Genes altered in major depressive disorder
Genes altered in major depressive disorder
Positive relationships between PIK3R1 and other components at different levels (count: 0)
Positive relationship network of PIK3R1 in MK4MDD
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1. The different color of the nodes denotes the level of the nodes.
Genetic/Epigenetic Locus
Protein and Other Molecule
Cell and Molecular Pathway
Neural System
Cognition and Behavior
Symptoms and Signs
Environment
MDD
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Negative relationships between PIK3R1 and MDD (count: 0)
Negative relationships between PIK3R1 and other components at different levels (count: 0)
Cell-matrix adhesions play essential roles in important biol......
Cell-matrix adhesions play essential roles in important biological processes including cell motility, cell proliferation, cell differentiation, regulation of gene expression and cell survival. At the cell-extracellular matrix contact points, specialized structures are formed and termed focal adhesions, where bundles of actin filaments are anchored to transmembrane receptors of the integrin family through a multi-molecular complex of junctional plaque proteins. Some of the constituents of focal adhesions participate in the structural link between membrane receptors and the actin cytoskeleton, while others are signalling molecules, including different protein kinases and phosphatases, their substrates, and various adapter proteins. Integrin signaling is dependent upon the non-receptor tyrosine kinase activities of the FAK and src proteins as well as the adaptor protein functions of FAK, src and Shc to initiate downstream signaling events. These signalling events culminate in reorganization of the actin cytoskeleton; a prerequisite for changes in cell shape and motility, and gene expression. Similar morphological alterations and modulation of gene expression are initiated by the binding of growth factors to their respective receptors, emphasizing the considerable crosstalk between adhesion- and growth factor-mediated signalling.More...
Chronic myelogenous leukaemia (CML) is a biphasic disease, i......
Chronic myelogenous leukaemia (CML) is a biphasic disease, initiated by expression of the BCR/ABL fusion gene product in self-renewing, haematopoietic stem cells (HSCs). HSCs can differentiate into common myeloid progenitors (CMPs), which then differentiate into granulocyte/macrophage progenitors (GMPs). HSCs can also differentiate into common lymphoid progenitors (CLPs), which are the progenitors of lymphocytes such as T cells and B cells. The initial chronic phase of CML (CML-CP) is characterized by a massive expansion of the granulocytic-cell series. Acquisition of additional genetic mutations beyond expression of BCR/ABL causes the progression of CML from chronic phase to blast phase (CML-BP), characterized by an accumulation of myeloid or lymphoid blast cells. The BCR/ABL fusion gene encodes p210BCR/ABL, an oncoprotein, which, unlike the normal p145 c-Abl, has constitutive tyrosine kinase activity and is predominantly localized in the cytoplasm. The tyrosine kinase activity is essential for cell transformation and the cytoplasmic localization of BCR/ABL allows the assembly of phosphorylated substrates in multiprotein complexes that transmit mitogenic and antiapoptotic signals. Additional cytogenetic and molecular changes are frequently found in patients with CML during the progression of the disease from chronic to blast phase. Some of the genetic changes include mutations in TP53, RB, and CDKN2A (also known as p16INK4A), or overexpression of genes such as EVI1. Additional chromosome translocations are also observed, such as t(3;21)(q26;q22), which generates AML1/EVI1. AML1/EVI-1 represses TGF-beta-mediated growth inhibitory signal.More...
Insulin resistance is strongly associated with type II diabe......
Insulin resistance is strongly associated with type II diabetes. Diabetogenic factors including FFA, TNFalpha and cellular stress induce insulin resistance through inhibition of IRS1 functions. Serine/threonine phosphorylation, interaction with SOCS, regulation of the expression, modification of the cellular localization, and degradation represent the molecular mechanisms stimulated by them. Various kinases (ERK, JNK, IKKbeta, PKCzeta, PKCtheta and mTOR) are involved in this process. The development of type II diabetes requires impaired beta-cell function. Chronic hyperglycemia has been shown to induce multiple defects in beta-cells. Hyperglycemia has been proposed to lead to large amounts of reactive oxygen species (ROS) in beta-cells, with subsequent damage to cellular components including PDX-1. Loss of PDX-1, a critical regulator of insulin promoter activity, has also been proposed as an important mechanism leading to beta-cell dysfunction. Although there is little doubt as to the importance of genetic factors in type II diabetes, genetic analysis is difficult due to complex interaction among multiple susceptibility genes and between genetic and environmental factors. Genetic studies have therefore given very diverse results. Kir6.2 and IRS are two of the candidate genes. It is known that Kir6.2 and IRS play central roles in insulin secretion and insulin signal transmission, respectively.More...
Xenopus oocytes are naturally arrested at G2 of meiosis I. E......
Xenopus oocytes are naturally arrested at G2 of meiosis I. Exposure to either insulin/IGF-1 or the steroid hormone progesterone breaks this arrest and induces resumption of the two meiotic division cycles and maturation of the oocyte into a mature, fertilizable egg. This process is termed oocyte maturation. The transition is accompanied by an increase in maturation promoting factor (MPF or Cdc2/cyclin B) which precedes germinal vesicle breakdown (GVBD). Most reports point towards the Mos-MEK1-ERK2 pathway and the polo-like kinase/CDC25 pathway as responsible for the activation of MPF in meiosis, most likely triggered by a decrease in cAMP.More...
Fc epsilon RI-mediated signaling pathways in mast cells are ......
Fc epsilon RI-mediated signaling pathways in mast cells are initiated by the interaction of antigen (Ag) with IgE bound to the extracellular domain of the alpha chain of Fc epsilon RI. The activation pathways are regulated both positively and negatively by the interactions of numerous signaling molecules. Mast cells that are thus activated release preformed granules which contain biogenic amines (especially histamines) and proteoglycans (especially heparin). The activation of phospholipase A2 causes the release of membrane lipids followed by development of lipid mediators such as leukotrienes (LTC4, LTD4 and LTE4) and prostaglandins (especially PDG2). There is also secretion of cytokines, the most important of which are TNF-alpha, IL-4 and IL-5. These mediators and cytokines contribute to inflammatory responses.More...
There is now much evidence that VEGFR-2 is the major mediato......
There is now much evidence that VEGFR-2 is the major mediator of VEGF-driven responses in endothelial cells and it is considered to be a crucial signal transducer in both physiologic and pathologic angiogenesis. The binding of VEGF to VEGFR-2 leads to a cascade of different signaling pathways, resulting in the up-regulation of genes involved in mediating the proliferation and migration of endothelial cells and promoting their survival and vascular permeability. For example, the binding of VEGF to VEGFR-2 leads to dimerization of the receptor, followed by intracellular activation of the PLCgamma;PKC-Raf kinase-MEK-mitogen-activated protein kinase (MAPK) pathway and subsequent initiation of DNA synthesis and cell growth, whereas activation of the phosphatidylinositol 3' -kinase (PI3K)-Akt pathway leads to increased endothelial-cell survival. Activation of PI3K, FAK, and p38 MAPK is implicated in cell migration signaling.More...
Leukocyte migaration from the blood into tissues is vital fo......
Leukocyte migaration from the blood into tissues is vital for immune surveillance and inflammation. During this diapedesis of leukocytes, the leukocytes bind to endothelial cell adhesion molecules (CAM) and then migrate across the vascular endothelium. A leukocyte adherent to CAMs on the endothelial cells moves forward by leading-edge protrusion and retraction of its tail. In this process, alphaL /beta2 integrin activates through Vav1, RhoA, which subsequently activates the kinase p160ROCK. ROCK activation leads to MLC phosphorylation, resulting in retraction of the actin cytoskeleton. Moreover, Leukocytes activate endothelial cell signals that stimulate endothelial cell retraction during localized dissociation of the endothelial cell junctions. ICAM-1-mediated signals activate an endothelial cell calcium flux and PKC, which are required for ICAM-1 dependent leukocyte migration. VCAM-1 is involved in the opening of the endothelial passage through which leukocytes can extravasate. In this regard, VCAM-1 ligation induces NADPH oxidase activation and the production of reactive oxygen species (ROS) in a Rac-mediated manner, with subsequent activation of matrix metallopoteinases and loss of VE-cadherin-mediated adhesion.More...
Normal duct epithelium progresses to infiltrating cancer thr......
Normal duct epithelium progresses to infiltrating cancer through a series of histologically defined precursors (PanINs). The overexpression of HER-2/neu and activating point mutations in the K-ras gene occur early, inactivation of the p16 gene at an intermediate stage, and the inactivation of p53, SMAD4, and BRCA2 occur relatively late. Activated K-ras engages multiple effector pathways. Although EGF receptors are conventionally regarded as upstream activators of RAS proteins, they can also act as RAS signal transducers via RAS-induced autocrine activation of the EGFR family ligands. Pancreatic ductal adenocarcinoma (PDA) show elevated expression of EGF receptors (e.g. HER2/neu) and their ligands (e.g.TGF-alpha) consistent with the presence of this autocrine loop. Moreover, PDA shows extensive genomic instability and aneuploidy. Telomere attrition and mutations in p53 and BRCA2 are likely to contribute to these phenotypes. Inactivation of the SMAD4 tumour suppressor gene leads to loss of the inhibitory influence of the transforming growth factor-beta signalling pathway.More...
Five distinct stages have been proposed in the evolution of ......
Five distinct stages have been proposed in the evolution of melanoma on the basis of histological criteria: common acquired and congenital nevi without dysplastic changes; dysplastic nevi with structural and architectural atypia; radial-growth phase (RGP) melanoma; vertical-growth phase (VGP) melanoma; and metastatic melanoma. Oncogenic NRAS mutations activate both effector pathways Raf-MEK-ERK and PI3K-Akt. The Raf-MEK-ERK pathway may also be activated via mutations in the BRAF gene. The PI3K-Akt pathway may be activated through loss or mutation of the inhibitory tumor suppressor gene PTEN. These mutations arise early during melanoma pathogenesis and are preserved throughout tumor progression. Moreover, melanoma development is strongly associated with inactivation of the p16INK4a/CDK4,6/pRb and p14ARF/HMD2/p53 tumor suppressor pathways. The vertical-growth phase and metastatic melanoma are notable for striking changes in the control of cell adhesion. Recently, amplification of the MITF gene was demonstrated in 10% of primary melanomas and 20% of metastatic melanomas, suggesting that MITF is a melanoma oncogene.More...
Renal cell carcinoma (RCC) is a heterogenous term comprising......
Renal cell carcinoma (RCC) is a heterogenous term comprising a group of neoplasms of renal origin. There are 4 major histologic subtypes of RCC: conventional (clear cell RCC, 75%), papillary (15%), chromophobic (5%), and collecting duct (2%). Multiple genes are involved in the molecular pathogenesis of RCC. VHL is a tumor suppressor gene responsible for hereditary (von Hippel-Lindau) and sporadic variants of conventional (clear cell) RCC. In the absence of VHL, hypoxia-inducible factor alpha (HIF-alpha) accumulates, leading to production of several growth factors, including vascular endothelial growth factor and platelet-derived growth factor. An oncogene, MET has been found to be mutant in cases of hereditary papillary renal cancer (HPRC), although the incidence of c-MET mutations is low in sporadic papillary RCC. Once activated, MET mediates a number of biological effects including motility, invasion of extracellular matrix, cellular transformation, prevention of apoptosis and metastasis formation. Mutations in the fumarate hydratase (FH) gene cause hereditary leiomyomatosis and renal cancer syndrome (HLRCC) papillary renal tumors, although the incidence of FH mutations in sporadic tumors is unknown. Loss of functional FH leads to accumulation of fumarate in the cell, triggering inhibition of HPH and preventing targeted pVHL-mediated degradation of HIF-alpha. BHD mutations cause the Birt-Hogg-Dube syndrome and its associated chromophobe, hybrid oncocytic, and conventional (clear cell) RCC. The incidence of BHD mutations in sporadic renal tumors is not known.More...
Non-small-cell lung cancer (NSCLC) accounts for approximatel......
Non-small-cell lung cancer (NSCLC) accounts for approximately 80% of lung cancer and represents a heterogeneous group of cancers, consisting mainly of squamous cell (SCC), adeno (AC) and large-cell carcinoma. Molecular mechanisms altered in NSCLC include activation of oncogenes, such as K-RAS and c-erbB-2, and inactivation of tumorsuppressor genes, such as p53, p16INK4a, RAR-beta, and RASSF1. Point mutations within the K-RAS gene inactivate GTPase activity and the p21-RAS protein continuously transmits growth signals to the nucleus. Overexpression of c-erbB-2 or EGFR leads to a proliferative advantage. Inactivating mutation of p53 can lead to more rapid proliferation and reduced apoptosis. The protein encoded by the p16INK4a inhibits formation of CDK-cyclin-D complexes by competitive binding of CDK4 and CDK6. Loss of p16INK4a expression is a common feature of NSCLC RAR-beta is a nuclear receptor that bears vitamin-A-dependent transcriptional activity. RASSF1A is able to form heterodimers with Nore-1, an RAS effector.Therefore loss of RASSF1A might shift the balance of RAS activity towards a growth-promoting effect.More...
Activation of T lymphocytes is a key event for an efficient ......
Activation of T lymphocytes is a key event for an efficient response of the immune system. It requires the involvement of the T-cell receptor (TCR) as well as costimulatory molecules such as CD28. Engagement of these receptors through the interaction with a foreign antigen associated with major histocompatibility complex molecules and CD28 counter-receptors B7.1/B7.2, respectively, results in a series of signaling cascades. These cascades comprise an array of protein-tyrosine kinases, phosphatases, GTP-binding proteins and adaptor proteins that regulate generic and specialised functions, leading to T-cell proliferation, cytokine production and differentiation into effector cells.More...
B cells are an important component of adaptive immunity. The......
B cells are an important component of adaptive immunity. They produce and secrete millions of different antibody molecules, each of which recognizes a different (foreign) antigen. The B cell receptor (BCR) is an integral membrane protein complex that is composed of two immunoglobulin (Ig) heavy chains, two Ig light chains and two heterodimers of Ig-alpha and Ig-beta. After BCR ligation by antigen, three main protein tyrosine kinases (PTKs) -the SRC-family kinase LYN, SYK and the TEC-family kinase BTK- are activated. Phosphatidylinositol 3-kinase (PI3K) and phospholipase C-gamma 2 (PLC-gamma 2) are important downstream effectors of BCR signalling. This signalling ultimately results in the expression of immediate early genes that further activate the expression of other genes involved in B cell proliferation, differentiation and Ig production as well as other processes.More...
Phagocytosis plays an essential role in host-defense mechani......
Phagocytosis plays an essential role in host-defense mechanisms through the uptake and destruction of infectious pathogens. Specialized cell types including macrophages, neutrophils, and monocytes take part in this process in higher organisms. After opsonization with antibodies (IgG), foreign extracellular materials are recognized by Fc gamma receptors. Cross-linking of Fc gamma receptors initiates a variety of signals mediated by tyrosine phosphorylation of multiple proteins, which lead through the actin cytoskeleton rearrangements and membrane remodeling to the formation of phagosomes. Nascent phagosomes undergo a process of maturation that involves fusion with lysosomes. The acquisition of lysosomal proteases and release of reactive oxygen species are crucial for digestion of engulfed materials in phagosomes.More...
Two major types of genetic events are crucial for the molecu......
Two major types of genetic events are crucial for the molecular pathogenesis of acute myeloid leukemias (AML) : activating mutations of signal transduction intermediates and alterations in myeloid transcription factors governing hematopoietic differentiation. Both aberrant and constitutive activation of signal transduction molecules are found in about 50% of primary AML bone marrow samples, and seem to contribute to the increased proliferation and apoptosis resistance. The most common of these activating events were observed in the RTK Flt3, in N-Ras and K-Ras, in Kit, and sporadically in other RTKs. Specific haematopoietic transcription factors are crucial for differentiation to particular lineages during normal differentiation, but are frequently disrupted in AML. Some mechanisms of disruption involve the effect of fusion proteins that are generated by chromosomal translocations on haematopoietic transcription factors. In other cases, the transcription factors themselves are mutated.More...
Classically, colorectal cancer (CRC) has been believed to de......
Classically, colorectal cancer (CRC) has been believed to develop from normal mucosa through the premalignant adenoma by the step-wise accumulation of mutations. All CRC display either microsatellite instability (MSI) or chromosome instability (CIN). MSI occurs in 15% of colon cancers and results from inactivation of the DNA mismatch repair (MMR) system by either MMR gene mutations or hypermethylation of the MLH1 promoter. MSI promotes tumorigenesis through generating mutations in target genes that possess coding microsatellite repeats, such as beta-catenin, TGFBR2 and BAX. CIN is found in the majority of colon cancers and leads to a different pattern of gene alterations that contribute to tumor formation. Genes involved in CIN are those coding for APC, K-ras, SMAD4 and p53.More...
The identification of key molecular alterations in prostate-......
The identification of key molecular alterations in prostate-cancer cells implicates carcinogen defenses (GSTP1), growth-factor-signaling pathways (NKX3.1, PTEN, and p27), and androgens (AR) as critical determinants of the phenotype of prostate-cancer cells. Glutathione S-transferases (GSTP1) are detoxifying enzymes that catalyze conjunction of glutathione with harmful, electrophilic molecules, thereby protecting cells from carcinogenic factors. Cells of prostatic intraepithelial neoplasia, devoid of GSTP1, undergo genomic damage mediated by such carcinogens. NKX3.1, PTEN, and p27 regulate the growth and survival of prostate cells in the normal prostate. Inadequate levels of PTEN and NKX3.1 lead to a reduction in p27 levels and to increased proliferation and decreased apoptosis. After therapeutic reduction in the levels of testosterone and dihydrotestosterone, the emergence of androgen-independent prostate cancer has been associated with mutations in the androgen receptor (AR) that permit receptor activation by other ligands, increased expression of androgen receptors accompanying AR amplification, and ligand-independent androgen-receptor activation.More...
The ErbB family of receptor tyrosine kinases (RTKs) couples ......
The ErbB family of receptor tyrosine kinases (RTKs) couples binding of extracellular growth factor ligands to intracellular signaling pathways regulating diverse biologic responses, including proliferation, differentiation, cell motility, and survival. Ligand binding to the four closely related members of this RTK family -epidermal growth factor receptor (EGFR, also known as ErbB-1 or HER1), ErbB-2 (HER2), ErbB-3 (HER3), and ErbB-4 (HER4)-induces the formation of receptor homo- and heterodimers and the activation of the intrinsic kinase domain, resulting in phosphorylation on specific tyrosine residues (pY) within the cytoplasmic tail. Signaling effectors containing binding pockets for pY-containing peptides are recruited to activated receptors and induce the various signaling pathways. The Shc- and/or Grb2-activated mitogen-activated protein kinase (MAPK) pathway is a common target downstream of all ErbB receptors. Similarly, the phosphatidylinositol-3-kinase (PI-3K) pathway is directly or indirectly activated by most ErbBs. Several cytoplasmic docking proteins appear to be recruited by specific ErbB receptors and less exploited by others. These include the adaptors Crk, Nck, the phospholipase C gamma (PLCgamma), the intracellular tyrosine kinase Src, or the Cbl E3 ubiquitin protein ligase.More...
Small cell lung carcinoma (SCLC) is a highly aggressive neop......
Small cell lung carcinoma (SCLC) is a highly aggressive neoplasm, which accounts for approximately 20% of all lung cancer cases. Molecular mechanisms altered in SCLC include induced expression of oncogene, MYC, and loss of tumorsuppressor genes, such as p53, PTEN, RB, and FHIT. The overexpression of MYC proteins in SCLC is largely a result of gene amplification. Such overexpression leads to more rapid proliferation and loss of terminal differentiation. Mutation or deletion of p53 or PTEN can lead to more rapid proliferation and reduced apoptosis. The retinoblastoma gene RB1 encodes a nuclear phosphoprotein that helps to regulate cell-cycle progression. The fragile histidine triad gene FHIT encodes the enzyme diadenosine triphosphate hydrolase, which is thought to have an indirect role in proapoptosis and cell-cycle control.More...
Insulin binding to its receptor results in the tyrosine phos......
Insulin binding to its receptor results in the tyrosine phosphorylation of insulin receptor substrates (IRS) by the insulin receptor tyrosine kinase (INSR). This allows association of IRSs with the regulatory subunit of phosphoinositide 3-kinase (PI3K). PI3K activates 3-phosphoinositide-dependent protein kinase 1 (PDK1), which activates Akt, a serine kinase. Akt in turn deactivates glycogen synthase kinase 3 (GSK-3), leading to activation of glycogen synthase (GYS) and thus glycogen synthesis. Activation of Akt also results in the translocation of GLUT4 vesicles from their intracellular pool to the plasma membrane, where they allow uptake of glucose into the cell. Akt also leads to mTOR-mediated activation of protein synthesis by eIF4 and p70S6K. The translocation of GLUT4 protein is also elicited through the CAP/Cbl/TC10 pathway, once Cbl is phosphorylated by INSR. Other signal transduction proteins interact with IRS including GRB2. GRB2 is part of the cascade including SOS, RAS, RAF and MEK that leads to activation of mitogen-activated protein kinase (MAPK) and mitogenic responses in the form of gene transcription. SHC is another substrate of INSR. When tyrosine phosphorylated, SHC associates with GRB2 and can thus activate the RAS/MAPK pathway independently of IRS-1.More...
The Janus kinase/signal transducers and activators of transc......
The Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway is one of a handful of pleiotropic cascades used to transduce a multitude of signals for development and homeostasis in animals, from humans to flies. In mammals, the JAK/STAT pathway is the principal signaling mechanism for a wide array of cytokines and growth factors. Following the binding of cytokines to their cognate receptor, STATs are activated by members of the JAK family of tyrosine kinases. Once activated, they dimerize and translocate to the nucleus and modulate the expression of target genes. In addition to the activation of STATs, JAKs mediate the recruitment of other molecules such as the MAP kinases, PI3 kinase etc. These molecules process downstream signals via the Ras-Raf-MAP kinase and PI3 kinase pathways which results in the activation of additional transcription factors.More...
Natural killer (NK) cells are lymphocytes of the innate immu......
Natural killer (NK) cells are lymphocytes of the innate immune system that are involved in early defenses against both allogeneic (nonself) cells and autologous cells undergoing various forms of stress, such as infection with viruses, bacteria, or parasites or malignant transformation. Although NK cells do not express classical antigen receptors of the immunoglobulin gene family, such as the antibodies produced by B cells or the T cell receptor expressed by T cells, they are equipped with various receptors whose engagement allows them to discriminate between target and nontarget cells. Activating receptors bind ligands on the target cell surface and trigger NK cell activation and target cell lysis. However Inhibitory receptors recognize MHC class I molecules (HLA) and inhibit killing by NK cells by overruling the actions of the activating receptors. This inhibitory signal is lost when the target cells do not express MHC class I and perhaps also in cells infected with virus, which might inhibit MHC class I exprssion or alter its conformation. The mechanism of NK cell killing is the same as that used by the cytotoxic T cells generated in an adaptive immune response; cytotoxic granules are released onto the surface of the bound target cell, and the effector proteins they contain penetrate the cell membrane and induce programmed cell death.More...
Glioblastoma multiforme (GBM) formation is either de novo (p......
Glioblastoma multiforme (GBM) formation is either de novo (primary GBMs) or due to the progression of a lower grade glioma to a higher grade one through the acquisition of additional mutations (secondary GBMs). In primary GBM, disruption of the p53 pathway often occurs through loss of ARF, or less frequently through amplification of MDM2. Disruption of the RB pathway occurs through loss of INK4A. Amplification and/or mutation of the epidermal growth factor receptor (EGFR) is the most frequently detected genetic defect that is associated with primary GBM. In secondary GBM, loss of p53 and activation of the growth-factorreceptor-tyrosine-kinase signalling pathway (such as through overexpression of PDGF/PDGFR ) initiates tumour formation,whereas disruption of the retinoblastoma (RB) pathway contributes to the progression of tumour development. Loss of PTEN has been implicated in both pathways, although it is much more common in the pathogenesis of primary GBM.More...
Sodium transport across the tight epithelia of Na+ reabsorbi......
Sodium transport across the tight epithelia of Na+ reabsorbing tissues such as the distal part of the kidney nephron and colon is the major factor determining total-body Na+ levels, and thus, long-term blood pressure. Aldosterone plays a major role in sodium and potassium metabolism by binding to epithelial mineralocorticoid receptors (MR) in the renal collecting duct cells localized in the distal nephron, promoting sodium resorption and potassium excretion. Aldosterone enters a target cell and binds MR, which translocates into the nucleus and regulates gene transcription. Activation of MR leads to increased expression of Sgk-1, which phosphorylates Nedd4-2, an ubiquitin-ligase which targets ENAC to proteosomal degradation. Phosphorylated Nedd4-2 dissociates from ENAC, increasing its apical membrane abundance. Activation of MR also leads to increased expression of Na+/K+-ATPase, thus causing a net increase in sodium uptake from the renal filtrate. The specificity of MR for aldosterone is provided by 11beta-HSD2 by the rapid conversion of cortisol to cortisone in renal cortical collecting duct cells. Recently, besides genomic effects mediated by activated MR, rapid aldosterone actions that are independent of translation and transcription have been documented.More...
Inflammatory immune response requires the recruitment of leu......
Inflammatory immune response requires the recruitment of leukocytes to the site of inflammation upon foreign insult. Chemokines are small chemoattractant peptides that provide directional cues for the cell trafficking and thus are vital for protective host response. In addition, chemokines regulate plethora of biological processes of hematopoietic cells to lead cellular activation, differentiation and survival. The chemokine signal is transduced by chemokine receptors (G-protein coupled receptors) expressed on the immune cells. After receptor activation, the alpha- and beta-gamma-subunits of G protein dissociate to activate diverse downstream pathways resulting in cellular polarization and actin reorganization. Various members of small GTPases are involved in this process. Induction of nitric oxide and production of reactive oxygen species are as well regulated by chemokine signal via calcium mobilization and diacylglycerol production.More...
Specific families of pattern recognition receptors are respo......
Specific families of pattern recognition receptors are responsible for detecting microbial pathogens and generating innate immune responses. Toll-like receptors (TLRs) are membrane-bound receptors identified as homologs of Toll in Drosophila. Mammalian TLRs are expressed on innate immune cells, such as macrophages and dendritic cells, and respond to the membrane components of Gram-positive or Gram-negative bacteria. Pathogen recognition by TLRs provokes rapid activation of innate immunity by inducing production of proinflammatory cytokines and upregulation of costimulatory molecules. TLR signaling pathways are separated into two groups: a MyD88-dependent pathway that leads to the production of proinflammatory cytokines with quick activation of NF-{kappa}B and MAPK, and a MyD88-independent pathway associated with the induction of IFN-beta and IFN-inducible genes, and maturation of dendritic cells with slow activation of NF-{kappa}B and MAPK.More...
Apoptosis is a genetically controlled mechanisms of cell dea......
Apoptosis is a genetically controlled mechanisms of cell death involved in the regulation of tissue homeostasis. The 2 major pathways of apoptosis are the extrinsic (Fas and other TNFR superfamily members and ligands) and the intrinsic (mitochondria-associated) pathways, both of which are found in the cytoplasm. The extrinsic pathway is triggered by death receptor engagement, which initiates a signaling cascade mediated by caspase-8 activation. Caspase-8 both feeds directly into caspase-3 activation and stimulates the release of cytochrome c by the mitochondria. Caspase-3 activation leads to the degradation of cellular proteins necessary to maintain cell survival and integrity. The intrinsic pathway occurs when various apoptotic stimuli trigger the release of cytochrome c from the mitochondria (independently of caspase-8 activation). Cytochrome c interacts with Apaf-1 and caspase-9 to promote the activation of caspase-3. Recent studies point to the ER as a third subcellular compartment implicated in apoptotic execution. Alterations in Ca2+ homeostasis and accumulation of misfolded proteins in the ER cause ER stress. Prolonged ER stress can result in the activation of BAD and/or caspase-12, and execute apoptosis.More...
Neurotrophins are a family of trophic factors involved in di......
Neurotrophins are a family of trophic factors involved in differentiation and survival of neural cells. The neurotrophin family consists of nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), and neurotrophin 4 (NT-4). Neurotrophins exert their functions through engagement of Trk tyrosine kinase receptors or p75 neurotrophin receptor (p75NTR). Neurotrophin/Trk signaling is regulated by connecting a variety of intracellular signaling cascades, which include MAPK pathway, PI-3 kinase pathway, and PLC pathway, transmitting positive signals like enhanced survival and growth. On the other hand, p75NTR transmits both positive and nagative signals. These signals play an important role for neural development and additional higher-order activities such as learning and memory.More...
Two types of endometrial carcinoma are distinguished with re......
Two types of endometrial carcinoma are distinguished with respect to biology and clinical course. Type-I carcinoma is related to hyperestrogenism by association with endometrial hyperplasia, frequent expression of estrogen and progesterone receptors and younger age, whereas type-II carcinoma is unrelated to estrogen, associated with atrophic endometrium, frequent lack of estrogen and progesterone receptors and older age. This classification has also been justified at the molecular level with Type 1 tumours being more commonly associated with abnormalities of DNA-mismatch repair genes, K-ras, PTEN and beta-catenin, and Type 2 tumours with abnormalities of p53 and HER2/neu.More...
The T Cell Receptor plays a key role in the immune system. T......
The T Cell Receptor plays a key role in the immune system. The specificity of the receptor is governed by the binding site formed from the mature alpha and beta chains (shown here) or gamma and delta chains in gamma/delta T Cells. It is the ability of this receptor to bind a complex of foreign peptide in the groove of an MHC molecule that leads to T cell activation. Upon activation the T cell can assist in activating other cells or carry out cytolytic attacks depending on the particular T cell type. The CD3 complex and CD4 (Th cells) or CD8 (Tc cells) work to transmit the activation signal to the T cell's transcriptional machinary upon engagement of the receptor.More...
To replicate in the host cell, viruses commandeer cellular s......
To replicate in the host cell, viruses commandeer cellular signaling pathways. Cytomegalovirus (CMV) is a DNA virus with that is widespread in the population but usually causes disease only in immunocompromised individuals and is also a viral cause of birth defects. One of the actions of CMV in the host cell is to stimulate MAP kinase pathways. Both p38 and ERK kinases are activated by CMV infection through activation map kinase kinases and inhibition of phosphatases. One result of Map kinase activation by CMV is activation of transcription of viral genes, increasing the production of viral gene products. Both p38 and ERK kinases contribute to the activation of viral genes by cellular transcription factors acting through the viral UL4 promoter at upstream and basal transcription elements. Another target of prolonged p38 activation during infection is Rb, contributing to viral replication. Activation of MKK1 and MKK2 leads to Erk1 and Erk2 activation, and phosphorylation of downstream targets. The MEKK1 kinase regulates the immediate early promoter indirectly through downstream kinase signaling and perhaps more directly through activation of NF-kB. Map kinase pathways activated by CMV converge on increased transcription of viral genes and increased replication of the viral genome. Better understanding of the mechanisms involved in the interaction of CMV with cellular signaling machinery will provide improved ways to treat CMV-mediated disease.More...
Ras-Independent pathway in NK cell-mediated cytotoxicity
NK (natural killer) cells are lymphocytes distinct from B an......
NK (natural killer) cells are lymphocytes distinct from B and T cells that induce perforin-mediated lysis of tumor cells and virus-infected cells. NK cell-mediated cytotoxicity is activated by glycoproteins on the cell surface (activating receptors) and inhibited by MHC-1 with self-peptide bound. The MHC-1 inhibitory signal through Ig-family or lectin receptors prevents NK cells from killing normal cells. Abnormal MHC-1 expression in infected or tumor cells results in the release of perforin, the lysis of the abnormal cell and the release of cytokines that stimulate the immune response. MAP kinase inhibitors but not ras inhibitors are able to block NK cell cytotoxicity, indicating that the pathway can function by a ras-independent manner that involves the MAP kinase pathway. This pathway includes phosphoinositide-3-kinase (PI3K) as a key component, followed by Rac1 and the exchange factor Vav. The tyrosine kinase SYK and LAT may provide an additional pathway for activation of MAP kinases leading to NK cell activation, and also Pyk-2 activation by integrins. The protein tyrosine phosphatase SHP-1 appears to mediate the cytotoxicity inhibitory signal that blocks lysis of normal cells. The balance of these positive and negative signaling pathways regulates the role of NK cells in the immune response.More...
Role of PI3K subunit p85 in regulation of Actin Organization and Cell Migration
Migration of cells is involved in essential functions such a......
Migration of cells is involved in essential functions such as development, invasiveness of cancer cells, leukocyte movement toward chemotactic signals, and fibroblast response to injury. Cells can migrate in a specific direction in response to extracellular signals through pathways that trigger changes in the cytoskeleton, particularly actin filaments, increasing lamellipodia and filopodia formation and decreasing focal adhesions. Factors like PDGF activate PI3 kinase and multiple pathways downstream to stimulate cell migration. One pathway regulating migration through the p85 regulatory subunit of PI3 kinase does not require PI3-kinase activity. In this pathway, p85 of PI3-kinase activates cdc42, which activates N-Wasp (Wiskott-Aldrich Syndrome Protein) to regulate ARP-2/3. ARP-2/3 is a complex of proteins localized at the leading edge of moving cells that nucleates the formation of new actin fibers and interacts with Wasp to stimulate migration. The cdc42 pathway also regulates p21-activate kinase 1 (PAK1). Another pathway by which PI3 kinase regulates migration is through the small GTPase Rac. PAK1 is a downstream target of Rac as well as cdc42. Downstream of Rac and PAK1, Myosin light chain kinase (MLCK) phosphorylates myosin light chain to increase cell migration. The regulation of the localization and activity of signaling factors creates coordinated pathways linking extracellular signals and cellular migration.More...
The IL-2 receptor is a key component of immune signaling and......
The IL-2 receptor is a key component of immune signaling and is required for the activation, proliferation, and survival of T cells. This receptor is composed of three polypeptide chains, the alpha, beta and gamma chains. The IL-2 receptor gamma chain is a common component for several other cytokine receptors, including IL-4, IL-7, IL-9 and IL-15. The IL-2 receptor beta chain is essential for IL-2 signaling and is also a component of the IL-15 receptor complex. The polypeptides of the IL-2 receptor do not themselves have intrinsic catalytic activity, but interact with cytoplasmic signaling proteins to transduce signals. br>Different regions of the cytoplasmic domain of the IL-2 receptor beta chain interact and couple with distinct signaling pathways and cellular responses. JAK1 associates with the beta chain, and JAK3 with the gamma chain. Binding of IL-2 induces heterodimerization of receptor subunits, and activation of JAK kinase activity. Tyrosine residues in the beta chain cytoplasmic domain are phosphorylated during activation, recruiting other factors to the phosphorylated tyrosine residues through src homology 2 (SH2) domains. The adaptor protein Shc binds to phosphorylated tyrosine 338 of the beta chain. When bound, Shc is phosphorylated and couples through Grb2 and Sos-1 to activate Ras and stimulate T cell proliferation. Another key proliferative pathway activated by IL-2 is phosphorylation of STAT-5 by JAK kinases. STAT-5 is recruited to IL-2 beta phosphorylated tyrosines at multiple positions, including Y338, Y392 and Y510. Once phosphorylated, STAT-5 enters the nucleus to regulate the transcription of several genes, some proliferative such as cyclin genes and others that are involved in T cell immune function such as cytokine genes. The suppressors of cytokine activation, SOCS-3 and SOCS-1, oppose phosphorylation and activation of STAT-5 and JAK1 caused by IL-2. PI3 kinase is another protein recruited to IL-2 receptor beta chain tyrosines when phosphorylated. Activation of PI3 Kinase also contributes to the proliferative activity of IL-2 in T cells. The role of other tyrosines in the IL-2 receptor beta chain, Y355, Y358 and Y361, is not yet clear, but may be involved in signaling by the protein kinase p56lck. In addition to stimulating T cell activation and proliferation, IL-2 activation blocks T cell apoptosis through multiple pathways. Among the genes activated by STAT-5 are BCL-xL, an inhibitor of apoptosis, and fas-ligand, an activator of apoptosis in cells expressed the fas receptor. PI3 kinase also contributes to anti-apoptotic activity of IL-2 through AKT activation. T cell responses to IL-2 must be coordinated in part in the complex protein-protein interactions with the IL-2 receptor beta chain.More...
The drug Gleevec (also known as imatinib mesylate or STI-571......
The drug Gleevec (also known as imatinib mesylate or STI-571) was approved by the FDA in 2001 for the treatment of CML, chronic myeloid leukemia. While traditional cytotoxic cancer treatments such as chemotherapy or radiation therapy kill all dividing cells, Gleevec acts on a molecular target by a mechanism that is more specific to cancer cells. Traditional cytotoxic cancer agents have serious side effects such as nausea, weight loss, hair loss and severe fatigue that result from their lack of specificity in killing cells. Gleevec was designed as an inhibitor of a specific receptor associated with CML, and so produces less severe side effects than other cancer agents. CML is associated in most cases with a specific chromosomal defect, a translocation between chromosomes 9 and 22 that creates the Philadelphia chromosome. This translocation occurs at the site in the genome of a protein tyrosine kinase called abl, creating the abnormal bcr-abl protein, a fusion of the abl gene with another gene called bcr. The kinase activity of abl in the bcr-abl fusion is activated and unregulated, driving the uncontrolled cell growth observed in CML. White blood cells containing the bcr-abl mutation become able to proliferate in the absence of growth factors they normally require. Gleevec inhibits abl kinase activity, helping to reverse uncontrolled cell growth. Gleevec also inhibits the PDGF tyrosine kinase and the c-kit tyrosine kinase. There are a variety of cellular substrates of the bcr-abl kinase that may be involved in cellular transformation. Bcr-abl is associated with the cytoplasm as part of a large signaling complex. Some of the downstream factors in bcr-abl signaling include PI3 kinase/AKT and STAT transcription factors. The activation of bcr-abl also represses apoptosis through induction of anti-apoptosis factors such as Bad, allowing transformed cells to divide. JAK2 kinase activity appears to be one target of bcr-abl. Grb-2 phosphorylation by bcr-abl may play a role in down-regulation of tyrosine kinase signaling. STAT5 may be involved in the failure of apoptosis in bcr-abl cells. In addition to supporting the idea that cancer therapies targeting specific molecular targets should be efficacious with fewer side effects, Gleevec has also demonstrated that drugs inhibiting protein kinases can be developed successfully. Tyrosine kinases are important in a range of cellular processes, including other cancers, and will provide additional drug targets. Gleevec itself has already demonstrated potential in other cancers such as gastrointestinal stromal tumor that do not respond to existing treatments. Although Gleevec has produced very strong clinical responses in patients with early stage CML, patients with late stage disease have had an initial response followed by a relapse of drug resistant CML cells. Cancer cells in patients with Gleevec resistant cancer either had amplification of the bcr-abl gene, or mutation of a key amino acid involved in binding drug from threonine to isoleucine.More...
Role of nicotinic acetylcholine receptors in the regulation of apoptosis
Nicotinic acetylcholine receptors are essential for neuromus......
Nicotinic acetylcholine receptors are essential for neuromuscular signaling and are also expressed in non-neuronal tissues, where their function is less clear. Although nicotinic acetylcholine receptors are primarily known for their action as ligand-gated ion channels transducing action potentials across synapses, they may have other actions. Nicotinic acetylcholine receptors in neurons alter apoptotic signaling, protecting against cell death in some settings, and this action may in some cases be directed through alternative signaling pathways. In neurons the alpha-7 nicotinic receptor activates PI3 kinase through a src-family kinase, activating the anti-apoptotic kinase AKT. One pathway involved in AKT signaling involves phosphorylation of the forkhead transcription factor FKHRL1, causing its retention in the cytoplasm associated with 14-3-3, and blocking expression of the apoptotic fas protein. The PI3 kinase/AKT pathway protects a broad range of neurons against apoptotic cell death and may block apoptosis triggered by beta-amyloid fragments that contributes to the progression of Alzheimers disease. If so, nicotinic agents may prove useful in the treatment of this and other neurodegenerative conditions. There are several proteins that modulate the response of nicotinic acetylcholine receptors, include synapse formation. Prior to synapse formation, nicotinic receptors are randomly dispersed in the post-synaptic membrane. A neuronal protein, agrin, binds to the Musk receptor in the muscle membrane, stimulating clustering of nicotinic receptors and synapse formation. Rapsyn is present at high levels at synapses with nicotinic receptors, bringing them together at high densities and anchoring clustered receptors to the cytoskeleton. Members of the Src family of tyrosine kinases also play a role in clustering caused by Rapsyn, phosphorylating the nicotinic receptors, rapsyn, and other targets. Nicotinic receptors expressed in non-neuronal tissues may also be involved in the response to smoking. In lung epithelial cells, nicotine from cigarette smoke blocks apoptosis by activating the anti-apoptotic kinase AKT, contributing perhaps to carcinogenesis and resistance to chemotherapy. Activation of nicotinic acetylcholine receptors in dermal fibroblasts may contribute to the altered wound healing and skin elasticity related to smoking. Activation of keratinocyte nicotinic receptors may also alter the properties of skin.More...
Thrombopoietin (TPO) binds to its receptor inducing aggregat......
Thrombopoietin (TPO) binds to its receptor inducing aggregation and activation. TPO signals its growth regulating effects to the cell through several major pathways including MAPK (ERK and JNK), Protein Kinase C, and JAK/Stat.More...
Sphingosine-1-phosphate (S1P) is an example of lipid messeng......
Sphingosine-1-phosphate (S1P) is an example of lipid messengers with both intracellular and extracellular functions. Intracellularly S1P regulates proliferation and survival; extracellularly S1P is a ligand for EDG1 (also known as S1P1). Activation of sphingosine kinase (SPHK), the enzyme that catalyzes the phosphorylation of sphingosine, increases cellular levels of S1P. Inhibitors of SPHK block formation of S1P and inhibit cellular proliferation induced by a variety of factors, including as an example platelet-derived growth factor (PDGF) and PMA. In a study using endothelial cells it was demonstrated that S1P induces activation of alpha-v and B3 integrins via RhoA. S1P also activates Akt via Gi and PI3K. The activated Akt phosphorlyates the Edg1 receptor on threonine 236 leading to the activation of Rac1 and subsequent signals leading to actin assembly, chemotaxis and lamellipodia formation. Edg1 stimulation also leads to the activation of the ERK signaling cascade resulting in anti-apoptotic reversal, proliferation and cell survival.More...
Her2 or ERBB2 belongs to a class of proteins having high hom......
Her2 or ERBB2 belongs to a class of proteins having high homology with epidermal growth factor receptor (EGFR or ERBB1). It encodes a protein with the molecular weight of 185 KDa. Unlike other members of EGFR family, no ligand for Her2 has been found and it usually associates with members of ERBB1 family to form functional heterodimers. It has been shown that it can form dimers with ERBB (EGFR), ERBB3 and ERBB4 as well as gp130 subunits of IL-6 receptor. In at least some cell types, the association between gp130 and HRBB2 is essential for HRBB2-ERBB3 phosphorylation and subsequent MAP kinase signaling. Although ERBB1 can form homodimers, the signaling for ERBB1 is usually transient and the receptor undergoes internalization after ligand binding and activation. EGFR-HER2 complex increases the signaling capacity of EGFR by increasing the ligand affinity as well as the recycling of the heterodimer. Of all the ERBB heterodimers, ERBB2-ERBB3 heterodimers perhaps elicit the strongest signal. Removing ERBB3 from the cell has a drastic effect on ERBB2 mediated signaling and downstream effectors. The clinical importance of HER2 cannot be overstated. In addition, monoclonal antibody (Herceptin) against this receptor has been shown to be an effective treatment of breast cancer patients who have a high level of HER2 over expression.More...
Transcription factor CREB and its extracellular signals
The transcription factor CREB binds the cyclic AMP response ......
The transcription factor CREB binds the cyclic AMP response element (CRE) and activates transcription in response to a variety of extracellular signals including neurotransmitters, hormones, membrane depolarization, and growth and neurotrophic factors. Protein kinase A and the calmodulin-dependent protein kinases CaMKII stimulate CREB phosphorylation at Ser133, a key regulatory site controlling transcriptional activity. Growth and neurotrophic factors also stimulate CREB phosphorylation at Ser133. Phosphorylation occurs at Ser133 via p44/42 MAP Kinase and p90RSK and also via p38 MAP Kinase and MSK1. CREB exhibit deficiencies in spatial learning tasks, while flies overexpressing or lacking CREB show enhanced or diminished learning, respectively.More...
Nerve growth factor (NGF) is one of a family of neurotrophin......
Nerve growth factor (NGF) is one of a family of neurotrophins that induce the survival and proliferation of neurons. In cell culture NGF induces the formation of neurite projections and in vivo may stimulate the innervation of tissues. NGF plays a role in the repair, regeneration, and protection of neurons, and as such could serve as a therapeutic agent in neurodegenerative conditions such as Alzheimer's disease. One potential method of NGF application would be through gene therapy or through implantation of cells that have been genetically modified ex vivo. NGF has also been suggested to play a role in other physiological systems and tissues such as the immune system. NGF has two receptors, TrkA and the p75(NTR). NGF may signal its neuroprotective actions through the tyrosine kinase TrkA receptor and trigger apoptosis in some cells through the p75 receptor. High-affinity binding of NGF requires both TrkA and p75(NTR). Binding of NGF to the TrkA receptor causes activation of the receptor tyrosine kinase and downstream signaling cascades. One of the downstream signaling pathways of NGF activates phospholipase C, releasing DAG and IP3 and activating associated downstream pathways such as protein kinase C. Another NGF-activated pathway is the ras-mediated activation of the map kinase pathway. This pathway is initiated through recruitment and activation of Shc, which leads to ras activation through Grb-2 and Sos-1. The Map kinase cascade includes raf, Mek and Erk. The downstream effectors of the ras pathway include activation of fos and jun to form AP-1, activating genes through this transcription factor. Other transcription factors involved in NGF responses include Egr and CREB. The Egr family of transcription factors as well as the Mek/Erk pathway contribute to NGF-induced neurite formation. The CREB family of transcription factors are involved in NGF-induced survival of sympathetic neurons. Further understanding of NGF signaling may be applied to the modulation of NGF responses in neurodegenerative conditions.More...
Influence of Ras and Rho proteins on G1 to S Transition
The cell cycle transition from G1 to S phase is a key regula......
The cell cycle transition from G1 to S phase is a key regulatory point in the cell cycle. This transition is regulated by the checkpoint kinase cdk2 that activates the G1 to S transition when it is associated with cyclin E. Cdk2/Cyclin E causes the G1 to S transition through phosphorylation of the tumor suppressor Rb, releasing the transcription factor E2F-1. Other pathways acting through Rac, Ras and Rho also regulate the G1 to S transition. Ras regulates cyclin D1 expression to affect the G1 to S transition. Transforming forms of Ras or Raf induce cyclin D1 expression and cause early entry into S phase. Signaling from Ras to Raf to MEK to ERKs induces Cyclin D1 expression, allowing Cyclin D1 to complex with Cdk4 and Cdk6 and phosphorylate Rb. Rac-1 and PAK appear to induce Cyclin D1 expression and induce the G1 to S transition primarily through activation of NF-kB to activate the Cyclin D1 promoter. Rho activates cdk2 and also inhibits p21 and p27 to induce cyclin D1 and stimulate the G1 to S transition. Rho represses p21 expression to block p21 induction by Ras and to allow Ras induced progression from G1 to S. Cells that lack p21 do not require Rho for Ras to induce cell cycle progression from G1 to S phase. The cooperative action of Ras, Rac and Rho to induce Cyclin D1 expression is a key component of oncogenic transformation.More...
The epidermal growth factor (EGF) peptide induces cellular p......
The epidermal growth factor (EGF) peptide induces cellular proliferation through the EGF receptor, which has a tyrosine kinase cytoplasmic domain, a single transmembrane domain and an extracellular domain involved in EGF binding and receptor dimerization. Inhibitors of the EGF receptor are being pursued as potential cancer therapies and EGF may stimulate wound healing. Mutation of the EGF receptor has been associated with cancer in humans. The proliferative effects of EGF are signaled through several pathways. Binding of EGF results in EGF receptor dimerization, autophosphorylation of the receptor, and tyrosine phosphorylation of other proteins. The EGF receptor activates ras and the MAP kinase pathway, ultimately causing phosphorylation of transcription factors such as c-Fos to create AP-1 and ELK-1 that contribute to proliferation. Activation of STAT-1 and STAT-3 transcription factors by JAK kinases in response to EGF contributes to proliferative signaling. Phosphatidylinositol signaling and calcium release induced by EGF activate protein kinase C, another component of EGF signaling. Crosstalk of EGF signaling with other pathways make the EGF receptor a junction point between signaling systems.More...
Erk and PI-3 Kinase Are Necessary for Collagen Binding in Corneal Epithelia
Activation of the MAPK kinase pathway has been identified as......
Activation of the MAPK kinase pathway has been identified as a mechanism that integrins use to regulate gene expression leading to cell shape changes during cell spreading or migration Epithelial cells respond to extracellular matrix (ECM) cause integrin-mediated FAK phosphorylation that in turn phosphorylates the surrounding proteins (paxillin, Fyn/shc, and src) and leads to signal amplification. FAK also binds PI-3 kinase and is upstream of the MAP kinase pathway. When MAPkinase or PI-3 kinase was inhibited, actin reorganization was blocked. Src phosphorylates p190RhoGAP, inactivating its GAP function that may allow RhoGTP to stay active longer, promoting further signal amplification. Activated RhoGTP binds to downstream kinases such as Rho-associated coiled coil-containing protein kinase (p160ROCK) and p140 diaphanous (p140Dia) to increase actin polymerization and contraction. Actin reorganization assists integrin clustering, allowing more ECM binding that increase FAK phosphorylation and other signal transduction events.More...
Axons extend significant distances to innervate target tissu......
Axons extend significant distances to innervate target tissues. At the site of innervation, target tissues release neurotrophins including NGF, BDNF and neurotrophin-3 that stimulate the survival of the associated neuron. Local signaling by activated Trk receptors at the synaptic terminus mediates some presynaptic neuronal responses to neurotrophins. Map kinase pathways activated by Trk receptor activate Erk1 and Erk2 at the terminus stimulating axonal growth, and PI3K activates AKT in the terminus as well. Activation of these kinases does not propagate a signal to the cell body though and does not induce a transcriptional response. This local signaling at the terminus or local signaling at the cell body appears distinct from the signaling pathway that transduces the survival signal from the target tissue. Retrograde axonal transport plays an essential role in neuronal survival induced by neurotrophins released at the target tissue. Failure of retrograde neurotrophin signaling may play a role in neurodegenerative conditions. The neuronal survival signal is initiated by binding of neurotrophins to Trk receptors in the presynaptic membrane, then travels back along the axon to the neuronal cell body. To transmit the signal back along the axon, activated Trk receptors are internalized through receptor-mediated endocytosis and receptor containing vesicles then rapidly travel back to the cell body along axonal microtubules. Several reports indicate that neurotrophins remain receptor-bound during the retrograde axonal transport to the cell body, but recently it was reported that retrograde transport of NGF was not required to induce neuronal survival. Once in the cell body, Trk receptors activate multiple pathways. A key pathway activated by Trk after retrograde transport involves Erk5, also called BMK1. Trk activates Mek5, which activates Erk5, inducing phosphorylation of the CREB and Mef2 transcription factors. Erk5 does not directly phosphorylate CREB, but translocates into the nucleus and phosphorylates the kinase Rsk, which phosphorylates CREB in turn. Both CREB and Mef2 induce a transcriptional program that contributes to neuronal survival. Local activation of Erk5 on the cell body does not appear to induce the same signaling system or neuronal survival, indicating that the retrograde transport is an essential part of the survival signaling system. Also, activation of Erk1 and Erk2 in the cell body can induce CREB activation and neuronal survival, but these kinases are not activated by neurotrophins applied to the axonal terminus. Another pathway activated by retrograde neurotrophin signaling though Erk5 is PI3 Kinase.More...
Physical interactions between intergrin alpha4beta1 heterodi......
Physical interactions between intergrin alpha4beta1 heterodimer expressed on B cells and counter receptors on stroma cells are key mediators of the survival of normal and malignant B cells. Recent data indicate that integrin stimulation increases FBI-1, XIAP, surviving, and CCT4 expression but inhibits Requiem, c-Fos, and caspase 3 and 7 induction.More...
IL-7 is a key cytokine in the immune system, essential for n......
IL-7 is a key cytokine in the immune system, essential for normal development of B cells and T cells. Mice with the IL-7 receptor deleted lack B and T cells. Some humans with SCID (severe combined immunodeficiency disease) also have mutation of their IL-7 receptor gene leading to an absence of T cells and greatly impaired B cell production. The IL-7 receptor includes two polypeptides, a gamma chain and an alpha chain. The alpha-chain is unique to the IL-7 receptor while several other cytokines use the same gamma receptor chain as IL-7, including IL-2, IL-4, IL-9, IL-15 and IL-21. Binding of IL-7 to the alpha chain leads to dimerization of the alpha and gamma chains. JAK3 associated with the gamma chain tyrosine phosphorylates the alpha chain after dimerization. The importance of JAK3 in IL-7 signaling is supported by the similarity of the immune defects in JAK3 knockout mice and IL-7 knockout mice. The phosphorylated alpha chain serves as the site for recruiting other signaling molecules to the complex to be phosphorylated and activated, including STAT5, src kinases, PI3 kinase, Pyk2 and Bcl2 proteins. Some targets of IL-7 signaling contribute to cellular survival, including Bcl2 and Pyk2. Other targets contribute to cellular proliferation, including PI3 kinase, src family kinases (lck and fyn) and STAT5. The transcription factor STAT5 contributes to activation of multiple different downstream genes in B and T cells and may contribute to VDJ recombination through alteration of chromatin structure. The cell survival and cell proliferation signals induced by IL-7 combine to induce normal B and T cell development.More...
NFAT and Hypertrophy of the heart (Transcription in the broken heart)
Hypertrophy associated with both hypertension and obstructio......
Hypertrophy associated with both hypertension and obstruction to ventricular outflow leads to pathologic cardiac growth and it is associated with increase morbidity and mortality. Symptomatic ventricular disease takes a growing toll on the health of nations. As other cardiovascular diseases such as stroke and myocardial infraction are in decline as causes of mortality, the heart failure problem becomes increasingly urgent. Congenital heart defects occur in 1% of live births and fetal heart malformations are implicated in many pregnancies that end in still-birth or spontaneous abortion. The current paradigm suggests that the heart adapts to excess of hemodynamic loading by compensatory hypertrophy, which under condition of persistent stress, over time evolves into dysfunction and myocardial failure. There is considerable evidence that direct effects of increased mechanical stress are sensed within the ventricular wall and that signals critical for the generation of growth responses. Despite compelling statistics we still do not understand biochemically why heart defects are so prevalent. A single transcriptional regulator initially associated with the activation of the T-cellsMore...
Rac-1 is a small G-protein in the Rho family that regulates ......
Rac-1 is a small G-protein in the Rho family that regulates cell motility in response to extracellular signals. Several changes in cytoskeletal structure and other aspects of cell structure are involved in cell motility. Rac-1 is activated by GEF factors, and repressed by GAPs. GEFs are guanine nucleotide exchange factors, including Trio and Vav. Sos-1 is involved in Ras signaling and also acts as a GEF for Rac to transduce signals between Ras and Rac. SWAP-70 is a Rac GEF that binds IP3 and transduces signals from tyrosine kinases to Rac to modulate the cytoskeleton and cause membrane ruffling. GAPs are GTPase- activating proteins. Rac stimulates the formation of actin-based structures such as filopodia and lamellopodia, while GAPs such as chimerin oppose the formation of these Rac dependent structures. Several different factors downstream of Rac act on cytoskeletal structure and other aspects of cell motility. Pak1 provides a direct link from Rac to cell motility through phosphorylation of the myosin light chain. Pak1 also phosphorylates and activates LIM kinase, which phosphorylates cofilin as one target. Cofilin stimulates actin depolymerization and changes in cell structure, and phosphorylation of cofilin by LIM kinase represses its activity. In neurons, Rac acts through the protein kinase cdk5 and p35 to phosphorylate and downregulate Pak1, increasing neuronal migration. Rac-1 also interacts with several other factors to regulate a variety of processes. Interaction of Por1 with Rac-1 is involved in membrane ruffling. WAVE is a member of the WASP family of proteins that regulate actin organization and that is involved in Rac signaling to cause membrane ruffling. Interaction of Rac-1 with MEKK1 integrates Rac signaling with pathways signaling through map kinases.More...
Mechanism of Gene Regulation by Peroxisome Proliferators via PPARa(alpha)
The most recognized mechanism by which peroxisome proliferat......
The most recognized mechanism by which peroxisome proliferators regulated gene expresssion is through a PPAR/RXR heterodimeric complex binding to a peroxisome proliferator-response element (PPRE) (classical mechanism). However, there are the possibility of several variations on this theme: 1). The peroxisome proliferator interacts with PPAR that preexists as a DNA complex with associated corepressors proteins. The interaction with ligand causes release of the corepressor and association with a coactivator, resulting in the classical mechanism. 2). The peroxisome proliferator interacts with PPAR as a soluble member of the nucleus. The binding of ligand results in RXR heterodimerization, DNA binding and coactivator recruitment. 3). In this scenario, PPAR exists in the cytosol, perhaps complexed to heat shock protein 90 and/or other chaperones. Binding of peroxisome proliferator causes a conformational change and translocation into the nucleus. Scenarios 4 and 5 require regulation of gene expression via non-classical mechanisms: 4). PPAR is capable of interacting with, and forming DNA binding heterodimers with, several nuclear receptors including the thyroid hormone receptor. The binding site for this non-RXR heterodimer need not be the classic DR-1 motif found in the PPRE. 5). PPAR may participate in the regulation of gene expression witout binding to DNA. By association with transcription factors such as c-jun or p65, PPAR diminishes the ability of AP1 or NFB to bind to their cognate DNA sequences, respectively. Also shown in this scheme are two means to modify the peroxisome proliferator response. Most importantly, growth factor signaling has a pronounced affect on PPAR via post-translational modification. PPAR is a phosphoprotein and its activity is affected by insulin. Several kinase pathways affects PPARa's activity, although the specific kinases and phosphorylation sites have not been conclusively determined.More...
CTCF is central to signaling pathways in immature B cells el......
CTCF is central to signaling pathways in immature B cells elicited by cross-linking the Ig BCR and stimulation with TGF. Both stimuli result in induction of cell cycle arrest and apoptosis. BCR ligation stimulates a transient induction of MYC that leads to high level CTCF expression and feedback suppression of MYC transcription. BCR ligation also activates PTEN opposing PI3K activation of MYC. Pharmacologic inactivation of PI3K or mTOR/FRAP results in suppression of S6K resulting in activation of CTCF and suppression of MYC. CTCF activation induces transcriptional activation of p19ARF, with its downstream consequences, and of p27. Growth arrest is occasioned by co-expression of p21 and p27 and inhibition of MYC. CTCF, is bona fide multivalent DNA-sequence binder which specificity is mediated by different sets of zinc fingers (ZFs). For three different DNA target sites, particular groups of ZFs which cannot be deleted from the 11 ZF domain without loosing binding to a given site, are shown by a rainbow in the box on the left.More...
Myocardial infarction damages heart tissue both during the i......
Myocardial infarction damages heart tissue both during the initial ischemia and the subsequent reperfusion of tissues with oxygen. Corticosteroids can protect cardiac tissue from damage following a heart attack, but the mechanisms by which corticosteroids are cardioprotective have not been clear and negative side effects such as reduced wound healing may result from their use. Corticosteroids exert a variety of actions through binding to the glucocorticoid receptor (GR), a member of the steroid hormone receptor gene family. GR acts as a ligand-dependent transcription factor, but some of the cardioprotective effects mediated by GR-bound corticosteroids are non-transcriptional in nature. Glucocorticoids are commonly used as anti-inflammatory drugs in a variety of conditions, and some of their effects in the heart result from inhibition of the inflammatory response of heart tissue to ischemia and reperfusion. NF-kB is a transcription factor involved in signaling by inflammatory factors such as TNF, and is repressed by glucocorticoids. Annexin-1 is a calcium-dependent phospholipid binding protein whose expression is induced by corticosteroids and inhibits the infiltration of neutrophils into tissue, blocking reperfusion-induced inflammatory heart damage. A non-transcriptional cardioprotective effect of glucocorticoids is activation of NO production by endothelial nitric oxide synthase (eNOS). Glucocorticoids activate eNOS through activation of PI3 kinase and AKT and increased NO produced by eNOS can diffuse into surrounding tissues to prevent clotting and cause vasodilation. The beta-2 adrenergic receptor can also activate PI3 kinase and may synergize with glucocorticoids in this pathway. The atrial natriuretic factor (ANF) is a peptide secreted by the atrial wall in response to increased atrial pressure such as occurs during cardiac failure and to be decreased by myocardial infarction. Glucocorticoids increase the secretion of ANF by acting at the transcriptional level to increase expression of the pro-ANF peptide, perhaps inducing increased water excretion in the kidneys to reduce blood volume and reduce atrial pressure. The exploration of glucorticoid responses may allow the identification of compounds that retain the cardioprotective activities but do not inhibit wound healing. Alternative mechanisms of eNOS activation may also provide a route to identify cardioprotective drugs.More...
Control of skeletal myogenesis by HDAC and calcium/calmodulin-dependent kinase (CaMK)
The differentiation of muscle cells is transcriptionally reg......
The differentiation of muscle cells is transcriptionally regulated, in part by the myocyte enhancer factor-2, MEF2. During myogenesis MEF2 binds to MyoD and other basic helix-loop-helix factors to activate transcription of genes involved in muscle cell differentiation. Transcriptional activation by MEF2 is blocked by interaction with HDAC5 and other histone deacetylases. In undifferentiated myoblasts, HDAC5 is present in the nucleus where it binds to MEF2 to block activation of muscle genes. When activated by IGF-1 signaling, CaM kinase phosphorylates HDAC proteins, causing them to be exported from the nucleus, releasing the block on MEF2 transcriptional activation and allowing differentiation to proceed. Transcription cofactors also interact with MEF2 to contribute to gene regulation and myogenesis. The transcriptional regulator NFAT, for example, acts as a cofactor for MEF2 when calcium and calcineurin signaling activate it. There are four members of the Mef2 gene family, Mef2a-2d. Mef2a is expressed in brain, heart and skeletal muscle. Mef2c is involved in myogenesis in cardiac and skeletal muscle. Mef2d is widely expressed, and may be involved in the regulation of T cell function as well as muscle. Several factors regulate Mef2 transcription factors, including Map kinases and histone deacetylase (HDAC) enzymes. Mef2 is phosphorylated by p38 map kinase, and phosphorylation of Mef2c by p38 contributes to skeletal muscle differentiation. BMK-1 (also called Erk5) is another member of the Map kinase family that regulates the activity of Mef2 family members and is unique in that it appears itself to possess a transcriptional activation domain and act as a transcriptional coactivator. Mekk3 disruption prevented normal cardiovascular development in mice and appears to signal through p38 and Mef2c in normal cardiovascular development.More...
A demonstrated means to increase lifespan in a wide range of......
A demonstrated means to increase lifespan in a wide range of organisms is through the restriction of caloric intake. Reducing the consumption of calories increases the lifespan of many different organisms, including mice. Although caloric restriction has not been demonstrated experimentally to increase human lifespan, short-term changes in physiological measures like insulin responsiveness have been observed. Caloric restriction not only increases lifespan, but decreases age-related deterioration of systems and physiological responses, reducing age related diseases like cancer and neurodegenerative disease. Caloric restriction in animals reduces the levels of plasma glucose and insulin and reduces inflammatory responses and may reduce oxidative stress through reduced oxidative metabolism, further contributing to the health benefits of reduced calorie intake. The reduction in inflammation may be related to reduces plasma glucose and in humans could reduce an inflammation connection to cancer, heart disease, and Alzheimers disease. Genetic analysis has indicated several genes that influence lifespan, particularly those that alter pituitary development, reduce growth hormone secretion, reduce food intake, and reduce apoptosis (p66 Shc). All of these appear to converge on an IGF-1 receptor pathway and to reproduce many of the effects of caloric restriction. Although dwarf mice with defective growth hormone or IGF-1 signaling also have significantly increased lifespan, humans with defects in growth hormone signaling tend to develop diseases that shorten their lifespan. One of the downstream targets of IGF-1 signaling is to repress stress resistance proteins including antioxidant enzymes like superoxide dismutase, and heat shock proteins, so a reduction in IGF signaling may extend lifespan by increasing the expression of stress resistance genes. The link between caloric restriction and IGF signaling may be that a reduction in food intake reduces the expression of IGF-1, increasing the expression of stress resistance proteins. In addition to the IGF-1R mutation, p66 Shc mutation also increases lifespan without significant aberration of other systems. Shc is a target of IGF-1R phosphorylation, and a major inducer of cellular responses to oxidative stress. Shc increases levels of intracellular reactive oxygen species, repressing the forkhead factor FKHRL1. Alhtough FKHRL1 is also involved in apoptosis, in the absence of Shc, FKHRL1 mediates increased resistance to oxidative stress. Exploration of the genes that induce longevity in animals models may enlighten the role of these genes in human disease and lifespan.More...
Vascular endothelial growth factor (VEGF) plays a key role i......
Vascular endothelial growth factor (VEGF) plays a key role in physiological blood vessel formation and pathological angiogenesis such as tumor growth and ischemic diseases. Hypoxia is a potent inducer of VEGF in vitro. The increase in secreted biologically active VEGF protein from cells exposed to hypoxia is partly because of an increased transcription rate, mediated by binding of hypoxia-inducible factor-1 (HIF1) to a hypoxia responsive element in the 5'-flanking region of the VEGF gene. bHLH-PAS transcription factor that interacts with the Ah receptor nuclear translocator (Arnt), and its predicted amino acid sequence exhibits significant similarity to the hypoxia-inducible factor 1alpha (HIF1a) product. HLF mRNA expression is closely correlated with that of VEGF mRNA.. The high expression level of HLF mRNA in the O2 delivery system of developing embryos and adult organs suggests that in a normoxic state, HLF regulates gene expression of VEGF, various glycolytic enzymes, and others driven by the HRE sequence, and may be involved in development of blood vessels and the tubular system of lung. VEGF expression is dramatically induced by hypoxia due in large part to an increase in the stability of its mRNA. HuR binds with high affinity and specificity to the VRS element that regulates VEGF mRNA stability by hypoxia. In addition, an internal ribosome entry site (IRES) ensures efficient translation of VEGF mRNA even under hypoxia. The VHL tumor suppressor (von Hippel-Lindau) regulates also VEGF expression at a post-transcriptional level. The secreted VEGF is a major angiogenic factor that regulates multiple endothelial cell functions, including mitogenesis. Cellular and circulating levels of VEGF are elevated in hematologic malignancies and are adversely associated with prognosis. Angiogenesis is a very complex, tightly regulated, multistep process, the targeting of which may well prove useful in the creation of novel therapeutic agents. Current approaches being investigated include the inhibition of angiogenesis stimulants (e.g., VEGF), or their receptors, blockade of endothelial cell activation, inhibition of matrix metalloproteinases, and inhibition of tumor vasculature. Preclinical, phase I, and phase II studies of both monoclonal antibodies to VEGF and blockers of the VEGF receptor tyrosine kinase pathway indicate that these agents are safe and offer potential clinical utility in patients with hematologic malignancies.More...
Inactivation of Gsk3 by AKT causes accumulation of b-catenin in Alveolar Macrophages
Lipopolysaccharide. One of the key actions of AKT is to bloc......
Lipopolysaccharide. One of the key actions of AKT is to block apoptosis. AKT phosphorylation of NF-kB promotes the survival and activation of macrophages responding to LPS. Another substrate of AKT is the protein kinase Gsk3-beta. AKT phosphorylates and deactivates Gsk3-beta. Non-phosphorylated Gsk3-beta is active and phosphorylates beta-catenin, leading to its degradation in the ubiquitin dependent proteosome pathway. Stimulation by LPS causes the accumulation of beta-catenin in the nucleus and the activation of genes in concert with the transcription factor LEF1. This pathway is probably not restricted to alveolar pathway, but leads to the activation of beta-catenin dependent genes by LPS in other cells as well. Other pathways regulate this pathway also, such as the modulation of PI3 kinase activity by ceramide, and the inhibition of Gsk3-beta activity by the Wnt/frizzled/disheveled (DSH) pathway.More...
The Co-Stimulatory Signal During T-cell Activation
For a T cell to be activated by a specific antigen, the T ce......
For a T cell to be activated by a specific antigen, the T cell receptor must recognize complexes of MHCI with the antigen on the surface of an antigen-presenting cell. T cells and the T cell receptor complex do not respond to antigen in solution, but even for the specific antigen they only respond to antigen-MHC-1 complexes on the cell surface. This interaction is necessary for T cell activation, but it is not sufficient. T cell activation also requires a co-stimulatory signal involving interaction of CD28 on the T cell with CD80 or CD86 (B7 family genes) on the antigen-presenting cell. CD28 activates a signal transduction pathway acting through PI-3K, Lck and Grb-2/ITK to provide its co-stimulatory signal for T cell activation. Another means to control T cell activation is by expressing factors that down-regulate T cell activation. Signaling by activated T cell receptors induces expression of CTLA-4, a receptor that opposes T cell activation. CTLA-4 has a higher affinity than CD28 for B7 proteins, terminating T cell activation. ICOS is a protein related to CD28 that is only expressed on activated T cells, and that provides another important co-stimulatory signal. The requirement for co-stimulatory signals provides additional control mechanisms that prevent inappropriate and hazardous T cell activation.More...
The Fc Epsilon Receptor 1 signaling pathway in mast cells us......
The Fc Epsilon Receptor 1 signaling pathway in mast cells uses multiple core signal path to achieve its necessary ends. Through the BTK protein and PKC Mast cells are able to degranulate, through the PKC and MAPK paths the cells are able to alter cytokine expression and arachidonic acid release.More...
Ras activates many signaling cascades. Here we illustrate so......
Ras activates many signaling cascades. Here we illustrate some of the well-characterized cascades in a generic compilation of effector molecules. The effectors mediate Ras stimulation to a diverse set of cellular signals. Many of these signals are interpreted differently depending on the cell type or microenvironment receiving the stimulus. Not all of these effectors are activated in any given cell type. The primary method of activation is to promote the translocation of the molecule to the plasma membrane where additional interactions lead to the activation of the molecule. RalGDS is a Guanine Exchange Factor (GEF) for Ral but also has other independent functions. RalGDS activates RalA/B-related small GTPases. RalBP1 is a GTPase activating protein that leads to the inhibition of the Rac and CDC42 GTPases. Ral can also interact with phospholipase D1 (PLD1) that can also be activated by RhoA. Ras stimulation of the lipid kinase activity of PI3K occurs through an interaction with the p110 catalytic subunit. PI3K phosphorylates the D3 position of phosphatidylinositides. In this example Pip2 is converted to PIP3. PIP3 stimulates the AKT/PKB kinase and several of the Rac-GEFs such as Sos1 AND Vav. AKT activation inhibits apoptosis by inhibiting the actions of Bad, Caspase9 and AFX. AKT further hinders apoptosis by phosphorylating the IkB repressor of NFkB. Stimulus of Rac causes among other things the activation of NFkB. Ras also stimulates the mitogen-activated kinases ERK1/2 via the Raf1 cascade. The Erk kinases translocate to the nucleus where they phosphorylate various transcription factors such as ELK1More...
Maintaining the integrity of the gastrointestinal tract desp......
Maintaining the integrity of the gastrointestinal tract despite the continual presence of microbial flora and injurious agents is essential. Epithelial repair requires restitution and regeneration. During restitution, epithelial cells spread and migrate across the basement membrane to re-establish surface-cell continuity, a process that is independent of cell proliferation. Epithelial continuity depends on a family of small abundant secreted proteins, the trefoil factors (TFFs). The trefoil factor (TFF) family comprises the gastric peptides pS2/TFF1 and spasmolytic peptide (SP)/TFF2, and the intestinal trefoil factor (ITF)/TFF3. Their fundamental action is to promote epithelial-cell restitution within the gastrointestinal tract. TFFs are abundantly secreted onto the mucosal surface by mucus-secreting cells. Their expression is rapidly and coordinately upregulated at the margins of mucosal injury. Secreted TFF acts on adjacent mucosal cell populations either extracellularly (augmenting barrier function) or intracellularly (transcriptional and signalling events). TFF response elements in TFF gene promoters allow increases in TFF expression through auto-induction and cross-induction of other TFFs, in addition to mucin expression and possibly tumor suppression. Cell migration is the result of integrated disruption of cellcell and cellsubstratum adhesion and prevention of apoptosis through cell detachment. Epithelial movement therefore requires integration of motogenic and cell-survival signals. This is achieved by activation of several intracellular signalling pathways that converge on ERK/MAPK and possibly NF-B activation. Serine phosphorylation of the extracellular signal-regulated kinases (ERKs)/mitogen-activated protein kinases (MAPKs) 1 and 2 is central to trefoil factor -mediated signalling, lying downstream of EGFR activation and possibly FAK activation (through recruitment of GRB2 and SOS). Cell migration might result from cooperation between ERK/MAPKs and Rho proteins, FAK activation, beta-integrin clustering and beta-catenin activation. Abrogation of cell death has been shown to require both PI3K activation and ERK/MAPK activation; the former operates through serine/threonine phosphorylation of AKT/protein kinase B, serine phosphorylation of BAD (BCL-2 agonist of cell death) and inhibition of mitochondrial cytochrome c release and formation of the apoptosome (APAF1, caspase-9 (CASP9) and cytochrome c (CYT-c). Translocation of phosphorylated ERK/MAPK to the nucleus leads to amplification and de-restriction of TFF expression to ensure sustained action.More...
The appropriate signaling through the insulin pathway is cri......
The appropriate signaling through the insulin pathway is critical for the regulation of glucose levels and the avoidance of diabetes. Insulin forms a complex with the Insulin Receptor (IR) and b chains to form the active signaling complex. Through recruitment of adaptor molecules and the activation of RAS, the activated IR can cause transcriptional activation.More...
Nerve growth factor (NGF) is a neurotrophic factor that stim......
Nerve growth factor (NGF) is a neurotrophic factor that stimulates neuronal survival and growth through TrkA, a member of the trk family of tyrosine kinase receptors that also includes TrkB and TrkC. Some NGF responses are also mediated or modified by p75LNTR, a low affinity neurotrophin receptor. Binding of NGF to TrkA stimulates neuronal survival, and also proliferation. Pathways coupled to these responses are linked to TrkA through association of signaling factors with specific amino acids in the TrkA cytoplasmic domain. Cell survival through inhibition of apoptosis is signaled through activation of PI3-kinase and AKT. Ras-mediated signaling and phospholipase C both activate the MAP kinase pathway to stimulate proliferation.More...
Cyclin-dependent kinase inhibitor-2A (CDKN2A) goes by the co......
Cyclin-dependent kinase inhibitor-2A (CDKN2A) goes by the colloquial designation p16, which is sometimes referred to as p16(INK4). The alpha transcript of CDKN2A has been shown to encode p16(INK4a), a recognized tumor suppressor that induces a G1 cell cycle arrest by inhibiting the phosphorylation of the RB protein by the cyclin-dependent kinases CDK4 and CDK6. The beta transcript of CDKN2A encodes p14(ARF). The predicted 132-amino acid p14(ARF) is shorter than the corresponding mouse protein, p19(ARF), and the 2 proteins share only 50% identity. However, both proteins have the ability to elicit a p53 response, manifest in the increased expression of both CDKN1A and MDM2, and resulting in a distinctive cell cycle arrest in both the G1 and G2/M phases. Two unrelated proteins encoded by the INK4A-ARF locus function in tumor suppression. ARF binds to MDM2 and promotes the rapid degradation of MDM2. This interaction is mediated by the E1-beta-encoded N-terminal domain of ARF and a C-terminal region of MDM2. ARF-promoted MDM2 degradation is associated with MDM2 modification and concurrent p53 stabilization and accumulation. The p19(Arf) tumor suppressor inhibits production of ribosomal RNA, retarding processing of 47/45S and 32S precursors. These effects correlate with but do not strictly depend upon inhibition of rRNA biosynthesis or cell cycle arrest, are not mimicked by p53, and require neither p53 nor Mdm2. Arf mutants lacking conserved amino acid residues 2-14 do not block rRNA synthesis and processing or inhibit cell proliferation. Evolution may have linked a primordial nucleolar Arf function to Mdm2 and p53, creating a more efficient checkpoint-signaling pathway for coordinating ribosomal biogenesis and cell cycle progression.More...
Many cell-surface receptors induce production of second mess......
Many cell-surface receptors induce production of second messengers like PIP3, phosphatidylinositol 3,4,5-trisphosphate, that convey signals to the cytoplasm from the cell surface. PIP3 signals activates the kinase PDK1, 3-phosphoinositide-dependent protein kinase-1, which in turn activates the kinase AKT, also known as protein kinase B. Proteins phosphorylated by activated AKT promote cell survival. Phosphorylation of Ikappa-B kinase leads to activation of the transcription factor NF-kB to oppose apoptosis. Bad is a protein in the Bcl-2 gene family that opposes Bcl-2 to induce apoptosis. Phosphorylation of Bad by AKT blocks anti-apoptotic activity to promote cell survival. Similarly, phosphorylation of the protease caspase 9 or forkhead transcription factors by AKT block the induction of apoptosis by these factors. AKT promotes cell survival and opposes apoptosis by a variety of routes.More...
Skeletal muscle hypertrophy is regulated via AKT/mTOR pathway
Skeletal muscle atrophies with disuse while with increased u......
Skeletal muscle atrophies with disuse while with increased use and increased load skeletal muscle exhibits hypertrophy, with an increase in the size of existing muscle fibers. One signaling pathway involved in regulating skeletal muscle atrophy and hypertrophy is the AKT/mTOR pathway. The mTOR pathway activity increases in response to muscle activity during hypertrophy and decreases in activity during atrophy. Blocking this pathway genetically or with the mTOR inhibitor rapamycin blocks hypertrophy and genetic activation of the pathway induces hypertrophy. One agent that promotes muscle hypertrophy is the growth factor IGF-1. IGF-1 activates AKT, GSK-3beta and mTOR to promote hypertrophy. In contrast, the calcineurin pathway is not involved in hypertrophy and is down-regulated by agents such as IGF-1 that promote hypertrophy. Calcineurin may modulate other aspects of muscle function such as the development of slow muscle fibers through transcriptional regulation. These pathways lead to regulation of protein translation, with increased translation apparently acting as a key regulatory point in skeletal muscle hypertrophy. Agents such as IGF-1 that stimulate skeletal muscle hypertrophy may provide treatments for muscle atrophy and wasting.More...
PTEN is a tumor suppressor gene. Recombinant PTEN is capable......
PTEN is a tumor suppressor gene. Recombinant PTEN is capable of dephosphorylating phosphatidylinositol 3,4,5-triphosphate, the product of phosphatidylinositol 3 -kinase. Many of the cancer-related mutations have been mapped to the phosphatase catalytic domain, it has been suggested that the phosphatase activity of PTEN is required for its tumor suppressor function. The activation of PKB/AKT is regulated in a complex manner via phosphorylation of AKT on Thr308 and Ser473 by PDK1 and ILK(integrin-linked kinase) respectively. Inactivation of PTEN will constitutively activate PKB/AKT pathway. In addition to its role in regulating the PI 3-K/AKT cell survival pathway, PTEN also inhibits growth factor-induced Shc phosphorylation and suppresses the mitogen-activated protein (MAP) kinase signaling pathway. PTEN also interact with FAK, a key molecule implicated in integrin signaling pathways, and it directly dephosphorylates tyrosine-phosphorylated FAK. PTEN down-regulation of p130CAS through FAK results in inhibition of cell migration and spreading.More...
CXCR4 is a chemokine receptor in the GPCR gene family, and i......
CXCR4 is a chemokine receptor in the GPCR gene family, and is expressed by cells in the immune system and the central nervous system. In response to binding its ligand SDF-1 (stromal cell-derived factor-1), CXCR4 triggers the migration and recruitment of immune cells. This ligand-receptor pair may also play a role in development of the nervous system. In addition to acting as a chemokine receptor, CXCR4 is a co-receptor for entry of HIV into T cells and ligands of CXCR4, including SDF-1 may help to block HIV infection. Early in the infection of an individual, HIV viruses often are tropic for the CCR5 coreceptor that provides for macrophage entry, then later in infection are tropic for CXCR4 and T cell entry. Viruses that are tropic for CXCR4 are generally syncitium forming, causing T cells to aggregate and be destroyed at a rapid rate. CXCR4 induces downstream signaling by several different pathways. As a GPCR, CXCR4 binding of SDF-1 activates G-protein mediated signaling, including downstream pathways such as ras, and PI3 kinase. PI3 kinase activated by SDF-1 and CXCR4 plays a role in lymphocyte chemotaxis in response to these signals. One endpoint of CXCR4 signaling is the activation of transcription factors such as AP-1 and chemokine regulated genes. JAK/STAT signaling pathways also appear to play a role in SDF-1/CXCR4 signaling. Delineation of the signaling mechanisms utilized by CXCR4 may assist in determining the role of CXCR4 in HIV infection and in the immune response.More...
The function of the pro-apoptotic molecule BAD is regulated ......
The function of the pro-apoptotic molecule BAD is regulated by phosphorylation of three sites (ser 112,136 and 155). Phosphorylation at these sites results in loss of the ability of BAD to heterodimerize with the survival proteins BCL-XL or BCL-2. Phosphorylated BAD binds to 14-3-3 and is sequestered in the cytoplasm. While ser-136 phosphorylation is concordant with the activation of Akt, Ser-112 phosphorylation requires activation of the Ras-MAPK pathway. BAD Ser 155 was found to be a major site of phosphorylation induced following stimulation by growth factors and prevented by protein kinase A inhibitors.More...
Thrombin signaling and protease-activated receptors
Thrombin is an extracellular protease that is involved in th......
Thrombin is an extracellular protease that is involved in the clotting of blood and inflammation through its action on platelets and endothelial cells in the vasculature and that plays a role in thrombosis and myocardial infarction. The protease activated receptors PAR1 and PAR4 are cellular targets of thrombin signaling and members of the G-protein coupled receptor gene family. Both of these receptors are cleaved in their N-terminus by thrombin, unmasking a portion of the receptor sequence that acts itself as a tethered peptide ligand that activates the receptor. The tethered ligand that activates PAR1 is SFLLRN and the tethered ligand that activates PAR4 is GYPGQV. Other members of the family include PAR2 which is activated by trypsin rather than thrombin and PAR3 which seems to play a role in the activation of other PARs but does not itself transduce a signal directly. Addition of peptide agonist exogenously in solution can also activate PAR1, PAR2 and PAR4. PAR1 activation may be involved in the dilation of arteries during inflammation through the action of thrombin on endothelial cells and in platelet activation by thrombin during clotting. PAR1 and PAR2 activation cause bronchodilation in airway and may protect against asthma. PAR 4 activation by thrombin activates platelets during clotting and mice lacking PAR4 have impaired clotting and platelets that do not respond to thrombin signaling. The action of thrombin on PAR1 and PAR4 on platelets and endothelial cells may also contribute to vascular permeability and inflammation. Activated PARs appear to couple primarily through Gq-mediated stimulation of inositol phosphate metabolism and intracellular calcium levels to activate platelets. PAR1 and PAR4 also appear to couple to multiple G-proteins and transduce signals through more than one G-protein mediated pathway in some circumstances. Signaling by PAR1 and PAR4 through Galpha12 pathways couples to Rho signaling and changes in cytoskeletal structure and cell shape. Gi activation does not appear necessary for platelet activation by PAR1 or PAR4, and platelet activation by these receptors requires an ADP signal perhaps acting through the platelet-associated purinergic receptor P2Y12. Gi-coupled signaling may play a role in mitogenic PAR signaling in some settings through Map kinase activation. Activation of Rho by PAR1 can induce cellular transformation through a Galpha12 mediated mechanism and sustained rho-dependent phosphorylation of the myosin light chain by PAR1 contributes to cytoskeletal changes and activation of platelets. Since the activation of PARs by protease cleavage is irreversible the primary mechanism for down-regulation of the PAR signaling cascade appears to be internalization and degradation of PAR receptors.More...
mTOR (mammalian target of rapamycin) appears to play a centr......
mTOR (mammalian target of rapamycin) appears to play a central role in signaling caused by nutrients and mitogens such as growth factors to regulate translation. The drug rapamycin acts on mammalian cells through the mTOR protein kinase, also known as FRAP. When bound to the immunophilin binding protein FKBP12, rapamycin inhibits mTOR kinase activity and has immunosuppressant activity. Rapamycin and the mTOR inhibitor CCI-779 are being tested as anti-cancer agents, acting to block mitogenic signaling. Recently, mTOR was also found to act as an ATP sensor to regulate cell growth. Upstream activation of PI 3 kinase activity that leads to oncogenic transformation can be blocked by inhibition of mTOR by rapamycin. Growth factor receptors first stimulate PI 3 kinase, and through inositol phosphates activate PDK-1 and AKT (protein kinase B). AKT phosphorylates mTOR. The phosphorylation of p70S6K and 4EBP by mTOR and the phosphorylation downstream of RPS6 and EIF-4B stimulate translational initiation and contribute to cell growth.More...
Platelet Derived Growth Factor (PDGF) plays a critical role ......
Platelet Derived Growth Factor (PDGF) plays a critical role in cellular proliferation and development. The biologically active form is a dimer formed from the A and B chains. PDGF is active to a differing degree depending on which dimer is formed (AA, AB, or BB). The PDGF Receptor (PDGFR) is also a dimer and can form from the combination of the alpha and beta chains in any order (alpha-alpha, alpha-beta, beta-beta). The PDGFR dimer is only formed after ligand binding so the alpha/beta composition of the receptor can be influenced by the form of PDGF that is present. Upon binding of ligand the PDGFR is tyrosine phosphorylated and leads to the phosphorylation of several other cellular proteins.More...
Insulin like growth factor 1 (IGF-1) and its receptor (IGF-1......
Insulin like growth factor 1 (IGF-1) and its receptor (IGF-1R) provide a potent proliferative signaling system that stimulates growth in many different cell types and blocks apoptosis. In vivo IGF-1 acts as an intermediate of many growth hormone responses, and may stimulate the growth of some types of cancer. IGF-1 also provides a mitogenic signal to act as a growth factor for many tissue culture cells. One component of IGF-1 mitogenic signaling is association of the receptor tyrosine kinase with Shc, Grb2, and Sos-1 to activate ras and the Map kinase cascade (raf, Mek, Erk). An endpoint of the Map kinase pathway is modification of transcription factor activity, such as activation of ELK transcription factors. Serum response factor (SRF) and AP-1 contribute to mitogenic signaling by many factors. Phosphorylation of IRS-1 and PI3 kinase activation are also involved in IGF-1 signaling, similar to insulin signaling.More...
Growth hormone plays a major role in regulating growth durin......
Growth hormone plays a major role in regulating growth during childhood and adolescence and also regulates metabolism. Defects in growth hormone signaling can result in dwarfism and decreases in growth hormone levels with age have been suggested to play a role in the reduced function of some physiological systems. Growth hormone signals a response in cells through the growth hormone receptor, a member of the cytokine receptor gene family. Growth hormone causes the receptor to dimerize, activating the JAK2 protein kinase. The activity of JAK2 mediates many of the downstream responses to growth hormone through phosphorylation of STAT transcription factors, MAP kinases, other kinase cascades and molecules involved in metabolism like IRS-1. Factors like SOCS and SHP-1 appear to play a role in the down regulation of signaling by growth hormone and cytokines.More...
eIF-4F and p70 S6 kinase play critical roles in translationa......
eIF-4F and p70 S6 kinase play critical roles in translational regulation. eIF-4F is a complex whose functions include the recognition of the mRNA 5' cap structure (eIF-4E), delivery of an RNA helicase to the 5' region (eIF-4A), bridging of the mRNA and the ribosome (eIF-4G), and circularization of the mRNA via interaction between eIF-4G and the poly(A) binding protein (PABP). Several stimuli, including growth factors and cytokines, regulate the eIF-4 complex and p70 S6 kinase by initiating a phosphorylation cascade involving the sequential activation of PI3-K, PDK1/2, Akt/PKB, and FRAP/mTOR kinase. FRAP/mTOR, together with an unidentified kinase, phosphorylates 4E-BP, leading to its dissociation from and activation of eIF-4E. MNK1/2, activated by ERK and p38 MAPK, phosphorylates and activates eIF-4E. Both processes contribute to the association of eIF-4E and eIF-4G to form the active eIF-4F complex, a necessary component of the 48S initiation complex. Phosphorylation of ribosomal protein S6 by p70 S6 kinase stimulates the translation of mRNAs with a 5' oligopyrimidine tract which typically encode components of the protein synthesis.More...
The hepatocyte growth factor receptor, also called c-Met, is......
The hepatocyte growth factor receptor, also called c-Met, is activated by HGF and stimulates proliferation of hepatocytes and other cell types. Mutated forms of the HGF receptor are associated with oncogenesis and metastasis, making the HGF receptor a potential therapeutic target for cancer drugs. Changes in cell motility, cell shape, adhesion, resistance to apoptosis, and anchorage independent growth all contribute to the role of c-Met in cancer. The HGF receptor is a heterodimer with tyrosine kinase activity and associates with a multiprotein complex involved in downstream signal transduction. The HGF receptor can associate with several different signaling systems, including src, Grb2/SOS, PI3 kinase and Gab1. One of the major substrates of the activated HGF receptor tyrosine kinase is the adaptor protein Gab1. Gab1 interacts with Crk and CrkL, two proteins with SH2 and SH3 protein interaction domains that couple to signaling further downstream. The actions of HGF on paxillin, DOCK180 and Rap1 mediated through GAB1 and other members of this complex alter cell motility. Regulation of Rho, Rac1 and CDC42 pathways in response to HGF all contribute to changes in cellular motility. Another target of the HGF receptor kinase is the focal adhesion kinase, FAK. The activation of FAK induces the formation of focal adhesions, a preliminary step to increased cell motility and tissue invasion by transformed cells, and paxillin phosphorylation may also alter cell adhesion of Met transformed cells. Src and p130cas are required for the role of FAK in HGF induced cellular transformation. HGF also blocks anoikis, the induction of apoptosis through suspension of cells, by acting on Erk and AKT kinases. This activity may contribute to anchorage independent growth of Met transformed cells. Signaling by integrins also plays a key role in the activation of tissue invasive growth by HGF. The alpha6beta4 integrin acts as a cofactor along with Meta to participate in cell growth and proliferation. In addition to altering cell adhesion, proliferation and cell motility, HGF alters cellular transcription through activation of STAT3. STAT3 activation by HGF is independent of PI3 kinase or map kinases and alters gene expression leading to changes in cellular shape. Although HGF is associated with cellular proliferation and survival, in rat liver epithelial cells HGF induces apoptosis and inhibits cell growth.More...
Multiple antiapoptotic pathways from IGF-1R signaling lead to BAD phosphorylation
IGF-1R, the type 1 receptor for insulin-like growth factor, ......
IGF-1R, the type 1 receptor for insulin-like growth factor, mediates cell survival and growth in response to its ligands IGF-1 and IGF-2. This tyrosine kinase receptor is widely expressed in many cell types and is a key mediator of growth. Overexpression or activation of IGF-1R may be involved in the proliferation of transformed cells, making inhibition of IGF-1R signaling a strategy for the development of cancer drugs. IGF-1R activates three signaling pathways that converge to phosphorylate BAD protein and block apoptosis. The first pathway activated by IGF-1R stimulates PI3-kinase and the AKT pathway to phosphorylate BAD and block apoptosis. A second pathway activated by IGF-1R involves ras mediated activation of the map kinase pathway to block apoptosis. A third pathway involves interaction of raf with mitochondria in response to IGF-1R activation. The convergence of these pathways to block apoptosis may enhance the IGF-1R response.More...
PI3Ks can be activated by a number of different receptors, i......
PI3Ks can be activated by a number of different receptors, including the TcR (T cell receptor), co-stimulatory receptors (CD28), cytokine receptors and chemokine receptors. However, the specific roles of PI3Ks downstream of these receptors vary. CD28 contains the YMNM consensus PI3K-binding motif, and PI3K recruitment by CD28 contributes to or complements TCR-dependent PI3K signaling. Activation of PI3K promotes PIP3 production at the plasma membrane and several potential target molecules for this phospholipid have been implicated in PI3K pathways downstream of the TcR and CD28. Of these targets, at least Vav and Akt have been implicated in CD28 costimulation of T cell activation. AKT/PKB connects PI3K to signaling pathways that promote cytokine transcription, survival, cell-cycle entry and growth.More...
Signaling via FGFRs is mediated via direct recruitment of si......
Signaling via FGFRs is mediated via direct recruitment of signaling proteins that bind to tyrosine auto-phosphorylation sites on the activated receptor and via closely linked docking proteins that become tyrosine phosphorylated in response to FGF-stimulation and form a complex with additional complement of signaling proteins. The activation loop in the catalytic domain of FGFR maintains the PTK domain in an inactive or low activity state. The activation-loop of FGFR1, for instance, contains two tyrosine residues that must be autophosphorylated for maintaining the catalytic domain in an active state. In the autoinhibited configuration, a kinase invariant proline residue at the C-terminal end of the activation loop interferes with substrate binding while allowing access to ATP in the nucleotidebinding site. Iin addition to the catalytic PTK core, the cytoplasmic domain of FGFR contains several regulatory sequences. The juxtamembrane domain of FGFRs is considerably longer than that of other receptor tyrosine kinases. This region contains a highly conserved sequence that serves as a binding site for the phosphotyrosine binding (PTB) domain of FRS2. A variety of signaling proteins are phosphorylated in response to FGF stimulation, including Shc, phospholipase-C gamma and FRS2 leading to stimulation of intracellular signaling pathways that control cell proliferation, cell differentiation, cell migration, cell survival and cell shape.More...
In naive T cells, CD28 costimulation enhances cell cycle ent......
In naive T cells, CD28 costimulation enhances cell cycle entry, potently stimulates expression of both the mitogenic lymphokine interleukin-2 (IL-2) and its receptor, and stimulates the activation of an antiapoptotic program. CD28 engages with one or both members of the B7 receptor family, B7.1 and B7.2. Upon ligand binding the tyrosines and proline-rich motifs present in the cytoplasmic tail of CD28 are phosphorylated by Lck or Fyn. Upon phosphorylation CD28 recruits and induces phosphorylation and activation of a more restricted set of intracellular signaling components that, together with those mobilized by the TCR, contribute to convert membrane-based biochemical and biophysical changes into gene activation events. Proteins like PI3K, Vav-1, Tec and Itk kinases, AKT, and the Dok-1 adaptor have been identified as elements of the CD28 signaling pathway by biochemical or genetic approaches or both.More...
The GPVI receptor is a complex of the GPVI protein with Fc e......
The GPVI receptor is a complex of the GPVI protein with Fc epsilon R1 gamma (FcR). The Src family kinases Fyn and Lyn constitutively associate with the GPVI-FcR complex in platelets and initiate platelet activation through phosphorylation of the immunoreceptor tyrosine-based activation motif (ITAM) in the FcR gamma chain, leading to binding and activation of the tyrosine kinase Syk. Downstream of Syk, a series of adapter molecules and effectors lead to platelet activation. The GPVI receptor signaling cascade is similar to that of T- and B-cell immune receptors, involving the formation of a signalosome composed of adapter and effector proteins. At the core of the T-cell receptor signalosome is the transmembrane adapter LAT and two cytosolic adapters SLP-76 and Gads. While LAT is essential for signalling to PLCgamma1 downstream of the T-cell receptor, the absence of LAT in platelets only impairs the activation of PLCgamma2, the response to collagen and GPVI receptor ligands remains sufficient to elicit a full aggregation response. In contrast, GPVI signalling is almost entirely abolished in the absence of SLP-76.More...
Platelet activation begins with the initial binding of adhes......
Platelet activation begins with the initial binding of adhesive ligands and of the excitatory platelet agonists. Intracellular signaling reactions will then enhance the adhesive and procoagulant properties of tethered platelets or of platelets circulating in the proximity. From the subendothelial adhesive substrates, collagen and possibly vWF are the main inducers of platelet activation. GP VI is the most potent collagen receptor initiating signal generation, an ability derived from its interaction with the FcRI gamma chain. This results in the phosphorylation of the gamma-chain by the non-receptor tyrosine kinases of the Src family. The phosphotyrosine motif is recognized by the SH2 domains of Syk, a tyrosine kinase. This association activates the Syk enzyme, leading to activation. Four PARs are identified, of which PARs 1 ,3 and 4 are substrates for thrombin. PAR 1 is the predominant thrombin receptor, PAR 3 is minimally expressed and PAR 4 is less responsive to thrombin. Platelets do not store PAR1, due to limited protein synthesis, they are capable of responding to thrombin only once. Platelet activation further results in the scramblase-mediated transport of negatively-charged phospholipids to the platelet surface. These phospholipids provide a catalytic surface (with the charge provided by phosphatidylserine and phosphatidylethanolamine) for the tenase complex (formed by the activated forms of the blood coagulation factors factor VIII and factor I).More...
The TCR is a multisubunit complex that consists of clonotypi......
The TCR is a multisubunit complex that consists of clonotypic alpha/beta chains noncovalently associated with the invariant CD3 delta/epsilon/gamma and TCR zeta chains. T cell activation by antigen presenting cells (APCs) results in the activation of protein tyrosine kinases (PTKs) that associate with CD3 and TCR zeta subunits and the co-receptor CD4. Members of the Src kinases (Lck), Syk kinases (ZAP-70), Tec (Itk) and Csk families of nonreceptor PTKs play a crucial role in T cell activation. Activation of PTKs following TCR engagement results in the recruitment and tyrosine phosphorylation of enzymes such as phospholipase C gamma1 and Vav as well as critical adaptor proteins such as LAT, SLP-76 and Gads. These proximal activation leads to reorganization of the cytoskeleton as well as transcription activation of multiple genes leading to T lymphocyte proliferation, differentiation and/or effector function.More...
Leukocyte extravasation is a rigorously controlled process t......
Leukocyte extravasation is a rigorously controlled process that guides white cell movement from the vascular lumen to sites of tissue inflammation. The powerful adhesive interactions that are required for leukocytes to withstand local flow at the vessel wall is a multistep process mediated by different adhesion molecules. Platelets adhered to injured vessel walls form strong adhesive substrates for leukocytes. For instance, the initial tethering and rolling of leukocytes over the site of injury are mediated by reversible binding of selectins to their cognate cell-surface glycoconjugates. Endothelial cells are tightly connected through various proteins, which regulate the organization of the junctional complex and bind to cytoskeletal proteins or cytoplasmic interaction partners that allow the transfer of intracellular signals. An important role for these junctional proteins in governing the transendothelial migration of leukocytes under normal or inflammatory conditions has been established. This pathway describes some of the key interactions that assist in the process of platelet and leukocyte interaction with the endothelium, in response to injury.More...
The epidermal growth factor receptor (EGFR) is one member of......
The epidermal growth factor receptor (EGFR) is one member of the ErbB family of transmembrane glycoprotein tyrosine receptor kinases (RTK). Binding of EGFR to its ligands leads to autophosphorylation of tyrosine residues on the receptor and subsequent activation of signal transduction pathways that are involved in regulating cellular proliferation, differentiation, and survival. Ligand binding with EGFR results in receptor homo- or heterodimerization at the cell surface. Trans-autophosphorylation of the EGFR tyrosine kinase domains occurs and the phosphorylated tyrosine kinase residues serve as binding sites for the recruitment of signal transducers and activators of intracellular substrates, such as Ras, which then stimulate an intracellular signal transduction cascade.More...
The alpha subunits of G12 and 13 bind RhoGEFs (guanine nucle......
The alpha subunits of G12 and 13 bind RhoGEFs (guanine nucleotide exchange factors, which activate small G proteins) providing a path to Rho-mediated cytoskeletal responses that are likely involved in shape change in platelets.More...
The Tie2/Tek receptor tyrosine kinase plays a pivotal role i......
The Tie2/Tek receptor tyrosine kinase plays a pivotal role in vascular and hematopoietic development and is expressed exclusively on endothelial lineage. Tie2 interacts with a group of ligands belonging to angiopoietin family and undergoes activation. These ligands show opposing actions, angiopoietin 1 and angiopoietin 4 stimulate the Tie2 phosphorylation and angiopoietin 2 inhibits it. Upon tyrosine phosphorylation Tie2 acts as a scaffold for various signaling proteins involved in different signal transduction cascades that can effect survival of endothelium and angiogenic sprout formation.More...
Hemostasis is a physiological response that culminates in th......
Hemostasis is a physiological response that culminates in the arrest of bleeding from an injured vessel. Acute vessel injury results in its constriction to reduce the loss of blood. Under normal conditions vascular endothelium supports vasodilation, inhibits platelet adhesion and activation, suppresses coagulation, enhances fibrin cleavage and is anti-inflammatory in character. Under acute vascular trauma vasoconstrictor mechanisms predominate and the endothelium becomes prothrombotic, procoagulatory and proinflammatory in nature. This is achieved by a reduction of endothelial dilating agents: adenosine, NO and prostacyclin; and the direct action of ADP, serotonin and thromboxane on vascular smooth muscle cells to elicit their contraction. The chief trigger for the change in endothelial function that leads to the formation of haemostatic thrombus is the loss of the endothelial cell barrier between blood and ECM components. Circulating platelets identify and discriminate areas of endothelial lesions; here, they adhere to the exposed sub endothelium. Their interaction with the various thrombogenic substrates and locally generated or released agonists results in platelet activation. This process is described as possessing two stages, firstly, adhesion - the initial tethering to a surface, and secondly aggregation - the platelet-platelet cohesion.More...
Platelet-derived Growth Factor (PDGF) is a potent stimulator......
Platelet-derived Growth Factor (PDGF) is a potent stimulator of growth and motility of connective tissue cells such as fibroblasts and smooth muscle cells as well as other cells such as capillary endothelial cells and neurons.The PDGF family of growth factors is composed of four different polypeptide chains encoded by four different genes. The classical PDGF chains, PDGF-A and PDGF-B, and more recently discovered PDGF-C and PDGF-D. The four PDGF chains assemble into disulphide-bonded dimers via homo- or heterodimerization, and five different dimeric isoforms have been described so far; PDGF-AA, PDGF-AB, PDGF-BB, PDGF-CC and PDGF-DD. It is notable that no heterodimers involving PDGF-C and PDGF-D chains have been described. PDGF exerts its effects by binding to, and activating, two protein tyrosine kinase (PTK) receptors, alpha and beta. These receptors dimerize and undergo autophosphorylation. The phosphorylation sites then attract downstream effectors to transduct the signal into the cell.More...
Humans are exposed to millions of potential pathogens daily,......
Humans are exposed to millions of potential pathogens daily, through contact, ingestion, and inhalation. Our ability to avoid infection depends on the adaptive immune system and during the first critical hours and days of exposure to a new pathogen, our innate immune system.More...
The classic signalling route for G alpha (q) is activation o......
The classic signalling route for G alpha (q) is activation of phospholipase C beta thereby triggering phosphoinositide hydrolysis, calcium mobilization and protein kinase C activation. This provides a path to calcium-regulated kinases and phosphatases, GEFs, MAP kinase cassettes and other proteins that mediate cellular responses ranging from granule secretion, integrin activation, and aggregation in platelets. Gq participates in many other signalling events including direct interaction with RhoGEFs that stimulate RhoA activity and inhibition of PI3K. Both in vitro and in vivo, the G-protein Gq seems to be the predominant mediator of the activation of platelets.More...
G protein-coupled receptors. The beta:gamma G-protein dimer ......
G protein-coupled receptors. The beta:gamma G-protein dimer is also involved in downstream signaling , and some receptors form part of metastable complexes of receptor and accessory proteins such as the arrestins. GPCRs are involved in many diverse signaling events , using a variety of pathways that include modulation of adenylyl cyclase, phospholipase C, the mitogen activated protein kinases (MAPKs), extracellular signal regulated kinase (ERK) c-Jun-NH2-terminal kinase (JNK) and p38 MAPK.More...
IRS is one of the mediators of insulin signalling events. It......
IRS is one of the mediators of insulin signalling events. It is activated by phosphorylation and triggers a cascade of events involving PI3K, SOS, RAF and the MAP kinases. The proteins mentioned under IRS are examples of IRS family members acting as indicated. More family members are to be confirmed and added in the future.More...
Two principal mechanisms limit blood loss after vascular inj......
Two principal mechanisms limit blood loss after vascular injury. Initially, platelets are activated, adhere to the site of the injury, and aggregate into a plug that limits blood loss. Proteins and small molecules released from activated platelets stimulate the plug formation process, and fibrinogen from the plasma forms bridges between activated platelets. These events allow the initiation of the clotting cascade, the second mechanism to limit blood loss. Negatively charged phospholipids exposed on cell surfaces at the site of injury and on activated platelets interact with tissue factor, setting off a cascade of reactions leading to generation of fibrin and the formation of an insoluble fibrin clot that strengthens the platelet plug.More...
Neurotrophins (NGF, BDNF, NT-3, NT-4/5) play pivotal roles i......
Neurotrophins (NGF, BDNF, NT-3, NT-4/5) play pivotal roles in survival, differentiation, and plasticity of neurons in the peripheral and central nervous system. They are produced, and secreted in minute amounts, by a variety of tissues. They signal through two types of receptors: TRK tyrosine kinase receptors (TRKA, TRKB, TRKC), which specifically interact with the different neurotrophins, and p75NTR, which interacts with all neurotrophins. TRK receptors are reported in a variety of tissues in addition to neurons. p75NTRs are also widespread. Neurotrophins and their receptors are synthesized as several different splice variants, which differ in terms of their biological activities. The nerve growth factor (NGF) was the first growth factor to be identified and has served as a model for studying the mechanisms of action of neurotrophins and growth factors. The mechanisms by which NGF generates diverse cellular responses have been studied extensively in the rat pheochromocytoma cell line PC12. When exposed to NGF, PC12 cells exit the cell cycle and differentiate into sympathetic neuron-like cells. Current data show that signalling by the other neurotrophins is similar to NGF signalling.More...
Trk receptors signal from the plasma membrane and from intra......
Trk receptors signal from the plasma membrane and from intracellular membranes, particularly from early endosomes. Signalling from the plasma membrane is fast but transient; signalling from endosomes is slower but long lasting. Signalling from the plasma membrane is annotated here. TRK signalling leads to proliferation in some cell types and neuronal differentiation in others. Proliferation is the likely outcome of short term signalling, as observed following stimulation of EGFR (EGF receptor). Long term signalling via TRK receptors, instead, was clearly shown to be required for neuronal differentiation in response to neurotrophins.More...
Optimal activation of T-lymphocytes requires at least two si......
Optimal activation of T-lymphocytes requires at least two signals. A primary one is delivered by the T-cell receptor (TCR) complex after antigen recognition and additional costimulatory signals are delivered by the engagement of costimulatory receptors such as CD28. The best-characterized costimulatory pathways are mediated by a set of cosignaling molecules belonging to the CD28 superfamily, including CD28, CTLA4, ICOS, PD1 and BTLA receptors. These proteins deliver both positive and negative second signals to T-cells by interacting with B7 family ligands expressed on antigen presenting cells. Different subsets of T-cells have very different requirements for costimulation. CD28 family mediated costimulation is not required for all T-cell responses in vivo, and alternative costimulatory pathways also exist. Different receptors of the CD28 family and their ligands have different regulation of expression. CD28 is constitutively expressed on naive T cells whereas CTLA4 expression is dependent on CD28/B7 engagement and the other receptor members ICOS, PD1 and BTLA are induced after initial T-cell stimulation. The positive signals induced by CD28 and ICOS molecules are counterbalanced by other members of the CD28 family, including cytotoxic T-lymphocyte associated antigen (CTLA)4, programmed cell death (PD)1, and B and T lymphocyte attenuator (BTLA), which dampen immune responses. The balance of stimulatory and inhibitory signals is crucial to maximize protective immune responses while maintaining immunological tolerance and preventing autoimmunity. The costimulatory receptors CD28, CTLA4, ICOS and PD1 are composed of single extracellular IgV-like domains, whereas BTLA has one IgC-like domain. Receptors CTLA4, CD28 and ICOS are covalent homodimers, due to an interchain disulphide linkage. The costimulatory ligands B71, B72, B7H2, B7H1 and B7DC, have a membrane proximal IgC-like domain and a membrane distal IgV-like domain that is responsible for receptor binding and dimerization. CD28 and CTLA4 have no known intrinsic enzymatic activity. Instead, engagement by their physiologic ligands B71 and B72 leads to the physical recruitment and activation of downstream T-cell effector molecules.More...
In the initial response to injury, platelets adhere to damag......
In the initial response to injury, platelets adhere to damaged blood vessels, responding to the exposure of collagen from the vascular epithelium. Once adhered they degranulate, releasing agents such as serotonin and ADP and synthesize Thromboxane A2, all of which amplify the response, recruiting further platelets to the area and promoting platelet aggregation.More...
PI3K/AKT signalling is a major regulator of neuron survival.......
PI3K/AKT signalling is a major regulator of neuron survival. It blocks cell death by both impinging on the cytoplasmic cell death machinery and by regulating the expression of genes involved in cell death and survival. In addition, it may also use metabolic pathways to regulate cell survival.The PI3K/AKT pathway also affects axon diameter and branching and regulates small G proteins like RhoA , which control the behaviour of the F-actin cytoskeleton. Moreover, through its connection with the TOR pathway, it promotes translation of a subset of mRNAs.More...
The role of autophosphorylation sites on PDGF receptors are ......
The role of autophosphorylation sites on PDGF receptors are to provide docking sites for downstream signal transduction molecules which contain SH2 domains. The SH2 domain is a conserved motif of around 100 amino acids that can bind a phosphorylated tyrosine residue. These downstream molecules are activated upon binding to, or phosphorylated by, the receptor kinases intrinsic to PDGF receptors. Some of the dowstream molecules are themselves enzymes, such as phosphatidylinositol 3'-kinase (PI3K), phospholipase C (PLC-gamma), the Src family of tyrosine kinases, the tyrosine phosphatase SHP2, and a GTPase activating protein (GAP) for Ras. Others such as Grb2 are adaptor molecules which link the receptor with downstream catalytic molecules.More...
Changes in gene expression are required for the T cell to ga......
Changes in gene expression are required for the T cell to gain full proliferative competence and to produce effector cytokines. Three transcription factors in particular have been found to play a key role in TCR-stimulated changes in gene expression, namely NF-kB, NFAT and AP-1. A key step in NF-kB activation is the stimulation and translocation of PKC theta. The critical element that effects PKC theta activation is PI3K. This enzyme complex translocates to the plasma membrane by interacting with phospho-tyrosines on CD28 via its two SH2 domains located in p85 subunit. The p110 subunit of PI3K phosphorylates the inositol ring of PIP2 to generate PIP3 (steps 17-18). PIP3 may also be dephosphorylated by the phosphatase SHIP to generate PI-3,4-P2. PIP3 and PI-3,4-P2 acts as binding sites to the PH domain of PKB/Akt and PDK1 (steps 19, 21 and 22). PKB is activated in response to PI3K stimulation by PDK1 (step 23). PDK1 has an essential role in regulating the activation of PKC theta and recruitment of CBM complex to the immune synapse. PKC theta is a member of novel class (DAG dependent, Ca++ independent) of PKC and the only member known to translocate to this synapse. Prior to TCR stimulation PKC theta exists in an inactive closed conformation. Upon release of DAG, it binds to PKC theta via the C1 domain and undergoes phosphorylation on tyrosine 90 by Lck to attain an open conformation. PKC theta is further phosphorylated by PDK1 on threonine 538. This step is critical for PKC activity (steps 24-26). CARMA1 translocates to the plasma membrane following the interaction of its SH3 domain with the 'PxxP' motif on PDK1. CARMA1 is phosphorylated by PKC-theta on residue S552, leading to the oligomerization of CARMA1. This complex acts as a scaffold, recruiting Bcl10 to the synapse by interacting with their CARD domains. Bcl10 undergoes phosphorylation mediated by the enzyme RIP2. Activated Bcl10 then mediates the ubiquitination of NEMO by recruiting MALT1 and TRAF6. MALT1 binds to Bcl10 with its Ig-like domains and undergoes oligomerization. TRAF6 binds to the oligomerized MALT1 and also undergoes oligomerization. Oligomerized TRAF6 acts as a ubiquitin-protein ligase, catalyzing auto-K63-linked polyubiquitination (steps 27-33). This K-63 ubiquitinated TRAF6 activates TAK1 kinase bound to TAB2 and also ubiquitinates NEMO/IKK-gamma in the IKK complex. TAK1 undergoes autophosphorylation on residues T184 and T187 and gets activated. Activated TAK1 kinase phosphorylates IKK-beta on residues S177 and S181 in the activation loop and activates the IKK kinase activity. IKK-beta phosphorylates the IkB-alpha bound to the NF-kB heterodimer, on residues S19 and S23 and directs IkB-beta to 26S proteasome degradation (step 34-38 and 40). The NF-kB heterodimer with a free NTS sequence finally migrates to the nucleus to regulate gene transcription (step 39).More...
The ability of growth factors to protect from apoptosis is p......
The ability of growth factors to protect from apoptosis is primarily due to the activation of the AKT survival pathway. P-I-3-kinase dependent activation of PDK leads to the activation of AKT which in turn affects the activity or expression of pro-apoptotic factors, which contribute to protection from apoptosis. AKT activation also blocks the activity of GSK-3b which could lead to additional antiapoptotic signals.More...
PIK3R1 related interactors from protein-protein interaction data in HPRD (count: 128)
Basic Information
Positive relationships between PIK3R1 and other components at different levels (count: 0)
