Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.24 (mitogen-activated protein kinase)
95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

PI3K was originally discovered as a lipid kinase involved in the phosphorylation of the inositol ring in position -3, leading to the synthesis of phosphatidyl-inositol-3-4 bisphosphate. The enzyme purified from rat liver is an heterodimer of two subunits of 85 and 110 KD respectively: it phosphorylates the D3 hydroxyl of phosphoinositides to produce phosphatidyl-inositol-3-phosphate. So far the function of the 3-phospho-inositide is unclear. It is likely that the entire phospholipid serves as a second messenger, since no phospholipase C has yet been found that can cleave the inositol group with a 3 phosphate residue. However the activation targets of this second messenger are still poorly known. Recently a novel/serine/theronine kinase was insolated by three groups and called differently RAC, PKB and AKT. It exhibits sequence homology with protein kinase A and C at the carboxyl terminal, whereas the aminoterminal domain has a plectrin homology. Activation of ATK is inhibited by wortmannin, a specific inhibitor of PI3K at very low concentrations. Furthermore inositol-3-phosphate can activate ATK in vitro. In addition very recently, a linkage of G-protein coupled receptors to the MAP kinase signalled pattern through PI3K has been discovered. But what is downstream of this pathway? 70S6 kinase is an attractive candidate since this kinase, involved in protein synthesis, is activated by AKT in vivo. Interestingly AKT is the cellular protooncogene of v-ATK and this implies that ATK induces a pathway of oncogenic transformation. AKT is inhibited by dominant negative mutants of ras and thus involved in the ras-raf-MAP kinase pathway. The role of PI3K is still indefinite but it must have a paramount importance in cell signalling since nearly all growth factor receptors recruit this enzyme and that the activity of fundamental growth factor receptors like PDGF, EGF and insulin are blocked by the specific inhibitor wortmannin, leading to the conclusion that the PI3K signal is much important in mitogenesis, protein synthesis, membrane ruffling, cell transformation and cell cycle progression.
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PMID:PI3K signal and DNA repair: a short commentary. 926 40

The loss of integrin-mediated cell-matrix contact induces apoptosis ('anoikis') in certain cell types. Recently it has been shown that protein kinase signaling pathways control anoikis both positively and negatively. Focal adhesion kinase, when activated by integrins, can suppress anoikis. Phosphatidylinositol 3-kinase and the AKT oncoprotein may mediate the anoikis-suppressing effects of focal adhesion kinase. Conversely, the stress-activated protein kinase/Jun amino-terminal kinase pathway promotes anoikis. Latest results indicate that caspase-mediated cleavage of the first component of this latter pathway, MEKK-1, may trigger activation of this pathway in anoikis. In addition, certain integrins may regulate bcl-2 expression levels, possibly adjusting the threshold for anoikis.
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PMID:Integrins and anoikis. 933 Aug 74

Activated insulin receptor (IR) interacts with its substrates, IRS-1, IRS-2, and Shc via the NPXY motif centered at Y960. This interaction is important for IRS-1 phosphorylation. Studies using the yeast two-hybrid system and sequence identity analysis between IRS-1 and IRS-2 have identified two putative elements, the PTB and SAIN domains, between amino acids 108 and 516 of IRS-1 that are sufficient for receptor interaction. However, their precise function in mediating insulin's bioeffects is not understood. We expressed the PTB and SAIN domains of IRS-1 in HIRcB fibroblasts and 3T3-L1 adipocytes utilizing replication-defective adenoviral infection to investigate their role in insulin signalling. In both cell types, overexpression of either the PTB or the SAIN protein caused a significant decrease in insulin-induced tyrosine phosphorylation of IRS-1 and Shc proteins, IRS-1-associated phosphatidylinositol 3-kinase (PI 3-K) enzymatic activity, p70s6k activation, and p44 and p42 mitogen-activated protein kinase (MAPK) phosphorylation. However, epidermal growth factor-induced Shc and MAPK phosphorylation was unaffected by the overexpressed proteins. These findings were associated with a complete inhibition of insulin-stimulated cell cycle progression. In 3T3-L1 adipocytes, PTB or SAIN expression extinguished IRS-1 phosphorylation with a corresponding 90% decrease in IRS-1-associated PI 3-K activity. p70s6k is a downstream target of PI 3-K, and insulin-stimulated p70s6k was inhibited by PTB or SAIN expression. Interestingly, overexpression of either PTB or SAIN protein did not affect insulin-induced AKT activation or insulin-stimulated 2-deoxyglucose transport, even though both of these bioeffects are inhibited by wortmannin. Thus, interference with the IRS-1-IR interaction inhibits insulin-stimulated IRS-1 and Shc phosphorylation, PI 3-K enzymatic activity, p70s6k activation, MAPK phosphorylation and cell cycle progression. In 3T3-L1 adipocytes, interference with the IR-IRS-1 interaction did not cause inhibition of insulin-stimulated AKT activation or glucose transport. These results indicate a bifurcation or subcompartmentalization of the insulin signalling pathway whereby some targets of PI 3-K (i.e., p70s6k) are dependent on IRS-1-associated PI 3-K and other targets (i.e., AKT and glucose transport) are not. IR-IRS-1 interaction is not essential for insulin's effect on glucose transport, and alternate, or redundant, pathways exist in these cells.
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PMID:Adenovirus-mediated overexpression of IRS-1 interacting domains abolishes insulin-stimulated mitogenesis without affecting glucose transport in 3T3-L1 adipocytes. 937 69

Activation and recruitment of eosinophils in allergic inflammation is in part mediated by chemoattractants and T-helper 2 (Th2)-derived cytokines. However, little is known concerning the signal transduction mechanisms by which this activation occurs. We have investigated tyrosine kinase-mediated activation of phosphatidylinositol 3-kinase (PI3K) and compared this with the activation of the p21ras-ERK signaling pathway in human eosinophils. The related cytokines interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF), all induced PI3K activity detected in antiphosphotyrosine immunoprecipitates. Furthermore, the chemoattractants platelet-activating factor (PAF), RANTES, and C5a were also able to induce phosphotyrosine-associated PI3K activity. Protein kinase B (PKB) is a downstream target of PI3K activation by growth factors. Induction of PKB phosphorylation in human eosinophils was transiently induced on activation with the cytokines IL-4 and IL-5, as well as the chemoattractants PAF, C5a, and RANTES showing a broad activation profile. Surprisingly, analysis of the activation of the mitogen-activated protein (MAP) kinases p44(ERK1) and p42(ERK2), showed that ERK2, but not ERK1, was transiently activated in human eosinophils after stimulation with IL-5 or PAF. Activation kinetics correlated with activation of p21ras by both cytokines and chemoattractants as measured by a novel assay for guanosine triphosphate (GTP)-loading. Finally, using specific inhibitors of both the p21ras-ERK and PI3K signaling pathways, a role was demonstrated for PI3K, but not p21ras-ERK, in activation of the serum-treated zymosan (STZ)-mediated respiratory burst in IL-5 and PAF-primed eosinophils. In summary, these data show that in human eosinophils, Th2-derived cytokines differentially activate both PI3K and MAP kinase signal transduction pathways with distinct functional consequences showing complex regulation of eosinophil effector functions.
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PMID:Analysis of signal transduction pathways in human eosinophils activated by chemoattractants and the T-helper 2-derived cytokines interleukin-4 and interleukin-5. 951 56

The effects of insulin and platelet-derived growth factor (PDGF) on glycogen synthase activation were compared in 3T3-L1 fibroblasts and adipocytes. In the fibroblasts, PDGF elicited a stronger phosphorylation of mitogen-activated protein kinase (MAPK) and AKT than did insulin. Both agents caused a comparable stimulation of receptor autophosphorylation, MAPK, and phosphatidylinositol 3-kinase (PI3-K) activation in the adipocytes. However, adipogenesis resulted in the uncoupling of PI3-K activation by PDGF from subsequent AKT phosphorylation. The relative contributions of glycogen synthase kinase-3 (GSK-3) inactivation and protein phosphatase-1 (PP1) activation in the regulation of glycogen synthase in both cell types were evaluated. Insulin and PDGF caused a small increase in glycogen synthase a activity in the fibroblasts. Additionally, both agents caused a similar inhibition of GSK-3, while having no effect on PP1 activity. Following differentiation, insulin treatment resulted in a 5-fold stimulation of glycogen synthase, whereas PDGF was without effect. Both agents caused a comparable inhibition of GSK-3 activity in the adipocytes, whereas only insulin activated PP1. Finally, wortmannin completely blocked the stimulation of PP1 by insulin in 3T3-L1 adipocytes, indicating that PI3-K inhibition can impinge on PP1 activation. Cumulatively these results suggest that the weak activation of glycogen synthase in 3T3-L1 fibroblasts is mediated by GSK-3 inactivation, whereas in the more metabolically active adipocytes, the insulin-specific activation of glycogen synthase is mediated by PP1 activation.
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PMID:The activation of glycogen synthase by insulin switches from kinase inhibition to phosphatase activation during adipogenesis in 3T3-L1 cells. 960

Protein kinase B (PKB) isoforms became activated [and glycogen synthase kinase-3 (GSK3) became inhibited] when mouse Swiss 3T3 fibroblasts were exposed to oxidative stress (H2O2) or heat shock, but not when they were exposed to osmotic shock (0.5 M sorbitol or 0. 7 M NaCl), chemical stress (sodium arsenite), the protein-synthesis inhibitor anisomycin, or UV radiation. In contrast, all seven stimuli activated mitogen-activated protein kinase-activated protein kinase-2 (MAPKAP-K2). The activation of MAPKAP-K2 was suppressed by the drug SB 203580, but not by inhibitors of phosphoinositide (phosphatidylinositide, PI) 3-kinase. In contrast, the activation of PKB isoforms and the inhibition of GSK3 by oxidative stress or heat shock were prevented by inhibitors of PI 3-kinase, but not by SB 203580. Thus the activation of PKB by oxidative stress or heat shock is mediated by PI 3-kinase and not by MAPKAP-K2. PKBalpha and PKBgamma were also activated by heat shock and oxidative stress in human embryonic kidney 293 cells and PKBgamma was activated by heat shock in NIH 3T3 cells; in each case activation was suppressed by inhibitors of PI 3-kinase. The activation of PKB isoforms by H2O2 may underlie some of the insulin-mimetic effects of this compound.
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PMID:The activation of protein kinase B by H2O2 or heat shock is mediated by phosphoinositide 3-kinase and not by mitogen-activated protein kinase-activated protein kinase-2. 980 7

Proliferation of airway smooth muscle results from persistent inflammatory cytokine and growth factor stimulation and is a critical component of airway luminal narrowing in chronic asthma. Using primary cultures of bovine tracheal smooth muscle (BTSM) cells to examine the signaling basis of cell proliferation, platelet-derived growth factor (PDGF)-BB and thrombin (which act through distinct receptor types) were found to induce DNA synthesis in BTSM cells. Mitogen-induced DNA synthesis could be completely inhibited by LY294002, a selective phosphoinositide 3-kinase (PtdIns 3-kinase) inhibitor. Exposure of BTSM cells to PDGF-BB or thrombin resulted in rapid activation of PtdIns 3-kinase and accumulation of phosphoinositide-3,4,5-trisphosphate. Protein kinase B, a novel signaling protein kinase, was identified in BTSM cells and was activated by PDGF-BB and thrombin in a PtdIns 3-kinase-dependent manner; this may underlie mitogen-stimulated activation of p70(s6k). PD98059, a mitogen-activated protein kinase kinase 1 inhibitor, also partially inhibited PDGF-BB- and thrombin-stimulated DNA synthesis, indicating a modulatory role for mitogen-activated protein kinase in proliferation. GF109203X, Ro 31-8220, calphostin C, and chelerythrine (selective protein kinase C inhibitors) had no effect on PDGF-BB- or thrombin-stimulated DNA synthesis, suggesting that, despite abolishment of mitogen-stimulated protein kinase C activity, cell proliferation stimulated by PDGF-BB and thrombin is protein kinase C-independent. These data demonstrate that the PtdIns 3-kinase/protein kinase B pathway represents a key signaling route in airway smooth muscle proliferation, with the mitogen-activated protein kinase kinase 1/mitogen-activated protein kinase cascade providing a complementary signal required for the full mitogenic response.
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PMID:Platelet-derived growth factor-BB and thrombin activate phosphoinositide 3-kinase and protein kinase B: role in mediating airway smooth muscle proliferation. 985 29

Macrophage stimulating protein (MSP) belongs to the plasminogen-related kringle domain family. In addition to stimulation of macrophages, MSP acts on other cell types including epithelial and hematopoietic cells. The MSP receptor is a transmembrane tyrosine kinase called RON in humans and STK in mice. MSP/receptor interaction induces activation of signal transduction pathways that mediate MSP biological activities. Cytoplasmic kinases are intracellular messengers occupying an important role in signal transduction. We have identified kinases that participate in RON signaling. In addition to previously identified involvement of phosphatidylinositol 3-kinase (PI3-K), JNK, and MAPK, we found that FAK, c-Src, and AKT are rapidly and transiently activated by MSP. FAK, MAPK, and c-Src are involved in MSP-induced cell proliferation. MAPK and c-Src are components of one signal transduction cascade, and MAPK is downstream of c-Src. FAK also regulates MSP-induced cell growth, but via a path different from c-Src/MAPK. AKT kinase is a component of a separate branch of the RON/PI3-K pathway that mediates the MSP anti-apoptotic effect on epithelial cells. PI3-K regulates MSP-induced adhesion and motility but via downstream components different from AKT. Thus, occupancy of the RON receptor by MSP activates distinct signal transduction pathways that mediate several cellular responses.
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PMID:Kinases involved in MSP/RON signaling. 1008 May 38

The role of cbl-b in signaling by the epidermal growth factor receptor (EGFR) was studied and compared with c-cbl. We demonstrate in vivo, that cbl-b, like c-cbl, is phosphorylated and recruited to the EGFR upon EGF stimulation and both cbl proteins can bind to the Grb2 adaptor protein. To investigate the functional role of cbl proteins in EGFR signaling, we transfected cbl-b or c-cbl into 32D cells overexpressing the EGFR (32D/EGFR). This cell line is absolutely dependent on exogenous IL-3 or EGF for sustained growth. 32D/EGFR cells overexpressing cbl-b showed markedly inhibited growth in EGF compared to c-cbl transfectants and vector controls. This growth inhibition by cbl-b was the result of a dramatic increase in the number of cells undergoing apoptosis. Consistent with this finding, cbl-b overexpression markedly decreased the amplitude and duration of AKT activation upon EGF stimulation compared to either vector controls or c-cbl overexpressing cells. In addition, the duration of EGF mediated MAP kinase and Jun kinase activation in cells overexpressing cbl-b is shortened. These data demonstrate that cbl-b inhibits EGF-induced cell growth and that cbl-b and c-cbl have distinct roles in EGF mediated signaling.
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PMID:cbl-b inhibits epidermal growth factor receptor signaling. 1008 40

Protein kinase B lies "downstream" of phosphatidylinositide (PtdIns) 3-kinase and is thought to mediate many of the intracellular actions of insulin and other growth factors. Here we show that FKHR, a human homologue of the DAF16 transcription factor in Caenorhabditis elegans, is rapidly phosphorylated by human protein kinase Balpha (PKBalpha) at Thr-24, Ser-256, and Ser-319 in vitro and at a much faster rate than BAD, which is thought to be a physiological substrate for PKB. The same three sites, which all lie in the canonical PKB consensus sequences (Arg-Xaa-Arg-Xaa-Xaa-(Ser/Thr)), became phosphorylated when FKHR was cotransfected with either PKB or PDK1 (an upstream activator of PKB). All three residues became phosphorylated when 293 cells were stimulated with insulin-like growth factor 1 (IGF-1). The IGF-1-induced phosphorylation was abolished by the PtdIns 3-kinase inhibitor wortmannin but not by PD 98059 (an inhibitor of the mitogen-activated protein kinase cascade) or by rapamycin. These results indicate that FKHR is a physiological substrate of PKB and that it may mediate some of the physiological effects of PKB on gene expression. DAF16 is known to be a component of a signaling pathway that has been partially dissected genetically and includes homologues of the insulin/IGF-1 receptor, PtdIns 3-kinase and PKB. The conservation of Thr-24, Ser-256, and Ser-319 and the sequences surrounding them in DAF16 therefore suggests that DAF16 is also a direct substrate for PKB in C. elegans.
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PMID:Phosphorylation of the transcription factor forkhead family member FKHR by protein kinase B. 1035 75


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