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)

The signal transduction pathway by which insulin stimulates glucose transport is largely unknown, but a role for tyrosine and serine/threonine kinases has been proposed. Since mitogen-activated protein (MAP) kinase is activated by insulin through phosphorylation on both tyrosine and threonine residues, we investigated whether MAP kinase and its upstream regulator, p21ras, are involved in insulin-mediated glucose transport. We did this by examining the time- and dose-dependent stimulation of glucose uptake in relation to the activation of Ras-GTP formation and MAP kinase by thrombin, epidermal growth factor (EGF), and insulin in 3T3-L1 adipocytes. Ras-GTP formation was stimulated transiently by all three agonists, with a peak at 5 to 10 min. Thrombin induced a second peak at approximately 30 min. The activation of p21ras was paralleled by both the phosphorylation and the activation of MAP kinase: transient for insulin and EGF and biphasic for thrombin. However, despite the strong activation of Ras-GTP formation and MAP kinase by EGF and thrombin, glucose uptake was not stimulated by these agonists, in contrast to the eightfold stimulation of 2-deoxy-D-[14C]glucose uptake by insulin. In addition, insulin-mediated glucose transport was not potentiated by thrombin or EGF. Although these results cannot exclude the possibility that p21ras and/or MAP kinase is needed in conjunction with other signaling molecules that are activated by insulin and not by thrombin or EGF, they show that the Ras/MAP kinase signaling pathway alone is not sufficient to induce insulin-mediated glucose transport.
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PMID:Activation of the Ras/mitogen-activated protein kinase signaling pathway alone is not sufficient to induce glucose uptake in 3T3-L1 adipocytes. 751 Dec 5

Thrombin stimulates G protein-coupled signaling pathways in target cells by proteolytic cleavage of its seven transmembrane domain receptor. Protein tyrosine phosphorylation is also stimulated by the protease via poorly defined mechanisms. In human platelets, thrombin has been shown to activate the nonreceptor tyrosine kinase Src. To elucidate the signal transduction pathways involved in transmission of thrombin's cellular effects, we have examined the ability of thrombin to activate Src family tyrosine kinases in a growth-responsive line of lung fibroblasts (CCL39 cells). We report here that thrombin induces a rapid (< or = 30 s) and transient increase in the kinase activity of Src and Fyn as determined by autophosphorylation in immune complex kinase assays. Activation is mediated by the G protein-coupled thrombin receptor since a synthetic peptide agonist of the receptor mimics thrombin action. The involvement of one or more G proteins in this response was confirmed by the observation that thrombin's effect is partially sensitive to pertussis toxin. Furthermore, both alpha 2-adrenergic and muscarinic m1 receptors are able to increase Src kinase activity via pertussis toxin-sensitive and -insensitive G proteins, respectively. These findings suggest that nonreceptor tyrosine kinases of the Src family may represent a novel effector system linking G protein-coupled receptors to downstream activation of Ras and the mitogen-activated protein kinase cascade.
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PMID:Activation of Src family kinase activity by the G protein-coupled thrombin receptor in growth-responsive fibroblasts. 752 55

Thrombin is known to evoke numerous inflammatory and proliferative responses in a wide variety of its target cells. Recent studies have demonstrated morphoregulatory and mitogenic effects of thrombin on astroglial cells (astrocytes). The present study deals with thrombin-induced activation of mitogen-activated protein (MAP) kinase in primary cultures of rat astrocytes. Treatment of serum-starved astrocytes with thrombin resulted in a rapid activation of tyrosine (Tyr) phosphorylation of a set of proteins including a prominent one with a molecular mass of 42 kDa (p42). The identity of p42 with MAP kinase was confirmed by MAP kinase-immunoreactivity of isolated [i.e., immunoprecipitated with anti-phosphotyrosine (PY) antibodies] p42 and by increased myelin basic protein (MBP) kinase activity present in MAP kinase immunoprecipitates of thrombin-treated cultures. Pertussis toxin (PTX) pretreatment failed to inhibit thrombin stimulation of p42 phosphorylation, indicating the lack of involvement of PTX sensitive G proteins in the mechanism of activation of MAP kinase by thrombin. Chronic exposure of cultures to phorbol 12-myristate 13-acetate to down-regulate PKC resulted in an attenuation of thrombin-induced p42 Tyr phosphorylation, although H-7, a known PKC inhibitor, failed to block thrombin effect. However, staurosporine, a nonspecific protein kinase inhibitor, prevented the activation of p42 phosphorylation. It is concluded that thrombin induces MAP kinase activation in astrocytes by a mechanism involving a staurosporine-sensitive pathway.
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PMID:Thrombin activates mitogen-activated protein kinase in primary astrocyte cultures. 759 20

alpha-Thrombin (thrombin), a potent mitogen for CCL39 hamster lung fibroblasts, stimulates phosphoinositide-specific phospholipase C (PI-PLC) and inhibits adenylate cyclase via cleavage of a specific G-protein-coupled receptor (TH-R), recently cloned from human and hamster cells. This action can be entirely mimicked by the synthetic peptide SFFLRNP, referred to here as TMP (thrombin-mimicking peptide). TMP corresponds to the first seven amino acids of the new N-terminus generated by thrombin cleavage of the hamster TH-R. Although thrombin and TMP apparently generate identical early transmembrane signals, only thrombin is mitogenic on its own. TMP needs to be associated with fibroblast growth factor (FGF), a tyrosine kinase-activating growth factor, to induce cell-cycle re-entry. Here, we have examined the early and late phase of p44 MAP kinase (p44mapk) activation in G0-arrested CCL39 cells after stimulation by thrombin, TMP, FGF or TMP+FGF. We found that: (i) both thrombin and TMP rapidly activate p44mapk in a dose-dependent manner with maximum activation at around 5 min, (ii) after the initial burst of activation, a second and long-lasting wave of activation is observed in response to thrombin (10-100 nM) but not to TMP (up to 300 microM), (iii) FGF alone (25 ng/ml), like thrombin, rapidly and persistently activates p44mapk (20-fold at 5 min and about 3-fold after 2 h), (iv) TMP added together with FGF strongly potentiates the second and sustained phase of p44mapk activation. From these results we propose that: (1) thrombin-induced mitogenesis is mediated only in part by the TH-R recently cloned and (2) activation of p44mapk, in particular the long-lasting phase that correlates with DNA synthesis, is an obligatory event for cell-cycle re-entry.
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PMID:Differential activation of p44mapk (ERK1) by alpha-thrombin and thrombin-receptor peptide agonist. 838 Sep 83

Previous studies established that thrombin stimulates phosphoinositide hydrolysis and modulates contractile function in neonatal rat ventricular myocytes. The present study further defines the signaling pathways activated by the thrombin receptor and their role in thrombin's actions in cardiac myocytes. The thrombin receptor-derived agonist peptide (TRAP, a portion of the tethered ligand created by thrombin's proteolytic activity) stimulates the rapid and transient accumulation of inositol bis- and tris-phosphates (IP2 and IP3, respectively), which is followed by the more gradual and sustained accumulation of inositol monophosphate (IP1). TRAP elicits a larger and more sustained accumulation of IP1 than does thrombin. Thrombin and TRAP also activate mitogen-activated protein kinase (MAPK) in cultured neonatal rat ventricular myocytes. Differences in the kinetics and magnitude of thrombin- and TRAP-dependent inositol phosphate (IP) accumulation are paralleled by differences in the kinetics and magnitude of thrombin- and TRAP-dependent activation of MAPK. Pretreatment with phorbol 12-myristate 13-acetate (PMA) to downregulate protein kinase C (PKC) attenuates thrombin- and TRAP-dependent activation of MAPK, although small and equivalent effects of thrombin and TRAP to stimulate MAPK persist in PMA-pretreated cells. These results support the notion that the thrombin receptor activates MAPK through PKC-dependent pathways and that the incremental activation of MAPK by TRAP over that induced by thrombin is the consequence of enhanced activation through the PKC limb of the phosphoinositide lipid pathway. TRAP also increases the beating rate of spontaneously contracting ventricular myocytes and elevates cytosolic calcium in myocytes electrically driven at a constant basic cycle length. The effects of TRAP to modulate contractile function and elevate intracellular calcium are not inhibited by tricyclodecan-9-yl-xanthogenate (D609, to block TRAP-dependent IP accumulation) or pretreatment with PMA (to downregulate PKC). The TRAP-dependent rise in intracellular calcium also is not inhibited by verapamil or removal of extracellular calcium but is markedly attenuated by depletion of sarcoplasmic reticular calcium stores by caffeine. Patch-clamp experiments demonstrate that TRAP elevates intracellular calcium in cells held at a membrane potential of -70 mV. Taken together, these results support the conclusion that the thrombin receptor modulates contractile function by mobilizing intracellular calcium through an IP3-independent mechanism and that this response does not require activation of voltage-gated ion channels.
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PMID:Thrombin receptor actions in neonatal rat ventricular myocytes. 863 12

p38 mitogen-activated protein kinase (MAPK) was identified in platelets on the basis of (a) its reactivity with antibodies to C-terminal and N-terminal peptides, and (b) its ability to activate MAPK-activated protein kinase-2, which phosphorylates the small heat shock protein, hsp27. p38 MAPK was activated in platelets by collagen fibers, a collagen-related cross-linked peptide, thrombin, or the thromboxane analogue U46619. A highly specific inhibitor of p38 MAPK, a pyridinyl imidazole known as SB203580, inhibited the platelet enzyme in vitro (IC50 approximately 0.5 microM). At similar concentrations it also inhibited agonist-stimulated phosphorylation of hsp27 in platelets, and platelet aggregation and secretion induced by minimal aggregatory concentrations of collagen or U46619, but not thrombin. Inhibition of aggregation was overcome by increasing agonist dose. SB203580 might act by inhibiting thromboxane generation, but this was only inhibited by 10-20% at low agonist concentrations. p38 MAPK provides a crucial signal, which is necessary for aggregation caused by minimal concentrations of collagen fibers or U46619. Thrombin or high doses of these agonists generate signals that bypass the enzyme, or render the enzyme no longer rate-limiting.
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PMID:Role for p38 mitogen-activated protein kinase in platelet aggregation caused by collagen or a thromboxane analogue. 863 72

The mitogenic activity of thrombin on fibroblasts and smooth muscle cells may contribute to embryonic development and normal wound healing, and it may also play a role in pathological responses to vascular injury. To examine the importance of thrombin signaling in vivo and to define the cloned thrombin receptor's role, we disrupted the thrombin receptor gene (tr) in mice. Platelets from tr-/- mice responded normally to thrombin, but tr-/- fibroblasts showed no thrombin-induced calcium mobilization or phosphoinositide hydrolysis. Thus distinct thrombin receptors act in different tissues. This study focuses on the role of the thrombin receptor in thrombin-induced mitogenesis and mitogen-activated protein (MAP) kinase activation in mesenchymal cells. Thrombin and thrombin receptor agonist peptide both stimulated DNA synthesis and MAP kinase activation in fibroblasts derived from wild-type mice. These responses were selectively lost in fibroblasts from tr-/- mice. Activation of the cloned thrombin receptor is therefore necessary and sufficient for thrombin-induced mitogenesis and MAP kinase activation in mouse lung fibroblasts. The tr-/- mouse thus provides a valuable model for defining the role of thrombin-induced proliferative events in vivo. Because thrombin-induced MAP kinase activation was attributable to a single receptor expressed at natural levels, mouse lung fibroblasts presented an opportunity to define the pathways that normally mediate activation of MAP kinase by the thrombin receptor. Elimination of phorbol-sensitive protein kinase C by prolonged exposure to phorbol ester only partially inhibited MAP kinase activation by thrombin but completely blocked c-Raf kinase activation. Pertussis toxin partially inhibited MAP kinase activation by thrombin but had no significant effect on c-Raf kinase activation. Thus in mouse lung fibroblasts, one thrombin receptor utilizes two pathways for MAP kinase activation: one is protein kinase C- and c-Raf dependent, and a second is Gi-dependent and c-Raf-independent.
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PMID:The cloned thrombin receptor is necessary and sufficient for activation of mitogen-activated protein kinase and mitogenesis in mouse lung fibroblasts. Loss of responses in fibroblasts from receptor knockout mice. 870 39

In 1321N1 astrocytoma cells, thrombin, but not carbachol, induces AP-1-mediated gene expression and DNA synthesis. To understand the divergent effects of these G protein-coupled receptor agonists on cellular responses, we examined Gq-dependent signaling events induced by thrombin receptor and muscarinic acetylcholine receptor stimulation. Thrombin and carbachol induce comparable changes in phosphoinositide and phosphatidylcholine hydrolysis, mobilization of intracellular Ca2+, diglyceride generation, and redistribution of protein kinase C; thus, activation of these Gq-signaling pathways appears to be insufficient for gene expression and mitogenesis. Thrombin increases Ras and mitogen-activated protein kinase activation to a greater extent than carbachol in 1321N1 cells. The effects of thrombin are not mediated through Gi, since ribosylation of Gi/Go proteins by pertussis toxin does not prevent thrombin-induced gene expression or thrombin-stimulated DNA synthesis. We recently reported that the pertussis toxin-insensitive G12 protein is required for thrombin-induced DNA synthesis. We demonstrate here, using transfection of receptors and G proteins in COS-7 cells, that G alpha 12 selectively couples the thrombin receptor to AP-1-mediated gene expression. This does not appear to result from increased mitogen-activated protein kinase activity but may reflect activation of a tyrosine kinase pathway. We suggest that preferential coupling of the thrombin receptor to G12 accounts for the selective ability of thrombin to stimulate Ras, mitogen-activated protein kinase, gene expression, and mitogenesis in 1321N1 cells.
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PMID:Coupling of the thrombin receptor to G12 may account for selective effects of thrombin on gene expression and DNA synthesis in 1321N1 astrocytoma cells. 893 Aug 92

Vascular endothelial growth factor (VEGF) stimulated the tyrosine phosphorylation of multiple components in confluent human umbilical vein endothelial cells (HUVECs) including bands of Mr 205,000, corresponding to the VEGF receptors Flt-1 and KDR, and Mr 145,000, 120,000, 97,000, and 65,000-70,000. VEGF caused a striking and transient increase in mitogen-activated protein (MAP) kinase activity and stimulated phospholipase C-gamma tyrosine phosphorylation, but it had no effect on phosphatidylinositol 3'-kinase activity. VEGF caused a marked increase in tyrosine phosphorylation of p125 focal adhesion kinase (p125(FAK)), which was both rapid and concentration-dependent. VEGF produced similar effects on p125(FAK) in the endothelial cell line ECV.304. VEGF stimulated tyrosine phosphorylation of the 68-kDa focal adhesion-associated component, paxillin, with similar kinetics and concentration dependence to that for p125(FAK). Thrombin and the phorbol ester, phorbol 12-myristate 13-acetate, also increased p125(FAK) tyrosine phosphorylation in HUVECs. The effect of VEGF on p125(FAK) tyrosine phosphorylation was completely inhibited by the actin filament-disrupting agent cytochalasin D and was partially inhibited by the protein kinase C inhibitor GF109203X. Inhibition of the MAP kinase pathway using a specific inhibitor of MAP kinase kinase had no effect on p125(FAK) tyrosine phosphorylation. VEGF stimulated migration and actin stress fiber formation in confluent HUVEC, and VEGF-induced p125(FAK)/paxillin tyrosine phosphorylation was accompanied by increased immunofluorescent staining of p125(FAK), paxillin, and phosphotyrosine in focal adhesions in confluent cultures of HUVECs. These findings identify p125(FAK) and paxillin as components in a VEGF-stimulated signaling pathway and suggest a novel mechanism for VEGF regulation of endothelial cell functions.
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PMID:Vascular endothelial growth factor stimulates tyrosine phosphorylation and recruitment to new focal adhesions of focal adhesion kinase and paxillin in endothelial cells. 918 76

We investigated the role of thrombin in the pathogenesis in atherosclerosis and restenosis. First we examined the effect of thrombin on cultured human vascular smooth muscle cells (VSMC). We showed that thrombin acts as a mitogen on VSMC through thrombin receptor. The expression of thrombin receptor was increased in the cell lines of VSMC established from directional coronary atherectomy (DCA). This is more pronounced in the cells from patients with restenosis after PTCA. Next we investigated the signaling pathway from thrombin/thrombin receptor. Thrombin activates thrombin receptor resulting in the exposing of the agonist peptide domain (thrombin receptor agonist peptide, TRAP). The signal from thrombin/thrombin receptor activated protein C kinase, tyrosine kinase, and MAP kinase and resulted in NF-kappa B activation. Furthermore, treatment of the cells with antisense p65 oligodeoxynucleotides of NF-kappa B inhibited the thrombin-stimulated growth of VSMC in vitro. These results suggest that thrombin may have a role in the pathogenesis of atherosclerosis and restenosis after PTCA through the thrombin receptor.
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PMID:Thrombin activates NF-kappa B through thrombin receptor and results in proliferation of vascular smooth muscle cells: role of thrombin in atherosclerosis and restenosis. 918 20


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