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)

To evaluate a possible mechanism for the chronic regulation of MAPK/ERK kinase-1 (MEK-1) and p42 mitogen-activated protein kinase (MAPK) we studied the long-term effects of the G-protein-coupled receptor agonist endothelin-1 (ET-1) and the protein tyrosine kinase-coupled receptor agonist platelet-derived growth factor BB (PDGF BB) on MEK-1 and p42 MAPK in glomerular mesangial cells (GMCs). ET-1 and PDGF BB led to a time-dependent increase in MEK-1 mRNA expression without altering p42 MAPK mRNA levels. The effect of ET-1 and PDGF BB on MEK-1 mRNA expression was maximal after 24 h (3.3-fold) or 6 h (2.9-fold). Furthermore, the effect of ET-1 and PDGF BB on MEK-1 mRNA expression was additive (4.2-fold after 6 h) and was inhibited by actinomycin D (5 micrograms/ml). Cycloheximide (10 micrograms/ml) inhibited MEK-1 mRNA induction but stimulated p42 MAPK mRNA expression in both the absence and the presence of ET-1 and/or PDGF BB. The ET-1 and PDGF BB-induced increase in MEK-1 mRNA was accompanied by sustained enhancement of both p45 MEK protein expression after 12 h and by elevation of p42 MAPK activity for up to 24 h. We conclude that, in GMCs, MEK-1 acts like a delayed-early gene, whereas p42 MAPK resembles an immediate-early gene. MEK-1 mRNA and protein levels, as well as p42 MAPK activity, can be chronically regulated by both a seven-transmembrane domain receptor-coupled peptide such as ET-1 and by an agonist binding to a receptor with intrinsic protein tyrosine kinase activity, such as PDGF BB.
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PMID:ET-1 and PDGF BB induce MEK mRNA and protein expression in mesangial cells. 858 80

PTP2C (also known as Syp/SH-PTP2/PTPlD) is a soluble protein tyrosine phosphatase present in most cell types. It interacts directly with activated PDGF receptor via its SH2 domains, which results in its phosphorylation on tyrosine residue(s). The phosphorylated PTP2C in turn binds to the SH2 domain of GRB2, serving as an adaptor in the transduction of mitogenic signals from the growth factor receptor to the Ras and MAP kinase signaling pathways. We investigated the interaction of PTP2C with the PDGF receptor by examining the localization of both proteins after PDGF stimulation of 293 cells which stably express the human PDGF receptor. In resting cells, transiently expressed PTP2C was distributed throughout the cytoplasm. Upon stimulation with PDGF, PTP2C was translocated from the cytoplasm to membrane ruffles. Immunofluorescence examination revealed that PTP2C colocalized with actin, the PDGF receptors, and hyper-tyrosine- phosphorylated protein(s). Neither deletion of the SH2 domains nor point mutations at either the catalytic site or the major phosphorylation site affected membrane ruffling or the localization of PTP2C to the ruffles of PDGF-stimulated cells. However, the expression of a catalytically inactive mutant PTP2C substantially prolonged ruffling activity following PDGF stimulation. These results suggest that PTP2C is involved in the down-regulation of the membrane ruffling pathway, and in contrast to its positive function in the MAP kinase pathway, the phosphatase activity negatively regulates ruffling activity.
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PMID:Localization and down-regulating role of the protein tyrosine phosphatase PTP2C in membrane ruffles of PDGF-stimulated cells. 860 24

The mechanisms responsible for altered vascular smooth muscle cell (VSMC) function in hypertension remain unknown. In the spontaneously hypertensive rat (SHR) model of genetic hypertension, there are multiple abnormalities in VSMC function, including increased growth, Na(+)-H+ exchange, and increased signal transduction by protein kinase C. The family of kinases termed mitogen-activated protein (MAP) kinases has recently been shown to be essential mediators of growth factor signal transduction. In the present study, alterations in MAP kinase function in the hypertensive phenotype were investigated using early-passage SHR and Wistar-Kyoto (WKY) VSMCs stimulated with angiotensin II (Ang II, 100 nmol/L) or platelet-derived growth factor-BB (PDGF-BB, 10 ng/mL). MAP kinase activity was measured by in-gel kinase assays and Western blot analysis. Two differences between SHR and WKY rats were observed for Ang II-mediated MAP kinase activation: (1) Inactivation after Ang II stimulation was more rapid in SHR than WKY VSMCs. (2) Activity in SHR VSMCs showed a greater dependence on Ca2+ mobilization, since chelation of intracellular Ca2+ with BAPTA inhibited maximal activity by 95% in SHR VSMCs but by only 50% in WKY VSMCs. In contrast to the results with Ang II, no differences in PDGF-stimulated MAP kinase activity were observed. These findings establish activation of MAP kinase by Ang II as a feature that distinguishes SHR VSMCs from WKY VSMCs and suggest that differences in regulation of MAP kinase signaling may alter cellular events that are increased in the SHR genetic model of hypertension.
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PMID:Ca(2+)-dependent mitogen-activated protein kinase activation in spontaneously hypertensive rat vascular smooth muscle defines a hypertensive signal transduction phenotype. 863 46

Treatment of quiescent rat aortic smooth muscle cells with either alpha-thrombin or a thrombin receptor-derived agonist peptide (SFLLRNP) resulted in pronounced increases in [3H]thymidine incorporation that were concentration dependent and reached a maximum of approximately 15-fold above serum-starved controls. However, in contrast to FBS, PDGF-BB, or basic fibroblast growth factor (bFGF), that initiated DNA synthesis promptly after 16-19 h, thymidine incorporation in response to thrombin was delayed by an additional 3-6 h. Delayed mitogenesis correlated with the appearance of a potent mitogenic activity in conditioned media samples obtained from thrombin-stimulated rat aortic smooth muscle cells, as assayed using Swiss 3T3 fibroblasts. This activity was not inhibited by neutralizing antibodies directed against PDGF or bFGF. Furthermore, in the Swiss 3T3 cells, simple addition of either alpha-thrombin or SFLLRNP failed to elicit a significant mitogenic response. In signal transduction studies, both thrombin and SFLLRNP treatment led to rapid tyrosine phosphorylation of proteins with apparent molecular masses of 42, 44, 75, 120, and 190 kD, respectively, as assessed by antiphosphotyrosine immunoblotting. The overall pattern of protein tyrosine phosphorylation was distinct from that observed after PDGF-BB addition. Activation of Raf-1 and the mitogen-activated protein (MAP) kinases p44mapk and p42mapk was also observed. However, the time course and duration of Raf-1/MAP kinase activation after thrombin stimulation were similar to those elicited by PDGF-BB. Taken together, our results indicate that thrombin-stimulated vascular smooth muscle proliferation is delayed and requires the de novo expression of one or more autocrine mitogens. In addition, the rapid induction of discrete intracellular signaling mechanisms by thrombin, including the Raf-1/MAP kinase pathway, appears to be insufficient alone to promote vascular smooth muscle cell mitogenesis.
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PMID:Thrombin receptor activation elicits rapid protein tyrosine phosphorylation and stimulation of the raf-1/MAP kinase pathway preceding delayed mitogenesis in cultured rat aortic smooth muscle cells: evidence for an obligate autocrine mechanism promoting cell proliferation induced by G-protein-coupled receptor agonist. 863 28

As previous studies showed, PDGF-AA exerts a poor mitogenic effect on vascular smooth muscle cells. Simultaneous addition of insulin-like growth factor 1 (IGF-1), itself also poorly mitogenic, led to a significant increase in [3H]thymidine incorporation into the cell DNA as well as a strong increase in cell number. To explain the synergistic effect of PDGF-AA and IGF-1 on VSMC proliferation, we describe the effects of the two growth factors on distinct intracellular signals: on the activation of the signal proteins mitogen-activated protein kinase (MAPK) isoforms p42 and p44 and on the protein kinase C (PKC) isoforms alpha, delta, and epsilon, and on the induction of the transcription factor c-fos. PDGF-AA strongly activated the MAPK isoforms and PKC delta as well as the induction of c-fos. In contrast, IGF-1 exerted no effect on the signals induced by PDGF-AA, but strongly activated PKC epsilon isoform. Comparing this signal pattern to the one of the mitogenically potent PDGF isoform PDGF-BB, we found that PDGF-BB activated all of the signal proteins investigated.
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PMID:The synergistic effect of PDGF-AA and IGF-1 on VSMC proliferation might be explained by the differential activation of their intracellular signaling pathways. 866 Sep 39

The PDGF beta-receptor in which the active-site lysine in the kinase domain has been mutated to arginine (K634R) tacks intrinsic kinase activity. When expressed in HepG2 cells, the kinase-inactive PDGF beta-receptor was tyrosine phosphorylated in response to PDGF-BB. Previously, HepG2 cells were thought to be devoid of PDGF alpha-receptor primarily due to lack of specific antibody which precluded detection of the PDGF alpha-receptor. In fact, these cells express low levels of PDGF alpha-receptor. In HepG2 cells that express the kinase-inactive PDGF beta-receptor, PDGF-BB activates the PDGF alpha-receptors to trans phosphorylate the kinase-inactive PDGF beta-receptor in an intermolecular fashion. As a result, stimulation of HepG2 cells that express the kinase-inactive receptor leads to activation of serine/threonine kinases of the MAP kinase cascade which include RAF-1, MEK-1 and p42 MAP kinase. In contrast, the kinase-inactive receptor does not activate any signaling pathways when it is expressed in PC12 cells which do not express the endogenous PDGF alpha-receptor. Thus, the kinase-inactive K634R PDGF beta-receptor is able to enhance PDGF-BB signaling in HepG2 cells that express the PDGF alpha-receptor.
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PMID:The kinase-inactive PDGF beta-receptor mediates activation of the MAP kinase cascade via the endogenous PDGF alpha-receptor in HepG2 cells. 870 May 41

In an effort to determine the role of protein kinase C-delta (PKC-delta) in cellular transformation mediated by the sis proto-oncogene, we cotransfected expression vectors containing cDNAs that encode for c-sis with an ATP binding mutant of PKC-delta (PKC-delta K376R) or wild type PKC-delta (PKC-delta WT) into NIH3T3 cells. Our results showed that expression of PKC-delta K376R severely impaired Sis-induced focus formation, whereas cotransfection of PKC-delta WT cDNA had no effect on Sis-mediated transformation. Consistent with this result, PKC-delta K376R expression also inhibited PDGF-BB-mediated anchorage-independent colony formation. While cotransfection of a vector containing a dominant negative mutant of ras (N17 ras) cDNA potently inhibited Sis-induced transformation, the expression of PKC-delta K376R did not block transformation mediated by v-H-Ras or v-Raf. In addition, PDGF-BB-induced Raf and mitogen-activated protein kinase activation, which are known to be downstream molecules in the Ras cascade, were not affected by the expression of PKC-delta K376R, indicating that PKC-delta and Ras are segregated in mediating Sis-induced transformation. Interestingly, expression of PKC-delta K376R strongly reduced TPA responsive element (TRE) transactivation induced by PDGF stimulation, suggesting that activation of TRE-containing genes, which may be involved in Sis-mediated transformation, are negatively regulated by expression of PKC-delta K376R.
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PMID:Expression of an ATP binding mutant of PKC-delta inhibits Sis-induced transformation of NIH3T3 cells. 876 Dec 94

The duration of extracellular signal-regulated protein kinase (ERK) activation is critical for cell signaling decisions and probably determines whether a stimulus elicits proliferation or differentiation. We studied the intracellular signals regulating sustained ERK-2 activity in glomerular mesangial cells (GMC), utilizing combination of GMC mitogens of different potency. Incubation of GMC with both endothelin-1 (ET-1) and platelet-derived growth factor BB (PDGF-BB) led to a long-lasting, monophasic increase in ERK-2 activity. In contrast, when ET-1 was administered together with epidermal growth factor (EGF), a less pronounced and shorter activation occurred. Long-term stimulation of ERK-2 was accompanied by an increase in p45 MEK activity, which again was more pronounced when ET-1 was administered together with PDGF-BB compared with EGF. In the presence of actinomycin D (Act D), an inhibitor of RNA synthesis, ERK-2 activity induced by ET-1 and PDGF-BB but not by ET-1 and EGF remained elevated more than sixfold throughout the whole incubation period of 6 h. The effect of Act D on ET-1- and PDGF-BB-induced ERK-2 activation was mimicked by the protein phosphatase inhibitor sodium orthovanadate. In addition, vanadate also unmarked an ET-1- and EGF-induced ERK-2 activity after 6 h. The serine/threonine phosphatase inhibitor okadaic acid (OA) did neither alter agonist-induced ERK-2 activity after 6 h (0.5 nM OA) nor after 10 min or 1 h (250 nM). Together these results suggest that, in GMC, long-term activation of the mitogen-activated protein kinase ERK-2 is differentially regulated, depending on the combination of agonists administered. ET-1- and PDGF-BB-induced long-term activation of ERK-2 is regulated by a vanadate-sensitive protein phosphatase(s) and by a transcriptionally regulated protein(s). In contrast, ET-1- and EGF-induced sustained ERK-2 stimulation is regulated by a vanadate-sensitive protein phosphatase(s) but not by a transcriptionally regulated protein. Agonist-specific and time-dependent stimulation of ERK-2-regulating protein phosphatases may be critical for the length of ERK-2 activation in GMC and could thus be of pathophysiological significance in glomerular diseases associated with alterations in cell proliferation or cell differentiation.
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PMID:Sustained ERK-2 activation in rat glomerular mesangial cells: differential regulation by protein phosphatases. 877 Jan 75

Constitutive stimulation of the mitogen-activated protein kinase (MAPK) activator MAPK/ERK kinase (MEK) is sufficient to promote long-term events such as cell differentiation, proliferation, and transformation. To evaluate a possible mechanism for the chronic regulation of MEK and p42 MAPK, we studied the long-term effects of fetal bovine serum (FBS), the G protein-coupled receptor agonist endothelin-1 (ET-1), and the protein tyrosine kinase-coupled receptor agonist platelet-derived growth factor BB (PDGF BB) on MEK and p42 MAPK in glomerular mesangial cells (GMC). FBS, ET-1, and PDGF BB led to a time-dependent increase in MEK-1 mRNA and protein expression without altering p42 MAPK mRNA and protein levels. FBS also induced MEK-1 mRNA expression in diverse cell types, including NIH/3T3 fibroblasts, A7r5 vascular smooth muscle cells, and Chinese hamster ovary cells. In GMC, cycloheximide inhibited MEK-1 mRNA induction but stimulated p42 MAPK mRNA expression in the absence and presence of FBS, ET-1, or PDGF. The FBS-induced increase in MEK-1 mRNA was accompanied by a sustained enhancement of MEK activity, as assessed by the ability of immunoprecipitated p45 MEK to activate recombinant p42 MAPK and hence phosphorylate myelin basic protein, and p42 MAPK activity. We conclude that, in GMC, MEK-1 acts like a delayed-early gene and that it can be chronically induced at the mRNA and protein level.
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PMID:Differential long-term regulation of MEK and of p42 MAPK in rat glomerular mesangial cells. 877 28

To summarize the regulation of cPLA2, we have proposed a model for the activation of cPLA2 based both on our previous studies (Clark et al., 1991; Lin et al., 1993) and the work of many others (Fig. 5). In this model, cPLA2 is tightly regulated by multiple pathways, including those that control Ca2+ concentration, phosphorylation states and cPLA2 protein levels, to exert both rapid and prolonged effects on cellular processes, such as inflammation. cPLA2 is rapidly activated by increased intracellular Ca2+ concentration and phosphorylation by MAP kinase. When cells are stimulated with a ligand for a receptor, such as ATP or PDGF, PLC is activated via either a G protein-dependent or -independent process, leading to the production of diacylglycerol (DAG) and inositol triphosphate (IP3). The rise in these intracellular messengers cause the activation of PKC and mobilization of intracellular Ca2+. Alternatively, the increase in intracellular Ca2+ can result from a Ca2+ influx. Increased Ca2+ acts through the CaLB domain to cause translocation of cPLA2 from the cytosol to the membrane where its substrate, phospholipid, is localized. This step is essential for the activation of cPLA2 and may account for the partial activation of cPLA2 in the absence of phosphorylation. MAP kinase activation can occur through both PKC-dependent and -independent mechanisms (Cobb et al., 1991; Posada and Cooper, 1992; Qiu and Leslie, 1994). In many cases, this pathway is also G protein-dependent. Activated MAP kinase phosphorylates cPLA2 at Ser-505, causing increased enzymatic activity of cPLA2, which is realized only upon translocation of cPLA2 to the membrane. Therefore, full activation of cPLA2 requires both increased cytosolic Ca2+ and cPLA2 phosphorylation at Ser-505. In a more delayed response, cPLA2 activity in the cells can be controlled by changes in its expression levels, such as in response to inflammatory cytokines and certain growth factors. Thus the expression level of cPLA2 is regulated by both transcriptional and post-transcriptional mechanisms.
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PMID:Cytosolic phospholipase A2. 877 86


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