Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.12.2 (MEK)
 18,161 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Interstitial fibroblast proliferation is an elemental feature in the development of cardiac fibrosis. The effects of inhibitors of the intracellular signalling proteins, MEK, a kinase involved in the mitogen-activated protein kinase (MAPK) pathway and phosphatidylinositol 3-kinase (PI3-K), were tested on growth of cultured human cardiac fibroblasts. 2. Cardiac fibroblasts were isolated from transplant recipient myocardium and made quiescent by serum deprivation for 48 h. Cells were incubated for 24 h with the inhibitors PD 098059 (0.3-30 mumol/L) and LY294002 (1-25 mumol/L) in the presence and absence of platelet-derived growth factor-AB (PDGF-AB, 10 ng/mL). DNA synthesis was measured by [3H]-thymidine incorporation assay (20-24 h). 3. Both compounds markedly inhibited both basal and PDGF-stimulated increases in DNA synthesis in a concentration-dependent manner. Cardiac fibroblast DNA synthesis was reduced to near control levels by PD 098059, while it was inhibited completely by LY294002. 4. These results implicate the importance of MAPK and PI3-K activation in the signal transduction pathways necessary for cardiac fibroblast replication.
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PMID:Inhibition of human cardiac fibroblast mitogenesis by blockade of mitogen-activated protein kinase and phosphatidylinositol 3-kinase. 1040 75

Multiple biological functions have been ascribed to the Ras-related G protein R-Ras. These include the ability to transform NIH 3T3 fibroblasts, the promotion of cell adhesion, and the regulation of apoptotic responses in hematopoietic cells. To investigate the signaling mechanisms responsible for these biological phenotypes, we compared three R-Ras effector loop mutants (S61, G63, and C66) for their relative biological and biochemical properties. While the S61 mutant retained the ability to cause transformation, both the G63 and the C66 mutants were defective in this biological activity. On the other hand, while both the S61 and the C66 mutants failed to promote cell adhesion and survival in 32D cells, the G63 mutant retained the ability to induce these biological activities. Thus, the ability of R-Ras to transform cells could be dissociated from its propensity to promote cell adhesion and survival. Although the transformation-competent S61 mutant bound preferentially to c-Raf, it only weakly stimulated the mitogen-activated protein kinase (MAPK) activity, and a dominant negative mutant of MEK did not significantly perturb R-Ras oncogenicity. Instead, a dominant negative mutant of phosphatidylinositol 3-kinase (PI3-K) drastically inhibited the oncogenic potential of R-Ras. Interestingly, the ability of the G63 mutant to induce cell adhesion and survival was closely associated with the PI3-K-dependent signaling cascades. To further delineate R-Ras downstream signaling events, we observed that while a dominant negative mutant of Akt/protein kinase inhibited the ability of R-Ras to promote cell survival, both dominant negative mutants of Rac and Ral suppressed cell adhesion stimulated by R-Ras. Thus, the biological actions of R-Ras are mediated by multiple effectors, with PI3-K-dependent signaling cascades being critical to its functions.
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PMID:Differential roles of Akt, Rac, and Ral in R-Ras-mediated cellular transformation, adhesion, and survival. 1045 80

T-lymphocyte migration into tissues requires focal degradation of the basement membrane. In this study, we show that transient adherence to fibronectin induces the production of activated forms of matrix metalloproteinase-2 (MMP-2) and MMP-9, as well as downregulation of tissue inhibitor of metalloproteinase-2 (TIMP-2) by T-cell lines. MMP-2 activation was likely achieved by inducing a coordinated expression of membrane-type matrix metalloproteinase-1 (MMP-14), a major activator of MMP-2. Blocking monoclonal antibodies against alpha4, alpha5, and alphav integrins strongly reduced MMP-2 and MMP-9 production induced by fibronectin. Disrupting actin cytoskeleton organization by cytochalasin D strongly enhanced fibronectin-induced MMP-2 and MMP-9 expression. Inhibiting Src tyrosine kinases with herbimycin A reduced MMP-2 and MMP-9 production with no effect on cell attachment. By contrast, G-protein inhibition by pertussis toxin, or transfection with a dominant negative mutant of Ha-Ras strongly increased fibronectin-induced MMP-2 and MMP-9. Inhibition of PI3 kinase, MAPkinase (MEK1), or p38 MAPkinase by wortmannin, PD 98059, or SB 202190, respectively, strongly promoted fibronectin-induced MMP2 and MMP-9. Cells at high density lost their ability to synthesize MMP-2 and MMP-9 in response to fibronectin and MMP expression was restored by transfection with a dominant-negative mutant of Ha-Ras or by treatment with wortmannin, PD 98059, or SB 202190. Our findings suggest that adhesion to fibronectin transduces both stimulatory (through Src-type tyrosin kinases) and inhibitory signals (through Ras/MAPKinase signaling pathways) for MMP-2 and MMP-9 expression by T lymphocytes and that their relative predominance is regulated by additional stimuli related to cell adhesion, motility, and growth.
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PMID:Fibronectin upregulates gelatinase B (MMP-9) and induces coordinated expression of gelatinase A (MMP-2) and its activator MT1-MMP (MMP-14) by human T lymphocyte cell lines. A process repressed through RAS/MAP kinase signaling pathways. 1051 79

The mechanisms by which inorganic salts of the trace element vanadium mediate their insulinomimetic effects are not clearly understood and were investigated. We have shown previously that vanadium salts activate mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase activities (PI3-K) via a pathway that does not involve the insulin receptor (IR) tyrosine kinase function [Pandey, S. K., Anand-Srivastava, M. B., and Srivastava, A. K. (1998) Biochemistry 37, 7006-7014]. Herein, we have examined a possible role of PI3-K in the vanadyl sulfate (VS)-mediated increase in the level of ras-MAPK activation as well as the contribution of signaling components upstream to MAPK in this VS response. Treatment of IR-overexpressing cells with VS resulted in an increased level of tyrosine phosphorylation of p44(mapk) (ERK-1) and p42(mapk) (ERK-2) along with stimulation of MAPK, MAPK kinase (MEK), and C-raf-1 activities, and ras activation. Preincubation with wortmannin and LY294002, two structurally and mechanistically different inhibitors of PI3-K, blocked the VS-mediated increase in MAPK activity and phosphorylation of ERK-1 and ERK-2. Furthermore, wortmannin inhibited activation of ras, C-raf-1, and MEK in response to VS. The addition of a farnesyltransferase inhibitor, B581, to cells reduced the level of MAPK activation as well as ERK-1 and ERK-2 phosphorylation stimulated by VS. Finally, VS increased PI3-K activity in ras immunoprecipitates. A VS-mediated increase in p70(s6k) activity was also found to be inhibited by wortmannin. Taken together, these results demonstrate that the insulinomimetic effects of VS may be mediated, in part, by PI3-K-dependent stimulation of the ras-MAPK and p70(s6k) pathways.
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PMID:Phosphatidylinositol 3-kinase requirement in activation of the ras/C-raf-1/MEK/ERK and p70(s6k) signaling cascade by the insulinomimetic agent vanadyl sulfate. 1054 92

In this report, we examine how the Ras protein regulates neuronal survival, focusing on sympathetic neurons. Adenovirus-expressed constitutively activated Ras (RasV12) enhanced survival and the phosphorylation of Akt (protein kinase B) and MAP kinase (MAPK), two targets of Ras activity. Functional inhibition of endogenous Ras by adenovirus-expressed dominant-inhibitory Ras (N17Ras) decreased nerve growth factor (NGF)-dependent survival and both Akt and MAPK phosphorylation as well. To determine the signaling pathways through which Ras mediates survival, we used Ras effector mutants and pharmacological inhibitors that selectively suppress phosphatidylinositol 3-kinase (PI3-K)/Akt or MAP kinase kinase (MEK)/MAPK pathways. The Ras effector mutant Ras(V12)Y40C, which selectively stimulates PI3-K and Akt, rescued survival in the absence of NGF, and the PI3-K inhibitor LY 294002 inhibited both Ras- and NGF-dependent survival. Ras(V12)T(35)S, which activates MEK/MAPK but not PI3-K/Akt, was less effective at rescuing survival, whereas the MEK inhibitor PD 098059 also partially suppressed Ras-dependent survival. To investigate the mechanisms by which Ras suppresses neuronal death, we examined whether Ras functions by inhibiting the proapoptotic p53 pathway (Jun-N-terminal kinase/p53/BAX) that is necessary for neuronal death after NGF withdrawal and p75NTR activation. We found that RasV12 suppressed c-jun, BAX, and p53 levels, whereas inhibition of NGF-induced Ras-survival activity via N17Ras increased the levels of these proteins. Furthermore, the E1B55K protein, which suppresses p53 activity, blocked N17Ras-induced neuronal death. Together, these results indicate that Ras is, in part, both necessary and sufficient for survival of sympathetic neurons and that this effect is mediated by activation of both the PI3-K- and MEK-signaling cascades, which in turn suppress a proapoptotic p53 pathway.
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PMID:Ras regulates sympathetic neuron survival by suppressing the p53-mediated cell death pathway. 1055 81

Non-esterified fatty acids are thought to be one of the causes for insulin resistance. However, the molecular mechanism of fatty acid-induced insulin resistance is not clearly known. In this study, we first examined the effect of palmitate on insulin signaling in 3T3-L1 adipocytes. We found that 1h treatment with 1 mmol/l palmitate had no effect on insulin binding, tyrosine phosphorylation of insulin receptors, 185 kDa proteins and Shc, and PI3 kinase activity in 3T3-L1 adipocytes. Then, the effects of palmitate on MAP kinase activity and glucose uptake in fully differentiated 3T3-L1 adipocytes were compared with those in poorly differentiated 3T3-L1 cells and in HIRc-B cells. Palmitate treatment had no effect on MAP kinase activity in fully differentiated 3T3-L1 adipocytes, while it inhibited MAP kinase in poorly differentiated 3T3-L1 cells and HIRc-B cells. Glucose transport in 3T3-L1 adipocytes treated with palmitate for 1 h, 4 h and 16 h was higher than that in control cells, but palmitate treatment caused a rightward shift of the insulin-dose responsive curve for glucose uptake in HIRc-B cells. Palmitate treatment did not significantly affect basal and insulin-stimulated GLUT4 translocation. When the cells were treated with PD98059, a specific MEK inhibitor, insulin-stimulated glucose uptake was not affected in 3T3-L1 adipocytes, while it was almost completely inhibited in HIRc-B cells. These results suggest the primary effect of palmitate on adipocytes may not involve insulin resistance of adipocytes themselves.
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PMID:Differential effects of palmitate on glucose uptake in rat-1 fibroblasts and 3T3-L1 adipocytes. 1059 63

Using digoxigenin (DIG)-based differential hybridization, a series of immediate early genes (IEG) was identified following the adipogenic stimulation in 3T3-L1 preadipocyte cells. Most of the known IEGs were identified as well as new members such as zf9 and Stra13. To delineate possible signaling pathways accounting for these gene expression, a subset of specific kinase inhibitors, SB203580, PD98059, rapamycin, LY294002, and Ro-32-0432, which inhibit p38 (HOG), MEK (MAPKK), S6 kinase, PI3 kinase, and protein kinase C (PKC), respectively, were employed. The IEGs were classified into three categories according to their susceptibility to the inhibitors. Expression of the first group (c-fos, jun-B, egr-1, tis11, tis21, thrombospondin-1, erp, thyroid hormone receptor [N-10], cyr61, and zf9) was mainly dependent on PKC and MEK pathways, while that of the second class (gene33 and tis10) exhibited an additional dependence on PI3 kinase pathways. The third one (Id-3, gly96, and Stra13) was characterized in that none of these inhibitors interfered with gene expression. Our results suggest that the induction of IEGs by the adipogenic stimuli is mediated by common as well as distinct signaling pathways.
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PMID:Differential regulation of immediate early gene expression in preadipocyte cells through multiple signaling pathways. 1060 Apr 78

We investigated the role of MEK1 signaling in MMP-2 activation by use of constitutive active/dominant negative forms of MEK1 and MEK1-specific inhibitor. We found that cell transformation with active forms of MEK1 dramatically increased secretion and proteolytic activation of MMP-2 and subsequently stimulated invasiveness of cells. Contrary, expression of dominant negative form of MEK1 in v-src-transformed cells or in Con A-activated cells resulted in the suppression of the augmented secretion and proteolytic activation of MMP-2. In addition, treatment of v-src-transformed cells with PD98059, a MEK1-specific inhibitor, strongly suppressed the secretion and activation of MMP-2, whereas treatment with wortmannin, a PI3 kinase inhibitor, showed no clear effect on MMP-2 secretion. Taken together, these results strongly suggest that MEK-MAP kinase signaling, but not PI3 kinase signaling, plays a critical role in the activation of MMP-2 secretion and, subsequently, in the invasiveness of v-src-transformed cells.
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PMID:Constitutive activation of MAP kinase kinase (MEK1) is critical and sufficient for the activation of MMP-2. 1062 78

Expression of oncogenic Ras in thyroid cells results in loss of expression of several thyroid-specific genes and inactivation of TTF-1, a homeodomain-containing transcription factor required for normal development of the thyroid gland. In an effort to understand how signal transduction pathways downstream of Ras may be involved in suppression of the differentiated phenotype, we have tested mutants of the Ras effector region for their ability to affect TTF-1 transcriptional activity in a transient-transfection assay. We find that V12S35 Ras, a mutant known to interact specifically with Raf but not with RalGDS or phosphatidylinositol 3-kinase (PI3 kinase) inhibits TTF-1 activity. Expression of an activated form of Raf (Raf-BXB) also inhibits TTF-1 function to a similar extent, while the MEK inhibitors U0126 and PD98059 partially relieve Ras-mediated inactivation of TTF-1, suggesting that the extracellular signal-regulated kinase (ERK) pathway is involved in this process. Indeed, ERK directly phosphorylates TTF-1 at three serine residues, and concomitant mutation of these serines to alanines completely abolishes ERK-mediated phosphorylation both in vitro and in vivo. Since activation of the Raf/MEK/ERK pathway accounts for only part of the activity elicited by oncogenic Ras on TTF-1, other downstream pathways are likely to be involved in this process. We find that activation of PI3 kinase, Rho, Rac, and RalGDS has no effect on TTF-1 transcriptional activity. However, a poorly characterized Ras mutant, V12N38 Ras, can partially repress TTF-1 transcriptional activity through an ERK-independent pathway. Importantly, concomitant expression of constitutive activated Raf and V12N38 Ras results in almost complete loss of TTF-1 activity. Our data indicate that the Raf/MEK/ERK cascade may act in concert with an as-yet-uncharacterized signaling pathway activated by V12N38 Ras to repress TTF-1 function and ultimately to inhibit thyroid cell differentiation.
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PMID:Multiple ras downstream pathways mediate functional repression of the homeobox gene product TTF-1. 1073 81

Overexpression of epidermal growth factor receptor (EGFR) and establishment of transforming growth factor alpha (TGF alpha)/EGF autocrine system are frequently detected in tumor cells. In addition to mitogenic ability, we demonstrate in this report that EGF protects a human esophageal carcinoma (CE) cell line, CE81T/VGH, from staurosporine-induced apoptosis. The anti-apoptotic signal of EGF is alleviated by a MEK inhibitor PD98059 or an ERK2 dominant negative mutant but not by a phosphatidylinositol-3'-kinase (PI-3K) inhibitor wortmannin. Furthermore, v-raf blocks apoptosis induced by staurosporine. This evidence implies that the survival signal of EGF is mediated via the Raf-MEK-ERK pathway but not the PI3-K pathway. The survival effect of EGF is coincident with the induction of mcl-1, an antiapoptotic gene in the bcl-2 family. PD98059 also suppresses the induction of Mcl-1 by EGF, implying that EGF may up-regulate Mcl-1 via the MAP kinase pathway. Overexpression of mcl-1 is sufficient to protect against apoptosis, while transfection of a mcl-1 antisense plasmid causes cell death. The expression of mcl-1 antisense plasmid also suppresses the anti-apoptotic effect of EGF. Taken together, these results indicate that EGF may up-regulate Mcl-1 through the MAP kinase pathway to suppress apoptosis.
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PMID:Epidermal growth factor (EGF) suppresses staurosporine-induced apoptosis by inducing mcl-1 via the mitogen-activated protein kinase pathway. 1076 23


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