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

The calcium-sensing receptor (CaR) activation has recently been shown to modulate the ERK1 and ERK2 cascade in different cell lines. The present study investigated this pathway in human normal and tumoral parathyroid cells. In cells from normal parathyroids and almost all hyperplasia increasing extracellular calcium concentrations (Ca(o)(2+)) induced a significant activation of ERK1 and -2, the percent stimulation over basal activity (at 0.5 mM Ca(o)(2+)) being 545 +/- 140 and 800 +/- 205 in normal cells and 290 +/- 71 and 350 +/- 73 in hyperplasia at 1 and 2 mM Ca(o)(2+), respectively. This effect was mediated by CaR because it was mimicked by the receptor agonist gadolinium and neomycin. Basal and Ca(o)(2+)-stimulated ERK1 and -2 activity was nearly abolished by the PKC inhibitor calphostin C, and PKA changes did not affect ERK1 and -2 activity. PI3K blockade by wortmannin, known to prevent G protein betagamma subunit effect on ERK1 and -2, induced a 30% reduction of the Ca(o)(2+)-stimulated ERK1 and -2 activity. Adenomatous cells showed high PKC-dependent ERK1 and -2 activity in resting conditions that was unresponsive to high Ca(o)(2+). A role of MAPK on PTH secretion was suggested by the finding that PD98059, a specific MEK inhibitor, abolished the inhibitory effect of 1.5 mM Ca(o)(2+) on PTH release from normal parathyroid cells. In conclusion, these data first demonstrate that CaR activation, through the PKC pathway and, to a lesser extent, PI3K, increases ERK1 and -2 activity in normal parathyroid cells and this cascade seems to be involved in the modulation of PTH secretion by Ca(o)(2+). Interestingly, this signaling pathway is disrupted in parathyroid tumors.
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PMID:Mitogen-activated protein kinase cascade in human normal and tumoral parathyroid cells. 1199 64

Cell dissociation and cell migration are the two main components of epithelium-mesenchyme transitions (EMT). We previously demonstrated that Ras is required for the accomplishment of both of these processes during the EGF-induced EMT of the NBT-II rat carcinoma cell line in vitro. In this study, we examined the downstream targets of Ras that are responsible for the dissociation and motility of NBT-II cells. Overexpression of activated forms of c-Raf and MEK1 (a component of the mitogen-activated protein kinase pathway, MAPK) led to cell dissociation, as inferred by the loss of desmosomes from the cell periphery. By contrast, active PI3K, RalA and RalB did not induce desmosome breakdown. The MEK1 inhibitor PD098059 inhibited EGF- and Ras-induced cell dispersion, whereas the PI3K inhibitor LY294002 had no effect. Accordingly, among the partial loss-of-function mutants of Ras (RasV12) that were used to distinguish between downstream targets of Ras, we found that the Raf-specific Ras mutants RasV12S35 and RasV12E38 induced cell dissociation. The PI3K- and RalGDS-activating Ras mutants had, in contrast, no effect on cell dispersion. However, MEK1 was unable to promote cell motility, whereas RasV12S35 and RasV12E38 induced cell migration, suggesting that another Ras effector was responsible for cell motility. We found that the small GTPase Rac is necessary for EGF-mediated cell dispersion since overexpression of a dominant-negative mutant of Rac1 (Rac1N17) inhibited EGF-induced NBT-II cell migration. All stimuli that promoted cell migration also induced Rac activation. Finally, coexpression of active Rac1 and active MEK1 induced the motility of NBT-II cells, suggesting that Ras mediates NBT-II cell scattering through the coordinate activation of Rac and the Raf/MAPK pathway.
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PMID:Ras induces NBT-II epithelial cell scattering through the coordinate activities of Rac and MAPK pathways. 1204 29

The role of monocyte chemoattractant protein-1 (MCP-1) in mediating the infiltration and activation of monocytes/macrophages into the sites of inflammation or tumor growth is well documented, but the molecular mechanism(s) involved in the process is poorly understood. In the current investigation, we demonstrate activation of the p42/44 MAPK-mediated signal transduction in murine peritoneal macrophages on stimulation with MCP-1 (10-100 ng/ml) in vitro. The p42/44 MAPK activation was determined by studying the expression of the phosphorylated p42/44 MAPK (Thr202/Tyr204) in the MCP-1-treated macrophages. This response was found to be rapid and time dependent, detectable within 5 min of MCP-1 stimulation. PD98058 (5-50 microM), a specific inhibitor of MAPK kinase (MEK) inhibited the p42/44 MAPK phosphorylation, indicating the specificity of the response. Furthermore, the MCP-1-induced phosphorylation of p42/44 MAPK was found to be blocked by pertussis toxin (100 ng/ml), tyrosine kinase inhibitor-genestein (10 ng/ml), PI3K inhibitor-wortmannin (20-200 microM), and anti-CCR2 antibody (2.5 microg/ml). Additionally, phosphorylation of JNK and activation of the transcription factor, c-Jun, were also noted in response to MCP-1 treatment. Lastly, the MCP1-induced p42/44 MAPK activity was correlated with the functional activation of macrophages by demonstrating the dose-specific inhibition of actin polymerization, macrophage-mediated tumor cell cytotoxicity, and tumor necrosis factor-alpha (TNF-alpha) transcription/production afforded by PD98059 in the MCP-1-treated macrophages. Taken together, these data suggest the involvement of the p42/44 MAPK/c-Jun pathway in the signal transduction process, leading to activation of murine peritoneal macrophages.
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PMID:Monocyte chemoattractant protein-1-induced activation of p42/44 MAPK and c-Jun in murine peritoneal macrophages: a potential pathway for macrophage activation. 1206 Apr 90

Transformation by ras oncogenes induces the deregulation of intracellular signalling cascades that are critical elements in cell growth control. Ras proteins are molecular switches with the ability to interact and activate several effector molecules. Among those, Raf-1 kinase, PI3K and Ral-GDS are the best characterised. Raf activates the mitogenic MEK/ERK kinases pathway, while PI3K regulates the PKB/Akt cascade, involved in the control of proliferation, metabolism and apoptotic responses. Finally, Ral-GDS belongs to a family of guanine nucleotide exchange factors that activate Ral GTPases. While Raf and PI3K have emerged as critical elements in regulating cell growth and apoptosis, little is known about the role of the Ral-GDS family. We have previously reported that Ras proteins are critical elements in the regulation of phospholipase D (PLD), a proposed target for the Ral-GDS/RalA pathway. Physiological regulation of PLD by growth factors requires the simultaneous activation of the endogenous, wild-type Ras proteins, and a PKC-dependent mechanism. Transformation by ras oncogenes induces drastic alterations in PLD activity and the usual response to external stimuli, through a PKC-independent mechanism. Here we provide further evidence on the mechanisms by which oncogenic Ras proteins induces the deregulation of PLD and here we try to identify the specific effectors involved. A complex system for PLD regulation is unravelled which implies the existence of two positive regulatory pathways, mediated by Ral-GDS and PI3K, and two negative feedback mechanisms mediated by Raf and Ral-GDS. These results strongly support participation of PLD in Ras-mediated signalling. Furthermore, we provide evidence that oncogenic Ras proteins constitutively activate PLD by mechanisms different to those used by normal Ras proteins.
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PMID:Modulation of phospholipase D by Ras proteins mediated by its effectors Ral-GDS, PI3K and Raf-1. 1216 89

Extracellular signals transduced via receptor tyrosine kinases, G-protein-coupled receptors or integrins activate Ras, a key switch in cellular signalling. Although Ras can activate multiple downstream effectors (PI3K, Ral em leader ) one of the major activated pathway is a conserved sequential protein kinase cascade referred to as the mitogen activated protein (MAP) kinase module: Raf>MEK>ERK. The fidelity of signalling among protein kinases and the spatio-temporal activation are certainly key determinants for generating precise biological responses. The fidelity is ensured by scaffold proteins, a sort of protein kinase "insulators" and/or specific docking sites among the members of the signalling cascade. These docking sites are found in upstream and downstream regulators and MAPK substrates [Nat Cell Biol 2 2000 110]. The duration and the intensity of the response are in part controlled by the compartmentalisation of the signalling molecules. Growth factors promote nuclear accumulation and persistent activation of ERK (p42/p44 MAP kinases) during the entire G1 period with an extinction during S-phase. These features are exquisitely well controlled by (i) the temporal induction of the MAP kinase phosphatases, MKP1-3, and (ii) the compartmentalisation of the signalling molecules. We have shown that MKP1-2 induction is strictly controlled by the activation of the MAP kinase module providing evidence for an autoregulatory mechanism. This negative regulatory loop was further enhanced by the capacity of ERK to phosphorylate MKP1 and 2. This action reduced the degradation rate of these MKPs through the ubiquitin-proteasomal system [Science 286 1999 2514]. Whereas the two upstream kinases of the module, Raf and MEK remained cytoplasmic, ERK anchored to MEK in the cytoplasm of resting cells, rapidly translocated to the nucleus upon mitogenic stimulation. This process was rapid, reversible, and controlled by the strict activation of the MAPK cascade. Prevention of this nuclear translocation, by overexpression of a cytoplasmic ERK-docking molecule (inactive MKP3) prevented growth factor-stimulated DNA replication [EMBO J 18 1999 664]. Following long term stimulation, ERK progressively accumulated in the nucleus in an inactive form. This nuclear retention relied on the neosynthesis of short-lived nuclear anchoring proteins. Nuclear inactivation and sequestration was likely to be controlled by MAP kinase phosphatases 1 and 2. Therefore we propose that the nucleus represents a site for ERK action, sequestration and signal termination [J Cell Sci 114 2001 3433]. In addition, with the generation of mice invalidated for each of the ERK isoforms, we will illustrate that besides controlling cell proliferation the ERK cascade also controls cell differentiation and cell behaviour [Science 286 1999 1374].
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PMID:Fidelity and spatio-temporal control in MAP kinase (ERKs) signalling. 1221 67

Signaling events involving angiotensin IV (ANG IV)-mediated pulmonary artery endothelial cell (PAEC) proliferation were examined. ANG IV significantly increased upstream phosphatidylinositide (PI) 3-kinase (PI3K), PI-dependent kinase-1 (PDK-1), extracellular signal-related kinases (ERK1/2), and protein kinase B-alpha/Akt (PKB-alpha) activities, as well as downstream p70 ribosomal S6 kinase (p70S6K) activities and/or phosphorylation of these proteins. ANG IV also significantly increased 5-bromo-2'-deoxy-uridine incorporation into newly synthesized DNA in a concentration- and time-dependent manner. Pretreatment of cells with wortmannin and LY-294002, inhibitors of PI3K, or rapamycin, an inhibitor of the mammalian target of rapamycin kinase and p70S6K, diminished the ANG IV-mediated activation of PDK-1 and PKB-alpha as well as phosphorylation of p70S6K. Although an inhibitor of mitogen-activated protein kinase kinase, PD-98059, but not rapamycin, blocked ANG IV-induced phosphorylation of ERK1/2, both PD-98059 and rapamycin independently caused partial reduction in ANG IV-mediated cell proliferation. However, simultaneous treatment with PD-98059 and rapamycin resulted in total inhibition of ANG IV-induced cell proliferation. These results demonstrate that ANG IV-induced DNA synthesis is regulated in a coordinated fashion involving multiple signaling modules in PAEC.
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PMID:Activation of multiple signaling modules is critical in angiotensin IV-induced lung endothelial cell proliferation. 1222 47

In isolated rat adipocytes, the insulin stimulation of pyruvate dehydrogenase can be partially inhibited by inhibitors of PI3K (phosphoinositide 3-kinase) and MEK1/2 (mitogen-activated protein kinase/extracellular signal-regulated kinase kinase). In combination, U0126 and wortmannin completely block the insulin stimulation of pyruvate dehydrogenase. It is concluded that the effect of insulin on pyruvate dehydrogenase in rat adipocytes involves two distinct signalling pathways: one is sensitive to wortmannin and the other to U0126. The synthetic phosphoinositolglycan PIG41 can activate pyruvate dehydrogenase but the activation is only approx. 30% of the maximal effect of insulin. This modest activation can be completely blocked by wortmannin alone, suggesting that PIG41 acts through only one of the pathways leading to the activation of pyruvate dehydrogenase.
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PMID:Insulin stimulation of pyruvate dehydrogenase in adipocytes involves two distinct signalling pathways. 1237 70

Platelet factor 4 (PF-4) is a member of the chemokine family with powerful antiangiogenic properties. The mechanism by which PF-4 inhibits endothelial cell proliferation is unclear. We investigated the effects of PF-4 on the intracellular signal transduction induced by basic fibroblast growth factor (FGF2). We found that PF-4 (10 microg/mL) inhibited the FGF2-induced proliferation of adrenal cortex capillary endothelial (ACE) cells. The inhibition of MEK1/2 (mitogen-activated protein kinase kinase) by PD98059 or of PI3K (phosphatidylinositol 3-kinase) by Ly294002 abolished the proliferation induced by FGF2, suggesting that ACE cell proliferation required dual signaling through both the extracellular signal-regulated kinase (ERK) and PI3K pathways. Ly294002 had no significant effect on ERK phosphorylation, whereas PD98059 had a weak effect on the phosphorylation of Akt, suggesting that 2 separate cascades are required for ACE cell proliferation. The addition of PF-4 (10 microg/mL) significantly inhibited ERK phosphorylation (95%), showing that PF-4 acted directly on or upstream from this kinase. Surprisingly, PF-4 did not affect FGF2-induced Akt phosphorylation. This suggests that PF-4 disrupts FGF2 signaling via an intracellular mechanism of inhibition. To exclude the possibility that PF-4 inhibited the binding of FGF2 to only one FGF receptor, preferentially activating the ERK pathway, we investigated the effect of PF-4 on FGF2-induced ERK and Akt phosphorylation, using mutant heparan sulfate-deficient Chinese hamster ovary cells transfected with the FGF-R1 cDNA. The addition of PF-4 (1 microg/mL) significantly inhibited ERK phosphorylation (90%), with no effect on Akt phosphorylation, suggesting that PF-4 acts downstream from the FGF-R1 receptor. In conclusion, this is the first report showing that PF-4 inhibits FGF2 activity downstream from its receptor.
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PMID:Platelet factor 4 inhibits FGF2-induced endothelial cell proliferation via the extracellular signal-regulated kinase pathway but not by the phosphatidylinositol 3-kinase pathway. 1238 3

Neuroblastomas are the most common extracranial solid tumors of childhood. These tumors are associated with an overall poor prognosis, particularly for advanced stage disease. The benzoquinone ansamycin antibiotic, geldanamycin (GA), exhibits potent antitumor activity in certain cancer cell lines by destabilizing important signal transduction proteins (e.g., Raf-1 and Akt). The purpose of our study was to determine whether GA can alter the expression of Raf-1 and Akt, which have been shown to be critical for neuronal cell survival, and induce apoptosis of neuroblastoma cells. Human neuroblastoma cells (SH-SY5Y, SK-N-SH and LAN-1) were treated with GA for a variable period of time. Cell viability was assessed with MTT assays. Apoptosis was assessed with DNA fragmentation ELISA, TUNEL-flow cytometric assay, Western blot and caspase activities. We found that GA decreases cell viability and induces apoptosis in the SH-SY5Y human neuroblastoma cell line. These effects were mediated through activation of caspase-9 and -3, mitochondrial release of cytochrome c and subsequent PARP cleavage. GA-induced apoptosis was associated with a reduction in the level and activity of Raf-1 and Akt. The importance of these proteins was further demonstrated by induction of apoptosis in SH-SY5Y cells by a combination of U0126 (MEK1/2 inhibitor) and LY294002 (an inhibitor of PI3K). Similar to SH-SY5Y cells, other human neuroblastoma cells (SK-N-SH and LAN-1) were sensitive to the effects of GA-induced apoptosis. Taken together, our findings suggest that GA may be a novel therapeutic agent, which may be effective in the treatment of neuroblastomas.
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PMID:Geldanamycin decreases Raf-1 and Akt levels and induces apoptosis in neuroblastomas. 1247 18

Interleukin 1beta(IL-1beta), a proinflammatory cytokine, is related with inflammatory diseases and it up-regulates MUC2 gene expression and mucin secretion. This study was designed to investigate the signal transduction pathway of the IL-1beta-mediated MUC2 gene expression and mucin secretion in human airway epithelial cells. In cultured human airway NCI-H292 epithelial cells, the steady state of the mRNA level of MUC2 gene expression and mucin secretion induced by IL-1beta were determined by reverse transcriptase-polymerase chain reaction (RT-PCR), enzyme immunoassay, and immunoblot analysis. To observe the signal pathway of the IL-1beta-mediated MUC2 gene expression and mucin secretion, we used several specific inhibitors. PD98059 (MEK/ERK inhibitor) suppressed IL-1beta-mediated MUC2 gene expression and mucin secretion, while SB203580 (p38 inhibitor) did not. Ro31-8220 (PKC inhibitor) inhibited IL-1beta-mediated MUC2 gene expression and mucin secretion. It inhibited ERK phosphorylation, but did not inhibit p38 phosphorylation. LY294002 (PI3K inhibitor) also suppressed MUC2 expression, but did not inhibit any MAPKs phosphorylation. These results suggest that the IL-1beta-mediated MUC2 gene expression and mucin secretion in NCI-H292 cells are regulated through activation of the PKC-MEK/ERK pathway, and that PI3K is also involved in the IL-1beta-mediated MUC2 gene expression and mucin secretion.
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PMID:Interleukin-1beta induces MUC2 gene expression and mucin secretion via activation of PKC-MEK/ERK, and PI3K in human airway epithelial cells. 1248 99


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