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)

Rat T lymphoblasts arrested in the G1 phase of the cell cycle by interleukin-2 (IL-2) deprivation can be forced to proceed to the S phase when they are stimulated with IL-2 or the phorbol ester phorbol 12,13-dibutyrate (PDBu). When PDBu is used as a stimulus, extracellular regulated kinase 2 (ERK2) is activated by threonine and tyrosine phosphorylation by the dual-specificity kinase MEK. Here we have studied the regulation of ERK2 dephosphorylation as a mechanism for inactivation of this kinase. In vivo inhibition of ERK2 dephosphorylation observed after preincubation with translation or transcription inhibitors (cycloheximide or actinomycin, respectively) indicates the involvement of at least one inducible phosphatase, the best candidate for which is the dual-specificity phosphatase PAC-1. Other noninducible phosphatases must act as well, however, because sodium orthovanadate is a more effective dephosphorylation blocker than cycloheximide. In addition, the okadaic acid effect in ERK2 dephosphorylation indicates that Ser/Thr phosphatases are also involved, directly and/or indirectly.
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PMID:Regulation of ERK2 dephosphorylation in G1-stimulated rat T lymphoblasts. 941 90

Intestinal trefoil factor (ITF), a small, compact protease-resistant peptide, is abundantly expressed in goblet cells of large and small intestine. Although several biological activities of ITF have been identified, including promotion of wound healing, stimulation of epithelial cell migration, and protection of intestinal epithelial barrier, little is known about signaling events through which ITF mediates its physiological function. In this study, the effects of exogenous ITF on mitogen-activated protein kinase (MAPK) signaling cascades were examined in IEC-6 cells, a nontransformed intestinal epithelial cell line that does not express endogenous trefoil peptides. Stimulation with ITF resulted in rapid decrease in extracellular signal-related protein kinase (ERK) activity and concomitant reduced ERK tyrosine phosphorylation. ITF also decreased activation of ERK activity induced by either transforming growth factor-alpha, which links extracellular stimuli to the Ras/Raf/MEK/ERK pathway via the epidermal growth factor receptor, or phorbol 12-myristate 13-acetate, which activates Raf through protein kinase C. ITF-induced inhibition of ERK activity was blocked by an inhibitor of tyrosine and dual-specific phosphatases, sodium orthovanadate. In summary, ITF leads to inhibition of ERK and the MAPK pathway through activation of tyrosine or dual-specific phosphatase.
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PMID:Intestinal trefoil factor induces inactivation of extracellular signal-regulated protein kinase in intestinal epithelial cells. 941 49

The tumor promoter palytoxin has been found to activate the stress-activated protein kinase/c-Jun NH2-terminal kinase 1 (SAPK/JNK1), and it also potentiates, as demonstrated here, the p38/HOG1 mitogen-activated protein kinase and the upstream activator of SAPK/JNK1, SEK1/MKK4. In search of possible mechanisms for both the cytotoxicity and the activation of stress kinases by palytoxin, we found that palytoxin is a potent inhibitor of cellular protein synthesis. The inhibition of translation by palytoxin does not result from its direct binding to the translational apparatus. We have previously demonstrated that ribotoxic stressors (Iordanov, M. S., Pribnow, D., Magun, J. L., Dinh, T.-H., Pearson, J. A., Chen, S. L.-Y., and Magun, B. E. (1997) Mol. Cell. Biol. 17, 3373-3381) signal the activation of SAPK/JNK1 by binding to or covalently modifying 28 S rRNA in ribosomes that are active at the time of exposure to the stressor. Palytoxin acted as a ribotoxic stressor, inasmuch as it required actively translating ribosomes at the time of exposure to activate SAPK/JNK1. Palytoxin has been shown to augment ion fluxes by binding to the Na+/K+-ATPase in the plasma membrane of cells. To determine whether altered fluxes of either Na+ or K+ could be responsible for the effects of palytoxin on translation and on activation of SAPK/JNK1, cells were exposed to palytoxin in modified culture medium in which a major portion of the Na+ was replaced by either K+ or by choline+. The substitution of Na+ by K+ strongly inhibited the ability of palytoxin both to inhibit protein translation and to activate SAPK/JNK1, whereas the substitution of Na+ by choline+ did not. These results suggest that palytoxin-induced efflux of cellular K+ mimics ribotoxic stress by provoking both translational inhibition and activation of protein kinases associated with cellular defense against stress.
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PMID:Loss of cellular K+ mimics ribotoxic stress. Inhibition of protein synthesis and activation of the stress kinases SEK1/MKK4, stress-activated protein kinase/c-Jun NH2-terminal kinase 1, and p38/HOG1 by palytoxin. 945 78

Epidermal growth factor (EGF), which plays an important role in normal and tumoral cell growth regulation, displays an ambivalent dose-dependent effect on the proliferation of epithelial cells overexpressing EGF receptor. However, the underlying molecular mechanisms remain obscure. In this study we have examined the regulation of amphiregulin (AR) gene expression by growth inhibitory (10(-9) M) and stimulatory (10(-12) M) EGF concentrations in A431 cells. The time course of AR messenger RNA (mRNA) accumulation was different with 10(-12) and 10(-9) M EGF; AR induction by 10(-9) M EGF peaked between 1 and 1.5 h, then decreased to the basal level within 2 h. Conversely, the induction by 10(-12) M EGF was slightly delayed, but persisted for 4 h. The involvement of tyrosine phosphorylation in AR induction by EGF was suggested by the ability of the tyrosine phosphatase inhibitor sodium orthovanadate to prolong AR expression induced by 10(-12) or 10(-9) M EGF. In the presence of the protein phosphatase 2A inhibitor, okadaic acid, 10(-9) M EGF induced a persistent accumulation of AR mRNA. On the contrary, okadaic acid abrogated the stimulation of AR mRNA level induced by a low EGF concentration, suggesting that both EGF concentrations activated distinct regulatory mechanisms. The signaling components involved in the differential activities of EGF in A431 cells were then examined. We previously reported a relationship between the ambivalent activity of EGF and the p42-mitogen-activated protein (MAP) kinase activity. Thus, 10(-12) M EGF induced a sustained MAP kinase activation, whereas 10(-9) M EGF led to a sharp, but transitory, activation. The MAP kinases are activated by MAP kinase kinases (MEK1 and MEK2). Whereas no significant effect of 10(-12) M EGF could be detected, 10(-9) M EGF was shown to activate MEK1 and, to a lesser extent, MEK2. Also, both MAP kinase activation and AR induction by 10(-9) M, but not by 10(-12) M, EGF were inhibited by the MEK1 inhibitor PD98059. Moreover, the involvement of c-Raf-1 in the signaling pathway induced by EGF was verified. A concentration of 10(-9) M EGF induced stimulation of c-Raf-1 kinase activity, whereas 10(-12) M EGF not only failed to activate c-Raf-1, but led to a moderate decrease in its kinase activity. These results demonstrate that in EGF receptor-overexpressing cells, EGF may differently affect gene expression and cell proliferation through distinct mechanisms of regulation.
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PMID:Differential dose-dependent effects of epidermal growth factor on gene expression in A431 cells: evidence for a signal transduction pathway that can bypass Raf-1 activation. 956 49

Hydrogen peroxide (H2O2) is a potent stimulator of signal-responsive phospholipase A2 (PLA2) in vascular smooth muscle and cultured endothelial cells. We investigated whether H2O2 plays a similar regulatory role in neurons. H2O2 did not stimulate a release of arachidonic acid from cultured neurons when applied alone but strongly enhanced the liberation of arachidonic acid evoked by maximally effective concentrations of either glutamate, the glutamate receptor agonist N-methyl-D-aspartate (NMDA), the muscarinic receptor agonist carbachol, the Na+-channel opener veratridine, or the Ca2+-ionophore ionomycin. The potentiating effects of H2O2 were strongly inhibited in the presence of the PLA2 inhibitor mepacrine, suggesting that the site of action was within the signal responsive arachidonic acid cascade. The enhancing effect of H2O2 was not reversed by protein kinase C inhibitors (chelerythrine chloride or GF 109203X) nor was it mimicked by phorbol ester treatment. H2O2 alone strongly enhanced the levels of immunodetectable activated mitogen-activated protein kinase (activated MAP kinases ERK1 and ERK2) in a Ca2+-dependent manner and this effect was additive with increases in the levels of activated MAP kinase evoked by glutamate. The enhanced release of arachidonic acid, however, was not clearly reversed by the MAP kinase kinase (MEK) inhibitor PD 98059, although this treatment effectively abolished H2O2 activation of MAP kinase. Thus, MAP kinase activation and Ca2+-dependent arachidonic acid release are regulated by oxidative stress in cultured striatal neurons.
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PMID:Hydrogen peroxide enhances signal-responsive arachidonic acid release from neurons: role of mitogen-activated protein kinase. 957 94

We showed before that in neonatal rat cardiac myocytes partial inhibition of Na+/K+-ATPase by nontoxic concentrations of ouabain causes hypertrophic growth and transcriptional regulations of genes that are markers of cardiac hypertrophy. In view of the suggested roles of Ras and p42/44 mitogen-activated protein kinases (MAPKs) as key mediators of cardiac hypertrophy, the aim of this work was to explore their roles in ouabain-initiated signal pathways regulating four growth-related genes of these myocytes, i.e. those for c-Fos, skeletal alpha-actin, atrial natriuretic factor, and the alpha3-subunit of Na+/K+-ATPase. Ouabain caused rapid activations of Ras and p42/44 MAPKs; the latter was sustained longer than 90 min. Using high efficiency adenoviral-mediated expression of a dominant-negative Ras mutant, and a specific inhibitor of MAPK kinase (MEK), activation of Ras-Raf-MEK-p42/44 MAPK cascade by ouabain was shown. The effects of the mutant Ras, an inhibitor of Ras farnesylation, and the MEK inhibitor on ouabain-induced changes in mRNAs of the four genes indicated that (a) skeletal alpha-actin induction was dependent on Ras but not on p42/44 MAPKs, (b) alpha3 repression was dependent on the Ras-p42/44 MAPK cascade, and (c) induction of c-fos or atrial natriuretic factor gene occurred partly through the Ras-p42/44 MAPK cascade, and partly through pathways independent of Ras and p42/44 MAPKs. All ouabain effects required extracellular Ca2+, and were attenuated by a Ca2+/calmodulin antagonist or a protein kinase C inhibitor. The findings show that (a) signal pathways linked to sarcolemmal Na+/K+-ATPase share early segments involving Ca2+ and protein kinase C, but diverge into multiple branches only some of which involve Ras, or p42/44 MAPKs, or both; and (b) there are significant differences between this network and the related gene regulatory pathways activated by other hypertrophic stimuli, including those whose responses involve increases in intracellular free Ca2+ through different mechanisms.
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PMID:Multiple signal transduction pathways link Na+/K+-ATPase to growth-related genes in cardiac myocytes. The roles of Ras and mitogen-activated protein kinases. 961 40

Reperfusion of cardiac tissue after an ischemic episode is associated with metabolic and contractile dysfunction, including reduced tension development and activation of the Na+-H+ exchanger (NHE). Oxygen-derived free radicals are key mediators of reperfusion abnormalities, although the cellular mechanisms involved have not been fully defined. In the present study, the effects of free radicals on mitogen-activated protein (MAP) kinase function were investigated using cultured neonatal rat ventricular myocytes. Acute exposure of spontaneously beating myocytes to 50 micromol/L hydrogen peroxide (H2O2) caused a sustained decrease in contraction amplitude (80% of control). MAP kinase activity was measured by in-gel kinase assays and Western blot analysis. Acute exposure to H2O2 (100 micromol/L, 5 minutes) resulted in sustained MAP kinase activation that persisted for 60 minutes. Catalase, but not superoxide dismutase, completely inhibited MAP kinase activation by H2O2. Pretreatment with chelerythrine (10 micromol/L, 45 minutes), a protein kinase C inhibitor, or genistein (75 micromol/L, 45 minutes) or herbimycin A (3 micromol/L, 45 minutes), tyrosine kinase inhibitors, caused significant inhibition of H2O2-stimulated MAP kinase activity (51%, 78%, and 45%, respectively, at 20 minutes). Brief exposure to H2O2 also stimulated NHE activity. This effect was completely abolished by pretreatment with the MAP kinase kinase inhibitor PD 98059 (30 micromol/L, 60 minutes). These results suggest that low doses of H2O2 induce MAP kinase-dependent pathways that regulate NHE activity during reperfusion injury.
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PMID:Hydrogen peroxide activates mitogen-activated protein kinases and Na+-H+ exchange in neonatal rat cardiac myocytes. 962 58

The influence of osmolarity and compatible organic osmolytes on the phosphorylation of the MAP-kinases Erk-1 and Erk-2 and on the expression of taurine transporter (TAUT) and lipopolysaccharide (LPS)-induced nitric oxide synthetase (iNOS) was studied in RAW 264.7 mouse macrophages. Hypoosmolarity (205 mosmol/l) but not hyperosmolarity (405 mosmol/l) or challenge of the cells with betaine or taurine increased phosphorylation of Erk-1 and Erk-2. Hypoosmotic Erk-phosphorylation was blocked by the MEK-inhibitor PD098059 but was resistant to depletion of extracellular calcium and to inhibition of PLC, PKC, erbstatin-sensitive tyrosine kinases and elevation of intracellular cAMP. Hyperosmolarity stimulated Na+-dependent taurine uptake and led to an increase of TAUT mRNA levels, whereas hypoosmotic exposure diminished both and induced a rapid efflux of the osmolyte from taurine-preloaded cells. The hyperosmotic elevation of TAUT mRNA levels was antagonized upon addition of taurine but not of betaine or myo-inositol. Hyperosmolarity increased the LPS-induced iNOS expression at the mRNA and the protein level. This was suppressed by betaine but not by taurine or myo-inositol. The osmotic regulation of taurine transport and iNOS expression appeared independent of the MEK-Erk pathway and the p38MAPK.
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PMID:Compatible organic osmolytes and osmotic modulation of inducible nitric oxide synthetase in RAW 264.7 mouse macrophages. 970 50

Stimulation of pheochromocytoma (PC12) cells with the mitogen epidermal growth factor (EGF) produced a rapid and robust accumulation of intracellular reactive oxygen species (ROS), an accumulation which, in other systems, has been shown to be essential for mitogenesis. Brief pretreatment of the cells with nerve growth factor (NGF) suppressed the EGF-mediated ROS increase. EGF failed to produce elevations in ROS in a PC12 variant stably expressing a dominant-negative p21(ras) construct (PC12-N17) or in cells pretreated with the MEK inhibitor PD098059. NGF failed to suppress the increase in ROS in the PC12 variant nnr5, which lacks p140(trk) receptors. The suppression of the increase in ROS by NGF was restored in nnr5 cells stably expressing p140(trk) (nnr5-trk), but NGF failed to prevent the increase in ROS in nnr cells expressing mutant p140(trk) receptors that lack binding sites for Shc and phospholipase Cgamma. Among several inhibitors of superoxide-generating enzymes, only the lipoxygenase inhibitor, nordihydroguaiaretic acid reduced EGF-mediated ROS accumulation. The inhibitory action of NGF on ROS production was mimicked by the nitric oxide donor, sodium nitroprusside, and was blocked by an inhibitor of nitric-oxide synthetase, L-nitroarginine methyl ester. These results suggest a novel mechanism for the rapid interruption of mitogenic signaling by the neurotrophin NGF.
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PMID:Nerve growth factor treatment prevents the increase in superoxide produced by epidermal growth factor in PC12 cells. 971 26

Angiotensin II (Ang II) is a potent pressor hormone, a stimulus for vascular smooth muscle hypertrophy and an activator of multiple tyrosine kinases. The physiological effects of Ang II are mediated through activation of AT1 and AT2 receptors, receptors that have been coupled to tyrosine kinase(s) and tyrosine phosphatases, respectively. Agonists of G protein-coupled receptors, of which Ang II is one, have recently been shown to stimulate smooth muscle contraction in part via activation tyrosine kinases. We tested the hypothesis that Ang II-induced contraction in the rat aorta was dependent on activation of tyrosine kinase(s) and specifically investigated the role of the tyrosine kinase mitogen-activated protein kinase kinase (MEK), a kinase important to the mitogen activated protein kinase (MAPK) pathway. Rat thoracic aortic strips denuded of endothelium and cultured aortic smooth muscle cells were used in isolated tissue baths for measurement of isometric contractile force and Western analyses of protein tyrosyl-phosphorylation. Ang II (0.1-100 nM)-induced contraction in the aorta was completely blocked by the AT1 receptor antagonist losartan (1 microM) but unaffected by the AT2 receptor antagonist PD123319 (100 nM) or tyrosine phosphatase inhibitor sodium orthovanadate (1 microM), indicating an AT1 receptor mediates aortic contraction to Ang II. Neither the tyrosine kinase inhibitor genistein (5 microM), inactive tyrosine kinase inhibitor daidzein (5 microM) nor MEK inhibitor PD098059 (10 microM) reduced Ang II-induced contraction; the concentrations of inhibitors used maximally reduced contraction stimulated by other agonists of G protein-coupled receptors such as serotonin. Moreover, Ang II-induced contraction was not altered by the combination of PD098059 and PD123319, indicating that it is unlikely AT2 receptor stimulation masks activation of the MAPK pathway through AT1 receptor activation. The nonflavone tyrosine kinase inhibitor tyrphostin B42 (30 microM) reduced Ang II-induced maximal contraction (to 11.2% control) but, unlike the other tyrosine kinase inhibitors, also reduced KCl-induced contraction (to 55.2% control), indicating a probable nonselectivity of tyrphostin B42. Ang IIinduced maximal contraction was reduced by the L-type voltage gated calcium channel antagonist nifedipine (50 nM), consistent with the activation of calcium channels by Ang II. In cultured rat aortic smooth muscle cells, Ang II (0.1-1000 nM) stimulated concentration-dependent tyrosyl-phosphorylation of the extracellular signal regulated kinase (Erk) mitogen activated protein kinases (maximal stimulation, fold basal: Erk-1 = 17-fold, Erk-2 = 3-fold), indicating that Ang II can activate MEK. Losartan (1 microM) abolished Ang II (10 nM)-induced Erk tyrosyl-phosphorylation and PD098059 (10 microM), which did not diminish Ang II-induced aortic contraction, reduced Ang II (10 nM)-stimulated phosphorylation of Erk-2 by 72%. Finally, Ang II (1 microM) increased tyrosyl-phosphorylation of the Erk proteins in isolated aorta exposed to Ang II for 5 min. Thus, while Ang II can stimulate both MEK activation and vascular contraction via interaction with AT1 receptors, stimulation of MEK does not appear to be important for Ang II-induced contraction. These findings dissociate the process of Ang II-stimulated Erk protein tyrosyl-phosphorylation from Ang II-induced contraction in the rat aorta.
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PMID:Dissociation of angiotensin II-stimulated activation of mitogen-activated protein kinase kinase from vascular contraction. 973 8


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