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)

Mitogen-activated protein kinase (MAPK) cascades are central components of signal transduction pathways induced by mitogens and stresses. They consist of a three-kinase module in which a mitogen-activated protein kinase kinase kinase (MAP3K) activates a mitogen-activated protein kinase kinase (MAP2K), which in turn activates MAPK. The molecular determinants that underlie specific MAP3K-MAP2K interactions are poorly understood. In this study, we examined the interaction between the MAP3K MEKK1 and MKK4, a MAP2K of the JNK pathway. Select point mutations in subdomain X of the catalytic domain of MEKK1 (MEKK1delta) were found to impair the ability of MEKK1delta to bind to and activate MKK4. Such mutations were also found to impair MEKK1delta-induced activation of an AP1 reporter gene. These studies point to a critical role for subdomain X in the interaction of MEKK1 with MKK4.
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PMID:A subdomain of MEKK1 that is critical for binding to MKK4. 1240 21

MEKK1 is a MAPK kinase kinase that is activated in response to stimuli that alter the cytoskeleton and cell shape. MEKK1 phosphorylates and activates MKK1 and MKK4, leading to ERK1/2 and JNK activation. MEKK1 has a plant homeobox domain (PHD) that has been shown to have E3 ligase activity. (Lu, Z., Xu, S., Joazeiro, C., Cobb, M. H., and Hunter, T. (2002) Mol. Cell 9, 945-956). MEKK1 kinase activity is required for ubiquitylation of MEKK1. MEKK1 ubiquitylation is inhibited by mutation of cysteine 441 to alanine (C441A) within the PHD. The functional consequence of MEKK1 ubiquitylation is the inhibition of MEKK1 catalyzed phosphorylation of MKK1 and MKK4 resulting in inhibition of ERK1/2 and JNK activation. The C441A mutation within the PHD of MEKK1 prevents ubiquitylation and preserves the ability of MEKK1 to catalyze MKK1 and MKK4 phosphorylation. MEKK1 ubiquitylation represents a mechanism for inhibiting the ability of a protein kinase to phosphorylate substrates and regulate downstream signaling pathways.
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PMID:Ubiquitylation of MEKK1 inhibits its phosphorylation of MKK1 and MKK4 and activation of the ERK1/2 and JNK pathways. 1245 88

We have previously demonstrated that hydrogen peroxide (H(2)O(2)) treatment of murine 70Z/3 pre-B lymphocytes inhibits the immune response to lipopolysaccharide by attenuating signaling through c-Jun N-terminal kinase (JNK) activation. In the present study, we further examined the signaling intermediates responsible for immunosuppression by H(2)O(2), focusing on NF-kappaB, a dimeric transcription factor whose activation is implicated in a number of immune response. Treatment of 70Z/3 pre-B cells with H(2)O(2) caused activation of NF-kappaB in the nuclei by detection of NF-kappaB specific DNA binding, concomitant with phosphorylation of IkappaBalpha. H(2)O(2) stimulation of NF-kappaB occurred within 20 min of treatment, reached maximum level at 60 min, and sustained for 2 h or more. Especially, MEK1 may contribute to H(2)O(2)-induced NF-kappaB activation as shown in the inhibition of NF-kappaB binding activity by the MEK1 inhibitor, PD 98059, and H(2)O(2)-induced MEK1 activation. However, H(2)O(2) exhibited no effect on the activity of Raf-1 kinase, which was an upstream activator of MEK1. Furthermore, B-58l and alpha-hydroxyfarnesylphosphonic acid, two inhibitors of Ras, did not block NF-kappaB activation. In addition, the transient transfection of a dominant negative Ras (RasN17) construct showed a negligible inhibitory effect on the activation of NF-kappaB by H(2)O(2). Instead, treatment of 70Z/3 cells with H(2)O(2) resulted in the activation of MAPK kinase kinase 1 (MEKK1) as well as JNK. Therefore, our data suggest that H(2)O(2) regulates the activity of NF-kappaB by MEK1 activation through MEKK1-dependent but Ras/Raf-independent mechanism.
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PMID:Raf-independent and MEKK1-dependent activation of NF-kappaB by hydrogen peroxide in 70Z/3 pre-B lymphocyte tumor cells. 1253 30

MAP kinase pathways comprise a group of parallel protein phosphorylation cascades, which are involved in signaling triggered by a variety of stimuli. Previous findings suggested that the ERK and the JNK pathways have opposing roles in regulating proliferation and survival or apoptosis and that apoptosis can be promoted by inhibiting the ERK pathway or by activation of the JNK pathway. In order to test this hypothesis and explore whether it can be exploited as a strategy for killing human cancer cells, we used gene transfer experiments with a range of cancer cell lines. We expressed the catalytic fragment of human MEKK1 to activate JNK and the Ras-binding domain (RBD) of Raf-1 to inhibit the Ras-ERK pathway. In addition, we designed several RBD-MEKK1 fusion proteins aiming to simultaneously activate the JNK and block the ERK pathway. We found that the MEKK1 proteins as well as the RBD alone could reduce colony formation in all cell lines. The survival time of MEKK1-expressing cells depended on the cell line. In HeLa cells, survival could be prolonged by inhibition of caspases but not by coexpression of the anti-apoptotic protein Bcl-2. Due to a lower kinase activity the RBD-MEKK1 fusion proteins were less effective in apoptosis induction than the MEKK1 kinase domain alone. Using mutant forms of Ras and Raf-1 we could show that the reduced kinase activity of RBD-MEKK1 fusion proteins was caused by binding to the Ras protein. The expression of lethal doses of MEKK1 resulted in a strong activation of all three major MAP kinase families JNK, ERK, and p38. Blocking these pathways either by coexpressing a dominant negative form of MKK4 or with inhibitors of MEK or p38 failed to inhibit apoptosis. This suggests that MEKK1 induces apoptosis by causing a general deregulation of MAP kinase signaling rather than by the activation of a single pathway.
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PMID:The kinase domain of MEKK1 induces apoptosis by dysregulation of MAP kinase pathways. 1256 21

In skin, the profibrotic protein connective tissue growth factor (CTGF) is not normally expressed. However, when skin cells are exposed to transforming growth factor-beta (TGF-beta), CTGF is induced in fibroblasts but not in epithelial cells. We have begun to investigate the requirements for the fibroblast-selective induction of CTGF by TGF-beta. Previously we found that this response was Smad-dependent. Now we show that protein kinase C and Ras/MEK/ERK are necessary for the TGF-beta induction of the CTGF promoter but not of a generic Smad-responsive promoter (SBE-lux). Induction of the CTGF promoter is antagonized by c-Jun or by MEKK1, suggesting that a proper balance between the Ras/MEK/ERK and JNK MAPK cascades is necessary for TGF-beta induction of CTGF. We identify the minimal CTGF promoter element necessary and sufficient to confer TGF-beta responsiveness to a heterologous promoter and show that a tandem repeat of a consensus transcription enhancer factor binding element, 5'-GAGGAATGG-3', is necessary for this induction. This element has not been previously shown to play a role in TGF-beta induction of gene expression in fibroblasts. Gel shift analysis shows that this sequence binds nuclear factors that are greatly enriched in fibroblasts relative to epithelial cells. Thus Smads, Ras/MEK/ERK, protein kinase C, and fibroblast-enriched factors that bind GAGGAATGG act together to drive the TGF-beta-mediated induction of CTGF in fibroblasts.
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PMID:Connective tissue growth factor gene regulation. Requirements for its induction by transforming growth factor-beta 2 in fibroblasts. 1257 Dec 53

Vascular endothelial cells (ECs) are constantly exposed to flow-induced shear stress. Shear stress is known to induce signaling cascades, including the extracellular signal-regulated protein kinase (ERK) pathway. STAT3 transcription factor plays a key role in cytokine stimulation. Recent studies indicate that STAT3 is involved in growth factor-induced cell cycle. In the present study, we have examined STAT3 activation of ECs under conditions of shear flow. Bovine aortic ECs cultured with serum at static state show a serum concentration-dependent phosphorylation at Tyr-705 of STAT3, whereas there is a constant basal phosphorylation at Ser-727. In ECs subjected to shear flow, a shear dose-dependent phosphorylation of Ser-727 and ERK1/2 was observed. In contrast, a concomitantly shear dose-dependent inhibition of phosphorylation at Tyr-705 was exhibited. Shear stress on ECs increased the association of ERK1/2 to STAT3. ECs treated with MEK inhibitor (U0126 or PD98059) consistently and significantly reduced the shear-induced ERK1/2 and Ser-727 phosphorylation, indicating that ERK1/2 is upstream of Ser-727 phosphorylation. Interestingly, shear-induced inhibition in Tyr-705 phosphorylation was abolished in these same inhibitor-treated ECs. Similarly, ECs transfected with a dominant positive mutant of MEK1 enhanced the phosphorylation of Ser-727 with the attenuation of the Tyr-705 phosphorylation. In contrast, when ECs were transfected with dominant positive mutant of MEKK1, JNK upstream, no change in the phosphorylation of Ser-727 and Tyr-705 was observed. These results indicate that shear flow induces the phosphorylation of Ser-727 via ERK1/2 pathway, and this Ser-727 phosphorylation inhibits Tyr-705 phosphorylation in STAT3. As a result, shear flow reduced the translocation of STAT3 into nucleus. This study shows for the first time that shear flow may play a significant role by attenuating STAT3 activation and thus may reduce inflammatory responses and/or serum-induced endothelial proliferation.
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PMID:Shear flow attenuates serum-induced STAT3 activation in endothelial cells. 1263 10

MAPK/ERK kinase kinase 2 (MEKK2) is a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family of protein kinases. MAP3Ks are components of a three-tiered protein kinase pathway in which a MAP3K phosphorylates and activates a mitogen-activated protein kinase kinase (MAP2K), which in turn activates a mitogen-activated protein kinase (MAPK). We have previously identified residues within protein kinase subdomain X in the MAP3K, MEKK1, that are critical for its interaction with the MAP2K, MKK4, and MEKK1-induced MKK4 activation. We report here that kinase subdomain X also plays a critical role in MEKK2 activity. Select point mutations in subdomain X impair MEKK2 phosphorylation of the MAP2Ks, MKK7 and MEK5, abolish MEKK2-induced activation of the MAPKs, JNK1 and ERK5, and diminish MEKK2-dependent activation of an AP-1 reporter gene. Interestingly, the spectrum of mutations in subdomain X of MEKK2 that affects its activity is overlapping with but not identical to those that have effects on MEKK1. Thus, mutations in subdomain X differentially affect MEKK2 and MEKK1.
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PMID:Mutations in protein kinase subdomain X differentially affect MEKK2 and MEKK1 activity. 1265 51

We previously reported that the alpha-subunit of heterotrimeric G13 protein induces either mitogenesis and neoplastic transformation or apoptosis in a cell-dependent manner. Here, we analyzed which signaling pathways are required for G alpha 13-induced mitogenesis or apoptosis using a novel mutant of G alpha 13. We have identified that in human cell line LoVo, the mutation encoding substitution of Arg260 to stop codon in mRNA of G alpha 13 subunit produced a mutant protein (G alpha 13-T) that lacks a COOH terminus and is endogenously expressed in LoVo cells as a polypeptide of 30 kDa. We found that G alpha 13-T lost its ability to promote proliferation and transformation but retained its ability to induce apoptosis. We found that full-length G alpha 13 could stimulate Elk1 transcription factor, whereas truncated G alpha 13 lost this ability. G alpha 13-dependent stimulation of Elk1 was inhibited by dominant-negative extracellular signal-regulated kinase (MEK) but not by dominant-negative MEKK1. Similarly, MEK inhibitor PD-98059 blocked G alpha 13-induced Elk1 stimulation, whereas JNK inhibitor SB-203580 was ineffective. In Rat-1 fibroblasts, G alpha 13-induced cell proliferation and foci formation were also inhibited by dominant-negative MEK and PD-98059 but not by dominant-negative MEKK1 and SB-203580. Whereas G alpha 13-T alone did not induce transformation, coexpression with constitutively active MEK partially restored its ability to transform Rat-1 cells. Importantly, full-length but not G alpha 13-T could stimulate Src kinase activity. Moreover, G alpha 13-dependent stimulation of Elk1, cell proliferation, and foci formation were inhibited by tyrosine kinase inhibitor, genistein, or by dominant-negative Src kinase, suggesting the involvement of a Src-dependent pathway in the G alpha 13-mediated cell proliferation and transformation. Importantly, truncated G alpha 13 retained its ability to stimulate apoptosis signal-regulated kinase ASK1 and c-Jun terminal kinase, JNK. Interestingly, the apoptosis induced by G alpha 13-T was inhibited by dominant-negative ASK1 or by SB-203580.
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PMID:G alpha 13-mediated transformation and apoptosis are permissively dependent on basal ERK activity. 1273 37

Tumour necrosis factor (TNF) induces death of oligodendrocytes, the putative cell target in multiple sclerosis. We defined that the intracellular transduction pathway involved in TNF-induced death of human adult oligodendrocytes (hOLs) is dependent on c-jun NH(2)-terminal kinase (JNK) activation, but not the other mitogen-activated protein kinase (MAPK), p38. JNK activation, measured by c-jun phosphorylation and induction of the phosphorylated form of JNK, was enhanced, prolonged and correlated with cell death in hOLs exposed to TNF. Comparative autoradiographic analysis revealed that JNK-3, but not JNK-1 or JNK-2, is responsible for prolonged JNK activation in TNF exposed hOLs. Expression of a dominant-negative mutant of JNK upstream kinase, MKK4/SEK1, inhibited apoptosis induced by TNF, whereas expression of a constitutive active mutant of MEKK1, an upstream kinase to JNK, accelerates TNF-induced apoptosis. JNK activation occurred prior to changes of mitochondrial membrane potential in hOLs exposed to TNF. These results demonstrate that TNF-induced death in adult hOLs depends on prolonged JNK-3 activation, and that this apoptosis requires the mitochondrial dysfunction that occurs after JNK activation. This is the first evidence that a JNK-3 isoform is involved in oligodendrocyte death and might have significant importance in designing new molecules to protect hOLs demise in multiple sclerosis.
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PMID:TNF-induced death of adult human oligodendrocytes is mediated by c-jun NH2-terminal kinase-3. 1276 57

To study the signaling pathway involved in the regulation of galectin-3 expression we used phorbol ester to stimulate macrophage differentiation of THP-1 cells. Treatment with phorbol 12-myristate 13-acetate (PMA) increased significantly the level of expression of galectin-3 in THP-1 cells. PMA-induced galectin-3 overexpression was blocked by: protein kinase C inhibitors staurosporine, calphostin C, and apigenin; tyrosine-specific protein kinase inhibitors genistein and tyrphostin A25; PD 98059, a selective inhibitor of mitogen-activated protein kinase (MAPK) kinase 1 (MEK1 or MKK1); and SB 203580, a specific inhibitor of p38 MAPK. Galectin-3 up-regulation was not affected by exposure to two inhibitors of cAMP-dependent protein kinase (PKA), H-89 and KT5720. Co-transfection of pPG3.5, a plasmid vector containing the rabbit galectin-3 promoter and the constructs pMCL-MKK1 N3 or pRC-RSV-MKK3Glu that constitutively express MKK1 and MKK3, raised the activity of galectin-3 promoter by 185% and 110%, respectively. Co-transfection with a Ha-Ras expression vector stimulated galectin-3 promoter activity approximately 10-fold. Expression of c-Jun or v-Jun raised the level of galectin-3 promoter activity more the three- and fourfold, respectively. Co-transfection of c-Jun and pPG3.5 5'-upstream deletion mutants resulted in a reduction of the galectin-3 promoter activity by 50% to 80%. Transfection of c-Jun, v-Jun or Ha-Ras increased significantly galectin-3 protein in THP-1 cells. These findings indicated that Ras/MEKK1/MKK1-dependent/AP-1 signal transduction pathway plays an important role in the expression of galectin-3 in PMA-stimulated macrophages. We further investigated the effect of modified lipoproteins on galectin-3 expression in macrophages. Murine resident peritoneal macrophages loaded with acetylated low-density lipoprotein (AcLDL) or oxidized LDL (OxLDL) showed increased galectin-3 protein and mRNA. These results showed that treatment of macrophages with PMA or modified lipoproteins results in galectin-3 overexpression. These findings may explain the enhanced expression of galectin-3 in atherosclerotic foam cells and suggest that Ras/MAPK signal transduction pathway is involved in controlling this gene.
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PMID:Galectin-3 expression in macrophages is signaled by Ras/MAP kinase pathway and up-regulated by modified lipoproteins. 1278 25


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