Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.25 (MEKK1)
 1,856 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Various elements of the MAP kinase module have been isolated in plants. We describe here the characterisation of 14 new plant cDNAs and genes encoding putative MAP kinase kinase kinases (MAP3Ks) related to the MEKK/STE11 and RAF protein kinases. Plant MAP3Ks are characterised by a variety of primary structures conserved within closely related proteins. Southern blot analysis suggests that plant MAP3Ks are heterogenous in their genomic structure, existing either as single copy genes or as small gene families. An RT-PCR analysis showed that in Arabidopsis thaliana, all organs studied contain detectable levels of transcripts of each of the MAP3K genes identified; however, signals obtained with mature pollen were weak or non-existent except for AtMAP3Kgamma. None of the reported genes share a cell-cycle or a cold stress regulated expression.
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PMID:Characterisation of novel plant genes encoding MEKK/STE11 and RAF-related protein kinases. 1009 17

The transcription factor nuclear factor (NF)-kappaB is activated by oxidative stress or cytokines and is critical to the activation of inflammatory genes. Here, we report that hydrogen peroxide or 3-morpholinosydnonimine, which simultaneously releases nitric oxide and superoxide, synergize with the cytokine tumor necrosis factor (TNF)-alpha to activate NF-kappaB in rat lung epithelial cells, suggesting that signaling pathways elicited by reactive oxygen species (ROS)/reactive nitrogen species (RNS) are different from TNF-induced signaling. These findings were substantiated by observations that levels of IkappaB-alpha did not change after exposure to ROS/RNS, whereas a rapid depletion of IkappaB-alpha was observed in cells exposed to TNF. In addition, the proteosome inhibitor MG132 did not affect activation of NF-kappaB by ROS/RNS, whereas it abolished the TNF response. Transfection of a dominant negative Ras construct prevented the activation of NF-kappaB by ROS/RNS, demonstrating the requirement for Ras in the activation of NF-kappaB by oxidants. In contrast, TNF activated NF-kappaB in a Ras-independent fashion. Evaluation of members of the mitogen-activated protein kinase (MAPK) family as downstream effectors of Ras revealed the requirement of MAPK/ extracellular-regulated kinase (ERK) kinase kinase (MEKK)1 and c-Jun N-terminal kinases in the induction of NF-kappaB by both oxidants and TNF, whereas the MEK-ERK pathway negatively regulates NF-kappaB. Our findings demonstrate that cytokines and oxidants cooperate in the activation of transcription factors through distinct pathways, and suggest that anti-inflammatory and antioxidant therapies may be required in concert to prevent the activation of NF-kappaB-regulated genes important in the development of inflammatory diseases.
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PMID:Cooperativity between oxidants and tumor necrosis factor in the activation of nuclear factor (NF)-kappaB: requirement of Ras/mitogen-activated protein kinases in the activation of NF-kappaB by oxidants. 1022 64

We demonstrated previously that in bovine tracheal myocytes, pretreatment with either forskolin or histamine significantly reduces both platelet-derived growth factor (PDGF)- and epidermal growth factor- induced Raf-1 activation but fails to inhibit extracellular signal-regulated kinase (ERK) activation substantially, evidence of a Raf-1-independent ERK activation pathway. To identify Raf-1-independent upstream signaling intermediates of mitogen-activated protein kinase/ERK kinase-1 (MEK1), the dual-function kinase required and sufficient for ERK activation in these cells, lysates from forskolin and PDGF-treated bovine tracheal myocytes were resolved using ion exchange chromatography. Kinase activity for MEK1 was assessed by in vitro phosphorylation assay. In all experiments, the major peak of MEK1 phosphorylation activity was detected in fractions 18 through 26 (80 to 160 mM NaCl), with the peak fraction eluting at a NaCl concentration of 140 mM. The ability of these fractions to activate MEK1 was confirmed by examining the phosphorylation of myelin basic protein, a known substrate for ERKs, in the presence of functional MEK1 and ERK1. Fractions containing kinase activity were also probed with antibodies against MEK kinase-1, Raf-1, A-Raf, B-Raf, Mos, and Tpl-2. None of these proteins was detected in fractions containing peak kinase activity, suggesting the presence of a novel PDGF-stimulated, forskolin-insensitive MEK1 kinase. Further separation of fractions holding peak MEK phosphorylation activity by gel filtration suggested an apparent molecular mass of 40 to 45 kD. We conclude that PDGF-induced activation of MEK1 in bovine tracheal myocytes is mediated at least in part by a novel kinase.
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PMID:Partial characterization of a novel mitogen-activated protein kinase/extracellular signal-regulated kinase activator in airway smooth-muscle cells. 1022 75

Effects of inhibitors of PI 3-kinase and MEK kinases were investigated on histamine, leukotriene C4(LTC4), and cytokine release from human basophils stimulated with anti-IgE. The PI 3-kinase antagonists wortmannin (> 10 nM) and LY 294002 (>1 microM) strongly inhibited anti-IgE-induced release of all mediators by 40-100%. This was contrasted by the effects of the MEK kinase inhibitor PD 098059, which weakly inhibited histamine, interleukin (IL)-4, and IL-13 release but was substantially more efficacious at blocking LTC4 production (>70% at 10 microM). Previous studies have shown that arachidonic acid synthesis is controlled by MEK kinases. We observed that wortmannin, LY 294002, and PD 098059 reduce basophil ERK-1,2 activation, thus implying that, with regard to arachidonic acid metabolism, MEK kinases are a downstream target for PI-3-kinase. Our results demonstrate a universal regulatory role played by PI 3-kinases in basophil mediator production and release, whereas MEK kinase signaling is largely limited to controlling arachidonic acid metabolism.
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PMID:Inhibitors of PI 3-kinase and MEK kinase differentially affect mediator secretion from immunologically activated human basophils. 1038 Sep 14

Raf-1 activation and Bcl-2 hyperphosphorylation following treatment with paclitaxel (Taxol) or other microtubule-active drugs is associated with mitotic arrest. Here we show that microtubule-active drugs do not activate the mitogen-activated protein kinase (MAPK) pathway in leukemia cells. PD98059, a MEK inhibitor, and SB202190, a p38 MAP kinase inhibitor, do not abrogate Bcl-2 phosphorylation nor apoptosis. Simultaneously with PARP cleavage, paclitaxel induces cleavage of Bcl-2 protein yielding a potentially pro-apoptotic 22 kDa product. In comparison, the stimulation of Raf-1 by phorbol ester (TPA) activates the MAPK pathway, causes MAPK-dependent p21WAF1/CIP1 induction, Rb dephosphorylation and growth arrest without Bcl-2 phosphorylation or apoptosis. Like TPA, cAMP induces p21WAF1/CIP1 but does not cause Bcl-2 phosphorylation. MEKK1 and Ras, upstream activators of JNK and ERK MAPK, also fail to induce Bcl-2 hyperphosphorylation. Although Lck tyrosine kinase has been recently implicated in Raf-1 activation during mitotic arrest, microtubule-active drugs induce Raf-1/Bcl-2 hyperphosphorylation and apoptosis in a Lck-deficient Jurkat cells. Therefore, microtubule-active drugs induce apoptosis which is associated with Raf-1 and Bcl-2 phosphorylation and Bcl-2 cleavage but is independent of the MAPK pathway. In contrast, TPA-activated MAPK pathway causes p21WAF1/CIP1-dependent growth arrest without apoptosis.
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PMID:Mitogen-activated protein kinase pathway is dispensable for microtubule-active drug-induced Raf-1/Bcl-2 phosphorylation and apoptosis in leukemia cells. 1040 Apr 18

In this study we describe that platelet-derived growth factor (PDGF), 12-O-tetradecanoyl-phorbol-acetate (TPA), and forskolin induced CREB (cAMP-responsive element-binding protein) Ser-133 phosphorylation with comparable magnitude and kinetics in NIH 3T3 cells. While forskolin was the most potent activator of CREB, TPA or PDGF modestly increased CREB activity. The role of protein kinase C, protein kinase A, and the Raf-MEK kinase pathway in the activation and Ser-133 phosphorylation of CREB by these three stimuli was investigated. We found that inhibition of the Raf-MEK kinase pathway efficiently blocks transcriptional activation of CREB by all three stimuli. This dominant involvement of Raf-MEK in CREB transcriptional activation seems to be uncoupled from CREB Ser-133 phosphorylation. We further demonstrate that although inhibition of Raf-MEK represses forskolin-induced CREB activation, forskolin by itself failed to activate ERK1/2 and Elk-1 mediated transcription. These results suggest that a basal level of Raf-MEK activity is necessary for both PDGF- and forskolin-induced CREB activation, independent of CREB Ser-133 phosphorylation.
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PMID:A dominant role for the Raf-MEK pathway in forskolin, 12-O-tetradecanoyl-phorbol acetate, and platelet-derived growth factor-induced CREB (cAMP-responsive element-binding protein) activation, uncoupled from serine 133 phosphorylation in NIH 3T3 cells. 1040 59

c-Jun N-terminal protein kinase (JNK), a member of the mitogen-activated protein (MAP) kinase family, regulates gene expression in response to various extracellular stimuli. JNK is activated by JNK-activating kinase (JNKK1 and JNKK2), a subfamily of the dual specificity MAP kinase kinase (MEK) family, through phosphorylation on threonine (Thr) 183 and tyrosine (Tyr) 185 residues. The physiological functions of the JNK pathway, however, are not completely understood. A major obstacle is the lack of specific and activated kinase components that can stimulate the JNK pathway in the absence of any stimulus. Here we show that fusion of JNK1 to its upstream activator JNKK2 resulted in its constitutive activation. In HeLa cells, the JNKK2-JNK1 fusion protein showed significant JNK activity, which was comparable with that of JNK1 activated by many stimuli and activators, including EGF, TNF-alpha, anisomycin, UV irradiation, MEKK1, and small GTP binding proteins Rac1 and Cdc42Hs. Immunoblotting analysis indicated that JNK1 was phosphorylated by JNKK2 in the fusion protein on both Thr(183) and Tyr(185) residues. Like JNKK2, the JNKK2-JNK1 fusion protein was highly specific for the JNK pathway and did not activate either p38 or ERK2. Transient transfection assays demonstrated that the JNKK2-JNK1 fusion protein was sufficient to stimulate c-Jun transcriptional activity in the absence of any stimulus. Immunofluorescence analysis revealed that the JNKK2-JNK1 fusion protein was predominantly located in the nucleus of transfected HeLa cells. These results indicate that the JNKK2-JNK1 fusion protein is a constitutively active Jun kinase, which will facilitate the investigation of the physiological roles of the JNK pathway.
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PMID:The JNKK2-JNK1 fusion protein acts as a constitutively active c-Jun kinase that stimulates c-Jun transcription activity. 1050 43

Mitogen-activated protein kinases (MAPKs) are inactivated by dual-specificity and protein tyrosine phosphatases (PTPs) in yeasts. In Saccharomyces cerevisiae, two PTPs, Ptp2 and Ptp3, inactivate the MAPKs, Hog1 and Fus3, with different specificities. To further examine the functions and substrate specificities of Ptp2 and Ptp3, we tested whether they could inactivate a third MAPK, Mpk1, in the cell wall integrity pathway. In vivo and in vitro evidence indicates that both PTPs inactivate Mpk1, but Ptp2 is the more effective negative regulator. Multicopy expression of PTP2, but not PTP3, suppressed growth defects due to the MEK kinase mutation, BCK1-20, and the MEK mutation, MKK1-386, that hyperactivate this pathway. In addition, deletion of PTP2, but not PTP3, exacerbated growth defects due to MKK1-386. Other evidence supported a role for Ptp3 in this pathway. Expression of MKK1-386 was lethal in the ptp2Delta ptp3Delta strain but not in either single PTP deletion strain. In addition, the ptp2Delta ptp3Delta strain showed higher levels of heat stress-induced Mpk1-phosphotyrosine than the wild-type strain or strains lacking either PTP. The PTPs also showed differences in vitro. Ptp2 was more efficient than Ptp3 at binding and dephosphorylating Mpk1. Another factor that may contribute to the greater effectiveness of Ptp2 is its subcellular localization. Ptp2 is predominantly nuclear whereas Ptp3 is cytoplasmic, suggesting that active Mpk1 is present in the nucleus. Last, PTP2 but not PTP3 transcript increased in response to heat shock in a Mpk1-dependent manner, suggesting that Ptp2 acts in a negative feedback loop to inactivate Mpk1.
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PMID:Differential regulation of the cell wall integrity mitogen-activated protein kinase pathway in budding yeast by the protein tyrosine phosphatases Ptp2 and Ptp3. 1052 53

In haploid Saccharomyces cerevisiae, the mating and invasive growth (IG) pathways use the same mitogen-activated protein kinase kinase kinase kinase (MAPKKKK, Ste20), MAPKKK (Ste11), MAPKK (Ste7), and transcription factor (Ste12) to promote either G(1) arrest and fusion or foraging in response to distinct stimuli. This exquisite specificity is the result of pathway-specific receptors, G proteins, scaffold protein, and MAPKs. It is currently not thought that the shared signaling components function under the basal conditions of vegetative growth. We tested this hypothesis by searching for mutations that cause lethality when the STE11 gene is deleted. Strikingly, we found that Ste11, together with Ste20, Ste7, Ste12, and the IG MAPK Kss1, functions in a third pathway that promotes vegetative growth and is essential in an och1 mutant that does not synthesize mannoproteins. We term this pathway the STE vegetative growth (SVG) pathway. The SVG pathway functions, in part, to promote cell wall integrity in parallel with the protein kinase C pathway. During vegetative growth, the SVG pathway is inhibited by the mating MAPK Fus3. By contrast, the SVG pathway is constitutively activated in an och1 mutant, suggesting that it senses intracellular changes arising from the loss of mannoproteins. We predict that general proliferative functions may also exist for other MAPK cascades thought only to perform specialized functions.
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PMID:The MAPKKK Ste11 regulates vegetative growth through a kinase cascade of shared signaling components. 1053 82

We previously reported the identification of Mkh1, a MEK kinase in Schizosaccharomyces pombe that is required for cell wall integrity, and we presented genetic evidence that Pmk1/Spm1, a MAP kinase, functions downstream from Mkh1 in the same pathway. Here, we report the identification of Skh1, a MEK (MAP kinase kinase) in S. pombe. The sequence of Skh1 is nearly identical to that of the recently reported Pek1 sequence. We present biochemical and genetic evidence that Skh1 is the MEK component of the Mkh1-Spm1 MAP kinase cascade. Our yeast two-hybrid results indicate that Mkh1, Skh1, and Spm1 physically interact to form a ternary complex. Deletion of mkh1, skh1 or spm1 results in identical phenotypes, including sensitivity to (beta)-glucanase treatment, growth inhibition on media containing KCl, and filamentous growth on medium containing caffeine. Double mutant strains exhibit phenotypes that are identical to the single mutant strains. Furthermore, expression of an activated HA-Skh1(DD )protein suppressed these defects in mkh1(delta) cells, and overexpression of Spm1 suppressed these defects in skh1(delta) cells. We also show that HA-Spm1 is hyper-phosphorylated on tyrosine residues in cells co-expressing the activated HA-Skh1(DD) protein. Furthermore, we found the phosphorylated/activated form of GFP-HA-Spm1 at detectable levels in wild-type cells, but not at appreciable levels in mkh1(delta) or skh1(delta) cells expressing this fusion protein. Together, our results indicate that Mkh1, Skh1 and Spm1 constitute a MAPK cascade in fission yeast.
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PMID:Skh1, the MEK component of the mkh1 signaling pathway in Schizosaccharomyces pombe. 1059 34


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