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 pleiotropic cytokine tumor necrosis factor-alpha (TNF alpha) controls the expression of multiple gene products in macrophages and plays an important role in host defense. TNF alpha is recognized by the receptors, CD120a (p55) and CD120b (p75). Ligation of CD120a (p55) by TNF alpha or by anti-receptor agonistic antibodies initiates signal transduction leading to the activation of mitogen-activated protein kinases (MAPKs) (p42mapk/erk2 and p44mapk/erk1). Phosphorylation and activation of MAPK are mediated by MAPK kinase (MEK), a family of Thr/Tyr kinases. In this study, we investigated the preferential involvement of the MEK isoforms MEK1 and MEK2 in the activation of p42mapk/erk2 in mouse macrophages stimulated with TNF alpha. Exposure of macrophages to TNF alpha stimulated a time-dependent increase in the activity of MEK1 as measured by an in vitro kinase assay using kinase-inactive p42mapk/erk2 (rMAPKkd) as substrate in the presence of gamma-[32P]ATP. Maximal activation of MEK1 was detected at 10 min poststimulation and coincided with maximal transphosphorylation of Tyr and Thr residues of rMAPKkd. By contrast, there was no evidence of MEK2 activation in macrophages in response to TNF alpha. These data suggest that MEK1 is the preferred substrate for MEK kinase, the upstream kinase implicated in activation of the MAPK pathway in macrophages by TNF alpha.
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PMID:Preferential involvement of MEK1 in the tumor necrosis factor-alpha-induced activation of p42mapk/erk2 in mouse macrophages. 749 90

Recent evidence suggests that reactive oxygen species (ROS) may function as second messengers in intracellular signal transduction pathways. We explored the possibility that ROS were involved in lysophosphatidic acid (LPA)-induced mitogen-activated protein (MAP) kinase signaling pathway in HeLa cells. Antioxidant N-acetylcysteine inhibited the LPA-stimulated MAP kinase kinase activity. Direct exposure of HeLa cells to hydrogen peroxide resulted in a concentration- and time-dependent activation of MAP kinase kinase. Inhibition of catalase with aminotriazole enhanced the effect of LPA on induction of MAP kinase kinase. Further, LPA stimulated ROS production in HeLa cells. These findings suggest that ROS participate in the LPA-elicited MAP kinase signaling pathway.
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PMID:Participation of reactive oxygen species in the lysophosphatidic acid-stimulated mitogen-activated protein kinase kinase activation pathway. 749 58

The prototype mitogen-activated protein (MAP) kinase module is a three-kinase cascade consisting of the MAP kinase, extracellular signal-regulated protein kinase (ERK) 1 or ERK2, the MAP/ERK kinase (MEK) MEK1 or MEK2, and the MEK kinase, Raf-1 or B-Raf. This and other MAP kinase modules are thought to be critical signal transducers in major cellular events including proliferation, differentiation, and stress responses. To identify novel mammalian MAP kinase modules, polymerase chain reaction was used to isolate a new MEK family member, MEK5, from the rat. MEK5 is more closely related to MEK1 and MEK2 than to the other known mammalian MEKs, MKK3 and MKK4. MEK5 is thought to lie in an uncharacterized MAP kinase pathway, because MEK5 does not phosphorylate the ERK/MAP kinase family members ERK1, ERK2, ERK3, JNK/SAPK, or p38/HOG1, nor will Raf-1, c-Mos, or MEKK1 highly phosphorylate it. Alternative splicing results in a 50-kDa alpha and a 40-kDa beta isoform of MEK5. MEK5 beta is ubiquitously distributed and primarily cytosolic. MEK5 alpha is expressed most highly in liver and brain and is particulate. The 23 amino acids encoded by the 5' exon in the larger alpha isoform are similar to a sequence found in certain proteins believed to associate with the actin cytoskeleton; this alternatively spliced modular domain may lead to the differential subcellular localization of MEK5 alpha.
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PMID:Isolation of MEK5 and differential expression of alternatively spliced forms. 749 18

The p53 tumor suppressor protein is tightly regulated in the cell and is phosphorylated at multiple sites by several different protein kinases. We have investigated the phosphorylation of p53 by mitogen-activated protein (MAP) kinase, a protein kinase that plays a central role in mediating many mitogenic and differentiation signals. Recombinant wild-type mouse p53 was phosphorylated in vitro by activated recombinant p42-MAP kinase but not by inactive MAP kinase or by the activating protein, MAP kinase kinase. Phosphorylation of p53 by MAP kinase occurred at two N-terminal sites, threonine residues 73 and 83. Tryptic phosphopeptides of recombinant p53 phosphorylated in vitro by MAP kinase comigrated on two-dimensional maps with p53 from SV3T3 cells labeled in vivo with [32P]orthophosphate, suggesting that MAP kinase targets a site in p53 that is phosphorylated in the cell. Following serum stimulation of quiescent C57MG cells, two p53 kinases, which were resolved by chromatography on Mono Q, were stimulated 15-20-fold within 5 min. Each of these kinase activities co-eluted with myelin basic protein kinase activity and could be inactivated following treatment with protein phosphatase 2A, a serine/threonine phosphatase, or leukocyte antigen receptor, a protein tyrosine phosphatase, suggesting that these activities were members of the MAP kinase family. The two kinase activities from the lysates targeted the same phosphorylation sites on p53 as the purified recombinant MAP kinase. These protein kinase activities were also stimulated following exposure of the cells to ultraviolet radiation, but with slightly delayed kinetics. Phorbol ester treatment of SV3T3 cells led to increased phosphorylation of the peptide containing the residues targeted by MAP kinase. The data suggest that p53 may be phosphorylated by MAP kinase physiologically and that this interaction may be involved in the cell's response to UV exposure, growth factor stimulation, or transformation by oncogenes.
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PMID:Phosphorylation of the tumor suppressor protein p53 by mitogen-activated protein kinases. 751 Jul 6

We have purified 42- and 44-kilodalton (kDa) isoforms of the mitogen-activated protein (MAP) kinase family from bovine brain. The kinases were assayed with myelin basic protein as the substrate and detected by anti-sea star p44mpk antibody. Purification was achieved using phenyl-Sepharose, polylysine-agarose, hydroxylapatite, and Mono-Q column chromatography. Both myelin basic protein and smooth muscle caldesmon, but not histone H1, served as good substrates. Based on chromatographic behaviors and specific activities toward myelin basic protein, it is likely that the 42-kDa brain isoform is similar to that of brain tau kinase. The 44-kDa enzyme, however, is a novel brain MAP kinase isoform not reported previously. Although it has been demonstrated that p44mpk can be activated in vitro through phosphorylation by the tyrosine kinase p56lck, neither of the brain kinases were significantly stimulated by the tyrosine kinases p56lck, p56lyn, or p59fyn. However, based on antibody cross-reactivity, a MAP kinase kinase is present in the crude brain extract. Both brain MAP kinases were capable of autophosphorylation which occurred, at least in part, on tyrosine residues. However, only the 44-kDa isoform showed a significant degree of coincident activation.
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PMID:MAP kinases from bovine brain: purification and characterization. 751 82

T-cell antigen receptor (TCR) ligation of an Lck-deficient Jurkat mutant, J.CaM1, with anti-CD3 or anti-TCR beta monoclonal antibodies failed to induce tyrosine phosphorylation and activation of p42MAPK. The same stimuli activated mitogen-activated protein (MAP) kinase in J.CaM1 cells transfected with Lck, demonstrating that Lck plays a critical role in MAP kinase activation. Utilizing immunocomplex kinase assays, we demonstrated that TCR/CD3 ligation activated a MAP kinase kinase kinase (Raf-1) as well as a MAP kinase kinase (MEK-1) in Jurkat but not in J.CaM1 cells. It was possible, however, to activate Raf-1, MEK-1, and p42MAPK in J.CaM1 cells during treatment with the phorbol ester phorbol 12-myristate 13-acetate, which activates protein kinase C (PKC). This demonstrates the presence of a PKC-dependent pathway which functions independently from Lck in MAP kinase activation. Stimulation of Jurkat cells with either anti-TCR beta or anti-CD3 monoclonal antibody failed to induce substantial tyrosine phosphorylation of Shc proteins or their association with Grb2 which forms a complex with the guanine nucleotide exchange factor hSOS. However, the same stimuli induced tyrosine phosphorylation of another putative guanine nucleotide exchange factor, p95Vav, in Jurkat but not J.CaM1 cells. Moreover, Lck was reversibly co-immunoprecipitated with p95Vav, and the stoichiometry of binding increased in anti-CD3-treated Jurkat cells. Phorbol 12-myristate 13-acetate did not induce tyrosine phosphorylation of p95Vav. These data show that the TCR activates MAP kinase by way of a signaling cascade, which depends upon Lck, and may be mediated by downstream events involving PKC or p95Vav which act on Raf-1 and MEK-1.
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PMID:The T-cell antigen receptor utilizes Lck, Raf-1, and MEK-1 for activating mitogen-activated protein kinase. Evidence for the existence of a second protein kinase C-dependent pathway in an Lck-negative Jurkat cell mutant. 751 37

Interferons (IFNs) exert antiproliferative effects on many types of cells. The underlying molecular mechanism, however, is unclear. One possibility is that IFNs block growth factor-induced mitogenic signaling, which involves activation of Ras/Raf-1/MEK/mitogen-activated protein kinase. We have tested this hypothesis by using HER14 cells (NIH 3T3 cell expressing both platelet-derived growth factor [PDGF] and epidermal growth factor [EGF] receptors) as a model system. Our studies showed that IFNs (alpha/beta and gamma) blocked PDGF-and phorbol ester- but not EGF-stimulated DNA synthesis and cell proliferation. While the ligand-stimulated receptor tyrosine phosphorylation and interaction with downstream signaling molecules, such as GRB2, were not affected, IFNs specifically blocked PDGF- and phorbol ester- but not EGF-stimulated activation of Raf-1, mitogen-activated protein kinases, and tyrosine phosphorylation of an unidentified 34-kDa protein. This inhibition could be detected as early as 5 min after IFN treatments and was insensitive to cycloheximide, indicating that de novo protein synthesis is not required. The IFN-induced inhibition acted upstream of Raf-1 kinase and downstream of diacyl glycerol/phorbol ester, suggesting that protein kinase C (PKC) is the potential primary target. Consistently, downregulation of PKC by chronic phorbol myristate acetate treatment or inhibition of PKC by H7 and staurosporine blocked PDGF- and phorbol myristate acetate- but not EGF-induced signaling and DNA synthesis. Moreover, incubating cells with antisense oligodeoxyribonucleotides of PKC delta eliminated production of PKC delta protein and specifically blocked PDGF- but not EGF-stimulated mitogenesis in these cells. Thus, these studies have elucidated a major difference in the early events of EGF-and PDGF-stimulated signal transduction and, more importantly, revealed a novel mechanism by which IFNs may execute their antiproliferative function.
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PMID:Interferons block protein kinase C-dependent but not-independent activation of Raf-1 and mitogen-activated protein kinases and mitogenesis in NIH 3T3 cells. 862 73

In the renal medulla during antidiuresis, the extracellular fluid becomes hyperosmotic. Madin-Darby canine kidney (MDCK) epithelial cells adapt in hyperosmotic conditions and serve as a useful tissue culture model for cellular responses to hyperosmolality. We demonstrate that hyperosmolality stimulates phospholipase C, Raf-1 kinase mitogen-activated protein (MAP) kinase kinase, MAP kinase, and S6 kinase activities and that it increases phosphorylation of Raf-1 kinase, and p42 MAP kinase in MDCK cells. Stimulation of these kinases is osmolality-dependent (from 300 to 600 mosm/kg H2O). The time course of activation is sequential; the peak stimulation for Raf-1 kinase is at 5 min, at 10 min for MAP kinase kinase and MAP kinase, and at 20 min for S6 kinase. The activation of Raf-1 kinase and MAP kinase is inhibited by phorbol 12-myristate 13-acetate pretreatment in the presence of calphostin C or H-7. Tyrosine kinase inhibitors (genistein, herbimycin) do not significantly suppress hyperosmolality-induced MAP kinase activity. The increase of Ins-1,4,5-P3 levels by hyperosmolality suggests that activation of these kinases is mediated at least partially via activation of phospholipase C. Thus, hyperosmolality stimulates the serine/threonine kinases, Raf-1 kinase, MAP kinase kinase, MAP kinase, and S6 kinase, via predominantly protein kinase C-dependent, tyrosine kinase-independent pathways in MDCK cells.
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PMID:Sequential activation of Raf-1 kinase, mitogen-activated protein (MAP) kinase kinase, MAP kinase, and S6 kinase by hyperosmolality in renal cells. 752 42

In KB epidermoid cells, we previously showed that interleukin-1 alpha (IL-1) and various mitogens activate the mitogen-activated protein (MAP) kinases ERK1 and ERK2, which phosphorylate both myelin basic protein (MBP) and a peptide containing Thr669 of the epidermal growth factor receptor. In cell-free extracts made from gingival fibroblasts treated with platelet-derived growth factor or HepG2 hepatoma cells stimulated with phorbol myristate acetate, MBP and Thr669 kinase were both elevated 4-fold, and ERK1 and ERK2 were tyrosine-phosphorylated. In these cells IL-1 activated a kinase(s) that phosphorylated Thr669 peptide but not MBP and failed to cause tyrosine phosphorylation of ERK1/ERK2. Ceramide has been proposed as an intracellular mediator of IL-1 action, but C2-ceramide or sphingosine stimulated predominantly MBP-specific kinase activity in fibroblasts and had no effect in HepG2 cells. p54 MAP kinase (also called stress-activated protein kinase) is a c-Jun kinase first isolated from livers of cycloheximide-treated rats. After IL-1 stimulation, immunoprecipitates of lysates made from all three cell types with specific anti-p54 MAP kinase serum contained Thr669 and c-Jun phosphorylating activity, whereas precipitates from unstimulated cells contained no detectable p54 kinase activity. The major peak of IL-1-stimulated HepG2 Thr669 kinase activity co-chromatographed on Mono Q and phenyl-Superose with immunodetectable p54 MAP kinase. IL-1 did not cause p21ras activation in any cell type. Induction of Thr 669 kinase activity was not abrogated by elevation of cAMP levels, which has been shown to interfere with the activation of Raf-1. We could not detect MAP kinase kinase phosphorylating activity in unfractionated lysates made from IL-1-stimulated fibroblasts or HepG2 cells. KB cells contained a small amount of this activity, but it was not precipitated with an anti-Raf-1 antibody. We conclude that most of the IL-1-activated Thr669 kinase activity in fibroblasts and HepG2 cells, and a portion in KB cells, is due to p54 MAP kinase and that its activation is Ras-, Raf-, and MAP kinase kinase-independent.
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PMID:Interleukin-1 activates p54 mitogen-activated protein (MAP) kinase/stress-activated protein kinase by a pathway that is independent of p21ras, Raf-1, and MAP kinase kinase. 752 98

A temperature-sensitive mutant of the v-Abl protein has previously been shown to exhibit tyrosine protein kinase activity in Interleukin 3 (IL-3)-dependent IC.DP cells grown at the permissive temperature (32 degrees C) but not at the restrictive temperature (39 degrees C). These IC.DP cells are dependent on IL-3 for suppression of apoptosis at 39 degrees C, but at 32 degrees C cells will survive without added growth factor. Both IL-3 and v-Abl stimulated the tyrosine phosphorylation of SHC and GTPase-activating protein. However, while IL-3 stimulated similar levels of tyrosine phosphorylation in p46shc and p52shc, v-Abl preferentially phosphorylated p52shc, an event that occurred within 1 h of temperature switch. v-Abl also differentially associated with p46shc in a temperature-independent manner. In contrast, only IL-3 stimulated detectable increases in both myelin basic protein kinase and mitogen-activated protein (MAP) kinase kinase in in vitro assays, although in more specific MAP kinase activity assays a very slight increase in the activity of this enzyme was observed after 6 h at the permissive temperature. Time course studies suggest that phosphorylation and association of SHC with v-Abl is insufficient to lead to significant activation of MAP kinase and that activation of the MAP kinase kinase/MAP kinase pathway is not required for apoptotic suppression.
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PMID:v-Abl-mediated apoptotic suppression is associated with SHC phosphorylation without concomitant mitogen-activated protein kinase activation. 753 3


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