Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

MEK is a family of dual specific protein kinases which activate the extracellular signal-regulated kinases by phosphorylation of threonine and tyrosine residues. MEK itself is activated via serine phosphorylation by upstream activator kinases, including c-raf, mos and MEK kinase. Here, we report the activation phosphorylation sites of human MEK1 and yeast STE7 kinase as determined by a combination of biochemical and genetic approaches. In human MEK1, substitution of either serine residue 218 or 222 with alanine completely abolished its activation by epidermal growth factor-stimulated Swiss 3T3 cell lysates or immunoprecipitated c-raf, suggesting that both serine residues are required for MEK1 activation. Phosphopeptide analysis demonstrated that serine residues 218 and 222 of human MEK1 are the primary sites for phosphorylation by c-raf. These two serine residues are highly conserved in all members of the MEK family, including the yeast STE7 gene product, a MEK homolog in the yeast mating pheromone response pathway. Mutation of the corresponding residues in STE7 completely abolished the biological functions of this gene. These data demonstrate that MEK is activated by phosphorylation of two adjacent serine/threonine residues and this activation mechanism is conserved in the MEK family kinases.
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PMID:Activation of MEK family kinases requires phosphorylation of two conserved Ser/Thr residues. 813 46

Many growth factors whose receptors are protein tyrosine kinases stimulate the MAP kinase pathway by activating first the GTP-binding protein Ras and then the protein kinase p74raf-1. p74raf-1 phosphorylates and activates MAP kinase kinase (MAPKK). To understand the mechanism of activation of MAPKK, we have identified Ser217 and Ser221 of MAPKK1 as the sites phosphorylated by p74raf-1. This represents the first characterization of sites phosphorylated by this proto-oncogene product. Ser217 and Ser221 lie in a region of the catalytic domain where the activating phosphorylation sites of several other protein kinases are located. Among MAPKK family members, this region is the most conserved, suggesting that all members of the family are activated by the phosphorylation of these sites. A 'kinase-dead' MAPKK1 mutant was phosphorylated at the same residues as the wild-type enzyme, establishing that both sites are phosphorylated directly by p74raf-1, and not by autophosphorylation. Only the diphosphorylated form of MAPKK1 (phosphorylated at both Ser217 and Ser221) was detected, even when the stoichiometry of phosphorylation by p74raf-1 was low, indicating that phosphorylation of one of these sites is rate limiting, phosphorylation of the second then occurring extremely rapidly. Ser217 and Ser221 were both phosphorylated in vivo within minutes when PC12 cells were stimulated with nerve growth factor. Analysis of MAPKK1 mutants in which either Ser217 or Ser221 were changed to glutamic acid, and the finding that inactivation of maximally activated MAPKK1 required the dephosphorylation of both serines, shows that phosphorylation of either residue is sufficient for maximal activation.
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PMID:Identification of the sites in MAP kinase kinase-1 phosphorylated by p74raf-1. 815

Activation of extracellular signal-regulated kinase (ERK) or mitogen-activated protein kinase by MEK (mitogen-activated protein kinase or extracellular signal-regulated kinase kinase) is an essential event in the mitogenic growth factor signal transduction. We now demonstrate that three recombinant MEKs (MEK1, MEK2, MEK3) show remarkably different activity toward recombinant ERK1 and ERK2. MEK2 is the most active ERK activator. The recombinant MEK1 has an activity approximately seven times lower than that of MEK2. MEK3, which is identical to MEK1 except for missing an internal 26-amino acid residue and probably represents an alternative splicing product of MEK1, shows neither autophosphorylation nor ERK-activating activity. Recombinant MEK1 and MEK2 can be activated by epidermal growth factor-stimulated SWISS3T3 cell lysate. MEK1 and MEK2 can also be activated by autophosphorylation. Autophosphorylation of MEKs correlates with their ability to phosphorylate and activate ERKs. Phosphorylation of MEK is also stimulated by ERK. Phosphoamino acid analysis showed that ERK1 preferentially phosphorylated threonine residue of MEKs. MEKs complex with ERKs in vitro. Interestingly, MEK3 also forms a complex with ERK1, although it is totally inactive as an ERK activator.
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PMID:Properties of MEKs, the kinases that phosphorylate and activate the extracellular signal-regulated kinases. 822 33

Interaction with SV40 small tumor antigen (small t) compromised the ability of multimeric protein phosphatase 2A to inactivate the mitogen-activated protein kinase ERK1 and the mitogen-activated protein kinase kinase MEK1. Transient expression of small t in CV-1 cells activated MEK and ERK but did not affect Raf activity. Small t stimulated the growth of quiescent CV-1 cells almost as effectively as did serum. Coexpression of kinase-deficient ERK2 blocked most, but not all, of the proliferation caused by small t. Activation of the mitogen-activated protein kinase pathway and stimulation of cell growth were dependent on the interaction of small t with protein phosphatase 2A. These findings indicate that SV40 small t is capable of inducing cell growth through blockade of protein phosphatase and deregulation of the mitogen-activated protein kinase cascade.
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PMID:The interaction of SV40 small tumor antigen with protein phosphatase 2A stimulates the map kinase pathway and induces cell proliferation. 825 25

MEK1 is a dual specificity kinase that phosphorylates and activates the Erk/MAP kinases Erk-1 and Erk-2 by phosphorylating them on threonine and tyrosine. We report the cloning of a second MEK-like complementary DNA, Mek2, which predicts a protein of a molecular weight of 44,500. The MEK2 protein bears substantial sequence homology to MEK1, except at its amino terminus, and at a proline-rich region insert between the conserved kinase subdomains 9 and 10. MEK1 and MEK2 are shown to be encoded by different genes and are located on murine chromosomes 9 and 10, respectively. Northern analysis indicates that Mek2 is expressed at low levels in adult mouse brain and heart tissue, and at higher levels in other tissues examined. Low expression levels of Mek2 in brain tissue are in contrast to the high levels of Mek1 expressed in brain. Mek2 is expressed at high levels in neonatal brain, however. Recombinant MEK2 produced in bacteria phosphorylates a kinase-inactive Erk-1 on tyrosine and threonine, whereas a kinase-inactive mutant MEK2 does not. These findings suggest that MEK2 is a member of a multigene family.
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PMID:MEK2 is a kinase related to MEK1 and is differentially expressed in murine tissues. 829 98

Mitogen-induced signal transduction is mediated by a cascade of protein phosphorylation and dephosphorylation. One of the immediate responses of mitogen stimulation is the activation of a family of protein kinases known as mitogen-activated protein kinase or extracellular signal-regulated kinase (ERK). MEK (MAP kinase or ERK kinase) is the immediate upstream activator kinase of ERK. Two cDNAs, MEK1 and MEK2, were cloned and sequenced. MEK1 and MEK2 encode 393 and 400 amino acid residues, respectively. The human MEK1 shares 99% amino acid sequence identity with the murine MEK1 and 80% with human MEK2. Both MEK1 and MEK2 were expressed in Escherichia coli and shown to be able to activate recombinant human ERK1 in vitro. The purified MEK2 protein stimulated threonine and tyrosine phosphorylation on ERK1 and concomitantly activated ERK1 kinase activity more than 100-fold. The recombinant MEK2 showed lower activity as an ERK activator as compared with MEK purified from tissue. However, the recombinant MEK2 can be activated by serum-stimulated cell extract in vitro. MEKs, in a manner similar to ERKs, are likely to consist of a family of related proteins playing critical roles in signal transduction.
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PMID:Cloning and characterization of two distinct human extracellular signal-regulated kinase activator kinases, MEK1 and MEK2. 838 92

Mitogen-activated protein (MAP) kinases are serine/threonine protein kinases activated by dual phosphorylation on threonine and tyrosine residues. A MAP kinase kinase (MKK1 or MEK1) has been identified as a dual-specificity protein kinase that is sufficient to phosphorylate MAP kinases p42mapk and p44mapk on the regulatory threonine and tyrosine residues. Because of the multiplicity of MAP kinase isoforms and the diverse circumstances and agonists leading to their activation, we thought it unlikely that a single MKK could accommodate this complexity. Indeed, two protein bands with MKK activity have previously been identified after renaturation following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We now report the molecular cloning and characterization of a second rat MAP kinase kinase cDNA, MKK2. MKK2 cDNA contains an open reading frame encoding a protein of 400 amino acids, 7 residues longer than MKK1 (MEK1). The amino acid sequence of MKK2 is 81% identical to that of MKK1, but nucleotide sequence differences occur throughout the aligned MKK2 and MKK1 cDNAs, indicating that MKK2 is the product of a distinct gene. MKK1 and MKK2 mRNAs are expressed differently in rat tissues. Both cDNAs when expressed in COS cells displayed the ability to phosphorylate and activate p42mapk and p44mapk, both MKK1 and MKK2 were activated in vivo in response to serum, and both could be phosphorylated and activated by the v-Raf protein in vitro. However, differences between MKK1 and MKK2 in sites of phosphorylation by proline-directed protein kinases predict differences in feedback regulation.
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PMID:Identification and characterization of a new mammalian mitogen-activated protein kinase kinase, MKK2. 839 35

Mutants defective in meiotic recombination were isolated from a disomic haploid strain of Saccharomyces cerevisiae by examining recombination within the leu2 and his4 heteroalleles located on chromosome III. The mutants were classified into two new complementation groups (MRE2 and MRE11) and eight previously identified groups, which include SPO11, HOP1, REC114, MRE4/MEK1 and genes in the RAD52 epistasis group. All of the mutants, in which the mutations in the new complementation groups are homozygous and diploid, can undergo premeiotic DNA synthesis and produce spores. The spores are, however, not viable. The mre2 and mre11 mutants produce viable spores in a spo13 background, in which meiosis I is bypassed, suggesting that these mutants are blocked at an early step in meiotic recombination. The mre2 mutant does not exhibit any unusual phenotype during mitosis and it is, thus, considered to have a mutation in a meiosis-specific gene. By contrast, the mre11 mutant is sensitive to damage to DNA by methyl methanesulfonate and exhibits a hyperrecombination phenotype in mitosis. Among six alleles of HOP1 that were isolated, an unusual pattern of intragenic complementation was observed.
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PMID:Identification of new genes required for meiotic recombination in Saccharomyces cerevisiae. 841 89

Mitogen-activated protein (MAP) kinase kinase (MAPKK) is a recently characterized activator of MAP kinase (MAPK), and is considered to be regulated by a protooncogene product c-Raf-1. It is, however, unclear whether the signals originating from c-Raf-1 utilize this phosphorylation cascade to lead to oncogenesis. To clarify this point, we isolated rat MAPKK cDNAs, and identified two distinct cDNAs encoding MAPKK and a highly related kinase, both with molecular weights of approximately 45 kDa (MEK1 and MEK2). Genomic Southern blot analyses suggested that MAPKK may form a large gene family.
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PMID:Isolation of two members of the rat MAP kinase kinase gene family. 839 17

Mitogen-activated protein kinase kinase (MAPKK) is a dual-specificity protein kinase which phosphorylates and activates mitogen-activated protein kinase (MAPK). cDNAs encoding two isoforms of MAPKK, MAPKK1 and MAPKK2 (also known as MEK1 and MEK2), have been cloned in mammalian cells. To analyze the characteristics of MAPKK1 and MAPKK2 individually, we have produced specific anti-MAPKK serum against each isoform. MAPKK1 and MAPKK2 have apparent molecular masses of 45 kDa and 47 kDa, respectively, on SDS/polyacrylamide gel electrophoresis. In mouse tissues, MAPKK1 was highly enriched in brain, while MAPKK2 was present relatively evenly. In rat fibroblastic 3Y1 cells, epidermal growth factor (EGF) treatment induced activation of both MAPKK1 and MAPKK2. Immunoprecipitation experiments have shown that the time courses of activation and deactivation of both isoforms of MAPKK were superimposed. In PC12 cells, both MAPKK1 and MAPKK2 were activated in response to nerve growth factor (NGF) as well as EGF, and the time courses of activation and deactivation of both isoforms were indistinguishable from each other in the NGF-stimulated cells and also in the EGF-stimulated cells. Furthermore, localization of both MAPKK1 and MAPKK2 in the cytoplasm was unchanged in response to EGF and NGF. Thus, the same or quite similar mechanisms may operate in the regulation of the activation and deactivation of two isoforms of MAPKK, and both kinases might have redundant functions when expressed in the same cell.
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PMID:Activation of two isoforms of mitogen-activated protein kinase kinase in response to epidermal growth factor and nerve growth factor. 852 59


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