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Query: EC:2.7.11.24 (mitogen-activated protein kinase)
 95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Growth hormone (GH) influences a number of tissue-specific biological activities in diverse cell types. However, little is known about the biochemical pathway by which the signal initiated by GH binding to its cell-surface receptor is transduced. The GH receptor has been reported to be phosphorylated on tyrosine in 3T3-F442A cells, a cell line in which GH promotes differentiation and inhibits mitogen-stimulated growth; however, it is not known whether tyrosine phosphorylation plays a role in GH signal transduction. We report that GH treatment of 3T3-F442A cells resulted in the rapid tyrosine phosphorylation of at least four proteins. These included 42- (pp42) and 45-kDa (pp45) proteins immunologically related to ERK1 (extracellular signal-regulated kinase 1), a member of a family of serine/threonine protein kinases that are phosphorylated on tyrosine in response to mitogens. Prolonged phorbol ester pretreatment attenuated the tyrosine phosphorylation of pp42 and pp45 in platelet-derived growth factor-treated cells, but not in GH-treated cells. Maximal GH-stimulated tyrosine phosphorylation of pp42 and pp45 coincided with peak levels of a 42-kDa renaturable MBP kinase activity in lysates of GH-treated cells resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The observation that multiple cellular proteins are rapidly phosphorylated on tyrosine in response to physiological concentrations of GH suggests that tyrosine phosphorylation plays a role in GH signal transduction. Moreover, the stimulation of tyrosine phosphorylation of ERK-related proteins by GH suggests that mitogens and nonmitogens may employ common phosphotyrosyl proteins in the activation of ultimately distinct cellular programs.
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PMID:Growth hormone stimulates the tyrosine phosphorylation of 42- and 45-kDa ERK-related proteins. 153 56

The phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1 and ERK2) in response to insulin in Rat 1 HIRc B cells and in response to nerve growth factor (NGF) in PC12 cells has been examined. ERK1 and ERK2 are phosphorylated on serine in the absence of the stimuli and additionally on tyrosine and threonine residues after exposure to NGF and insulin. NGF stimulates tyrosine phosphorylation of ERK1 more rapidly than threonine phosphorylation. Two-dimensional phosphopeptide maps of both ERK1 and ERK2 phosphorylated in intact cells treated with NGF or with insulin display the same three predominant phosphopeptides that comigrate when digests of ERK1 and ERK2 are mixed. As many as five additional phosphopeptides are detected under certain conditions. Autophosphorylated recombinant ERK2 also contains the three tryptic phosphopeptides found in ERKs labeled in intact cells. These experiments demonstrate that ERK1 and ERK2 are phosphorylated on related sites in response to two distinct extracellular signals. The data also support the possibility that autophosphorylation may be involved in the activation of the ERKs.
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PMID:Extracellular signal-regulated kinases 2 autophosphorylates on a subset of peptides phosphorylated in intact cells in response to insulin and nerve growth factor: analysis by peptide mapping. 162 31

Soluble, monomeric simian virus 40 (SV40) small-t antigen (small-t) was purified from bacteria and assayed for its ability to form complexes with protein phosphatase 2A (PP2A) and to modify its catalytic activity. Different forms of purified PP2A, composed of combinations of regulatory subunits (A and B) with a common catalytic subunit (C), were used. The forms used included free A and C subunits and AC and ABC complexes. Small-t associated with both the free A subunit and the AC form of PP2A, resulting in a shift in mobility during nondenaturing polyacrylamide gel electrophoresis. Small-t did not interact with the free C subunit or the ABC form. These data demonstrate that the primary interaction is between small-t and the A subunit and that the B subunit of PP2A blocks interaction of small-t with the AC form. The effect of small-t on phosphatase activity was determined by using several exogenous substrates, including myosin light chains phosphorylated by myosin light-chain kinase, myelin basic protein phosphorylated by microtubule-associated protein 2 kinase/ERK1, and histone H1 phosphorylated by protein kinase C. With the exception of histone H1, small-t inhibited the dephosphorylation of these substrates by the AC complex. With histone H1, a small stimulation of dephosphorylation by AC was observed. Small-t had no effect on the activities of free C or the ABC complex. A maximum of 50 to 75% inhibition was obtained, with half-maximal inhibition occurring at 10 to 20 nM small-t. The specific activity of the small-t/AC complex was similar to that of the ABC form of PP2A with myosin light chains or histone H1 as the substrate. These results suggested that small-t and the B subunit have similar qualitative and quantitative effects on PP2A enzyme activity. These data show that SV40 small-antigen binds to purified PP2A in vitro, through interaction with the A subunit, and that this interaction inhibits enzyme activity.
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PMID:Control of protein phosphatase 2A by simian virus 40 small-t antigen. 170 74

Meiotic maturation of Xenopus and sea star oocytes involves the activation of a number of protein-serine/threonine kinase activities, including a myelin basic protein (MBP) kinase. A 44-kDa MBP kinase (p44mpk) purified from mature sea star oocytes is shown here to be phosphorylated at tyrosine. Antiserum to purified sea star p44mpk was used to identify antigenically related proteins in Xenopus oocytes. Two tyrosine-phosphorylated 42-kDa proteins (p42) were detected with this antiserum in Xenopus eggs. Xenopus p42 chromatographs with MBP kinase activity on a Mono Q ion-exchange column. Tyrosine phosphorylation of Xenopus p42 approximately parallels MBP kinase activity during meiotic maturation. These results suggest that related MBP kinases are activated during meiotic maturation of Xenopus and sea star oocytes. Previous studies have suggested that Xenopus p42 is related to the mitogen-activated protein (MAP) kinases of culture mammalian cells. We have cloned a MAP kinase relative from a Xenopus ovary cDNA library and demonstrate that this clone encodes the Xenopus p42 that is tyrosine phosphorylated during oocyte maturation. Comparison of the sequences of Xenopus p42 and a rat MAP kinase (ERK1) and peptide sequences from sea star p44mpk indicates that these proteins are close relatives. The family members appear to be tyrosine phosphorylated, and activated, in different contexts, with the murine MAP kinase active during the transition from quiescence to the G1 stage of the mitotic cell cycle and the sea star and Xenopus kinases being active during M phase of the meiotic cell cycle.
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PMID:Tyrosine phosphorylation and activation of homologous protein kinases during oocyte maturation and mitogenic activation of fibroblasts. 170 93

Microtubule-associated protein 2 kinase (MAP kinase), which exists in several forms, is a protein serine/threonine kinase that participates in a growth factor-activated protein kinase cascade in which it activates a ribosomal protein S6 kinase (pp90rsk) while being regulated itself by a cytoplasmic factor (MAP kinase activator). Experiments with recombinant MAP kinase, ERK2, purified from Escherichia coli in a nonactivated form revealed a self-catalyzed phosphate incorporation into both tyrosine and threonine residues. Another MAP kinase, ERK1, purified from insulin-stimulated cells also autophosphorylated on tyrosine and threonine residues. Autophosphorylation of ERK2 correlated with its autoactivation, although both autophosphorylation and autoactivation were slow compared to that occurring in the presence of MAP kinase activator. Therefore, we propose that autophosphorylation is probably involved in the MAP kinase activation process in vitro, but it may not be sufficient for full activation. The specificity toward tyrosine and threonine residues indicates that the MAP kinases ERK1 and ERK2 are members of a group of kinases with specificity for tyrosine as well as serine and threonine residues.
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PMID:Microtubule-associated protein 2 kinases, ERK1 and ERK2, undergo autophosphorylation on both tyrosine and threonine residues: implications for their mechanism of activation. 171 80

Mitogen activated protein (MAP) kinases (MAPKs) are a family of protein-serine/threonine kinases activated as an early intracellular response to a variety of hormones and growth factors. They are unique in requiring both serine/threonine and tyrosine phosphorylation to become active and are the only examples of protein-serine/threonine kinases activated by tyrosine phosphorylation. Nerve growth factor (NGF) promotes differentiation of phaeochromocytoma (PC12) cells, which respond by conversion within hours from a chromaffin-like to a sympathetic neuron-like phenotype. NGF stimulation of PC12 cells increases the activity of two protein kinases by greater than 20-fold within minutes, both strikingly similar to MAPKs. They are inactivated by either protein-tyrosine phosphatases or the protein-serine/threonine phosphatase termed protein phosphatase 2A (ref. 8), they activate protein S6 kinase-II (refs 9, 10), and they phosphorylate identical threonine residues on myelin basic protein (our unpublished results) to those phosphorylated by other MAPKs. Immunological data indicate that these protein kinases, termed peak-I and peak-II (Fig. 1a) are probably ERK2 and ERK1, respectively, two widely expressed MAPK isoforms. Here we identify the 'MAP kinase kinases' (MAPKKs) in PC12 cells which are activated by NGF and report that MAPKKs are dependent on serine/threonine phosphorylation for activity and promote phosphorylation of serine/threonine and tyrosine residues on MAPKs.
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PMID:Dissection of the protein kinase cascade by which nerve growth factor activates MAP kinases. 171 48

We have isolated and characterized brain cDNA clones encoding microtubule-associated protein-2 (MAP-2) kinase for rat (rMNK1) and mouse (mMNK1). The nucleotide sequences diverged by only 5% whereas the amino acid sequences were identical except for one conservative residue change. Conservation of the expressed sequence extended into other mammalian species. These findings constitute the first demonstration of a strict evolutionary conservation of MAP-2 kinase. Genomic restriction patterns revealed a single MAP-2 kinase gene that shares homology with other genomic sequences. The 3' terminal half of the gene appears to be encoded by four exons. rMNK1 and mMNK1 differed from a recently reported MAP-2 kinase cDNA, termed ERK1, because of a nonconservative change in position 82, from Gly in ERK1 to Arg in rMNK1. The rMNK1 gene was found to be expressed mainly as a 1.8-kb transcript that was highest in brain and in lung. In contrast to ERK1, rMNK1 showed two equally prominent mRNA species in liver, at 1.8 kb and 5 kb, which imply differential processing of the primary transcript. Results derived from the immunological screening of an expression library showed that MAP-2 kinase might share epitopes with two prominent protein kinase C substrates, MARCKS (an 80-kD protein kinase C substrate) and GAP-43, suggesting the possibility that MAP-2 kinase could interact with kinase C.
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PMID:Molecular analysis of microtubule-associated protein-2 kinase cDNA from mouse and rat brain. 171 39

We have approached the functioning of a MAP kinase, which is thought to be a "switch kinase" in the phosphorylation cascade initiated from various receptor tyrosine kinases including the insulin receptor. To do so, antipeptide antibodies were raised against the C-terminal portion of ERK1 (extracellular signal-regulated kinase 1), a protein kinase belonging to the family of MAP kinases. With these antipeptide antibodies, we observed the following: (i) a 44-kDa protein can be specifically recognized both under native and denaturing conditions; (ii) a 44-kDa phosphoprotein can be revealed in 32P-labeled cells; its phosphorylation is stimulated by insulin, sodium orthovanadate, and okadaic acid; (iii) a MBP kinase activity can be precipitated, which phosphorylates MBP on threonine residues, and which is stimulated by insulin, sodium orthovanadate, okadaic acid, and fetal calf serum; (iv) this MBP kinase activity appears to be correlated with the in vivo induced phosphorylation of the 44-kDa protein. We next studied the in vitro phosphorylation of this 44-kDa/ERK1-immunoreactive protein. A time- and manganese-dependent phosphorylation was stimulated by the in vitro addition of sodium orthovanadate. Phosphoamino acid analysis of the in vitro phosphorylated 44-kDa protein revealed both threonine and tyrosine phosphorylation. Importantly, this in vitro phosphorylation of MAP kinase results in activation of phosphorylation of added MBP substrate. As a whole, our data indicate that the 44-kDa phosphoprotein identified by our antipeptide antibodies very likely corresponds to a MAP kinase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Tyrosine and threonine phosphorylation of an immunoaffinity-purified 44-kDa MAP kinase. 171 57

Bacterial expression of mouse gene Erk-1 yielded an active kinase with the same substrate specificity shown for ERK1 protein purified from rat cells. Although rat gene ERK1 is believed to encode a serine/threonine kinase based on sequence data and known ERK1 substrate phosphorylation sites, bacterially-produced mouse Erk-1 (bt-Erk-1) autophosphorylated on tyrosine in addition to serine and threonine residues. The bt-Erk-1 protein also had the capacity to reactivate the ribosomal protein S6 kinase (S6KII). Furthermore, treatment of bt-Erk-1 with either serine/threonine-specific phosphatase 2A or tyrosine-specific phosphatase 1B significantly decreased its kinase activity. These findings predict that autophosphorylation may play an important role in Erk-1/ERK1 regulation.
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PMID:Mouse Erk-1 gene product is a serine/threonine protein kinase that has the potential to phosphorylate tyrosine. 171 89

The Raf-1 proto-oncogene protein kinase can be phosphorylated and activated after stimulation of cells with insulin and a variety of other growth factors and mitogens. We recently presented evidence that insulin and certain other growth factors activated one or more Raf-1 kinase kinase activities (Lee, R.M., Rapp, U. R., and Blackshear, P.J. (1991) J. Biol. Chem. 266, 10351-10357). In the present study, four peaks of Raf-1 kinase kinase activity were identified after anion-exchange chromatography of cell lysates, and two of these were activated by insulin. Further chromatographic characterization of these two peaks of insulin-activated kinase activity indicated that they contained three apparently distinct kinase activities. Two of these activities comigrated with immunoreactive extracellular signal-regulated kinases (ERK) 1 and 2 (mitogen-activated protein kinase) through three different chromatographic separations. Both ERK1 and ERK2 phosphorylated Raf-1 with reasonably high affinity (Km for ERK1 = 90 nM; Km for ERK2 = 120 nM), and produced similar, complex phosphopeptide maps; both kinases also phosphorylated myelin basic protein. The third kinase activity also phosphorylated Raf-1 and myelin basic protein but did not comigrate exactly with either immunoreactive ERK1 or ERK2. We conclude that two and possibly three insulin-activated Raf-1 kinase kinases are members of the ERK family.
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PMID:Evidence that extracellular signal-regulated kinases are the insulin-activated Raf-1 kinase kinases. 173 Jun 37


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