Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51812 (mitogen-activated protein)
 10,636 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In mammalian melanocytes, melanin synthesis is controlled by tyrosinase, the critical enzyme in the melanogenic pathway. We and others showed that the stimulation of melanogenesis by cAMP is due to an increased tyrosinase expression at protein and mRNA levels. However, the molecular events connecting the rise of intracellular cAMP and the increase in tyrosinase activity remain to be elucidated. In this study, using B16 melanoma cells, we showed that cAMP-elevating agents stimulated mitogen-activated protein (MAP) kinase, p44mapk. This effect was mediated by the activation of MAP kinase kinase. cAMP-elevating agents induced a translocation of p44mapk to the nucleus and an activation of the transcription factor AP-1. cAMP-induced AP-1 contained FOS-related antigen-2 in association with JunD, while after phorbol ester stimulation AP-1 complexes consist mainly of JunD/c-Fos heterodimers. In an attempt to connect these molecular events to the control of tyrosinase expression that appears to be the pivotal point of melanogenesis regulation, we hypothesized that following its activation by cAMP, p44mapk activates AP-1. Then AP-1 could stimulate tyrosinase expression through the interaction with specific DNA sequences present in the mouse tyrosinase promoter.
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PMID:Mitogen-activated protein kinase pathway and AP-1 are activated during cAMP-induced melanogenesis in B-16 melanoma cells. 759 42

The molecular mechanism underlying the cAMP inhibition of nuclear activation events in T lymphocytes is unknown. Recently, the activation of fibroblasts and muscle cells are shown to be antagonized by cAMP through the inhibition of mitogen-activated protein (MAP) kinases signaling pathway. Whether a similar antagonism may account for the late inhibitory effect of cAMP in T cell was examined. Surprisingly, extracellular signal regulated kinase 2 (ERK1, ERK2, and ERK3) of MAP kinase were poorly inhibited by cAMP. High concentration of cAMP also only weakly antagonized Raf-1 in T cells. The resistance of ERK and Raf-1 to cAMP clearly distinguishes T cells from fibroblasts. In contrast, another MAP kinase homologue c-Jun N-terminal kinase (JNK) was inhibited by cAMP in good correlation with that of IL-2 suppression. Moreover, JNK was antagonized by a delayed kinetics which is characteristic of cAMP inhibition. Despite that both ERK and JNK are essential for T cell activation, selective inhibition by cAMP further supports the specific role of JNK in T cell activation.
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PMID:c-Jun N-terminal kinase but not mitogen-activated protein kinase is sensitive to cAMP inhibition in T lymphocytes. 762 20

p44erk1 is a member of a family of tyrosyl-phosphorylated and mitogen-activated protein (MAP) kinases that participate in cell cycle control. A full-length erk1 cDNA was isolated from a human hepatoma cell line (Hep G2) library. The erk1 cDNA clone shared approximately 96% predicted amino acid identity with partial sequences of rodent erk1 cognates, and the erk1 gene was assigned to human chromosome 16 by hybrid panel analysis. Human erk1 expressed in Escherichia coli as a glutathione S-transferase fusion (GST-Erk1) protein was substantially phosphorylated on tyrosine in vivo. It underwent further autophosphorylation in vitro (up to 0.01 mol of P per mol) at the regulatory Tyr-204 site and at additional tyrosine and serine residues. Threonine autophosphorylation, presumably at the regulatory Thr-202 site, was also detected weakly when the recombinant kinase was incubated in the presence of manganese, but not in the presence of magnesium. Before and after cleavage of the GST-Erk1 protein with thrombin, it exhibited a relatively high level of myelin basic protein phosphotransferase activity, which could be reduced eightfold by treatment of the kinase with the protein-tyrosine phosphatase CD45, but not by treatment with the protein-serine/threonine phosphatase 2A. The protein-tyrosine kinase p56lck catalyzed phosphorylation of GST-Erk1 at two autophosphorylations sites, including Tyr-204, and at a novel site. A further fivefold stimulation of the myelin basic protein phosphotransferase activity of the GST-Erk1 was achieved in the presence of a partially purified MAP kinase kinase from sheep platelets. Under these circumstances, there was primarily an enhancement of the tyrosine phosphorylation of GST-Erk1. This MAP kinase kinase also similarly phosphorylated a catalytically compromised version of GST-Erk1 in which Lys-71 was converted to Ala by site-directed mutagenesis.
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PMID:Molecular cloning, expression, and characterization of the human mitogen-activated protein kinase p44erk1. 768 43

Although tumor necrosis factor (TNF)-alpha stimulation of human neutrophils does not result in a significant release of arachidonic acid, it primes the cell for arachidonic acid release when cells are further stimulated by agents that induce an intracellular calcium increase. We demonstrate that TNF-alpha stimulation of neutrophils induces the phosphorylation of cytosolic phospholipase A2 (cPLA2) and also increases its activity. These results indicate that although TNF-alpha, by itself, does not cause the release of arachidonic acid in intact cells, it increases the phosphorylation and activation of the enzyme cPLA2. Since we recently found that TNF-alpha stimulation of neutrophils does not increase the tyrosine phosphorylation or activation of the p42erk2 and p44erk1 mitogen-activated protein kinases (MAPKs), the present studies demonstrate the involvement of a MAPK independent pathway in the phosphorylation and activation of cPLA2.
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PMID:A mitogen-activated protein kinase independent pathway involved in the phosphorylation and activation of cytosolic phospholipase A2 in human neutrophils stimulated with tumor necrosis factor-alpha. 772 46

In response to heat-shock and chemical treatments, cells undergo profound biochemical changes such as modifications in protein phosphorylation in order to resist the new, unfavorable growth conditions. We have previously shown that in HeLa cells a protein kinase (HS-CTD kinase) activity is induced rapidly after a heat or sodium arsenite shock. This kinase activity is able to phosphorylate a synthetic peptide composed of four repeats of the motif Ser-Pro-Thr-Ser-Pro-Ser-Tyr, a motif highly repeated in the carboxyl-terminal domain (CTD) of the largest subunit of eukaryotic RNA polymerase II. In this paper, we designed a new experimental procedure to characterize the substrate specificity of this kinase activity. We show that HS-CTD kinase activity phosphorylates a consensus sequence (-P-X-S/T-P-) which is similar to the sequence phosphorylated by extracellular regulated protein kinases (also called mitogen-activated protein kinases). However, there is a slight but reproducible difference between these kinases in their use of serine or threonine as the phosphate acceptor. Mono Q chromatography allows the separation of five stress-induced CTD kinase activities, two of which coelute with active mitogen-activated protein kinase forms revealed by Western blotting with anti ERK1-ERK2 antibodies. The other three CTD kinase activities induced after a stress are distinct from ERK1 and ERK2 and have different enzymatic properties. The molecular nature of these HS-CTD kinases and the physiological significance of their activation during stress remain to be determined.
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PMID:Different carboxyl-terminal domain kinase activities are induced by heat-shock and arsenite. Characterization of their substrate specificity, separation by Mono Q chromatography, and comparison with the mitogen-activated protein kinases. 776 4

The thrombin receptor agonist peptide SFLLRN was less effective than thrombin in eliciting the liberation of arachidonic acid and the generation of thromboxane A2 by human platelets. We found that while SFLLRN evokes an initial transient increase in cystolic free calcium concentration ([Ca2+]i) of similar magnitude as that caused by thrombin, the SFLLRN-induced elevation of [Ca2+]i declines more rapidly to near resting levels than that evoked by thrombin, suggesting that disparate levels of [Ca2+]i may contribute to the attenuated arachidonic acid release. Furthermore, we observed that SFLLRN is less effective than thrombin in mediating the "activating" phosphorylation of cytolic phospholipase A2 (cPLA2). Both thrombin and SFLLRN rapidly and transiently activated kinases that phosphorylate the 21-residue synthetic peptide Thr669 derived from the epidermal growth factor receptor, but the maximal activation of proline-directed kinases by SFLLRN was less pronounced than that by thrombin. MonoQ chromatography and immunoblot analysis of extracts from stimulated platelets revealed that while thrombin induced a prominent activation of the mitogen-activated protein kinases ERK1 and ERK2, SFLLRN completely failed to do so. On the other hand, SFLLRN, like thrombin, stimulated the activity of a proline-directed kinase distinct from ERK1/2, but the activation of this kinase was less pronounced following stimulation of platelets with SFLLRN compared with thrombin. We conclude 1) that the partial activation of cPLA2 and the subsequent attenuated mobilization of arachidonic acid in response to SFLLRN may be the consequence of a less prolonged elevation of [Ca2+]i and insufficient activation of proline-directed kinase(s) by SFLLRN and 2) that the ability of SFLLRN to mediate the activating phosphorylation of cPLA2 in the absence of ERK1/2 stimulation suggest that, at least in human platelets, proline-directed kinases other than ERK1/2 may phosphorylate and activate cPLA2.
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PMID:Differential activation of cytosolic phospholipase A2 (cPLA2) by thrombin and thrombin receptor agonist peptide in human platelets. Evidence for activation of cPLA2 independent of the mitogen-activated protein kinases ERK1/2. 778 48

Exposure of mesangial cells to platelet-derived growth factor (PDGF) BB caused a significant stimulation of cell proliferation and protein synthesis, as measured by [3H]thymidine incorporation and [3H]leucine incorporation respectively. In contrast, cells treated with angiotensin II had no significant increase in [3H]thymidine incorporation, but demonstrated a marked increase in [3H]leucine incorporation. Furthermore, angiotensin II significantly increased total protein content per cell. These data show that, whereas PDGF-BB is a mitogen and stimulates mesangial-cell hyperplasia, angiotensin II causes hypertrophy of the cells without hyperplasia. Treatment of mesangial cells with PDGF and angiotensin II rapidly and dose-dependently stimulated mitogen-activated protein (MAP) kinase activity, as shown by an assay for activity in vitro using myelin basic protein as a substrate, and by immunoprecipitation of 32P-labelled cells with specific antibodies against the 42 kDa and 44 kDa mitogen-activated protein kinases p42mapk and p44mapk, respectively. Whereas stimulation with PDGF-BB caused a potent and sustained (for more than 30 min) phosphorylation and activation of p42mapk and p44mapk, as well as of the upstream activators MAP kinase kinase and c-Raf, the effect of angiotensin II was less potent, reaching a peak at 5-10 min and thereafter declining rapidly. In summary, these results suggest that PDGF-BB and angiotensin II differ in their potency and duration of activation of the MAP kinase cascade, which may explain why PDGF-BB is a potent mitogen for mesangial cells, whereas angiotensin II only triggers mesangial-cell hypertrophy.
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PMID:Platelet-derived growth factor and angiotensin II stimulate the mitogen-activated protein kinase cascade in renal mesangial cells: comparison of hypertrophic and hyperplastic agonists. 784 76

We have examined porcine granulosa cells (pGCs) for the presence of immunodetectable mitogen-activated protein (MAP) kinases (extracellular signal-regulated kinases, ERK) and have further studied the effects of epidermal growth factor (EGF) on the activation of these kinases. Cell lysates prepared from untreated monolayer cultures of pGCs were subjected to Western immunoblotting analysis using monoclonal antibodies to ERK1, ERK2 and pan-specific ERK. MAP kinases were detected having mol wts of 87K (ERK87), 54K (ERK54), 44K (ERK1), and 42K (ERK2). Treatment of pGCs with increasing concentrations (1-10 ng/ml) of EGF for 10 min resulted in electrophoretic mobility shifts of ERK1 and ERK2 suggesting hyperphosphorylation. Immunoprecipitation with an antiphosphotyrosine antibody (PY20), followed by Western analysis using pan-ERK, revealed a marked concentration-dependent increase in tyrosine phosphorylation of ERK2 in response to EGF treatment. The mobility shift and tyrosine phosphorylation of ERK2 was observed as early as 1 min after treatment with 10 ng/ml EGF. In-gel myelin basic protein (MBP) kinase assays revealed significant MBP kinase activity associated with ERK1 and ERK2 in total cell lysates and ERK2 in PY20 immunoprecipitates. Although ERK1 displayed a moderate mobility shift in response to EGF, tyrosine phosphorylation of this MAP kinase was not appreciably increased by EGF. Furthermore, PY20 immunoprecipitates demonstrated minimal MBP kinase associated with ERK1 in response to EGF treatment. Electrophoretic migration, tyrosine phosphorylation, and MBP kinase activity of the ERK54 and ERK87 was not effected regardless of EGF concentration or duration of treatment. These data demonstrate for the first time that pGCs contain immunodetectable MAP kinases. EGF, in a concentration- and time-dependent manner, increases tyrosine phosphorylation and MBP kinase activity (i.e. activation) of ERK2, and to a lesser degree ERK1, suggesting that the activation of MAP kinase may mediate the mitogenic action of EGF in pGCs.
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PMID:Effects of epidermal growth factor on the tyrosine phosphorylation of mitogen-activated protein kinases in monolayer cultures of porcine granulosa cells. 786 73

We have previously shown that hypoxia causes the activation of nuclear factor-kappa B (NF-kappa B), and the phosphorylation of its inhibitory subunit, I kappa B alpha, on tyrosine residues. With the use of dominant negative mutants of Ha-Ras and Raf-1, we investigated some of the early signaling events leading to the activation of NF-kappa B by hypoxia. Both dominant negative alleles of Ha-Ras and Raf-1 inhibited NF-kappa B induction by hypoxia, suggesting that the hypoxia-induced pathway of NF-kappa B induction is dependent on Ras and Raf-1 kinase activity. Furthermore, although conditions of low oxygen can also activate mitogen-activated protein kinases (ERK1 and ERK2), these kinases do not appear to be involved in regulating NF-kappa B by low oxygen conditions, as dominant negative mutants of mitogen-activated protein kinase do not inhibit NF-kappa B activation by hypoxia. Since Ras and Raf-1 have been previously shown to work downstream from membrane-associated tyrosine kinases such as Src, we determined if the Src membrane-associated kinase was also activated by low oxygen conditions. We detected an increase in Src proto-oncogene activity within 15-30 min of cellular exposure to hypoxia. We postulate that Src activation by hypoxia may be one of the earliest events that precedes Ras activation in the signaling cascade which ultimately leads to the phosphorylation and dissociation of the inhibitory subunit of NF-kappa B, I kappa B alpha.
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PMID:Hypoxic activation of nuclear factor-kappa B is mediated by a Ras and Raf signaling pathway and does not involve MAP kinase (ERK1 or ERK2). 792 53

The effect of insulin and epidermal growth factor on the phosphorylation of CTP:phosphocholine cytidylyltransferase (EC 2.7.7.15) was investigated in HeLa cells. For the first time, cytidylyltransferase phosphorylation was shown to be influenced by growth factors in cell culture experiments. The rephosphorylation of cytidylyltransferase after an oleate-mediated dephosphorylation and translocation to membranes was increased after 2 min in the presence of insulin or epidermal growth factor by 99% and 76%, respectively, compared with controls. However, the increased phosphorylation of cytidylyltransferase did not have an effect on its subcellular distribution. Furthermore, purified cytidylyltransferase preincubated with alkaline phosphatase is a substrate for p44mapk, a member of the mitogen-activated protein (MAP) kinase family downstream of the growth factor receptors, in vitro. In accordance with the in vivo data, in vitro phosphorylation of cytidylyltransferase by p44mapk occurred after 2 min.
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PMID:Growth factors stimulate phosphorylation of CTP:phosphocholine cytidylyltransferase in HeLa cells. 792 53


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