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Query: HUMANGGP:019459 (ERK2)
 3,473 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The erythropoietin receptor (EpoR) belongs to the cytokine receptor family, members of which lack a tyrosine kinase domain. Recent studies, however, have shown that a cytoplasmic tyrosine kinase, JAK2, interacts with the cytoplasmic domain of the EpoR and becomes activated upon binding of Epo to the receptor. Epo has also been shown to stimulate activation of Ras and Raf-1. The present studies were undertaken to examine the possible involvement of Epo-induced tyrosine phosphorylation in activation of the Ras/mitogen-activated protein kinase (MAP kinase) pathway and to determine its significance on the growth signaling from the EpoR. In an interleukin (IL)-3-dependent cell line expressing the transfected wild-type EpoR, Epo, or IL-3 induced tyrosine phosphorylation of Shc and its association with Grb2. These cytokines also induced tyrosine phosphorylation and activation of MAP kinase isoforms ERK1 and ERK2. A mutant EpoR with a carboxyl-terminal deletion of 108 amino acids (H mutant), which is mitogenically functional but lacks tyrosine phosphorylation sites in the carboxyl-terminal region, showed markedly diminished abilities to induce tyrosine phosphorylation of Shc and to phosphorylate and activate MAP kinases. A mutant receptor (PM4 mutant) inactivated by a point mutation, Trp282 to Arg, which abrogates the interaction with JAK2, failed to induce any effect on Shc or MAP kinases. In cells expressing a mutant EpoR that is constitutively activated by a point mutation, Arg129 to Cys, in the extracellular portion of the receptor, neither tyrosine phosphorylation of Shc nor activation of MAP kinases by phosphorylation was detectable without stimulation with Epo or IL-3. These results suggest that the carboxyl-terminal region of EpoR may play a crucial role in activation of MAP kinases through the Ras signaling pathway which may be activated by tyrosine phosphorylation of Shc and its association with Grb2. The activation of MAP kinases, however, failed to correlate with the mitogenic activity of mutant EpoRs and thus may not be required for growth signaling from the EpoR.
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PMID:Activation of the mitogen-activated protein kinase pathway by the erythropoietin receptor. 796 95

Triggering of the T cell antigen receptor (TCR) complex activates the serine/threonine kinase Raf-1 whose function is necessary for TCR induction of the interleukin 2 gene. Raf-1 has been identified as a candidate mitogen-activated protein (MAP) kinase kinase kinase (MKKK) and thus has the potential to couple the TCR to the activation of the MAP kinases such as ERK2. In the present study, the role of Raf-1 in ERK2 regulation of ERK2 in T cells has been explored. A constitutively active Raf-1 kinase, v-raf, or a dominant inhibitory Raf-1 mutant were expressed transiently from the pEF BOS vector in Jurkat cells and the effects of these Raf-1 mutants on a coexpressed ERK2 reporter was assessed. The action of the constitutively active Raf-1 was to stimulate the ERK2 kinase, whereas the dominant negative version of Raf-1 inhibited the ERK2 activation induced by triggering of the TCR. These data indicate a role for Raf-1 in the regulation of ERK2 in T cells.
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PMID:The role of Raf-1 in the regulation of extracellular signal-regulated kinase 2 by the T cell antigen receptor. 800 97

Uncontrolled proliferation of acute myeloid leukemia (AML) cells is an important step during leukemogenesis. However, little is known about the mechanisms leading to growth autonomy. Studies using immortalized murine hematopoietic cell lines have suggested that autocrine production of growth factors, or the constitutive activation of molecules in growth factor signalling pathways, are involved. We have established six spontaneous factor-independent cell lines from the human growth factor-dependent TF-1 cell line. The factor-independent cells showed no detectable growth factor activity. Immunoblotting analyses of tyrosine phosphorylation, Raf-1 and extracellular signal-regulated kinase 2 (ERK-2) showed a similar pattern in all the cell lines including TF-1 cells. Furthermore, somatic-cell hybrids between TF-1 and the factor-independent cells grew in absence of growth factor. Taken together this data demonstrates that the factor independence in this system is dominant and suggests that the molecular event is located either downstream of the Raf-1 and MAP kinases pathway or on an alternative pathway. Finally, the karyotype analysis of one factor-independent cell line TF-1i1 and TF-1H- (G418 resistant, HAT sensitive TF-1 cells) and their hybrids demonstrated an unstable derivative chromosome [der(19) t(19;?) (q13.1;?)] which seemed to correlate with the factor-independence capacity. This model may help in our understanding of autonomous proliferation by human myeloid leukemias.
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PMID:Characterization of spontaneous factor-independent cell lines derived from the human leukemic cell line TF-1: a dominant event. 805 74

We have studied the role of Raf-1 in mitogenesis and cellular transformation induced by G protein-coupled receptors in NIH 3T3 cells transfected with the human m1 muscarinic receptor. We have observed that in m1-expressing NIH 3T3 cells, the cholinergic agonist carbachol induces a dose- and time-dependent shift in the electrophoretic mobility of p72Raf-1, equivalent to that observed when using phorbol esters or platelet-derived growth factor as stimulants. Phosphoamino acid analysis of slower mobility forms of p72Raf-1 revealed both phosphoserine and phosphothreonine. Carbachol potently induced c-Raf activity as judged by its in vitro phosphorylating activity using MEK as a substrate. However, induction of Raf-1 kinase activity by carbachol occurred much earlier than changes in its electrophoretic mobility. Raf-1 kinase activation followed a kinetic similar to that exhibited by an epitope-tagged ERK2 protein when coexpressed in the same cells. Conventional protein kinase C (PKC) inactivation by means of sustained phorbol ester treatment or by a new nontoxic PKC-specific inhibitor, GF 109203X, abolished p72Raf-1 mobility shift induced by carbachol or by phorbol esters. However, c-Raf and ERK2 enzymatic activity in response to carbachol was at least 50-80% PKC-independent. Furthermore, inhibition of PKC failed to affect DNA synthesis or focus formation induced by carbachol in cells expressing m1 receptors. In contrast, cotransfection of NIH 3T3 cells with the Raf-1 dominant negative mutant Raf-301 (K375W) drastically decreased the transforming ability of m1 receptors. Thus, our findings implicate Raf-1 activation in transformation by G protein-coupled receptors. In addition, our data suggest that activation of p72Raf-1 and ERK2 by G protein-coupled receptors involves PKC-independent pathways.
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PMID:Signaling through transforming G protein-coupled receptors in NIH 3T3 cells involves c-Raf activation. Evidence for a protein kinase C-independent pathway. 806 29

We have identified, in Xenopus oocyte cytosol, a protein kinase named REKS (Ras-dependent extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase kinase (MEK) stimulator), which phosphorylates and activates recombinant ERK2 through recombinant MEK in a recombinant GTP gamma S (guanosine 5'-(3-O-thio)triphosphate)-Ras-dependent manner. We show here that this REKS activity is synergistically enhanced by a combination of mammalian recombinant GTP gamma S-KiRas and 14-3-3 protein purified from rat brain. 14-3-3 protein is known to activate tyrosine and tryptophan hydroxylases, to modulate the protein kinase C activity, to stimulate secretion, and to show phospholipase A2 activity per se. 14-3-3 protein did not affect the MEK activity. 14-3-3 protein neither interacted with Ki-Ras nor affected the neurofibromin activity to stimulate the GTPase activity of Ki-Ras under the conditions where the recombinant N-terminal fragment of c-Raf-1 inhibited it. These results suggest that 14-3-3 protein has an additional function in the regulation of the Ras-MEK-ERK cascade pathway through the activation of REKS.
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PMID:Synergistic activation by Ras and 14-3-3 protein of a mitogen-activated protein kinase kinase kinase named Ras-dependent extracellular signal-regulated kinase kinase stimulator. 808 86

The structure of the MAP kinase ERK2, a ubiquitous protein kinase target for regulation by Ras and Raf, has been solved in its unphosphorylated low-activity conformation to a resolution of 2.3 A. The two domains of unphosphorylated ERK2 are farther apart than in the active conformation of cAMP-dependent protein kinase and the peptide-binding site is blocked by tyrosine 185, one of the two residues that are phosphorylated in the active enzyme. Activation of ERK2 is thus likely to involve both global and local conformational changes.
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PMID:Atomic structure of the MAP kinase ERK2 at 2.3 A resolution. 810 61

The protein kinase cascade Raf-MAPKK/MEK-MAPK/ERK connects protein tyrosine kinase receptors in the membrane with control of transcription factor activity in the nucleus. We have examined whether Raf is obligatory for activation of this cascade and whether this signaling pathway is relevant to transformation. By use of transient assays with epitope-tagged ERK-1 cDNA and a dominant inhibitory mutant of Raf-1 we found that serum and 12-O-tetradecanoylphorbol-13-acetate as well as representatives of three classes of oncogenes (protein tyrosine kinases abl/src, Ras, and protein serine/threonine kinases mos/cot) were all Raf-dependent for stimulation of MAPK. All of the MAPK stimulating oncogenes were also activators of Raf kinase as judged by shift induction. It thus appears that there is little or no redundancy in pathways used by growth regulators for activation of MAPK/ERK. Furthermore, the ability to stimulate MAPK/ERK appears to be critical for transformation by oncogenic Raf-1 and ERK-1 and -2 synergized with v-raf in a focus induction assay on NIH3T3 cells and kinase dead mutants of ERK-2 were inhibitory. Raf/ERK synergism was also observed in transcriptional transactivation of the oncogene-response element in the polyoma enhancer. We conclude that this Raf signaling pathway, which connects to many upstream activators and downstream effectors, is essential for transformation by most oncogenes.
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PMID:Mitogen-activated protein kinase/extracellular signal-regulated protein kinase activation by oncogenes, serum, and 12-O-tetradecanoylphorbol-13-acetate requires Raf and is necessary for transformation. 812 67

Two cDNA clones, cATMPK1 and cATMPK2, encoding MAP kinases (mitogen-activated protein kinases) have been cloned from Arabidopsis thaliana and their nucleotide sequences have been determined. Putative proteins encoded by ATMPK1 and ATMPK2 genes, designated ATMPK1 and ATMPK2, contain 370 and 376 amino acid residues, respectively, and are 88.7% identical at the amino acid sequence level. ATMPK1 and ATMPK2 exhibit significant similarity to rat ERK2 (49%) and Xenopus MAP kinase (50%). The amino acid residues corresponding to the sites of phosphorylation (Thr-Glu-Tyr) that are involved in the activation of MAP kinases are conserved in ATMPK1 and ATMPK2. Northern blot analysis indicates that the ATMPK1 and ATMPK2 mRNAs are significantly present in all the organs except seeds. Genomic Southern blot analysis suggests that there are a few additional genes that are related to ATMPK1 and ATMPK2 in the Arabidopsis genome. Purified Xenopus MAP kinase kinase (MAPK kinase) phosphorylates ATMPK1 and ATMPK2 proteins that have been expressed in Escherichia coli, activating these enzymes. A rapid and transient activation of 46-kDa protein kinase activity that phosphorylated myelin basic protein (MBP) was detected when auxin-starved tobacco BY-2 cells were treated with synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D). Protein kinase activities which phosphorylated the recombinant ATMPK2 protein also increased rapidly after auxin treatment in the auxin-starved BY-2 cells. These results suggest that auxin may function as an activator of plant MAP kinase homologues, as do various mitogens in animal systems.
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PMID:Characterization of two cDNAs that encode MAP kinase homologues in Arabidopsis thaliana and analysis of the possible role of auxin in activating such kinase activities in cultured cells. 813 Jul 95

In fibroblasts, stimulation of receptor tyrosine kinases results in the activation of the extracellular signal-regulated kinase 2 (ERK2). The major signalling pathway employed by these receptors involves the activation of p21ras and raf-1 kinase. Here we show that in NIH3T3 and rat-1 fibroblasts, elevation of the intracellular cAMP level results in the inhibition of ERK2 activation induced by PDGF, EGF and insulin treatment. Analysis of various signalling intermediates shows that cAMP interferes at a site downstream of p21ras, but upstream of raf-1 kinase. Inhibition by cAMP depends on both the cAMP concentration and the absolute amount of p21ras molecules bound to GTP, suggesting a mechanism of competitive inhibition. Also TPA-induced, p21ras-independent, activation of raf-1 kinase and ERK2 is inhibited by cAMP. We have used the inhibitory effect of cAMP to investigate whether phosphorylation of mSos, a p21ras nucleotide exchange factor, is dependent on the activity of the raf-1 kinase/ERK2 pathway. We found that phosphorylation of mSos, as monitored by a mobility shift, is delayed with respect to p21ras and ERK2 activation and is inhibited by cAMP in a similar cell type- and concentration-dependent manner as the inactivation of ERK2. These results provide evidence for a model of p21ras-directed signalling towards ERK2 that feeds back on mSos by regulating its phosphorylation status and that can be negatively modulated by protein kinase A and positively modulated by protein kinase C action.
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PMID:cAMP antagonizes p21ras-directed activation of extracellular signal-regulated kinase 2 and phosphorylation of mSos nucleotide exchange factor. 822 35

RCR cells are NRK clones in which Raf-1 production is blocked by the expression of an antisense RNA, and consequently they are refractory to transformation by various oncogenes. In RCR cells, MAP kinases (ERK1 and ERK2) were activated to an extent and in a time course similar to those of the original NRK cells, irrespective of whether the stimulus was oncogenic or non-oncogenic. Moreover, there was no significant elevation of ERK activities in oncogene-transformed NRK cells. These results indicate that Raf-1 kinase is not the major upstream activator of ERK's in NRK cells and that neither ERK1 nor ERK2 are likely to mediate oncogenic signals from Raf-1 kinase.
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PMID:Raf-1 is not a major upstream regulator of MAP kinases in rat fibroblasts. 826 40


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