Gene/Protein Disease Symptom Drug Enzyme Compound
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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)

The purpose of the studies included in this chapter was to examine the role of the actin network in the propagation of insulin action leading to stimulation of glucose transport and activation of the mitogen-activated protein kinase cascade. The active insulin receptor phosphorylates tyrosine residues of intracellular proteins such as the insulin receptor substrate-1 (IRS-1) which acts as docking sites for molecules containing Src homology 2 (SH2) domains. One such molecule is phosphatidylinositol 3-kinase (PI 3-kinase) which becomes activated by binding to IRS-1. PI 3-kinase activity is required for the insulin-stimulation of glucose transport and glycogen synthesis. Grb2, a small adaptor molecule, can bind IRS-1 and, through the guanine nucleotide exchange factor Sos, leads to the activation of the small GTP binding protein Ras. Through a cascade of protein kinases, activation of Ras results in activation of the Erk 1 and 2 mitogen-activated protein kinases (MAPKs) which appear to control important nuclear and metabolic events. To investigate the role of the actin network in the propagation of insulin action leading to stimulation of glucose transport and the activation of the Erk MAPKs, we used the fungal metabolite cytochalasin D which disassembles the actin network. Actin disassembly abolished almost completely the ability of insulin to increase the rate of glucose transport into L6 muscle cells (myotubes) through prevention of the insulin-induced recruitment of glucose transporters to the plasma membrane which is the event that mediates the increase in the rate of transport. Actin disassembly did not affect either the insulin-mediated phosphorylation of IRS-1, the association of PI 3-kinase with this molecule, or the activation of IRS-1-associated PI 3-kinase. These results were also verified in another insulin responsive cell line, the 3T3-L1 adipocytes. In these cells, actin disassembly inhibited the insulin-induced recruitment of PI 3-kinase to intracellular membranes containing glucose transporters. Moreover, actin disassembly abolished the insulin-mediated phosphorylation of the Erk MAPKs. We conclude that the cellular actin network of insulin responsive cells is not required for the activation of PI 3-kinase but prevents its cellular redistribution. In contrast, intact actin filaments are essential for the propagation of insulin signals leading to the the activation of the MAPKs.
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PMID:Involvement of the actin network in insulin signalling. 921 Feb 35

SOS, the guanine nucleotide exchange factor for Ras, becomes phosphorylated on serine and threonine residues following stimulation of cells with growth factors. These phosphorylations may play a role in negative feedback of Ras stimulation and have been shown to be mediated in part by the MAP kinases Erk-1 and Erk-2. Here we show that in addition to MAP kinase, a major mitogen activated kinase for SOS is p90 Rsk-2, a downstream target of MAP kinase. p90 Rsk-2 phosphorylates SOS in an in gel assay and also in solution in vitro. The ability of p90 Rsk-2 to phosphorylate SOS increases greatly following EGF treatment of PC12 cells and is blocked by expression of N17 Ras or treatment with the MEK inhibitor PD98059. Phosphopeptide mapping revealed that the sites phosphorylated by p90 Rsk-2 in vitro were also phosphorylated in intact cells in response to EGF treatment. Several major sites of in vivo phosphorylation correlated with p90 Rsk-2 phosphorylation sites rather than MAP kinase sites. It is therefore likely that p90 Rsk-2 plays an important role in the down regulation of the Ras activation pathway through SOS.
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PMID:EGF induced SOS phosphorylation in PC12 cells involves P90 RSK-2. 924 73

Stimulation of the T cell antigen receptor (TCR) activates signaling pathways involving protein kinases, phospholipase Cgamma1, and Ras. How these second messengers interact to initiate distal activation events is an area of intense scrutiny. In this report, we confirm that TCR ligation results in phosphorylation of Sos, a guanine nucleotide exchange factor for Ras. This requires expression of both the CD45 tyrosine phosphatase and the Lck protein tyrosine kinase and depends upon signaling via protein kinase C. In contrast to previous studies examining requirements for Sos phosphorylation following insulin and epidermal growth factor receptor engagement, we show that TCR-induced phosphorylation of Sos does not require activation of the mitogen-activated protein kinase/extracellular-signal regulated kinase (MEK/ERK) pathway. However, the basal phosphorylation of Sos in T cells is affected by either MEK or MEK-dependent kinases. Although Sos phosphorylation results in its dissociation from Grb2 following insulin stimulation in Chinese hamster ovary cells, TCR engagement on the Jurkat T cell line fails to elicit a similar effect. These data demonstrate that the kinases responsible for Sos phosphorylation differ following ligation of various cell surface receptors and that the consequences of Sos phosphorylation relies, at least in part, on sites of its phosphorylation.
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PMID:T cell receptor-induced phosphorylation of Sos requires activity of CD45, Lck, and protein kinase C, but not ERK. 926 Nov 85

Faciogenital dysplasia (FGDY; MIM 305400), or Aarskog syndrome, is an X-linked developmental disorder that adversely affects the formation of specific skeletal structures including elements of the face, the cervical vertebrae, and the distal extremities. FGD1, the gene responsible for faciogenital dysplasia, encodes a guanine nucleotide exchange factor that specifically activates Cdc42, a member of the Rho (Ras homology) family of p21 GTPases. By activating Cdc42, FGD1 stimulates fibroblasts to form filopodia, cytoskeletal elements involved in cellular signaling and migration, and through Cdc42, FGD1 also activates the stress-activated protein kinase/c-Jun N-terminal kinase signaling cascade, a pathway that regulates cell growth and differentiation. Here, we report a detailed characterization of the genomic organization of the FGD1 gene. The FGD1 gene is composed of 18 exons that range in size from 31 to 1240 bp. These exons span over 51 kb of genomic DNA within region Xp11.21. Flanking intronic sequences and the sequence of the 5' and 3' untranslated regions were determined to facilitate the detection of FGDY patient mutations. Analyses show that FGD1 transcripts are differentially spliced; in brain and placenta an alternatively spliced form of the FGD1 transcript removes part of the Cdc42GEF domain to encode a null Cdc42 activator.
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PMID:Genomic organization of the faciogenital dysplasia (FGD1; Aarskog syndrome) gene. 926 45

The ability of insulin to stimulate protein synthesis and cellular growth is mediated through the insulin receptor (IR), which phosphorylates Tyr residues in the insulin receptor substrate-signaling proteins (IRS-1 and IRS-2), Gab-1, and Shc. These phosphorylated substrates directly bind and activate enzymes such as phosphatidylinositol 3'-kinase (PI3K) and the guanine nucleotide exchange factor for p21Ras (GRB-2/SOS), which are in turn required for insulin-stimulated protein synthesis, cell cycle progression, and prevention of apoptosis. We have now shown that one or more members of the atypical protein kinase C group, as exemplified by the zeta isoform (PKC zeta), are downstream of IRS-1 and P13K and mediate the effect of insulin on general protein synthesis. Ectopic expression of constitutively activated PKC zeta eliminates the requirement of IRS-1 for general protein synthesis but not for insulin-stimulated activation of 70-kDa S6 kinase (p70S6K), synthesis of growth-regulated proteins (e.g., c-Myc), or mitogenesis. The fact that PKC zeta stimulates general protein synthesis but not activation of p70S6K indicates that PKC zeta activation does not involve the proto-oncogene Akt, which is also activated by PI3K. Yet insulin is still required for the stimulation of general protein synthesis in the presence of constitutively active PKC zeta and in the absence of IRS-1, suggesting a requirement for the convergence of the IRS-1/PI3K/PKC zeta pathway with one or more additional pathways emanating from the IR, e.g., Shc/SOS/p21Ras/mitogen-activated protein kinase. Thus, PI3K appears to represent a bifurcation in the insulin signaling pathway, one branch leading through PKC zeta to general protein synthesis and one, through Akt and the target of rapamycin (mTOR), to growth-regulated protein synthesis and cell cycle progression.
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PMID:Requirement of protein kinase C zeta for stimulation of protein synthesis by insulin. 927 96

The functional role of Cbl in regulating T cell receptor (TCR)-mediated signal transduction pathways is unknown. This study uses Cbl overexpression in conjunction with a Ras-sensitive AP1 reporter construct to examine its role in regulating TCR-mediated activation of the Ras pathway. Cbl overexpression in Jurkat T cells inhibited AP1 activity after TCR ligation. However, AP1 induction by 4beta-phorbol 12-myristate 13-acetate, which up-regulates Ras activity in a protein kinase C-dependent, TCR/tyrosine kinase-independent manner, was not affected by Cbl overexpression. Cbl overexpression also did not affect AP1 induction by an activated Ras protein or a membrane-bound form of the guanine nucleotide exchange factor Sos. In addition, activation of the mitogen-activated protein kinase Erk2 was decreased by Cbl overexpression. Therefore, Cbl regulates events that are required for full TCR-mediated Ras activation, and data are presented to support a model whereby Cbl regulates events required for Ras activation via its association with Grb2.
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PMID:Cbl-mediated regulation of T cell receptor-induced AP1 activation. Implications for activation via the Ras signaling pathway. 938 22

We have studied the functional importance of the N terminus of mouse Sos1 (mSos1), a ubiquitously expressed Ras-specific guanine nucleotide exchange factor whose C-terminal sequences bind Grb-2. Consistent with previous reports, addition of a myristoylation signal to mSos1 (MyrSos1) rendered it transforming for NIH 3T3 cells and deletion of the mSos C terminus (MyrSos1-deltaC) did not interfere with this activity. However, an N-terminally deleted myristoylated mSos1 protein (MyrSos1-deltaN) was transformation defective, although the protein was stable and localized to the membrane. Site-directed mutagenesis was used to examine the role of the Dbl and pleckstrin homology (PH) domains located in the N terminus. When mutations in the PH domain were introduced into two conserved amino acids either singly or together in MyrSos1 or MyrSos1-deltaC, the transforming activity was severely impaired. An analogous reduction in biological activity was seen when a cluster of point mutations was engineered into the Dbl domain. The mitogen-activation protein (MAP) kinase activities induced by the various Dbl and PH mutants of MyrSos1 correlated with their biological activities. When NIH 3T3 cells were transfected with a myristoylated Sos N terminus, their growth response to epidermal growth factor (EGF), platelet-derived growth factor, lysophosphatidic acid or serum was greatly impaired. The dominant inhibitory biological activity of the N terminus correlated with its ability to impair EGF-dependent activation of GTP-Ras and of MAP kinase, as well with the ability of endogenous Sos to form a stable complex with activated EGF receptors. The N terminus with mutations in the Dbl and PH domains was much less inhibitory in these biological and biochemical assays. In contrast to wild-type Sos1, nonmyristoylated versions of Sos1-deltaN and Sos1-deltaC did not form a stable complex with activated EGF receptors. We conclude that the Dbl and PH domains are critical for Sos function and that stable association of Sos with activated EGF receptors requires both the Sos N and C termini.
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PMID:N terminus of Sos1 Ras exchange factor: critical roles for the Dbl and pleckstrin homology domains. 944 73

Stimulation of the interleukin (IL)-3 receptor provokes rapid activation of the Ras pathway in various hematopoietic cell lines. Also, a wide range of G-protein-coupled receptors induce Ras activation following ligand stimulation. In this report, we investigate the mechanism underlying Ras activation upon stimulation of these two types of receptors in hematopoietic cells. Thrombin, a G-protein-coupled receptor ligand, was found to stimulate extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) in IL-3-dependent BaF3 cells, suggesting a significant function of thrombin receptor-mediated signaling. We show that the Ras-guanine nucleotide exchange factor mSos is indispensable for activation of the Ras pathway in IL-3- or thrombin-stimulated BaF3 cells. The activation of Ras in response to IL-3 as defined by accumulation of the GTP-bound form was impaired by conditional overexpression of a dominant-negative mutant of mSos (DeltamSos1). Furthermore, following induction of DeltamSos1, IL-3 enhancement of the kinase activities of c-Raf-1, ERK2, and JNK1 downstream of Ras was almost completely blocked. Similarly, thrombin-induced Ras-dependent ERK2 activation was diminished by DeltamSos1. However, the tyrosine phosphorylation pattern of cellular substrates upon thrombin stimulation was entirely different from the pattern of IL-3-induced tyrosine phosphorylation. Collectively, these results provide evidence that mSos plays a crucial role in both IL-3 and thrombin activation of the Ras pathway in hematopoietic cells, although molecules (including tyrosine kinases) mediating the signal to mSos are likely to be different between the two types of receptors.
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PMID:Functional involvement of mSos in interleukin-3 and thrombin stimulation of the Ras, mitogen-activated protein kinase pathway in BaF3 murine hematopoietic cells. 953 58

Tyr-762 is an autophosphorylation site in the human platelet-derived growth factor (PDGF) alpha-receptor. In order to investigate whether phosphorylated Tyr-762 serves as a docking site for downstream signal transduction molecules, affinity purification using an immobilized synthetic peptide containing phosphorylated Tyr-762 and its surrounding amino acid residues was performed. Proteins in HeLa cell lysate of molecular sizes 27, 38 and 40 kDa bound to the phosphorylated, but not to the unphosphorylated peptide. Analyses of partial amino acid sequences of the purified proteins indicated that they were identical to CrkI, CrkII and CrkL respectively. The wild-type PDGF alpha-receptor, when expressed in porcine aortic endothelial cells, formed complexes with CrkII and CrkL upon ligand stimulation, which was specifically inhibited by a synthetic peptide containing phosphorylated Tyr-762. Replacement of Tyr-762 with a phenylalanine residue in the PDGF alpha-receptor abrogated ligand-induced binding of Crk proteins. Tyrosine phosphorylation of CrkII and CrkL increased by 1.8- and 1.3-fold, respectively, upon ligand stimulation of the wild-type alpha-receptor. In contrast, the Y762F mutant PDGF alpha-receptor failed to induce tyrosine phosphorylation of Crk proteins. CrkII and CrkL constitutively formed complex with the guanine nucleotide exchange factor C3G, in unstimulated as well as PDGF-stimulated cells. Moreover, the activated wild-type PDGF alpha-receptor but not the Y762F mutant receptor was found in a C3G immunoprecipitate, suggesting that a ternary complex between the activated PDGF alpha-receptor, Crk and C3G was formed. DNA synthesis stimulated by PDGF-BB as well as PDGF-induced MAP kinase activation was similar in cells expressing wild-type and mutant receptors. Interestingly, the activated PDGF beta-receptor was found not to bind Crk proteins. Instead, Tyr-771 of the beta-receptor, which is localized at an analogous position to Tyr-762 in the alpha-receptor, binds RasGAP. RasGAP is not bound to the alpha-receptor. Thus, this region in the kinase inserts of the two receptors may be important for the divergency in signaling from the two PDGF receptors.
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PMID:Identification of Tyr-762 in the platelet-derived growth factor alpha-receptor as the binding site for Crk proteins. 954 24

The Ras signaling pathway is rapidly activated and then down-regulated following stimulation of multiple cell-surface receptors including the insulin receptor (IR). Much recent attention has focused on elucidating the mechanism of Ras inactivation following IR engagement. Previous data suggest that IR-mediated serine/threonine phosphorylation of the Ras guanine nucleotide exchange factor Sos correlates with its decreased affinity for the adapter protein Grb2. This phosphorylation-induced disassembly of the Grb2.Sos complex is thought to be responsible, at least in part, for diminishing Ras activity in Chinese hamster ovary cells. In this report, we confirm the causal relationship between Sos phosphorylation and Grb2/Sos dissociation. We then examine several putative phosphorylation sites of Sos that could potentially regulate this event. Since a number of reports suggest that extracellular signal-regulated kinase (ERK) phosphorylates Sos, we generated a Sos mutant lacking all seven canonical phosphorylation sites for ERK. This mutant is a poor substrate of activated ERK in vitro and fails to undergo a change in its electrophoretic mobility following IR stimulation. It is, however, phosphorylated after IR stimulation when expressed in Chinese hamster ovary cells. Interestingly, the mutant protein still dissociates from Grb2 following insulin stimulation, suggesting that ERK is not the kinase responsible for regulating the stability of the Grb2.Sos complex.
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PMID:Insulin receptor-mediated dissociation of Grb2 from Sos involves phosphorylation of Sos by kinase(s) other than extracellular signal-regulated kinase. 957 48


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