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)

Activity of the ubiquitously expressed Na+-H+ exchanger subtype NHE1 is stimulated upon activation of receptor tyrosine kinases and G protein-coupled receptors. The intracellular signaling pathways mediating receptor regulation of the exchanger, however, are poorly understood. Using transient expression of dominant interfering and constitutively active alleles in CCL39 fibroblasts, we determined that the GTPases Ha-Ras and Galpha 13 stimulate NHE1 through distinct signaling cascades. Exchange activity stimulated by constitutively active RasV12 occurs through a Rafl- and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase kinase (MEK)-dependent mechanism. Constitutively active Galpha 13QL, recently shown to stimulate the Jun kinase cascade, activates NHE1 through a Cdc42- and MEK kinase (MEKK1)-dependent mechanism that is independent of Rac1. Constitutively active Rac1V12 does stimulate NHE1 through a MEKK1-dependent mechanism, but dominant interfering Rac1N17 does not inhibit Galpha 13QL-mediated or constitutively active Cdc42V12-mediated stimulation of the exchanger. Conversely, Cdc42NI7 does not inhibit Rac1V12 activation of NHE1, suggesting that Rae I and Cdc42 independently regulate a MEKK1-dependent activation of the exchanger. Rapid (<10 min) stimulation of NHE1 with a Ga13/Gaz chimera also was inhibited by a kinase-inactive MEKK. Galpha 13QL, but not RasV12, also stimulates NHE1 through a RhoA-dependent pathway that is independent of MEKK, and microinjection of mutationally active Galpha 13 results in a Rho phenotype of increased stress fiber formation. These findings indicate a new target for Rho-like proteins: the regulation of H+ ex- change and intracellular pH. Our findings also suggest that a MEKK cascade diverges to regulate effectors other than transcription factors.
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PMID:G alpha 13 stimulates Na+-H+ exchange through distinct Cdc42-dependent and RhoA-dependent pathways. 862 3

Treatment of human platelets with phorbol 12-myristate 13-acetate (PMA) and arginine vasopressin (AVP) increase the phosphorylation and activation of mitogen-activated protein kinase (MAPK). Electrophoretic retardation of MAPK mobility on SDS-polyacrylamide gels was used for determination of MAPK phosphorylation. The activity of MAPK was tested in myelin basic protein (MBP)-containing polyacrylamide gels. In this study we compared the PMA and AVP signal transduction pathways leading to the activation of MAPKs and Na+/H+ exchanger (NHE). Both agonists stimulate MAPK and NHE activities in a similar time frame and concentration dependence. The MAPK and NHE activities induced by PMA were inhibited by staurosporine, a potent inhibitor for protein kinase C (PKC), and by MAPK kinase (MEK) inhibitor, PD98059, but were not affected by the tyrosine kinase inhibitor genistein. In contrast, both AVP-induced MAPK and NHE activities were inhibited by genistein and MEK inhibitor but were not affected by staurosporine. Immunoprecipitation studies demonstrate that PMA, but not AVP, enhances the basal phosphorylation of the NHE-1. In this study, MAPKs are suggested to be a part of converging signaling leading to NHE activation by PKC-dependent and AVP-tyrosine kinase-dependent pathways. We propose that the MAPK activation of the NHE-1 does not involve phosphorylation of this exchanger protein. On the other hand, PKC can lead to phosphorylation and to additional activation of the NHE-1 through a MAPK-independent pathway.
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PMID:Stimulation of mitogen-activated protein kinase and Na+/H+ exchanger in human platelets. Differential effect of phorbol ester and vasopressin. 866

Replacement of external NaCl with LiCl induced cytoplasmic alkalinization in CCL-39 cells and rat L6 myoblasts expressing the endogenous Na+/H+ exchanger isoform NHE1. This Li+-induced alkalinization is due to activation of the Na+/H+ exchanger because it was completely inhibited by 100 microM ethylisopropylamiloride (apparent Kd=1 microM) and because it did not occur in exchanger-deficient PS120 cells. The effect of Li+ was not mimicked by Na+, K+, Cs+ and choline+. Li+ caused cytoplasmic alkalinization in PS120 cells expressing NHE1 or NHE2, but not NHE3, when Li+ was added to cells at a concentration high enough to saturate their external transport sites as predicted from Li+ affinities. Li+ did not induce phosphatidylinositol (PI) turnover or intracellular Ca2+ mobilization. Li+-induced alkalinization was not affected by protein kinase C down-regulation, loss of glycogen synthase kinase 3beta caused by antisense oligonucleotide treatment, or pretreatment with calphostin C, pertussis toxin, MEK inhibitor PD98059 and PI3-kinase inhibitor LY294002. However, it was markedly suppressed by the tyrosine kinase inhibitor genistein (10 microM). Thus, externally added Li+ activates NHE1 and NHE2 via a mechanism possibly involving a tyrosine kinase, causing an increase in cytoplasmic pH that could potentially affect various cell functions.
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PMID:Lithium activates mammalian Na+/H+ exchangers: isoform specificity and inhibition by genistein. 1067 42

Activity of the Na+/H+ exchanger (NHE) isoform 1 (NHE1) is increased by intracellular acidosis through the interaction of intracellular H+ with an allosteric modifier site in the transport domain. Additional regulation is achieved via kinase-mediated modulation of the NHE1 regulatory domain. To determine if intracellular acidosis stimulates NHE1 activity solely by the allosteric mechanism, we subjected cultured neonatal rat ventricular myocytes (NRVM) with native NHE1 expression to intracellular acidosis (pHi approximately 6.6) for up to 6 min by transient exposure to NH4Cl and its washout in the presence of NHE inhibition (by zero [Na+]o or the NHE1 inhibitor cariporide) in HCO3- -free medium. After the desired duration of acidosis, NHE was reactivated (by reintroduction of [Na+]o or removal of cariporide), and the rate of recovery of pHi (dpHi/dt) was measured as the index of NHE activity. Regardless of the method used when intracellular acidosis was sustained for > or =3 min, subsequent NHE activity was significantly increased (>4-fold). Similar NHE stimulatory effects of sustained acidosis were observed in adult rat ventricular myocytes and COS-7 cells. Sustained (3 min) intracellular acidosis activated several NHE1 kinases in NRVM, in an in-gel kinase assay using as substrate a glutathione S-transferase fusion protein of the NHE1 regulatory domain. Detailed investigation of ERK and its downstream effector p90RSK, two putative NHE1 kinases, revealed time-dependent activation of both by intracellular acidosis in NRVM. Furthermore, inhibition of MEK1/2 by pretreatment of NRVM with two structurally distinct inhibitors, PD98059 (30 microM) or UO126 (3 microM), inhibited the activation of ERK and p90RSK and abolished the stimulation of NHE activity by sustained (3 min) intracellular acidosis. Our data show that not only the extent but also the duration of intracellular acidosis regulates NHE1 activity and suggest that the stimulatory effect of sustained intracellular acidosis occurs through a novel mechanism mediated by activation of the ERK pathway.
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PMID:Stimulation of the plasma membrane Na+/H+ exchanger NHE1 by sustained intracellular acidosis. Evidence for a novel mechanism mediated by the ERK pathway. 1279 86

The purposes of this study were to test 1) the relationship between two widely studied mitogenic effector pathways, and 2) the hypothesis that sodium-proton exchanger type 1 (NHE-1) is a regulator of extracellular signal-regulated protein kinase (ERK) activation in rat aortic smooth muscle (RASM) cells. Angiotensin II (Ang II) and 5-hydroxytryptamine (5-HT) stimulated both ERK and NHE-1 activities, with activation of NHE-1 preceding that of ERK. The concentration-response curves for 5-HT and Ang II were superimposable for both processes. Inhibition of NHE-1 with pharmacological agents or by isotonic replacement of sodium in the perfusate with choline or tetramethylammonium greatly attenuated ERK activation by 5-HT or Ang II. Similar maneuvers significantly attenuated 5-HT- or Ang II-mediated activation of MEK and Ras but not transphosphorylation of the epidermal growth factor (EGF) receptor. EGF receptor blockade attenuated ERK activation, but not NHE-1 activation by 5-HT and Ang II, suggesting that the EGF receptor and NHE-1 work in parallel to stimulate ERK activity in RASM cells, converging distal to the EGF receptor but at or above the level of Ras in the Ras-MEK-ERK pathway. Receptor-independent activation of NHE-1 by acute acid loading of RASM cells resulted in the rapid phosphorylation of ERK, which could be blocked by pharmacological inhibitors of NHE-1 or by isotonic replacement of sodium, closely linking the proton transport function of NHE-1 to ERK activation. These studies identify NHE as a new regulator of ERK activity in RASM cells.
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PMID:ERK is regulated by sodium-proton exchanger in rat aortic vascular smooth muscle cells. 1460 Jan 56

The sodium hydrogen exchanger isoform 1 (NHE1) is present in nearly all cells. Regulation of proton flux via the exchanger is a permissive step in cell growth and tumorgenesis and is vital in control of cell volume. The regulation of NHE1 by growth factors involves the Ras-extracellular signal regulated kinase (ERK) pathway, however, the mechanism for G protein-coupled receptor (GPCR) activation of NHE1 is not well established. In this report, the relationship between GPCRs, ERK, and NHE1 in CCL39 cells is investigated. We give evidence that two agonists, the specific alpha(1)-adrenergic agonist, phenylephrine and the water-soluble lipid mitogen, lysophosphatidic acid (LPA) activate NHE1 in CCL39 cells. Activation of ERK by phenylephrine and LPA occurs in a dose- and time-dependent manner. Optimal ERK activation was observed at 10 min and displayed a maximum stimulation at 100 microM phenylephrine and 10 microM LPA. alpha(1)-Adrenergic stimulation also led to a rise in steady-state pH(i) of 0.16+/-0.02 pH units, and incubation with LPA induced a 0.43+/-0.06 pH unit increase in pH(i). Phenylephrine-induced activation of NHE1 transport and ERK activity was inhibited by pretreating the cells with the MEK inhibitor PD98059. While only half of the LPA activatable exchange activity was abolished by PD98059 and U0126. To further demonstrate the specificity of the phenylephrine and LPA regulation of NHE1 and ERK, CCL39 cells were transfected with a kinase inactive MEK. The data indicate that ERK activation is essential for phenylephrine stimulation of NHE1, and that ERK and RhoA are involved in LPA stimulation of NHE1 by more than one mechanism. In addition, evidence of the convergence of these two pathways is shown by the loss of NHE1 activity when both pathways are inhibited and by the partial additivity of the two agonists on ERK and NHE1 activity. These studies indicate a direct involvement of ERK in the alpha(1)-adrenergic activation of NHE1 and a significant role for both ERK and RhoA in LPA stimulation of NHE1 in CCL39 fibroblasts.
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PMID:Two G protein-coupled receptors activate Na+/H+ exchanger isoform 1 in Chinese hamster lung fibroblasts through an ERK-dependent pathway. 1549 14

The present study evaluated the effect of interferon-gamma (IFN-gamma) on intestinal Na+/H+ exchange (NHE) activity and the intracellular signaling pathways set into motion after IFN-gamma receptor activation. Caco-2 cells express endogenous NHE1, NHE2 and NHE3 proteins, as detected by immunoblotting. Short- (0.5 h) and long- (24 h) term exposure of Caco-2 cells to IFN-gamma resulted in a concentration-dependent decrease in NHE activity. Inhibition of NHE activity by IFN-gamma was absent in cariporide-treated cells, but not in cells treated with S-3226. The long-term exposure to IFN-gamma was accompanied by a 20% increase in surface NHE1 abundance and no changes in total NHE1 abundance. Inhibition of Raf1, mitogen-activated protein kinase kinase (MAPKK/MEK) and p38 MAPK with, respectively, GW 5074, PD 98059 and SB 203580 and downregulation of protein kinase C (PKC) with phorbol-12,13-dibutyrate (100 nM for 24 h) prevented inhibition of NHE activity by IFN-gamma (0.5 and 24 h exposure). The signal transducer and activator transcription factor 1 (STAT1) inhibitor epigallocatechin-3-gallate (EGCG) prevented inhibition of NHE activity by long- but not the short-term treatment with IFN-gamma. Treatment with IFN-gamma activated phospho-p38 MAPK, this effect being detected as early as 1 h, persisting over 3 h and decreasing after 24 h. IFN-gamma produced a sustained action of phospho-STAT1 that was prevented by EGCG and partially attenuated by SB 203580 and insensitive to downregulation of PKC. In conclusion, short- and long-term inhibition of NHE1 activity by IFN-gamma involves a complex signaling pathway that includes PKC activation and STAT1 phosphorylation, respectively, but is not accompanied by downregulation of NHE1.
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PMID:Signaling of short- and long-term regulation of intestinal epithelial type 1 Na+/H+ exchanger by interferon-gamma. 1572 92

We studied pathways involved in the proliferation of rat C6 glioma cells induced by lysophosphatidic acid (LPA), a phospholipid with diverse biological functions. LPA induced a dose-responsive proliferation of C6 cells after 48 h. Proliferation was blocked by inhibitors of the sodium/proton exchanger type 1 (NHE1), Rho-associated kinase, the phosphatidylinositol 3-kinase/Akt pathway (PI3K/Akt), protein kinase C (PKC) and extracellular signal regulated kinase kinase (MEK). Phospho-specific antibodies were used to investigate the pathways involved. LPA induced transient (10 min) phosphorylations of ERK 1/2, Akt and the transcription factor CREB. The LPA-induced phosphorylation of ERK 1/2 and CREB was blocked by inhibition of PI3K, PKC and MEK, but that of Akt was only inhibited by wortmannin, the PI3K inhibitor. Inhibition of Rho kinase or NHE1 did not reduce the LPA-induced phosphorylation of ERK, Akt or CREB. The results were compared with the effects of LPA on transduction pathways in other cell types.
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PMID:Signal transduction mechanisms involved in the proliferation of C6 glioma cells induced by lysophosphatidic acid. 1617 63

Epidermal growth factor (EGF) is predominantly secreted by salivary glands and activates Na(+)/H(+) exchanger-1 (NHE-1), which regulates intracellular pH (pH(i)). We investigated the roles of EGF and NHE-1 in esophageal epithelial defense against acid using human esophageal epithelial cell lines and a rat chronic esophagitis model. Esophageal epithelial cells were incubated with acidified medium in the absence or presence of EGF. Cell viability and changes in pH(i) were measured. Chronic acid reflux esophagitis was induced in rats with and without sialoadenectomy. Esophageal lesion index, epithelial proliferation, and expression of EGF receptors and NHE-1 were examined. EGF protected esophageal epithelial cells against acid in a dose-dependent manner, and the cytoprotective effect of EGF was completely blocked by treatment with NHE-1 inhibitors. Tyrosine kinase, calmodulin, and PKC inhibitors significantly inhibited cytoprotection by EGF, whereas MEK, phosphatidylinositol 3-kinase, and PKA inhibitors had no effect. EGF significantly increased pH(i) recovery after NH(4)Cl pulse acidification, and this increase in pH(i) recovery was significantly blocked by inhibitors of calmodulin and PKC. Sialoadenectomy led to an increase in the severity of chronic esophagitis but affected neither epithelial proliferation nor expression of EGF receptors. Expression of NHE-1 mRNA was increased in esophagitis and upregulated in rats with sialoadenectomy. The increasing severity of esophagitis in rats with sialoadenectomy was prevented by exogenous administration of EGF. In conclusion, EGF protects esophageal epithelial cells against acid through NHE activation via Ca(2+)/calmodulin and the PKC pathway. Deficiency in endogenous EGF is associated with increased severity of esophagitis. EGF and NHE-1 play crucial roles in esophageal epithelial defense against acid.
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PMID:Roles of epidermal growth factor and Na+/H+ exchanger-1 in esophageal epithelial defense against acid-induced injury. 1630 34

Low density lipoproteins (LDL) inhibit the Na+/H+ antiport and thereby sensitize platelet towards agonist. However, mechanisms underlying the suppressing effect of LDL on Na+/H+ exchange are unclear. We here show that the lowering of intracellular pH and the suppression of the sodium propionate-induced Na+/H+ exchange in the presence of LDL are abolished by SKF86002, a selective inhibitor of p38MAP kinase (p38MAPK). The inhibitory effect of LDL on Na+/H+ exchange was mimicked by H2O2, which directly activates p38MAPK. Exposure of platelets to LDL or H2O2 led to phosphorylation of p38MAPK, its upstream regulator MAP kinase kinase 3/6 (MKK 3/6), and its downstream target heat shock protein 27 (HSP27), and this effect was abrogated in SKF86002-pretreated platelets. In addition, both LDL and H2O2 produced the SKF86002-sensitive phosphorylation of an oligopeptide encompassing p38MAPK phosphorylation sequence derived from NHE-1, a major Na+/H+ exchanger in platelets. We further show that the sensitizing effects of LDL on the thrombin-induced platelet activation, as reflected by aggregation and granule secretion, are abolished in cells pretreated with SKF86002. We conclude that activation of p38MAPK is required for the inhibitory effect of LDL on Na+/H+ antiport and thereby for LDL-dependent sensitization in human platelets.
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PMID:Low density lipoproteins inhibit the Na+/H+ antiport in human platelets via activation of p38MAP kinase. 1638 78


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