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)

We showed before that partial inhibition of Na/K-ATPase by non-toxic concentrations of ouabain caused hypertrophic growth of neonatal rat cardiac myocytes, and induced several early- and late-response genes that are markers of cardiac hypertrophy. The aim of this study was to determine if the genes of the alpha-subunit isoforms of Na/K-ATPase were among those regulated by ouabain; and if so, to begin the characterization of the pathways regulating these genes. When neonatal myocytes, expressing alpha1- and alpha3-isoform messages, were exposed to 5-100 micro M ouabain, alpha1 mRNA was not affected, but alpha3 mRNA was decreased in a dose- and time-dependent manner. Ouabain-induced down-regulation of alpha3 mRNA was accompanied by a decrease in alpha3-protein content in these myocytes. There was a significant correlation between ouabain effects on alpha3-repression and skeletal alpha-actin induction; also, ouabain's transcriptional effects on both genes were antagonised by retinoic acid. These findings suggested the association of alpha3 repression with ouabain-induced hypertrophy. Phenylephrine and a phorbol ester, two hypertrophic stimuli that do not inhibit Na/K-ATPase, also down-regulated alpha3 mRNA without affecting alpha1 mRNA, suggesting that alpha3-repression is a common feature of the hypertrophic phenotype in these myocytes. Ouabain-induced repression of alpha3 required the influx of extracellular Ca2+, and was antagonized by inhibitors of protein kinase C, Ca2+-calmodulin kinase, and mitogen-activated protein kinase but not by inhibition of protein kinase A. These data, and prior findings on the mechanisms of hypertrophic effects of phenylephrine and phorbol esters, suggest that transcriptional repression of alpha3 by ouabain and other hypertrophic stimuli involves a common step regulated by a mitogen-activated protein kinase.
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PMID:Differential regulation of Na/K-ATPase alpha-subunit isoform gene expressions in cardiac myocytes by ouabain and other hypertrophic stimuli. 940 89

We showed before that in neonatal rat cardiac myocytes partial inhibition of Na+/K+-ATPase by nontoxic concentrations of ouabain causes hypertrophic growth and transcriptional regulations of genes that are markers of cardiac hypertrophy. In view of the suggested roles of Ras and p42/44 mitogen-activated protein kinases (MAPKs) as key mediators of cardiac hypertrophy, the aim of this work was to explore their roles in ouabain-initiated signal pathways regulating four growth-related genes of these myocytes, i.e. those for c-Fos, skeletal alpha-actin, atrial natriuretic factor, and the alpha3-subunit of Na+/K+-ATPase. Ouabain caused rapid activations of Ras and p42/44 MAPKs; the latter was sustained longer than 90 min. Using high efficiency adenoviral-mediated expression of a dominant-negative Ras mutant, and a specific inhibitor of MAPK kinase (MEK), activation of Ras-Raf-MEK-p42/44 MAPK cascade by ouabain was shown. The effects of the mutant Ras, an inhibitor of Ras farnesylation, and the MEK inhibitor on ouabain-induced changes in mRNAs of the four genes indicated that (a) skeletal alpha-actin induction was dependent on Ras but not on p42/44 MAPKs, (b) alpha3 repression was dependent on the Ras-p42/44 MAPK cascade, and (c) induction of c-fos or atrial natriuretic factor gene occurred partly through the Ras-p42/44 MAPK cascade, and partly through pathways independent of Ras and p42/44 MAPKs. All ouabain effects required extracellular Ca2+, and were attenuated by a Ca2+/calmodulin antagonist or a protein kinase C inhibitor. The findings show that (a) signal pathways linked to sarcolemmal Na+/K+-ATPase share early segments involving Ca2+ and protein kinase C, but diverge into multiple branches only some of which involve Ras, or p42/44 MAPKs, or both; and (b) there are significant differences between this network and the related gene regulatory pathways activated by other hypertrophic stimuli, including those whose responses involve increases in intracellular free Ca2+ through different mechanisms.
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PMID:Multiple signal transduction pathways link Na+/K+-ATPase to growth-related genes in cardiac myocytes. The roles of Ras and mitogen-activated protein kinases. 961 40

We previously demonstrated that the marine toxin and skin tumor promoter palytoxin activates the stress-activated protein kinase/c-Jun N-terminal kinase (JNK), but not the extracellular signal-regulated kinase (ERK), which is typically activated by mitogenic agents. JNK, ERK, and p38, another stress-activated protein kinase, are members of the mitogen-activated protein (MAP) kinase family of serine/threonine kinases, which coordinate the transmission of various signals through the cell. The Na+,K+-ATPase is the putative palytoxin receptor. Therefore, we hypothesized that the Na+,K+-ATPase inhibitor ouabain might also stimulate signaling pathways that activate MAP kinases. Using HeLa and COS7 cells, we found that, although there are similarities between the protein kinase cascades by which palytoxin and ouabain activate JNK, there are also significant differences between the activation of specific MAP kinases by palytoxin and ouabain. Transient expression of dominant negative mutants indicates that ouabain, like palytoxin, activates JNK through a protein kinase cascade that involves the JNK kinase SEK1 but does not require the GTPase Ras. Palytoxin activates JNK and p38 to a greater extent than ouabain. By contrast, ouabain activates ERK to a greater extent than palytoxin. Ouabain blocked palytoxin-stimulated activation of JNK and p38, but not anisomycin-stimulated activation of these kinases, supporting the conclusion that ouabain and palytoxin bind to the same site on the Na+,K+-ATPase. These results suggest that the Na+,K+-ATPase can differentially mediate the activation of MAP kinases by two diverse ligands, palytoxin and ouabain.
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PMID:Differential activation of mitogen-activated protein kinases by palytoxin and ouabain, two ligands for the Na+,K+-ATPase. 970 14

This study examines the involvement of RNA and protein synthesis in the modulation of apoptosis in vascular smooth muscle cells (VSMC) by intracellular monovalent cations. In VSMC transfected with E1A adenovirus (VSMC-E1A), inversion of the [Na(+)](i)/[K(+)](i) ratio by an inhibitor of the Na(+),K(+) pump, ouabain, prevented the development of apoptosis triggered by serum withdrawal. Inhibition of apoptosis by ouabain was abolished by inhibitors of RNA and protein synthesis, actinomycin D, and cycloheximide, respectively. In VSMC-E1A, incubation with ouabain for 4 and 24 hours augmented RNA synthesis by 20% to 50% and 3-fold to 4-fold, respectively. In quiescent VSMC, the effect of ouabain and serum on RNA synthesis was additive. Ouabain did not affect the level of phosphorylation of ERK, JNK, and p38 MAP kinases and blocked apoptosis independent of the presence of the MAPK kinase inhibitors PD98059 and SB 202190. Equimolar substitution of NaCl with KCl in the incubation medium abolished the effect of ouabain on intracellular Na(+) and K(+) concentration, apoptosis, and RNA synthesis. Thus, our results demonstrate that the antiapoptotic effect of the inverted [Na(+)](i)/[K(+)](i) ratio is mediated by MAPK-independent induction of de novo synthesis of RNA species encoding inhibitor(s) of programmed cell death.
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PMID:Inversion of the intracellular Na(+)/K(+) ratio blocks apoptosis in vascular smooth muscle cells by induction of RNA synthesis. 1081 65

Nontoxic concentrations of ouabain, causing partial inhibition of the cardiac myocyte Na(+)/K(+)-ATPase, induce hypertrophy and several growth-related genes through signal pathways that include the activation of Ras and p42/44 mitogen-activated protein kinase (MAPK). The aim of this work was to examine the ouabain-induced events upstream of the Ras/MAPK cascade. Treatment of myocytes with genistein antagonized ouabain-induced activation of the MAPK, suggesting that protein tyrosine phosphorylation has a role. Tyrosine phosphorylation of several myocyte proteins was increased rapidly upon cell exposure to ouabain. Lowering of extracellular K(+) had a similar ouabain-like effect. Ouabain also increased protein tyrosine phosphorylation in A7r5, HeLa, and L929 cells. In cardiac myocytes and A7r5 cells, herbimycin A antagonized the ouabain-induced increase in protein tyrosine phosphorylation and MAPK activation. In both cell types, ouabain stimulated Src kinase activity, Src translocation to the Triton-insoluble fraction, Src association with the epidermal growth factor receptor, and the tyrosine phosphorylation of this receptor on site(s) other than its major autophosphorylation site, Tyr(1173). The findings suggest that (a) the ouabain-induced activation of Src and the Src-induced phosphorylation of the growth factor receptor provide the scaffolding for the recruitment of adaptor proteins and Ras and the activation of Ras/MAPK cascade; and (b) the activation of such pathways may be a common feature of the signal-transducing function of Na(+)/K(+)-ATPase in most cells.
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PMID:Involvement of Src and epidermal growth factor receptor in the signal-transducing function of Na+/K+-ATPase. 1087 30

Ouabain is a well known inhibitor of the Na+ pump in all mammalian cells. We have demonstrated that ouabain at concentrations below those which inhibit the pump, i.e. 0.1 nM and 1.0 nM, induce proliferation of saphenous vein smooth muscle cells as measured by bromodeoxyuridine (BrdU) uptake. Ouabain at these low concentrations also activated MAPK. Proliferating concentrations of the drug did not increase levels of Ca(i)2+, suggesting no effect of this ion in the process. In addition, incubation of the cells in low levels of K+, which has been shown to inhibit the pump, had no effect on proliferation. These data show that low concentrations of ouabain that do not inhibit the Na+ pump can activate proliferation of vascular smooth muscle cells, suggesting that the pump complex may act as a transducing receptor.
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PMID:Low concentrations of ouabain induce vascular smooth muscle cell proliferation. 1135 10

We have shown before that Na(+)/K(+)-ATPase acts as a signal transducer, through protein-protein interactions, in addition to being an ion pump. Interaction of ouabain with the enzyme of the intact cells causes activation of Src, transactivation of EGFR, and activation of the Ras/ERK1/2 cascade. To determine the role of protein kinase C (PKC) in this pathway, neonatal rat cardiac myocytes were exposed to ouabain and assayed for translocation/activation of PKC from cytosolic to particulate fractions. Ouabain caused rapid and sustained stimulation of this translocation, evidenced by the assay of Ca(2+)-dependent and Ca(2+)-independent PKC activities and by the immunoblot analysis of the alpha, delta, and epsilon isoforms of PKC. Dose-dependent stimulation of PKC translocation by ouabain (1-100 microm) was accompanied by no more than 50% inhibition of Na(+)/K(+)-ATPase and doubling of [Ca(2+)](i), changes that do not affect myocyte viability and are known to be associated with positive inotropic, but not toxic, effects of ouabain in rat cardiac ventricles. Ouabain-induced activation of ERK1/2 was blocked by PKC inhibitors calphostin C and chelerythrine. An inhibitor of phosphoinositide turnover in myocytes also antagonized ouabain-induced PKC translocation and ERK1/2 activation. These and previous findings indicate that ouabain-induced activation of PKC and Ras, each linked to Na(+)/K(+)-ATPase through Src/EGFR, are both required for the activation of ERK1/2. Ouabain-induced PKC translocation and ERK1/2 activation were dependent on the presence of Ca(2+) in the medium, suggesting that the signal-transducing and ion-pumping functions of Na(+)/K(+)-ATPase cooperate in activation of these protein kinases and the resulting regulation of contractility and growth of the cardiac myocyte.
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PMID:Role of protein kinase C in the signal pathways that link Na+/K+-ATPase to ERK1/2. 1156 72

The hypothesis of this study is that the sodium pump complex acts as an intracellular signal-transducing molecule in canine vascular smooth muscle cells through its interaction with other membrane and cytoskeletal proteins. We have demonstrated that 1 nm ouabain induced transactivation of the epidermal growth factor receptor (EGFR), resulting in increased proliferation and bromodeoxyuridine (BrdUrd) uptake. Immunoprecipitation and Western blotting showed that the EGFR and Src were phosphorylated within 5 min of 10(-9) m ouabain stimulation. Both ouabain-induced DNA synthesis (BrdUrd uptake) and MAPK42/44 phosphorylation were inhibited by the Src inhibitor PP2, the EGFR kinase inhibitor AG1478, the tyrosine kinase inhibitor genistein, and the MEK1 inhibitor PD98059. Ouabain concentrations higher than 1 nm had little or no stimulating effect on proliferation or BrdUrd uptake but did minimally activate ERK1/2. Thus, low concentrations of ouabain, which do not inhibit the sodium pump sufficiently to perturb the resting cellular ionic milieu, initiate a transactivational signaling cascade leading to vascular smooth muscle cell proliferation.
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PMID:Ouabain-induced signaling and vascular smooth muscle cell proliferation. 1157 90

Binding of ouabain to Na(+)/K(+)-ATPase activates tyrosine phosphorylation of the epidermal growth factor receptor (EGFR), Src, and p42/44 mitogen-activated protein kinases (MAPKs) in both cardiac myocytes and A7r5 cells. Here, we explored the roles of Src and the EGFR in the ouabain-invoked pathways that lead to the activation of MAPKs. Exposure of A7r5 and LLC-PK1 cells to ouabain caused a dose-dependent inhibition of Na(+)/K(+)-ATPase activity, which correlated well with ouabain-induced activation of Src and MAPKs in these cells. Immunoprecipitation experiments showed that ouabain stimulated Src binding to Na(+)/K(+)-ATPase in a dose- and time-dependent manner and increased phosphorylation of Src at Tyr(418) but had no effect on Tyr(529) phosphorylation. Ouabain failed to activate MAPKs in A7r5 cells that were pretreated with the Src inhibitor PP2 and in SYF cells in which Src family kinases are knocked out. Preincubation with AG1478, but not AG1295, also blocked the effects of ouabain on p42/44 MAPKs in A7r5 cells. Significantly, both herbimycin A and PP2 abrogated ouabain-induced but not epidermal growth factor-induced Src binding to the EGFR and the subsequent EGFR tyrosine phosphorylation. Ouabain also failed to affect tyrosine phosphorylation of the EGFR in SYF cells. In addition, unlike epidermal growth factor, ouabain did not increase EGFR autophosphorylation at Tyr(1173). These findings clearly indicate that ouabain transactivates the EGFR by activation of Src and stimulation of Src binding to the EGFR. Furthermore, we found that the transactivated EGFR was capable of recruiting and phosphorylating the adaptor protein Shc. This resulted in increased binding of another adaptor protein Grb2 to the Src-EGFR complex and the subsequent activation of Ras and MAPKs. Taken together, these new findings suggest that Src mediates the inter-receptor cross-talk between Na(+)/K(+)-ATPase and the EGFR to transduce the signals from ouabain to the Ras/MAPK cascade.
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PMID:Src-mediated inter-receptor cross-talk between the Na+/K+-ATPase and the epidermal growth factor receptor relays the signal from ouabain to mitogen-activated protein kinases. 1190 28

Ouabain binding to Na(+)/K(+)-ATPase activates Src/epidermal growth factor receptor (EGFR) to initiate multiple signal pathways that regulate growth. In cardiac myocytes and the intact heart, the early ouabain-induced pathways that cause rapid activations of ERK1/2 also regulate intracellular Ca(2+) concentration ([Ca(2+)](i)) and contractility. The goal of this study was to explore the role of caveolae in these early signaling events. Subunits of Na(+)/K(+)-ATPase were detected by immunoblot analysis in caveolae isolated from cardiac myocytes, cardiac ventricles, kidney cell lines, and kidney outer medulla by established detergent-free procedures. Isolated rat cardiac caveolae contained Src, EGFR, ERK1/2, and 20-30% of cellular contents of alpha(1)- and alpha(2)-isoforms of Na(+)/K(+)-ATPase, along with nearly all of cellular caveolin-3. Immunofluorescence microscopy of adult cardiac myocytes showed the presence of caveolin-3 and alpha-isoforms in peripheral sarcolemma and T tubules and suggested their partial colocalization. Exposure of contracting isolated rat hearts to a positive inotropic dose of ouabain and analysis of isolated cardiac caveolae showed that ouabain caused 1) no change in total caveolar ERK1/2, but a two- to threefold increase in caveolar phosphorylated/activated ERK1/2; 2) no change in caveolar alpha(1)-isoform and caveolin-3; and 3) 50-60% increases in caveolar Src and alpha(2)-isoform. These findings, in conjunction with previous observations, show that components of the pathways that link Na(+)/K(+)-ATPase to ERK1/2 and [Ca(2+)](i) are organized within cardiac caveolae microdomains. They also suggest that ouabain-induced recruitments of Src and alpha(2)-isoform to caveolae are involved in the manifestation of the positive inotropic effect of ouabain.
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PMID:Role of caveolae in signal-transducing function of cardiac Na+/K+-ATPase. 1260 14


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