p38 Kinase Is a Negative Regulator of Angiotensin II Signal Transduction in Vascular Smooth Muscle Cells

Abstract

Activation of the Na /H exchanger isoform-1 (NHE-1) by angiotensin II is an early signal transduction event that may regulate vascular smooth muscle cell (VSMC) growth and migration. Many signal transduction events stimulated by angiotensin II are mediated by the mitogen-activated protein (MAP) kinases. To define their roles in angiotensin II-mediated NHE-1 activity, VSMCs were treated with angiotensin II and the activities of p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinases 1 and 2 (ERK1/2) were measured. Angiotensin II rapidly (peak, 5 minutes) activated p38 and ERK1/2, whereas JNK was activated more slowly (peak, 30 minutes). Because angiotensin II stimulated Na /H exchange within 5 minutes, the effects of p38 and ERK1/2 antagonists on Na /H exchange were studied. The MEK-1 inhibitor PD98059 decreased ERK1/2 activity and Na /H exchange stimulated by angiotensin II. In contrast, the specific p38 antagonist SKF-86002 increased Na /H exchange. Two mechanisms were identified that may mediate the effects of p38 and SKF-86002 on angiotensin II-stimulated Na /H exchange. First, angiotensin II activation of ERK1/2 was increased 1.5-to 2.5-fold (depending on assay technique) in the presence of SKF-86002, demonstrating that p38 negatively regulates ERK1/2. Second, the ability of angiotensin II-stimulated MAP kinases to phosphorylate a glutathione S-transferase fusion protein containing amino acids 625 to 747 of NHE-1 in vitro was analyzed. The relative activities of endogenous immunoprecipitated p38, ERK1/2, and JNK were 1.0, 2.0, and 0.05 versus control, respectively suggesting that p38 and ERK1/2, but not JNK, may phosphorylate NHE-1 in VSMC. These data indicate important roles for p38 and ERK1/2 in angiotensin II-mediated regulation of the Na /H exchanger in VSMC. (Circ Res. 1998;83:824-831.) Key Words: mitogen-activated protein kinase Na /H exchange angiotensin II vascular smooth muscle A ngiotensin II is a multifunctional agonist for vascular smooth muscle cells (VSMC), stimulating ion fluxes, protein phosphorylation, contractility, gene expression, and cell growth. Our laboratory has characterized the signal transduction events stimulated by angiotensin II in VSMC to gain insight into its mechanisms of action. Many of the signal transduction events stimulated by angiotensin II are mediated by members of mitogen-activated protein (MAP) kinase family of protein kinases. 1-4 Characterization of substrates for the MAP kinases should provide important insights into the mechanisms by which angiotensin II regulates VSMC function. The Na /H exchanger isoform-1 (NHE-1) is an important membrane protein whose activity may be regulated by protein kinases activated by angiotensin II. Stimulation of Na /H exchange by angiotensin II is an early event that is required for VSMC growth, migration, and contraction. 2,5-7 In fact, inhibiting Na /H exchange with specific amiloride-derivative antagonists decreases neointimal proliferation in the rat carotid injury model. 7 The Na /H exchanger is a phospho...

Acute effects of 17β-estradiol on myocardial pH, Na+, and Ca2+ and ischemia-reperfusion injury

“…These include studies from isolated hepatocytes that suggest a preconditioning effect limiting increases in [Na ϩ ] i during hypoxia is mediated by NO through cGK and p38 MAPK (11) and furthermore that atrial natriuretic peptide diminishes hypoxia-induced increases in [Na ϩ ] i by a similar pathway that inhibits NHE1 (10). These results are also consistent with studies that suggest activation of p38 MAPK inhibits the response of NHE1 to angiotensin II in vascular smooth muscle cells by phosphorylating the NHE1 at serine/threonine residues located between amino acids 671 and 714 (27).…”

Mechanisms of hepatocyte protection against hypoxic injury by atrial natriuretic peptide

“…32,33 The possible involvement of p38 MAPK in down-modulating Na ϩ /H ϩ exchanger is suggested by the observation that p38 MAPK is able to phosphorylate a fusion protein containing the 625 to 747 amino acid sequence of Na ϩ /H ϩ exchanger isoform 1 and that Na ϩ /H ϩ exchanger isoform 1 phosphorylation affects Na ϩ exchange activity. 34 These observations do not exclude that ANP-mediated signals might also activate other cytoprotective mechanisms, because NPs have been shown to modulate cell apoptosis in various tissues. 35 In conclusion, the results show that ANP is capable of increasing hepatocyte tolerance to hypoxia by activating 2 independent signal pathways: one mediated by cGMP and cGK and the other involving G i protein, phospholipase C, and PKC-␦.…”

Activation and signaling of the p38 MAP kinase pathway

“…cPLA2, Na+/H+ exchanger isoform-1 (NHE-1), tau and keratin 8 have also been reported as substrates for p38α [78][79][80][81]. Furthermore, stathmin is another substrate for p38α [27].…”