P38 KINASE IS A NEGATIVE REGULATOR OF ANGIOTENSIN-II SIGNAL-TRANSDUCTION IN VASCULAR SMOOTH-MUSCLE CELLS - EFFECTS ON NA+ H+ EXCHANGE AND ERK1/2/

Activation of the Na+/H+ exchanger isoform-1 (NHE-1) by angiotensin II is an early signal transduction event that may regulate vascular smoo th muscle cell (VSMC) growth and migration. Many signal transduction e vents stimulated by angiotensin II are mediated by the mitogen-activat ed protein (MAP) kinases. To define their roles in angiotensin II-medi ated NHE-1 activity, VSMCs were treated with angiotensin II and the ac tivities of p38, c-Jun N-terminal kinase (JNK), and extracellular sign al-regulated kinases 1 and 2 (ERK1/2) were measured. Angiotensin II ra pidly (peak, 5 minutes) activated p38 and ERK1/2, whereas JNK was acti vated more slowly (peak, 30 minutes). Because angiotensin II stimulate d Na+/H+ exchange within 5 minutes, the effects of p38 and ERK1/2 anta gonists on Na+/H+ exchange were studied. The MEK-1 inhibitor PD98059 d ecreased ERK1/2 activity and Na+/H+ exchange stimulated by angiotensin II. In contrast, the specific p38 anlagonist SKF-86002 increased Na+/ H+ exchange. Two mechanisms were identified that may mediate the effec ts 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-f old (depending on assay technique) in the presence of SKF-86002, demon strating 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 immunopr ecipitated 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 phosph olylate 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.