Two distinct mechanisms of angiotensin II-induced negative regulation of the mitogen-activated protein kinases in cultured cardiac myocytes

Increasing evidence has suggested that mitogen-activated protein kinases (M APKs) play important roles in the development of cardiac hypertrophy. We an d others have reported that the activity of MAPKs is tightly regulated by a ngiotensin II (Ang II) in cardiac myocytes. In the present study, we determ ined the molecular mechanism of Ang H-induced inactivation of MAPKs in rat neonatal cardiac myocytes. Ang II increased MAPK phosphatase 1 (MKP-1) gene expressions within 10 min. Levels of MKP-1 transcripts peaked at 30 min an d gradually decreased thereafter. The increase in MKP-1 mRNA levels was Ang II-concentration dependent. An Ang II type 1 receptor (AT1)-specific antag onist, CV-11974, completely suppressed the Ang II-induced increase in MKP-1 gene expression, while a type 2 receptor (AT2)-specific antagonist, PD-123 319, had no significant effects. Induction of MKP-1 gene expressions by Ang II was inhibited by pretreatment with an intracellular Ca2+ chelator, BAPT A-AM, or with the protein kinase C inhibitors, H-7 and Calphostin C. Phorbo l ester and Ca2+ ionophore both significantly increased MKP-1 mRNA levels a nd showed synergistic action. Overexpression of MKP-1 cDNA blocked the Ang II-Induced increase in expressions of immediate early response genes. In ad dition, Ang II-induced MAPK activation was significantly inhibited by pretr eatment with CV-11974, but significantly enhanced by pretreatment with PD-1 23319. Addition of the AT2 agonist, CGP42112A, reduced basal MAPK activitie s, and pretreatment with PD-123319 abolished MAPK inactivation by CGP42112A . In conclusion, these observations suggest that Ang II negatively regulate s MAPKs through AT1 receptors by increasing MKP-1 mRNA levels and through A T2 receptors by unknown mechanisms.