Studies on the mechanism of the novel stimulatory effect of angiotensin-II on adenylate cyclase in rat fetal skin fibroblasts.

Abstract

In contrast to other systems in which angiotensin-II (AII) inhibits adenylyl cyclase, in fetal skin fibroblasts the peptide stimulates cAMP accumulation. The mechanism of this novel effect was studied by analysis of the actions of AII and other regulators on the adenylyl cyclase system in cultured cells. In the presence of phosphodiesterase inhibitors, AII, isoproterenol (ISO), choleratoxin (CTx), and forskolin (Fk) stimulated cAMP accumulation by 2.0 +/- 0.26-, 26 +/- 0.9-, 75 +/- 5.6-, and 88 +/- 3.3-fold, respectively. AII potentiated the stimulatory effect of ISO and CTx by 1.5 +/- 0.1- and 1.25 +/- 0.03-fold, respectively, but had no effect on that of Fk. Preincubation of the cells with PTx did not prevent the stimulatory effect of AII on basal and ISO- and CTx-stimulated cAMP, indicating that the effect of AII was not due to interaction with Gi. Unexpectedly, pretreatment of the cells with PTx for 18 h inhibited cAMP production stimulated by ISO and Fk. Similar inhibition by PTx was observed in adult rat skin fibroblasts, but not in adult human fibroblasts, in which pretreatment with PTx resulted in potentiation of Fk-stimulated cAMP production. ADP ribosylation studies showed that the optical density of the band corresponding to Gs was less than 20% that of Gi and Go in rat fetal cells, suggesting that excess release of the beta-gamma-subunit is responsible for the inhibition of cAMP production by PTx. However, immunoblot analysis of G-proteins showed that the content of Gs alpha was similar to that of Gi alpha and Go alpha in rat and human, fetal and adult cells. In contrast to the effect in intact cells, AII had no effect on basal or stimulated adenylyl cyclase activity in cell homogenates, suggesting that the stimulatory effect observed in intact cells is indirect. The stimulatory action of AII on cAMP production was not blocked by indomethacin, indicating that the effect is not mediated by prostaglandin formation. The stimulation of cAMP by AII was mimicked by 10-min incubation with phorbol 12-myristate 13-acetate (PMA), and prevented after cellular protein kinase-C (PKC) depletion by 4- or 6-h preincubation with PMA. However, the stimulation was not prevented by the PKC inhibitors staurosporine and H7 or 24-h preincubation with PMA, suggesting that the effect is not mediated by a traditional PKC-dependent mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)