Angiotensin II modulates ANP-R2/ANP-C receptor-mediated inhibition of adenylyl cyclase in vascular smooth muscle cells: Role of protein kinase 2

In the present studies, we have investigated the modulation of atrial natriuretic peptide (ANP) receptor of R2 subtype (ANP-R2/ANP-C) coupled to adenylyl cyclase/cAMP signal transduction system by angiotensin II (angII). C-ANF(4-23) [des(Gln(18), Ser(19), Gln(20), Leu(21), Gly(22))ANF(4-23)-NH2] and AngII inhibited adenylyl cyclase activity in a concentration-dependent manner in vascular smooth muscle cells (VSMC A-10). The maximal inhibitions observed were about 40 and 30%, respectively, with an apparent K-i of about 1 and 10 nM. Pretreatment of the cells with AngII resulted in the attenuation of both C-ANF(4-23) and AngII-mediated inhibitions of adenylyl cyclase, without altering [I-125]-ANF binding. The levels of G(i alpha-2) and G(i alpha-3) proteins as determined by immunoblotting were also augmented by AngII treatment. In addition, AngII treatment stimulated the phosphorylation of G(i alpha 2) but not of G(i alpha 3) or ANP-C receptor, as revealed by immunoprecipitation of the proteins using specific antibodies after prelabelling the cells with [P-32]orthophosphate. Staurosporine and chelerythrine, protein kinase C (PKC) inhibitors at 1 and 100 nM, respectively prevented the AngII-mediated desensitization of C-ANF(4-23)-sensitive adenylyl cyclase. In addition, the AngII-mediated phosphorylation of G(i alpha 2) protein was also inhibited partially by about 35% by staurosporine treatment. These results suggest that the attenuation of C-ANF(4-23)-mediated inhibition of adenylyl cyclase activity by AngII may not be attributed to the downregulation of receptors or to the decreased levels of G-proteins, and may involve PKC-dependent mechanisms, (C) 1998 Academic Press