Angiotensin AT(1) receptor phosphorylation and desensitization in a hepatic cell line. Roles of protein kinase C and phosphoinositide 3-kinase

Desensitization and phosphorylation of the endogenous angiotensin II AT(1) receptor were studied in clone 9 liver cells. Agonist activation of AT(1) r eceptors blunted the response to subsequent addition of angiotensin II. Par tial inhibition of the angiotensin II-induced calcium response was observed when cells were pretreated with dibutyryl cyclic AMP, tetradecanoyl phorbo l acetate (TPA), vasopressin, or lysophosphatidic acid. All of these desens itization processes were associated with receptor phosphorylation. Angioten sin II-induced AT(1) receptor phosphorylation was partially blocked by the protein kinase C inhibitor bisindolylmaleimide I and by phosphoinositide 3- kinase inhibitors (wortmannin and LY294002); the actions of these inhibitor s were not additive. Pertussis toxin pretreatment of cells also partially i nhibited angiotensin II-induced AT(1) receptor phosphorylation. TPA-induced AT(1) receptor phosphorylation was completely blocked by bisindolylmaleimi de I. AT(1) receptor phosphorylation was also induced by vasopressin and ly sophosphatidic acid, and these effects were partially inhibited by bisindol ylmaleimide I. Angiotensin II increased Akt/PKB (protein kinase B) phosphor ylation and protein kinase C membrane association. The effect on Akt/PKB ph osphorylation was blocked by phosphoinositide 3-kinase inhibitors. These fi ndings indicate that clone 9 cells exhibit both homologous and heterologous desensitization in association with AT(1) receptor phosphorylation. In the se hepatic cells, angiotensin II-induced receptor phosphorylation involves pertussis toxin-sensitive and -snsensitive G proteins, and is mediated in p art through protein kinase C and phosphoinositide 3-kinase.