Regulation of type 1 angiotensin II receptor messenger ribonucleic acid expression in human adrenocortical carcinoma H295 cells.

We have studied the hormonal regulation of type 1 angiotensin-II receptor (AT1-R) mRNA expression and [125I]angiotensin-II ([125I]AII) binding in human adrenocortical carcinoma H295 cells, which exhibit predominantly AT1-subtype receptors. Activation of the cAMP signaling pathway with forskolin or (Bu)2cAMP caused a rapid decrease in AT1-R mRNA levels (decreased 65% within 3 h). This preceded a time-dependent (maximal, 70% within 12 h) and dose-dependent (IC50, 2 microM forskolin) loss of [125I]AII binding together with decreased phosphoinositidase-C activation (72% decrease) on subsequent AII challenge. Thus, the decreases in AT1-R mRNA levels and functional receptor expression parallel each other in response to activation of protein kinase-A. AII treatment also caused a rapid loss in AT1-R mRNA (maximal, 80% decrease within 3 h), but 48-h treatment caused both [125I]AII binding and the subsequent phosphoinositidase-C response to decrease by only 6% (P < 0.05) and 22% (P < 0.05), respectively. The effect of AII on AT1-R mRNA levels was fully reproduced by the combination of calcium ionophore (A23187) and phorbol ester (12-O-tetradecanoylphorbol 13-acetate), suggesting that AII action was through protein kinase-C and possibly other Ca(2+)-sensitive protein kinases. The effect of AII, but not forskolin, was reversed by treatment in the presence of cycloheximide. In conclusion, control of AT1-R expression is differentially regulated by adenylate cyclase and phosphoinositidase-C signaling pathways, which act at multiple levels in human adrenocortical cells.