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 (ATI-R) mRNA expression and [I-125]angiotensin-II ([I-125]AII) binding in human adrenocortical carcinoma H295 cells, which exhibit predominantly AT(1)-subtype receptors. Activation of the cAMP signaling pathway with forskolin or (Bu)(2)cAMP caused a rapid decrease in ATI-R mRNA levels (decreased 65% within 3 h). This preceded a time-dependent (maximal, 70% within 12 h) and dose-dependent (IC50, 2 mu M forskolin) loss of [I-125]AII binding together with decreased phosphoinositidase-C activation (72% decrease) on subsequent ALI challenge. Thus, the decreases in AT(1)-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 ATI-R mRNA (maximal, 80% decrease within 3 h), but 48-h treatment caused both [I-125]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 AT(1)-R mRNA levels was fully reproduced by the combination of calcium ionophore (A23187) and phorbol eater (12-O-tetradecanoylphorbol 13-acetate), suggesting that AII action was through protein kinase-C and possibly other Ca2+-sensitive protein kinases. The effect of AII, but not forskolin, was reversed by treatment in the presence of cycloheximide. In conclusion, control of ATI-R expression is differentially regulated by adenylate cyclase and phosphoinositidase-C signaling pathways, which act at multiple levels in human adrenocortical cells.