Angiotensin II and cyclic adenosine 3',5'-monophosphate induce human steroidogenic acute regulatory protein...

Steroidogenic acute regulatory protein (StAR) synthesis and steroidogenesis are stimulated by activation of divergent signaling pathways in the adrenal cortex. The two major physiological regulators of aldosterone synthesis in the adrenal zona glomerulosa are angiotensin II (AII) and extracellular K+, which both mediate an increase in intracellular calcium levels, although by distinct mechanisms. Previously, we demonstrated that increased mineralocorticoid synthesis by N6,2'-O-dibutyryl cAMP (Bt2cAMP), AII, and K+ treatment is paralleled by an increase in StAR protein in the H295R human adrenocortical cell line. We now show that StAR steady state messenger RNA levels are increased by Bt2cAMP and AII, but not by K+ or 12-O-tetradecanoylphorbol-13-acetate, treatment of H295R cells. Northern analysis detected two major transcripts of 1.7 and 2.7 kb present in H295R cells, with the most prominent effect of agonist treatment on induction of the 1.7-kb messenger RNA. Similarly, StAR promoter activity in transient transfections of H295R cells with a luciferase reporter gene driven by 1.3 kb of the human promoter was increased only by Bt2cAMP and AII treatment. 5'-Deletion analysis of the StAR promoter indicates that both the cAMP- and AII-responsive elements are within 150 bases of the transcriptional start site. Mutation of a steroidogenic factor-1/AdBP4 element localized at -95 abolishes both Bt2cAMP- and AII-induced luciferase activity in these transient transfection assays. Thus, transcriptional activation of the StAR gene by a steroidogenic factor-1-dependent mechanism may represent a common pathway for ACTH (protein kinase A) and AII action in stimulating steroid production in the adrenal fasciculata and glomerulosa.