Adenylate Cyclase Activity in Adrenocorticotropic Hormone-sensitive and Mutant Adrenocortical Tumor Cell Lines

Adenylate cyclase activity has been examined in adrenocortical tumor cell cultures which exhibit adrenocorticotropic hormone (ACTH)-stimulated steroidogenesis (Y-1) and in mutant adrenal cell lines which are insensitive to added ACTH (Y-6 and OS3). Adenylate cyclase activity is stimulated by ACTH in Y-1 cells but not in Y-6 or OS3 cells. The absence of hormone-sensitive adenylate cyclase activity accounts for the variant phenotypes of Y-6 and OS3 cells, and provides evidence for the obligatory roles of adenylate cyclase and adenosine 3',5'-monophosphate in ACTH-stimulated adrenal steroidogenesis. Adenylate cyclase is present in Y-6 and OS3 cells as evidenced by F--stimulated activity. The enzyme activities in the ACTH responsive and mutant cell lines are indistinguishable with respect to requirements for fluoride ion, pH optima, stability at 37°, optimum ATP:Mg2+ ratio, and apparent Km values. The enzyme from each of the three cell lines appears to utilize ATP·Mg as substrate. The lack of hormone-sensitive adenylate cyclase activity in Y-6 and OS3 cells results from defects in ACTH receptors and/or in processes whereby the formation of ACTH receptor complexes is coupled to activation of adenylate cyclase. The dissociation of ACTH-stimulated adenylate cyclase activity from fluoride-stimulated activity in adrenal cell mutants indicates that ACTH and fluoride act on adenylate cyclase at different sites.