Adenylate cyclase activity and steroidogenesis in phenotypic revertants of an ACTH-insensitive adrenal tumour cell line

Abstract

A LARGE body of evidence implicates adenylate cyclase and cyclic AMP as mediators of adrenocorticotropic hormone (ACTH)-stimulated adrenal steroidogenesis (see ref. 1 for review). Recent observations, however, suggest that ACTH acts at separate sites to increase steroidogenesis and cyclic AMP accumulation, and that cyclic AMP may not be an important component of ACTH-stimulated steroidogenesis^2–5. An ACTH-responsive adrenocortical tumour cell line⁶ (clone Y1) and a derivative clone insensitive to ACTH⁷ (clone Y6), have been used to examine the role of adenylate cyclase and cyclic AMP in adrenal steroidogenesis^1,7. Y6 cells do not respond to ACTH with increased steroidogenesis but do respond to added cyclic AMP⁷. In addition, these cells have an adenylate cyclase system insensitive to ACTH, probably accounting for their variant phenotype¹. Y6 cells, when grown as tumours, regain the ability to respond to ACTH with increased steroidogenesis, and continue to express the ACTH-sensitive phenotype after prolonged periods in culture and extensive dilution⁷. Y6 cells, after animal passage, provide a system of phenotypic revertants to examine the linkage of different biochemical events to ACTH insensitivity^7,8. We have now examined adenylate cyclase activity in phenotypic revertants of Y6 cells induced by animal passage to assess the role of this enzyme in steroidogenesis. After animal passage, Y6 cells regained the ability to respond to ACTH both with increased steroidogenesis and with increased adenylate cyclase activity. These data indicate that the actions of ACTH on adenylate cyclase activity and steroidogenesis are closely linked.