Abstract
Abstract 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.
Highlights
Adenylate cyclase activity has been examined in adrenocortical tumor cell cultures which exhibit adrenocorticotropic hormone (ACTH)-stimulated steroidogenesis (Y-l) and in mutant adrenal cell lines which are insensitive to added
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 K, values
Summary
Adenylate cyclase activity has been examined in adrenocortical tumor cell cultures which exhibit adrenocorticotropic hormone (ACTH)-stimulated steroidogenesis (Y-l) and in mutant adrenal cell lines which are insensitive to added. This study examines the :ldcnylate cyclasc systems of Y-6 and OS3 cells directly The results of this communicatiou dcmonstrntJe that the nbuorm:ll phenotypes in t,he two mutant cell linrs arc the result of an adenylate cyclase system which, present, is insensitil-e to 11CTI-I. These observations provide evidence for the obligatory role of adenylate cyclase in ACTI-I-stimulated steroidogcnesis
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