Isolation of mutant adrenocortical tumor cells resistant to cyclic nucleotides.

A somatic cell genetic approach was used to study the role of cyclic nucleotides in adrenal steroidogenesis. 8-Bromoadenosine 3',5'-monophosphate (8BrcAMP) stimulated steroidogenesis (K'd=0.1 mM) in cultured mouse adrenocortical tumor cells (Clone Y1). In addition, 8BrcAMP inhibited Y1 cell growth and caused Y1 cell monolayers to assume a rounded morphology. As a consequence, 8BrcAMP (at concentrations greater than or equal to 0.4 mM) reduced the relative plating efficiency of Y1 cells to less than 10(-5). Y1 cells were mutagenized with ethyl methanesulfonate (300 microgram/ml) and grown in the presence of 0.4 mM 8BrcAMP. A surviving colony (8BrcAMPr-1) was shown to be resistant to growth inhibition (relative plating efficiency at 1.0 mM 8BrcAMP=50 percent)) and to morphological changes induced by 8BrcAMP. 8BrcAMPr-1 cells had diminished steroidogenic responses to cyclic nucleotides and to ACTH (less than or equal to 33 percent of maximum). In 8BrcAMP(R)-1 cells, adenylate cyclase activity remained responsive to ACTH, and cyclic AMP phosphodiesterase activity was not increased. These data suggest that 8BrcAMPr-1 cells are defective at a point common to cyclic AMP action on growth, morphology and steroidogenesis. The associated decrease in responsiveness of the steroidogenic pathway to ACTH suggests that ACTH-regulated steroidogenesis is via a cyclic nucleotide-mediated mechanism.