Induction of Synthesis of Mitochondrial Steroidogenic Enzymes of Bovine Adrenocortical Cells by Analogs of Cyclic AMP

The long term action of cyclic AMP analogs to stimulate the synthesis of cytochromes P-450scc, P-45011 beta, and adrenodoxin has been studied utilizing confluent monolayers of adult bovine adrenocortical cells maintained for periods of time up to 72 h in the absence or presence of dibutyryl cyclic AMP (1 mM), 8-bromo cyclic AMP (1 mM), or ACTH (adrenocorticotropin) (10(-6) M). The synthesis of these proteins was examined by radiolabeling cellular proteins with [35S]methionine or else by translating RNA extracted from such cells in a cell-free system in the presence of [35S]methionine. In each case, the protein under study was immunoprecipitated utilizing specific antisera, or IgG fractions prepared from such antisera. ACTH and both analogs of cyclic AMP caused an increase in the synthesis of cytochrome P-450scc which reached a maximum 36-48 h after addition, and then declined. On the other hand, butyric acid (1 mM) had no effect on the synthesis of cytochrome P-450scc. Cytochrome P-450scc activity measured as pregnenolone production by both intact cells or isolated mitochondria from such cells was increased following incubation of cells with either dibutyryl cyclic AMP or ACTH. The binding of rabbit anti-cytochrome P-450scc IgG was also increased in cells incubated with dibutyryl cyclic AMP or ACTH as estimated by immunofluorescence microscopy using fluorescein-tagged anti-rabbit IgG. Furthermore, dibutyryl cyclic AMP and ACTH both increased the synthesis of adrenodoxin and of cytochrome P-45011 beta, as well as the activity of 11 beta-hydroxylase. In addition, ACTH stimulated the secretion of cyclic AMP in a time- and concentration-dependent fashion. Thus, it is concluded that analogs of cyclic AMP can mimic the long term actions of ACTH to induce the synthesis of steroidogenic enzymes, and that this action of ACTH is likely mediated by cyclic AMP.