ROLE OF CYCLIC-AMP AND PROTEIN-KINASE ON STEROIDOGENIC ACTION OF ACTH, PROSTAGLANDIN-E1 AND DIBUTYRYL CYCLIC-AMP IN NORMAL ADRENAL-CELLS AND ADRENAL TUMOR-CELLS FROM HUMANS

Abstract

The role of the cyclic[c]AMP-protein kinase system in mediating the steroidogenic effect of ACTH, prostaglandin E1 [PGE1] and dibutyryl cAMP was studied using human cells isolated from normal adrenal gland and adrenocortical secreting tumors. At high concentrations of ACTH complete activation of protein kinase of normal adrenal cells was observed within 3 min, at the time when cAMP production was slightly increased and there was still no stimulation of steroidogenesis. At supramaximal concentrations of ACTH, PGE1 and dibutyryl cAMP similar stimulations of protein kinase activity, cAMP and cortisol productions were induced in adrenal cells isolated from normal and from 1 adrenocortical tumor. In 1 tumor in which the adenylate cyclase activity was insensitive to ACTH the hormone was unable to stimulate protein kinase or steroidogenesis; the cells did respond to both PGE1 and dibutyryl cAMP. In another tumor in which the adenylate cyclase was insensitive to PGE1, this compound also did not increase protein kinase activity or steroidogenesis; both parameters were stimulated by ACTH and dibutyryl cAMP. After incubation of normal adrenal cells with increasing concentrations of ACTH (0.01-100 nM) marked differences were found between cAMP formation and cortisol production. However, at the lowest concentrations of ACTH which exerted an effect on steroid production a close linked correlation was found between protein kinase activation and cortisol production; half-maximal and maximal cortisol porduction occurred at a lower concentration of ACTH than necessary to induce the same stimulation of protein kinase. Similar findings were made after incubating the adrenal cells with dibutyryl cAMP (0.01-10 mM). An important role of the cAMP-protein kinase system during activation of adrenal cell steroidogenesis by low concentrations of steroidogenic compounds is implicated.