REGULATION OF C-FOS, C-JUN AND JUN-B MESSENGER RIBONUCLEIC-ACIDS BY ANGIOTENSIN-II AND CORTICOTROPIN IN OVINE AND BOVINE ADRENOCORTICAL-CELLS

Previous work has shown that corticotropin (ACTH) and angiotensin-II (A-II), in addition to their acute steroidogenic effects, exert long-term influences on adrenal cell differentiated function, stimulatory or inhibitory, respectively. Certain nuclear proto-oncogenes have been implicated in the regulation of gene expression in many cell systems. We have investigated the effects of ACTH and A-II on the levels of c-fos, c-jun, and jun-B messenger RNAs (mRNAs), in bovine and ovine (OAC) adrenal fasciculata cells. In both cell types ACTH produced time- (maximum at 1 h) and dose-dependent (ED50 congruent-to 10(-12) M) increase in c-fos (2- to 4-fold) and jun-B (10- to 20-fold) mRNA levels but did not affect c-jun. The concentrations required to induce half-maximal mRNA accumulation and cortisol production were similar. A-II also produced a dose-dependent increase in c-fos and jun-B mRNAs but also in c-jun in both cell types, despite the fact that OAC are resistant to the steroidogenic action of the hormone. The stimulatory effects of A-II on c-fos mRNA were higher than those produced by ACTH, whereas the effects on jun-B were similar but ACTH abolished (OAC) or decreased (bovine adrenal fasciculata cells) the stimulatory effects of A-II on c-jun mRNA. The effects of ACTH and A-II on cortisol production and proto-oncogene mRNAs were in part mimicked by 8Bromo-cAMP and the phorbol ester phorbol-12-myristate-13 acetate plus calcium ionophore A23187, respectively. In the presence of cycloheximide, which blocks the steroidogenic effects of both hormones, proto-oncogene mRNAs were superinduced by both hormones. This result, together with the fact that dexamethasone failed to affect the mRNA levels suggests that the stimulatory effects of ACTH and A-II on proto-oncogene expression were not related to an autocrine/intracrine action of cortisol. Taken together, these findings show that the proto-oncogene mRNAs in normal adrenal cells are regulated by ACTH and A-II, acting through different intracellular pathways. They also demonstrate differential responsiveness of the Jun family to both hormones. Thus, the opposite long-term action of ACTH and A-II on adrenal cell differentiated function could be mediated by its different initial effects on proto-oncogene expression, in particular in the members of the Jun family.