Adrenocorticotropin increases expression of c-fos and beta-actin genes in the rat adrenals.

It is widely accepted that expression of protooncogenes is coupled with cellular proliferation and differentiation. Since ACTH stimulates not only steroidogenesis but also cellular proliferation, we investigated whether ACTH affects the expression of c-fos, c-myc, and beta-actin genes. The effect of ACTH on adrenal glands was studied in hypophysectomized rats. Changes in the mRNA levels were studied by Northern and dot blot analyses. It was demonstrated that ACTH induces increases in mRNAs encoding c-fos and beta-actin in adrenal glands of hypophysectomized rats. When stimulated by ACTH (5 IU/100 g BW), the mRNA levels of both genes increase rapidly; the maximum levels are observed at 30 min for c-fos and 6 h for beta-actin. Both mRNAs declined to near-control levels by 6-24 h. The levels of mRNAs encoding cholesterol side-chain cleavage cytochrome P-450 and 21-hydroxylase cytochrome P-450 began to increase 3 and 12 h after ACTH administration, respectively. This increase continued for 24 h after ACTH treatment. Increases in total adrenal RNA and adrenal weight occurred slowly after ACTH treatment. On the other hand, the levels of c-myc mRNA were very low and were not increased by ACTH administration. These results suggest that increased expression of c-fos and beta-actin genes by ACTH may have important roles in mediating its action on adrenals.