Corticotropin regulation of 3 beta-hydroxysteroid dehydrogenase/delta 5----4-isomerase in ovine adrenocortical cells: inhibition by transforming growth factor beta.

In the steroidogenic pathway, 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD) is a key enzyme which controls the formation of delta 4-3-ketosteroids from delta 5-3-beta-hydroxysteroids. Herein, we used primary cultures of ovine adrenocortical (OAC) cells to study the effects of ACTH and transforming growth factor beta (TGF-beta) on 3 beta-HSD activity, protein and mRNA levels. TGF-beta has been previously reported to be a potent inhibitor of steroid formation in OAC cells. By using an antibody against human placental 3 beta-HSD, we showed that ACTH-treatment had a dose- and time-dependent stimulatory effect on 3 beta-HSD protein amount. This effect was maximal using 10(-9) M ACTH after a 48 h treatment. When included in the treatment medium, TFG-beta inhibited this stimulation by ACTH in a dose- and time-dependent manner. We also used a human 3 beta-HSD cDNA probe to demonstrate that the effect of both ACTH and TFG-beta were exerted at the mRNA level with maximal effects observed using 10(-9) M for ACTH and 1 ng/ml for TGF-beta. Bu2cAMP mimicked the effects of ACTH, and TGF-beta had an inhibitory effect on this stimulation. It appears from these data that TGF-beta is a negative regulator of 3 beta-HSD expression in OAC cells. The inhibitory effect of TGF-beta on 3 beta-HSD was contrasted to the TGF-beta effect on 17 alpha-hydroxylase cytochrome P-450 (P-45017 alpha). While the levels of both enzymes decreased, that of 3 beta-HSD was less sensitive than that of P-45017 alpha which decreased following TGF-beta treatment to non-detectable levels. The different sensitivities of steroidogenic enzymes to factors which regulate growth and differentiation such as TGF-beta may play a role in determining the nature of steroids released from adrenocortical cells.