Transforming growth factor-α inhibition of luteinizing hormone-stimulated androgen production by ovarian theca-interstitial cells: mechanism of action

Abstract

We have previously demonstrated that TGFα inhibits theca-interstitial cell (TIC) androgen production by specifically blocking LH stimulation of 17α-hydroxylase/C_17–20 lyase (P450_17α) activity. The purpose of the present studies was to examine the mechanism by which this block occurs. TIC were isolated from hypophysectomized immature rats by Percoll gradient centrifugation and cultured up to 6 days in serum-free medium with LH (0–100 ng/ml) and TGFα (0–100 ng/ml). When freshly isolated TIC were treated with TGFα alone (100 ng/ml) there was no change in PKA activity from basal levels. LH (100 ng/ml) stimulated a significant increase in PKA activity that was abolished by TGFα. TGFα did not diminish LH stimulation of cAMP production. TGFα alone did not alter the basal expression of cholesterol side-chain cleavage (P450_scc), 3β-hydroxysteroid dehydrogenase (3β-HSD) or P450_17α mRNAs. LH stimulated dose-related increases in P450_scc (80-fold), 3β-HSD (5-fold) and P450_17α (35-fold) mRNAs. Concomitant treatment with TGFα (100 ng/ml) inhibited LH stimulation of P450_17α mRNA >90% and P450_scc mRNA 35% while 3β-HSD mRNA was stimulated 2-fold. Time course studies demonstrated that the effects of TGFα were present at 2 days in culture. At 4 and 6 days in culture there were small, if any, increases in mRNA levels stimulated by LH. There were no significant effects of TGFα at 4 or 6 days. Our data demonstrate that TGFα inhibition of TIC androgen production involves suppression of P450_scc and P450_17α mRNA expression by inhibiting LH stimulation of PKA activity.