Inhibition of CYP17 expression by adrenal androgens and transforming growth factor beta in adrenocortical cells.
Transforming growth factor beta1 (TGFbeta1) has been shown to exert strong inhibitory effects on adrenocortical cell steroidogenesis. However, the molecular targets of TGFbeta1 in adrenocortical cells appear to differ between species. Here, we report the first characterization of the regulatory effects of TGFbeta1 on the steroidogenic functions of the human adrenocortical tumor cell line NCI-H295R. After treatment with 2 ng/ml TGFbeta1 for 24 h, basal production of corticosterone, cortisol and androstenedione was dramatically decreased. When TGFbeta1 was added simultaneously with forskolin, the production of cortisol and 11-hydroxyandrostenedione was decreased by 85% whereas that of deoxycortisol was increased. When TGFbeta1 was added simultaneously with angiotensin II, aldosterone production was reduced by 80%. We observed that TGFbeta1 strongly inhibits forskolin-induced steroid 11beta-hydroxylase activity and CYP11B1 mRNA levels, as well as angiotensin II-induced aldosterone synthase activity and CYP11B2 mRNA levels. CYP11B1 and CYP11B2 gene products thus appear as the major steroidogenic enzymes down-regulated by TGFbeta1 in the human adrenocortical tumor cell line NCI-H295R.