INTERACTION OF INSULIN-LIKE GROWTH FACTOR-II AND ESTRADIOL DIRECTS STEROIDOGENESIS IN THE HUMAN FETAL ADRENAL TOWARD DEHYDROEPIANDROSTERONE-SULFATE PRODUCTION

We examined the regulation of steroid production in fetal zone cells from midgestation (16-21 weeks) human fetal adrenal glands to elucidate the mechanism by which these cells secrete large quantities of dehydroepiandrosterone sulfate (DHAS) and little cortisol in response to ACTH. Our underlying hypothesis is that estrogen and insulin-like growth factor-II (IGF-II) modulate the steroidogenic response of fetal zone cells to ACTH, driving steroid production toward DHAS rather than cortisol. We also hypothesize that the effects of IGF-II and estrogen on steroidogenesis are achieved by modulating the expression of key enzymes in the steroidogenic pathway. Basal cortisol secretion by cultured fetal zone cells was below the limit of assay sensitivity (< 0.54 pmol/10(5) cells . 24 h), whereas basal DHAS secretion was 210.8 +/- 41.0 pmol/10(5) cells . 24 h (mean +/- SE). ACTH-(1-24) increased the secretion of cortisol to 228.96 +/- 6.75 pmol/10(5) cells . 24 h and that of DHAS to 2039.8 +/- 121.7 pmol/10(5) cells . 24 h. Neither IGF-II nor estradiol (E2) affected basal (no added ACTH) steroid secretion by fetal zone cells. IGF-II increased ACTH-stimulated cortisol and DHAS secretion by fetal zone cells in a dose-dependent fashion. In contrast, E2 at high concentrations (1-10 mumol/L) decreased ACTH-stimulated cortisol production to basal levels, but increased ACTH-stimulated DHAS production 1.5- to 2-fold. Combinations of IGF-II (100 ng/mL) and E2 (1 mumol/L) increased ACTH-stimulated cortisol and DHAS secretion by 1.5- to 2-fold compared with control values. However, compared with cultures exposed to IGF-II alone, inclusion of E2 decreased ACTH-stimulated cortisol secretion by about 60% and increased ACTH-stimulated DHAS secretion by about 50%. IGF-II increased the abundance of ACTH-stimulated mRNAs encoding cholesterol side-chain cleavage cytochrome P450 (P450scc), 17alpha hydroxylase/17,20 lyase P450 (P450c17), and 3beta-hydroxysteroid dehydrogenase (3betaHSD). In addition, IGF-II increased the abundance of mRNA encoding P450c17 under basal conditions, but did not affect the basal expression of P450scc or 3betaHSD. E2 had no effect on basal expression of these steroidogenic enzymes, but increased the abundance of ACTH-stimulated mRNA encoding P450scc and P450c17. The abundance of mRNA encoding 3betaHSD was not affected by E2. The effect of IGF-II and E2 in combination on steroidogenic enzyme mRNA abundance was not different from that of IGF-II alone. These data indicate that IGF-II increases ACTH-stimulated steroid production in fetal zone cells by increasing the expression of key steroidogenic enzymes. Estrogen may increase ACTH-stimulated DHAS secretion by increasing the expression of P450scc and P450c17. Although the mechanism by which estrogen inhibits cortisol production is uncertain, our data clearly show that this effect is not due to an inhibition of 3betaHSD expression. These data indicate that IGF-II and E2 can influence the steroidogenic activity of fetal zone cells. As the human fetal adrenal is exposed to high concentrations of these substances, it is likely that they influence the steroidogenic response of fetal zone cells to ACTH in vivo, resulting in the production of DHAS rather than cortisol.