INSULIN-LIKE GROWTH-FACTORS AUGMENT STEROID-PRODUCTION AND EXPRESSIONOF STEROIDOGENIC ENZYMES IN HUMAN FETAL ADRENAL-CORTICAL CELLS - IMPLICATIONS FOR ADRENAL ANDROGEN REGULATION

The fetal zone is a unique adrenal cortical compartment that exists on ly during fetal life in humans and higher primates and produces large amounts of the adrenal androgen dehydroepiandrosterone sulfate !DHEA-S ). Growth of the fetal zone is primarily regulated by ACTH, the action s of which are mediated in part by locally produced autocrine/paracrin e growth factors. We previously demonstrated that one of these growth factors, insulin-like growth factor II (IGF-II), is mitogenic for cult ured fetal zone cells and is produced in high abundance by these cells in response to ACTH. In the present study, we determined whether IGF- II also modulates the differentiated function of fetal zone cells. We examined the effects of recombinant human IGF-II and the closely relat ed peptide, IGF-I, on 1) basal and agonist-stimulated [ACTH-(1-24), fo rskolin, or 8-bromo-cAMP] cortisol and DKEA-S production, 2) basal and ACTH-stimulated steady state abundance of messenger ribonucleic acids (mRNAs) encoding the steroidogenic enzymes cytochrome P450 side-chain cleavage (P450scc) and cytochrome P450 17 alpha-hydroxylase/17,20-lya se (P450c17), and 3) basal and ACTH-stimulated steady state abundance of mRNA encoding the ACTH receptor. Basal cortisol (23.93 +/- 1.20 pmo yl/10(5) cells.24 h) and DHEA-S (548.87 +/- 43.17 pmol/10(5) cells.24 h) productions were significantly (P < 0.05) increased by IGF-I (2.3- and 1.8-fold, respectively) and IGF-II (2.8- and 1.8-fold, respectivel y). As expected, ACTH, forskolin, and cAMP markedly increased the prod uction of cortisol by 26-, 10-, and 13-fold, respectively. and that of DHEA-S by 5.4-, 4.6-, and 5.5-fold, respectively, compared with basal levels. IGF-II (100 ng/mL) significantly (P < 0.001) increased ACTH-. forskolin-, and cAMP-stimulated production of cortisol by 2.4-, 4.3-, and 3.2-fold, respectively, and that of DHEA-S by 1.4, 1.6-, and 1.4- fold, respectively IGF-I (100 ng/mL) had similar effects as IGF-II and significantly (P < 0.001) increased ACTH-, forskolin-, and cAMP-stimu lated production of cortisol by 2.8-, 3.9-, and 3.1-fold, respectively , and that of DHEA-S by 1.3-, 1.6-, and 1.4-fold, respectively. The si milar potencies of IGF-I and IGF-II suggest that the actions of these factors were mediated via a common receptor, most likely the type I IG F receptor. The effects of IGF-II on ACTH-stimulated steroid productio n were dose-dependent (EC,,, 0.5-1.0 nmol/L), and IGF-II markedly incr eased the steroidogenic responsiveness of fetal zone cells to ACTH. Wi th respect to cortisol production, IGF-II shifted the ACTH dose-respon se curve to the left by 1 log(10) order of magnitude. IGF-II also incr eased ACTH-stimulated abundance of mRNA encoding P450scc (1.9-fold) an d P450c17 (2.2-fold). Basal expression of P450scc was not affected by IGF-II. In contrast, basal expression of P450c17 was increased 2.2-fol d by IGF-II and IGF-I in a dose-responsive fashion. Neither IGF-I nor IGF-II affected basal or ACTH-stimulated abundance of mRNA encoding th e ACTH receptor, suggesting that the increase in ACTH responsiveness w as not mediated by an increase in ACTH-binding capacity. Taken togethe r, these data indicate that activation of the type I IGF receptor incr eases ACTH responsiveness in fetal zone cells by modulating ACTH signa l transduction at some point distal to ACTH receptor activation. These data also indicate that locally produced IGF-II modulates fetal adren al cortical cell function by increasing responsiveness to ACTH and pos sibly (based on its direct stimulation of P450c17 expression) augmenti ng the potential for adrenal androgen synthesis. Thus, activation of t he type I IGF receptor on adrenal cortical cells may play a pivotal ro le in adrenal androgen production, both physiologically in utero and a t adrenarche, and in pathophysiological conditions of hyperandrogenemi a, such as the polycystic ovary syndrome.