Regulation of Human 3b-Hydroxysteroid Dehydrogenase Type 2 by Adrenal Corticosteroids and Product-Feedback by Androstenedione in Human Adrenarche

In human adrenarche during childhood, the secretion of dehydroepiandrosterone (DHEA) from the adrenal gland increases due to its increased synthesis and/or decreased metabolism. DHEA is synthesized by 17a-hydroxylase/17,20-lyase, and is metabolized by 3b-hydroxysteroid dehydrogenase type 2 (3bHSD2). In this study, the inhibition of purified human 3bHSD2 by the adrenal steroids, androstenedione, cortisone, and cortisol, was investigated and related to changes in secondary enzyme structure. Solubilized, purified 3bHSD2 was inhibited competitively by androstenedione with high affinity, by cortisone at lower affinity, and by cortisol only at very high, nonphysiologic levels. When purified 3bHSD2 was bound to lipid vesicles, the competitive Ki values for androstenedione and cortisone were slightly decreased, and the Ki value of cortisol was decreased 2.5-fold, although still at a nonphysiologic level. The circular dichroism spectrum that measured 3bHSD2 secondary structure was significantly altered by the binding of cortisol, but not by androstenedione and cortisone. Our import studies show that 3bHSD2 binds in the intermitochondrial space as a membraneassociated protein. Androstenedione inhibits purified 3bHSD2 at physiologic levels, but similar actions for cortisol and cortisone are not supported. In summary, our results have clarified the mechanisms for limiting the metabolism of DHEA during human adrenarche.