Characterization of the oxidative 3alpha-hydroxysteroid dehydrogenase activity of human recombinant 11-cis-retinol dehydrogenase.

11-cis-Retinol dehydrogenase catalyzes the oxidation of cis-retinols, a rate-limiting step in the biosynthesis of 9-cis-retinoic acid. It is also active toward 3alpha-hydroxysteroids, and thus might be involved in steroid metabolism. To better understand the role of this enzyme, we produced stable transfectants expressing 11-cis-retinol dehydrogenase in human embryonic kidney 293 cells. In vitro enzymatic assays have demonstrated that, with an appropriate exogenous cofactor, the enzyme catalyzes the interconversion of 5alpha-androstane-3alpha,17beta-diol and dihydrotestosterone and that of androsterone and androstanedione. However, using intact transfected cells, we found that the enzyme catalyzes reactions only in the oxidative direction. Thus, it is possible that 5alpha-androstane-3alpha,17beta-diol (an inactive androgen) can be converted into dihydrotestosterone, the most potent androgen, by the action of 11-cis-retinol dehydrogenase. This reaction could constitute a non-classical pathway of production of active androgens in the peripheral tissues. We also showed that all-trans-, 9-cis- and 13-cis-retinol inhibit the oxidative 3alpha-hydroxysteroid steroid activity of 11-cis-retinol dehydrogenase with similar K(i) values. Since all-trans-retinol is a precursor of cis-retinols, its inhibitory effect on the activity suggests that it could play an important role in modulating the formation of 9-cis-retinoic acid. In addition, we examined the effect of several known enzyme modulators, namely carbenoxolone, phenylarsine oxide and phosphatidylcholine, on 11-cis-retinol dehydrogenase activity. Taken together, our results suggest that, in humans, this enzyme might play a role in the biosynthesis of both 9-cis-retinoic acid and dihydrotestosterone.