Modulation of the androgenic response by recombinant human 11- cis retinol dehydrogenase

Abstract

The 11- cis retinol dehydrogenase (11- cis-RoDH) enzyme catalyzes the oxidation of cis-retinols to their respective retinals, a rate limiting step in the formation of retinoic acids. Earlier, we have shown that the enzyme also exhibits an oxidative 3α-hydroxysteroid dehydrogenase (3α-HSD) activity that can convert 5α-androstane-3α,17β-diol (3α-diol) into dihydrotestosterone (DHT), the most potent natural androgen. 11- cis-RoDH could thus control the formation of two active hormones, namely 9- cis retinoic acid and DHT. Therefore, depending upon the substrate availability in the various tissues, this enzyme could provide different metabolites for specific cell functions. To further investigate the role of 11- cis-RoDH in the formation of DHT from 3α-diol, we stably expressed the enzyme in the human embryonic kidney cell line 293 (HEK-293). The transformation of 3α-diol by these cells was evaluated by assays using both microsomal fractions and intact cultured cells stably expressing 11- cis-RoDH. The results show that in the intact cells 11- cis-RoDH only catalyzes the oxidation of 3α-diol into DHT whereas the microsomal fraction catalyzes both the oxidation and the reduction reactions depending upon whether NAD + or NADH is added. Furthermore, we examined the ability of 11- cis-RoDH, through the production from 3α-diol of the active androgen DHT, to activate the androgen-responsive promoter of the prostate-specific antigen (PSA) gene. The co-transfection of the pCMV expression vector containing 11- cis-RoDH (pCMV-11- cisRoDH), a luciferase reporter gene driven by a PSA promoter (pCMV-PSA-Luc) and an androgen receptor (pCMV-hAR) showed that, in the presence of 3α-diol, the expression of the PSA promoter is increased by five to six-fold. Moreover, this stimulatory effect is inhibited by hydroxyflutamide, a well-known antiandrogen. These results suggest that 11- cis-RoDH could be involved in a non-classical pathway of androgen formation and might play a role in the modulation of the androgenic response in some peripheral tissues.