Expression Cloning and Regulation of Steroid 5α-Reductase, an Enzyme Essential for Male Sexual Differentiation

The conversion of testosterone into the more potent androgen, dihydrotestosterone, catalyzed by the enzyme steroid 5α-reductase, is required for the differentiation of male external genitalia. Here, we report the isolation of cDNA clones encoding the rat steroid 5α-reductase using expression cloning in Xenopus oocytes. DNA sequence analysis demonstrates that the liver and ventral prostate forms of steroid 5α-reductase are identical hydrophobic proteins of 29 kDa. The amount of steroid 5α-reductase mRNA in liver increased in response to castration, but remained unchanged in the prostate. Testosterone administration to castrates induced expression of mRNA in the prostate but had no effect on liver. The data suggest that the steroid 5α-reductase gene is differentially regulated by testosterone in androgen-responsive versus non-responsive tissues.