Steroid-sensitive gene-1 is an androgen-regulated gene expressed in prostatic smooth muscle cells in vivo

Steroid-sensitive gene-1 (SSG1) is a novel gene ne cloned, found regulated by 17 beta -estradiol in the rat uterus and mammary gland, and over-express ed in 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors. We show he re that SSG1 mRNA and protein expression are regulated by androgens in the rat ventral prostate. Increases in SSG1 mRNA levels were detected bq: North ern blotting after 24 h and reached a 27-fold peak 96 h following castratio n, relative to SSG1 mRNA expression in sham-operated rats. Dihydrotestoster one or testosterone supplementation of castrated rats prevented this rise i n SSG1 mRNA. In contrast with SSG1 mRNA expression, SSG1 protein was decrea sed 16-fold 2 weeks following castration but was at control levels in the p rostates of castrated rats receiving dihydrotestosterone or testosterone. A lthough SSG1 is regulated by androgens in vivo, treatment of LnCap cells wi th dihydrotestosterone, cyproterone acetate or flutamide did not result in the regulation of SSG1 protein levels in vitro. Immunofluorescence studies show that SSG1 is mainly expressed in prostatic smooth muscle cells. These results indicate that SSG1 is an androgen-regulated gene that is expressed in the smooth muscle component of the rat ventral prostate in vivo.