Blocking BRE expression in Leydig cells inhibits steroidogenesis by down-regulating 3β-hydroxysteroid dehydrogenase

Abstract

Conversion of cholesterol to biologically active steroids is a multi-step enzymatic process. Along with some important enzymes, like cholesterol side-chain cleavage enzyme (P450scc) and 3β-hydroxysteroid dehydrogenase/isomerase (3β-HSD), several proteins play key role in steroidogenesis. The role of steroidogenic acute regulatory (StAR) protein is well established. A novel protein, BRE, found mainly in brain, adrenals and gonads, was highly expressed in hyperplastic rat adrenals with impaired steroidogenesis, suggesting its regulation by pituitary hormones. To further elucidate its role in steroidogenic tissues, mouse Leydig tumor cells (mLTC-1) were transfected with BRE antisense probes. Morphologically the BRE antisense cells exhibited large cytoplasmic lipid droplets and failed to shrink in response to human chorionic gonadotropin. Although cAMP production, along with StAR and P450scc mRNA expression, was unaffected in BRE antisense clones, progesterone and testosterone yields were significantly decreased, while pregnenolone was increased in response to human chorionic gonadotropin stimulation or in the presence of 22(R)OH-cholesterol. Furthermore, whereas exogenous progesterone was readily converted to testosterone, pregnenolone was not, suggesting impairment of pregnenolone-to-progesterone conversion, a step metabolized by 3β-HSD. That steroidogenesis was compromised at the 3β-HSD step was further confirmed by the reduced expression of 3β-HSD type I (3ß-HSDI) mRNA in BRE antisense cells compared with controls. Our results suggest that BRE influences steroidogenesis through its effects on 3β-HSD action, probably affecting its transcription.