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Departments of Surgery and
¹ Chemical Pathology, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
² Department of Biology, Xiamen University, Xiamen, People’s Republic of China
³ Molecular Pathology, University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA

(Requests for offprints should be addressed to N S Panesar; Email: nspanesar{at}cuhk.edu.hk)

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 3ß-hydroxysteroid dehydrogenase/isomerase (3ß-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 3ß-HSD. That steroidogenesis was compromised at the 3ß-HSD step was further confirmed by the reduced expression of 3ß-HSD type I (3ß-HSDI) mRNA in BRE antisense cells compared with controls. Our results suggest that BRE influences steroidogenesis through its effects on 3ß-HSD action, probably affecting its transcription.