REGULATION BY ADRENOCORTICOTROPIC HORMONE OF THE IN-VIVO EXPRESSION OF SCAVENGER RECEPTOR CLASS-B TYPE-I (SR-BI), A HIGH-DENSITY-LIPOPROTEIN RECEPTOR, IN STEROIDOGENIC CELLS OF THE MURINE ADRENAL-GLAND

The class B, type I scavenger receptor, SR-BI, binds high density lipo protein (HDL) and can mediate selective uptake of HDL cholesteryl este rs by cultured cells. The high levels of expression of SR-BI in steroi dogenic tissues and the importance of selective uptake from HDL as a s ource of cholesterol for steroidogenesis raised the possibility that S R-BI may participate in cholesterol delivery to steroidogenic tissues in vivo. We have used immunoblotting and immunohistochemical methods t o show that SR-BI is specifically expressed in a distinctive pattern o n the surfaces of steroid-producing cells in the murine adrenal gland' s cortex and that its expression in vivo is induced by adrenocorticotr opic hormone and suppressed by glucocorticoids. Thus, expression of SR -BI protein is coordinately regulated with adrenal steroidogenesis. Th ese data provide strong support for the hypothesis that SR-BI is a phy siologically relevant HDL receptor that provides substrate cholesterol for steroid hormone synthesis.