ROLE OF STEROIDOGENIC-FACTOR-1 IN BASAL AND 3',5'-CYCLIC ADENOSINE MONOPHOSPHATE-MEDIATED REGULATION OF CYTOCHROME-P450 SIDE-CHAIN CLEAVAGEENZYME IN THE MOUSE

The orphan receptor steroidogenic factor-1 (SF-1) plays a major role i n adrenal and gonadal development and sexual differentiation, and it h as been shown to interact with shared promoter elements to increase th e expression of cytochrome P450 side-chain cleavage (P450(scc)) and ot her steroid hydroxylases in vitro. We took a step-wise approach to def ine the role of SF-1 in regulation of hormone-induced steroidogenesis. In a mouse Leydig cell line (MA-10) we show that hCG and forskolin ar e effective inducers of progesterone production and P450(scc) expressi on. In contrast, endogenous SF-1 expression was not increased by eithe r hCG or forskolin. Similarly, these agents did not enhance the activi ty of SF-1 promoter transfected into MA-10 cells. The transcriptional activity of SF-1, measured by induction of an SF-1 synthetic reporter, was only minimally increased by forskolin. Within the context of the rat P450(scc) promoter, mutation of the two SF-1-binding sites caused a dramatic decrease in constitutive activity of this promoter, but the degree of induction by 8-bromo-cAMP was only reduced from 7.9-fold to 5.9-fold. We conclude that SF-1 is required for the constitutive acti vity of P450(scc), but that it does not play a direct role in the earl y induction of steroidogenesis by hCG or forskolin in MA-10 cells.