STEROIDOGENIC FACTOR-I BINDING AND TRANSCRIPTIONAL ACTIVITY OF THE CHOLESTEROL SIDE-CHAIN CLEAVAGE PROMOTER IN RAT GRANULOSA-CELLS

The cholesterol side-chain cleavage cytochrome P450 (CYP11A; P450scc) gene is expressed in rat ovarian follicles in response to gonadotropins (FSH/LH) and cAMP. To identify functional regions within the rat P450scc promoter, 894 basepairs (bp) of 5'-flanking sequence and 5'-deletions (at -379, -101, -73, and -38 bp) were linked to the human GH reporter gene and transfected into cultured rat granulosa cells. cAMP inducibility of the rat promoter was localized to a region (between -73/-38 bp) that contains one of two AGGT/ CC/TA motifs, designated SCC1 (-51/-43 bp) and SCC2 (-79/-71 bp), within the rat promoter. One of the nuclear proteins in granulosa cells that binds to SCC1 was identified as the orphan receptor, steroidogenic factor-1 (SF-1). In contrast, multiple protein-DNA complexes formed with SCC2, only one of which was clearly identified as SF-1. Nuclear extract binding was sequence specific; SCC1 bound SF-1 more strongly than did SCC2. Thus, the two AGGT/CC/TA motifs of the rat promoter appear to differ structurally and functionally. Furthermore, because the expression of SF-1 mRNA precedes hormonal/cAMP induction of P450scc mRNA and is not regulated in vitro by cAMP, the functional role of SF-1 in transcriptional regulation of the P450scc gene, including its induction by cAMP, is not entirely clear and is probably dependent on other factors and/or the modification (phosphorylation?) of SF-1.