NUCLEAR RECEPTOR STEROIDOGENIC FACTOR-1 DIRECTS EMBRYONIC STEM-CELLS TOWARD THE STEROIDOGENIC LINEAGE

The orphan nuclear receptor steroidogenic factor 1 (SF-1) is expressed in the adrenal gland and gonads and is an important regulator of the expression of cytochrome P-450 steroidogenic enzymes in cultured cells , Targeted disruption of the SF-1 gene in mice shows that it is a crit ical participant in the genetic program that promotes the development of urogenital mesoderm into the adrenal gland and gonads, To assess th e ability of SF-I to regulate this differentiation pathway, we ectopic ally expressed SF-I in murine embryonic stem (ES) cells. We found that stable expression of SF-1 is sufficient to alter ES cell morphology, permit cyclic AMP (cAMP) and retinoic acid-induced expression of the e ndogenous side chain cleavage enzyme gene, and consequently, promote s teroidogenesis, While steroid production is dependent upon SF-1, cAMP induction of steroidogenesis does not enhance the responsiveness of an SF-1-specific reporter, Furthermore, the activity of a P450(SCC) prom oter/luciferase reporter construct, which is induced by cAMP in steroi dogenic cells and ES cells converted by stable expression of SF-1, is not induced by cAMP in wild-type ES cells transiently transfected with SF-1, suggesting that the induction of downstream gene products is re quired before steroidogenesis can occur. We demonstrate that mutants w hich disrupt the DNA binding domain or the AF2 transcriptional activat ion domain of SF-1 do not confer the steroidogenic phenotype to ES cel ls, Interestingly, however, AF2 mutants fused to the VP16 activation d omain do confer the steroidogenic phenotype to ES cells, but only in t he presence of a portion of the ligand binding domain, These studies e xtend the role of SF-1 in steroidogenic tissues to that of a dominant regulator of the steroidogenic cell phenotype.