Estrogen-related receptor γ (ERR γ) mediates oxygen-dependent induction of aromatase (cyp19) gene expression during human trophoblast differentiation

Differentiation of human cytotrophoblasts to syncytiotrophoblast and the associated induction of aromatase/hCYP19 gene expression are dependent upon a critical O2 tension; however, the underlying molecular mechanisms remain undefined. In this study, we provide compelling evidence that expression of the orphan nuclear receptor, estrogen-related receptor γ (ERR γ), is also O2 dependent, induced during human syncytiotrophoblast differentiation, and plays an obligatory role in the induction of placenta-specific hCYP19I.1 gene expression. Treatment with the selective ERR γ agonist, DY131, or overexpression of ERR γ, stimulated hCYP19 expression in syncytiotrophoblast. Overexpression of ERR γ prevented effects of hypoxia to repress hCYP19 gene expression in cultured trophoblasts. Conversely, small interfering RNA-mediated knockdown of endogenous ERR γ in primary trophoblasts markedly inhibited hCYP19 expression. Promoter and site-directed mutagenesis studies in transfected placental cells identified a nuclear receptor element within placenta-specific hCYP19 promoter I.1 required for ERR γ -stimulated activity. Recruitment of endogenous ERR γ to the nuclear receptor element region in hCYP19 promoter during trophoblast differentiation, assessed by chromatin immunoprecipitation, was prevented by hypoxia. Deferoxamine-induced hypoxia-inducible factor-1α (HIF- 1 α) levels decreased ERR γ expression, whereas knockdown of endogenous HIF-1 α prevented ERR γ suppression by hypoxia. Chromatin immunoprecipitation analysis of trophoblasts cultured in hypoxia revealed recruitment of HIF-1 α to one of two putative hypoxia response elements in the ERR γ promoter, providing in vivo evidence of a direct HIF-1 α involvement in ERR γ expression. Collectively, these novel findings identify ERR γ as an O2-dependent transcription factor and HIF-1 α target gene that serves a critical role in the induction of hCYP19 expression during human trophoblast differentiation.