Regulation of human estrogen receptor α-mediated gene transactivation in Saccharomyces cerevisiae by human coactivator and corepressor proteins

Human estrogen receptor α (ERα)-mediated transcription activation was evaluated in the yeast Saccharomyces cerevisiae using both the native ERα and a G400V variant. A previous study [1] demonstrated that coexpression of human SRC-1, a potent stimulator of ERα function in mammalian cells, potentiated ERα-mediated gene expression in yeast over five-fold in an E2-dependent manner. In the present study, two additional human coactivator proteins were shown to potentiate ERα-mediated gene expression in yeast. SRC2 potentiated transactivation two- to three-fold while SRC3 potentiated transactivation five- to eight-fold. Both human coactivators potentiated both the native ERα and the G400V variant in an E2-dependent manner. The effect of a human corepressor protein was also evaluated in yeast. Repressor of estrogen receptor activity (REA) did not affect E2-induced transactivation by ERα (either isoform). However, in a strain that coexpressed human SRC1, REA reduced E2-induced transactivation to that observed with ERα alone. Furthermore, repression of SRC1 potentiation was specific for the native ERα since REA had no effect on SRC1 potentiation of the G400V variant. Additionally, REA repression was specific for SRC1 since potentiation of ERα (either isoform) transactivation by SRC2 and SRC3 was unaffected by coexpression of REA. These results support previous observations in mammalian cells that REA does not prevent ERα from binding to DNA but does inhibit potentiation of ERα-mediated transactivation by SRC1. The results in the present study further characterize REA-mediated repression, and demonstrate the utility of this yeast system for dissecting molecular mechanisms involved in regulating gene transactivation by human ERα.