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

J Steroid Biochem Mol Biol 103(2):7 (2007) PMID 17194583

Human estrogen receptor @a (ER@a)-mediated transcription activation was evaluated in the yeast Saccharomyces cerevisiae using both the native ER@a and a G400V variant. A previous study [1] demonstrated that coexpression of human SRC-1, a potent stimulator of ER@a function in mammalian cells, potentiated ER@a-mediated gene expression in yeast over five-fold in an E"2-dependent manner. In the present study, two additional human coactivator proteins were shown to potentiate ER@a-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 ER@a and the G400V variant in an E"2-dependent manner. The effect of a human corepressor protein was also evaluated in yeast. Repressor of estrogen receptor activity (REA) did not affect E"2-induced transactivation by ER@a (either isoform). However, in a strain that coexpressed human SRC1, REA reduced E"2-induced transactivation to that observed with ER@a alone. Furthermore, repression of SRC1 potentiation was specific for the native ER@a since REA had no effect on SRC1 potentiation of the G400V variant. Additionally, REA repression was specific for SRC1 since potentiation of ER@a (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 ER@a from binding to DNA but does inhibit potentiation of ER@a-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 ER@a.