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

Human estrogen receptor alpha (ER alpha)-mediated transcription activation was evaluated in the yeast Saccharomyces cerevisiae using both the native ER alpha and a G400V variant. A previous study [1] demonstrated that coexpression of human SRC-1, a potent stimulator of ER alpha function in mammalian cells, potentiated ER alpha-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 alpha-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 alpha 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 alpha (either isoform). However, in a strain that coexpressed human SRC1, REA reduced E2-induced transactivation to that observed with ER alpha alone. Furthermore, repression of SRC1 potentiation was specific for the native ERa since REA had no effect on SRC I potentiation of the G400V variant. Additionally, REA repression was specific for SRC I since potentiation of ER alpha (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 alpha from binding to DNA but does inhibit potentiation of ER alpha-mediated transactivation by SRC L 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 alpha. (c) 2006 Elsevier Ltd. All rights reserved.