Comparison of transcriptional synergy of estrogen receptors alpha and betafrom multiple tandem estrogen response elements

Estrogen receptors alpha and beta (ER alpha and ER beta) act as ligand-depe ndent transcriptional enhancers. We reported that ER alpha induces synergis tic activation of luciferase reporter gene activity in response to E-2 from three or four tandem copies of a consensus estrogen response element (ERE) in transiently transfected MCF-7 cells. Here we addressed three questions: (1) is the synergistic activation of reporter gene activity from multiple tandem EREs by ER alpha restricted to MCF-7 cells?; (2) does ER beta induce synergistic activation of reporter activity from multiple tandem EREs?; an d (3) does ER beta bind cooperatively to multiple tandem EREs? To address t he first two questions, ER-negative CHO-K1 cells were co-transfected with E R alpha or ER beta and ERE-driven reporter plasmids. Both ER alpha and ER b eta activated ERE-driven luciferase gene activity in an estradiol-dependent manner. Induction by ER beta was lower than ER alpha from each ERE. We dem onstrate that both ER alpha and ER beta induce transcriptional synergy with three or four, but not two, tandem copies of an ERE. Electrophoretic mobil ity shift assays (EMSA) indicated an increase in ER-ERE binding affinity as sociated with cooperative binding of ER alpha and ER beta to multiple EREs that may be responsible for transcriptional synergy in transiently transfec ted cells. We also postulate that interaction of ER alpha and ER beta with coactivators may also play a role in transcriptional synergy. (C) 2000 Else vier Science Ireland Ltd. All rights reserved.