Comparison of transcriptional synergy of estrogen receptors α and β from multiple tandem estrogen response elements

Estrogen receptors alpha and beta (ER alpha and ER beta) act as ligand-dependent transcriptional enhancers. We reported that ER alpha induces synergistic 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?; and (3) does ER beta bind cooperatively to multiple tandem EREs? To address the first two questions, ER-negative CHO-K1 cells were co-transfected with ER alpha or ER beta and ERE-driven reporter plasmids. Both ER alpha and ER beta activated ERE-driven luciferase gene activity in an estradiol-dependent manner. Induction by ER beta was lower than ER alpha from each ERE. We demonstrate that both ER alpha and ER beta induce transcriptional synergy with three or four, but not two, tandem copies of an ERE. Electrophoretic mobility shift assays (EMSA) indicated an increase in ER-ERE binding affinity associated with cooperative binding of ER alpha and ER beta to multiple EREs that may be responsible for transcriptional synergy in transiently transfected cells. We also postulate that interaction of ER alpha and ER beta with coactivators may also play a role in transcriptional synergy. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.