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

Abstract

Estrogen receptors α and β (ERα and ERβ) act as ligand-dependent transcriptional enhancers. We reported that ERα 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 ERα restricted to MCF-7 cells?; (2) does ERβ induce synergistic activation of reporter activity from multiple tandem EREs?; and (3) does ERβ bind cooperatively to multiple tandem EREs? To address the first two questions, ER-negative CHO-K1 cells were co-transfected with ERα or ERβ and ERE-driven reporter plasmids. Both ERα and ERβ activated ERE-driven luciferase gene activity in an estradiol-dependent manner. Induction by ERβ was lower than ERα from each ERE. We demonstrate that both ERα and ERβ 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 ERα and ERβ to multiple EREs that may be responsible for transcriptional synergy in transiently transfected cells. We also postulate that interaction of ERα and ERβ with coactivators may also play a role in transcriptional synergy.