Estrogen Response Elements Alter Coactivator Recruitment through Allosteric Modulation of Estrogen Receptor β Conformation

Estrogen receptor β (ERβ) activates transcription by binding to estrogen response elements (EREs) and coactivator proteins that act as bridging proteins between the receptor and the basal transcription machinery. Although the imperfect vitellogenin B1, pS2, and oxytocin (OT) EREs each differ from the consensus vitellogenin A2 ERE sequence by a single base pair, ERβ activates transcription of reporter plasmids containing A2, pS2, B1, and OT EREs to different extents. To explain how these differences in transactivation might occur, we have examined the interaction of ERβ with these EREs and monitored recruitment of the coactivators amplified in breast cancer (AIB1) and transcription intermediary factor 2 (TIF2). Protease sensitivity, antibody interaction, and DNA pull-down assays demonstrated that ERβ undergoes ERE-dependent changes in conformation resulting in differential recruitment of AIB1 and TIF2 to the DNA-bound receptor. Overexpression of TIF2 or AIB1 in transient transfection assays differentially enhanced ERβ-mediated transcription of reporter plasmids containing the A2, pS2, B1, and OT EREs. Our studies demonstrate that individual ERE sequences induce changes in conformation of the DNA-bound receptor and influence coactivator recruitment. DNA-induced modulation of receptor conformation may contribute to the ability of ERβ to differentially activate transcription of genes containing divergent ERE sequences.