ESTROGEN RESPONSE ELEMENTS FUNCTION AS ALLOSTERIC MODULATORS OF ESTROGEN-RECEPTOR CONFORMATION

The estrogen receptor (ER) is a ligand-dependent transcription factor that regulates the expression of estrogen-responsive genes, ER-mediate d transcriptional changes are brought about by interaction of the ER w ith the estrogen response element (ERE), In this study, we examined th e interaction of the Xenopus laevis ER DNA binding domain (DBD) and th e intact ER with the X. laevis vitellogenin A2 ERE and the human pS2 E RE, Using gel mobility shift, DNase I footprinting, and methylation in terference assays, we demonstrated that the DBD bound only as a dimer to the A2 ERE, However, the DBD bound as a monomer to the consensus pS 2 ERE half site at Lower DBD concentrations and then as a homodimer to the consensus and imperfect pS2 ERE half site at higher DBD concentra tions, Antibody supershift experiments carried out with partially puri fied, yeast-expressed full-length ER demonstrated that three ER-specif ic antibodies interacted differentially with A2 and pS2 ERE bound ER, indicating that receptor epitopes were differentially exposed, Further more, partial digestion of the A2 and pS2 ERE-bound ER with chymotryps in or trypsin produced distinct protease cleavage patterns, Taken toge ther, these data provide Evidence that differential interaction of the DBD with the A2 and pS2 EREs brings about global changes in ER confor mation, The conformational changes in ER induced by individual ERE seq uences could lead to association off the receptor with different trans cription factors and assist in the differential modulation of estrogen -responsive genes in target cells.