Estrogen response element sequence impacts the conformation and transcriptional activity of estrogen receptor alpha

Estrogens play a critical role in mammary gland development, bone homeostas is, reproduction, and the pathogenesis of breast cancer by activating estro gen receptors (ERs) alpha and beta. Ligand-activated ER stimulates the expr ession of target proteins by interacting with specific DNA sequences: estro gen response elements (EREs). We have demonstrated that the ERE sequence an d the nucleotide sequences flanking the ERE impact ER alpha binding affinit y and transcriptional activation. Here, we examined whether the sequence of the ERE modulates ER alpha conformation by measuring changes in sensitivit y to protease digestion. ER alpha, occupied by estradiol (E-2) or 4-hydroxy tamoxifen (4-OHT), was incubated with select EREs and digested by chymotryp sin followed by a Western analysis with antibodies to ER alpha. ERE binding increased the sensitivity of ER alpha to chymotrypsin digestion. We found both ligand-specific and ERE-specific differences in ER alpha sensitivity t o chymotrypsin digestion. The ERE-mediated increase in ER alpha sensitivity to chymotrypsin digestion correlates with E-2-stimulated transcriptional a ctivity from the same EREs in transiently transfected cells. Transcriptiona l activity also correlates with the affinity of ER alpha -ERE binding in vi tro. Our results support the hypothesis that the ERE sequence acts as an al losteric effector, altering ER conformation. We speculate that ERE-induced alterations in ER alpha conformation modulate interaction with co-regulator y proteins. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.