Estrogens play a critical role in mammary gland development, bone homeostasis, reproduction, and the pathogenesis of breast cancer by activating estrogen receptors (ERs) α and β. Ligand-activated ER stimulates the expression of target proteins by interacting with specific DNA sequences: estrogen response elements (EREs). We have demonstrated that the ERE sequence and the nucleotide sequences flanking the ERE impact ERα binding affinity and transcriptional activation. Here, we examined whether the sequence of the ERE modulates ERα conformation by measuring changes in sensitivity to protease digestion. ERα, occupied by estradiol (E2) or 4-hydroxytamoxifen (4-OHT), was incubated with select EREs and digested by chymotrypsin followed by a Western analysis with antibodies to ERα. ERE binding increased the sensitivity of ERα to chymotrypsin digestion. We found both ligand-specific and ERE-specific differences in ERα sensitivity to chymotrypsin digestion. The ERE-mediated increase in ERα sensitivity to chymotrypsin digestion correlates with E2-stimulated transcriptional activity from the same EREs in transiently transfected cells. Transcriptional activity also correlates with the affinity of ERα-ERE binding in vitro. Our results support the hypothesis that the ERE sequence acts as an allosteric effector, altering ER conformation. We speculate that ERE-induced alterations in ERα conformation modulate interaction with co-regulatory proteins.
- Estrogen receptor
- Estrogen response element
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism