Bisphenol A derivatives act as novel coactivator binding inhibitors for estrogen receptor β

Bisphenol A and its derivatives are recognized endocrine disruptors based on their complex effects on estrogen receptor (ER) signaling. While the effects of bisphenol derivatives on ERα have been thoroughly evaluated, how these chemicals affect ERβ signaling is not well understood. Herein, we identified novel ERβ ligands by screening a chemical library of bisphenol derivatives. Many of the compounds identified showed intriguing dual activities as ERα agonists and ERβ antagonists. Docking simulations suggested that these compounds act as coactivator binding inhibitors (CBIs). Direct binding experiments using wild-type and mutated ERβ demonstrated the presence of a second ligand interaction position at the coactivator binding site in ERβ. Our study is the first to propose that bisphenol derivatives act as CBIs, presenting a critical view point for future ER signaling-based drug development.

Coactivator Proteins as Determinants of Estrogen Receptor Structure and Function: Spectroscopic Evidence for a Novel Coactivator-Stabilized Receptor Conformation

The direct regulation of gene transcription by nuclear receptors, such as the estrogen receptor (ER), involves not just ligand and DNA binding but the recruitment of coregulators. Typically, recruitment of p160 coactivator proteins to agonist-liganded ER is considered to be unidirectional, with ligand binding stabilizing an ER ligand binding domain (LBD) conformation that favors coactivator interaction. Using fluorophore-labeled ERα-LBDs, we present evidence for a pronounced stabilization of ER conformation that results from coactivator binding, manifest by decreased ER sensitivity to proteases and reduced conformational dynamics, as well as for the formation of a novel coactivator-stabilized (costabilized) receptor conformation, that can be conveniently monitored by the generation of an excimer emission from pyrene-labeled ERα-LBDs. This costabilized conformation may embody features required to support ER transcriptional activity. Different classes of coactivator proteins combine with estrogen agonists of different structure to elicit varying degrees of this receptor stabilization, and antagonists and coactivator binding inhibitors disfavor the costabilized conformation. Remarkably, high concentrations of coactivators engender this conformation even in apo- and antagonist-bound ERs (more so with selective ER modulators than with pure antagonists), providing an in vitro model for the development of resistance to hormone therapy in breast cancer.