A mutant form of ERα associated with estrogen insensitivity affects the coupling between ligand binding and coactivator recruitment

Abstract

A homozygous missense mutation in the gene encoding the estrogen receptor α (ERα) was previously identified in a female patient with estrogen insensitivity syndrome. We investigated the molecular features underlying the impaired transcriptional response of this mutant (ERα-Q375H) and four other missense mutations at this position designed to query alternative mechanisms. The identity of residue 375 greatly affected the sensitivity of the receptor to agonists without changing the ligand binding affinity. Instead, the mutations caused changes in the affinity of coactivator binding and alterations in the balance of coactivator and corepressor recruitment. Comparisons among the transcriptional regulatory responses of these six ERα genotypes to a set of ER agonists showed that both steric and electrostatic factors contributed to the functional deficits in gene regulatory activity of the mutant ERα proteins. ERα–coregulator peptide binding in vitro and RIME (rapid immunoprecipitation mass spectrometry of endogenous) analysis in cells showed that the degree of functional impairment paralleled changes in receptor-coregulator binding interactions. These findings uncover coupling between ligand binding and coregulator recruitment that affects the potency rather than the efficacy of the receptor response without substantially altering ligand binding affinity. This highlights a molecular mechanism for estrogen insensitivity syndrome involving mutations that perturb a bidirectional allosteric coupling between ligand binding and coregulator binding that determines receptor transcriptional output.

Asymmetric Allostery in Estrogen Receptor-α Homodimers Drives Responses to the Ensemble of Estrogens in the Hormonal Milieu

“…Protein conformational heterodimers presented structural differential transcriptional coregulator binding surfaces compared to heterodimers( Fig.7F ). This illustrates a new mode by which receptor activity can be modulated, which has not been visualized by previous simulations of monomeric ER (14, 21), or conceptualized within the framework of steroid receptors as homodimer signaling molecules.…”

“…7F). This illustrates a new mode by which receptor activity can be modulated, which has not been visualized by previous simulations of monomeric ER (14,21), or conceptualized within the framework of steroid receptors as homodimer signaling molecules.…”

“…While allostery between ligand binding and the coregulator binding site has been studied in the context of individual receptor monomers (8,9,(14)(15)(16)(17)(18)(19)(20)(21), it has not been investigated with respect to cross-dimer signaling in ER homodimers or of asymmetrical ER dimers, those only partially occupied by ligand or bound by two different ligands (3,22). Such ER species with varied stoichiometries are likely involved in the actions of ER in vivo, in complex environments with widely varying levels of different endogenous and exogenous estrogens as during pregnancy, hormone therapy, and environmental exposures (23)(24)(25)(26).…”

Role of estrogen receptor coregulators in endocrine resistant breast cancer

“…Taken together, these data suggest that ESR1 mutations in the LBD maintain the ERα-driven transcriptional program within these cancer cells, even in the absence of estrogenic ligand; thus contributing to endocrine resistance [30]. ERα mutations are also associated with estrogen insensitivity by affecting the coupling between ligand binding and coactivator recruitment [103]. A recent proteomics-based study suggested differential coactivator recruitment such as SRC1, 2, or 3 may be partly responsible for the ability of mtERα proteins to drive metastatic BC [104].…”