Research ArticleBiochemistry

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

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Science Signaling  22 Sep 2020:
Vol. 13, Issue 650, eaaw4653
DOI: 10.1126/scisignal.aaw4653

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Coupling ligand binding to coregulator recruitment

Like other nuclear hormone receptors, the estrogen receptor (ER) recruits transcriptional coactivators and corepressors in a ligand-dependent manner. Mutations that affect the ER can cause estrogen insensitivity. Li et al. compared ligand binding, transcriptional regulatory activity, and coregulator recruitment of a patient-derived missense mutation in ERα (Q375H) and four other missense mutations at this same position with wild-type ERα. The substitutions did not affect ligand affinity, but they affected the potency with which agonists induced a transcriptional response. The mutant proteins differed in the strength of their interactions with coregulators in vitro and in which specific coactivators and corepressors they recruited in cells. These findings identify a coupling between ligand binding and coregulator recruitment that is important for fine-tuning the responses to agonists and results in hormonal insensitivity when disrupted.

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.

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