The Androgen Receptor Recruits Nuclear Receptor CoRepressor (N-CoR) in the Presence of Mifepristone via Its N and C Termini Revealing a Novel Molecular Mechanism for Androgen Receptor Antagonists

Inna Astapova,Manon C Verhoeven,Myles C Hodgson,Anthony N Hollenberg,Larissa J Lee,Steven P Balk,Eunis Choi,Shinta Cheng

doi:10.1074/jbc.m408972200

Inna Astapova, Manon C Verhoeven + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m408972200

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Abstract

The androgen receptor (AR) activates target gene expression in the presence of agonist ligands via the recruitment of transcriptional coactivators, but recent work shows that overexpression of the nuclear corepressors NCoR and SMRT attenuates this agonist-mediated AR activation. Here we demonstrate using NCoR siRNA and chromatin immunoprecipitation that endogenous NCoR is recruited to and represses the dihydrotestosterone (DHT)-liganded AR. Furthermore this study shows that NCoR and coactivators compete for AR in the presence of DHT. AR antagonists such as bicalutamide that are currently in use for prostate cancer treatment can also mediate NCoR recruitment, but mifepristone (RU486) at nanomolar concentrations is unique in its ability to markedly enhance the AR-NCoR interaction. The RU486-liganded AR interacted with a C-terminal fragment of NCoR, and this interaction was mediated by the two most C-terminal nuclear receptor interacting domains (RIDs) present in NCoR. Significantly, in addition to the AR ligand binding domain, the AR N terminus was also required for this interaction. Mutagenesis studies demonstrate that the N-terminal surface of the AR-mediating NCoR recruitment was distinct from tau5 and from the FXXLF motif that mediates agonist-induced N-C-terminal interaction. Taken together these data demonstrate that NCoR is a physiological regulator of the AR and reveal a new mechanism for AR antagonism that may be exploited for the development of more potent AR antagonists.

Highlights

The androgen receptor (AR),1 a member of the steroid/nuclear receptor superfamily, plays a critical role in normal male
The AR plays a critical role in prostate cancer development and progression, and hormonal therapies that ablate androgen action remain as critical mainstays of therapy
We and others have previously demonstrated that the corepressors NCoR and SMRT can associate with the AR and inhibit AR transcriptional activity, but the roles these corepressors play in mediating AR responses to physiological agonists or to antagonists used for prostate cancer treatment have not been determined (24 –27)

Summary

Introduction

The androgen receptor (AR), a member of the steroid/nuclear receptor superfamily, plays a critical role in normal male. The addition of an agonist ligand leads initially to the DNA binding of the receptor, followed by the ordered recruitment of both transcriptional coactivators and other mediators to the ligand binding domain. This leads to histone modifications including acetylation, and to transcriptional activation [10]. Bicalutamide, which is widely used for prostate cancer treatment, can stimulate the AR to bind DNA, but fails to recruit coactivators and can mediate the recruitment of NCoR to the androgen-regulated PSA gene, indicating that corepressor recruitment may contribute to antagonist activity (30 –32). As enhancement of corepressor recruitment to the AR may be an effective approach for blocking AR signaling in prostate cancer, this study further examines corepressor recruitment by AR agonists and antagonists

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