RETRACTION: Structural and Functional Analysis of Androgen Receptor in Chromatin

Dept. of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030.
Molecular Endocrinology (Impact Factor: 4.02). 02/2007; DOI: 10.1210/me.2006-0221
Source: PubMed


Androgen receptor (AR), a member of the nuclear receptor superfamily, is a modular protein comprised of a N-terminal domain (NTD), a central DNA binding domain (DBD) and a C-terminal ligand-binding domain (LBD). Previous structural and functional studies have shown that deletion of the LBD generates an AR molecule with full transcriptional activity in many transient transfection assays. In this study we show that deletion of either the NTD1-478 (ARDeltaN) or LBD680-919 (ARDeltaC) cripples AR transcriptional activity in chromatin. Both ARDeltaN and ARDeltaC mutants are impaired in binding to target genes in chromatin. Overexpression of SRC-1 coactivator partially rescued transcriptional and chromatin-binding defects of ARDeltaN and ARDeltaC mutants. Expression of SRC-1 also enhances the binding of the wild-type AR to chromatin, thus revealing a role of SRC-1 in promoting binding of AR to chromatin. We also demonstrate that expression of the AR NTD1-501 in trans can substantially rescue the chromatin binding, but not the transcriptional defect of ARDeltaN, indicating that binding of AR to chromatin is a step separable from AR induced transcriptional activation. Finally we present evidence that, in contrast to transient transfection, AR NTD alone cannot efficiently activate transcription in chromatin.

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    • "The predominant activation function in the AR appears to be AF-1, since deletion of AF-2 and the LBD results in a constitutively active receptor with similar activity to the wild-type receptor in the presence of agonist [34, 35]. Recently, however, it has been demonstrated that AF-2 plays a significant role in chromatin and hence its importance in transcriptional regulation may have been underestimated [36]. "
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    ABSTRACT: Prostate tumour growth is almost always dependent upon the androgen receptor pathway and hence therapies aimed at blocking this signalling axis are useful tools in the management of this disease. Unfortunately such therapies invariably fail; and the tumour progresses to an "androgen-independent" stage. In such cases androgen receptor expression is almost always maintained and much evidence exists to suggest that it may still be driving growth. One mechanism by which the receptor is thought to remain active is mutation. This review summarises the present data on androgen receptor mutations in prostate cancer, and how such substitutions offer a growth advantage by affecting cofactor interactions or by reducing ligand specificity. Such alterations appear to have a subsequent effect upon gene expression suggesting that tumours may "behave" differently dependent upon the ligand promoting growth and if a mutation is present.
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    • "One contributing factor is likely to be that differences in co-activator complexes recruited by different receptors could affect the rate of transcription from a given promoter under control of a given steroid receptor, hence be a mechanism to control receptor specificity (Li et al., 2003), and our data are supportive of this. Mutations of the AR have been found in 10–40% of cases of advanced, hormone independent prostate cancer (Taplin, 2007). Those that reduce ligand specificity , as presented here, may promote AR activation hence tumour growth in the absence of conventional AR ligands, explaining the failure of androgen blockade therapy. "
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    ABSTRACT: Prostate tumour growth depends on androgens; hence treatment includes androgen ablation and anti-androgens. Eventually tumours progress and in approximately 30% of patients this is associated with mutation of the androgen receptor. Several receptor variants associated with advanced disease show promiscuous activation by other hormones and anti-androgens. Such loss of specificity could promote receptor activation, hence tumour growth, in the absence of conventional ligands, explaining therapy failure. We aimed to elucidate mechanisms by which alternative ligands promote receptor activation. The three most commonly identified variants in tumours (with amino-acid substitutions H874Y, T877A and T877S) and wild-type receptor showed differences in co-activator recruitment dependent upon ligand and the interaction motif utilized. Co-expression and knockdown of co-activators that bind via leucine or phenylalanine motifs, combined with chromatin immunoprecipitation and quantitative PCR, revealed these preferences extend to co-activator recruitment in vivo and affect receptor activity at the transcriptional level, with subsequent effects on target gene regulation. The findings suggest that mutant receptors, activated by alternative ligands, drive growth via different mechanisms to androgen-activated wild-type receptor. Tumours may hence behave differently dependent upon any androgen receptor mutation present and what ligand is driving growth, as distinct subsets of genes may be regulated.
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    ABSTRACT: Androgen receptor (AR) exerts its diverse biological functions primarily through its ability to regulate gene expression. As a member of nuclear receptor superfamily, AR recruits various coactivators to facilitate its transcriptional activity. The ligand-binding domains (LBD) of AR is believed to play a role in coactivator recruitment through a direct interaction between a hydrophobic coactivator binding groove in the LBD and a FXXLF or LXXLL motif within coactivators. In this study, we provide multiple lines of evidence showing that the FXXLF motif-containing ARA70 and ARA54 exhibit strong hormone-dependent interaction with the AR LBD but poorly with full-length AR. This drastic difference in interaction with ARA70 and ARA54 between the AR LBD and full-length AR is due to the hormone-dependent N-C interaction of AR. Like the AR LBD, full-length AR mutants defective in the N-C interaction exhibit strong hormone-dependent interaction with ARA70 and ARA54. Thus, our results suggest that in the full-length context the hydrophobic coactivator binding groove in the LBD is normally engaged in the liganded induced AR N-C interaction and thus restricted from interaction with other proteins. This finding raises fundamental question as to how AR recruits coactivators to regulate gene transcription.
    Preview · Article · Feb 2007 · Molecular Endocrinology
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