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: 4.2). 02/2007; DOI: 10.1210/me.2006-0221
Source: PubMed

ABSTRACT 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.

  • Source
    [Show abstract] [Hide abstract]
    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.
    Oncogene 06/2008; 27(21):2941-50. DOI:10.1038/sj.onc.1210955 · 8.56 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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.
    Molecular Endocrinology 02/2007; DOI:10.1210/me.2006-0228 · 4.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Androgens control male sexual development and maintenance of the adult male phenotype. They have very divergent effects on their target organs like the reproductive organs, muscle, bone, brain and skin. This is explained in part by the fact that different cell types respond differently to androgen stimulus, even when all these responses are mediated by the same intracellular androgen receptor. To understand these tissue- and cell-specific readouts of androgens, we have to learn the many different steps in the transcription activation mechanisms of the androgen receptor (NR3C4). Like all nuclear receptors, the steroid receptors have a central DNA-binding domain connected to a ligand-binding domain by a hinge region. In addition, all steroid receptors have a relatively large amino-terminal domain. Despite the overall structural homology with other nuclear receptors, the androgen receptor has several specific characteristics which will be discussed here. This receptor can bind two types of androgen response elements (AREs): one type being similar to the classical GRE/PRE-type elements, the other type being the more divergent and more selective AREs. The hormone-binding domain has low intrinsic transactivation properties, a feature that correlates with the low affinity of this domain for the canonical LxxLL-bearing coactivators. For the androgen receptor, transcriptional activation involves the alternative recruitment of coactivators to different regions in the amino-terminal domain, as well as the hinge region. Finally, a very strong ligand-induced interaction between the amino-terminal domain and the ligand-binding domain of the androgen receptor seems to be involved in many aspects of its function as a transcription factor. This review describes the current knowledge on the structure-function relationships within the domains of the androgen receptor and tries to integrate the involvement of different domains, subdomains and motifs in the functioning of this receptor as a transcription factor with tissue- and cell-specific readouts.
    Nuclear Receptor Signaling 02/2008; 6:e008. DOI:10.1621/nrs.06008


Available from