title: Differential modulation of androgen receptor transcriptional activity by the nuclear receptor co-repressor (N-CoR).
abstract: Antiandrogens are widely used agents in the treatment of prostate cancer, as inhibitors of AR (androgen receptor) action. Although the precise mechanism of antiandrogen action is not yet elucidated, recent studies indicate the involvement of nuclear receptor co-repressors. In the present study, the regulation of AR transcriptional activity by N-CoR (nuclear receptor co-repressor), in the presence of different ligands, has been investigated. Increasing levels of N-CoR differentially affected the transcriptional activity of AR occupied with either agonistic or antagonistic ligands. Small amounts of co-transfected N-CoR repressed CPA (cyproterone acetate)- and mifepristone (RU486)-mediated AR activity, but did not affect agonist (R1881)-induced AR activity. Larger amounts of co-transfected N-CoR repressed AR activity for all ligands, and converted the partial agonists CPA and RU486 into strong AR antagonists. In the presence of the agonist R1881, co-expression of the p160 co-activator TIF2 (transcriptional intermediary factor 2) relieved N-CoR repression up to control levels. However, in the presence of RU486 and CPA, TIF2 did not functionally compete with N-CoR, suggesting that antagonist-bound AR has a preference for N-CoR. The AR mutation T877A (Thr877-->Ala), which is frequently found in prostate cancer and affects the ligand-induced conformational change of the AR, considerably reduced the repressive action of N-CoR. The agonistic activities of CPA- and hydroxyflutamide-occupied T877A-AR were hardly affected by N-CoR, whereas TIF2 strongly enhanced their activities. These results indicate that lack of N-CoR action allows these antiandrogens to act as strong agonists on the mutant AR.
authors.affiliation: Department of Reproduction and Development, Erasmus MC, University Medical Center Rotterdam, 3000 DR Rotterdam, Netherlands. c.berrevoets@erasmusmc.nl
authors.forename: Cor A
authors.initials: CA
authors.lastname: Berrevoets
authors.forename: Arzu
authors.initials: A
authors.lastname: Umar
authors.forename: Jan
authors.initials: J
authors.lastname: Trapman
authors.forename: Albert O
authors.initials: AO
authors.lastname: Brinkmann
mesh_terms: D000726:Androgen Antagonists / Q000494:pharmacology*; D059002:Androgen Receptor Antagonists; D000818:Animals; D001667:Binding, Competitive; D016466:CHO Cells; D045744:Cell Line, Tumor; D006224:Cricetinae; D017373:Cyproterone Acetate / Q000494:pharmacology; D015536:Down-Regulation; D005786:Gene Expression Regulation; D008024:Ligands; D008297:Male; D015741:Metribolone / Q000037:antagonists & inhibitors / Q000494:pharmacology; D051379:Mice; D015735:Mifepristone / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism*; D056971:Nuclear Receptor Co-Repressor 1; D051958:Nuclear Receptor Coactivator 2; D011401:Promoter Regions, Genetic / Q000235:genetics; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D000726:Androgen Antagonists; D059002:Androgen Receptor Antagonists; D008024:Ligands; C498002:Ncoa2 protein, mouse; C539128:Ncor1 protein, mouse; D009687:Nuclear Proteins; D056971:Nuclear Receptor Co-Repressor 1; D051958:Nuclear Receptor Coactivator 2; D011944:Receptors, Androgen; D012097:Repressor Proteins; D014157:Transcription Factors; D015741:Metribolone; D015735:Mifepristone; D017373:Cyproterone Acetate