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.

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.

Identification of hypoxia-inducible factor-1alpha (HIF-1alpha) polymorphism as a mutation in prostate cancer that prevents normoxia-induced degradation.

BACKGROUND: Hypoxia-inducible factor-1alpha (HIF-1alpha) regulates cellular responses to hypoxia and is rapidly degraded under normoxia through von Hippel-Lindau (VHL) mediated ubiquitination. Although HIF-1alpha stabilization appears to be the molecular basis for VHL-associated cancers, stabilizing mutations in HIF-1alpha have not been reported. METHODS: A series of 15 metastatic androgen independent prostate cancers were examined for mutations in the oxygen-dependent domain (ODD) of HIF-1alpha by PCR amplification and DNA sequencing. RESULTS: A somatic proline to serine mutation in codon 582 (P582S) was identified in one sample. Transfection studies with a HIF-1alpha regulated reporter gene showed increased transcriptional activity that correlated with higher mutant HIF-1alpha protein expression. Increased expression of the P582S mutant induced by iron chelation, which blocks proline hydroxylation of wild-type HIF-1alpha, was markedly attenuated. The mutant also showed increased stability under normoxic versus hypoxic conditions. CONCLUSION: The P582S HIF-1alpha is a stable variant and HIF-1alpha mutation is a mechanism for enhancing HIF-1alpha activity in human cancer. The recent identification of the identical P582S HIF-1alpha as a polymorphism suggests that this variant may increase tumor susceptibility or cause more aggressive biological behavior.

Recruitment of beta-catenin by wild-type or mutant androgen receptors correlates with ligand-stimulated growth of prostate cancer cells.

Prostate cancers respond to treatments that suppress androgen receptor (AR) function, with bicalutamide, flutamide, and cyproterone acetate (CPA) being AR antagonists in clinical use. As CPA has substantial agonist activity, it was examined to identify AR coactivator/corepressor interactions that may mediate androgen-stimulated prostate cancer growth. The CPA-liganded AR was coactivated by steroid receptor coactivator-1 (SRC-1) but did not mediate N-C terminal interactions or recruit beta-catenin, indicating a nonagonist conformation. Nonetheless, CPA did not enhance AR interaction with nuclear receptor corepressor, whereas the AR antagonist RU486 (mifepristone) strongly stimulated AR-nuclear receptor corepressor binding. The role of coactivators was further assessed with a T877A AR mutation, found in LNCaP prostate cancer cells, which converts hydroxyflutamide (HF, the active flutamide metabolite) into an agonist that stimulates LNCaP cell growth. The HF and CPA-liganded T877A ARs were coactivated by SRC-1, but only the HF-liganded T877A AR was coactivated by beta-catenin. L-39, a novel AR antagonist that transcriptionally activates the T877A AR, but still inhibits LNCaP growth, similarly mediated recruitment of SRC-1 and not beta-catenin. In contrast, beta-catenin coactivated a bicalutamide-responsive mutant AR (W741C) isolated from a bicalutamide-stimulated LNCaP subline, further implicating beta-catenin recruitment in AR-stimulated growth. Androgen-stimulated prostate-specific antigen gene expression in LNCaP cells could be modulated by beta-catenin, and endogenous c-myc expression was repressed by dihydrotestosterone, but not CPA. These results indicate that interactions between AR and beta-catenin contribute to prostate cell growth in vivo, although specific growth promoting genes positively regulated by AR recruitment of beta-catenin remain to be identified.