Androgen receptor overexpression in prostate cancer linked to Purα loss from a novel repressor complex

Abstract

Increased androgen receptor (AR) expression and activity are pivotal for androgen-independent (AI) prostate cancer (PC) progression and resistance to androgen-deprivation therapy. We show that a novel transcriptional repressor complex that binds a specific sequence (repressor element) in the AR gene 5′-untranslated region contains Purα and hnRNP-K. Purα expression, its nuclear localization, and its AR promoter association, as determined by chromatin immunoprecipitation analysis, were found to be significantly diminished in AI-LNCaP cells and in hormone-refractory human PCs. Transfection of AI cells with a plasmid that restored Purα expression reduced AR at the transcription and protein levels. Purα knockdown in androgen-dependent cells yielded higher AR and reduced p21, a gene previously shown to be under negative control of AR. These changes were linked to increased proliferation in androgen-depleted conditions. Treatment of AI cells with histone deacetylase and DNA methylation inhibitors restored Purα protein and binding to the AR repressor element. This correlated with decreased AR mRNA and protein levels and inhibition of cell growth. Purα is therefore a key repressor of AR transcription and its loss from the transcriptional repressor complex is a determinant of AR overexpression and AI progression of PC. The success in restoring Purα and the repressor complex function by pharmacologic intervention opens a promising new therapeutic approach for advanced PC. ©2008 American Association for Cancer Research.