Androgen receptor (AR) is a hormone-activated transcription factor that plays important roles in prostate development and function, as well as malignant transformation. The downstream pathways of AR, however, are incompletely understood. AR has been primarily known as a transcriptional activator inducing prostate-specific gene expression. Through integrative analysis of genome-wide AR occupancy and androgen-regulated gene expression, here we report AR as a globally acting transcriptional repressor. This repression is mediated by androgen-responsive elements (ARE) and dictated by Polycomb group protein EZH2 and repressive chromatin remodeling. In embryonic stem cells, AR-repressed genes are occupied by EZH2 and harbor bivalent H3K4me3 and H3K27me3 modifications that are characteristic of differentiation regulators, the silencing of which maintains the undifferentiated state. Concordantly, these genes are silenced in castration-resistant prostate cancer rendering a stem cell–like lack of differentiation and tumor progression. Collectively, our data reveal an unexpected role of AR as a transcriptional repressor inhibiting non-prostatic differentiation and, upon excessive signaling, resulting in cancerous dedifferentiation.

Androgen receptor (AR) has essential roles during prostate cancer progression. With genome-wide AR-binding sites mapped to high resolution, studies have recently reported AR as a transcriptional repressor. How AR inhibits gene expression and how this contributes to prostate cancer, however, are incompletely understood. Through meta-analysis of microarray data, here we nominate nephroblastoma overexpressed (NOV) as a top androgen-repressed gene. We show that NOV is directly suppressed by androgen through the AR. AR occupies the NOV enhancer and communicates with the NOV promoter through DNA looping. AR activation recruits the polycomb group protein EZH2, which subsequently catalyzes histone H3 lysine 27 tri-methylation around the NOV promoter, thus leading to repressive chromatin remodeling and epigenetic silencing. Concordantly, AR and EZH2 inhibition synergistically restored NOV expression. NOV is downregulated in human prostate cancer wherein AR and EZH2 are upregulated. Functionally, NOV inhibits prostate cancer cell growth in vitro and in vivo. NOV reconstitution reverses androgen-induced cell growth and NOV knockdown drives androgen-independent cell growth. In addition, NOV expression is restored by hormone-deprivation therapies in mice and prostate cancer patients. Therefore, using NOV as a model gene we gained further understanding of the mechanisms underlying AR-mediated transcriptional repression. Our findings establish a tumor-suppressive role of NOV in prostate cancer and suggest that one important, but previously underestimated, manner by which AR contributes to prostate cancer progression is through inhibition of key tumor-suppressor genes.

Androgen receptor (AR) is a hormone-activated transcription factor that plays important roles in prostate development, function, as well as malignant transformation. The downstream pathways of AR, however, are incompletely understood. AR has been primarily known as a transcriptional activator inducing prostate-specific gene expression. Although androgen stimulation has been shown to also suppress genes, little attention has been paid to the mechanisms and functions of AR-mediated gene repression. Through integrative analysis of genome-wide AR occupancy and androgen-regulated gene expression, here we report AR as a globally acting transcriptional repressor. This repression is dictated, at least in part, by the Polycomb group protein EZH2 and repressive chromatin remodeling. In embryonic stem cells (ESC), AR-repressed genes harbor bivalent H3K4me3 and H3K27me3 modifications that are characteristic of developmental regulators, the silencing of which maintains the undifferentiated ESC state. Similarly, these genes are down-regulated in poorlydifferentiated, castration-resistant prostate tumors rendering a stem cell-like cellular state. To characterize the function of AR-repressed genes, we nominated NOV as a top AR-repressed gene. We show that NOV is robustly suppressed by androgen through the AR. Using NOV as a model gene we present evidence that AR directly inhibits gene expression through physically binding to the enhancer, establishing promoter-enhancer DNA looping, and inducing repressive chromatin remodeling. We further demonstrate that NOV is down-regulated in aggressive prostate cancer. Concordantly, NOV expression inhibits prostate cancer cell growth, migration, and invasion in vitro and xenograft tumor growth in mice. Collectively, our data reveal an unexpected role of AR in inhibiting non-prostatic differentiation and, upon aberrant signaling, promoting cancerous de-differentiation. Our findings support AR-mediated inhibition of tumor suppressors as a novel mechanism to prostate cancer progression. Citation Format: Jonathan C. Zhao, Christine Runkle, Jianjun Yu, Longtao Wu, Hongjian Jin, Timothy Kuzel, Chung Lee, Jindan Yu. Cooperation between androgen receptor and Polycomb in prostate cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr IA19.

Transcriptional regulation by the androgen receptor (AR) is critical to prostate cancer development and progression. Through integrative analysis of genome-wide AR occupancy and androgen-regulated gene expression, we have recently reported AR as a globally acting transcriptional repressor. This repression is mediated by androgen responsive elements (ARE) and dictated by Polycomb group protein EZH2 and repressive chromatin remodeling. In addition, AR-repressed genes are enriched for developmental regulators controlling cell differentiation. They tend to get down-regulated in advanced prostate cancer probably accountable for stem cell-like de-differentiation and thus tumor progression. However, critical AR-repressed genes of functional relevance are yet to be identified and their roles to be carefully characterized. Through meta-analysis of several expression microarray data, we nominate one top candidate AR-repressed gene. Using this gene as a model, we present further evidence that AR directly inhibits gene expression through physically binding to the enhancer, establishing promoter-enhancer DNA looping, and inducing repressive chromatin remodeling. Further, overexpression of this gene inhibits prostate cancer cell growth, migration, and invasion in vitro and xenograft tumor growth in mice, thus exhibiting a tumor suppressive role. In addition, the loss of this gene drives castration-resistant prostate cancer. Therefore, our findings support that AR-mediated inhibition of tumor suppressors plays important roles during prostate cancer progression. Our study provides an innovative mechanism for AR in castration resistance, which may eventually lead to novel therapeutic targets for treatment of advanced prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-273. doi:1538-7445.AM2012-LB-273