CCN3/NOV gene expression in human prostate cancer is directly suppressed by the androgen receptor

Abstract

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.

Polycomb-Mediated Disruption of an Androgen Receptor Feedback Loop Drives Castration-Resistant Prostate Cancer

“…We have recently reported CCN3 as a prototype target gene of AR-mediated transcriptional repression(7). To gain insights into the potential functions of CCN3, we generated doxycycline (Dox)-inducible CCN3 overexpression in LNCaP cells, which express a relative lower level of endogenous CCN3 compared to benign cell lines, and performed microarray analysis (Fig.…”

“…AR-full length and AR fragments were cloned into the pcDNA3.1 vector. pGIPZ Non-silencing Lentiviral shRNA Control (RHS4346) and CCN3-targeting shRNA (V2LHS_152302) were purchased from Open Biosystems as used in previous study (7). Lentiviral supernatants were collected from 293T cells that were transfected with lentiviral constructs along with packaging plasmids pSPAX2 and pMD2G for 48 hours.…”

“…We and other have reported that, in addition to its conventional role in transcriptional activation, AR also acts as a transcriptional repressor that directly inhibits target gene expression, an activity that is collaborated by the epigenetic silencer EZH2 (5,6). Our previous study has nominated CCN3/NOV as one of the most strongly repressed genes by AR and EZH2 (7). …”

The lncRNA PCAT29 Inhibits Oncogenic Phenotypes in Prostate Cancer

“…In fact, there have been only a handful of lncRNAs identified to date which function in repression of cancer phenotypes, and, to our knowledge, none of these are targets downregulated by known oncogenes (12). A recent study identifies a protein-coding gene, CCN3/NOV, as a tumor suppressor that is repressed by AR (15). Thus, our study represents the first identification of an AR-repressed lncRNA functioning as a tumor suppressor.…”

CCN family of proteins: critical modulators of the tumor cell microenvironment

“…Wu et al (2014) performed meta-analysis of microarray data and identified CCN3 as a top androgen-repressed gene. Methylation analysis around the CCN3 promoter established epigenetic regulation.…”