Abstract 1849: Androgen receptor transcriptionally represses genes mediating DNA synthesis and repair in prostate cancer
Authors: Gao Yanfei , Gao Shuai , He Housheng , Liu Xiaming , Chen Sen , Ma Fen , Liu X. Shirley , Brown Myles , Balk Steven P. , Chen Shaoyong , Cai Changmeng 
Published: August 2015

Abstract
In the U.S., prostate cancer (PCa) ranked second for cancer related deaths for men. It has been well established that androgen receptor (AR) plays an essential role in the development of primary PCa and its activity is restored in castration resistant prostate cancers (CRPC). While AR has been extensively characterized as a transcriptional activator, it can also function by direct or indirect mechanisms to suppress gene expression. Despite the critical role AR plays in PCa, mechanisms by which it functions as a transcriptional repressor are poorly understood. Using VCaP and VCaP derived CRPC cell lines, we have reported that androgen-repressed genes were functionally enriched for DNA synthesis and repair, while AR stimulated genes were associated with lipid/sterol synthesis and other aspects of cellular metabolism. Significantly, a subset of the genes that were androgen-repressed in VCaP cells were consistently increased in CRPC clinical samples, and this 53-gene subset was also highly enriched for genes mediating DNA synthesis and repair. Using AR ChIP-seq and transcriptome profiling in VCaP cells, we found that the majority of this AR-suppressed gene subset (39/53) have one or more AR binding sites within the gene locus. The expression level of these direct AR-suppressed genes is associated with poor survival of disease in clinical cohorts. Interestingly, although the suppression activity of AR on this subset of genes is direct, in other PCa cell lines such as LNCaP, there is a secondary mechanism that allows AR to indirectly stimulate the expression of these genes. Importantly, the direct AR mediated repression of these genes is enhanced in PCa cells expressing higher levels of AR, and overexpression of AR in LNCaP cells resulted in increased and more persistent AR binding to these genes, and also enhanced the direct AR repression of this gene subset.
Mechanistically, we found that the indirect activation of these DNA synthesis genes by AR is mediated through transcriptionally stimulating lipid synthesis, which could subsequently drive the G1/S cell cycle progression and RB1 phosphorylation. Indeed, this indirect stimulatory effect of AR on these genes could be suppressed by cyclin dependent kinase inhibition or by preventing the AR stimulation of mTOR (rapamycin) or sterol synthesis (statins). Taken together, these findings indicate that the ability of AR to repress this gene set mediating DNA synthesis may persist in CRPC, and may be exploited therapeutically by combination therapies that stimulate AR while repressing its metabolic functions.
Citation Format: Yanfei Gao, Shuai Gao, Housheng He, Xiaming Liu, Sen Chen, Fen Ma, X. Shirley Liu, Myles Brown, Steven P. Balk, Shaoyong Chen, Changmeng Cai. Androgen receptor transcriptionally represses genes mediating DNA synthesis and repair in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1849. doi:10.1158/1538-7445.AM2015-1849