Abstract 5375: Androgen excess induces aberrant DNA methylation in the prostate.

Aberrant DNA methylation is deeply involved in prostate carcinogenesis. However, inducers of aberrant DNA methylation in the prostate are almost unknown. Here, we investigated whether androgen excess can induce aberrant DNA methylation or not, using a rat prostate cancer model. First, by analysis of reported data of expression microarray after treatment of a prostate cancer cell line with a demethylating agent, we isolated two marker genes (Mmp23, Nkx3.1) whose promoter CpG islands were aberrantly methylated in testosterone and 3,2′-dimethyl-4-aminobiphenyl-induced invasive adenocarcinomas. These two genes and three genes previously isolated (Aebp1, Amn1, Tgfbr2) [Yamashita et al. Cancer Res. 2008] were used as markers. Then, we analyzed temporal profiles of DNA methylation levels of the five genes in the dorsolateral lobe of rats treated with excessive androgen. Testosterone was administrated every five weeks for 15, 30, 40 and 50 weeks from six weeks old by subcutaneous implantation of a Silastic tube containing 40 mg testosterone propionate. Aberrant DNA methylation of two genes (Amn1, Mmp23) was gradually induced during the testosterone treatment while that of the other three genes was not. The former two genes had lower mRNA expression levels in the normal prostate than the latter three genes, which was in accordance with the known fact that genes with low transcription are susceptible to DNA methylation. Third, we investigated molecular mechanisms for aberrant DNA methylation induction by androgen excess. Androgen excess did not induce mRNA expression of DNA methyltransferases; Dnmt1, Dnmt3a or Dnmt3b in the rat prostrate. As for histone modifications, it did not induce significant changes in either H3K4me3 or H3K27me3 levels of the five genes methylated in rat prostate cancer. In contrast, it induced infiltration of lymphocytes and neutrophils in the prostate. Temporal profiles of expression levels of specific inflammation-related genes (Cxcl2, Il1b, Nos2 and Tnf) paralleled the methylation levels of Amn1 and Mmp23. Androgen excess did not induce bacterial infection as determined by copy number of bacterial DNA, but induced increase in Ki67-positive cells in regions with and without infiltration of inflammatory cells. The inflammatory response, known as a major mechanism for aberrant DNA methylation induction, along with cell proliferation was likely to be the cause of aberrant DNA methylation induction in the rat prostate with androgen excess. These results demonstrated that androgen excess can induce aberrant DNA methylation in the prostate, and suggested that inflammatory response underlies aberrant DNA methylation induction by androgen excess. Citation Format: Satoshi Yamashita, Satoru Takahashi, Yasunori Matsuda, Ken Gyobu, Toshikazu Ushijima. Androgen excess induces aberrant DNA methylation in the prostate. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5375. doi:10.1158/1538-7445.AM2013-5375