Abstract PL01-02: Functional biomarkers that promote African American prostate cancer through epigenetic regulation

Abstract Prostate cancer is the most commonly diagnosed malignancy in men, with African American men experiencing a rate 60% higher than white patients. At the time of diagnosis, approximately 50% of men have clinically advanced disease. African American men have almost twice the incidence and death rates related to prostate cancer compared to Caucasian men. Several studies have suggested that some of these differences may be attributed to the elevated expression of different genes. Many factors have been associated with why prostate tumors in AA patients are more aggressive. However there is a lack of knowledge, whether this is the result of genes that promote aggressiveness or promote tumor development. Methylation profiling of prostate tumors has demonstrated that the loss of a number of key regulatory genes are not via mutation, but rather hypermethylation. This is particularly evident in the AA patients where hypermethylation of a number of genes in normal or pre-malignant areas are thought to predispose a full-blown malignancy. However the underlining mechanism of these acquired methylation patterns is poorly understood. To better understand the epigenetic regulation of genes associated with promoting aggressiveness and specifically to determine if this can explain the more aggressive nature of AA tumors , we conducted 662 microRNA microarray profiling utilizing novel isogenic non-malignant and malignant cell lines derived from both AA and CA tumor patients. Utilizing multiple criteria, included pathological stage and race, we were able to determine a distinct microRNA signature that was unique the AA derived cell lines, independent of tumor status. Validation by q-PCR of the 10 most significantly differentially expressed miRNA's across our 11 cell line panel demonstrated that loss of miR-152 expression was associated with aggressiveness. Restoring miR-152 expression in miR-152 deficient cell lines, resulted in decreased proliferation, and S phase arrest of the cell cycle. In silico informatics analysis predicted that miR-152 contains a significant number of CpG islands within the promoter region upstream of the start site. We confirmed this analysis with bisulfite conversion and sequencing of the promoter, as well as treatment with demethylation agent 5-Aza-2′-deoxycytidine. Furthermore, we observed an inverse relationship of miR-152 with predicted target DNA methyltransferase-1 (DNMT1), suggesting a reciprocal maintenance of hypermethylation for not only miR-152, but also a number of other methylated genes. This is plausible given the well-established role of DNMT1 in methylation of a large number of genes found to promote aggressiveness in prostate tumors . Lastly, a comparison of normal/tumor ratios of miR-152 expression in 20 CA and 20 AA prostate cancer patients, we observed significantly decreased expression in tumors from CA patients as expected, however this was not observed in AA patients. AA patients also displayed an overall lower expression compared to CA tumors. In summary, these results are the first to identify unique miRNAs that contribute to aggressive prostate cancers in AA patients. Furthermore epigenetic regulation of the miR-152/DNMT1 regulatory loop may play an import ant role in multiple events that contribute to the aggressiveness of PCa tumors. Citation Format: Shaniece C. Theodore, Honghe Wang, Jhong Rhim, Timothy Turner, Melissa Davis, William Grizzle, Clayton C. Yates. Functional biomarkers that promote African American prostate cancer through epigenetic regulation. [abstract]. In: Proceedings of the Sixth AACR Conference: The Science of Cancer Health Disparities; Dec 6–9, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2014;23(11 Suppl):Abstract nr PL01-02. doi:10.1158/1538-7755.DISP13-PL01-02