Abstract 282: MicroRNAs located at chromosome 8p21-22 region as novel factors underlying racial disparities in prostate cancer aggressiveness
Authors: Bhagirath Divya , Patel Nikhil , Ghosh Santu , Bollag Roni , Saini Sharanjot 
Published: September 2020

Abstract
The mechanistic basis of racial disparities in prostate cancer (PCa) aggressiveness between African American (AA) and Caucasian (CA) men are not yet fully understood. Further, molecular biomarkers to predict aggressive disease at its onset have been studied primarily in CAs, the relevance of these biomarkers to AAs are largely unknown. We propose a novel, paradigm-shifting hypothesis that expression of microRNA (miRNA) genes-miR-3622a and miR-383-located within frequently deleted chr8p21-22 region constitute important molecular factors contributing to racial disparities in PCa aggressiveness in AA vs CA men. Chromosome 8p deletions are a frequent alteration of PCa genome, with a common region of loss of heterozygosity at the chr8p21-22 locus. We previously showed that this region is associated with a set of tumor suppressive miRNAs (miR-3622a/b, -383, -4288) that are downregulated in PCa with important causal roles in tumor progression, recurrence and metastasis. Chr8p deletions increase significantly with tumor grade and are associated with poor prognosis. These deletions are well studied in CA men. However, there have been conflicting reports on frequency of chr8p deletions in AA men. In view of these conflicting studies and in light of our paradigm-shifting studies establishing the link between chr8p deletions and loss of miRNA genes in this region, we examined the expression of these miRNAs in AA vs CA clinical PCa tissues. We found that miR-3622a and miR-383 expression is significantly lower in AA men as compared to age, tumor stage and grade matched CAs. To examine if these miRNAs constitute causal factors contributing to PCa racial disparities, we overexpressed miR-3622a/miR-383/control miR in AA and CA PCa cell lines followed by functional assays. We found that these miRNAs exert more prominent effects on cellular proliferation and apoptosis in AA cell lines. To understand molecular mechanisms contributing to disparate functional effects of these miRNAs in AA vs CA cell lines, we examined potential miRNA target genes and found that miR-3622a regulates PCa stem cell marker, CD44 while miR-383 represses LEF1 and ZEB1 in a race-specific manner. Further, we determined the mechanistic basis of differential expression of miR-3622a in AAs vs CAs by examining copy number alterations (CNAs) and methylation at this locus using PCa clinical samples. Our analyses showed that while this locus is genomically altered at a lower frequency in AAs, significantly increased frequency of miRNA promoter hypermethylation was found in AAs as compared to CAs. In conclusion, our data suggests that miRNAs located in frequently deleted chr8p21-22 region constitute important causal factors contributing to racial disparities in PCa aggressiveness and clinical outcomes and are potential biomarkers to predict PCa aggressiveness and tumor recurrence in AA men.
Citation Format: Divya Bhagirath, Nikhil Patel, Santu Ghosh, Roni Bollag, Sharanjot Saini. MicroRNAs located at chromosome 8p21-22 region as novel factors underlying racial disparities in prostate cancer aggressiveness [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 282.