Abstract B016: MicroRNA drivers of TMPRSS2 fusion-negative prostate cancer in African Americans
Authors: Siddappa Manjunath , White Jason , Wang Honghe , Sucheston-Campbell Lara E. , Yates Clayton , Campbell Moray J. 
Published: February 2019

TMPRSS2:ERG fusions are being pursued as genomic biomarkers to define disease state and predict treatment responses in prostate cancer (PCa). Successful biomarker exploitation depends on the frequency of TMPRSS2 fusions, which are very common in European American (EA) men with both high-grade PIN, and in at least 50% PCa patients. However, the incidence is far lower in men from other ethnicities, and as low as 10% among African American (AA) patients. Therefore in AA patients, TMPRSS2:ERG fusion events are unlikely to either explain the elevated incidence of PCa or be relevant as a biomarker.

To seek novel biomarkers of TMPRSS2 fusion-negative PCa we have considered a role for miRNA drivers. Previously, we analyzed miRNA expression in various PCa cohorts, to identify differentially expressed miRNA in TMPRSS2 fusion-negative disease in AA men. These cohorts included PCa in AA men, PCa progression in EA men following surgery, and mining of TCGA-PRAD and MSKCC cohorts to identify TMPRSS2 fusion-negative associated miRNA.

We have now complemented this by a genome-wide miRNA screen in serum samples using the NanoString platform of 97 aged matched EA and AA men with HGPIN, ~30% of whom progressed to PCa (SWOG S9917). Serum levels of 22 miRNA significantly distinguished AA men who progressed to PCa, from those whose HGPIN remained stable; these miRNA included miR-25-3p, miR-93-5p, and miR-423-5p.

Combining the findings identified 38 miRNA, and we sought to identify shared and unique links between these miRNA associated with PCa progression and TMPRSS2 fusion-negative status. Although the PCa drivers in AA men remain obscured, strong links are emerging between vitamin D receptor (VDR) signaling and AA PCa. Epidemiologic studies have established links between low serum vitamin D3 levels and PCa incidence and progression in AA men. VDR signaling has also been linked to altered local immune responses in AA PCa patients. Remarkably, we found strong evidence from our studies and those of others that 29 of the 38 miRNA identified were regulated by 1,25(OH)2D3 in prostate cells, including the miR-25-miR-93-miR-106b cluster, miR-152 and miR-423-5p.

As this regulation includes both direct and indirect effects, we examined how these miRNA genes, or host genes, were targeted by the vitamin D receptor (VDR). Previously, we identified VDR binding at the MCM7 host gene for the miR-25-miR-93-miR-106b cluster used ChIP-PCR in nonmalignant RWPE-1 cells. We have now mined publicly available VDR ChIP-Seq in LNCaP cells (GSE64656); these cells are TMPRSS2 fusion negative. Selecting all binding sites within +/- 7.5 kb of a TSS, we identified VDR associated with 8/29 miRNA, including NSRP1 (miR-423-5p host gene) and COPZ2 (miR-152 host gene).

To measure associations with TMPRSS2 fusion-negative PCa, we identified the most commonly altered of the 38 miRNA in the TCGA-PRAD cohort. Specifically, we identified 18 miRNA altered by more than 2 Z scores in more than 25% tumors, which included miR-25-3p, miR-93-5p, miR-152, and miR-423-5p. Expression of these miRNA clustered tumors into two groups that significantly distinguished TMPRSS2 fusion status (p=0.007) and race (p=0.01). 15/18 miRNA were known to be regulated by 1,25(OH)2D3, and 5/8 were bound by VDR in LNCaP cells. Currently, we are measuring how these 18 miRNA are regulated by 1,25(OH)2D3 in AA and EA nonmalignant and malignant prostate cell models: AA-RC77T, RC43T; EA-HPr-1AR, LNCaP, VCaP (TMPRSS2 fusion positive), PC-3.

Together these data suggest that a distinct PCa subtype, independent of TMPRSS2 fusion, arises more frequently in AA men due to reduced 1,25(OH)2D3 levels that disrupts VDR regulation of miRNA, including miR-25-3p, miR-93, miR-152, and miR-423-5p. Understanding the miRNA regulated gene networks has the potential to illuminate the cancer drivers in TMPRSS2 fusion-negative AA PCa, and expression of these miRNA may predict progression risks.

Citation Format: Manjunath Siddappa, Jason White, Honghe Wang, Lara E. Sucheston-Campbell, Clayton Yates, Moray J. Campbell. MicroRNA drivers of TMPRSS2 fusion-negative prostate cancer in African Americans [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B016.