Abstract PO-134: Intracellular calcium regulates androgen receptor expression and basal-luminal features in prostate cancer from African American men
Authors: Ramakrishnan Swathi , Peng Xuan , Gomez Eduardo C. , Attwood Kristopher , Maly Ivan V. , Hoffmann Wilma A. , Huss Wendy , Azabdaftari Gissou , Yan Li , Wang Jianmin , Woloszynska Anna 
Published: December 2020

Abstract
Background: Disparities in prostate cancer (PrCa) incidence and mortality between African American (AA) and European American (EA) men are partially mediated by underlying disease biology. The goal of this study was to determine how DNA methylation and transcriptomic changes drive PrCa health disparities in AA men.
Methods: Transcriptomic alterations potentially mediated by DNA methylation were identified by Illumina arrays and RNA-sequencing in PrCa from 30 AA and 32 EA men. Androgen receptor (AR) protein expression was measured using tissues microarray of matched PrCa tissues from 95 EA and 92 AA men. In vitro, MDA PCa 2a (2a)/MDA PCa 2b (2b) cells derived from an AA man and LNCaP/LaPC-4 cells derived from EA men were stimulated with ionomycin, a calcium ionophore to measure intracellular calcium using fluorescent-based live imaging. Results: Unsupervised hierarchical clustering revealed DNA methylation clusters (Cluster A and Cluster B) with differential methylation of loci that regulate intracellular calcium levels including RYR2, TRPC6, and TRPA1. Increased methylation of calcium regulatory genes in Cluster A was associated with reduced disease-free time (DFT) (21.65 vs 46.71 months, p&lt;0.05) only in AA men with PrCa. RYR2 (-0.122 vs -0.004, p=0.69), TRPC6 (0.006 vs -0.639, p=0.06) and TRPA1 (-0.070 vs -0.269, p&lt;0.05) transcript levels were lower in Cluster A compared to Cluster B. These data suggest DNA methylation can regulate expression of calcium regulating genes. In vitro, we found AA PrCa derived 2b cells have reduced RNA levels of RYR2, TRPV6 and CALB1 compared to EA PrCa derived LNCaP cells. Reduced transcription can result in lower protein expression and thus activity of calcium regulatory genes. To test this, we stimulated cells with ionomycin and found a rapid increase in intracellular calcium in 2a/2b cells (within 60 seconds) compared to LNCaP/LAPC-4 cells (120-300 seconds). This suggests that decreased transcription correlates to reduced buffering capacity of calcium regulatory genes. Others have shown that increased intracellular calcium reduces AR protein levels. Therefore, we analyzed AR protein expression in a subset of tumors from Cluster A and B. AR levels were lower in adjacent non-tumor and tumor tissue in these overlapping samples. AR low PrCa are associated with basal like features and respond poorly to androgen deprivation therapy. Therefore, we analyzed the PAM50 basal/luminal gene sets and AR target genes and found differentially expression of these genes in AA PrCa derived 2b and EA PrCa derived LNCaP cells. Conclusions: Our study shows that AA men with PrCa have epigenetically dysregulated calcium signaling that is associated with worse DFT. Our ongoing work seeks to identify how these alterations regulate AR expression and thus basal/luminal features. Our long- term goal is to establish novel molecular subtypes using calcium-AR-basal/luminal features that can guide design of rationale therapies in a subset of AA men with PrCa.
Citation Format: Swathi Ramakrishnan, Xuan Peng, Eduardo C. Gomez, Kristopher Attwood, Ivan V. Maly, Wilma A. Hoffmann, Wendy Huss, Gissou Azabdaftari, Li Yan, Jianmin Wang, Anna Woloszynska. Intracellular calcium regulates androgen receptor expression and basal-luminal features in prostate cancer from African American men [abstract]. In: Proceedings of the AACR Virtual Conference: Thirteenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2020 Oct 2-4. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(12 Suppl):Abstract nr PO-134.