Abstract B087: Role of GATA-4-Androgen-AR axis in prostate cancer from African American men
Authors: Ramakrishnan Swathi , Peng Xuan , Gomez Eduardo Cortes , Attwood Kristopher , Yan Li , Wilton John , Azabdaftari Gissou , Mohler James , Wang Jianmin , Woloszynska Anna 
Published: September 2020

Abstract
Background: African American (AA) men are 1.7 times more likely to develop and 2.4 times more likely to die of prostate cancer (PrCa) than their European American (EA) counterparts, however the underlying biology causing this disparity is unknown. Here, we show how epigenetic dysregulation of calcium signaling genes affect GATA-4, androgen receptor (AR), androgen metabolism and associate with clinical outcomes in AA men with PrCa. Methods: Using Illumina arrays we identified DNA methylation differences between 32 EA and AA PrCa patients. We used RNA-sequencing to discover transcriptomic changes potentially mediated by DNA methylation. We measured GATA-4 and AR protein expression in a tissue microarray (TMA) of 95 EA and 92 AA PrCa patients. We measured testosterone (T) and dihydrotestosterone (DHT) in serum of the same AA and EA PrCa patients. In vitro, we treated MDA PCa 2a (2a) and LaPC4 cells derived from AA and EA prostate tumors, respectively with a calcium chelator (BAPTA-AM) and T. We measured GATA-4 and AR protein expression in control and treated cells. Results: Our DNA methylation analysis showed that AA but not EA prostate tumors enriched for hypermethylated sites in calcium sensing genes was associated with worse disease-free time (21.6 vs 46.7 months, p&lt;0.05). DNA hypermethylation of calcium signaling genes, which correlated with decreased transcript levels, can potentially raise intracellular calcium. Calcium levels regulate stability of proteins including AR and GATA-4. Therefore, we tested potential calcium mediated changes in GATA-4 and AR expression in vitro and in patient samples. In vitro, depleting calcium in the presence of T increased GATA-4 protein expression by 1.5 times and AR expression only in AA prostate tumor derived 2a cells. DNA hypermethylation of calcium sensing genes was associated with lower GATA-4 and AR expression in PrCa and adjacent non-tumor tissues of AA men. The role of GATA-4 in PrCa is unknown, but it is a known transcriptional regulator of androgen metabolizing enzymes (AME). AMEs are important for androgen metabolism that result in T and DHT production through the primary and alternative pathways. AME transcripts in the primary and alternative pathways were one of the top 5 transcriptionally dysregulated pathways in AA compared to EA prostate tumors. We found that T but not DHT is significantly lower (p&lt;0.05) in serum samples from AA (3.64ng/ml) compared to EA (3.99ng/ml) PrCa patients. T and DHT bioavailability in prostate tumors affect AR expression and function. In our studies, AA adjacent non-tumor tissues had higher percent AR positive nuclei (p&lt;0.05) compared to EA adjacent non-tumor tissues. Conclusion: Epigenetic alteration of calcium signaling can affect GATA-4 mediated changes in androgen metabolism and AR signaling that are well-established therapeutic targets in PrCa. This molecular alteration, unique to AA prostate tumors, can be used to rationalize specific androgen deprivation and AR-targeted therapies in these patients.
Citation Format: Swathi Ramakrishnan, Xuan Peng, Eduardo Cortes Gomez, Kristopher Attwood, Li Yan, John Wilton, Gissou Azabdaftari, James Mohler, Jianmin Wang, Anna Woloszynska. Role of GATA-4-Androgen-AR axis in prostate cancer from African American men [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr B087.