Abstract B083: Dysregulation of the AR-Nrdp1-ErbB3 axis occurs in African American prostate cancer patients and is associated with worse outcomes

• Published in: Cancer epidemiology, biomarkers & prevention biomarkers & prevention, 2020-06, Vol.29 (6_Supplement_2), p.B083-B083
• Main Authors: Sam, Anhao, Evans, Shawna, Browning, Elizabeth, Krig, Sheryl, Batra, Neelu, Steele, Thomas, Siddqui, Salma, Ghosh, Paramita, Vinall, Ruth
• Format: Article
• Language: English
• ISSN: 1055-9965; 1538-7755
• DOI: 10.1158/1538-7755.DISP19-B083

Background: We previously showed that Nrdp1, an E3 ubiquitin ligase, is transcriptionally regulated by the androgen receptor (AR) in prostate cancer (CaP) cells and that Nrdp1 can post-translationally regulate ErbB3 (an EGFR family member) levels via ubiquitination and subsequent proteasomal degradation. Increased levels of ErbB3 are associated with worse CaP patient outcome. The goal of the current study was to determine whether dysregulation of the AR-Nrdp1-ErbB3 axis contributes to prostate cancer health disparities for African American (AA) men, and to identify the underlying mechanisms involved. Methods: Expression levels and localization of AR, Nrdp1, and ErbB3 were assessed in a total of 208 CaP patient samples (50 African American (AA) and 158 Caucasian (CA) CaP patients) and two cell lines (LNCaP (CA) and MDAPCa2b (AA)). Expression levels and localization of these molecules were determined by immunohistochemistry (IHC) and subcellular fractionation and western blot. A combination of knockdown (siRNA), forced overexpression (Nrdp1-FLAG construct), and treatment with enzalutamide or synthetic androgen (R1881) experiments were employed to investigate the relationship between AR, Nrdp1, and ErbB3 expression levels and localization and to identify differences in AA and CA cell lines. Immunoprecipitation allowed for investigation of the mechanisms which facilitate nuclear transport of Nrdp1. Results: A statistically significant negative association between cytoplasmic levels of AR (AR C) and nuclear Nrdp1 (Nrdp1 N) exists in both Caucasian (CA) and African American (AA) prostate cancer (CaP) patients, but this association was stronger in AA patients compared to CA patients (Spearman correlation coefficient of -0.62 for AA patients, and -0.36 for CA patients). Increased nuclear Nrdp1 expression levels were associated with increased 5-year survival rates, and reduced nuclear Nrdp1 expression levels predicted biochemical recurrence (AUC 0.63). Dysregulation of the AR-Nrdp1-ErbB3 axis in AA CaP cells was also observed in cell line studies; AA CaP cells expressed significantly lower levels of both total and nuclear Nrdp1 compared to their CA CaP counterparts. Manipulation of AR expression levels and localization via knockdown and inhibition with enzalutamide had a lesser impact on Nrdp1 expression levels and localization in AA versus CA CaP cells. Immunoprecipitation studies demonstrated that Nrdp1 can bind to AR in CA CaP cells but not AA CaP cells. Conclus