Abstract 3535: Differential expression and localization of the E3 ubiquitin ligase Nrdp1 in African American versus Caucasian American prostate cancer cells
Authors: Batra Neelu , Krig Sheryl , Sam Anhao , Macias Katelyn , Savoy Rosalinda , Siddiqui Salma , Melgoza Frank , D'Abronzo Leandro , Hazari Sidhartha , Durbin-Johnson Blythe , Ghosh Paramita , Vinall Ruth L. 
Published: August 2018

Abstract
Despite a recent decrease in overall incidence of prostate cancer (CaP), CaP incidence continues to be much higher among men of African origin living in the United States (223.9 men per 100,000) compared to those of European origin (139.9 men per 100,000). Also, the CaP age-specific mortality rates are 2.4 times greater among African-American (AA) compared with European American (EA) men. The causes for these differences are multifactorial, but include genetic effects that contribute to CaP-associated health disparity. We previously showed that the androgen receptor (AR) can suppress levels of the receptor tyrosine kinase ErbB3, a molecule that is known to drive CaP progression, by stimulating the E3 ubiquitin ligase Nrdp1 (also called RNF41 or FLRF). The goals of the current study were to determine whether differential expression and/or localization of Nrdp1 contribute to CaP-associated health disparities, and to further elucidate the mechanisms by which regulation of Nrdp1 levels and localization occurs. Immunohistochemistry (IHC) in prostate tissue determined that nuclear Nrdp1 levels are significantly lower in AA CaP patients (n=19) versus CA CaP patients (n=121) with localized disease (p=0.008). A similar association was observed in CaP cell lines; immunofluorescence (IF) analyses demonstrated MDAPCa2b and E006 (cell lines derived from AA CaP patients) express significantly lower levels of nuclear Nrdp1 compared to LNCaP, CWR22Rv1, C4-2, and C4-2B (cell lines derived from CA CaP patients). Western blot and qPCR determined that Nrdp1 levels are lower in AA versus CA CaP cells (MDAPCa2b express ~2-fold less Nrdp1 protein and mRNA levels compared to LNCaP), and that androgen withdrawal has a bigger impact on Nrdp1 expression levels in AA CaP cells (2-fold decrease in MDAPCa2b compared to ~1.2-fold decrease in LNCaP). Proteasomal regulation of Nrdp1 also occurs; treatment with MG132 resulted in accumulation of Nrdp1 in both AA and CA CaP cell lines. Interestingly, altering androgen and/or AR levels also affected Nrdp1 localization (IF analyses) as well as the ability of Nrdp1 to mediate CaP cell apoptosis (flow cytometry). In summary, we demonstrate that Nrdp1 is differentially expressed in AA versus CA CaP patients as well as in AA versus CA CaP-patient derived cell lines, and that androgen withdrawal has a bigger impact on Nrdp1 expression in AA CaP cell lines. We also demonstrate that androgen/AR is involved in determining Nrdp1 localization, and that Nrdp1 can mediate CaP cell apoptosis in the presence of AR. The combined data, and the knowledge that Nrdp1 regulates ErbB3 levels, suggest that differential expression of Nrdp1 in AA versus CA CaP may contribute to CaP-associated health disparities and may occur as a result of dysregulation of the regulation of Nrdp1 by androgen/AR.
Citation Format: Neelu Batra, Sheryl Krig, Anhao Sam, Katelyn Macias, Rosalinda Savoy, Salma Siddiqui, Frank Melgoza, Leandro D'Abronzo, Sidhartha Hazari, Blythe Durbin-Johnson, Paramita Ghosh, Ruth L. Vinall. Differential expression and localization of the E3 ubiquitin ligase Nrdp1 in African American versus Caucasian American prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3535.