Abstract 5326: EZH2 regulation through lysine 63 linked ubiquitination in prostate cancer

Abstract

Abstract Enhancer of zeste homolog 2 (EZH2) plays crucial roles on the development of cells and tissues as well as the progression of prostate cancer (PCa) and castration resistant prostate cancer (CRPC). EZH2 can upregulate and activate progenitor genes including androgen receptor (AR) and the target genes. However, the mechanisms by which EZH2 is regulated in PCa remain elusive. Literature reports that tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6) is essential for both normal tissue development and regulation of oncogenic signaling pathways in cancers. In this study, we reported that EZH2 is regulated by PTEN and SKP2 network in PCa. Specifically, we showed that the aberrant upregulation of EZH2 and histone H3 lysine 27 trimethylation (H3K27me3) in both Pten null mouse embryonic fibroblasts (MEFs) in vitro and prostate tumors of Pten null mice in vivo, as compared to the controls. EZH2 levels were negatively correlated with TRAF6 in human PCa cells upon SKP2 dysregulation. Immunofluorescence (IF) staining results showed a co-localization of EZH2 and TRAF6 in nucleus of PC3 cells, and co-immunoprecipitation (co-IP) analysis further confirmed a physical binding of EZH2 and TRAF6 in PC3 cells. Ectopic expression of TRAF6 promoted the K63-linked polyubiquitination of EZH2 to decrease EZH2 and H3K27me3 levels in PCa cells. Conversely, TRAF6 knockdown resulted in a reduction of EZH2 polyubiquitination with an increase of EZH2 and H3K27me3 levels in PCa cells. Furthermore, the catalytically dead mutant TRAF6 C70A abolished the TRAF6-mediated polyubiquitination of human EZH2 in vivo in 293T cells and in vitro in the recombinant human EZH2 protein, as compared with TRAF6 WT. Together, we report for the first time a novel mechanism on EZH2 ubiquitination and an important signaling network of SKP2-TRAF6-EZH2-H3K27me3 in PCa cells. Our findings provide valuable clues on the mechanism and efficiency of targeting EZH2 in PCa and CRPC . Note: This abstract was not presented at the meeting. Citation Format: Wenfu Lu, Shenji Lu, Bo Li, Yingqiu Xie, Michael G. Izban, Billy R. Ballard, Sandeep A. Sathyanarayana, Samuel E. Adunyah, Robert J. Matusik, Zhenbang Chen. EZH2 regulation through lysine 63 linked ubiquitination in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5326. doi:10.1158/1538-7445.AM2017-5326