Abstract 5350: Enhancer of zeste homolog 2 (EZH2) promotes progression of cholangiocarcinoma by regulating cell cycle and apoptosis.

Abstract

Abstract Background: Enhancer of zeste homolog 2 (EZH2) is a catalytic subunit of the polycomb repressive complex 2 (PRC2). When present in PRC2, EZH2 catalyzes trimethylation on lysine 27 residue of histone H3(H3K27Me3), resulting in epigenetic silencing of gene expression and cancer progression. Here, we investigated the expression and the function of EZH2 in intrahepatic and extrahepatic cholangiocarcinoma (ICC and ECC). Methods: The influence of EZH2 on cell growth and apoptosis was assessed by knockdown experiments using siRNA in cholangiocarcinoma cell lines, RBE and TFK-1. Target genes of EZH2 in cholangiocarcinoma cell lines were searched by real time PCR. The clinical significance of EZH2 in 84 cholangiocarcinoma patients (ICC and ECC in 45 and 41, respectively) who underwent a curative surgery was examined by immunohistochemistry. Results: In vitro analysis, a knockdown of EZH2 reduced cell growth and induced G1 arrest, and induced apoptosis confirmed by Annexin V staining and increasing sub-G1 population of two cholangiocarcinoma cell lines. Moreover, a knockdown of EZH2 increased the expression of p16INK4A and p27KIP1, in real time PCR. In immunohistochemical study, The upregulation of EZH2 was correlated with tumor diameter (P = 0.0103) in ICC, lymph node metastasis (P=0.0292) in ECC, and Ki67 index in both ICC (P=0.0364) and ECC (P=0.0017). In addition, EZH2 expression was correlated with the poor prognosis in both ICC (P=0.0447) and ECC (P=0.0227). Conclusion: The current study demonstrates that the high expression of EZH2 results in acceleration of cell cycle and anti-apoptosis in vitro analysis, and is related to poor prognosis in patients with ICC or ECC by IHC study. These results suggest that EZH2 is a potential target for cholangiocarcinoma therapeutics. Citation Format: Shigeki Nakagawa, Hirohisa Okabe, Yasuo Sakamoto, Hiromitsu Hayashi, Daisuke Hashimoto, Hideyuki Kuroki, Katsunori Imai, Hidetoshi Nitta, Akira Chikamoto, Masayuki Watanabe, Toru Beppu, Hideo Baba. Enhancer of zeste homolog 2 (EZH2) promotes progression of cholangiocarcinoma by regulating cell cycle and apoptosis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5350. doi:10.1158/1538-7445.AM2013-5350