EZH2-Mediated Concordant Repression of Wnt Antagonists Promotes beta-Catenin-Dependent Hepatocarcinogenesis

Institute of Digestive Disease, The Chinese University of Hong Kong, Hong Kong SAR, China.
Cancer Research (Impact Factor: 9.28). 06/2011; 71(11):4028-39. DOI: 10.1158/0008-5472.CAN-10-3342
Source: PubMed

ABSTRACT Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of the Polycomb-repressive complex 2 (PRC2) that represses gene transcription through histone H3 lysine 27 trimethylation (H3K27me3). Although EZH2 is abundantly present in various cancers, the molecular consequences leading to oncogenesis remain unclear. Here, we show that EZH2 concordantly silences the Wnt pathway antagonists operating at several subcellular compartments, which in turn activate Wnt/β-catenin signaling in hepatocellular carcinomas (HCC). Chromatin immunoprecipitation promoter array and gene expression analyses in HCCs revealed EZH2 occupancy and reduced expression of Wnt antagonists, including the growth-suppressive AXIN2, NKD1, PPP2R2B, PRICKLE1, and SFRP5. Knockdown of EZH2 reduced the promoter occupancy of PRC2, histone deacetylase 1 (HDAC1), and H3K27me3, whereas the activating histone marks were increased, leading to the transcriptional upregulation of the Wnt antagonists. Combinatorial EZH2 and HDAC inhibition dramatically reduced the levels of nuclear β-catenin, T-cell factor-dependent transcriptional activity, and downstream pro-proliferative targets CCND1 and EGFR. Functional analysis revealed that downregulation of EZH2 reduced HCC cell growth, partially through the inhibition of β-catenin signaling. Conversely, ectopic overexpression of EZH2 in immortalized hepatocytes activated Wnt/β-catenin signaling to promote cellular proliferation. In human HCCs, concomitant overexpression of EZH2 and β-catenin was observed in one-third (61/179) of cases and significantly correlated with tumor progression. Our data indicate that EZH2-mediated epigenetic silencing contributes to constitutive activation of Wnt/β-catenin signaling and consequential proliferation of HCC cells, thus representing a novel therapeutic target for this highly malignant tumor.

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    • "Meanwhile, GSK-3β is considered playing a negative role in this pathway by degradation of β-catenin (Liu et al., 2002). Several studies reported that EZH2 contributed to constitutive activation of Wnt/β-catenin signaling pathway and induced tumorigenesis of breast cancer and hepatocellular carcinomas (Shi et al., 2007; Li et al., 2009; Cheng et al., 2011). To the best of our knowledge, there is no article referring the relationship between EZH2 and Wnt/β-catenin pathway in the oncogenesis of RCC. "
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