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

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/b-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 b-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 b-catenin signaling. Conversely, ectopic overexpression of EZH2 in immortalized hepatocytes activated Wnt/b-catenin signaling to promote cellular proliferation. In human HCCs, concomitant overexpression of EZH2 and b-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/b-catenin signaling and consequential proliferation of HCC cells, thus representing a novel therapeutic target for this highly malignant tumor. Cancer Res; 71(11); 4028-39. Ó2011 AACR.

Epigenetic Regulation of Cell Adhesion and Communication by Enhancer of Zeste Homolog 2 in Human Endothelial Cells

“…7, 43 Our results, however, also add complexity because WNT5B represents a ligand for noncanonical WNT signaling, which may counteract canonical WNT signaling. 44 …”

A Positive Feedback Loop Regulates the Expression of Polycomb Group Protein BMI1 via WNT Signaling Pathway

“…Hence, during breast cancer development, PcG proteins such as BMI1 are likely to target other tumor suppressors and/or growth-regulatory pathways. Indeed, PcG protein EZH2 was recently reported to promote hepatocellular carcinoma via regulation of the WNT pathway (36), and cross-talk between EZH2 and the WNT pathway has been reported (37).…”

Polycomb repressive complex 2 is required for MLL-AF9 leukemia

“…Loss of function of PRC2 has been evaluated in several cancer models (14,15). However, shRNA technologies used in these studies will leave in place some residual expression and function of the protein in question, obscuring the interpretation of experimental results.…”