EZH2-Mediated Concordant Repression of Wnt Antagonists Promotes beta-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/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. "
ABSTRACT: Although enhancer of zeste homolog 2 (EZH2) has been reported as an independent prognostic factor in renal cell carcinoma (RCC), little is known about the exact mechanism of EZH2 in promoting the genesis of RCC. However, several studies have shown that dysregulation of the Wnt/β-catenin signaling pathway plays a crucial role. Therefore, we determined whether EZH2 could affect ACHN human RCC cell proliferation and invasion via the Wnt/β-catenin pathway. In the present study, we investigated the effects of short interfering RNA (siRNA)-mediated EZH2 gene silencing on Wnt/β-catenin signaling in ACHN cells. EZH2-siRNA markedly inhibited the proliferation and invasion capabilities of ACHN, while also reducing the expression of EZH2, Wnt3a and β-catenin. In contrast, cellular expression of GSK-3β (glycogen synthase kinase-3β), an inhibitor of the Wnt/β-catenin pathway, was conspicuously higher after transfection of EZH2 siRNA. These preliminary findings suggest EZH2 may promote proliferation and invasion of ACHN cells via action on the Wnt/β-catenin signaling pathway.Asian Pacific journal of cancer prevention: APJCP 12/2012; 13(12):6197-201. DOI:10.7314/APJCP.2012.13.12.6197 · 2.51 Impact Factor
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ABSTRACT: Latent HIV proviruses are silenced as the result of deacetylation and methylation of histones located at the viral long terminal repeat (LTR). Inhibition of histone deacetylases (HDACs) leads to the reemergence of HIV-1 from latency, but the contribution of histone lysine methyltransferases (HKMTs) to maintaining HIV latency remains uncertain. Chromatin immunoprecipitation experiments using latently infected Jurkat T-cell lines demonstrated that the HKMT enhancer of Zeste 2 (EZH2) was present at high levels at the LTR of silenced HIV proviruses and was rapidly displaced following proviral reactivation. Knockdown of EZH2, a key component of the Polycomb repressive complex 2 (PRC2) silencing machinery, and the enzyme which is required for trimethyl histone lysine 27 (H3K27me3) synthesis induced up to 40% of the latent HIV proviruses. In contrast, there was less than 5% induction of latent proviruses following knockdown of SUV39H1, which is required for H3K9me3 synthesis. Knockdown of EZH2 also sensitized latent proviruses to external stimuli, such as T-cell receptor stimulation, and slowed the reversion of reactivated proviruses to latency. Similarly, cell populations that responded poorly to external stimuli carried HIV proviruses that were enriched in H3K27me3 and relatively depleted in H3K9me3. Treating latently infected cells with the HKMT inhibitor 3-deazaneplanocin A, which targets EZH2, led to the reactivation of silenced proviruses, whereas chaetocin and BIX01294 showed only minimal reactivation activities. These findings suggest that PRC2-mediated silencing is an important feature of HIV latency and that inhibitors of histone methylation may play a useful role in induction strategies designed to eradicate latent HIV pools.Journal of Virology 06/2011; 85(17):9078-89. DOI:10.1128/JVI.00836-11 · 4.65 Impact Factor
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ABSTRACT: The biological pathways and functional properties by which misexpressed microRNAs (miRNAs) contribute to liver carcinogenesis have been intensively investigated. However, little is known about the upstream mechanisms that deregulate miRNA expressions in this process. In hepatocellular carcinoma (HCC), hepatitis B virus (HBV) X protein (HBx), a transcriptional trans-activator, is frequently expressed in truncated form without carboxyl-terminus but its role in miRNA expression and HCC development is unclear. Human non-tumorigenic hepatocytes were infected with lentivirus-expressing full-length and carboxyl-terminal truncated HBx (Ct-HBx) for cell growth assay and miRNA profiling. Chromatin immunoprecipitation microarray was performed to identify the miRNA promoters directly associated with HBx. Direct transcriptional control was verified by luciferase reporter assay. The differential miRNA expressions were further validated in a cohort of HBV-associated HCC tissues using real-time PCR. Hepatocytes expressing Ct-HBx grew significantly faster than the full-length HBx counterparts. Ct-HBx decreased while full-length HBx increased the expression of a set of miRNAs with growth-suppressive functions. Interestingly, Ct-HBx bound to and inhibited the transcriptional activity of some of these miRNA promoters. Notably, some of the examined repressed-miRNAs (miR-26a, -29c, -146a and -190) were also significantly down-regulated in a subset of HCC tissues with carboxyl-terminal HBx truncation compared to their matching non-tumor tissues, highlighting the clinical relevance of our data. Our results suggest that Ct-HBx directly regulates miRNA transcription and in turn promotes hepatocellular proliferation, thus revealing a viral contribution of miRNA deregulation during hepatocarcinogenesis.PLoS ONE 08/2011; 6(8):e22888. DOI:10.1371/journal.pone.0022888 · 3.53 Impact Factor