title: EZH2 represses target genes through H3K27-dependent and H3K27-independent mechanisms in hepatocellular carcinoma.
abstract: Alterations of polycomb group (PcG) genes directly modulate the trimethylation of histone H3 lysine 27 (H3K27me3) and may thus affect the epigenome of hepatocellular carcinoma (HCC), which is crucial for controlling the HCC cell phenotype. However, the extent of downstream regulation by PcGs in HCC is not well defined. Using cDNA microarray analysis, we found that the target gene network of PcGs contains well-established genes, such as cyclin-dependent kinase inhibitors (CDKN2A), and genes that were previously undescribed for their regulation by PcG, including E2F1, NOTCH2, and TP53. Using chromatin immunoprecipitation assays, we demonstrated that EZH2 occupancy coincides with H3K27me3 at E2F1 and NOTCH2 promoters. Interestingly, PcG repress the expression of the typical tumor suppressor TP53 in human HCC cells, and an increased level of PcG was correlated with the downregulation of TP53 in certain HCC specimens. Unexpectedly, we did not find obvious H3K27me3 modification or an EZH2 binding signal at the TP53 promoters, suggesting that PcG regulates TP53 expression in an H3K27me3-independent manner. Finally, the reduced expression of PcGs effectively blocked the aggressive signature of liver cancer cells in vitro and in vivo.
  
  
  CONCLUSIONS
  Taken together, our results establish the functional and mechanistic significance of certain gene regulatory networks that are regulated by PcGs in HCC.
authors.affiliation: Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen, P.R. China. Fujian Provincial Key Laboratory of Chronic Liver Disease and Hepatocellular Carcinoma, Xiamen University, Xiamen, P.R. China.
authors.forename: Shu-Bin
authors.initials: SB
authors.lastname: Gao
authors.affiliation: Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen, P.R. China. Fujian Provincial Key Laboratory of Chronic Liver Disease and Hepatocellular Carcinoma, Xiamen University, Xiamen, P.R. China.
authors.forename: Qi-Fan
authors.initials: QF
authors.lastname: Zheng
authors.affiliation: Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen, P.R. China. Fujian Provincial Key Laboratory of Chronic Liver Disease and Hepatocellular Carcinoma, Xiamen University, Xiamen, P.R. China.
authors.forename: Bin
authors.initials: B
authors.lastname: Xu
authors.affiliation: Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen, P.R. China.
authors.forename: Chang-Bao
authors.initials: CB
authors.lastname: Pan
authors.affiliation: Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen, P.R. China.
authors.forename: Kang-Li
authors.initials: KL
authors.lastname: Li
authors.affiliation: Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen, P.R. China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen, P.R. China.
authors.forename: Qi-Lin
authors.initials: QL
authors.lastname: Zheng
authors.affiliation: Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen, P.R. China. Fujian Provincial Key Laboratory of Chronic Liver Disease and Hepatocellular Carcinoma, Xiamen University, Xiamen, P.R. China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Lin
authors.affiliation: Department of Biochemistry and Molecular Biology, Health Science Center, Peking University, Beijing, P.R. China.
authors.forename: Li-Xiang
authors.initials: LX
authors.lastname: Xue
authors.affiliation: Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen, P.R. China. Fujian Provincial Key Laboratory of Chronic Liver Disease and Hepatocellular Carcinoma, Xiamen University, Xiamen, P.R. China. ghjin@xmu.edu.cn.
authors.forename: Guang-Hui
authors.initials: GH
authors.lastname: Jin
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000473:pathology; D002465:Cell Movement; D049109:Cell Proliferation; D000071221:Enhancer of Zeste Homolog 2 Protein; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006657:Histones / Q000378:metabolism*; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics* / Q000473:pathology; D008239:Lysine / Q000378:metabolism*; D008745:Methylation; D008819:Mice, Nude; D063151:Polycomb Repressive Complex 2 / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D006657:Histones; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; C498409:EZH2 protein, human; D000071221:Enhancer of Zeste Homolog 2 Protein; D063151:Polycomb Repressive Complex 2; D008239:Lysine