title: EZH2-mediated epigenetic silencing in germinal center B cells contributes to proliferation and lymphomagenesis.
abstract: EZH2 is the catalytic subunit of the PRC2 Polycomb complex and mediates transcriptional repression through its histone methyltransferase activity. EZH2 is up-regulated in normal germinal center (GC) B cells and is implicated in lymphomagenesis. To explore the transcriptional programs controlled by EZH2, we performed chromatin immunoprecipitation (ChIP-on-chip) in GC cells and found that it binds approximately 1800 promoters, often associated with DNA sequences similar to Droso-phila Polycomb response elements. While EZH2 targets overlapped extensively between GC B cells and embryonic stem cells, we also observed a large GC-specific EZH2 regulatory program. These genes are preferentially histone 3 lysine 27-trimethylated and repressed in GC B cells and include several key cell cycle-related tumor suppressor genes. Accordingly, siRNA-mediated down-regulation of EZH2 in diffuse large B-cell lymphoma (DLBCL) cells resulted in acute cell cycle arrest at the G(1)/S transition and up-regulation of its tumor suppressor target genes. At the DNA level, EZH2-bound promoters are hypomethylated in GC B cells, but many of them are aberrantly hypermethylated in DLBCL, suggesting disruption of normal epigenetic processes in these cells. EZH2 is thus involved in regulating a specific epigenetic program in normal GCs, including silencing of antiproliferative genes, which may contribute to the malignant transformation of GC B cells into DLBCLs.
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY, USA.
authors.forename: Irina
authors.initials: I
authors.lastname: Velichutina
authors.forename: Rita
authors.initials: R
authors.lastname: Shaknovich
authors.forename: Huimin
authors.initials: H
authors.lastname: Geng
authors.forename: Nathalie A
authors.initials: NA
authors.lastname: Johnson
authors.forename: Randy D
authors.initials: RD
authors.lastname: Gascoyne
authors.forename: Ari M
authors.initials: AM
authors.lastname: Melnick
authors.forename: Olivier
authors.initials: O
authors.lastname: Elemento
mesh_terms: D001402:B-Lymphocytes / Q000473:pathology; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D004268:DNA-Binding Proteins / Q000502:physiology*; D000071221:Enhancer of Zeste Homolog 2 Protein; D044127:Epigenesis, Genetic; D020868:Gene Silencing / Q000502:physiology*; D018858:Germinal Center / Q000473:pathology; D006801:Humans; D016403:Lymphoma, Large B-Cell, Diffuse / Q000209:etiology* / Q000473:pathology; D063151:Polycomb Repressive Complex 2; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000502:physiology*; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; D014157:Transcription Factors; C498409:EZH2 protein, human; D000071221:Enhancer of Zeste Homolog 2 Protein; D063151:Polycomb Repressive Complex 2