DNA Methyltransferase 1 and DNA Methylation Patterning Contribute to Germinal Center B-Cell Differentiation
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE31671 | GEO | 2011/09/01
SECONDARY ACCESSION(S): PRJNA145385
REPOSITORIES: GEO
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Project description:We performed DNA methylation (HELP) and gene expression profiling in 17 samples of purified Germinal center B cells (GCBs) and Naive B cells (NBC). We performed supervised analysis using HELP data and defined DNA methylation signature differentiting 2 subgroups of B cvells. Study included purification of human B cells form reactive tonsils, DNA purification and DNA methylation analysis using HELP assay.
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Project description:The phenotype of germinal center (GC) B cells includes the unique ability to tolerate rapid proliferation and the mutagenic actions of activation induced cytosine deaminase (AICDA). Given the importance of epigenetic patterning in determining cellular phenotypes, we examined DNA methylation and the role of DNA methyltransferases in the formation of GCs. DNA methylation profiling revealed a marked shift in DNA methylation patterning in GC B cells versus resting/naive B cells. This shift included significant differential methylation of 235 genes, with concordant inverse changes in gene expression affecting most notably genes of the NFkB and MAP kinase signaling pathways. GC B cells were predominantly hypomethylated compared with naive B cells and AICDA binding sites were highly overrepresented among hypomethylated loci. GC B cells also exhibited greater DNA methylation heterogeneity than naive B cells. Among DNA methyltransferases (DNMTs), only DNMT1 was significantly up-regulated in GC B cells. Dnmt1 hypomorphic mice displayed deficient GC formation and treatment of mice with the DNA methyltransferase inhibitor decitabine resulted in failure to form GCs after immune stimulation. Notably, the GC B cells of Dnmt1 hypomorphic animals showed evidence of increased DNA damage, suggesting dual roles for DNMT1 in DNA methylation and double strand DNA break repair.
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Project description:Protection against deadly pathogens requires the production of high-affinity antibodies by B cells, which are generated in germinal centers (GCs). Alteration of the GC developmental program is common in many B cell malignancies. Identification of regulators of the GC response is crucial to develop targeted therapies for GC B cell dysfunctions, including lymphomas. The histone H3 lysine 27 methyltransferase enhancer of zeste homolog 2 (EZH2) is highly expressed in GC B cells and is often constitutively activated in GC-derived non-Hodgkin lymphomas (NHLs). The function of EZH2 in GC B cells remains largely unknown. Herein, we show that Ezh2 inactivation in mouse GC B cells caused profound impairment of GC responses, memory B cell formation, and humoral immunity. EZH2 protected GC B cells against activation-induced cytidine deaminase (AID) mutagenesis, facilitated cell cycle progression, and silenced plasma cell determinant and tumor suppressor B-lymphocyte-induced maturation protein 1 (BLIMP1). EZH2 inhibition in NHL cells induced BLIMP1, which impaired tumor growth. In conclusion, EZH2 sustains AID function and prevents terminal differentiation of GC B cells, which allows antibody diversification and affinity maturation. Dysregulation of the GC reaction by constitutively active EZH2 facilitates lymphomagenesis and identifies EZH2 as a possible therapeutic target in NHL and other GC-derived B cell diseases.
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Project description:We performed DNA methylation (HELP) and gene expression profiling in 69 samples of diffuse large B cell lymphoma (DLBCL). First, by gene expression, two molecular subtypes of DLBCL termed as germinal center B cell-like (GCB) and activated B cell-like (ABC) DLBCL were assigned to the 69 DLBCL cases. Then, we performed supervised analysis using HELP data and defined DNA methylation signature differentiating 2 subgroups of DLBCLs. Keywords: DNA methylation profiling
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Project description:Diffuse Large B-Cell Lymphoma (DLBCL) is the most common aggressive form of non-Hodgkin lymphoma with variable biology and clinical behavior. The current classification does not fully explain the biological and clinical heterogeneity of DLBCLs. In this study we carried out genome-wide DNA methylation profiling of 140 DLBCL samples and 10 normal germinal center B-cells (NGCBs) using the HELP assay and hybridization to a custom Roche NimbleGen promoter array. We defined methylation disruption as a main epigenetic event in DLBCLs and designed a method for measuring the methylation variability of individual cases. We then used a novel approach for unsupervised hierarchical clustering based on the extent of DNA methylation variability. This approach identified 6 clusters (A-F). The extent of methylation variability was associated with survival outcomes, with significant differences in overall and progression-free survival. The novel clusters are characterized by disruption of specific biological pathways like cytokine-mediated signaling, ephrin signaling and pathways associated with apoptosis and cell cycle regulation. In a subset of patients, we profiled gene expression and genomic variation to investigate their interplay with methylation changes. This study is the first to identify novel epigenetic clusters of DLBCLs and their aberrantly methylated genes, molecular associations and survival.
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Project description:Changes in DNA methylation are required for the formation of germinal centers (GC), but the mechanisms of such changes are poorly understood. Activation-induced cytidine deaminase (AID) has been recently implicated recently in DNA demethylation through its deaminase activity coupled with DNA repair. We investigated the epigenetic function of AID in vivo in germinal center B cells (GCB) isolated from wild type (WT) and AID-deficient (Aicda-/-) mice. We determined that the transit of B cells through the GC is associated with marked locus-specific loss of methylation and increased methylation diversity, both of which are lost in Aicda-/- animals. Differentially methylated cytosines (DMCs) between GCB and naïve B cells (NB) are enriched in genes that are targeted for somatic hypermutation (SHM) by AID and these genes form networks required for B cell development and proliferation. Finally, we observed significant conservation of AID-dependent epigenetic reprogramming between mouse and human B cells. ERRBS and RNA-seq of wild type and Aicda knockout murine naive and germinal center B cells. ERRBS of human naive and germinal center B cells
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Project description:We performed DNA methylation (HELP array) and gene expression profiling in 69 samples of diffuse large B cell lymphoma (DLBCL). First, by gene expression, two molecular subtypes of DLBCL termed as "germinal center B cell-like" (GCB) and "activated B cell-like" (ABC) DLBCL were assigned to the 69 DLBCL cases. Then, the supervised analysis using HELP data revealed strikingly different DNA promoter methylation patterns in the two molecular DLBCL subtypes. These data provide epigenetic evidence that the DLBCL subtypes are distinct diseases that utilize different oncogenic pathways.
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Project description:Changes in DNA methylation are required for the formation of germinal centers (GC), but the mechanisms of such changes are poorly understood. Activation-induced cytidine deaminase (AID) has been recently implicated recently in DNA demethylation through its deaminase activity coupled with DNA repair. We investigated the epigenetic function of AID in vivo in germinal center B cells (GCB) isolated from wild type (WT) and AID-deficient (Aicda-/-) mice. We determined that the transit of B cells through the GC is associated with marked locus-specific loss of methylation and increased methylation diversity, both of which are lost in Aicda-/- animals. Differentially methylated cytosines (DMCs) between GCB and naïve B cells (NB) are enriched in genes that are targeted for somatic hypermutation (SHM) by AID and these genes form networks required for B cell development and proliferation. Finally, we observed significant conservation of AID-dependent epigenetic reprogramming between mouse and human B cells.
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