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Gene expression profile analysis of germinal center B cells from conditional Crebbp knockout mice and littermate controls

ABSTRACT: Inactivating mutations of the gene encoding for the CREBBP acetyltransferase are highly frequent in diffuse large B cell lymphoma (DLBCL, 30% of cases) and follicular lymphoma (FL, 60% of cases), the two most common cancers derived from thegerminal-center (GC). However, the role of CREBBP inactivation in lymphomagenesisremains unclear. Using functional epigenomics and mouse genetics, here we definethe program modulated by CREBBP in primary human GC B cells and show thatCREBBP regulates enhancer/super-enhancer networks, with specific roles in GC/post-GC cell fate decisions. Conditional GC-specific deletion of Crebbp in the mouseperturbs the expression of a limited set of genes involved in the regulation of signaltransduction (BCR, TLR and CD40), lineage specification (NF-κB and BCL6) andterminal B cell differentiation (PRDM1, IRF4). Consistently, Crebbp-deficient B cellsexhibit proliferative advantage and show impaired plasma cell differentiation. WhileGC-specific loss of Crebbp was not sufficient to initiate malignant transformation,compound Crebbp-haploinsufficient/BCL2-transgenic mice, mimicking the genetics ofFL and DLBCL, display an increased incidence of clonal lymphoid malignanciesrecapitulating the features of the human diseases. These findings establish CREBBPas a haploinsufficient tumor suppressor gene in GC B cells and provide insights intothe mechanisms and targes by which loss of CREBBP contributes to lymphomagenesis.

ORGANISM(S): Mus musculus

PROVIDER: GSE88799 | GEO | 2017/01/11

SECONDARY ACCESSION(S): PRJNA348677

REPOSITORIES: GEO

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Project description:Somatic mutations of the MLL2 methyltransferase gene represent a common genetic lesion in multiple cancer types. In diffuse large B cell lymphoma (DLBCL) and follicular lymphoma (FL) (collectively, over 70% of all lymphoma diagnoses), these mutations are highly recurrent and appear early during transformation, possibly in pre-malignant precursors. Here we show that FL- and DLBCL-associated MLL2 mutations impair its enzymatic activity and lead to diminished global H3K4 methylation in normal germinal-center (GC) B cells and DLBCL, consistent with the enrichment of MLL2 binding at enhancer and promoter regions marked by mono- and tri-methylation. Conditional deletion of Mll2 early during B cell development, but not after initiation of the GC reaction, leads to increased percentages and numbers of GC B cells, which feature a distinct transcriptional profile defined by the enrichment of cell-cycle regulatory and B-cell receptor signaling genes. Consistently, Mll2-deficient B cells exhibit proliferative advantage and accumulation in the S phase of the cell cycle, which is influenced by the number of cell divisions. While GC-specific loss of Mll2 was not sufficient to initiate malignant transformation, compound Mll2-deficient/BCL2-transgenic mice displayed an increased incidence of clonal lymphoproliferations resembling the features of human FL and DLBCL. These findings suggest that early MLL2 loss favors BCL2-induced lymphomagenesis by remodeling the epigenetic landscape of the cancer precursor cells. Eradication of MLL2-deficient cells may represent a rational therapeutic approach targeting early tumorigenic events. Murine germinal center B cells (B220+CD95+PNA+) were sorted from the spleen of conditional Mll2 knock-out, Mll2 heterozygous and Mll2 wild type mice (crossed with CD19-Cre or Cg1-Cre deletor strains) and sacrificed at day 12 after immunization with sheep red blood cells (SRBC)(n=3 mice per genotype). Total RNA was extracted from single cell suspensions and processed according to the Ovation RNA Amplification System and Encore® Biotin Module protocols (both from NuGEN). Samples were analyzed on Affymetrix Mouse Genome 430 2.0 arrays.

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Gene expression profile analysis of germinal center B cells from conditional Crebbp knockout mice and littermate controls

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