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

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. Overall design: Murine germinal center B cells (B220+CD95+PNA+) were sorted from the spleen of conditional Crebbp knock-out, Crebbp heterozygous and Crebbp wild type mice (crossed with the Cg1-Cre deletor strain) and sacrificed at day 12 after immunization with sheep red blood cells (SRBC)(n=4WT, 5HET and 5KO). 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.