[PMC free article] [PubMed] [Google Scholar]Wang T, Wei JJ, Sabatini DM, and Lander ES (2014). well as compensatory functions for these acetyltransferases in individual compartments of the germinal center and exploit this notion to document an EP300-dependency in CREBBP-deficient lymphoma cells that can be targeted ANK2 therapeutically. Graphical Abstract INTRODUCTION Diffuse large B cell lymphoma (DLBCL) and follicular lymphoma (FL) are the most common lymphoid malignancies, together accounting for ~60% of B cell lymphoma diagnoses (Swerdlow et al, 2016). Despite the significant progress made in the therapeutic management of these diseases, both remain partially unmet clinical needs. In particular, a substantial portion of DLBCL patients do not accomplish total remission with current first-line chemo-immunotherapeutic methods (Gisselbrecht et al., 2010) and FL, although indolent, is essentially incurable. Moreover, as many as 45% of FL cases transform into a high-grade malignancy, typically a DLBCL (also known as transformed FL or tFL), with dismal overall survival (Montoto et al., 2007). The development of treatments that can eradicate the reservoir of initiating cells responsible for resistance and transformation remains a high priority in the field. Over the past decade, genomic analyses of FL and DLBCL have uncovered highly recurrent somatic mutations and deletions in the histone acetyl-transferase gene (60% of FL and 25% of DLBCL); its paralogue is usually targeted at much lower frequencies (5% of FL and DLBCL) (Chapuy et al., 2018; Morin et al., 2011; Okosun et al., 2014; Pasqualucci et al., 2011a; Pasqualucci et al., 2014; Pasqualucci et al., 2011b; Schmitz et al., 2018). encode for ubiquitously expressed mammalian enzymes that act as global transcriptional co-activators by interacting with more than 400 transcription factors and by catalyzing the modification of lysines on both histone and non-histone proteins in a cell-context-dependent manner (Bannister and Kouzarides, 1996; Bedford et al., 2010; Dancy and Cole, 2015; Goodman and Smolik, 2000; Ogryzko et al., 1996). In germinal center (GC) B cells, the normal counterpart of FL and DLBCL, two critical non-histone substrates of CREBBP- and EP300-mediated acetylation are the tumor suppressor p53, which requires acetylation for its transcriptional activity (Avantaggiati et al., 1997; Gu and Roeder, 1997; Lill et al., 1997), and the proto-oncogene BCL6, a potent transcriptional repressor that regulates the GC reaction and is functionally impaired by this modification (Bereshchenko et al., 2002). Additionally, by catalyzing H3K18 and H3K27 acetylation at promoter and enhancer regions, CREBBP modulates the expression of a selected quantity of genes that are implicated in GC exit including signaling pathways brought on by engagement of the B cell receptor (BCR) and CD40 receptor, the plasma cell regulator IRF4, and antigen processing and presentation Fludarabine Phosphate (Fludara) through the major histocompatibility complex class II (MHC-II) complex (Green et al., 2015; Hashwah et al., 2017; Jiang et al., 2017; Zhang et al., 2017). Of notice, the GC-specific CREBBP transcriptional network encompasses almost all BCL6 direct target genes, suggesting a critical role for this acetyltransferase in opposing the oncogenic activity of BCL6 while Fludarabine Phosphate (Fludara) ensuring the quick activation of programs that sustain terminal differentiation in the GC light zone (LZ) (Jiang et al., 2017; Fludarabine Phosphate (Fludara) Zhang et al., 2017). Mutations of and inactivate the enzymatic function of these proteins by generating truncated forms that lack the histone acetyl-transferase (HAT) domain name or by introducing amino acid changes, also within the HAT domain name, which severely impair their affinity for AcetylCoA (Pasqualucci et al., 2011a). These mutations are acquired at Fludarabine Phosphate (Fludara) an early stage of FL development by a common ancestral clone that subsequently progresses to FLor tFL throughdivergent development(Greenet al., 2015; Okosun et al., 2014; Pasqualucci et al., 2014). Accordingly, CREBBP-mutated B cells have been found in a pre-malignant condition known as FL often togetherwith the hallmark t(14;18) translocation deregulating BCL2 (Schmidt et al., 2018). Mutations in are mono-allelic in 80% of DLBCL and over 50% of FL cases, leaving the residual wild-type (WT) allele expressed (Garca-Ramrez et al., 2017; Pasqualucci et al., 2011a). In mouse models, conditional GC-directed inactivation of in both heterozygosis and homozygosis significantly increases the incidence of Bcl2-driven lymphomas (Jiang et al., 2017; Zhang et al., 2017). Reduced dosage of CREBBP (and EP300) is usually thus thought to facilitate malignant transformation by dysregulating signaling pathways that are important for terminal differentiation and by favoring the constitutive activity of the BCL6 oncogene at the expense of the p53 tumor suppressor. Genetic alterations of and mutations, has revealed a synthetic lethal role for EP300 in CREBBP-mutated cells, where its pharmacologic inhibition exerts anti-proliferative and anti-survival effects, although at very high concentrations of a tool compound with limited potency and selectivity (Ogiwara et al., 2016). Here, we used mouse models where and/or were specifically deleted in GC B cells to explore the relationship between CREBBP and EP300 in.