Inactivation of CREBBP expands the germinal center B cell compartment, down-regulates MHCII expression and promotes DLBCL growth

Abstract

The genes encoding the histone acetyl-transferases (HATs) CREB binding protein (CREBBP) and EP300 are recurrently mutated in the activated B cell-like and germinal center (GC) B cell-like subtypes of diffuse large B cell lymphoma (DLBCL). Here, we introduced a patient mutation into a human DLBCL cell line using CRISPR and deleted and in the GC B cell compartment of mice. CREBBP-mutant DLBCL clones exhibited reduced histone H3 acetylation, expressed significantly less MHCII, and grew faster than wild-type clones in s.c. and orthotopic xenograft models. Mice lacking Crebbp in GC B cells exhibited hyperproliferation of their GC compartment upon immunization, had reduced MHCII surface expression on GC cells, and developed accelerated MYC-driven lymphomas. Ep300 inactivation reproduced some, but not all, consequences of Crebbp inactivation. MHCII deficiency phenocopied the effects of CREBBP loss in spontaneous and serial transplantation models of MYC-driven lymphomagenesis, supporting the idea that the mutational inactivation of CREBBP promotes immune evasion. Indeed, the depletion of CD4 T cells greatly facilitated the engraftment of lymphoma cells in serial transplantation models. In summary, we provide evidence that both HATs are bona fide tumor suppressors that control MHCII expression and promote tumor immune control; mutational inactivation of CREBBP, but not of EP300, has additional cell-intrinsic engraftment and growth-promoting effects.

The IL ‐6 signaling complex is a critical driver, negative prognostic factor, and therapeutic target in diffuse large B‐cell lymphoma

“…AID ‐Cre × Il6ra fl/fl mice were additionally crossed with a mouse strain that expresses MYC under the control of the immunoglobulin heavy chain enhancer ( Emu ‐MYC) (Adams et al , ). Immunization of the resulting offspring induced GC formation, AID ‐Cre activity, and Il6ra deletion in GC B cells as reported previously (Hashwah et al , ). In the absence of the MYC transgene, none of the mice of this line developed lymphomas.…”

Germinal center‐derived lymphomas: The darkest side of humoral immunity

“…CD40 engagement with its ligand (CD40L) F I G U R E 5 Immune surveillance evasion. Mono-and bi-allelic deletions of CREBBP increase the proportion of GC B cells and these GC B cells feature reduced MHC II protein levels 164. Escape: Loss of MHC II expression caused by CIITA or CREBBP inactivation prevents antigen presentation to CD4+ T cells.…”

Molecular pathogenesis of germinal center‐derived B cell lymphomas

“…Moreover, CREBBP-mediated acetylation is an essential requirement for the activation of the p53 tumor suppressor, which is itself a target of BCL6. 52,86 A comprehensive characterization of the transcriptional network modulated by CREBBP in the GC has been recently obtained and revealed a preferential enrichment in GC LZ signature genes, 84,85 including components of the BCR and CD40 signaling cascade, master regulators of terminal differentiation, the CIITA transactivator, multiple MHC-class II loci, and additional genes involved in antigen presentation/processing 84,85,87 (Figure 3). CREBBP therefore appears to be particularly important in the decision making of B cells that exit the GC.…”

“…176,177 Of note, the CIITA enhancer is bound and acetylated by CREBBP in GC B cells, and expression of MHC-II was significantly reduced in mice with conditional GCspecific deletion of Crebbp, as well as in human FL samples harboring CREBBP mutations. 84,85,87,139 Thus, genetic inactivation of CREBBP may represent an important contributor to this phenotype.…”

“…The frequent observation of concurrent HLA-I and CD58 loss in the same cases suggests that tumors have co-selected these lesions to escape both CTL-mediated and NK cell-mediated immune surveillance mechanisms 173. Of note, the CIITA enhancer is bound and acetylated by CREBBP in GC B cells, and expression of MHC-II was significantly reduced in mice with conditional GCspecific deletion of Crebbp, as well as in human FL samples harboring CREBBP mutations 84,85,87,139. The underlying mechanism involves in part the genetic inactivation of CIITA, which is targeted by ASHM in 23% of cases, and has been occasionally implicated in promiscuous chromosomal rearrangements leading to gene disruption or to dominant negative fusion proteins (3% of cases) 176,177.…”