AID-associated DNA repair pathways regulate malignant transformation in a murine model of BCL6-driven diffuse large B-cell lymphoma

Abstract

• The combined effects of AIDassociated base excision and MMR delay the development of BCL6-driven DLBCL.• UNG single deficiency prevents the development of BCL6-driven DLBCL.Somatic hypermutation and class-switch recombination of the immunoglobulin (Ig) genes occur in germinal center (GC) B cells and are initiated through deamination of cytidine to uracil by activation-induced cytidine deaminase (AID). Resulting uracil-guanine mismatches are processed by uracil DNA glycosylase (UNG)-mediated base-excision repair and MSH2-mediated mismatch repair (MMR) to yield mutations and DNA strand lesions.Although off-target AID activity also contributes to oncogenic point mutations and chromosome translocations associated with GC and post-GC B-cell lymphomas, the role of downstream AID-associated DNA repair pathways in the pathogenesis of lymphoma is unknown. Here, we show that simultaneous deficiency of UNG and MSH2 or MSH2 alone causes genomic instability and a shorter latency to the development of BCL6-driven diffuse large B-cell lymphoma (DLBCL) in a murine model. The additional development of several BCL6-independent malignancies in these mice underscores the critical role of MMR in maintaining general genomic stability. In contrast, absence of UNG alone is highly protective and prevents the development of BCL6-driven DLBCL. We further demonstrate that clonal and nonclonal mutations arise within non-Ig AID target genes in the combined absence of UNG and MSH2 and that DNA strand lesions arise in an UNG-dependent manner but are offset by MSH2. These findings lend insight into a complex interplay whereby potentially deleterious UNG activity and general genomic instability are opposed by the protective influence of MSH2, producing a net protective effect that promotes immune diversification while simultaneously attenuating malignant transformation of GC B cells. (Blood. 2016;127(1):102-112) Introduction Acquired somatic mutations and chromosome translocations are a hallmark of cancer that arise as a pathological result of a DNA repair response to a genotoxic event.1 In contrast, the introduction of nontemplated nucleotides and DNA double-strand breaks (DSBs) is part of the normal developmental program in germinal center (GC) B cells. Somatic hypermutation (SHM) and class-switch recombination (CSR) of the immunoglobulin (Ig) genes promotes antibody diversification in GC B cells, but the nature of these genetic remodeling events makes these cells uniquely vulnerable to malignant transformation.2 Numerous types of B-cell malignancies arise from GC and post-GC B cells including diffuse large B-cell lymphoma (DLBCL), Burkitt lymphoma, follicular lymphoma (FL), lymphoplasmacytic lymphoma, multiple myeloma, and Hodgkin lymphoma. 3 SHM and CSR are both initiated by activation-induced cytidine deaminase (AID), 4 a GC B-cell enzyme that lacks strict target specificity and is also able to introduce mutations and DSBs into non-Ig genes throughout the genome.5-12 A role for AID in lymphomagenesis is supported by the presence of cha...

UNG protects B cells from AID-induced telomere loss

“…Thus, our results predict that UNG deficiency could in fact protect from GC-derived B cell lymphoma. Indeed, a recent study found that UNG deficiency protected Iμ-HABcl6 mice from DLBCL ( Gu et al, 2016 ), which was previously shown to be AID dependent in that mouse model ( Pasqualucci et al, 2008 ). In contrast, Iμ-HABcl6 Ung −/− Msh2 −/− and Iμσ-HABcl6 Msh2 −/− mice developed DLBCL faster than Iμ-HABcl6 mice ( Gu et al, 2016 ).…”

TEOA Inhibits Proliferation and Induces DNA Damage of Diffuse Large B-Cell Lymphoma Cells Through Activation of the ROS-Dependent p38 MAPK Signaling Pathway

“…DLBCL is a heterogeneous disease characterized by high levels of genomic instability (Barlow et al, 2013), and activation of DNA damage repair pathways, including the activation of nucleotide excision DNA repair (NER) and DNA damage response kinases (Shaheen et al, 2011;Gu et al, 2015). Studies have shown that inhibition of the process of DNA damage repair, such as inhibitors of kinase WEE1, could effectively prevent the progress of DLBCL (Knittel et al, 2018;Jong et al, 2020).…”

Optimized high‐fidelity 3DPCR to assess potential mitochondrial targeting by activation‐induced cytidine deaminase

“…Analysis of mutation frequency and hotspot enrichment was performed as previously described [3,25]. Statistical comparison of mutation frequencies was performed using Fisher's exact test (one-tailed), and the significance of AID hotspot and CpG motif enrichment was assessed using the binomial test.…”