Aid-Initiated DNA Lesions Are Differentially Processed in Distinct B Cell Differentiation Stages in a Locus-Dependent Manner.

Abstract 2376 Activation induced deaminase (AID) initiates U:G mismatches that are subsequently converted into point mutations or DNA double-stranded breaks. AID-mediated DNA alterations in switch (S) regions at the Igh locus frequently occur in both antigen-stimulated germinal center (GC) B cells and cytokine-activated B cells. To investigate whether AID-initiated U:G lesions are differentially processed in a differentiation stage-specific manner at non-Ig loci to maintain genome stability, we established a knock-in model by inserting an Sg2b region into the first intron of proto-oncogene c-myc . We found that the inserted Sg2b region mutated at an extremely low level and did not enhance genomic instability of c-myc locus in antigen-stimulated GC B cells. In contrast, the inserted Sg2b region mutated more frequently and increased c-myc locus abnormalities in cytokine-activated B cells. Furthermore, uracil glycosylase deficiency led to increased mutation frequency at the c-myc locus. These results reveal that AID-initiated lesions are differentially processed via error-free or error-prone repair in a differentiation stage-specific and locus-dependent manner. Our data might provide mechanistic explanation for differential frequency of AID-mediated genetic alterations in distinct subtypes of common B cell lymphomas. Disclosures: No relevant conflicts of interest to declare.