Novel ubiquitination-like modifications that regulate recombination of immunoglobulin loci gene segments leading to antibody diversification (IRM8P.711)

Abstract

Abstract Programmed DNA mutagenesis events in the immunglobulin (Ig) loci of B cells utilize the common and conserved mechanism of ubiquitination of proteins prior to proteasomal degradation to generate the required antigen-receptor diversity. Recombinase proteins RAG1 and RAG2, required for V(D)J recombination, and activation-induced cytidine deaminase (AID), an essential mutator protein for catalyzing somatic hypermutation (SHM) and class switch recombination (CSR), are regulated by various ubiquitination events affecting protein stability and activity. AID associates with transcribing RNA polII and non-coding RNA processing complex RNA exosome to introduce DNA lesions in the IgH locus that are required for CSR and SHM. Failure in regulating AID’s DNA mutagenic activity is considered as a primary cause for B cell lymphomagenesis, especially Diffuse Large B cell Lymphoma (DLBCL). Here, we present our recent observations that demonstrate that the AID/RNA exosome/RNA polymerase II complex is regulated by ubiquitination and neddylation modifications. Using proteomics based experiments we have identified AID associated protein factors that promote ubiquitin-like modification of AID/RNA polII/RNA exosome complex. Using various biochemical assays, knockdown experiments and genetically mutated mouse models, we demonstrate the ubiquitin-like modification of AID-protein complex is important for regulating AID activity during CSR and overall maintenance of B cell genomic integrity.