A genome guardian role for RAG-mediated restriction of repair pathway choice (42.10)

Abstract

Abstract The V(D)J recombinase, which includes the RAG 1/2 proteins, retains broken DNA intermediates in a post-cleavage complex, restricting repair to the canonical nonhomologous end joining (NHEJ) pathway. Previously, we described a C-terminal RAG2 truncation mutant that ablates repair pathway restriction, allowing RAG-generated DNA double strand breaks (DSBs) to access alternative NHEJ, an error-prone pathway characterized by junctional microhomologies and associated with oncogenic chromosome translocations. In “core” RAG2 knock in mice, which lack RAG2’s dispensable C-terminus, V(D)J junctions show characteristics of alternative NHEJ and thymocytes display genomic instability. RAG2 core/core p53-/- mice rapidly succumb to thymic lymphomas bearing complex chromosome translocations involving antigen receptor loci. Because the C-terminus of RAG2 contains multiple regulatory motifs, it remained unclear whether pathway choice restriction per se contributes to genomic stability. We now show that deleting or altering a C-terminal acidic “hinge” region destabilizes the post-cleavage complex, allows repair by alternative NHEJ, and promotes genomic instability. These data identify a novel regulatory region in RAG2 and show that the post-cleavage complex plays a genome guardian role by restricting repair pathway choice.