RAG1 and RAG2 non-core regions are implicated in leukemogenesis and off-target V(D)J recombination in BCR-ABL1-driven B-cell lineage lymphoblastic leukemia.

Abstract

The evolutionary conservation of non-core RAG regions suggests significant roles that might involve quantitative or qualitative alterations in RAG activity. Off-target V(D)J recombination contributes to lymphomagenesis and is exacerbated by RAG2' C-terminus absence in <i>Tp53^-/-</i> mice thymic lymphomas. However, the genomic stability effects of non-core regions from both <i>Rag1^c/c</i> and <i>Rag2^c/c</i> in <i>BCR-ABL1</i>⁺ B-lymphoblastic leukemia (<i>BCR-ABL1</i>⁺ B-ALL), the characteristics, and mechanisms of non-core regions in suppressing off-target V(D)J recombination remain unclear. Here, we established three mouse models of <i>BCR-ABL1</i>⁺ B-ALL in mice expressing full-length RAG (Rag^f/f), core RAG1 (Rag1^c/c), and core RAG2 (Rag2^c/c). The <i>Rag^c/c</i> (<i>Rag1^c/c</i> and <i>Rag2^c/c</i>) leukemia cells exhibited greater malignant tumor characteristics compared to <i>Rag^f/f</i> cells. Additionally, <i>Rag^c/c</i> cells showed higher frequency of off-target V(D)J recombination and oncogenic mutations than <i>Rag^f/f</i>. We also revealed decreased RAG cleavage accuracy in <i>Rag^c/c</i> cells and a smaller recombinant size in <i>Rag1^c/c</i> cells, which could potentially exacerbate off-target V(D)J recombination in <i>Rag^c/c</i> cells. In conclusion, these findings indicate that the non-core RAG regions, particularly the non-core region of RAG1, play a significant role in preserving V(D)J recombination precision and genomic stability in <i>BCR-ABL1</i>⁺ B-ALL.