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Irradiation promotes V(D)J joining and RAG-dependent neoplastic transformation in SCID T-cell precursors
C J Williams1, I Grandal, D J Vesprini
1Hospital for Sick Children Research Institute and Department of Immunology, University of Toronto, Toronto, Ontario, Canada.
Abstract:
Defects in the nonhomologous end-joining (NHEJ) pathway of double-stranded DNA break repair severely impair V(D)J joining and selectively predispose mice to the development of lymphoid neoplasia. This connection was first noted in mice with the severe combined immune deficient (SCID) mutation in the DNA-dependent protein kinase (DNA-PK). SCID mice spontaneously develop thymic lymphoma with low incidence and long latency. However, we and others showed that low-dose irradiation of SCID mice dramatically increases the frequency and decreases the latency of thymic lymphomagenesis, but irradiation does not promote the development of other tumors. We have used this model to explore the mechanistic basis by which defects in NHEJ confer selective and profound susceptibility to lymphoid oncogenesis. Here, we show that radiation quantitatively and qualitatively improves V(D)J joining in SCID cells, in the absence of T-cell receptor-mediated cellular selection. Furthermore, we show that the lymphocyte-specific endonuclease encoded by the recombinase-activating genes (RAG-1 and RAG-2) is required for radiation-induced thymic lymphomagenesis in SCID mice. Collectively, these data suggest that irradiation induces a DNA-PK-independent NHEJ pathway that facilitates V(D)J joining, but also promotes oncogenic misjoining of RAG-1/2-induced breaks in SCID T-cell precursors.
Insights
Defects in DNA repair pathways like nonhomologous end-joining (NHEJ) increase lymphoid cancer risk. Irradiation enhances DNA repair in SCID mice, promoting thymic lymphoma by activating a DNA-PK-independent NHEJ pathway.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Defects in nonhomologous end-joining (NHEJ) DNA repair impair V(D)J recombination and predispose to lymphoid cancers.
- Severe combined immunodeficient (SCID) mice with DNA-dependent protein kinase (DNA-PK) mutations develop thymic lymphoma spontaneously at low rates.
- Low-dose irradiation dramatically increases thymic lymphomagenesis frequency and decreases latency in SCID mice without affecting other tumor types.
Purpose of the Study:
- To investigate the mechanistic basis for the selective susceptibility of SCID mice to lymphoid oncogenesis following irradiation.
- To explore how defects in NHEJ confer a profound susceptibility to lymphoid cancers.
Main Methods:
- Utilized a SCID mouse model with DNA-PK deficiency.
- Administered low-dose irradiation to SCID mice.
- Analyzed V(D)J joining in SCID cells post-irradiation.
- Assessed the requirement of recombinase-activating genes (RAG-1 and RAG-2) in radiation-induced lymphomagenesis.
Main Results:
- Irradiation quantitatively and qualitatively improved V(D)J joining in SCID cells, independent of T-cell receptor selection.
- The lymphocyte-specific endonuclease RAG-1/2 was essential for radiation-induced thymic lymphomagenesis in SCID mice.
- Irradiation appears to induce a DNA-PK-independent NHEJ pathway.
Conclusions:
- Irradiation-induced DNA-PK-independent NHEJ facilitates V(D)J joining in SCID mice.
- This pathway also promotes oncogenic misjoining of RAG-1/2-induced DNA breaks in SCID T-cell precursors, leading to thymic lymphoma.
- NHEJ pathway defects confer selective susceptibility to lymphoid oncogenesis.