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Molecular and Cellular Biology, January 2001, p. 400-413, Vol. 21, No. 2
Hospital for Sick Children Research Institute
and Department of Immunology, University of Toronto, Toronto,
Ontario, Canada
Received 31 July 2000/Returned for modification 8 September
2000/Accepted 17 October 2000
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.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.2.400-413.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Irradiation Promotes V(D)J Joining and
RAG-Dependent Neoplastic Transformation in SCID T-Cell
Precursors

*
Corresponding author. Mailing address: Program in
Developmental Biology, Rm. 8104, Hospital for Sick Children Research
Institute, 555 University Ave., Toronto, Ontario M5G 1X8, Canada.
Phone: (416) 813-8810. Fax: (416) 813-8823. E-mail:
guidos{at}sickkids.on.ca.
Present address: Cutaneous Biology Research Center, Massachusetts
General Hospital East, Charlestown, MA 02129.
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