Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 109, Issue 10, Pages 3903-3908Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1120160109
Keywords
Ataxia-Telangiectasia-Mutated; XRCC4-like factor; classical nonhomologous end joining
Categories
Funding
- National Institutes of Health/National Cancer Institute [CA158073]
- St. Baldrick Foundation
- John Driscoll Jr. Children's Medical Award
- Leukemia and Lymphoma Society
- Pathobiology and Molecular Medicine graduate program
- Columbia University
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Nonhomologous end joining (NHEJ), a major pathway of DNA double-strand break (DSB) repair, is required during lymphocyte development to resolve the programmed DSBs generated during Variable, Diverse, and Joining [V(D)J] recombination. XRCC4-like factor (XLF) (also called Cernunnos or NHEJ1) is a unique component of the NHEJ pathway. Although germ-line mutations of other NHEJ factors abrogate lymphocyte development and lead to severe combined immunodeficiency (SCID), XLF mutations cause a progressive lymphocytopenia that is generally less severe than SCID. Accordingly, XLF-deficient murine lymphocytes show no measurable defects in V(D) J recombination. We reported earlier that ATM kinase and its substrate histone H2AX are both essential for V(D) J recombination in XLF-deficient lymphocytes, despite moderate role in V(D) J recombination in WT cells. p53-binding protein 1 (53BP1) is another substrate of ATM. 53BP1 deficiency led to small reduction of peripheral lymphocyte number by compromising both synapse and end-joining at modest level during V(D) J recombination. Here, we report that 53BP1/XLF double deficiency blocks lymphocyte development at early progenitor stages, owing to severe defects in end joining during chromosomal V(D) J recombination. The unrepaired DNA ends are rapidly degraded in 53BP1(-/-)XLF(-/-) cells, as reported for H2AX(-/-)XLF(-/-) cells, revealing an end protection role for 53BP1 reminiscent of H2AX. In contrast to the early embryonic lethality of H2AX(-/-)XLF(-/-) mice, 53BP1(-/-)XLF(-/-) mice are born alive and develop thymic lymphomas with translocations involving the T-cell receptor loci. Together, our findings identify a unique function for 53BP1 in end-joining and tumor suppression.
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