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53BP1 facilitates long-range DNA end-joining during V(D)J recombination
Simone Difilippantonio1, Eric Gapud, Nancy Wong
1Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-1360, USA.
Nature
|October 22, 2008
Summary
53BP1 protein is crucial for DNA repair during V(D)J recombination in lymphocytes. Its absence causes coding end degradation and genomic instability, leading to T-cell defects and lymphopenia.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Variable, diversity and joining (V(D)J) recombination and class-switch recombination are critical immune processes relying on non-homologous end joining (NHEJ) pathways for DNA double-strand break repair.
- 53BP1 (p53-binding protein 1) is a key DNA-damage-response protein recruited to double-strand break sites, involved in ATM, H2AX, and MDC1-dependent pathways.
- A previously identified 53BP1-dependent NHEJ pathway is essential for class-switch recombination but not V(D)J recombination.
Purpose of the Study:
- To investigate the role of 53BP1 in the joining phase of V(D)J recombination.
- To characterize the specific defects in V(D)J recombination occurring in the absence of 53BP1.
- To elucidate the broader function of 53BP1 in maintaining genomic stability during DNA joining processes.
Main Methods:
- Analysis of V(D)J recombination in 53BP1-deficient lymphocytes.
- Assessment of DNA double-strand break repair intermediates and junctions.
- Evaluation of lymphocyte apoptosis and T-cell receptor alpha locus integrity.
- Investigation of the impact of impaired apoptotic checkpoints on lymphocyte propagation.
Main Results:
- 53BP1 deficiency leads to a previously unrecognized defect in the joining stage of V(D)J recombination, distinct from other NHEJ-related deficiencies.
- Absence of 53BP1 results in impaired distal V-DJ joining, extensive degradation of unrepaired coding ends, and episomal signal joint reintegration.
- These defects cause lymphocyte apoptosis, loss of T-cell receptor alpha locus integrity, and lymphopenia.
- Further compromising the apoptotic checkpoint exacerbates the propagation of lymphocytes with antigen receptor breaks.
Conclusions:
- 53BP1 plays a critical, previously unrecognized role in the joining phase of V(D)J recombination.
- 53BP1 is essential for preventing degradation of coding ends and maintaining genomic integrity during long-range DNA joining.
- These findings suggest a more general role for 53BP1 in safeguarding genomic stability across different DNA repair contexts.
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