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PAXX promotes KU accumulation at DNA breaks and is essential for end-joining in XLF-deficient mice
Xiangyu Liu1, Zhengping Shao1, Wenxia Jiang1
1Department of Pathology and Cell Biology, College of Physicians and Surgeons, Institute for Cancer Genetics, Columbia University, 1130 Saint Nicholas Avenue, Room 501, New York City, New York 10032, USA.
Abstract:
Non-homologous end-joining (NHEJ) is the most prominent DNA double strand break (DSB) repair pathway in mammalian cells. PAXX is the newest NHEJ factor, which shares structural similarity with known NHEJ factors-XRCC4 and XLF. Here we report that PAXX is dispensable for physiological NHEJ in otherwise wild-type mice. Yet Paxx-/- mice require XLF and Xlf-/- mice require PAXX for end-ligation. As such, Xlf-/-Paxx-/- mice display severe genomic instability and neuronal apoptosis, which eventually lead to embryonic lethality. Despite their structural similarities, only Xlf-/- cells, but not Paxx-/- cells require ATM/DNA-PK kinase activity for end-ligation. Mechanistically, PAXX promotes the accumulation of KU at DSBs, while XLF enhances LIG4 recruitment without affecting KU dynamics at DNA breaks in vivo. Together these findings identify the molecular functions of PAXX in KU accumulation at DNA ends and reveal distinct, yet critically complementary functions of PAXX and XLF during NHEJ.
Insights
PAXX is dispensable for DNA repair in mice, but XLF and PAXX are complementary. Loss of both leads to severe genomic instability and embryonic lethality, revealing their distinct roles in DNA double-strand break repair.
Area of Science:
- Molecular Biology
- Genetics
- Cellular Biology
Background:
- Non-homologous end-joining (NHEJ) is a major DNA double-strand break (DSB) repair pathway in mammals.
- PAXX is a recently identified NHEJ factor with structural similarities to XRCC4 and XLF.
Purpose of the Study:
- To investigate the in vivo function of PAXX in NHEJ.
- To elucidate the distinct and complementary roles of PAXX and XLF in DNA repair.
Main Methods:
- Generation and analysis of knockout mouse models (Paxx-/- and Xlf-/-).
- Assessment of genomic instability and neuronal apoptosis in mutant mice.
- Investigation of kinase dependency and protein recruitment dynamics at DSBs in vitro.
Main Results:
- PAXX is dispensable for NHEJ in wild-type mice but essential for end-ligation in Xlf-/- cells.
- XLF is essential for end-ligation in Paxx-/- cells, and combined deficiency leads to embryonic lethality.
- PAXX promotes KU accumulation at DSBs, while XLF facilitates LIG4 recruitment, with distinct kinase dependencies.
Conclusions:
- PAXX and XLF have distinct yet complementary functions in NHEJ.
- PAXX is crucial for KU recruitment, and XLF is vital for LIG4 recruitment, highlighting their cooperative roles in DSB repair.
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