DNA ligase IV-deficient cells are more resistant to ionizing radiation in the absence of Ku70: Implications for DNA double-strand break repair

AUTOR(ES)

Adachi, Noritaka

FONTE

The National Academy of Sciences

RESUMO

Vertebrate cells have evolved two major pathways for repairing DNA double-strand breaks (DSBs), homologous recombination (HR) and nonhomologous DNA end-joining (NHEJ). To investigate the role of DNA ligase IV (Lig4) in DSB repair, we knocked out the Lig4 gene (LIG4) in the DT40 chicken B-lymphocyte cell line. The LIG4−/− cells showed a marked sensitivity to X-rays, bleomycin, and VP-16 and were more x-ray-sensitive in G1 than late S or G2/M, suggesting a critical role of Lig4 in DSB repair by NHEJ. In support of this notion, HR was not impaired in LIG4−/− cells. LIG4−/− cells were more x-ray-sensitive when compared with KU70−/− DT40 cells, particularly at high doses. Strikingly, however, the x-ray sensitivity of KU70−/−/LIG4−/− double-mutant cells was essentially the same as that of KU70−/− cells, showing that Lig4 deficiency has no effect in the absence of Ku. These results indicate that Lig4 is exclusively required for the Ku-dependent NHEJ pathway of DSB repair and that other DNA ligases (I and III) do not substitute for this function. Our data may explain the observed severe phenotype of Lig4-deficient mice as compared with Ku-deficient mice.

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