Host: The Japan Radiation Research Society
To investigate a role of 53BP1 in repair of X-ray induced DNA damage in vertebrate cells, we established, by using hyper-recombinogenic chicken B cell line DT40, a 53BP1 knockout cell line and double knockout cell lines deficient in 53BP1 and either Ku, DNA ligase IV, ATM or Artemis. 53BP1-/- cells showed intact intra-S and G2/M phase checkpoints for X-ray induced DNA damage. We carried out an epistasis analysis, using colony formation assay with cells irradiated in the G1 phase, and revealed that there are at least four sub-pathways in repair of X-ray induced DNA damage: 1) the core non-homologous end-joining (core NHEJ) which is dependent on Ku/DNA-PK, 2) Artemis-dependent pathway which includes ATM, 3) 53BP1-dependent pathway, and 4) DNA ligase IV-independent pathway. In contrast to the core NHEJ and Artemis-dependent pathways, the 53BP1-dependent pathway was resistant to PI-3 kinase inhibitor Wortmannin. Furthermore, Ku70-/-53BP1-/- double mutant cells were more sensitive than Ku70-/- cells to low dose rate X-ray irradiation (0.3 or 0.5 Gy/day), providing further evidence that 53BP1 plays a role in a different pathway from the core NHEJ pathway.
