@article{oai:repo.qst.go.jp:00044605,
 author = {Okayasu, Ryuichi and Okada, Maki and Okabe, Atsushi and Noguchi, Miho and Takakura, Kaoru and Takahashi, Sentaro and 岡安 隆一 and 岡田 真希 and 岡部 篤史 and 野口 実穂 and 高倉 かほる and 高橋 千太郎},
 issue = {1},
 journal = {Radiation Research},
 month = {Jan},
 note = {Human and rodent cells proficient and deficient in non-homologous end joining (NHEJ) were irradiated with X rays, 70 keV/mum carbon ions, and 200 keV/mum iron ions, and the biological effects on these cells were compared. For wild-type CHO and normal human fibroblast (HFL III) cells, exposure to iron ions yielded the lowest cell survival, followed by carbon ions and then X rays. NHEJ-deficient xrs6 (a Ku80 mutant of CHO) and 180BR human fibroblast (DNA ligase IV mutant) cells showed similar cell survival for X and carbon-ion irradiation (RBE = approximately 1.0). This phenotype is likely to result from a defective NHEJ protein because xrs6-hamKu80 cells (xrs6 cells corrected with the wild-type KU80 gene) exhibited the wild-type response. At doses higher than 1 Gy, NHEJ-defective cells showed a lower level of survival with iron ions than with carbon ions or X rays, possibly due to inactivation of a radioresistant subpopulation. The G(1) premature chromosome condensation (PCC) assay with HFL III cells revealed LET-dependent impairment of repair of chromosome breaks. Additionally, iron-ion radiation induced non-repairable chromosome breaks not observed with carbon ions or X rays. PCC studies with 180BR cells indicated that the repair kinetics after exposure to carbon and iron ions behaved similarly for the first 6 h, but after 24 h the curve for carbon ions approached that for X rays, while the curve for iron ions remained high. These chromosome data reflect the existence of a slow NHEJ repair phase and severe biological damage induced by iron ions. The auto-phosphorylation of DNA-dependent protein kinase catalytic subunits (DNA-PKcs), an essential NHEJ step, was delayed significantly by high-LET carbon- and iron-ion radiation compared to X rays. This delay was further emphasized in NHEJ-defective 180BR cells. Our results indicate that high-LET radiation induces complex DNA damage that is not easily repaired or is not repaired by NHEJ even at low radiation doses such as 2 Gy.},
 pages = {59--67},
 title = {Repair of DNA damage induced by accelerated heavy ions in mammalian cells proficient and deficient in the Non-homologous End-joining pathway},
 volume = {165},
 year = {2006}
}