量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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DNA double strand breaks (DSBs) are the most deleterious and lethal form of DNA damage. DSBs are rejoined or repaired by two major pathways in mammalian cells: i.e. homologous recombination (HR) and non-homologous end-joining (NHEJ). DNA-PK is a nuclear, serine/threonine protein kinase consisting of three subunits of DNA-PKcs, Ku70 and Ku80, and involved in the NHEJ, V(D)J recombination and modulation of transcription [1]. Cells lacking DNA-PKcs activity are highly sensitive to DSBs-inducing agents such as ionizing radiations [2]. Douglas et al [3] identified 4 phosphorylation sites in the DNA-PKcs protein: i.e. Thr-2609, Ser-2612, Thr-2638 and Thr-2647. These sites were autophosphorylated with own DNA-PKcs. Chan et al [4] demonstrated that autophosphorylation of DNA-PKcs was required for the rejoining of DSBs.
Radiation sensitivities of 31 human esophageal squamous cell carcinoma (ESCC) cell lines were investigated with a colony-formation assay. There was a large variation in radiosensitivity among 31 cell lines. In particular, the radiation sensitivity of one cell line (KYSE190) was distinct from a cluster of radiation sensitivities of other 30 cell lines. In order to understand the mechanism behind this hypersensitivity, we investigated the expression of ATM and DNA-PKcs proteins with a western-blotting method and the phosphorylation of DNA-PKcs with a immunohistochemical staining methd. The phosphorylation of DNA-PKcs was not observed in KYSE190 cells. No mutation was detected in the four phosphorylation sites, but one base change in FAT domain of DNA-PKcs gene was observed. These data seem to indicate that the high radiosensitivity of KYSE 190 cells results from the defect in the autophosphorylation of the DNA-PKcs protein.
雑誌名
Proceedings of the Japan-France Workshop on Radiobiology and Isotopic Imaging
A deficiency in the phosphorylation of DNA-PKcs in a radiosensitive human ESCC cell line
