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Objective: Radiosensitivity is mainly determined by the number of DNA double-strand breaks (DSBs) induced by ionizing radiation and the extent of its repair. The DNA-PK complex formation is one of the major pathways by which the mammalian cells respond to DSBs repairing. Our previous study suggested that CNE1 is more radioresistant than CNE2. This study was designed to answer whether the radiosensitive difference of Nasopharyngeal Carcinoma cell lines CNE 1/CNE2 was related to the expression and localization of Ku70/Ku80/DNA-PKcs. Methods: Immunohistochemistry was performed to detect the subcellular localization of Ku70/Ku80/DNA-PKcs in NPC cells lines CNE1 and CNE2. Western-blot was used to determine the expression of Ku protein in total extract of CNE1 and CNE2 and semi-quantitative assay of protein expression was performed to estimate the optic density (OD) value of each band using automatic image analysis system. Results:Ku70/Ku80/DNA-PKcs primarily located in the nuclei. A part of nucleolus in CNE1 and CNE2 showed positive dyeing of DNA-PKcs. Protein expression of Ku70/Ku80/DNA-PKcs was detected in CNE1 and CNE2, and the integral optical density (IOD) of Ku70 protein was 22.03 ± 7.56 and 19.98 ± 6.04 respectively (t=0.021, P＞0.05), while the IODs of Ku80 protein in the two cell lines were 33.44 ± 12.87 and 28.98 ± 9.24 respectively (t=0.24, P＞0.05), and the IODs of DNA-PKcs protein were 45.03 ± 1.77 and 40.87 ± 4.19 (t=1.58, P＞0.05). The above results suggested that the basic expression of Ku70/Ku80/DNA-PKcs had no statistic difference between the different radiosensitive NPC cell lines CNE1 and CNE2.Conclusion: The variation of radiosensitivity in NPC cell lines CNE1 and CNE2 has no obviously correlation with the subcellular localization and basic expression of DNA-PK protein. So we presumed that the difference of radiosensitivity between CNE1 and CNE2 may be on account of some other factors than subcellular localization and basic expression of DNA-PK.