Abstract
[Purpose] It is known that Ku70 protein, a subunit of DNA-dependent protein kinase, plays an important role in a repair of DNA double strand breaks (DSB). We have reported that more than 70% of Ku70 proteins existed in the cytoplasm compartment of unirradiated fibroblasts of normal rat and Ku70 protein translocated into nuclei after X-irradiation. The translocation into nuclei is necessary for DSB repair. In contrast, substantially all Ku70 proteins were found in the nuclei of unirradiated and irradiated human fibroblasts. In this study we investigated the localization of Ku70 proteins in unirradiated and X-irradiated fibroblasts derived from various mammalian species. [Materials and Methods] Fibroblasts from 5 primates and 10 non-primates were subjected to immunofluorescence observation of Ku70 protein using conforcal laser microscopy with and without X-irradiation (4 Gy). [Results and Discussion] In the fibroblasts from all primates, substantially all Ku70 proteins were found in the nuclei of both unirradiated and irradiated cells. In contrast, more than 50% of Ku70 proteins were found in the cytoplasm of unirradiated fibroblasts other than primate cells. Most of Ku 70 proteins were also found in the nuclei of the non-primate cells at 20 min post-irradiation. These results suggest that radiation-induced nuclear translocation occured in the non-primate cells and initial stage of DSB repair are different between primate cells and non-primate cells.
