Deficiency in nuclear accumulation of G22p1 and Xrcc5 proteins in hyper-radiosensitive Long-Evans Cinnamon (LEC) rat cells after X irradiation.
The DNA-dependent protein kinase (DNA-PK) complex has been implicated in the repair of DNA double-strand breaks (DSBs). DNA-PK is a heterotrimeric protein complex comprised of two components: a large catalytic subunit, Prkdc, with serine/threonine kinase activity and a DNA-targeting component, G22p1 and Xrcc5. In previous report, we showed that approximately 80% of the G22p1 and Xrcc5 proteins were observed in the cytoplasm of rat fibroblasts, and that nuclear translocation of the proteins from the cytoplasm is important for the repair of DNA DSBs. In the present study, we showed that nuclear accumulation of the G22p1 and Xrcc5 proteins was not observed in fibroblasts from a mutant strain of Long-Evans Cinnamon (LEC) rat that has an enhanced radiosensitivity and a reduced level of repair of DSBs after X irradiation. Nuclear translocation of the proteins was observed in both LEC rat cells and control rat cells with normal radiosensitivity at 5 min after X irradiation. Although high levels of G22p1 and Xrcc5 proteins were observed in the nuclei of control rat cells until 60 min postirradiation, the amounts of the proteins decreased rapidly in the nuclei of LEC rat cells in the first 10 min after X irradiation. These findings suggest that there are some defects in maintaining the levels of G22p1 and Xrcc5 proteins in the nuclei of LEC rat cells. An analysis of fibroblasts from backcross rats showed that the deficiency in nuclear accumulation of G22p1 and Xrcc5 proteins is genetically linked to enhanced radiosensitivity. Since the nucleotide sequences of the G22p1 and Xrcc5 genes of the LEC rats coincided with those of the control rats, the deficiency in nuclear accumulation may not be caused by mutations of the G22p1 and Xrcc5 proteins.
Okui
Toyo
T
Hokkaido Institute of Public Health, Sapporo 060-0819, Japan.
Endoh
Daiji
D
Kon
Yasuhiro
Y
Hayashi
Masanobu
M
D021581:Active Transport, Cell Nucleus / Q000528:radiation effects*; D000818:Animals; D034961:Antigens, Nuclear; D002467:Cell Nucleus / Q000502:physiology / Q000528:radiation effects*; D002478:Cells, Cultured; D004249:DNA Damage; D004265:DNA Helicases; D004260:DNA Repair / Q000528:radiation effects; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000528:radiation effects*; D005347:Fibroblasts / Q000378:metabolism / Q000528:radiation effects; D005456:Fluorescent Dyes; D000072200:Ku Autoantigen; D009687:Nuclear Proteins / Q000378:metabolism* / Q000528:radiation effects*; D011836:Radiation Tolerance / Q000528:radiation effects*; D051381:Rats; D020332:Rats, Inbred LEC; D014965:X-Rays
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D005456:Fluorescent Dyes; D009687:Nuclear Proteins; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; C000606511:Xrcc6 protein, rat; D000072200:Ku Autoantigen