Suppression of Ku80 Correlates with Radiosensitivity andTelomere Shortening in the U2OS Telomerase-negativeOsteosarcoma Cell Line

Ku70/80 heterodimer is a central element in the nonhomologous end joining (NHEJ) DNA repair pathway,Ku80 playing a key role in regulating the multiple functions of Ku proteins. It has been found that the Ku80 proteinlocated at telomeres is a major contributor to radiosensitivity in some telomerase positive human cancer cells.However, in ALT human osteosarcoma cells, the precise function in radiosensitivity and telomere maintenance isstill unknown. The aim of this study was to investigate the effects of Ku80 depletion in the U2OS ALT cell line cellline. Suppression of Ku80 expression was performed using a vector-based shRNA and stable Ku80 knockdownin cells was verified by Western blotting. U2OS cells treated with shRNA-Ku80 showed lower radiobiologicalparameters (D0, Dq and SF2) in clonogenic assays. Furthermore, shRNA-Ku80 vector transfected cells displayedshortening of the telomere length and showed less expression of TRF2 protein. These results demonstrated thatdown-regulation of Ku80 can sensitize ALT cells U2OS to radiation, and this radiosensitization is related totelomere length shortening.