Radioresistance in a tumour cell line correlates with radiation inducible Ku 70/80 end-binding activity

PURPOSE: The aims of the present study were to better understand the role of Ku80, which is involved in double-strand break repair in mammalian cells in themechanism of radiation resistance and to verify the possibility of increasingcell radiosensitivity by targeted inhibition of Ku autoantigen 80 (Ku 80).MATERIALS AND METHODS: Western blot and electrophoretic mobility shift assay (EMSA) were performed on the human bladder carcinoma cell line RT112(radioresistant) and on the human colorectal carcinoma cell line SW48(radiosensitive) to assess the expression levels of DNA-dependent protein kinase(DNA-PK) components and the DNA-binding activity of the Ku 70/80 heterodimerafter exposure to radiation, respectively. Ku 80 silencing was carried out withthe use of small interfering RNA (siRNA). RESULTS: Greater differences in theDNA-binding activity of Ku 70/80 and Ku 80 phosphorylation level were observed inRT112 as compared to SW48 after X-ray treatment. There is no correlation betweenKu expression and DNA-binding activity at lower doses. A significant increase innuclear Ku 80 expression was observed one hour after the exposure, only at thehigher doses, while the DNA-PK catalytic subunits (DNA-PKcs) and Ku 70 levels didnot change significantly. Inhibition of Ku 80 expression by siRNA inducedradiosensitivity in the RT112 cell line. CONCLUSIONS: Our data demonstrate thatin a bladder tumour cell line up-regulation of Ku end-binding activity withoutany marked change in Ku expression underlie radiation resistance