Purpose. It has been reported in several studies that the absence in cancer cells of the p53 tumor suppressor gene, mutations of which are frequently found in bladder cancer, increases their resistance to ionizing radiation. Other studies, however, suggest that mutations of the p53 gene could increase the radiosensitivity of cancer cells, although the evidence is still inconclusive. In the present study, we investigated the relationship between p53 status and radiation response in five different bladder cancer cell lines. Materials and Methods. Five different human bladder cancer cell lines (KK47: with wt- p53, RT4: with wt- p53, T24: with mutated p53, 5637: with mutated p53, UM-UC-3: with mutated p53) were used in the study. Cells were irradiated with 0, 2, 4, 6 or 8 Gy, then trypsinized and re-plated for clonogenic survival assay, quantitative RT-PCR assay, flow-cytometry analysis and TUNEL assay. Results. The clonogenic assay demonstrated that KK47 and RT4 had significantly higher radiosensitivity than other cell lines. Quantitative RT-PCR analysis showed that radiation induced increased expression of p53, Bax, and p21 mRNA in KK47 and RT4. After irradiation, G1 cell-cycle arrest was observed in KK47 and RT4 under flow cytometry analysis, while T24, 5637, and UM-UC-3 showed an increase in the proportion of G2 cells. Increased cell apoptosis was also observed under TUNEL assay in KK47 and RT4, but not in other cell lines.
Conclusions: It was demonstrated that ionizing radiation induces p53-dependent cell apoptosis in bladder cancer cells with wt- p53 but not in those with mutated p53.