Analysis of apoptosis-related gene expression after X-ray irradiation in human tongue squamous cell carcinoma cells harboring wild-type or mutated p53 gene.

Mutations in the p53 tumor suppressor gene have recently been reported to have an impact on clinical trials of several human tumors, including head and neck cancers. To confirm the p53-dependence of X-ray induced apoptosis, we used two cell lines derived from a human squamous cell carcinoma (SAS) with identical genetic backgrounds, except for the p53 gene, which are SAS/mp53 cells with mp53 and SAS/neo cells with wtp53. We previously reported that the radiosensitivity, Caspase-3 activity and apoptosis frequency in SAS/neo cells were clearly high as compared with SAS/mp53 cells. In order to elucidate the expression of apoptosis-related genes after irradiation, we used cDNA array analysis. The expressions of apoptosis-inductive genes, such as DFF40, Caspase-3, Caspase-8, Caspase-9, Caspase-10 and CRADD, were increased by X-ray irradiation in SAS cells with wtp53, but not in SAS cells expressing mp53. These results suggest that the X-ray sensitivity of wtp53 cells may come from the expression of these apoptosis-related genes.