Dynamics of delayed p53 mutations in mice given whole-body irradiation at 8 weeks

Purpose: Ionizing irradiation might induce delayed genotoxic effects in a p53-dependent manner. However, a few reports have shown a p53 mutation as a delayed effect of radiation. In this study, we investigated the p53 gene mutation by the translocation frequency in chromosome 11, loss of p53 alleles, p53 gene methylation, p53 nucleotide sequence, and p53 protein expression/phosphorylation in p53 ^+/+ and p53 ^+/- mice after irradiation at a young age. Methods and Materials: p53 ^+/+ and p53 ^+/- mice were exposed to 3 Gy of whole-body irradiation at 8 weeks of age. Chromosome instability was evaluated by fluorescence in situ hybridization analysis. p53 allele loss was evaluated by polymerase chain reaction, and p53 methylation was evaluated by methylation-specific polymerase chain reaction. p53 sequence analysis was performed. p53 protein expression was evaluated by Western blotting. Results: The translocation frequency in chromosome 11 showed a delayed increase after irradiation. In old irradiated mice, the number of mice that showed p53 allele loss and p53 methylation increased compared to these numbers in old non-irradiated mice. In two old irradiated p53 ^+/- mice, the p53 sequence showed heteromutation. In old irradiated mice, the p53 and phospho-p53 protein expressions decreased compared to old non-irradiated mice. Conclusion: We concluded that irradiation at a young age induced delayed p53 mutations and p53 protein suppression.