TP53 and cancer: We also compared the dynamics of p53 protein in USP22−/− and the parent A549 cells after irradiation treatment, the results show only a slightly more p53 protein was found in USP22−/− A549 cells at 6, 12 h post-irradiation (Additional file 1: Figure S6), indicating p53 may not play a crucial role in the process for USP22−/− cancer cells.