USP22 and cancer: Apoptosis analysis showed that both 5 and 10 Gy irradiation induced more apoptosis at 48 h post-irradiation in both USP22−/− A549 (Fig. 6a, lower panel) and USP22−/− H1299 (Fig. 6b, lower panel) cancer cells than the parent A549 (Fig. 6a, upper panel) and H1299 (Fig. 6b, upper panel) cancer cells, respectively.