ATM and nasopharyngeal carcinoma: EdU staining was applied to measure the effect of E2F-1 on the proliferation of DDP-resistant NPC cells via regulation of ATM (Fig. 5A, B) and compared with the blank group; CNE2/DDP and HNE1/DDP cells decreased proliferation after transfection with E2F-1 shRNAs but increased proliferation with ATM lentiviral activation particles (both P < 0.05), while those in the E2F-1 shRNA#1 + ATM group and E2F-1 shRNA#2 + ATM group showed no significant difference (P > 0.05).