E2F1 and nasopharyngeal carcinoma: The expression of the cycle-related genes cyclin E1 and cyclin-dependent kinase 2 (CDK2) in DDP-resistant NPC cells was further detected, and the results (Fig. 4B) showed that compared to the control shRNA group, the expression of cyclin E1 and CDK2 was downregulated after the inhibition of E2F-1 but upregulated after ATM overexpression (all P < 0.05).