Repression of CDK4 elevates expression of let-7c by modulating G1/S cell cycle signaling in NPC. A. Let-7c expression was significantly increased in NPC cells after stable knockown of CDK4 expression. B. Knocking down the expression of CDK4 decreased the CCND1, CDK6, and E2F1 as well as activated p21 expression. C. E2F1 expression was markedly suppressed using specific siRNA-E2F1. D. Knocking down E2F1 by specific siRNA-E2F1 elevated the expression of let-7c.