Rb-E2F signaling is involved in miR-503-regulated G1/S transition. (A) phosphorylation of Rb protein on Ser780 and Ser811 is inhibited by miR-503. 48 h after transfection with the indicated RNA duplex, cells were subjected to Western blot analysis. Rb, total Rb protein; pRb, phosphorylated Rb. (B) effect of miR-503 on the expression of endogenous genes. miR-503 inhibited significantly the expression of CDK6 and the downstream genes of E2F3. Gene expression was examined by Western blot. β-actin, internal control. (C) signaling pathways that regulate the cell cycle control in HCC involving miR-503.