SMAD4 is a validated target of miR-224. (A) The wild-type and mutated 3′UTR of SMAD4, with the seed region (site1, site2 and site3) and base substitutions (bold). (B) Dual luciferase report assays were performed on HEK 293T cells. Each bar represents mean values ± SD from three independent experiments. **P<0.01.