miR-3690 suppressed DKK3 expression by directly targeting its 3′-UTR and altered levels of proteins related to cell proliferation and cell cycle in K1 cells. (A) Predicted miR-3690 target sequence in the 3′-UTR of DKK3 (DKK3-3′-UTR) and positions of three mutated nucleotides (red) in the 3′-UTR of miR-3690 (miR-3690-mut). (B) Validation of miR-3690 expression levels after transfection with miR-3690-mut by PCR analysis. (C) Western blotting analysis of DKK3 expression in K1 cells transfected with miR-3690 or the miR-3690-in, α-tubulin served as the loading control. (D) Luciferase reporter assay of the indicated cells transfected with the pGL3-DKK3-3′-UTR reporter and miR-3690 or miR-3690-in or miR-3690-mut. (E) Reverse transcription PCR analysis of expression of Cyclin E and c-myc in indicated K1 cells. (F) Western blotting analysis of expression of Cyclin E and c-myc protein in K1 cells. α-tubulin served as the loading control. *P<0.05 vs. NC group or vector group. miR, microRNA; 3′-UTR, 3′-untranslated region; DKK3, Dickkopf-related protein 3; miR-3690-mut, microRNA-3690-mutant; miR-3690-in, microRNA-3690-inhibitor; NC, negative control.