(A) Schematic representation of the pGL3-TopFlash reporter. Eight tandem repeats of TCF/LEF response elements were introduced upstream of the SV40 promoter and firefly luciferase gene (Luc) in pGL3 promoter vector. (B) Screening for inhibitors of Wnt/β-catenin signaling. Plasmids pGL3-TopFlash, pRL-TK and miRNA-expressing vectors were cotransfected into HEK293T cells. Cells were treated with 25 mM LiCl 6 h posttransfection, and lysed 24 h posttransfection for dual-luciferase analysis (RLUs, Fluc/Rluc). (C, E) miR-142 inhibits the activated Wnt/β-catenin signaling. Wnt/β-catenin signaling was activated by 25 mM LiCl (C) or increasing doses of Wnt3a (E). TopFlash-mediated firefly luciferase activities (B, C, E) were normalized to the activity of Renilla luciferase (pRL-TK); error bars mark the SEM (n = 3; **P < 0.01, *P < 0.05, t test). (D) miR-142 represses expression of Axin2. miR-142 expressing vector or empty vector (EF) was transfected into HEK293T cells with or without 25 mM LiCl treatment. Axin2 mRNA expression was analyzed by quantitative RT-PCR, the data shown were normalized by Actb expression; error bars mark the SEM (n = 2; *P < 0.05, t test).