For mutant luciferase reporter vector construction, the mutant CCND1 3'UTR (replaced TGTTACA with AAAAACA) were cloned into the MCS region of pMir-GLO luciferase reporter vector with Sac I and Xba I.
The primers for wildtype and mutant CCND1 3'UTR were as follows, F: 5'-gggagctcCTGTCCCACTC CTACGATAC-3', R1 (wildtype): 5'-tctctagaTGTAACATCAAAGGCAGAAGG-3', R2 (Mutant): 5'-tctctagaTGTTTTTTCAAAGGCAGAAGGTTTGTGT-3'. The luciferase reporter assay was conducted as we previously described before [14] . Brie y, the BGC823 cells were seeded into 12-well-tissue plates 24h before transfection, and then co-transfected with 5 nM siRNA and 1mg plasmid using the Lipofectamine 2000 Reagent (Invitrogen), according to the manufacturer's instructions. After another 48h, cells were assayed using the Dual-Luciferase reporter assay system kit (GeneCopoeia, USA). All experiments were performed in triplicate and data were pooled from three independent experiments.