2.3 MTT assay
All cells were maintained in low serum, containing 2% FBS (Invitrogen) with starvation for 10 hours before the experiments were performed. An aliquot of cells (1 *103 cells/well) was seeded in a 96-well plate with 2% FBS and serum-starved for 10 hours, transfected with corresponding vector or siRNA and cultured in normal medium. At 24, 48, 72, and 96 hours after transfection, MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl-tetrazolium bromide) solution (5 mg/mL, 20 mL) was added to each well. After incubation for 4 hours, the medium was removed and 100 mL dimethyl sulfoxide was added to each well. The relative number of surviving cells was assessed by measuring the optical density of cell lysates at 570 nm. All assays were performed 5 times.