Cell viability assay and cytotoxicity assay (Cell Counting Kit-8, CCK8 assay)

MDA-MB-453 and HepG2 cells were seeded in sextuplicate in a 96-well plate with 3000 cells per well, respectively, 1 day prior to transfection. The cells were transfected with different miR mimic, inhibitor or non-specific control (NC) in the following day. On the third day half of cells were treated with PS-341 (50 nM) for 24 h. Then the CCK8 assay was used to determine cell viability 48 hours after transfection. The absorbance at 450 nm was measured with a Quant Universal Microplate Spectrophotometer (BioTek, Winooski, VT, USA). Three independent experiments were performed and the data were presented as the mean ± SD.