2.1 Cell lines and media
HeLa carcinoma cells were purchased from American Type Culture Collection (ATCC, Manassas, VA, USA). Cells were cultured in dulbecco’s modified eagle medium (DMEM) (Gibco, 11995-065, USA) supplemented with 10% fetal bovine serum (Gibco, 10099-141, USA), 100 IU/mL penicillin and 100 mg/mL streptomycin (B540732, Sangon Biotech, Shanghai, CN). Cells were maintained in 75 cm2 flasks in a 37°C, 5% carbon dioxide incubator (Thermo Fisher Scientific, Waltham, MA, USA) and passaged when the confluence of cells reached 80%–90%.