2.2. Cell culture and maintenance

Human breast adenocarcinoma cells MDA-MB-231, MCF7 and human breast epithelial cells MCF10A were purchased from America Type Culture Collection (ATCC). Both human breast adenocarcinoma cells were cultured in DMEM and supplemented with 10% fetal bovine serum (FBS) (Sigma, USA) and 1% penicillin-streptomycin (Pen-Strep) (Gibco, USA). MCF10A was maintained in MCF10A complete media which consisted of DMEM/F12 (Cellgro, USA) and supplemented with 5% horse serum (Gibco, USA), 20 ng/μL of human epidermal growth factor (hEGF) (Sigma, USA), 0.5 μg/mL of hydrocortisone (Nacalai Tesque, Japan), 10 mg/mL of insulin (Sigma, USA) and 1% Pen-Strep as described in previous studies (Chung et al., 2017). MCF10A was starved with MCF10A complete media without 20 ng/μL hEGF one day prior to any experiment. The cells were maintained in an incubator at 37°C and supplied with 5% carbon dioxide.