Media, sera and antibiotics were purchased from GIBCO (Thermo Fischer Scientific, Waltham, MA, USA) and from BioWhittaker (Lonza, Basel, Switzerland). Antibody against phospho-ERK1/ERK2 was purchased from Cell Signaling Technology (Cell Signaling Technology, Danvers, MA, USA) and antibody against ERK was obtained from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) reagents were acquired from Bio-Rad (Hercules, CA, Usa).