Protein extraction and Western blot analysis were performed according to the procedures described previously.16 (link) Briefly, the proteins of the cells on the membrane were incubated with a primary mouse monoclonal antibody against human RRM2 (1:1000 dilution; ab57653; Abcam) at 4 °C overnight. The mouse monoclonal antibody against human β-actin (1:5000 dilution; ab6276; Abcam) was used as a control.