SiRNA or lentivirus transfected cells were harvested and washed with PBS. Next, 75% ethanol was used to fix cells at −20°C overnight. Then, DNA in cells was stained by Hank's balanced salt solution including 50 mg/mL propidium iodide and 50 mg/mL RNaseA for 1 h at room temperature. Cell cycle of these cells was analyzed by Gallios flow cytometer (Beckman Countler).