As previously described,[15 (link)] flow cytometry (FCM) was used to analyze cell cycle and apoptosis. The cell cycle was analyzed by ethanol-fixed cells stained with propidium iodide (PI) in buffer containing RNase A (Cat: FXP0211, 4A Biotech Co., Ltd, Beijing, China). The DNA content was assessed with a FACS Calibur flow cytometer (BD Biosciences, USA). Cell apoptosis was detected using the Annexin V-FITC Apoptosis Detection Kit (Cat: FXP022, 4A Biotech Co., Ltd, Beijing, China). The percentage of apoptotic cells were calculated with CellQuest 6.0 (BD Biosciences, USA).