Western blot analysis was conducted as previously described.23 (link) Primary antibodies, including Flotillin-1 (ab41927), Tsg101 (ab125011), CD63 (ab217345), p21 (ab188224), p16INK4a (ab211542), and β-actin (ab179467) were purchased from Abcam. PNUTS (14171) was purchased from Cell Signaling Technology.