RIPA lysis buffer (KeyGEN, Jiangsu, China) was used to extract proteins from cells. Equal amounts of protein were separated by SDS-PAGE, followed by electrotransfer onto polyvinylidene difluoride membranes (Thermo Fisher Scientific, Massachusetts, USA). Immunoblot analysis used the following primary antibodies: CBX7 (ab21873), HDAC2 (ab12169), Cyclin E1 (ab3927), p16 (ab51243), p53 (ab28), Actin (ab8226), Tubulin (ab7291) and GAPDH (ab9485) were obtained from Abcam (Cambridge, UK). P21 (#2946), acetyl-histone H3 (Lys56) (#4243), acetyl-histone H2B (Lys20) (#2571) were purchased from Cell Signaling Technology (Massachusetts, USA).