SiRNA or lentivirus transfected cells were collected and lysed using lysis buffer supplemented with PMSF. Then, equal amounts of protein was subjected was subjected to anti-CBX7 antibody or anti-HDAC2 antibody following overnight incubation at 4°C. Then, protein-antibody immunoprecipitates were collected by protein A/G plus-agarose (Santa Cruz Biotechnology, Texas, USA).