CBX4 and osteosarcoma: However, the chromodomain mutant of CDM-CBX4 could not increase Runx2 at both mRNA and protein levels, neither migration nor invasion (Fig. 1o–q), and depletion of Ring1b did not impact the down-regulation of Runx2 induced by CBX4 knockdown (Supplementary Fig. 3A), indicating that such effects of CBX4 is dependent on its chromodomain, but not the PCR1 complex, in osteosarcoma cells.