EZH2 is the catalytic component of PRC2 (ref. 38) and KDM2B is a member of a variant PRC1 complex that binds GC rich DNA regions and represses transcription.39 Quantitative proteomic studies have also shown that KDM2B and EZH2 are members of other complexes.40 Some of the proteins in these complexes, such as KDM6A, are encoded by genes that are frequently mutated in invasive bladder cancer.19,41,42 Moreover, some bladder cancer mutations inactivate enzymes, which erase histone marks that are catalyzed by KDM2B or EZH2. This evidence concerns the gene PRC1 and urinary bladder cancer.