BMI1 and cancer: In agreement with these observations, genes encoding histone E3 ubiquitin ligases and deubiquitinases (DUBs) are also frequently altered in cancers [4], and many of the enzymes possess tumor suppressor potential (e.g., BAP1, USP16 and RNF20) or oncogenic potential (e.g., BMI1 and USP22) [5–8].