BMI1 and cancer: Moreover, the genes encoding histone E3 ubiquitin ligases and DUBs are also frequently altered in cancers, and many of the enzymes possess tumor suppressor (e.g., BAP1 and RNF20) or oncogenic potential (e.g., BMI1 and USP22) (Melo-Cardenas et al., 2018), identifying possible mechanism(s) accounting for the aberrant histone ubiquitination levels observed within those cancers.