PRC1 and cancer: Polycomb repressive complex 1 (PRC1), composed of four subunits PHC, BMI-1, CBX, and Ring 1A/B, is an E3 ubiquitin ligase that monoubiquitinates histone H2A lysine 119 (H2AK119ub1), which silences target gene expression and promotes dedifferentiation and stemness during development and cancer [148].