Component of a Polycomb group (PcG) multiprotein PRC1-like complex, a complex class required to maintain the transcriptionally repressive state of many genes, including Hox genes, throughout development. PcG PRC1 complex acts via chromatin remodeling and modification of histones; it mediates monoubiquitination of histone H2A 'Lys-119', rendering chromatin heritably changed in its expressibility. In the PRC1 complex, it is required to stimulate the E3 ubiquitin-protein ligase activity of RNF2/RING2.
 The polycomb gene product BMI1 contributes to the maintenance of tumor-initiating side population cells in hepatocellular carcinoma.
Chiba, T., et al. (2008). Cancer Res 68(19): 7742-7749.. [ 18829528 ]
 Hedgehog signaling and Bmi-1 regulate self-renewal of normal and malignant human mammary stem cells.
Liu, S., et al. (2006). Cancer Res 66(12): 6063-6071.. [ 16778178 ]