Cancer stem cells have been identified in numerous tumor types as a subpopulation of tumor cells which have co-opted many characteristics of normal stem cells that have the ability to initiate a tumor, produce other cancer cell types, move freely and proliferate throughout the body without attaching to other cells or surfaces and resist chemotherapy and radiotherapy. Their resistance to chemotherapy and radiotherapy is believed to be a key factor in the failure of current cancer treatments.
The BMI1 (B-cell-specific Moloney murine leukemia virus integration site 1) protein, which is overexpressed in many tumor subtypes, is a critical component of the polycomb repressive complex 1, or PRC1. PRC1 modulates gene expression that is important for cancer stem cell survival, maintenance, stabilization and differentiation. PRC1 is epigenetic, meaning that it is able to modify DNA directly to modulate gene expression without altering the nucleotide sequence in the genetic code. As a critical component of PRC1, the BMI1 protein regulates the self-renewal of adult blood and central nervous system stem cells that regulate cell growth.