BMI1 as a novel target for drug discovery in cancer

Growing evidence has demonstrated that clonogenic cancer stem (initiating) cells are responsible for tumor regrowth and disease relapse. Bmi-1 plays a critical role in the self-renewal of adult stem cells. The Bmi-1 protein is elevated in many types of cancers, and experimental reduction of Bmi-1 protein levels by small interfering RNA (siRNA) causes apoptosis and/or senescence in tumor cells in vitro and increases susceptibility to cytotoxic agents. The Bmi-1 protein has no known enzymatic activity, but serves as the key regulatory component of the PRC1 complex (polycomb repressive complex-1). This complex influences chromatin structure and regulates transcriptional activity of a number of important loci including the Ink4a locus which encodes the tumor suppressor proteins p16Ink4a and p14Arf. In this prospective study, we will discuss the implication of BMI1 in cancers, the biology of BMI1, and the regulatory control of BMI1 expression. The target validation and the future prospects of targeting BMI1 in cancer therapy are also discussed. J. Cell. Biochem. 112: 2729–2741, 2011. © 2011 Wiley-Liss, Inc.