Polycomb group (PcG)
proteins are transcriptional repressors that regulate several crucial developmental and physiological processes in the cell. More recently, they have been found to play important roles in human
carcinogenesis and
cancer development and progression. The deregulation and dysfunction of PcG
proteins often lead to blocking or inappropriate activation of developmental pathways, enhancing cellular proliferation, inhibiting apoptosis, and increasing the cancer stem cell population. Genetic and molecular investigations of PcG
proteins have long been focused on their PcG functions. However, PcG
proteins have recently been shown to exert non-classical-Pc-functions, contributing to the regulation of diverse cellular functions. We and others have demonstrated that PcG
proteins regulate the expression and function of several oncogenes and tumor suppressor genes in a PcG-independent manner, and PcG
proteins are associated with the survival of patients with
cancer. In this review, we summarize the recent advances in the research on PcG
proteins, including both the Pc-repressive and non-classical-Pc-functions. We specifically focus on the mechanisms by which PcG
proteins play roles in
cancer initiation, development, and progression. Finally, we discuss the potential value of PcG
proteins as molecular
biomarkers for the diagnosis and prognosis of
cancer, and as molecular targets for
cancer therapy.