Polycomb Group (PcG) proteins are epi-genetic transcriptional repressors that play a central role during development via chromatin-modifying activities. In mammals, dosage variations in the PcG protein levels are tightly associated with tumorigenesis, and aberrant expression or PcG mutations are found in many human cancer types. However, the relationship between PcG genes and cancerogenesis in vertebrates is complex because of the high context dependency and partial redundancy of PcG functions. Indeed, PcG genes can behave either as oncogenes or as tumor-suppressors. PcG proteins participate in distinct multiprotein complexes, the Polycomb repressive complexes 1 and 2 (PRC1 and PRC2) being the best characterized. PRC1 components repress transcription of the INK4a tumor suppressor locus. Overexpression of some PcG proteins also correlates with the severity and invasiveness of several cancer types. In contrast, some PcG members like Mell8 may have a tumor suppressor function.
展开▼
