Polycomb group proteins and their roles in carcinogenesis

In the cell nucleus, DNA is wound around histone proteins, which are then packed together to form chromatin. Histones can be chemically tagged by methyl and acetyl groups. Polycomb group (PcG) proteins attach methyl groups to genes, which block their activity. This is similar to the attachment of methyl groups to gene promoters by DNA methyltransferases (DNMTs). This action is directly linked with tumor initiation and metastasis via the promotion of anti-senescence and anti-apoptosis pathways, and by facilitating epithelial mesenchymal transition (EMT). Cell fate transcriptional factors (CFTFs) and long non-coding RNAs (long ncRNAs) recruit PcG proteins to the promoters of tumor suppressor genes, resulting in epigenetic gene silencing by influencing chromatin structure and DNA accessibility. Thus, PcG proteins are potential diagnostic markers and targets for new chemoprevention and therapeutic strategies.