Polycomb group (PcG) proteins remodel chromatin and regulate the binding of transcription factors to promoter sites in DNA. In many cases, PcG proteins maintain stem cell-like characteristics in cells and may thus promote cancer. Classen et al. now report that a PcG complex called Polycomb repressive complex 1 (PRC1) suppresses tumor formation in the Drosophila imaginal disc. Mutations to the PcG proteins cause cell hyperproliferation and, consequently, abnormal tissue architecture. This phenotype depends upon activation of JAK-STAT, a pathway that responds to environmental cues to regulate cell proliferation, differentiation and death. The authors show that PRC1 usually represses the expression of Unpaired family ligands, which activate the JAK-STAT pathway. Thus, PRC1 inhibits imaginal disc growth and acts as a tumor suppressor by inducing epigenetic modifications in the fly.
Classen AK, Bunker BD, Harvey KF, Vaccari T, Bilder D (2009). A tumor suppressor activity of Drosophila Polycomb genes mediated by JAK-STAT signaling. Nat Genet. 41, 1150– 1155.
