A virus linked to many human cancers may promote the growth of uninfected neighbouring cells by mediating the transfer of key signalling and gene-regulatory molecules from infected cancer cells. These molecules are packaged in tiny sacs called exosomes, which are taken up by the nearby cells.
Nancy Raab-Traub and her team at the University of North Carolina at Chapel Hill isolated exosomes from cancer cells that had been infected with Epstein–Barr virus. They found that these contained high levels of LMP1, a protein encoded by the virus that enhances cell growth and is found in many cancers. After incubating normal cells with the exosomes, the authors found LMP1 and activated growth-signalling pathways in the cells. The cells also contained viral microRNAs, which regulate gene expression, suggesting that the virus uses exosomes to manipulate its environment.