The protein Ras plays an important role in cellular growth control. Researchers have focused on the protein because mutations in its gene are found in more than 30 percent of all cancers, making it the most prevalent human oncogene.
University of North Carolina Lineberger Comprehensive Cancer Center and Harvard researchers have discovered an alternative mechanism for activating Ras that does not require mutation or hormonal stimulus. In healthy cells, Ras transmits hormone signals into the cell that prompt responses such as cell growth and the development of organs and tissues. A mutation on the RAS gene can chronically activate those signals, leading to tumor initiation and progression.
In an article published on-line in a November issue of Nature Structural and Molecular Biology, the UNC and Harvard teams discovered that modification of Ras at a specific site with a small protein known as ubiquitin can also lock Ras into an active signaling state. Thus, modification of Ras with a single ubiquitin - a process known as monoubiquitination - switches Ras to an active signaling state by disrupting the action of another protein known as the GTPase activating protein, or GAP. Work by two of the papers co-authors, Atsuo Sasaki and Lewis Cantley of Harvard, had previously found evidence for Ras's potential to become activated and promote Ras-mediated tumorigenesis by monoubiquitination.
Because of the strong link between Ras and cancer, Ras should be an attractive target for drug discovery efforts. Despite considerable efforts at developing treatments targeting the protein, Ras itself is now considered to be 'undruggable', leading researchers to try new approaches to developing drugs that target activated Ras. This could lead to benefits beyond cancer therapies, as the RAS gene has also been linked to developmental disorders such as Noonan syndrome, Costello syndrome and autoimmune lymphoproliferative syndrome.