RAS unplugged: negative feedback and oncogene-induced senescence.

Many normal cells respond to certain stresses, such as oncogene activation, by undergoing a permanent form of growth arrest known as senescence, an intrinsic tumor suppressor program. The predominant view has been that senescence is caused in some settings through a mutant oncogene's ability to induce activation of high levels of sustained MAP kinase and PI3 kinase signaling. A new study in this issue of Cancer Cell has challenged this model with the surprising finding that aberrant activation of the RAS/RAF pathway can induce a negative feedback loop that globally attenuates MAPK and PI3K signaling and that the reduction of signaling in these pathways is required for senescence.