Stopping ras in its tracks.

Ras interacts with many downstream effectors that regulate complex cytoplasmic signaling networks. In this issue, Gupta et al. (2007) use mouse models of Ras-mediated tumorigenesis to show that the interaction of Ras with a single isoform of phosphatidylinositol 3-kinase (PI3K), called p110alpha (PIK3CA), is critical for tumor formation. This result will stimulate re-evaluation of pharmacological approaches to target Ras for cancer treatment.