Semaphorins—not just for axons

An axon guidance factor can work with growth factor receptors to trigger invasive growth, according to a recent article by Silvia Giordano, Paolo Comoglio, and colleagues (Institute for Cancer Research, University of Torino, Torino, Italy).

The guidance cues are semaphorins, soluble and cell surface molecules that have homology to Met, a scatter factor (SF) receptor tyrosine kinase. Met and semaphorins also share homology with the extracellular domain of semaphorin receptors, known as plexins. Because plexins and semaphorins are expressed outside the nervous system, Giordano et al. examined what function they might control in other tissues.

They found that ligand stimulation of a plexin in epithelial cells caused invasive growth, including scattering and anchorage-independent growth. Met is the only kinase known to trigger invasive growth and, as expected, without Met, this plexin-stimulated growth was blocked. Epithelial...