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Trends Cell Biol. 2005 Feb;15(2):61-4.

R-Ras fills another GAP in semaphorin signalling.

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Department of Pharmacology and Anatomy, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.


Plexins are cell-surface receptors for the semaphorin family of neuronal guidance cues. Following semaphorin binding, the plexin cytoplasmic region initiates poorly understood signal-transduction events that lead to modifications of the cytoskeleton. Recent findings shed new light on the signalling network downstream of semaphorins and plexins by demonstrating that one of the plexins, plexin-B1, possesses an intrinsic GTPase-activating protein (GAP) activity towards R-Ras. Inactivation of R-Ras by the plexin-B1 GAP domains is required for plexin-B1-mediated effects on the cytoskeleton. These results indicate that plexins not only bind to but also regulate directly the activity of some of their downstream effectors.

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