The DIX domain targets dishevelled to actin stress fibres and vesicular membranes

Colorectal cancer results from mutations in components of the Wnt pathway that regulate β-catenin levels1. Dishevelled (Dvl or Dsh) signals downstream of Wnt receptors and stabilizes β-catenin during cell proliferation1 and embryonic axis formation2. Moreover, Dvl contributes to cytoskeletal reorganization during gastrulation3,4,5 and mitotic spindle orientation during asymmetric cell division6. Dvl belongs to a family of eukaryotic signalling proteins that contain a conserved 85-residue module of unknown structure and biological function called the DIX domain7. Here we show that the DIX domain mediates targeting to actin stress fibres and cytoplasmic vesicles in vivo. Neighbouring interaction sites for actin and phospholipid are identified between two helices by nuclear magnetic resonance spectroscopy (NMR). Mutation of the actin-binding motif abolishes the cytoskeletal localization of Dvl, but enhances Wnt/β-catenin signalling and axis induction in Xenopus. By contrast, mutation of the phospholipid interaction site disrupts vesicular association of Dvl, Dvl phosphorylation, and Wnt/β-catenin pathway activation. We propose that partitioning of Dvl into cytoskeletal and vesicular pools by the DIX domain represents a point of divergence in Wnt signalling.