β-arrestin is a necessary component of Wnt/β-catenin signaling in vitro and in vivo

The Wnt/beta-catenin signaling pathway is crucial for proper embryonic development and tissue homeostasis. The phosphoprotein dishevelled (Dvl) is an integral part of Wnt signaling and has recently been shown to interact with the multifunctional scaffolding protein beta-arrestin. Using Dvl deletion constructs, we found that P-arrestin binds a region N-terminal of the PDZ domain of Dvl, which contains casein kinase 1 (CK1) phosphorylation sites. Inhibition of Wnt signaling by CKII inhibitors reduced the binding of beta-arrestin to Dvl. Moreover, mouse embryonic fibroblasts lacking beta-arrestins were able to phosphorylate LRP6 in response to Wnt-3a but decreased the activation of Dvl and blocked beta-catenin signaling. In addition, we found that beta-arrestin can bind axin and forms a trimeric complex with axin and Dvl. Furthermore, treatment of Xenopus laevis embryos with beta-arrestin morpholinos reduced the activation of endogenous beta-catenin, decreased the expression of the P-catenin target gene, Xnr3, and blocked axis duplication induced by X-Wnt-8, CK1 epsilon, or Dsh Delta DEP, but not by beta-catenin. Thus, our results identify beta-arrestin as a necessary component for Wnt/ beta-catenin signaling, linking DO and axin, and open a vast array of signaling avenues and possibilities for cross-talk with other beta-arrestin-dependent signaling pathways.