Function Of The C-terminal Region Of Dishevelled Protein In Wnt Signaling Pathways

Dishevelled(Dvl or Dsh)is a key intracellular signaling molecule that mediates the activation of divergent Wnt pathways,it contains three highly conserved domains known as DIX,PDZ and DEP.DIX domain mediates canonical Wnt signalling,DEP domain functions in non-canonical Wnt signaling,while the central PDZ domain functions in both two pathways.The C-terminal region is also highly conserved from invertebrates to vertebrates.However,its function in regulating the activation of different Wnt signals remains unclear.Here,we use Dv1 deletion mutants to examine the function of the C-terminal region in canonical and non-canonical Wnt signaling pathways.Our results show that deletion of the C-terminal region results in a decrease in the activity of Dvl in canonical Wnt signaling.In particular,a Dvl mutant lacking the last 8 amino acids(Xdsh-C?8)shows an obvious reduced capacity to activate canonical Wnt/?-catenin signaling.However,the same mutant is more potent to affect convergence and extension movements and induces PCP defects during gastrulation in zebrafish,due to an increased activation of Wnt/PCP signaling.These results indicate that the Dvl C-terminus differentially regulates the Wnt signaling pathways.We previously reported that Dvl conformational change triggered by the highly conserved PDZ-binding C-terminus is important for the pathway specificity.Here,we provide further evidence demonstrating that binding of the C-terminus to PDZ domain results in Dvl auto-inhibition in the Wnt signaling pathways.Therefore,forced binding of the C-terminus to PDZ domain(mutant Xdsh268/735C forming a closed conformation)reduces the activity of Dvl in canonical and Wnt/PCP signaling,while obstruction of this interaction(mutant Xdsh-RFP,Xdsh-GFP or Xdsh-C?8 forming an open conformation)releases Dvl auto-inhibition,impairs its functional interaction with LRP6 in canonical Wnt signaling,and increases Dvl specificity in Wnt/PCP signaling,which is closely correlated with an enhanced Dvl membrane localization.Thus,our finding suggests that auto-inhibition of Dvl regulated by its extreme C-terminus plays a distinct regulatory role in Wnt/?-catenin and Wnt/PCP signaling pathways.All together,our present results highlight the importance of the C-terminus in keeping Dv1 in appropriate auto-inhibition state,accessible for regulations by other interaction partners to switch pathway specificity.More importantly,our results indicate that C-terminally tagged-Dvl fusion proteins that have been widely used to study the function and the cellular localization of Dvl may not truly represent the wild-type Dvl because those proteins cannot be auto-inhibited.