N-terminal part of Dishevelled DEP domain is required for Wnt/β-catenin signaling in mammalian cells.

Dishevelled (DVL) proteins are key mediators of Wnt/β-catenin signaling pathway. All DVL proteins contain three conserved domains -- DIX, PDZ and DEP. There is a consensus in the field that DIX domain is critical for Wnt/β-catenin signaling but contradictory evidence exists regarding the function of the DEP domain. It has been difficult until recently to test the importance of the DEP domain rigorously because of the interference with endogenous DVL, expressed in all Wnt-responsive cell lines. In this study, we took advantage of DVL KO (DVL1/DVL2/DVL3-triple knockout) cells, fully deficient in Wnt3a-induced signaling events, and performed series of rescue experiments. Using this complementation assays we analyze the role of individual DVL isoforms. Further domain mapping of DVL1 showed that DVL1 DEP domain, and especially its N-terminal region, is both required and sufficient for Wnt3a-induced phosphorylation of LRP6 and TopFlash reporter activation. On the contrary, multiple DEP domain mutants deficient in the planar cell polarity (PCP) pathway could fully rescue the Wnt3a response. This study provides conclusive evidence that DVL DEP domain is essential for Wnt/β-catenin signaling in mammalian cells and establishes an experimental system suitable for further functional testing of DVL.