Dapper 1 Antagonizes Wnt Signaling by Promoting Dishevelled Degradation

Ye-Guang Chen,Jun Wen,Xia Gao,Yuanheng Ning,Long Zhang

doi:10.1074/jbc.m600274200

Abstract

Wnt signaling plays pivotal roles in the regulation of embryogenesis and cancer development. Xenopus Dapper (Dpr) was identified as an interacting protein for Dishevelled (Dvl), a Wnt signaling mediator, and modulates Wnt signaling. However, it is largely unclear how Dpr regulates Wnt signaling. Here, we present evidence that human Dpr1, the ortholog of Xenopus Dpr, inhibits Wnt signaling. We have identified the regions responsible for the Dpr-Dvl interaction in both proteins and found that the interaction interface is formed between the DEP (Dishevelled, Egl-10, and pleckstrin) domain of Dvl and the central and the C-terminal regions of Dpr1. The inhibitory function of human Dpr1 requires both its N and C terminus. Overexpression of the C-terminal region corresponding to the last 225 amino acids of Dpr1, in contrast to wild-type Dpr1, enhances Wnt signaling, suggesting a dominant negative function of this region. Furthermore, we have shown that Dpr1 induces Dvl degradation via a lysosome inhibitor-sensitive and proteasome inhibitor-insensitive mechanism. Knockdown of Dpr1 by RNA interference up-regulates endogenous Dvl2 protein. Taken together, our data indicate that the inhibitory activity of Dpr on Wnt signaling is conserved from Xenopus to human and that Dpr1 antagonizes Wnt signaling by inducing Dvl degradation.

Highlights

To further define the functions of Dpr1, we have cloned human Dpr1 and mouse Dpr1
We have shown that mammalian Dpr1 inhibits expression of the Wnt-responsive reporters lymphoid enhancer factor (LEF)-luciferase and TopFlash-luciferase
Wnt signaling plays a key role in embryogenesis, and its dysregulation leads to cancer development [1, 2]

Summary

Introduction

To further define the functions of Dpr1, we have cloned human Dpr1 and mouse Dpr1. In this report, we have shown that mammalian Dpr1 inhibits expression of the Wnt-responsive reporters lymphoid enhancer factor (LEF)-luciferase and TopFlash-luciferase. To test whether the inhibitory function of Dpr on Wnt signaling is conserved in mammalian cells, the cDNAs encoding human and mouse Dpr1 were cloned and examined for their activities with Wnt-responsive reporters. Overexpression of human or mouse Dpr1 interfered with Wnt- and Dvl-induced expression of the reporters LEF-luciferase [16, 17] and Topflash-luciferase [18] in a dose-dependent manner (Fig. 1, A–C), whereas they had no effect on the control reporter Fopflash-luciferase (data not shown).

Results

Conclusion