Functions Of Dpr1 And Dpr2 Proteins In Modulating Wnt/TGFβ Signaling

Dapper1 and Dapper2, two divergent members of the Dapper family, have been suggested to modulate Wnt and TGFβ/Nodal signaling in Xenopus and zebrafish. To get a better understanding of Dapper function in mammals, we have cloned the mouse ortholog of zebrafish Dapper2, mDpr2 and investigated its function in regulating TGFβsignaling activity. Here, we showed that, like zebrafish Dapper2, overexpression of mDpr2 inhibited the TGFβ-induced expression of the Smad-responsive reporters and targeted TGFβtype I receptor ALK5 for degradation in mammalian cells, and knocking down of Dpr2 by RNA interference up-regulates TGFβreporter gene activity, which implying that mDpr2 may have an intrinsic in vivo activity similar to fish Dapper2 activity. Our data indicate that the function of Dpr2 as a negative regulator of the TGFβ/Nodal signal pathway is evolutionally conserved, at least in part, in fish and mammals.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 whether and how Dpr1 regulates Wnt signaling and whether like Dpr2, it still has inhibitory effect on TGFβsignaling. Here, we firstly cloned the human Dapper1 and mouse Dapper1 gene and present evidence that human Dpr1, the ortholog of Xenopus Dpr, inhibits both canonical and none-canonical 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.To deeply elucidate the biological function of Dapper protein family. Yeast two hybrid were carried out by using Dpr1/Dpr2 protein as baits and Fetal brain cDNA as libray. These findings provides basis for further study.