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Development ePress online publication date 12 Dec 2007
doi: 10.1242/dev.013540
Research article
Initiation of Wnt signaling: control of Wnt coreceptor Lrp6 phosphorylation/activation via frizzled, dishevelled and axin functions
Xin Zeng,
He Huang,
Keiko Tamai,
Xinjun Zhang,
Yuko Harada,
Chika Yokota,
Karla Almeida,
Jianbo Wang,
Brad Doble,
Jim Woodgett,
Anthony Wynshaw-Boris,
Jen-Chieh Hsieh,
and
Xi He*
* Author for correspondence (e-mail: xi.he{at}childrens.harvard.edu)
Canonical Wnt/
-catenin signaling has central roles in development and diseases, and is initiated by the action of the frizzled (Fz) receptor, its coreceptor LDL receptor-related protein 6 (Lrp6), and the cytoplasmic dishevelled (Dvl) protein. The functional relationships among Fz, Lrp6 and Dvl have long been enigmatic. We demonstrated previously that Wnt-induced Lrp6 phosphorylation via glycogen synthase kinase 3 (Gsk3) initiates Wnt/
-catenin signaling. Here we show that both Fz and Dvl functions are critical for Wnt-induced Lrp6 phosphorylation through Fz-Lrp6 interaction. We also show that axin, a key scaffolding protein in the Wnt pathway, is required for Lrp6 phosphorylation via its ability to recruit Gsk3, and inhibition of Gsk3 at the plasma membrane blocks Wnt/
-catenin signaling. Our results suggest a model that upon Wnt-induced Fz-Lrp6 complex formation, Fz recruitment of Dvl in turn recruits the axin-Gsk3 complex, thereby promoting Lrp6 phosphorylation to initiate
-catenin signaling. We discuss the dual roles of the axin-Gsk3 complex and signal amplification by Lrp6-axin interaction during Wnt/
-catenin signaling.

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