title: A mechanism for Wnt coreceptor activation.
abstract: LDL receptor related proteins 5 and 6 (LRP5/6) and their Drosophila homolog Arrow are single-span transmembrane proteins essential for Wnt/beta-catenin signaling, likely via acting as Wnt coreceptors. How Wnt activates LRP5/6/Arrow to initiate signal transduction is not well defined. Here we show that a PPPSP motif, which is reiterated five times in the LRP5/6/Arrow intracellular domain, is necessary and sufficient to trigger Wnt/beta-catenin signaling. A single PPPSP motif, upon transfer to the LDL receptor, fully activates the Wnt pathway, inducing complete axis duplication in Xenopus and TCF/beta-catenin-responsive transcription in human cells. We further show that Wnt signal-ing stimulates, and requires, phosphorylation of the PPPSP motif, which creates an inducible docking site for Axin, a scaffolding protein controlling beta-catenin stability. Our study identifies a critical signaling module and a key phosphorylation-dependent activation step of the Wnt receptor complex and reveals a unifying logic for transmembrane signaling by Wnts, growth factors, and cytokines.
authors.affiliation: Division of Neuroscience, Children's Hospital, Department of Neurology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Keiko
authors.initials: K
authors.lastname: Tamai
authors.forename: Xin
authors.initials: X
authors.lastname: Zeng
authors.forename: Chunming
authors.initials: C
authors.lastname: Liu
authors.forename: Xinjun
authors.initials: X
authors.lastname: Zhang
authors.forename: Yuko
authors.initials: Y
authors.lastname: Harada
authors.forename: Zhijie
authors.initials: Z
authors.lastname: Chang
authors.forename: Xi
authors.initials: X
authors.lastname: He
mesh_terms: D000409:Alanine / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D060466:Axin Protein; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004625:Embryo, Nonmammalian; D008954:Models, Biological; D010766:Phosphorylation; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D011973:Receptors, LDL / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D015533:Transcriptional Activation; D051153:Wnt Proteins; D029867:Xenopus Proteins / Q000378:metabolism; D014982:Xenopus laevis / Q000196:embryology; D029961:Zebrafish Proteins; D051176:beta Catenin
chemical_list: D060466:Axin Protein; C495266:CTNNB1 protein, Xenopus; D003598:Cytoskeletal Proteins; D011518:Proto-Oncogene Proteins; D011973:Receptors, LDL; D012097:Repressor Proteins; D015534:Trans-Activators; D051153:Wnt Proteins; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; C555454:axin1 protein, Xenopus; D051176:beta Catenin; D000409:Alanine