title: Wnt-4 activates the canonical beta-catenin-mediated Wnt pathway and binds Frizzled-6 CRD: functional implications of Wnt/beta-catenin activity in kidney epithelial cells.
abstract: The Wnt signaling pathway is central to the development of all animals and to cancer progression, yet largely unknown are the pairings of secreted Wnt ligands to their respective Frizzled transmembrane receptors or, in many cases, the relative contributions of canonical (beta-catenin/LEF/TCF) versus noncanonical Wnt signals. Specifically, in the kidney where Wnt-4 is essential for the mesenchymal to epithelial transition that generates the tissue's collecting tubules, the corresponding Frizzled receptor(s) and downstream signaling mechanism(s) are unclear. In this report, we addressed these issues using Madin-Darby Canine Kidney (MDCK) cells, which are competent to form tubules in vitro. Employing established reporter constructs of canonical Wnt/beta-catenin pathway activity, we have determined that MDCK cells are highly responsive to Wnt-4, -1, and -3A, but not to Wnt-5A and control conditions, precisely reflecting functional findings from Wnt-4 null kidney mesenchyme ex vivo rescue studies. We have confirmed that Wnt-4's canonical signaling activity in MDCK cells is mediated by downstream effectors of the Wnt/beta-catenin pathway using beta-Engrailed and dnTCF-4 constructs that suppress this pathway. We have further found that MDCK cells express the Frizzled-6 receptor and that Wnt-4 forms a biochemical complex with the Frizzled-6 CRD. Since Frizzled-6 did not appear to transduce Wnt-4's canonical signal, data supported recently by Golan et al., there presumably exists another as yet unknown Frizzled receptor(s) mediating Wnt-4 activation of beta-catenin/LEF/TCF. Finally, we report that canonical Wnt/beta-catenin signals cells help maintain cell growth and survival in MDCK cells but do not contribute to standard HGF-induced (nonphysiologic) tubule formation. Our results in combination with work from Xenopus laevis (not shown) lead us to believe that Wnt-4 binds both canonical and noncanonical Frizzled receptors, thereby activating Wnt signaling pathways that may each contribute to kidney tubulogenesis.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Jon P
authors.initials: JP
authors.lastname: Lyons
authors.forename: Ulrich W
authors.initials: UW
authors.lastname: Mueller
authors.forename: Hong
authors.initials: H
authors.lastname: Ji
authors.forename: Christopher
authors.initials: C
authors.lastname: Everett
authors.forename: Xiang
authors.initials: X
authors.lastname: Fang
authors.forename: Jen-Chih
authors.initials: JC
authors.lastname: Hsieh
authors.forename: AngelaI M
authors.initials: AM
authors.lastname: Barth
authors.forename: Pierre D
authors.initials: PD
authors.lastname: McCrea
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence / Q000235:genetics; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004285:Dogs; D004627:Embryonic Induction / Q000502:physiology; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D051157:Frizzled Receptors; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D007684:Kidney Tubules / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D038081:Organogenesis / Q000502:physiology*; D011485:Protein Binding / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism*; D051153:Wnt Proteins; D060528:Wnt4 Protein; D029867:Xenopus Proteins; D051176:beta Catenin
chemical_list: C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; C080330:En1 protein, mouse; D051157:Frizzled Receptors; C111048:Fzd6 protein, mouse; D018398:Homeodomain Proteins; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D015534:Trans-Activators; D051153:Wnt Proteins; D060528:Wnt4 Protein; C555584:Wnt4 protein, Xenopus; C555582:Wnt4 protein, mouse; D029867:Xenopus Proteins; D051176:beta Catenin