title: TSPAN12 regulates retinal vascular development by promoting Norrin- but not Wnt-induced FZD4/beta-catenin signaling.
abstract: Mutations in the genes encoding the Wnt receptor Frizzled-4 (FZD4), coreceptor LRP5, or the ligand Norrin disrupt retinal vascular development and cause ophthalmic diseases. Although Norrin is structurally unrelated to Wnts, it binds FZD4 and activates the canonical Wnt pathway. Here we show that the tetraspanin Tspan12 is expressed in the retinal vasculature, and loss of Tspan12 phenocopies defects seen in Fzd4, Lrp5, and Norrin mutant mice. In addition, Tspan12 genetically interacts with Norrin or Lrp5. Overexpressed TSPAN12 associates with the Norrin-receptor complex and significantly increases Norrin/beta-catenin but not Wnt/beta-catenin signaling, whereas Tspan12 siRNA abolishes transcriptional responses to Norrin but not Wnt3A in retinal endothelial cells. Signaling defects caused by Norrin or FZD4 mutations that are predicted to impair receptor multimerization are rescued by overexpression of TSPAN12. Our data indicate that Norrin multimers and TSPAN12 cooperatively promote multimerization of FZD4 and its associated proteins to elicit physiological levels of signaling.
authors.affiliation: Tumor Biology and Angiogenesis Department, Genentech Inc., 1 DNA Way, South San Francisco, CA 94080, USA.
authors.forename: Harald J
authors.initials: HJ
authors.lastname: Junge
authors.forename: Stacey
authors.initials: S
authors.lastname: Yang
authors.forename: Jeremy B
authors.initials: JB
authors.lastname: Burton
authors.forename: Kim
authors.initials: K
authors.lastname: Paes
authors.forename: Xiao
authors.initials: X
authors.lastname: Shu
authors.forename: Dorothy M
authors.initials: DM
authors.lastname: French
authors.forename: Mike
authors.initials: M
authors.lastname: Costa
authors.forename: Dennis S
authors.initials: DS
authors.lastname: Rice
authors.forename: Weilan
authors.initials: W
authors.lastname: Ye
mesh_terms: D000818:Animals; D004224:Diterpenes; D042783:Endothelial Cells / Q000378:metabolism; D051157:Frizzled Receptors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000196:embryology*; D015398:Signal Transduction; D059470:Tetraspanins; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
chemical_list: D004224:Diterpenes; D051157:Frizzled Receptors; C498581:Fzd4 protein, mouse; D008565:Membrane Proteins; D043562:Receptors, G-Protein-Coupled; D059470:Tetraspanins; C544733:Tspan12 protein, mouse; D051176:beta Catenin; C485194:norrisolide