title: Wnt signaling requires sequestration of glycogen synthase kinase 3 inside multivesicular endosomes.
abstract: Canonical Wnt signaling requires inhibition of Glycogen Synthase Kinase 3 (GSK3) activity, but the molecular mechanism by which this is achieved remains unclear. Here, we report that Wnt signaling triggers the sequestration of GSK3 from the cytosol into multivesicular bodies (MVBs), so that this enzyme becomes separated from its many cytosolic substrates. Endocytosed Wnt colocalized with GSK3 in acidic vesicles positive for endosomal markers. After Wnt addition, endogenous GSK3 activity decreased in the cytosol, and GSK3 became protected from protease treatment inside membrane-bounded organelles. Cryoimmunoelectron microscopy showed that these corresponded to MVBs. Two proteins essential for MVB formation, HRS/Vps27 and Vps4, were required for Wnt signaling. The sequestration of GSK3 extended the half-life of many other proteins in addition to β-Catenin, including an artificial Wnt-regulated reporter protein containing GSK3 phosphorylation sites. We conclude that multivesicular endosomes are essential components of the Wnt signal-transduction pathway.
authors.affiliation: Howard Hughes Medical Institute and Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, CA 90095-1662, USA.
authors.forename: Vincent F
authors.initials: VF
authors.lastname: Taelman
authors.forename: Radoslaw
authors.initials: R
authors.lastname: Dobrowolski
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Plouhinec
authors.forename: Luis C
authors.initials: LC
authors.lastname: Fuentealba
authors.forename: Peggy P
authors.initials: PP
authors.lastname: Vorwald
authors.forename: Iwona
authors.initials: I
authors.lastname: Gumper
authors.forename: David D
authors.initials: DD
authors.lastname: Sabatini
authors.forename: Edward M
authors.initials: EM
authors.lastname: De Robertis
mesh_terms: D000818:Animals; D002460:Cell Line; D004625:Embryo, Nonmammalian / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D006801:Humans; D051379:Mice; D057146:Multivesicular Bodies / Q000378:metabolism* / Q000648:ultrastructure; D010766:Phosphorylation; D055550:Protein Stability; D015398:Signal Transduction; D051153:Wnt Proteins / Q000378:metabolism*; D014981:Xenopus
chemical_list: D051153:Wnt Proteins; D038362:Glycogen Synthase Kinase 3