title: Endocytic Adaptor Protein Tollip Inhibits Canonical Wnt Signaling.
abstract: Many adaptor proteins involved in endocytic cargo transport exhibit additional functions in other cellular processes which may be either related to or independent from their trafficking roles. The endosomal adaptor protein Tollip is an example of such a multitasking regulator, as it participates in trafficking and endosomal sorting of receptors, but also in interleukin/Toll/NF-κB signaling, bacterial entry, autophagic clearance of protein aggregates and regulation of sumoylation. Here we describe another role of Tollip in intracellular signaling. By performing a targeted RNAi screen of soluble endocytic proteins for their additional functions in canonical Wnt signaling, we identified Tollip as a potential negative regulator of this pathway in human cells. Depletion of Tollip potentiates the activity of β-catenin/TCF-dependent transcriptional reporter, while its overproduction inhibits the reporter activity and expression of Wnt target genes. These effects are independent of dynamin-mediated endocytosis, but require the ubiquitin-binding CUE domain of Tollip. In Wnt-stimulated cells, Tollip counteracts the activation of β-catenin and its nuclear accumulation, without affecting its total levels. Additionally, under conditions of ligand-independent signaling, Tollip inhibits the pathway after the stage of β-catenin stabilization, as observed in human cancer cell lines, characterized by constitutive β-catenin activity. Finally, the regulation of Wnt signaling by Tollip occurs also during early embryonic development of zebrafish. In summary, our data identify a novel function of Tollip in regulating the canonical Wnt pathway which is evolutionarily conserved between fish and humans. Tollip-mediated inhibition of Wnt signaling may contribute not only to embryonic development, but also to carcinogenesis. Mechanistically, Tollip can potentially coordinate multiple cellular pathways of trafficking and signaling, possibly by exploiting its ability to interact with ubiquitin and the sumoylation machinery.
authors.affiliation: International Institute of Molecular and Cell Biology, 02-109, Warsaw, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Toruń
authors.affiliation: International Institute of Molecular and Cell Biology, 02-109, Warsaw, Poland.
authors.forename: Ewelina
authors.initials: E
authors.lastname: Szymańska
authors.affiliation: Department of Biochemistry, University of Geneva, 1211, Geneva, Switzerland.
authors.forename: Irinka
authors.initials: I
authors.lastname: Castanon
authors.affiliation: International Institute of Molecular and Cell Biology, 02-109, Warsaw, Poland.
authors.forename: Lidia
authors.initials: L
authors.lastname: Wolińska-Nizioł
authors.affiliation: International Institute of Molecular and Cell Biology, 02-109, Warsaw, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Bartosik
authors.affiliation: International Institute of Molecular and Cell Biology, 02-109, Warsaw, Poland.
authors.forename: Kamil
authors.initials: K
authors.lastname: Jastrzębski
authors.affiliation: International Institute of Molecular and Cell Biology, 02-109, Warsaw, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Miętkowska
authors.affiliation: Department of Biochemistry, University of Geneva, 1211, Geneva, Switzerland.
authors.forename: Marcos
authors.initials: M
authors.lastname: González-Gaitán
authors.affiliation: International Institute of Molecular and Cell Biology, 02-109, Warsaw, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Miaczynska
mesh_terms: D000818:Animals; D063646:Carcinogenesis / Q000235:genetics; D047108:Embryonic Development / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D060449:Wnt Signaling Pathway / Q000235:genetics*; D015027:Zebrafish; D051176:beta Catenin / Q000378:metabolism
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; C410602:TOLLIP protein, human; D051176:beta Catenin