title: Structure, Dynamics, and Functionality of Tankyrase Inhibitor-Induced Degradasomes.
abstract: Tankyrase (TNKS) enzymes, due to their poly(ADP-ribose) polymerase activity, have emerged as potential targets in experimental cancer therapy. However, the functional consequences of TNKS inhibition remain incompletely resolved because of the binding promiscuity of TNKS. One of the hallmarks of small-molecule TNKS inhibitors (TNKSi) is the stabilization of AXIN, which plays a pivotal role in the WNT/β-catenin signaling pathway. The present study focused on the known ability of TNKSi to induce cytoplasmic puncta (degradasomes) consisting of components of the signal-limiting WNT/β-catenin destruction complex. Using the colorectal cancer cell line SW480 stably transfected with GFP-TNKS1, it was demonstrated that a TNKS-specific inhibitor (G007-LK) induces highly dynamic and mobile degradasomes that contain phosphorylated β-catenin, ubiquitin, and β-TrCP. Likewise, G007-LK was found to induce similar degradasomes in other colorectal cancer cell lines expressing wild-type or truncated versions of the degradasome component APC. Super-resolution and electron microscopy revealed that the induced degradasomes in SW480 cells are membrane-free structures that consist of a filamentous assembly of high electron densities and discrete subdomains of various destruction complex components. Fluorescence recovery after photobleaching experiments further demonstrated that β-catenin-mCherry was rapidly turned over in the G007-LK-induced degradasomes, whereas GFP-TNKS1 remained stable. In conclusion, TNKS inhibition attenuates WNT/β-catenin signaling by promoting dynamic assemblies of functional active destruction complexes into a TNKS-containing scaffold even in the presence of an APC truncation.
  
  
  CONCLUSIONS
  This study demonstrates that β-catenin is rapidly turned over in highly dynamic assemblies of WNT destruction complexes (degradasomes) upon tankyrase inhibition and provides a direct mechanistic link between degradasome formation and reduced WNT signaling in colorectal cancer cells.
authors.affiliation: Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Montebello, Oslo, Norway. Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, Oslo, Norway.
authors.forename: Tor Espen
authors.initials: TE
authors.lastname: Thorvaldsen
authors.affiliation: Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Montebello, Oslo, Norway. Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, Oslo, Norway.
authors.forename: Nina Marie
authors.initials: NM
authors.lastname: Pedersen
authors.affiliation: Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Montebello, Oslo, Norway. Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, Oslo, Norway.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Wenzel
authors.affiliation: Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Montebello, Oslo, Norway. Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, Oslo, Norway.
authors.forename: Sebastian W
authors.initials: SW
authors.lastname: Schultz
authors.affiliation: Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Montebello, Oslo, Norway. Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, Oslo, Norway.
authors.forename: Andreas
authors.initials: A
authors.lastname: Brech
authors.affiliation: Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Montebello, Oslo, Norway. Department of Informatics, University of Oslo, Oslo, Norway.
authors.forename: Knut
authors.initials: K
authors.lastname: Liestøl
authors.affiliation: Department of Microbiology, Unit for Cell Signaling, Oslo University Hospital, Forskningsparken, Oslo, Norway.
authors.forename: Jo
authors.initials: J
authors.lastname: Waaler
authors.affiliation: Department of Microbiology, Unit for Cell Signaling, Oslo University Hospital, Forskningsparken, Oslo, Norway.
authors.forename: Stefan
authors.initials: S
authors.lastname: Krauss
authors.affiliation: Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Montebello, Oslo, Norway. Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, Oslo, Norway. stenmark@ulrik.uio.no.
authors.forename: Harald
authors.initials: H
authors.lastname: Stenmark
mesh_terms: D060465:Axin Signaling Complex / Q000378:metabolism*; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism; D006801:Humans; D013450:Sulfones / Q000494:pharmacology*; D038501:Tankyrases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D014230:Triazoles / Q000494:pharmacology*; D060449:Wnt Signaling Pathway / Q000187:drug effects*
chemical_list: D060465:Axin Signaling Complex; D013450:Sulfones; D038501:Tankyrases; D014230:Triazoles; C582305:G007-LK; C418109:TNKS protein, human