title: Ubiquitin ligase RNF146 regulates tankyrase and Axin to promote Wnt signaling.
abstract: Canonical Wnt signaling is controlled intracellularly by the level of β-catenin protein, which is dependent on Axin scaffolding of a complex that phosphorylates β-catenin to target it for ubiquitylation and proteasomal degradation. This function of Axin is counteracted through relocalization of Axin protein to the Wnt receptor complex to allow for ligand-activated Wnt signaling. AXIN1 and AXIN2 protein levels are regulated by tankyrase-mediated poly(ADP-ribosyl)ation (PARsylation), which destabilizes Axin and promotes signaling. Mechanistically, how tankyrase limits Axin protein accumulation, and how tankyrase levels and activity are regulated for this function, are currently under investigation. By RNAi screening, we identified the RNF146 RING-type ubiquitin E3 ligase as a positive regulator of Wnt signaling that operates with tankyrase to maintain low steady-state levels of Axin proteins. RNF146 also destabilizes tankyrases TNKS1 and TNKS2 proteins and, in a reciprocal relationship, tankyrase activity reduces RNF146 protein levels. We show that RNF146, tankyrase, and Axin form a protein complex, and that RNF146 mediates ubiquitylation of all three proteins to target them for proteasomal degradation. RNF146 is a cytoplasmic protein that also prevents tankyrase protein aggregation at a centrosomal location. Tankyrase auto-PARsylation and PARsylation of Axin is known to lead to proteasome-mediated degradation of these proteins, and we demonstrate that, through ubiquitylation, RNF146 mediates this process to regulate Wnt signaling.
authors.affiliation: Department of Cancer Targets, Genentech Research and Early Development, South San Francisco, California, United States of America.
authors.forename: Marinella G
authors.initials: MG
authors.lastname: Callow
authors.forename: Hoanh
authors.initials: H
authors.lastname: Tran
authors.forename: Lilian
authors.initials: L
authors.lastname: Phu
authors.forename: Ted
authors.initials: T
authors.lastname: Lau
authors.forename: James
authors.initials: J
authors.lastname: Lee
authors.forename: Wendy N
authors.initials: WN
authors.lastname: Sandoval
authors.forename: Peter S
authors.initials: PS
authors.lastname: Liu
authors.forename: Sheila
authors.initials: S
authors.lastname: Bheddah
authors.forename: Janet
authors.initials: J
authors.lastname: Tao
authors.forename: Jennie R
authors.initials: JR
authors.lastname: Lill
authors.forename: Jo-Anne
authors.initials: JA
authors.lastname: Hongo
authors.forename: David
authors.initials: D
authors.lastname: Davis
authors.forename: Donald S
authors.initials: DS
authors.lastname: Kirkpatrick
authors.forename: Paul
authors.initials: P
authors.lastname: Polakis
authors.forename: Mike
authors.initials: M
authors.lastname: Costa
mesh_terms: D060466:Axin Protein / Q000378:metabolism*; D018385:Centrosome / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D055550:Protein Stability; D021381:Protein Transport; D059748:Proteolysis; D015398:Signal Transduction; D038501:Tankyrases / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination; D051153:Wnt Proteins / Q000378:metabolism*
chemical_list: D060466:Axin Protein; D046988:Proteasome Endopeptidase Complex; D038501:Tankyrases; D044767:Ubiquitin-Protein Ligases; D051153:Wnt Proteins; C555451:AXIN1 protein, human; C491761:AXIN2 protein, human; C561932:RNF146 protein, human; C437334:TNKS2 protein, human; C418109:TNKS protein, human