An F-box protein, FWD1, mediates ubiquitin-dependent proteolysis of beta-catenin.
beta-catenin plays an essential role in the Wingless/Wnt signaling cascade and is a component of the cadherin cell adhesion complex. Deregulation of beta-catenin accumulation as a result of mutations in adenomatous polyposis coli (APC) tumor suppressor protein is believed to initiate colorectal neoplasia. beta-catenin levels are regulated by the ubiquitin-dependent proteolysis system and beta-catenin ubiquitination is preceded by phosphorylation of its N-terminal region by the glycogen synthase kinase-3beta (GSK-3beta)/Axin kinase complex. Here we show that FWD1 (the mouse homologue of Slimb/betaTrCP), an F-box/WD40-repeat protein, specifically formed a multi-molecular complex with beta-catenin, Axin, GSK-3beta and APC. Mutations at the signal-induced phosphorylation site of beta-catenin inhibited its association with FWD1. FWD1 facilitated ubiquitination and promoted degradation of beta-catenin, resulting in reduced cytoplasmic beta-catenin levels. In contrast, a dominant-negative mutant form of FWD1 inhibited the ubiquitination process and stabilized beta-catenin. These results suggest that the Skp1/Cullin/F-box protein FWD1 (SCFFWD1)-ubiquitin ligase complex is involved in beta-catenin ubiquitination and that FWD1 serves as an intracellular receptor for phosphorylated beta-catenin. FWD1 also links the phosphorylation machinery to the ubiquitin-proteasome pathway to ensure prompt and efficient proteolysis of beta-catenin in response to external signals. SCFFWD1 may be critical for tumor development and suppression through regulation of beta-catenin protein stability.
Kitagawa
M
M
Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Hatakeyama
S
S
Shirane
M
M
Matsumoto
M
M
Ishida
N
N
Hattori
K
K
Nakamichi
I
I
Kikuchi
A
A
Nakayama
K
K
Nakayama
K
K
D025601:Adenomatous Polyposis Coli Protein; D000818:Animals; D060466:Axin Protein; D002352:Carrier Proteins / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D009154:Mutation; D009363:Neoplasm Proteins / Q000378:metabolism; D010453:Peptide Synthases / Q000378:metabolism; D011485:Protein Binding; D011506:Proteins / Q000302:isolation & purification; D011994:Recombinant Proteins / Q000378:metabolism; D012097:Repressor Proteins; D044843:SKP Cullin F-Box Protein Ligases; D015534:Trans-Activators; D014452:Ubiquitins / Q000378:metabolism*; D051176:beta Catenin; D044844:beta-Transducin Repeat-Containing Proteins
D025601:Adenomatous Polyposis Coli Protein; D060466:Axin Protein; C471643:Btrc protein, mouse; C495267:CTNNB1 protein, mouse; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D009363:Neoplasm Proteins; D011506:Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014452:Ubiquitins; D051176:beta Catenin; D044844:beta-Transducin Repeat-Containing Proteins; D044843:SKP Cullin F-Box Protein Ligases; D019204:GTP-Binding Proteins; D010453:Peptide Synthases