title: Direct ubiquitination of beta-catenin by Siah-1 and regulation by the exchange factor TBL1.
abstract: Beta-catenin is a key component of the Wnt signaling pathway that functions as a transcriptional co-activator of Wnt target genes. Upon UV-induced DNA damage, beta-catenin is recruited for polyubiquitination and subsequent proteasomal degradation by a unique, p53-induced SCF-like complex (SCF(TBL1)), comprised of Siah-1, Siah-1-interacting protein (SIP), Skp1, transducin beta-like 1 (TBL1), and adenomatous polyposis coli (APC). Given the complexity of the various factors involved and the novelty of ubiquitination of the non-phosphorylated beta-catenin substrate, we have investigated Siah-1-mediated ubiquitination of beta-catenin in vitro and in cells. Overexpression and purification protocols were developed for each of the SCF(TBL1) proteins, enabling a systematic analysis of beta-catenin ubiquitination using an in vitro ubiquitination assay. This study revealed that Siah-1 alone was able to polyubiquitinate beta-catenin. In addition, TBL1 was shown to play a role in protecting beta-catenin from Siah-1 ubiquitination in vitro and from Siah-1-targeted proteasomal degradation in cells. Siah-1 and TBL1 were found to bind to the same armadillo repeat domain of beta-catenin, suggesting that polyubiquitination of beta-catenin is regulated by competition between Siah-1 and TBL1 during Wnt signaling.
authors.affiliation: Department of Biochemistry, Vanderbilt University, Nashville, Tennessee 37232, USA.
authors.forename: Yoana N
authors.initials: YN
authors.lastname: Dimitrova
authors.forename: Jiong
authors.initials: J
authors.lastname: Li
authors.forename: Young-Tae
authors.initials: YT
authors.lastname: Lee
authors.forename: Jessica
authors.initials: J
authors.lastname: Rios-Esteves
authors.forename: David B
authors.initials: DB
authors.lastname: Friedman
authors.forename: Hee-Jung
authors.initials: HJ
authors.lastname: Choi
authors.forename: William I
authors.initials: WI
authors.lastname: Weis
authors.forename: Cun-Yu
authors.initials: CY
authors.lastname: Wang
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Chazin
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002474:Cell-Free System; D006801:Humans; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D015293:Transducin / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology*; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*; D000098563:Seven in Absentia Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D025601:Adenomatous Polyposis Coli Protein; C111922:Cacybp protein, mouse; D002135:Calcium-Binding Proteins; C484351:EFS protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D044786:S-Phase Kinase-Associated Proteins; C119542:TBL1X protein, human; C495901:TP53 protein, human; C485613:Tbl1x protein, mouse; D016159:Tumor Suppressor Protein p53; D051153:Wnt Proteins; D051176:beta Catenin; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins; D046988:Proteasome Endopeptidase Complex; D015293:Transducin