title: The APC tumor suppressor binds to C-terminal binding protein to divert nuclear beta-catenin from TCF.
abstract: Adenomatous polyposis coli (APC) is an important tumor suppressor in the colon. APC antagonizes the transcriptional activity of the Wnt effector beta-catenin by promoting its nuclear export and its proteasomal destruction in the cytoplasm. Here, we show that a third function of APC in antagonizing beta-catenin involves C-terminal binding protein (CtBP). APC is associated with CtBP in vivo and binds to CtBP in vitro through its conserved 15 amino acid repeats. Failure of this association results in elevated levels of beta-catenin/TCF complexes and of TCF-mediated transcription. Notably, CtBP is neither associated with TCF in vivo nor does mutation of the CtBP binding motifs in TCF-4 alter its transcriptional activity. This questions the idea that CtBP is a direct corepressor of TCF. Our evidence indicates that APC is an adaptor between beta-catenin and CtBP and that CtBP lowers the availability of free nuclear beta-catenin for binding to TCF by sequestering APC/beta-catenin complexes.
authors.affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom.
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Hamada
authors.forename: Mariann
authors.initials: M
authors.lastname: Bienz
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000429:Alcohol Oxidoreductases; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry*; D017124:Conserved Sequence; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila / Q000196:embryology / Q000378:metabolism; D029721:Drosophila Proteins / Q000378:metabolism / Q000502:physiology*; D005816:Genetic Complementation Test; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism / Q000502:physiology*; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D051176:beta Catenin
chemical_list: D025601:Adenomatous Polyposis Coli Protein; C495270:CTNNB1 protein, human; C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051176:beta Catenin; C115159:pan protein, Drosophila; D000429:Alcohol Oxidoreductases; C096794:C-terminal binding protein; D008156:Luciferases; D005982:Glutathione Transferase