title: Deconstructing the ßcatenin destruction complex: mechanistic roles for the tumor suppressor APC in regulating Wnt signaling.
abstract: Negatively regulating signaling by targeting key effectors for ubiquitination/destruction is essential for development and oncogenesis. The tumor suppressor adenomatous polyposis coli (APC), an essential negative regulator of Wnt signaling, provides a paradigm. APC mutations occur in most colon cancers. Acting in the "destruction complex" with Axin, glycogen synthase kinase 3, and casein kinase, APC targets ßcatenin (ßcat) for phosphorylation and recognition by an E3 ubiquitin-ligase. Despite 20 years of work, the internal workings of the destruction complex and APC's role remain largely mysterious. We use both Drosophila and colon cancer cells to test hypotheses for APC's mechanism of action. Our data are inconsistent with current models suggesting that high-affinity ßcat-binding sites on APC play key roles. Instead, they suggest that multiple ßcat-binding sites act additively to fine-tune signaling via cytoplasmic retention. We identify essential roles for two putative binding sites for new partners--20-amino-acid repeat 2 and conserved sequence B--in destruction complex action. Finally, we demonstrate that APC interacts with Axin by two different modes and provide evidence that conserved sequence B helps ensure release of APC from Axin, with disassembly critical in regulating ßcat levels. Using these data, we suggest a new model for destruction complex action in development, which also provides new insights into functions of truncated APC proteins in cancer.
authors.affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Roberts
authors.forename: Mira I
authors.initials: MI
authors.lastname: Pronobis
authors.forename: John S
authors.initials: JS
authors.lastname: Poulton
authors.forename: Jon D
authors.initials: JD
authors.lastname: Waldmann
authors.forename: Elise M
authors.initials: EM
authors.lastname: Stephenson
authors.forename: Shahnaz
authors.initials: S
authors.lastname: Hanna
authors.forename: Mark
authors.initials: M
authors.lastname: Peifer
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D060466:Axin Protein; D001665:Binding Sites / Q000235:genetics; D045744:Cell Line, Tumor; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D007814:Larva / Q000235:genetics / Q000378:metabolism; D008297:Male; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism; D030781:Organisms, Genetically Modified; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D015398:Signal Transduction; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
chemical_list: C118001:APC protein, Drosophila; D048868:Adaptor Proteins, Signal Transducing; D060466:Axin Protein; C118000:Axn protein, Drosophila; D003598:Cytoskeletal Proteins; D029721:Drosophila Proteins; D051153:Wnt Proteins; D051176:beta Catenin