Supramolecular assembly of the beta-catenin destruction complex and the effect of Wnt signaling on its localization, molecular size, and activity in vivo

• Published in: PLoS genetics Vol. 14; no. 4; p. e1007339
• Main Authors: Schaefer, Kristina N, Bonello, Teresa T, Zhang, Shiping, Williams, Clara E, Roberts, David M, McKay, Daniel J, Peifer, Mark
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 11.04.2018; Public Library of Science (PLoS)
• Subjects: Adenomatous polyposis coli; Animals; Animals, Genetically Modified; Apc1 Subunit, Anaphase-Promoting Complex-Cyclosome - chemistry; Apc1 Subunit, Anaphase-Promoting Complex-Cyclosome - genetics; Apc1 Subunit, Anaphase-Promoting Complex-Cyclosome - metabolism; Armadillo Domain Proteins - chemistry; Armadillo Domain Proteins - genetics; Armadillo Domain Proteins - metabolism; Axin Protein - chemistry; Axin Protein - genetics; Axin Protein - metabolism; Axin Signaling Complex - chemistry; Axin Signaling Complex - genetics; Axin Signaling Complex - metabolism; Binding proteins; Biology and Life Sciences; Cancer; Cell Line; Colorectal cancer; Curricula; Dishevelled protein; Drosophila; Drosophila melanogaster - embryology; Drosophila melanogaster - genetics; Drosophila melanogaster - metabolism; Drosophila Proteins - chemistry; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; Embryogenesis; Embryos; Funding; Genes; Genetic disorders; Genetic engineering; Glycogen; Glycogen synthase; Glycogen Synthase Kinase 3 - genetics; Glycogen Synthase Kinase 3 - metabolism; Health aspects; Homeostasis; Insects; Kinases; Localization; Medicine and Health Sciences; Microscopy; Molecular biology; Multiprotein Complexes - chemistry; Multiprotein Complexes - genetics; Multiprotein Complexes - metabolism; Phosphorylation; Polymerization; Polyps; Proteins; Proteolysis; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Regulation; Research and Analysis Methods; RNA, Messenger - genetics; RNA, Messenger - metabolism; Stem cells; Stoichiometry; Transcription Factors - chemistry; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription, Genetic; Tumor Suppressor Proteins - chemistry; Tumor Suppressor Proteins - genetics; Tumor Suppressor Proteins - metabolism; Ubiquitination; Wnt protein; Wnt proteins; Wnt Signaling Pathway; Wnt1 Protein - genetics; Wnt1 Protein - metabolism; β-Catenin; United States > US
• ISSN: 1553-7404; 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1007339

Wnt signaling provides a paradigm for cell-cell signals that regulate embryonic development and stem cell homeostasis and are inappropriately activated in cancers. The tumor suppressors APC and Axin form the core of the multiprotein destruction complex, which targets the Wnt-effector beta-catenin for phosphorylation, ubiquitination and destruction. Based on earlier work, we hypothesize that the destruction complex is a supramolecular entity that self-assembles by Axin and APC polymerization, and that regulating assembly and stability of the destruction complex underlie its function. We tested this hypothesis in Drosophila embryos, a premier model of Wnt signaling. Combining biochemistry, genetic tools to manipulate Axin and APC2 levels, advanced imaging and molecule counting, we defined destruction complex assembly, stoichiometry, and localization in vivo, and its downregulation in response to Wnt signaling. Our findings challenge and revise current models of destruction complex function. Endogenous Axin and APC2 proteins and their antagonist Dishevelled accumulate at roughly similar levels, suggesting competition for binding may be critical. By expressing Axin:GFP at near endogenous levels we found that in the absence of Wnt signals, Axin and APC2 co-assemble into large cytoplasmic complexes containing tens to hundreds of Axin proteins. Wnt signals trigger recruitment of these to the membrane, while cytoplasmic Axin levels increase, suggesting altered assembly/disassembly. Glycogen synthase kinase3 regulates destruction complex recruitment to the membrane and release of Armadillo/beta-catenin from the destruction complex. Manipulating Axin or APC2 levels had no effect on destruction complex activity when Wnt signals were absent, but, surprisingly, had opposite effects on the destruction complex when Wnt signals were present. Elevating Axin made the complex more resistant to inactivation, while elevating APC2 levels enhanced inactivation. Our data suggest both absolute levels and the ratio of these two core components affect destruction complex function, supporting models in which competition among Axin partners determines destruction complex activity.