title: Adenomatous polyposis coli (APC) differentially regulates beta-catenin phosphorylation and ubiquitination in colon cancer cells.
abstract: Most colorectal cancers have mutations of the adenomatous polyposis coli (APC) gene or the beta-catenin gene that stabilize beta-catenin and activate beta-catenin target genes, leading ultimately to cancer. The molecular mechanisms of APC function in beta-catenin degradation are not completely known. APC binds beta-catenin and is involved in the Axin complex, suggesting that APC regulates beta-catenin phosphorylation. Some evidence also suggests that APC regulates beta-catenin nuclear export. Here, we examine the effects of APC mutations on beta-catenin phosphorylation, ubiquitination, and degradation in the colon cancer cell lines SW480, DLD-1, and HT29, each of which contains a different APC truncation. Although the current models suggest that beta-catenin phosphorylation should be inhibited by APC mutations, we detected significant beta-catenin phosphorylation in these cells. However, beta-catenin ubiquitination and degradation were inhibited in SW480 but not in DLD-1 and HT29 cells. The ubiquitination ofbeta-catenin in SW480 cells can be rescued by exogenous expression of APC. The APC domains required for beta-catenin ubiquitination were analyzed. Our results suggest that APC regulates beta-catenin phosphorylation and ubiquitination by distinct domains and by separate molecular mechanisms.
authors.affiliation: Sealy Center for Cancer Cell Biology and Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77555, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
authors.forename: Wen
authors.initials: W
authors.lastname: Zhang
authors.forename: Paul M
authors.initials: PM
authors.lastname: Evans
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.forename: Xi
authors.initials: X
authors.lastname: He
authors.forename: Chunming
authors.initials: C
authors.lastname: Liu
mesh_terms: D011125:Adenomatous Polyposis Coli / Q000235:genetics / Q000378:metabolism*; D025601:Adenomatous Polyposis Coli Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism*; D018900:Dinucleotide Repeats; D019073:HT29 Cells; D006801:Humans; D009154:Mutation; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D025801:Ubiquitin / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
chemical_list: D025601:Adenomatous Polyposis Coli Protein; D025801:Ubiquitin; D051176:beta Catenin