title: The ubiquitin-proteasome pathway and serine kinase activity modulate adenomatous polyposis coli protein-mediated regulation of beta-catenin-lymphocyte enhancer-binding factor signaling.
abstract: The tumor suppressor function of the adenomatous polyposis coli protein (APC) depends, in part, on its ability to bind and regulate the multifunctional protein, beta-catenin. beta-Catenin binds the high mobility group box transcription factors, lymphocyte enhancer-binding factor (LEF) and T-cell factor, to directly regulate gene transcription. Using LEF reporter assays we find that APC-mediated down-regulation of beta-catenin-LEF signaling is reversed by proteasomal inhibitors in a dose-dependent manner. APC down-regulates signaling induced by wild type beta-catenin but not by the non-ubiquitinatable S37A mutant, beta-catenin. Bisindoylmaleimide-type protein kinase C inhibitors, which prevent beta-catenin ubiquitination, decrease the ability of APC to down-regulate beta-catenin-LEF signaling. All these effects on LEF signaling are paralleled by changes in beta-catenin protein levels. Lithium, an inhibitor of glycogen synthase kinase-3beta, does not alter the ability of APC to down-regulate beta-catenin protein and beta-catenin-LEF signaling in the colon cancer cells that were tested. These results point to a role for beta-catenin ubiquitination, proteasomal degradation, and potentially a serine kinase other than glycogen synthase kinase-3beta in the tumor-suppressive actions of APC.
authors.affiliation: Department of Cell Biology, Georgetown University School of Medicine and Lombardi Cancer Research Center, Washington, D.C. 20007, USA.
authors.forename: V
authors.initials: V
authors.lastname: Easwaran
authors.forename: V
authors.initials: V
authors.lastname: Song
authors.forename: P
authors.initials: P
authors.lastname: Polakis
authors.forename: S
authors.initials: S
authors.lastname: Byers
mesh_terms: D025601:Adenomatous Polyposis Coli Protein; D019943:Amino Acid Substitution; D018938:Caco-2 Cells; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008094:Lithium / Q000494:pharmacology; D051821:Lymphoid Enhancer-Binding Factor 1; D008301:Maleimides / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014452:Ubiquitins / Q000378:metabolism*; D051176:beta Catenin
chemical_list: D025601:Adenomatous Polyposis Coli Protein; C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D007211:Indoles; D051821:Lymphoid Enhancer-Binding Factor 1; D008301:Maleimides; D009097:Multienzyme Complexes; D015534:Trans-Activators; D014157:Transcription Factors; D014452:Ubiquitins; D051176:beta Catenin; D008094:Lithium; D017346:Protein Serine-Threonine Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C070515:bisindolylmaleimide I