title: The APC tumour suppressor has a nuclear export function.
abstract: The adenomatous polpyposis coli (APC) protein is mutated in most colorectal tumours. Nearly all APC mutations are truncations, and many of these terminate in the mutation cluster region located halfway through the protein. In cancer cells expressing mutant APC, beta-catenin is stabilized and translocates into the nucleus to act as a transcriptional co-activator of T-cell factor. During normal development, APC also promotes the destabilization of beta-catenin and Drosophila Armadillo. It does so by binding to the Axin complex which earmarks beta-catenin/Armadillo for degradation by the proteasome pathway. APC has a regulatory role in this process, which is poorly understood. Here we show that APC contains highly conserved nuclear export signals 3' adjacent to the mutation cluster region that enable it to exit from the nucleus. This ability is lost in APC mutant cancer cells, and we provide evidence that beta-catenin accumulates in the nucleus as a result. Thus, the ability of APC to exit from the nucleus appears to be critical for its tumour suppressor function.
authors.affiliation: Laboratory of Molecular Biology, Cambridge, UK.
authors.forename: R
authors.initials: R
authors.lastname: Rosin-Arbesfeld
authors.forename: F
authors.initials: F
authors.lastname: Townsley
authors.forename: M
authors.initials: M
authors.lastname: Bienz
mesh_terms: D025601:Adenomatous Polyposis Coli Protein; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D019556:COS Cells; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D017930:Genes, Reporter; D005816:Genetic Complementation Test; D006801:Humans; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D010446:Peptide Fragments / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators; D014162:Transfection; D014407:Tumor Cells, Cultured; D051176:beta Catenin
chemical_list: D025601:Adenomatous Polyposis Coli Protein; C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D005231:Fatty Acids, Unsaturated; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D051176:beta Catenin; C038753:leptomycin B