title: Phosphorylation near nuclear localization signal regulates nuclear import of adenomatous polyposis coli protein.
abstract: Mutation of the adenomatous polyposis coli (APC) gene is an early step in the development of colorectal carcinomas. APC protein is located in both the cytoplasm and the nucleus. The objective of this study was to define the nuclear localization signals (NLSs) in APC protein. APC contains two potential NLSs comprising amino acids 1767-1772 (NLS1(APC)) and 2048-2053 (NLS2(APC)). Both APC NLSs are well conserved among human, mouse, rat, and fly. NLS1(APC) and NLS2(APC) each were sufficient to target the cytoplasmic protein beta-galactosidase to the nucleus. Mutational analysis of APC demonstrated that both NLSs were necessary for optimal nuclear import of full-length APC protein. Alignment of NLS2(APC) with the simian virus 40 large T antigen NLS (NLS(SV40 T-ag)) revealed sequence similarity extending to adjacent phosphorylation sites. Changing a serine residue (Ser(2054)) to aspartic acid mutated the potential protein kinase A site adjacent to NLS2(APC), resulting in both inhibition of the NLS2(APC)-mediated nuclear import of a chimeric beta-galactosidase fusion protein and a reduction of full-length APC nuclear localization. Our data provide evidence that control of APC's nuclear import through phosphorylation is a potential mechanism for regulating APC's nuclear activity.
authors.affiliation: Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, 2000 Circle of Hope, Building 555, Room 5263, Salt Lake City, UT 84112, USA.
authors.forename: F
authors.initials: F
authors.lastname: Zhang
authors.forename: R L
authors.initials: RL
authors.lastname: White
authors.forename: K L
authors.initials: KL
authors.lastname: Neufeld
mesh_terms: D025601:Adenomatous Polyposis Coli Protein; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D000957:Antigens, Viral, Tumor / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport; D019556:COS Cells; D047390:Casein Kinase II; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D017124:Conserved Sequence; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007739:L Cells; D051379:Mice; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000235:genetics / Q000378:metabolism; D013539:Simian virus 40; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D025601:Adenomatous Polyposis Coli Protein; D000957:Antigens, Viral, Tumor; D003598:Cytoskeletal Proteins; D019913:Nuclear Localization Signals; D012694:Serine; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D001616:beta-Galactosidase