title: Transactivation activity and nucleocytoplasmic transport of β-catenin are independently regulated by its C-terminal end.
abstract: The key protein in the canonical Wnt pathway is β-catenin, which is phosphorylated both in absence and presence of Wnt signals by different kinases. Upon activation in the cytoplasm, β-catenin can enter into the nucleus to transactivate target gene expression, many of which are cancer-related genes. The mechanism governing β-catenin's nucleocytoplasmic transport has been recently unvealed, although phosphorylation at its C-terminal end and its functional consequences are not completely understood. Serine 646 of β-catenin is a putative CK2 phosphorylation site and lies in a region which has been proposed to be important for its nucleocytoplasmic transport and transactivation activity. This residue was mutated to aspartic acid mimicking CK2-phosphorylation and its effects on β-catenin activity as well as localization were explored. β-Catenin S6464D did not show significant differences in both transcriptional activity and nuclear localization compared to the wild-type form, but displayed a characteristic granular nuclear pattern. Three-dimensional models of nuclei were constructed which showed differences in number and volume of granules, being those from β-catenin S646D more and smaller than the wild-type form. FRAP microscopy was used to compare nuclear export of both proteins which showed a slightly higher but not significant retention of β-catenin S646D. Altogether, these results show that C-terminal phosphorylation of β-catenin seems to be related with its nucleocytoplasmic transport but not transactivation activity.
authors.affiliation: Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: J L
authors.initials: JL
authors.lastname: Maturana
authors.affiliation: Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: I
authors.initials: I
authors.lastname: Niechi
authors.affiliation: Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: E
authors.initials: E
authors.lastname: Silva
authors.affiliation: Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: H
authors.initials: H
authors.lastname: Huerta
authors.affiliation: Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: R
authors.initials: R
authors.lastname: Cataldo
authors.affiliation: Laboratory for Scientific Image Analysis (SCIAN-Lab), ICBM, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: S
authors.initials: S
authors.lastname: Härtel
authors.affiliation: Centro de Estudios Cientificos, Valdivia, Chile.
authors.forename: L F
authors.initials: LF
authors.lastname: Barros
authors.affiliation: Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: M
authors.initials: M
authors.lastname: Galindo
authors.affiliation: Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile. Electronic address: jtapia@med.uchile.cl.
authors.forename: J C
authors.initials: JC
authors.lastname: Tapia
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017386:Sequence Homology, Amino Acid; D015533:Transcriptional Activation; D051176:beta Catenin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D051176:beta Catenin
keywords: CK2; Nucleocytoplasmic; Phosphorylation; β-Catenin