title: Rac1 augments Wnt signaling by stimulating β-catenin-lymphoid enhancer factor-1 complex assembly independent of β-catenin nuclear import.
abstract: β-Catenin transduces the Wnt signaling pathway and its nuclear accumulation leads to gene transactivation and cancer. Rac1 GTPase is known to stimulate β-catenin-dependent transcription of Wnt target genes and we confirmed this activity. Here we tested the recent hypothesis that Rac1 augments Wnt signaling by enhancing β-catenin nuclear import; however, we found that silencing/inhibition or up-regulation of Rac1 had no influence on nuclear accumulation of β-catenin. To better define the role of Rac1, we employed proximity ligation assays (PLA) and discovered that a significant pool of Rac1-β-catenin protein complexes redistribute from the plasma membrane to the nucleus upon Wnt or Rac1 activation. More importantly, active Rac1 was shown to stimulate the formation of nuclear β-catenin-lymphoid enhancer factor 1 (LEF-1) complexes. This regulation required Rac1-dependent phosphorylation of β-catenin at specific serines, which when mutated (S191A and S605A) reduced β-catenin binding to LEF-1 by up to 50%, as revealed by PLA and immunoprecipitation experiments. We propose that Rac1-mediated phosphorylation of β-catenin stimulates Wnt-dependent gene transactivation by enhancing β-catenin-LEF-1 complex assembly, providing new insight into the mechanism of cross-talk between Rac1 and canonical Wnt/β-catenin signaling.
authors.affiliation: Center for Cancer Research, The Westmead Millennium Institute for Medical Research, The University of Sydney, Westmead, New South Wales 2145, Australia.
authors.forename: Cara
authors.initials: C
authors.lastname: Jamieson
authors.affiliation: Center for Cancer Research, The Westmead Millennium Institute for Medical Research, The University of Sydney, Westmead, New South Wales 2145, Australia.
authors.forename: Christina
authors.initials: C
authors.lastname: Lui
authors.affiliation: Center for Cancer Research, The Westmead Millennium Institute for Medical Research, The University of Sydney, Westmead, New South Wales 2145, Australia.
authors.forename: Mariana G
authors.initials: MG
authors.lastname: Brocardo
authors.affiliation: Center for Cancer Research, The Westmead Millennium Institute for Medical Research, The University of Sydney, Westmead, New South Wales 2145, Australia.
authors.forename: Estefania
authors.initials: E
authors.lastname: Martino-Echarri
authors.affiliation: Center for Cancer Research, The Westmead Millennium Institute for Medical Research, The University of Sydney, Westmead, New South Wales 2145, Australia beric.henderson@sydney.edu.au.
authors.forename: Beric R
authors.initials: BR
authors.lastname: Henderson
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000235:genetics / Q000502:physiology; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D045325:HCT116 Cells; D006801:Humans; D047468:Immunoprecipitation; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells; D060888:Real-Time Polymerase Chain Reaction; D060449:Wnt Signaling Pathway / Q000235:genetics / Q000502:physiology; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D051821:Lymphoid Enhancer-Binding Factor 1; D051176:beta Catenin; D020830:rac1 GTP-Binding Protein
keywords: Proximity ligation assay; Rac1; Wnt signaling; β-Catenin