title: Molecular association between beta-catenin degradation complex and Rac guanine exchange factor DOCK4 is essential for Wnt/beta-catenin signaling.
abstract: The canonical Wnt/beta-catenin pathway is a highly conserved signaling cascade that is involved in development and stem cell renewal. The deregulation of this pathway is often associated with increased cell growth and neoplasia. The small GTPase Rac has been shown to influence canonical Wnt signaling by regulating beta-catenin stability through an unknown mechanism. We report that DOCK4, a guanine nucleotide exchange factor (GEF) for Rac and a member of the CDM family of unconventional GEFs, mediates Wnt-induced Rac activation in the canonical Wnt/beta-catenin pathway. DOCK4 expression regulates cellular beta-catenin levels in response to the Wnt signal, in vitro. Biochemical studies demonstrate that DOCK4 interacts with the beta-catenin degradation complex, consisting of the proteins adenomatosis polyposis coli, Axin and glycogen synthase kinase 3beta (GSK3beta). This molecular interaction enhances beta-catenin stability and Axin degradation. Furthermore, we observe that DOCK4 is phosphorylated by GSK3beta, which enhances Wnt-induced Rac activation. Using a T-cell factor reporter zebrafish we confirm that DOCK4 is required for Wnt/beta-catenin activity, in vivo. These results elucidate a novel intracellular signaling mechanism in which a Rac GEF, DOCK4 acts as a scaffold protein in the Wnt/beta-catenin pathway.
authors.affiliation: Department of Medicine, Gastrointestinal Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA. gu6@georgetown.edu
authors.forename: G
authors.initials: G
authors.lastname: Upadhyay
authors.forename: W
authors.initials: W
authors.lastname: Goessling
authors.forename: T E
authors.initials: TE
authors.lastname: North
authors.forename: R
authors.initials: R
authors.lastname: Xavier
authors.forename: L I
authors.initials: LI
authors.lastname: Zon
authors.forename: V
authors.initials: V
authors.lastname: Yajnik
mesh_terms: D000818:Animals; D060466:Axin Protein; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051379:Mice; D012097:Repressor Proteins / Q000378:metabolism; D015398:Signal Transduction; D051153:Wnt Proteins / Q000378:metabolism*; D015027:Zebrafish; D051176:beta Catenin / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
chemical_list: D060466:Axin Protein; C510122:DOCK4 protein, human; D020690:GTPase-Activating Proteins; D012097:Repressor Proteins; D051153:Wnt Proteins; D051176:beta Catenin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D020830:rac1 GTP-Binding Protein