title: Glycogen synthase kinase-3 phosphorylates CdGAP at a consensus ERK 1 regulatory site.
abstract: Rho GTPases regulate a multitude of cellular processes from cytoskeletal reorganization to gene transcription and are negatively regulated by GTPase-activating proteins (GAPs). Cdc42 GTPase-activating protein (CdGAP) is a ubiquitously expressed GAP for Rac1 and Cdc42. In this study, we set out to identify CdGAP-binding partners and, using a yeast two-hybrid approach, glycogen synthase kinase 3alpha (GSK-3alpha) was identified as a partner for CdGAP. GSK-3 exists in two isoforms, alpha and beta, and is involved in regulating many cellular functions from insulin response to tumorigenesis. We show that GSK-3alpha and -beta interact with CdGAP in mammalian cells. We also demonstrate that GSK-3 phosphorylates CdGAP both in vitro and in vivo on Thr-776, which we have previously shown to be an ERK 1/2 phosphorylation site involved in CdGAP regulation. We report that the mRNA and protein levels of CdGAP are increased upon serum stimulation and that GSK-3 activity is necessary for the up-regulation of the protein levels of CdGAP but not for the increase in mRNA. We conclude that GSK-3 is an important regulator of CdGAP and that regulation of CdGAP protein levels by serum presents a novel mechanism for cells to control Cdc42/Rac1 GTPase signaling pathways.
authors.affiliation: Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec H3A 2B2, Canada.
authors.forename: Eric Ian
authors.initials: EI
authors.lastname: Danek
authors.forename: Joseph
authors.initials: J
authors.lastname: Tcherkezian
authors.forename: Ibtissem
authors.initials: I
authors.lastname: Triki
authors.forename: Mayya
authors.initials: M
authors.lastname: Meriane
authors.forename: Nathalie
authors.initials: N
authors.lastname: Lamarche-Vane
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D016384:Consensus Sequence; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051379:Mice; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011392:Proline / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism
chemical_list: C514543:ARHGAP31 protein, human; D020690:GTPase-Activating Proteins; D010750:Phosphoproteins; D011392:Proline; D000071679:Glycogen Synthase Kinase 3 beta; D048052:Mitogen-Activated Protein Kinase 3; D038362:Glycogen Synthase Kinase 3; C448021:glycogen synthase kinase 3 alpha; D020764:cdc42 GTP-Binding Protein