title: Identification of RhoGAP22 as an Akt-dependent regulator of cell motility in response to insulin.
abstract: Insulin exerts many of its metabolic actions via the canonical phosphatidylinositide 3 kinase (PI3K)/Akt pathway, leading to phosphorylation and 14-3-3 binding of key metabolic targets. We previously identified a GTPase-activating protein (GAP) for Rac1 called RhoGAP22 as an insulin-responsive 14-3-3 binding protein. Insulin increased 14-3-3 binding to RhoGAP22 fourfold, and this effect was PI3K dependent. We identified two insulin-responsive 14-3-3 binding sites (pSer(16) and pSer(395)) within RhoGAP22, and mutagenesis studies revealed a complex interplay between the phosphorylation at these two sites. Mutating Ser(16) to alanine blocked 14-3-3 binding to RhoGAP22 in vivo, and phosphorylation at Ser(16) was mediated by the kinase Akt. Overexpression of a mutant RhoGAP22 that was unable to bind 14-3-3 reduced cell motility in NIH-3T3 fibroblasts, and this effect was dependent on a functional GAP domain. Mutation of the catalytic arginine of the GAP domain of RhoGAP22 potentiated growth factor-stimulated Rac1 GTP loading. We propose that insulin and possibly growth factors such as platelet-derived growth factor may play a novel role in regulating cell migration and motility via the Akt-dependent phosphorylation of RhoGAP22, leading to modulation of Rac1 activity.
authors.affiliation: Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia.
authors.forename: Alexander F
authors.initials: AF
authors.lastname: Rowland
authors.forename: Mark
authors.initials: M
authors.lastname: Larance
authors.forename: William E
authors.initials: WE
authors.lastname: Hughes
authors.forename: David E
authors.initials: DE
authors.lastname: James
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D020134:Catalytic Domain; D002460:Cell Line; D002465:Cell Movement; D017124:Conserved Sequence; D006224:Cricetinae; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D007328:Insulin / Q000494:pharmacology / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034622:RNA Interference; D051381:Rats
chemical_list: D048948:14-3-3 Proteins; D020690:GTPase-Activating Proteins; D007328:Insulin; C568926:RhoGAP22 protein, human; D051057:Proto-Oncogene Proteins c-akt