title: Regulation of Tiam1 nucleotide exchange activity by pleckstrin domain binding ligands.
abstract: Rho family GTPases play roles in cytoskeletal organization and cellular transformation. Tiam1 is a member of the Dbl family of guanine nucleotide exchange factors that activate Rho family GTPases. These exchange factors have in common a catalytic Dbl homology and adjacent pleckstrin homology domain. Previous structural studies suggest that the pleckstrin domain, a putative phosphoinositide-binding site, may serve a regulatory function. We identified ascorbyl stearate as a compound that binds to the pleckstrin domain of p120 Ras GTPase-activating protein. Furthermore, ascorbyl stearate appears to be a general pleckstrin domain ligand, perhaps by mimicking an endogenous amphiphilic ligand. Tiam1 nucleotide exchange activity was greatly stimulated by ascorbyl stearate. Certain phosphoinositides also stimulated Tiam1 activity but were less potent than ascorbyl stearate. Tiam1 contains an additional N-terminal pleckstrin domain, but only the C-terminal pleckstrin domain was required for activation. Our results suggest that the pleckstrin domains of Dbl-type proteins may not only be involved in subcellular localization but may also directly regulate the nucleotide exchange activity of an associated Dbl homology domain. In addition, this paper introduces ascorbyl stearate as a pleckstrin domain ligand that can modulate the activity of certain pleckstrin domain-containing proteins.
authors.affiliation: Onyx Pharmaceuticals, Richmond, California 94806, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Crompton
authors.forename: L H
authors.initials: LH
authors.lastname: Foley
authors.forename: A
authors.initials: A
authors.lastname: Wood
authors.forename: W
authors.initials: W
authors.lastname: Roscoe
authors.forename: D
authors.initials: D
authors.lastname: Stokoe
authors.forename: F
authors.initials: F
authors.lastname: McCormick
authors.forename: M
authors.initials: M
authors.lastname: Symons
authors.forename: G
authors.initials: G
authors.lastname: Bollag
mesh_terms: D000818:Animals; D001011:Aorta / Q000378:metabolism; D001205:Ascorbic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D016367:Baculoviridae / Q000378:metabolism; D001798:Blood Proteins / Q000737:chemistry / Q000378:metabolism*; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D008024:Ligands; D008956:Models, Chemical; D016296:Mutagenesis; D009711:Nucleotides / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013552:Swine; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D013997:Time Factors; D018631:ras Proteins / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D018076:DNA, Complementary; D020662:Guanine Nucleotide Exchange Factors; D007295:Inositol Phosphates; D008024:Ligands; D009711:Nucleotides; D010455:Peptides; D019269:Phosphatidylinositol 4,5-Diphosphate; D010750:Phosphoproteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C087334:TIAM1 protein, human; C039077:platelet protein P47; C081655:inositol-1,3,4,5-tetrakisphosphate; C036225:ascorbyl monostearate; D006160:Guanosine Triphosphate; D005982:Glutathione Transferase; D018631:ras Proteins; D001205:Ascorbic Acid