title: D3 phosphoinositides and outside-in integrin signaling by glycoprotein IIb-IIIa mediate platelet actin assembly and filopodial extension induced by phorbol 12-myristate 13-acetate.
abstract: Phorbol 12-myristate 13-acetate (PMA) uncaps a small number of the fast-growing (barbed) ends of actin filaments, thereby eliciting slow actin assembly and extension of filopodia in human blood platelets. These reactions, which also occur in response to immunologic perturbation of the integrin glycoprotein (GP) IIb-IIIa, are sensitive to the phosphoinositide 3-kinase inhibitor wortmannin. Platelets deficient in GPIIb-IIIa integrins or with GPIIb-IIIa function inhibited by calcium chelation or the peptide RGDS have diminished PMA responsiveness. The effects of PMA contrast with thrombin receptor stimulation by >/=5 microM thrombin receptor-activating peptide (TRAP), which causes rapid and massive wortmannin-insensitive actin assembly and lamellar and filopodial extension. However, we show here that wortmannin can inhibit filopod formation if the thrombin receptor is ligated using suboptimal doses (<1 microM) of TRAP. Phosphatidylinositol 3,4-bisphosphate inhibits actin filament severing and capping by human gelsolin in vitro. The findings implicate D3 polyphosphoinositides and integrin signaling in PMA-mediated platelet stimulation and implicate D3 containing phosphoinositides generated in response to protein kinase C activation and GPIIb-IIIa signaling as late-acting intermediates leading to filopodial actin assembly.
authors.affiliation: Divisions of Experimental Medicine and Hematology-Oncology, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Hartwig
authors.forename: S
authors.initials: S
authors.lastname: Kung
authors.forename: T
authors.initials: T
authors.lastname: Kovacsovics
authors.forename: P A
authors.initials: PA
authors.lastname: Janmey
authors.forename: L C
authors.initials: LC
authors.lastname: Cantley
authors.forename: T P
authors.initials: TP
authors.lastname: Stossel
authors.forename: A
authors.initials: A
authors.lastname: Toker
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000648:ultrastructure*; D000199:Actins / Q000378:metabolism*; D000730:Androstadienes / Q000494:pharmacology; D001792:Blood Platelets / Q000502:physiology* / Q000648:ultrastructure; D003571:Cytochalasin B / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018260:Gelsolin / Q000378:metabolism; D006801:Humans; D009842:Oligopeptides / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000502:physiology*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000502:physiology*; D018179:Receptors, Thrombin / Q000502:physiology*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D000077191:Wortmannin
chemical_list: D000199:Actins; D000730:Androstadienes; D004791:Enzyme Inhibitors; D018260:Gelsolin; D009842:Oligopeptides; D019269:Phosphatidylinositol 4,5-Diphosphate; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D018179:Receptors, Thrombin; D003571:Cytochalasin B; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D013755:Tetradecanoylphorbol Acetate; D000077191:Wortmannin