title: C-terminal peptide of thrombospondin-1 induces platelet aggregation through the Fc receptor gamma-chain-associated signaling pathway and by agglutination.
abstract: A peptide from the C-terminal domain of thrombospondin-1 (Arg-Phe-Tyr-Val-Val-Met-Trp-Lys; known as 4N1-1) has been reported to induce platelet aggregation and to bind to the integrin-associated protein (IAP), which is also known as CD47. In this study, it was discovered that 4N1-1 or its derivative peptide, 4N1K, induces rapid phosphorylation of the Fc receptor (FcR) gamma chain, Syk, SLP-76, and phospholipase C gamma2 in human platelets. A specific inhibitor of Src family kinases, 4-amino-4-(4-methylphenyl)-7-(t-butyl) pyrazola[3,4-d]pyrimidine, prevented phosphorylation of these proteins, abolished platelet secretion, and reduced aggregation by approximately 50%. A similar inhibition of aggregation to 4N1-1 was obtained in the presence of Arg-Gly-Asp-Ser in mouse platelets deficient in FcR gamma chain or SLP-76 and in patients with type I Glanzmann thrombasthenia. These results show that 4N1-1 signals through a pathway similar to that used by the collagen receptor glycoprotein (GP) VI. The alphaIIbbeta3-independent aggregation induced by 4N1-1 was also observed in fixed platelets and platelets from patients with Bernard-Soulier syndrome, which are deficient in GPIbalpha. Surprisingly, the ability of 4N1-1 to stimulate aggregation and tyrosine phosphorylation was not altered in platelets pretreated with anti-IAP antibodies and in IAP-deficient mice. These results show that the C-terminal peptide of thrombospondin induces platelet aggregation through the FcR gamma-chain signaling pathway and through agglutination. The latter pathway is independent of signaling events and does not use GPIbalpha or alphaIIbbeta3. Neither of these pathways is mediated by IAP.
authors.affiliation: Department of Pharmacology, University of Oxford, United Kingdom. david.tulasne@pharmacology.oxford.ac.uk
authors.forename: D
authors.initials: D
authors.lastname: Tulasne
authors.forename: B A
authors.initials: BA
authors.lastname: Judd
authors.forename: M
authors.initials: M
authors.lastname: Johansen
authors.forename: N
authors.initials: N
authors.lastname: Asazuma
authors.forename: D
authors.initials: D
authors.lastname: Best
authors.forename: E J
authors.initials: EJ
authors.lastname: Brown
authors.forename: M
authors.initials: M
authors.lastname: Kahn
authors.forename: G A
authors.initials: GA
authors.lastname: Koretzky
authors.forename: S P
authors.initials: SP
authors.lastname: Watson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D001792:Blood Platelets / Q000502:physiology; D051928:CD47 Antigen; D002352:Carrier Proteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D010974:Platelet Aggregation / Q000187:drug effects*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000502:physiology; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000502:physiology; D017452:Receptors, IgG / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism; D015398:Signal Transduction; D019700:Thrombospondin 1 / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D015703:Antigens, CD; D051928:CD47 Antigen; C497894:CD47 protein, human; D002352:Carrier Proteins; C497895:Cd47 protein, mouse; D010446:Peptide Fragments; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D017452:Receptors, IgG; D019700:Thrombospondin 1; D019000:Phosphotyrosine; D012701:Serotonin