title: The cleaved peptide of the thrombin receptor is a strong platelet agonist.
abstract: Thrombin cleaves its G-protein-linked seven-transmembrane domain receptor, thereby releasing a 41-aa peptide and generating a new amino terminus that acts as a tethered ligand for the receptor. Peptides corresponding to the new amino terminal end of the proteolyzed seven-transmembrane domain thrombin receptor [TR42-55, SFLLRNPNDKYEPF, also known as TRAP (thrombin receptor-activating peptide)], previously have been demonstrated to activate the receptor. In this study, we demonstrate that the 41-aa cleaved peptide, TR1-41 (MGPRRLLLVAACFSLCGPLLSARTRARRPESKATNATLDPR) is a strong platelet agonist. TR1-41 induces platelet aggregation. In whole-blood flow cytometric studies, TR1-41 was shown to be more potent than TR42-55 and almost as potent as thrombin, as determined by the degree of increase in: (i) platelet surface expression of P-selectin (reflecting alpha granule secretion); (ii) exposure of the fibrinogen binding site on the glycoprotein (GP) IIb-IIIa complex; and (iii) fibrinogen binding to the activated GPIIb-IIIa complex. As determined by experiments with inhibitors [prostaglandin I2, staurosporine, wortmannin, the endothelium-derived relaxing factor congener S-nitroso-N-acetylcysteine (SNAC), EDTA, EGTA, and genestein], and with Bernard-Soulier or Glanzmann's platelets, we demonstrated that TR1-41-induced platelet activation is: (i) inhibited by cyclic AMP; (ii) mediated by protein kinase C, phosphatidyl inositol-3-kinase, myosin light chain kinase, and intracellular protein tyrosine kinases; (iii) dependent on extracellular calcium; and (iv) independent of the GPIb-IX and GPIIb-IIIa complexes. TR1-41-induced platelet activation was synergistic with TR42-55. In summary, the cleaved peptide of the seven-transmembrane domain TR (TR1-41) is a strong platelet agonist.
authors.affiliation: Center for Platelet Function Studies, University of Massachusetts Medical Center, Worcester, MA 01655, USA. Mark.Furman@banyan.ummed.edu
authors.forename: M I
authors.initials: MI
authors.lastname: Furman
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.forename: S E
authors.initials: SE
authors.lastname: Benoit
authors.forename: R C
authors.initials: RC
authors.lastname: Becker
authors.forename: M R
authors.initials: MR
authors.lastname: Barnard
authors.forename: A D
authors.initials: AD
authors.lastname: Michelson
mesh_terms: D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology; D006801:Humans; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000494:pharmacology*; D015539:Platelet Activation / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D019311:Staurosporine / Q000494:pharmacology; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D004791:Enzyme Inhibitors; D010446:Peptide Fragments; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; C111242:thrombin receptor peptide (1-41); C072032:thrombin receptor peptide (42-55); D019833:Genistein; D019311:Staurosporine; D000077191:Wortmannin