The cleaved peptide of the thrombin receptor is a strong platelet agonist

Proc Natl Acad Sci U S A. 1998 Mar 17;95(6):3082-7. doi: 10.1073/pnas.95.6.3082.


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.

MeSH terms

  • Amino Acid Sequence
  • Androstadienes / pharmacology
  • Blood Platelets / drug effects*
  • Dose-Response Relationship, Drug
  • Drug Synergism
  • Enzyme Inhibitors / pharmacology
  • Genistein / pharmacology
  • Humans
  • Molecular Sequence Data
  • Peptide Fragments / pharmacology*
  • Platelet Activation / physiology*
  • Platelet Glycoprotein GPIIb-IIIa Complex / metabolism
  • Platelet Glycoprotein GPIb-IX Complex / metabolism
  • Signal Transduction / drug effects
  • Staurosporine / pharmacology
  • Wortmannin


  • Androstadienes
  • Enzyme Inhibitors
  • Peptide Fragments
  • Platelet Glycoprotein GPIIb-IIIa Complex
  • Platelet Glycoprotein GPIb-IX Complex
  • thrombin receptor peptide (1-41)
  • thrombin receptor peptide (42-55)
  • Genistein
  • Staurosporine
  • Wortmannin