Rapid stimulation of tyrosine phosphorylation signals downstream of G-protein-coupled receptors for thromboxane A2 in human platelets

Pietro Minuz, Laura Fumagalli, Stefania Gaino, Rosa M. Tommasoli, Maurizio Degan, Chiara Cavallini, Anna Lecchi, Marco Cattaneo, Clara Lechi Santonastaso, Giorgio Berton

Research output: Contribution to journalArticlepeer-review


Signals ensuing from trimeric G-protein-coupled receptors synergize to induce platelet activation. At low doses, the thromboxane A2 analogue U46619 does not activate integrin αIIbβ3 or trigger platelet aggregation, but it induces shape changes. In the present study, we addressed whether low doses of U46619 trigger tyrosine phosphorylation independently of integrin αIIbβ3 activation and ADP secretion, and synergize with adrenaline (epinephrine) to induce aggregation in acetylsalicylic acid (aspirin)-treated platelets. Low doses of U46619 triggered tyrosine phosphorylation of different proteins, including FAK (focal adhesion kinase), Src and Syk, independently of signals ensuing from integrin αIIbβ3 or ADP receptors engaged by secreted ADP. The G12/13-mediated Rho/Rho-kinase pathway was also increased by low doses of U46619; however, this pathway was not upstream of tyrosine phosphorylation, because this occurred in the presence of the Rho-kinase inhibitor Y-27632. Although low doses of U46619 or adrenaline alone were unable to trigger platelet aggregation and integrin αIIbβ3 activation, the combination of the two stimuli effectively induced these responses. PP2, a tyrosine kinase inhibitor, and Y-27632 inhibited platelet activation induced by low doses of U46619 plus adrenaline and, when used in combination, totally suppressed this platelet response. In addition, the two inhibitors selectively blocked tyrosine kinases and the Rho/Rho-kinase pathway respectively. These findings suggest that both tyrosine phosphorylation and the Rho/Rho-kinase pathway are required to activate platelet aggregation via G12/13 plus Gz signalling.

Original languageEnglish
Pages (from-to)127-134
Number of pages8
JournalBiochemical Journal
Issue number1
Publication statusPublished - Nov 15 2006


  • G-protein
  • Platelet
  • Rho
  • Rho kinase
  • Thromboxane A (TXA )
  • Tyrosine phosphorylation

ASJC Scopus subject areas

  • Biochemistry


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