Glyeoproteins VI and Ib-IX-V stimulate tyrosine phosphorylation of tyrosine kinase Syk and phospholipase Cγ2 at distinct sites

Katsue Suzuki-Inoue, Jonathan I. Wilde, Robert K. Andrews, Jocelyn M. Auger, Reuben P. Siraganian, Fujio Sekiya, Sue Goo Rhee, Steve P. Watson

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Glycoproteins GPVI and GPIb-IX-V stimulate robust tyrosine phosphorylation of Syk and PLCγ2 (phospholipase Cγ2) in washed platelets, but only the former stimulates pronounced activation of phospholipase. Using phospho-specific antibodies, we demonstrate that GPVI, but not GPIb-IX-V, stimulates significant tyrosine phosphorylation of Syk at the autophosphorylation site pY525/526, a marker of Syk activity. In addition, GPVI stimulates tyrosine phosphorylation of PLCγ2 at Tyr753 and Tyr759, whereas GPIb-IX-V only induces significant phosphorylation at Tyr753. Both receptors stimulate tyrosine phosphorylation of Btk at the regulatory Tyr223 and Tyr551. Syk and Btk phosphorylate peptides from PLCγ2 containing Tyr753 and Tyr759 respectively, suggesting that they may stimulate phosphorylation at these sites in phospholipase. Studies using PLCγ2-deficient platelets demonstrated that phospholipase is not required for the activation of integrin αIIbβ3 by GPIb-IX-V. Our results demonstrate fundamental differences between GPVI and GPIb-IX-V in the regulation of tyrosine phosphorylation of Syk and PLCγ2 consistent with the functional impairment of phospholipase in signalling by GPIb-IX-V.

Original languageEnglish
Pages (from-to)1023-1029
Number of pages7
JournalBiochemical Journal
Issue number3
Publication statusPublished - 15 Mar 2004
Externally publishedYes


  • Blood platelet
  • Collagen
  • Glycoprotein Ib-IX-V (GPIB-IX-V)
  • Glycoprotein VI (GPVI)
  • Phospholipase Cγ2 (PLCγ2)
  • von Willebrand factor (vWF)

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