title: Glycoproteins VI and Ib-IX-V stimulate tyrosine phosphorylation of tyrosine kinase Syk and phospholipase Cgamma2 at distinct sites.
abstract: Glycoproteins GPVI and GPIb-IX-V stimulate robust tyrosine phosphorylation of Syk and PLCg2 (phospholipase Cg2) 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 PLCg2 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 PLCg2 containing Tyr753 and Tyr759 respectively, suggesting that they may stimulate phosphorylation at these sites in phospholipase. Studies using PLCg2-deficient platelets demonstrated that phospholipase is not required for the activation of integrin aIIbb3 by GPIb-IX-V. Our results demonstrate fundamental differences between GPVI and GPIb-IX-V in the regulation of tyrosine phosphorylation of Syk and PLCg2 consistent with the functional impairment of phospholipase in signalling by GPIb-IX-V.
authors.affiliation: Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK. katsuei@yamanashi.ac.jp
authors.forename: Katsue
authors.initials: K
authors.lastname: Suzuki-Inoue
authors.forename: Jonathan I
authors.initials: JI
authors.lastname: Wilde
authors.forename: Robert K
authors.initials: RK
authors.lastname: Andrews
authors.forename: Jocelyn M
authors.initials: JM
authors.lastname: Auger
authors.forename: Reuben P
authors.initials: RP
authors.lastname: Siraganian
authors.forename: Fujio
authors.initials: F
authors.lastname: Sekiya
authors.forename: Sue Goo
authors.initials: SG
authors.lastname: Rhee
authors.forename: Steve P
authors.initials: SP
authors.lastname: Watson
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004792:Enzyme Precursors / Q000737:chemistry* / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D051966:Phospholipase C gamma; D010766:Phosphorylation; D010974:Platelet Aggregation; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000737:chemistry* / Q000378:metabolism*; D012310:Ristocetin / Q000494:pharmacology; D000072377:Syk Kinase; D010738:Type C Phospholipases / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D014443:Tyrosine / Q000378:metabolism; D014841:von Willebrand Factor / Q000494:pharmacology
chemical_list: D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D014841:von Willebrand Factor; D012310:Ristocetin; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D010738:Type C Phospholipases; D051966:Phospholipase C gamma