title: Collagen-stimulated activation of Syk but not c-Src is severely compromised in human platelets lacking membrane glycoprotein VI.
abstract: Activation of circulating platelets by subendothelial collagen is an essential event in vascular hemostasis. In human platelets, two membrane glycoprotein (GP) abnormalities, integrin alpha2 beta1 deficiency and GPVI deficiency, have been reported to result in severe hyporesponsiveness to fibrillar collagen. Although it has been well established that integrin alpha2 beta1, also known as the GPIa-IIa complex, functions as a primary platelet adhesion receptor for collagen, the mechanism by which GPVI contributes to collagen-platelet interaction has been ill defined to date. However, our recent observation that GPVI cross-linking couples to cyclic AMP-insensitive activation of c-Src and Syk tyrosine kinases suggested a potential role for GPVI in regulating protein-tyrosine phosphorylation by collagen (Ichinohe, T., Takayama, H., Ezumi, Y., Yanagi, S., Yamamura, H., and Okuma, M. (1995) J. Biol. Chem. 270, 28029-28036). To further investigate this hypothesis, here we examined the collagen-induced protein-tyrosine phosphorylation in GPVI-deficient platelets expressing normal amounts of alpha2 beta1. In response to collagen, these platelets exhibited alpha2 beta1-dependent c-Src activation accompanied by tyrosine phosphorylation of several substrates including cortactin. In contrast, severe defects were observed in collagen-stimulated Syk activation and tyrosine phosphorylation of phospholipase C-gamma2, Vav, and focal adhesion kinase, implicating a specific requirement of GPVI for recruiting these molecules to signaling cascades evoked by collagen-platelet interaction.
authors.affiliation: Department of Hematology and Oncology, Clinical Sciences for Pathological Organs, Graduate School of Medicine, Kyoto University, Sakyo-ku, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ichinohe
authors.forename: H
authors.initials: H
authors.lastname: Takayama
authors.forename: Y
authors.initials: Y
authors.lastname: Ezumi
authors.forename: M
authors.initials: M
authors.lastname: Arai
authors.forename: N
authors.initials: N
authors.lastname: Yamamoto
authors.forename: H
authors.initials: H
authors.lastname: Takahashi
authors.forename: M
authors.initials: M
authors.lastname: Okuma
mesh_terms: D000328:Adult; D015815:Cell Adhesion Molecules / Q000378:metabolism; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D003094:Collagen / Q000502:physiology; D051356:Cortactin; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D016023:Integrins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D051966:Phospholipase C gamma; D010750:Phosphoproteins / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins / Q000172:deficiency*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051567:Proto-Oncogene Proteins c-vav; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D038981:Receptors, Collagen; D015398:Signal Transduction; D000072377:Syk Kinase; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: C495868:CTTN protein, human; D015815:Cell Adhesion Molecules; D018797:Cell Cycle Proteins; D051356:Cortactin; D004792:Enzyme Precursors; D016023:Integrins; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D008840:Microfilament Proteins; D010750:Phosphoproteins; D010980:Platelet Membrane Glycoproteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D038981:Receptors, Collagen; C496618:VAV1 protein, human; C098341:platelet membrane glycoprotein VI; D019000:Phosphotyrosine; D003094:Collagen; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D016392:Proto-Oncogene Proteins pp60(c-src); C000606896:SYK protein, human; D000072377:Syk Kinase; D010738:Type C Phospholipases; D051966:Phospholipase C gamma