Tyrosine phosphorylation of the Fc receptor gamma-chain in collagen-stimulated platelets.
Stimulation of platelets by the extracellular matrix protein collagen leads to activation of a tyrosine kinase-dependent mechanism resulting in secretion and aggregation. Tyrosine phosphorylation of the tyrosine kinase Syk and phospholipase Cgamma2 are early events in collagen-induced activation. We recently proposed that collagen-signaling in platelets involves a receptor or a receptor-associated protein containing an immunoreceptor tyrosine-based activation motif (ITAM) enabling interaction with Syk. In this report we show that collagen stimulation of platelets causes rapid tyrosine phosphorylation of the ITAM containing Fc receptor gamma-chain and that this is precipitated by the tandem Src homology 2 (SH2) domains of Syk expressed as a fusion protein. In addition we demonstrate an association between the Fc receptor gamma-chain with endogenous Syk in collagen-stimulated platelets. The Fc receptor gamma-chain undergoes tyrosine phosphorylation in platelets stimulated by a collagen-related peptide which does not bind the integrin alpha2beta1 and by the lectin wheat germ agglutinin. In contrast, cross-linking of the platelet low affinity receptor for immune complexes, FcgammaRIIA, or stimulation by thrombin does not induce phosphorylation of the Fc receptor gamma-chain. The present results provide a molecular basis for collagen activation of platelets which is independent of the integrin alpha2beta1 and involves phosphorylation of the Fc receptor gamma-chain, its association with Syk and subsequent phosphorylation of phospholipase Cgamma2. Collagen is the first example of a nonimmune receptor stimulus to signal through a pathway closely related to signaling by immune receptors.
Gibbins
J
J
Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, United Kingdom.
Asselin
J
J
Farndale
R
R
Barnes
M
M
Law
C L
CL
Watson
S P
SP
D001792:Blood Platelets / Q000187:drug effects*; D003094:Collagen / Q000494:pharmacology*; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D010766:Phosphorylation; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D017452:Receptors, IgG / Q000378:metabolism*; D011993:Recombinant Fusion Proteins; D015398:Signal Transduction; D000072377:Syk Kinase; D014443:Tyrosine / Q000378:metabolism; D018909:src Homology Domains
D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D017452:Receptors, IgG; D011993:Recombinant Fusion Proteins; D014443:Tyrosine; D003094:Collagen; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase