title: Identification of FcgammaRIIa as the ITAM-bearing receptor mediating alphaIIbbeta3 outside-in integrin signaling in human platelets.
abstract: Immunoreceptor tyrosine-based activation motif (ITAM)-containing proteins have recently been demonstrated in macrophages and neutrophils to be required for cell surface integrins to transmit activation signals into the cell. To identify ITAM-bearing proteins that mediate signaling via the platelet-specific integrin alphaIIbbeta3, fibrinogen binding was induced by (1) allowing platelets to spread directly on immobilized fibrinogen, or (2) activating the PAR1 thrombin receptor on platelets in suspension. Both initiated strong, ligand binding-dependent tyrosine phosphorylation of the ITAM-bearing platelet Fc receptor, FcgammaRIIa, as well as downstream phosphorylation of the protein tyrosine kinase Syk and activation of phospholipase Cgamma2 (PLCgamma2). Addition of Fab fragments of an FcgammaRIIa-specific monoclonal antibody strongly inhibited platelet spreading on immobilized fibrinogen, as well as downstream tyrosine phosphorylation of FcgammaRIIa, Syk, and PLCgamma2, and platelets from a patient whose platelets express reduced levels of FcgammaRIIa exhibited markedly reduced spreading on immobilized fibrinogen. Finally, fibrinogen binding-induced FcgammaRIIa phosphorylation did not occur in human platelets expressing a truncated beta3 cytoplasmic domain. Taken together, these data suggest that ligand binding to platelet alphaIIbbeta3 induces integrin cytoplasmic domain-dependent phosphorylation of FcgammaRIIa, which then enlists selected components of the immunoreceptor signaling cascade to transmit amplification signals into the cell.
authors.affiliation: Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Boylan
authors.forename: Cunji
authors.initials: C
authors.lastname: Gao
authors.forename: Vipul
authors.initials: V
authors.lastname: Rathore
authors.forename: Joan C
authors.initials: JC
authors.lastname: Gill
authors.forename: Debra K
authors.initials: DK
authors.lastname: Newman
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Newman
mesh_terms: D020816:Amino Acid Motifs; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D002460:Cell Line; D002465:Cell Movement / Q000187:drug effects; D002648:Child; D005340:Fibrinogen / Q000494:pharmacology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008024:Ligands; D051966:Phospholipase C gamma / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D015539:Platelet Activation / Q000187:drug effects; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D017452:Receptors, IgG / Q000737:chemistry* / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D012995:Solubility / Q000187:drug effects; D000072377:Syk Kinase
chemical_list: C080568:Fc gamma receptor IIA; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D017452:Receptors, IgG; D005340:Fibrinogen; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D051966:Phospholipase C gamma