title: The N-terminal SH2 domain of Syk is required for (hem)ITAM, but not integrin, signaling in mouse platelets.
abstract: We have used a novel knockin mouse to investigate the effect of disruption of phosphotyrosine binding of the N-terminal SH2 domain of Syk on platelet activation by GPVI, CLEC-2, and integrin αIIbβ3. The Syk(R41Afl/fl) mouse was crossed to a PF4-Cre(+) mouse to induce expression of the Syk mutant in the megakaryocyte/platelet lineage. Syk(R41Afl/fl;PF4-Cre) mice are born at approximately 50% of the expected frequency and have a similar phenotype to Syk(fl/fl;PF4-Cre) mice, including blood-lymphatic mixing and chyloascites. Anastomosis of the venous and lymphatic vasculatures can be seen in the mesenteric circulation accounting for rapid and continuous mixing of the 2 vasculatures. Platelet activation by CLEC-2 and GPVI is abolished in Syk(R41Afl/fl;PF4-Cre) platelets. Syk phosphorylation on Tyr519/20 is blocked in CLEC-2-stimulated platelets, suggesting a model in which binding of Syk via its N-terminal SH2 domain regulates autophosphorylation. In contrast, outside-in signaling by integrin αIIbβ3 is not altered, but it is inhibited in the presence of inhibitors of Src and Syk tyrosine kinases. These results demonstrate that αIIbβ3 regulates Syk through an ITAM-independent pathway in mice and provide novel insight into the course of events underlying Syk activation and hemITAM phosphorylation by CLEC-2.
authors.affiliation: Centre for Cardiovascular Sciences, Institute for Biomedical Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom; and.
authors.forename: Craig E
authors.initials: CE
authors.lastname: Hughes
authors.affiliation: Centre for Cardiovascular Sciences, Institute for Biomedical Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom; and.
authors.forename: Brenda A
authors.initials: BA
authors.lastname: Finney
authors.affiliation: Ozgene Pty Ltd, Bentley, WA, Australia.
authors.forename: Frank
authors.initials: F
authors.lastname: Koentgen
authors.affiliation: Centre for Cardiovascular Sciences, Institute for Biomedical Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom; and.
authors.forename: Kate L
authors.initials: KL
authors.lastname: Lowe
authors.affiliation: Centre for Cardiovascular Sciences, Institute for Biomedical Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom; and.
authors.forename: Steve P
authors.initials: SP
authors.lastname: Watson
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D037181:Lectins, C-Type / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D015539:Platelet Activation; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D000072377:Syk Kinase; D018909:src Homology Domains
chemical_list: C529518:CLEC-2 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D037181:Lectins, C-Type; D010750:Phosphoproteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse