title: SHPS-1 negatively regulates integrin alphaIIbbeta3 function through CD47 without disturbing FAK phosphorylation.
abstract: CD47 (integrin-associated protein) serves as a receptor for thrombospondin-1 (TSP-1) and Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 (SHPS-1), and the TSP-1/CD47 interaction has been believed to augment integrin-mediated platelet function. Here, employing SHPS-1-immunoglobulin (Ig) as a ligand, we have newly demonstrated that CD47 acts as an inhibitory receptor for platelet function. The binding of SHPS-1-Ig was solely mediated by CD47, because CD47-deficient platelets failed to bind murine SHPS-1-Ig. The human SHPS-1/CD47 interaction inhibited the platelet aggregation induced by several kinds of agonists at a low concentration. Moreover, human SHPS-1 expressed on the cell surface as well as soluble SHPS-1-Ig markedly inhibited the platelet spreading on, but not initial adhesion to, immobilized fibrinogen. Again, neither murine SHPS-1 expressed on the cell surface nor murine SHPS-1-Ig inhibited the spreading of CD47-deficient platelets. We further investigated the tyrosine phosphorylation of signaling proteins during platelet spreading on immobilized fibrinogen. Unexpectedly, SHPS-1 inhibited alpha(IIb)beta(3)-mediated platelet spreading without disturbing focal adhesion kinase (FAK) tyrosine phosphorylation. Further examination revealed that SHPS-1 inhibited the tyrosine phosphorylation of alpha-actinin, a downstream effector of FAK, but not of cortactin. Thus, it is likely that the SHPS-1/CD47 interaction inhibits alpha(IIb)beta(3)-mediated outside-in signaling by interfering with the downstream pathway of FAK. Taken together, our data suggest that SHPS-1 negatively regulates platelet function via CD47, especially alpha(IIb)beta(3)-mediated outside-in signaling.
authors.affiliation: Department of Internal Medicine and Molecular Science, Graduate School of Medicine B5, Osaka University, Osaka, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Kato
authors.forename: Shigenori
authors.initials: S
authors.lastname: Honda
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Yoshida
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Kashiwagi
authors.forename: Masamichi
authors.initials: M
authors.lastname: Shiraga
authors.forename: Nakayuki
authors.initials: N
authors.lastname: Honma
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kurata
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Tomiyama
mesh_terms: D000185:Actinin / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis*; D000943:Antigens, Differentiation / Q000378:metabolism / Q000502:physiology*; D001792:Blood Platelets / Q000378:metabolism; D051928:CD47 Antigen; D016466:CHO Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D051356:Cortactin; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D005340:Fibrinogen / Q000737:chemistry / Q000378:metabolism; D005434:Flow Cytometry; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005786:Gene Expression Regulation; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism; D010766:Phosphorylation; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D014443:Tyrosine / Q000737:chemistry
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D051928:CD47 Antigen; C497894:CD47 protein, human; C495868:CTTN protein, human; C497895:Cd47 protein, mouse; D051356:Cortactin; C495869:Cttn protein, mouse; D008562:Membrane Glycoproteins; D008840:Microfilament Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C501922:Sirpa protein, mouse; D011971:Receptors, Immunologic; C501920:SIRPA protein, human; D000185:Actinin; D014443:Tyrosine; D005340:Fibrinogen; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; C496051:Ptk2 protein, mouse