title: Thy-1 binds to integrin beta(3) on astrocytes and triggers formation of focal contact sites.
abstract: BACKGROUND
  Thy-1 is an abundant neuronal glycoprotein in mammals. Despite such prevalence, Thy-1 function remains largely obscure in the absence of a defined ligand. Astrocytes, ubiquitous cells of the brain, express a putative Thy-1 ligand that prevents neurite outgrowth. In this paper, a ligand molecule for Thy-1 was identified, and the consequences of Thy-1 binding for astrocyte function were investigated.
  
  
  RESULTS
  Thy-1 has been implicated in cell adhesion and, indeed, all known Thy-1 sequences were found to contain an integrin binding, RGD-like sequence. Thy-1 interaction with beta3 integrin on astrocytes was demonstrated in an adhesion assay using a thymoma line (EL-4) expressing high levels of Thy-1. EL-4 cells bound to astrocytes five times more readily than EL-4(-f), control cells lacking Thy-1. Binding was blocked by either anti-Thy-1 or anti-beta3 antibodies, by RGD-related peptides, or by soluble Thy-1-Fc chimeras. However, neither RGE/RLE peptides nor Thy-1(RLE)-Fc fusion protein inhibited the interaction. Immobilized Thy-1-Fc, but not Thy-1(RLE)-Fc fusion protein supported the attachment and spreading of astrocytes in a Mn(2+)-dependent manner. Binding to Thy-1-Fc was inhibited by RGD peptides. Moreover, vitronectin, fibrinogen, denatured collagen (dcollagen), and a kistrin-derived peptide, but not fibronectin, also mediated Mn(2+)-dependent adhesion, suggesting the involvement of beta3 integrin. The addition of Thy-1 to matrix-bound astrocytes induced recruitment of paxillin, vinculin, and focal adhesion kinase (FAK) to focal contacts and increased tyrosine phosphorylation of proteins such as p130(Cas) and FAK. Furthermore, astrocyte binding to immobilized Thy-1-Fc alone was sufficient to promote focal adhesion formation and phosphorylation on tyrosine.
  
  
  CONCLUSIONS
  Thy-1 binds to beta3 integrin and triggers tyrosine phosphorylation of focal adhesion proteins in astrocytes, thereby promoting focal adhesion formation, cell attachment, and spreading.
authors.affiliation: ICBM-Faculty of Medicine, University of Chile, Santiago, Chile. lleyton@machi.med.uchile.cl
authors.forename: L
authors.initials: L
authors.lastname: Leyton
authors.forename: P
authors.initials: P
authors.lastname: Schneider
authors.forename: C V
authors.initials: CV
authors.lastname: Labra
authors.forename: C
authors.initials: C
authors.lastname: Rüegg
authors.forename: C A
authors.initials: CA
authors.lastname: Hetz
authors.forename: A F
authors.initials: AF
authors.lastname: Quest
authors.forename: C
authors.initials: C
authors.lastname: Bron
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D015703:Antigens, CD / Q000276:immunology / Q000378:metabolism*; D001253:Astrocytes / Q000378:metabolism*; D001921:Brain / Q000378:metabolism; D002448:Cell Adhesion; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D022001:Focal Adhesions / Q000378:metabolism*; D039661:Integrin beta3; D051379:Mice; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D019000:Phosphotyrosine / Q000378:metabolism; D010980:Platelet Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism*; D051381:Rats; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D018800:Thy-1 Antigens / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D003598:Cytoskeletal Proteins; D016326:Extracellular Matrix Proteins; D039661:Integrin beta3; D009842:Oligopeptides; D010980:Platelet Membrane Glycoproteins; D018800:Thy-1 Antigens; D019000:Phosphotyrosine; C047981:arginyl-glycyl-aspartic acid