RESUMO
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.
Assuntos
Antígenos CD/metabolismo , Astrócitos/metabolismo , Adesões Focais/metabolismo , Glicoproteínas da Membrana de Plaquetas/metabolismo , Antígenos Thy-1/metabolismo , Antígenos Thy-1/fisiologia , Sequência de Aminoácidos , Animais , Anticorpos Monoclonais/imunologia , Antígenos CD/imunologia , Encéfalo/metabolismo , Adesão Celular , Células Cultivadas , Proteínas do Citoesqueleto/metabolismo , Proteínas da Matriz Extracelular/metabolismo , Integrina beta3 , Camundongos , Dados de Sequência Molecular , Neurônios/metabolismo , Oligopeptídeos/farmacologia , Fosfotirosina/metabolismo , Glicoproteínas da Membrana de Plaquetas/imunologia , Ratos , Homologia de Sequência de Aminoácidos , Transdução de Sinais , Antígenos Thy-1/química , Células Tumorais CultivadasRESUMO
We designed a trap system to isolate different amino acid sequences which could target proteins to the cell surface via GPI anchor transfer. This selection procedure is based on the insertion of various sequences which regenerate a functional GPI anchor signal sequence and therefore provoke re-expression at the surface of a reporter molecule. Using this trap for cell surface targeting sequences, we could show the importance of the defined elements essential for GPI anchor addition. Such a system could be used for an exhaustive analysis of the carboxyl terminus structural requirements for GPI membrane anchoring.
Assuntos
Antígenos de Superfície/metabolismo , Glicosilfosfatidilinositóis/biossíntese , Glicoproteínas de Membrana/metabolismo , Sequência de Aminoácidos , Antígenos de Superfície/química , Células Cultivadas , Citometria de Fluxo , Vetores Genéticos , Humanos , Glicoproteínas de Membrana/química , Peptídeos/metabolismo , Sinais Direcionadores de Proteínas , TransfecçãoRESUMO
We designed a trap system to isolate different amino acid sequences which could target proteins to the cell surface via GPI anchor transfer. This selection procedure is based on the insertion of various sequences which regenerate a functional GPI anchor signal sequence and therefore provoke re-expression at the surface of a reporter molecule. Using this trap for cell surface targeting sequences, we could show the importance of the defined elements essential for GPI anchor addition. Such a system could be used for an exhaustive analysis of the carboxyl terminus structural requeriments for GPI membrane anchoring