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Thrombospondin Mediates Focal Adhesion Disassembly through Interactions with Cell Surface Calreticulin

2000; Elsevier BV; Volume: 275; Issue: 46 Linguagem: Inglês

10.1074/jbc.m005951200

1083-351X

Silvia M. Goicoechea, A. Wayne Orr, Manuel A. Pallero, Paul Eggleton, Joanne E. Murphy-Ullrich,

Apelin-related biomedical research

Thrombospondin induces reorganization of the actin cytoskeleton and restructuring of focal adhesions. This activity is localized to amino acids 17–35 in the N-terminal heparin-binding domain of thrombospondin and can be replicated by a peptide (hep I) with this sequence. Thrombospondin/hep I stimulate focal adhesion disassembly through a mechanism involving phosphoinositide 3-kinase activation. However, the receptor for this thrombospondin sequence is unknown. We now report that calreticulin on the cell surface mediates focal adhesion disassembly by thrombospondin/hep I. A 60-kDa protein from endothelial cell detergent extracts has homology and immunoreactivity to calreticulin, binds a hep I affinity column, and neutralizes thrombospondin/hep I-mediated focal adhesion disassembly. Calreticulin on the cell surface was confirmed by biotinylation, confocal microscopy, and by fluorescence-activated cell sorting analyses. Thrombospondin and calreticulin potentially bind through the hep I sequence, since thrombospondin-calreticulin complex formation can be blocked specifically by hep I peptide. Antibodies to calreticulin and preincubation of thrombospondin/hep I with glutathione S -transferase-calreticulin block thrombospondin/hep I-mediated focal adhesion disassembly and phosphoinositide 3-kinase activation, suggesting that calreticulin is a component of the thrombospondin-induced signaling cascade that regulates cytoskeletal organization. These data identify both a novel receptor for the N terminus of thrombospondin and a distinct role for cell surface calreticulin in cell adhesion.