title: Vimentin exposed on activated platelets and platelet microparticles localizes vitronectin and plasminogen activator inhibitor complexes on their surface.
abstract: Type 1 plasminogen activator inhibitor (PAI-1), the primary inhibitor of tissue-type plasminogen activator (t-PA), is found in plasma and platelets. PAI-1 circulates in complex with vitronectin (Vn), an interaction that stabilizes PAI-1 in its active conform. In this study, we examined the binding of platelet-derived Vn and PAI-1 to the surface of isolated platelets. Flow cytometry indicate that, like P-selectin, PAI-1, and Vn are found on the surface of thrombin- or calcium ionophore-activated platelets and platelet microparticles. The binding of PAI-1 to the activated platelet surface is Vn-dependent. Vn mediates the binding of PAI-1 to platelet surfaces through a high affinity (K(d) of 80 nm) binding interaction with the NH(2) terminus of vimentin, and this Vn-binding domain is expressed on the surface of activated platelets and platelet microparticles. Immunological and functional assays indicate that only -5% of the total PAI-1 in platelet releasates is functionally active, and it co-precipitates with Vn, and the vimentin-enriched cytoskeleton fraction of activated platelet debris. The remaining platelet PAI-1 is inactive, and does not associate with the cytoskeletal debris of activated platelets. Confocal microscopic analysis of platelet-rich plasma clots confirm the co-localization of PAI-1 with Vn and vimentin on the surface of activated platelets, and platelet microparticles. These findings suggest that platelet vimentin may regulate fibrinolysis in plasma and thrombi by binding platelet-derived Vn.PAI-1 complexes.
authors.affiliation: Department of Pathology and Molecular Medicine, McMaster University and the Hamilton Civic Hospitals Research Centre, 711 Concession Street, Hamilton, Ontario L8V 1C3, Canada. podort@mcmaster.ca
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Podor
authors.forename: Davindra
authors.initials: D
authors.lastname: Singh
authors.forename: Paul
authors.initials: P
authors.lastname: Chindemi
authors.forename: Denise M
authors.initials: DM
authors.lastname: Foulon
authors.forename: Robert
authors.initials: R
authors.lastname: McKelvie
authors.forename: Jeffrey I
authors.initials: JI
authors.lastname: Weitz
authors.forename: Richard
authors.initials: R
authors.lastname: Austin
authors.forename: Ghislain
authors.initials: G
authors.lastname: Boudreau
authors.forename: Richard
authors.initials: R
authors.lastname: Davies
mesh_terms: D000818:Animals; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism*; D015153:Blotting, Western; D002417:Cattle; D003902:Detergents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D006801:Humans; D007150:Immunohistochemistry; D007700:Kinetics; D008024:Ligands; D018613:Microscopy, Confocal; D008957:Models, Genetic; D017830:Octoxynol / Q000494:pharmacology; D019007:P-Selectin / Q000378:metabolism; D010949:Plasma / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D017395:Plasminogen Activator Inhibitor 1 / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D013917:Thrombin / Q000378:metabolism; D013997:Time Factors; D014746:Vimentin / Q000737:chemistry* / Q000378:metabolism*; D019096:Vitronectin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D003902:Detergents; D008024:Ligands; D019007:P-Selectin; D017395:Plasminogen Activator Inhibitor 1; D011994:Recombinant Proteins; D014746:Vimentin; D019096:Vitronectin; D017830:Octoxynol; D013917:Thrombin