Identification of and partial characterization of platelet vitronectin: evidence for complex formation with platelet-derived plasminogen activator inhibitor-1.
Vitronectin (VN; = complement S-protein), a plasma glycoprotein that is also associated with extracellular sites, was identified in washed human platelets contaminated with less than 0.05% of plasma VN. A specific enzyme-linked immunosorbent assay (ELISA) for VN has been developed and was used to detect and to quantitate VN in detergent extracts of washed platelets with 8.1 +/- 4.6 micrograms/10(9) platelets (n = 10), representing about 0.8% of the plasma VN pool. Platelet and plasma VN were similar by immunochemical criteria using Western-blot analysis, although platelet VN was mainly found as partially proteolyzed polypeptide. Total release of platelet VN occurred at optimal doses of Ca-ionophore 23187 or thrombin, whereas no VN was released by platelet treatment with digitonin or Staphylococcus alpha-toxin. During stimulation of washed platelets with various concentrations of thrombin, the nearly concomitant release of VN and plasminogen activator inhibitor-1 (PAI-1) together with platelet factor 4 indicated the association of VN with inner-platelet storage granules. Furthermore, platelet VN and PAI-1 in Ca-ionophore releasates comigrated during ultracentrifugation in high mol wt fractions of sucrose density gradients, indicating a possible association of both components. Complex formation of platelet VN and PAI-1 was verified by a sensitive enzyme-linked immunosorbent assay (ELISA) and accounts at least in part for a high molecular form of platelet VN. The identification of platelet VN and its binding to platelet PAI-1 raises the possibility that VN, in contrast to other adhesive proteins, may participate in localized regulatory functions of blood coagulation and fibrinolysis in platelet-matrix interactions and the protection of the matrix against proteolysis.
Preissner
K T
KT
Clinical Research Unit for Blood Coagulation and Thrombosis of the Max-Planck-Gesellschaft Justus-Liebig-Universität, Giessen, FRG.
Holzhüter
S
S
Justus
C
C
Müller-Berghaus
G
G
D001427:Bacterial Toxins / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism*; D015153:Blotting, Western; D000001:Calcimycin / Q000494:pharmacology; D002448:Cell Adhesion; D004072:Digitonin / Q000494:pharmacology; D006023:Glycoproteins / Q000097:blood* / Q000378:metabolism; D006460:Hemolysin Proteins; D006801:Humans; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008970:Molecular Weight; D015849:Plasminogen Inactivators / Q000378:metabolism*; D015539:Platelet Activation; D010978:Platelet Factor 4 / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D019096:Vitronectin
D001427:Bacterial Toxins; D006023:Glycoproteins; D006460:Hemolysin Proteins; D046911:Macromolecular Substances; D015849:Plasminogen Inactivators; D019096:Vitronectin; C021091:staphylococcal alpha-toxin; D010978:Platelet Factor 4; D000001:Calcimycin; D013917:Thrombin; D004072:Digitonin