Type 1 Plasminogen Activator Inhibitor Induces Multimerization of Plasma Vitronectin
A SUGGESTED MECHANISM FOR THE GENERATION OF THE TISSUE FORM OF VITRONECTIN IN VIVO*
- ‡To whom correspondence should be addressed: Dept. of Vascular Biology (VB-3), The Scripps Research Institute, 10666 N. Torrey Pines Rd., La Jolla, CA 92037. Tel.: 619-784-7153; Fax: 619-784-7353; E-mail: Seiffert{at}Scripps.edu.
Abstract
The conformation and degree of multimerization of vitronectin (Vn) appears to be of critical importance for its functions, but little is known about the underlying mechanisms that control Vn multimerization. We report that Vn secreted by cultured hepatoma cells is present as a mixture of monomeric and multimeric forms. A single protein of Mr 45,000 co-purified with hepatoma cell-derived Vn, which was immunologically identified as type 1 plasminogen activator inhibitor (PAI-1). The possibility that PAI-1 may modulate Vn multimerization was investigated. The addition of active PAI-1 to unfractionated plasma containing Vn monomers resulted in the formation of covalently and noncovalently associated Vn multimers and expression of conformationally sensitive epitopes. In contrast, inactive forms of PAI-1 did not efficiently induce Vn multimerization and conformational change. Gel filtration analysis revealed that Vn remained multimeric after dissociation from PAI-1. Vn multimers were also assembled using purified monomeric Vn and PAI-1, suggesting that a plasma cofactor was not required to induce Vn multimerization. This study provides insights into physiological mechanism responsible for the generation of homomultimeric Vn, a multimeric form of Vn that is not in complex with other proteins and which expresses a functional repertoire distinct from that of plasma Vn.
Footnotes
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↵* This work was supported by California Tobacco-related Disease Research Program Grant 4KT-0192 and National Institutes of Health Grants HL50704 and HL31950. This is publication 9845-VB from the Department of Vascular Biology. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 The abbreviations used are:
- Vn
-
vitronectin
- CM
-
conditioned medium
- mAb
-
monoclonal antibody
- PAGE
-
polyacrylamide gel electrophoresis
- PAI-1
-
type 1 plasminogen activator inhibitor
- PBS
-
phosphate-buffered saline
- uPA
-
urinary-type plasminogen activator
- tPA
-
tissue-type plasminogen activator
- ELISA
-
enzyme-linked immunosorbent assay
- PPP
-
platelet-poor plasma
- TBS
-
Tris-buffered saline.
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↵2D. Seiffert, unpublished observation.
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- Received June 27, 1996.
- Revision received September 9, 1996.
- © 1996 by The American Society for Biochemistry and Molecular Biology, Inc.
