α1-Proteinase Inhibitor, α1-Antichymotrypsin, or α2-Macroglobulin Is Required for Vascular Smooth Muscle Cell Spreading in Three-dimensional Fibrin Gel

• Published in: The Journal of biological chemistry 2000-04, Vol.275 (17), p.12799-12805
• Main Authors: Ikari, Yuji, Fujikawa, Kazuo, Yee, Karen O., Schwartz, Stephen M.
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.275.17.12799

It is assumed that vitronectin and other adhesion molecules induce cell spreading. We found that vascular smooth muscle cells require unidentified plasma components besides adhesion molecules to spread in fibrin gel, a likely provisional matrix at wound sites. By purification, the plasma components were found to be α1-proteinase inhibitor, α1-antichymotrypsin, and α2-macroglobulin. The chemically inactivated α1-proteinase inhibitor and α2-macroglobulin lose the spreading activity, indicating that these proteins function as proteinase inhibitors but not as adhesion molecules. Not only anti-integrin (αvβ3 and α5β1) antibodies but also anti-fibronectin antibodies inhibit the cell spreading. The spreading occurs without the addition of fibronectin and integrins, suggesting that cells produce these molecules. In the absence of the proteinase inhibitors, Western blot analysis shows that the fibronectin is degraded in fibrin gel, while it is intact in the presence of the inhibitors. Thus, the proteinase inhibitors prevent adhesion molecules such as fibronectin from being degraded by a cell-derived proteinase(s) and thus play a role in cell spreading.