MODULATION OF CELL-SURFACE FIBRONECTIN ASSEMBLY SITES BY LYSOPHOSPHATIDIC ACID

Lysophosphatidic acid is a product of activated platelets and has dive rse actions on cells. We have characterized the effect of lysophosphat idic acid on cell-mediated binding and assembly of fibronectin, an ext racellular matrix protein. Serum made from whole blood, but neither pl atelet-poor plasma nor serum made from platelet-poor plasma, caused en hanced binding of fibronectin to cultured fibroblastic cells. The abil ity of whole blood serum to enhance binding of fibronectin was abolish ed by phospholipase B. These results indicate that lysophosphatidic ac id derived from platelets is the principal component in whole blood se rum that is active in the fibronectin binding assay. 1-oleoyl lysophos phatidic acid, 20-200 nM, was as active as 0.1-0.2% whole blood serum. The stimulatory effect of lysophosphatidic acid on the binding of fib ronectin or the amino-terminal 70-kD fragment of fibronectin was rapid , sustained, and lost upon removal of lysophosphatidic acid. The stimu latory effect on binding could not be duplicated by bradykinin, platel et-activating factor, bombesin, or a peptide agonist of the thrombin r eceptor. Enhanced binding of the 70-kD fragment was due to increases i n both the number and affinity of binding sites. Enhanced binding and assembly of fibronectin correlated with changes in cell shape and acti n-containing cytoskeleton. The binding sites for fibronectin on lysoph osphatidic acid-stimulated cells, as assessed by fluorescence, video, and scanning electron microscopy, were on areas of cell membrane conta ining numerous filopodia that extended between cells or between cells and substratum. These observations suggest that lysophosphatidic acid functions as a powerful and specific modulator of cell shape and early matrix assembly during wound healing.