The effect of Arg-Gly-Asp-containing peptides on fibrinogen and von Willebrand factor binding to platelets.

Abstract

The Arg-Gly-Asp sequence resides in the cell attachment region offibronectin. Arg-Gly-Asp-containing peptides support fibroblast attachment, inhibit fibroblast adhesion to fibronectin, and inhibit fibronectin binding to thrombinstimulated platelets. In view of the similarities between the binding of fibronectin, fibrinogen, and von Willebrand factor to stimulated platelets, we have examined the effects of ArgGly-Asp-containing peptides on the interaction of these latter two adhesive proteins with platelets. Gly-Arg-Gly-Asp-Ser-Pro was used as a prototype peptide, and this hexapeptide inhibited fibrinogen binding to ADP and thrombin-stimulated platelets in the 10-200 jaM range. The inhibition exceeded 90% at high concentrations of peptide and was observed in the presence of either calcium or magnesium. Platelet aggregation was also inhibited by the peptide in this dose range. The hexapeptide inhibited fibrinogen binding to platelets with receptors fixed in an exposed state, indicating direct interference with the ligand-platelet interaction. The peptide was 1/2 to 1/3rd as potent in inhibiting fibrinogen as fibronectin binding to platelets, but fibrinogen and von Willebrand factor binding were inhibited to an identical extent. Conservative amino acid substitutions for the arginine, glycine, or aspartic acid markedly reduced inhibitory activity and the Asp-Gly-Arg sequence was inactive. These results indicate that Arg-Gly-Asp-containing peptides can inhibit the binding of the three adhesive proteins to stimulated platelets, establishing a basic common feature between the interaction of these molecules with platelets.Platelet attachment, spreading, and aggregation on extracellular matrices are central events in thrombus formation. These events can be regulated by a family ofplatelet adhesive glycoproteins-fibrinogen, fibronectin, and von Willebrand factor (vWF). Fibrinogen is a cofactor for platelet aggregation (1-3), fibronectin supports platelet attachment and spreading reactions (4-7), and vWF is important in platelet attachment to and spreading on subendothelial matrices (7-9). At a mechanistic level, the role of these adhesive proteins in platelet functions can be attributed to their interaction with specific binding sites on the cell surface. Although binding of these proteins to resting platelets is not detected, saturable interactions can be demonstrated with platelets stimulated by agonists such as thrombin (10-15). The binding of all three proteins to thrombin-stimulated platelets is divalent ion dependent (11,14,16,17), and platelets from patients with Glanzmann thrombasthenia exhibit decreased capacity to bind all three proteins (11,18,19). Synthetic peptides corresponding in sequence to the carboxyl-terminal region of the y chain of fibrinogen inhibit the binding of all three molecules to platelets (20), suggesting that common mechanisms may be involved in these interactions.Recent studies have demonstrated that the Arg-Gly-Asp sequence within fibronectin is involved in the cell attachment func...

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