Abstract
Fibronectin has been shown to bind to integrin alphaIIbbeta3 in Arg-Gly-Asp (RGD)-dependent and -independent manners. A recent study has indicated that a 29-kDa dispase-digestive fragment from the C-terminal heparin-binding domain of human plasma fibronectin (lacking RGD sequence) inhibits binding of fibronectin to thrombin-stimulated platelets and ADP-induced aggregation (Tanabe, J. , Fujita, H., Iwamatsu, A., Mohri, H., and Ohkubo, T.(1993) J. Biol. Chem. 268, 27143-27147). We provide here the evidence that a peptide corresponding to residues from Ala1704 to Glu1718 (designated F1) from this fragment inhibited binding of 125I-labeled 29-kDa fragment of fibronectin to thrombin-stimulated platelets and ADP-induced aggregation. The F1 peptide bound directly to alphaIIbbeta3 integrin receptor. These results indicate that a novel binding site in the C-terminal heparin-binding region of fibronectin is localized within the residues from Ala1704 to Glu1718. Binding of 125I-labeled 29-kDa fragment of fibronectin to thrombin-stimulated platelets was not inhibited by RGDS peptide and the 12-residue peptide from the cell-binding domain of fibronectin, suggesting that binding site in the C-terminal heparin-binding domain may be different from those of RGDS and the 12-residue peptide. This additional alphaIIbbeta3-binding domain(s) in fibronectin may also play some role for prevention of thrombus formation by direct interaction with alphaIIbbeta3.
Highlights
RGD-containing peptides block binding of fibronectin to unstimulated platelets [13]
We have studied the interaction of synthetic peptides derived from the C-terminal heparin-binding domain of fibronectin with integrin receptor ␣IIb3
There are three key findings: (a) an active binding site of the C-terminal heparinbinding domain of fibronectin that inhibited binding of the 29-kDa fragment to ␣IIb3 was a sequence corresponding to the residues from Ala1704 to Glu1718; (b) a peptide including this binding site inhibited both bindings of fibronectin and fibrinogen to ␣IIb3 in a dose-dependent manner; (c) a binding site of this peptide on ␣IIb3 may be different from that of RGDS and of the 12-residue peptide in the cell-binding domain of fibronectin
Summary
(Received for publication, November 29, 1995, and in revised form, March 11, 1996). From The First Department of Internal Medicine, Yokohama City University School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama 236, Japan. The F1 peptide bound directly to ␣IIb3 integrin receptor These results indicate that a novel binding site in the C-terminal heparin-binding region of fibronectin is localized within the residues from Ala1704 to Glu1718. One site is located in the N-terminal region of the cellbinding domain of fibronectin corresponding to the residues from Ile1359 to Ser1436 This recombinant fragment of fibronectin inhibited binding of fibronectin to ␣IIb3 and ADP-induced platelet aggregation [14]. Responding to residues from Ala1597 to Glu1963 [15] This fragment lacks RGD sequence, inhibits binding of fibronectin to thrombin-stimulated platelets as well as heparin and ADPinduced platelet aggregation and binds to immobilized ␣IIb3. These results suggest that three different binding sites in fi-. The binding site of this peptide on ␣IIb3 might be different from those of RGDS and the sequence in the N-terminal region of cell-binding domain of fi-
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