Divalent cation-dependent platelet adhesion to fibronectin (FN) is mediated by the integrin receptors α5β1 (GP Ic-IIa) and α(IIb)β3 (GP IIb-IIIa), which recognize the RGD (Arg-Gly-Asp) sequence in the cell- binding domain. However, FN can also support divalent cation-independent platelet adhesion. To determine which domain of FN mediates divalent cation- independent adhesion, proteolysis with thermolysin and affinity chromatography were used to isolate the cell-binding, gelatin-binding, and heparin-binding domains of FN. Unactivated and thrombin-activated platelets adhered to intact FN and the 45-Kd gelatin-binding domain in the presence of either Ca2+ or EDTA. Platelet spreading was mediated only by the 105-Kd cell-binding domain and required divalent cations. The heparin-binding domains did not support platelet adhesion. Reduction of intrachain disulfide bonds or removal of carbohydrate side chains on the gelatin-binding domain did not alter the ability to support platelet adhesion. Divalent cation- independent adhesion to the 45-Kd gelatin-binding domain was not inhibited by RGDS (Arg-Gly-Asp-Ser) synthetic peptides or monoclonal antibodies (MoAbs) directed against known platelet receptors. We conclude that platelets can adhere but not spread on the gelatin-binding domain of FN by a novel divalent cation-independent mechanism.
|Number of pages||9|
|State||Published - 1993|