Cytoskeletal regulation of the platelet glycoprotein Ib/V/IX-von Willebrand factor interaction

Shear-induced binding of von Willebrand factor (vWf) to the platelet glycop rotein (GP) Ib/V/IX complex plays a key role in initiating platelet adhesio n and aggregation at sites of vascular injury. This study demonstrated that pretreating human platelets with inhibitors of actin polymerization, cytoc halasin D or latrunculin B, dramatically enhances platelet aggregation indu ced by vWf, The effects of these inhibitors were specific to the vWf-GBIb a lpha interaction because they enhanced vWf- induced aggregation of Glanzman n thrombasthenic platelets and Chinese hamster ovary (CHO) cells transfecte d with GPIb/V/IX, Moreover, cytochalasin D enhanced the extent of platelet aggregation induced by high shear stress (5000 s(-1)) and also lowered the shear threshold required to induce aggregation from 3000 s(-1) to as low as 500 s(-)1. Studies of CHO cells expressing GPIb alpha cytoplasmic tail tru ncation mutants that failed to bind actin-binding protein-280 (deletion of residues 569-610 or 535-568) demonstrated that the linkage between GPIb and actin-binding protein-280 was not required for vWf-induced actin polymeriz ation, but was critical for the enhancing effects of cytochalasin D on vWf- induced cell aggregation. Taken together, these studies suggest a fundament ally important role for the cytoskeleton in regulating the adhesive functio n of GPIb/V/IX, (C) 2000 by The American Society of Hematology.