Small GTPase Rho regulates thrombin-induced platelet aggregation

Platelets play essential roles in hemostasis and thrombosis by aggregating with each other. However, the molecular mechanism governing platelet aggreg ation is not yet fully understood. Here, we established an assay system usi ng platelets permeabilized with streptolysin-O to analyze mechanism of the thrombin-induced aggregation, focusing upon a controversial issue in the he ld whether small GTPase Rho regulates the aggregation. Incubation of the pe rmeabilized platelets with Rho GDP-dissociation inhibitor, an inhibitory re gulator for Rho family GTPases, extracted Rho family proteins extensively f rom the plasma and intracellular membranes, and inhibited the thrombin-indu ced aggregation. Incubation of the permeabilized platelets with botulinum e xoenzyme C3, which specifically inhibits Rho function by ADP-ribosylating i t, abolished the thrombin-induced aggregation. Thus, Rho is involved in thr ombin-induced aggregation of platelets. (C) 2001 Academic Press.