INTEGRIN ALPHA(IIB)BETA(3)-MEDIATED TRANSLOCATION OF CDC42HS TO THE CYTOSKELETON IN STIMULATED HUMAN PLATELETS

To investigate the function of the human Ras-related CDC42 GTP-binding protein (CDC42Hs) we studied its subcellular redistribution in platel ets stimulated by thrombin-receptor activating peptide (TRAP) or ADP. In resting platelets CDC42Hs was detected exclusively in the membrane skeleton (9.6 +/- 1.5% of total) and the detergent soluble fraction (9 0 +/- 4%). When platelets were aggregated with TRAP or ADP, CDC42Hs (1 0% of total) appeared in the cytoskeleton and decreased in the membran e skeleton, whereas RhoGDI (guanine-nucleotide dissociation inhibitor) and CDC42HsGAP (GTPase-activating protein) remained exclusively in th e detergent-soluble fraction. Upon prolonged platelet stimulation CDC4 2Hs disappeared from the cytoskeleton and reappeared in the membrane s keleton. Rac translocated to the cytoskeleton with a similar time cour se as CDC42Hs. When platelets were stimulated under conditions that pr ecluded the activation of the alpha(IIb)beta(3) integrin and platelet aggregation, cytoskeletal association of CDC42Hs was abolished. Transl ocation of CDC42Hs to the cytoskeleton but not aggregation was also pr evented by cytochalasins B or D or the protein tyrosine kinase inhibit or genistein. Platelet secretion and thromboxane formation were not re quired but facilitated the cytoskeletal association of CDC42Hs. The re sults indicate that in platelets stimulated by TRAP or ADP, a fraction of CDC42Hs translocates from the membrane skeleton to the cytoskeleto n. This process is reversible and is mediated by activation of the alp ha(IIb)beta(3) integrin and subsequent actin polymerization and protei n-tyrosine kinase stimulation. CDC42Hs might be a new component of a s ignaling complex containing specific cytoskeletal proteins and protein -tyrosine kinases that forms after activation of the alpha(IIb)beta(3) integrin in platelets.