A rho gene product in human blood platelets. II. Effects of the ADP-ribosylation by botulinum C3 ADP-ribosyltransferase on platelet aggregation.
In the accompanying paper (Nemoto, Y., Namba, T., Teru-uchi, T., Ushikubi, F., Morii, N., and Narumiya, S. (1992) J. Biol. Chem. 267, 20916-20920), we have identified rhoA protein as the sole substrate protein for botulinum C3 ADP-ribosyltransferase (C3 exoenzyme) in human blood platelets. Here we examined the role of rhoA protein in platelet functions. C3 exoenzyme added to washed platelets dose- and time-dependently ADP-ribosylated rhoA protein in situ in the cells. Concomitant with this modification, inhibition of thrombin-induced platelet aggregation was observed. This inhibition was not reversed by washing the treated platelets, but was not found when C3 exoenzyme was pretreated with mouse monoclonal anti-C3 exoenzyme antibody. C3 exoenzyme treatment did not affect thrombin-induced inositol 1,4,5-trisphosphate production. Secretion of preloaded [14C]serotonin was delayed by the enzyme treatment, but the extent of the secretion was not influenced. In addition, the enzyme treatment did not change the expression of the glycoprotein IIb-IIIa complex on the platelet surface. The enzyme treatment also suppressed platelet aggregation induced by phorbol myristate acetate. These results suggest that rhoA protein plays a role mainly in the aggregation process downstream from receptor-phospholipase C coupling. This, together with the previous finding that rhoA protein modulates stress fiber formation in cultured fibroblasts (Paterson, H. F., Self, A. J., Garrett, M. D., Just, I., Aktories, K., and Hall, A. (1990) J. Cell Biol. 111, 1001-1007), suggests that rhoA protein regulates the assembly of actin filaments and the avidity of the platelet integrin (glycoprotein IIb-IIIa) in the aggregation process.
Morii
N
N
Department of Pharmacology, Kyoto University Faculty of Medicine, Japan.
Teru-uchi
T
T
Tominaga
T
T
Kumagai
N
N
Kozaki
S
S
Ushikubi
F
F
Narumiya
S
S
D036002:ADP Ribose Transferases / Q000494:pharmacology*; D000246:Adenosine Diphosphate Ribose / Q000097:blood; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000097:blood; D007700:Kinetics; D008954:Models, Biological; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D012701:Serotonin / Q000097:blood; D013917:Thrombin / Q000494:pharmacology; D013997:Time Factors; D020742:rhoA GTP-Binding Protein
D010975:Platelet Aggregation Inhibitors; D000246:Adenosine Diphosphate Ribose; D012701:Serotonin; D015544:Inositol 1,4,5-Trisphosphate; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D013917:Thrombin; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein