Ionophore A23187-induced protein-tyrosine phosphorylation of human platelets: possible synergism between Ca2+ mobilization and protein kinase C activation.
Addition of ionophore A23187 to washed human platelets caused a time- and dose-dependent increase in the phosphotyrosyl content of 135, 124 and 76 kDa proteins. Platelets loaded with intracellular Ca2+ chelator 5,5'-dimethyl-bis-(o-aminophenoxy)-ethane-N, N, N', N'-tetraacetic acid before addition of A23187 exhibited no protein-tyrosine phosphorylation. Replenishment of such platelets with extracellular CaCl2 restored A23187-induced protein-tyrosine phosphorylation. Upon stimulation with A23187, both aspirin and ADP scavengers-treated platelets exhibited protein-tyrosine phosphorylation without phosphoinositide hydrolysis and protein kinase C activation. These data show (a) that A23187 stimulates protein-tyrosine phosphorylation by the elevation of intracellular Ca2+, and (b) that A23187-induced protein-tyrosine phosphorylation is independent of formation of endoperoxides/thromboxane A2, released ADP, phosphoinositide hydrolysis and protein kinase C activation. Furthermore, a synergistic effect of A23187 and protein kinase C activators in stimulating protein-tyrosine phosphorylation is suggested.
Takayama
H
H
First Department of Internal Medicine, Fukui Medical School, Japan.
Nakamura
T
T
Yanagi
S
S
Taniguchi
T
T
Nakamura
S
S
Yamamura
H
H
D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000097:blood*; D002122:Calcium Chloride / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology / Q000031:analogs & derivatives; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D010766:Phosphorylation; D019000:Phosphotyrosine; D011493:Protein Kinase C / Q000097:blood*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
D019000:Phosphotyrosine; D000001:Calcimycin; D014443:Tyrosine; D004533:Egtazic Acid; C058180:5,5'-dimethyl-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate; D011493:Protein Kinase C; D002122:Calcium Chloride; D002118:Calcium