Synergistic phosphorylation of the focal adhesion-associated vasodilator-stimulated phosphoprotein in intact human platelets in response to cGMP- and cAMP-elevating platelet inhibitors.
The mechanism underlying the synergistic inhibition of platelet activation by cGMP- and cAMP-elevating vasodilators was investigated using washed human platelets and platelet-rich plasma. With both types of human platelet preparations, low concentrations of sodium nitroprusside increased the cAMP-elevating potency of low concentrations of prostaglandin E1 (PG-E1). Using threshold concentrations of both sodium nitroprusside and PG-E1, the NO-donor potentiated the effect of PG-E1 with respect to the phosphorylation of the focal adhesion-associated vasodilator-stimulated phosphoprotein (VASP) at serine157. In contrast, threshold concentrations of cell-membrane permeant selective activators of the platelet cGMP-dependent protein kinase or the cAMP-dependent protein kinase had only additive effects on VASP serine157 phosphorylation in washed human platelets. The data demonstrate that low intracellular levels of cGMP effectively inhibit type III cGMP-inhibited phosphodiesterase in human platelets despite the high levels of cGMP-dependent protein kinase present in this cell type. This study provides the first evidence that the simultaneous activation of both cGMP- and cAMP-dependent protein kinase results in additive effects on VASP serine157 phosphorylation, whereas the supra-additive effects observed with the combination of sodium nitroprusside and PG-E1 are due to cGMP-mediated inhibition of type III phosphodiesterase. VASP phosphorylation at serine157 may be an important component underlying the synergistic inhibition of human platelets by cGMP-and cAMP-elevating agents.
Medizinische Universitätsklinik, Klinische Forschergruppe, Würzburg, Germany.
C
C
Nolte
M
M
Eigenthaler
K
K
Horstrup
P
P
Hönig-Liedl
U
U
Walter
D000527:Alprostadil / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D004357:Drug Synergism; D006801:Humans; D008956:Models, Chemical; D009599:Nitroprusside / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011494:Protein Kinases / Q000378:metabolism
D010726:Phosphodiesterase Inhibitors; D010750:Phosphoproteins; D010975:Platelet Aggregation Inhibitors; D009599:Nitroprusside; D000242:Cyclic AMP; D011494:Protein Kinases; D000527:Alprostadil; D006152:Cyclic GMP