Protease-activated receptors 1 and 4 do not stimulate G(i) signaling pathways in the absence of secreted ADP and cause human platelet aggregation independently of G(i) signaling.
Thrombin is an important agonist for platelet activation and plays a major role in hemostasis and thrombosis. Thrombin activates platelets mainly through protease-activated receptor 1 (PAR1), PAR4, and glycoprotein Ib. Because adenosine diphosphate and thromboxane A(2) have been shown to cause platelet aggregation by concomitant signaling through G(q) and G(i) pathways, we investigated whether coactivation of G(q) and G(i) signaling pathways is the general mechanism by which PAR1 and PAR4 agonists also activate platelet fibrinogen receptor (alphaIIbbeta3). A PAR1-activating peptide, SFLLRN, and PAR4-activating peptides GYPGKF and AYPGKF, caused inhibition of stimulated adenylyl cyclase in human platelets but not in the presence of either Ro 31-8220, a protein kinase C selective inhibitor that abolishes secretion, or AR-C66096, a P2Y12 receptor-selective antagonist; alpha-thrombin-induced inhibition of adenylyl cyclase was also blocked by Ro 31-8220 or AR-C66096. In platelets from a P2Y12 receptor-defective patient, alpha-thrombin, SFLLRN, and GYPGKF also failed to inhibit adenylyl cyclase. In platelets from mice lacking the P2Y12 receptor, neither alpha-thrombin nor AYPGKF caused inhibition of adenylyl cyclase. Furthermore, AR-C66096 caused a rightward shift of human platelet aggregation induced by the lower concentrations of alpha-thrombin and AYPGKF but had no effect at higher concentrations. Similar results were obtained with platelets from mice deficient in the P2Y12. We conclude that (1) thrombin- and thrombin receptor-activating peptide-induced inhibition of adenylyl cyclase in platelets depends exclusively on secreted adenosine diphosphate that stimulates G(i) signaling pathways and (2) thrombin and thrombin receptor-activating peptides cause platelet aggregation independently of G(i) signaling.
Kim
Soochong
S
Department of Physiology and the Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Foster
Carolyn
C
Lecchi
Anna
A
Quinton
Todd M
TM
Prosser
Dina M
DM
Jin
Jianguo
J
Cattaneo
Marco
M
Kunapuli
Satya P
SP
D000244:Adenosine Diphosphate / Q000378:metabolism / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D009842:Oligopeptides / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics; D010446:Peptide Fragments / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D058919:Purinergic P2 Receptor Antagonists; D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000502:physiology; D058925:Receptors, Purinergic P2Y12; D018179:Receptors, Thrombin / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D015398:Signal Transduction; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
C092108:2-propylthio-D-beta,gamma-difluoromethylene ATP; D008565:Membrane Proteins; D009842:Oligopeptides; C548576:P2RY12 protein, human; C548577:P2ry12 protein, mouse; D010446:Peptide Fragments; D010975:Platelet Aggregation Inhibitors; D058919:Purinergic P2 Receptor Antagonists; D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D018048:Receptors, Purinergic P2; D058925:Receptors, Purinergic P2Y12; D018179:Receptors, Thrombin; C455901:alanyl-tyrosyl-prolyl-glycyl-lysyl-phenylalanine; C082835:thrombin receptor peptide (42-47); D015016:Yohimbine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D013917:Thrombin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000262:Adenylyl Cyclases