The P2Y₁₂ receptor induces platelet aggregation through weak activation of the α_IIbβ₃ integrin – a phosphoinositide 3‐kinase‐dependent mechanism

Abstract

High concentrations of adenosine-5P P-diphosphate ADP are able to induce partial aggregation without shape change of P2Y 1 receptor-deficient mouse platelets through activation of the P2Y 12 receptor. In the present work we studied the transduction pathways selectively involved in this phenomenon. Flow cytometric analyses using R-phycoerythrin-conjugated JON/A antibody (JON/A-PE), an antibody which recognizesAdrenaline induced no such activation but strongly potentiated the effect of ADP in a dose-dependent manner. Global phosphorylation of 32 P-labeled platelets showed that P2Y 12 -mediated aggregation was not accompanied by an increase in the phosphorylation of myosin light chain (P 20 ) or pleckstrin (P 47 ) and was not affected by the protein kinase C (PKC) inhibitor staurosporine. On the other hand, two unrelated phosphoinositide 3-kinase inhibitors, wortmannin and LY294002, inhibited this aggregation. Our results indicate that (i) the P2Y 12 receptor is able to trigger a P2Y 1 receptor-independent inside-out signal leading to K K IIb L L 3 integrin activation and platelet aggregation, (ii) ADP and adrenaline use different signaling pathways which synergize to activate the K K IIb L L 3 integrin, and (iii) the transduction pathway triggered by the P2Y 12 receptor is independent of PKC but dependent on phosphoinositide 3-kinase. ß

Signaling pathways mediating adhesion and spreading through extracellular ADP and the P2Y12 receptor

“…ADP signaling via the P2Y 12 receptor has been implicated in the regulation of cell adhesion and motility in a variety of cell types, in particular in microglia cells and platelets [4,5]. Interestingly and as evidenced by the above-presented highlights, ADP-P2Y 12 -initiated signaling may play various roles in the regulation of adhesion, the functional outcome of which may be dependent on the cell type.…”

PKC inhibitors RO 31-8220 and Gö 6983 enhance epinephrine-induced platelet aggregation in catecholamine hypo-responsive platelets by enhancing Akt phosphorylation

“…This should be further investigated in relation to future advancements in specific agonists and antagonists of each PKC isoform. Epinephrine-mediated α2A-adrenoceptor-coupled Gz signaling alone is known to be incapable of inducing full platelet aggregation, and activation of P2Y12 receptor-coupled Gi signaling, which leads to inhibition of adenylyl cyclase, is required (22)(23)(24). An elevated plasma level of NO has been observed in CA-HY compared to CA-GR (10), and NO is known to raise cAMP levels in platelets (25).…”

Central role of the P2Y12 receptor in platelet activation

“…Ex vivo studies used platelets treated with clopidogrel or reversible antagonists of the P2Y 12 receptor and led to the conclusion that the P2Y 12 receptor is crucial to several platelet functions. Thus far, studies have identified a potentiating role for the P2Y 12 receptor in dense granule secretion (9), fibrinogen-receptor activation (10)(11)(12)(13)(14), and, as reported in a recent issue of the JCI, thrombus formation (15, 16), identifying it as a central mediator of the hemostatic response. This receptor is also important for the irreversible platelet aggregation induced not only by ADP, but also by thromboxane A 2 and the PAR1-selective peptide agonist SFLLRN (17,18).…”