αIIbβ3-integrin mediated adhesion of human platelets to a fibrinogen matrix triggers phospholipase C activation and phosphatidylinositol 3′,4′-bisphosphate accumulation

Abstract

This study focused on the variations in phosphoinositide metabolism depending upon α_IIbβ₃-integrin/fibrinogen interaction without previous activation of platelet agonist receptors. We found that adhesion of resting human platelets to immobilized fibrinogen stimulates phosphatidic acid production and a concomitant decrease in phosphatidylinositol 4′,5′-bisphosphate. These results, and the absence of a transphosphatidylation reaction, argue in favor of the activation of a phospholipase C. Moreover, we observed the accumulation of phosphatidylinositol 3′,4′-bisphosphate in adherent platelets as a consequence of the activation of a phosphatidylinositol 3-kinase. This effect was inhibited by ADP scavengers. Our results demonstrate that in adherent platelets, whereas phosphatidylinositol 3-kinase activation is controlled by both α_IIbβ-integrin engagement and released ADP, phospholipase C stimulation is triggered only by α_IIbβ-integrin/fibrinogen interaction.