TY - JOUR T1 - Purinergic P2Y<sub>12</sub> Receptor Blockade Inhibits Shear-Induced Platelet Phosphatidylinositol 3-Kinase Activation JF - Molecular Pharmacology JO - Mol Pharmacol SP - 639 LP - 645 DO - 10.1124/mol.63.3.639 VL - 63 IS - 3 AU - Julio C. Reséndiz AU - Shuju Feng AU - Guilan Ji AU - Ketia A. Francis AU - Michael C. Berndt AU - Michael H. Kroll Y1 - 2003/03/01 UR - http://molpharm.aspetjournals.org/content/63/3/639.abstract N2 - Pathologically elevated shear stress triggers aspirin-insensitive platelet thrombosis. Signaling mechanisms involved in shear-induced platelet thrombosis are not well understood. To investigate these, we examined the hypothesis that functionally important platelet phosphatidylinositol 3-kinase (PI3-K) activity is stimulated by an in vitro shear stress of 120 dynes/cm2 (shear rate of 6000 sec−1). Phosphatidylinositol 3,4,5-trisphosphate (PIP3) production was examined in washed human platelets subjected to pathological shear stress in a cone-plate viscometer. PIP3 production peaks 30 s after shear begins and is initiated by von Willebrand factor (VWF) binding to the glycoprotein (Gp) Ib-IX-V complex. Inhibiting PI3-K with wortmannin or 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) results in the inhibition of shear-induced platelet aggregation. In resting platelets, class IA PI3-K associates with the tyrosine kinase Syk. Within 30 s of beginning shear, PI3-K-associated Syk becomes tyrosine phosphorylated. Inhibiting Syk activation with piceatannol results in the inhibition of PIP3 production and aggregation. Selective blockade of the P2Y12 receptor results in the inhibition of Syk phosphorylation, PIP3 production, and aggregation. These results indicate that shear-induced VWF binding to platelet GpIb-IX-V stimulates functionally important PI3-K activity. PI3-K activation is signaled by rapid feedback amplification that involves P2Y12 receptor-mediated activation of Syk. ER -