Phosphoinositide 3-kinase inhibition reverses platelet aggregation triggered by the combination of the neutrophil proteinases elastase and cathepsin G without impairing αIIbβ3 integrin activation

Neutrophil elastase (NE) upregulates the fibrinogen binding activity of the platelet integrin alpha (IIb)beta (3) through proteolysis of the alpha (IIb) subunit, This cleavage allows a strong potentiation of platelet aggregation induced by ion concentrations of cathepsin G (CG), another neutrophil serine proteinase, During this activation process, we observed a strong fibrinogen binding and aggregation-dependent phosphatidylinositol 3,4-bis-phosphate (PtdIns(3,4)P-2) accumulation. PtdIns(3,4)P-2 has been suggested to play a role in the stabilization of platelet aggregation, possibly through the control of a maintained alpha (IIb)beta (3) integrin activation, Here we show that inhibition of phosphoinositide 3-kinase (PI 3-K) by very low concentrations of wortmannin of LY294002 transformed the irreversible platelet aggregation induced by a combination of NE and low concentrations of CG into a reversible aggregation. However, although inhibition of PI 3-K was very efficient in inducing platelet disaggregation, it did not modify the level of alpha (IIb)beta (3) activation as assessed by binding of an activation-dependent antibody. These results indicate that PI 3-K activity can control the irreversibility of platelet aggregation even under conditions where alpha (IIb)beta (3) integrin remains activated. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V, All rights reserved.