Platelet-derived-growth-factor-induced signalling in human platelets: phosphoinositide-3-kinase-dependent inhibition of platelet activation

• Published in: Biochemical journal Vol. 350 Pt 2; no. 2; pp. 469 - 475
• Main Authors: Selheim, F, Fukami, M H, Holmsen, H, Vassbotn, F S
• Format: Journal Article
• Language: English
• Published: England 01.09.2000
• Subjects: Androstadienes - pharmacology; Blood Platelets - enzymology; Blood Platelets - metabolism; Chromatography, High Pressure Liquid; Chromones - pharmacology; Collagen - metabolism; Enzyme Inhibitors - pharmacology; Flow Cytometry; Humans; Immunoblotting; Morpholines - pharmacology; Phosphatidylinositol 3-Kinases - metabolism; Phosphatidylinositol Phosphates - metabolism; Phosphorylation; Platelet Activation - drug effects; Platelet-Derived Growth Factor - metabolism; Recombinant Proteins - metabolism; Signal Transduction; Tyrosine - metabolism
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/0264-6021:3500469

Human platelets release platelet-derived growth factor (PDGF) from alpha-granules during platelet activation. We have previously shown that platelets have PDGF alpha-receptors, a transmembrane tyrosine kinase that takes part in negative feedback regulation during platelet activation. Here we have described a study of PDGF-induced tyrosine phosphorylation of platelet substrates and phosphoinositide 3-kinase (PI-3K) activity in collagen-stimulated platelets. By immunoblotting with phosphotyrosine antibodies of collagen-activated platelets we found that PDGF increased the phosphorylation of several platelet substrates, e.g. pp140, pp120 and pp85. PDGF inhibited collagen-induced platelet activation in the presence of inhibitors of autocrine stimulation, thus blocking the pure collagen-induced signal transduction. PDGF enhanced the collagen-induced formation of PtdIns(3,4)P(2) and PtdIns(3,4,5)P(3) as measured by HPLC. Wortmannin and LY294002, two unrelated inhibitors of PI-3K, were used to investigate the role of PI-3K in PDGF-induced platelet signalling. Incubation of platelets with wortmannin and LY294002 blocked the formation of three phosphorylated inositides as well as the inhibitory effect of PDGF on collagen-induced platelet activation. We conclude that the inhibitory effect of PDGF on platelet activation is PI-3K dependent. This is the first demonstration of a negative regulatory function of 3-phosphorylated inositides in platelets.