RAFTK/Pyk2 involvement in platelet activation is mediated by phosphoinositide 3‐kinase

• Published in: British journal of haematology Vol. 114; no. 1; pp. 134 - 140
• Main Authors: Koziak, K., Kaczmarek, E., Park, S. Y., Fu, Y., Avraham, S., Avraham, H.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.07.2001; Blackwell; Blackwell Publishing Ltd
• Subjects: Adenosine Diphosphate - pharmacology; Biological and medical sciences; Blood coagulation. Blood cells; Chromones - pharmacology; Collagen - pharmacology; Enzyme Inhibitors - pharmacology; Fibrinogen - pharmacology; Focal Adhesion Kinase 2; Fundamental and applied biological sciences. Psychology; Hematology; Humans; Intracellular Signaling Peptides and Proteins; Molecular and cellular biology; Morpholines - pharmacology; Phosphatidylinositol 3-Kinases - antagonists & inhibitors; Phosphatidylinositol 3-Kinases - metabolism; Phosphoric Monoester Hydrolases - antagonists & inhibitors; Phosphorylation; PI3K; Platelet; Platelet Activation - physiology; Precipitin Tests; Protein Phosphatase 2; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Protein Tyrosine Phosphatase, Non-Receptor Type 6; Protein Tyrosine Phosphatases - metabolism; Protein-Tyrosine Kinases - metabolism; RAFTK/Pyk2; SHP‐2; Signal Transduction - physiology; Thrombin - pharmacology; thrombin receptor; Vanadates - pharmacology; Human; Phosphorylation; Serine endopeptidases; Enzyme; Transferases; Phosphoric monoester hydrolases; Thrombin; Esterases; EC 2.7.1.37; 1-Phosphatidylinositol 3-kinase; Peptidases; Platelet; Hemostasis; Protein kinase; Platelet function; Hydrolases; EC 3.1.3.48; EC 3.4.21.5; Protein-tyrosine-phosphatase
• ISSN: 0007-1048; 1365-2141
• DOI: 10.1046/j.1365-2141.2001.02894.x

Platelet activation by different agonists initiates a signalling cascade involving the phosphorylation of several protein kinases, which control key regulatory events. Previously, we demonstrated that the related adhesion focal tyrosine kinase (RAFTK, Pyk2) was involved in an early phase of platelet activation, independent of integrin and glycoprotein IIb–IIIa activation. In this study, we demonstrate that RAFTK is co‐immunoprecipitated with phosphoinositide 3‐kinase (PI3K) upon platelet activation, and that thrombin, ADP and collagen induced the phosphorylation of both PI3K and RAFTK. A low dose of thrombin (0·015 U/ml) induced RAFTK phosphorylation and platelet aggregation in a PI3K activity‐dependent manner, whereas a high dose of thrombin (0·1 U/ml) induced these events in a PI3K activity‐independent manner. ADP and collagen also induced RAFTK phosphorylation and platelet aggregation in a PI3K activity‐dependent manner, similar to that of the low‐dose thrombin. Furthermore, protein tyrosine phosphatase activity was associated with RAFTK in response to platelet activation, and was found to be that of protein tyrosine phosphatase‐2 (SHP‐2). The association of SHP‐2 with RAFTK was PI3K‐dependent and was increased upon RAFTK phosphorylation. Taken together, our results strongly suggest that the involvement of RAFTK in platelet activation is mediated via the PI3K pathway.