Key role of integrin α(IIb)β          (3) signaling to Syk kinase in tissue factor-induced thrombin generation.
The fibrin(ogen) receptor, integrin α(IIb)β(3), has a well-established role in platelet spreading, aggregation and clot retraction. How α(IIb)β(3) contributes to platelet-dependent coagulation is less well resolved. Here, we demonstrate that the potent suppressing effect of clinically used α(IIb)β(3) blockers on tissue factor-induced thrombin generation is linked to diminished platelet Ca(2+) responses and phosphatidylserine (PS) exposure. The same blockers suppress these responses in platelets stimulated with collagen and thrombin receptor agonists, whereas added fibrinogen potentiates these responses. In platelets spreading on fibrinogen, outside-in α(IIb)β(3) signaling similarly enhances thrombin-induced Ca(2+) rises and PS exposure. These responses are reduced in α(IIb)β(3)-deficient platelets from patients with Glanzmann's thrombasthenia. Furthermore, the contribution of α(IIb)β(3) to tissue factor-induced platelet Ca(2+) rises, PS exposure and thrombin generation in plasma are fully dependent on Syk kinase activity. Tyrosine phosphorylation analysis confirms a key role of Syk activation, which is largely but not exclusively dependent on α(IIb)β(3) activation. It is concluded that the majority of tissue factor-induced procoagulant activity of platelets relies on Syk activation and ensuing Ca(2+) signal generation, and furthermore that a considerable part of Syk activation relies on α(IIb)β(3) signaling. These results hence point to a novel role of Syk in integrin-dependent thrombin generation.
Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, Maastricht, The Netherlands. p.vandermeijden@maastrichtuniversity.nl
Paola E J
PE
van der Meijden
Marion A H
MA
Feijge
Frauke
F
Swieringa
Karen
K
Gilio
Reyhan
R
Nergiz-Unal
Karly
K
Hamulyák
Johan W M
JW
Heemskerk
D001777:Blood Coagulation / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D015153:Blotting, Western; D005340:Fibrinogen / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D010768:Phosphoserine / Q000378:metabolism; D010974:Platelet Aggregation / Q000187:drug effects; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase; D013915:Thrombasthenia / Q000097:blood*; D013917:Thrombin / Q000378:metabolism*; D013925:Thromboplastin / Q000494:pharmacology*
D047908:Intracellular Signaling Peptides and Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010768:Phosphoserine; D005340:Fibrinogen; D013925:Thromboplastin; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D013917:Thrombin