1. Integrin alpha2beta1 mediates outside-in regulation of platelet spreading on collagen through activation of Src kinases and PLCgamma2.
- Author
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Inoue O, Suzuki-Inoue K, Dean WL, Frampton J, and Watson SP
- Subjects
- Adaptor Proteins, Signal Transducing, Animals, Blood Coagulation drug effects, Blood Platelets cytology, Calcium Signaling drug effects, Calcium Signaling physiology, Calcium-Transporting ATPases metabolism, Cation Transport Proteins, Cell Movement drug effects, Cells, Cultured, Enzyme Precursors metabolism, Humans, Intracellular Signaling Peptides and Proteins, Mice, Peptide Fragments pharmacology, Phospholipase C gamma, Phosphoproteins metabolism, Plasma Membrane Calcium-Transporting ATPases, Platelet Adhesiveness drug effects, Platelet Membrane Glycoproteins deficiency, Protein-Tyrosine Kinases metabolism, Pseudopodia metabolism, Pseudopodia ultrastructure, Receptors, Fc deficiency, Signal Transduction physiology, Syk Kinase, Type C Phospholipases genetics, Tyrosine metabolism, src-Family Kinases antagonists & inhibitors, Blood Coagulation physiology, Blood Platelets metabolism, Cell Movement physiology, Collagen metabolism, Integrin alpha2beta1 metabolism, Platelet Adhesiveness physiology, Type C Phospholipases deficiency, src-Family Kinases metabolism
- Abstract
Collagen plays a critical role in hemostasis by promoting adhesion and activation of platelets at sites of vessel injury. In the present model of platelet-collagen interaction, adhesion is mediated via the inside-out regulation of integrin alpha2beta1 and activation through the glycoprotein VI (GPVI)-Fc receptor (FcR) gamma-chain complex. The present study extends this model by demonstrating that engagement of alpha2beta1 by an integrin-specific sequence from within collagen or by collagen itself generates tyrosine kinase-based intracellular signals that lead to formation of filopodia and lamellipodia in the absence of the GPVI-FcR gamma-chain complex. The same events do not occur in platelet suspensions. alpha2beta1 activation of adherent platelets stimulates tyrosine phosphorylation of many of the proteins in the GPVI-FcR gamma-chain cascade, including Src, Syk, SLP-76, and PLCgamma2 as well as plasma membrane calcium ATPase and focal adhesion kinase. alpha2beta1-mediated spreading is dramatically inhibited in the presence of the Src kinase inhibitor PP2 and in PLCgamma2-deficient platelets. Spreading is abolished by chelation of intracellular Ca2+. Demonstration that adhesion of platelets to collagen via alpha2beta1 generates intracellular signals provides a new insight into the mechanisms that control thrombus formation and may explain the unstable nature of beta1-deficient thrombi and why loss of the GPVI-FcR gamma-chain complex has a relatively minor effect on bleeding.
- Published
- 2003
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