Integrin alpha2beta1 mediates outside-in regulation of platelet spreading on collagen through activation of Src kinases and PLCgamma2.
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.
Inoue
Osamu
O
Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, UK. osamu.inoue@pharm.ox.ac.uk
Suzuki-Inoue
Katsue
K
Dean
William L
WL
Frampton
Jon
J
Watson
Steve P
SP
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001777:Blood Coagulation / Q000187:drug effects / Q000502:physiology*; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D027682:Cation Transport Proteins; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism; D006801:Humans; D038982:Integrin alpha2beta1 / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D010446:Peptide Fragments / Q000494:pharmacology; D051966:Phospholipase C gamma; D010750:Phosphoproteins / Q000378:metabolism; D053499:Plasma Membrane Calcium-Transporting ATPases; D010973:Platelet Adhesiveness / Q000187:drug effects / Q000502:physiology*; D010980:Platelet Membrane Glycoproteins / Q000172:deficiency; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism / Q000648:ultrastructure; D011961:Receptors, Fc / Q000172:deficiency; D015398:Signal Transduction / Q000502:physiology; D000072377:Syk Kinase; D010738:Type C Phospholipases / Q000172:deficiency* / Q000235:genetics; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D027682:Cation Transport Proteins; D004792:Enzyme Precursors; D038982:Integrin alpha2beta1; D047908:Intracellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D010750:Phosphoproteins; D010980:Platelet Membrane Glycoproteins; D011961:Receptors, Fc; C092947:SLP-76 signal Transducing adaptor proteins; C098341:platelet membrane glycoprotein VI; D014443:Tyrosine; D003094:Collagen; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D019061:src-Family Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D053499:Plasma Membrane Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases