Murine GPVI stimulates weak integrin activation in PLCgamma2-/- platelets: involvement of PLCgamma1 and PI3-kinase.
Collagen stimulates platelet activation through a tyrosine kinase-based pathway downstream of the glycoprotein VI (GPVI)-Fc receptor (FcR) gamma-chain complex. Genetic ablation of FcR gamma-chain results in a complete inhibition of aggregation to collagen. In contrast, a steady increase in light transmission is induced by collagen in phospholipase Cgamma2-deficient (PLCgamma2-/-) platelets in a Born aggregometer, indicating a weak level of activation. This increase is inhibited partially in the presence of an alpha2beta1-blocking antibody or an alphaIIbbeta3 antagonist and completely by a combination of the 2 inhibitors. It is also abolished by the Src kinase inhibitor PP1 and reduced in the presence of the phosphatidylinositol (PI) 3-kinase inhibitor wortmannin. The GPVI-specific agonists convulxin and collagen-related peptide (CRP) also stimulate weak aggregation in PLCgamma2-/- platelets, which is inhibited by wortmannin and PP1. Collagen and CRP stimulate tyrosine phosphorylation of PLCgamma1 at its regulatory site, Tyr 783, in murine but not in human platelets through a Src kinase-dependent pathway. Adhesion of PLCgamma2-/- platelets to a collagen monolayer is severely reduced at a shear rate of 800 s-1, relative to controls, whereas it is abolished in FcR gamma-chain-/- platelets. These results provide strong evidence that engagement of GPVI stimulates limited integrin activation in PLCgamma2-/- platelets via PLCgamma1 and PI3-kinase.
Department of Pharmacology, University of Oxford, United Kingdom. katsue.inoue@pharm.ox.ac.uk
Katsue
K
Suzuki-Inoue
Osamu
O
Inoue
Jon
J
Frampton
Steve P
SP
Watson
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology*; D003094:Collagen / Q000378:metabolism / Q000494:pharmacology; D003435:Crotalid Venoms / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D038982:Integrin alpha2beta1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D037181:Lectins, C-Type; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000097:blood*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051966:Phospholipase C gamma; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors; D010980:Platelet Membrane Glycoproteins / Q000819:agonists* / Q000494:pharmacology; D011961:Receptors, Fc / Q000378:metabolism; D010738:Type C Phospholipases / Q000097:blood* / Q000172:deficiency; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D003094:Collagen; D003435:Crotalid Venoms; D004791:Enzyme Inhibitors; D005340:Fibrinogen; D038982:Integrin alpha2beta1; D037181:Lectins, C-Type; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051966:Phospholipase C gamma; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; D011961:Receptors, Fc; D010738:Type C Phospholipases; D014443:Tyrosine; D019061:src-Family Kinases; C028890:convulxin