Vav1, but not Vav2, contributes to platelet aggregation by CRP and thrombin, but neither is required for regulation of phospholipase C.
We have investigated the role of the Rho and Rac family small guanine triphosphate (GTP) exchange factors (RhoGEFs), Vav1 and Vav2, in the activation of platelets by the immunoreceptor tyrosine-based activation motif (ITAM)-coupled collagen receptor GPVI and by the G protein-coupled receptor agonist thrombin. The glycoprotein VI (GPVI)-specific agonist collagen-related peptide (CRP) and thrombin stimulated tyrosine phosphorylation of Vav1 but not Vav2 in human platelets. Surprisingly, however, CRP did not activate the low-molecular-weight G protein Rac and stimulated only a small increase in activity of p21-associated kinase 2 (PAK2), despite the fact that both proteins are regulated downstream of Vav1 in other cells. Further, activation of Rac and PAK2 by thrombin was maintained in platelets from mice deficient in Vav1. Activation of phospholipase C (PLC) by GPVI and thrombin was unaltered in Vav1-, Vav2-, and Vav1/Vav2-deficient platelets. A weak inhibition of late-stage aggregation to CRP and thrombin was observed in platelets deficient in Vav1 but not Vav2, whereas spreading on fibrinogen was not changed. The present results demonstrate that neither Vav1 nor Vav2 lie upstream of PLC or Rac in platelets, highlighting an important difference in their role in signaling by ITAM-coupled receptors in other cell types. The present study has provided evidence for a possible role of Vav1 but not Vav2 in the later stages of platelet aggregation.
Pearce
Andrew C
AC
Department of Pharmacology, University of Oxford, United Kingdom. andrew.pearce@spc.ox.ac.uk
Wilde
Jonathan I
JI
Doody
Gina M
GM
Best
Denise
D
Inoue
Osamu
O
Vigorito
Elena
E
Tybulewicz
Victor L J
VL
Turner
Martin
M
Watson
Steve P
SP
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D002352:Carrier Proteins / Q000494:pharmacology; D018797:Cell Cycle Proteins; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D015513:Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D010455:Peptides; D051966:Phospholipase C gamma; D010766:Phosphorylation; D010973:Platelet Adhesiveness / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D051567:Proto-Oncogene Proteins c-vav; D015398:Signal Transduction / Q000187:drug effects; D013917:Thrombin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000187:drug effects / Q000378:metabolism*
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D015513:Oncogene Proteins; D010455:Peptides; D010980:Platelet Membrane Glycoproteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; C496618:VAV1 protein, human; C093651:VAV2 protein, human; C496619:Vav1 protein, mouse; C490565:Vav2 protein, mouse; C435908:collagen-related peptide; C098341:platelet membrane glycoprotein VI; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D013917:Thrombin