Platelet activation via the collagen receptor GPVI is not altered in platelets from chronic myeloid leukaemia patients despite the presence of the constitutively phosphorylated adapter protein CrkL.
In this study, we show that the adapter proteins CrkL and Cbl undergo increases in tyrosine phosphorylation and form an intracellular complex in platelets stimulated with the snake venom toxin convulxin, a selective agonist at the collagen receptor glycoprotein VI (GPVI). Constitutive tyrosine phosphorylation of CrkL has previously been reported in platelets from chronic myeloid leukaemia (CML) patients. This was confirmed in the present study, and shown to result in a weak constitutive association of CrkL with Cbl and a number of other unidentified tyrosine-phosphorylated proteins. There was no further increase in phosphorylation of CrkL in CML platelets in response to GPVI activation, whereas phosphorylation of Cbl and its association with CrkL were potentiated. In addition, this was accompanied by a small increase in p42/ 44 mapkinase (MAPK) activity in CML platelets. The functional consequence of the presence of constitutively phosphorylated proteins in CML platelets was investigated by measurement of aminophospholipid exposure and alpha-granule secretion. This revealed little alteration in the concentration-response curves for either in CML platelets stimulated via GPVI, although maximal levels of P-selectin were depressed. Despite the minimal effect on platelet activation in CML patients, we cannot exclude a role for CrkL or Cbl in signal transduction pathways stimulated via GPVI.
Department of Pharmacology, University of Oxford, Mansfield, Oxford OX1 3QT, UK. denise.best@pharm.ox.ac.uk
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Best
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Pasquet
T J
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Littlewood
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Brunskill
C J
CJ
Pallister
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Watson
D048868:Adaptor Proteins, Signal Transducing; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D016022:Case-Control Studies; D003094:Collagen / Q000378:metabolism*; D003435:Crotalid Venoms / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D037181:Lectins, C-Type; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000097:blood*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D050722:Oncogene Protein v-cbl; D010766:Phosphorylation; D015539:Platelet Activation; D010980:Platelet Membrane Glycoproteins / Q000819:agonists*; D015682:Retroviridae Proteins, Oncogenic / Q000378:metabolism; D013268:Stimulation, Chemical
D048868:Adaptor Proteins, Signal Transducing; C082869:CRKL protein; D003435:Crotalid Venoms; D037181:Lectins, C-Type; D009687:Nuclear Proteins; D050722:Oncogene Protein v-cbl; D010980:Platelet Membrane Glycoproteins; D015682:Retroviridae Proteins, Oncogenic; C098341:platelet membrane glycoprotein VI; C028890:convulxin; D003094:Collagen; D019950:Mitogen-Activated Protein Kinase 1