Platelet alpha IIb-beta 3 integrin engagement induces the tyrosine phosphorylation of Cbl and its association with phosphoinositide 3-kinase and Syk.
Agonist-induced platelet activation triggers 'inside-out' signalling which activates alpha IIb-beta 3, the most abundant integrin in platelet membranes. The engagement of activated alpha IIb-beta 3 integrin by linking fibrinogen is necessary for platelet aggregation, and this induces subsequent outside-in signalling, which enhances platelet activation. Here we studied the involvement of Cbl during alpha IIb-beta 3-integrin-mediated signal transduction. During thrombin-induced platelet activation, Cbl was tyrosine phosphorylated, and phosphoinositide 3-kinase (PI 3-kinase) activity measured in Cbl immunoprecipitates was increased. Both Cbl phosphorylation and its association with PI 3-kinase were dependent on alpha IIb-beta 3 engagement by linking fibrinogen. The P256 and anti-LIBS6 (ligand-induced binding site 6) antibodies, which activate platelets directly through alpha IIb-beta 3, induced Cbl phosphorylation and increased the PI 3-kinase activity associated with Cbl. Both thrombin and antibodies to alpha IIb-beta 3 induced association of Cbl with the tyrosine kinase, Syk. Experiments performed with inhibitors of tyrosine kinases indicated that both Src-family kinases and Syk contribute to phosphorylation of Cbl and its consequent association with PI 3-kinase. The results show that, following integrin alpha IIb-beta 3 engagement, Cbl is tyrosine phosphorylated, recruits PI 3-kinase to this integrin signalling pathway and possibly enhances PI 3-kinase activity, downstream of Src-family tyrosine kinases and Syk activation.
Saci
A
A
INSERM-U428, Faculté de Pharmacie (Université Paris-V), 4 av. de l'Observatoire, F-75270 Paris Cedex 06, France.
Rendu
F
F
Bachelot-Loza
C
C
D000199:Actins / Q000378:metabolism; D001792:Blood Platelets / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D050722:Oncogene Protein v-cbl; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D015539:Platelet Activation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015682:Retroviridae Proteins, Oncogenic / Q000378:metabolism*; D000072377:Syk Kinase; D014443:Tyrosine / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism
D000199:Actins; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D050722:Oncogene Protein v-cbl; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D015682:Retroviridae Proteins, Oncogenic; D014443:Tyrosine; D005340:Fibrinogen; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D019061:src-Family Kinases