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.
SciCrunch is a data sharing and display platform. Anyone can create a custom portal where they can select searchable subsets of hundreds of data sources, brand their web pages and create their community. SciCrunch will push data updates automatically to all portals on a weekly basis. User communities can also add their own data to scicrunch, however this is not currently a free service.