Role of the p110d PI 3-kinase in integrin and ITAM receptor signalling in platelets.

We have investigated the function of the p110d catalytic subunit of phosphoinositide 3-kinase (PI 3-kinase) in platelets using p110d knock-out (p110d –/– ) mice and p110d knock-in (p110d D910A/D910A ) mice, which express a catalytically inactive form of the enzyme. Aggregation to threshold concentrations of the GPVI-specific agonist, CRP, was partially reduced in p110d –/– and p110d D910A/D910A platelets. This inhibition was overcome by higher concentrations of CRP. The degree of inhibition was considerably weaker than that induced by LY294002 and wortmannin, which inhibit all isoforms of PI 3-kinase. p110d –/– platelets showed decreased spreading on fibrinogen- or von Willebrand factor (VWF)-coated surfaces under static conditions, whereas they spread normally on collagen. LY294002 had a more pronounced inhibitory effect on spreading on all three surfaces. Adhesion and aggregate formation of p110d –/– platelets to collagen or fibrinogen/VWF at intermediate/high rates of shear were normal. This study demonstrates a minor role for the p110d catalytic subunit in mediating platelet activation by the collagen receptor GPVI and integrin aIIbß3. The more pronounced inhibitory effect of LY294002 and wortmannin indicates that other isoforms of PI 3-kinase play a more significant role in signalling by the two platelet glycoprotein receptors. [ABSTRACT FROM AUTHOR]