Abstract
We examined the role of phosphoinositide 3-kinase (PI3K) in integrin-mediated eosinophil adhesion. Deltap85, a dominant-negative form of the class IA PI3K adaptor subunit, was fused to an HIV-TAT protein transduction domain (TAT-Deltap85). Recombinant TAT-Deltap85 inhibited interleukin (IL)-5-stimulated phosphorylation of protein kinase B, a downstream target of PI3K. beta(2)-Integrin-dependent adhesion caused by IL-5 to the plated intracellular adhesion molecule-1 surrogate, bovine serum albumin, was inhibited by TAT-Deltap85 in a concentration-dependent manner. Similarly, two PI3K inhibitors, wortmannin and LY294002, blocked eosinophil adhesion to plated bovine serum albumin. By contrast, beta(1)-integrin-mediated eosinophil adhesion to vascular cell adhesion moelcule-1 was not blocked by TAT-Deltap85, wortmannin, or LY294002. Rottlerin, a protein kinase C (PKC)-delta inhibitor, also blocked beta(2)-integrin adhesion of eosinophils caused by IL-5, whereas beta(1) adhesion to vascular cell adhesion molecule-1 was not affected. IL-5 caused translocation of PKCdelta from the cytosol to cell membrane; inhibition of PI3K by wortmannin blocked translocation of PKCdelta. Western blot analysis demonstrated that extracellular signal-regulated kinase phosphorylation, a critical intermediary in adhesion elicited by IL-5, was blocked by inhibition of either PI3K or PKC-delta. These data suggest that extracellular signal-regulated kinase-mediated adhesion of beta(2)-integrin caused by IL-5 is mediated in human eosinophils by a class IA PI3K through activation of a PKCdelta pathway.