A critical role for PI 3-kinase in cytokine-induced Fcα-receptor activation

Abstract

AbstractFc-receptors, such as FcR and FcγRII, play an important role in leukocyte activation, and rapid modulation of ligand binding (“activation”) is critical for receptor regulation. We have previously demonstrated that ligand binding to Fc-receptors on human eosinophils is dependent on cytokine stimulation. Utilization of pharmacological inhibitors provided evidence that the phenomenon of interleukin (IL)-5 induced immunoglobulin A (IgA) binding to human eosinophils requires activation of phosphatidylinositol 3-kinase (PI3K). However, eosinophils are refractory to manipulation by molecular techniques such as DNA transfection or viral infection. Here we utilize an IL-3 dependent pre-B cell line to investigate the molecular mechanism of cytokine-mediated ligand binding to FcR. In this system, IgA binding is dependent on IL-3, similarly to the requirement for IL-5 of eosinophils. We show that IL-3-mediated activation of FcR (CD89) requires the activation of PI3K, independent of p21ras activation. Co-expression of dominant negative (▵p85) and active (p110_K227E) forms of PI3K demonstrate that the affinity switch regulating FcR activation requires PI3K. Moreover, overexpression of PI3K is both necessary and sufficient for activation of FcR. Furthermore, we show that IL-3/IL-5/GM-CSF induced inside-out signaling pathways activating FcR require the involvement of protein kinase C downstream of PI3K. Finally, we show that these inside-out signaling pathways responsible for Fc-receptor modulation require CD89, independent of its association with the FcRγ chain.