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

Fc-receptors, such as Fc alpha R and Fc gamma RII, play an important role i n leukocyte activation, and rapid modulation of ligand binding ("activation ") is critical for receptor regulation. We have previously demonstrated tha t ligand binding to Fc-receptors on human eosinophils is dependent on cytok ine stimulation. Utilization of pharmacological inhibitors provided evidenc e 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 molec ular techniques such as DNA transfection or viral infection. Here we utiliz e an IL-3 dependent pre-B cell line to investigate the molecular mechanism of cytokine-mediated ligand binding to Fc alpha R, In this system, IgA bind ing is dependent on IL-3, similarly to the requirement for IL-5 of eosinoph ils. We show that IL-3-mediated activation of Fc alpha R (CD89) requires th e activation of PI3K, independent of p21ras activation. Go-expression of do minant negative (Delta p85) and active (p110_K227E) forms of PI3K demonstra te that the affinity switch regulating Fc alpha R activation requires PI3K, Moreover, overexpression of PI3K is both necessary and sufficient for acti vation of Fc alpha R, Furthermore, we show that IL-3/IL-5/GM-CSF induced in side-out signaling pathways activating Fc alpha R require the involvement o f protein kinase C downstream of PI3K, Finally, we show that these inside-o ut signaling pathways responsible for Feat-receptor modulation require CD89 , independent of its association with the FcR gamma chain. (C) 2000 by The American Society of Hematology.