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Association of interleukin-4 receptor (IL-4R) with phosphatidylinositol 3-kinase (PI3-kinase) has been demonstrated as the proximal event of IL-4 signaling. We investigated the role of this enzyme in the IL-4 signaling pathway in a human Burkitt lymphoma B cell line, DND39, that expresses germline C epsilon transcripts in response to IL-4. Stimulation of DND39 cells with IL-4 resulted in an accumulation of PI-3-monophosphate as well as a decrease of PI-4,5-bisphosphate, which were abrogated by wortmannin, a potent inhibitor of PI3-kinase. Activation of PI3-kinase was further confirmed by the finding that IL-4 caused an increase in PI3-kinase activity coimmunoprecipitated with anti-IL-4R and with anti-JAK3 kinase antibodies. As a possible downstream event of PI3-kinase activation, the translocation of a zeta isoform of protein kinase C (PKC) from the cytosol to the membrane fraction was observed after IL-4 stimulation, and wortmannin also suppressed this translocation. Moreover, IL-4-induced expression of germline C epsilon transcription was inhibited not only by wortmannin, but also by a PKC inhibitor, K252a. These results suggest that the signaling pathway involving PI3-kinase and PKC zeta plays an important role in induction of germline C epsilon transcription in DND39 cells by IL-4.

Despite the recent advances in knowledge of the molecular mechanism by which interleukin-4 (IL-4) induces IgE production, little is known about the signal transduction pathway that leads to this event. This study investigated the signal transduction mechanism responsible for IL-4-induced expression of germ-line C epsilon transcripts with use of a human Burkitt lymphoma B-cell line, DND39, which is known to express germ-line C epsilon transcripts in response to IL-4. On stimulation with IL-4, the generation of inositol triphosphate was observed in the cells. In addition, this generation was associated with activation of phospholipase C-gamma 1 (PLC-gamma 1). Although herbimycin A, a potent inhibitor of tryosine kinase, inhibited IL-4-induced activation of PLC-gamma 1 and generation of inositol triphosphate, direct phosphorylation of PCL-gamma 1 was not determined. Nevertheless, IL-4 stimulation could induce activation of FYN but not LYN kinase, suggesting that additional molecule(s) might link FYN kinase to PLC-gamma 1. Interestingly, herbimycin A almost completely inhibited IL-4-induced expression of germ-line C epsilon transcripts when present during the entire culture period. These results indicate that the induction of germ-line C epsilon transcripts in IL-4-stimulated DND39 cells is essentially dependent on the activation of tyrosine kinase, possibly FYN kinase.