Evidence for a Role of Phosphatidylinositol 3-Kinase in IL-4-Induced Germline Cϵ Transcription

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 Cϵ 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 ζ 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 Cϵ 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 PKCζ plays an important role in induction of germline Cϵ transcription in DND39 cells by IL-4.