Interleukin-4 Signals Regulating CD23 Gene Expression in Human B Cells: Protein Kinase C-Independent Signaling Pathways

Signal transduction by IL-4 leading to the activation of CD23(FcϵRII) gene expression using human tonsillar B cells was studied. IL-4 stimulated CD23 mRNA transcription within hours (1-4 hr) which preceded the later induction of cell surface CD23. The induction of CD23 gene transcription by IL-4 was not adversely affected by cycloheximide, suggesting that post-translational modifications are accounted for the gene activation. PKC activators (PMA, diacylglycerol, indolactam) were effective inducers of CD23 gene expression, whereas calcium ionophores were not. PMA and IL-4 also displayed similar induction kinetics for CD23 mRNA. However, the signaling pathways utilized by the two agents appear distinct as shown by (1) cotreatment of IL-4 and PMA caused CD23 gene expression over the maximum level inducible by each agent alone and (2) unlike the PMA-induced CD23 expression, the IL-4-induced expression was not affected by PKC inhibitors. These results strongly suggest that IL-4 signals leading to CD23 gene activation are mediated via a PKC-independent pathway. A possible role of tyrosine kinases in the regulation of CD23 expression is discussed.