Regulation of the expression of human C epsilon germline transcript. Identification of a novel IL-4 responsive element.

Transcriptional regulation for Ig H chain germline transcripts induced by cytokines is a topic of recent interest for the understanding of the mechanism of class switch recombination. Among human B cell lines examined, we have found that a human IgM-producing B cell line, DND39 (EBV negative) expressed germ-line transcripts of epsilon constant gene (C epsilon) when stimulated with IL-4. In our study, the regulatory element responsible for the expression of IL-4-induced human C epsilon germ-line transcript was determined using DND39 cells. To identify the IL-4 responsive promoter/enhancer element, deletion analysis of the upstream region of the germ-line exon (I epsilon) of the C epsilon germ-line transcript which is located 5' to the switch region, was performed by using a luciferase gene as a reporter. Deletion analysis showed that a DNA fragment which lies between -215 and -154 bp upstream from the most 3' transcriptional initiation site of human I epsilon gene is fully responsible for the induction of germ-line transcripts by IL-4. According to a mutational analysis, the DNA fragment between -163 and -152 bp, was identified to be a novel IL-4 responsive element in a human C epsilon gene. Electrophoretic gel mobility shift assay showed the presence of IL-4-induced nuclear factor that specifically bound to this IL-4 responsive element. This novel IL-4 responsive element and an IL-4-induced DNA binding protein may play an important role for the induction of C epsilon germ-line transcript as well as class switching to IgE.