Characterization of an interleukin 4 (IL-4) responsive region in the immunoglobulin heavy chain germline ε promoter: Regulation by NF-IL-4, a C/EBP family member and NF-κB/p50

Abstract

A large body of data indicate that antibody class switching is directed by cytokines by inducing or repressing transcription from unrearranged, or germline, C(H) genes. Interleukin 4 (IL-4) induces transcription of the germline Cε genes in activated B cells and subsequently, cells in this population will undergo switch recombination to immunoglobulin E. Furthermore, the data suggest that transcription of germline Cε genes is required for class switching. In this paper we define DNA elements required for induction of transcription of the germline Cε genes by IL-4. To do this, segments of DNA from the 5' flank of the initiation sites for germline ε RNA were ligated to a luciferase reporter gene and transfected into two mouse B cell lines, one of which can be induced to switch to IgE. By analysis of a series of 5' deletion constructs and linker-scanning mutations, we demonstrate that a 46-bp segment (residing at -126/-79 relative to the first RNA initiation site) contains an IL-4 responsive region. By electrophoretic mobility shift assays, we find that this segment binds three transcription factors: the recently described NF-IL4, one or more members of the C/EBP family of transcription factors, and NF-κB/p50. Mutation of any of the binding sites for these three factors abolishes or reduces IL-4 inducibility of the ε promoter. A 27-bp segment within this IL-4 response region containing binding sites for NF-IL4 and a C/EBP factor is sufficient to transfer IL-4 inducibility to a minimal c-fos promoter.