CD40 cross-linking induces Ig epsilon germline transcripts in B cells via activation of NF-kappaB: synergy with IL-4 induction
Department of Molecular Genetics and Microbiology
Animals; Antigens, CD40; B-Lymphocytes; Base Sequence; Binding Sites; CD40 Ligand; DNA-Binding Proteins; *Genes, Immunoglobulin; Immunoglobulin E; Interleukin-4; Membrane Glycoproteins; Mice; Molecular Sequence Data; NF-kappa B; *Promoter Regions (Genetics); STAT6 Transcription Factor; Signal Transduction; Trans-Activators; Transcription, Genetic
Life Sciences | Medicine and Health Sciences | Women's Studies
Transcription of unrearranged (germline) Ig heavy chain C region (C(H)) genes is required before Ab class switch recombination. Although the cytokine IL-4 is well known to induce transcription of unrearranged C epsilon and C gamma1 genes, it has been shown recently that CD40 signaling also induces these transcripts in mouse B cells. We report in this study that treatment of mouse M12.4.1 B lymphoma cells with soluble CD40 ligand (CD40L)-CD8alpha fusion protein modestly induces the promoter for germline epsilon transcripts, and that this induction synergizes with IL-4. CD40L induces binding of nuclear factor (NF)-kappaB/Rel proteins to two tandem kappaB sites located immediately 3' to the IL-4-responsive region of the mouse germline epsilon promoter. The epsilon-124/-56 promoter segment containing the IL-4 response region and the two kappaB sites is sufficient to transfer CD40L and IL-4 inducibility to a minimal c-fos promoter when transiently transfected into M12.4.1 cells. Mutation of the two kappaB sites eliminates induction by CD40L or by IL-4, and treatment of M12.4.1 cells with inhibitors of NF-kappaB activation prevents induction of endogenous germline epsilon transcripts in M12.4.1 cells. In addition to the NF-kappaB/Rel complexes induced by CD40L, two nuclear complexes, each which contain both STAT6 and NF-kappaB/Rel proteins, are induced in splenic B cells by a combination of CD40L and IL-4, and bind to the CD40L/IL-4-responsive region of the germline epsilon promoter. The presence of these complexes may explain the synergistic induction of transcription by CD40L and IL-4 mediated through this promoter segment.
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Citation: J Immunol. 1997 May 15;158(10):4769-79.