CD40 cross-linking induces Ig epsilon germline transcripts in B cells via activation of NF-kappaB: synergy with IL-4 induction.
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.
Iciek
L A
LA
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655, USA.
Delphin
S A
SA
Stavnezer
J
J
D000818:Animals; D001402:B-Lymphocytes / Q000502:physiology*; D001483:Base Sequence; D001665:Binding Sites; D019013:CD40 Antigens / Q000502:physiology*; D023201:CD40 Ligand; D004268:DNA-Binding Proteins / Q000502:physiology; D005803:Genes, Immunoglobulin; D007073:Immunoglobulin E / Q000235:genetics*; D015847:Interleukin-4 / Q000502:physiology; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000502:physiology*; D011401:Promoter Regions, Genetic; D050800:STAT6 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000502:physiology; D014158:Transcription, Genetic
D019013:CD40 Antigens; D004268:DNA-Binding Proteins; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D050800:STAT6 Transcription Factor; C494100:Stat6 protein, mouse; D015534:Trans-Activators; D023201:CD40 Ligand; D015847:Interleukin-4; D007073:Immunoglobulin E