NF-κB elements associated with the Stat6 site in the germline γ1 immunoglobulin promoter are not necessary for the transcriptional response to CD40 ligand

Both germline transcription and switch recombination of heavy chain genes are likely to be regulated by cis elements binding transcription factors in the promoter regions of germline immunoglobulin genes. To identify cis-acting elements important in germline transcription of the murine γ1 heavy chain gene, we have used a transgenic approach. Seventeen kb γ1 immunoglobulin transgenes with mutations in three NF-κB sites in the γ1 proximal promoter, a putative CD40 response element, are expressed well. Compared to wild-type transgenes, there is no deficiency in the expression of the transgenes with mutations of the three NF-κB sites after induction of splenic B cells with IL-4 alone, CD40L, or CD40L + IL-4. There may be a small reduction in the response of these mutant transgenes after induction with LPS + IL-4. We also prepared transgenes that were truncated at -150 (rather than -2100) and therefore included the wild-type Stat6 binding site at -123 and the three wild-type NF-κB sites. Nevertheless, γ1 germline transcripts were not expressed from these transgenes. We conclude that the three proximal NF-κB sites are dispensable for expression of γ1 germline transcripts under most conditions. However, cis-acting elements distal to -150 must be critical to this transcription.