Single Nucleotide Variations Between the I gamma 1 and I gamma 4 Promoters Result in Biased Recruitment of Transcription Factors in Response to CD40 Signaling (35.7)

Abstract

Abstract IgG subclass expression is highly biased in human IgM+ B cells activated with CD40L and IL-4. This bias is clearly reflected at the level of germline (Iγ) transcription despite extensive homology throughout the four Iγ promoters. Our current aim is to define the underlying mechanism by which Iγ1 transcripts are preferentially expressed relative to Iγ4 transcripts in order to extend our understanding of CD40 mediated humoral responses. Characterization of both promoters using defined regions of the Iγ1 and Iγ4 promoters revealed a marked decrease in Iγ4 transcriptional activity when compared to Iγ1 activity despite similar regulation. Expression studies have further shown that exchanging a previously defined 36 bp region of the Iγ1 promoter that is essential for Iγ1 transcription and binds NF-κB and various co-activators, can elevate Iγ4 transcription. This increase can be attributed to single nucleotide changes in either a putative CREB site or a putative NF-κB site within this region that renders this element CD40 inducible, and increases recruitment of p50, p65, c-Rel, CREB, and p300. Together, these data indicate that a single base pair change in a key regulatory region can contribute to differences in promoter strength. Competition assays and site-directed mutagenesis are currently in progress to further our understanding of the effect of these variances on Iγ transcription targeting. Supported by AI37081