Coordinated Regulation of the Promoter and Enhancer Regions of Human CD23 Gene by Signal Through IL-4R and CD40, and the Role of Ku70/80 in the Enhancer Activity

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CD23 has roles in proliferation, antigen uptake and presentation, and the generation of IgE. Signals through IL-4R and CD40 stimulate transcription of CD23 in B cells and are necessary for immunoglobulin class switch (IgCS). The same signals induce nuclear translocation of Ku, which is also required for IgCS, in human resting B cells, suggesting that these signaling pathways are connected. We examined the regulation of CD23 gene, and located the minimal promoter at -132+80 region. A pair of 188bp inverted repeats inhibited its activity. The intronic region including EBV responsive element (EBVRE) and the surrounding sequence, required the gene specific promoter to enhance the reporter gene activity. Western blotting and FACS analysis using subclones of DND39 B cells infected with recombinant EBV, revealed that CD23 upregulation did not necessarily correlate with EBNA 2 and LMP 1 expression. Although the specific binding of Ku to EBVRE was not demonstrated, dominant negative Ku80 suppressed IL-4 + anti-CD40-driven CD23 expression. These results suggest that Ku is involved in gene regulation as a signal transducer and gene enhance. Detailed analysis of CD23 gene regulation would lead to a better understanding of disorders such as allergy and lymphoproliferation.