Multiple transcription factors regulate the inducible expression of the human complement receptor 2 promoter

Complement receptor 2 (CR2) is regulated at the transcriptional level, but the promoter elements and the transcription factors that bind to them and c ontribute to its regulation are unknown. After documenting that PMA and CAM P induced the activity of the CR2 promoter by 10-fold, we conducted promote r truncation and mutagenesis experiments, in conjunction with shift assays, to determine the functionally important regions of the promoter and the pr oteins that bind to them. We identified two regions, separated by similar t o 900 nucleotides, which together were responsible for inducible promoter a ctivity. Mutagenesis of single promoter elements demonstrated a functional upstream stimulatory factor/E box in the TATA box-proximal region and three equally important, closely spaced, CREB/AP-1 half-sites in the upstream pr omoter region. The cAMP response element-binding protein (CREB)/AP-1 half-s ites bound in vitro Jun and CREB that are induced by protein kinases A and/ or C. The 900-nucleotide segment stretching between the above two regions h ad no functional impact on the induced transcription, and its deletion incr eased the promoter activity. Finally, a region upstream of the distal site had a repressor activity on CR2 transcription. Moreover, IL-4 induced bindi ng of CREB and AP-1 to the upstream promoter elements and resulted in incre ased CR2 surface protein expression. These studies have characterized regio ns of the CR2 promoter and the transcription factors that bind to them and are crucial to induced CR2 expression. Our studies may provide insights to novel approaches to modulate B cell function by regulating CR2 gene transcr iption.