High level transcription of the complement regulatory protein CD59 requires an enhancer located in intron 1

CD59 is a complement regulatory protein and may also act as a signal-transd ucing molecule. CD59 transgenic mice have been generated using a CD59 minig ene (CD59 minigene-1). Although this minigene contained a 4.6-kilobase pair 5'-flanking region from the human CD59 gene as a promoter, the expression levels of the CD59 mRNA were substantially lower than those observed in hum ans, suggesting that CD59 gene expression might also require other transcri ptional regulatory elements such as an enhancer. To investigate the transcr iptional regulation of the CD59 gene, we used three cell lines that express CD59 at different levels. We have identified DNase 1-hypersensitive sites in intron 1 in HeLa cells, which express CD59 at high levels, but not in Ju rkat (intermediate level) or Raji cells (low level). Furthermore, cell line -specific enhancer activity was detected in a fragment containing these DNa se 1-hypersensitive sites. The CD59 enhancer was mapped to between -1155 an d -888 upstream of the 5'-end of exon 2. To investigate the enhancer activi ty in vivo, a new CD59 minigene was constructed by the addition of the enha ncer fragment, into CD59 minigene-1, High expressor CD59 transgenic mice we re generated using the new minigene.