Transcriptional regulation by retinoic acid of interleukin-2 alpha receptors in human B cells.

In this study, we demonstrated that retinoic acid (RA) up-regulated interleukin-2 receptor-alpha (IL-2R alpha) expression on two human B-cell lines, IE8.6 and SKW6.4. Deleted forms of the human IL-2R alpha promoter linked to the bacterial chloramphenicol acetyltransferase reporter gene were transfected into IE8.6 cells in order to define RA-responsive regulatory domains. Experiments using the -1.6 kb construct, which contains all known regulatory regions in the IL-2R alpha promoter, indicated that RA could induce IL-2R alpha promoter activity. The basal activity of the -471 construct was initially low, but was markedly enhanced by the addition of RA. Deletion of promoter sequences between -471 and -317 resulted in a significant augmentation of basal promoter activity and abolished promoter induction by RA. This finding revealed a requirement for sequences 5' of base -317 for RA-induced promoter activation, raising the possibility of the presence of both a RA response element and a negative regulatory element (NRE) upstream of base -317. Transfection studies with internal deletion mutants with the putative NRE removed resulted in increases in basal promoter activity and unresponsiveness to RA similar to the -317 construct. In contrast, an internal deletion mutant with the NRE intact had low basal activity and was inducible by RA similar to the -471 construct. Taken together, our results suggested that RA-induced activation of the IL-2R alpha promoter was through changes in the function of a NRE present between bases -400 and -368. This 31-base pair element may interact with an adjacent RA-responsive regulatory site as well as being responsible for down-regulation of basal IL-2R alpha expression under certain conditions.