Regulation of interleukin 2 receptor alpha subunit (Tac or CD25 antigen) gene expression: binding of inducible nuclear proteins to discrete promoter sequences correlates with transcriptional activation.

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Abstract
Transfection of deleted forms of the human interleukin 2 receptor alpha subunit (IL-2R alpha; also called CD25 or Tac antigen) gene (IL2RA) promoter revealed a requirement for sequences 3' of base -317 for phytohemagglutinin- and phorbol 12-myristate 13-acetate (PMA)-induced promoter activation in CD4+ Jurkat T cells. In contrast, sequences 3' of base -271 were sufficient for promoter induction in CD4-/CD8- YT-1 T cells or Jurkat cells expressing the transactivator protein (tat-I) of human T-cell lymphotropic virus type I (HTLV-I). Gel retardation assays revealed that nuclear extracts from induced, but not uninduced, Jurkat and YT-1 cells mediated the formation of two specific DNA-protein complexes with oligonucleotides spanning the region of the IL2RA promoter from position -291 to -245, which contains two imperfect direct repeats (IDRs). Consistent with the different 5' sequence requirements for promoter activation in Jurkat and YT-1 cells, oligonucleotides corresponding to the region from -267 to -243 (downstream IDR and flanking region) formed only one complex with induced Jurkat extracts but two complexes with induced YT-1 extracts. Oligonucleotides containing the region of the IL2RA promoter from -293 to -270 (upstream IDR and flanking region) failed to bind protein in either cell type. In further support of the biological significance of these DNA-protein interactions, the IL2RA oligonucleotide from -291 to -245 proved to be sufficient in either orientation to confer PMA inducibility to the mitogen-insensitive thymidine kinase gene promoter in Jurkat cells. Together, these findings suggest that the interaction of inducible DNA binding proteins with the IL2RA promoter between bases -291 and -245 plays an important role in mitogen-induced changes in the transcriptional activity of this receptor gene. Furthermore, the requisite 5' sequences appear to differ in T cells depending upon the nature of the activation signal and perhaps the stage of cellular maturation.