Nuclear factor of activated T cells and YY1 combine to repress IL-5 expression in a human T-cell line

Background: IL-5 is an inducible T-cell cytokine with the unique ability to induce eosinophilia without increases in other cell compartments. Regulati on of IL-5 expression is controlled primarily at the level of transcription . The role of eosinophilia in allergic disorders indicates IL-5 as a target for therapy. Objective: This report aims to increase our understanding of IL-5 gene regu lation by identifying distal control elements in the human (h) IL-5 promote r, determining the transcription factors that bind these elements and eluci dating their role in control of hIL-5 gene expression, Methods: Methods used in this study include deoxyribonuclease I footprint analysis, electrophoretic mobility shift assay, and functional analysis by transfecti on of PER-117 cells with site-directed mutants of the hIL-5 promoter. Results: We have identified a protected region in the distal hIL-5 promoter that has sequence homology to the previously identified negative regulator y element within BR3, This protected region has not been previously reporte d and is shown to contain overlapping binding sites for YY1 and nuclear fac tor of activated cells. The binding sites exist between positions -447 and -459, and this sequence was named hPRE2-IL5, Substitution mutations that ab olish binding of these proteins to hPRE2-IL5 result in a 2- to 3-fold incre ase in hIL-5 promoter activity in activated human T cells. Conclusion: We report the novel combination of YY1 and nuclear factor of ac tivated T cells transcription factors binding to a distal hIL-5 promoter el ement where both factors are involved in down-regulation of hIL-5 gene expr ession in human T cell.