Transcriptional Regulation of the Human IL5 Gene by Ionizing Radiation in Jurkat T Cells: Evidence for Repression by an NF-AT-Like Element

Eosinophilia is often observed in patients with parasitic infections and atopic diseases like allergic asthma and atopic dermatitis. Additionally, it is a typical feature of the inflammatory reaction after therapeutic and accidental exposure to ionizing radiation. This uniquely specific phenomenon regulated by the cytokine interleukin 5 (IL-5) suggests specific control for IL5 gene expression. In this study, we generated promoter-CAT constructs containing different human IL-5 promoter regions spanning from positions -507 to +43. Transfection experiments in Jurkat T cells revealed that the promoter sequence from -57 to +43 was required for constitutive and inducible IL-5 promoter activity. Low baseline CAT activity could be enhanced by treatment with phenylmercuric acetate (PMA) or the combination of PMA and calcium ionophore. The promoter region between positions -97 and +43 showed responsiveness to low-dose X rays. Electrophoretic mobility shift assays demonstrated that the region from -117 to -97 was responsive to irradiation. Transcription factors specifically bound to this sequence showed a dose-dependent response to single doses of X rays between 1 and 8 Gy. Competition analysis indicated that the protein-DNA complexes at this region were related to the nuclear factor of activated T cells (NF-AT). Further confirmation was obtained by the addition of specific antibodies into protein-DNA reactions. For the first time, we have demonstrated that specific DNA binding of NF-ATp at the promoter region from -117 to -97 is involved in transcriptional regulation of the human IL5 gene in response to ionizing radiation.