Nuclear Factor of Activated T Cells 1 (NFAT1)-induced Permissive Chromatin Modification Facilitates Nuclear Factor-κB (NF-κB)-mediated Interleukin-9 (IL-9) Transactivation

IL-9 regulates diverse inflammatory immune responses. Although the functional importance of IL-9 has been investigated in various pathophysiological conditions, molecular mechanisms by which TCR stimulation induced IL-9 gene expression are still unclear. In this study, we investigated the functional importance of the NFAT1 and NF-kappa B (p65) in IL-9 gene transcription in CD4(+) T cells. In vivo binding of NFAT1 and NF-kappa B (p65) to the IL-9 promoter was observed. NFAT1 binding induced a transcriptionally active chromatin configuration at the IL-9 promoter locus, whereas NF-kappa B (p65) binding transactivated the IL-9 promoter. Mouse deficient in NFAT1 shows a significant down-regulation of IL-9 expression that resulted from an inaccessible chromatin configuration at the IL-9 promoter. In parallel, knockdown of NF-kappa B (p65) also resulted in reduced IL-9 expression. In this process, NFAT1 plays a pivotal role as a core protein that creates an accessible platform for the assembly of transcription activators. The presence of NFAT1 correlates with recruitment of NF-kappa B (p65), p300, and active histone markers on the IL-9 promoter, resulting in a transcriptionally competent promoter. NFAT1 deficiency significantly reduced the recruitment of the above activation complex to the IL-9 promoter. In summary, our data suggest that functional cooperation of NFAT1 and NF-kappa B synergistically enhances IL-9 transcription in CD4(+) T cells.