Multiple transcription factors are required for activation of human interleukin 9 gene in T cells. 
The genetic elements and regulatory mechanisms responsible for human interleukin 9 (IL-9) gene expression in a human T cell leukemia virus type I-transformed human T cell line, C5MJ2, were investigated. We demonstrated that IL-9 gene expression is controlled, at least in part, by transcriptional activation. Transient expression of the luciferase reporter gene linked to serially deleted sequences of the 5'-flanking region of the IL-9 gene has revealed several positive and negative regulatory elements involved in the basal and inducible expression of the IL-9 gene in C5MJ2 cells. An AP-1 site at -146 to -140 was shown to be involved in the expression of the IL-9 gene. A proximal region between -46 and -80 was identified as the minimum sequence for the basal and inducible expression of the IL-9 gene in C5MJ2 cells. Within this region, an NF-kappaB site at -59 to -50 and its adjacent 20-base pair upstream sequence were demonstrated to play a critical role for the IL-9 promoter activity. DNA-protein binding studies indicated that NF-kappaB, c-Jun, and potentially novel proteins (around 35 kDa) can bind to this important sequence. Mutations at different sites within this proximal promoter region abolished the promoter activity as well as the DNA binding. Taken together, these results suggest that the cooperation of different transcription factors is essential for IL-9 gene expression in T cells.