Human Tumor Necrosis Factor-α Gene 3′ Untranslated Region Confers Inducible Toxin Responsiveness to Homologous Promoter in Monocytic THP-1 Cells

To better define the role of 3′ untranslated region (3′UTR) on transcriptional regulation of the human tumor necrosis factor (TNF)-α gene, monocytic human THP-1 cells were transfected with two TNF-α promoter constructs spanning base pairs −1897/−1 and −1214/−1, respectively, and linked to the rabbit β-globin gene. Quantitative globin gene expression of chimerae was measured by reverse transcription-polymerase chain reaction. A construct linking the chicken β-actin promoter and a deleted portion of the β-globin gene was cotransfected and used as internal standard. Unexpectedly, when THP-1 cells were stimulated with lipopolysaccharide or toxic shock syndrome toxin-1, gene regulation was hardly detected. In contrast, endogenous TNF-α gene regulation measured by the same reverse transcription-polymerase chain reaction procedure was vigorous. Remarkably, ligation of 3′UTR to chimeric constructs led to a drastic drop in the basal level of chimeric gene expression, resulting in a 15- to 40-fold induction of the reporter gene. Consistently, when the TNF-α promoter was replaced by the cytomegalovirus early immediate promoter, gene expression was also uniformly reduced but was no longer up-regulated upon stimulation with lipopolysaccharide and toxic shock syndrome toxin-1. These data provide the first line of evidence that, in addition to its role in TNF-α transcript stability and translation, human TNF-α 3′UTR also participates in modulating gene expression at the transcriptional level.