Identification and functional characterization of a novel binding site on TNF-α promoter

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Abstract
Transcription of the tumor necrosis factor (TNF) gene is rapidly and transiently induced by lipopolysaccharide in cells of monocytemacrophage lineage. Previous studies have suggested that in the mouse, multiple NF-kappaBRel-binding sites contribute to the TNF transcriptional response to LPS. But the role of these regulatory elements in transcriptional activation of the TNF-alpha gene in human monocytes remains unclear. Previously, a transcription factor, termed lipopolysaccharide-induced TNF-alpha factor (LITAF), was found to regulate TNF-alpha gene expression. However, the specific protein domain(s) of human (h)LITAF that interact with the hTNF-alpha promoter had not been identified. In this study, we identify by footprinting a sequence motif, CTCCC (-515 to -511), within the TNF-alpha promoter that binds to hLITAF. We also identify the region of hLITAF (amino acids 165-180) that was named peptide B and specifically mediates binding to the hTNF-alpha promoter. When THP-1 cells were stimulated with this peptide B, it was sufficient to induce TNF-alpha secretion. Induction of TNF-alpha transcription by LPS or peptide B depended on the presence of the -515 to -511 promoter region, which was found to be essential for hLITAF binding. Together, these findings help to clarify the mechanism of hLITAFhTNF-alpha interaction and the manner by which hLITAF contributes to hTNF-alpha regulation in an attempt to design new pharmacological interventions to address TNF-related diseases.