A novel lipopolysaccharide-induced transcription factor regulating tumor necrosis factor α gene expression: Molecular cloning sequencing characterization and chromosomal assignment

摘要

Lipopolysaccharide (LPS) is a potent stimulator of monocytes and macrophages, causing secretion of tumor necrosis factor α (TNF-α) and other inflammatory mediators. Given the deleterious effects to the host of TNF-α, it has been postulated that TNF-α gene expression must be tightly regulated. The nature of the nuclear factor(s) that control TNF-α gene transcription in humans remains obscure, although NF-κB has been suggested. Our previous studies pertaining to macrophage response to LPS identified a novel DNA-binding domain located from −550 to −487 in the human TNF-α promoter that contains transcriptional activity, but lacks any known NF-κB-binding sites. We have used this DNA fragment to isolate and purify a 60-kDa protein binding to this fragment and obtained its amino-terminal sequence, which was used to design degenerate probes to screen a cDNA library from THP-1 cells. A novel cDNA clone (1.8 kb) was isolated and fully sequenced. Characterization of this cDNA clone revealed that its induction was dependent on LPS activation of THP-1 cells; hence, the name LPS-induced TNF-alpha factor (LITAF). Inhibition of LITAF mRNA expression in THP-1 cells resulted in a reduction of TNF-α transcripts. In addition, high level of expression of LITAF mRNA was observed predominantly in the placenta, peripheral blood leukocytes, lymph nodes, and the spleen. Finally, chromosomal localization using fluorescence in situ hybridization revealed that LITAF mapped to chromosome 16p12–16p13.3. Together, these findings suggest that LITAF plays an important role in the activation of the human TNF-α gene and proposes a new mechanism to control TNF-α gene expression.