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

Lipopolysaccharide (LPS) is a potent stimulator of monocytes and macrophage s, causing secretion of tumor necrosis factor alpha (TNF-alpha) and other i nflammatory mediators. Given the deleterious effects to the host of TNF-alp ha, it has been postulated that TNF-alpha gene expression must be tightly r egulated. The nature of the nuclear factor(s) that control TNF-alpha gene t ranscription in humans remains obscure, although NF-kappa B has been sugges ted. Our previous studies pertaining to macrophage response to LPS identifi ed a novel DNA-binding domain located from -550 to -487 in the human TNF-al pha promoter that contains transcriptional activity, but lacks any known NF -kappa B-binding sites. We have used this DNA fragment to isolate and purif y a 60-kDa protein binding to this fragment and obtained its aminoterminal sequence, which was used to design degenerate probes to screen a cDNA libra ry from THP-1 cells. A novel cDNA done (1.8 kb) was isolated and fully sequ enced. 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 r esulted in a reduction of TNF-alpha transcripts. In addition, high level of expression of LITAF mRNA was observed predominantly in the placenta, perip heral blood leukocytes, lymph nodes, and the spleen. Finally, chromosomal l ocalization using fluorescence in situ hybridization revealed that LITAF ma pped to chromosome 16p12-16p13.3. Together, these findings suggest that LIT AF plays an important role in the activation of the human TNF-alpha gene an d proposes a new mechanism to control TNF-alpha gene expression.