Involvement of NF-kappa B pathway in TL1A gene expression induced by lipopolysaccharide

Backgrounds: Recent studies have shown that TL1A (TNFSF15) is one of the definitive susceptibility genes to Crohn's disease (CD). To determine the immunological contribution of TL1A to CD, it is essential to investigate the transcriptional regulation of TL1A. Methods/Results: We analyzed the transcriptional mechanisms of TL1A induced by lipopolysaccharide (LPS) using the human monocytic cell line U937. RT-PCR revealed that LPS induced TL1A mRNA expression. Transient transfection assays using the promoter-reporter construct which contained 5′ flanking region of TL1A revealed that LPS induce transcription of TL1A. Serial deletion constructs revealed that the positive regulatory elements involved with LPS-induced transcriptional activation were located between -247 and -135 in TL1A, in which one putative NF-kappa B binding site was predicted. Overexpressions of I-kappa Bα inhibited LPS-induced transcriptional activation. Mutation of the predicted NF-kappa B binding site abolished the LPS-induced transcriptional activation. The binding of NF-kappa B to the predicted NF-kappa B motif was demonstrated by electrophoretic mobility shift assays. Conclusion: (1) LPS induces TL1A expression through the transcriptional activation via a NF-kappa B pathway. (2) The NF-kappa B binding site in the 5′ flanking region of TL1A was identified.