Multiple activating and repressive cis-promoter regions regulate TNFSF15 expression in human primary mononuclear cells

•PMA/ionomycin activates TNFSF15 transcription in human monocytes.•A minimal −74/26 promoter fragment mediates a 30-fold increase in transactivation.•AP1/c-jun binds to the TNFSF15 5′UTR and mutation of this site inhibits TNFSF15 promoter activity.•NFκB binds to TNFSF15 −210 bp region, although mutation of this site enhances promoter activity.•Global inhibition of AP1 or NFκB pathways downregulates TL1A mRNA and protein expression in human monocytes.

TL1A/TNFSF15 has been associated with IBD (inflammatory bowel disease) in GWAS (genome-wide association study) and plays a role mediating mucosal inflammation in IBD. Higher TL1A expression is associated with disease severity in both patients and mouse models. Although TL1A has been studied extensively for IBD-associated SNPs, the cis/trans-regulatory regions are poorly defined. Herein we identify response elements regulating TNFSF15 in primary human myeloid cells. Peripheral mononuclear cells transfected with TNFSF15 promoter constructs displayed 30-fold enhanced promoter activity in a minimal −74 bp region. Transactivation was mediated partly by AP-1, since mutation of the AP-1 site resulting in loss of promoter activity. Monocytes transfected with c-Jun siRNA or treated with TAT-TI-JIP (JNK Inhibitor VII TAT-TI-JIP) demonstrated reduced TL1A mRNA and protein levels. Surprisingly, constructs larger than −74 bp did not increase promoter expression (expression of −1275 bp construct was 25% of −74 bp activity), suggesting the presence of both activating and repressing TL1A promoter elements. In fact, mutation of the −210 bp NFκB site enhanced promoter activity (60-fold) suggesting a repressive role for this site. DNA–protein binding to the TL1A AP-1 and NFκB elements was inhibited by excess consensus or TL1A oligonucleotides and binding and confirmed by chromatin immuno-precipitation analysis. Yet, despite the fact that the −210 bp NFκB site acts as a suppressor element, overall mRNA and protein expression were inhibited in monocytes treated with MG132 (NFκB/proteasome inhibitor) or SN50 (NFκB-p50 blocking peptide), suggesting that NFκB acts as both an activator and silencer of TL1A expression. These data suggest that modulation of TL1A expression involves a complex interplay between positive and negative signals, binding to distinct regulatory regions.