Therefore, we wondered whether TSLP expression
in human IECs was regulated in a similar fashion. Although we also observed that TSLP was regulated by NF-κB in Caco-2 and HT-29 cell lines in response to IL-1, we found contradictory results concerning the precise promoter site responsible for the NF-κB-dependent regulation of TSLP. The in silico analysis of a 4 kb-long region of human TSLP promoter allowed us to identify four potential NF-κB sites. Although human and murine TSLP promoters do not share significant ABT-263 cost sequence homology, one of these putative sites is conserved in mice TSLP promoter as well as in other mammals. Moreover, in mice a site corresponding to NF2 exerts the same biological function as that observed CHIR-99021 in vivo in human
TSLP regulation and expression (P. Chambon, unpublished data and ). In our study, we used different strategies to demonstrate that NF2, a newly identified NF-κB responsive element located in the proximal region of TSLP promoter, is functionally important for the NF-κB-dependent regulation of human TSLP in IECs. We also demonstrated the functional importance of NF2 in regulating TSLP expression in other epithelial cells, including lung, cervical and kidney epithelial cells. Despite the fact that both NF1 and NF2 sites showed similar binding capacities for p65 and p50 subunits of NF-κB, as revealed by EMSA experiments using nuclear extracts from IL-1-, TNF- or PMA- stimulated Caco-2 and HT-29 cells, they produced a different impact on TSLP modulation. First, we assumed that both NF1 and NF2 sites were necessary to support the full transcriptional activity
of NF-κB complexes in response to the different ligands. However, TSLP promoter lacking a functional NF1 site was still able to respond to IL-1 in IECs as well as in other epithelial cells, including the lung cell line, A549, which has Idoxuridine been used in the previously published paper . By contrast, all the IL-1-induced activity was lost following NF2 site mutation, demonstrating the absolute requirement of NF2 for the NF-κB-dependent regulation of TSLP driven by IL-1. We speculate that the presence of two NF-κB sites, one of which fails to respond to inflammatory agonist IL-1, could be necessary for constitutive expression of TSLP, while the other responses to upregulate TSLP expression under specific conditions. Overall, our data did not reveal other regulatory elements, other than NF2, that are absolutely essential for the IL-1-induced expression of TSLP. In accordance with previous studies [16, 17], we showed that TSLP promoter contains several putative AP-1 binding sites. These sites either cooperate with NF-κB sites to mediate the effects of IL-1 via ERK pathway or are involved in PKC signaling via PMA.