NF-kappa B-inducing kinase is a common mediator of IL-17-, TNF-alpha-, and IL-1 beta-induced chemokine promoter activation in intestinal epithelial cells

IL-17 expression is restricted to activated T cells, whereas the IL-17R is expressed in a variety of cell types including intestinal epithelial cells. However, the functional responses of intestinal epithelial cells to stimulation with IL-17 are unknown. Moreover, the signal transduction pathways activated by the IL-17R have not been characterized. IL-17 induced NF-kappa B protein-DNA complexes consisting of p65/p50 heterodimers in the rat intestinal epithelial cell line IEC-6. The induction of NF-kappa B correlated with the induction of CXC and CC chemokine mRNA expression in IEC-6 cells. IL-17 acted in a synergistic fashion with IL-1 beta to induce the NF-kappa B site-dependent CINC promoter. Induction of the CINC promoter by IL-17 in IEC-6 cells was TNF receptor-associated factor-6 (TRAF6), but not TRAF2, dependent. Furthermore, IL-17 induction of the CINC promoter could be inhibited by kinase-negative mutants of NF-kappa B-inducing kinase and I kappa B kinase-alpha. In addition to activation of the NF-kappa B, IL-17 regulated the activities of extracellular regulated kinase, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinases in IEC-6 cells. Whereas the IL-17-mediated activation of extracellular regulated kinase mitogen-activated protein kinases was mediated through ras, c-Jun N-terminal kinase activation was dependent on functional TRAF6. These data suggest that NF-kappa B-inducing kinase serves as the common mediator in the NF-kappa B signaling cascades triggered by IL-17, TNF-alpha, and IL-1 beta in intestinal epithelial cells.     

IFN-gamma-induced SOCS-1 regulates STAT6-dependent eotaxin production triggered by IL-4 and TNF-alpha

The production of eotaxin, which is a critical mediator for airway inflammation, is inhibited by IFN-gamma. Here, we investigated the precise mechanisms underlying IFN-gamma-dependent inhibition of eotaxin production using mouse embryonic fibroblasts (MEF). MEF produced high levels of eotaxin in STAT6-dependent manner when they were cultured with both IL-4 and TNF-alpha. However, the eotaxin production by MEF was strongly inhibited by addition of IFN-gamma. Western-blotting analysis demonstrated that IFN-gamma downmodulated STAT6 phosphorylation induced by IL-4 and TNF-alpha. Moreover, IFN-gamma did not exhibit its inhibitory effect on both STAT6-phosphorylation and eotaxin production in MEF obtained from deficient mice in STAT1, a key molecule of IFN-gamma signaling. We also demonstrated that SOCS-1, a potent inhibitory molecule of IL-4 signaling, was induced by IFN-gamma in STAT1-dependent manner. This indicated that SOCS-1 might be involved in IFN-gamma-mediated STAT1-dependent inhibition of eotaxin production. In SOCS-1(-/-) MEF, IFN-gamma inhibited neither STAT6 phosphorylation nor eotaxin production induced by IL-4 and TNF-alpha. Conversely, retroviral transduction of SOCS-1 into MEF inhibited STAT6 phosphorylation and eotaxin production induced by IL-4 and TNF-alpha, in the absence of IFN-gamma. Thus, we demonstrated that IFN-gamma-induced inhibition of STAT6 phosphorylation and eotaxin production were mediated by SOCS-1 induced in STAT1-dependent manner.