NF-κB-inducing kinase is a common mediator of IL-17-, TNF-α-, and IL- 1β-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-κB protein-DNA complexes consisting of p65/p50 heterodimers in the rat intestinal epithelial cell line IEC-6. The induction of NF-κB correlated with the induction of CXC and CC chemokine mRNA expression in IEC-6 cells. IL-17 acted in a synergistic fashion with IL-1β to induce the NF-κB 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-κB-inducing kinase and IκB kinase-α. In addition to activation of the NF-κB, 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-κB-inducing kinase serves as the common mediator in the NF-κB signaling cascades triggered by IL-17, TNF-α, and IL-1β in intestinal epithelial cells.