Requirement of Tumor Necrosis Factor Receptor–Associated Factor (Traf)6 in Interleukin 17 Signal Transduction

Signaling through its widely distributed cell surface receptor, interleukin (IL)-17 enhances the transcription of genes encoding proinflammatory molecules. Although it has been well documented that IL-17 activates the transcription factor nuclear factor (NF)-κB and c-Jun NH₂-terminal kinase (JNK), the upstream signaling events are largely unknown. Here we report the requirement of tumor necrosis factor receptor–associated factor (TRAF)6 in IL-17–induced NF-κB and JNK activation. In embryonic fibroblasts (EFs) derived from TRAF6 knockout mice, IL-17 failed to activate the IκB kinases (IKKs) and JNK. Consequently, IL-17–induced IL-6 and intercellular adhesion molecule 1 expression in the TRAF6-deficient cells was abolished. Lack of TRAF6 appeared to be the sole defect responsible for the observed failure to respond to IL-17, because transient transfection of TRAF6 expression plasmid into the TRAF6-deficient cells restored IL-17–induced NF-κB activation in a luciferase reporter assay. Furthermore, the levels of IL-17 receptor (IL-17R) on the TRAF6-deficient EFs were comparable to those on the wild-type control cells. Defect in IL-17 response was not observed in TRAF2-deficient EFs. Moreover, when TRAF6 and IL-17R were coexpressed in 293 cells, TRAF6 coimmunoprecipitated with IL-17R. Together, these results indicate that TRAF6, but not TRAF2, is a crucial component in the IL-17 signaling pathway leading to proinflammatory responses.