Involvement of TNF Receptor-Associated Factor 6 in IL-25 Receptor Signaling

Abstract

IL-25 (IL-17E) induces IL-4, IL-5, and IL-13 production from an unidentified non-T/non-B cell population and subsequently induces Th2-type immune responses such as IgE production and eosinophilic airway inflammation. IL-25R is a single transmembrane protein with homology to IL-17R, but the IL-25R signaling pathways have not been fully understood. In this study, we investigated the signaling pathway under IL-25R, especially the possible involvement of TNFR-associated factor (TRAF)6 in this pathway. We found that IL-25R cross-linking induced NF-κB activation as well as ERK, JNK, and p38 activation. We also found that IL-25R-mediated NF-κB activation was inhibited by the expression of dominant negative TRAF6 but not of dominant negative TRAF2. Furthermore, IL-25R-mediated NF-κB activation, but not MAPK activation, was diminished in TRAF6-deficient murine embryonic fibroblast. In addition, coimmunoprecipitation assay revealed that TRAF6, but not TRAF2, associated with IL-25R even in the absence of ligand binding. Finally, we found that IL-25R-mediated gene expression of IL-6, TGF-β, G-CSF, and thymus and activation-regulated chemokine was diminished in TRAF6-deficient murine embryonic fibroblast. Taken together, these results indicate that TRAF6 plays a critical role in IL-25R-mediated NF-κB activation and gene expression.

Identification of Functional Roles for Both IL-17RB and IL-17RA in Mediating IL-25-Induced Activities

“…IL-17RB has been shown previously to bind IL-25 and to induce activation of multiple signaling molecules in response to IL-25 stimulation (11,12,14). Our experiments using IL-17RB KO mice and an antagonistic Ab to IL-17RB provide additional functional data supporting a role for IL-17RB in mediating IL-25-induced activities.…”

“…For example, stimulation of different cell types with either IL-17A or IL-25 activates TNFR-associated factor 6 (TRAF6), ERK, JNK, and p38, but the mechanisms by which these signaling pathways are activated have been reported to be different (12)(13)(14). For example, IL-17RA does not contain a TRAF6-binding motif but it has been reported to recruit TRAF6 by directly associating with the adaptor protein Act1 which does contain a TRAF6-binding motif (29).…”

“…IL-25 binds with high affinity to and activates signaling pathways through IL-17RB (11)(12)(13)(14). It has, however, recently been reported that IL-17A and IL-17F signal through a heteromeric receptor complex containing IL-17RA and IL-17RC (15).…”

The roles and functional mechanisms of interleukin-17 family cytokines in mucosal immunity

“…57 Moreover, the adaptor protein TRAF6 is recruited by IL-17RB and mediates IL-17E-induced NF-κB activation. 58 Recently, IL-17RB was shown to recruit another TRAF molecule (TRAF4) in an Act1-dependent manner. Mechanistically, TRAF4 recruits the E3-ligase SMURF2 to degrade DAZAP2, which is an IL-17RB-inhibitory protein.…”

IL-17 signaling in host defense and inflammatory diseases

“…Similar to IL-17 signaling, TRAF6 has been shown to be involved in IL-25-mediated signaling. 60 We recently reported that Act1 is also an essential signaling molecule for IL-25 receptor signaling. Mice deficient in Act1 have abolished IL-25-induced expression of cytokines (IL-4, IL-5 and IL-13) and chemokines (eotaxin, TARC and RANTES) in the airway and reduced allergen-induced pulmonary eosinophilia.…”