Interleukin 17 (IL-17) plays a critical role in the pathogenesis of inflammatory and autoimmune diseases. Here we report that Act1, the key adaptor for IL-17R, forms a complex with IKKi upon IL-17 stimulation. Using IKKi-deficient mice, we show that IKKi was required for IL-17-induced inflammatory gene expression in primary airway epithelial cells, neutrophilia and pulmonary inflammation. IKKi deficiency abolished IL-17-induced Act1-TRAF2/5 complex formation, MAPK activation and mRNA stability, whereas the Act1-TRAF6-NFκB axis was retained. IKKi was required for IL-17-induced Act1 phosphorylation on serine 311, adjacent to a putative TRAF binding motif. S311A mutation impaired IL-17-mediated Act1-TRAF2/5 interaction and gene expression. Thus, IKKi is a novel kinase modulating IL-17 signaling through its impact on Act1 phosphorylation and consequent function.
A novel cytokine IL-33, an IL-1 family member, signals via ST2 receptor and promotes Th2 responses, through the activation of NF-κB and MAP kinases. Previous studies reported that single Ig IL-1R-related molecule (SIGIRR)/Toll IL-1R8 acts as negative regulator for TLR-IL-1R-mediated signaling. We now found that SIGIRR formed a complex with ST2 upon IL-33 stimulation and specifically inhibited IL-33/ST2-mediated signaling in cell culture model. Furthermore, IL-33-induced Th2 response was enhanced in SIGIRR-deficient mice compared with that in wild-type control mice, suggesting a negative regulatory role of SIGIRR in IL-33/ST2 signaling in vivo. Similar to ST2, SIGIRR was highly expressed in in vitro polarized Th2 cells, but not Th1 cells. SIGIRR-deficient Th2 cells produce higher levels of Th2 cytokines, including IL-5, IL-4, and IL-13, than that in wild-type cells. Moreover, SIGIRR-deficient mice developed stronger Th2 immune response in OVA-challenged asthma model. Taken together, our results suggest that SIGIRR plays an important role in the regulation of Th2 response in vivo, possibly through its impact on IL-33-ST2-mediated signaling.
IL-17, a potent proinflammatory cytokine, has been shown to intimately contribute to the formation, growth, and metastasis of a wide range of malignancies. Recent studies implicate IL-17 as a link among inflammation, wound healing, and cancer. While IL-17–mediated production of inflammatory mediators mobilizes immune-suppressive and angiogenic myeloid cells, emerging studies reveal that IL-17 can directly act on tissue stem cells to promote tissue repair and tumorigenesis. Here, we review the pleotropic impacts of IL-17 on cancer biology, focusing how IL-17–mediated inflammatory response and mitogenic signaling are exploited to equip its cancer-promoting function and discussing the implications in therapies.
Mechanisms that degrade inflammatory mRNAs are well-known, however
stabilizing mechanisms are poorly understood. Here we show that Act1, an
interleukin-17 (IL-17) receptor complex adaptor, binds and stabilizes mRNAs
encoding key inflammatory proteins. The Act1 SEFIR domain binds a stem-loop
structure, SBE (SEFIR-binding element), in the inflammatory chemokine
Cxcl1 3’ UTR. mRNA-bound Act1 directs formation of
three compartmentally-distinct protein-RNA complexes (RNPs) that regulate three
disparate events in inflammatory mRNA metabolism: preventing mRNA decay in the
nucleus, inhibiting mRNA decapping in P-bodies, and promoting translation. SBE
RNA aptamers reduced IL-17-mediated mRNA stabilization in
vitro, IL-17-induced skin inflammation and airway inflammation in a
mouse asthma model, providing a therapeutic strategy for autoimmune diseases.
These results reveal a network in which Act1 assembles RNPs on the 3’
UTRs of select mRNAs to control receptor-mediated mRNA stabilization and
translation during inflammation.
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