IL-17-receptor-associated adaptor Act1 directly stabilizes mRNAs to mediate IL-17 inflammatory signaling

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, the SEFIR-binding element (SBE), in the 3′ untranslated region (UTR) of Cxcl1 mRNA, encoding an inflammatory chemokine. mRNA-bound Act1 directs formation of three compartmentally distinct RNA–protein 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 decreased IL-17-mediated mRNA stabilization in vitro, IL-17-induced skin inflammation and airway inflammation in a mouse asthma model, thus providing a therapeutic strategy for autoimmune diseases. These results reveal a network in which Act1 assembles RNPs on the 3′ UTRs of select mRNAs and consequently controls receptor-mediated mRNA stabilization and translation during inflammation. Act1 is an adaptor protein that associates with the IL-17 receptor at the cell membrane. Li and colleagues show that Act1 also exhibits unexpected RNA-binding activity and directly stabilizes select mRNAs encoding inflammatory cytokines and chemokines.