The m6A reader IMP2 directs autoimmune inflammation through an IL-17– and TNFα-dependent C/EBP transcription factor axis
IL-17 makes its m6A marks
IL-17 and related cytokines not only support host defense against certain pathogens but also contribute to the development of autoimmune diseases. A holistic understanding of how IL-17 initiates and propagates inflammation is needed to identify additional therapeutic opportunities in autoimmunity. Bechara et al. probed the role of N6-methyladenosine (m6A) modifications of IL-17–induced transcripts in enhancing their stability and translation. Epitranscriptomic m6A marks were detected on the mRNAs for the C/EBPβ and C/EBPδ transcription factors involved in IL-17 signaling. The noncanonical m6A reader protein IMP2 was implicated in binding these m6A marks. Mice lacking IMP2 were less susceptible to an autoantibody-induced model of kidney disease driven by IL-17 signaling. These findings establish posttranscriptional modifications of mRNAs involved in proinflammatory cytokine signaling as potential targets for therapeutic intervention.
Abstract
Excessive cytokine activity underlies many autoimmune conditions, particularly through the interleukin-17 (IL-17) and tumor necrosis factor–α (TNFα) signaling axis. Both cytokines activate nuclear factor κB, but appropriate induction of downstream effector genes requires coordinated activation of other transcription factors, notably, CCAAT/enhancer binding proteins (C/EBPs). Here, we demonstrate the unexpected involvement of a posttranscriptional “epitranscriptomic” mRNA modification [N6-methyladenosine (m6A)] in regulating C/EBPβ and C/EBPδ in response to IL-17A, as well as IL-17F and TNFα. Prompted by the observation that C/EBPβ/δ-encoding transcripts contain m6A consensus sites, we show that Cebpd and Cebpb mRNAs are subject to m6A modification. Induction of C/EBPs is enhanced by an m6A methylase “writer” and suppressed by a demethylase “eraser.” The only m6A “reader” found to be involved in this pathway was IGF2BP2 (IMP2), and IMP2 occupancy of Cebpd and Cebpb mRNA was enhanced by m6A modification. IMP2 facilitated IL-17–mediated Cebpd mRNA stabilization and promoted translation of C/EBPβ/δ in response to IL-17A, IL-17F, and TNFα. RNA sequencing revealed transcriptome-wide IL-17–induced transcripts that are IMP2 influenced, and RNA immunoprecipitation sequencing identified the subset of mRNAs that are directly occupied by IMP2, which included Cebpb and Cebpd. Lipocalin-2 (Lcn2), a hallmark of autoimmune kidney injury, was strongly dependent on IL-17, IMP2, and C/EBPβ/δ. Imp2−/− mice were resistant to autoantibody-induced glomerulonephritis (AGN), showing impaired renal expression of C/EBPs and Lcn2. Moreover, IMP2 deletion initiated only after AGN onset ameliorated disease. Thus, posttranscriptional regulation of C/EBPs through m6A/IMP2 represents a previously unidentified paradigm of cytokine-driven autoimmune inflammation.
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