The m6A reader IMP2 directs autoimmune inflammation through an IL-17- and TNFα-dependent C/EBP transcription factor axis

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.