Oxygen enhances antiviral innate immunity through maintenance of EGLN1-catalysed proline hydroxylation of IRF3
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ABSTRACT: Oxygen is essential for aerobic organisms, but little is known about its role in antiviral immunity. Here, we report that during responses to viral infection, the hypoxic conditions repress antiviral-responsive genes independently of HIF signalling. EGLN1 was identified as a key mediator of the enhancement exerted by the oxygen on antiviral innate immune responses. Under sufficient oxygen conditions, EGLN1 maintains its prolyl hydroxylase activity to catalyse hydroxylation of IRF3 at proline 10. This modification enhances IRF3 phosphorylation, dimerisation, and nuclear translocation, leading to subsequent IRF3 activation. Furthermore, mice and zebrafish with Egln1 deletion, treatment with the EGLN inhibitor, FG4592, or mice carrying an Irf3 P10A mutation are more susceptible to viral infections. These findings not only reveal a direct link between oxygen and antiviral responses, but also provide insights into the mechanisms by which oxygen regulates innate immunity
Project description:Ischemic preconditioning is the phenomenon whereby brief periods of sublethal ischemia protect against a subsequent, more prolonged, ischemic insult. In remote ischemic preconditioning (RIPC), ischemia to one organ protects other organs at a distance. We developed mouse models to ask if inhibition of EglN1, which senses oxygen and regulates the HIF transcription factor, could suffice to mediate local and remote ischemic preconditioning. We used microarrays to detail the global expression changes induced when the oxygen sensor EglN1 is genetically deleted from skeletal muscle cells. We also used microarrays to assess the transcriptome alterations that occur in mouse hearts with pharmacologic inhibition of EglN1, using the EglN inhibitor FG-4497. We generated mice with a tamoxifen-inducible model of EglN1 loss using a floxxed EglN1 locus with skeletal muscle-specific CRE recombinase. WT mice and mice with the floxxed EglN1 locus were exposed to tamoxifen. Mouse skeletal muscle was isolated for RNA extraction and hybridization on Affymetrix microarrays. In a related experiment, mice were treated with the EglN inhibitor FG-4497, and RNA from their heart tissue was analyzed by microarray for transcriptome alterations compared to control hearts.
Project description:Ischemic preconditioning is the phenomenon whereby brief periods of sublethal ischemia protect against a subsequent, more prolonged, ischemic insult. In remote ischemic preconditioning (RIPC), ischemia to one organ protects other organs at a distance. We developed mouse models to ask if inhibition of EglN1, which senses oxygen and regulates the HIF transcription factor, could suffice to mediate local and remote ischemic preconditioning. We used microarrays to detail the global expression changes induced when the oxygen sensor EglN1 is genetically deleted from skeletal muscle cells. We also used microarrays to assess the transcriptome alterations that occur in mouse hearts with pharmacologic inhibition of EglN1, using the EglN inhibitor FG-4497.
Project description:Hypoxia is a hallmark of solid tumors. Mitochondria play essential roles in cellular adaptation to hypoxia, but the underlying mechanisms are not fully understood. Through mitochondrial proteomic profiling, we find that the prolyl hydroxylase EglN1 accumulates on mitochondria under hypoxia. EglN1 substrate binding region 23 loop is responsible for its mitochondrial translocation and contributes to tumor growth. Furthermore, we identify AMPK as an EglN1 substrate on mitochondria. The EglN1-AMPK interaction is essential for their mutual mitochondrial translocation. EglN1 prolyl-hydroxylates AMPK under normoxia, then they rapidly dissociate following prolyl-hydroxylation, leading to their immediate release from mitochondria. While hypoxia results in constant EglN1-AMPK interaction and accumulation on mitochondria, leading to the formation of CaMKK2-EglN1-AMPK complex to activate AMPK phosphorylation, consequently ensuring metabolic homeostasis and tumor growth. Our findings demonstrate EglN1 as an oxygen-sensitive metabolic checkpoint signaling hypoxic stress to mitochondria through its 23 loop, revealing a therapeutic target for solid tumors.
Project description:Viral inflammation contributes to pathogenesis and mortality during respiratory virus infections. We recently uncovered Irf3, a critical component of innate antiviral immune responses, interacts with pro-inflammatory transcription factor NF-kB, and inhibits its activity. Irf3, using this mechanism, suppresses inflammatory gene expression in virus-infected cells and mice. In this study, we evaluated the cells responsible for Irf3-mediated suppression of viral inflammation using newly engineered conditional Irf3Δ/Δ mice. Irf3Δ/Δ mice, upon respiratory virus infection, showed increased susceptibility and mortality. Irf3 deficiency caused enhanced inflammatory gene expression, lung inflammation, immunopathology, and damage, which were accompanied by increased infiltration of pro-inflammatory macrophages. Deletion of Irf3 in macrophages (Irf3-MKO) displayed, similar to Irf3Δ/Δ mice, increased inflammatory responses, macrophage infiltration, lung damage, and lethality, indicating Irf3 in these cells suppressed lung inflammation. RNA-seq analyses revealed enhanced NF-kB-dependent gene expression along with activation of inflammatory signaling pathways in infected Irf3MKO lungs. Targeted analyses revealed activated MAPK signaling in Irf3MKO lungs. Therefore, Irf3 inhibited inflammatory signaling pathways in myeloid cellsmacrophages to prevent viral inflammation and pathogenesis.
Project description:mRNA m6A modification is involved in regulation of immune system. However, its function in antiviral immunity is controversial, and how immune responses regulate m6A modification is unknown. We here found TBK1, a key kinase of antiviral pathways, phosphorylated the core m6A methyltransferase METTL3 at Serine 67. The phosphorylated METTL3 interacted with translational complex and enhanced proteins translation, including IRF3, and facilitated antiviral responses. TBK1 also promoted METTL3 activation and m6A modification, which is required for stabilizing IRF3 mRNA. Type I IFN induction was severely impaired in METTL3 deficient cells. Mettl3flfl-lyz2-Cre mice were significantly more susceptible to IAV-induced lethality than control mice. Consistently, Ythdf1—/— mice cannot control viral infection and showed higher mortality than control mice due to decreased IRF3 expression. Together, we demonstrated that innate signals activated METTL3 via TBK1, and METTL3 and m6A modification secured antiviral immunity by promoting mRNA stability and protein translation.
Project description:mRNA m6A modification is involved in regulation of immune system. However, its function in antiviral immunity is controversial, and how immune responses regulate m6A modification is unknown. We here found TBK1, a key kinase of antiviral pathways, phosphorylated the core m6A methyltransferase METTL3 at Serine 67. The phosphorylated METTL3 interacted with translational complex and enhanced proteins translation, including IRF3, and facilitated antiviral responses. TBK1 also promoted METTL3 activation and m6A modification, which is required for stabilizing IRF3 mRNA. Type I IFN induction was severely impaired in METTL3 deficient cells. Mettl3flfl-lyz2-Cre mice were significantly more susceptible to IAV-induced lethality than control mice. Consistently, Ythdf1-/- mice cannot control viral infection and showed higher mortality than control mice due to decreased IRF3 expression. Together, we demonstrated that innate signals activated METTL3 via TBK1, and METTL3 and m6A modification secured antiviral immunity by promoting mRNA stability and protein translation.
Project description:mRNA m6A modification is involved in regulation of immune system. However, its function in antiviral immunity is controversial, and how immune responses regulate m6A modification is unknown. We here found TBK1, a key kinase of antiviral pathways, phosphorylated the core m6A methyltransferase METTL3 at Serine 67. The phosphorylated METTL3 interacted with translational complex and enhanced proteins translation, including IRF3, and facilitated antiviral responses. TBK1 also promoted METTL3 activation and m6A modification, which is required for stabilizing IRF3 mRNA. Type I IFN induction was severely impaired in METTL3 deficient cells. Mettl3flfl-lyz2-Cre mice were significantly more susceptible to IAV-induced lethality than control mice. Consistently, Ythdf1—/— mice cannot control viral infection and showed higher mortality than control mice due to decreased IRF3 expression. Together, we demonstrated that innate signals activated METTL3 via TBK1, and METTL3 and m6A modification secured antiviral immunity by promoting mRNA stability and protein translation.