Project description:Cells infected by influenza virus mount a large-scale antiviral response and most cells ultimately initiate cell-death pathways in an attempt to suppress viral replication. We performed a CRISPR/Cas9-knockout selection designed to identify host factors required for replication following viral entry. We identified a large class of presumptive antiviral factors that unexpectedly act as important pro-viral enhancers during influenza virus infection. One of these, IFIT2, is an interferon-stimulated gene with well-established antiviral activity but limited mechanistic understanding. As opposed to suppressing infection, we show here that IFIT2 is instead repurposed by influenza virus to promote viral gene expression. CLIP‐seq demonstrated that IFIT2 binds directly to viral and cellular mRNAs in AU‐rich regions, with bound cellular transcripts enriched in interferon‐stimulated mRNAs. Polysome and ribosome profiling revealed that IFIT2 prevents ribosome pausing on bound mRNAs. Together, the data link IFIT2 binding to enhanced translational efficiency for viral and cellular mRNAs and ultimately viral replication. Our findings establish a model for the normal function of IFIT2 as a protein that increases translation of cellular mRNAs to support antiviral responses and explain how influenza virus uses this same activity to redirect a classically antiviral protein into a pro-viral effector.
Project description:Cells infected by influenza virus mount a large-scale antiviral response and most cells ultimately initiate cell-death pathways in an attempt to suppress viral replication. We performed a CRISPR-Cas9-knockout selection designed to identify host factors required for replication after viral entry. We identified a large class of presumptive antiviral factors that unexpectedly act as important proviral enhancers during influenza virus infection. One of these, IFIT2, is an interferon-stimulated gene with well-established antiviral activity but limited mechanistic understanding. As opposed to suppressing infection, we show in the present study that IFIT2 is instead repurposed by influenza virus to promote viral gene expression. CLIP-seq demonstrated that IFIT2 binds directly to viral and cellular messenger RNAs in AU-rich regions, with bound cellular transcripts enriched in interferon-stimulated mRNAs. Polysome and ribosome profiling revealed that IFIT2 prevents ribosome pausing on bound mRNAs. Together, the data link IFIT2 binding to enhanced translational efficiency for viral and cellular mRNAs and ultimately viral replication. Our findings establish a model for the normal function of IFIT2 as a protein that increases translation of cellular mRNAs to support antiviral responses and explain how influenza virus uses this same activity to redirect a classically antiviral protein into a proviral effector.
Project description:Recognition of non-self nucleic acids, including cytoplasmic dsDNA, dsRNA, or mRNAs lacking proper 5' cap structures, is critical for the induction of innate immunity against viruses. Here, we demonstrate that short 5’ untranslated regions (UTRs), a characteristic of many viral mRNAs, can also serve as molecular pattern for innate immune recognition via the interferon-induced proteins, IFIT2 and IFIT3. The IFIT2-IFIT3 heterodimer, formed through an intricate domain swap structure, mediates viral mRNA 5' end recognition, translation inhibition, and ultimately antiviral activity. Critically, 5' UTR lengths <50 nucleotides are necessary and sufficient to sensitize an mRNA to translation inhibition by the IFIT2-IFIT3 complex. Thus, diverse viruses whose mRNAs contain short 5’ UTRs, such as vesicular stomatitis virus and parainfluenza virus 3, are sensitive to IFIT2-IFIT3-mediated antiviral activity. Our work reveals a new size-restricted pattern of nucleic acid innate immune recognition for the selective repression of viral replication.
Project description:In response to foreign and endogenous double-stranded RNA (dsRNA), protein kinase R (PKR) and ribonuclease L (RNase L) reprogram translation in mammalian cells. PKR inhibits translation initiation through eIF2 phosphorylation, which triggers stress granule (SG) formation and promotes translation of stress responsive mRNAs. The mechanisms of RNase L-driven translation repression, its contribution to SG assembly, and its regulation of dsRNA stress-induced mRNAs are unknown. We demonstrate that RNase L drives translational shut-off in response to dsRNA by promoting widespread turnover of mRNAs. This alters stress granule assembly and reprograms translation by only allowing for the translation of mRNAs resistant to RNase L degradation, including numerous antiviral mRNAs such as IFN- . Individual cells differentially activate dsRNA responses revealing variation that can affect cellular outcomes. This identifies bulk mRNA degradation and the resistance of antiviral mRNAs as the mechanism by which RNaseL reprograms translation in response to dsRNA.
Project description:Interferon-induced protein with tetratricopeptide repeat 2 (IFIT2) is known for its antiviral activity and has recently been implicated in the defense against Mycobacterium tuberculosis (M. tb). This study employed global transcriptomics to investigate the downstream effects of IFIT2 induction in THP-1 macrophages infected with R179 M. tb, aiming to elucidate its role and downstream contributing factors that aid it in intracellular M. tb killing. Using a vector-based overexpression approach, IFIT2 expression was induced in THP-1 cells infected with R179 M. tb, followed by RNA extraction 12 hours postinfection and AmpliSeq-based targeted transcriptome sequencing. Bioinformatics analysis identified 282 differentially expressed genes (DEGs), of which 189 were upregulated and 90 were downregulated (FDR <0.05). Filtering for highly significant DEGs (|log2(fold change) | > 1.5) yielded 70 genes, predominantly upregulated, with functional enrichment in pathways such as defense response to viruses and cytokine-mediated signaling. Signaling pathway impact analysis highlighted pathway activation and inhibition of the tuberculosis (TB) pathway. RT-qPCR validation confirmed the upregulation of selected DEGs (ISG15, CMPK2, RSAD2, IFI44L, IFI44), corroborating the AmpliSeq data. This study provides comprehensive insights into the transcriptomic profile induced by IFIT2 in TB, revealing critical downstream contributors and pathways that underpin IFIT2’s ability to combat M. tb infection.
Project description:IFit2 is highly induced in response to type I and type II interferons, dsRNA, LPS, viral and bacterial infections and it is als found in several chronic diseases.A possible role for the protein in cell proliferation, virion assembly/transport and microtubule dynamices was described. This study focus on IFIT2 proinflammatory cytokine response which might be involved in the development of septic shock. In the IFIT2 knockout mice gene expression levels before and after OVA challenge were analysed. Total RNA obtained from 3-4 male mutant mice (challenged/un-challenged) was compared to 4 wild type controls (challenged/unchallenged).
Project description:IFit2 is highly induced in response to type I and type II interferons, dsRNA, LPS, viral and bacterial infections and it is als found in several chronic diseases.A possible role for the protein in cell proliferation, virion assembly/transport and microtubule dynamices was described. This study focus on IFIT2 proinflammatory cytokine response which might be involved in the development of septic shock. In the IFIT2 knockout mice gene expression levels before and after OVA challenge were analysed.
Project description:Upon detection of viral infections, cells activate the expression of type I interferons (IFNs) and pro-inflammatory cytokines to control viral dissemination. As part of their antiviral response, cells also trigger the translational shutoff response which prevents translation of viral mRNAs and cellular mRNAs in a non-selective manner. Intriguingly, mRNAs encoding for antiviral factors bypass this translational shutoff, suggesting the presence of additional regulatory mechanisms enabling expression of the self-defence genes. Here, we identified the dsRNA binding protein ILF3 as an essential host factor required for efficient translation of the central antiviral cytokine, IFNB1, and a subset of interferon-stimulated genes. By combining polysome profiling and next-generation sequencing, ILF3 was also found to be necessary to establish the dsRNA-induced transcriptional and translational programs. We propose a central role for the host factor ILF3 in enhancing expression of the antiviral defence mRNAs in cellular conditions where cap-dependent translation is compromised. In this dataset we use polysome profiling in combination with RNA-seq to investigate the effect of ILF3 on the translation of mRNAs in HeLa cells in homeostasis and the antiviral response.