Project description:Cytosolic foreign DNA is detected by pattern recognition receptors and mainly induces Type-I IFN production. We found that transfection of different types of DNA into various untreated cells induces Type-III IFN (IFN-lambda1) rather than Type-I IFN, indicating the presence of uncharacterized DNA sensor(s). A pull-down assay using cytosolic proteins identified that Ku70 and Ku80 are the DNA binding proteins. The knockdown studies and the reporter assay revealed that Ku70 is a novel DNA sensor inducing the IFN-lambda1 activation. The functional analysis of IFNL1 promoter revealed that PRDI and ISRE sites are predominantly involved in the DNA-mediated IFNL1 activation. A pull-down assay using nuclear proteins demonstrated that the IFN-lambda1 induction is associated with the activation of IRF-1 and IRF-7. This is the first report of a specific induction of Type-III rather than Type-I IFN and of Ku70 that plays a key role in the activation of innate immune responses. To identify the nature of the anti-HIV mediators associated with the empty vector transfection, we compared patterns of gene expression between untreated and pCMV9-transfected HEK293 cells, using DNA microarray analysis.
Project description:Cytosolic foreign DNA is detected by pattern recognition receptors and mainly induces Type-I IFN production. We found that transfection of different types of DNA into various untreated cells induces Type-III IFN (IFN-lambda1) rather than Type-I IFN, indicating the presence of uncharacterized DNA sensor(s). A pull-down assay using cytosolic proteins identified that Ku70 and Ku80 are the DNA binding proteins. The knockdown studies and the reporter assay revealed that Ku70 is a novel DNA sensor inducing the IFN-lambda1 activation. The functional analysis of IFNL1 promoter revealed that PRDI and ISRE sites are predominantly involved in the DNA-mediated IFNL1 activation. A pull-down assay using nuclear proteins demonstrated that the IFN-lambda1 induction is associated with the activation of IRF-1 and IRF-7. This is the first report of a specific induction of Type-III rather than Type-I IFN and of Ku70 that plays a key role in the activation of innate immune responses.
Project description:The innate immune system recognizes nucleic acids as a signature of microbial infection and initiates host-protective responses, including the production of type I IFN and proinflammatory cytokines. Z-DNA binding protein 1 (ZBP1, also known as DLM-1 or DAI) was previously identified as a dsDNA binding protein, triggering DNA-mediated activation of innate immune responses. However, mice or cells lacking ZBP1 produce normal levels of type I IFN in response to dsDNA. Therefore, the classification of ZBP1 as a true DNA sensor remains to be resolved. Here, we report that the single stranded RNA virus, influenza A virus (IAV) is a trigger of the cytosolic sensor ZBP1. Sensing of IAV infection by ZBP1 engages a novel NLRP3 inflammasome pathway that is not defined by the conventions of the canonical and non-canonical NLRP3 inflammasome pathways. Surprisingly, IAV-induced cell death was not prevented by the absence of the NLRP3 inflammasome. Instead, we identified parallel contributions from pyroptosis, necroptosis and apoptosis in the execution of ZBP1-dependent cell death, mediated by the kinase RIPK3. Overall, the ability of ZBP1 to sense IAV infection signifies a point of divergence for IAV-induced programmed cell death pathways and inflammasome activation. We used microarrays to explore the gene expression profiles differentially expressed in influenza-infected bone marrow derived macrophages (BMDM) isolated from Ifnar1-/- and wild-type mice.
Project description:We report that IFI16, which was previously identified as a cytosolic DNA sensor, is essential for the activation of programmed cell death pathways in IAV infected cells. We have identified IFI16 as an innate immune sensor of the influenza A virus. We find that IFI16 recognizes viral genomic RNA upon infection. The activation of IFI16, in turn, triggers the production of type I, III interferons, and also other pro-inflammatory cytokines via the STING-TBK1 and Pro-caspase-1 signalling axis, thereby promoting cell death (apoptosis and pyroptosis in IAV infected cells).
Project description:The innate immune system recognizes nucleic acids as a signature of microbial infection and initiates host-protective responses, including the production of type I IFN and proinflammatory cytokines. Z-DNA binding protein 1 (ZBP1, also known as DLM-1 or DAI) was previously identified as a dsDNA binding protein, triggering DNA-mediated activation of innate immune responses. However, mice or cells lacking ZBP1 produce normal levels of type I IFN in response to dsDNA. Therefore, the classification of ZBP1 as a true DNA sensor remains to be resolved. Here, we report that the single stranded RNA virus, influenza A virus (IAV) is a trigger of the cytosolic sensor ZBP1. Sensing of IAV infection by ZBP1 engages a novel NLRP3 inflammasome pathway that is not defined by the conventions of the canonical and non-canonical NLRP3 inflammasome pathways. Surprisingly, IAV-induced cell death was not prevented by the absence of the NLRP3 inflammasome. Instead, we identified parallel contributions from pyroptosis, necroptosis and apoptosis in the execution of ZBP1-dependent cell death, mediated by the kinase RIPK3. Overall, the ability of ZBP1 to sense IAV infection signifies a point of divergence for IAV-induced programmed cell death pathways and inflammasome activation.
Project description:STING plays a key role in detecting cytosolic DNA and induces type I interferon responses for host defense against pathogens. Although T cells highly express STING, its physiological role remains unknown. In this study, we show that costimulation of T cells via TCR and STING ligand induce type I IFN responses like innate immune cells.
Project description:Type I interferon (IFN) signalling is tightly controlled. Upon recognition of DNA by cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING) translocates along the endoplasmic reticulum (ER)-Golgi axis to induce IFN signalling. Afterwards, signal termination is achieved through autophagic degradation of STING, or STING recycling by retrograde COPI-mediated transport. Here we identify the GTPase ARF1 as a negative regulator of cGAS-STING signaling. Heterozygous ARF1 missense mutations cause a novel type I interferonopathy associated with enhanced IFN stimulated gene production. Expression of patient-derived, GTPase-defective, ARF1 in cell lines and primary cells results in increased cGAS-STING dependent type I IFN signalling. Mechanistically, mutated ARF1 both induces activation of cGAS by aberrant mitochondrial DNA, and promotes accumulation of active STING at the Golgi/ERGIC due to defective COPI retrograde transport. Our data establish ARF1 as a key factor in cGAS-STING homeostasis, which is required to maintain mitochondrial integrity and promote STING recycling.
Project description:Cytosine-5 methylation (m5C) is one of the most prevalent modifications of RNA, playing important roles in RNA metabolism, nuclear export, and translation. However, the potential role of RNA m5C methylation in innate immunity remains elusive. Here we show that depletion of NSUN2, an m5C methyltransferase, significantly inhibits the replication and gene expression of a wide range of RNA and DNA viruses. Notably, we found that this antiviral effect is largely driven by an enhanced type I interferon (IFN) response. The antiviral signaling pathway is dependent on the cytosolic RNA sensor RIG-I but not MDA5. Transcriptome-wide mapping of m5C following NSUN2 depletion in human A549 cells revealed a marked reduction in the m5C methylation of several abundant non-coding RNAs (ncRNAs). However, m5C methylation of viral RNA was not noticeably altered by NSUN2 depletion. In NSUN2-depleted cells, the host RNA polymerase (Pol) III transcribed ncRNAs, in particular RPPH1 and 7SL RNAs, were substantially upregulated, leading to an increased level in unshielded 7SL RNA in cytoplasm, which served as direct ligands for the RIG-I mediated IFN response. In NSUN2 depleted cells, inhibition of Pol III transcription or silencing of RPPH1 and 7SL RNA dampened IFN signaling, partially rescuing viral replication and gene expression. Finally, depletion of NSUN2 in an ex vivo human lung model and a mouse model inhibits viral replication and reduces pathogenesis which is accompanied by enhanced type I IFN responses. Collectively, our data demonstrate that RNA m5C methylation controls antiviral innate immunity through modulating m5C methylome of ncRNAs and their expression.
Project description:Ku70 and Ku80 form Ku , a ring-shaped protein that initiates the non-homologous end-joining (NHEJ) DNA repair pathway. Specifically, Ku binds to double-stranded DNA (dsDNA) ends and recruits other NHEJ factors (e.g., DNA-PKcs and LIG4). While Ku binds to double-stranded RNA (dsRNA) and traps mutated-DNA-PKcs on ribosomal RNA in vivo, the physiological significance of Ku-dsRNA interactions in otherwise wild-type cells remains elusive. Intriguingly, while dispensable for murine development, Ku is essential in human cells. Despite similar genome sizes, human cells express ~100-fold more Ku than mouse cells, implying functions beyond NHEJ, possibly through a dose-sensitive interaction with dsRNA, which is 10~100 times weaker than with dsDNA. While investigating the essentiality of Ku in human cells, we found that depletion of Ku - unlike LIG4 - induces profound interferon (IFN) and NF-kB signaling via dsRNA-sensor MDA5/RIG-I and adaptor MAVS. Prolonged Ku-degradation also activates other dsRNA-sensors, e.g. PKR that suppresses protein translation, and OAS/RNaseL that cleaves rRNAs and eventually induces growth arrest and cell death. MAVS, RIG-I, or MDA5 knockouts suppressed IFN signaling and, like PKR knockouts, all partially rescued Ku-depleted human cells. Ku-irCLIP analyses revealed that Ku binds to diverse dsRNA, predominantly stem-loops in primate-specific Alu elements at anti-sense orientation in introns and 3’-UTRs. Ku expression rose sharply in higher primates tightly correlating with Alu-expansion (r = 0.94/0.95). Together, our study identified a vital role of Ku in accommodating Alu-expansion in primates by mitigating a dsRNA-induced innate immune response, explaining the rise of Ku levels and its essentiality in human cells.
Project description:DNA-PK is a heterotrimeric complex that consists of Ku70 (XRCC6), Ku80 (XRCC5) and DNA-PKcs (PRKDC) subunits. DNA-PK complex is a major player in DNA double strand break (DSB) repair via non-homologous end joining pathway. This process requires all of DNA-PK subunits. Ku70/Ku80 heterodimers firstly bind to DNA-ends at DSB, that increase affinity of DNA-PKcs to DNA-ends. Recruitment of DNA-PKcs subunit to DSB leads to phosphorylation events near DSB, recruitment of another NHEJ-related genes that restore DNA integrity. However, today a lot of evidence demonstrate participation of DNA-PK components in other cellular process, e.g. cytosolic DNA sensing, apoptosis regulation, cellular movement and adhesion. It is important to note that not all subunits of DNA-PK complex are necessary for these process. This demonstrate the independent functions of DNA-PK subunits. Here we for the first time using NGS-sequencing analyzed the transcriptional changes in HEK293T cells under depletion of Ku70, Ku80 or DNA-PKcs to characterize the independent functions of each subunit.