Self-Recognition of an Inducible Host lncRNA by RIG-I Feedback Restricts Innate Immune Response.

The innate RNA sensor RIG-I is critical in the initiation of antiviral type I interferons (IFNs) production upon recognition of "non-self" viral RNAs. Here, we identify a host-derived, IFN-inducible long noncoding RNA, lnc-Lsm3b, that can compete with viral RNAs in the binding of RIG-I monomers and feedback inactivate the RIG-I innate function at late stage of innate response. Mechanistically, binding of lnc-Lsm3b restricts RIG-I protein's conformational shift and prevents downstream signaling, thereby terminating type I IFNs production. Multivalent structural motifs and long-stem structure are critical features of lnc-Lsm3b for RIG-I binding and inhibition. These data reveal a non-canonical self-recognition mode in the regulation of immune response and demonstrate an important role of an inducible "self" lncRNA acting as a potent molecular decoy actively saturating RIG-I binding sites to restrict the duration of "non-self" RNA-induced innate immune response and maintaining immune homeostasis, with potential utility in inflammatory disease management.

The long noncoding RNA Lnczc3h7a promotes a TRIM25-mediated RIG-I antiviral innate immune response.

The helicase RIG-I initiates an antiviral immune response after recognition of pathogenic RNA. TRIM25, an E3 ubiquitin ligase, mediates K63-linked ubiquitination of RIG-I, which is crucial for RIG-I downstream signaling and the antiviral innate immune response. The components and mode of the RIG-I-initiated innate signaling remain to be fully understood. Here we identify a novel long noncoding RNA (Lnczc3h7a) that binds to TRIM25 and promotes RIG-I-mediated antiviral innate immune responses. Depletion of Lnczc3h7a impairs RIG-I signaling and the antiviral innate response to RNA viruses in vitro and in vivo. Mechanistically, Lnczc3h7a binds to both TRIM25 and activated RIG-I, serving as a molecular scaffold for stabilization of the RIG-I-TRIM25 complex at the early stage of viral infection. Lnczc3h7a facilitates TRIM25-mediated K63-linked ubiquitination of RIG-I and thus promotes downstream signaling transduction. Our findings reveal that host RNAs can enhance the response of innate immune sensors to foreign RNAs, ensuring effective antiviral defense.

Nuclear RNF2 inhibits interferon function by promoting K33-linked STAT1 disassociation from DNA.

Prolonged activation of interferon-STAT1 signaling is closely related to inflammatory autoimmune disorders, and therefore the identification of negative regulators of these pathways is important. Through high-content screening of 115 mouse RING-domain E3 ligases, we identified the E3 ubiquitin ligase RNF2 as a potent inhibitor of interferon-dependent antiviral responses. RNF2 deficiency substantially enhanced interferon-stimulated gene (ISG) expression and antiviral responses. Mechanistically, nuclear RNF2 directly bound to STAT1 after interferon stimulation and increased K33-linked polyubiquitination of the DNA-binding domain of STAT1 at position K379, in addition to promoting the disassociation of STAT1/STAT2 from DNA and consequently suppressing ISG transcription. Our study provides insight into the regulation of interferon-dependent responses via a previously unrecognized post-translational modification of STAT1 in the nucleus.

Cis-acting lnc-Cxcl2 restrains neutrophil-mediated lung inflammation by inhibiting epithelial cell CXCL2 expression in virus infection.

Chemokine production by epithelial cells is important for neutrophil recruitment during viral infection, the appropriate regulation of which is critical for restraining inflammation and attenuating subsequent tissue damage. Epithelial cell expression of long noncoding RNAs (lncRNAs), RNA-binding proteins, and their functional interactions during viral infection and inflammation remain to be fully understood. Here, we identified an inducible lncRNA in the Cxcl2 gene locus, lnc-Cxcl2, which could selectively inhibit Cxcl2 expression in mouse lung epithelial cells but not in macrophages. lnc-Cxcl2-deficient mice exhibited increased Cxcl2 expression, enhanced neutrophils recruitment, and more severe inflammation in the lung after influenza virus infection. Mechanistically, nucleus-localized lnc-Cxcl2 bound to Cxcl2 promoter, recruited a ribonucleoprotein La, which inhibited the chromatin accessibility of chemokine promoters, and consequently inhibited Cxcl2 transcription in cis However, unlike mouse lnc-Cxcl2, human lnc-CXCL2-4-1 inhibited multiple immune cytokine expressions including chemokines in human lung epithelial cells. Together, our results demonstrate a self-protecting mechanism within epithelial cells to restrain chemokine and neutrophil-mediated inflammation, providing clues for better understanding chemokine regulation and epithelial cell function in lung viral infection.

LncRNA Malat1 inhibition of TDP43 cleavage suppresses IRF3-initiated antiviral innate immunity.

Long noncoding RNAs (lncRNAs) involved in the regulation of antiviral innate immune responses need to be further identified. By functionally screening the lncRNAs in macrophages, here we identified lncRNA Malat1, abundant in the nucleus but significantly down-regulated after viral infection, as a negative regulator of antiviral type I IFN (IFN-I) production. Malat1 directly bound to the transactive response DNA-binding protein (TDP43) in the nucleus and prevented activation of TDP43 by blocking the activated caspase-3-mediated TDP43 cleavage to TDP35. The cleaved TDP35 increased the nuclear IRF3 protein level by binding and degrading Rbck1 pre-mRNA to prevent IRF3 proteasomal degradation upon viral infection, thus selectively promoting antiviral IFN-I production. Deficiency of Malat1 enhanced antiviral innate responses in vivo, accompanying the increased IFN-I production and reduced viral burden. Importantly, the reduced MALAT1, augmented IRF3, and increased IFNA mRNA were found in peripheral blood mononuclear cells (PBMCs) from systemic lupus erythematosus (SLE) patients. Therefore, the down-regulation of MALAT1 in virus-infected cells or in human cells from autoimmune diseases will increase host resistance against viral infection or lead to autoinflammatory interferonopathies via the increased type I IFN production. Our results demonstrate that the nuclear Malat1 suppresses antiviral innate responses by targeting TDP43 activation via RNA-RBP interactive network, adding insight to the molecular regulation of innate responses and autoimmune pathogenesis.

Nuclear translocation of RIG-I promotes cellular apoptosis.

Cell death is important in the elimination of damaged cells such as virus-infected cells and also is closely involved in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus (SLE). The retinoic acid-inducible gene-I (RIG-I), one cytosolic RNA innate sensor, can trigger antiviral innate response by inducing production of type I interferons (IFN-I). However, the function of RIG-I, once translocated from cytoplasm to nucleus at the late stage of viral infection when IFN-I production is almost terminated, remains poorly understood. Here, we reported that RIG-I is accumulated in the nucleus of macrophages and fibroblasts after virus infection, and nuclear RIG-I is present in peripheral blood mononuclear cells (PBMCs) from SLE patients. We found that nuclear RIG-I interacts with the first 20 amino acids of apurinic/apyrimidinic endodeoxyribonuclease 1 (APEX1) and attenuates the anti-apoptotic properties of APEX1, therefore promoting apoptosis of virus-infected cells to suppress viral infection through an IFN-I-independent way at the late stage of viral infection. Together, our findings reveal a non-canonical role of nuclear RIG-I in the induction of cellular apoptosis, besides its activation of IFN-I expression as the cytosolic innate sensor. This study provides new insight to the regulation of infection, IFN-I and autoimmune diseases by nuclear RIG-I-APEX1 interaction.

RNA-binding protein hnRNP UL1 binds κB sites to attenuate NF-κB-mediated inflammation.

Heterogeneous nuclear ribonucleoproteins (hnRNPs), a family of RNA-binding proteins, play important roles in various biological processes. However, the roles of hnRNPs members in immunity and inflammation remain to be fully understood. By a functional screening for hnRNPs members in LPS-stimulated macrophage inflammatory response, we identified hnRNP UL1 as a negative regulator of NF-κB-mediated inflammation. hnRNP UL1 constrains NF-κB-triggered transcriptional expression of pro-inflammatory cytokines in response to innate stimuli. Perturbation of hnRNP UL1 enhanced pro-inflammatory cytokine production in macrophages. In vivo deficiency of hnRNP UL1 increased the pro-inflammatory cytokine production once challenged with LPS. Accordingly, the expression of hnRNP UL1 decreased in peripheral blood mononuclear cells of rheumatoid arthritis patients. Mechanistically, hnRNP UL1 competes with NF-κB to bind κB sites to constrain the magnitude and duration of inflammatory response. Meanwhile, the broadly and dynamically binding of hnRNP UL1 on the target genes' promoter during inflammatory response is unraveled. Our study adds new insight into the functions of hnRNPs in NF-κB-mediated inflammation, proposing a potential therapeutic strategy for controlling inflammatory autoimmune diseases.

Tuning Topological Orders by a Conical Magnetic Field in the Kitaev Model.

We show that a conical magnetic field H=(1,1,1)H can be used to tune the topological order and hence, anyon excitations of the Z_{2} quantum spin liquid in the isotropic antiferromagnetic Kitaev model. A novel topological order, featured with Chern number C=4 and Abelian anyon excitations, is induced in a narrow range of intermediate fields H_{c1}≤H≤H_{c2}. On the other hand, the C=1 Ising-topological order with non-Abelian anyon excitations, as previously known to be present at small fields, is found here to survive up to H_{c1}. The results are obtained by developing and applying a Z_{2} mean field theory that works at finite fields and is asymptotically exact in the zero field limit and the associated variational quantum Monte Carlo.

RNF122 suppresses antiviral type I interferon production by targeting RIG-I CARDs to mediate RIG-I degradation.

The activation of retinoic acid-inducible gene 1 (RIG-I), a cytoplasmic innate sensor for viral RNA, is tightly regulated to maintain immune homeostasis properly and prevent excessive inflammatory reactions other than initiation of antiviral innate response to eliminate RNA virus effectively. Posttranslational modifications, particularly ubiquitination, are crucial for regulation of RIG-I activity. Increasing evidence suggests that E3 ligases play important roles in various cellular processes, including cell proliferation and antiviral innate signaling. Here we identify that E3 ubiquitin ligase RING finger protein 122 (RNF122) directly interacts with mouse RIG-I through MS screening of RIG-I-interacting proteins in RNA virus-infected cells. The transmembrane domain of RNF122 associates with the caspase activation and recruitment domains (CARDs) of RIG-I; this interaction effectively triggers RING finger domain of RNF122 to deliver the Lys-48-linked ubiquitin to the Lys115 and Lys146 residues of RIG-I CARDs and promotes RIG-I degradation, resulting in a marked inhibition of RIG-I downstream signaling. RNF122 is widely expressed in various immune cells, with preferential expression in macrophages. Deficiency of RNF122 selectively increases RIG-I-triggered production of type I IFNs and proinflammatory cytokines in macrophages. RNF122-deficient mice exhibit more resistance against lethal RNA virus infection, with increased production of type I IFNs. Thus, we demonstrate that RNF122 acts as a selective negative regulator of RIG-I-triggered antiviral innate response by targeting CARDs of RIG-I and mediating proteasomal degradation of RIG-I. Our study outlines a way for E3 ligase to regulate innate sensor RIG-I for the control of antiviral innate immunity.

Rhomboid domain-containing protein 3 is a negative regulator of TLR3-triggered natural killer cell activation.

Rhomboid domain-containing protein 3 (Rhbdd3), which belongs to a family of proteins with rhomboid domain, is widely expressed in immune cells; however, the roles of the Rhbdd members, including Rhbdd3, in immunity remain unknown. Natural killer (NK) cells are critical for host immune defense and also can mediate inflammatory diseases such as hepatitis. Although much is known about how NK cells are activated, the detailed mechanisms for negative regulation of NK cell activation remain to be fully understood. Using Rhbdd3-deficient mice, we reveal that Rhbdd3, selectively up-regulated in NK cells upon Toll-like receptor 3 (TLR3) stimulation, negatively regulates TLR3-mediated NK cell activation in a feedback manner. Rhbdd3 inhibits TLR3-triggered IFN-γ and granzyme B expression of NK cells in cell-cell contact dependence of accessory cells such as dendritic cells and Kupffer cells. Rhbdd3 interacts with DNAX activation protein of 12 kDa and promotes its degradation, inhibiting MAPK activation in TLR3-triggered NK cells. Furthermore, Rhbdd3 plays a critical role in attenuating TLR3-triggered acute inflammation by controlling NK cell activation and accumulation in liver and disrupting NK cell-Kupffer cell interaction. Therefore, Rhbdd3 is a feedback inhibitor of TLR3-triggered NK cell activation. Our study outlines a mechanism for the negative regulation of NK cell activation and also provides clues for the function of the rhomboid proteins in immunity.

Death domain-associated protein 6 (Daxx) selectively represses IL-6 transcription through histone deacetylase 1 (HDAC1)-mediated histone deacetylation in macrophages.

As a multifunctional nuclear protein, death domain-associated protein 6 (Daxx) regulates a wide range of biological processes, including cell apoptosis and gene transcription. However, the function of Daxx in innate immunity remains unclear. In our study, we show that Daxx is highly expressed in macrophages and localized in nucleus of macrophages. The expression of Daxx is significantly up-regulated by stimulation with TLR ligands LPS and poly(I:C). Silence of Daxx selectively represses IL-6 expression at transcription level in LPS-activated macrophages. Upon stimulation of LPS, Daxx specifically binds to the promoter of IL-6 and inhibits histone acetylation at IL-6 promoter region. Further mechanism analyses show that histone deacetylase 1 (HDAC1) interacts with Daxx and binds to the promoter of IL-6. Daxx silencing decreases the association of HDAC1 to IL-6 promoter. Therefore, our data reveal that Daxx selectively represses IL-6 transcription through HDAC1-mediated histone deacetylation in LPS-induced macrophages, acting as a negative regulator of IL-6 during innate immunity and potentially preventing inflammatory response because of overproduction of IL-6.

Human CD14+ CTLA-4+ regulatory dendritic cells suppress T-cell response by cytotoxic T-lymphocyte antigen-4-dependent IL-10 and indoleamine-2,3-dioxygenase production in hepatocellular carcinoma.

UNLABELLED: Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide with limited therapeutic options. HCC-induced immunosuppression often leads to ineffectiveness of immuno-promoting therapies. Currently, suppressing the suppressors has become the potential strategy for cancer immunotherapy. So, figuring out the immunosuppressive mechanisms induced and employed by HCC will be helpful to the design and application of HCC immunotherapy. Here, we identified one new subset of human CD14(+) CTLA-4(+) regulatory dendritic cells (CD14(+) DCs) in HCC patients, representing ∼13% of peripheral blood mononuclear cells. CD14(+) DCs significantly suppress T-cell response in vitro through interleukin (IL)-10 and indoleamine-2,3-dioxygenase (IDO). Unexpectedly, CD14(+) DCs expressed high levels of cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed death-1, and CTLA-4 was found to be essential to IL-10 and IDO production. So, we identified a novel human tumor-induced regulatory DC subset, which suppresses antitumor immune response through CTLA-4-dependent IL-10 and IDO production, thus indicating the important role of nonregulatory T-cell-derived CTLA-4 in tumor-immune escape or immunosuppression. CONCLUSIONS: These data outline one mechanism for HCC to induce systemic immunosuppression by expanding CD14(+) DCs, which may contribute to HCC progression. This adds new insight to the mechanism for HCC-induced immunosuppression and may also provide a previously unrecognized target of immunotherapy for HCC.

Identification of resting and type I IFN-activated human NK cell miRNomes reveals microRNA-378 and microRNA-30e as negative regulators of NK cell cytotoxicity.

NK cells are important innate immune cells with potent cytotoxicity that can be activated by type I IFN from the host once infected. How NK cell cytotoxicity is activated by type I IFN and then tightly regulated remain to be fully elucidated. MicroRNAs (miRNAs, or miRs) are important regulators of innate immune response, but the full scale of miRNome in human NK cells remains to be determined. In this study, we reported an in-depth analysis of miRNomes in resting and IFN-α-activated human NK cells, found two abundant miRNAs, miR-378 and miR-30e, markedly decreased in activated NK cells by IFN-α, and further proved that miR-378 and miR-30e directly targeted granzyme B and perforin, respectively. Thus, IFN-α activation suppresses miR-378 and miR-30e expression to release cytolytic molecule mRNAs for their protein translation and then augments NK cell cytotoxicity. Importantly, the phenomena are also confirmed in human NK cells activated by other cytokines and even in the sorted CD16(+)CD56(dim)CD69(+) human NK cell subset. Finally, miR-378 and miR-30e were proved to be suppressors of human NK cell cytotoxicity. Taken together, our results reveal that downregulated miR-378 and miR-30e during NK cell activation are negative regulators of human NK cell cytotoxicity, providing a mechanistic explanation for regulation of NK cell function by miRNAs.

Down-regulation of miR-301a suppresses pro-inflammatory cytokines in Toll-like receptor-triggered macrophages.

In many types of tumours, especially pancreatic adenocarcinoma, miR-301a is over-expressed. This over-expression results in negative regulation of the target gene of miR-301a, the nuclear factor-κB (NF-κB) repressing factor (NKRF), increasing the activation of NF-κB and production of NF-κB-responsive pro-inflammatory cytokines such as interleukin-8, interferon-ß, nitric oxide synthase 2A and cytochrome oxidase subunit 2 (COX-2). However, in immune cells, mechanisms that regulate miR-301a have not been reported. Similar to tumour cells, Toll-like receptor (TLR) -activated macrophages produce NF-κB-responsive pro-inflammatory cytokines. Therefore, it is of considerable interest to determine whether miR-301a regulates the secretion of cytokines by immune cells. In the present study, we demonstrate that the expression of miR-301a was decreased in TLR-triggered macrophages. Through targeting NKRF, miR-301a affected the activity of NF-κB and the expression of pro-inflammatory genes downstream of NF-κB such as COX-2, prostaglandin E2 and interleukin-6. In addition, when lipopolysaccharide-treated macrophages were simultaneously stimulated with trichostatin A, an inhibitor of histone deacetylases, the expression of miR-301a increased, whereas NKRF and pro-inflammatory cytokine expression decreased. However, further investigation revealed that there was no correlation between the induction of miR-301a and the inhibitory effect of trichostatin A on lipopolysaccharide-induced gene expression in macrophages. In summary, our study indicates a new mechanism by which miR-301a regulates inflammatory cytokine expression in macrophages, which may clarify the regulatory role of microRNAs in immune-mediated inflammatory responses.

RNF138 inhibits late inflammatory gene transcription through degradation of SMARCC1 of the SWI/SNF complex.

As one of the core components of the switching or sucrose non-fermentable (SWI/SNF) complex, SMARCC1 (BAF155, SRG3) plays essential roles in activation of late inflammatory genes in response to microbial challenge. However, little is known about the mechanism of how SMARCC1 regulates the inflammatory innate response. Via functional screening, we identify the nuclear E3 ubiquitin ligase RNF138 as a negative regulator in the inflammatory innate response and show that RNF138 interacts with SMARCC1 and mediates its K48-linked polyubiquitination at position Lys643 and proteasomal degradation. As a result, the catalytic activity of RNF138 fine-tunes the kinetics of late inflammatory gene transcription by inhibiting chromatin remodeling at SWI/SNF-regulated gene loci. Reduced RNF138 and increased SMARCC1 in monocytes of rheumatoid arthritis patients are observed. These results provide mechanistic insight into the interplay among nucleosome remodeling, inflammation, and ubiquitylation and underscore the important role of the E3 ubiquitin ligases in controlling the extent and duration of inflammatory responses.

Oxidized galectin-1 in SLE fails to bind the inhibitory receptor VSTM1 and increases reactive oxygen species levels in neutrophils.

Inhibitory immune receptors set thresholds for immune cell activation, and their deficiency predisposes a person to autoimmune responses. However, the agonists of inhibitory immune receptors remain largely unknown, representing untapped sources of treatments for autoimmune diseases. Here, we show that V-set and transmembrane domain-containing 1 (VSTM1) is an inhibitory receptor and that its binding by the competent ligand soluble galectin-1 (Gal1) is essential for maintaining neutrophil viability mediated by downregulated reactive oxygen species production. However, in patients with systemic lupus erythematosus (SLE), circulating Gal1 is oxidized and cannot be recognized by VSTM1, leading to increased intracellular reactive oxygen species levels and reduced neutrophil viability. Dysregulated neutrophil function or death contributes significantly to the pathogenesis of SLE by providing danger molecules and autoantigens that drive the production of inflammatory cytokines and the activation of autoreactive lymphocytes. Interestingly, serum levels of glutathione, an antioxidant able to convert oxidized Gal1 to its reduced form, were negatively correlated with SLE disease activity. Taken together, our findings reveal failed inhibitory Gal1/VSTM1 pathway activation in patients with SLE and provide important insights for the development of effective targeted therapies.

Degradation of HDAC10 by autophagy promotes IRF3-mediated antiviral innate immune responses.

Histone deacetylases (HDACs) play important roles in immunity and inflammation. Through functional screening, we identified HDAC10 as an inhibitor of the type I interferon (IFN) response mediated by interferon regulatory factor 3 (IRF3). HDAC10 abundance was decreased in mouse macrophages in response to innate immune stimuli and was reduced in peripheral blood mononuclear cells (PBMCs) from patients with systemic lupus erythematosus (SLE) compared with that in PBMCs from healthy donors. Deficiency in HDAC10 in mouse embryonic fibroblasts and in mice promoted the expression of genes encoding type I IFNs and of IFN-stimulated genes (ISGs), leading to enhanced antiviral responses in vitro and in vivo. HDAC10 bound in a deacetylase-independent manner to IRF3 in uninfected cells to inhibit the phosphorylation of IRF3 at Ser396 by TANK-binding kinase 1 (TBK1). Upon viral infection, HDAC10 was targeted for autophagy-mediated degradation through its interaction with LC3-II. Consequently, IRF3 phosphorylation was increased, which resulted in enhanced type I IFN production and antiviral responses. Our findings identify a potential target for improving host defense responses against pathogen infection and for treating autoimmune disease.

Synergistic antitumor effect of AAV-mediated TRAIL expression combined with cisplatin on head and neck squamous cell carcinoma.

BACKGROUND: Adeno-associated virus-2 (AAV-2)-mediated gene therapy is quite suitable for local or regional application in head and neck cancer squamous cell carcinoma (HNSCC). However, its low transduction efficiency has limited its further development as a therapeutic agent. DNA damaging agents have been shown to enhance AAV-mediated transgene expression. Cisplatin, one of the most effective chemotherapeutic agents, has been recognized to cause cancer cell death by apoptosis with a severe toxicity. This study aims to evaluate the role of cisplatin in AAV-mediated tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) expression and the effect on HNSCC both in vitro and in vivo. METHODS: Five human HNSCC cell lines were treated with recombinant soluble TRAIL (rsTRAIL) and infected with AAV/TRAIL to estimate the sensitivity of the cancer cells to TRAIL-induced cytotoxicity. KB cells were infected with AAV/EGFP with or without cisplatin pretreatment to evaluate the effect of cisplatin on AAV-mediated gene expression. TRAIL expression was detected by ELISA and Western blot. Cytotoxicity was measured by MTT assay and Western blot analysis for caspase-3 and -8 activations. Following the in vitro experiments, TRAIL expression and its tumoricidal activity were analyzed in nude mice with subcutaneous xenografts of HNSCC. RESULTS: HNSCC cell lines showed different sensitivities to rsTRAIL, and KB cells possessed both highest transduction efficacy of AAV and sensitivity to TRAIL among five cell lines. Preincubation of KB cells with subtherapeutic dosage of cisplatin significantly augmented AAV-mediated transgene expression in a heparin sulfate proteoglycan (HSPG)-dependent manner. Furthermore, cisplatin enhanced the killing efficacy of AAV/TRAIL by 3-fold on KB cell line. The AAV mediated TRAIL expression was observed in the xenografted tumors and significantly enhanced by cisplatin. AAV/TRAIL suppressed the tumors growth and cisplatin augmented the tumoricidal activity by two-fold. Furthermore, Combination treatment reduced cisplatin-caused body weight loss in nude mice. CONCLUSION: The combination of AAV-mediated TRAIL gene expression and cisplatin had synergistic therapeutic effects on head and neck cancers and reduced the potential toxicity of cisplatin. These findings suggest that the combination of AAV/TRAIL and cisplatin may be a promising strategy for HNSCC therapy.

IRF3-binding lncRNA-ISIR strengthens interferon production in viral infection and autoinflammation.

Interferon regulatory factor 3 (IRF3) is an essential transductor for initiation of many immune responses. Here, we show that lncRNA-ISIR directly binds IRF3 to promote its phosphorylation, dimerization, and nuclear translocation, along with enhanced target gene productions. In vivo lncRNA-ISIR deficiency results in reduced IFN production, uncontrolled viral replication, and increased mortality. The human homolog, AK131315, also binds IRF3 and promotes its activation. More important, AK131315 expression is positively correlated with type I interferon (IFN-I) level and severity in patients with lupus. Mechanistically, in resting cells, IRF3 is bound to suppressor protein Flightless-1 (Fli-1), which keeps its inactive state. Upon infection, IFN-I-induced lncRNA-ISIR binds IRF3 at DNA-binding domain in cytoplasm and removes Fli-1's association from IRF3, consequently facilitating IRF3 activation. Our results demonstrate that IFN-I-inducible lncRNA-ISIR feedback strengthens IRF3 activation by removing suppressive Fli-1 in immune responses, revealing a method of lncRNA-mediated modulation of transcription factor (TF) activation.