Breaking the barrier: membrane fusion triggers innate antiviral immunity.

The sensing of viral infection by the innate immune system is dominated by the recognition of nucleic acids. New data now demonstrate that the fusion of viral and target-cell membranes leads to the activation of an immune response dependent on the adaptor STING.

The RIG-I agonist M8 triggers cell death and natural killer cell activation in human papillomavirus-associated cancer and potentiates cisplatin cytotoxicity.

Although the activation of innate immunity to treat a wide variety of cancers is gaining increasing attention, it has been poorly investigated in human papillomavirus (HPV)-associated malignancies. Because these tumors harbor a severely impaired cGAS-STING axis, but they still retain a largely functional RIG-I pathway, another critical mediator of adaptive and innate immune responses, we asked whether RIG-I activation by the 5'ppp-RNA RIG-I agonist M8 would represent a therapeutically viable option to treat HPV+ cancers. Here, we show that M8 transfection of two cervical carcinoma-derived cell lines, CaSki and HeLa, both expressing a functional RIG-I, triggers intrinsic apoptotic cell death, which is significantly reduced in RIG-I KO cells. We also demonstrate that M8 stimulation potentiates cisplatin-mediated cell killing of HPV+ cells in a RIG-I dependent manner. This combination treatment is equally effective in reducing tumor growth in a syngeneic pre-clinical mouse model of HPV16-driven cancer, where enhanced expression of lymphocyte-recruiting chemokines and cytokines correlated with an increased number of activated natural killer (NK) cells in the tumor microenvironment. Consistent with a role of RIG-I signaling in immunogenic cell killing, stimulation of NK cells with conditioned medium from M8-transfected CaSki boosted NK cell proliferation, activation, and migration in a RIG-I-dependent tumor cell-intrinsic manner. Given the highly conserved molecular mechanisms of carcinogenesis and genomic features of HPV-driven cancers and the remarkably improved prognosis for HPV+ oropharyngeal cancer, targeting RIG-I may represent an effective immunotherapeutic strategy in this setting, favoring the development of de-escalating strategies.

Identification of Anti-Influenza A Compounds Inhibiting the Viral Non-Structural Protein 1 (NS1) Using a Type I Interferon-Driven Screening Strategy.

There is an urgent need to identify efficient antiviral compounds to combat existing and emerging RNA virus infections, particularly those related to seasonal and pandemic influenza outbreaks. While inhibitors of the influenza viral integral membrane proton channel protein (M2), neuraminidase (NA), and cap-dependent endonuclease are available, circulating influenza viruses acquire resistance over time. Thus, the need for the development of additional anti-influenza drugs with novel mechanisms of action exists. In the present study, a cell-based screening assay and a small molecule library were used to screen for activities that antagonized influenza A non-structural protein 1 (NS1), a highly conserved, multifunctional accessory protein that inhibits the type I interferon response against influenza. Two potential anti-influenza agents, compounds 157 and 164, were identified with anti-NS1 activity, resulting in the reduction of A/PR/8/34(H1N1) influenza A virus replication and the restoration of IFN-ß expression in human lung epithelial A549 cells. A 3D pharmacophore modeling study of the active compounds provided a glimpse of the structural motifs that may contribute to anti-influenza virus activity. This screening approach is amenable to a broader analysis of small molecule compounds to inhibit other viral targets.

SAMHD1 phosphorylation and cytoplasmic relocalization after human cytomegalovirus infection limits its antiviral activity.

SAMHD1 is a host restriction factor that functions to restrict both retroviruses and DNA viruses, based on its nuclear deoxynucleotide triphosphate (dNTP) hydrolase activity that limits availability of intracellular dNTP pools. In the present study, we demonstrate that SAMHD1 expression was increased following human cytomegalovirus (HCMV) infection, with only a modest effect on infectious virus production. SAMHD1 was rapidly phosphorylated at residue T592 after infection by cellular cyclin-dependent kinases, especially Cdk2, and by the viral kinase pUL97, resulting in a significant fraction of phosho-SAMHD1 being relocalized to the cytoplasm of infected fibroblasts, in association with viral particles and dense bodies. Thus, our findings indicate that HCMV-dependent SAMHD1 cytoplasmic delocalization and inactivation may represent a potential novel mechanism of HCMV evasion from host antiviral restriction activities.

Human Papillomavirus E7 Oncoprotein Subverts Host Innate Immunity via SUV39H1-Mediated Epigenetic Silencing of Immune Sensor Genes.

Subversion of innate immunity by oncoviruses, such as human papillomavirus (HPV), favors carcinogenesis because the mechanism(s) of viral immune evasion can also hamper cancer immunosurveillance. Previously, we demonstrated that high-risk (hr) HPVs trigger simultaneous epigenetic silencing of multiple effectors of innate immunity to promote viral persistence. Here, we expand on those observations and show that the HPV E7 oncoprotein upregulates the H3K9-specific methyltransferase, whose action shuts down the host innate immune response. Specifically, we demonstrate that SUV39H1 contributes to chromatin repression at the promoter regions of the viral nucleic acid sensors RIG-I and cGAS and the adaptor molecule STING in HPV-transformed cells. Inhibition of SUV39H1 leads to transcriptional activation of these genes, especially RIG-I, followed by increased beta interferon (IFN-ß) and IFN-λ1 production after poly(dA·dT) or RIG-I agonist M8 transfection. Collectively, our findings provide new evidence that the E7 oncoprotein plays a central role in dampening host innate immunity and raise the possibility that targeting the downstream effector SUV39H1 or the RIG-I pathway is a viable strategy to treat viral and neoplastic disease.IMPORTANCE High-risk HPVs are major viral human carcinogens responsible for approximately 5% of all human cancers. The growth of HPV-transformed cells depends on the ability of viral oncoproteins to manipulate a variety of cellular circuits, including those involved in innate immunity. Here, we show that one of these strategies relies on E7-mediated transcriptional activation of the chromatin repressor SUV39H1, which then promotes epigenetic silencing of RIG-I, cGAS, and STING genes, thereby shutting down interferon secretion in HPV-transformed cells. Pharmacological or genetic inhibition of SUV39H1 restored the innate response in HPV-transformed cells, mostly through activation of RIG-I signaling. We also show that IFN production upon transfection of poly(dA·dT) or the RIG-I agonist M8 predominantly occurs through RIG-I signaling. Altogether, the reversible nature of the modifications associated with E7-mediated SUV39H1 upregulation provides a rationale for the design of novel anticancer and antiviral therapies targeting these molecules.

Dengue Virus Targets Nrf2 for NS2B3-Mediated Degradation Leading to Enhanced Oxidative Stress and Viral Replication.

Dengue virus (DENV) is a mosquito-borne virus that infects upward of 300 million people annually and has the potential to cause fatal hemorrhagic fever and shock. While the parameters contributing to dengue immunopathogenesis remain unclear, the collapse of redox homeostasis and the damage induced by oxidative stress have been correlated with the development of inflammation and progression toward the more severe forms of disease. In the present study, we demonstrate that the accumulation of reactive oxygen species (ROS) late after DENV infection (>24 hpi) resulted from a disruption in the balance between oxidative stress and the nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent antioxidant response. The DENV NS2B3 protease complex strategically targeted Nrf2 for degradation in a proteolysis-independent manner; NS2B3 licensed Nrf2 for lysosomal degradation. Impairment of the Nrf2 regulator by the NS2B3 complex inhibited the antioxidant gene network and contributed to the progressive increase in ROS levels, along with increased virus replication and inflammatory or apoptotic gene expression. By 24 hpi, when increased levels of ROS and antiviral proteins were observed, it appeared that the proviral effect of ROS overcame the antiviral effects of the interferon (IFN) response. Overall, these studies demonstrate that DENV infection disrupts the regulatory interplay between DENV-induced stress responses, Nrf2 antioxidant signaling, and the host antiviral immune response, thus exacerbating oxidative stress and inflammation in DENV infection.IMPORTANCE Dengue virus (DENV) is a mosquito-borne pathogen that threatens 2.5 billion people in more than 100 countries annually. Dengue infection induces a spectrum of clinical symptoms, ranging from classical dengue fever to severe dengue hemorrhagic fever or dengue shock syndrome; however, the complexities of DENV immunopathogenesis remain controversial. Previous studies have reported the importance of the transcription factor Nrf2 in the control of redox homeostasis and antiviral/inflammatory or death responses to DENV. Importantly, the production of reactive oxygen species and the subsequent stress response have been linked to the development of inflammation and progression toward the more severe forms of the disease. Here, we demonstrate that DENV uses the NS2B3 protease complex to strategically target Nrf2 for degradation, leading to a progressive increase in oxidative stress, inflammation, and cell death in infected cells. This study underlines the pivotal role of the Nrf2 regulatory network in the context of DENV infection.

The mitochondrial proteins NLRX1 and TUFM form a complex that regulates type I interferon and autophagy.

The mitochondrial protein MAVS (also known as IPS-1, VISA, and CARDIF) interacts with RIG-I-like receptors (RLRs) to induce type I interferon (IFN-I). NLRX1 is a mitochondrial nucleotide-binding, leucine-rich repeats (NLR)-containing protein that attenuates MAVS-RLR signaling. Using Nlrx1(-/-) cells, we confirmed that NLRX1 attenuated IFN-I production, but additionally promoted autophagy during viral infection. This dual function of NLRX1 paralleled the previously described functions of the autophagy-related proteins Atg5-Atg12, but NLRX1 did not associate with Atg5-Atg12. High-throughput quantitative mass spectrometry and endogenous protein-protein interaction revealed an NLRX1-interacting partner, mitochondrial Tu translation elongation factor (TUFM). TUFM interacted with Atg5-Atg12 and Atg16L1 and has similar functions as NLRX1 by inhibiting RLR-induced IFN-I but promoting autophagy. In the absence of NLRX1, increased IFN-I and decreased autophagy provide an advantage for host defense against vesicular stomatitis virus. This study establishes a link between an NLR protein and the viral-induced autophagic machinery via an intermediary partner, TUFM.

SIRT1 Modulates the Sensitivity of Prostate Cancer Cells to Vesicular Stomatitis Virus Oncolysis.

Oncolytic virotherapy represents a promising experimental anticancer strategy, based on the use of genetically modified viruses to selectively infect and kill cancer cells. Vesicular stomatitis virus (VSV) is a prototypic oncolytic virus (OV) that induces cancer cell death through activation of the apoptotic pathway, although intrinsic resistance to oncolysis is found in some cell lines and many primary tumors, as a consequence of residual innate immunity to the virus. In the effort to improve OV therapeutic efficacy, we previously demonstrated that different agents, including histone deacetylase inhibitors (HDIs), functioned as reversible chemical switches to dampen the innate antiviral response and improve the susceptibility of resistant cancer cells to VSV infection. In the present study, we demonstrated that the NAD+-dependent histone deacetylase SIRT1 (silent mating type information regulation 2 homolog 1) plays a key role in the permissivity of prostate cancer PC-3 cells to VSVΔM51 replication and oncolysis. HDI-mediated enhancement of VSVΔM51 infection and cancer cell killing directly correlated with a decrease of SIRT1 expression. Furthermore, pharmacological inhibition as well as silencing of SIRT1 by small interfering RNA (siRNA) was sufficient to sensitize PC-3 cells to VSVΔM51 infection, resulting in augmentation of virus replication and spread. Mechanistically, HDIs such as suberoylanilide hydroxamic acid (SAHA; Vorinostat) and resminostat upregulated the microRNA miR-34a that regulated the level of SIRT1. Taken together, our findings identify SIRT1 as a viral restriction factor that limits VSVΔM51 infection and oncolysis in prostate cancer cells.IMPORTANCE The use of nonpathogenic viruses to target and kill cancer cells is a promising strategy in cancer therapy. However, many types of human cancer are resistant to the oncolytic (cancer-killing) effects of virotherapy. In this study, we identify a host cellular protein, SIRT1, that contributes to the sensitivity of prostate cancer cells to infection by a prototypical oncolytic virus. Knockout of SIRT1 activity increases the sensitivity of prostate cancer cells to virus-mediated killing. At the molecular level, SIRT1 is controlled by a small microRNA termed miR-34a. Altogether, SIRT1 and/or miR-34a levels may serve as predictors of response to oncolytic-virus therapy.

Activation of Latent HIV-1 T Cell Reservoirs with a Combination of Innate Immune and Epigenetic Regulators.

The presence of T cell reservoirs in which human immunodeficiency virus (HIV) establishes latency by integrating into the host genome represents a major obstacle to an HIV cure and has prompted the development of strategies aimed at the eradication of HIV from latently infected cells. The "shock-and-kill" strategy is one of the most pursued approaches to the elimination of viral reservoirs. Although several latency-reversing agents (LRAs) have shown promising reactivation activity, they have failed to eliminate the cellular reservoir. In this study, we evaluated a novel immune system-mediated approach to clearing the HIV reservoir, based on a combination of innate immune stimulation and epigenetic reprogramming. The combination of the STING agonist cGAMP (cyclic GMP-AMP) and the FDA-approved histone deacetylase inhibitor resminostat resulted in a significant increase in HIV proviral reactivation and specific apoptosis in HIV-infected cells in vitro Reductions in the proportion of HIV-harboring cells and the total amount of HIV DNA were also observed in CD4+ central memory T (TCM) cells, a primary cell model of latency, where resminostat alone or together with cGAMP induced high levels of selective cell death. Finally, high levels of cell-associated HIV RNA were detected ex vivo in peripheral blood mononuclear cells (PBMCs) and CD4+ T cells from individuals on suppressive antiretroviral therapy (ART). Although synergism was not detected in PBMCs with the combination, viral RNA expression was significantly increased in CD4+ T cells. Collectively, these results represent a promising step toward HIV eradication by demonstrating the potential of innate immune activation and epigenetic modulation for reducing the viral reservoir and inducing specific death of HIV-infected cells.IMPORTANCE One of the challenges associated with HIV-1 infection is that despite antiretroviral therapies that reduce HIV-1 loads to undetectable levels, proviral DNA remains dormant in a subpopulation of T lymphocytes. Numerous strategies to clear residual virus by reactivating latent virus and eliminating the reservoir of HIV-1 (so-called "shock-and-kill" strategies) have been proposed. In the present study, we use a combination of small molecules that activate the cGAS-STING antiviral innate immune response (the di-cyclic nucleotide cGAMP) and epigenetic modulators (histone deacetylase inhibitors) that induce reactivation and HIV-infected T cell killing in cell lines, primary T lymphocytes, and patient samples. These studies represent a novel strategy for HIV eradication by reducing the viral reservoir and inducing specific death of HIV-infected cells.

Alternate NF-κB-Independent Signaling Reactivation of Latent HIV-1 Provirus.

Current combination antiretroviral therapies (cART) are unable to eradicate HIV-1 from infected individuals because of the establishment of proviral latency in long-lived cellular reservoirs. The shock-and-kill approach aims to reactivate viral replication from the latent state (shock) using latency-reversing agents (LRAs), followed by the elimination of reactivated virus-producing cells (kill) by specific therapeutics. The NF-κB RelA/p50 heterodimer has been characterized as an essential component of reactivation of the latent HIV-1 long terminal repeat (LTR). Nevertheless, prolonged NF-κB activation contributes to the development of various autoimmune, inflammatory, and malignant disorders. In the present study, we established a cellular model of HIV-1 latency in J-Lat CD4+ T cells that stably expressed the NF-κB superrepressor IκB-α 2NΔ4 and demonstrate that conventional treatments with bryostatin-1 and hexamethylenebisacetamide (HMBA) or ionomycin synergistically reactivated HIV-1 from latency, even under conditions where NF-κB activation was repressed. Using specific calcineurin phosphatase, p38, and MEK1/MEK2 kinase inhibitors or specific short hairpin RNAs, c-Jun was identified to be an essential factor binding to the LTR enhancer κB sites and mediating the combined synergistic reactivation effect. Furthermore, acetylsalicylic acid (ASA), a potent inhibitor of the NF-κB activator kinase IκB kinase ß (IKK-ß), did not significantly diminish reactivation in a primary CD4+ T central memory (TCM) cell latency model. The present work demonstrates that the shock phase of the shock-and-kill approach to reverse HIV-1 latency may be achieved in the absence of NF-κB, with the potential to avoid unwanted autoimmune- and or inflammation-related side effects associated with latency-reversing strategies.IMPORTANCE The shock-and-kill approach consists of the reactivation of HIV-1 replication from latency using latency-reversing agents (LRAs), followed by the elimination of reactivated virus-producing cells. The cellular transcription factor NF-κB is considered a master mediator of HIV-1 escape from latency induced by LRAs. Nevertheless, a systemic activation of NF-κB in HIV-1-infected patients resulting from the combined administration of different LRAs could represent a potential risk, especially in the case of a prolonged treatment. We demonstrate here that conventional treatments with bryostatin-1 and hexamethylenebisacetamide (HMBA) or ionomycin synergistically reactivate HIV-1 from latency, even under conditions where NF-κB activation is repressed. Our study provides a molecular proof of concept for the use of anti-inflammatory drugs, like aspirin, capable of inhibiting NF-κB in patients under combination antiretroviral therapy during the shock-and-kill approach, to avoid potential autoimmune and inflammatory disorders that can be elicited by combinations of LRAs.

Crosstalk between Cytoplasmic RIG-I and STING Sensing Pathways.

Detection of evolutionarily conserved molecules on microbial pathogens by host immune sensors represents the initial trigger of the immune response against infection. Cytosolic receptors sense viral and intracellular bacterial genomes, as well as nucleic acids produced during replication. Once activated, these sensors trigger multiple signaling cascades, converging on the production of type I interferons and proinflammatory cytokines. Although distinct classes of receptors are responsible for the RNA and DNA sensing, the downstream signaling components are physically and functionally interconnected. This review highlights the importance of the crosstalk between retinoic acid inducible gene-I (RIG-I)-mitochondrial antiviral-signaling protein (MAVS) RNA sensing and the cyclic GMP-AMP synthase (cGAS)- stimulator of interferon genes (STING) DNA sensing pathways in potentiating efficient antiviral responses. The potential of cGAS-STING manipulation as a component of cancer immunotherapy is also reviewed.

An optimized retinoic acid-inducible gene I agonist M8 induces immunogenic cell death markers in human cancer cells and dendritic cell activation.

RIG-I is a cytosolic RNA sensor that recognizes short 5' triphosphate RNA, commonly generated during virus infection. Upon activation, RIG-I initiates antiviral immunity, and in some circumstances, induces cell death. Because of this dual capacity, RIG-I has emerged as a promising target for cancer immunotherapy. Previously, a sequence-optimized RIG-I agonist (termed M8) was generated and shown to stimulate a robust immune response capable of blocking viral infection and to function as an adjuvant in vaccination strategies. Here, we investigated the potential of M8 as an anti-cancer agent by analyzing its ability to induce cell death and activate the immune response. In multiple cancer cell lines, M8 treatment strongly activated caspase 3-dependent apoptosis, that relied on an intrinsic NOXA and PUMA-driven pathway that was dependent on IFN-I signaling. Additionally, cell death induced by M8 was characterized by the expression of markers of immunogenic cell death-related damage-associated molecular patterns (ICD-DAMP)-calreticulin, HMGB1 and ATP-and high levels of ICD-related cytokines CXCL10, IFNß, CCL2 and CXCL1. Moreover, M8 increased the levels of HLA-ABC expression on the tumor cell surface, as well as up-regulation of genes involved in antigen processing and presentation. M8 induction of the RIG-I pathway in cancer cells favored dendritic cell phagocytosis and induction of co-stimulatory molecules CD80 and CD86, together with increased expression of IL12 and CXCL10. Altogether, these results highlight the potential of M8 in cancer immunotherapy, with the capacity to induce ICD-DAMP on tumor cells and activate immunostimulatory signals that synergize with current therapies.

Sphingosine 1-Phosphate Lyase Enhances the Activation of IKKε To Promote Type I IFN-Mediated Innate Immune Responses to Influenza A Virus Infection.

Sphingosine 1-phosphate (S1P) lyase (SPL) is an intracellular enzyme that mediates the irreversible degradation of the bioactive lipid S1P. We have previously reported that overexpressed SPL displays anti-influenza viral activity; however, the underlying mechanism is incompletely understood. In this study, we demonstrate that SPL functions as a positive regulator of IKKε to propel type I IFN-mediated innate immune responses against viral infection. Exogenous SPL expression inhibited influenza A virus replication, which correlated with an increase in type I IFN production and IFN-stimulated gene accumulation upon infection. In contrast, the lack of SPL expression led to an elevated cellular susceptibility to influenza A virus infection. In support of this, SPL-deficient cells were defective in mounting an effective IFN response when stimulated by influenza viral RNAs. SPL augmented the activation status of IKKε and enhanced the kinase-induced phosphorylation of IRF3 and the synthesis of type I IFNs. However, the S1P degradation-incompetent form of SPL also enhanced IFN responses, suggesting that SPL's pro-IFN function is independent of S1P. Biochemical analyses revealed that SPL, as well as the mutant form of SPL, interacts with IKKε. Importantly, when endogenous IKKε was downregulated using a small interfering RNA approach, SPL's anti-influenza viral activity was markedly suppressed. This indicates that IKKε is crucial for SPL-mediated inhibition of influenza virus replication. Thus, the results illustrate the functional significance of the SPL-IKKε-IFN axis during host innate immunity against viral infection.

Human Monocyte Subsets Are Transcriptionally and Functionally Altered in Aging in Response to Pattern Recognition Receptor Agonists.

Age-related alterations in immunity have been linked to increased incidence of infections and decreased responses to vaccines in the aging population. Human peripheral blood monocytes are known to promote Ag presentation and antiviral activities; however, the impact of aging on monocyte functions remains an open question. We present an in-depth global analysis examining the impact of aging on classical (CD14+CD16-), intermediate (CD14+CD16+), and nonclassical (CD14dimCD16+) monocytes. Monocytes sorted from nonfrail healthy adults (21-40 y) and old (≥65 y) individuals were analyzed after stimulation with TLR4, TLR7/8, and retinoic acid-inducible gene I agonists. Our data showed that under nonstimulated conditions, monocyte subsets did not reveal significant age-related alternations; however, agonist stimulated-monocytes from adults and old subjects did show differences at the transcriptional and functional levels. These alternations in many immune-related transcripts and biological processes resulted in reduced production of IFN-α, IFN-γ, IL-1ß, CCL20, and CCL8, and higher expression of CX3CR1 in monocytes from old subjects. Our findings represent a comprehensive analysis of the influence of human aging on pattern recognition receptors signaling and monocyte functions, and have implications for strategies to enhance the immune response in the context of infection and immunization.

Activation of Nrf2 Signaling Augments Vesicular Stomatitis Virus Oncolysis via Autophagy-Driven Suppression of Antiviral Immunity.

Oncolytic viruses (OVs) offer a promising therapeutic approach to treat multiple types of cancer. In this study, we show that the manipulation of the antioxidant network via transcription factor Nrf2 augments vesicular stomatitis virus Δ51 (VSVΔ51) replication and sensitizes cancer cells to viral oncolysis. Activation of Nrf2 signaling by the antioxidant compound sulforaphane (SFN) leads to enhanced VSVΔ51 spread in OV-resistant cancer cells and improves the therapeutic outcome in different murine syngeneic and xenograft tumor models. Chemoresistant A549 lung cancer cells that display constitutive dominant hyperactivation of Nrf2 signaling are particularly vulnerable to VSVΔ51 oncolysis. Mechanistically, enhanced Nrf2 signaling stimulated viral replication in cancer cells and disrupted the type I IFN response via increased autophagy. This study reveals a previously unappreciated role for Nrf2 in the regulation of autophagy and the innate antiviral response that complements the therapeutic potential of VSV-directed oncolysis against multiple types of OV-resistant or chemoresistant cancer.

Inhibition of dengue virus replication by novel inhibitors of RNA-dependent RNA polymerase and protease activities.

Dengue virus (DENV) is the leading mosquito-transmitted viral infection in the world. With more than 390 million new infections annually, and up to 1 million clinical cases with severe disease manifestations, there continues to be a need to develop new antiviral agents against dengue infection. In addition, there is no approved anti-DENV agents for treating DENV-infected patients. In the present study, we identified new compounds with anti-DENV replication activity by targeting viral replication enzymes - NS5, RNA-dependent RNA polymerase (RdRp) and NS3 protease, using cell-based reporter assay. Subsequently, we performed an enzyme-based assay to clarify the action of these compounds against DENV RdRp or NS3 protease activity. Moreover, these compounds exhibited anti-DENV activity in vivo in the ICR-suckling DENV-infected mouse model. Combination drug treatment exhibited a synergistic inhibition of DENV replication. These results describe novel prototypical small anti-DENV molecules for further development through compound modification and provide potential antivirals for treating DENV infection and DENV-related diseases.

Mapping of transcription factor motifs in active chromatin identifies IRF5 as key regulator in classical Hodgkin lymphoma.

Deregulated transcription factor (TF) activities are commonly observed in hematopoietic malignancies. Understanding tumorigenesis therefore requires determining the function and hierarchical role of individual TFs. To identify TFs central to lymphomagenesis, we identified lymphoma type-specific accessible chromatin by global mapping of DNaseI hypersensitive sites and analyzed enriched TF-binding motifs in these regions. Applying this unbiased approach to classical Hodgkin lymphoma (HL), a common B-cell-derived lymphoma with a complex pattern of deregulated TFs, we discovered interferon regulatory factor (IRF) sites among the top enriched motifs. High-level expression of the proinflammatory TF IRF5 was specific to HL cells and crucial for their survival. Furthermore, IRF5 initiated a regulatory cascade in human non-Hodgkin B-cell lines and primary murine B cells by inducing the TF AP-1 and cooperating with NF-κB to activate essential characteristic features of HL. Our strategy efficiently identified a lymphoma type-specific key regulator and uncovered a tumor promoting role of IRF5.

Aryl Hydrocarbon Receptor Interacting Protein Targets IRF7 to Suppress Antiviral Signaling and the Induction of Type I Interferon.

The transcription factor IRF7 (interferon regulatory factor 7) is a key regulator of type I interferon and plays essential roles in restricting virus infection and spread. IRF7 activation is tightly regulated to prevent excessive inflammation and autoimmunity; however, how IRF7 is suppressed by negative regulators remains poorly understood. Here, we have identified AIP (aryl hydrocarbon receptor interacting protein) as a new binding partner of IRF7. The interaction between AIP and IRF7 is enhanced upon virus infection, and AIP potently inhibits IRF7-induced type I IFN (IFNα/ß) production. Overexpression of AIP blocks virus-induced activation of IFN, whereas knockdown of AIP by siRNA potentiates virally activated IFN production. Consistently, AIP-deficient murine embryonic fibroblasts are highly resistant to virus infection because of increased production of IFNα/ß. AIP inhibits IRF7 function by antagonizing the nuclear localization of IRF7. Together, our study identifies AIP as a novel inhibitor of IRF7 and a negative regulator of innate antiviral signaling.

Mouse superkiller-2-like helicase DDX60 is dispensable for type I IFN induction and immunity to multiple viruses.

IFN-α/ß allow cells to fight virus infection by inducing the expression of many genes that encode effectors of antiviral defense. One of these, the Ski2-like DExH-box helicase DDX60, was recently implicated in resistance of human cells to hepatitis C virus, as well as in induction of IFN-α/ß by retinoic acid inducible gene 1-like receptors (RLRs) that detect the presence of RNA viruses in a cell-intrinsic manner. Here, we sought to investigate the role of DDX60 in IFN-α/ß induction and in resistance to virus infection. Analysis of fibroblasts and myeloid cells from Ddx60-deficient mice revealed no impairment in IFN-α/ß production in response to RLR agonists, RNA viruses, or other stimuli. Moreover, overexpression of DDX60 did not potentiate IFN induction and DDX60 did not interact with RLRs or capture RLR agonists from virally infected cells. We also failed to identify any impairment in Ddx60-deficient murine cells or mice in resistance to infection with influenza A virus, encephalomyocarditis virus, Sindbis virus, vaccinia virus, or herpes simplex virus-1. These results put in question the reported role of DDX60 as a broad-acting positive regulator of RLR responses and hint at the possibility that it may function as a restriction factor highly specific for a particular virus or class of viruses.

RAIDD Mediates TLR3 and IRF7 Driven Type I Interferon Production.

BACKGROUND/AIMS: Viral infections represent a global health problem with the need for new viral therapies and better understanding of the immune response during infection. The most immediate and potent anti-viral defense mechanism is the production of type I interferon (IFN-I) which are activated rapidly following recognition of viral infection by host pathogen recognition receptors (PRR). The mechanisms of innate cellular signaling downstream of PRR activation remain to be fully understood. In the present study, we demonstrate that CASP2 and RIPK1 domain-containing adaptor with death domain (CRADD/RAIDD) is a critical component in type I IFN production. METHODS: The role of RAIDD during IFN-I production was investigated using western blot, shRNA mediated lentiviral knockdown, immunoprecipitation and IFN-I driven dual luciferase assay. RESULTS: Immunoprecipitation analysis revealed the molecular interaction of RAIDD with interferon regulatory factor 7 (IRF7) and its phosphorylating kinase IKKε. Using an IFN-4α driven dual luciferase analysis in RAIDD deficient cells, type I IFN activation by IKKε and IRF7 was dramatically reduced. Furthermore, deletion of either the caspase recruitment domain (CARD) or death domain (DD) of RAIDD inhibited IKKε and IRF7 mediated interferon-4α activation. CONCLUSION: We have identified that the adaptor molecule RAIDD coordinates IKKε and IRF7 interaction to ensure efficient expression of type I interferon.