IRF1 Maintains Optimal Constitutive Expression of Antiviral Genes and Regulates the Early Antiviral Response

lncRNA CARINH regulates expression and function of innate immune transcription factor IRF1 in macrophages

The discovery of long non-coding RNAs (lncRNAs) has provided a new perspective on the centrality of RNA in gene regulation and genome organization. Here, we screened for lncRNAs with putative functions in the host response to single-stranded RNA respiratory viruses. We identify CARINH as a conserved cis-acting lncRNA up-regulated in three respiratory diseases to control the expression of its antisense gene IRF1, a key transcriptional regulator of the antiviral response. CARINH and IRF1 are coordinately increased in the circulation of patients infected with human metapneumovirus, influenza A virus, or SARS-CoV-2, and in macrophages in response to viral infection or TLR3 agonist treatment. Targeted depletion of CARINH or its mouse ortholog Carinh in macrophages reduces the expression of IRF1/Irf1 and their associated target gene networks, increasing susceptibility to viral infection. Accordingly, CRISPR-mediated deletion of Carinh in mice reduces antiviral immunity, increasing viral burden upon sublethal challenge with influenza A virus. Together, these findings identify a conserved role of lncRNA CARINH in coordinating interferon-stimulated genes and antiviral immune responses.

Interference without interferon: interferon-independent induction of interferon-stimulated genes and its role in cellular innate immunity

Interferons (IFNs) are multifaceted proteins that play pivotal roles in orchestrating robust antiviral immune responses and modulating the intricate landscape of host immunity. The major signaling pathway activated by IFNs is the JAK/STAT (Janus kinase/signal transducer and activator of transcription) pathway, which leads to the transcription of a battery of genes, collectively known as IFN-stimulated genes (ISGs). While the well-established role of IFNs in coordinating the innate immune response against viral infections is widely acknowledged, recent years have provided a more distinct comprehension of the functional significance attributed to non-canonical, IFN-independent induction of ISGs. In this review, we summarize the non-conventional signaling pathways of ISG induction. These alternative pathways offer new avenues for developing antiviral strategies or immunomodulation in various diseases.

The multiple roles of interferon regulatory factor family in health and disease

Interferon Regulatory Factors (IRFs), a family of transcription factors, profoundly influence the immune system, impacting both physiological and pathological processes. This review explores the diverse functions of nine mammalian IRF members, each featuring conserved domains essential for interactions with other transcription factors and cofactors. These interactions allow IRFs to modulate a broad spectrum of physiological processes, encompassing host defense, immune response, and cell development. Conversely, their pivotal role in immune regulation implicates them in the pathophysiology of various diseases, such as infectious diseases, autoimmune disorders, metabolic diseases, and cancers. In this context, IRFs display a dichotomous nature, functioning as both tumor suppressors and promoters, contingent upon the specific disease milieu. Post-translational modifications of IRFs, including phosphorylation and ubiquitination, play a crucial role in modulating their function, stability, and activation. As prospective biomarkers and therapeutic targets, IRFs present promising opportunities for disease intervention. Further research is needed to elucidate the precise mechanisms governing IRF regulation, potentially pioneering innovative therapeutic strategies, particularly in cancer treatment, where the equilibrium of IRF activities is of paramount importance.

Early human migration determines the risk of being attacked by wolves: ethnic gene diversity on the development of systemic lupus erythematosus

The prevalence of systemic lupus erythematosus (SLE) varies significantly based on ethnicity rather than geographic distribution; thus, the prevalence is higher in Asian, Hispanic, and Black African populations than in European populations. The risk of developing lupus nephritis (LN) is the highest among Asian populations. Therefore, we hypothesize that human genetic diversity between races has occurred through the early human migration and human genetic adaptation to various environments, with a particular focus on pathogens. Additionally, we compile the currently available evidence on the ethnic gene diversity of SLE and how it relates to disease severity. The human leukocyte antigen (HLA) locus is well established as associated with susceptibility to SLE; specific allele distributions have been observed across diverse populations. Notably, specific amino acid residues within these HLA loci demonstrate significant associations with SLE risk. The non-HLA genetic loci associated with SLE risk also varies across diverse ancestries, implicating distinct immunological pathways, such as the type-I interferon and janus kinase-signal transducers and activators of transcription (JAK-STAT) pathways in Asians, the type-II interferon signaling pathway in Europeans, and B cell activation pathway in Africans. Furthermore, assessing individual genetic susceptibility using genetic risk scores (GRS) for SLE helps to reveal the diverse prevalence, age of onset, and clinical phenotypes across different ethnicities. A higher GRS increases the risk of LN and the severity of SLE. Therefore, understanding ethnic gene diversity is crucial for elucidating disease mechanisms and SLE severity, which could enable the development of novel drugs specific to each race.

Opposing tumor-cell-intrinsic and -extrinsic roles of the IRF1 transcription factor in antitumor immunity

Type I interferon (IFN-I) and IFN-γ foster antitumor immunity by facilitating T cell responses. Paradoxically, IFNs may promote T cell exhaustion by activating immune checkpoints. The downstream regulators of these disparate responses are incompletely understood. Here, we describe how interferon regulatory factor 1 (IRF1) orchestrates these opposing effects of IFNs. IRF1 expression in tumor cells blocks Toll-like receptor- and IFN-I-dependent host antitumor immunity by preventing interferon-stimulated gene (ISG) and effector programs in immune cells. In contrast, expression of IRF1 in the host is required for antitumor immunity. Mechanistically, IRF1 binds distinctly or together with STAT1 at promoters of immunosuppressive but not immunostimulatory ISGs in tumor cells. Overexpression of programmed cell death ligand 1 (PD-L1) in Irf1-/- tumors only partially restores tumor growth, suggesting multifactorial effects of IRF1 on antitumor immunity. Thus, we identify that IRF1 expression in tumor cells opposes host IFN-I- and IRF1-dependent antitumor immunity to facilitate immune escape and tumor growth.

Predisposal of Interferon Regulatory Factor 1 Deficiency to Accumulate DNA Damage and Promote Osteoarthritis Development in Cartilage

OBJECTIVE

Interferon regulatory factor 1 (IRF1) is a transcriptional regulator conventionally associated with immunomodulation. Recent molecular analyses mapping DNA binding sites of IRF1 have suggested its potential function in DNA repair. However, the physiologic significance of this noncanonical function remains unexplored. Here, we investigated the role of IRF1 in osteoarthritis (OA), a condition marked by senescence and chronic joint inflammation.

METHODS

OA progression was examined in wild-type and Irf1-/- mice using histologic assessments and microcomputed tomography analysis of whole-joint OA manifestations and behavioral assessments of joint pain. An integrated analysis of assay for transposase-accessible chromatin with sequencing and whole transcriptome data was conducted for the functional assessment of IRF1 in chondrocytes. The role of IRF1 in DNA repair and senescence was investigated by assaying γ-H2AX foci and senescence-associated beta-galactosidase activity.

RESULTS

Our genome-wide investigation of IRF1 footprinting in chondrocytes revealed its primary occupancies in the promoters of DNA repair genes without noticeable footprint patterns in those of interferon-responsive genes. Chondrocytes lacking IRF1 accumulated irreversible DNA damage under oxidative stress, facilitating their entry into cellular senescence. IRF1 was down-regulated in the cartilage of human and mouse OA. Although IRF1 overexpression did not elicit an inflammatory response in joints or affect OA development, genetic deletion of Irf1 caused enhanced chondrocyte senescence and exacerbated post-traumatic OA in mice.

CONCLUSION

IRF1 offers DNA damage surveillance in chondrocytes, protecting them from oxidative stress associated with OA risk factors. Our study provides a crucial and cautionary perspective that compromising IRF1 activity renders chondrocytes vulnerable to cellular senescence and promotes OA development.

Cytosolic DNA sensors activation of human astrocytes inhibits herpes simplex virus through IRF1 induction

Introduction

While astrocytes participate in the CNS innate immunity against herpes simplex virus type 1 (HSV-1) infection, they are the major target for the virus. Therefore, it is of importance to understand the interplay between the astrocyte-mediated immunity and HSV-1 infection.

Methods

Both primary human astrocytes and the astrocyte line (U373) were used in this study. RT-qPCR and Western blot assay were used to measure IFNs, the antiviral IFN-stimulated genes (ISGs), IFN regulatory factors (IRFs) and HSV-1 DNA. IRF1 knockout or knockdown was performed with CRISPR/Cas9 and siRNA transfection techniques.

Results

Poly(dA:dT) could inhibit HSV-1 replication and induce IFN-β/IFN-λs production in human astrocytes. Poly(dA:dT) treatment of astrocytes also induced the expression of the antiviral ISGs (Viperin, ISG56 and MxA). Among IRFs members examined, poly(dA:dT) selectively unregulated IRF1 and IRF9, particularly IRF1 in human astrocytes. The inductive effects of poly(dA:dT) on IFNs and ISGs were diminished in the IRF1 knockout cells. In addition, IRF1 knockout attenuated poly(dA:dT)-mediated HSV-1 inhibition in the cells.

Conclusion

The DNA sensors activation induces astrocyte intracellular innate immunity against HSV-1. Therefore, targeting the DNA sensors has potential for immune activation-based HSV-1 therapy.

Non-transcriptional IRF7 interacts with NF-κB to inhibit viral inflammation

Interferon (IFN) regulatory factors (IRF) are key transcription factors in cellular antiviral responses. IRF7, a virus-inducible IRF, expressed primarily in myeloid cells, is required for transcriptional induction of interferon α and antiviral genes. IRF7 is activated by virus-induced phosphorylation in the cytoplasm, leading to its translocation to the nucleus for transcriptional activity. Here, we revealed a nontranscriptional activity of IRF7 contributing to its antiviral functions. IRF7 interacted with the pro-inflammatory transcription factor NF-κB-p65 and inhibited the induction of inflammatory target genes. Using knockdown, knockout, and overexpression strategies, we demonstrated that IRF7 inhibited NF-κB-dependent inflammatory target genes, induced by virus infection or toll-like receptor stimulation. A mutant IRF7, defective in transcriptional activity, interacted with NF-κB-p65 and suppressed NF-κB-induced gene expression. A single-action IRF7 mutant, active in anti-inflammatory function, but defective in transcriptional activity, efficiently suppressed Sendai virus and murine hepatitis virus replication. We, therefore, uncovered an anti-inflammatory function for IRF7, independent of transcriptional activity, contributing to the antiviral response of IRF7.

Strategies to reduce the risks of mRNA drug and vaccine toxicity

mRNA formulated with lipid nanoparticles is a transformative technology that has enabled the rapid development and administration of billions of coronavirus disease 2019 (COVID-19) vaccine doses worldwide. However, avoiding unacceptable toxicity with mRNA drugs and vaccines presents challenges. Lipid nanoparticle structural components, production methods, route of administration and proteins produced from complexed mRNAs all present toxicity concerns. Here, we discuss these concerns, specifically how cell tropism and tissue distribution of mRNA and lipid nanoparticles can lead to toxicity, and their possible reactogenicity. We focus on adverse events from mRNA applications for protein replacement and gene editing therapies as well as vaccines, tracing common biochemical and cellular pathways. The potential and limitations of existing models and tools used to screen for on-target efficacy and de-risk off-target toxicity, including in vivo and next-generation in vitro models, are also discussed.

Cooperative interaction of interferon regulatory factor -1 and bromodomain-containing protein 4 on RNA polymerase activation for intrinsic innate immunity

Introduction

The human orthopneumovirus, Respiratory Syncytial Virus (RSV), is the causative agent of severe lower respiratory tract infections (LRTI) and exacerbations of chronic lung diseases. In immune competent hosts, RSV productively infects highly differentiated epithelial cells, where it elicits robust anti-viral, cytokine and remodeling programs. By contrast, basal cells are relatively resistant to RSV infection, in part, because of constitutive expression of an intrinsic innate immune response (IIR) consisting of a subgroup of interferon (IFN) responsive genes. The mechanisms controlling the intrinsic IIR are not known.

Methods

Here, we use human small airway epithelial cell hSAECs as a multipotent airway stem cell model to examine regulatory control of an intrinsic IIR pathway.

Results

We find hSAECs express patterns of intrinsic IIRs, highly conserved with pluri- and multi-potent stem cells. We demonstrate a core intrinsic IIR network consisting of Bone Marrow Stromal Cell Antigen 2 (Bst2), Interferon Induced Transmembrane Protein 1 (IFITM1) and Toll-like receptor (TLR3) expression are directly under IRF1 control. Moreover, expression of this intrinsic core is rate-limited by ambient IRF1• phospho-Ser 2 CTD RNA Polymerase II (pSer2 Pol II) complexes binding to their proximal promoters. In response to RSV infection, the abundance of IRF1 and pSer2 Pol II binding is dramatically increased, with IRF1 complexing to the BRD4 chromatin remodeling complex (CRC). Using chromatin immunoprecipitation in IRF1 KD cells, we find that the binding of BRD4 is IRF1 independent. Using a small molecule inhibitor of the BRD4 acetyl lysine binding bromodomain (BRD4i), we further find that BRD4 bromodomain interactions are required for stable BRD4 promoter binding to the intrinsic IIR core promoters, as well as for RSV-inducible pSer2 Pol II recruitment. Surprisingly, BRD4i does not disrupt IRF1-BRD4 interactions, but disrupts both RSV-induced BRD4 and IRF1 interactions with pSer2 Pol II.

Conclusions

We conclude that the IRF1 functions in two modes- in absence of infection, ambient IRF1 mediates constitutive expression of the intrinsic IIR, whereas in response to RSV infection, the BRD4 CRC independently activates pSer2 Pol II to mediates robust expression of the intrinsic IIR. These data provide insight into molecular control of anti-viral defenses of airway basal cells.

Unraveling the dynamics of hepatitis C virus adaptive mutations and their impact on antiviral responses in primary human hepatocytes

Hepatitis C virus (HCV) infection progresses to chronicity in the majority of infected individuals. Its high intra-host genetic variability enables HCV to evade the continuous selection pressure exerted by the host, contributing to persistent infection. Utilizing a cell culture-adapted HCV population (p100pop) which exhibits increased replicative capacity in various liver cell lines, this study investigated virus and host determinants that underlie enhanced viral fitness. Characterization of a panel of molecular p100 clones revealed that cell culture adaptive mutations optimize a range of virus-host interactions, resulting in expanded cell tropism, altered dependence on the cellular co-factor micro-RNA 122 and increased rates of virus spread. On the host side, comparative transcriptional profiling of hepatoma cells infected either with p100pop or its progenitor virus revealed that enhanced replicative fitness correlated with activation of endoplasmic reticulum stress signaling and the unfolded protein response. In contrast, infection of primary human hepatocytes with p100pop led to a mild attenuation of virion production which correlated with a greater induction of cell-intrinsic antiviral defense responses. In summary, long-term passage experiments in cells where selective pressure from innate immunity is lacking improves multiple virus-host interactions, enhancing HCV replicative fitness. However, this study further indicates that HCV has evolved to replicate at low levels in primary human hepatocytes to minimize innate immune activation, highlighting that an optimal balance between replicative fitness and innate immune induction is key to establish persistence.

IMPORTANCE

Hepatitis C virus (HCV) infection remains a global health burden with 58 million people currently chronically infected. However, the detailed molecular mechanisms that underly persistence are incompletely defined. We utilized a long-term cell culture-adapted HCV, exhibiting enhanced replicative fitness in different human liver cell lines, in order to identify molecular principles by which HCV optimizes its replication fitness. Our experimental data revealed that cell culture adaptive mutations confer changes in the host response and usage of various host factors. The latter allows functional flexibility at different stages of the viral replication cycle. However, increased replicative fitness resulted in an increased activation of the innate immune system, which likely poses boundary for functional variation in authentic hepatocytes, explaining the observed attenuation of the adapted virus population in primary hepatocytes.

Differential signaling by type-I and type-III interferons in mucosa

Mucosal surfaces are barrier sites that protect the body from the outside environment. They have developed mechanisms to handle microbiota-associated triggers while remaining responsive to pathogens. Cells at mucosal surfaces rely on both the type-I and -III interferons (IFNs) as key cytokines to protect the epithelium itself and to prevent systemic spread of viral infections. Type-I and -III IFNs have been shown to use distinct receptors but similar JAK/STAT signaling cascades to elicit the induction of IFN-stimulated genes. These overlapping cascades led to the original hypothesis that both IFNs provided redundant functions at mucosal surfaces. However, accumulating evidence points toward a different model where each IFN provides a unique protective and homeostatic function as well as distinct antiviral protection to epithelial cells. This review will highlight recent work shedding light on the differences in how both type -I and -III IFNs induce receptor-mediated signaling to protect mucosal surfaces.

Feedback loop regulation between viperin and viral hemorrhagic septicemia virus through competing protein degradation pathways

Viperin is an antiviral protein that exhibits a remarkably broad spectrum of antiviral activity. Viperin-like proteins are found all kingdoms of life, suggesting it is an ancient component of the innate immune system. However, viruses have developed strategies to counteract viperin's effects. Here, we describe a feedback loop between viperin and viral hemorrhagic septicemia virus (VHSV), a common fish pathogen. We show that Lateolabrax japonicus viperin (Ljviperin) is induced by both IFN-independent and IFN-dependent pathways, with the C-terminal domain of Ljviperin being important for its anti-VHSV activity. Ljviperin exerts an antiviral effect by binding both the nucleoprotein (N) and phosphoprotein (P) of VHSV and induces their degradation through the autophagy pathway, which is an evolutionarily conserved antiviral mechanism. However, counteracting viperin's activity, N protein targets and degrades transcription factors that up-regulate Ljviperin expression, interferon regulatory factor (IRF) 1 and IRF9, through ubiquitin-proteasome pathway. Together, our results reveal a previously unknown feedback loop between viperin and virus, providing potential therapeutic targets for VHSV prevention.

Importance

Viral hemorrhagic septicaemia (VHS) is a contagious disease caused by the viral hemorrhagic septicaemia virus (VHSV), which poses a threat to over 80 species of marine and freshwater fish. Currently, there are no effective treatments available for this disease. Understanding the mechanisms of VHSV-host interaction is crucial for preventing viral infections. Here, we found that, as an ancient antiviral protein, viperin degrades the N and P proteins of VHSV through the autophagy pathway. Additionally, the N protein also impacts the biological functions of IRF1 and IRF9 through the ubiquitin-proteasome pathway, leading to the suppression of viperin expression. Therefore, the N protein may serve as a potential virulence factor for the development of VHSV vaccines and screening of antiviral drugs. Our research will serve as a valuable reference for the development of strategies to prevent VHSV infections.

AGC kinase inhibitors regulate STING signaling through SGK-dependent and SGK-independent mechanisms

Type 1 IFN expression is critical in the innate immune response, but aberrant expression is associated with autoimmunity and cancer. Here, we identify N-[4-(1H46 pyrazolo[3,4-b] pyrazin-6-yl)-phenyl]-sulfonamide (Sanofi-14h), a compound with preference for inhibition of the AGC family kinase SGK3, as an inhibitor of Ifnb1 gene expression in response to STING stimulation of macrophages. Sanofi-14h abrogated SGK activity and also impaired activation of the critical TBK1/IRF3 pathway downstream of STING activation, blocking interaction of STING with TBK1. Deletion of SGK1/3 in a macrophage cell line did not block TBK1/IRF3 activation but decreased expression of transcription factors, such as IRF7 and STAT1, required for the innate immune response. Other AGC kinase inhibitors blocked TBK1 and IRF3 activation suggesting common action on a critical regulatory node in the STING pathway. These studies reveal both SGK-dependent and SGK-independent mechanisms in the innate immune response and indicate an approach to block aberrant Ifnb1 expression.

Inhibition of the lysine demethylase LSD1 modulates the balance between inflammatory and antiviral responses against coronaviruses

Innate immune responses to coronavirus infections are highly cell specific. Tissue-resident macrophages, which are infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in patients but are inconsistently infected in vitro, exert critical but conflicting effects by secreting both antiviral type I interferons (IFNs) and tissue-damaging inflammatory cytokines. Steroids, the only class of host-targeting drugs approved for the treatment of coronavirus disease 2019 (COVID-19), indiscriminately suppress both responses, possibly impairing viral clearance. Here, we established in vitro cell culture systems that enabled us to separately investigate the cell-intrinsic and cell-extrinsic proinflammatory and antiviral activities of mouse macrophages infected with the prototypical murine coronavirus MHV-A59. We showed that the nuclear factor κB-dependent inflammatory response to viral infection was selectively inhibited by loss of the lysine demethylase LSD1, which was previously implicated in innate immune responses to cancer, with negligible effects on the antiviral IFN response. LSD1 ablation also enhanced an IFN-independent antiviral response, blocking viral egress through the lysosomal pathway. The macrophage-intrinsic antiviral and anti-inflammatory activity of Lsd1 inhibition was confirmed in vitro and in a humanized mouse model of SARS-CoV-2 infection. These results suggest that LSD1 controls innate immune responses against coronaviruses at multiple levels and provide a mechanistic rationale for potentially repurposing LSD1 inhibitors for COVID-19 treatment.

Immune-epithelial cell cross-talk enhances antiviral responsiveness to SARS-CoV-2 in children

The risk of developing severe COVID-19 rises dramatically with age. Schoolchildren are significantly less likely than older people to die from SARS-CoV-2 infection, but the molecular mechanisms underlying this age-dependence are unknown. In primary infections, innate immunity is critical due to the lack of immune memory. Children, in particular, have a significantly stronger interferon response due to a primed state of their airway epithelium. In single-cell transcriptomes of nasal turbinates, we find increased frequencies of immune cells and stronger cytokine-mediated interactions with epithelial cells, resulting in increased epithelial expression of viral sensors (RIG-I, MDA5) via IRF1. In vitro, adolescent peripheral blood mononuclear cells produce more cytokines, priming A549 cells for stronger interferon responses to SARS-CoV-2. Taken together, our findings suggest that increased numbers of immune cells in the airways of children and enhanced cytokine-based interactions with epithelial cells tune the setpoint of the epithelial antiviral system. Our findings shed light on the molecular basis of children's remarkable resistance to COVID-19 and may suggest a novel concept for immunoprophylactic treatments.

Hepatitis C virus cell culture adaptive mutations enhance cell culture propagation by multiple mechanisms but boost antiviral responses in primary human hepatocytes

Hepatitis C virus (HCV) infection progresses to chronicity in the majority of infected individuals. Its high intra-host genetic variability enables HCV to evade the continuous selection pressure exerted by the host, contributing to persistent infection. Utilizing a cell culture adapted HCV population (p100pop) which exhibits increased replicative capacity in various liver cell lines, this study investigated virus and host determinants which underlie enhanced viral fitness. Characterization of a panel of molecular p100 clones revealed that cell culture adaptive mutations optimize a range of virus-host interactions, resulting in expanded cell tropism, altered dependence on the cellular co-factor micro-RNA 122 and increased rates of virus spread. On the host side, comparative transcriptional profiling of hepatoma cells infected either with p100pop or its progenitor virus revealed that enhanced replicative fitness correlated with activation of endoplasmic reticulum stress signaling and the unfolded protein response. In contrast, infection of primary human hepatocytes with p100pop led to a mild attenuation of virion production which correlated with a greater induction of cell-intrinsic antiviral defense responses. In summary, long-term passage experiments in cells where selective pressure from innate immunity is lacking improves multiple virus-host interactions, enhancing HCV replicative fitness. However, this study further indicates that HCV has evolved to replicate at low levels in primary human hepatocytes to minimize innate immune activation, highlighting that an optimal balance between replicative fitness and innate immune induction is key to establishing persistence.

Author Summary

HCV infection remains a global health burden with 58 million people currently chronically infected. However, the detailed molecular mechanisms which underly persistence are incompletely defined. We utilized a long-term cell culture adapted HCV, exhibiting enhanced replicative fitness in different human liver cell lines, in order to identify molecular principles by which HCV optimizes its replication fitness. Our experimental data revealed that cell culture adaptive mutations confer changes in the host response and usage of various host factors. The latter allows functional flexibility at different stages of the viral replication cycle. However, increased replicative fitness resulted in an increased activation of the innate immune system, which likely poses boundary for functional variation in authentic hepatocytes, explaining the observed attenuation of the adapted virus population in primary hepatocytes.

Induction of antiviral gene expression by cyclosporine A, but not inhibition of cyclophilin A or B, contributes to its restriction of human coronavirus 229E infection in a lung epithelial cell line

The development of antivirals with an extended spectrum of activity is an attractive possibility to protect against future emerging coronaviruses (CoVs). Cyclosporine A (CsA), a clinically approved immunosuppressive drug, has established antiviral activity against diverse unrelated viruses, including several CoVs. However, its antiviral mechanisms of action against CoV infection have remained elusive, precluding the rational design of non-immunosuppressive derivatives with improved antiviral activities. In this study, we evaluated the mechanisms of CsA against HCoV-229E infection in a human lung epithelial cell line. We demonstrate that the antiviral activity of CsA against HCoV-229E is independent of classical CsA target proteins, cyclophilin A or B, which are not required host factors for HCoV-229E in A549 cells. Instead, CsA treatment induces expression of antiviral genes in a manner dependent on interferon regulatory factor 1, but independent of classical interferon responses, which contributes to its inhibitory effect against HCoV-229E infection. Our results also point to a role for the HCoV-229E nucleoprotein in antagonizing activation of type I interferon, but we show that CsA treatment does not affect evasion of innate immune signalling pathways by HCoV-229E. Overall, our findings further the understanding of the antiviral mechanisms of CsA against CoV infection and highlight a novel immunomodulatory strategy to inhibit CoV infection that may inform future drug development efforts.

IRF1 regulates self-renewal and stress responsiveness to support hematopoietic stem cell maintenance

Hematopoietic stem cells (HSCs) are tightly controlled to maintain a balance between blood cell production and self-renewal. While inflammation-related signaling is a critical regulator of HSC activity, the underlying mechanisms and the precise functions of specific factors under steady-state and stress conditions remain incompletely understood. We investigated the role of interferon regulatory factor 1 (IRF1), a transcription factor that is affected by multiple inflammatory stimuli, in HSC regulation. Our findings demonstrate that the loss of IRF1 from mouse HSCs significantly impairs self-renewal, increases stress-induced proliferation, and confers resistance to apoptosis. In addition, given the frequent abnormal expression of IRF1 in leukemia, we explored the potential of IRF1 expression level as a stratification marker for human acute myeloid leukemia. We show that IRF1-based stratification identifies distinct cancer-related signatures in patient subgroups. These findings establish IRF1 as a pivotal HSC controller and provide previously unknown insights into HSC regulation, with potential implications to IRF1 functions in the context of leukemia.

A bacterial quorum sensing signal is a potent inhibitor of de novo pyrimidine biosynthesis in the globally abundant Emiliania huxleyi

Interactions between marine phytoplankton, viruses, and bacteria drive biogeochemical cycling, shape marine trophic structures, and impact global climate. Microbially produced compounds have emerged as key players in influencing eukaryotic organismal physiology, and in turn, remodel microbial community structure. This work aimed to reveal the molecular mechanism by which the bacterial quorum sensing molecule 2-heptyl-4-quinolone (HHQ), produced by the marine gammaproteobacterium Pseudoalteromonas spp., arrests cell division and confers protection from virus-induced mortality in the bloom-forming coccolithophore Emiliania huxleyi. Previous work has established alkylquinolones as inhibitors of dihydroorotate dehydrogenase (DHODH), a fundamental enzyme catalyzing the fourth step in pyrimidine biosynthesis and a potential antiviral drug target. An N-terminally truncated version of E. huxleyi DHODH was heterologously expressed in E. coli, purified, and kinetically characterized. Here, we show HHQ is a potent inhibitor (Ki of 2.3 nM) of E. huxleyi DHODH. E. huxleyi cells exposed to brequinar, the canonical human DHODH inhibitor, experienced immediate, yet reversible cellular arrest, an effect which mirrors HHQ-induced cellular stasis previously observed. However, brequinar treatment lacked other notable effects observed in HHQ-exposed E. huxleyi including significant changes in cell size, chlorophyll fluorescence, and protection from virus-induced lysis, indicating HHQ has additional as yet undiscovered physiological targets. Together, these results suggest a novel and intricate role of bacterial quorum sensing molecules in tripartite interdomain interactions in marine ecosystems, opening new avenues for exploring the role of microbial chemical signaling in algal bloom regulation and host-pathogen dynamics.

Syphilis and the host: multi-omic analysis of host cellular responses to Treponema pallidum provides novel insight into syphilis pathogenesis

Introduction

Syphilis is a chronic, multi-stage infection caused by the extracellular bacterium Treponema pallidum ssp. pallidum. Treponema pallidum widely disseminates through the vasculature, crosses endothelial, blood-brain and placental barriers, and establishes systemic infection. Although the capacity of T. pallidum to traverse the endothelium is well-described, the response of endothelial cells to T. pallidum exposure, and the contribution of this response to treponemal traversal, is poorly understood.

Methods

To address this knowledge gap, we used quantitative proteomics and cytokine profiling to characterize endothelial responses to T. pallidum.

Results

Proteomic analyses detected altered host pathways controlling extracellular matrix organization, necroptosis and cell death, and innate immune signaling. Cytokine analyses of endothelial cells exposed to T. pallidum revealed increased secretion of interleukin (IL)-6, IL-8, and vascular endothelial growth factor (VEGF), and decreased secretion of monocyte chemoattractant protein-1 (MCP-1).

Discussion

This study provides insight into the molecular basis of syphilis disease symptoms and the enhanced susceptibility of individuals infected with syphilis to HIV co-infection. These investigations also enhance understanding of the host response to T. pallidum exposure and the pathogenic strategies used by T. pallidum to disseminate and persist within the host. Furthermore, our findings highlight the critical need for inclusion of appropriate controls when conducting T. pallidum-host cell interactions using in vitro- and in vivo-grown T. pallidum.

RSV replication modifies the XBP1s binding complex on the IRF1 upstream enhancer to potentiate the mucosal anti-viral response

Introduction

The unfolded protein response (UPR) has emerged as an important signaling pathway mediating anti-viral defenses to Respiratory Syncytial Virus (RSV) infection. Earlier we found that RSV replication predominantly activates the evolutionarily conserved Inositol Requiring Enzyme 1α (IRE1α)-X-Box Binding Protein 1 spliced (XBP1s) arm of the Unfolded Protein Response (UPR) producing inflammation, metabolic adaptation and cellular plasticity, yet the mechanisms how the UPR potentiates inflammation are not well understood.

Methods

To understand this process better, we examined the genomic response integrating RNA-seq and Cleavage Under Targets and Release Using Nuclease (CUT&RUN) analyses. These data were integrated with an RNA-seq analysis conducted on RSV-infected small airway cells ± an IRE1α RNAse inhibitor.

Results

We identified RSV induced expression changes in ~3.2K genes; of these, 279 required IRE1α and were enriched in IL-10/cytokine signaling pathways. From this data set, we identify those genes directly under XBP1s control by CUT&RUN. Although XBP1s binds to ~4.2 K high-confidence genomic binding sites, surprisingly only a small subset of IL10/cytokine signaling genes are directly bound. We further apply CUT&RUN to find that RSV infection enhances XBP1s loading on 786 genomic sites enriched in AP1/Fra-1, RELA and SP1 binding sites. These control a subset of cytokine regulatory factor genes including IFN response factor 1 (IRF1), CSF2, NFKB1A and DUSP10. Focusing on the downstream role of IRF1, selective knockdown (KD) and overexpression experiments demonstrate IRF1 induction controls type I and -III interferon (IFN) and IFN-stimulated gene (ISG) expression, demonstrating that ISG are indirectly regulated by XBP1 through IRF1 transactivation. Examining the mechanism of IRF1 activation, we observe that XBP1s directly binds a 5' enhancer sequence whose XBP1s loading is increased by RSV. The functional requirement for the enhancer is demonstrated by targeting a dCas9-KRAB silencer, reducing IRF1 activation. Chromatin immunoprecipitation shows that XBP1 is required, but not sufficient, for RSV-induced recruitment of activated phospho-Ser2 Pol II to the enhancer.

Discussion

We conclude that XBP1s is a direct activator of a core subset of IFN and cytokine regulatory genes in response to RSV. Of these IRF1 is upstream of the type III IFN and ISG response. We find that RSV modulates the XBP1s binding complex on the IRF1 5' enhancer whose activation is required for IRF1 expression. These findings provide novel insight into how the IRE1α-XBP1s pathway potentiates airway mucosal anti-viral responses.

Time-dependent recruitment of GAF, ISGF3 and IRF1 complexes shapes IFNα and IFNγ-activated transcriptional responses and explains mechanistic and functional overlap

To understand in detail the transcriptional and functional overlap of IFN-I- and IFN-II-activated responses, we used an integrative RNAseq-ChIPseq approach in Huh7.5 cells and characterized the genome-wide role of pSTAT1, pSTAT2, IRF9 and IRF1 in time-dependent ISG expression. For the first time, our results provide detailed insight in the timely steps of IFNα- and IFNγ-induced transcription, in which pSTAT1- and pSTAT2-containing ISGF3 and GAF-like complexes and IRF1 are recruited to individual or combined ISRE and GAS composite sites in a phosphorylation- and time-dependent manner. Interestingly, composite genes displayed a more heterogeneous expression pattern, as compared to GAS (early) and ISRE genes (late), with the time- and phosphorylation-dependent recruitment of GAF, ISGF3 and IRF1 after IFNα stimulation and GAF and IRF1 after IFNγ. Moreover, functional composite genes shared features of GAS and ISRE genes through transcription factor co-binding to closely located sites, and were able to sustain IFN responsiveness in STAT1-, STAT2-, IRF9-, IRF1- and IRF9/IRF1-mutant Huh7.5 cells compared to Wt cells. Thus, the ISRE + GAS composite site acted as a molecular switch, depending on the timely available components and transcription factor complexes. Consequently, STAT1, STAT2 and IRF9 were identified as functional composite genes that are part of a positive feedback loop controlling long-term IFNα and IFNγ responses. More important, in the absence of any one of the components, the positive feedback regulation of the ISGF3 and GAF components appeared to be preserved. Together, these findings provide further insight in the existence of a novel ISRE + GAS composite-dependent intracellular amplifier circuit prolonging ISG expression and controlling cellular responsiveness to different types of IFNs and subsequent antiviral activity. It also offers an explanation for the existing molecular and functional overlap between IFN-I- and IFN-II-activated ISG expression.

Pleiotropic effects of BAFF on the senescence-associated secretome and growth arrest

Senescent cells release a variety of cytokines, proteases, and growth factors collectively known as the senescence-associated secretory phenotype (SASP). Sustained SASP contributes to a pattern of chronic inflammation associated with aging and implicated in many age-related diseases. Here, we investigated the expression and function of the immunomodulatory cytokine BAFF (B-cell activating factor; encoded by the TNFSF13B gene), a SASP protein, in multiple senescence models. We first characterized BAFF production across different senescence paradigms, including senescent human diploid fibroblasts (WI-38, IMR-90) and monocytic leukemia cells (THP-1), and tissues of mice induced to undergo senescence. We then identified IRF1 (interferon regulatory factor 1) as a transcription factor required for promoting TNFSF13B mRNA transcription in senescence. We discovered that suppressing BAFF production decreased the senescent phenotype of both fibroblasts and monocyte-like cells, reducing IL6 secretion and SA-β-Gal staining. Importantly, however, the influence of BAFF on the senescence program was cell type-specific: in monocytes, BAFF promoted the early activation of NF-κB and general SASP secretion, while in fibroblasts, BAFF contributed to the production and function of TP53 (p53). We propose that BAFF is elevated across senescence models and is a potential target for senotherapy.

Phospholipase A and acyltransferase 4/retinoic acid receptor responder 3 at the intersection of tumor suppression and pathogen restriction

Phospholipase A and acyltransferase (PLAAT) 4 is a class II tumor suppressor with phospholipid metabolizing abilities. It was characterized in late 2000s, and has since been referred to as 'tazarotene-induced gene 3' (TIG3) or 'retinoic acid receptor responder 3' (RARRES3) as a key downstream effector of retinoic acid signaling. Two decades of research have revealed the complexity of its function and regulatory roles in suppressing tumorigenesis. However, more recent findings have also identified PLAAT4 as a key anti-microbial effector enzyme acting downstream of interferon regulatory factor 1 (IRF1) and interferons (IFNs), favoring protection from virus and parasite infections. Unveiling the molecular mechanisms underlying its action may thus open new therapeutic avenues for the treatment of both cancer and infectious diseases. Herein, we aim to summarize a brief history of PLAAT4 discovery, its transcriptional regulation, and the potential mechanisms in tumor prevention and anti-pathogen defense, and discuss potential future directions of PLAAT4 research toward the development of therapeutic approaches targeting this enzyme with pleiotropic functions.

The innate and T-cell mediated immune response during acute and chronic gammaherpesvirus infection

Immediately after entry into host cells, viruses are sensed by the innate immune system, leading to the activation of innate antiviral effector mechanisms including the type I interferon (IFN) response and natural killer (NK) cells. This innate immune response helps to shape an effective adaptive T cell immune response mediated by cytotoxic T cells and CD4+ T helper cells and is also critical for the maintenance of protective T cells during chronic infection. The human gammaherpesvirus Epstein-Barr virus (EBV) is a highly prevalent lymphotropic oncovirus that establishes chronic lifelong infections in the vast majority of the adult population. Although acute EBV infection is controlled in an immunocompetent host, chronic EBV infection can lead to severe complications in immunosuppressed patients. Given that EBV is strictly host-specific, its murine homolog murid herpesvirus 4 or MHV68 is a widely used model to obtain in vivo insights into the interaction between gammaherpesviruses and their host. Despite the fact that EBV and MHV68 have developed strategies to evade the innate and adaptive immune response, innate antiviral effector mechanisms still play a vital role in not only controlling the acute infection but also shaping an efficient long-lasting adaptive immune response. Here, we summarize the current knowledge about the innate immune response mediated by the type I IFN system and NK cells, and the adaptive T cell-mediated response during EBV and MHV68 infection. Investigating the fine-tuned interplay between the innate immune and T cell response will provide valuable insights which may be exploited to design better therapeutic strategies to vanquish chronic herpesviral infection.

Genetic adaptation to pathogens and increased risk of inflammatory disorders in post-Neolithic Europe

Ancient genomics can directly detect human genetic adaptation to environmental cues. However, it remains unclear how pathogens have exerted selective pressures on human genome diversity across different epochs and affected present-day inflammatory disease risk. Here, we use an ancestry-aware approximate Bayesian computation framework to estimate the nature, strength, and time of onset of selection acting on 2,879 ancient and modern European genomes from the last 10,000 years. We found that the bulk of genetic adaptation occurred after the start of the Bronze Age, <4,500 years ago, and was enriched in genes relating to host-pathogen interactions. Furthermore, we detected directional selection acting on specific leukocytic lineages and experimentally demonstrated that the strongest negatively selected candidate variant in immunity genes, lipopolysaccharide-binding protein (LBP) D283G, is hypomorphic. Finally, our analyses suggest that the risk of inflammatory disorders has increased in post-Neolithic Europeans, possibly because of antagonistic pleiotropy following genetic adaptation to pathogens.

Human IRF1 governs macrophagic IFN-γ immunity to mycobacteria

Inborn errors of human IFN-γ-dependent macrophagic immunity underlie mycobacterial diseases, whereas inborn errors of IFN-α/β-dependent intrinsic immunity underlie viral diseases. Both types of IFNs induce the transcription factor IRF1. We describe unrelated children with inherited complete IRF1 deficiency and early-onset, multiple, life-threatening diseases caused by weakly virulent mycobacteria and related intramacrophagic pathogens. These children have no history of severe viral disease, despite exposure to many viruses, including SARS-CoV-2, which is life-threatening in individuals with impaired IFN-α/β immunity. In leukocytes or fibroblasts stimulated in vitro, IRF1-dependent responses to IFN-γ are, both quantitatively and qualitatively, much stronger than those to IFN-α/β. Moreover, IRF1-deficient mononuclear phagocytes do not control mycobacteria and related pathogens normally when stimulated with IFN-γ. By contrast, IFN-α/β-dependent intrinsic immunity to nine viruses, including SARS-CoV-2, is almost normal in IRF1-deficient fibroblasts. Human IRF1 is essential for IFN-γ-dependent macrophagic immunity to mycobacteria, but largely redundant for IFN-α/β-dependent antiviral immunity.

Transcriptomic analysis of the innate immune response to in vitro transfection of plasmid DNA

The innate immune response to cytosolic DNA is intended to protect the host from viral infections, but it can also inhibit the delivery and expression of therapeutic transgenes in gene and cell therapies. The goal of this work was to use mRNA sequencing to identify genes that may influence transfection efficiency in four different cell types (PC-3, Jurkat, HEK-293T, and primary T cells). The highest transfection efficiency was observed in HEK-293T cells, which upregulated only 142 genes with no known antiviral functions after transfection with lipofectamine. Lipofection upregulated 1,057 cytokine-stimulated genes (CSGs) in PC-3 cells, which exhibited a significantly lower transfection efficiency. However, when PC-3 cells were transfected in serum-containing media or electroporated, the observed transfection efficiencies were significantly higher while the expression levels of cytokines and CSGs decreased. In contrast, lipofection of Jurkat and primary T cells only upregulated a few genes, but several of the antiviral CSGs that were absent in HEK-293T cells and upregulated in PC-3 cells were observed to be constitutively expressed in T cells, which may explain the relatively low Lipofection efficiencies observed with T cells (8%-21% GFP⁺). Indeed, overexpression of one CSG (IFI16) significantly decreased transfection efficiency in HEK-293T cells.

IRF2 Cooperates with Phosphoprotein of Spring Viremia of Carp Virus to Suppress Antiviral Response in Zebrafish

IFN regulatory factor (IRF) 2 belongs to the IRF1 subfamily, and its functions are not yet fully understood. In this study, we showed that IRF2a was a negative regulator of the interferon (IFN) response induced by spring viremia of carp virus (SVCV). Irf2a^-/- knockout zebrafish were less susceptible to SVCV than wild-type fish. Transcriptomic analysis reveals that differentially expressed genes (DEGs) in the irf2a^-/- and irf2a^+/+ cells derived caudal fins were mainly involved in cytokine-cytokine receptor interaction, mitogen-activated protein kinase (MAPK) signaling pathway, and transforming growth factor-beta (TGF-beta) signaling pathway. Interestingly, the basal expression levels of interferon stimulating genes (ISGs), including pkz, mx, apol, and stat1 were higher in the irf2a^-/- cells than irf2a^+/+ cells, suggesting that they may contribute to the increased viral resistance of the irf2a^-/- cells. Overexpression of IRF2a inhibited the activation of ifnφ1 and ifnφ3 induced by SVCV and poly(I:C) in the epithelioma papulosum cyprini (EPC) cells. Further, it was found that SVCV phosphoprotein (SVCV-P) could interact with IRF2a to promote IRF2a nuclear translocation and protein stability via suppressing K48-linked ubiquitination of IRF2a. Both IRF2a and SVCV-P not only destabilized STAT1a but reduced its translocation into the nucleus. Our work demonstrates that IRF2a cooperates with SVCV-P to suppress host antiviral response against viral infection in zebrafish. IMPORTANCE Interferon regulatory factors (IRFs) are central in the regulation of interferon-mediated antiviral immunity. Here, we reported that IRF2a suppressed interferon response and promoted virus replication in zebrafish. The suppressive effects were enhanced by the phosphoprotein of the spring viremia of carp virus (SVCV) via inhibition of K48-linked ubiquitination of IRF2a. IRF2a and SVCV phosphoprotein cooperated to degrade STAT1 and block its nuclear translocation. Our work demonstrated that IRFs and STATs were targeted by the virus through posttranslational modifications to repress interferon-mediated antiviral response in lower vertebrates.

DNA-PKcs restricts Zika virus spreading and is required for effective antiviral response

Zika virus (ZIKV) is a single-strand RNA mosquito-borne flavivirus with significant public health impact. ZIKV infection induces double-strand DNA breaks (DSBs) in human neural progenitor cells that may contribute to severe neuronal manifestations in newborns. The DNA-PK complex plays a critical role in repairing DSBs and in the innate immune response to infection. It is unknown, however, whether DNA-PK regulates ZIKV infection. Here we investigated the role of DNA-PKcs, the catalytic subunit of DNA-PK, during ZIKV infection. We demonstrate that DNA-PKcs restricts the spread of ZIKV infection in human epithelial cells. Increased ZIKV replication and spread in DNA-PKcs deficient cells is related to a notable decrease in transcription of type I and III interferons as well as IFIT1, IFIT2, and IL6. This was shown to be independent of IRF1, IRF3, or p65, canonical transcription factors necessary for activation of both type I and III interferon promoters. The mechanism of DNA-PKcs to restrict ZIKV infection is independent of DSB. Thus, these data suggest a non-canonical role for DNA-PK during Zika virus infection, acting downstream of IFNs transcription factors for an efficient antiviral immune response.

Long noncoding RNA CHROMR regulates antiviral immunity in humans

An effective innate immune response to virus infection requires the induction of type I interferons and up-regulation of hundreds of interferon-stimulated genes (ISGs) that instruct antiviral functions and immune regulation. Deciphering the regulatory mechanisms that direct expression of the ISG network is critical for understanding the fundamental organization of the innate immune response and the development of antiviral therapies. We define a regulatory role for the primate-specific long noncoding RNA CHROMR in coordinating ISG transcription. CHROMR sequesters the interferon regulatory factor (IRF)-2/IRF2BP2 complex that restrains ISG transcription and thus is required to restrict influenza virus replication. These data identify a novel regulator of the antiviral gene program in humans and provide insights into the multilayered regulatory network that controls the innate immune response.

Long noncoding RNAs (lncRNAs) have emerged as critical regulators of gene expression, yet their contribution to immune regulation in humans remains poorly understood. Here, we report that the primate-specific lncRNA CHROMR is induced by influenza A virus and SARS-CoV-2 infection and coordinates the expression of interferon-stimulated genes (ISGs) that execute antiviral responses. CHROMR depletion in human macrophages reduces histone acetylation at regulatory regions of ISG loci and attenuates ISG expression in response to microbial stimuli. Mechanistically, we show that CHROMR sequesters the interferon regulatory factor (IRF)-2-dependent transcriptional corepressor IRF2BP2, thereby licensing IRF-dependent signaling and transcription of the ISG network. Consequently, CHROMR expression is essential to restrict viral infection of macrophages. Our findings identify CHROMR as a key arbitrator of antiviral innate immune signaling in humans.

Bifurcation of signalling in human innate immune pathways to NF-kB and IRF family activation

The human innate immune response can be activated through a wide range of stimuli. This multi-faceted system can be triggered by a range of immunostimulants including pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). These stimuli drive intracellular signalling pathways that branch off downstream to activate several distinct transcription factors. The two most impactful of which in innate immune outcomes are the NF-κB and the IRF family members. Both transcription factor families play defining roles in driving inflammation as well as the antiviral response. Pathways leading to their simultaneous activation share common upstream components but eventually distinct regulators which directly facilitate their activation. This review will discuss the current state of knowledge about what is known about how these pathways bifurcate to activate NF-κB and IRF family members.

Re-Examining Rotavirus Innate Immune Evasion: Potential Applications of the Reverse Genetics System

Rotaviruses represent one of the most successful pathogens in the world, with high infectivity and efficient transmission between the young of many animal species, including humans. To overcome host defenses, rotaviruses have evolved a plethora of strategies to effectively evade the innate immune response, establish initial infection in the small intestine, produce progeny, and shed into the environment. Previously, studying the roles and relative contributions of specific rotaviral factors in innate immune evasion had been challenging without a plasmid-only reverse genetics system. Although still in its infancy, current reverse genetics technology will help address important research questions regarding rotavirus innate immune evasion, host range restriction, and viral pathogenesis. In this review, we summarize the current knowledge about the antiviral host innate immune defense mechanisms, countermeasures of rotavirus-encoded factors, and strategies to better understand these interactions using the rotavirus reverse genetics system.

Toosendanin suppresses African swine fever virus replication through upregulating interferon regulatory factor 1 in porcine alveolar macrophage cultures

African swine fever virus (ASFV) is a highly infectious and lethal swine pathogen that causes severe socio-economic consequences in affected countries. Unfortunately, effective vaccine for combating ASF is unavailable so far, and the prevention and control strategies for ASFV are still very limited. Toosendanin (TSN), a triterpenoid saponin extracted from the medicinal herb Melia toosendan Sieb. Et Zucc, has been demonstrated to possess analgesic, anti-inflammatory, anti-botulism and anti-microbial activities, and was used clinically as an anthelmintic, while the antiviral effect of TSN on ASFV has not been reported. In this study, we revealed that TSN exhibited a potent inhibitory effect on ASFV GZ201801-38 strain in porcine alveolar macrophages (PAMs; EC₅₀ = 0.085 μM, SI = 365) in a dose-dependent manner. TSN showed robust antiviral activity in different doses of ASFV infection and reduced the transcription and translation levels of ASFV p30 protein, viral genomic DNA quantity as well as viral titer at 24 and 48 h post-infection. In addition, TSN did not affect virion attachment and release but intervened in its internalization in PAMs. Further investigations disclosed that TSN played its antiviral role by upregulating the host IFN-stimulated gene (ISG) IRF1 rather than by directly inactivating the virus particles. Overall, our results suggest that TSN is an effective antiviral agent against ASFV replication in vitro and may have the potential for clinical use.

XAF1 Protects Host against Emerging RNA Viruses by Stabilizing IRF1-Dependent Antiviral Immunity

XIAP-associated factor 1 (XAF1) is an interferon (IFN)-stimulated gene (ISG) that enhances IFN-induced apoptosis. However, it is unexplored whether XAF1 is essential for the host fighting against invaded viruses. Here, we find that XAF1 is significantly upregulated in the host cells infected with emerging RNA viruses, including influenza, Zika virus (ZIKV), and SARS-CoV-2. IFN regulatory factor 1 (IRF1), a key transcription factor in immune cells, determines the induction of XAF1 during antiviral immunity. Ectopic expression of XAF1 protects host cells against various RNA viruses independent of apoptosis. Knockout of XAF1 attenuates host antiviral innate immunity in vitro and in vivo, which leads to more severe lung injuries and higher mortality in the influenza infection mouse model. XAF1 stabilizes IRF1 protein by antagonizing the CHIP-mediated degradation of IRF1, thus inducing more antiviral IRF1 target genes, including DDX58, DDX60, MX1, and OAS2. Our study has described a protective role of XAF1 in the host antiviral innate immunity against RNA viruses. We have also elucidated the molecular mechanism that IRF1 and XAF1 form a positive feedback loop to induce rapid and robust antiviral immunity. IMPORTANCE Rapid and robust induction of antiviral genes is essential for the host to clear the invaded viruses. In addition to the IRF3/7-IFN-I-STAT1 signaling axis, the XAF1-IRF1 positive feedback loop synergistically or independently drives the transcription of antiviral genes. Moreover, XAF1 is a sensitive and reliable gene that positively correlates with the viral infection, suggesting that XAF1 is a potential diagnostic marker for viral infectious diseases. In addition to the antitumor role, our study has shown that XAF1 is essential for antiviral immunity. XAF1 is not only a proapoptotic ISG, but it also stabilizes the master transcription factor IRF1 to induce antiviral genes. IRF1 directly binds to the IRF-Es of its target gene promoters and drives their transcriptions, which suggests a unique role of the XAF1-IRF1 loop in antiviral innate immunity, particularly in the host defect of IFN-I signaling such as invertebrates.

CD24 Expression Dampens the Basal Antiviral State in Human Neuroblastoma Cells and Enhances Permissivity to Zika Virus Infection

Zika virus (ZIKV) exhibits distinct selectivity for infection of various cells and tissues, but how host cellular factors modulate varying permissivity remains largely unknown. Previous studies showed that the neuroblastoma cell line SK-N-AS (expressing low levels of cellular protein CD24) was highly restricted for ZIKV infection, and that this restriction was relieved by ectopic expression of CD24. We tested the hypothesis that CD24 expression allowed ZIKV replication by suppression of the antiviral response. SK-N-AS cells expressing an empty vector (termed CD24-low cells) showed elevated basal levels of phosphorylated STAT1, IRF-1, IKKE, and NFκB. In response to exogenously added type I interferon (IFN-I), CD24-low cells had higher-level induction of antiviral genes and activity against two IFN-I-sensitive viruses (VSV and PIV5-P/V) compared to SK-N-AS cells with ectopic CD24 expression (termed CD24-high cells). Media-transfer experiments showed that the inherent antiviral state of CD24-low cells was not dependent on a secreted factor such as IFN-I. Transcriptomics analysis revealed that CD24 expression decreased expression of genes involved in intracellular antiviral pathways, including IFN-I, NFκB, and Ras. Our findings that CD24 expression in neuroblastoma cells represses intracellular antiviral pathways support the proposal that CD24 may represent a novel biomarker in cancer cells for susceptibility to oncolytic viruses.

Lipopolysaccharide-induced interferon response networks at birth are predictive of severe viral lower respiratory infections in the first year of life

Appropriate innate immune function is essential to limit pathogenesis and severity of severe lower respiratory infections (sLRI) during infancy, a leading cause of hospitalization and risk factor for subsequent asthma in this age group. Employing a systems biology approach to analysis of multi-omic profiles generated from a high-risk cohort (n=50), we found that the intensity of activation of an LPS-induced interferon gene network at birth was predictive of sLRI risk in infancy (AUC=0.724). Connectivity patterns within this network were stronger among susceptible individuals, and a systems biology approach identified IRF1 as a putative master regulator of this response. These findings were specific to the LPS-induced interferon response and were not observed following activation of viral nucleic acid sensing pathways. Comparison of responses at birth versus age 5 demonstrated that LPS-induced interferon responses but not responses triggered by viral nucleic acid sensing pathways may be subject to strong developmental regulation. These data suggest that the risk of sLRI in early life is in part already determined at birth, and additionally that the developmental status of LPS-induced interferon responses may be a key determinant of susceptibility. Our findings provide a rationale for the identification of at-risk infants for early intervention aimed at sLRI prevention and identifies targets which may be relevant for drug development.

SARS-CoV-2 infection impairs the insulin/IGF signaling pathway in the lung, liver, adipose tissue, and pancreatic cells via IRF1

BACKGROUND

COVID-19 can cause multiple organ damages as well as metabolic abnormalities such as hyperglycemia, insulin resistance, and new onset of diabetes. The insulin/IGF signaling pathway plays an important role in regulating energy metabolism and cell survival, but little is known about the impact of SARS-CoV-2 infection. The aim of this work was to investigate whether SARS-CoV-2 infection impairs the insulin/IGF signaling pathway in the host cell/tissue, and if so, the potential mechanism and association with COVID-19 pathology.

METHODS

To determine the impact of SARS-CoV-2 on insulin/IGF signaling pathway, we utilized transcriptome datasets of SARS-CoV-2 infected cells and tissues from public repositories for a wide range of high-throughput gene expression data: autopsy lungs from COVID-19 patients compared to the control from non-COVID-19 patients; lungs from a human ACE2 transgenic mouse infected with SARS-CoV-2 compared to the control infected with mock; human pluripotent stem cell (hPSC)-derived liver organoids infected with SARS-CoV-2; adipose tissues from a mouse model of COVID-19 overexpressing human ACE2 via adeno-associated virus serotype 9 (AAV9) compared to the control GFP after SARS-CoV-2 infection; iPS-derived human pancreatic cells infected with SARS-CoV-2 compared to the mock control. Gain and loss of IRF1 function models were established in HEK293T and/or Calu3 cells to evaluate the impact on insulin signaling. To understand the mechanistic regulation and relevance with COVID-19 risk factors, such as older age, male sex, obesity, and diabetes, several transcriptomes of human respiratory, metabolic, and endocrine cells and tissue were analyzed. To estimate the association with COVID-19 severity, whole blood transcriptomes of critical patients with COVID-19 compared to those of hospitalized noncritical patients with COVID-19.

RESULTS

We found that SARS-CoV-2 infection impaired insulin/IGF signaling pathway genes, such as IRS, PI3K, AKT, mTOR, and MAPK, in the host lung, liver, adipose tissue, and pancreatic cells. The impairments were attributed to interferon regulatory factor 1 (IRF1), and its gene expression was highly relevant to risk factors for severe COVID-19; increased with aging in the lung, specifically in men; augmented by obese and diabetic conditions in liver, adipose tissue, and pancreatic islets. IRF1 activation was significantly associated with the impaired insulin signaling in human cells. IRF1 intron variant rs17622656-A, which was previously reported to be associated with COVID-19 prevalence, increased the IRF1 gene expression in human tissue and was frequently found in American and European population. Critical patients with COVID-19 exhibited higher IRF1 and lower insulin/IGF signaling pathway genes in the whole blood compared to hospitalized noncritical patients. Hormonal interventions, such as dihydrotestosterone and dexamethasone, ameliorated the pathological traits in SARS-CoV-2 infectable cells and tissues.

CONCLUSIONS

The present study provides the first scientific evidence that SARS-CoV-2 infection impairs the insulin/IGF signaling pathway in respiratory, metabolic, and endocrine cells and tissues. This feature likely contributes to COVID-19 severity with cell/tissue damage and metabolic abnormalities, which may be exacerbated in older, male, obese, or diabetic patients.

Revisiting IRF1-mediated antiviral innate immunity

Many studies have been conducted over the last few decades to understand better the functions of IRF3 and IRF7 in antiviral immune responses. However, the precise underlying molecular mechanism of IRF1-mediated immune response remains largely unknown. Recent studies indicate that IRF1 exerts strong antiviral activities against several viral infections through diverse mechanisms, both in IFN-dependent and IFN-independent manners. Nevertheless, the efficacy and kinetics of inducing IFNs and ISGs remain unknown. Here we summarize the recent advances in IRF1 research and highlight its potential roles in initiating IFN immune responses and subsequent IRF1-triggering antiviral responses. Challenges regarding the IFN positive feedback mediated by IRF7 during infection will be discussed; this classical loop may also be mediated in part by IRF1. Therefore, we propose a revised model that may help decipher the functional roles of IRF1 in antiviral immunity.

Transient Increases in Inflammation and Proapoptotic Potential Are Associated with the HESN Phenotype Observed in a Subgroup of Kenyan Female Sex Workers

Interferon (IFN) -stimulated genes (ISGs) are critical effectors of IFN response to viral infection, but whether ISG expression is a correlate of protection against HIV infection remains elusive. A well-characterized subcohort of Kenyan female sex workers, who, despite being repeatedly exposed to HIV-1 remain seronegative (HESN), exhibit reduced baseline systemic and mucosal immune activation. This study tested the hypothesis that regulation of ISGs in the cells of HESN potentiates a robust antiviral response against HIV. Transcriptional profile of a panel of ISGs with antiviral function in PBMC and isolated CD4+ T cells from HESN and non-HESN sex worker controls were defined following exogenous IFN-stimulation using relative RT-qPCR. This study identified a unique profile of proinflammatory and proapoptotic ISGs with robust but transient responses to exogenous IFN-γ and IFN-α2 in HESN cells. In contrast, the non-HESN cells had a strong and prolonged proinflammatory ISG profile at baseline and following IFN challenge. Potential mechanisms may include augmented bystander apoptosis due to increased TRAIL expression (16-fold), in non-HESN cells. The study also identified two negative regulators of ISG induction associated with the HESN phenotype. Robust upregulation of SOCS-1 and IRF-1, in addition to HDM2, could contribute to the strict regulation of proinflammatory and proapoptotic ISGs in HESN cells. As reducing IRF-1 in the non-HESN cells resulted in the identified HESN ISG profile, and decreased HIV susceptibility, the unique HESN ISG profile could be a correlate of protection against HIV infection.

Poly(I:C) transfection induces a pro-inflammatory cascade in murine mammary carcinoma and fibrosarcoma cells

Germline-encoded pattern recognition receptors [PRRs] in mammalian cells function in the detection of molecular patterns associated with pathogen invasion or cellular damage. A PRR subset is activated by the atypical presence and location of double-stranded RNA [dsRNA] or its synthetic analogue polyinosinic-polycytidylic acid [poly(I:C)], triggering pro-inflammatory signalling and death in many cell types. Poly(I:C) has been tested as a sole or combination cancer therapy in preclinical studies and clinical trials. The purpose of this study was to evaluate the effects of poly(I:C) transfection via electroporation on cell lines from a cancer of epithelial origin, 4T1 mammary carcinoma, and a cancer of mesenchymal origin, WEHI 164 fibrosarcoma. The effects of the poly(I:C) delivery on cell metabolism implicate the induction of cell death. A pro-inflammatory response was demonstrated by mRNA upregulation and the secretion of Type I interferon and several cytokines and chemokines. The mRNAs of dsRNA sensor DExD/H-box helicase 58/retinoic acid-inducible gene I protein [Ddx58/RIG-I] and sensor/co-sensor DEAH-box helicase 9 [Dhx9] were not regulated, but the mRNAs of RNA sensors toll-like receptor 3 [TLR3], interferon-induced with helicase C domain 1/melanoma differentiation-associated protein 5 [Ifih1/MDA5] and Z-DNA binding protein 1 [Zbp1] and co-sensors DEAD (Asp-Glu-Ala-Asp) box polypeptide 60 [Ddx60] and interferon-inducible protein 204 [Ifi204] were upregulated in both cell lines. The mRNAs encoding signalling pathways components were present or upregulated in both cell types. These data demonstrate that RNA sensing effects can be amplified by electroporation delivery, potentially expanding the practicality of this immunotherapeutic approach.

Overexpression screen of interferon-stimulated genes identifies RARRES3 as a restrictor of Toxoplasma gondii infection

Toxoplasma gondii is an important human pathogen infecting an estimated one in three people worldwide. The cytokine interferon gamma (IFNγ) is induced during infection and is critical for restricting T. gondii growth in human cells. Growth restriction is presumed to be due to the induction of interferon-stimulated genes (ISGs) that are upregulated to protect the host from infection. Although there are hundreds of ISGs induced by IFNγ, their individual roles in restricting parasite growth in human cells remain somewhat elusive. To address this deficiency, we screened a library of 414 IFNγ induced ISGs to identify factors that impact T. gondii infection in human cells. In addition to IRF1, which likely acts through the induction of numerous downstream genes, we identified RARRES3 as a single factor that restricts T. gondii infection by inducing premature egress of the parasite in multiple human cell lines. Overall, while we successfully identified a novel IFNγ induced factor restricting T. gondii infection, the limited number of ISGs capable of restricting T. gondii infection when individually expressed suggests that IFNγ-mediated immunity to T. gondii infection is a complex, multifactorial process.

Candidate genes of SARS-CoV-2 gender susceptibility

The severe acute respiratory syndrome coronavirus (SARS-CoV-2) initiated a global viral pandemic since late 2019. Understanding that Coronavirus disease (COVID-19) disproportionately affects men than women results in great challenges. Although there is a growing body of published study on this topic, effective explanations underlying these sex differences and their effects on the infection outcome still remain uncertain. We applied a holistic bioinformatics method to investigate molecular variations of known SARS-CoV-2 interacting human proteins mainly expressed in gonadal tissues (testis and ovary), allowing for the identification of potential genetic targets for this infection. Functional enrichment and interaction network analyses were also performed to better investigate the biological differences between testicular and ovarian responses in the SARS-CoV-2 infection, paying particular attention to genes linked to immune-related pathways, reactions of host cells after intracellular infection, steroid hormone biosynthesis, receptor signaling, and the complement cascade, in order to evaluate their potential association with sexual difference in the likelihood of infection and severity of symptoms. The analysis revealed that within the testis network TMPRSS2, ADAM10, SERPING1, and CCR5 were present, while within the ovary network we found BST2, GATA1, ENPEP, TLR4, TLR7, IRF1, and IRF2. Our findings could provide potential targets for forthcoming experimental investigation related to SARS-CoV-2 treatment.

KrasG12D induces changes in chromatin territories that differentially impact early nuclear reprogramming in pancreatic cells

BACKGROUND

Pancreatic ductal adenocarcinoma initiation is most frequently caused by Kras mutations.

RESULTS

Here, we apply biological, biochemical, and network biology methods to validate GEMM-derived cell models using inducible KrasG12D expression. We describe the time-dependent, chromatin remodeling program that impacts function during early oncogenic signaling. We find that the KrasG12D-induced transcriptional response is dominated by downregulated expression concordant with layers of epigenetic events. More open chromatin characterizes the ATAC-seq profile associated with a smaller group of upregulated genes and epigenetic marks. RRBS demonstrates that promoter hypermethylation does not account for the silencing of the extensive gene promoter network. Moreover, ChIP-Seq reveals that heterochromatin reorganization plays little role in this early transcriptional program. Notably, both gene activation and silencing primarily depend on the marking of genes with a combination of H3K27ac, H3K4me3, and H3K36me3. Indeed, integrated modeling of all these datasets shows that KrasG12D regulates its transcriptional program primarily through unique super-enhancers and enhancers, and marking specific gene promoters and bodies. We also report chromatin remodeling across genomic areas that, although not contributing directly to cis-gene transcription, are likely important for KrasG12D functions.

CONCLUSIONS

In summary, we report a comprehensive, time-dependent, and coordinated early epigenomic program for KrasG12D in pancreatic cells, which is mechanistically relevant to understanding chromatin remodeling events underlying transcriptional outcomes needed for the function of this oncogene.

Integrated transcriptome profiling in THP-1 macrophages infected with bunyavirus SFTSV

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne bunyavirus that causes an emerging hemorrhagic fever termed SFTS with high mortality. However, knowledge of SFTSV-host interactions is largely limited. Here, we performed a global transcriptome analysis of mRNAs and lncRNAs in THP-1 macrophages infected with SFTSV for 24 and 48 h. A total of 2,334 differentially expressed mRNAs and 154 differentially expressed lncRNAs were identified with 577 mRNAs and 31 lncRNAs commonly changed at both time points. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that differentially expressed mRNAs were mainly associated with innate immune, cytokine signaling, systemic lupus erythematosus, and alcoholism. Differentially expressed lncRNAs were enriched in systemic lupus erythematosus, alcoholism, and ribosome. Bioinformatic analysis also revealed hub regulatory mRNAs including IL6, TNF, UBA52, SRC, IL10, CXCL10, and CDK1 and core regulatory lncRNAs including XLOC_083027 and XLOC_113317. Transcription factor analysis of the differentially expressed mRNAs revealed that IRF1, SPI1, SPIB, ELF5, and FEV were enriched during SFTSV infection. Taken together, our studies illustrate the complex interaction between THP-1 macrophages and SFTSV.

Comparative Analysis of Six IRF Family Members in Alveolar Epithelial Cell-Intrinsic Antiviral Responses

Host cell-intrinsic antiviral responses are largely mediated by pattern-recognition receptor (PRR) signaling and the interferon (IFN) system. The IFN regulatory factor (IRF) family of transcription factors takes up a central role in transcriptional regulation of antiviral innate immunity. IRF3 and IRF7 are known to be key players downstream of PRRs mediating the induction of type I and III IFNs. IFN signaling then requires IRF9 for the expression of the full array of interferon stimulated genes (ISGs) ultimately defining the antiviral state of the cell. Other members of the IRF family clearly play a role in mediating or modulating IFN responses, such as IRF1, IRF2 or IRF5, however their relative contribution to mounting a functional antiviral response is much less understood. In this study, we systematically and comparatively assessed the impact of six members of the IRF family on antiviral signaling in alveolar epithelial cells. We generated functional knockouts of IRF1, -2, -3, -5, -7, and -9 in A549 cells, and measured their impact on the expression of IFNs and further cytokines, ISGs and other IRFs, as well as on viral replication. Our results confirmed the vital importance of IRF3 and IRF9 in establishing an antiviral state, whereas IRF1, 5 and 7 were largely dispensable. The previously described inhibitory activity of IRF2 could not be observed in our experimental system.

Comparison of transcriptional responses between pathogenic and nonpathogenic hantavirus infections in Syrian hamsters using NanoString

BACKGROUND

Syrian hamsters infected with Andes virus (ANDV) develop a disease that recapitulates many of the salient features of human hantavirus pulmonary syndrome (HPS), including lethality. Infection of hamsters with Hantaan virus (HTNV) results in an asymptomatic, disseminated infection. In order to explore this dichotomy, we examined the transcriptome of ANDV- and HTNV-infected hamsters.

RESULTS

Using NanoString technology, we examined kinetic transcriptional responses in whole blood collected from ANDV- and HTNV-infected hamsters. Of the 770 genes analyzed, key differences were noted in the kinetics of type I interferon sensing and signaling responses, complement activation, and apoptosis pathways between ANDV- and HTNV-infected hamsters.

CONCLUSIONS

Delayed activation of type I interferon responses in ANDV-infected hamsters represents a potential mechanism that ANDV uses to subvert host immune responses and enhance disease. This is the first genome-wide analysis of hantavirus-infected hamsters and provides insight into potential avenues for therapeutics to hantavirus disease.

The single-cell epigenomic and transcriptional landscape of immunity to influenza vaccination

Emerging evidence indicates a fundamental role for the epigenome in immunity. Here, we mapped the epigenomic and transcriptional landscape of immunity to influenza vaccination in humans at the single-cell level. Vaccination against seasonal influenza induced persistently diminished H3K27ac in monocytes and myeloid dendritic cells (mDCs), which was associated with impaired cytokine responses to Toll-like receptor stimulation. Single-cell ATAC-seq analysis revealed an epigenomically distinct subcluster of monocytes with reduced chromatin accessibility at AP-1-targeted loci after vaccination. Similar effects were observed in response to vaccination with the AS03-adjuvanted H5N1 pandemic influenza vaccine. However, this vaccine also stimulated persistently increased chromatin accessibility at interferon response factor (IRF) loci in monocytes and mDCs. This was associated with elevated expression of antiviral genes and heightened resistance to the unrelated Zika and Dengue viruses. These results demonstrate that vaccination stimulates persistent epigenomic remodeling of the innate immune system and reveal AS03's potential as an epigenetic adjuvant.

Multi-omics analysis of respiratory specimen characterizes baseline molecular determinants associated with SARS-CoV-2 outcome

Rapid diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection still remains a major challenge. A multi-omic approach was adopted to analyze the respiratory specimens of 20 SARS-CoV-2-positive, 20 negative and 15 H1N1 pdm 2009 positive cases. Increased basal level of MX1 (MX dynamin-like GTPase 1) and WARS (tryptophan-tRNA ligase) correlated with SARS-CoV-2 infection and its outcome. These markers were further validated in 200 suspects. MX1>30pg/ml and WARS>25ng/ml segregated virus positives [AUC = 94% CI: (0.91–0.97)] and severe patients [AUC>0.85%]. Our results documented significant increase in immune activation; metabolic reprograming and decrease in oxygen transport, wound healing and others linked proteins and metabolites in patients with coronavirus disease 2019 (COVID-19). Multi-omics profiling correlated with viremia and segregated asymptomatic patients with COVID-19. Additionally, we identified increased respiratory pathogens (Burkholderiales, Klebsiella pneumonia) and decreased lactobacillus salivarius (FDR<0.05) in COVID-19 specimens. In conclusion, increased basal MX1 and WARS levels correlates with SARS-CoV-2 infection and could aid in the identification of patient's predisposed to higher severity.

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Multi-omics analysis of respiratory specimen is distinct in SARS-CoV-2 infection

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Change in oropharyngeal metaproteome correlates with SARS-CoV-2 infection

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Multi-omics analysis reveals various process regulated by SARS-CoV-2 infection

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Increased basal MX1 and WARS could segregate patients with severe and positive SARS-CoV-2