Structural insights into interferon regulatory factor activation

Crystal Structures of DNA-bound Fish IRF10 and IRF11 Reveal the Determinants of IFN Regulation

IFN regulatory factors (IRFs) are transcription factors that mediate homeostatic mechanisms of host defense against pathogens. In addition to IRF1-9, which are conserved across vertebrates, teleost fishes have two other IRFs, IRF10 and IRF11. In zebrafish (Danio rerio), IRF10 represses the expression of IFNφ1 and IFNφ3, whereas IRF11 exerts the opposite effect. In this study, we found IRF10 could significantly inhibit the expression of IFNφ1 and IFNφ3 induced by IFN11 to synergistically regulate type I IFN expression. To clarify the synergistically regulatory mechanism of IRF10 and IRF11 in type I IFN expression, we determined and analyzed the crystal structures of the DNA-binding domains (DBDs) of zebrafish IRF10 and IRF11 bound to DNA, as well as IRF11 DBD in apo form. The interactions of IRF10-DBD and IRF11-DBD with DNA backbone were elaborated in detail. Further analysis showed that IRF10 and IRF11 have the same binding patterns and comparable affinities with the IFN-sensitive response elements of IFNφ1 and IFNφ3 promoters. Therefore, IRF10 could function as a controlling factor for IRF11 by competitive binding of the IFN-sensitive response elements to coregulate the host IFN response. Accordingly, similar to IRF1 and IRF2 in mammals, IRF10 and IRF11 act as another pair of negative and positive regulators to balance the antiviral responses in fish.

IRF7 Exacerbates Candida albicans Infection by Compromising CD209-Mediated Phagocytosis and Autophagy-Mediated Killing in Macrophages

IFN regulatory factor 7 (IRF7) exerts anti-infective effects by promoting the production of IFNs in various bacterial and viral infections, but its role in highly morbid and fatal Candida albicans infections is unknown. We unexpectedly found that Irf7 gene expression levels were significantly upregulated in tissues or cells after C. albicans infection in humans and mice and that IRF7 actually exacerbates C. albicans infection in mice independent of its classical function in inducing IFNs production. Compared to controls, Irf7-/- mice showed stronger phagocytosis of fungus, upregulation of C-type lectin receptor CD209 expression, and enhanced P53-AMPK-mTOR-mediated autophagic signaling in macrophages after C. albicans infection. The administration of the CD209-neutralizing Ab significantly hindered the phagocytosis of Irf7-/- mouse macrophages, whereas the inhibition of p53 or autophagy impaired the killing function of these macrophages. Thus, IRF7 exacerbates C. albicans infection by compromising the phagocytosis and killing capacity of macrophages via regulating CD209 expression and p53-AMPK-mTOR-mediated autophagy, respectively. This finding reveals a novel function of IRF7 independent of its canonical IFNs production and its unexpected role in enhancing fungal infections, thus providing more specific and effective targets for antifungal therapy.

Transcriptional control of metabolism by interferon regulatory factors

Interferon regulatory factors (IRFs) comprise a family of nine transcription factors in mammals. IRFs exert broad effects on almost all aspects of immunity but are best known for their role in the antiviral response. Over the past two decades, IRFs have been implicated in metabolic physiology and pathophysiology, partly as a result of their known functions in immune cells, but also because of direct actions in adipocytes, hepatocytes, myocytes and neurons. This Review focuses predominantly on IRF3 and IRF4, which have been the subject of the most intense investigation in this area. IRF3 is located in the cytosol and undergoes activation and nuclear translocation in response to various signals, including stimulation of Toll-like receptors, RIG-I-like receptors and the cGAS-STING pathways. IRF3 promotes weight gain, primarily by inhibiting adipose thermogenesis, and also induces inflammation and insulin resistance using both weight-dependent and weight-independent mechanisms. IRF4, meanwhile, is generally pro-thermogenic and anti-inflammatory and has profound effects on lipogenesis and lipolysis. Finally, new data are emerging on the role of other IRF family members in metabolic homeostasis. Taken together, data indicate that IRFs serve as critical yet underappreciated integrators of metabolic and inflammatory stress.

Interferon regulatory factor 7 in inflammation, cancer and infection

Interferon regulatory factor 7 (IRF7), a member of the interferon regulatory factors (IRFs) family, is located downstream of the pattern recognition receptors (PRRs)-mediated signaling pathway and is essential for the production of type I interferon (IFN-I). Activation of IRF7 inhibits various viral and bacterial infections and suppresses the growth and metastasis of some cancers, but it may also affect the tumor microenvironment and promote the development of other cancers. Here, we summarize recent advances in the role of IRF7 as a multifunctional transcription factor in inflammation, cancer and infection by regulating IFN-I production or IFN-I-independent signaling pathways.

Transglutaminase type 2-dependent crosslinking of IRF3 in dying melanoma cells

cGAS/STING axis is the major executor of cytosolic dsDNA sensing that leads to the production of type I interferon (IFNI) not only upon bacterial infection, but also in cancer cells, upon DNA damage. In fact, DNA damage caused by ionizing radiations and/or topoisomerase inhibitors leads to a release of free DNA into the cytosol, which activates the cGAS/STING pathway and the induction of IFNI expression. Doxorubicin-induced apoptotic cancer cells release damage-associated molecular patterns (DAMPs), including IFNI, which are able to stimulate the immune system. Our results indicate that Transglutaminase type 2 (TG2) is directly involved in the formation of a covalent cross-linked IRF3 (Interferon regulatory factor 3) dimers, thereby limiting the production of IFNI. Indeed, we demonstrated that upon doxorubicin treatment TG2 translocates into the nucleus of apoptotic melanoma cells interacting with IRF3 dimers. Interestingly, we show that both the knockdown of the enzyme as well as the inhibition of its transamidating activity lead to a decrease in the dimerization of IRF3 correlated with an increase in the IFNI mRNA levels. Taken together, these data demonstrate that TG2 negatively regulates the IRF3 pathway in human melanoma cells suggesting a so far unknown TG2-dependent mechanism by which cancer cells reduce the IFNI production after DNA damage to limit the immune system response.

Negative regulation of interferon regulatory factor 6 (IRF6) in interferon and NF-κB signalling pathways of common carp (Cyprinus carpio L.)

BACKGROUND

Interferon (IFN) regulatory factors (IRFs) is a kind of transcription factors, which play an important role in regulating the expression of type I IFN and related genes. In mammals, IRF6 is not relevant with IFN expression, while zebrafish IRF6 was reported to be a positive regulator of IFN expression and could be phosphorylated by both MyD88 and TBK1. However, the role of IRF6 in the immune response and IFN transcription of common carp is unknown.

RESULTS

In the present study, the cDNA of IRF6 gene (CcIRF6) was cloned from common carp using RACE technique, with a total length of 1905 bp, encoding 471 amino acid residues, which possesses two functional domains of DBD and IAD. Similarity analysis showed that CcIRF6 had more than 50% similarity with IRFs of other vertebrates, and had the highest similarity with grass carp and zebrafish, among which the DBD domain was much more conserved. The phylogenetic analysis showed that CcIRF6 is in the branch of Osteichthyes and has the closest relationship with grass carp. In healthy common carp, the CcIRF6 was expressed in all the examined tissues, with the highest level in the oral epithelium, and the lowest level in the head kidney. After intraperitoneal injection of poly(I:C) or Aeromonas hydrophila, the expression of CcIRF6 increased in spleen, head kidney, foregut and hindgut of common carp. Moreover, poly(I:C), LPS, PGN and flagellin induced the expression of CcIRF6 in peripheral leukocytes and head kidney leukocytes of common carp in vitro. In EPC cells, CcIRF6 inhibited the expression of some IFN-related genes and pro-inflammatory cytokines, and dual luciferase reporter assay showed that CcIRF6 reduced the activity of IFN and NF-κB reporter genes.

CONCLUSIONS

The present study suggests that CcIRF6 is involved in the antiviral and antibacterial immune response of common carp, and negatively regulate the expression of IFN and NF-κB signalling pathways, which provides a theoretical basis for the study and prevention of fish disease pathogenesis.

Avian IRF1 and IRF7 Play Overlapping and Distinct Roles in Regulating IFN-Dependent and -Independent Antiviral Responses to Duck Tembusu Virus Infection

Avian interferon regulatory factors 1 and 7 (IRF1 and IRF7) play important roles in the host’s innate immunity against viral infection. Our previous study revealed that duck tembusu virus (DTMUV) infection of chicken fibroblasts (DF1) and duck embryo fibroblasts (DEFs) induced the expression of a variety of IFN-stimulated genes (ISGs), including VIPERIN, IFIT5, CMPK2, IRF1, and IRF7. IRF1 was further shown to play a significant role in regulating the up-expression of VIPERIN, IFIT5, and CMPK2 and inhibiting DTMUV replication. In this study, we confirm, through overexpression and knockout approaches, that both IRF1 and IRF7 inhibit DTMUV replication, mainly via regulation of type I IFN expression, as well as the induction of IRF1, VIPERIN, IFIT5, CMPK2, and MX1. In addition, IRF1 directly promoted the expression of VIPERIN and CMPK2 in an IFN-independent manner when IRF7 and type I IFN signaling were undermined. We also found that non-structural protein 2B (NS2B) of DTMUV was able to inhibit the induction of IFN-β mRNA triggered by Newcastle disease virus (NDV) infection or poly(I:C) treatment, revealing a strategy employed by DTMUV to evade host’s immunosurveillance. This study demonstrates that avian IRF7 and IRF1 play distinct roles in the regulation of type I IFN response during DTMUV infection.

Modulation of fish immune response by interferon regulatory factor 4 in redlip mullet (Liza haematocheilus): Delineation through expression profiling, antiviral assay, and macrophage polarization analysis

Interferon regulatory factor 4 (IRF4) is a crucial member of IRF family, which acts as an imperative transcription factor in the development and maturation of multiple lineages of blood cells and also plays a pivotal role in host defense against microbial infections. In the present study, we aimed to investigate the detailed structural and functional aspects of a redlip mullet IRF4 homolog (LhIRF4). The LhIRF4 open reading frame consists of 1347 base pairs encoding 449 amino acids, with the DNA-binding domain sharing significant homology with that of other vertebrate IRF4 homologs. The highest transcription levels of LhIRF4 were observed in the mullet intestine and spleen under normal physiological conditions. Furthermore, a time-dependent upregulation of LhIRF4 transcription was observed in the spleen and head kidney tissues upon pathogenic challenges. When overexpressed in mullet cells, LhIRF4 was localized to the nucleus and significantly stimulated the transcription of several host antiviral genes. Moreover, the overexpression of LhIRF4 strongly inhibited the replication of viral hemorrhagic septicemia virus (VHSV) in vitro. The function of LhIRF4 in regulation of macrophage M2 polarization has also been evidently demonstrated in RAW 264.7 cells. Taken together, our findings indicate the profound role of LhIRF4 in modulating immune responses against microbial infections in redlip mullet.

Structure and expression identification of Cherry Valley duck IRF8

Interferon regulatory factor 8 (IRF8) is also known as interferon (IFN) consensus sequence binding protein (ICSBP), which plays an important role in IFN signal transduction. In this study, we cloned the full-length coding sequence of Cherry Valley duck IRF8 (duIRF8) and analyzed its structure. In addition, we tested the distribution of IRF8 in the tissues of healthy Cherry Valley ducks, and the changes in IRF8 expression levels in the tissues after virus infection. The results show that the open reading frame (ORF) of IRF8 is 1293 bp, encodes 430 amino acids, and have 3 conserved domains: the N-terminal DBD domain, the C-terminal IAD domain, and the NLS domain. Besides, from the analysis of the phylogenetic tree, it can be known that the duIRF8 has the highest homology with the anser cygnoides, and has less homology with the fish. Analyzing the distribution level of IRF8 in the tissues, it is found that the expression level of IRF8 in the liver of Cherry Valley duck is the highest. However, after infection with duck Tambusu virus, novel duck reovirus, and duck plague virus, the expression of IRF8 in the spleen and brain all showed up-regulation. These data indicate that IRF8 is involved in the host's innate immune response against virus in Cherry Valley duck.

Regulation of antiviral innate immune signaling and viral evasion following viral genome sensing

A harmonized balance between positive and negative regulation of pattern recognition receptor (PRR)-initiated immune responses is required to achieve the most favorable outcome for the host. This balance is crucial because it must not only ensure activation of the first line of defense against viral infection but also prevent inappropriate immune activation, which results in autoimmune diseases. Recent studies have shown how signal transduction pathways initiated by PRRs are positively and negatively regulated by diverse modulators to maintain host immune homeostasis. However, viruses have developed strategies to subvert the host antiviral response and establish infection. Viruses have evolved numerous genes encoding immunomodulatory proteins that antagonize the host immune system. This review focuses on the current state of knowledge regarding key host factors that regulate innate immune signaling molecules upon viral infection and discusses evidence showing how specific viral proteins counteract antiviral responses via immunomodulatory strategies.

Chicken interferon regulatory factor 7 (IRF7) can control ALV-J virus infection by triggering type I interferon production through affecting genes related with innate immune signaling pathway

In order to breed new birds with strong disease resistance, it is necessary to first understand the mechanism of avian antiviral response. Interferon regulatory factor 7 (IRF7) is not only a member of type I interferons (IFNs) regulatory factor (IRFs) family, but also a major regulator of the IFN response in mammals. However, whether IRF7 is involved in the host innate immune response remains unclear in poultry, due to the absence of IRF3. Here, we first observed by HE stains that with the increase of the time of ALV-J challenge, the thymus was obviously loose and swollen, the arrangement of liver cell was disordered, and the bursa of fabricius formed vacuolated. Real-time PCR detection showed that the expression level of IRF7 gene and related immune genes in ALV-J group was significantly higher than that in control group (P < 0.05). To further study the role of chicken IRF7 during avian leukosis virus subgroup J (ALV-J) infection, we constructed an induced IRF7 overexpression and interfered chicken embryo fibroblasts (CEFs) cell and performed in vitro infection using low pathogenic ALV-J and virus analog poly(I:C). In ALV-J and poly(I:C) stimulated CEFs cells, the expression level of STAT1, IFN-α, IFN-β, TLR3 and TLR7 were increased after IRF7 overexpressed, while the results were just the opposite after IRF7 interfered, which indicating that IRF7 may be associated with Toll-like receptor signaling pathway and JAK-STAT signaling pathway. These findings suggest that chicken IRF7 is an important regulator of IFN and is involved in chicken anti-ALV-J innate immunity.

Host Interferon-Stimulated Gene 20 Inhibits Pseudorabies Virus Proliferation

Host interferon-stimulated gene 20 (ISG20) exerts antiviral effects on viruses by degrading viral RNA or by enhancing IFN signaling. Here, we examined the role of ISG20 during pseudorabies virus (PRV) proliferation. We found that ISG20 modulates PRV replication by enhancing IFN signaling. Further, ISG20 expression was upregulated following PRV infection and poly(I:C) treatment. Ectopic expression of ISG20 inhibited PRV proliferation in PK15 cells, whereas knockdown of ISG20 promoted PRV proliferation. In addition, ISG20 expression upregulated IFN-β expression and enhanced IFN downstream signaling during PRV infection. Notably, PRV UL24 suppressed the transcription of ISG20, thus antagonizing its antiviral effect. Further domain mapping analysis showed that the N terminus (amino acids 1-90) of UL24 was responsible for the inhibition of ISG20 transcription. Collectively, these findings characterize the role of ISG20 in suppressing PRV replication and increase the understanding of host-PRV interplay.

Involvement of Interleukin-1 Receptor-Associated Kinase 4 and Interferon Regulatory Factor 5 in the Immunopathogenesis of SARS-CoV-2 Infection: Implications for the Treatment of COVID-19

Interleukin-1 receptor-associated kinase 4 (IRAK4) and interferon regulatory factor 5 (IRF5) lie sequentially on a signaling pathway activated by ligands of the IL-1 receptor and/or multiple TLRs located either on plasma or endosomal membranes. Activated IRF5, in conjunction with other synergistic transcription factors, notably NF-κB, is crucially required for the production of proinflammatory cytokines in the innate immune response to microbial infection. The IRAK4-IRF5 axis could therefore have a major role in the induction of the signature cytokines and chemokines of the hyperinflammatory state associated with severe morbidity and mortality in COVID-19. Here a case is made for considering IRAK4 or IRF5 inhibitors as potential therapies for the "cytokine storm" of COVID-19.

Evolution of the IRF Family in Salmonids

Interferon regulatory factors (IRFs) as a family, are major regulators of the innate antiviral response in vertebrates principally involved in regulating the expression of interferons (IFNs) and interferon-stimulated genes (ISGs). To date, nine IRFs have been identified in mammals with a 10th member also found in several avian and fish species. Through genome mining and phylogenetic analysis, we identified and characterised 23 irf genes in 6 salmonid species. This larger repertoire of IRF in salmonids results from two additional whole-genome duplications which occurred in early teleosts and salmonids, respectively. Synteny analysis was then used to identify and confirm which paralogues belonged to each subgroup and a new nomenclature was assigned to the salmonid IRFs. Furthermore, we present a full set of Real-Time PCR primers for all rainbow trout IRFs, confirmed by sequencing to ensure paralogue specificity. RT PCR was then used to examine the response of all trout irf genes in vivo, following Vibrio anguillarum and poly I:C stimulation, indicating potential functional divergence between paralogues. Overall, this study presents a comprehensive overview of the IRF family in salmonids and highlights some novel roles for the salmonid-specific IRFs in immunity.

Metabolic and Molecular Mechanisms of Macrophage Polarisation and Adipose Tissue Insulin Resistance

Inflammation plays a key role in the development and progression of type-2 diabetes (T2D), a disease characterised by peripheral insulin resistance and systemic glucolipotoxicity. Visceral adipose tissue (AT) is the main source of inflammation early in the disease course. Macrophages are innate immune cells that populate all peripheral tissues, including AT. Dysregulated AT macrophage (ATM) responses to microenvironmental changes are at the root of aberrant inflammation and development of insulin resistance, locally and systemically. The inflammatory activation of macrophages is regulated at multiple levels: cell surface receptor stimulation, intracellular signalling, transcriptional and metabolic levels. This review will cover the main mechanisms involved in AT inflammation and insulin resistance in T2D. First, we will describe the physiological and pathological changes in AT that lead to inflammation and insulin resistance. We will next focus on the transcriptional and metabolic mechanisms described that lead to the activation of ATMs. We will discuss more novel metabolic mechanisms that influence macrophage polarisation in other disease or tissue contexts that may be relevant to future work in insulin resistance and T2D.

Molecular characterization of yellow catfish (Pelteobagrus fulvidraco) IRF7 suggests involvement in innate immune response

Interferon regulatory factor 7 (IRF7) serves as a critical mediator in the regulation of type Ι interferon (IFN) response to invading pathogens. Here, an ortholog of IRF7 was characterized in yellow catfish (Pelteobagrus fulvidraco). The full-length cDNA of PfIRF7 consisted of 1516 bp encoding a polypeptide of 425 amino acids. PfIRF7 protein comprised a typical IRF structural architecture, including a DNA binding domain (DBD), an IRF association domain (IAD) and a serine-rich domain (SRD). PfIRF7 was expressed predominantly in the immune-related tissues and transcriptionally upregulated by PolyI:C, LPS, and Edwardsiella ictaluri. Ectopic expression of PfIRF7 led to activation of fish type I IFN promoters and induction of IFN and Vig1, thereby conferring a strong antiviral effect against spring viremia of carp virus (SVCV). Overall, the present data suggest that PfIRF7 may play an essential role in type I IFN response of yellow catfish.

Of Keeping and Tipping the Balance: Host Regulation and Viral Modulation of IRF3-Dependent IFNB1 Expression

The type I interferon (IFN) response is a principal component of our immune system that allows to counter a viral attack immediately upon viral entry into host cells. Upon engagement of aberrantly localised nucleic acids, germline-encoded pattern recognition receptors convey their find via a signalling cascade to prompt kinase-mediated activation of a specific set of five transcription factors. Within the nucleus, the coordinated interaction of these dimeric transcription factors with coactivators and the basal RNA transcription machinery is required to access the gene encoding the type I IFN IFNβ (IFNB1). Virus-induced release of IFNβ then induces the antiviral state of the system and mediates further mechanisms for defence. Due to its key role during the induction of the initial IFN response, the activity of the transcription factor interferon regulatory factor 3 (IRF3) is tightly regulated by the host and fiercely targeted by viral proteins at all conceivable levels. In this review, we will revisit the steps enabling the trans-activating potential of IRF3 after its activation and the subsequent assembly of the multi-protein complex at the IFNβ enhancer that controls gene expression. Further, we will inspect the regulatory mechanisms of these steps imposed by the host cell and present the manifold strategies viruses have evolved to intervene with IFNβ transcription downstream of IRF3 activation in order to secure establishment of a productive infection.

Pollen exposure weakens innate defense against respiratory viruses

BACKGROUND

Hundreds of plant species release their pollen into the air every year during early spring. During that period, pollen allergic as well as non-allergic patients frequently present to doctors with severe respiratory tract infections. Our objective was therefore to assess whether pollen may interfere with antiviral immunity.

METHODS

We combined data from real-life human exposure cohorts, a mouse model and human cell culture to test our hypothesis.

RESULTS

Pollen significantly diminished interferon-λ and pro-inflammatory chemokine responses of airway epithelia to rhinovirus and viral mimics and decreased nuclear translocation of interferon regulatory factors. In mice infected with respiratory syncytial virus, co-exposure to pollen caused attenuated antiviral gene expression and increased pulmonary viral titers. In non-allergic human volunteers, nasal symptoms were positively correlated with airborne birch pollen abundance, and nasal birch pollen challenge led to downregulation of type I and -III interferons in nasal mucosa. In a large patient cohort, numbers of rhinoviruspositive cases were correlated with airborne birch pollen concentrations.

CONCLUSION

The ability of pollen to suppress innate antiviral immunity, independent of allergy, suggests that high-risk population groups should avoid extensive outdoor activities when pollen and respiratory virus seasons coincide.

Mechanisms of Macrophage Polarization in Insulin Signaling and Sensitivity

Type-2 diabetes (T2D) is a disease of two etiologies: metabolic and inflammatory. At the cross-section of these etiologies lays the phenomenon of metabolic inflammation. Whilst metabolic inflammation is characterized as systemic, a common starting point is the tissue-resident macrophage, who's successful physiological or aberrant pathological adaptation to its microenvironment determines disease course and severity. This review will highlight the key mechanisms in macrophage polarization, inflammatory and non-inflammatory signaling that dictates the development and progression of insulin resistance and T2D. We first describe the known homeostatic functions of tissue macrophages in insulin secreting and major insulin sensitive tissues. Importantly we highlight the known mechanisms of aberrant macrophage activation in these tissues and the ways in which this leads to impairment of insulin sensitivity/secretion and the development of T2D. We next describe the cellular mechanisms that are known to dictate macrophage polarization. We review recent progress in macrophage bio-energetics, an emerging field of research that places cellular metabolism at the center of immune-effector function. Importantly, following the advent of the metabolically-activated macrophage, we cover the known transcriptional and epigenetic factors that canonically and non-canonically dictate macrophage differentiation and inflammatory polarization. In closing perspectives, we discuss emerging research themes and highlight novel non-inflammatory or non-immune roles that tissue macrophages have in maintaining microenvironmental and systemic homeostasis.

Expression, subcellular localization, and potential antiviral function of three interferon regulatory factors in the big-belly seahorse (Hippocampus abdominalis)

Interferon regulatory factors (IRFs) are among the most important transcription mediators and have multiple biological functions, such as antiviral and antimicrobial defense, cell differentiation, immune modulation, and apoptosis. Three IRF family members (HaIRF4-like, HaIRF6, and HaIRF8) of the big belly seahorse (Hippocampus abdominalis) were molecularly and functionally characterized at the sequence and transcriptional level. The coding sequences of HaIRF4-like, HaIRF6, and HaIRF8 were 1214, 1485, and 1266 bp in length, encoding proteins of size 46.21, 55.32, and 47.56 kDa, respectively. Potential viral transcription and replication was detected against VHSV infection using qPCR in HaIRFs-transfected FHM cells. IRFs significantly reduced viral gene expression at 24 h and 48 h post infection and the expression of interferon-stimulated genes (ISGs) was modulated at transcriptional level upon HaIRF overexpression in FHM cells. Subcellular HaIRF localization was observed using GFP-tagged expression vectors in FHM cells. HaIRF4-like and HaIRF8 were localized to the nucleus, whereas HaIRF6 was observed in the cytoplasm. All three IRFs were ubiquitously expressed in all analyzed tissues of the big belly seahorse. The mRNA expression of IRF4-like, IRF6, and IRF8 increased significantly post injection in the blood and gills following LPS, poly (I:C), and Streptococcus iniae challenge. These findings demonstrate that seahorse IRFs are involved in host defense mechanisms against immune stimulants and HaIRFs induce interferon and ISGs which trigger antiviral activity against viral infections in the host.

Protein kinases involved in epidermal barrier formation: The AKT family and other animals

Formation of a stratified epidermis is required for the performance of the essential functions of the skin; to act as an outside-in barrier against the access of microorganisms and other external factors, to prevent loss of water and solutes via inside-out barrier functions and to withstand mechanical stresses. Epidermal barrier function is initiated during embryonic development and is then maintained throughout life and restored after injury. A variety of interrelated processes are required for the formation of a stratified epidermis, and how these processes are both temporally and spatially regulated has long been an aspect of dermatological research. In this review, we describe the roles of multiple protein kinases in the regulation of processes required for epidermal barrier formation.

Inactivating Mutation in IRF8 Promotes Osteoclast Transcriptional Programs and Increases Susceptibility to Tooth Root Resorption

This is the first study to our knowledge to report a novel mutation in the interferon regulatory factor 8 gene (IRF8G388S ) associated with multiple idiopathic tooth root resorption, a form of periodontal disease. The IRF8G388S variant in the highly conserved C-terminal motif is predicted to alter the protein structure, likely impairing IRF8 function. Functional assays demonstrated that the IRF8G388S mutant promoted osteoclastogenesis and failed to inhibit NFATc1-dependent transcriptional activation when compared with IRF8WT control. Further, similar to subjects with heterozygous IRF8G388S mutation, Irf8+/- mice exhibited increased osteoclast activity in the mandibular alveolar bone surrounding molar teeth. Immunohistochemistry illustrated increased NFATc1 expression in the dentoalveolar region of Irf8-/- and Irf8+/- mice when compared with Irf8+/+ controls. Genomewide analyses revealed that IRF8 constitutively bound to regulatory regions of several thousand genes in osteoclast precursors, and genetic aberration of IRF8 significantly enhanced many osteoclast-specific transcripts. Collectively, this study delineates the critical role of IRF8 in defining osteoclast lineage and osteoclast transcriptional program, which may help in better understanding of various osteoclast-mediated disorders, including periodontal disease. © 2019 American Society for Bone and Mineral Research.

Transcriptional control of macrophage polarisation in type 2 diabetes

Type-2 diabetes (T2D) is considered today as an inflammatory disease. Inflammatory processes in T2D are orchestrated by macrophage activation in different organs. Macrophages undergo classical M1 pro-inflammatory or alternative M2 anti-inflammatory activation in response to tissue microenvironmental signals. These subsets of macrophages are characterised by their expression of cell surface markers, secreted cytokines and chemokines. Transcriptional regulation is central to the polarisation of macrophages, and several major pathways have been described as essential to promote the expression of specific genes, which dictate the functional polarisation of macrophages. In this review, we summarise the current knowledge of transcriptional control of macrophage polarisation and the role this plays in development of insulin resistance.

Interferon-Stimulated Genes-Mediators of the Innate Immune Response during Canine Distemper Virus Infection

The demyelinating canine distemper virus (CDV)-leukoencephalitis represents a translational animal model for multiple sclerosis. The present study investigated the expression of type I interferon (IFN-I) pathway members in CDV-induced cerebellar lesions to gain an insight into their role in lesion development. Gene expression of 110 manually selected genes in acute, subacute and chronic lesions was analyzed using pre-existing microarray data. Interferon regulatory factor (IRF) 3, IRF7, signal transducer and activator of transcription (STAT) 1, STAT2, MX protein, protein kinase R (PKR), 2'-5'-oligoadenylate synthetase (OAS) 1 and interferon-stimulated gene (ISG) 15 expression were also evaluated using immunohistochemistry. Cellular origin of STAT1, STAT2, MX and PKR were determined using immunofluorescence. CDV infection caused an increased expression of the antiviral effector proteins MX, PKR, OAS1 and ISG15, which probably contributed to a restricted viral replication, particularly in neurons and oligodendrocytes. This increase might be partly mediated by IRF-dependent pathways due to the lack of changes in IFN-I levels and absence of STAT2 in astrocytes. Nevertheless, activated microglia/macrophages showed a strong expression of STAT1, STAT2 and MX proteins in later stages of the disease, indicating a strong activation of the IFN-I signaling cascade, which might be involved in the aggravation of bystander demyelination.

Therapeutic Targeting of IRFs: Pathway-Dependence or Structure-Based?

The interferon regulatory factors (IRFs) are a family of master transcription factors that regulate pathogen-induced innate and acquired immune responses. Aberration(s) in IRF signaling pathways due to infection, genetic predisposition and/or mutation, which can lead to increased expression of type I interferon (IFN) genes, IFN-stimulated genes (ISGs), and other pro-inflammatory cytokines/chemokines, has been linked to the development of numerous diseases, including (but not limited to) autoimmune and cancer. What is currently lacking in the field is an understanding of how best to therapeutically target these transcription factors. Many IRFs are regulated by post-translational modifications downstream of pattern recognition receptors (PRRs) and some of these modifications lead to activation or inhibition. We and others have been able to utilize structural features of the IRFs in order to generate dominant negative mutants that inhibit function. Here, we will review potential therapeutic strategies for targeting all IRFs by using IRF5 as a candidate targeting molecule.

Duck interferon regulatory factor 7 (IRF7) can control duck Tembusu virus (DTMUV) infection by triggering type I interferon production and its signal transduction pathway

Human interferon regulatory factor 7 (IRF7) plays an important role in the innate antiviral immune response. To date, the characteristics and functions of waterfowl IRF7 have not been clarified. This study reports the cDNA sequence, tissue distribution, and antiviral function of duck IRF7. The duck IRF7 gene has a 1536-bp open read frame (ORF) and encodes a 511-amino acid polypeptide. IRF7 is highly expressed in the blood and pancreas of 5-day-old ducklings and in the small intestine, large intestine and liver of 60-day-old adult ducks. Indirect immunofluorescence assay (IFA) showed that over-expressed duck IRF7 was located in both the cytoplasm and nucleus of transfected duck embryo fibroblasts (DEFs), which was also observed in poly(I:C)-stimulated or duck Tembusu virus (DTMUV)-infected DEFs. Titres and copies of DTMUV were significantly reduced in DEFs overexpressing IRF7. Moreover, overexpression of duck IRF7 significantly induced IFNα/β, but not IFNγ, mRNA expression, and transcription of downstream interferon-stimulated genes (ISGs), such as MX, OASL and IL-6, which were significantly induced by poly(I:C) co-stimulation, was enhanced. Additionally, duck IRF7 overexpression can significantly activate the IFNβ promoter in DEFs. Collectively, duck IRF7 plays an important role in host anti-DTMUV immune regulation, which depends on type I interferons and associated signal transduction pathway(s).

Expression Levels of Interferon Regulatory Factor 5 (IRF5) and Related Inflammatory Cytokines Associated with Severity, Prognosis, and Causative Pathogen in Patients with Community-Acquired Pneumonia

Background

Community-acquired pneumonia (CAP) is a common disease with significant morbidity and mortality. Interferon regulatory factor 5 (IRF5), which induces type I interferons (IFNs) and cytokines such as interleukin (IL)-6, tumor necrosis factor (TNF)-α, IL-10, and interferon gamma-induced protein (IP)10, is a key transcription factor involved in controlling the expression of proinflammatory cytokines and responses to infection. Here, we carefully investigated the role of IRF5 in regulating immune responses to CAP.

Material/Methods

QRT-PCR was used to detect the mRNA levels of IRF5, IL-6, IL-10, IP10, TNF-α, and IFN-α in the peripheral blood of 71 CAP patients and 31 healthy controls, as well as in the bronchoalveolar lavage cells of 20 patients with CAP and 23 patients with lung cancer (using samples from the unaffected lung). Flow cytometry was performed to detect the protein level of IRF5, and a CBA flex set was used to detect the levels of these cytokines in the volunteers.

Results

The expression levels of IRF5 and its related cytokines were significantly increased in CAP patients compared with the controls. Additionally, IRF5, IL-6, IL-10, and IP10 levels were found to be related with the severity of CAP. Furthermore, the levels of IRF5 and IFN-α increased significantly in the early phase of pneumonia caused by influenza virus infection.

Conclusions

IRF5 and its related inflammatory cytokines are associated with the severity, prognosis, and causative pathogen of CAP patients. This finding may provide new drug targets for the prevention and treatment of severe pneumonia caused by influenza virus.

A conserved interferon regulation factor 1 (IRF-1) from Pacific oyster Crassostrea gigas functioned as an activator of IFN pathway

Interferon regulatory factors (IRFs), a family of transcription factors with a novel helix-turn-helix DNA-binding motif, play important roles in regulating the expression of interferons (IFNs) and IFN-stimulated genes. In the present study, an interferon regulation factor 1 was identified from oyster Crassostrea gigas (designated CgIRF-1), and its immune function was characterized to understand the regulatory mechanism of interferon system against viral infection in invertebrates. The open reading frame (ORF) of CgIRF-1 was 990 bp, encoding a polypeptide of 329 amino acids with a typical IRF domain (also known as DNA-binding domain). The mRNA transcripts of CgIRF-1 were detected in all the tested tissues with the highest expression level in hemocyte. CgIRF-1 protein was distributed in both nucleus and cytoplasm of the oyster hemocyte. The mRNA expression of CgIRF-1 in hemocytes was significantly up-regulated at 48 h after poly (I:C) stimulation (p < 0.05). The recombinant CgIRF-1 (rCgIRF-1) could interact with classically IFN-stimulated response elements (ISRE) in vitro. The relative luciferase activity of interferon-like protein promotor reporter gene (pGL-CgIFNLP promotor) was significantly (p < 0.05) enhanced in HEK293T cell after transfection of CgIRF-1. These results indicated that CgIRF-1 could bind ISRE and regulate the expression of CgIFNLP as a transcriptional regulatory factor, and participated in the antiviral immune response of oysters.

Composition and transcription of all interferon regulatory factors (IRFs), IRF1‒11 in a perciform fish, the mandarin fish, Siniperca chuatsi

Interferon regulatory factors (IRFs) are a family of mediators in various biological processes including immune modulation of interferon (IFN) and proinflammatory cytokine expression. However, the data on the complete composition of IRFs is rather limited in teleost fish. In the present study, all IRF members, i.e. IRF1‒11 with two IRF4, IRF4a and IRF4b have been characterised in an aquaculture species of fish, the mandarin fish, Siniperca chuatsi, in addition to the previous report of IRF1, IRF2, IRF3 and IRF7 from the fish. These IRFs are constitutively expressed in various organs/tissues of the fish, and their expression can be induced following the stimulation of polyinosinic:polycytidylic acid (poly(I:C)) and the infection of infectious spleen and kidney necrosis virus (ISKNV), a viral pathogen of mandarin fish in aquaculture. The ISKNV infection induced the significant increase in the expression of some IRF genes, i.e. IRF2, IRF4a, IRF7, IRF9, IRF10 at 24 or 36 h post-infection (hpi) in spleen and head-kidney, and the significant increase of some other IRF genes, e.g. IRF1, IRF3, IRF4b, IRF5, IRF6, IRF8 at later stage of infection from 72, or 96, or even 120 hpi, which may imply the inhibitory effect of ISKNV on fish immune response. It is considered that the present study provides the first detailed analysis on all IRF members in an aquaculture species of fish, and can be served as the base for further investigation on the role of IRFs in teleost fish.

Genetic variants of interferon regulatory factor 5 associated with chronic hepatitis B infection

AIM

To investigate possible effects of IRF5 polymorphisms in the 3’ UTR region of the IFR5 locus on susceptibility to hepatitis B virus (HBV) infection and progression of liver diseases among clinically classified Vietnamese patients.

METHODS

Four IFR5 SNPs (rs13242262A/T, rs77416878C/T, rs10488630A/G, and rs2280714T/C) were genotyped in clinically classified HBV patients [chronic hepatitis B (CHB). n = 99; liver cirrhosis (LC), n = 131; hepatocellular carcinoma (HCC), n = 149] and in 242 healthy controls by direct sequencing and TaqMan real-time PCR assays.

RESULTS

Comparing patients and controls, no significant association was observed for the four IFR5 variants. However, the alleles rs13242262T and rs10488630G contributed to an increased risk of liver cirrhosis (LC vs CHB: OR = 1.5, 95%CI: 1.1-2.3, adjusted P = 0.04; LC vs CHB: OR = 1.7, 95%CI: 1.1-2.6, adjusted P = 0.019). Haplotype IRF5*TCGT constructed from 4 SNPs was observed frequently in LC compared to CHB patients (OR = 2.1, 95%CI: 1.2-3.3, adjusted P = 0.008). Haplotype IRF5*TCAT occurred rather among CHB patients than in the other HBV patient groups (LC vs CHB: OR = 0.4, 95%CI: 0.2-0.8, adjusted P = 0.03; HCC vs CHB: OR = 0.3, 95%CI: 0.15-0.7, adjusted P = 0.003). The IRF5*TCAT haplotype was also associated with increased levels of ALT, AST and bilirubin.

CONCLUSION

Our study shows that IFR5 variants may contribute as a host factor in determining the pathogenesis in chronic HBV infections.

IFN Regulatory Factors and Antiviral Innate Immunity: How Viruses Can Get Better

The interferon regulatory factor (IRF) family consists of transcriptional regulators that exert multifaceted and versatile functions in multiple biological processes. Their crucial role as central mediators in the establishment and execution of host immunity in response to pathogen-derived signals downstream pattern recognition receptors (PRRs) makes IRFs a hallmark of the host antiviral response. They function as hub molecules at the crossroad of different signaling pathways for the induction of interferon (IFN) and inflammatory cytokines, as well as of antiviral and immunomodulatory genes even in an IFN-independent manner. By regulating the development and activity of immune cells, IRFs also function as a bridge between innate and adaptive responses. As such, IRFs represent attractive and compulsive targets in viral strategies to subvert antiviral signaling. In this study, we discuss current knowledge on the wide array of strategies put in place by pathogenic viruses to evade, subvert, and/or hijack these essential components of host antiviral immunity.

Role of interferon regulatory factor-1 in lipopolysaccharide-induced mitochondrial damage and oxidative stress responses in macrophages

Sepsis causes many early deaths; both macrophage mitochondrial damage and oxidative stress responses are key factors in its pathogenesis. Although the exact mechanisms responsible for sepsis-induced mitochondrial damage are unknown, the nuclear transcription factor, interferon regulatory factor-1 (IRF-1) has been reported to cause mitochondrial damage in several diseases. Previously, we reported that in addition to promoting systemic inflammation, IRF-1 promoted the apoptosis of and inhibited autophagy in macrophages. In the present study, we hypothesized that lipopolysaccharide (LPS)-induced IRF-1 activation in macrophages may promote mitochondrial damage and oxidative stress. In vitro, LPS was found to promote IRF-1 activation, reactive oxygen species (ROS) production, adenosine triphosphate (ATP) depletion, superoxide dismutase (SOD) consumption, malondialdehyde (MDA) accumulation and mitochondrial depolarization in macrophages in a time- and dose-dependent manner. These effects were abrogated in cells in which IRF-1 was knocked down. Furthermore, IRF-1 overexpression increased LPS-induced oxidative stress responses and mitochondrial damage. In vivo, peritoneal macrophages obtained from IRF-1 knockout (KO) mice produced less ROS and had less mitochondrial depolarization and damage following the administration of LPS, when compared to their wild-type (WT) counterparts. In addition, IRF-1 KO mice exhibited a decreased release of mitochondrial DNA (mtDNA) following the administration of LPS. Thus, IRF-1 may be a critical factor in augmenting LPS-induced oxidative stress and mitochondrial damage in macrophages.

Periderm: Life-cycle and function during orofacial and epidermal development

Development of the secondary palate involves a complex series of embryonic events which, if disrupted, result in the common congenital anomaly cleft palate. The secondary palate forms from paired palatal shelves which grow initially vertically before elevating to a horizontal position above the tongue and fusing together in the midline via the medial edge epithelia. As the epithelia of the vertical palatal shelves are in contact with the mandibular and lingual epithelia, pathological fusions between the palate and the mandible and/or the tongue must be prevented. This function is mediated by the single cell layered periderm which forms in a distinct and reproducible pattern early in embryogenesis, exhibits highly polarised expression of adhesion complexes, and is shed from the outer surface as the epidermis acquires its barrier function. Disruption of periderm formation and/or function underlies a series of birth defects that exhibit multiple inter-epithelial adhesions including the autosomal dominant popliteal pterygium syndrome and the autosomal recessive cocoon syndrome and Bartsocas Papas syndrome. Genetic analyses of these conditions have shown that IRF6, IKKA, SFN, RIPK4 and GRHL3, all of which are under the transcriptional control of p63, play a key role in periderm formation. Despite these observations, the medial edge epithelia must rapidly acquire the capability to fuse if the palatal shelves are not to remain cleft. This process is driven by TGFβ3-mediated, down-regulation of p63 in the medial edge epithelia which allows periderm migration out of the midline epithelial seam and reduces the proliferative potential of the midline epithelial seam thereby preventing cleft palate. Together, these findings indicate that periderm plays a transient but fundamental role during embryogenesis in preventing pathological adhesion between intimately apposed, adhesion-competent epithelia.

Disrupted IRF6-NME1/2 Complexes as a Cause of Cleft Lip/Palate

Mutations and common polymorphisms in interferon regulatory factor 6 ( IRF6) are associated with both syndromic and nonsyndromic forms of cleft lip/palate (CLP). To date, much of the focus on this transcription factor has been on identifying its direct targets and the gene regulatory network in which it operates. Notably, however, IRF6 is found predominantly in the cytoplasm, with its import into the nucleus tightly regulated like other members of the IRF family. To provide further insight into the role of IRF6 in the pathogenesis of CLP, we sought to identify direct IRF6 protein interactors using a combination of yeast 2-hybrid screens and co-immunoprecipitation assays. Using this approach, we identified NME1 and NME2, well-known regulators of Rho-type GTPases, E-cadherin endocytosis, and epithelial junctional remodeling, as bona fide IRF6 partner proteins. The NME proteins co-localize with IRF6 in the cytoplasm of primary palatal epithelial cells in vivo, and their interaction with IRF6 is significantly enhanced by phosphorylation of key serine residues in the IRF6 C-terminus. Furthermore, CLP associated IRF6 missense mutations disrupt the ability of IRF6 to bind the NME proteins and result in elevated activation of Rac1 and RhoA, compared to wild-type IRF6, when ectopically expressed in 293T epithelial cells. Significantly, we also report the identification of 2 unique missense mutations in the NME proteins in patients with CLP (NME1 R18Q in an IRF6 and GRHL3 mutation-negative patient with van der Woude syndrome and NME2 G71V in a patient with nonsyndromic CLP). Both variants disrupted the ability of the respective proteins to interact with IRF6. The data presented suggest an important role for cytoplasmic IRF6 in regulating the availability or localization of the NME1/2 complex and thus the dynamic behavior of epithelia during lip/palate development.

Reprogramming Interferon Regulatory Factor Signaling in Cardiometabolic Diseases

Interferon regulatory factors (IRFs) are evolutionarily conserved proteins expressed not only in immune cells but also in other tissues and organs outside the immune system. In this review, we discuss mechanisms responsible for IRF-mediated innate immune responses and the function and mechanism of IRFs in cardiometabolic diseases. We focus on the role of IRFs in innate immunity and cardiometabolic homeostasis, and highlight reprogrammed IRF signaling.

Identification of an IRF-1 splicing transcript in APL cells sharing similar transactivation activity of the full length one

Interferon regulatory factor-1 (IRF-1) is a member of the interferon regulatory factor family. It acts as a transcriptional activator and plays a critical role in antiviral defense, immune response, cell growth regulation, apoptosis and cell differentiation. Deletions, mutations or aberrant splicing of IRF-1 would result in its functional inactivation, and closely related to the tumorigenesis. In this work, we identified an IRF-1 splicing transcript (IRF-1-s) in all-trans retinoic acid (ATRA)-treated acute promyelocytic leukemia (APL) cell line NB4 cells. It lost the exon 8 and 9 of the full length IRF-1, expressed in numerous cell types and could be induced to expression by ATRA in NB4 cells. It turned out similar biological activity as full length IRF-1 to enhance the transcription of interferon stimulated response element (ISRE)-containing target genes. Identification of IRF-1-s in NB4 cells would be benefit for our further exploring the signaling pathway of ATRA and interferons, as well as the mechanisms of differentiation of APL cells.

HIV-1 and hijacking of the host immune system: the current scenario

Human immunodeficiency virus (HIV) infection is a major health burden across the world which leads to the development of acquired immune deficiency syndrome (AIDS). This review article discusses the prevalence of HIV, its major routes of transmission, natural immunity, and evasion from the host immune system. HIV is mostly prevalent in Sub-Saharan Africa and low income countries. It is mostly transmitted by sharing syringe needles, blood transfusion, and sexual routes. The host immune system is categorized into three main types; the innate, the adaptive, and the intrinsic immune system. Regarding the innate immune system against HIV, the key players are mucosal membrane, dendritic cells (DCs), complement system, interferon, and host Micro RNAs. The major components of the adaptive immune system exploited by HIV are T cells mainly CD4+ T cells and B cells. The intrinsic immune system confronted by HIV involves (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G) APOBEC3G, tripartite motif 5-α (TRIM5a), terherin, and (SAM-domain HD-domain containing protein) SAMHD1. HIV-1 efficiently interacts with the host immune system, exploits the host machinery, successfully replicates and transmits from one cell to another. Further research is required to explore evasion strategies of HIV to develop novel therapeutic approaches against HIV.

Pestivirus Npro Directly Interacts with Interferon Regulatory Factor 3 Monomer and Dimer

Interferon regulatory factor 3 (IRF3) is a transcription factor involved in the activation of type I alpha/beta interferon (IFN-α/β) in response to viral infection. Upon viral infection, the IRF3 monomer is activated into a phosphorylated dimer, which induces the transcription of interferon genes in the nucleus. Viruses have evolved several ways to target IRF3 in order to subvert the innate immune response. Pestiviruses, such as classical swine fever virus (CSFV), target IRF3 for ubiquitination and subsequent proteasomal degradation. This is mediated by the viral protein N(pro) that interacts with IRF3, but the molecular details for this interaction are largely unknown. We used recombinant N(pro) and IRF3 proteins and show that N(pro) interacts with IRF3 directly without additional proteins and forms a soluble 1:1 complex. The full-length IRF3 but not merely either of the individual domains is required for this interaction. The interaction between N(pro) and IRF3 is not dependent on the activation state of IRF3, since N(pro) binds to a constitutively active form of IRF3 in the presence of its transcriptional coactivator, CREB-binding protein (CBP). The results indicate that the N(pro)-binding site on IRF3 encompasses a region that is unperturbed by the phosphorylation and subsequent activation of IRF3 and thus excludes the dimer interface and CBP-binding site.

IMPORTANCE

The pestivirus N-terminal protease, N(pro), is essential for evading the host's immune system by facilitating the degradation of interferon regulatory factor 3 (IRF3). However, the nature of the N(pro) interaction with IRF3, including the IRF3 species (inactive monomer versus activated dimer) that N(pro) targets for degradation, is largely unknown. We show that classical swine fever virus N(pro) and porcine IRF3 directly interact in solution and that full-length IRF3 is required for interaction with N(pro) Additionally, N(pro) interacts with a constitutively active form of IRF3 bound to its transcriptional cofactor, the CREB-binding protein. This is the first study to demonstrate that N(pro) is able to bind both inactive IRF3 monomer and activated IRF3 dimer and thus likely targets both IRF3 species for ubiquitination and proteasomal degradation.

Down-Regulation of IRF6 Protects Cortical Neurons Against Traumatic Neuronal Injury Through Activating Akt-eNOS Pathway

Interferon regulatory factor 6 (IRF6) is a novel and unique member of the IRF family of transcription factors, and the regulation and function of IRF6 remain unknown. Recently, IRF6 was shown to be upregulated after TBI and could promote neuronal apoptosis under oxidative stress conditions. This study aimed to investigate the role of IRF6 in traumatic neuronal injury (TNI) in primary cultured mouse cortical neurons. We found that the expression of IRF6 was significantly increased within 48 after TNI, and peaked at 24 h. Knockdown of IRF6 using specific targeted small interfering RNA (siRNA) attenuated TNI-induced loss of neuronal viability and release of lactate dehydrogenase. The results of TUNEL staining showed that IRF6 knockdown markedly reduced neuronal apoptosis, which was accompanied by decreased activity of caspase-3. Furthermore, downregulation of IRF6 inhibited lipid peroxidation, promoted the activity of endogenous antioxidative enzymes, and differently regulated the expression of inflammatory cytokines after TNI. In addition, IRF6 knockdown significantly increased phosphorylation of Akt and endothelial nitric oxide synthase (eNOS), whereas blocking Akt-eNOS pathway via selective antagonists partly prevented the protective effects of IRF6 knockdown. These data show that downregulation of IRF6 affords protection against TNI through Akt-eNOS pathway-mediated antioxidative and anti-inflammatory activity.

Regulation of TBK1 activity by Optineurin contributes to cell cycle-dependent expression of the interferon pathway

The innate immune system has evolved to detect and neutralize viral invasions. Triggering of this defense mechanism relies on the production and secretion of soluble factors that stimulate intracellular antiviral defense mechanisms. The Tank Binding Kinase 1 (TBK1) is a serine/threonine kinase in the innate immune signaling pathways including the antiviral response and the host defense against cytosolic infection by bacteries. Given the critical roles of TBK1, important regulatory mechanisms are required to regulate its activity. Among these, Optineurin (Optn) was shown to negatively regulate the interferon response, in addition to its important role in membrane trafficking, protein secretion, autophagy and cell division. As Optn does not carry any enzymatic activity, its functions depend on its precise subcellular localization and its interaction with other proteins, especially with components of the innate immune pathway. This review highlights advances in our understanding of Optn mechanisms of action with focus on the relationships between Optn and TBK1 and their implication in host defense against pathogens. Specifically, how the antiviral immune system is controlled during the cell cycle by the Optn/TBK1 axis and the physiological consequences of this regulatory mechanism are described. This review may serve to a better understanding of the relationships between the different functions of Optn, including those related to immune responses and its associated pathologies such as primary open-angle glaucoma, amyotrophic lateral sclerosis and Paget's disease of bone.

Sequence and Expression Analysis of Interferon Regulatory Factor 10 (IRF10) in Three Diverse Teleost Fish Reveals Its Role in Antiviral Defense

BACKGROUND

Interferon regulatory factor (IRF) 10 was first found in birds and is present in the genome of other tetrapods (but not humans and mice), as well as in teleost fish. The functional role of IRF10 in vertebrate immunity is relatively unknown compared to IRF1-9. The target of this research was to clone and characterize the IRF10 genes in three economically important fish species that will facilitate future evaluation of this molecule in fish innate and adaptive immunity.

MOLECULAR CHARACTERIZATION OF IRF10 IN THREE FISH SPECIES

In the present study, a single IRF10 gene was cloned in grass carp Ctenopharyngodon idella and Asian swamp eel Monopterus albus, and two, named IRF10a and IRF10b, in rainbow trout Oncorhynchus mykiss. The fish IRF10 molecules share highest identities to other vertebrate IRF10s, and have a well conserved DNA binding domain, IRF-associated domain, and an 8 exon/7 intron structure with conserved intron phase. The presence of an upstream ATG or open reading frame (ORF) in the 5'-untranslated region of different fish IRF10 cDNA sequences suggests potential regulation at the translational level, and this has been verified by in vitro transcription/translation experiments of the trout IRF10a cDNA, but would still need to be validated in fish cells.

EXPRESSION ANALYSIS OF IRF10 IN VIVO AND IN VITRO

Both trout IRF10 paralogues are highly expressed in thymus, blood and spleen but are relatively low in head kidney and caudal kidney. Trout IRF10b expression is significantly higher than IRF10a in integumentary tissues i.e. gills, scales, skin, intestine, adipose fin and tail fins, suggesting that IRF10b may be more important in mucosal immunity. The expression of both trout IRF10 paralogues is up-regulated by recombinant IFN-γ. The expression of the IRF10 genes is highly induced by Poly I:C in vitro and in vivo, and by viral infection, but is less responsive to peptidoglycan and bacterial infection, suggesting an important role of fish IRF10 in antiviral defense.

Knockdown of IRF6 Attenuates Hydrogen Dioxide-Induced Oxidative Stress via Inhibiting Mitochondrial Dysfunction in HT22 Cells

Oxidative stress-induced cell damage is involved in many neurological diseases. Interferon regulatory factor 6 (IRF6), a member of the IRF family of transcription factors, is required for the differentiation of skin, breast epithelium, and oral epithelium. However, the regulation and function of IRF6 in central nervous system remain unknown. This study aimed to investigate the role of IRF6 in hydrogen peroxide (H2O2)-induced oxidative neuronal injury in HT22 mouse hippocampal cells. Treatment with H2O2 significantly increased the expression of IRF6 at both mRNA and protein levels, and knockdown of IRF6 using specific small interfering RNA reduced H2O2-induced cytotoxicity, as evidenced by increased cell viability and decreased apoptosis. Knockdown of IRF6 attenuated intracellular reactive oxygen species (ROS) generation and lipid peroxidation, and also preserved endogenous antioxidant enzyme activities. The inhibitory effect of IRF6 knockdown on mitochondrial dysfunction was demonstrated by reduced mitochondrial oxidative level, preserved mitochondrial membrane potential (MMP) and ATP generation, as well as attenuated mitochondrial swelling. In addition, down-regulation of IRF6 inhibited the activation of mitochondrial apoptotic factors, whereas IRF6 knockdown together with caspase inhibitors had no extra effect on cell viability and LDH release. These results suggest that knockdown of IRF6 has protective effects against H2O2-induced oxidative stress by reducing ROS accumulation and apoptosis, and these protective effects are dependent on preservation of mitochondrial function.

Genome-Wide Mapping of the Binding Sites and Structural Analysis of Kaposi's Sarcoma-Associated Herpesvirus Viral Interferon Regulatory Factor 2 Reveal that It Is a DNA-Binding Transcription Factor

The oncogenic herpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV) is known to encode four viral interferon regulatory factors (vIRF1 to -4) to subvert the host antiviral immune response, but their detailed DNA-binding profiles as transcription factors in the host remain uncharacterized. Here, we first performed genome-wide vIRF2-binding site mapping in the human genome using chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-seq). vIRF2 was capable of binding to the promoter regions of 100 putative target genes. Importantly, we confirmed that vIRF2 can specifically interact with the promoters of the genes encoding PIK3C3, HMGCR, and HMGCL, which are associated with autophagosome formation or tumor progression and metastasis, and regulate their transcription in vivo. The crystal structure of the vIRF2 DNA-binding domain (DBD) (referred to here as vIRF2DBD) showed variable loop conformations and positive-charge distributions different from those of vIRF1 and cellular IRFs that are associated with DNA-binding specificities. Structure-based mutagenesis revealed that Arg82 and Arg85 are required for the in vitro DNA-binding activity of vIRF2DBD and can abolish the transcription regulation function of vIRF2 on the promoter reporter activity of PIK3C3, HMGCR, and HMGCL. Collectively, our study provided unique insights into the DNA-binding potency of vIRF2 and suggested that vIRF2 could act as a transcription factor of its target genes in the host antiviral immune response.

IMPORTANCE

The oncogenic herpesvirus KSHV is the etiological agent of Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. KSHV has developed a unique mechanism to subvert the host antiviral immune responses by encoding four homologues of cellular interferon regulatory factors (vIRF1 to -4). However, none of their DNA-binding profiles in the human genome have been characterized until now, and the structural basis for their diverse DNA-binding properties remain poorly understood. In this study, we performed the first genome-wide vIRF2-binding site mapping in the human genome and found vIRF2 can bind to the promoter regions of 100 target cellular genes. X-ray structure analysis and functional studies provided unique insights into its DNA-binding potency and regulation of target gene expression. Our study suggested that vIRF2 could act as a transcription factor of its target genes and contribute to KSHV infection and pathogenesis through versatile functions.

Activation of Vago by interferon regulatory factor (IRF) suggests an interferon system-like antiviral mechanism in shrimp

There is a debate on whether invertebrates possess an antiviral immunity similar to the interferon (IFN) system of vertebrates. The Vago gene from arthropods encodes a viral-activated secreted peptide that restricts virus infection through activating the JAK-STAT pathway and is considered to be a cytokine functionally similar to IFN. In this study, the first crustacean IFN regulatory factor (IRF)-like gene was identified in Pacific white shrimp, Litopenaeus vannamei. The L. vannamei IRF showed similar protein nature to mammalian IRFs and could be activated during virus infection. As a transcriptional regulatory factor, L. vannamei IRF could activate the IFN-stimulated response element (ISRE)-containing promoter to regulate the expression of mammalian type I IFNs and initiate an antiviral state in mammalian cells. More importantly, IRF could bind the 5′-untranslated region of L. vannamei Vago4 gene and activate its transcription, suggesting that shrimp Vago may be induced in a similar manner to that of IFNs and supporting the opinion that Vago might function as an IFN-like molecule in invertebrates. These suggested that shrimp might possess an IRF-Vago-JAK/STAT regulatory axis, which is similar to the IRF-IFN-JAK/STAT axis of vertebrates, indicating that invertebrates might possess an IFN system-like antiviral mechanism.

Innate immunity against HIV-1 infection

During acute HIV-1 infection, viral pathogen-associated molecular patterns are recognized by pathogen-recognition receptors (PRRs) of infected cells, which triggers a signaling cascade that initiates innate intracellular antiviral defenses aimed at restricting the replication and spread of the virus. This cell-intrinsic response propagates outward via the action of secreted factors such as cytokines and chemokines that activate innate immune cells and attract them to the site of infection and to local lymphatic tissue. Antiviral innate effector cells can subsequently contribute to the control of viremia and modulate the quality of the adaptive immune response to HIV-1. The concerted actions of PRR signaling, specific viral-restriction factors, innate immune cells, innate-adaptive immune crosstalk and viral evasion strategies determine the outcome of HIV-1 infection and immune responses.