Structure and function of IRF-7

Insight into the role of IRF7 in skin and connective tissue diseases

Interferons (IFNs) are signalling proteins primarily involved in initiating innate immune responses against pathogens and promoting the maturation of immune cells. Interferon Regulatory Factor 7 (IRF7) plays a pivotal role in the IFNs signalling pathway. The activation process of IRF7 is incited by exogenous or abnormal nucleic acids, which is followed by the identification via pattern recognition receptors (PRRs) and the ensuing signalling cascades. Upon activation, IRF7 modulates the expression of both IFNs and inflammatory gene regulation. As a multifunctional transcription factor, IRF7 is mainly expressed in immune cells, yet its presence is also detected in keratinocytes, fibroblasts, and various dermal cell types. In these cells, IRF7 is critical for skin immunity, inflammation, and fibrosis. IRF7 dysregulation may lead to autoimmune and inflammatory skin conditions, including systemic scleroderma (SSc), systemic lupus erythematosus (SLE), Atopic dermatitis (AD) and Psoriasis. This comprehensive review aims to extensively elucidate the role of IRF7 and its signalling pathways in immune cells and keratinocytes, highlighting its significance in skin-related and connective tissue diseases.

IRF7: role and regulation in immunity and autoimmunity

Interferon regulatory factor (IRF) 7 was originally identified as master transcriptional factor that produced IFN-I and regulated innate immune response, subsequent studies have revealed that IRF7 performs a multifaceted and versatile functions in multiple biological processes. In this review, we provide a comprehensive overview on the current knowledge of the role of IRF7 in immunity and autoimmunity. We focus on the latest regulatory mechanisms of IRF7 in IFN-I, including signaling pathways, transcription, translation, and post-translational levels, the dimerization and nuclear translocation, and the role of IRF7 in IFN-III and COVID-19. In addition to antiviral immunity, we also discuss the role and mechanism of IRF7 in autoimmunity, and the further research will expand our understanding of IRF7.

Immunomodulatory Role of Interferons in Viral and Bacterial Infections

Interferons are a group of immunomodulatory substances produced by the human immune system in response to the presence of pathogens, especially during viral and bacterial infections. Their remarkably diverse mechanisms of action help the immune system fight infections by activating hundreds of genes involved in signal transduction pathways. In this review, we focus on discussing the interplay between the IFN system and seven medically important and challenging viruses (herpes simplex virus (HSV), influenza, hepatitis C virus (HCV), lymphocytic choriomeningitis virus (LCMV), human immunodeficiency virus (HIV), Epstein-Barr virus (EBV), and SARS-CoV coronavirus) to highlight the diversity of viral strategies. In addition, the available data also suggest that IFNs play an important role in the course of bacterial infections. Research is currently underway to identify and elucidate the exact role of specific genes and effector pathways in generating the antimicrobial response mediated by IFNs. Despite the numerous studies on the role of interferons in antimicrobial responses, many interdisciplinary studies are still needed to understand and optimize their use in personalized therapeutics.

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.

Avian Metapneumovirus Subgroup C Phosphoprotein Suppresses Type I Interferon Production by Blocking Interferon Regulatory Factor 3 Nuclear Translocation

Avian metapneumovirus subgroup C (aMPV/C) is an important pathogen that causes upper respiratory symptoms and egg production decline in turkeys and chickens. aMPV/C infection leads to inhibition of the host antiviral immune response. However, our understanding of the molecular mechanisms underlying host immune response antagonized by aMPV/C infection is limited. In this study, we demonstrated that the aMPV/C phosphoprotein (P) inhibits the IFN antiviral signaling pathway triggered by melanoma differentiation gene 5 (MDA5) and reduces interferon β (IFN-β) production and IFN-stimulated genes (ISGs) by targeting IFN regulatory factor 7 (IRF7) but not nuclear factor κB (NF-κB) in DF-1 cells. Moreover, we found that aMPV/C P protein only blocks the nuclear translocation of IRF3 by interacting with IRF3 in HEK-293T cells, instead of affecting IRF3 phosphorylation and inducing IRF3 degradation, which suppresses IRF3 signaling activation and results in a decrease in IFN-β production. Collectively, these results reveal a novel mechanism by which aMPV/C infection disrupts IFN-β production in the host. IMPORTANCE The innate immune response is the first defense line of host cells and organisms against viral infections. When RNA viruses infect cells, viral RNA induces activation of retinoic acid-induced gene I and melanoma differentiation gene 5, which initiates downstream molecules and finally produces type I interferon (IFN-I) to regulate antiviral immune responses. The mechanism for avian metapneumovirus (aMPV) modulating IFN-I production to benefit its replication remains unknown. Here, we demonstrate that phosphoprotein of aMPV subgroup C (aMPV/C) selectively inhibits the nuclear translocation of interferon regulatory 3 (IRF3), instead of affecting the expression and phosphorylation of IRF3, which finally downregulates IFN-I production. This study showed a novel mechanism for aMPV/C infection antagonizing the host IFN response.

Evolution and emergence of primate-specific interferon regulatory factor 9

The binding of interferon (IFN) to its receptors leads to formation of IFN-stimulated gene factor 3 (ISGF3) complex that activates the transcription of cellular IFN-regulated genes. IFN regulatory factor 9 (IRF9, also called ISGF3γ or p48) is a key component of ISGF3. However, there is limited knowledge regarding the molecular evolution of IRF9 among vertebrates. In this study, we have identified the existence of the IRF9 gene in cartilaginous fish (sharks). Among primates, several isoforms unique to old world moneys and great apes are identified. These IRF9 isoforms are named as primate-specific IRF9 (PS-IRF9) to distinguish from canonical IRF9. PS-IRF9 originates from a unique exon usage and differential splicing in the IRF9 gene. Although the N-terminus are identical for all IRF9s, the C-terminal regions of the PS-IRF9 are completely different from canonical IRF9. In humans, two PS-IRF9s are identified and their RNA transcripts were detected in human primary peripheral blood mononuclear cells. In addition, human PS-IRF9 proteins were detected in human cell lines. Sharing the N-terminal exons with the canonical IRF9 proteins, PS-IRF9 is predicted to bind to the same DNA sequences as the canonical IRF9 proteins. As the C-terminal regions of IRFs are the determinants of IRF functions, PS-IRF9 may offer unique biological functions and represent a novel signaling molecule involved in the regulation of the IFN pathway in a primate-specific manner.

Combining a nanoparticle-mediated immunoradiotherapy with dual blockade of LAG3 and TIGIT improves the treatment efficacy in anti-PD1 resistant lung cancer

BACKGROUND

While improvements in immunoradiotherapy have significantly improved outcomes for cancer patients, this treatment approach has nevertheless proven ineffective at controlling the majority of malignancies. One of the mechanisms of resistance to immunoradiotherapy is that immune cells may be suppressed via the myriad of different immune checkpoint receptors. Therefore, simultaneous blockade of multiple immune checkpoint receptors may enhance the treatment efficacy of immunoradiotherapy.

METHODS

We combined NBTXR3-enhanced localized radiation with the simultaneous blockade of three different checkpoint receptors: PD1, LAG3, and TIGIT, and tested the treatment efficacy in an anti-PD1-resistant lung cancer model in mice. 129 Sv/Ev mice were inoculated with fifty thousand αPD1-resistant 344SQR cells in the right leg on day 0 to establish primary tumors and with the same number of cells in the left leg on day 4 to establish the secondary tumors. NBTXR3 was intratumorally injected into the primary tumors on day 7, which were irradiated with 12 Gy on days 8, 9, and 10. Anti-PD1 (200 µg), αLAG3 (200 µg), and αTIGIT (200 µg) were given to mice by intraperitoneal injections on days 5, 8, 11, 14, 21, 28, 35, and 42.

RESULTS

This nanoparticle-mediated combination therapy is effective at controlling the growth of irradiated and distant unirradiated tumors, enhancing animal survival, and is the only one that led to the destruction of both tumors in approximately 30% of the treated mice. Corresponding with this improved response is robust activation of the immune response, as manifested by increased numbers of immune cells along with a transcriptional signature of both innate and adaptive immunity within the tumor. Furthermore, mice treated with this combinatorial therapy display immunological memory response when rechallenged by the same cancer cells, preventing tumor engraftment.

CONCLUSION

Our results strongly attest to the efficacy and validity of combining nanoparticle-enhanced radiotherapy and simultaneous blockade of multiple immune checkpoint receptors and provide a pre-clinical rationale for investigating its translation into human patients.

Goose IRF7 is involved in antivirus innate immunity by mediating IFN activation

Interferon regulatory factor (IRF) 3 and IRF7 are the most important nuclear transcription factors regulating type-I interferon (IFN) production in mammals and the IRF3 is missing in birds. Our previous study found that IFR7 is the most important IRF in chickens, however, its functions in geese remain unknown. We cloned goose IRF7 (GoIRF7) and conducted bioinformatics analyses to compare the chromosomal location and protein homology of IRF7 in different species. Overexpression of GoIRF7 in DF-1 cells induced the activation of IFN-β, and this activation correlated positively with the dosage of transfected plasmids. Overexpression of GoIRF7 in goose embryonic fibroblasts (GEFs) induced the expression of IFNs, proinflammatory cytokines, and IFN-stimulated genes (ISGs); it also inhibited replication of Newcastle disease virus (NDV) and vesicular stomatitis virus (VSV). Our results suggest that GoIRF7 is an important regulator of IFNs, proinflammatory cytokines, and ISGs and plays a role in antiviral innate immunity in geese.

Regulation of STAT3 signaling in IFNγ and IL10 pathways and in their cross-talk

The pro-inflammatory IFNγ-STAT1 pathway and anti-inflammatory IL10-STAT3 pathway elicit cellular responses primarily utilizing their canonical STATs. However IL10 mediated STAT1 and IFNγ mediated STAT3 activation is also observed, suggesting crosstalk of these functionally opposing signaling pathways can potentially reshape the canonical dynamics both STATs and alter the expression of their target genes. Herein, we measured the dynamics of STATs in response to different doses of IL10 or IFNγ and in their co-stimulation and employed quantitative modeling to understand the regulatory mechanisms controlling signal responses in individual and co-simulation scenarios. Our experiments show, STAT3 in particular, exhibits a bell-shaped dose-response while treated with IFNγ or IL10 and our model quantiatively captured the dose-dependent dynamics of both the STATs in both pathways. The model next predicted and subsequent experiments validated that STAT3 dynamics would robustly remain IL10 specific when subjected to a co-stimulation of both IFNγ and IL10. Genes common to both pathways also exhibited IL10 specific expression during the co-stimulation. The findings thus uncover anovel feature of the IL10-STAT3 signaling axis during pathway crosstalk. Finally, parameter sampling coupled to information theory based analysis showed that bell-shaped signal-response of STAT3 in both pathways is primarily dependent on receptor concentration whereas robustness of IL10-STAT3 signaling axis in co-stimulation results from the negative regulation of the IFNγ pathway.

The role of interferon regulatory factor 7 in the pathogenicity and immunogenicity of rabies virus in a mouse model

Rabies is a zoonotic disease caused by the rabies virus (RABV). RABV can lead to fatal encephalitis and is still a serious threat in most parts of the world. Interferon regulatory factor 7 (IRF7) is the main transcriptional regulator of type I IFN, and it is crucial for the induction of IFNα/β and the type I IFN-dependent immune response. In this study, we focused on the role of IRF7 in the pathogenicity and immunogenicity of RABV using an IRF7^-/- mouse model. The results showed that the absence of IRF7 made mice more susceptible to RABV, because IRF7 restricted the replication of RABV in the early stage of infection. IRF7 deficiency affected the recruitment of plasmacytoid dendritic cells to the draining lymph nodes (dLNs), reduced the production of type I IFN and expression of IFN-stimulated genes. Furthermore, we found that the ability to produce specific RABV-neutralizing antibody was impaired in IRF7^-/- mice. Consistently, IRF7 deficiency affected the recruitment of germinal-centre B cells to dLNs, and the generation of plasma cells and RABV-specific antibody secreting cells. Moreover, the absence of IRF7 downregulated the induction of IFN-γ and reduced type 1 T helper cell (Th1)-dependent antibody production. Collectively, our findings demonstrate that IRF7 promotes humoral immune responses and compromises the pathogenicity of RABV in a mouse model.

Evasion of Antiviral Innate Immunity by Porcine Reproductive and Respiratory Syndrome Virus

Innate immunity is the front line for antiviral immune responses and bridges adaptive immunity against viral infections. However, various viruses have evolved many strategies to evade host innate immunity. A typical virus is the porcine reproductive and respiratory syndrome virus (PRRSV), one of the most globally devastating viruses threatening the swine industry worldwide. PRRSV engages several strategies to evade the porcine innate immune responses. This review focus on the underlying mechanisms employed by PRRSV to evade pattern recognition receptors signaling pathways, type I interferon (IFN-α/β) receptor (IFNAR)-JAK-STAT signaling pathway, and interferon-stimulated genes. Deciphering the antiviral immune evasion mechanisms by PRRSV will enhance our understanding of PRRSV’s pathogenesis and help us to develop more effective methods to control and eliminate PRRSV.

Role of Alternative Splicing in Regulating Host Response to Viral Infection

The importance of transcriptional regulation of host genes in innate immunity against viral infection has been widely recognized. More recently, post-transcriptional regulatory mechanisms have gained appreciation as an additional and important layer of regulation to fine-tune host immune responses. Here, we review the functional significance of alternative splicing in innate immune responses to viral infection. We describe how several central components of the Type I and III interferon pathways encode spliced isoforms to regulate IFN activation and function. Additionally, the functional roles of splicing factors and modulators in antiviral immunity are discussed. Lastly, we discuss how cell death pathways are regulated by alternative splicing as well as the potential role of this regulation on host immunity and viral infection. Altogether, these studies highlight the importance of RNA splicing in regulating host-virus interactions and suggest a role in downregulating antiviral innate immunity; this may be critical to prevent pathological inflammation.

Identification and functional characterization of three irf7 transcript variants in obscure puffer (Takifugu obscurus)

Interferon regulatory factor 7 (IRF7) is a key mediator in regulating the type Ι IFN response. Although irf7 has been identified in more than twenty fish species, alternative splicing has not been found in teleost irf7. Alternative splicing is an important mechanism expanding the transcriptomic and proteomic diversity, and has been found in several IRF family members. Here, three alternative splicing variants of irf7 were identified and characterized in obscure puffer. The first splicing transcript (Toirf7v1) was predicted to encode 428 amino acids with a DNA-binding domain (DBD), an interaction-associated domain (IAD) and a serine-rich domain (SRD). Toirf7v2 encoded 430 amino acids caused by the intron retention, and contained the whole conserved domains. Toirf7v3 encoded a truncated protein with 337 amino acids resulting from the alternative 5' splice-site selection, and lacked part of IAD domain and the entire SRD domain. Functional studies demonstrated that all of the three isoforms could activate the expression of type I IFN and IFN-stimulated genes (ISGs). Nevertheless, the two variants (Toirf7v2 and Toirf7v3) exhibited much less ability to induce transcription of IFN and ISGs compared to the Toirf7v1. Our findings suggest that these splicing variants may have distinct roles in the regulation of immune response. These results will be beneficial to understand the functional characteristics of irf7 variants in fish.

Alternative mRNA Processing of Innate Response Pathways in Respiratory Syncytial Virus (RSV) Infection

The innate immune response (IIR) involves rapid genomic expression of protective interferons (IFNs) and inflammatory cytokines triggered by intracellular viral replication. Although the transcriptional control of the innate pathway is known in substantial detail, little is understood about the complexity of alternative splicing (AS) and alternative polyadenylation (APA) of mRNAs underlying the cellular IIR. In this study, we applied single-molecule, real-time (SMRT) sequencing with mRNA quantitation using short-read mRNA sequencing to characterize changes in mRNA processing in the epithelial response to respiratory syncytial virus (RSV) replication. Mock or RSV-infected human small-airway epithelial cells (hSAECs) were profiled using SMRT sequencing and the curated transcriptome analyzed by structural and quality annotation of novel transcript isoforms (SQANTI). We identified 113,082 unique isoforms; 28,561 represented full splice matches, and 45% of genes expressed six or greater AS mRNA isoforms. Identification of differentially expressed AS isoforms was accomplished by mapping a short-read RNA sequencing expression matrix to the curated transcriptome, and 905 transcripts underwent differential polyadenylation site analysis enriched in protein secretion, translation, and mRNA degradation. We focused on 355 genes showing differential isoform utilization (DIU), indicating where a new AS isoform becomes a major fraction of mRNA isoforms expressed. In pathway and network enrichment analyses, we observed that DIU transcripts are substantially enriched in cell cycle control and IIR pathways. Interestingly, the RelA/IRF7 innate regulators showed substantial DIU where major transcripts included distinct isoforms with exon occlusion, intron inclusion, and alternative transcription start site utilization. We validated the presence of RelA and IRF7 AS isoforms as well as their induction by RSV using eight isoform-specific RT-PCR assays. These isoforms were identified in both immortalized and primary small-airway epithelial cells. We concluded that the cell cycle and IIR are differentially spliced in response to RSV. These data indicate that substantial post-transcriptional complexity regulates the antiviral response.

Epstein-Barr Virus (EBV) Tegument Protein BGLF2 Suppresses Type I Interferon Signaling To Promote EBV Reactivation

Interferon alpha (IFN-α) and IFN-β are type I IFNs that are induced by virus infection and are important in the host's innate antiviral response. EBV infection activates multiple cell signaling pathways, resulting in the production of type I IFN which inhibits EBV infection and virus-induced B-cell transformation. We reported previously that EBV tegument protein BGLF2 activates p38 and enhances EBV reactivation. To further understand the role of BGLF2 in EBV infection, we used mass spectrometry to identify cellular proteins that interact with BGLF2. We found that BGLF2 binds to Tyk2 and confirmed this interaction by coimmunoprecipitation. BGLF2 blocked type I IFN-induced Tyk2, STAT1, and STAT3 phosphorylation and the expression of IFN-stimulated genes (ISGs) IRF1, IRF7, and MxA. In contrast, BGLF2 did not inhibit STAT1 phosphorylation induced by IFN-γ. Deletion of the carboxyl-terminal 66 amino acids of BGLF2 reduced the ability of the protein to repress type I IFN signaling. Treatment of gastric carcinoma and Raji cells with IFN-α blocked BZLF1 expression and EBV reactivation; however, expression of BGLF2 reduced the ability of IFN-α to inhibit BZLF1 expression and enhanced EBV reactivation. In summary, EBV BGLF2 interacts with Tyk2, inhibiting Tyk2, STAT1, and STAT3 phosphorylation and impairs type I IFN signaling; BGLF2 also counteracts the ability of IFN-α to suppress EBV reactivation.IMPORTANCE Type I interferons are important for controlling virus infection. We have found that the Epstein-Barr virus (EBV) BGLF2 tegument protein binds to a protein in the type I interferon signaling pathway Tyk2 and inhibits the expression of genes induced by type I interferons. Treatment of EBV-infected cells with type I interferon inhibits reactivation of the virus, while expression of EBV BGLF2 reduces the ability of type I interferon to inhibit virus reactivation. Thus, a tegument protein delivered to cells during virus infection inhibits the host's antiviral response and promotes virus reactivation of latently infected cells. Therefore, EBV BGLF2 might protect virus-infected cells from the type I interferon response in cells undergoing lytic virus replication.

Adaptations of Interferon Regulatory Factor 3 with Transition from Terrestrial to Aquatic Life

Interferon regulatory factor 3 (IRF3) and IRF7 are closely related IRF members and the major factors for the induction of interferons, a key component in vertebrate innate immunity. However, there is limited knowledge regarding the evolution and adaptation of those IRFs to the environments. Two unique motifs in IRF3 and 7 were identified. One motif, GASSL, is highly conserved throughout the evolution of IRF3 and 7 and located in the signal response domain. Another motif, DPHK, is in the DNA-binding domain. The ancestral protein of IRF3 and 7 seemed to possess the DPHK motif. In the ray-finned fish lineage, while the DPHK is maintained in IRF7, the motif in IRF3 is changed to NPHK with a D → N amino acid substitution. The D → N substitution are also found in amphibian IRF3 but not in amphibian IRF7. Terrestrial animals such as reptiles and mammals predominantly use DPHK sequences in both IRF3 and 7. However, the D → N substitution in IRF3 DPHK is again found in cetaceans such as whales and dolphins as well as in marsupials. These observations suggest that the D → N substitutions in the IRF3 DPHK motif is likely to be associated with vertebrate's adaptations to aquatic environments and other environmental changes.

Identification and evaluation of hub mRNAs and long non-coding RNAs in neutrophils during sepsis

OBJECTIVE

To reveal the systematic response of neutrophils to sepsis and to study the hub lncRNAs in sepsis.

MATERIALS AND METHODS

Neutrophils taken from the femur and tibia of male C57 BL/6 mice were used in this study. And neutrophils were treated for 0 h, 0.5 h, 1 h, and 4 h with or without 1 µg/mL lipopolysaccharide (LPS) for further chip detection. In addition, cecal ligation and perforation were used to simulate sepsis. Here, we used different bioinformatics analyses, including differential expression analysis, weighted gene co-expression network analysis (WGCNA), and gene regulatory network analysis, to analyze the systemic response of neutrophils to sepsis.

RESULTS

We identified nine modules and found hub lncRNAs in each module. The blue and pink modules were closely related to the inflammatory state of sepsis. Some hub lncRNAs (NONMMUT005259, KnowTID_00004196, and NR_003507) may have functions related to the inflammatory state in sepsis.

CONCLUSIONS

Based on a new biological approach, our research results revealed the systemic-level response of neutrophils to sepsis and identified several hub lncRNAs with potential regulatory effects on this condition.

Differential and Overlapping Immune Programs Regulated by IRF3 and IRF5 in Plasmacytoid Dendritic Cells

We examined the signaling pathways and cell type-specific responses of IFN regulatory factor (IRF) 5, an immune-regulatory transcription factor. We show that the protein kinases IKKα, IKKβ, IKKε, and TANK-binding kinase 1 each confer IRF5 phosphorylation/dimerization, thus extending the family of IRF5 activator kinases. Among primary human immune cell subsets, we found that IRF5 is most abundant in plasmacytoid dendritic cells (pDCs). Flow cytometric cell imaging revealed that IRF5 is specifically activated by endosomal TLR signaling. Comparative analyses revealed that IRF3 is activated in pDCs uniquely through RIG-I-like receptor (RLR) signaling. Transcriptomic analyses of pDCs show that the partitioning of TLR7/IRF5 and RLR/IRF3 pathways confers differential gene expression and immune cytokine production in pDCs, linking IRF5 with immune regulatory and proinflammatory gene expression. Thus, TLR7/IRF5 and RLR-IRF3 partitioning serves to polarize pDC response outcome. Strategies to differentially engage IRF signaling pathways should be considered in the design of immunotherapeutic approaches to modulate or polarize the immune response for specific outcome.

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).

Molecular cloning and functional characterization of interferon regulatory factor 7 of the barbel chub, Squaliobarbus curriculus

The interferon regulatory factor 7 (IRF7) is a critical regulator of type-I interferon-dependent immune reaction that defense against virus. To investigate the antiviral function of IRF7 of barbel chub Squaliobarbus curriculus (ScIRF7), the cDNA of ScIRF7 was cloned and characterized. The full length cDNA of ScIRF7 was 1870 bp, consisted of 41 bp 5'-UTR, 560 bp 3'-UTR and a 1269 bp open reading frame (ORF). The ORF encoded 423 amino acids with a molecular weight of 49.426 KDa and a theoretical isoelectric point of 5.71. The putative ScIRF7 protein possesses typical domains of IRF family including a conserved N-terminal DBD-binding domain (DBD), a C-terminal IRF association domain and a serine-rich domain. In the DBD, four tryptophans were found to be highly conserved among all species, whilst in another conserved tryptophan site of mammals, the corresponding amino acids were methionine for fishes. The expression level of ScIRF7 was highest in the spleen and lowest in the liver. The expression level of IFN-β was highest in the gill and lowest in the liver. After GCRV infection, expression levels changes of ScIRF7 showed an overall tendency of firstly up-regulation and then down-regulation in the spleen and the gill; and expression levels of ScIRF7 in peripheral blood lymphocyte at 24 h post-infection was highest among all time points. In pEGFP-ScIRF7 overexpressing cells, the mRNA level of ScIRF7 was firstly up-regulation and then down-regulation; and the expression of IFN-β was significantly up-regulated at 12 h post-infection than that of control group (P < 0.05), which was significantly higher than those in pEGFP-N1 overexpressing cells. The results indicated that ScIRF7 may play a key role in immune responses of barbel chub Squaliobarbus curriculus against GCRV and may also functions in the Ctenopharyngodon idellus kidney cells.

Tumor Suppressor p53 Stimulates the Expression of Epstein-Barr Virus Latent Membrane Protein 1

Epstein-Barr virus (EBV) is associated with multiple human malignancies. EBV latent membrane protein 1 (LMP1) is required for the efficient transformation of primary B lymphocytes in vitro and possibly in vivo The tumor suppressor p53 plays a seminal role in cancer development. In some EBV-associated cancers, p53 tends to be wild type and overly expressed; however, the effects of p53 on LMP1 expression is not clear. We find LMP1 expression to be associated with p53 expression in EBV-transformed cells under physiological and DNA damaging conditions. DNA damage stimulates LMP1 expression, and p53 is required for the stimulation. Ectopic p53 stimulates endogenous LMP1 expression. Moreover, endogenous LMP1 blocks DNA damage-mediated apoptosis. Regarding the mechanism of p53-mediated LMP1 expression, we find that interferon regulatory factor 5 (IRF5), a direct target of p53, is associated with both p53 and LMP1. IRF5 binds to and activates a LMP1 promoter reporter construct. Ectopic IRF5 increases the expression of LMP1, while knockdown of IRF5 leads to reduction of LMP1. Furthermore, LMP1 blocks IRF5-mediated apoptosis in EBV-infected cells. All of the data suggest that cellular p53 stimulates viral LMP1 expression, and IRF5 may be one of the factors for p53-mediated LMP1 stimulation. LMP1 may subsequently block DNA damage- and IRF5-mediated apoptosis for the benefits of EBV. The mutual regulation between p53 and LMP1 may play an important role in EBV infection and latency and its related cancers.IMPORTANCE The tumor suppressor p53 is a critical cellular protein in response to various stresses and dictates cells for various responses, including apoptosis. This work suggests that an Epstein-Bar virus (EBV) principal viral oncogene is activated by cellular p53. The viral oncogene blocks p53-mediated adverse effects during viral infection and transformation. Therefore, the induction of the viral oncogene by p53 provides a means for the virus to cope with infection and DNA damage-mediated cellular stresses. This seems to be the first report that p53 activates a viral oncogene; therefore, the discovery would be interesting to a broad readership from the fields of oncology to virology.

Interferon activates promoter of Nmi gene via interferon regulator factor-1

N-Myc interactor (Nmi) is reported to participate in many activities, such as signaling transduction, transcription regulation, and antiviral responses. As Nmi may play important roles in interferon (IFN)-induced responses, we investigated the mechanism how Nmi protein is regulated. We identified and cloned the promoter of Nmi gene. Sequence analysis and luciferase assays shown that an IFN-stimulated response element (ISRE) and a GC box in the promoter were essential for the basal transcription activity of Nmi gene. We also found that interferon regulatory factor 1 (IRF-1) could activate transcription of Nmi by binding to the ISRE in the promoter. Knockdown of IRF-1 decreases IFN-induced Nmi transcription. These results revealed that IRF-1 is involved in the IFN-inducible expression of Nmi.

Persistent Cytomegalovirus Infection in Amniotic Membranes of the Human Placenta

Human cytomegalovirus (HCMV) is the leading viral cause of birth defects, including microcephaly, neurological deficits, hearing impairment, and vision loss. We previously reported that epithelial cells in amniotic membranes of placentas from newborns with intrauterine growth restriction and underlying congenital HCMV infection contain viral proteins in cytoplasmic vesicles. Herein, we immunostained amniotic membranes from 51 placentas from symptomatic and asymptomatic congenital infection with HCMV DNA in amniotic fluid and/or newborn saliva, intrauterine growth restriction, preterm deliveries, and controls. We consistently observed HCMV proteins in amniotic epithelial cells (AmEpCs) from infected placentas, sometimes with aberrant morphology. Primary AmEpCs isolated from mid-gestation placentas infected with pathogenic VR1814 proliferated and released infectious progeny for weeks, producing higher virus titers than late-gestation cells that varied by donor. In contrast to intact virion assembly compartments in differentiated retinal pigment epithelial cells, infected AmEpCs made dispersed multivesicular bodies. Primary AmEpCs and explants of amniochorionic membranes from mid-gestation placentas formed foci of infection, and interferon-β production was prolonged. Infected AmEpCs up-regulated anti-apoptotic proteins survivin and Bcl-x_L by mechanisms dependent and independent of the activated STAT3. Amniotic membranes naturally expressed both survivin and Bcl-x_L, indicating that fetal membranes could foster persistent viral infection. Our results suggest strengthening innate immune responses and reducing viral functions could suppress HCMV infection in the fetal compartment.

The Foot-and-Mouth Disease Carrier State Divergence in Cattle

The pathogenesis of persistent foot-and-mouth disease virus (FMDV) infection was investigated in 46 cattle that were either naive or had been vaccinated using a recombinant, adenovirus-vectored vaccine 2 weeks before challenge. The prevalence of FMDV persistence was similar in both groups (62% in vaccinated cattle, 67% in nonvaccinated cattle), despite vaccinated cattle having been protected from clinical disease. Analysis of antemortem infection dynamics demonstrated that the subclinical divergence between FMDV carriers and animals that cleared the infection had occurred by 10 days postinfection (dpi) in vaccinated cattle and by 21 dpi in nonvaccinated animals. The anatomic distribution of virus in subclinically infected, vaccinated cattle was restricted to the pharynx throughout both the early and the persistent phases of infection. In nonvaccinated cattle, systemically disseminated virus was cleared from peripheral sites by 10 dpi, while virus selectively persisted within the nasopharynx of a subset of animals. The quantities of viral RNA shed in oropharyngeal fluid during FMDV persistence were similar in vaccinated and nonvaccinated cattle. FMDV structural and nonstructural proteins were localized to follicle-associated epithelium of the dorsal soft palate and dorsal nasopharynx in persistently infected cattle. Host transcriptome analysis of tissue samples processed by laser capture microdissection indicated suppression of antiviral host factors (interferon regulatory factor 7, CXCL10 [gamma interferon-inducible protein 10], gamma interferon, and lambda interferon) in association with persistent FMDV. In contrast, during the transitional phase of infection, the level of expression of IFN-λ mRNA was higher in follicle-associated epithelium of animals that had cleared the infection. This work provides novel insights into the intricate mechanisms of FMDV persistence and contributes to further understanding of this critical aspect of FMDV pathogenesis.

IMPORTANCE The existence of a prolonged, asymptomatic carrier state is a political impediment for control and potential eradication of foot-and-mouth disease (FMD). When FMD outbreaks occur, they are often extinguished by massive depopulation of livestock due to the fear that some animals may have undiagnosed subclinical infection, despite uncertainty over the biological relevance of FMD virus (FMDV) persistence. The work described here elucidates aspects of the FMDV carrier state in cattle which may facilitate identification and/or abrogation of asymptomatic FMDV infection. The divergence between animals that clear infection and those that develop persistent infection was demonstrated to occur earlier than previously established. The host antiviral response in tissues maintaining persistent FMDV was downregulated, whereas upregulation of IFN-λ mRNA was found in the epithelium of cattle that had recently cleared the infection. This suggests that the clearing of FMDV infection is associated with an enhanced mucosal antiviral response, whereas FMDV persistence is associated with suppression of the host antiviral response.

3C Protease of Enterovirus D68 Inhibits Cellular Defense Mediated by Interferon Regulatory Factor 7

Human enterovirus 68 (EV-D68) is a member of the EV-D species, which belongs to the EV genus of the Picornaviridae family. Over the past several years, clusters of EV-D68 infections have occurred worldwide. A recent outbreak in the United States is the largest one associated with severe respiratory illness and neurological complication. Although clinical symptoms are recognized, the virus remains poorly understood. Here we report that EV-D68 inhibits innate antiviral immunity by downregulation of interferon regulatory factor 7 (IRF7), an immune factor with a pivotal role in viral pathogenesis. This process depends on 3C(pro), an EV-D68-encoded protease, to mediate IRF7 cleavage. When expressed in host cells, 3C(pro) targets Q167 and Q189 within the constitutive activation domain, resulting in cleavage of IRF7. Accordingly, wild-type IRF7 is fully active. However, IRF7 cleavage abrogated its capacity to activate type I interferon expression and limit replication of EV-D68. Notably, IRF7 cleavage strictly requires the protease activity of 3C(pro). Together, these results suggest that a dynamic interplay between 3C(pro) and IRF7 may determine the outcome of EV-D68 infection.

IMPORTANCE

EV-D68 is a globally emerging pathogen, but the molecular basis of EV-D68 pathogenesis is unclear. Here we report that EV-D68 inhibits innate immune responses by targeting an immune factor, IRF7. This involves the 3C protease encoded by EV-D68, which mediates the cleavage of IRF7. These observations suggest that the 3C(pro)-IRF7 interaction may represent an interface that dictates EV-D68 infection.

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.

Interferon regulatory factor 7 functions as a novel negative regulator of pathological cardiac hypertrophy

Cardiac hypertrophy is a complex pathological process that involves multiple factors including inflammation and apoptosis. Interferon regulatory factor 7 (IRF7) is a multifunctional regulator that participates in immune regulation, cell differentiation, apoptosis, and oncogenesis. However, the role of IRF7 in cardiac hypertrophy remains unclear. We performed aortic banding in cardiac-specific IRF7 transgenic mice, IRF7 knockout mice, and the wild-type littermates of these mice. Our results demonstrated that IRF7 was downregulated in aortic banding-induced animal hearts and cardiomyocytes that had been treated with angiotensin II or phenylephrine for 48 hours. Accordingly, heart-specific overexpression of IRF7 significantly attenuated pressure overload-induced cardiac hypertrophy, fibrosis, and dysfunction, whereas loss of IRF7 led to opposite effects. Moreover, IRF7 protected against angiotensin II-induced cardiomyocyte hypertrophy in vitro. Mechanistically, we identified that IRF7-dependent cardioprotection was mediated through IRF7 binding to inhibitor of κB kinase-β, and subsequent nuclear factor-κB inactivation. In fact, blocking nuclear factor-κB signaling with cardiac-specific inhibitors of κBα(S32A/S36A) super-repressor transgene counteracted the adverse effect of IRF7 deficiency. Conversely, activation of nuclear factor-κB signaling via a cardiac-specific conditional inhibitor of κB kinase-β(S177E/S181E) (constitutively active) transgene negated the antihypertrophic effect of IRF7 overexpression. Our data demonstrate that IRF7 acts as a novel negative regulator of pathological cardiac hypertrophy by inhibiting nuclear factor-κB signaling and may constitute a potential therapeutic target for pathological cardiac hypertrophy.

Genetics of the type I interferon pathway in systemic lupus erythematosus

Genetic studies of systemic lupus erythematosus (SLE) have been successful, identifying numerous risk factors for human disease. While the list is not yet complete, it is clear that important immune system pathways are represented, one of which being type I interferon (IFN). Circulating type I IFN levels are high in SLE patients and this IFN pathway activation is heritable in families with SLE. We summarize our current understanding of the genetics of the type I IFN pathway in SLE, with an emphasis on studies that demonstrate an impact of the SLE-risk alleles upon type I IFN pathway activation in SLE patients. These studies illustrate that variations in type I IFN pathway genes represent a common genetic feature of SLE. By understanding the genetic regulation of type I IFN, we may be able to intervene in a more personalized fashion, based upon the molecular dysregulation present in a given individual.

IRF-7: an antiviral factor and beyond

This review will summarize main characteristics and functions of IRF-7. IRF-7 and the highly homologous IRF-3 are two members of the IRF family of transcription factors that have emerged as crucial regulators of type I interferon (IFN) in response to pathogenic infections downstream pathogen recognition receptors. IRF-7 is also part of a positive-feedback regulatory loop essential for sustained IFN responses. Thus, tight regulation of its expression and activity is necessary to balance IFN-mediated beneficial effects and unwanted pathological consequences of IFN overproduction. Its role as an antiviral factor independent of IFN expression, and its involvement in other cellular functions beyond antiviral functions, including regulation of oncogenesis and metabolism, underscore its important role in the regulation of cellular homeostasis.

Distinct roles of Kaposi's sarcoma-associated herpesvirus-encoded viral interferon regulatory factors in inflammatory response and cancer

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent associated with Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman disease (MCD). Similar to other herpesviruses, KSHV has two life cycles, latency and lytic replication. In latency, the KSHV genome persists as a circular episome in the nucleus of the host cell and only a few viral genes are expressed. In this review, we focus on oncogenic, antiapoptotic, and immunomodulating properties of KSHV-encoded homologues of cellular interferon regulatory factors (IRFs)--viral IRF1 (vIRF1) to vIRF4--and their possible role in the KSHV-mediated antiviral response, apoptosis, and oncogenicity.

The association of CD81 polymorphisms with alloimmunization in sickle cell disease

The goal of the present work was to identify the candidate genetic markers predictive of alloimmunization in sickle cell disease (SCD). Red blood cell (RBC) transfusion is indicated for acute treatment, prevention, and abrogation of some complications of SCD. A well-known consequence of multiple RBC transfusions is alloimmunization. Given that a subset of SCD patients develop multiple RBC allo-/autoantibodies, while others do not in a similar multiple transfusional setting, we investigated a possible genetic basis for alloimmunization. Biomarker(s) which predicts (predict) susceptibility to alloimmunization could identify patients at risk before the onset of a transfusion program and thus may have important implications for clinical management. In addition, such markers could shed light on the mechanism(s) underlying alloimmunization. We genotyped 27 single nucleotide polymorphisms (SNPs) in the CD81, CHRNA10, and ARHG genes in two groups of SCD patients. One group (35) of patients developed alloantibodies, and another (40) had no alloantibodies despite having received multiple transfusions. Two SNPs in the CD81 gene, that encodes molecule involved in the signal modulation of B lymphocytes, show a strong association with alloimmunization. If confirmed in prospective studies with larger cohorts, the two SNPs identified in this retrospective study could serve as predictive biomarkers for alloimmunization.

The applied basic research of systemic lupus erythematosus based on the biological omics

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by the production of autoantibodies directed against nuclear self-antigens and circulating immune complexes. This results in damages to various organs or systems, including skin, joints, kidneys and the central nervous system. Clinical manifestations of SLE could be diverse, including glomerulonephritis, dermatitis, thrombosis, vasculitis, seizures and arthritis. The complicated pathogenesis and varied clinical symptoms of SLE pose great challenges in the diagnosis and monitoring of this disease. Unfortunately, the etiological factors and pathogenesis of SLE are still not completely understood. It is noteworthy that recent advances in our understanding of the biological omics and emerging technologies have been providing new tools in the analyses of SLE, such as genomics, epigenomics, transcriptomics, proteomics, metabolomics and so on. In this article, we summarize our current knowledge in this field for a better understanding of the pathogenesis, diagnosis and treatment for SLE.

The bile acid sensor FXR is required for immune-regulatory activities of TLR-9 in intestinal inflammation

BACKGROUND

Toll like receptors (TLRs) sense the intestinal microbiota and regulate the innate immune response. A dysregulation of TLRs function participates into intestinal inflammation. Farnesoid X Receptor (FXR) is a nuclear receptor and bile acid sensor highly expressed in entero-hepatic tissues. FXR regulates lipid metabolism and innate immunity.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we have investigated whether FXR gene expression/function in the intestine is modulated by TLRs. We found that in human monocytes activation of membrane TLRs (i.e. TLR2, 4, 5 and 6) downregulates, while activation of intracellular TLRs (i.e. TLR3, 7, 8 and 9) upregulates the expression of FXR and its target gene SHP, small heterodimer partner. This effect was TLR9-dependent and TNFα independent. Intestinal inflammation induced in mice by TNBS downregulates the intestinal expression of FXR in a TLR9-dependent manner. Protection against TNBS colitis by CpG, a TLR-9 ligand, was lost in FXR(-/-) mice. In contrast, activation of FXR rescued TLR9(-/-) and MyD88(-/-) mice from colitis. A putative IRF7 response element was detected in the FXR promoter and its functional characterization revealed that IRF7 is recruited on the FXR promoter under TLR9 stimulation.

CONCLUSIONS/SIGNIFICANCE

Intestinal expression of FXR is selectively modulated by TLR9. In addition to its role in regulating type-I interferons and innate antiviral immunity, IRF-7 a TLR9-dependent factor, regulates the expression of FXR, linking microbiota-sensing receptors to host's immune and metabolic signaling.

Association of a functional IRF7 variant with systemic lupus erythematosus

OBJECTIVE

A previous genome-wide association study conducted in a population of European ancestry identified rs4963128, a KIAA1542 single-nucleotide polymorphism (SNP) 23 kb telomeric to IRF7 (the gene for interferon regulatory factor 7 [IRF-7]), to be strongly associated with systemic lupus erythematosus (SLE). This study was undertaken to investigate whether genetic polymorphism within IRF7 is a risk factor for the development of SLE.

METHODS

We genotyped one KIAA1542 SNP (rs4963128) and one IRF7 SNP (rs1131665 [Q412R]) in an Asian population (1,302 cases, 1,479 controls), to assess their association with SLE. Subsequently, rs1131665 was further genotyped in independent panels of Chinese subjects (528 cases, 527 controls), European American subjects (446 cases, 461 controls), and African American subjects (159 cases, 115 controls) by TaqMan genotyping assay, to seek confirmation of association in various ethnic groups. A luciferase reporter assay was used to assess the effect of Q412R polymorphism on the activation of IRF-7.

RESULTS

Consistent association of rs1131665 (Q412R) with SLE was identified in Asian, European American, and African American populations (total 2,435 cases and 2,582 controls) (P(meta) = 6.18 × 10(-6) , odds ratio 1.42 [95% confidence interval 1.22-1.65]). Expression of the IRF7 412Q risk allele resulted in a 2-fold increase in interferon-stimulated response element transcriptional activity compared with expression of IRF7 412R (P = 0.0003), suggesting that IRF7 412Q confers elevated IRF-7 activity and may therefore affect a downstream interferon pathway.

CONCLUSION

These findings show that the major allele of a nonsynonymous SNP, rs1131665 (412Q) in IRF7, confers elevated activation of IRF-7 and predisposes to the development of SLE in multiple ethnic groups. This result provides direct genetic evidence that IRF7 may be a risk gene for human SLE.

Interferon-γ upregulates expression of IFP35 gene in HeLa cells via interferon regulatory factor-1

Background

Interferon-induced 35-kDa protein (IFP35) plays important roles in antiviral defense and the progression of some skin cancer diseases. It can be induced by interferon-γ (IFN-γ) in multiple human cells. However, the mechanisms by which IFN-γ contributes to IFP35 induction remain to be elucidated.

Methods/Principal Findings

We identified the transcription start sites of IFP35 by 5′ rapid amplification of cDNA ends (RACE) and cloned the promoter of IFP35. Sequence analysis and luciferase assays revealed two GC boxes and an IFN-stimulated response element (ISRE) in the 5′ upstream region of the transcription start sites, which were important for the basal transcription of IFP35 gene. Furthermore, we found that interferon regulatory factor 1 (IRF-1) and IRF-2 could bind to IFP35 promoter and upregulate endogenous IFP35 protein level. Depletion of endogenous IRF-1 by interfering RNA reduced the constitutive and IFN-γ-dependent expression of IFP35, whereas depletion of IRF-2 had little effect on IFN-γ-inducible IFP35 expression. Moreover, IRF-1 was recruited to the ISRE site in IFP35 promoter in IFN-γ treated HeLa cells, as demonstrated by electrophoretic mobility shift and chromatin immunoprecipitation assays.

Conclusions/Significance

These findings provide the first evidence that IRF-1 and IRF-2 are involved in constitutive IFP35 expression in HeLa cells, while IRF-1 also activates IFP35 expression in an IFN-γ-inducible manner. Our data therefore identified a new IRF-1 and IRF-2 target gene, which may expand our current understanding of the versatile functions of IRF-1 and IRF-2.

Epstein-Barr virus latent membrane protein 1 regulates the function of interferon regulatory factor 7 by inducing its sumoylation

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) induces multiple signal transduction pathways during latent EBV infection via its C-terminal activating region 1 (CTAR1), CTAR2, and the less-studied CTAR3. One mechanism by which LMP1 regulates cellular activation is through the induction of protein posttranslational modifications, including phosphorylation and ubiquitination. We recently documented that LMP1 induces a third major protein modification by physically interacting with the SUMO-conjugating enzyme Ubc9 through CTAR3 and inducing the sumoylation of cellular proteins in latently infected cells. We have now identified a specific target of LMP1-induced sumoylation, interferon regulatory factor 7 (IRF7). We hypothesize that during EBV latency, LMP1 induces the sumoylation of IRF7, limiting its transcriptional activity and modulating the activation of innate immune responses. Our data show that endogenously sumoylated IRF7 is detected in latently infected EBV lymphoblastoid cell lines. LMP1 expression coincided with increased sumoylation of IRF7 in a CTAR3-dependent manner. Additional experiments show that LMP1 CTAR3-induced sumoylation regulates the expression and function of IRF7 by decreasing its turnover, increasing its nuclear retention, decreasing its DNA binding, and limiting its transcriptional activation. Finally, we identified that IRF7 is sumoylated at lysine 452. These data demonstrate that LMP1 CTAR3 does in fact function in intracellular signaling, leading to biologic effects. We propose that CTAR3 is an important signaling region of LMP1 that regulates protein function by sumoylation. We have shown specifically that LMP1 CTAR3, in cooperation with CTAR2, can limit the ability of IRF7 to induce innate immune responses by inducing the sumoylation of IRF7.

Toll-like receptor 7 stimulates the expression of Epstein-Barr virus latent membrane protein 1

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus. Toll-like receptor 7 (TLR7) is involved in host innate immunity against pathogens, and its aberrant activation is linked to the development of systemic lupus erythematosus (SLE, also called “lupus”). Type I interferons (IFN) are apparently driving forces for lupus pathogenesis. Previously, we found that EBV latent membrane protein 1 (LMP1) primes cells for IFN production. In this report, the relationship among EBV LMP1, TLRs, and IFN production are examined. We find that TLR7 activation increases the expression of EBV LMP1, and IFN regulatory factor 7 (IRF7) is involved in the stimulation process. TLR7 activation did not induce IFNs from EBV-infected cells, but potentiates those cells for IFN production by TLR3 or TLR9 activation. In addition, we find that LMP1 and IFNs are co-expressed in the same cells in some lupus patients. Therefore, the aberrant activation of TLR7 might induce LMP1 expression and LMP1-expression cells may be producing IFNs in lupus patients. These results suggest EBV might be an exacerbating factor in some lupus patients via promoting IFN production.

Role of cytokines in systemic lupus erythematosus: recent progress from GWAS and sequencing

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder, known to have a strong genetic component. Concordance between monozygotic twins is approximately 30-40%, which is 8-20 times higher than that of dizygotic twins. In the last decade, genome-wide approaches to understanding SLE have yielded many candidate genes, which are important to understanding the pathophysiology of the disease and potential targets for pharmaceutical intervention. In this paper, we focus on the role of cytokines and examine how genome-wide association studies, copy number variation studies, and next-generation sequencing are being employed to understand the etiology of SLE. Prominent genes identified by these approaches include BLK, FCγR3B, and TREX1. Our goal is to present a brief overview of genomic approaches to SLE and to introduce some of the key discussion points pertinent to the field.

Cd14 SNPs regulate the innate immune response

CD14 is a monocytic differentiation antigen that regulates innate immune responses to pathogens. Here, we show that murine Cd14 SNPs regulate the length of Cd14 mRNA and CD14 protein translation efficiency, and consequently the basal level of soluble CD14 (sCD14) and type I IFN production by murine macrophages. This has substantial downstream consequences for the innate immune response; the level of expression of at least 40 IFN-responsive murine genes was altered by this mechanism. We also observed that there was substantial variation in the length of human CD14 mRNAs and in their translation efficiency. sCD14 increased cytokine production by human dendritic cells (DCs), and sCD14-primed DCs augmented human CD4T cell proliferation. These findings may provide a mechanism for exploring the complex relationship between CD14 SNPs, serum sCD14 levels, and susceptibility to human infectious and allergic diseases.

IRF6 is a mediator of Notch pro-differentiation and tumour suppressive function in keratinocytes

While the pro-differentiation and tumour suppressive functions of Notch signalling in keratinocytes are well established, the underlying mechanisms remain poorly understood. We report here that interferon regulatory factor 6 (IRF6), an IRF family member with an essential role in epidermal development, is induced in differentiation through a Notch-dependent mechanism and is a primary Notch target in keratinocytes and keratinocyte-derived SCC cells. Increased IRF6 expression contributes to the impact of Notch activation on growth/differentiation-related genes, while it is not required for induction of 'canonical' Notch targets like p21(WAF1/Cip1), Hes1 and Hey1. Down-modulation of IRF6 counteracts differentiation of primary human keratinocytes in vitro and in vivo, promoting ras-induced tumour formation. The clinical relevance of these findings is illustrated by the strikingly opposite pattern of expression of Notch1 and IRF6 versus epidermal growth factor receptor in a cohort of clinical SCCs, as a function of their grade of differentiation. Thus, IRF6 is a primary Notch target in keratinocytes, which contributes to the role of this pathway in differentiation and tumour suppression.

Absent in Melanoma 2 (AIM2) is an important mediator of interferon-dependent and -independent HLA-DRA and HLA-DRB gene expression in colorectal cancers

Absent in Melanoma 2 (AIM2) is a member of the HIN-200 family of hematopoietic, IFN-inducible, nuclear proteins, associated with both, infection defense and tumor pathology. Recently, AIM2 was found to act as a DNA sensor in innate immunity. In addition, we and others have previously demonstrated a high frequency of AIM2-alterations in microsatellite unstable (MSI-H) tumors. To further elucidate AIM2 function in colorectal tumors, we here addressed AIM2-responsive target genes by microarray based gene expression profiling of 22 244 human genes. A total of 111 transcripts were significantly upregulated, whereas 80 transcripts turned out to be significantly downregulated in HCT116 cells, constitutively expressing AIM2, compared with AIM2-negative cells. Among the upregulated genes that were validated by quantitative PCR and western blotting we recognized several interferon-stimulated genes (ISGs: IFIT1, IFIT2, IFIT3, IFI6, IRF7, ISG15, HLA-DRA, HLA-DRB, TLR3 and CIITA), as well as genes involved in intercellular adhesion and matrix remodeling. Expression of ISGs correlated with expression of AIM2 in 10 different IFN-γ treated colorectal cancer cell lines. Moreover, small interfering RNA-mediated knock-down of AIM2 resulted in reduced expression of HLA-DRA, HLA-DRB and CIITA in IFN-γ-treated cells. IFN-γ independent induction of HLA-DR genes and their encoded proteins was also demonstrated upon doxycyclin-regulated transient induction of AIM2. Luciferase reporter assays revealed induction of the HLA-DR promoter upon AIM2 transfection in different cell lines. STAT-signaling was not involved in IFN-γ independent induction of ISGs, arguing against participation of cytokines released in an autostimulating manner. Our data indicate that AIM2 mediates both IFN-γ dependent and independent induction of several ISGs, including genes encoding the major histocompatibility complex (MHC) class II antigens HLA-DR-α and -β. This suggests a novel role of the IFN/AIM2/ISG cascade likewise in cancer cells.

Evasion and subversion of interferon-mediated antiviral immunity by Kaposi's sarcoma-associated herpesvirus: an overview

Viral invasion of a host cell triggers immune responses with both innate and adaptive components. The innate immune response involving the induction of type I interferons (alpha and beta interferons [IFN-α and -β]) constitutes the first line of antiviral defenses. The type I IFNs signal the transcription of a group of antiviral effector proteins, the IFN-stimulated genes (ISGs), which target distinct viral components and distinct stages of the viral life cycle, aiming to eliminate invading viruses. In the case of Kaposi's sarcoma-associated herpesvirus (KSHV), the etiological agent of Kaposi's sarcoma (KS), a sudden upsurge of type I IFN-mediated innate antiviral signals is seen immediately following both primary de novo infection and viral lytic reactivation from latency. Potent subversion of these responses thus becomes mandatory for the successful establishment of a primary infection following viral entry as well as for efficient viral assembly and egress. This review gives a concise overview of the induction of the type I IFN signaling pathways in response to viral infection and provides a comprehensive understanding of the antagonizing effects exerted by KSHV on type I IFN pathways wielded at various stages of the viral life cycle. Information garnered from this review should result in a better understanding of KSHV biology essential for the development of immunotherapeutic strategies targeted toward KSHV-associated malignancies.

Interferon regulatory factors in human lupus pathogenesis

Systemic lupus erythematosus (SLE) is a severe multisystem autoimmune disease that results from both genetic predisposition and environmental factors. Many lines of investigation support interferon alpha (IFN-α) as a causal agent in human lupus, and high levels of serum IFN-α are a heritable risk factor for SLE. Interferon regulatory factors (IRFs) are a family of transcription factors involved in host defense, which can induce transcription of IFN-α and other immune response genes after activation. In SLE, circulating immune complexes that contain nucleic acid are prevalent. These complexes are recognized by endosomal Toll-like receptors, resulting in activation of downstream IRF proteins. Genetic variants in the IRF5 and IRF7 genes have been associated with SLE susceptibility, and these same variants are associated with increased serum IFN-α in SLE patients. The increase in serum IFN-α related to IRF5 and 7 genotypes is observed only in patients with particular antibody specificities. This suggests that chronic stimulation of the endosomal Toll-like receptors by autoantibody immune complexes is required for IRF SLE-risk variants to cause elevation of circulating IFN-α and subsequent risk of SLE. Recently, genetic variation in the IRF8 gene has been associated with SLE and multiple sclerosis, and studies support an impact of IRF8 genotype on the IFN-α pathway. In summary, the SLE-associated polymorphisms in the IRF family of proteins seem to be gain-of-function variants, and understanding the impact of these variants on the IFN-α pathway in vivo may guide therapeutic strategies directed at the Toll-like receptor/IRF/IFN-α pathway in SLE.

IRF7: activation, regulation, modification and function

Interferon regulatory factor 7 (IRF7) was originally identified in the context of Epstein-Barr virus (EBV) infection, and has since emerged as the crucial regulator of type I interferons (IFNs) against pathogenic infections, which activate IRF7 by triggering signaling cascades from pathogen recognition receptors (PRRs) that recognize pathogenic nucleic acids. Moreover, IRF7 is a multifunctional transcription factor, underscored by the fact that it is associated with EBV latency, in which IRF7 is induced as well as activated by the EBV principal oncoprotein latent membrane protein-1 (LMP1). Aberrant production of type I IFNs is associated with many types of diseases such as cancers and autoimmune disorders. Thus, tight regulation of IRF7 expression and activity is imperative in dictating appropriate type I IFN production for normal IFN-mediated physiological functions. Posttranslational modifications have important roles in regulation of IRF7 activity, exemplified by phosphorylation, which is indicative of its activation. Furthermore, mounting evidence has shed light on the importance of regulatory ubiquitination in activation of IRF7. Albeit these exciting findings have been made in the past decade since its discovery, many questions related to IRF7 remain to be addressed.

Nickel-induced down-regulation of ΔNp63 and its role in the proliferation of keratinocytes

Epidemiological, animal, and cell studies have demonstrated that nickel compounds are human carcinogens. The mechanisms of their carcinogenic actions remain to be investigated. p63, a close homologue of the p53 tumor suppressor protein, has been linked to cell fate determination and/or maintenance of self-renewing populations in several epithelial tissues, including skin, mammary gland, and prostate. ΔNp63, a dominant negative isoform of p63, is amplified in a variety of epithelial tumors including squamous cell carcinomas and carcinomas of the prostate and mammary glands. The present study shows that nickel suppressed ΔNp63 expression in a short-time treatment (up to 48 h). Nickel treatment caused activation of NF-κB. Blockage of NF-κB partially reversed nickel-induced ΔNp63 suppression. Nickel decreased interferon regulatory factor (IRF) 3 and IRF7, IKKε, and Sp100. Over-expression of IRF3 increased ΔNp63 expression suppressed by nickel. Nickel was able to activate p21, and its activation was offset by the over-expression of ΔNp63. In turn, elevated p63 expression counteracted the ability of nickel to restrict cell growth. The present study demonstrated that nickel decreased interferon regulatory proteins IRF3 and IRF7, and activated NF-κB, resulting in ΔNp63 suppression and then p21 up-regulation. ΔNp63 plays an important role in nickel-induced cell proliferation.

An intronic polymorphism in the porcine IRF7 gene is associated with better health and immunity of the host during Sarcocystis infection, and affects interferon signalling

Interferon regulatory factor 7 (IRF7), as a key regulator of type I interferon response, plays an important role during innate response against viral infection. Although well conserved across species, the structure of IRF7 and its function during parasite infection are not well documented in farm animals, such as the pig. To bridge this gap, we have determined the porcine IRF7 gene structure and identified two intronic single nucleotide polymorphisms (SNPs), SNP g.748G>C and SNP g.761A>G, in commercial pig breeds. The distribution of SNP g.761A>G in multiple breeds suggested that it was in Hardy-Weinberg equilibrium and allowed us to map it at the top of SSC2. We found that during Sarcocystis miescheriana infection, the G allele was associated with high lymphocyte levels (P < 0.02), reduced drop in platelet levels (P < 0.002) and IgG1-Th2-dominated response (P < 0.05). This suggests that the G allele was associated with better health and immunity of the host during Sarcocystis infection. Furthermore, we have also provided suggestive evidence that the G allele of SNPc.761A>G enhances the transactivation activity of IRF7, possibly by improving IRF7 transcript splicing of intron-3. These findings would suggest that IRF7, as a transcriptional regulator, is involved in the defence mechanism against a larger spectrum of pathogens, and in more host species, than initially anticipated.

Getting the message direct manipulation of host mRNA accumulation during gammaherpesvirus lytic infection

The Gammaherpesvirinae subfamily of herpesviruses comprises lymphotropic viruses, including the oncogenic human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus. During lytic infection, gammaherpesviruses manipulate host gene expression to optimize the cellular environment for viral replication and to evade the immune response. Additionally, although a lytically infected cell will itself be killed in the process of viral replication, lytic infection can contribute to pathogenesis by inducing the secretion of paracrine factors with functions in cell survival and proliferation, and angiogenesis. The mechanisms by which these viruses manipulate host gene expression are varied and target the accumulation of cellular mRNAs and their translation, signaling pathways, and protein stability. Here, we discuss how gammaherpesviral proteins directly influence host mRNA biogenesis and stability, either selectively or globally, in order to fine-tune the cellular environment to the advantage of the virus. Appreciation of the mechanisms by which these viruses interface with and adapt normal cellular processes continues to inform our understanding of gammaherpesviral biology and the regulation of mRNA accumulation and turnover in our own cells.

Specific and shared targets of ephrin A signaling in epidermal keratinocytes

Both ephrins (EFNs) and their receptors (Ephs) are membrane-bound, restricting their interactions to the sites of direct cell-to-cell interfaces. They are widely expressed, often co-expressed, and regulate developmental processes, cell adhesion, motility, survival, proliferation, and differentiation. Both tumor suppressor and oncogene activities are ascribed to EFNs and Ephs in various contexts. A major conundrum regarding the EFN/Eph system concerns their large number and functional redundancy given the promiscuous cross-activation of ligands and receptors and the overlapping intracellular signaling pathways. To address this issue, we treated human epidermal keratinocytes with five EFNAs individually and defined the transcriptional responses in the cells. We found that a large set of genes is coregulated by all EFNAs. However, although the responses to EFNA3, EFNA4, and EFNA5 are identical, the responses to EFNA1 and EFNA2 are characteristic and distinctive. All EFNAs induce epidermal differentiation markers and suppress cell adhesion genes, especially integrins. Ontological analysis showed that all EFNAs induce cornification and keratin genes while suppressing wound healing-associated, signaling, receptor, and extracellular matrix-associated genes. Transcriptional targets of AP1 are selectively suppressed by EFNAs. EFNA1 and EFNA2, but not the EFNA3, EFNA4, EFNA5 cluster, regulate the members of the ubiquitin-associated proteolysis genes. EFNA1 specifically induces collagen production. Our results demonstrate that the EFN-Eph interactions in the epidermis, although promiscuous, are not redundant but specific. This suggests that different members of the EFN/Eph system have specific, clearly demarcated functions.