We previously found that enveloped virus binding and penetration are necessary to initiate an interferon-independent, IRF3-mediated antiviral response. To investigate whether membrane perturbations that accompany membrane fusion-dependent enveloped-virus entry are necessary and sufficient for antiviral-state induction, we utilized a reovirus fusion-associated small transmembrane (FAST) protein. Membrane disturbances during FAST protein-mediated fusion, in the absence of additional innate immune response triggers, are sufficient to elicit interferon-stimulated gene induction and establishment of an antiviral state. Using sensors of membrane disruption to activate an IRF3-dependent, interferon-independent antiviral state may provide cells with a rapid, broad-spectrum innate immune response to enveloped-virus infections.

Protein arginine methyltransferases (PRMTs) regulate mRNA processing and maturation by modulating the activity of RNA-binding proteins through methylation. The cDNA for human PRMT1 (HRMT1L2) was recently identified. In this paper, we describe the complete genomic organization of the human PRMT1 gene (GenBank Accession No. AF222689), together with its precise chromosomal localization in relation to other neighboring genes. We have also examined its expression in a total RNA panel of 26 human tissues, the BT-474 breast carcinoma cell line, and 16 breast tumors. PRMT1, which spans 11.2 kb of genomic sequence on chromosome 19q13.3, is located in close proximity to the IRF3 and RRAS genes and is transcribed in the opposite direction. It is formed of 12 coding exons and 11 intervening introns, and shows structural similarity to other PRMT genes. Three PRMT1 isoforms exist as a result of alternative mRNA splicing. Amino acid sequence comparison of the splicing variants indicates that they are all enzymatically active methyl transferases, but with different N-terminal hydrophobic regions. PRMT1 expression was detected in a variety of tissues. We have shown that the relative prevalence of alternatively spliced forms of PRMT1 is different between normal and cancerous breast tissues. Although PRMT1 was not found to be hormonally regulated by steroid hormones in breast cancer cells, our results suggest that two variants of PRMT1 are down regulated in breast cancer.

The innate immune response constitutes the first line of host defence that limits viral spread and plays an important role in the activation of adaptive immune response. Viral components are recognized by specific host pathogen recognition receptors triggering the activation of IRF3. IRF3, along with NF-κB, is a key regulator of IFN-β expression. Until now, the role of IRF3 in the activation of the innate immune response during Varicella-Zoster Virus (VZV) infection has been poorly studied. In this work, we demonstrated for the first time that VZV rapidly induces an atypical phosphorylation of IRF3 that is inhibitory since it prevents subsequent IRF3 homodimerization and induction of target genes. Using a mutant virus unable to express the viral kinase ORF47p, we demonstrated that (i) IRF3 slower-migrating form disappears; (ii) IRF3 is phosphorylated on serine 396 again and recovers the ability to form homodimers; (iii) amounts of IRF3 target genes such as IFN-β and ISG15 mRNA are greater than in cells infected with the wild-type virus; and (iv) IRF3 physically interacts with ORF47p. These data led us to hypothesize that the viral kinase ORF47p is involved in the atypical phosphorylation of IRF3 during VZV infection, which prevents its homodimerization and subsequent induction of target genes such as IFN-β and ISG15.

The transcription factors IRF3 and NF-κB are required for the expression of many genes involved in antiviral innate immune response, including type I interferons (IFNs) and proinflammatory cytokines. It is well established that TBK1 is an essential kinase engaged downstream of multiple pattern-recognition receptors (PRRs) to mediate IRF3 phosphorylation and activation, whereas the precise mechanisms of TBK1 activation have not been fully elucidated yet. Here, we identified tripartite motif 26 (TRIM26) as an important regulator for RNA virus-triggered innate immune response. Knockdown of TRIM26 impaired virus-triggered IRF3, NF-κB activation, IFN-β induction, and cellular antiviral response. TRIM26 was physically associated with TBK1 independent of viral infection. As an E3 ligase, TRIM26 underwent autoubiquitination upon viral infection. Ubiquitinated TRIM26 subsequently associated with NEMO, thus bridging TBK1-NEMO interaction, which is critical for the recruitment of TBK1 to the VISA signalsome and activation of TBK1. Our findings suggest that TRIM26 is an important regulator of innate immune responses against RNA viruses, which functions by bridging TBK1 to NEMO and mediating the activation of TBK1.

Sensing viruses by pattern recognition receptors (PRR) triggers the innate immune system of the host cell and activates immune signaling cascades such as the RIG-I/IRF3 pathway. Mitochondrial antiviral-signaling protein (MAVS, also known as IPS-1, Cardif, and VISA) is the crucial adaptor protein of this pathway localized on mitochondria, peroxisomes and mitochondria-associated membranes of the endoplasmic reticulum. Activation of MAVS leads to the production of type I and type III interferons (IFN) as well as IFN stimulated genes (ISGs). To refine the role of MAVS subcellular localization for the induction of type I and III IFN responses in hepatocytes and its counteraction by the hepatitis C virus (HCV), we generated various functional and genetic knock-out cell systems that were reconstituted to express mitochondrial (mito) or peroxisomal (pex) MAVS, exclusively. Upon infection with diverse RNA viruses we found that cells exclusively expressing pexMAVS mounted sustained expression of type I and III IFNs to levels comparable to cells exclusively expressing mitoMAVS. To determine whether viral counteraction of MAVS is affected by its subcellular localization we employed infection of cells with HCV, a major causative agent of chronic liver disease with a high propensity to establish persistence. This virus efficiently cleaves MAVS via a viral protease residing in its nonstructural protein 3 (NS3) and this strategy is thought to contribute to the high persistence of this virus. We found that both mito- and pexMAVS were efficiently cleaved by NS3 and this cleavage was required to suppress activation of the IFN response. Taken together, our findings indicate comparable activation of the IFN response by pex- and mitoMAVS in hepatocytes and efficient counteraction of both MAVS species by the HCV NS3 protease.

Humans have a distinct combination of IFIT (IFN-induced protein with tetratricopeptide repeats) family orthologs, including IFIT1 (ISG56), IFIT2 (ISG54), IFIT3 (ISG60), and IFIT5 (ISG58). The function of IFIT1/IFIT2/IFIT3 has been intensively investigated. However, little is known about the role of IFIT5 in any cellular processes. In this study, we reported that both the mRNA and protein levels of IFIT5 are up-regulated in response to RNA virus infection or polyinosinic-cytidylic acid stimulation. Ectopic expression of IFIT5 could synergize IRF3- and NF-κB-mediated gene expression, whereas knockdown of IFIT5 impairs the transcription of these genes. Consistently, anti-viral responses of host cells are significantly increased or decreased in the presence or absence of IFIT5. Mechanistically, IFIT5 co-localizes partly with mitochondria and interacts with RIG-I and MAVS. Our study identified that IFIT5 is an important enhancer in innate immune response.

Although molecular components that execute noninflammatory apoptotic cell death are well defined, molecular pathways that trigger necrotic cell death remain poorly characterized. Here, we show that in response to infection with adenovirus or Listeria monocytogenes, macrophages in vivo undergo rapid proinflammatory necrotic death that is controlled by interferon-regulatory factor 3 (IRF3). The transcriptional activity of IRF3 is, surprisingly, not required for the induction of necrosis, and it proceeds normally in mice deficient in all known regulators of necrotic death or IRF3 activation, including RIPK3, caspases 1, 8, or 11, STING, and IPS1/MAVS. Although L. monocytogenes triggers necrosis to promote the infection, IRF3-dependent necrosis is required for reducing pathogen burden in the models of disseminated infection with adenovirus. Therefore, our studies implicate IRF3 as a principal and nonredundant component of a physiologically regulated necrotic cell-death pathway that operates as an effective innate immune mechanism of host protection against disseminated virus infection.

DNA vaccination is an attractive approach to induce antigen-specific cytotoxic CD8(+) T lymphocytes (CTLs), which can mediate protective antitumor immunity. The potency of DNA vaccines encoding weakly immunogenic tumor-associated antigens (TAAs) can be enhanced by codelivering gene-encoded adjuvants. Pattern recognition receptors (PRRs) that sense intracellular DNA could potentially be used to harness intrinsic immune-stimulating properties of plasmid DNA vaccines. Consequently, the cytosolic DNA sensor, DNA-dependent activator of interferon (IFN) regulatory factors (DAI), was used as a genetic adjuvant. In vivo electroporation (EP) of mice with a DAI-encoding plasmid (pDAI) promoted transcription of genes encoding type I IFNs, proinflammatory cytokines, and costimulatory molecules. Coimmunization with pDAI and antigen-encoding plasmids enhanced in vivo antigen-specific proliferation, and induction of effector and memory CTLs. Moreover, codelivery of pDAI effectively promoted CTL and CD4(+) Th1 responses to the TAA survivin. The DAI-enhanced CTL induction required nuclear factor κB (NF-κB) activation and type I IFN signaling, but did not involve the IFN regulatory factor 3 (IRF3). Codelivery of pDAI also increased CTL responses to the melanoma-associated antigen tyrosinase-related protein-2 (TRP2), enhanced tumor rejection and conferred long-term protection against B16 melanoma challenge. This study constitutes "proof-of-principle" validating the use of intracellular PRRs as genetic adjuvants to enhance DNA vaccine potency.

Exacerbation of disease in systemic lupus erythematosus (SLE) is associated with bacterial infection. In conventional dendritic cells (cDCs), the TLR4 ligand bacterial LPS induces IFN-beta gene expression but does not induce IFN-alpha. We hypothesized that when cDCs are primed by cytokines, as may frequently be the case in SLE, LPS would then induce the production of IFN-alpha, a cytokine believed to be important in lupus pathogenesis. In this study we show that mouse cDCs and human monocytes produce abundant IFN-alpha following TLR4 engagement whether the cells have been pretreated either with IFN-beta or with a supernatant from DCs activated by RNA-containing immune complexes from lupus patients. This TLR4-induced IFN-alpha induction is mediated by both an initial TRIF-dependent pathway and a subsequent MyD88-dependent pathway, in contrast to TLR3-induced IFN-alpha production, which is entirely TRIF-dependent. There is also a distinct requirement for IFN regulatory factors (IRFs), with LPS-induced IFN-alpha induction being entirely IRF7- and partially IRF5-dependent, in contrast to LPS-induced IFN-beta gene induction which is known to be IRF3-dependent but largely IRF7-independent. This data demonstrates a novel pathway for IFN-alpha production by cDCs and provides one possible explanation for how bacterial infection might precipitate disease flares in SLE.

The severity of urinary tract infection (UTI) reflects the quality and magnitude of the host response. While strong local and systemic innate immune activation occurs in patients with acute pyelonephritis, the response to asymptomatic bacteriuria (ABU) is low. The immune response repertoire in ABU has not been characterized, due to the inherent problem to distinguish bacterial differences from host-determined variation. In this study, we investigated the host response to ABU and genetic variants affecting innate immune signaling and UTI susceptibility. Patients were subjected to therapeutic urinary tract inoculation with E. coli 83972 to ensure that they were exposed to the same E. coli strain. The innate immune response repertoire was characterized in urine samples, collected from each patient before and after inoculation with bacteria or PBS, if during the placebo arm of the study. Long-term E. coli 83972 ABU was established in 23 participants, who were followed for up to twelve months and the innate immune response was quantified in 233 urine samples. Neutrophil numbers increased in all but two patients and in an extended urine cytokine/chemokine analysis (31 proteins), the chemoattractants IL-8 and GRO-α, RANTES, Eotaxin-1 and MCP-1, the T cell chemoattractant and antibacterial peptide IP-10, inflammatory regulators IL-1-α and sIL-1RA and the T lymphocyte/dendritic cell product sIL-2Rα were detected and variably increased, compared to sterile samples. IL-6, which is associated with symptomatic UTI, remained low and numerous specific immune mediators were not detected. The patients were also genotyped for UTI-associated IRF3 and TLR4 promoter polymorphisms. Patients with ABU associated TLR4 polymorphisms had low neutrophil numbers, IL-6, IP-10, MCP-1 and sIL-2Rα concentrations. Patients with the ABU-associated IRF3 genotype had lower neutrophils, IL-6 and MCP-1 responses than the remaining group. The results suggest that the host-specific, low immune response to ABU mainly includes innate immune mediators and that host genetics directly influence the magnitude of this response.

Psoriasis is an immune-mediated skin disease, the aetiology of which remains poorly understood. In recent years, genome-wide association studies (GWAS) have helped to illuminate the molecular basis of this condition, by demonstrating the pathogenic involvement of multiple genes from the IL-23 and NF-κB pathways. A GWAS carried out by our group also identified RNF114, a gene encoding a novel ubiquitin binding protein, as a determinant for psoriasis susceptibility. Although the function of RNF114 is unknown, its paralogue RNF125 has been shown to regulate the RIG-I/MDA5 innate antiviral response. This signalling cascade, which is activated by the presence of double-stranded RNA (dsRNA) within the cytoplasm, induces the production of type I interferon (IFN) through the activation of the IRF3 and NF-κB transcription factors. Here, we explore the hypothesis that RNF114 may also modulate RIG-I/MDA5 signalling. We show that RNF114 associates with ubiquitinated proteins and that it is a soluble cytosolic protein that can be induced by interferons and synthetic dsRNA. Moreover, we demonstrate that RNF114 over-expression enhances NF-κb and IRF3 reporter activity and increases type I and type III IFN mRNA levels. These results indicate that RNF114 regulates a positive feedback loop that enhances dsRNA induced production of type I IFN. Thus, our data point to a novel pathogenic pathway, where dysregulation of RIG-I/MDA5 signalling leads to the over-production of type I IFN, a key early mediator of epithelial inflammation.

Epidermal growth factor receptor (EGFR) overexpression plays an important oncogenic role in cancer. Regular EGFR protein levels are increased in cancer cells and the receptor then becomes constitutively active. However, downstream signals generated by constitutively activated EGFR are unknown. Here we report that the overexpressed EGFR oscillates between two distinct and mutually exclusive modes of signalling. Constitutive or non-canonical EGFR signalling activates the transcription factor IRF3 leading to expression of IFI27, IFIT1 and TRAIL. Ligand-mediated activation of EGFR switches off IRF3-dependent transcription, activates canonical extracellular signal-regulated kinase (ERK) and Akt signals, and confers sensitivity to chemotherapy and virus-induced cell death. Mechanistically, the distinct downstream signals result from a switch of EGFR-associated proteins. EGFR constitutively complexes with IRF3 and TBK1 leading to TBK1 and IRF3 phosphorylation. Addition of epidermal growth factor dissociates TBK1, IRF3 and EGFR leading to a loss of IRF3 activity, Shc-EGFR association and ERK activation. Finally, we provide evidence for non-canonical EGFR signalling in glioblastoma.

Pathogens are sensed by Toll-like receptors (TLRs) and a growing number of non-TLR receptors. Integrins constitute a family of signaling receptors exploited by viruses and bacteria to access cells. By gain- and loss-of-function approaches we found that αvβ3-integrin is a sensor of and plays a crucial role in the innate defense against herpes simplex virus (HSV). αvβ3-integrin signaled through two pathways. One concurred with TLR2, affected activation/induction of interferons type 1 (IFNs-1), NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells), and a polarized set of cytokines and receptors. The virion glycoproteins gH/gL sufficed to induce IFN1 and NF-κB via this pathway. The other pathway was TLR2-independent, involved sarcoma (SRC)-spleen tyrosine kinase (SYK)-Caspase recruitment domain-containing protein 9 (CARD9)-TRIF (TIR-domain-containing adapter-inducing interferon-β), and affected interferon regulatory factor 3 and 7 (IRF3-IRF7). The importance of αvβ3-integrin-mediated defense is reflected in the observation that HSV evolved the immediate-early infected cellular protein 0 (ICP0) protein to counteract it. We propose that αvβ3-integrin is considered a class of non-TLR pattern recognition receptors, a role likely exerted toward viruses and bacteria that interact with integrins and mount an innate response.

ISG15 is an interferon-stimulated, linear di-ubiquitin-like protein, with anti-viral activity. The role of ISG15 during bacterial infection remains elusive. We show that ISG15 expression in nonphagocytic cells is dramatically induced upon Listeria infection. Surprisingly this induction can be type I interferon independent and depends on the cytosolic surveillance pathway, which senses bacterial DNA and signals through STING, TBK1, IRF3 and IRF7. Most importantly, we observed that ISG15 expression restricts Listeria infection in vitro and in vivo. We made use of stable isotope labeling in tissue culture (SILAC) to identify ISGylated proteins that could be responsible for the protective effect. Strikingly, infection or overexpression of ISG15 leads to ISGylation of ER and Golgi proteins, which correlates with increased secretion of cytokines known to counteract infection. Together, our data reveal a previously uncharacterized ISG15-dependent restriction of Listeria infection, reinforcing the view that ISG15 is a key component of the innate immune response.

The transition of mammalian cells from quiescence to proliferation is accompanied by the differential expression of several microRNAs (miRNAs) and transcription factors. However, the interplay between transcription factors and miRNAs in modulating gene regulatory networks involved in human cell proliferation is largely unknown. Here we show that the miRNA miR-22 promotes proliferation in primary human cells, and through a combination of Argonaute-2 immunoprecipitation and reporter assays, we identified multiple novel targets of miR-22, including several cell-cycle arrest genes that mediate the effects of the tumor-suppressor p53. In addition, we found that miR-22 suppresses interferon gene expression by directly targeting high mobility group box-1 and interferon regulatory factor (IRF)-5, preventing activation of IRF3 and NF-κB, which are activators of interferon genes. The expression of interferon genes is elevated in quiescent cells and their expression is inhibitory for cell proliferation. In addition, we find that miR-22 is activated by the transcription factor Myc when quiescent cells enter proliferation and that miR-22 inhibits the Myc transcriptional repressor MXD4, mediating a feed-forward loop to elevate Myc expression levels. Our results implicate miR-22 in downregulating the anti-proliferative p53 and interferon pathways and reveal a new transcription factor-miRNA network that regulates the transition of primary human cells from quiescence to proliferation.

Metabolic stress in obesity induces endothelial inflammation and activation, which initiates adipose tissue inflammation, insulin resistance, and cardiovascular diseases. However, the mechanisms underlying endothelial inflammation induction are not completely understood. Stimulator of interferon genes (STING) is an important molecule in immunity and inflammation. In the present study, we sought to determine the role of STING in palmitic acid-induced endothelial activation/inflammation.

In cultured endothelial cells, palmitic acid treatment activated STING, as indicated by its perinuclear translocation and binding to interferon regulatory factor 3 (IRF3), leading to IRF3 phosphorylation and nuclear translocation. The activated IRF3 bound to the promoter of ICAM-1 (intercellular adhesion molecule 1) and induced ICAM-1 expression and monocyte-endothelial cell adhesion. When analyzing the upstream signaling, we found that palmitic acid activated STING by inducing mitochondrial damage. Palmitic acid treatment caused mitochondrial damage and leakage of mitochondrial DNA into the cytosol. Through the cytosolic DNA sensor cGAS (cyclic GMP-AMP synthase), the mitochondrial damage and leaked cytosolic mitochondrial DNA activated the STING-IRF3 pathway and increased ICAM-1 expression. In mice with diet-induced obesity, the STING-IRF3 pathway was activated in adipose tissue. However, STING deficiency (Stinggt/gt ) partially prevented diet-induced adipose tissue inflammation, obesity, insulin resistance, and glucose intolerance.

The mitochondrial damage-cGAS-STING-IRF3 pathway is critically involved in metabolic stress-induced endothelial inflammation. STING may be a potential therapeutic target for preventing cardiovascular diseases and insulin resistance in obese individuals.

Virus infection elicits a robust innate antiviral response dominated by the production of type 1 IFN. In nonprofessional innate immune cells such as fibroblasts, type 1 IFN is rapidly produced following the recognition of viral dsRNA and the subsequent activation of the constitutively expressed transcription factor IFN regulatory factor 3 (IRF3). Although origin, localization, and length are factors in mediating dsRNA recognition and binding by cellular dsRNA-binding proteins, the biological significance of differential dsRNA binding is unclear, since the subsequent signaling pathways converge on IRF3. In this study, we show a dsRNA length-dependent activation of IRFs, IFNs, and IFN-stimulated genes in mouse fibroblasts. The length dependence was exacerbated in fibroblasts deficient in the mitochondria-associated adaptor IFN-beta promoter stimulator 1 and IRF3, suggesting that antiviral gene induction mediated by short and long dsRNA molecules is predominantly IFN-beta promoter stimulator 1 and IRF3 dependent and independent, respectively. Furthermore, we provide evidence of an innate antiviral response in fibroblasts in the absence of both IRF3 and type 1 IFN induction. Even with these key modulators missing, a 60-90% inhibition of virus replication was observed following 24-h treatment with short or long dsRNA molecules, respectively. These data provide evidence of a novel antiviral pathway that is dependent on dsRNA length, but independent of the type 1 IFN system.

During viral infection, extracellular dsRNA is a potent signaling molecule that activates many innate immune cells, including macrophages. TLR3 is a well-known receptor for extracellular dsRNA, and internalization of extracellular dsRNA is required for endosomal TLR3 activation. Preserved inflammatory responses of TLR3-deficient macrophages to extracellular dsRNA strongly support a TLR3-independent mechanism in dsRNA-mediated immune responses. The present study demonstrated that CD11b/CD18 (Mac-1 [macrophage-1 Ag]), a surface integrin receptor, recognized extracellular dsRNA and induced macrophage immune responses. CD11b deficiency reduced inflammatory cytokine induction elicited by polyinosinic:polycytidylic acid (poly I:C; a synthetic dsRNA) in mouse sera and livers, as well as in cultured peritoneal macrophages. dsRNA-binding assay and confocal immunofluorescence showed that Mac-1, especially the CD11b subunit, interacted and colocalized with poly I:C on the surface of macrophages. Further mechanistic studies revealed two distinct signaling events following dsRNA recognition by Mac-1. First, Mac-1 facilitated poly I:C internalization through the activation of PI3K signaling and enhanced TLR3-dependent activation of IRF3 in macrophages. Second, poly I:C induced activation of phagocyte NADPH oxidase in a TLR3-independent, but Mac-1-dependent, manner. Subsequently, phagocyte NADPH oxidase-derived intracellular reactive oxygen species activated MAPK and NF-κB pathways. Our results indicate that extracellular dsRNA activates Mac-1 to enhance TLR3-dependent signaling and to trigger TLR3-independent, but Mac-1-dependent, inflammatory oxidative signaling, identifying a novel mechanistic basis for macrophages to recognize extracellular dsRNA to regulate innate immune responses. This study identifies Mac-1 as a novel surface receptor for extracellular dsRNA and implicates it as a potential therapeutic target for virus-related inflammatory diseases.

The production of type I interferons (IFNs) in response to viral infections is critical for antiviral immunity. However, IFN production is transient, and continued expression can lead to inflammatory or autoimmune diseases. Thus, understanding the mechanisms underlying the negative regulation of IFN expression could lead to the development of novel therapeutic approaches to the treatment of these diseases. We report that the transcription factor IRF3 plays a central role in the negative regulation of interferon-β (IFNβ) expression during both acute and persistent (chronic) virus infections. We show that the degradation of IRF3 during acute infections, rather than the activation of transcriptional repressors, leads to the down regulation of IFNβ expression. We also show that the block to IFNβ expression in mouse embryonic fibroblasts that are persistently infected with Sendai virus (SeV) correlates with the absence of transcriptionally active IRF3. Remarkably, ongoing protein synthesis and viral replication are required to maintain repression of the IFNβ gene in persistently infected cells, as the gene can be activated by the protein synthesis inhibitor cycloheximide, or by the antiviral drug ribavirin. Finally, we show that the SeV V protein inhibits IRF3 activity in persistently infected cells. Thus, in conjunction with the known interference with STAT1 by the SeV C protein, both IFN activation and its signaling pathways are blocked in persistently infected cells. We conclude that the transcription factor IRF3 is targeted for turnover and inactivation through distinct mechanisms from both the host cells and virus, leading to the inhibition of IFNβ gene expression during acute and persistent viral infections. These observations show that IRF3 plays a critical role, not only in the activation of the IFNβ gene, but also in the controlling the duration of its expression. (284 words).

The infected cell protein 0 (bICP0) encoded by Bovine herpesvirus 1 (BHV-1) stimulates viral gene expression and productive infection. As bICP0 is expressed constitutively during productive infection, it is considered to be the major viral regulatory protein. Like other alphaherpesvirus ICP0 homologues, bICP0 contains a zinc RING finger near its N terminus that activates transcription and regulates subcellular localization. In this study, evidence is provided that bICP0 represses the human beta interferon (IFN-beta) promoter and a simple promoter with consensus IFN-stimulated response elements following stimulation with double-stranded RNA (polyinosinic-polycytidylic acid), IFN regulatory factor 3 (IRF3) or IRF7. bICP0 also inhibits the ability of two protein kinases (TBK1 and IKK epsilon) to activate IFN-beta promoter activity. The zinc RING finger is necessary for inhibiting IFN-dependent transcription in certain cell types. Collectively, these studies suggest that bICP0 activates productive infection by stimulating viral gene expression and inhibiting IFN-dependent transcription.

The intracellular innate antiviral response in human cells is an essential component of immunity against virus infection. As obligate intracellular parasites, all viruses must evade the actions of the host cell's innate immune response in order to replicate and persist. Innate immunity is induced when pathogen recognition receptors of the host cell sense viral products including nucleic acid as "non-self". This process induces downstream signaling through adaptor proteins to activate latent transcription factors that drive the expression of genes encoding antiviral and immune modulatory effector proteins that restrict virus replication and regulate adaptive immunity. The interferon regulatory factors (IRFs) are transcription factors that play major roles in innate immunity. In particular, IRF3 is activated in response to infection by a range of viruses including RNA viruses, DNA viruses and retroviruses. Among these viruses, human immunodeficiency virus type 1 (HIV-1) remains a major global health problem mediating chronic infection in millions of people wherein recent studies show that viral persistence is linked with the ability of the virus to dysregulate and evade the innate immune response. In this review, we discuss viral pathogen sensing, innate immune signaling pathways and effectors that respond to viral infection, the role of IRF3 in these processes and how it is regulated by pathogenic viruses. We present a contemporary overview of the interplay between HIV-1 and innate immunity, with a focus on understanding how innate immune control impacts infection outcome and disease.

Virus-induced activation of the beta interferon (IFN-beta) gene requires orderly recruitment of chromatin-remodeling complexes and time-regulated acetylation of histone residues K8H4 and K14H3 on the promoter region. We have previously shown that transcription factor Yin Yang 1 (YY1) binds the murine IFN-beta promoter at two sites (-122 and -90) regulating promoter transcriptional capacity with a dual activator/repressor role. In this work we demonstrate that both YY1 -122 and -90 sites are required for CBP recruitment and K8H4/K14H3 acetylation to take place on the IFN-beta promoter region after virus infection. A single point mutation introduced at either one of these two sites inhibiting YY1 binding completely disrupted CBP recruitment and K8H4/K14H3 acetylation independently of HMGI or IRF3 binding to the promoter. We have previously demonstrated that YY1 represses the transcriptional capacity of the IFN-beta promoter through its -90 site via histone deacetylation. Here we demonstrate that, in vivo, the binding of YY1 to the -90 site is constant all through virus infection whereas the binding of YY1 to the -122 site is activated after infection. We discuss here the capacity of YY1 to either repress (through histone deacetylase recruitment) or activate (through CBP recruitment) IFN-beta gene expression according to the occupancy of either only its -90 site or both its -122 and -90 sites.

Toll-like receptors (TLRs) sense pathogen-associated molecular patterns to activate the production of inflammatory mediators. TLR4 recognizes lipopolysaccharide (LPS) and drives the secretion of inflammatory cytokines, often contributing to sepsis. We report that transient receptor potential melastatin-like 7 (TRPM7), a non-selective but Ca2+-conducting ion channel, mediates the cytosolic Ca2+ elevations essential for LPS-induced macrophage activation. LPS triggered TRPM7-dependent Ca2+ elevations essential for TLR4 endocytosis and the subsequent activation of the transcription factor IRF3. In a parallel pathway, the Ca2+ signaling initiated by TRPM7 was also essential for the nuclear translocation of NFκB. Consequently, TRPM7-deficient macrophages exhibited major deficits in the LPS-induced transcriptional programs in that they failed to produce IL-1β and other key pro-inflammatory cytokines. In accord with these defects, mice with myeloid-specific deletion of Trpm7 are protected from LPS-induced peritonitis. Our study highlights the importance of Ca2+ signaling in macrophage activation and identifies the ion channel TRPM7 as a central component of TLR4 signaling.

beta(2)-Microglobulin (beta(2)m) is a chaperone of major histocompatibility complex (MHC) class I (-like) molecules that play a central role in antigen presentation, immunoglobulin transport, and iron metabolism. It is therefore of importance that beta(2)m is adequately expressed in cells that perform these functions, such as hematopoietic cells. In this study, we investigated the transcriptional regulation of beta(2)m in lymphoid and myeloid cell lines through a promoter containing a putative E box, Ets/interferon-stimulated response element (ISRE), and kappa B site. Here we show that upstream stimulatory factor 1 (USF1) and USF2 bind to the E box and regulate beta(2)m transactivation. The nuclear factor kappa B (NF-kappa B) subunits p50 and p65 bind to the kappa B box and p65 transactivates beta(2)m. Interferon regulatory factor 1 (IRF1), IRF2, IRF4, and IRF8, but not PU.1, bind to the Ets/ISRE, and IRF1 and IRF3 are strong transactivators of beta(2)m. Together, all 3 boxes are important for the constitutive and cytokine-induced levels of beta(2)m expression in lymphoid and myeloid cell types. As such, beta(2)m transactivation is under the control of important transcriptional pathways, which are activated during injury, infection, and inflammation.