Activation of NF-kappaB by double-stranded RNA (dsRNA) in the absence of protein kinase R and RNase L demonstrates the existence of two separate dsRNA-triggered antiviral programs

Regulation of the antigen presentation machinery in cancer and its implication for immune surveillance

Evading immune destruction is one of the hallmarks of cancer. A key mechanism of immune evasion deployed by tumour cells is to reduce neoantigen presentation through down-regulation of the antigen presentation machinery. MHC-I and MHC-II proteins are key components of the antigen presentation machinery responsible for neoantigen presentation to CD8⁺ and CD4⁺ T lymphocytes, respectively. Their expression in tumour cells is modulated by a complex interplay of genomic, transcriptomic and post translational factors involving multiple intracellular antigen processing pathways. Ongoing research investigates mechanisms invoked by cancer cells to abrogate MHC-I expression and attenuate anti-tumour CD8⁺ cytotoxic T cell response. The discovery of MHC-II on tumour cells has been less characterized. However, this finding has triggered further interest in utilising tumour-specific MHC-II to harness sustained anti-tumour immunity through the activation of CD4⁺ T helper cells. Tumour-specific expression of MHC-I and MHC-II has been associated with improved patient survival in most clinical studies. Thus, their reactivation represents an attractive way to unleash anti-tumour immunity. This review provides a comprehensive overview of physiologically conserved or novel mechanisms utilised by tumour cells to reduce MHC-I or MHC-II expression. It outlines current approaches employed at the preclinical and clinical trial interface towards reversing these processes in order to improve response to immunotherapy and survival outcomes for patients with cancer.

The location of sensing determines the pancreatic β-cell response to the viral mimetic dsRNA

Viral infection is an environmental trigger that has been suggested to initiate pancreatic β-cell damage, leading to the development of autoimmune diabetes. Viruses potently activate the immune system and can damage β cells by either directly infecting them or stimulating the production of secondary effector molecules (such as proinflammatory cytokines) during bystander activation. However, how and where β cells recognize viruses is unclear, and the antiviral responses that are initiated following virus recognition are incompletely understood. In this study, we show that the β-cell response to dsRNA, a viral replication intermediate known to activate antiviral responses, is determined by the cellular location of sensing (intracellular versus extracellular) and differs from the cellular response to cytokine treatment. Using biochemical and immunological methods, we show that β cells selectively respond to intracellular dsRNA by expressing type I interferons (IFNs) and inducing apoptosis, but that they do not respond to extracellular dsRNA. These responses differ from the activities of cytokines on β cells, which are mediated by inducible nitric oxide synthase expression and β-cell production of nitric oxide. These findings provide evidence that the antiviral activities of type I IFN production and apoptosis are elicited in β cells via the recognition of intracellular viral replication intermediates and that β cells lack the capacity to respond to extracellular viral intermediates known to activate innate immune responses.

Effect of suboptimal temperature on the regulation of endogenous antigen presentation in a rainbow trout hypodermal fibroblast cell line

Rainbow trout (Oncorhynchus mykiss) face low environmental temperatures over winter months and during extreme low temperature events. Suboptimal temperatures are known to negatively impact the teleost immune system, although there is mixed evidence in rainbow trout as to the effect on the endogenous antigen processing and presentation pathway (EAPP). The EAPP is an important pathway for antiviral defense that involves the presentation of endogenous peptides on the cell surface for recognition by cytotoxic T cells. Using a rainbow trout hypodermal fibroblast (RTHDF) cell line as an in vitro model, we determined that constitutive EAPP transcript levels are not impaired at low temperature, but induction of up-regulation of these transcripts is delayed at the suboptimal temperature following exposure to poly(I:C) or viral haemorrhagic septicaemia virus IVb, which was still able to enter and replicate in the cell line at 4 °C, albeit with reduced efficiency. The delay in the induction of EAPP mRNA level up-regulation following poly(I:C) stimulation coincided with a delay in ifn1 transcript levels and secretion, which is important since interferon-stimulated response elements were identified in the promoter regions of the EAPP-specific members of the pathway, implying that IFN1 is involved in the regulation of these genes. Our results suggest that the ability of rainbow trout to mount an effective immune response to viral pathogens may be lessened at suboptimal temperatures.

CCR5 is a required signaling receptor for macrophage expression of inflammatory genes in response to viral double-stranded RNA

Double-stranded (ds) RNA, both synthetic and produced during virus replication, rapidly stimulates MAPK and NF-κB signaling that results in expression of the inflammatory genes inducible nitric oxide synthase, cyclooxygenase 2, and IL-1β by macrophages. Using biochemical and genetic approaches, we have identified the chemokine ligand-binding C-C chemokine receptor type 5 (CCR5) as a cell surface signaling receptor required for macrophage expression of inflammatory genes in response to dsRNA. Activation of macrophages by synthetic dsRNA does not require known dsRNA receptors, as poly(inosinic:cytidylic) acid [poly(I:C)] activates signaling pathways leading to expression of inflammatory genes to similar levels in wild-type and Toll-like receptor 3- or melanoma differentiation antigen 5-deficient macrophages. In contrast, macrophage activation in response to poly(I:C) is attenuated in macrophages isolated from mice lacking CCR5. These findings support a role for CCR5 as a cell surface signaling receptor that participates in activation of inflammatory genes in macrophages in response to the viral dsRNA mimetic poly(inosinic:cytidylic) acid by pathways that are distinct from classical dsRNA receptor-mediated responses.

The association of ribosomal protein L18 (RPL18) with infectious bursal disease virus viral protein VP3 enhances viral replication

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by IBD virus (IBDV). IBDV VP3 is a multifunctional protein playing a key role in virus assembly and pathogenesis. To investigate the role of VP3 in pathogenesis, we transfected DF-1 cells with pRK5-FLAG-vp3 and found that VP3 enhanced type I interferon expression and suppressed IBDV replication. Furthermore we found that VP3 interacted with chicken Ribosomal Protein L18 (chRPL18) in host cells and knockdown of chRPL18 by RNAi significantly promoted Type I interferon expression and inhibited IBDV replication. Moreover, our data show that chicken double-stranded RNA-activated protein kinase (chPKR) interacted with both VP3 and chRPL18. Thus chRPL18 in association with VP3 and chPKR affects viral replication.

Stress Beyond Translation: Poxviruses and More

Poxviruses are large double-stranded DNA viruses that form viral factories in the cytoplasm of host cells. These viruses encode their own transcription machinery, but rely on host translation for protein synthesis. Thus, poxviruses have to cope with and, in most cases, reprogram host translation regulation. Granule structures, called antiviral granules (AVGs), have been observed surrounding poxvirus viral factories. AVG formation is associated with abortive poxvirus infection, and AVGs contain proteins that are typically found in stress granules (SGs). With certain mutant poxviruses lack of immunoregulatory factor(s), we can specifically examine the mechanisms that drive the formation of these structures. In fact, cytoplasmic macromolecular complexes form during many viral infections and contain sensing molecules that can help reprogram transcription. More importantly, the similarity between AVGs and cytoplasmic structures formed during RNA and DNA sensing events prompts us to reconsider the cause and consequence of these AVGs. In this review, we first summarize recent findings regarding how poxvirus manipulates host translation. Next, we compare and contrast SGs and AVGs. Finally, we review recent findings regarding RNA- and especially DNA-sensing bodies observed during viral infection.

Macrophage Expression of Inflammatory Genes in Response to EMCV Infection

The expression and production of type 1 interferon is the classic cellular response to virus infection. In addition to this antiviral response, virus infection also stimulates the production of proinflammatory mediators. In this review, the pathways controlling the induction of inflammatory genes and the roles that these inflammatory mediators contribute to host defense against viral pathogens will be discussed. Specific focus will be on the role of the chemokine receptor CCR5, as a signaling receptor controlling the activation of pathways leading to virus-induced inflammatory gene expression.

MDA5 localizes to stress granules, but this localization is not required for the induction of type I interferon

Virus infection can initiate a type I interferon (IFN-α/β) response via activation of the cytosolic RNA sensors retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5). Furthermore, it can activate kinases that phosphorylate eukaryotic translation initiation factor 2α (eIF2α), which leads to inhibition of (viral) protein translation and formation of stress granules (SG). Most viruses have evolved mechanisms to suppress these cellular responses. Here, we show that a mutant mengovirus expressing an inactive leader (L) protein, which we have previously shown to be unable to suppress IFN-α/β, triggered SG formation in a protein kinase R (PKR)-dependent manner. Furthermore, we show that infection of cells that are defective in SG formation yielded higher viral RNA levels, suggesting that SG formation acts as an antiviral defense mechanism. Since the induction of both IFN-α/β and SG is suppressed by mengovirus L, we set out to investigate a potential link between these pathways. We observed that MDA5, the intracellular RNA sensor that recognizes picornaviruses, localized to SG. However, activation of the MDA5 signaling pathway did not trigger and was not required for SG formation. Moreover, cells that were unable to form SG-by protein kinase R (PKR) depletion, using cells expressing a nonphosphorylatable eIF2α protein, or by drug treatment that inhibits SG formation-displayed a normal IFN-α/β response. Thus, although MDA5 localizes to SG, this localization seems to be dispensable for induction of the IFN-α/β pathway.

Ccr5 regulates inflammatory gene expression in response to encephalomyocarditis virus infection

Encephalomyocarditis virus (EMCV) is capable of stimulating inflammatory gene expression by macrophages as a result of interactions between EMCV capsid proteins and cell surface receptors. In this study, biochemical and genetic approaches identified a role for Ccr5, a chemokine receptor, in transducing the signals of EMCV infection that result in the expression of inflammatory genes in macrophages. Antibody neutralization and gene knockout strategies were used to show that the presence of Ccr5 is required for EMCV-stimulated mitogen-activated protein (MAP) kinase and nuclear factor-kappa B (NF-κB) activation, and the subsequent expression of the inflammatory gene-inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2). Ccr5 appears to participate in the early control of virus replication: EMCV mRNA accumulates to sevenfold higher levels in Ccr5-deficient mice when compared to wild-type controls. These findings support a regulatory role for Ccr5 in the antiviral response to EMCV in which this chemokine receptor participates in regulation of inflammatory gene expression in response to virus infection.

Properties of cells with increased resistance to some picornaviruses

The resistance to picornaviral infection cells of susceptible lines has similar changes in the phenotype. They have decreased number of nucleoli and increased percentage of euploidy. Also the percentage of euploid cells those were resistant to the picornaviral infection increased in all highly transformed cultures. In resistant cells of all cultures has been found reduction of DNA. RNA amount also decreased both in nucleus and in cytoplasm. All these data correlated with the increased euploidy of the resistant population. The resistant cells had a less transformed phenotype, and decreased proliferative activity. Decreased nucleolar status became apparent by reduction of absolute and relative nucleolar indices. Consequently the reduction of viral titer (viral titters reduction) in resistant cells could be the direct result of diminished activity of the RNA synthesis machinery. It is important to note that the cells lose resistance while another type of virus, even from the same family, infects the culture once.

Sequence-non-specific effects of RNA interference triggers and microRNA regulators

RNA reagents of diverse lengths and structures, unmodified or containing various chemical modifications are powerful tools of RNA interference and microRNA technologies. These reagents which are either delivered to cells using appropriate carriers or are expressed in cells from suitable vectors often cause unintended sequence-non-specific immune responses besides triggering intended sequence-specific silencing effects. This article reviews the present state of knowledge regarding the cellular sensors of foreign RNA, the signaling pathways these sensors mobilize and shows which specific features of the RNA reagents set the responsive systems on alert. The representative examples of toxic effects caused in the investigated cell lines and tissues by the RNAs of specific types and structures are collected and may be instructive for further studies of sequence-non-specific responses to foreign RNA in human cells.

HERPES SIMPLEX VIRUS INFECTION AND APOPTOSIS

Consequences of human herpes simplex virus (HSV) infection include the induction of apoptosis and the concomitant synthesis of proteins which act to block this process from killing the infected cell. Recent data has clarified our current understanding of the mechanisms of induction and prevention of apoptosis by HSV. These findings emphasize the fact that modulation of apoptosis by HSV during infection is a multicomponent phenomenon. We review recent evidence showing how this important human pathogen modulates the fundamental cell death process.

IL-10-dependent S100A8 gene induction in monocytes/macrophages by double-stranded RNA

The S100 calcium-binding proteins S100A8 and S100A9 are elevated systemically in patients with viral infections. The S100A8-S100A9 complex facilitated viral replication in human CD4(+) T lymphocytes latently infected with HIV-1- and S100A8-induced HIV-1 transcriptional activity. Mechanisms inducing the S100 genes and the potential source of these proteins following viral activation are unknown. In this study, we show that S100A8 was induced in murine macrophages, and S100A8 and S100A9 in human monocytes and macrophages, by polyinosinic:polycytidylic acid, a dsRNA mimetic. Induction was at the transcriptional level and was IL-10 dependent. Similar to LPS-induced S100A8, induction by dsRNA was dependent on p38 and ERK MAPK. Protein kinase R (PKR) mediates antiviral defense and participates in MyD88-dependent/independent signaling triggered by TLR4 or TLR3. Like IL-10, S100 induction by polyinosinic:polycytidylic acid and by LPS was inhibited by the specific PKR inhibitor 2-aminopurine, indicating a novel IL-10, PKR-dependent pathway. Other mediators such as IFN-beta, which synergized with dsRNA, may also be involved. C/EBPbeta bound the defined promoter region in response to dsRNA. S100A8 was expressed in lungs of mice infected with influenza virus and was maximal at day 8 with strong immunoreactivity in epithelial cells lining the airways and in mononuclear cells and declined early in the recovery phase, implying down-regulation by mediator(s) up-regulated during resolution of the infection. IL-10 is implicated in viral persistence. Since S100A8/S100A9 levels are likely to be maintained in conditions where IL-10 is raised, these proteins may contribute to viral persistence in patients infected by some RNA viruses.

Characterization of interleukin-1beta mRNA expression in chicken macrophages in response to avian reovirus

Inhibitors of viral disassembly or RNA and protein synthesis, viral disassembly intermediates (infectious subviral particles, ISVP), binary ethylenimine-inactivated virions, and viral particles lacking genomic double-stranded (ds) RNA (empty particles) were used to assess the expression of interleukin-1beta (IL-1beta) mRNA in chicken (chIL-1beta) macrophages in response to avian reovirus. The results demonstrate that two distinct expression patterns of chIL-1beta mRNA mediated by different steps in viral replication were found. Viral disassembly was required for the induction of a rapid, transient expression pattern of chIL-1beta mRNA that was rapidly induced at 30 min, with maximal levels reached by 2 h, and fell to a low level within 6 h post-inoculation, while viral RNA synthesis rather than protein translation, which was subsequent to membrane penetration, was required to induce a stable, sustained expression pattern of chIL-1beta mRNA that occurred at and after 6 h post-inoculation. In addition, the induction of chIL-1beta mRNA expression by the empty particles and ISVP was extremely weak, compared with the active dsRNA(+) virions or binary ethylenimine-inactivated virions, suggesting that the presence of dsRNA, even if transcriptionally inactive, may be an important factor in this response.

Intracellular immune dysfunction in myalgic encephalomyelitis/chronic fatigue syndrome: state of the art and therapeutic implications

BACKGROUND

Evidence in support of intracellular immune dysfunctions in people with myalgic encephalomyelitis (ME)/chronic fatigue syndrome (CFS) is accumulating, but few studies have addressed intracellular immunity as a potential therapeutic target.

OBJECTIVE

To provide an overview of our present understanding of intracellular immunity in ME/CFS, to relate the intracellular immune dysfunctions to other aspects of the illness like decreased natural killer cell function, the presence of infections and poor exercise performance, and to point to potential therapeutic targets.

METHODS

An in-depth review of the scientific literature of intracellular immunity in people with ME/CFS was performed.

RESULTS/CONCLUSION

From the scientific literature it is concluded that proteolytic cleavage of the native RNase L enzyme is characteristic of the dysregulation of intracellular immunity in people with ME/CFS, but the origin of the dysregulation is speculative. There is increasing evidence for immune cell apoptosis and upregulation of various aspects of the 2'-5' oligoadenylate (2-5A) synthetase/RNase L pathway in ME/CFS. This review provides the theoretical rationale for conducting studies examining the effectiveness of direct or indirect drug targeting of the 2-5A synthetase/RNase L pathway in ME/CFS patients.

Effects of viral hemorrhagic septicemia virus (VHSV) on the rainbow trout (Oncorhynchus mykiss) monocyte cell line RTS-11

The effect of viral hemorrhagic septicemia virus (VHSV) was studied on the established rainbow trout (Oncorhynchus mykiss) monocyte/macrophage-like cell line RTS11. The virus was not able to complete its replication cycle as infectious viral particles were not released from the cells. However, in RTS11, the virus was capable of producing mRNA from at least its N and G genes. At the protein level, only N protein was detected 2 days post-infection, whereas a faint band corresponding to the G protein was also observed after 5 days post-infection. These results suggest an interruption of viral protein translation at some point. The expression of N mRNA was significantly inhibited in cells pre-treated with Poly I:C, but not affected by 2-aminopurine (2-AP), an inhibitor of the dsRNA-dependent protein kinase (PKR), thus indicating that PKR has no effect on mRNA expression directly. However, when cells were preincubated with Poly I:C in the presence of 2-AP, the levels of N mRNA were restored suggesting that Poly I:C can limit viral transcription through an antiviral mechanism dependent of PKR. The effect of VHSV on the expression of transcripts for different immune genes was determined, but significant induction was found only for genes related to the type I interferon (IFN) response, such as IFN-1 and -2 and the three Mx isoforms. Heat-inactivated virus failed to induce IFN-1 and -2, suggesting that early events in the VHSV life cycle were necessary for the type I IFN response. Poly I:C alone also induced transcripts for the antiviral Mx proteins. Prior exposure of RTS11 to VHSV did not prevent Poly I:C from inducing transcripts for Mx1, Mx2 and Mx3. Perhaps the failure of VHSV to disable antiviral mechanisms in RTS11 accounts for the aborted infections.

Protein kinase PKR plays a stimulus- and virus-dependent role in apoptotic death and virus multiplication in human cells

The protein kinase regulated by double-stranded RNA (dsRNA), PKR, is implicated in a range of biologic processes, including apoptotic death and interferon antiviral responses, based in part on studies with mouse cells genetically deficient in Pkr. To test the role of the PKR protein in human cells, an RNA interference silencing strategy was used to generate stable HeLa cell lines with less than 2% of the PKR protein (PKR deficient) compared to either parental or control knockdown HeLa lines. Phosphorylation of the alpha subunit of eukaryotic initiation factor 2 on serine 51 was not detectably increased in response to dsRNA in PKR-deficient HeLa cells but was elevated severalfold in PKR-sufficient cells. PKR-deficient cells displayed reduced dsRNA-induced apoptosis compared to PKR-sufficient cell lines, whereas tumor necrosis factor alpha (TNF-alpha)-induced apoptosis was comparable between the HeLa lines. NF-kappaB was activated to a comparable extent in PKR-deficient and PKR-sufficient HeLa cells upon treatment with either dsRNA or TNF-alpha. The antiviral response against vesicular stomatitis virus was reduced in interferon-treated PKR-deficient compared to PKR-sufficient HeLa cells. However, the growth of two human viruses, adenovirus and reovirus, was unaffected by the PKR knockdown. Surprisingly, the yield of mutant adenovirus that fails to encode VAI RNA was not enhanced in PKR-deficient cells, indicating the importance of host factors in addition to PKR in conferring the VAI RNA phenotype.

RNAi in primary human chondrocytes: efficiencies, kinetics, and non-specific effects of siRNA-mediated gene suppression

RNAi-mediated gene silencing is a recent, powerful tool to investigate gene function. Controlling for experimental factors such as transfection efficiencies, siRNA concentration, gene suppression levels, gene suppression kinetics, or non-specific effects is key to robust results. In this methods paper, we compare the efficiencies of different transfection reagents in primary human chondrocytes (PHCs). We investigated TAK1 gene suppression efficiencies and kinetics on the mRNA and protein level depending on the siRNA concentration used. Furthermore, we evaluated PKR, IL-6, and TNF-alpha induction, as well as IkappaB degradation and NFkappaB activation as control parameters of non-specific siRNA effects. PKR and IL-6 proved to be appropriate markers of cellular inflammatory responses resulting from siRNA transfection. In addition, we compared different siRNAs (silencing, non-silencing, classic 21-mer, and 25-mer stealth siRNA) with respect to their capacity to induce cellular inflammatory responses. We found the occurrence of cellular responses in PHCs to be a function of the specific siRNA sequence in use. Hence, it is essential to analyze and to compare gene silencing siRNAs and control siRNAs with respect to their off-target effects prior to any functional gene validation.

Suppression of proinflammatory signal transduction and gene expression by the dual nucleic acid binding domains of the vaccinia virus E3L proteins

Cells have evolved elaborate mechanisms to counteract the onslaught of viral infections. To activate these defenses, the viral threat must be recognized. Danger signals, or pathogen-associated molecular patterns, that are induced by pathogens include double-stranded RNA (dsRNA), viral single-stranded RNA, glycolipids, and CpG DNA. Understanding the signal transduction pathways activated and host gene expression induced by these danger signals is vital to understanding virus-host interactions. The vaccinia virus E3L protein is involved in blocking the host antiviral response and increasing pathogenesis, functions that map to separate C-terminal dsRNA- and N-terminal Z-DNA-binding domains. Viruses containing mutations in these domains allow modeling of the role of dsRNA and Z-form nucleic acid in the host response to virus infection. Deletions in the Z-DNA- or dsRNA-binding domains led to activation of signal transduction cascades and up-regulation of host gene expression, with many genes involved in the inflammatory response. These data suggest that poxviruses actively inhibit cellular recognition of viral danger signals and the subsequent cellular response to the viral threat.

Fas Ligand Elicits a Caspase-Independent Proinflammatory Response in Human Keratinocytes: Implications for Dermatitis

Fas ligand (FasL) causes apoptosis of epidermal keratinocytes and triggers the appearance of spongiosis in eczematous dermatitis. We demonstrate here that FasL also aggravates inflammation by triggering the expression of proinflammatory cytokines, chemokines, and adhesion molecules in keratinocytes. In HaCaT cells and in reconstructed human epidermis (RHE), FasL triggered a NF-kappaB-dependent mRNA accumulation of inflammatory cytokines (tumor necrosis factor-alpha, IL-6, and IL-1beta), chemokines (CCL2/MCP-1, CXCL1/GROalpha, CXCL3/GROgamma, and CXCL8/IL-8), and the adhesion molecule ICAM-1. Oligomerization of Fas was required both for apoptosis and for gene expression. Inhibition of caspase activity abolished FasL-dependent apoptosis; however, it failed to suppress the expression of FasL-induced genes. Additionally, in the presence of caspase inhibitors, but not in their absence, FasL triggered the accumulation of CCL5/RANTES (regulated on activation normal T cell expressed and secreted) mRNA. Our findings identify a novel proinflammatory role of FasL in keratinocytes that is independent of caspase activity and is separable from apoptosis. Thus, in addition to causing spongiosis, FasL may play a direct role in triggering and/or sustaining inflammation in eczemas.

A novel role for viral-defective interfering particles in enhancing dendritic cell maturation

Dendritic cell (DC) maturation is a crucial event in the development of adaptive immune responses that confer long-lasting protection against reinfection with the same virus. Sendai virus strain Cantell has a particularly strong ability to mature DCs independently of type I IFNs and TLR signaling, currently the best-described pathways for the induction of DC maturation. In this study, we demonstrate that defective-interfering (DI) particles present in Sendai virus-Cantell stocks are required for its robust DC maturation ability. DI particles contain incomplete genomes that are unable to replicate unless the viral polymerase is supplied by coinfection with complete virus. Accordingly, the improvement in the virus-induced maturation of DCs provided by DI particles requires standard virus coinfection and likely results from increased production of dsRNA replication intermediaries. This unique ability of DI particles to stimulate DC maturation cannot be mimicked by simply increasing the dose of standard virus. Furthermore, viruses with weak DC maturation abilities can be converted into potent DC stimulators with the addition of DI particles, supporting a potential application for DI particles as a novel natural adjuvant for viral immunizations.

Role of MAPK in the regulation of double-stranded RNA- and encephalomyocarditis virus-induced cyclooxygenase-2 expression by macrophages

In response to virus infection or treatment with dsRNA, macrophages express the inducible form of cyclooxygenase-2 (COX-2) and produce proinflammatory prostaglandins. Recently, we have shown that NF-kappaB is required for encephalomyocarditis virus (EMCV)- and dsRNA-stimulated COX-2 expression in mouse macrophages. The dsRNA-dependent protein kinase R is not required for EMCV-stimulated COX-2 expression, suggesting the presence of protein kinase R-independent pathways in the regulation of this antiviral gene. In this study, the role of MAPK in the regulation of macrophage expression of cyclooxygenase-2 (COX)-2 in response to EMCV infection was examined. Treatment of mouse macrophages or RAW-264.7 cells with dsRNA or infection with EMCV stimulates the rapid activation of the MAPKs p38, JNK, and ERK. Inhibition of p38 and JNK activity results in attenuation while ERK inhibition does not modulate dsRNA- and EMCV-induced COX-2 expression and PGE2 production by macrophages. JNK and p38 appear to selectively regulate COX-2 expression, as inhibition of either kinase fails to prevent dsRNA- or EMCV-stimulated inducible NO synthase expression by macrophages. Using macrophages isolated from TLR3-deficient mice, we show that p38 and JNK activation and COX-2 expression in response to EMCV or poly(IC) does not require the presence the dsRNA receptor TLR3. These findings support a role for p38 and JNK in the selective regulation of COX-2 expression by macrophages in response to virus infection.

Induction of chemokine and cytokine genes in astrocytes following infection with Theiler's murine encephalomyelitis virus is mediated by the Toll-like receptor 3

Theiler's murine encephalomyelitis virus (TMEV) infection in the central nervous system (CNS) induces a demyelinating disease similar to human multiple sclerosis. TMEV infection results in activation of various chemokine and cytokine genes that are important in the initiation of an inflammatory response. We have previously shown that the production of these chemokines and cytokines in astrocytes is induced via the NF-kappaB pathway following TMEV and Coxsackie virus infection. In this study, we investigated whether the NF-kappaB-dependent inflammatory responses after TMEV infection is triggered through TLR3 and/or TLR7. The activation of NF-kappaB or IRF/ISRE, as well as the production of both MCP-1/CCL2 and IL-8/CXCL8, was observed in only TLR3-transfected HEK 293 cells, but not in TLR7-tranfected cells. The potential involvement of TLR3 in mouse embryonic fibroblasts and primary astrocytes was further investigated following transfection with wildtype or dominant negative form of TLRs and MyD88, as well as astrocytes from TLR3- and MyD88-deficient mice. Similarly, the activation of transcription factors and chemokine genes is induced in these mouse cells through primarily TLR3 signaling pathway, but not TLR7 or other MyD88-mediated pathways following TMEV infection. However, the TLR3-mediated cellular activation does not appear to affect the level of viral replication in astrocytes. These results strongly suggest that TLR3-signaling by TMEV alone is sufficient to induce the initial inflammatory cytokine responses that could be very important for the outcome of virus-induced encephalitis and/or demyelinating diseases, such as multiple sclerosis.

The N-terminus of PKR is responsible for the activation of the NF-kappaB signaling pathway by interacting with the IKK complex

The interferon-induced double-stranded RNA (dsRNA)-activated protein kinase (PKR) has been shown to activate NF-kappaB independently of its kinase function after interaction with the IKK complex. In order to investigate the mechanism of NF-kappaB activation by PKR, we identified the domain of PKR responsible for stimulating the NF-kappaB pathway in PKR-deficient fibroblasts using an NF-kappaB dependent reporter assay. The N-terminal 1-265 AA of PKR activates NF-kappaB, whereas the 1-180 AA N-terminus restricted to the two dsRNA Binding Domains (DRBD), the third basic domain alone (AA 181-265), or the C-terminus of PKR (AA 266-550) were unable to stimulate the expression of the NF-kappaB dependent reporter gene. Using confocal microscopy, we confirmed that PKR full length as well as PKR N-terminus colocalized with IKKbeta. By GST-pulldown analysis, using different PKR domains, we then revealed the specific ability of the PKR N-terminus 1-265 to bind to and activate IKK and showed that this activation requires the integrity of the IKK complex. This activation is not only due to DRBDs since the DRBD fragment 1-180 failed to inhibit PKR 1-265 induced NF-kappaB activation. Our results therefore demonstrate that the ability of PKR to mediate NF-kappaB activation resides in its full N-terminus, and requires both DRBDs and the third basic domain.

Plant and animal pathogen recognition receptors signal through non-RD kinases

Plants and animals mediate early steps of the innate immune response through pathogen recognition receptors (PRRs). PRRs commonly associate with or contain members of a monophyletic group of kinases called the interleukin-1 receptor-associated kinase (IRAK) family that include Drosophila Pelle, human IRAKs, rice XA21 and Arabidopsis FLS2. In mammals, PRRs can also associate with members of the receptor-interacting protein (RIP) kinase family, distant relatives to the IRAK family. Some IRAK and RIP family kinases fall into a small functional class of kinases termed non-RD, many of which do not autophosphorylate the activation loop. We surveyed the yeast, fly, worm, human, Arabidopsis, and rice kinomes (3,723 kinases) and found that despite the small number of non-RD kinases in these genomes (9%-29%), 12 of 15 kinases known or predicted to function in PRR signaling fall into the non-RD class. These data indicate that kinases associated with PRRs can largely be predicted by the lack of a single conserved residue and reveal new potential plant PRR subfamilies.

Chronic fatigue syndrome: exercise performance related to immune dysfunction

PURPOSE

To date, the exact cause of abnormal exercise response in chronic fatigue syndrome (CFS) remains to be revealed, but evidence addressing intracellular immune deregulation in CFS is growing. Therefore, the aim of this cross-sectional study was to examine the interactions between several intracellular immune variables and exercise performance in CFS patients.

METHODS

After venous blood sampling, subjects (16 CFS patients) performed a maximal exercise stress test on a bicycle ergometer with continuous monitoring of cardiorespiratory variables. The following immune variables were assessed: the ratio of 37 kDa Ribonuclease (RNase) L to the 83 kDa native RNase L (using a radiolabeled ligand/receptor assay), RNase L enzymatic activity (enzymatic assay), protein kinase R activity assay (comparison Western blot), elastase activity (enzymatic-colorimetric assay), the percent of monocytes, and nitric oxide determination (for monocytes and lymphocytes; flow cytometry, live cell assay).

RESULTS

Forward stepwise multiple regression analysis revealed 1) that elastase activity was the only factor related to the reduction in oxygen uptake at a respiratory exchange ratio (RER) of 1.0 (regression model: R = 0.53, F (1,14) = 15.5, P < 0.002; elastase activity P < 0.002); 2) that the protein kinase R activity was the principle factor related to the reduction in workload at RER = 1.0; and 3) that elastase activity was the principle factor related to the reduction in percent of target heart rate achieved.

CONCLUSION

These data provide evidence for an association between intracellular immune deregulation and exercise performance in patients with CFS. To establish a causal relationship, further study of these interactions using a prospective longitudinal design is required.

Leukemia virus long terminal repeat activates NFkappaB pathway by a TLR3-dependent mechanism

The long terminal repeat (LTR) region of leukemia viruses plays a critical role in tissue tropism and pathogenic potential of the viruses. We have previously reported that U3-LTR from Moloney murine and feline leukemia viruses (Mo-MuLV and FeLV) upregulates specific cellular genes in trans in an integration-independent way. The U3-LTR region necessary for this action does not encode a protein but instead makes a specific RNA transcript. Because several cellular genes transactivated by the U3-LTR can also be activated by NFkappaB, and because the antiapoptotic and growth promoting activities of NFkappaB have been implicated in leukemogenesis, we investigated whether FeLV U3-LTR can activate NFkappaB signaling. Here, we demonstrate that FeLV U3-LTR indeed upregulates the NFkappaB signaling pathway via activation of Ras-Raf-IkappaB kinase (IKK) and degradation of IkappaB. LTR-mediated transcriptional activation of genes did not require new protein synthesis suggesting an active role of the LTR transcript in the process. Using Toll-like receptor (TLR) deficient HEK293 cells and PKR(-/-) mouse embryo fibroblasts, we further demonstrate that although dsRNA-activated protein kinase R (PKR) is not necessary, TLR3 is required for the activation of NFkappaB by the LTR. Our study thus demonstrates involvement of a TLR3-dependent but PKR-independent dsRNA-mediated signaling pathway for NFkappaB activation and thus provides a new mechanistic explanation of LTR-mediated cellular gene transactivation.

Encephalomyocarditis virus induces PKR-independent mitogen-activated protein kinase activation in macrophages

In this study, we provide evidence that the double-stranded RNA-dependent protein kinase (PKR) is not required for virus-induced expression of inducible nitric oxide synthase (iNOS) or the activation of specific signaling pathways in macrophages. The infection of RAW264.7 cells with encephalomyocarditis virus (EMCV) induces iNOS expression and nitric oxide production, which are unaffected by a dominant-negative mutant of PKR. EMCV infection also activates the mitogen-activated protein kinase, cyclic AMP response element binding protein, and nuclear factor kappaB (NF-kappaB) signaling cascades at 15 to 30 min postinfection in PKR+/+ and PKR-/- macrophages. Activation of these signaling cascades does not temporally correlate with PKR activity or the accumulation of EMCV RNA, suggesting that an interaction between a structural component of the virion and the cell surface may activate macrophages. Consistent with this hypothesis, empty EMCV capsids induced comparable levels of iNOS expression, nitrite production, and activation of these signaling cascades to those induced by intact virions. These findings support the hypothesis that virion-host cell interactions are primary mediators of the PKR-independent activation of signaling pathways that participate in the macrophage antiviral response of inflammatory gene expression.

Double-stranded RNA stimulates the expression of monocyte chemoattractant protein-1 in BEAS-2B bronchial epithelial cells

BEAS-2B bronchial epithelial cells were treated with polyinosinic-polycytidylic acid (poly IC), a synthetic double-stranded RNA (dsRNA) analog, and the expressions of monocyte chemoattractant protein-1 (MCP-1) mRNA and protein were analyzed by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay. Poly IC enhanced the expression of MCP-1 and release of mononuclear cell chemotactic activity, which were inhibited by dexamethasone pre-treatment. The poly IC-induced up-regulation of MCP-1 was blocked by 2-aminopurine, a specific inhibitor of dsRNA-dependent protein kinase, but not by nuclear factor (NF)-kappaB inhibitor SN50.

Genetic and pharmacologic evidence that calcium-independent phospholipase A2beta regulates virus-induced inducible nitric-oxide synthase expression by macrophages

Recent evidence supports a regulatory role for the calcium-independent phospholipase A2 (iPLA2) in the antiviral response of inducible nitric-oxide synthase (iNOS) expression by macrophages. Because two mammalian isoforms of iPLA2 (iPLA2beta and iPLA2gamma) have been cloned and characterized, the aim of this study was to identify the specific isoform(s) in macrophages that regulates the expression of iNOS in response to virus infection. Bromoenol lactone (BEL), a suicide substrate inhibitor of iPLA2, inhibits the activity of both isoforms at low micromolar concentrations. However, the R- and S-enantiomers of BEL display approximately 10-fold greater potency for inhibition of the enzymatic activity of iPLA2gamma and iPLA2beta, respectively. In this study, we show that the iPLA2beta-selective (S)-BEL inhibits encephalomyocarditis virus (EMCV)-induced iNOS expression, nitric oxide production, and iPLA2 enzymatic activity in macrophages in a concentration-related manner that closely resembles the inhibitory properties of racemic BEL. cAMP response element-binding protein (CREB) is one downstream target of iPLA2 that is required for the transcriptional activation of iNOS in response to virus infection, and consistent with the effects of BEL enantiomers on iNOS expression, (S)-BEL more effectively inhibits EMCV-induced CREB phosphorylation than (R)-BEL in macrophages. Using macrophages isolated from iPLA2beta-null mice, virus infection fails to stimulate iNOS mRNA accumulation and protein expression, thus providing genetic evidence that iPLA2beta is required for EMCV-induced iNOS expression. These findings provide evidence for a signaling role for iPLA2beta in virus-induced iNOS expression by macrophages.

Innate immune response induced by Theiler's murine encephalomyelitis virus infection

Although the causative agents of human multiple sclerosis (MS) are not known, it is suspected that a viral infection may be associated with the initiation of the disease. Several viral disease models in mice have been studied to understand the pathogenesis of demeylination. In particular, Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) has been extensively studied as a relevant model. Various cytokines and chemokines are produced upon viral infection by different cell types, including antigen-presenting cells (APCs) such as macrophages; dendritic cells (DCs); and glial cells, such as astrocytes, microglia, and oligoden-drocytes. The upregulation of the corresponding molecules are also found in MS and are likely to play an important role in the protection and/or pathogenesis of chronic inflammatory demyelinating disease. In this review, the type of cells and molecules, gene-activation mechanisms as well as their potential roles in protection and pathogenesis will be discussed.

Influenza A mutant viruses with altered NS1 protein function provoke caspase-1 activation in primary human macrophages, resulting in fast apoptosis and release of high levels of interleukins 1beta and 18

Several NS1 mutant viruses of human influenza A/PR/8/34 (H1N1) virus were tested for their ability to induce pro-inflammatory cytokines in primary human macrophages. The findings revealed a pronounced difference in the virus-induced cytokine pattern, depending on the functionality of the NS1 protein-encoded domains. The PR8/NS1-125 mutant virus, which encodes the first 125 aa of the NS1 protein, thus lacking the C-terminal domains, induced significantly higher amounts of beta interferon, interleukin (IL) 6, tumour necrosis factor alpha and CCL3 (MIP-1alpha) when compared with the A/PR/8/34 wild-type virus. However, this mutant virus was as efficient as wild-type virus in the inhibition of IL1beta and IL18 release from infected macrophages. Another group of viral mutants either lacking or possessing non-functional RNA-binding and dimerization domains induced 10-50 times more biologically active IL1beta and five times more biologically active IL18 than the wild-type or PR8/NS1-125 viruses. The hallmark of infection with this group of mutant viruses was the induction of rapid apoptosis in infected macrophages, which correlated with the enhanced activity of caspase-1. These results indicated that the NS1 protein, through the function of its N-terminal domains, might control caspase-1 activation, thus repressing the maturation of pro-IL1beta-, pro-IL18- and caspase-1-dependent apoptosis in infected primary human macrophages.

Two mechanisms of caspase 9 processing in double-stranded RNA- and virus-triggered apoptosis

Viral double-stranded RNA (dsRNA) is a ubiquitous intracellular "alert signal" used by cells to detect viral infection and to mount anti-viral responses. DsRNA triggers a rapid (complete within 2-4 h) apoptosis in the highly-susceptible HeLa cell line. Here, we demonstrate that the apical event in this apoptotic cascade is the activation of procaspase 8. Downstream of caspase 8, the apoptotic signaling cascade bifurcates into a mitochondria-independent caspase 8/caspase 3 arm and a mitochondria-dependent, caspase 8/Bid/Bax/Bak/cytochrome c arm. Both arms impinge upon, and activate, procaspase 9 via two different cleavage sites within the procaspase 9 molecule (D330 and D315, respectively). This is the first in vivo demonstration that the "effector" caspase 3 plays an "initiator" role in the regulation of caspase 9. The dsRNA-induced apoptosis is potentiated by the inhibition of protein synthesis, whose role is to accelerate the execution of all apoptosis steps downstream of, and including, the activation of caspase 8. Thus, efficient apoptosis in response to viral dsRNA results from the co-operation of the two major apical caspases (8 and 9) and the dsRNA-activated protein kinase R (PKR)/ribonuclease L (RNase L) system that is essential for the inhibition of protein synthesis in response to viral infection.

Requirement of type I interferon signaling for arthritis triggered by double-stranded RNA

OBJECTIVE

Arthralgias and overt arthritides are often associated with viral infections. Viral infections expose the infected host to proinflammatory double-stranded RNA (dsRNA), which can cause joint inflammation and is a potent activator of interferon-alpha (IFNalpha). The aim of this study was to determine the role of IFNalpha and dsRNA-related signaling molecules in the onset of joint inflammation induced by viral dsRNA.

METHODS

IFNalpha and different forms of RNA were injected into the knee joints of wild-type mice, mice lacking the type I interferon receptor (IFNAR(-/-)), and mice deficient in dsRNA-dependent protein kinase (PKR(-/-)). Histologic evidence of joint damage and the ability of splenocytes to produce cytokines in response to dsRNA or IFNalpha were assessed.

RESULTS

Viral dsRNA, but not short single-stranded RNA, induced arthritis. The arthritis was aggravated by intracellular delivery of dsRNA. The expression of PKR was not mandatory for dsRNA-induced joint inflammation. In contrast, IFNalpha/beta signaling was important for dsRNA-induced joint inflammation because IFNAR(-/-) mice did not develop arthritis. Furthermore, intraarticular deposition of IFNalpha induced arthritis in PKR(-/-) and control mice, whereas IFNAR(-/-) mice were protected. The arthritogenic effect of IFNalpha was attenuated by in vivo depletion of monocyte/macrophages.

CONCLUSION

Arthritis triggered by dsRNA is not dependent on the expression of the dsRNA-signaling molecule PKR (or Toll-like receptor 3, as previously shown), but is associated with the ability to produce type I IFN and is critically dependent on type I IFN receptor signaling. The intrinsic arthritogenic properties of IFNalpha implicate a role of this cytokine in joint manifestations triggered by various interferogenic stimuli.

Recruitment of TRADD, FADD, and caspase 8 to double-stranded RNA-triggered death inducing signaling complexes (dsRNA-DISCs)

Rapid elimination of virus-infected cells by apoptosis is an efficient anti-viral strategy. Double-stranded RNA (dsRNA), a viral product, is potently and rapidly apoptogenic in susceptible cells. Caspase 8 plays an important role in the dsRNA-induced apoptosis; however, the mechanisms of caspase 8 activation in response to dsRNA are unknown. We demonstrate here that, in HeLa cells, the dsRNA-triggered activation of caspase 8 is independent of ongoing proteins synthesis (and is, therefore, independent of changes in pro- and anti-apoptotic gene expression) and involves the formation of multiprotein dsRNA-triggered death inducing signaling complexes (dsRNA-DISCs). DsRNA-DISCs contain FADD, TRADD, and caspase 8; however, several experimental approaches suggest that death ligands and death receptors (such as Fas/Apo1 and DR4/Apo2) are not involved in the formation of dsRNA-DISCs.

Chronic fatigue syndrome: intracellular immune deregulations as a possible etiology for abnormal exercise response

The exacerbation of symptoms after exercise differentiates Chronic fatigue syndrome (CFS) from several other fatigue-associated disorders. Research data point to an abnormal response to exercise in patients with CFS compared to healthy sedentary controls, and to an increasing amount of evidence pointing to severe intracellular immune deregulations in CFS patients. This manuscript explores the hypothetical interactions between these two separately reported observations. First, it is explained that the deregulation of the 2-5A synthetase/RNase L pathway may be related to a channelopathy, capable of initiating both intracellular hypomagnesaemia in skeletal muscles and transient hypoglycemia. This might explain muscle weakness and the reduction of maximal oxygen uptake, as typically seen in CFS patients. Second, the activation of the protein kinase R enzyme, a characteristic feature in atleast subsets of CFS patients, might account for the observed excessive nitric oxide (NO) production in patients with CFS. Elevated NO is known to induce vasidilation, which may limit CFS patients to increase blood flow during exercise, and may even cause and enhanced postexercise hypotension. Finally, it is explored how several types of infections, frequently identified in CFS patients, fit into these hypothetical pathophysiological interactions.

Toll-like receptor ligands directly promote activated CD4+ T cell survival

Toll-like receptor (TLR) engagement by pathogen-associated molecular patterns (PAMPs) is an important mechanism for optimal cellular immune responses. APC TLR engagement indirectly enhances activated CD4(+) T cell proliferation, differentiation, and survival by promoting the up-regulation of costimulatory molecules and the secretion of proinflammatory cytokines. However, TLRs are also expressed on CD4(+) T cells, suggesting that PAMPs may also act directly on activated CD4(+) T cells to mediate functional responses. In this study, we show that activated mouse CD4(+) T cells express TLR-3 and TLR-9 but not TLR-2 and TLR-4. Treatment of highly purified activated CD4(+) T cells with the dsRNA synthetic analog poly(I:C) and CpG oligodeoxynucleotides (CpG DNA), respective ligands for TLR-3 and TLR-9, directly enhanced their survival without augmenting proliferation. In contrast, peptidoglycan and LPS, respective ligands for TLR-2 and TLR-4 had no effect. Enhanced survival mediated by either poly(I:C) or CpG DNA required NF-kappaB activation and was associated with Bcl-x(L) up-regulation. However, only CpG DNA, but not poly(I:C)-mediated effects on activated CD4(+) T cells required the TLR/IL-1R domain containing adaptor molecule myeloid differentiation factor 88. Collectively, our results demonstrate that PAMPs can directly promote activated CD4(+) T cell survival, suggesting that TLRs on T cells can directly modulate adaptive immune responses.

The exonuclease ISG20 is directly induced by synthetic dsRNA via NF-kappaB and IRF1 activation

Many interferon (IFN)-stimulated genes are also induced by double-stranded RNA (dsRNA), a component closely associated with the IFN system in the context of virus-host interactions. Recently, we demonstrated that the IFN-induced 3' --> 5' exonuclease ISG20 possesses antiviral activities against RNA viruses. Here we show that ISG20 induction by synthetic dsRNA (pIpC) is stronger and faster than its induction by IFN. Two families of transcription factors are implicated in the transcriptional activation of ISG20 by dsRNA. Initially, the NF-kappaB factors p50 and p65 bind and activate the kappaB element of the Isg20 promoter. This is followed by IRF1 binding to the ISRE. As pIpC often induces protein movements in the cells, we questioned whether it could influence ISG20 localization. Interestingly and contrary to IFN, dsRNA induces a nuclear matrix enrichment of the ISG20 protein. dsRNA induction of ISG20 via NF-kappaB and its antiviral activity led us to suggest that ISG20 could participate in the cellular response to virus infection.

Expression of Toll-like receptors in human endometrial epithelial cells and cell lines

PROBLEM

Are toll-like receptors (TLRs) expressed by human endometrium and endometrial cell lines?

METHODS OF STUDY

Expression of each TLR mRNA species was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of proliferative-phase human endometrium, separated endometrial epithelial cells, and the Ishikawa and RL95-2 endometrial epithelial cell lines. U-937 and SKW 6.4 cell lines were used as positive controls. Functional relevance of PCR findings was tested by enzyme-linked immunsorbent assay (ELISA)analysis of IL-8 production after stimulating cell lines with ligands for TLR2-5.

RESULTS

TLR1-6 and 9 mRNA species were detected in both whole endometrium and separated endometrial epithelial cells. Ishikawa cells expressed TLR2 and TLR5, while RL95-2 cells expressed TLR3, 5, and 9. Response of RL95-2, Ishikawa, and U-937 cells to TLR2-5 ligands was consistent with RT-PCR findings except response to flagellin by Ishikawa cells.

CONCLUSION

These studies provide the first evidence of TLR expression in the endometrium of any species and suggest the usefulness of endometrial cell lines to study TLR function.

The role and regulation of COX-2 during viral infection

Prostaglandins are lipid mediators, generated by cyclooxygenase (COX), that have been shown to participate in the regulation of virus replication and the modulation of inflammatory responses following infection. A number of studies support a role for PGE2 in the modulation of virus replication and virulence in a cell type and virus selective manner. Virus infection also stimulates the expression of a number of proinflammatory gene products, including COX-2, inducible nitric oxide synthase (iNOS) as well as proinflammatory cytokines. This review will focus on the mechanisms by which proinflammatory prostaglandin production regulates virus replication and virulence. In addition, the signaling pathways that are activated during a virus infection, and that regulate proinflammatory gene expression in macrophages will be reviewed. Specific attention will be placed on the ability of virus infection to activate multiple signaling cascades (such as PKR, MAPK, iPLA2, NF-kappaB) and how these pathways are integrated in the regulation of individual target gene expression.

Innate immune response against nonsegmented negative strand RNA viruses

Innate immune response represents the hallmark of host defense against foreign pathogens, including viruses. Not only does this response combat viruses during initial stages of infection, but it shapes the adaptive immune response as well. This review focuses on this critical host defense mechanism, the innate immune response, in the context of infection by nonsegmented negative strand RNA viruses of the Paramyxoviridae family. We specifically focus on the two critical transcription factors, nuclear factor-kappaB (NF-kappaB) and interferon (IFN) regulatory factor-3 (IRF-3), that play an important role in establishing an innate antiviral state. The antiviral cytokine IFN-alpha/beta (IFN type I) produced following viral infection as a result of activation of NF-kappaB or IRF-3 or both exerts an antiviral state by inducing the Janus kinases/signal transducer and activator (Jak-Stat) pathway. In that context, our review discusses various strategies adopted by these viruses to counteract and evade the antiviral action of IFN I for replicative advantages, especially after modulation of the Jak-Stat antiviral pathway. Understanding this interplay between the innate immune response and viral replication is fundamental to probing into the molecular basis of host-virus interaction.

The protein kinase PKR: a molecular clock that sequentially activates survival and death programs

Cell death and survival play a key role in the immune system as well as during development. The control mechanisms that balance cell survival against cell death are not well understood. Here we report a novel strategy used by a single protein to regulate chronologically cell survival and death. The interferon-induced protein kinase PKR acts as a molecular clock by using catalysis-dependent and -independent activities to temporally induce cell survival prior to cell death. We show that the proapoptotic protein PKR surprisingly activates a survival pathway, which is mediated by NF-kappaB to delay apoptosis. Cell death is then induced by PKR through the phosphorylation of eIF-2alpha. This unique temporal control might serve as a paradigm for other kinases whose catalytic activity is not required for all of their functions.

Viral dsRNA activates mucin transcription in airway epithelial cells

Double-stranded (ds) RNA is a biologically active component of many viruses including rhinoviruses infecting the upper respiratory tract. Mucus production is a common symptom of such infections. Here, we show that mucin, the glycoprotein subunit of mucus gels, is transcriptionally upregulated in an NF-kappaB- and p38-dependent manner when homogeneous cultures of epithelial cells are exposed to dsRNA. Furthermore, upstream of p38 in this system, dsRNA stimulates the extracellular release of ATP and activation of cell surface ATP receptors, which are G protein-coupled. This results in the stimulation of phospholipase C and protein kinase C. These findings suggest that ATP receptor antagonists could be used to modulate mucus production induced by virus.

Exploiting hepatitis C virus activation of NFkappaB to deliver HCV-responsive expression of interferons alpha and gamma

Chronic infection with hepatitis C virus (HCV) may lead to liver failure and hepatocellular carcinoma. Current treatment for HCV includes high systemic doses of interferonalpha (IFNalpha), which is effective in less than half of patients and may have severe side effects. We designed conditional IFNalpha and IFNgamma expression constructs to be triggered by HCV-induced activation of NFkappaB, and delivered these using highly efficient recombinant Tag-deleted SV40-derived vectors. NFkappaB activates the HIV-1NL4-3 long terminal repeat (HIVLTR) as a promoter, which accounts for the conditional transgene expression. Human hepatocyte lines and primary rat hepatocytes (PRH) were transduced with SV[HIVLTR](IFN) vectors, and transfected with HCV cDNA. Production of human and murine IFNalpha and IFNgamma in cytosol and culture supernatants was measured. HCV activated the HIVLTR to produce and secrete IFNs, and did so largely through the NFkappaB binding sites of the HIVLTR. Levels of IFNs secreted, and the magnitude of induction in response to HCV, were greater in hepatocyte lines than in primary cultured hepatocytes. However, even in the latter, supernatant IFNalpha concentrations achieved by this approach were similar to therapeutic serum concentrations sought in systemic IFNalpha-treated patients. In coculture studies, secreted IFNalpha activated its cognate response elements in untransduced cells, suggesting that its potential inhibitory effects on HCV may not be limited to transduced cells. Although HCV replication in culture is difficult to assess, HCV-induced IFNalpha production demonstrably reduced HCV transcription. Conditional expression of IFNs within the liver may represent an attractive approach to therapy of severe chronic HCV infection that could avoid the side effects of systemic treatment regimens.