A central role for RNA in the induction and biological activities of type 1 interferons

Inclusion body myositis, viral infections, and TDP-43: a narrative review

The ubiquitous RNA-processing molecule TDP-43 is involved in neuromuscular diseases such as inclusion body myositis, a late-onset acquired inflammatory myopathy. TDP-43 solubility and function are disrupted in certain viral infections. Certain viruses, high viremia, co-infections, reactivation of latent viruses, and post-acute expansion of cytotoxic T cells may all contribute to inclusion body myositis, mainly in an age-shaped immune landscape. The virally induced senescent, interferon gamma-producing cytotoxic CD8+ T cells with increased inflammatory, and cytotoxic features are involved in the occurrence of inclusion body myositis in most such cases, in a genetically predisposed host. We discuss the putative mechanisms linking inclusion body myositis, TDP-43, and viral infections untangling the links between viruses, interferon, and neuromuscular degeneration could shed a light on the pathogenesis of the inclusion body myositis and other TDP-43-related neuromuscular diseases, with possible therapeutic implications.

Application and prospect of targeting innate immune sensors in the treatment of autoimmune diseases

Dysregulation of auto-reactive T cells and autoantibody-producing B cells and excessive inflammation are responsible for the occurrence and development of autoimmune diseases. The suppression of autoreactive T cell activation and autoantibody production, as well as inhibition of inflammatory cytokine production have been utilized to ameliorate autoimmune disease symptoms. However, the existing treatment strategies are not sufficient to cure autoimmune diseases since patients can quickly suffer a relapse following the end of treatments. Pattern recognition receptors (PRRs), including Toll-like receptors (TLRs), Nod-like receptors (NLRs), RIG-I like receptors (RLRs), C-type lectin receptors (CLRs) and various nucleic acid sensors, are expressed in both innate and adaptive immune cells and are involved in the development of autoimmune diseases. Here, we have summarized advances of PRRs signaling pathways, association between PRRs and autoimmune diseases, application of inhibitors targeting PRRs and the corresponding signaling molecules relevant to strategies targeting autoimmune diseases. This review emphasizes the roles of different PRRs in activating both innate and adaptive immunity, which can coordinate to trigger autoimmune responses. The review may also prompt the formulation of novel ideas for developing therapeutic strategies against autoimmune diseases by targeting PRRs-related signals.

The Structure and Immune Regulatory Implications of the Ubiquitin-Like Tandem Domain Within an Avian 2'-5' Oligoadenylate Synthetase-Like Protein

Post-translational modification of host and viral proteins by ubiquitin and ubiquitin-like proteins plays a key role in a host’s ability to mount an effective immune response. Avian species lack a ubiquitin-like protein found in mammals and other non-avian reptiles; interferon stimulated gene product 15 (ISG15). ISG15 serves as a messenger molecule and can be conjugated to both host and viral proteins leading them to be stabilized, degraded, or sequestered. Structurally, ISG15 is comprised of a tandem ubiquitin-like domain (Ubl), which serves as the motif for post-translational modification. The 2’-5’ oligoadenylate synthetase-like proteins (OASL) also encode two Ubl domains in series near its C-terminus which binds OASL to retinoic acid inducible gene-I (RIG-I). This protein-protein interaction increases the sensitivity of RIG-I and results in an enhanced production of type 1 interferons and a robust immune response. Unlike human and other mammalian OASL homologues, avian OASLs terminate their tandem Ubl domains with the same LRLRGG motif found in ubiquitin and ISG15, a motif required for their conjugation to proteins. Chickens, however, lack RIG-I, raising the question of structural and functional characteristics of chicken OASL (chOASL). By investigating chOASL, the evolutionary history of viruses with deubiquitinases can be explored and drivers of species specificity for these viruses may be uncovered. Here we show that the chOASL tandem Ubl domains shares structural characteristics with mammalian ISG15, and that chOASL can oligomerize and conjugate to itself. In addition, the ISG15-like features of avian OASLs and how they impact interactions with viral deubiquitinases and deISGylases are explored.

Epigenetic regulation of RNA sensors: Sentinels of immune response

Living host system possess mechanisms like innate immune system to combat against inflammation, stress singling, and cancer. These mechanisms are initiated by PAMP and DAMP mediated recognition by PRR. PRR is consist of variety of nucleic acid sensors like-RNA sensors. They play crucial role in identifying exogenous and endogenous RNA molecules, which subsequently mediate pro/inflammatory cytokine, IFN and ISGs response in traumatized or tumorigenic conditions. The sensors can sensitize wide range of nucleic acid particle in term of size and structure, while each category sensors belongs subclasses with differentially expressed in cell and distinguished functioning mechanisms. They are also able to make comparison between self and non-self-nucleic acid molecules through specific mechanisms. Besides exhibiting anti-inflammatory and anti-tumorigenic responses, RNA sensors cover the broad spectrum of response mechanisms. Transcriptionally RNA sensors undergo with tight epigenetic regulations. In this review study, we will be going to discuss about the details of RNA sensors, their functional mechanisms and epi-transactional regulations.

The Japanese Encephalitis Virus NS1' Protein Inhibits Type I IFN Production by Targeting MAVS

Japanese encephalitis virus (JEV) is a mosquito-borne Flavivirus that causes severe neurologic disease in humans. NS1' is a NS1-related protein only reported in the Japanese encephalitis serogroup members of Flavivirus It is produced through programmed -1 ribosomal frameshift in NS2A. Our previous study demonstrated that JEV NS1' could antagonize type I IFN (IFN-I) production, but the mechanism is still unclear. In the current study, we found that JEV NS1' inhibits the expression of MAVS, and knockdown of MAVS hampers inhibition of IFN-β induction by NS1', suggesting that JEV NS1' inhibits IFN-I production by targeting MAVS. This finding is further supported by the result of the in vivo assay that showed the similar mortality caused by NS1'-deficient virus and its wild type virus in MAVS-deficient mice. Based on our previous sequencing results of noncoding RNA in JEV-infected cells, microRNA-22 (miR-22) was identified to be a key regulator for MAVS expression during JEV infection. Furthermore, we demonstrated that JEV NS1' could induce the expression of miR-22 by increasing the binding of transcriptional factors, CREB and c-Rel, to the promoter elements of miR-22. Taken together, our results reveal a novel mechanism by which JEV NS1' antagonizes host MAVS by regulating miR-22, thereby inhibiting the IFN-I production and facilitating viral replication.

CRISPR-Cas9 Mediated RNase L Knockout Regulates Cellular Function of PK-15 Cells and Increases PRV Replication

Ribonuclease L (RNase L) is an important antiviral endoribonuclease regulated by type I IFN. RNase L is activated by viral infection and dsRNA. Because the role of swine RNase L (sRNase L) is not fully understood, in this study, we generated a sRNase L knockout PK-15 (KO-PK) cell line through the CRISPR/Cas9 gene editing system to evaluate the function of sRNase L. After transfection with CRISPR-Cas9 followed by selection using puromycin, sRNase L knockout in PK-15 cells was further validated by agarose gel electrophoresis, DNA sequencing, and Western blotting. The sRNase L KO-PK cells failed to trigger RNA degradation and induced less apoptosis than the parental PK-15 cells after transfected with poly (I: C). Furthermore, the levels of ISGs mRNA in sRNase L KO-PK cells were higher than those in the parental PK-15 cells after treated with poly (I: C). Finally, both wild type and attenuated pseudorabies viruses (PRV) replicated more efficiently in sRNase L KO-PK cells than the parental PK-15 cells. Taken together, these findings suggest that sRNase L has multiple biological functions including cellular single-stranded RNA degradation, induction of apoptosis, downregulation of transcript levels of ISGs, and antiviral activity against PRV. The sRNase L KO-PK cell line will be a valuable tool for studying functions of sRNase L as well as for producing PRV attenuated vaccine.

The Role of Nucleic Acid Sensing in Controlling Microbial and Autoimmune Disorders

Innate immunity, the first line of defense against invading pathogens, is an ancient form of host defense found in all animals, from sponges to humans. During infection, innate immune receptors recognize conserved molecular patterns, such as microbial surface molecules, metabolites produces during infection, or nucleic acids of the microbe's genome. When initiated, the innate immune response activates a host defense program that leads to the synthesis proteins capable of pathogen killing. In mammals, the induction of cytokines during the innate immune response leads to the recruitment of professional immune cells to the site of infection, leading to an adaptive immune response. While a fully functional innate immune response is crucial for a proper host response and curbing microbial infection, if the innate immune response is dysfunctional and is activated in the absence of infection, autoinflammation and autoimmune disorders can develop. Therefore, it follows that the innate immune response must be tightly controlled to avoid an autoimmune response from host-derived molecules, yet still unencumbered to respond to infection. In this review, we will focus on the innate immune response activated from cytosolic nucleic acids, derived from the microbe or host itself. We will depict how viruses and bacteria activate these nucleic acid sensing pathways and their mechanisms to inhibit the pathways. We will also describe the autoinflammatory and autoimmune disorders that develop when these pathways are hyperactive. Finally, we will discuss gaps in knowledge with regard to innate immune response failure and identify where further research is needed.

Defining the Role of Stress Granules in Innate Immune Suppression by the Herpes Simplex Virus 1 Endoribonuclease VHS

In response to virus-induced shutoff host protein synthesis, dynamic aggregates containing mRNA, RNA-binding proteins and translation factors termed stress granules (SGs) often accumulate within the cytoplasm. SGs typically form following phosphorylation and inactivation of the eukaryotic translation initiation factor 2α (eIF2α), a substrate of the double-stranded RNA (dsRNA)-activated kinase protein kinase R (PKR). The detection of innate immune sensors and effectors like PKR at SGs suggests a role in pathogen nucleic acid sensing. However, the functional importance of SGs in host innate responses is unclear and has primarily been examined in response to infection with select RNA viruses. During infection with the DNA virus herpes simplex virus 1 (HSV-1), the virus-encoded virion host shutoff (VHS) endoribonuclease is required to restrict interferon production, PKR activation, and SG formation, although the relationship between these activities remains incompletely understood. Here, we show that in cells infected with a VHS-deficient HSV-1 (ΔVHS) dsRNA accumulated and localized to SGs. Surprisingly, formation of dsRNA and its concentration at SGs was not required for beta interferon mRNA induction, indicating that suppression of type I interferon induction by VHS does not stem from its control of dsRNA accumulation. Instead, STING signaling downstream of cGMP-AMP synthase (cGAS)-dependent DNA sensing is required for beta interferon induction. In contrast, significantly less PKR activation is observed when SG assembly is disrupted by ISRIB, an inhibitor of phosphorylated eIF2α-mediated translation repression, or depleting SG scaffolding proteins G3BP1 or TIA1. This demonstrates that PKR activation is intimately linked to SG formation and that SGs form important hubs to potentiate PKR activation during infection.IMPORTANCE Formation of cytoplasmic stress granules that are enriched for innate immune sensors and effectors is suppressed during many viral infections. It is unclear, however, to what extent this is a side effect of viral efforts to maintain protein synthesis or intentional disruption of a hub for innate immune sensing. In this study, we utilize a herpes simplex virus 1 mutant lacking the RNA nuclease VHS which upon infection induces SGs, PKR activation, and beta interferon to address this question. We show that dsRNA is localized to SGs and that SGs can function to promote PKR activation in the context of a DNA virus infection, but we find no evidence to support their importance for interferon induction during HSV-1 infection.

Interferon-related genetic markers of necroinflammatory activity in chronic hepatitis C

INTRODUCTION

Chronic hepatitis C (CHC) is a major cause of liver disease worldwide which often leads to progressive liver inflammation, fibrosis, cirrhosis and hepatocellular carcinoma (HCC). CHC displays heterogeneous progression depending on a broad set of factors, some of them intrinsic to each individual such as the patient's genetic profile. This study aims to evaluate the contribution of certain genetic variants of crucial interferon alpha and lambda signaling pathways to the hepatic necroinflammatory activity (NIA) grade of CHC patients.

METHODS

NIA was evaluated in 119 CHC patients by METAVIR scale and classified as low (NIA = 0-2, n = 80) or high grade (NIA = 3, n = 39). In a candidate gene approach, 64 SNPs located in 30 different genes related to interferon pathways (IL-28B, IFNAR1-2, JAK-STAT and OAS1-3, among others) were genotyped using the Illumina GoldenGate® Genotyping Assay. Statistical association was determined by logistic regression and expressed as OR and 95% CI. Those SNPs significantly associated were further adjusted by other covariates.

RESULTS

Seven SNPs located in IL-28B (rs12979860), JAK1 (rs11576173 and rs1497056), TYK2 (rs280519), OAS1 (rs2057778), SOCS1 (rs33932899) and RNASEL (rs3738579) genes were significantly related to severe NIA grade (p<0.05). Regarding to clinical variables, elevated NIA was notably associated with aspartate aminotransferase (AST) serum levels >40 IU/L (p<0.05) but not with other clinical factors. Multivariate logistic regression analysis of these factors reflected that AST (>40 IU/L), TYK2 rs280519 (G allele) and RNASEL rs3738579 (G allele) were factors independently associated with elevated NIA (p<0.05). AST concentration showed a moderate AUC value (AUC = 0.63), similar to TYK2 (rs280519) and RNASEL (rs3738579) SNPs (AUC = 0.61, both) in the ROC_AUC analysis. Interestingly, the model including all significant variables reached a considerable predictive value (AUC = 0.74).

CONCLUSION

The identified genetic variants in interferon signaling pathways may constitute useful prognostic markers of CHC progression. Further validation in larger cohorts of patients is needed.

Structural basis for 2'-5'-oligoadenylate binding and enzyme activity of a viral RNase L antagonist

Synthesis of 2'-5'-oligoadenylates (2-5A) by oligoadenylate synthetase (OAS) is an important innate cellular response that limits viral replication by activating the latent cellular RNase, RNase L, to degrade single-stranded RNA. Some rotaviruses and coronaviruses antagonize the OAS/RNase L pathway through the activity of an encoded 2H phosphoesterase domain that cleaves 2-5A. These viral 2H phosphoesterases are phylogenetically related to the cellular A kinase anchoring protein 7 (AKAP7) and share a core structure and an active site that contains two well-defined HΦ(S/T)Φ (where Φ is a hydrophobic residue) motifs, but their mechanism of substrate binding is unknown. Here, we report the structures of a viral 2H phosphoesterase, the C-terminal domain (CTD) of the group A rotavirus (RVA) VP3 protein, both alone and in complex with 2-5A. The domain forms a compact fold, with a concave β-sheet that contains the catalytic cleft, but it lacks two α-helical regions and two β-strands observed in AKAP7 and other 2H phosphoesterases. The cocrystal structure shows significant conformational changes in the R loop upon ligand binding. Bioinformatics and biochemical analyses reveal that conserved residues and residues required for catalytic activity and substrate binding comprise the catalytic motifs and a region on one side of the binding cleft. We demonstrate that the VP3 CTD of group B rotavirus, but not that of group G, cleaves 2-5A. These findings suggest that the VP3 CTD is a streamlined version of a 2H phosphoesterase with a ligand-binding mechanism that is shared among 2H phosphodiesterases that cleave 2-5A.

IMPORTANCE

The C-terminal domain (CTD) of rotavirus VP3 is a 2H phosphoesterase that cleaves 2'-5'-oligoadenylates (2-5A), potent activators of an important innate cellular antiviral pathway. 2H phosphoesterase superfamily proteins contain two conserved catalytic motifs and a proposed core structure. Here, we present structures of a viral 2H phosphoesterase, the rotavirus VP3 CTD, alone and in complex with its substrate, 2-5A. The domain lacks two α-helical regions and β-strands present in other 2H phosphoesterases. A loop of the protein undergoes significant structural changes upon substrate binding. Together with our bioinformatics and biochemical findings, the crystal structures suggest that the RVA VP3 CTD domain is a streamlined version of a cellular enzyme that shares a ligand-binding mechanism with other 2H phosphodiesterases that cleave 2-5A but differs from those of 2H phosphodiesterases that cleave other substrates. These findings may aid in the future design of antivirals targeting viral phosphodiesterases with cleavage specificity for 2-5A.

The Role of Phosphodiesterase 12 (PDE12) as a Negative Regulator of the Innate Immune Response and the Discovery of Antiviral Inhibitors

2',5'-Oligoadenylate synthetase (OAS) enzymes and RNase-L constitute a major effector arm of interferon (IFN)-mediated antiviral defense. OAS produces a unique oligonucleotide second messenger, 2',5'-oligoadenylate (2-5A), that binds and activates RNase-L. This pathway is down-regulated by virus- and host-encoded enzymes that degrade 2-5A. Phosphodiesterase 12 (PDE12) was the first cellular 2-5A- degrading enzyme to be purified and described at a molecular level. Inhibition of PDE12 may up-regulate the OAS/RNase-L pathway in response to viral infection resulting in increased resistance to a variety of viral pathogens. We generated a PDE12-null cell line, HeLaΔPDE12, using transcription activator-like effector nuclease-mediated gene inactivation. This cell line has increased 2-5A levels in response to IFN and poly(I-C), a double-stranded RNA mimic compared with the parental cell line. Moreover, HeLaΔPDE12 cells were resistant to viral pathogens, including encephalomyocarditis virus, human rhinovirus, and respiratory syncytial virus. Based on these results, we used DNA-encoded chemical library screening to identify starting points for inhibitor lead optimization. Compounds derived from this effort raise 2-5A levels and exhibit antiviral activity comparable with the effects observed with PDE12 gene inactivation. The crystal structure of PDE12 complexed with an inhibitor was solved providing insights into the structure-activity relationships of inhibitor potency and selectivity.

Emerging roles of interferon-stimulated genes in the innate immune response to hepatitis C virus infection

Infection with hepatitis C virus (HCV), a major viral cause of chronic liver disease, frequently progresses to steatosis and cirrhosis, which can lead to hepatocellular carcinoma. HCV infection strongly induces host responses, such as the activation of the unfolded protein response, autophagy and the innate immune response. Upon HCV infection, the host induces the interferon (IFN)-mediated frontline defense to limit virus replication. Conversely, HCV employs diverse strategies to escape host innate immune surveillance. Type I IFN elicits its antiviral actions by inducing a wide array of IFN-stimulated genes (ISGs). Nevertheless, the mechanisms by which these ISGs participate in IFN-mediated anti-HCV actions remain largely unknown. In this review, we first outline the signaling pathways known to be involved in the production of type I IFN and ISGs and the tactics that HCV uses to subvert innate immunity. Then, we summarize the effector mechanisms of scaffold ISGs known to modulate IFN function in HCV replication. We also highlight the potential functions of emerging ISGs, which were identified from genome-wide siRNA screens, in HCV replication. Finally, we discuss the functions of several cellular determinants critical for regulating host immunity in HCV replication. This review will provide a basis for understanding the complexity and functionality of the pleiotropic IFN system in HCV infection. Elucidation of the specificity and the mode of action of these emerging ISGs will also help to identify novel cellular targets against which effective HCV therapeutics can be developed.

Emerging roles of interferon-stimulated genes in the innate immune response to hepatitis C virus infection

Infection with hepatitis C virus (HCV), a major viral cause of chronic liver disease, frequently progresses to steatosis and cirrhosis, which can lead to hepatocellular carcinoma. HCV infection strongly induces host responses, such as the activation of the unfolded protein response, autophagy and the innate immune response. Upon HCV infection, the host induces the interferon (IFN)-mediated frontline defense to limit virus replication. Conversely, HCV employs diverse strategies to escape host innate immune surveillance. Type I IFN elicits its antiviral actions by inducing a wide array of IFN-stimulated genes (ISGs). Nevertheless, the mechanisms by which these ISGs participate in IFN-mediated anti-HCV actions remain largely unknown. In this review, we first outline the signaling pathways known to be involved in the production of type I IFN and ISGs and the tactics that HCV uses to subvert innate immunity. Then, we summarize the effector mechanisms of scaffold ISGs known to modulate IFN function in HCV replication. We also highlight the potential functions of emerging ISGs, which were identified from genome-wide siRNA screens, in HCV replication. Finally, we discuss the functions of several cellular determinants critical for regulating host immunity in HCV replication. This review will provide a basis for understanding the complexity and functionality of the pleiotropic IFN system in HCV infection. Elucidation of the specificity and the mode of action of these emerging ISGs will also help to identify novel cellular targets against which effective HCV therapeutics can be developed.

TDP-1, the Caenorhabditis elegans ortholog of TDP-43, limits the accumulation of double-stranded RNA

Caenorhabditis elegans mutants deleted for TDP-1, an ortholog of the neurodegeneration-associated RNA-binding protein TDP-43, display only mild phenotypes. Nevertheless, transcriptome sequencing revealed that many RNAs were altered in accumulation and/or processing in the mutant. Analysis of these transcriptional abnormalities demonstrates that a primary function of TDP-1 is to limit formation or stability of double-stranded RNA. Specifically, we found that deletion of tdp-1: (1) preferentially alters the accumulation of RNAs with inherent double-stranded structure (dsRNA); (2) increases the accumulation of nuclear dsRNA foci; (3) enhances the frequency of adenosine-to-inosine RNA editing; and (4) dramatically increases the amount of transcripts immunoprecipitable with a dsRNA-specific antibody, including intronic sequences, RNAs with antisense overlap to another transcript, and transposons. We also show that TDP-43 knockdown in human cells results in accumulation of dsRNA, indicating that suppression of dsRNA is a conserved function of TDP-43 in mammals. Altered accumulation of structured RNA may account for some of the previously described molecular phenotypes (e.g., altered splicing) resulting from reduction of TDP-43 function.

Integrative RNA-seq and microarray data analysis reveals GC content and gene length biases in the psoriasis transcriptome

Gene expression profiling of psoriasis has driven research advances and may soon provide the basis for clinical applications. For expression profiling studies, RNA-seq is now a competitive technology, but RNA-seq results may differ from those obtained by microarray. We therefore compared findings obtained by RNA-seq with those from eight microarray studies of psoriasis. RNA-seq and microarray datasets identified similar numbers of differentially expressed genes (DEGs), with certain genes uniquely identified by each technology. Correspondence between platforms and the balance of increased to decreased DEGs was influenced by mRNA abundance, GC content, and gene length. Weakly expressed genes, genes with low GC content, and long genes were all biased toward decreased expression in psoriasis lesions. The strength of these trends differed among array datasets, most likely due to variations in RNA quality. Gene length bias was by far the strongest trend and was evident in all datasets regardless of the expression profiling technology. The effect was due to differences between lesional and uninvolved skin with respect to the genome-wide correlation between gene length and gene expression, which was consistently more negative in psoriasis lesions. These findings demonstrate the complementary nature of RNA-seq and microarray technology and show that integrative analysis of both data types can provide a richer view of the transcriptome than strict reliance on a single method alone. Our results also highlight factors affecting correspondence between technologies, and we have established that gene length is a major determinant of differential expression in psoriasis lesions.

Enteropathogenic Escherichia coli inhibits type I interferon- and RNase L-mediated host defense to disrupt intestinal epithelial cell barrier function

Enteropathogenic Escherichia coli (EPEC) primarily infects children in developing countries and causes diarrhea that can be deadly. EPEC pathogenesis occurs through type III secretion system (T3SS)-mediated injection of effectors into intestinal epithelial cells (IECs); these effectors alter actin dynamics, modulate the immune response, and disrupt tight junction (TJ) integrity. The resulting compromised barrier function and increased gastrointestinal (GI) permeability may be responsible for the clinical symptoms of infection. Type I interferon (IFN) mediates anti-inflammatory activities and serves essential functions in intestinal immunity and homeostasis; however, its role in the immune response to enteric pathogens, such as EPEC, and its impact on IEC barrier function have not been examined. Here, we report that IFN-β is induced following EPEC infection and regulates IEC TJ proteins to maintain barrier function. The EPEC T3SS effector NleD counteracts this protective activity by inhibiting IFN-β induction and enhancing tumor necrosis factor alpha to promote barrier disruption. The endoribonuclease RNase L is a key mediator of IFN induction and action that promotes TJ protein expression and IEC barrier integrity. EPEC infection inhibits RNase L in a T3SS-dependent manner, providing a mechanism by which EPEC evades IFN-induced antibacterial activities. This work identifies novel roles for IFN-β and RNase L in IEC barrier functions that are targeted by EPEC effectors to escape host defense mechanisms and promote virulence. The IFN-RNase L axis thus represents a potential therapeutic target for enteric infections and GI diseases involving compromised barrier function.

Noncoding subgenomic flavivirus RNA: multiple functions in West Nile virus pathogenesis and modulation of host responses

Flaviviruses are a large group of positive strand RNA viruses transmitted by arthropods that include many human pathogens such as West Nile virus (WNV), Japanese encephalitis virus (JEV), yellow fever virus, dengue virus, and tick-borne encephalitis virus. All members in this genus tested so far are shown to produce a unique subgenomic flavivirus RNA (sfRNA) derived from the 3' untranslated region (UTR). sfRNA is a product of incomplete degradation of genomic RNA by the cell 5'–3' exoribonuclease XRN1 which stalls at highly ordered secondary RNA structures at the beginning of the 3'UTR. Generation of sfRNA results in inhibition of XRN1 activity leading to an increase in stability of many cellular mRNAs. Mutant WNV deficient in sfRNA generation was highly attenuated displaying a marked decrease in cytopathicity in cells and pathogenicity in mice. sfRNA has also been shown to inhibit the antiviral activity of IFN-α/β by yet unknown mechanism and of the RNAi pathway by likely serving as a decoy substrate for Dicer. Thus, sfRNA is involved in modulating multiple cellular pathways to facilitate viral pathogenicity; however the overlying mechanism linking all these multiple functions of sfRNA remains to be elucidated.

Specific RNA-protein interactions in the replication of foamy viruses (FVs)

The FV pathway of replication is fundamentally different from what we know about the strategy employed by all known other retroviruses. This unique pathway involves some distinctive RNA-protein interactions, which range from nuclear RNA export to activation of reverse transcription late in the viral replication cycle. Some peculiarities of this replication strategy will be summarized here.

The anti-HBV effect mediated by a novel recombinant eukaryotic expression vector for IFN-α

BACKGROUND

Chronic hepatitis B is a primary cause of liver-related death. Interferon alpha (IFN-α) is able to inhibit the replication of hepadnavirus, and the sustained and stable expression of IFN-α at appropriate level may be beneficial to HBV clearance. With the development of molecular cloning technology, gene therapy plays a more and more important role in clinical practice. In light of the findings, an attempt to investigate the anti-HBV effects mediated by a eukaryotic expression plasmid (pSecTagB-IFN-α) in vitro was carried out.

METHODS

HBV positive cell line HepG2.2.15 and its parental cell HepG2 were transfected with pSecTagB-IFN-α or empty plasmid by using Lipofectamine™ 2000 reagent. The expression levels of IFN-α were determined by reverse transcriptase polymerase chain reaction (RT-PCR) and ELISA methods. The effects of pSecTagB-IFN-α on HBV mRNA, DNA and antigens were analyzed by real-time fluorescence quantitative PCR (qRT-PCR) and ELISA assays. RT-PCR, qRT-PCR and western blot were employed to investigate the influence of pSecTagB-IFN-α on IFN-α-induced signal pathway. Furthermore, through qRT-PCR and ELISA assays, the suppressive effects of endogenously expressed IFN-α and the combination with lamivudine on HBV were also examined.

RESULTS

pSecTagB-IFN-α could express efficiently in hepatoma cells, and then inhibited HBV replication, characterized by the decrease of HBV S gene (HBs) and HBV C gene (HBc) mRNA, the reduction of HBV DNA load, and the low contents of hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg). Mechanism research showed that the activation of Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signal pathway, the up-regulation of IFN-α-induced antiviral effectors and double-stranded (ds) RNA sensing receptors by delivering pSecTagB-IFN-α, could be responsible for these phenomena. Furthermore, pSecTagB-IFN-α vector revealed effectively anti-HBV effect than exogenously added IFN-α. Moreover, lamivudine combined with endogenously expressed IFN-α exhibited stronger anti-HBV effect than with exogenous IFN-α.

CONCLUSION

Our results showed that endogenously expressed IFN-α can effectively and persistently inhibit HBV replication in HBV infected cells. These observations opened a promising way to design new antiviral genetic engineering drugs based on IFN-α.

A heat-shock protein axis regulates VEGFR2 proteolysis, blood vessel development and repair

Vascular endothelial growth factor A (VEGF-A) binds to the VEGFR2 receptor tyrosine kinase, regulating endothelial function, vascular physiology and angiogenesis. However, the mechanism underlying VEGFR2 turnover and degradation in this response is unclear. Here, we tested a role for heat-shock proteins in regulating the presentation of VEGFR2 to a degradative pathway. Pharmacological inhibition of HSP90 stimulated VEGFR2 degradation in primary endothelial cells and blocked VEGF-A-stimulated intracellular signaling via VEGFR2. HSP90 inhibition stimulated the formation of a VEGFR2-HSP70 complex. Clathrin-mediated VEGFR2 endocytosis is required for this HSP-linked degradative pathway for targeting VEGFR2 to the endosome-lysosome system. HSP90 perturbation selectively inhibited VEGF-A-stimulated human endothelial cell migration in vitro. A mouse femoral artery model showed that HSP90 inhibition also blocked blood vessel repair in vivo consistent with decreased endothelial regeneration. Depletion of either HSP70 or HSP90 caused defects in blood vessel formation in a transgenic zebrafish model. We conclude that perturbation of the HSP70-HSP90 heat-shock protein axis stimulates degradation of endothelial VEGFR2 and modulates VEGF-A-stimulated intracellular signaling, endothelial cell migration, blood vessel development and repair.

Pathologic effects of RNase-L dysregulation in immunity and proliferative control

The endoribonuclease RNase-L is the terminal component of an RNA cleavage pathway that mediates antiviral, antiproliferative and immunomodulatory activities. Inactivation or dysregulation of RNase-L is associated with a compromised immune response and increased risk of cancer, accordingly its activity is tightly controlled and requires an allosteric activator, 2',5'-linked oligoadenylates, for enzymatic activity. The biological activities of RNase-L are a result of direct and indirect effects of RNA cleavage and microarray analyses have revealed that RNase-L impacts the gene expression program at multiple levels. The identification of RNase-L-regulated RNAs has provided insights into potential mechanisms by which it exerts antiproliferative, proapoptotic, senescence-inducing and innate immune activities. RNase-L protein interactors have been identified that serve regulatory functions and are implicated as alternate mechanisms of its biologic functions. Thus, while the molecular details are understood for only a subset of RNase-L activities, its regulation by small molecules and critical roles in host defense and as a candidate tumor suppressor make it a promising therapeutic target.