Activation of the IFN-inducible enzyme RNase L causes apoptosis of animal cells

In silico modeling revealed new insights into the mechanism of action of enzyme 2'-5'-oligoadenylate synthetase in cattle

The innate immune system has an important role in developing the initial resistance to virus infection, and the ability of oligoadenylate synthetase to overcome viral evasion and enhance innate immunity is already established in humans. In the present study, we have tried to explore the molecular and structural variations present in Sahiwal (indigenous) and crossbred (Frieswal) cattle to identify the molecular mechanism of action of OAS1 gene in activation of innate immune response. The significant changes in structural alignment in terms of orientation of loops, shortening of β-sheets and formation of 3-10 α-helix was noticed in Sahiwal and Frieswal cattle. Further, it has been observed that OAS1 from Sahiwal had better binding with APC and DTP ligand than Frieswal OAS1. A remarkable change was seen in orientation at the nucleoside base region of both the ligands, which are bound with OAS1 protein from Frieswal and Sahiwal cattle. The Molecular Dynamic study of apo and ligand complex structures was provided more insight towards the stability of OAS1 from both cattle. This analysis displayed that the Sahiwal cattle protein has more steady nature throughout the simulation and has better binding towards Frieswal in terms of APC and DTP binding. Thus, OAS1 protein is the potential target for explaining the innate immune response in Sahiwal than Frieswal.Communicated by Ramaswamy H. Sarma.

The tumor suppressor MIR139 is silenced by POLR2M to promote AML oncogenesis

MIR139 is a tumor suppressor and is commonly silenced in acute myeloid leukemia (AML). However, the tumor-suppressing activities of miR-139 and molecular mechanisms of MIR139-silencing remain largely unknown. Here, we studied the poorly prognostic MLL-AF9 fusion protein-expressing AML. We show that MLL-AF9 expression in hematopoietic precursors caused epigenetic silencing of MIR139, whereas overexpression of MIR139 inhibited in vitro and in vivo AML outgrowth. We identified novel miR-139 targets that mediate the tumor-suppressing activities of miR-139 in MLL-AF9 AML. We revealed that two enhancer regions control MIR139 expression and found that the polycomb repressive complex 2 (PRC2) downstream of MLL-AF9 epigenetically silenced MIR139 in AML. Finally, a genome-wide CRISPR-Cas9 knockout screen revealed RNA Polymerase 2 Subunit M (POLR2M) as a novel MIR139-regulatory factor. Our findings elucidate the molecular control of tumor suppressor MIR139 and reveal a role for POLR2M in the MIR139-silencing mechanism, downstream of MLL-AF9 and PRC2 in AML. In addition, we confirmed these findings in human AML cell lines with different oncogenic aberrations, suggesting that this is a more common oncogenic mechanism in AML. Our results may pave the way for new targeted therapy in AML.

A genome-wide CRISPR screen identifies HuR as a regulator of apoptosis induced by dsRNA and virus

We performed an unbiased whole-genome CRISPR/Cas9 screen in A549 cells to identify potential regulators involved in cell death triggered by dsRNA. Of several top candidate genes, we identified the RNA binding protein ELAV like protein 1 (ELAVL1) that encodes Hu antigen R (HuR). Depletion of HuR led to less cell death induced by dsRNA. HuR is mainly involved in the apoptosis, and all of its RNA recognition motifs are essential for its proapoptotic function. We further showed that the HuR depletion had no influence on the mRNA level of an anti-apoptotic gene, BCL2, instead downregulated its translation in a cap-independent way. Polysome fractionation studies showed that HuR retarded the BCL2 mRNA in the non-translating pool of polysomes. Moreover, protection from dsRNA-induced apoptosis by HuR depletion required the presence of BCL2, indicating that the proapoptotic function of HuR is executed by suppressing BCL2. Consistently, HuR regulated apoptosis induced by infection of encephalomyocarditis or Semliki Forest virus. Collectively, our work identified a suite of proteins that regulate dsRNA-induced cell death, and elucidated the mechanism by which HuR acts as a pro-apoptotic factor.

African Swine Fever Virus CD2v Protein Induces β-Interferon Expression and Apoptosis in Swine Peripheral Blood Mononuclear Cells

African swine fever (ASF) is a hemorrhagic disease of swine characterized by massive lymphocyte depletion in lymphoid tissues due to the apoptosis of B and T cells, a process likely triggered by factors released or secreted by infected macrophages. ASFV CD2v (EP402R) has been implicated in viral virulence and immunomodulation in vitro; however, its actual function(s) remains unknown. We found that CD2v expression in swine PK15 cells induces NF-κB-dependent IFN-β and ISGs transcription and an antiviral state. Similar results were observed for CD2v protein treated swine PBMCs and macrophages, the major ASFV target cell. Notably, treatment of swine PBMCs and macrophages with CD2v protein induced apoptosis. Immunoprecipitation and colocalization studies revealed that CD2v interacts with CD58, the natural host CD2 ligand. Additionally, CD58 knockdown in cells or treatment of cells with an NF-κB inhibitor significantly reduced CD2v-mediated NF-κB activation and IFN-β induction. Further, antibodies directed against CD2v inhibited CD2v-induced NF-κB activation and IFN-β transcription in cells. Overall, results indicate that ASFV CD2v activates NF-κB, which induces IFN signaling and apoptosis in swine lymphocytes/macrophages. We propose that CD2v released from infected macrophages may be a significant factor in lymphocyte apoptosis observed in lymphoid tissue during ASFV infection in pigs.

Role of the chicken oligoadenylate synthase-like gene during in vitro Newcastle disease virus infection

The enzyme 2′-5′ oligoadenylate synthase (OAS) is one of the key interferon-induced antiviral factors that act through inhibition of viral replication. In chickens, there is a single well-characterized OAS gene, oligoadenylate synthase-like (OASL) that has been shown to be upregulated after infection with various viruses. However, a deeper understanding of how chicken OASL acts against viral infection is still necessary. In this study, we tested the hypothesis that OASL short interfering RNA (siRNA)–mediated knockdown would decrease the host gene expression response to the Newcastle disease virus (NDV) by impacting antiviral pathways. To assess our hypothesis, a chicken fibroblast cell line (DF-1) was infected with the NDV (LaSota strain) and OASL expression was knocked down using a specific siRNA. The level of NDV viral RNA in the cells and the expression of interferon response- and apoptosis-related genes were evaluated by quantitative PCR at 4, 8, and 24 h postinfection (hpi). Knockdown of OASL increased the level of NDV viral RNA at 4, 8, and 24 hpi (P < 0.05) and eliminated the difference between NDV-infected and noninfected cells for expression of interferon response- and apoptosis-related genes (P > 0.05). The lack of differential expression suggests that knockdown of OASL resulted in a decreased response to NDV infection. Within NDV-infected cells, OASL knockdown reduced expression of signal transducer and activator of transcription 1, interferon alfa receptor subunit 1, eukaryotic translation initiation factor 2 alpha kinase 2, ribonuclease L, caspase 8 (CASP8) and caspase 9 (CASP9) at 4 hpi, CASP9 at 8 hpi, and caspase 3, CASP8, and CASP9 at 24 hpi (P < 0.05). We suggest that the increased NDV viral load in DF-1 cells after OASL knockdown was the result of a complex interaction between OASL and interferon response- and apoptosis-related genes that decreased host response to the NDV. Our results provide comprehensive information on the role played by OASL during NDV infection in vitro. Targeting this mechanism could aid in future prophylactic and therapeutic treatments for Newcastle disease in poultry.

Development of a Novel Class of Self-Assembling dsRNA Cancer Therapeutics: A Proof-of-Concept Investigation

Cancer has proven to be an extremely difficult challenge to treat. Several fundamental issues currently underlie cancer treatment, including differentiating self from nonself, functional coupling of the recognition and therapeutic components of various therapies, and the propensity of cancerous cells to develop resistance to common treatment modalities via evolutionary pressure. Given these limitations, there is an increasing need to develop an all-encompassing therapeutic that can uniquely target malignant cells, decouple recognition from treatment, and overcome evolutionarily driven cancer resistance. We describe herein a new class of programmable self-assembling double-stranded RNA (dsRNA)-based cancer therapeutics that uniquely targets aberrant genetic sequences and in a functionally decoupled manner, undergoes oncogenic RNA-activated displacement (ORAD), initiating a therapeutic cascade that induces apoptosis and immune activation. As a proof of concept, we show that RNA strands targeting the EWS/Fli1 fusion gene in Ewing sarcoma cells that are end blocked with phosphorothioate bonds and additionally sealed with a 2'-deoxyuridine (2'-U)-modified DNA protector can be used to induce specific and potent killing of cells containing the target oncogenic sequence but not wild type.

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.

Characterization of a PKR inhibitor from the pathogenic ranavirus, Ambystoma tigrinum virus, using a heterologous vaccinia virus system

Ambystoma tigrinum virus (ATV) (family Iridoviridae, genus Ranavirus) was isolated from diseased tiger salamanders (Ambystoma tigrinum stebbinsi) from the San Rafael Valley in southern Arizona, USA in 1996. Genomic sequencing of ATV, as well as other members of the genus, identified an open reading frame that has homology to the eukaryotic translation initiation factor, eIF2α (ATV eIF2α homologue, vIF2αH). Therefore, we asked if the ATV vIF2αH could also inhibit PKR. To test this hypothesis, the ATV vIF2αH was cloned into vaccinia virus (VACV) in place of the well-characterized VACV PKR inhibitor, E3L. Recombinant VACV expressing ATV vIF2αH partially rescued deletion of the VACV E3L gene. Rescue coincided with rapid degradation of PKR in infected cells. These data suggest that the salamander virus, ATV, contains a novel gene that may counteract host defenses, and this gene product may be involved in the presentation of disease caused by this environmentally important pathogen.

New advances in our understanding of the "unique" RNase L in host pathogen interaction and immune signaling

Ever since the discovery of the existence of an interferon (IFN)-regulated ribonuclease, significant advances have been made in understanding the mechanism and associated regulatory effects of its action. What had been studied initially as a "unique" endoribonuclease is currently known as ribonuclease L (RNase L where "L" stands for latent). Some of the key developments include discovery of the RNase L signaling pathway, its structural characterization, and its molecular cloning. RNase L has been implicated in antiviral and antibacterial defense, as well as in hereditary prostate cancer. RNase L is activated by 2'-5' linked oligoadenylates (2-5A), which are synthesized by the oligoadenylate synthetases (OASs), a family of IFN-regulated pathogen recognition receptors that sense double-stranded RNAs. Activated RNase L cleaves single stranded RNAs, including viral RNAs and cellular RNAs. The catalytic activity of RNase L has been found to lead into the activation of several cellular signaling pathways, including those involved in autophagy, apoptosis, IFN-β production, NLRP3 inflammasome activation leading to IL-1β secretion, inhibition of cell migration, and cell adhesion. In this review, we will highlight the newest advances in our understanding of the catalytic role of RNase L in the context of different cellular pathways and extend the scope of these findings to discussion of potential therapeutic targets for antimicrobial drug development.

RNase L and the NLRP3-inflammasome: An old merchant in a new trade

The type I/III interferon (IFN)-inducible 2'-5'- oligoadenylate synthetase (OAS)/endoribonuclease L (RNase L) is a classical innate immune pathway that has been implicated in antiviral and antibacterial defense and also in hereditary prostate cancer. The OAS/RNase L pathway is activated when OAS senses double-stranded RNA and catalyzes the synthesis of 2'-5' linked oligodenylates (2-5A) from ATP. 2-5A then binds and activates RNase L, resulting cleavage of single-stranded RNAs. RNase L cleavage products are capable of activating RIG-like receptors such as RIG-I and MDA5 that leads to IFN-β expression during viral infection. Our recent findings suggest that beside the RLR pathway, RNase L cleavage products can also activate the NLRP3-inflammasome pathway, which requires DHX33 (DExD/H-box helicase) and the mitochondrial adaptor protein MAVS. Here we discuss this newly identified role of OAS-RNase L pathway in regulation of inflammasome signaling as an alternative antimicrobial mechanism that has potential as a target for development of new broad-spectrum antimicrobial and anti-inflammatory therapies.

Transfection of poly(I:C) can induce reactive oxygen species-triggered apoptosis and interferon-β-mediated growth arrest in human renal cell carcinoma cells via innate adjuvant receptors and the 2-5A system

Background

Synthetic double-stranded RNA poly(I:C) is a useful immune adjuvant and exhibits direct antitumor effects against several types of cancers. In this study, we elucidated the mechanisms underlying the effects induced in poly(I:C)-transfected human renal cell carcinoma (RCC) cells.

Results

In contrast to the lack of an effect of adding poly(I:C), poly(I:C) transfection drastically decreased RCC cell viability. Poly(I:C) transfection induced reactive oxygen species (ROS)-dependent apoptosis in RCC cells and decreased the mitochondrial membrane potential (ΔΨm). Treatment with N-acetyl-l-cysteine (NAC), a ROS scavenger, suppressed apoptosis and restored the ΔΨm. Although the levels of phosphorylated γH2A.X, an indicator of DNA damage, increased in poly(I:C)-transfected RCC cells, NAC treatment decreased their levels, suggesting ROS-mediated DNA damage. Furthermore, poly(I:C) transfection increased the levels of phosphorylated p53, NOXA, and tBid. Immunoblots and assays with a panel of caspase inhibitors revealed that poly(I:C) transfection-induced apoptosis was dependent on caspase-8 and -9, as well as caspase-2. Alternatively, poly(I:C) transfection increased mRNA expression of interferon (IFN)-β, and treatment with IFN-β suppressed growth of RCC cells without apoptosis. In addition, cyclinD1 and c-Myc expression decreased in poly(I:C)-transfected RCC cells. Moreover, RNA interference experiments revealed that poly(I:C) transfection exerted apoptotic effects on RCC cells through innate adjuvant receptors and the 2-5A system, the latter of which induces apoptosis in virus-infected cells.

Conclusions

These results suggest that poly(I:C) transfection induced two types of effects against RCC cells such as apoptosis, as a result of ROS-mediated DNA damage, and IFN-β-mediated growth arrest, both of which were exerted via innate adjuvant receptors and the 2-5A system.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-217) contains supplementary material, which is available to authorized users.

Role of type I interferons in inflammasome activation, cell death, and disease during microbial infection

Interferons (IFNs) were discovered over a half-century ago as antiviral factors. The role of type I IFNs has been studied in the pathogenesis of both acute and chronic microbial infections. Deregulated type I IFN production results in a damaging cascade of cell death, inflammation, and immunological host responses that can lead to tissue injury and disease progression. Here, we summarize the role of type I IFNs in the regulation of cell death and disease during different microbial infections, ranging from viruses and bacteria to fungal pathogens. Understanding the specific mechanisms driving type I IFN-mediated cell death and disease could aid in the development of targeted therapies.

Evasion of antiviral innate immunity by Theiler's virus L* protein through direct inhibition of RNase L

Theiler's virus is a neurotropic picornavirus responsible for chronic infections of the central nervous system. The establishment of a persistent infection and the subsequent demyelinating disease triggered by the virus depend on the expression of L*, a viral accessory protein encoded by an alternative open reading frame of the virus. We discovered that L* potently inhibits the interferon-inducible OAS/RNase L pathway. The antagonism of RNase L by L* was particularly prominent in macrophages where baseline oligoadenylate synthetase (OAS) and RNase L expression levels are elevated, but was detectable in fibroblasts after IFN pretreatment. L* mutations significantly affected Theiler's virus replication in primary macrophages derived from wild-type but not from RNase L-deficient mice. L* counteracted the OAS/RNase L pathway through direct interaction with the ankyrin domain of RNase L, resulting in the inhibition of this enzyme. Interestingly, RNase L inhibition was species-specific as Theiler's virus L* protein blocked murine RNase L but not human RNase L or RNase L of other mammals or birds. Direct RNase L inhibition by L* and species specificity were confirmed in an in vitro assay performed with purified proteins. These results demonstrate a novel viral mechanism to elude the antiviral OAS/RNase L pathway. By targeting the effector enzyme of this antiviral pathway, L* potently inhibits RNase L, underscoring the importance of this enzyme in innate immunity against Theiler's virus.

Theiler's virus is a murine picornavirus (same family as poliovirus) which has a striking ability to establish persistent infections of the central nervous system. To do so, the virus has to counteract the immune response of the host and particularly the potent response mediated by interferon. We observed that a protein encoded by Theiler's virus, the L* protein, inhibited the RNase L pathway, one of the best-characterized pathways mediating the antiviral IFN response. In contrast to previously identified viral antagonists of this pathway, L* was found to act directly on RNase L, the effector enzyme of the pathway. L* activity was found to be species-specific as it inhibited murine but not human RNase L. We confirmed the species-specificity and the direct interaction between L* and RNase L in vitro, using purified proteins. Acting at the effector step in the pathway allows L* to block RNase L activity efficiently. This suggests that RNase L is particularly important to control Theiler's virus replication in vivo. Another virus, mouse hepatitis virus (MHV), was recently shown to interfere with RNase L activation. Theiler's virus and MHV share a marked tropism for macrophages which may suggest that the RNase L pathway is particularly important in this cell type.

No association between XMRV or related gammaretroviruses in Australian prostate cancer patients

BACKGROUND

Xenotropic murine leukemia virus-related virus (XMRV) is a gammaretrovirus reported to be associated with prostate cancer (PC) and chronic fatigue syndrome (CFS). While the association of XMRV with CFS and PC has recently been discredited, no studies have been performed in Australian patients to investigate the association between PC and XMRV or related murine leukemia virus (MLV) in matched PC and normal tissue.

METHODS

Genomic DNA (gDNA) was purified from matched normal and cancer formalin-fixed paraffin-embedded (FFPE) prostate tissue from 35 Australian PC patients with Gleason scores ranging from 7 - 10. The presence of the ribonuclease L (RNase L) polymorphism R462Q was determined by allele specific PCR. Samples were screened for XMRV and related murine leukemia virus (MLV) variants by qPCR. Contaminating mouse DNA was detected using qPCR targeting mouse intracisternal A particle long terminal repeat DNA.

RESULTS

gDNA was successfully purified from 94% (66/70) of normal and cancer FFPE prostate tissues. RNase L typing revealed 8% were homozygous (QQ), 60% were heterozygous (RQ) and 32% were wild-type (RR) for the RNase L mutation. None of the 66 samples tested were positive for XMRV or related MLV sequences using broad MLV or XMRV specific primers with detection sensitivities of 1 viral copy of MLV/XMRV and XMRV DNA, respectively.

CONCLUSIONS

Using highly sensitive qPCR we found no evidence of XMRV or related gammaretroviruses in prostate tissues from 35 Australian PC patients. Our findings are consistent with other studies demonstrating that XMRV is a laboratory contaminant that has no role in the aetiology of PC.

ChemR23 dampens lung inflammation and enhances anti-viral immunity in a mouse model of acute viral pneumonia

Viral diseases of the respiratory tract, which include influenza pandemic, children acute bronchiolitis, and viral pneumonia of the elderly, represent major health problems. Plasmacytoid dendritic cells play an important role in anti-viral immunity, and these cells were recently shown to express ChemR23, the receptor for the chemoattractant protein chemerin, which is expressed by epithelial cells in the lung. Our aim was to determine the role played by the chemerin/ChemR23 system in the physiopathology of viral pneumonia, using the pneumonia virus of mice (PVM) as a model. Wild-type and ChemR23 knock-out mice were infected by PVM and followed for functional and inflammatory parameters. ChemR23^−/− mice displayed higher mortality/morbidity, alteration of lung function, delayed viral clearance and increased neutrophilic infiltration. We demonstrated in these mice a lower recruitment of plasmacytoid dendritic cells and a reduction in type I interferon production. The role of plasmacytoid dendritic cells was further addressed by performing depletion and adoptive transfer experiments as well as by the generation of chimeric mice, demonstrating two opposite effects of the chemerin/ChemR23 system. First, the ChemR23-dependent recruitment of plasmacytoid dendritic cells contributes to adaptive immune responses and viral clearance, but also enhances the inflammatory response. Second, increased morbidity/mortality in ChemR23^−/− mice is not due to defective plasmacytoid dendritic cells recruitment, but rather to the loss of an anti-inflammatory pathway involving ChemR23 expressed by non-leukocytic cells. The chemerin/ChemR23 system plays important roles in the physiopathology of viral pneumonia, and might therefore be considered as a therapeutic target for anti-viral and anti-inflammatory therapies.

Infections of the lower respiratory tract by single-stranded RNA viruses represent a major health problem worldwide. Animal models indicate that the severity of infections caused by these viruses is due essentially to an excessive primary immune response of the host, rather than the direct cytopathogenicity of the viruses. Plasmacytoid dendritic cells have been reported to play an important role in anti-viral immunity, but the factors responsible for the recruitment of these cells to the infected lung were unknown. This study depicts the roles of the G protein-coupled receptor ChemR23 in the recruitment of plasmacytoid dendritic cells and anti-viral immunity in a mouse model of acute viral pneumonia. The data also highlight the role of ChemR23 in dampening the lung inflammatory response. This latter effect is independent of pDC recruitment but involves non-leukocytic cells. This observation is of particular interest considering the established role of airway endothelial and epithelial cells in the immune responses following bacterial, viral and fungal infections. Our results suggest therefore that the chemerin/ChemR23 system might be considered as a target for anti-viral and anti-inflammatory therapies.

Equine torovirus (BEV) induces caspase-mediated apoptosis in infected cells

Toroviruses are gastroenteritis causing agents that infect different animal species and humans. To date, very little is known about how toroviruses cause disease. Here, we describe for the first time that the prototype member of this genus, the equine torovirus Berne virus (BEV), induces apoptosis in infected cells at late times postinfection. Observation of BEV infected cells by electron microscopy revealed that by 24 hours postinfection some cells exhibited morphological characteristics of apoptotic cells. Based on this finding, we analyzed several apoptotic markers, and observed protein synthesis inhibition, rRNA and DNA degradation, nuclear fragmentation, caspase-mediated cleavage of PARP and eIF4GI, and PKR and eIF2α phosphorylation, all these processes taking place after peak virus production. We also determined that both cell death receptor and mitochondrial pathways are involved in the apoptosis process induced by BEV. BEV-induced apoptosis at late times postinfection, once viral progeny are produced, could facilitate viral dissemination in vivo and contribute to viral pathogenesis.

Selective cell death mediated by small conditional RNAs

Cancer cells are characterized by genetic mutations that deregulate cell proliferation and suppress cell death. To arrest the uncontrolled replication of malignant cells, conventional chemotherapies systemically disrupt cell division, causing diverse and often severe side effects as a result of collateral damage to normal cells. Seeking to address this shortcoming, we pursue therapeutic regulation that is conditional, activating selectively in cancer cells. This functionality is achieved using small conditional RNAs that interact and change conformation to mechanically transduce between detection of a cancer mutation and activation of a therapeutic pathway. Here, we describe small conditional RNAs that undergo hybridization chain reactions (HCR) to induce cell death via an innate immune response if and only if a cognate mRNA cancer marker is detected within a cell. The sequences of the small conditional RNAs can be designed to accept different mRNA markers as inputs to HCR transduction, providing a programmable framework for selective killing of diverse cancer cells. In cultured human cancer cells (glioblastoma, prostate carcinoma, Ewing's sarcoma), HCR transduction mediates cell death with striking efficacy and selectivity, yielding a 20- to 100-fold reduction in population for cells containing a cognate marker, and no measurable reduction otherwise. Our results indicate that programmable mechanical transduction with small conditional RNAs represents a fundamental principle for exploring therapeutic conditional regulation in living cells.

Identification of cellular genes induced in human cells after activation of the OAS/RNaseL pathway by vaccinia virus recombinants expressing these antiviral enzymes

Interferon (IFN) type I induces the expression of antiviral proteins such as 2',5'-oligoadenylate synthetases (OAS). The enzyme OAS is activated by dsRNA to produce 5'-phosphorylated, 2-5-linked oligoadenylates (2-5A) that activate RNaseL which, in turn, triggers RNA breakdown, leading to multiple biological functions. Although RNaseL is required for IFN antiviral function, there are many aspects of the molecular mechanisms that remain obscure. Here, we have used microarray analyses from human HeLa cells infected with vaccinia virus (VACV) recombinants expressing OAS-RNaseL enzymes (referred as 2-5A system) with the aim to identify host genes that are up- or down-regulated in the course of infection by the activation of this antiviral pathway. We found that activation of the 2-5A system from VACV recombinants produces a remarkable stimulation of transcription for genes that regulate many cellular processes, like those that promote cell growth arrest, GADD45B and KCTD11, apoptosis as CUL2, PDCD6, and TNFAIP8L2, IFN-stimulated genes as IFI6, and related to tumor suppression as PLA2G2A. The 2-5A system activation produces down-regulation of transcription of some genes that promote cell growth as RUNX2 and ESR2 and of genes in charge to maintain mitochondria homeostasis as MIPEP and COX5A. These results reveal new genes induced in response to the activation of the 2-5A system with roles in apoptosis, translational control, cell growth arrest, and tumor suppression.

Ribosomal protein mRNAs are primary targets of regulation in RNase-L-induced senescence

The endoribonuclease RNase-L requires 2',5'-linked oligoadenylates for activation, and mediates antiviral and antiproliferative activities. We previously determined that RNase-L activation induces senescence; to determine potential mechanisms underlying this activity, we used microarrays to identify RNase-L-regulated mRNAs. RNase-L activation affected affected a finite number of transcripts, and thus does not lead to a global change in mRNA turnover. The largest classes of downregulated transcripts, that represent candidate RNase-L substrates, function in protein biosynthesis, metabolism and proliferation. Among these, mRNAs encoding ribosomal proteins (RPs) were particularly enriched. The reduced levels of four RP mRNAs corresponded with a decrease in their half lives and a physical association with an RNase-L-ribonucleoprotein (RNP) complex in cells, suggesting that they represent authentic RNase-L substrates. Sequence and structural analysis of the downregulated mRNAs identified a putative RNase-L target motif that was used for the in silico identification of a novel RNase-L-RNP-interacting transcript. The downregulation of RP mRNAs corresponded with a marked reduction in protein translation, consistent with the roles of RP proteins in ribosome function. Our data support a model in which the RNase-L-mediated degradation of RP mRNAs inhibits translation, and may contribute to its antiproliferative, senescence inducing and tumor suppressor activities.

RNase L downmodulation of the RNA-binding protein, HuR, and cellular growth

Ribonuclease L (RNase L) is an intracellular enzyme that is vital in innate immunity, but also is a tumor suppressor candidate. Here, we show that overexpression of RNase L decreases cellular growth and downmodulates the RNA-binding protein, HuR, a regulator of cell-cycle progression and tumorigenesis. The effect is temporal, occurring in specific cell-cycle phases and correlated with the cytoplasmic localization of RNase L. Both cellular growth and HuR were increased in RNASEL-null mouse fibroblast lines when compared to wild-type cells. Moreover, the stability of HuR mRNA was enhanced in RNASEL-null cells. The HuR 3' untranslated region (UTR), which harbors U-rich and adenylate-uridylate-rich elements, was potently responsive to RNase L when compared to control 3' UTR. Our results may offer a new explanation to the tumor suppressor function of RNase L.

[RNase L, a crucial mediator of innate immunity and other cell functions]

The 2-5A/RNase L pathway is one of the first cellular defences against viruses. RNase L is an unusual endoribonuclease which activity is strictly regulated by its binding to a small oligonucleotide, 2-5A. 2-5A itself is very unusual, consisting of a series of 5'- triphosphorylated oligoadenylates with 2'-5' bonds. But RNase L activity is not limited to viral RNA cleavage. RNase L plays a central role in innate immunity, apoptosis, cell growth and differentiation by regulating cellular RNA stability and expression. Default in its activity leads to increased susceptibility to virus infections and to tumor development. RNase L gene has been identified as HPC1 (Hereditary Prostate Cancer 1) gene. Study of RNase L variant R462Q in etiology of prostate cancer has led to the identification of the novel human retrovirus closely related to xenotropic murine leukemia viruses (MuLVs) and named XMRV.

The mitochondrial antiviral signaling protein, MAVS, is cleaved during apoptosis

Apoptosis of virus-infected cells is one important host strategy used to limit viral infection. Recently a member of the innate immune signaling pathway, MAVS, was localized to mitochondria, an organelle important for apoptosis regulation. Here we investigate what role MAVS may play in apoptosis. Induction of cell death led to the rapid cleavage of MAVS, resulting in its release from the outer mitochondrial membrane. This cleavage is blocked in cells incubated with proteasome or caspase inhibitors. Transfection of synthetic viral dsRNA and dsDNA also led to cleavage of MAVS, indicating that this process may be important during infection. Preventing apoptosis by over-expression of anti-apoptotic Bcl-xL blocks MAVS cleavage, placing this process downstream of caspase activation in the apoptotic program.

Enhanced expression of RNase L as a novel intracellular signal generated by NMDA receptors in mouse cortical neurons

Recently we showed that the level of mitochondrial mRNA was decreased prior to neuronal death induced by glutamate. As the level of mRNA is regulated by ribonuclease (RNase), we examined RNase activity and its expression in the primary cultures of cortical neurons after glutamate treatment in order to evaluate the involvement of RNase in glutamate-induced neuronal death. A 15-min exposure of the cultures to glutamate at the concentration of 100 microM produced marked neuronal damage (more than 70% of total cells) at 24-h post-exposure. Under the experimental conditions used, RNA degradation was definitely observed at a period of 4-12-h post-exposure, a time when no damage was seen in the neurons. Glutamate-induced RNA degradation was completely prevented by the N-methyl-d-aspartic acid (NMDA) receptor channel blocker MK-801 or the NR2B-containing NMDA receptor antagonist ifenprodil. Glutamate exposure produced enhanced expression of RNase L at least 2-12h later, which was absolutely abolished by MK-801. However, no significant change was seen in the level of RNase H1 mRNA at any time point post-glutamate treatment. Immunocytochemical studies revealed that RNase L expressed in response to glutamate was localized within the nucleus, mitochondria, and cytoplasm in the neurons. Taken together, our data suggest that expression of RNase L is a signal generated by NMDA receptor in cortical neurons. RNase L expression and RNA degradation may be events that cause neuronal damage induced by NMDA receptor activation.

Apoptotic signals induce specific degradation of ribosomal RNA in yeast

Organisms exposed to reactive oxygen species, generated endogenously during respiration or by environmental conditions, undergo oxidative stress. Stress response can either repair the damage or activate one of the programmed cell death (PCD) mechanisms, for example apoptosis, and finally end in cell death. One striking characteristic, which accompanies apoptosis in both vertebrates and yeast, is a fragmentation of cellular DNA and mammalian apoptosis is often associated with degradation of different RNAs. We show that in yeast exposed to stimuli known to induce apoptosis, such as hydrogen peroxide, acetic acid, hyperosmotic stress and ageing, two large subunit ribosomal RNAs, 25S and 5.8S, became extensively degraded with accumulation of specific intermediates that differ slightly depending on cell death conditions. This process is most likely endonucleolytic, is correlated with stress response, and depends on the mitochondrial respiratory status: rRNA is less susceptible to degradation in respiring cells with functional defence against oxidative stress. In addition, RNA fragmentation is independent of two yeast apoptotic factors, metacaspase Yca1 and apoptosis-inducing factor Aif1, but it relies on the apoptotic chromatin condensation induced by histone H2B modifications. These data describe a novel phenotype for certain stress- and ageing-related PCD pathways in yeast.

Lytic infection with vaccinia virus activates caspases in a Bcl-2-inhibitable manner

Vaccinia virus (VV) is considered to cause lytic infection of most cells, with lysis being regarded equivalent to necrosis. Activation of caspases has not been associated with necrosis. However, we observed the activation and activity of caspases in epithelial cells HeLa G and BSC-40 lytically infected with VV. Using three different flow-cytometric approaches, we characterized the distinct stages of caspase cascade in VV-infected cells: a cleaved, activated form of caspases detected using a fluorescent pan-caspase inhibitor; caspase activity assayed by cleavage of a non-fluorescent substrate into a fluorescent product; caspase-specific cleavage of death substrates characterized by a fluorescent antibody detecting a neo-epitope in cytokeratin-18. All of these approaches yielded an increased fluorescent signal in VV-infected cells compared to mock-infected controls. Additionally, the signal was decreased by the expression of Bcl-2. The cleavage of cytokeratin-18 was confirmed by western blotting, but another key protein involved in apoptosis, PARP, was not cleaved in VV-infected lytic cells. The necrotic phenotype of the cells was confirmed by increased cell membrane permeability and/or decreased mitochondrial membrane potential. In conclusion, our data suggest that VV infection of the epithelial cells HeLa G and BSC-40 initiates the apoptotic program, however, apoptosis is not completed and switches into necrosis.

Expression of the E3L gene of vaccinia virus in transgenic mice decreases host resistance to vaccinia virus and Leishmania major infections

The E3L gene of vaccinia virus (VACV) encodes the E3 protein that in cultured cells inhibits the activation of interferon (IFN)-induced proteins, double-stranded RNA-dependent protein kinase (PKR), 2'-5'-oligoadenylate synthetase/RNase L (2-5A system) and adenosine deaminase (ADAR-1), thus helping the virus to evade host responses. Here, we have characterized the in vivo E3 functions in a murine inducible cell culture system (E3L-TetOFF) and in transgenic mice (TgE3L). Inducible E3 expression in cultured cells conferred on cells resistance to the antiviral action of IFN against different viruses, while expression of the E3L gene in TgE3L mice triggered enhanced sensitivity of the animals to pathogens. Virus infection monitored in TgE3L mice by different inoculation routes (intraperitoneal and tail scarification) showed that transgenic mice became more susceptible to VACV infection than control mice. TgE3L mice were also more susceptible to Leishmania major infection, leading to an increase in parasitemia compared to control mice. The enhanced sensitivity of TgE3L mice to VACV and L. major infections occurred together with alterations in the host immune system, as revealed by decreased T-cell responses to viral antigens in the spleen and lymph nodes and by differences in the levels of specific innate cell populations. These results demonstrate that expression of the E3L gene in transgenic mice partly reverses the resistance of the host to viral and parasitic infections and that these effects are associated with immune alterations.

Characterization of the equine 2'-5' oligoadenylate synthetase 1 (OAS1) and ribonuclease L (RNASEL) innate immunity genes

Background

The mammalian OAS/RNASEL pathway plays an important role in antiviral host defense. A premature stop-codon within the murine Oas1b gene results in the increased susceptibility of mice to a number of flaviviruses, including West Nile virus (WNV). Mutations in either the OAS1 or RNASEL genes may also modulate the outcome of WNV-induced disease or other viral infections in horses. Polymorphisms in the human OAS gene cluster have been previously utilized for case-control analysis of virus-induced disease in humans. No polymorphisms have yet been identified in either the equine OAS1 or RNASEL genes for use in similar case-control studies.

Results

Genomic sequence for equine OAS1 was obtained from a contig assembly generated from a shotgun subclone library of CHORI-241 BAC 100I10. Specific amplification of regions of the OAS1 gene from 13 horses of various breeds identified 33 single nucleotide polymorphisms (SNP) and two microsatellites. RNASEL cDNA sequences were determined for 8 mammals and utilized in a phylogenetic analysis. The chromosomal location of the RNASEL gene was assigned by FISH to ECA5p17-p16 using two selected CHORI-241 BAC clones. The horse genomic RNASEL sequence was assembled. Specific amplification of regions of the RNASEL gene from 13 horses identified 31 SNPs.

Conclusion

In this report, two dinucleotide microsatellites and 64 single nucleotide polymorphisms within the equine OAS1 and RNASEL genes were identified. These polymorphisms are the first to be reported for these genes and will facilitate future case-control studies of horse susceptibility to infectious diseases.

Regulation of mitochondrial mRNA stability by RNase L is translation-dependent and controls IFNalpha-induced apoptosis

Interferons (IFNs) inhibit the growth of many different cell types by altering the expression of specific genes. IFNs activities are partly mediated by the 2'-5' oligoadenylates-RNase L RNA decay pathway. RNase L is an endoribonuclease requiring activation by 2'-5' oligoadenylates to cleave single-stranded RNA. Here, we present evidence that degradation of mitochondrial mRNA by RNase L leads to cytochrome c release and caspase 3 activation during IFNalpha-induced apoptosis. We identify and characterize the mitochondrial translation initiation factor (IF2mt) as a new partner of RNase L. Moreover, we show that specific inhibition of mitochondrial translation with chloramphenicol inhibits the IFNalpha-induced degradation of mitochondrial mRNA by RNase L. Finally, we demonstrate that overexpression of IF2mt in human H9 cells stabilizes mitochondrial mRNA, inhibits apoptosis induced by IFNalpha and partially reverses IFNalpha-cell growth inhibition. On the basis of our results, we propose a model describing how RNase L regulates mitochondrial mRNA stability through its interaction with IF2mt.

Diverse functions of RNase L and implications in pathology

The endoribonuclease L (RNase L) is the effector of the 2-5A system, a major enzymatic pathway involved in the molecular mechanism of interferons (IFNs). RNase L is a very unusual nuclease with a complex mechanism of regulation. It is a latent enzyme, expressed in nearly every mammalian cell type. Its activation requires its binding to a small oligonucleotide, 2-5A. 2-5A is a series of unique 5'-triphosphorylated oligoadenylates with 2'-5' phosphodiester bonds. By regulating viral and cellular RNA expression, RNase L plays an important role in the antiviral and antiproliferative activities of IFN and contributes to innate immunity and cell metabolism. The 2-5A/RNase L pathway is implicated in mediating apoptosis in response to viral infections and to several types of external stimuli. Several recent studies have suggested that RNase L could have a role in cancer biology and evidence of a tumor suppressor function of RNase L has emerged from studies on the genetics of hereditary prostate cancer.

Impact of protein kinase PKR in cell biology: from antiviral to antiproliferative action

The double-stranded RNA-dependent protein kinase PKR is a critical mediator of the antiproliferative and antiviral effects exerted by interferons. Not only is PKR an effector molecule on the cellular response to double-stranded RNA, but it also integrates signals in response to Toll-like receptor activation, growth factors, and diverse cellular stresses. In this review, we provide a detailed picture on how signaling downstream of PKR unfolds and what are the ultimate consequences for the cell fate. PKR activation affects both transcription and translation. PKR phosphorylation of the alpha subunit of eukaryotic initiation factor 2 results in a blockade on translation initiation. However, PKR cannot avoid the translation of some cellular and viral mRNAs bearing special features in their 5' untranslated regions. In addition, PKR affects diverse transcriptional factors such as interferon regulatory factor 1, STATs, p53, activating transcription factor 3, and NF-kappaB. In particular, how PKR triggers a cascade of events involving IKK phosphorylation of IkappaB and NF-kappaB nuclear translocation has been intensively studied. At the cellular and organism levels PKR exerts antiproliferative effects, and it is a key antiviral agent. A point of convergence in both effects is that PKR activation results in apoptosis induction. The extent and strength of the antiviral action of PKR are clearly understood by the findings that unrelated viral proteins of animal viruses have evolved to inhibit PKR action by using diverse strategies. The case for the pathological consequences of the antiproliferative action of PKR is less understood, but therapeutic strategies aimed at targeting PKR are beginning to offer promising results.

DT. Targeting lung cancer using an infectivity enhanced CXCR4-CRAd

Conventional treatments are not adequate for the majority of lung cancer patients. Conditionally replicating adenoviruses (CRAds) represent a promising new modality for the treatment of neoplastic diseases, including non-small cell lung cancer. Specifically, following cellular infection, the virus replicates selectively in the infected tumor cells and kills the cells by cytolysis. Next, the progeny virions infect a new population of surrounding target cells, replicate again and eradicate the infected tumor cells while leaving normal cells unaffected. However, to date, there have been two main limitations to successful clinical application of these CRAd agents; i.e. poor infectivity and poor tumor specificity. Here we report the construction of a CRAd agent, CRAd-CXCR4.RGD, in which the adenovirus E1 gene is driven by a tumor-specific CXCR4 promoter and the viral infectivity is enhanced by a capsid modification, RGD4C. This agent CRAd-CXCR4.RGD, as expected, improved both of the viral infectivity and tumor specificity as evaluated in an established lung tumor cell line and in primary tumor tissue from multiple patients. As an added benefit, the activity of the CXCR4 promoter was low in human liver as compared to three other promoters regularly used for targeting tumors. In addition, this agent has the potential of targeting multiple other tumor cell types. From these data, the CRAd-CXCR4.RGD appears to be a promising novel CRAd agent for lung cancer targeting with low host toxicity.

Role of 2-5A-dependent RNase-L in senescence and longevity

Senescence is a permanent growth arrest that restricts the lifespan of primary cells in culture, and represents an in vitro model for aging. Senescence functions as a tumor suppressor mechanism that can be induced independent of replicative crisis by diverse stress stimuli. RNase-L mediates antiproliferative activities and functions as a tumor suppressor in prostate cancer, therefore, we examined a role for RNase-L in cellular senescence and aging. Ectopic expression of RNase-L induced a senescent morphology, a decrease in DNA synthesis, an increase in senescence-associated beta-galactosidase activity, and accelerated replicative senescence. In contrast, senescence was retarded in RNase-L-null fibroblasts compared with wild-type fibroblasts. Activation of endogenous RNase-L by 2-5A transfection induced distinct senescent and apoptotic responses in parental and Simian virus 40-transformed WI38 fibroblasts, respectively, demonstrating cell type specific differences in the antiproliferative response to RNase-L activation. Replicative senescence is a model for in vivo aging; therefore, genetic disruption of senescence effectors may impact lifespan. RNase-L-/- mice survived 31.7% (P<0.0001) longer than strain-matched RNase-L+/+ mice providing evidence for a physiological role for RNase-L in aging. These findings identify a novel role for RNase-L in senescence that may contribute to its tumor suppressive function and to the enhanced longevity of RNase-L-/- mice.

Organization of the interferon-inducible 2',5'-oligoadenylate-dependent ribonuclease L (RNase L) gene of mouse

Interferons (IFNs) induce a 2',5'-oligoadenylate (2-5A)-dependent ribonuclease L (RNase L) following virus-infection of mammalian cells. RNase L degrades both viral and cellular RNAs and restricts virus-proliferation. We have studied organization of RNase L gene in genomic DNA from the mouse liver by Southern blot analysis. Several BamHI, BglII, EcoRI, HincII, HindIII, NcoI, PstI, SacI, and XbaI restriction fragments hybridized to (32)P-labeled mouse RNase L cDNA and the 5'-proximal exon probes. Mouse RNase L gene exists as a single copy (>16 kb DNA) gene. A 5 kb HindIII and a 2.5 kb EcoRI DNA were detected as 5'-upstream DNA of the gene which may contain mouse RNase L promoter. Our results will help studying mouse RNase L gene promoter in further details.

Role of mitochondria in apoptosis induced by the 2-5A system and mechanisms involved

The 2-5A system (2-5OAS/RNaseL) is composed of the 2',5'oligoadenylate synthetase 1 (2-5OAS1) and 2-5A-dependent RNase (RNaseL), enzymes that play a key role in antiviral defence mechanisms. Activation of the 2-5A system by double stranded RNA (dsRNA) induces degradation of ribosomal RNAs and apoptosis in mammalian cells. To obtain further information into the molecular mechanisms by which RNaseL induces apoptosis, we expressed human RNaseL and 2-5OAS in HeLa cells using recombinant vaccinia viruses as vectors and we analysed in detail different biochemical markers of apoptosis. In this expression virus-cell system the activation of RNaseL, as index of rRNA degradation, is an upstream event of apoptosis induction. RNaseL induces apoptosis in a caspase-dependent manner (caspases 8, 9 and 2). At the beginning of apoptosis RNaseL and 2-5OAS are localized in the mitochondria and cytosol fractions, while at the onset of apoptosis both enzymes are largely in mitochondria. The 2-5A system induces the release of Cytochrome c from mitochondria to cytosol in a caspase dependent manner. The onset of apoptosis elicits the disruption of mitochondrial membrane potential (delta psi m), as well as the generation of reactive oxygen species (ROS). Moreover, the activation of RNaseL induces morphological alterations in the mitochondria. Apoptosis induced by the 2-5A system involves mitochondrial proteins, such as the human anti-apoptotic protein Bcl-2, which blocks both the apoptosis and the change of delta psi m induced by the activation of RNaseL. These findings provide new insights into the molecular mechanisms of apoptosis induction by the 2-5A system, demonstrating the importance of mitochondria in 2-5OAS/RNaseL-induced apoptosis.

Involvement of PKR and RNase L in translational control and induction of apoptosis after Hepatitis C polyprotein expression from a vaccinia virus recombinant

Background

Hepatitis C virus (HCV) infection is of growing concern in public health with around 350 million chronically infected individuals worldwide. Although the IFN-α/rivabirin is the only approved therapy with 10–30% clinical efficacy, the protective molecular mechanism involved during the treatment is still unknown. To analyze the effect of HCV polyprotein expression on the antiviral response of the host, we developed a novel vaccinia virus (VV)-based delivery system (VT7-HCV7.9) where structural and nonstructural (except part of NS5B) proteins of HCV ORF from genotype 1b are efficiently expressed and produced, and timely regulated in mammalian cell lines.

Results

Regulated transcript production and viral polypeptide processing was demonstrated in various cell lines infected with the recombinant VT7-HCV7.9, indicating that the cellular and viral proteolytic machineries are functional within these cells. The inducible expression of the HCV polyprotein by VV inhibits the synthesis of both host and viral proteins over the time and also induces apoptosis in HeLa and HepG2-infected cells. These effects occur accompanying with the phosphorylation of the translation initiation factor eIF-2α. In cells co-infected with VT7-HCV7.9 and a recombinant VV expressing the dominant negative eIF-2α-S51A mutant in the presence of the inductor isopropyl-thiogalactoside (IPTG), protein synthesis is rescued. The IFN-inducible protein kinase PKR is responsible for the translational block, as demonstrated with PKR-/- and PKR+/+ cell lines. However, apoptosis induced by VT7-HCV7.9 is mediated by the RNase L pathway, in a PKR-independent manner.

Conclusion

These findings demonstrate the antiviral relevance of the proteins induced by interferon, PKR and RNase L during expression from a VV recombinant of the HCV polyprotein in human cell lines. HCV polyprotein expression caused a severe cytopathological effect in human cells as a result of inhibition of protein synthesis and apoptosis induction, triggered by the activation of the IFN-induced enzymes PKR and RNase L systems. Thus, the virus-cell system described here highlights the relevance of the IFN system as a protective mechanism against HCV infection.

The role of IFN regulatory factor-3 in the cytotoxic activity of NS-9, a polyinosinic-polycytidylic acid/cationic liposome complex, against tumor cells

NS-9 is a complex of polyinosinic-polycytidylic acid and a novel cationic liposome, LIC-101. The complex has strong cytotoxic activity against tumor cells derived from epithelial or fibroblastic cells. We have investigated the mechanism of the cytotoxic activity of NS-9 using knockdown cells in which the expression of proteins of interest was inhibited by RNA interference. NS-9 showed strong cytotoxic activity against knockdown cells with reduced expression of double-stranded RNA-dependent protein kinase, RNase L, or IFN-alpha/beta receptor, but showed no cytotoxic activity against IFN regulatory factor-3 (IRF3) knockdown cells. In IRF3-knockdown cells, NS-9 also did not induce either the DNA fragmentation or the rRNA degradation observed in negative control cells. We conclude that IRF3 plays a crucial role in the cytotoxic activity of NS-9 against tumor cells, whereas RNA-dependent protein kinase, RNase L, or type I IFNs are not important for its activity.

Arg462Gln sequence variation in the prostate-cancer-susceptibility gene RNASEL and age of onset of hereditary non-polyposis colorectal cancer: a case-control study

BACKGROUND

RNASEL is thought to be a susceptibility gene for hereditary prostate cancer and encodes the endoribonuclease RNase L, which has a role in apoptosis and is a candidate tumour-suppressor protein. A common sequence variation in RNASEL, Arg462Gln, has been associated with hereditary and sporadic prostate cancer, and the Gln variant has about three-fold reduced RNase activity in vitro. In view of the association between the age of onset of hereditary non-polyposis colorectal cancer and functionally different variants of P53, which play a key part in the apoptotic pathway, we aimed to assess whether the Arg462Gln variation of RNASEL affects the age of onset of hereditary non-polyposis colorectal cancer.

METHODS

We screened 251 patients with hereditary non-polyposis colorectal cancer who were unrelated, had pathogenic germline mutations in MSH2 (n=141) or MLH1 (n=110), and had colorectal carcinoma as the first tumour, for variation at codon 462 of RNASEL and compared them with 439 healthy controls.

FINDINGS

The median age of onset was 40 years (range 17-75) for patients with an Arg/Arg genotype at codon 462, 37 years (13-69) for patients with an Arg/Gln genotype, and 34 years (20-49) for those with a Gln/Gln genotype (p=0.0198). Only the RNASEL genotype had a significant effect on age of onset (p=0.0062) in an additive mode of inheritance. Pair-wise comparisons between genotype groups showed that the two homozygous groups (ie, Arg/Arg vs Gln/Gln) differed significantly in age of disease onset (mean age difference 4.8 years [SD 1.7], p=0.0044).

INTERPRETATION

A sequence variation in the prostate-cancer-susceptibility gene RNASEL has a role in a different, unassociated malignant disease. Genotypes at RNASEL codon 462 are associated with age of onset of hereditary non-polyposis colorectal cancer in a dose-dependent way, and might have a role in preventive strategies for this disease.

Modulation of CXCL14 (BRAK) expression in prostate cancer

BACKGROUND

Recent studies suggest inflammatory processes may be involved in the development or progression of prostate cancer. Chemokines are a family of cytokines that can play several roles in cancer progression including angiogenesis, inflammation, cell recruitment, and migration.

METHODS

Real-time quantitative RT-PCR, in situ RNA hybridization, laser capture microscopy, immunohistochemistry, and cDNA array based technologies were used to examine CXCL14 (BRAK) expression in paired normal and tumor prostate. To determine the role CXCL14 expression has on cancer progression, LAPC4 cells were engineered to overexpress mouse or human CXCL14, and xenograft studies were performed.

RESULTS

CXCL14 RNA expression was observed in normal and tumor prostate epithelium and focally in stromal cells adjacent to cancer. CXCL14 mRNA was significantly upregulated in localized prostate cancer and positively correlated with Gleason score. CXCL14 levels were unchanged in BPH specimens. LAPC4 cells expressing CXCL14 resulted in a 43% tumor growth inhibition (P = 0.019) in vivo compared to vector only xenografts.

CONCLUSIONS

CXCL14 mRNA upregulation is a common feature in prostate cancer. The finding that CXCL14 expression inhibits tumor growth suggests this gene has tumor suppressive functions.

Vaccinia virus recombinants as a model system to analyze interferon-induced pathways

The interferons (IFNs) are a family of cytokines with broad antiviral activities that also control cell proliferation and modulate immune responses. IFNs exert their pleiotropic actions through the regulation of multiple pathways that have been subjected to extensive study using diverse approaches. The scope of this review is to show how we can take advantage of vaccinia virus (VV) to study IFN-related pathways. We summarize and present the different VV models available for studying IFN function and the possibilities that they offer to analyze IFN-induced pathways, IFN modulators, and the biologic effects at the molecular and cellular levels. Emphasis is given to studies of dsRNA-activated signaling with VV lacking E3L (VV DeltaE3L) and in RNA-activated protein kinase (PKR)-related pathways, through the use of VV recombinants (VVr) with inducible PKR (VV PKR). The latest system is versatile, as expression of PKR can be regulated and induced at different times; similarly, VVr can be generated expressing other PKR modulators. As an example of the utility of VVr, we describe how this model has been used to analyze the antiviral and proapoptotic functions of PKR, the impact of PKR on translation, and the PKR-induced activation of the nuclear factor-kappaB (NF-kappaB) pathway.

RNase-L regulates the stability of mitochondrial DNA-encoded mRNAs in mouse embryo fibroblasts

Accelerated decrease in the levels of mitochondrial DNA-encoded mRNA (mt-mRNA) occurs in neuronal cells exposed either to the excitatory amino acid, glutamate or to the sodium ionophore, monensin, suggesting a role of mitochondrial RNase(s) on the stability of mt-mRNAs. Here we report that in mouse embryo fibroblasts that are devoid of the interferon-regulated RNase, RNase-L, the monensin-induced decrease in the half-life of mt-mRNA was reduced. In monensin (250 nM)-treated RNase-L(+/+) cells the average half-life of mt-mRNA, determined after termination of transcription with actinomycin D, was found to be 3h, whereas in monensin-treated RNase-L(-/-) cells the half-life of mt-mRNA was >6h. In contrast, the stability of nuclear DNA-encoded beta-actin mRNA was unaffected. Induction of RNase-L expression in mouse 3T3 fibroblasts further decreased the monensin-induced reduction in mt-mRNA half-life to 1.5h. The results indicate that the RNase-L-dependent decrease in mtDNA-encoded mRNA transcript levels occurs through a decrease in the half-life of mt-mRNA, and that RNase-L may play a role in the stability of mt-mRNA.

Apoptosis induced by a cytopathic hepatitis A virus is dependent on caspase activation following ribosomal RNA degradation but occurs in the absence of 2'-5' oligoadenylate synthetase

We have presented previously evidence that the cytopathogenic 18f strain of hepatitis A virus (HAV) induced degradation of ribosomal RNA (rRNA) in infected cells [Arch. Virol. 148 (2003) 1275–1300]. In contrast, the non-cytopathogenic parent virus HM175 clone 1 had no effect on rRNA integrity. We present here data showing that rRNA degradation is followed by apoptosis accompanied by characteristic DNA laddering in the cytoplasm of 18f infected cells. The DNA laddering coincided with the detection of caspase 3 and PARP-1 cleavage and was dependent upon activation of the caspase pathway, since treatment with Z-VAD-FMK, a pan-caspase inhibitor, inhibited both events. RNase L mRNA was present in both virus-infected and uninfected cells. Messenger RNA for the interferon inducible enzyme 2′–5′ oligoadenylate synthetase (2′–5′ OAS), which polymerizes ATP into 2′–5′ oligo adenylate (2–5A, the activator of RNase L) in the presence of double-stranded RNA, was not detected following virus infection. 2′–5′ OAS mRNA was induced by treatment of the cells with interferon-β (IFN-β). IFN-β mRNA was marginally induced following infection. However, phosphorylated STAT 1, a key regulator of interferon-stimulated gene transcription was not detected in virus infected cells. STAT 1 phosphorylation in response to IFN treatment was lower in virus-infected cells, compared to uninfected cells treated with interferon, suggesting that 18f virus infection interferes with interferon signaling. The results suggest that 18f infection causes the induction of a 2–5A independent RNase L like activity.

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.

Synthesis, characterization and antiviral activity against influenza virus of a series of novel manganese-substituted rare earth borotungstates heteropolyoxometalates

A series of novel manganese-substituted mixed-valence rare earth borotungsto-heteropoly blues, Ln2H3[BW9(VI)W2(V)Mn(H2O)O39] x 12H2O (Ln(2), Ln = La, Ce, Pr, Nd, Sm, Eu and Gd), as well as their corresponding heteropoly acids (Ln(0)), have been prepared and characterized by cyclic voltammetry (CV), infrared (IR), ultraviolet (UV), thermal gravimetric (TG) and differential thermal (DTA) analysis, X-ray photoelectron spectroscopy (XPS) and electrochemistry. It's shown that the heteropoly blues anion in Ln(2) still retains the alpha-Keggin structure but with a slight distortion as heteropoly acids do, and Mn and W atoms distribute statistically in the whole molecular. At the same time, the cell toxicity and antiviral activity of these rare earth borotungstateheteropoly blues against influenza virus type A and type B in MDCK cells have been investigated using plaque reduction assay. The results elucidated that these complexes exhibit a significantly inhibitory activity and almost no cytotoxicity comparable with those obtained from virazole, and the anti-virus activity depend on the structure of these complexes.

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.