A dominant negative mutant of 2-5A-dependent RNase suppresses antiproliferative and antiviral effects of interferon

ATP-dependent transporters: emerging players at the crossroads of immunity and metabolism

Nearly 50 ATP-binding cassette (ABC) transporters are encoded by mammalian genomes. These transporters are characterized by conserved nucleotide-binding and hydrolysis (i.e., ATPase) domains, and power directional transport of diverse substrate classes - ions, small molecule metabolites, xenobiotics, hydrophobic drugs, and even polypeptides - into or out of cells or subcellular organelles. Although immunological functions of ABC transporters are only beginning to be unraveled, emerging literature suggests these proteins have under-appreciated roles in the development and function of T lymphocytes, including many of the key effector, memory and regulatory subsets that arise during responses to infection, inflammation or cancers. One transporter in particular, MDR1 (Multidrug resistance-1; encoded by the ABCB1 locus in humans), has taken center stage as a novel player in immune regulation. Although MDR1 remains widely viewed as a simple drug efflux pump in tumor cells, recent evidence suggests that this transporter fills key endogenous roles in enforcing metabolic fitness of activated CD4 and CD8 T cells. Here, we summarize current understanding of the physiological functions of ABC transporters in immune regulation, with a focus on the anti-oxidant functions of MDR1 that may shape both the magnitude and repertoires of antigen-specific effector and memory T cell compartments. While much remains to be learned about the functions of ABC transporters in immunobiology, it is already clear that they represent fertile new ground, both for the definition of novel immunometabolic pathways, and for the discovery of new drug targets that could be leveraged to optimize immune responses to vaccines and cancer immunotherapies.

Orbivirus NS4 Proteins Play Multiple Roles to Dampen Cellular Responses

Non-structural protein 4 (NS4) of insect-borne and tick-borne orbiviruses is encoded by genome segment 9, from a secondary open reading frame. Though a protein dispensable for bluetongue virus (BTV) replication, it has been shown to counter the interferon response in cells infected with BTV or African horse sickness virus. We further explored the functional role(s) of NS4 proteins of BTV and the tick-borne Great Island virus (GIV). We show that NS4 of BTV or GIV helps an E3L deletion mutant of vaccinia virus to replicate efficiently in interferon-treated cells, further confirming the role of NS4 as an interferon antagonist. Our results indicate that ectopically expressed NS4 of BTV localised with caspase 3 within the nucleus and was found in a protein complex with active caspase 3 in a pull-down assay. Previous studies have shown that pro-apoptotic caspases (including caspase 3) suppress type I interferon response by cleaving mediators involved in interferon signalling. Our data suggest that orbivirus NS4 plays a role in modulating the apoptotic process and/or regulating the interferon response in mammalian cells, thus acting as a virulence factor in pathogenesis.

A pan-cancer analysis of the oncogenic role of ATP binding cassette subfamily E member 1 (ABCE1) in human tumors: An observational study

ATP-binding-cassette subfamily E member 1 (ABCE1) has been identified as an essential component of RNA translation and cell proliferation. However, studies on its role in pan-cancer are limited. Here, we aimed to characterize ABCE1 expression and its potential biological functions in cancer. ABCE1 expression was analyzed using RNA-seq data from The Cancer Genome Atlas (TCGA), the Genotype-Tissue Expression (GTEx) database, and the Clinical Proteomic Tumor Analysis Consortium database. The prognostic value of ABCE1 was analyzed using clinical survival data from TCGA. We downloaded the immune cell infiltration score of TCGA samples from published articles and online databases and performed a correlation analysis between immune cell infiltration levels, chemokines/chemokine receptors, and ABCE1 expression. We further assessed the association between ABCE1-correlated genes and their functions in pancreatic adenocarcinoma (PAAD). In general, ABCE1 gene expression was upregulated in most tumors. There were significant strong correlations between ABCE1 expression and tumor-infiltrating cells in cancers. Furthermore, RNA transport and ribosome biogenesis were significantly related to ABCE1 expression in PAAD. Our study revealed that ABCE1 may serve as a potential prognostic and immunological pan-cancer biomarker. Moreover, ABCE1 may be used in the development of a novel target for PAAD.

Analysis of ABC Transporter Gene Expression in Atherosclerosis

ABC transporters are a large family of membrane proteins that transport chemically diverse substrates across the cell membrane. Disruption of transport mechanisms mediated by ABC transporters causes the development of various diseases, including atherosclerosis. Methods: A bioinformatic analysis of a dataset from Gene Expression Omnibus (GEO) was performed. A GEO dataset containing data on gene expression levels in samples of atherosclerotic lesions and control arteries without atherosclerotic lesions from carotid, femoral, and infrapopliteal arteries was used for analysis. To evaluate differentially expressed genes, a bioinformatic analysis was performed in comparison groups using the limma package in R (v. 4.0.2) and the GEO2R and Phantasus tools (v. 1.11.0). Results: The obtained data indicate the differential expression of many ABC transporters belonging to different subfamilies. The differential expressions of ABC transporter genes involved in lipid transport, mechanisms of multidrug resistance, and mechanisms of ion exchange are shown. Differences in the expression of transporters in tissue samples from different arteries are established. Conclusions: The expression of ABC transporter genes demonstrates differences in atherosclerotic samples and normal arteries, which may indicate the involvement of transporters in the pathogenesis of atherosclerosis.

Activation of the antiviral factor RNase L triggers translation of non-coding mRNA sequences

Ribonuclease L (RNase L) is activated as part of the innate immune response and plays an important role in the clearance of viral infections. When activated, it endonucleolytically cleaves both viral and host RNAs, leading to a global reduction in protein synthesis. However, it remains unknown how widespread RNA decay, and consequent changes in the translatome, promote the elimination of viruses. To study how this altered transcriptome is translated, we assayed the global distribution of ribosomes in RNase L activated human cells with ribosome profiling. We found that RNase L activation leads to a substantial increase in the fraction of translating ribosomes in ORFs internal to coding sequences (iORFs) and ORFs within 5' and 3' UTRs (uORFs and dORFs). Translation of these alternative ORFs was dependent on RNase L's cleavage activity, suggesting that mRNA decay fragments are translated to produce short peptides that may be important for antiviral activity.

Structural and Hydrodynamic Characterization of Dimeric Human Oligoadenylate Synthetase 2

Oligoadenylate synthetases (OASs) are a family of interferon-inducible enzymes that require double-stranded RNA (dsRNA) as a cofactor. Upon binding dsRNA, OAS undergoes a conformational change and is activated to polymerize ATP into 2'-5'-oligoadenylate chains. The OAS family consists of several isozymes, with unique domain organizations to potentially interact with dsRNA of variable length, providing diversity in viral RNA recognition. In addition, oligomerization of OAS isozymes, potentially OAS1 and OAS2, is hypothesized to be important for 2'-5'-oligoadenylate chain building. In this study, we present the solution conformation of dimeric human OAS2 using an integrated approach involving small-angle x-ray scattering, analytical ultracentrifugation, and dynamic light scattering techniques. We also demonstrate OAS2 dimerization using immunoprecipitation approaches in human cells. Whereas mutation of a key active-site aspartic acid residue prevents OAS2 activity, a C-terminal mutation previously hypothesized to disrupt OAS self-association had only a minor effect on OAS2 activity. Finally, we also present the solution structure of OAS1 monomer and dimer, comparing their hydrodynamic properties with OAS2. In summary, our work presents the first, to our knowledge, dimeric structural models of OAS2 that enhance our understanding of the oligomerization and catalytic function of OAS enzymes.

Cellular Factors Targeting HIV-1 Transcription and Viral RNA Transcripts

Restriction factors are structurally and functionally diverse cellular proteins that constitute a first line of defense against viral pathogens. Exceptions exist, but typically these proteins are upregulated by interferons (IFNs), target viral components, and are rapidly evolving due to the continuous virus–host arms race. Restriction factors may target HIV replication at essentially each step of the retroviral replication cycle, and the suppression of viral transcription and the degradation of viral RNA transcripts are emerging as major innate immune defense mechanisms. Recent data show that some antiviral factors, such as the tripartite motif-containing protein 22 (TRIM22) and the γ-IFN-inducible protein 16 (IFI16), do not target HIV-1 itself but limit the availability of the cellular transcription factor specificity protein 1 (Sp1), which is critical for effective viral gene expression. In addition, several RNA-interacting cellular factors including RNAse L, the NEDD4-binding protein 1 (N4BP1), and the zinc finger antiviral protein (ZAP) have been identified as important immune effectors against HIV-1 that may be involved in the maintenance of the latent viral reservoirs, representing the major obstacle against viral elimination and cure. Here, we review recent findings on specific cellular antiviral factors targeting HIV-1 transcription or viral RNA transcripts and discuss their potential role in viral latency.

Mutual Regulation of RNA Silencing and the IFN Response as an Antiviral Defense System in Mammalian Cells

RNA silencing is a posttranscriptional gene silencing mechanism directed by endogenous small non-coding RNAs called microRNAs (miRNAs). By contrast, the type-I interferon (IFN) response is an innate immune response induced by exogenous RNAs, such as viral RNAs. Endogenous and exogenous RNAs have typical structural features and are recognized accurately by specific RNA-binding proteins in each pathway. In mammalian cells, both RNA silencing and the IFN response are induced by double-stranded RNAs (dsRNAs) in the cytoplasm, but have long been considered two independent pathways. However, recent reports have shed light on crosstalk between the two pathways, which are mutually regulated by protein–protein interactions triggered by viral infection. This review provides brief overviews of RNA silencing and the IFN response and an outline of the molecular mechanism of their crosstalk and its biological implications. Crosstalk between RNA silencing and the IFN response may reveal a novel antiviral defense system that is regulated by miRNAs in mammalian cells.

RNase L Is Involved in Liposaccharide-Induced Lung Inflammation

RNase L mediates interferon (IFN) function during viral infection and cell proliferation. Furthermore, the role of RNase L in the regulation of gene expression, cell apoptosis, autophagy, and innate immunity has been well established in the last decade. Tissue distribution reveals that RNase L is highly expressed in the lung and other organs. However, the physiological roles of RNase L in the lung are largely unknown. In this study, we found that polysaccharide (LPS)-induced acute lung injury (ALI) was remarkably intensified in mice deficient in RNase L compared to wild type mice under the same condition. Furthermore, we found that RNase L mediated the TLR4 signaling pathway, and regulated the expression of various pro- and anti-inflammatory genes in the lung tissue and blood. Most importantly, RNase L function in macrophages during LPS stimulation may be independent of the 2-5A system. These findings demonstrate a novel role of RNase L in the immune response via an atypical molecular mechanism.

Down-regulation of ABCE1 inhibits temozolomide resistance in glioma through the PI3K/Akt/NF-κB signaling pathway

The ATP binding cassette (ABC) E1 (ABCE1), a member of the ABC family, was originally described as the RNase L inhibitor. Through forming a heterodimer with RNase L, ABCE1 participates in the negative regulation of the 2-5A/RNase L system and thus mediates a wide range of biological functions. Recent evidence has shown the new roles of ABCE1 in tumorigenesis. However, there have been no investigations on the specific effect of ABCE1 on glioma. In the present study, we examined the expression pattern and possible role of ABCE1 in glioma. Our study demonstrated that ABCE1 was up-regulated in glioma tissues and cell lines. Down-regulation of ABCE1 inhibited temozolomide (TMZ) resistance of glioma cells in vitro and in vivo In addition, we found that the PI3K/Akt/NF-κB pathway was involved in ABCE1-mediated chemoresistance of glioma cells. Taken together, our study suggested ABCE1 as a promising target for glioma chemotherapy.

Synergistic Suppression of Melanoma Growth by a Combination of Natural dsRNA and Panaxadiolsaponins

Melanoma is one of the most lethal skin malignancies in the world. Interferons (IFNs) have been also demonstrated in response to tumor cell and IFNs such as IFN-α have been used for melanoma treatment. The long chain double-stranded RNA (dsRNA) (from a variety of nonviral sources) is a potent activator of the IFN system and an inducer of cell apoptosis. Panaxadiolsaponins (PDS) is a major Panax ginseng-derived active component with known antitumor activity and immune modulation. Here, we investigated a hypothesis that the combination of PDS and total natural dsRNA (as opposed to the synthetic dsRNA) will suppress tumor growth better than the individual agents. We have evaluated the antitumor and immunostimulatory effects of the combination of natural long chain dsRNA (derived from yeast) and PDS on melanoma cell line B16 and mice xenograft model. The underlying mechanisms of growth suppression were investigated by analyzing dsRNA-activated pathways, apoptosis, and cell cycle. Natural dsRNA and PDS exert superior anticancer effects than either agent alone. Natural dsRNA and PDS combination might be a promising strategy for treating malignancies, including melanoma.

The expression and correlation between chemokine CCL7 and ABCE1 in non-small cell lung cancer

Lung cancer is a malignant disease, and has the highest incidence and mortality worldwide. Lung cancer is also a popular subject in the field of cancer research. The molecular mechanisms of lung cancer development, invasion and metastasis need to be determined to prolong survival times and improve the quality of life. Recent studies have demonstrated that ATP-binding cassette sub-family E member 1 (ABCE1) is one of the factors that contributes to the development and metastasis of lung cancer, but the specific mechanism of this phenomenon remains unclear. A polymerase chain reaction microarray was used in the present study to screen for chemokine (C-C motif) ligand 7 (CCL7) expression in cell lines that highly expressed ABCE1, and the results showed that CCL7 was highly expressed in H1299 cells (P<0.01). The expression of CCL7 and ABCE1 in lung cancer tissues obtained from 30 patients with non-small cell lung cancer (NSCLC) was higher than that in adjacent normal lung tissues (P<0.01), and a positive correlation between the expression levels of the two genes in NSCLC was observed. These findings indicate that ABCE1 is involved in the development and progression of lung cancer through the CCL7 signaling pathway.

A conserved virus-induced cytoplasmic TRAMP-like complex recruits the exosome to target viral RNA for degradation

Here, Molleston et al. find that signals from viral infections repurpose TRAMP complex components to a cytoplasmic surveillance role where they selectively engage viral RNAs for degradation to restrict a broad range of viruses.

RNA degradation is tightly regulated to selectively target aberrant RNAs, including viral RNA, but this regulation is incompletely understood. Through RNAi screening in Drosophila cells, we identified the 3′-to-5′ RNA exosome and two components of the exosome cofactor TRAMP (Trf4/5–Air1/2–Mtr4 polyadenylation) complex, dMtr4 and dZcchc7, as antiviral against a panel of RNA viruses. We extended our studies to human orthologs and found that the exosome as well as TRAMP components hMTR4 and hZCCHC7 are antiviral. While hMTR4 and hZCCHC7 are normally nuclear, infection by cytoplasmic RNA viruses induces their export, forming a cytoplasmic complex that specifically recognizes and induces degradation of viral mRNAs. Furthermore, the 3′ untranslated region (UTR) of bunyaviral mRNA is sufficient to confer virus-induced exosomal degradation. Altogether, our results reveal that signals from viral infection repurpose TRAMP components to a cytoplasmic surveillance role where they selectively engage viral RNAs for degradation to restrict a broad range of viruses.

Whole-genome sequencing in multiplex families with psychoses reveals mutations in the SHANK2 and SMARCA1 genes segregating with illness

A current focus in psychiatric genetics is detection of multiple common risk alleles through very large genome-wide association study analyses. Yet families do exist, albeit rare, that have multiple affected members who are presumed to have a similar inherited cause to their illnesses. We hypothesized that within some of these families there may be rare highly penetrant mutations that segregate with illness. In this exploratory study, the genomes of 90 individuals across nine families were sequenced. Each family included a minimum of three available relatives affected with a psychotic illness and three available unaffected relatives. Twenty-six variants were identified that are private to a family, alter protein sequence, and are transmitted to all sequenced affected individuals within the family. In one family, seven siblings with schizophrenia spectrum disorders each carry a novel private missense variant within the SHANK2 gene. This variant lies within the consensus SH3 protein-binding motif by which SHANK2 may interact with post-synaptic glutamate receptors. In another family, four affected siblings and their unaffected mother each carry a novel private missense variant in the SMARCA1 gene on the X chromosome. Both variants represent candidates that may be causal for psychotic disorders when considered in the context of their transmission pattern and known gene and disease biology.

Genome-wide identification of ATP-binding cassette (ABC) transporters and conservation of their xenobiotic transporter function in the monogonont rotifer (Brachionus koreanus)

The ATP-binding cassette (ABC) transporter family is one of the largest gene family in animals, and members of this family are known to be involved in various biological processes due to their ability to transport a wide range of substrates across membranes using ATP cleavage-derived energy. We identified 61 ABC transporters in the genome of the monogonont rotifer Brachionus koreanus, and classified these into eight distinct subfamilies (A-H) by phylogenetic analysis. ABC transporters in the rotifer B. koreanus are comprised of 11 ABCA genes, 19 ABCB genes, 14 ABCC genes, 3 ABCD genes, 1 ABCE gene, 3 ABCF genes, 8 ABCG genes, and 2 ABCH genes. Extensive gene duplication and loss events in synteny were observed in several subfamilies. In particular, massive gene duplications of P-glycoproteins (P-gps), multidrug resistance proteins (MRPs), and Bk-Abcg-like proteins were observed. The ability of these B. koreanus proteins to function as multixenobiotic resistance (MXR) ABC transporters was validated using specific fluorescence substrates/inhibitors. The ABC transporter superfamily members identified in this study will be useful in future toxicological studies, and will facilitate comparative studies of the evolution of the ABC transporter superfamily in invertebrates.

Tumor metastatic promoter ABCE1 interacts with the cytoskeleton protein actin and increases cell motility

ABCE1, a member of the ATP-binding cassette (ABC) family, is a candidate tumor metastatic promoter in lung cancer. Overexpression of ABCE1 is correlated with aggressive growth and metastasis in lung cancer cells. However, the exact mechanism remains unclear. In the present study, GST pull-down assay provided evidence of the possible interaction between ABCE1 and β-actin using GST-ABCE1 as a bait protein. Co-immunoprecipitation manifested ABCE1 formed complexes with β-actin in vivo. ABCE1 overexpression significantly increased the migration of lung cancer cells which may be attributed to the promotion of F-actin rearrangements. Taken together, these data suggest that overexpression of ABCE1 produces an obvious effect on the motility of lung cancer cells through cytoskeleton rearrangement.

The Roles of RNase-L in Antimicrobial Immunity and the Cytoskeleton-Associated Innate Response

The interferon (IFN)-regulated endoribonuclease RNase-L is involved in multiple aspects of the antimicrobial innate immune response. It is the terminal component of an RNA cleavage pathway in which dsRNA induces the production of RNase-L-activating 2-5A by the 2′-5′-oligoadenylate synthetase. The active nuclease then cleaves ssRNAs, both cellular and viral, leading to downregulation of their expression and the generation of small RNAs capable of activating retinoic acid-inducible gene-I (RIG-I)-like receptors or the nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasome. This leads to IFNβ expression and IL-1β activation respectively, in addition to broader effects on immune cell function. RNase-L is also one of a growing number of innate immune components that interact with the cell cytoskeleton. It can bind to several cytoskeletal proteins, including filamin A, an actin-binding protein that collaborates with RNase-L to maintain the cellular barrier to viral entry. This antiviral activity is independent of catalytic function, a unique mechanism for RNase-L. We also describe here the interaction of RNase-L with the E3 ubiquitin ligase and scaffolding protein, ligand of nump protein X (LNX), a regulator of tight junction proteins. In order to better understand the significance and context of these novel binding partners in the antimicrobial response, other innate immune protein interactions with the cytoskeleton are also discussed.

Functional and Structural Consequences of Damaging Single Nucleotide Polymorphisms in Human Prostate Cancer Predisposition Gene RNASEL

A commonly diagnosed cancer, prostate cancer (PrCa), is being regulated by the gene RNASEL previously known as PRCA1 codes for ribonuclease L which is an integral part of interferon regulated system that mediates antiviral and antiproliferative role of the interferons. Both somatic and germline mutations have been implicated to cause prostate cancer. With an array of available Single Nucleotide Polymorphism data on dbSNP this study is designed to sort out functional SNPs in RNASEL by implementing different authentic computational tools such as SIFT, PolyPhen, SNPs&GO, Fathmm, ConSurf, UTRScan, PDBsum, Tm-Align, I-Mutant, and Project HOPE for functional and structural assessment, solvent accessibility, molecular dynamics, and energy minimization study. Among 794 RNASEL SNP entries 124 SNPs were found nonsynonymous from which SIFT predicted 13 nsSNPs as nontolerable whereas PolyPhen-2 predicted 28. SNPs found on the 3' and 5' UTR were also assessed. By analyzing six tools having different perspectives an aggregate result was produced where nine nsSNPs were found to be most likely to exert deleterious effect. 3D models of mutated proteins were generated to determine the functional and structural effect of the mutations on ribonuclease L. The initial findings were reinforced by the results from I-Mutant and Project HOPE as these tools predicted significant structural and functional instability of the mutated proteins. Expasy-ProSit tool defined the mutations to be situated in the functional domains of the protein. Considering previous analysis this study revealed a conclusive result deducing the available SNP data on the database by identifying the most damaging three nsSNP rs151296858 (G59S), rs145415894 (A276V), and rs35896902 (R592H). As such studies involving polymorphisms of RNASEL were none to be found, the results of the current study would certainly be helpful in future prospects concerning prostate cancer in males.

Expression of Interferon Lambda 4 Is Associated with Reduced Proliferation and Increased Cell Death in Human Hepatic Cells

Interferon lambda 4 (IFN-λ4) is a novel type-III interferon that can be generated only in individuals carrying a ΔG frame-shift allele of an exonic genetic variant (rs368234815-ΔG/TT). The rs368234815-ΔG allele is strongly associated with decreased clearance of hepatitis C virus (HCV) infection. Here, we further explored the biological function of IFN-λ4 expressed in human hepatic cells—a hepatoma cell line HepG2 and fresh primary human hepatocytes (PHHs). We performed live confocal imaging, cell death and proliferation assays, mRNA expression profiling, protein detection, and antibody blocking assays using transient and inducible stable in vitro systems. Not only did we observe significant intracellular retention of IFN-λ4 but also detected secreted IFN-λ4 in the culture media of expressing cells. Secreted IFN-λ4 induced strong activation of the interferon-stimulated genes (ISGs) in IFN-λ4-expressing and surrounding cells in transwell assays. Specifically, in PHHs, secreted IFN-λ4 induced expression of the CXCL10 transcript and a corresponding pro-inflammatory chemokine, IP-10. In IFN-λ4-expressing HepG2 cells, we also observed decreased proliferation and increased cell death. All IFN-λ4-induced phenotypes—activation of ISGs, decreased proliferation, and increased cell death—could be inhibited by an anti-IFN-λ4-specific antibody. Our study offers new insights into biology of IFN-λ4 and its possible role in HCV clearance.

RNase-L control of cellular mRNAs: roles in biologic functions and mechanisms of substrate targeting

RNase-L is a mediator of type 1 interferon-induced antiviral activity that has diverse and critical cellular roles, including the regulation of cell proliferation, differentiation, senescence and apoptosis, tumorigenesis, and the control of the innate immune response. Although RNase-L was originally shown to mediate the endonucleolytic cleavage of both viral and ribosomal RNAs in response to infection, more recent evidence indicates that RNase-L also functions in the regulation of cellular mRNAs as an important mechanism by which it exerts its diverse biological functions. Despite this growing body of work, many questions remain regarding the roles of mRNAs as RNase-L substrates. This review will survey known and putative mRNA substrates of RNase-L, propose mechanisms by which it may selectively cleave these transcripts, and postulate future clinical applications.

Viral phosphodiesterases that antagonize double-stranded RNA signaling to RNase L by degrading 2-5A

The host interferon (IFN) antiviral response involves a myriad of diverse biochemical pathways that disrupt virus replication cycles at many different levels. As a result, viruses have acquired and evolved genes that antagonize the host antiviral proteins. IFNs inhibit viral infections in part through the 2',5'-oligoadenylate (2-5A) synthetase (OAS)/RNase L pathway. OAS proteins are pathogen recognition receptors that exist at different basal levels in different cell types and that are IFN inducible. Upon activation by the pathogen-associated molecular pattern viral double-stranded RNA, certain OAS proteins synthesize 2-5A from ATP. 2-5A binds to the antiviral enzyme RNase L causing its dimerization and activation. Recently, disparate RNA viruses, group 2a betacoronaviruses, and group A rotaviruses, have been shown to produce proteins with 2',5'-phosphodiesterase (PDE) activities that eliminate 2-5A thereby evading the antiviral activity of the OAS/RNase L pathway. These viral proteins are members of the eukaryotic-viral LigT-like group of 2H phosphoesterases, so named for the presence of 2 conserved catalytic histidine residues. Here, we will review the biochemistry, biology, and implications of viral and cellular 2',5'-PDEs that degrade 2-5A. In addition, we discuss alternative viral and cellular strategies for limiting the activity of OAS/RNase L.

RNase L contributes to experimentally induced type 1 diabetes onset in mice

The cause of type 1 diabetes continues to be a focus of investigation. Studies have revealed that interferon α (IFNα) in pancreatic islets after viral infection or treatment with double-stranded RNA (dsRNA), a mimic of viral infection, is associated with the onset of type 1 diabetes. However, how IFNα contributes to the onset of type 1 diabetes is obscure. In this study, we found that 2-5A-dependent RNase L (RNase L), an IFNα-inducible enzyme that functions in the antiviral and antiproliferative activities of IFN, played an important role in dsRNA-induced onset of type 1 diabetes. Using RNase L-deficient, rat insulin promoter-B7.1 transgenic mice, which are more vulnerable to harmful environmental factors such as viral infection, we demonstrated that deficiency of RNase L in mice resulted in a significant delay of diabetes onset induced by polyinosinic:polycytidylic acid (poly I:C), a type of synthetic dsRNA, and streptozotocin, a drug which can artificially induce type 1-like diabetes in experimental animals. Immunohistochemical staining results indicated that the population of infiltrated CD8(+)T cells was remarkably reduced in the islets of RNase L-deficient mice, indicating that RNase L may contribute to type 1 diabetes onset through regulating immune responses. Furthermore, RNase L was responsible for the expression of certain proinflammatory genes in the pancreas under induced conditions. Our findings provide new insights into the molecular mechanism underlying β-cell destruction and may indicate novel therapeutic strategies for treatment and prevention of the disease based on the selective regulation and inhibition of RNase L.

RNase L interacts with Filamin A to regulate actin dynamics and barrier function for viral entry

The actin cytoskeleton and its network of associated proteins constitute a physical barrier that viruses must circumvent to gain entry into cells for productive infection. The mechanisms by which the physical signals of infection are sensed by the host to activate an innate immune response are not well understood. The antiviral endoribonuclease RNase L is ubiquitously expressed in a latent form and activated upon binding 2-5A, a unique oligoadenylate produced during viral infections. We provide evidence that RNase L in its inactive form interacts with the actin-binding protein Filamin A to modulate the actin cytoskeleton and inhibit virus entry. Cells lacking either RNase L or Filamin A displayed increased virus entry which was exacerbated in cells lacking both proteins. RNase L deletion mutants that reduced Filamin A interaction displayed a compromised ability to restrict virus entry, supporting the idea of an important role for the RNase L-Filamin A complex in barrier function. Remarkably, both the wild type and a catalytically inactive RNase L mutant were competent to reduce virus entry when transfected into RNase L-deficient cells, indicating that this novel function of RNase L is independent of its enzymatic activity. Virus infection and RNase L activation disrupt its association with Filamin A and release RNase L to mediate its canonical nuclease-dependent antiviral activities. The dual functions of RNase L as a constitutive component of the actin cytoskeleton and as an induced mediator of antiviral signaling and effector functions provide insights into its mechanisms of antiviral activity and opportunities for the development of novel antiviral agents.

Cells constantly face and sample pathogens on their outer surface. The actin cytoskeleton and interacting proteins associate with the cell membrane and constitute a barrier to infection. Disruption of the actin cytoskeleton allows viruses to enter the cell and induces innate immune responses to clear infections. The molecular mechanisms that link virus-induced physical perturbations to host defense pathways remain unclear. Our studies identified a novel interaction between the antiviral endoribonuclease RNase L and the actin-binding protein Filamin A that enhances host defense by preventing viral entry into naive cells. This role for RNase L is independent of its enzymatic function. Virus infection alters actin dynamics, disrupts the RNase L-Filamin A complex, and releases RNase L to mediate antiviral signaling and effector functions via its established nucleolytic activities. These dual roles for RNase L provide an efficient strategy to protect cells from infection and rapidly respond upon pathogen exposure.

RNase L attenuates mitogen-stimulated gene expression via transcriptional and post-transcriptional mechanisms to limit the proliferative response

The cellular response to mitogens is tightly regulated via transcriptional and post-transcriptional mechanisms to rapidly induce genes that promote proliferation and efficiently attenuate their expression to prevent malignant growth. RNase L is an endoribonuclease that mediates diverse antiproliferative activities, and tristetraprolin (TTP) is a mitogen-induced RNA-binding protein that directs the decay of proliferation-stimulatory mRNAs. In light of their roles as endogenous proliferative constraints, we examined the mechanisms and functional interactions of RNase L and TTP to attenuate a mitogenic response. Mitogen stimulation of RNase L-deficient cells significantly increased TTP transcription and the induction of other mitogen-induced mRNAs. This regulation corresponded with elevated expression of serum-response factor (SRF), a master regulator of mitogen-induced transcription. RNase L destabilized the SRF transcript and formed a complex with SRF mRNA in cells providing a mechanism by which RNase L down-regulates SRF-induced genes. TTP and RNase L proteins interacted in cells suggesting that RNase L is directed to cleave TTP-bound RNAs as a mechanism of substrate specificity. Consistent with their concerted function in RNA turnover, the absence of either RNase L or TTP stabilized SRF mRNA, and a subset of established TTP targets was also regulated by RNase L. RNase L deficiency enhanced mitogen-induced proliferation demonstrating its functional role in limiting the mitogenic response. Our findings support a model of feedback regulation in which RNase L and TTP target SRF mRNA and SRF-induced transcripts. Accordingly, meta-analysis revealed an enrichment of RNase L and TTP targets among SRF-regulated genes suggesting that the RNase L/TTP axis represents a viable target to inhibit SRF-driven proliferation in neoplastic diseases.

Curcumin, a natural antioxidant, acts as a noncompetitive inhibitor of human RNase L in presence of its cofactor 2-5A in vitro

Ribonuclease L (RNase L) is an antiviral endoribonuclease of the innate immune system, which is induced and activated by viral infections, interferons, and double stranded RNA (dsRNA) in mammalian cells. Although, RNase L is generally protective against viral infections, abnormal RNase L expression and activity have been associated with a number of diseases. Here, we show that curcumin, a natural plant-derived anti-inflammatory active principle, inhibits RNase L activity; hence, it may be exploited for therapeutic interventions in case of pathological situations associated with excess activation of RNase L.

The role of miR-29 family members in malignant hematopoiesis

AIMS

MicroRNAs of the miR-29 family members were one of the first microRNAs identified as possible therapeutic agents in malignant hematopoiesis. The aim of our review is to summarize the current state of knowledge on miR-29 family members.

METHODS

We performed literature searches involving miR-29 family members and their relationship to individual hematological malignancies, namely acute myeloid leukemia (AML), chronic lymphoblastic leukemia (CLL) and chronic myeloid leukemia (CML). We also searched for subgroups of hematological malignancies, e.g. multiple myeloma, that are regarded as members of the acute or chronic types of leukemias.

RESULTS

A number of genes appear to be regulated by miR-29 family members in various physiological and pathological situations. In our view regulation of Tcl-1, Mcl-1 and DNA methyltransferases is relevant in case of hematological malignancies, hence these are the focus of this review. miR-29 family members also function during normal T-cell and B-cell development.

CONCLUSION

MiR-29 family members appear to govern some general features in commonly heterogenous hematological malignancies and therefore form a potential target for treatment.

Can't RIDD off viruses

The mammalian genome has evolved to encode a battery of mechanisms, to mitigate a progression in the life cycle of an invasive viral pathogen. Although apparently disadvantaged by their dependence on the host biosynthetic processes, an immensely faster rate of evolution provides viruses with an edge in this conflict. In this review, I have discussed the potential anti-virus activity of inositol-requiring enzyme 1 (IRE1), a well characterized effector of the cellular homeostatic response to an overloading of the endoplasmic reticulum (ER) protein-folding capacity. IRE1, an ER-membrane-resident ribonuclease (RNase), upon activation catalyses regulated cleavage of select protein-coding and non-coding host RNAs, using an RNase domain which is homologous to that of the known anti-viral effector RNaseL. The latter operates as part of the Oligoadenylate synthetase OAS/RNaseL system of anti-viral defense mechanism. Protein-coding RNA substrates are differentially treated by the IRE1 RNase to either augment, through cytoplasmic splicing of an intron in the Xbp1 transcript, or suppress gene expression. This referred suppression of gene expression is mediated through degradative cleavage of a select cohort of cellular RNA transcripts, initiating the regulated IRE1-dependent decay (RIDD) pathway. The review first discusses the anti-viral mechanism of the OAS/RNaseL system and evasion tactics employed by different viruses. This is followed by a review of the RIDD pathway and its potential effect on the stability of viral RNAs. I conclude with a comparison of the enzymatic activity of the two RNases followed by deliberations on the physiological consequences of their activation.

RNASEL and MIR146A SNP-SNP interaction as a susceptibility factor for non-melanoma skin cancer

Immunity and inflammatory pathways are important in the genesis of non-melanoma skin cancers (NMSC). Functional genetic variation in immune modulators has the potential to affect disease etiology. We investigated associations between common variants in two key regulators, MIR146A and RNASEL, and their relation to NMSCs. Using a large population-based case-control study of basal cell (BCC) and squamous cell carcinoma (SCC), we investigated the impact of MIR146A SNP rs2910164 on cancer risk, and interaction with a SNP in one of its putative targets (RNASEL, rs486907). To examine associations between genotype and BCC and SCC, occurrence odds ratios (OR) and 95% confidence intervals (95%CI) were calculated using unconditional logistic regression, accounting for multiple confounding factors. We did not observe an overall change in the odds ratios for SCC or BCC among individuals carrying either of the RNASEL or MIR146A variants compared with those who were wild type at these loci. However, there was a sex-specific association between BCC and MIR146A in women (ORGC = 0.73, [95%CI = 0.52-1.03]; ORCC = 0.29, [95% CI = 0.14-0.61], p-trend<0.001), and a reduction in risk, albeit not statistically significant, associated with RNASEL and SCC in men (ORAG = 0.88, [95%CI = 0.65-1.19]; ORAA = 0.68, [95%CI = 0.43-1.08], p-trend = 0.10). Most striking was the strong interaction between the two genes. Among individuals carrying variant alleles of both rs2910164 and rs486907, we observed inverse relationships with SCC (ORSCC = 0.56, [95%CI = 0.38-0.81], p-interaction = 0.012) and BCC (ORBCC = 0.57, [95%CI = 0.40-0.80], p-interaction = 0.005). Our results suggest that genetic variation in immune and inflammatory regulators may influence susceptibility to NMSC, and novel SNP-SNP interaction for a microRNA and its target. These data suggest that RNASEL, an enzyme involved in RNA turnover, is controlled by miR-146a and may be important in NMSC etiology.

Regulation of human RNase-L by the miR-29 family reveals a novel oncogenic role in chronic myelogenous leukemia

The endoribonuclease RNase-L is the terminal component of an interferon-regulated RNA decay pathway known as the 2'-5'-oligoadenylate (2-5A) system, whose established functions include antimicrobial and tumor suppressive activities. RNase-L activity requires binding of the small molecule 2-5A, leading to RNase-L dimerization and cleavage of single-stranded RNA. RNase-L expression is controlled post-transcriptionally by its 3'-untranslated region (3' UTR), which exerts a strong negative effect on RNase-L levels. MicroRNAs (miRNAs) are a class of small noncoding RNAs that repress expression of target genes by binding to regions of complementarity often in the 3' UTR. The miR-29 family acts as a tumor suppressor in several cancers, including acute and chronic myelogenous leukemia (CML), and has many oncogenic targets. We report that the miR-29 family represses RNase-L protein expression across several cell types. Using a luciferase reporter, we showed that miR-29 acts via 4 target sites within the RNASEL 3' UTR. Mutation of all sites is required for abrogation of miR-29 repression. In light of the reported tumor suppressive role of miR-29 in K562 CML cells and miR-29 repression of RNase-L in these cells, we generated K562 cells with stable RNase-L knockdown and demonstrated that loss of RNase-L inhibits proliferation in vitro as well as tumor growth in a xenograft model. Our findings identify a previously unknown miRNA regulator of RNase-L expression and support a novel oncogenic role for RNase-L in CML and potentially other hematopoietic malignancies.

The association of elevated 2',5'-oligoadenylate-dependent RNase L with lung cancer correlated with deficient enzymatic activity and decreased capacity of RNase L dimerization

RNase L mediates critical cellular functions including antiviral, proapoptotic, antiproliferative and tumor suppressive activities. In this study, the expression and function of RNase L in lung cancer cells were examined. Interestingly we have found that the expression of RNase L in lung cancer cells was 3- and 9-fold higher in its mRNA and protein levels, but a significant decrease of its enzymatic activity when compared to that in corresponding normal lung cells. Further investigation revealed that 2-5A-induced dimerization of the RNase L protein, a necessary prerequisite for activation of RNase L, was inhibited, as a result of that RLI, a specific inhibitor of RNase L, was remarkably up-regulated in the cancer cells. Our findings provide new insight into how cancer cells escape normal growth-regulating mechanisms to form a tumor and the information may be useful for the design of novel strategies for treating lung cancer through regulating RNase L activity.

Expression, purification and characterization of the interferon-inducible, antiviral and tumour-suppressor protein, human RNase L

The interferon (IFN)-inducible, 2',5'-oligoadenylate (2-5A)-dependent ribonuclease L (RNase L) plays key role in antiviral defense of mammalian cells. Induction by IFN and activation by double-stranded RNA lead to 2-5A cofactor synthesis, which activates RNase L by causing its dimerization. Active RNase L degrades single-stranded viral as well as cellular RNAs causing apoptosis of virus-infected cells. Earlier, we had reported that expression of recombinant human RNase L caused RNA-degradation and cell-growth inhibition in E. coli without the need for exogenous 2-5A. Expression of human RNase L in E. coli usually leads to problems of leaky expression, low yield and degradation of the recombinant protein, which demands number of chromatographic steps for its subsequent purification thereby, compromising its biochemical activity. Here, we report a convenient protocol for expression of full-length, soluble and biochemically active recombinant human RNase L as GST-RNase L fusion protein from E. coli utilizing a single-step affinity purification with an appreciable yield of the highly purified protein. Recombinant RNase L was characterized by SDS-PAGE, immunoblotting and MALDI-TOF analysis. A semi-quantitative agarose-gel-based ribonuclease assay was developed for measuring its 2-5A-dependent RNase L activity against cellular large rRNAs as substrates. The optimized expression conditions minimized degradation of the protein, making it a convenient method for purification of RNase L, which can be utilized to study effects of various agents on the RNase L activity and its protein-protein interactions.

Regulation of p21/CIP1/WAF-1 mediated cell-cycle arrest by RNase L and tristetraprolin, and involvement of AU-rich elements

The p21^Cip1/WAF1 plays an important role in cell-cycle arrest. Here, we find that RNase L regulates p21-mediated G₁ growth arrest in AU-rich elements-dependent manner. We found a significant loss of p21 mRNA expression in RNASEL^−/− MEFs and that the overexpression of RNase L in HeLa cells induces p21 mRNA expression. The p21 mRNA half-life significantly changes as a result of RNase L modulation, indicating a post-transcriptional effect. Indeed, we found that RNase L promotes tristetraprolin (TTP/ZFP36) mRNA decay. This activity was not seen with dimerization- and nuclease-deficient RNase L mutants. Deficiency in TTP led to increases in p21 mRNA and protein. With induced ablation of RNase L, TTP mRNA and protein expressions were higher, while p21 expression became reduced. We further establish that TTP, but not C124R TTP mutant, binds to, and accelerates the decay of p21 mRNA. The p21 mRNA half-life was prolonged in TTP^−/− MEFs. The TTP regulation of p21 mRNA decay required functional AU-rich elements. Thus, we demonstrate a novel mechanism of regulating G₁ growth arrest by an RNase L-TTP-p21 axis.

[RNASEL study of genetics of prostate cancer and its relation to clinical staging]

OBJECTIVES

This study has aimed to find a possible genetic relationship between sporadic prostate cancers. An attempt is made to establish population subgroups in patients based on the genotype found and the aggressiveness of the cancer.

MATERIAL AND METHODS

A total of 231 patients with sporadic prostate cancer and 68 controls were selected. The subjects were selected by an urologist using clinical parameters such as PSA level and Gleason score. Both groups (patients and controls) were genotyped in RNASEL gene by sequencing the exons 1 and 3.

RESULTS

Statistically significant differences were found between controls and patients in some of the genotyped regions of the RNASEL gene (I97L, D541E and R462Q).

CONCLUSIONS

Thanks to the genetic profile in some regions of the genoma, such as the RNASEL gene, together with the combination of the clinical and environmental parameters, we can suggest a care and more personalized follow-up of each patient.

The tale of xenotropic murine leukemia virus-related virus

In 2006, a new retrovirus was isolated from prostate cancer patient tissue. Named xenotropic murine leukemia virus-related virus (XMRV), this was potentially the third class of retrovirus to be pathogenic in humans. XMRV made a more dramatic impact on the wider scientific community, and indeed the media, in 2009 when it was reported to be present in a remarkably high proportion of patients with chronic fatigue syndrome as well as a significant, albeit smaller, proportion of healthy controls. The apparent strong link to disease and the fear of a previously unknown retrovirus circulating in the general population lead to a surge in XMRV research. Subsequent studies failed to find an association of XMRV with disease and, in most cases, failed to find the virus in human samples. In 2011, the case against XMRV and human disease strengthened, ending with several decisive publications revealing the origin of the virus and demonstrating contamination of samples. In this review, we outline the passage of research on XMRV and its potential association with disease from its isolation to the present day, where we find ourselves at the end of a turbulent story.

Positive selection on the gene RNASEL: correlation between patterns of evolution and function

RNASEL is a 2-5A-dependent endoribonuclease that is a component of the interferon-induced 2-5A system, which plays a crucial role in the antiviral and apoptotic activities of interferons. In humans, many polymorphic sites within the RNASEL gene have been associated with an increased risk of developing prostate cancer. Here, we obtained coding sequences for the RNASEL gene from 11 primates and found evidence that positive selection has operated on the C-terminal endoribonuclease domain and the N-terminal ankyrin repeats domain of the protein, domains that directly interact with virus (i.e., ankyrin repeats are responsible for receiving environmental signals, and the endoribonuclease catalyses the destruction of the pathogenic viral RNA). To extend this finding, we studied variation within this gene in modern human populations by resequencing alleles from 144 individuals representing four separate populations. Interestingly, the frequency of the 541D allele shows a negative association with the incidence rate of prostate cancer in worldwide populations, and haplotypes containing the 541D polymorphisms demonstrate signatures of positive selection. RNASEL variants having the 541D haplotype likely have a greater ability to defend against infections by viruses, thus the loss of this activity may be associated with the development of prostate cancer. We provide evidence that positive selection has operated on the RNASEL gene, and its evolution is correlated with its function in pathogen defense and cancer association.

Role of the ABCE1 gene in human lung adenocarcinoma

ATP-binding cassette transporter E1 (ABCE1), also known as RLI (RNase L inhibitor), is a new type of endoribonuclease inhibitor, which can specifically bind to RNase L and abolish its effect. ABCE1 binds to eIF2α and eIF5 to form a pre-translation initiation complex, suggesting its crucial role in cell growth, development and certain pathological processes. To probe the role of ABCE1 in the development and progress of human lung adenocarcinoma, we first detected the changes of its mRNA and protein expression in tissues, and found a high expression level of ABCE1 in human lung adenocarcinoma tissues and metastatic lymph nodes, which was also correlated with clinical stages. Moreover, human lung adenocarcinoma A549 cells were infected with lentiviral vectors containing ABCE1-specific shRNA, and resulted in significant inhibition of cell growth. Using microarray assay, a number of differentially expressed genes were found after ABCE1 suppression. Our results demonstrated the potential role of ABCE1 in human lung adenocarcinoma, which may provide some molecular basis for the mechanisms of development and progress of human lung adenocarcinoma, and help to find new pharmacological targets.

Antitumor activity of type III interferon alone or in combination with type I interferon against human non-small cell lung cancer

The antitumor activities of type III interferon (IFN) (interleukin [IL]-28 and IL-29) and the combination of type III IFN and type I IFN (IFN-α) were evaluated using human non-small cell lung cancer (NSCLC). The expression of type III and type I receptor complexes was detected in NSCLC lines. IL-29 significantly inhibited the in vitro growth of a wide range of NSCLC lines in a dose-dependent fashion. To a lesser degree, IL-28A also displayed growth inhibitory activity. Antitumor activity of type III IFN is associated with cell cycle arrest at the G1 phase and apoptosis. IL-29 upregulated cyclin-dependent kinase inhibitor p21Waf1/Cip1 in cells sensitive, but not insensitive, to antiproliferative activity, and knockdown of p21 with small interfering RNA largely attenuated the antiproliferative effect. Intratumoral and systemic administration of IL-29 inhibited OBA-LK1 and LK-1, but not A549, tumor growth in severe combined immunodeficiency mice. Immunohistochemical analyses demonstrated marked upregulated p21 and downregulated Ki-67 expression in tumors treated with IL-29. The interferon combination of IL-29 and IFN-α displayed a more effective antiproliferative effect and a more intense p21 expression than each reagent alone in vitro. Furthermore, interferon combination therapy suppressed in vivo NSCLC growth more effectively than interferon monotherapy. These findings demonstrate that type III IFN can mediate direct antitumor activities via increased p21 expression and induction of apoptosis and cooperate with type I IFN to elicit more efficient direct antitumor activities, and suggest the possibility that type III IFN might improve the efficacy and reduce the side-effects of type I IFN cancer therapy.

Interferon-tau: current applications and potential in antiviral therapy

Interferon-tau (IFN-tau) was initially identified as an ovine pregnancy protein. Produced by the trophoblast, it is important in preventing degradation of the corpus luteum and has been used as an early marker for ovine pregnancy. As a member of the family of type I interferons, IFN-tau has demonstrated promising antiviral activity against human viral infections in vitro. Additionally, it displays high species cross-reactivity despite its absence in humans. To date, IFN-tau has shown efficacy in reducing replication of human immunodeficiency virus, feline immunodeficiency virus, and human papillomavirus. While IFN-tau shares similar antiviral activity to IFN-alpha, the current interferon of choice for treatment of viral infections, it lacks the associated toxicity. This may make IFN-tau an attractive alternative to IFN-alpha for the treatment of viral infections.

RNASEL -1385G/A polymorphism and cancer risk: a meta-analysis based on 21 case-control studies

Polymorphisms in the endoribonuclease L (RNASEL) gene have been hypothesized to increase the incidence of cancer. The common sequence variation in RNASEL, -1385G/A (rs486907) has been involved in several types of cancer risk. However, results of the related published studies remained conflicting rather than conclusive. To clarify the role of RNASEL -1385G/A genotype in global cancer, we performed a meta-analysis of all the available published studies involving 8,732 cancer patients and 8,748 control subjects. The overall results indicated that there was no major influence of the variant on cancer risk. However, stratified analysis by ethnicity showed that the RNASEL -1385G/A polymorphism has an increased cancer risk in African descendents in the homozygote comparison (OR = 2.59, 95% CI = 1.27-5.27), although no association was found in the analysis stratified by cancer type (OR = 1.12, 95% CI = 0.94-1.35). This meta-analysis suggested that the RNASEL -1385G/A polymorphism is associated with cancer risk in African descendents. To draw more comprehensive conclusions, further prospective studies with larger numbers of participants worldwide are still required to examine associations between RNASEL -1385G/A polymorphism and cancer risk.

New insights into the role of RNase L in innate immunity

The interferon (IFN)-inducible 2'-5'-oligoadenylate synthetase (OAS)/RNase L pathway blocks infections by some types of viruses through cleavage of viral and cellular single-stranded RNA. Viruses induce type I IFNs that initiate signaling to the OAS genes. OAS proteins are pathogen recognition receptors for the viral pathogen-associated molecular pattern, double-stranded RNA. Double-stranded RNA activates OAS to produce p(x)5'A(2'p5'A)(n); x = 1-3; n > 2 (2-5A) from ATP. Upon binding 2-5A, RNase L is converted from an inactive monomer to a potently active dimeric endoribonuclease for single-stranded RNA. RNase L contains, from N- to C-terminus, a series of 9 ankyrin repeats, a linker, several protein kinase-like motifs, and a ribonuclease domain homologous to Ire1 (involved in the unfolded protein response). In the past few years, it has become increasingly apparent that RNase L and OAS contribute to innate immunity in many ways. For example, small RNA cleavage products produced by RNase L during viral infections can signal to the retinoic acid-inducible-I like receptors to amplify and perpetuate signaling to the IFN-β gene. In addition, RNase L is now implicated in protecting the central nervous system against viral-induced demyelination. A role in tumor suppression was inferred by mapping of the RNase L gene to the hereditary prostate cancer 1 (HPC1) gene, which in turn led to discovery of the xenotropic murine leukemia-related virus. A broader role in innate immunity is suggested by involvement of RNase L in cytokine induction and endosomal pathways that suppress bacterial infections. These newly described findings about RNase L could eventually provide the basis for developing broad-spectrum antimicrobial drugs.

RNase L releases a small RNA from HCV RNA that refolds into a potent PAMP

Triggering and propagating an intracellular innate immune response is essential for control of viral infections. RNase L is a host endoribonuclease and a pivotal component of innate immunity that cleaves viral and cellular RNA within single-stranded loops releasing small structured RNAs with 5'-hydroxyl (5'-OH) and 3'-monophosphoryl (3'-p) groups. In 2007, we reported that RNase L cleaves self RNA to produce small RNAs that function as pathogen-associated molecular patterns (PAMPs). However, the precise sequence and structure of PAMP RNAs produced by RNase L is unknown. Here we used hepatitis C virus RNA as substrate to characterize RNase L mediated cleavage products [named suppressor of virus RNA (svRNA)] for their ability to activate RIG-I like receptors (RLR). The NS5B region of HCV RNA was cleaved by RNase L to release an svRNA that bound to RIG-I, displacing its repressor domain and stimulating its ATPase activity while signaling to the IFN-β gene in intact cells. All three of these RIG-I functions were dependent on the presence in svRNA of the 3'-p. Furthermore, svRNA suppressed HCV replication in vitro through a mechanism involving IFN production and triggered a RIG-I-dependent hepatic innate immune response in mice. RNase L and OAS (required for its activation) were both expressed in hepatocytes from HCV-infected patients, raising the possibility that the OAS/RNase L pathway might suppress HCV replication in vivo. It is proposed that RNase L mediated cleavage of HCV RNA generates svRNA that activates RIG-I, thus propagating innate immune signaling to the IFN-β gene.

Contribution of HPC1 (RNASEL) and HPCX variants to prostate cancer in a founder population

BACKGROUND

Prostate cancer is a genetically complex disease with locus and disease heterogeneity. The RNASEL gene and HPCX locus have been implicated in hereditary prostate cancer; however, their contributions to sporadic forms of this malignancy remain uncertain.

METHODS

Associations of prostate cancer with two variants in the RNASEL gene (a founder mutation, 471delAAAG, and a non-synonymous SNP, rs486907), and with five microsatellite markers in the HPCX locus, were examined in 979 cases and 1,251 controls of Ashkenazi Jewish descent. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression models.

RESULTS

There was an inverse association between RNASEL rs486907 and prostate cancer in younger men (<65 years) and those with a first-degree relative with prostate cancer; men with AA genotype had ORs of 0.64 and 0.47 (both P < 0.05), respectively, in comparison to men with GG genotype. Within the HPCX region, there were positive associations for allele 135 of bG82i1.1 marker (OR = 1.77, P = 0.01) and allele 188 of DXS1205 (OR = 1.65, P = 0.02). In addition, allele 248 of marker D33 was inversely associated (OR = 0.65, P = 0.05) with Gleason score ≥7 tumors.

CONCLUSIONS

Results suggest that variants in RNASEL contribute to susceptibility to early onset and familial forms of prostate cancer, whereas HPCX variants are associated with prostate cancer risk and tumor aggressiveness. The observation that a mutation predicted to completely inactivate RNASEL protein was not associated with prostate cancer, but that a missense variant was associated, suggests that the effect is due to either partial inactivation of the protein, and/or acquisition of a new protein activity.

Protein kinase R is responsible for the phosphorylation of eIF2alpha in rotavirus infection

The eukaryotic initiation translation factor 2 (eIF2) represents a key point in the regulation of protein synthesis. This factor delivers the initiator Met-tRNA to the ribosome, a process that is conserved in all eukaryotic cells. Many types of stress reduce global translation by triggering the phosphorylation of the α subunit of eIF2, which reduces the formation of the preinitiation translation complexes. Early during rotavirus infection, eIF2α becomes phosphorylated, and even under these conditions viral protein synthesis is not affected, while most of the cell protein synthesis is blocked. Here, we found that the kinase responsible for the phosphorylation of eIF2α in rotavirus-infected cells is PKR, since in mouse embryonic fibroblasts deficient in the kinase domain of PKR, or in MA104 cells where the expression of PKR was knocked down by RNA interference, eIF2α was not phosphorylated upon rotavirus infection. The viral component responsible for the activation of PKR seems to be viral double-stranded RNA, which is found in the cytoplasm of infected cells, outside viroplasms. Taken together, these results suggest that rotaviruses induce the PKR branch of the interferon system and have evolved a mechanism to translate its proteins, surpassing the block imposed by eIF2α phosphorylation.

Arg462Gln and Asp541Glu polymorphisms in ribonuclease L and prostate cancer risk: a meta-analysis

Objective

The association between ribonuclease L (RNASEL) gene polymorphisms and prostate cancer risk has been widely reported, but the results of these studies remained controversial and underpowered. We performed a meta-analysis of 28 studies to evaluate the association between Arg462Gln and Asp541Glu polymorphisms in the RNASEL gene and prostate cancer risk.

Methods

Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated to assess the association between RNASEL polymorphisms and prostate cancer risk.

Results

A significantly increased prostate cancer risk was found for the Arg462Gln polymorphism in Africans (Gln/Gln vs Arg/Arg: OR = 2.50, 95%CI = 1.28-4.87; Gln/Gln vs Gln/Arg + Arg/Arg: OR = 2.54, 95%CI = 1.30-4.95), but not in Europeans and Asians. Additionally, the Asp541Glu polymorphism was associated with increased total prostate cancer risk (Glu-allele vs Asp-allele: OR = 1.04, 95%CI = 1.01-1.07; Glu/Glu vs Asp/Asp: OR = 1.22, 95%CI = 1.03-1.46; Glu/Glu vs Glu/Asp + Asp/Asp: OR = 1.09, 95%CI = 1.02-1.16). In the stratified analysis for the Asp541Glu polymorphism, there was a significantly increased prostate cancer risk in Africans and Europeans, and in hospital-based prostate cancer cases.

Conclusion

The meta-analysis results showed evidence that RNASEL Arg462Gln and Asp541Glu polymorphisms are associated with prostate cancer risk and could be low-penetrance prostate cancer susceptibility biomarkers.

Single and multivariate associations of MSR1, ELAC2, and RNASEL with prostate cancer in an ethnic diverse cohort of men

Three genes, namely, ELAC2 (HPC2 locus) on chromosome 17p11, 2'-5'-oligoisoadenlyate-synthetase-dependent ribonuclease L (RNASEL, HPC1 locus), and macrophage scavenger receptor 1 (MSR1) within a region of linkage on chromosome 8p, have been identified as hereditary tumor suppressor genes in prostate cancer. We genotyped 41 tagged single nucleotide polymorphisms (SNPs) covering the three genes in a case-control cohort, which included 1,436 Caucasians, 648 Hispanics, and 270 African Americans. SNPs within MSR1, ELAC2, and RNASEL were significantly associated with risk of prostate cancer albeit with differences among the three ethnic groups (P = 0.043-1.0 x 10(-5)). In Caucasians, variants within MSR1 and ELAC2 are most likely to confer prostate cancer risk, and rs11545302 (ELAC2) showed a main effect independent of other significant SNPs (P = 2.03 x 10(-5)). A major haplotype G-A-C-G-C-G combining five SNPs within MSR1 was further shown to increase prostate cancer risk significantly in this study group. Variants in RNASEL had the strongest effects on prostate cancer risk estimates in Hispanics and also showed an interaction effect of family history. In African Americans, single SNPs within MSR1 were significantly associated with prostate cancer risk. A major risk haplotype C-G-G-C-G of five SNPs within ELAC2 was found in this group. Combining high-risk genotypes of MSR1 and ELAC2 in Caucasians and of RNASEL and MSR1 in Hispanics showed synergistic effects and suggest that an interaction between both genes in each ethnicity is likely to confer prostate cancer risk. Our findings corroborate the involvement of ELAC2, MSR1, and RNASEL in the etiology of prostate cancer even in individuals without a family history.

EBNA1 regulates cellular gene expression by binding cellular promoters

Epstein-Barr virus (EBV) is associated with several types of lymphomas and epithelial tumors including Burkitt's lymphoma (BL), HIV-associated lymphoma, posttransplant lymphoproliferative disorder, and nasopharyngeal carcinoma. EBV nuclear antigen 1 (EBNA1) is expressed in all EBV associated tumors and is required for latency and transformation. EBNA1 initiates latent viral replication in B cells, maintains the viral genome copy number, and regulates transcription of other EBV-encoded latent genes. These activities are mediated through the ability of EBNA1 to bind viral-DNA. To further elucidate the role of EBNA1 in the host cell, we have examined the effect of EBNA1 on cellular gene expression by microarray analysis using the B cell BJAB and the epithelial 293 cell lines transfected with EBNA1. Analysis of the data revealed distinct profiles of cellular gene changes in BJAB and 293 cell lines. Subsequently, chromatin immune-precipitation revealed a direct binding of EBNA1 to cellular promoters. We have correlated EBNA1 bound promoters with changes in gene expression. Sequence analysis of the 100 promoters most enriched revealed a DNA motif that differs from the EBNA1 binding site in the EBV genome.

The viral RNA recognition sensor RIG-I is degraded during encephalomyocarditis virus (EMCV) infection

RNA helicase-like receptors MDA-5 but not RIG-I has been shown to be essential for triggering innate immune responses against picornaviruses. However, virus-host co-evolution has selected for viruses capable of replicating despite host cells antiviral defences. In this report, we demonstrate that RIG-I is degraded during encephalomyocarditis virus (EMCV) infection. This effect is mediated by both the viral-encoded 3C protease and caspase proteinase. In addition, we show that RIG-I overexpression confers IFN-beta promoter activation during EMCV infection, in MDA-5 knockout (MDA-5(-/-)) mouse embryo fibroblasts. This induction is followed by a strong inhibition reflecting the ability of EMCV to disrupt RIG-I signalling. Taken together, our data strongly suggest that during evolution RIG-I has been involved for triggering innate immune response to picornavirus infections.