Anticellular and antiviral effects of pppA(2'p5'A)n

ABCE1 Regulates RNase L-Induced Autophagy during Viral Infections

Host response to a viral infection includes the production of type I interferon (IFN) and the induction of interferon-stimulated genes that have broad antiviral effects. One of the key antiviral effectors is the IFN-inducible oligoadenylate synthetase/ribonuclease L (OAS/RNase L) pathway, which is activated by double-stranded RNA to synthesize unique oligoadenylates, 2-5A, to activate RNase L. RNase L exerts an antiviral effect by cleaving diverse RNA substrates, limiting viral replication; many viruses have evolved mechanisms to counteract the OAS/RNase L pathway. Here, we show that the ATP-binding cassette E1 (ABCE1) transporter, identified as an inhibitor of RNase L, regulates RNase L activity and RNase L-induced autophagy during viral infections. ABCE1 knockdown cells show increased RNase L activity when activated by 2-5A. Compared to parental cells, the autophagy-inducing activity of RNase L in ABCE1-depleted cells is enhanced with early onset. RNase L activation in ABCE1-depleted cells inhibits cellular proliferation and sensitizes cells to apoptosis. Increased activity of caspase-3 causes premature cleavage of autophagy protein, Beclin-1, promoting a switch from autophagy to apoptosis. ABCE1 regulates autophagy during EMCV infection, and enhanced autophagy in ABCE1 knockdown cells promotes EMCV replication. We identify ABCE1 as a host protein that inhibits the OAS/RNase L pathway by regulating RNase L activity, potentially affecting antiviral effects.

Expression of the OAS Gene Family Is Highly Modulated in Subjects Affected by Juvenile Dermatomyositis, Resembling an Immune Response to a dsRNA Virus Infection

Background: Juvenile dermatomyositis (JDM) is a systemic, autoimmune, interferon (IFN)-mediated inflammatory muscle disorder that affects children younger than 18 years of age. JDM primarily affects the skin and the skeletal muscles. Interestingly, the role of viral infections has been hypothesized. Mammalian 2′-5′-oligoadenylate synthetase (OAS) genes have been thoroughly characterized as components of the IFN-induced antiviral system, and they are connected to several innate immune-activated diseases. The main purpose of the paper is to define the potential interrelationship between the OAS gene family network and the molecular events that characterize JDM along with double-stranded RNA (dsRNA) molecular pathways. Methods: We analyzed three microarray datasets obtained from the NCBI in order to verify the expression levels of the OAS gene family network in muscle biopsies (MBx) of JDM patients compared to healthy controls. Furthermore, From GSE51392, we decided to select significant gene expression profiles of primary nasal and bronchial epithelial cells isolated from healthy subjects and treated with polyinosinic-polycytidylic acid (poly(I:C)), a synthetic analog of double-stranded RNA (dsRNA), a molecular pattern associated with viral infection. Results: The analysis showed that all OAS genes were modulated in JDM muscle biopsies. Furthermore, 99% of OASs gene family networks were significantly upregulated. Of importance, 39.9% of modulated genes in JDM overlapped with those of primary epithelial cells treated with poly(I:C). Moreover, the microarray analysis showed that the double-stranded dsRNA virus gene network was highly expressed. In addition, we showed that the innate/adaptive immunity markers were significantly expressed in JDM muscles biopsies. and that their levels were positively correlated to OAS gene family expression. Conclusion: OAS gene expression is extremely modulated in JDM as well as in the dsRNA viral gene network. These data lead us to speculate on the potential involvement of a viral infection as a trigger moment for this systemic autoimmune disease. Further in vitro and translational studies are needed to verify this hypothesis in order to strategically plan treatment interventions.

Oligoadenylate synthase-like (OASL) proteins: dual functions and associations with diseases

The study of antiviral pathways to reveal methods for the effective response and clearance of virus is closely related to understanding interferon (IFN) signaling and its downstream target genes, IFN-stimulated genes. One of the key antiviral factors induced by IFNs, 2'-5' oligoadenylate synthase (OAS), is a well-known molecule that regulates the early phase of viral infection by degrading viral RNA in combination with RNase L, resulting in the inhibition of viral replication. In this review, we describe OAS family proteins from a different point of view from that of previous reviews. We discuss not only RNase L-dependent (canonical) and -independent (noncanonical) pathways but also the possibility of the OAS family members as biomarkers for various diseases and clues to non-immunological functions based on recent studies. In particular, we focus on OASL, a member of the OAS family that is relatively less well understood than the other members. We will explain its anti- and pro-viral dual roles as well as the diseases related to single-nucleotide polymorphisms in the corresponding gene.

Hepatitis C virus: standard-of-care treatment

Hepatitis C virus (HCV) infection is curable by therapy. The antiviral treatment of chronic hepatitis C has been based for decades on the use of interferon (IFN)-α, combined with ribavirin. More recently, new therapeutic approaches that target essential components of the HCV life cycle have been developed, including direct-acting antiviral (DAA) and host-targeted agents (HTA). A new standard-of-care treatment has been approved in 2011 for patients infected with HCV genotype 1, based on a triple combination of pegylated IFN-α, ribavirin, and either telaprevir or boceprevir, two inhibitors of the HCV protease. New triple and quadruple combination therapies including pegylated IFN-α, ribavirin, and one or two DAAs/HTAs, respectively, are currently being evaluated in Phase II and III clinical trials. In addition, various options for all-oral, IFN-free regimens are currently being evaluated. This chapter describes the characteristics of the different drugs used in the treatment of chronic hepatitis C and those currently in development and provides an overview of the current and future standard-of-care treatments of chronic hepatitis C.

Digital gene expression for non-model organisms

Next-generation sequencing technologies offer new approaches for global measurements of gene expression but are mostly limited to organisms for which a high-quality assembled reference genome sequence is available. We present a method for gene expression profiling called EDGE, or EcoP15I-tagged Digital Gene Expression, based on ultra-high-throughput sequencing of 27-bp cDNA fragments that uniquely tag the corresponding gene, thereby allowing direct quantification of transcript abundance. We show that EDGE is capable of assaying for expression in >99% of genes in the genome and achieves saturation after 6-8 million reads. EDGE exhibits very little technical noise, reveals a large (10(6)) dynamic range of gene expression, and is particularly suited for quantification of transcript abundance in non-model organisms where a high-quality annotated genome is not available. In a direct comparison with RNA-seq, both methods provide similar assessments of relative transcript abundance, but EDGE does better at detecting gene expression differences for poorly expressed genes and does not exhibit transcript length bias. Applying EDGE to laboratory mice, we show that a loss-of-function mutation in the melanocortin 1 receptor (Mc1r), recognized as a Mendelian determinant of yellow hair color in many different mammals, also causes reduced expression of genes involved in the interferon response. To illustrate the application of EDGE to a non-model organism, we examine skin biopsy samples from a cheetah (Acinonyx jubatus) and identify genes likely to control differences in the color of spotted versus non-spotted regions.

Human 2'-phosphodiesterase localizes to the mitochondrial matrix with a putative function in mitochondrial RNA turnover

The vertebrate 2-5A system is part of the innate immune system and central to cellular antiviral defense. Upon activation by viral double-stranded RNA, 5'-triphosphorylated, 2'-5'-linked oligoadenylate polyribonucleotides (2-5As) are synthesized by one of several 2'-5'-oligoadenylate synthetases. These unusual oligonucleotides activate RNase L, an unspecific endoribonuclease that mediates viral and cellular RNA breakdown. Subsequently, the 2-5As are removed by a 2'-phosphodiesterase (2'-PDE), an enzyme that apart from breaking 2'-5' bonds also degrades regular, 3'-5'-linked oligoadenylates. Interestingly, 2'-PDE shares both functionally and structurally characteristics with the CCR4-type exonuclease-endonuclease-phosphatase family of deadenylases. Here we show that 2'-PDE locates to the mitochondrial matrix of human cells, and comprise an active 3'-5' exoribonuclease exhibiting a preference for oligo-adenosine RNA like canonical cytoplasmic deadenylases. Furthermore, we document a marked negative association between 2'-PDE and mitochondrial mRNA levels following siRNA-directed knockdown and plasmid-mediated overexpression, respectively. The results indicate that 2'-PDE, apart from playing a role in the cellular immune system, may also function in mitochondrial RNA turnover.

Natural occurrence of 2',5'-linked heteronucleotides in marine sponges

2′,5′-oligoadenylate synthetases (OAS) as a component of mammalian interferon-induced antiviral enzymatic system catalyze the oligomerization of cellular ATP into 2′,5′-linked oligoadenylates (2-5A). Though vertebrate OASs have been characterized as 2′-nucleotidyl transferases under in vitro conditions, the natural occurrence of 2′,5′-oligonucleotides other than 2-5A has never been demonstrated. Here we have demonstrated that OASs from the marine sponges Thenea muricata and Chondrilla nucula are able to catalyze in vivo synthesis of 2-5A as well as the synthesis of a series 2′,5′-linked heteronucleotides which accompanied high levels of 2′,5′-diadenylates. In dephosphorylated perchloric acid extracts of the sponges, these heteronucleotides were identified as A2′p5′G, A2′ p5′U, A2′p5′C, G2′p5′A and G2′ p5′U. The natural occurrence of 2′-adenylated NAD⁺ was also detected. In vitro assays demonstrated that besides ATP, GTP was a good substrate for the sponge OAS, especially for OAS from C. nucula. Pyrimidine nucleotides UTP and CTP were also used as substrates for oligomerization, giving 2′,5′-linked homo-oligomers. These data refer to the substrate specificity of sponge OASs that is remarkably different from that of vertebrate OASs. Further studies of OASs from sponges may help to elucidate evolutionary and functional aspects of OASs as proteins of the nucleotidyltransferase family.

2'-5'-Oligoadenylate synthetase is activated by a specific RNA sequence motif

2'-5'-Oligoadenylate synthetase plays a central role in the cellular innate antiviral response. Although activation of 2'-5'-oligoadenylate synthetase by double stranded RNA was discovered more than 30 years ago it is still unclear which sequence features are required by an RNA to activate the enzyme. A pool of chemically synthesized short double stranded RNAs of specific sequence was used to probe 2'-5'-oligoadenylate synthetase activation. It was found that activating double stranded RNAs contain the following motif: NNWWNNNNNNNNNWGN. Verification of this sequence motif in a pool of 102 small double stranded RNAs demonstrated a false positive prediction rate of 8% and a false negative prediction rate of 12%. The sequence motif identified provides mechanistic insight into the mechanism of 2'-5'-oligoadenylate synthetase activation by double stranded RNA and allows theoretical predictions whether a given RNA molecule has the capability to activate 2'-5'-oligoadenylate synthetase.

Human leukocyte interferon and the antiviral factor (AVF) from virus-infected plants stimulate plant tissues to produce nucleotides with antiviral activity

Leaves of Nicotiana glutinosa and tobacco, as well as tobacco callus cultures, were treated with the plant antiviral factor AVF or with a purified subspecies of human leukocyte interferon. After incubation, a fraction containing short oligonucleotides was extracted directly from the plant tissue. In addition, a synthetase preparation was fractionated from treated tissues, which polymerized ATP in the presence of polyinosinic, polycytidylic acid (poly(I:C)). The various plant nucleotides were applied to tobacco mosaic virus (TMV)-infected leaf disks, the TMV content of which were determined by an enzyme-linked immunosorbent assay. The nucleotide fraction extracted directly from TMV-infected leaves exhibited a considerable antiviral activity, whereas similar fractions from AVF- or interferon-treated leaves did not, even though an antiviral state was induced in the tissue by these agents. However, when the synthetase fraction from TMV-infected, AVF-treated, or interferon-treated tissues was incubated with ATP and poly(I:C), the resultant, heat-stable, acid-soluble, polymerized ATP markedly inhibited TMV multiplication. It is concluded that the presence of double-stranded RNA is obligatory for the formation of the antiviral nucleotides. The analogy to interferon-induced resistance in animal tissues is discussed.

Interferon-based therapy of hepatitis C

In 2007, the world celebrated the 50th anniversary of the discovery of interferon (IFN). The first clinical trial of recombinant IFN-alpha in patients with chronic hepatitis C was published in 1986. This article reviews the classification of IFNs, IFN production during viral infections, IFN signaling pathways and the mechanisms of their antiviral and immunomodulatory properties. Hepatitis C virus infection treatment is currently based on the combination of pegylated IFN-alpha and ribavirin. The pegylated IFN-alpha molecules are described, as well as the putative mechanisms of action of ribavirin. Current treatment guidelines are discussed and new results suggesting that the treatment schedule should be tailored to the early virological response during therapy are presented. Finally, insights into new hepatitis C drug developments are given.

On the discovery of interferon-inducible, double-stranded RNA activated enzymes: the 2'-5'oligoadenylate synthetases and the protein kinase PKR

The demonstration that double-stranded (ds) RNA inhibits protein synthesis in cell-free systems prepared from interferon-treated cells, lead to the discovery of the two interferon-induced, dsRNA-dependent enzymes: the serine/threonine protein kinase that is referred to as PKR and the 2',5'-oligoadenylate synthetase (2',5'-OAS), which converts ATP to 2',5'-linked oligoadenylates with the unusual 2'-5' instead of 3'-5' phosphodiesterase bond. We raised monoclonal and polyclonal antibodies against human PKR and the two larger forms of the 2',5'-OAS. Such specific antibodies proved to be indispensable for the detailed characterization of these enzyme and the cloning of cDNAs corresponding to the human PKR and the 69-71 and 100 kDa forms of the 2',5'-OAS. When activated by dsRNA, PKR becomes autophosphorylated and catalyzes phosphorylation of the protein synthesis initiation factor eIF2, whereas the 2'-5'OAS forms 2',5'-oligoadenylates that activate the latent endoribonuclease, the RNAse L. By inhibiting initiation of protein synthesis or by degrading RNA, these enzymes play key roles in two independent pathways that regulate overall protein synthesis and the mechanism of the antiviral action of interferon. In addition, these enzymes are now shown to regulate other cellular events, such as gene induction, normal control of cell growth, differentiation and apoptosis.

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.

The human 2'-5'oligoadenylate synthetase family: unique interferon-inducible enzymes catalyzing 2'-5' instead of 3'-5' phosphodiester bond formation

The demonstration by Kerr and colleagues that double-stranded (ds) RNA inhibits drastically protein synthesis in cell-free systems prepared from interferon-treated cells, suggested the existence of an interferon-induced enzyme, which is dependent on dsRNA. Consequently, two distinct dsRNA-dependent enzymes were discovered: a serine/threonine protein kinase that nowadays is referred to as PKR and a 2'-5'oligoadenylate synthetase (2'-5'OAS) that polymerizes ATP to 2'-5'-linked oligomers of adenosine with the general formula pppA(2'p5'A)(n), n>or=1. The product is pppG2'p5'G when GTP is used as a substrate. Three distinct forms of 2'-5'OAS exist in human cells, small, medium, and large, which contain one, two, and three OAS units, respectively, and are encoded by distinct genes clustered on the 2'-5'OAS locus on human chromosome 12. OASL is an OAS like IFN-induced protein encoded by a gene located about 8 Mb telomeric from the 2'-5'OAS locus. OASL is composed of one OAS unit fused at its C-terminus with two ubiquitin-like repeats. The human OASL is devoid of the typical 2'-5'OAS catalytic activity. In addition to these structural differences between the various OAS proteins, the three forms of 2'-5'OAS are characterized by different subcellular locations and enzymatic parameters. These findings illustrate the apparent structural and functional complexity of the human 2'-5'OAS family, and suggest that these proteins may have distinct roles in the cell.

Anti-mitogenic function of interferon-induced (2'-5')oligo(adenylate) and growth-related variations in enzymes that synthesize and degrade this oligonucleotide

Addition of (2'5')ApApA to concanavalin-A-stimulated mouse spleen lymphocytes strongly inhibits the large increase in RNA and protein synthesis which takes place 24-48 h after stimulation. The inhibitory effect on protein synthesis precedes the effect on RNA synthesis and takes at least 6 h to be detected. Histone synthesis is preferentially inhibited at 48 h. No effect on protein synthesis was detected in unstimulated resting lymphocytes, or in stimulated lymphocytes during the first 24 h after concanavalin A treatment. The anti-mitogenic effect of the (2'-5')oligo(adenylate) seems to result, therefore, from inhibition of protein synthesis taking place before initiation of DNA replication. The mitogenic stimulus produced by the lectin enhances, in lymphocytes, the level of the 2'-phosphodiesterase which degrades (2'-5')oligo(adenylate). Enhancement of the 2'-phosphodiesterase was also observed after serum stimulation of confluent monkey kidney cells. Furthermore, the ratio of (2'-5')oligo(adenylate) synthetase to 2'-phosphodiesterase is ten-times lower in fast-growing kidney cells than in quiescent serum-starved cells. A model for the role of (2'-5')oligo(adenylate) synthesis and degradation in the regulation of cell proliferation by interferon and by mitogens is presented.

Interferon inhibits dengue virus infection by preventing translation of viral RNA through a PKR-independent mechanism

Previously, we demonstrated that pretreatment of cells with interferon (IFN) alpha + gamma or beta + gamma inhibited dengue virus (DV) replication. In this study, experiments were performed to better define the mechanism by which IFN blocks the accumulation of dengue virus (DV) RNA. Pretreatment of human hepatoma cells with IFN beta + gamma did not significantly alter virus attachment, viral entry, or nucleocapsid penetration into the cytoplasm. The inhibitory effect of IFN was retained even when naked DV RNA was transfected directly into cells, confirming that steps associated with viral entry were not the primary target of IFN action. Biosynthetic labeling experiments revealed that IFN abolished the translation of infectious viral RNA that occurred prior to RNA replication. Subcellular fractionation experiments demonstrated that IFN did not significantly alter the ability of viral RNA to attach to ribosomes. The antiviral effect of IFN appeared independent of the IFN-induced, double-stranded RNA-activated protein kinase (PKR) and RNase L, as genetically deficient PKR- RNase L- cells that were infected by DV retained sensitivity to inhibition by IFN. We conclude that IFN prevents DV infection by inhibiting translation of the infectious viral RNA through a novel, PKR-independent mechanism.

Antiviral actions of interferons

Tremendous progress has been made in understanding the molecular basis of the antiviral actions of interferons (IFNs), as well as strategies evolved by viruses to antagonize the actions of IFNs. Furthermore, advances made while elucidating the IFN system have contributed significantly to our understanding in multiple areas of virology and molecular cell biology, ranging from pathways of signal transduction to the biochemical mechanisms of transcriptional and translational control to the molecular basis of viral pathogenesis. IFNs are approved therapeutics and have moved from the basic research laboratory to the clinic. Among the IFN-induced proteins important in the antiviral actions of IFNs are the RNA-dependent protein kinase (PKR), the 2',5'-oligoadenylate synthetase (OAS) and RNase L, and the Mx protein GTPases. Double-stranded RNA plays a central role in modulating protein phosphorylation and RNA degradation catalyzed by the IFN-inducible PKR kinase and the 2'-5'-oligoadenylate-dependent RNase L, respectively, and also in RNA editing by the IFN-inducible RNA-specific adenosine deaminase (ADAR1). IFN also induces a form of inducible nitric oxide synthase (iNOS2) and the major histocompatibility complex class I and II proteins, all of which play important roles in immune response to infections. Several additional genes whose expression profiles are altered in response to IFN treatment and virus infection have been identified by microarray analyses. The availability of cDNA and genomic clones for many of the components of the IFN system, including IFN-alpha, IFN-beta, and IFN-gamma, their receptors, Jak and Stat and IRF signal transduction components, and proteins such as PKR, 2',5'-OAS, Mx, and ADAR, whose expression is regulated by IFNs, has permitted the generation of mutant proteins, cells that overexpress different forms of the proteins, and animals in which their expression has been disrupted by targeted gene disruption. The use of these IFN system reagents, both in cell culture and in whole animals, continues to provide important contributions to our understanding of the virus-host interaction and cellular antiviral response.

Interferon in oncological practice: review of interferon biology, clinical applications, and toxicities

For the past 40 years, various forms of interferon (IFN) have been evaluated as therapy in a number of malignant and non-malignant diseases. With the advent of gene cloning, large quantities of pure IFN became available for clinical study. This paper reviews the biology, pharmacology, and clinical applications of IFN formulations most commonly used in oncology. It then reviews the most common side effects seen in patients treated with IFN, and makes recommendations for the management of IFN-induced toxicity. The major oncological indications for IFN include melanoma, renal cell carcinoma, AIDS-related Kaposi's sarcoma, follicular lymphoma, hairy cell leukemia, and chronic myelogenous leukemia. Unfortunately, IFN therapy is associated with significant toxicity, which can be divided into constitutional, neuropsychiatric, hematologic, and hepatic effects. These toxicities have a major impact on the patient's quality of life, and on the physician's ability to optimally treat the patient. Careful attention to all aspects of patient care can result in improved tolerability of this difficult but promising therapy.

CONCLUSION

a better understanding of IFN biology, indications, side effect profiles, and toxicity management will aid in optimizing its use in the treatment of patients with cancer.

Identification of a novel gene with increasing rate of suppression in high grade prostate cancers

Prostate cancer is the second leading cause of cancer-related deaths in the United States. However, the underlying molecular events for prostate cancer development are not clear. In this study, we applied the recently developed technology known as differential subtraction chain (DSC) to identify a novel gene whose expression is inactivated in high grade prostate cancer. This gene, designated as SAPC, is expressed in normal prostate acinar cells. Its expression is dramatically down-regulated in high grade prostate cancers (4/4) but is unaltered in low grade prostate cancers. It encodes a 7.7-kd protein. Its sequence shares some homology with the cysteine-rich domain of 2-5A-dependent RNase L, which is a critical component of the interferon-induced apoptosis cascade. The selective inactivation in the more aggressive prostate cancers holds promise for SAPC as a potential prognostic marker for high grade prostate cancer.

Caspase-dependent apoptosis by 2',5'-oligoadenylate activation of RNase L is enhanced by IFN-beta

The 2',5'-oligoadenylate (2-5A) system is an interferon (IFN)-regulated RNA decay pathway that provides innate immunity against viral infections. The biologic action of the 2-5A system is mediated by RNase L, an endoribonuclease that becomes enzymatically active after binding to 2-5A. RNase L is also implicated in mediating apoptosis in response to both viral and nonviral inducers. To study the cellular effects of RNase L activation directly, 2-5A was transfected into the human ovarian cancer cell line, Hey1B. Activation of RNase L by 2-5A resulted in specific 18S rRNA cleavage and induction of apoptosis, as measured by TUNEL and annexin V binding assays. In contrast, the dimeric form of 2-5A, ppA2'p5'A, neither activated RNase L nor caused apoptosis. Treatment with IFN-beta prior to 2-5A transfection enhanced cellular RNase L levels (< or = 2.2-fold) and increased the proportion of cells undergoing apoptosis (by < or =40%). However, rRNA cleavages after 2-5A transfections were not enhanced by IFN-beta pretreatments, indicating that basal levels of RNase L were sufficient for this activity. Apoptosis in response to RNase L activation was accompanied by cytochrome c release from mitochondria. Induction of apoptosis by either 2-5A alone or by the combination of 2-5A and IFN-beta was effectively blocked with either the pancaspase inhibitor, Z-VAD-fmk, or with the caspase 3 inhibitor, DEVD-fmk. Therefore, activation of RNase L by 2-5A leads to cytochrome c release into the cytoplasm and then to caspase activation and apoptosis. These results suggest potential uses for 2-5A in augmenting the anticancer activities of IFN.

2',5'-oligoadenylate synthetase gene in chicken: gene structure, distribution of alleles and their expression

We have cloned the gene for chicken 2',5'-oligoadenylate synthetase (ChOAS) by the method of polymerase chain reaction with use of ChOAS cDNA sequence. The ChOAS gene is composed of five introns and six exons containing all of the sequence of the ChOAS cDNA from the start to the stop codon. The first five exons of ChOAS gene which encode the OAS catalytic domain have a similar structure to HuOAS1 gene including the exon-intron boundaries. However, the length of introns of ChOAS gene is only 1/7 of those of HuOAS1 gene. The sixth exon of the ChOAS gene encodes the ubiquitin-like (UbL) domain of two consecutive sequence (UbL1 and UbL2) homologous to ubiquitin. ChOAS encoded in a single copy gene has at least two alleles, OAS(*)A and OAS(*)B. The differences between these two alleles are in the sixth exon of the gene; a 96-nucleotide sequence in the UbL1 portion of OAS(*)A is deleted from OAS(*)B. No OAS(*)B gene was detected in nine lines of chickens tested other than Leghorns. Almost the same levels of ChOAS-A and -B proteins induced physiologically in erythrocytes were detected in infant chickens (2-week-old), but in grown-up chickens (6-month-old) the level of erythrocyte OAS-B was markedly reduced in most of B/B chickens. Thus, the UbL domain of ChOAS is responsible for the maintenance of the OAS level in the tissue.

Upregulation of type I interferon receptor by IFN-gamma

Type I interferon (IFN) receptor has a multichain structure composed of at least two distinct subunits, IFNAR-1 and IFNAR-2. In the present study, we demonstrated that IFN-gamma induced the expression of mRNA for IFNAR-1 and IFNAR-2 in a human hepatoma cell line, HepG2 cells. The induction was dose and time dependent. Because of this result, we examined the effect of combined treatment with type I IFN and IFN-gamma. The intracellular 2-5A-synthetase activity induced by combined treatment was significantly higher than that by type I IFN alone. This study suggests that combined treatment with type I IFN and IFN-gamma may be more effective than that of type I IFN alone and that the upregulation of type I IFN receptor may be one of the reasons. Our findings may have some relevance to the clinical use of IFN.

The expression of both domains of the 69/71 kDa 2',5' oligoadenylate synthetase generates a catalytically active enzyme and mediates an anti-viral response

The 2',5' oligoadenylate synthetase (OAS) represents a family of interferon-induced proteins which, when activated by double-stranded (ds) RNA, polymerizes ATP into 2',5'-linked oligomers with the general formula pppA(2'p5'A)n, where n >/= 1. The 69-kDa form of human OAS has two isoforms (p69 and p71) that are identical for their first 683 amino acids and consist of two homologous and adjacent domains, each homologous to the small 40-kDa OAS. Here, we demonstrate that mRNA species specific for the isoforms p69 and p71 are enhanced in interferon-treated cells, with the p69 mRNA being more abundant than that of p71. In transfected cells, both isoforms could be expressed independently to generate enzymes with similar catalytic activity, typical of the natural 69-kDa OAS from interferon-treated cells. On the other hand, deletion mutants expressing either the N- or C-terminal domain common in p69 and p71 were greatly unstable and were found to be devoid of catalytic activity, in spite of the capacity of the C-terminal domain to bind dsRNA. Finally, we show that murine cell lines stably expressing either p69 or p71 isoforms partially resist infection by the encephalomyocarditis virus. These results indicate that both isoforms of the 69-kDa form of 2',5' OAS are expressed in interferon-treated cells, and that each isoform could be implicated in the mechanism of the anti-viral action of interferon.

The human 2',5'-oligoadenylate synthetase family: interferon-induced proteins with unique enzymatic properties

2',5'-Oligoadenylate synthetase (2',5'-OAS) was discovered and characterized as an interferon (IFN)-induced enzyme that in the presence of double-stranded (ds) RNA converts ATP into 2',5'-linked oligomers of adenosine with the general formula pppA(2'p'A)n, n > or = 1. The product is pppG2'p5'G when GTP is used as a substrate. Now, 20 years later, this activity is attributed to several well-characterized, homologous, and IFN-induced proteins in human cells. Three distinct forms of 2',5'-OAS exist, small, medium, and large, which contain 1, 2, and 3 OAS units, respectively, and are encoded by distinct genes clustered on the 2',5'-OAS locus on human chromosome 12. Recently, other IFN-induced proteins homologous to the OAS unit but devoid of the typical 2',5'-OAS catalytic activity have been described. These OAS-related proteins are encoded by a gene located at the proximity of the 2',5'-OAS locus. These findings illustrate the apparent structural and functional complexity of the human 2',5'-OAS family.

The 100-kDa 2',5'-oligoadenylate synthetase catalyzing preferentially the synthesis of dimeric pppA2'p5'A molecules is composed of three homologous domains

The 2-5A synthetases represent a family of proteins implicated in the mechanism of the antiviral action of interferon. When activated by double-stranded RNA, these proteins polymerize ATP into 2'-5'-linked oligomers with the general formula pppA(2'p5'A)n, n >/= 1. Three forms of human 2-5A synthetases have been described corresponding to proteins of 40/46 (p40/p46), 69/71 (p69/p71), and 100 kDa (p100). Here we describe the molecular cloning and characterization of p100. By screening a cDNA expression library with a specific p100 polyclonal antibody, we first isolated a 590-nucleotide cDNA fragment which was subsequently used to isolate the full-length 6365-nucleotide cDNA. This cDNA recognizes a distinct interferon-induced messenger RNA of 7 kilobases. It has an open reading frame encoding a protein of 1087 amino acids including the sequence of seven peptides obtained by microsequencing of the natural p100 protein, which was purified from interferon-treated human cells. p100 is composed of three adjacent domains, each homologous to the previously defined catalytic unit of 350 amino acids, which is present as one unit in p40/p46 and as two units in p69/p71. The recombinant p100 synthesized preferentially dimeric 2', 5'-oligoadenylate molecules and displayed parameters for maximum enzyme activity similar to the natural p100. These results confirm that the enzymatic activity of p100 is distinct compared with that of p40/p46 and p69/p71.

Ultrastructural localization of interferon-inducible double-stranded RNA-activated enzymes in human cells

The protein kinase PKR and the 2',5'-oligoadenylate (2-5A) synthetase are two interferon-induced and double-stranded RNA-activated enzymes which are implicated in the mechanism of action of interferon. Their distribution was undertaken here at the ultrastructural level by the immunogold procedure, following the use of specific monoclonal antibodies directed against PKR and 69- and 100-kDa forms of the 2-5A synthetase. These enzymes were detected as a pool of nonaggregated proteins scattered throughout the cell and as aggregates often associated with electron-dense doughnut-like structures showing a similar aspect whatever their subcellular localization: the cytoplasm, the nuclear envelope, and the nucleus. In general, the 2-5A synthetases were present in much more lower amounts than the PKR, probably due to the difficulty of detecting traces of proteins by electron microscopy. To circumvent this, we used a human lymphoblastoid cell line overexpressing the 69-kDa form of the 2-5A synthetase. In such cells, the synthetase was then clearly observed in both the cytoplasm and the nucleus; isolated or small clusters of gold particles were numerous in the cell mainly over the RNP fibrils of the interchromatin space, nucleolus, and ribosomes. Interestingly, gold particles were also found to be associated with the membranes of nuclear envelope and rough endoplasmic reticulum probably due to the myristilated motif of this form of 2-5A synthetase. Finally, intensely labeled electron-opaque dots sometimes associated with the nuclear pore complexes were present in the nucleus and in the cytoplasm of cells which might suggest their transport from the nucleus to the cytoplasm or reciprocally through the nuclear pore complexes. These observations indicate the wider distribution of the dsRNA-activated enzymes in the cell, thus pointing out their potential implication in as yet undetermined physiological function(s) necessary for various cellular metabolic reactions.

Two types of chicken 2',5'-oligoadenylate synthetase mRNA derived from alleles at a single locus

We have isolated two types of chicken 2',5'-oligoadenylate synthetase cDNAs, A and B, which encode predicted proteins of 508 amino acids (58316 Da) and 476 amino acids (54336 Da), respectively. The region of A-protein comprising 33 amino acid residues from 385Ala to 417Cys is substituted by a single amino acid 385Tyr in B-protein. The homology between chicken and mammalian 2',5'-oligoadenylate synthetases is 49.5% over the amino-terminal 337 residues. Proteins expressed from A- and B-cDNAs in E. coli cells were both active in synthesizing 2',5'-oligoadenylate. However, the activity of B-protein was 10-15% of that of A-protein. Southern blotting hybridization indicated that the chicken synthetases are encoded by a single gene. RT-PCR and PCR analyses of RNA and DNA of chicken erythrocytes together with the sequence data of the PCR products showed that A- and B-mRNAs are derived from alleles at a single locus encoding chicken 2',5'-oligoadenylate synthetase, designated as OAS * A and OAS * B. Chickens carrying OAS * A/B produce two types of synthetase with molecular masses of 58 and 54 kDa, and those carrying OAS * A/A produce only a single type of 58 kDa.

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

The interferon (IFN)-induced enzyme RNase L produced by a recombinant vaccinia virus (VV) causes death of mammalian cells with morphological and biochemical characteristics of apoptosis. Coexpression of 2-5A-synthetase enhances apoptosis induced by RNase L Activation of endogenous RNase L by infection with a VV ts mutant (ts22) or with wild-type virus in the presence of the antipoxvirus drug isatin-beta-thiosemicarbazone, a treatment known to significantly increase the amount of double-stranded RNA late during infection, also causes pronounced apoptosis of infected cells. The effects observed with recombinant virus-derived RNase L or with the endogenous enzyme are specific, since apoptosis also occurs in cells derived from mice lacking the IFN-induced protein kinase (PKR). The apoptosis antagonist Bcl-2 prevents induction of cell death by RNase L activation. Apoptosis of mammalian cells by RNase L activation could be a mechanism mediating anticellular actions of IFN.

69-kDa and 100-kDa isoforms of interferon-induced (2'-5')oligoadenylate synthetase exhibit differential catalytic parameters

The (2'-5')oligoadenylate synthetase represents a family of interferon-induced proteins which when activated by double-stranded (ds)RNA polymerizes ATP into 2'-5'-linked oligomers with the general formula pppA(2'p5'A)n, where n > 1, which for convenience are referred to as 2-5A. We studied here the influence of pH, dsRNA concentration and time on oligomeric composition of 2-5A synthesized by purified 69-kDa and 100-kDa isoforms of (2'-5')oligo(adenylate) synthetase. In optimal conditions for activity, the 69-kDa form synthesized higher oligomers of 2-5A molecules whereas the 100 kDa form synthesized preferentially dimeric molecules, which are known not to be functional for the activation of RNase L. This difference does not reflect a differential affinity of the enzymes for the preformed 2-5A dimer, which is found to be a very poor substrate for both enzymes. This latter strongly suggests that the mechanism of elongation is more likely processive. Moreover, we show that both isoforms have efficient nucleotidyl-transferase activity and provide evidence that, in optimized conditions, GTP can be used alone as substrate by these enzymes to generate pppG2'p5'G. Our results clearly demonstrate that the 69-kDa and 100-kDa forms of (2'-5')oligoadenylate synthetase manifest various differential catalytic activities, and favor the hypothesis that these enzymes might have other functions in the cell besides those in the 2-5A system.

Activation of RNase L by 2',5'-oligoadenylates. Biophysical characterization

Ribonuclease L (RNase L) is an endoribonuclease that is activated upon binding of adenosine oligomers linked 2' to 5' to cleave viral and cellular RNAs. We recently proposed a model for activation in which activator A binds to monomer, E, to form EA, which subsequently dimerizes to the active form, E2A2 (Cole, J. L., Carroll, S. S., and Kuo, L. C. (1996) J. Biol. Chem. 271, 3978-3981). Here, we have employed this model to define the equilibrium constants for activator binding (Ka) and dimerization of EA to E2A2 (Kd) by equilibrium analytical ultracentrifugation and fluorescence measurements. Multi-wavelength sedimentation data were globally fit to the model above, yielding values of Ka = 1.69 microM and Kd = 17. 8 nM for 2',5'-linked adenosine trimer. Fluorescent conjugates of 2',5'-linked adenosine trimer with 7-hydroxycoumarin have been prepared. The coumarin emission anisotropy shows a large increases upon binding to RNase L. Analysis of anisotropy titrations yields values of Ka and Kd close to those obtained by sedimentation. The sedimentation parameters for unmodified 2',5'-linked adenosine trimer also agree with those obtained by enzyme kinetic methods (Carroll, S. S., Cole, J. L., Viscount, T., Geib, J., Gehman, J., and Kuo, L. C. (1997) J. Biol. Chem. 272, 19193-19198). Thus, the data presented here clearly define the energetics of RNase L activation and support the minimal activation model.

Activation of RNase L by 2',5'-oligoadenylates. Kinetic characterization

Ribonuclease L (RNase L), the 2',5'-oligoadenylate-dependent ribonuclease, is one of the cellular antiviral systems with enhanced activity in the presence of interferon. A reaction scheme has been developed to model the sequence of steps necessary for the activation of RNase L (Cole, J. L., Carroll, S. S., Blue, E. S., Viscount, T., and Kuo, L. C. (1997) J. Biol. Chem. 272, 19187-19192). The model comprises three sequential binding steps: the binding of activator to enzyme monomer, the subsequent dimerization of the activated monomer to form the active enzyme dimer, followed by the binding of substrate prior to catalysis. The model is used to evaluate the activation of RNase L by several synthetic analogs of the native activator. The 5'-phosphate of the activator has been determined to be an important structural determinant for the efficient activation of RNase L, and its loss caused a loss of activator affinity of 2-3 orders of magnitude. The length of activator is not an important determinant of activator potency for the activator analogs examined. The specific activity of the enzyme under conditions of saturation of activator binding and complete dimerization of the activated monomers varies only by about a factor of 3 for the activators examined, indicating that once dimerized in the presence of any of these activators, the enzyme exhibits a similar catalytic activity.

Cleavage of oligoribonucleotides by the 2',5'-oligoadenylate- dependent ribonuclease L

RNase L, the 2',5' oligoadenylate-dependent ribonuclease, is one of the enzyme systems important in the cellular response to interferon. When activated in the presence of 2',5'-linked oligoadenylates, RNase L can catalyze the cleavage of synthetic oligoribonucleotides that contain dyad sequences of the forms UU, UA, AU, AA, and UG, but it cannot catalyze the cleavage of an oligoribonucleotide containing only cytosines. The primary site of the cleavage reaction with the substrate C11UUC7 has been defined to be 3' of the UU dyad by labeling either the 5' or the 3' end of the oligoribonucleotide and by examining the reaction products on polyacrylamide sequencing gels. Reaction time courses have been used to determine the kinetic parameters of the cleavage reactions. The effect of the overall length of the oligomeric substrate as well as the sequence of the bases around the position of the cleavage site on the kinetics of the cleavage reaction has been examined. The efficiency with which activated RNase L catalyzes the cleavage of the substrate C11UUC7 is 1.9 x 10(7) m-1 s-1. Because the cleavage of the synthetic oligoribonucleotide can be used to monitor the steady-state kinetics of catalysis by activated RNase L, this method offers an advantage over previous methods of assay for RNase L activity.

Effects of interferons and tumour necrosis factor-alpha on human lung cancer cell lines and the development of an interferon-resistant lung cancer cell line

Thirteen human lung cancer cell lines, 7 representing small cell lung cancer (SCLC) and 6 different types of non-SCLC, were tested for sensitivity to tumour necrosis factor alpha (TNF-alpha) and interferon alpha and gamma (IFN-alpha and gamma) using an automated fluorometric microculture cytotoxicity assay (FMCA). One SCLC line (H-82) was found to be sensitive to IFN-alpha in short-term (72 h) culture, whereas after prolonged (5 days) culture two additional SCLC cell lines responded to IFN-gamma. TNF-alpha inhibited the growth of one large cell carcinoma cell line (H-157), whereas all SCLC lines were found to be insensitive. The combination of IFN-gamma and TNF-alpha produced no further response compared with the single agents used alone. By continuous cultivation of the IFN-alpha-sensitive cell line H-82 in the presence of increasing concentrations of IFN-alpha, an IFN-alpha-resistant subline (H-82) was established. This line displayed a high degree of resistance ( > 100 fold) to IFN-alpha and cross-resistance to IFN-gamma. There was no alteration in the number of IFN binding sites, in the growth rate, the expression of selected surface markers for SCLC or the expression of multidrug resistance markers in the H-82R subline compared with the parental H-82 cell line. The results demonstrate a heterogeneous response of SCLC cell lines to IFN-alpha and gamma and TNF-alpha with only a minority of the cell lines responding to these agents by growth inhibition. The IFN-alpha and gamma H-82R subline may serve as a valuable tool in future studies on the mechanisms of IFN antitumour activity.

Regulation of the interferon-inducible protein kinase PKR and (2'-5')oligo(adenylate) synthetase by a catalytically inactive PKR mutant through competition for double-stranded RNA binding

The interferon-inducible double-stranded RNA-dependent protein kinase PKR has been suggested to function as a tumour suppressor gene product. Catalytically inactive mutants of PKR give rise to a tumorigenic phenotype when overexpressed in NIH-3T3 fibroblasts and this has been attributed to a dominant negative effect on the activity of the wild-type enzyme. Here we show that the mutant with Lys296 replaced by Arg, [K296R]PKR, not only inhibits the protein kinase activity of wild-type PKR but is also inhibitory towards another double-stranded RNA-dependent enzyme, the 40-kDa form of (2'-5')oligo(adenylate) synthetase. Inhibition of both wild-type PKR and (2'-5')oligo(adenylate) synthetase is reversed by adding higher concentrations of double-stranded RNA. These results suggest competition between [K296R]PKR and wild-type PKR or (2'-5')oligo(adenylate) synthetase for limiting amounts of double-stranded RNA. Moreover, the data imply that the tumorigenic effect of this PKR mutant could be due to inhibition of additional pathways requiring low levels of double-stranded RNA for activation and cannot be unambiguously attributed to inhibition of endogenous PKR itself.

A sensitive assay for the IFN-regulated 2-5A synthetase enzyme

2-5A synthetase is the central enzyme of the 2-5A system, an important mediator of interferon action. An assay capable of detecting low, yet biologically important levels of 2-5A synthetase enzyme activity is described. The purification of enzyme reaction products on SepPak C-18 cartridges resulted in a significant reduction in background, when a high specific activity substrate was used to label the 2-5A. Quantitation of labeled 2-5A by chromatography and scintillation counting provided a means of detecting femptomolar amounts of 2-5A. The combination of these procedures accounts for a 3-4 log increase in sensitivity over existing assays. This degree of sensitivity should permit a more accurate determination of the 2-5A synthetase activity in vivo leading to a better understanding of the role of the 2-5A system in virus infection and other cellular processes.

Determination of 2-5A synthetase and 2-5A phosphodiesterase in neuroblastoma cells by analytical capillary isotachophoresis: effects of cytokines and comparison with radioenzymatic methods

2-5A Synthetase and 2-5A phosphodiesterase were determined by analytical capillary isotachophoresis in comparison to radioenzymatic methods. By means of isotachophoretic analysis, a frequently used radioenzymatic 2-5A synthetase assay was optimized and the results of both assays were compared. Using the isotachophoretic assay the influence of interferon-related cytokines (tumor necrosis factor-alpha and interleukin-2) on 2-5A synthetase induction in neuroblastoma cells was estimated. In contrast to mononuclear blood cells, the tumor necrosis factor induced 2-5A synthetase in these cells. 2-5A Phosphodiesterase was determined using an isotachophoretic assay and a radioenzymatic method. Degradation of A2'p5'A2'p5'A (trimeric form of 2-5A core) was measured by isotachophoresis whereas degradation of a mixture of phosphorus-32 labeled 2-5A cores was registered by radioenzymatic assay. Activity of 2-5A phosphodiesterase was only insignificantly enhanced by interferon in mononuclear blood and neuroblastoma cells. In contrast to the radioenzymatic assays, an accurate determination of 2-5A synthetase as well as of 2-5A phosphodiesterase is possible using the isotachophoretic method because the reactions are followed by measuring the substrates ATP and A2'p5'A2'p5'A, respectively.

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

2-5A-dependent RNase is the terminal factor in the interferon-regulated 2-5A system thought to function in both the molecular mechanism of interferon action and in the general control of RNA stability. However, direct evidence for specific functions of 2-5A-dependent RNase has been generally lacking. Therefore, we developed a strategy to block the 2-5A system using a truncated form of 2-5A-dependent RNase which retains 2-5A binding activity while lacking RNase activity. When the truncated RNase was stably expressed to high levels in murine cells, it prevented specific rRNA cleavage in response to 2-5A transfection and the cells were unresponsive to the antiviral activity of interferon alpha/beta for encephalomyocarditis virus. Remarkably, cells expressing the truncated RNase were also resistant to the antiproliferative activity of interferon. The truncated RNase is a dominant negative mutant that binds 2-5A and that may interfere with normal protein-protein interactions through nine ankyrin-like repeats.

2',5'-Oligoadenylate synthetase activity as a responsive marker during interferon therapy for chronic hepatitis C

The 2',5'-oligoadenylate (2-5A) synthetase is an intracellular enzyme induced by interferon (IFN). We evaluated the serum level of this enzyme in 25 patients affected by chronic hepatitis C and treated with recombinant IFN-alpha 2b. At the end of treatment, 14 patients were classified as responders and 11 as nonresponders. Before therapy initiation no significant differences in 2-5A synthetase levels among the patients were detected, while during therapy responders showed higher mean levels of 2-5A synthetase than nonresponders. An increase in the enzyme activity was observed after 1 month of therapy, and this trend was maintained in the following 2 months. The peak of 2-5A synthetase activity was found at the end of therapy. 2-5A synthetase levels were negatively correlated with serum alanine aminotransferase (ALT). This study suggests that 2-5A synthetase may be a useful marker to monitor IFN efficacy during treatment and to predict the clinical response.

Detection of protein kinase homologues and viral RNA-binding domains utilizing polyclonal antiserum prepared against a baculovirus-expressed ds RNA-activated 68,000-Da protein kinase

The P68 protein kinase (referred to as P68 based on its M(r) of 68,000 in human cells) is a serine/threonine kinase induced by interferon treatment and activated by dsRNAs. The kinase is under tight controls in virus-infected cells since once activated, it phosphorylates its natural substrate eukaryotic initiation factor 2 (elF-2), leading to potential limitations in functional elF-2 and decreases in protein synthesis initiation. To further delineate the molecular mechanisms underlying kinase regulation, we attempted to express the P68 protein kinase in insect cells using a baculovirus vector. Repeated efforts to isolate recombinant baculoviruses containing a wild-type kinase failed, whereas recombinants expressing a nonfunctional kinase with a catalytic domain II mutation were readily isolated. When used to infect Spodoptera frugiperda cells, the recombinant virus expressed the exogenous mutant protein at almost 5-10% of the total proteins synthesized. We then purified the kinase by immunoaffinity chromatography to raise monospecific antiserum which recognized not only the human native wild-type P68, but also kinase homologues in murine, bovine, and monkey cells as determined by immunoblot and immunoprecipitation analysis. Fortunately, kinase function also could be assayed using this antibody since the human and nonhuman kinase homologues, present in immunoprecipitates, were autophosphorylated and phosphorylated the natural substrate, elF-2 alpha. Further, this antiserum recognized epitopes throughout the molecule including the amino and carboxyl termini in contrast to the available monoclonal antibody. In vitro assays using the polyclonal antibody revealed the importance of the amino terminus, especially amino acids 1-97, in the binding of the kinase to viral RNA activators and inhibitors. Finally, we determined that the P68 amino terminus was both necessary and sufficient for binding dsRNA as we were able to transfer dsRNA-binding properties to a reporter gene product previously unable to bind RNA.

A proliferation-related constraint on endogenous and interferon-induced 2-5A synthetase activity in normal and neoplastic Syrian hamster cells

2-5A Synthetase is one of the most extensively characterized enzymes induced by interferon (IFN) and is the central enzyme in a pathway that may be involved in the control of cellular proliferation. We examined the activity of this enzyme in normal diploid Syrian hamster cells (FC13) and their neoplastically transformed derivatives (BP6T); the former cell strain possesses regulated proliferative control, while the latter cell line has escaped from this control. A significant threefold increase in 2-5A synthetase activity was observed in density-arrested versus proliferating FC13 cells, whereas endogenous enzyme activity was uniformly low in BP6T cultures. The increase in enzyme activity in FC13 cultures was not accompanied by the production of IFN at a detectable level, but was parallelled by an increase in the intracellular level of 2',5'-oligoadenylate. IFN treatment resulted in a differential induction of enzyme activity depending on the proliferative state of FC13 cells. After IFN treatment, BP6T cells and subconfluent FC13 cells responded similarly with a fivefold increase in enzyme activity, whereas confluent FC13 cells displayed only a 1.4-fold increase. 2-5A Synthetase enzyme activity reflected steady-state mRNA levels in BP6T and subconfluent FC13 cells. In contrast, a noncoordinate regulation of 2-5A synthetase mRNA expression and enzyme activity was detected in confluent FC13 cells, suggesting that posttranscriptional mechanisms may be involved. The different patterns of endogenous and IFN-induced 2-5A synthetase enzyme activity in FC13 and BP6T cells found in this comparative study may represent an alteration fundamental to the loss of proliferative control in transformed cells.

Interferon-induced and double-stranded RNA-activated enzymes: a specific protein kinase and 2',5'-oligoadenylate synthetases

Treatment of cells with interferon (IFN) results in the induction of two double-stranded RNA (dsRNA)-activated enzymes: a specific protein kinase and 2'-5' linked oligoadenylate [pppA(2'p5'A)n referred to as 2-5A] synthetases. The protein kinase, when activated by dsRNA, becomes autophosphorylated and catalyzes and phosphorylation of the protein synthesis initiation factor, eIF2. The 2-5A synthetases, when activated by dsRNA, form 2-5A molecules capable of activating a latent endoribonuclease that degrades RNA. By inhibiting initiation of protein synthesis or by degrading of RNA, these enzymes play key roles in two independent pathways that regulate overall protein synthesis.

Antiviral effects of 2',5'oligoadenylates (2-5As), and related compounds

Dephosphorylated "core" of 2',5'-oligoadenylate (2-5A) dimer (A2'p5'A), exogenously added to nonpermeabilized FL cells, inhibited the multiplication of Sindbis virus and vesicular stomatitis virus (VSV). The compound was shown to inhibit viral protein synthesis. The addition of A2'p5'A at the early stage of viral replication was more effective than that at the late stage. In contrast with the core, phosphorylated 2-5A (p5'A2'p5'A and ppp5'A2'p5'A) and 2-5A analogs containing cordycepin (3'-deoxyadenosine) did not show such antiviral effects. The rate of uptake of [3H]ppp5'A 2'p5'A into acid-soluble and acid-insoluble fractions, especially into the acid-insoluble fraction, was faster than that of [3H]A2'p5'A. These results suggest that the difference of antiviral activity between A2'p5'A and ppp5'A2'p5'A does not result from the different rate of uptake by cells, but from the different rate of from acid-soluble to acid-insoluble fractions.

Lymphokines and cytokines as cancer treatment. Immunotherapy realized

Human proteins with identified effects on host responses to malignant cells have been established as effective therapeutic techniques in cancer. Lymphokines, products of activated cells of the immune system, have pleiotropic biochemical and cellular effects. These include stimulation of immune effector cell proliferation, augmentation of cytotoxicity of immune effector cells for tumor cell targets, enhancement in antigen-recognition potential by monocytes, and modulation of tumor-associated antigen expression on neoplastic cells. Interferons (IFN) and interleukin-2 (IL-2), purified to homogeneity, can induce regression of metastatic malignancy. Recombinant DNA technology has facilitated large-scale production of these and other lymphokines and cytokines. It has also made possible analyses of physical structures of the molecules themselves and has enabled creation of mutated molecules with specific, desired substitutions in their amino acid sequence. Monoclonal antibodies, directed at tumor-associated antigens, can augment antibody-dependent cell-mediated cytotoxicity and can selectively deliver cytotoxic techniques to malignant cells. Molecules that modify the host resistance to malignant disease also have potential to augment effectiveness of other cancer treatment techniques. Lymphokines, cytokines, and monoclonal antibodies, all products of biotechnology, have resulted in fulfillment of the promise of the immune system for inhibition of growth of human malignancy.

Effect of 2',5'-oligoadenylate on herpes simplex virus-infected cells and preventive action of 2',5'-oligoadenylate on the lethal effect of HSV-2

Antiviral effects of ppp(A2'p)nA, (2-5A) on herpes simplex virus type 1 or type 2 (HSV-1 or HSV-2)-infected baby hamster kidney fibroblasts (BHK cells) and HSV-2-infected female guinea pigs were examined. 2-5A was introduced into BHK cells in the form of a calcium phosphate precipitate and as an ointment of polyethylene glycol (PEG) into guinea pig vagina. Under optimum conditions, 2-5A trimer and other 2-5A derivatives inhibited over 90% of HSV-1 syncytia formation and over 50% of HSV-2 plaque formation. The growth of uninfected cells was only slightly and transiently inhibited under these conditions. Northern analysis of viral immediate early mRNAs and cellular mRNAs showed that all transcripts determined were reduced in amount by the 2-5A trimer treatment. The reduction in level of viral mRNAs (ICP4, ICP22, and ICP47) by 2-5A trimer was significantly more than that of cellular mRNAs (represented by beta-actin). HSV-2 (strain 186) inoculation into the vagina of female guinea pigs causes severe symptoms in the genital area and high mortality. Topically applied 2-5A trimer almost completely prevented the lethal effect of HSV-2. These data are discussed from the viewpoint of mechanism of interferon action.

Induction of the 2-5A system by interferon and transmissible gastroenteritis virus

Interferon (IFN) treatment increased the level of 2',5'-oligoadenylate (2-5A) synthetase and inhibited replication of transmissible gastroenteritis virus (TGEV) in cultured swine testicular cells. Despite a minimal increase in TGEV titer in IFN-treated swine testicular cells, there was rapid cellular destruction. IFN-treated swine testicular cells had detectable levels of 2-5A (3.6 nM 6 h post-infection) after infection with 30 pfu TGEV/cell. Infection of neonatal pigs with a virulent strain of TGEV caused a significant increase in serum IFN and enterocyte 2-5A synthetase activity, as compared to control pigs. The level of enterocyte 2-5A synthetase in TGEV-infected pigs was increased 25-fold before viral-induced damage of the intestine consistently was present. 2-5A was not detected in enterocytes of either TGEV-infected or control pigs (less than 0.5 nM). Preparations of enterocytes contained two subpopulations of cells, one of which does not support replication of the virus. The considerable dilution of TGEV-infected cells (villous enterocytes) with uninfected cells (crypt cells) may be responsible for our inability to detect 2-5A in enterocytes from TGEV-infected pigs. These results indicate that the 2-5A system in porcine enterocytes and cultured testicular cells is modulated by TGEV infection and/or interaction with IFN.