Interferon action: inhibition of vesicular stomatitis virus RNA synthesis induced by virion-bound polymerase

Hydrodilatation with corticosteroids is the most effective conservative management for frozen shoulder

PURPOSE

The purpose of this overview is to summarise the findings of meta-analyses of randomised controlled trials that compare conservative treatment options for frozen shoulder.

METHODS

The authors conducted an electronic literature search for meta-analyses published using PubMed, Web of Science and the Cochrane Library. Two researchers independently applied selection criteria and assessed quality of meta-analyses using A MeaSurement Tool to Assess systematic Reviews (AMSTAR-2). Short-, medium- and long-term outcomes were synthesised narratively.

RESULTS

A total of 319 studies were identified, of which 8 meta-analyses were eligible for inclusion. All included meta-analyses were judged to be low or critically low quality according to AMSTAR-2, however, their data synthesis and interpretation was considered valid. Physiotherapy, intra-articular and subacromial corticosteroid injection (CSI), and arthrographic distension/hydrodilatation with corticosteroid were reported with sufficient evidence. Intra-articular CSI and arthrographic distension/hydrodilatation with corticosteroid provide advantages over placebo in short-term pain relief, range of motion (ROM) and shoulder function, with improvements in ROM continuing into the medium and long term. Arthrographic distension/hydrodilatation with corticosteroid provides medium-term and long-term improvements in ROM over intra-articular CSI and physiotherapy. Proprioceptive neuromuscular facilitation provides advantages over conventional physiotherapy for pain improvement and external rotation in the short term.

CONCLUSIONS

Arthrographic distension/hydrodilatation with corticosteroid provides superior pain relief in the short term and improvement in range of motion across all time frames for frozen shoulder when compared to CSI or physiotherapy.

LEVEL OF EVIDENCE

Level IV.

Herpes Simplex Virus Type 2 Inhibits Type I IFN Signaling Mediated by the Novel E3 Ubiquitin Protein Ligase Activity of Viral Protein ICP22

Type I IFNs play an important role in innate immunity against viral infections by inducing the expression of IFN-stimulated genes (ISGs), which encode effectors with various antiviral functions. We and others previously reported that HSV type 2 (HSV-2) inhibits the synthesis of type I IFNs, but how HSV-2 suppresses IFN-mediated signaling is less understood. In the current study, after the demonstration of HSV-2 replication resistance to IFN-β treatment in human epithelial cells, we reveal that HSV-2 and the viral protein ICP22 significantly decrease the expression of ISG54 at both mRNA and protein levels. Likewise, us1 del HSV-2 (ICP22-deficient HSV-2) replication is more sensitive to IFN-β treatment, indicating that ICP22 is a vital viral protein responsible for the inhibition of type I IFN-mediated signaling. In addition, overexpression of HSV-2 ICP22 inhibits the expression of STAT1, STAT2, and IFN regulatory factor 9 (IRF9), resulting in the blockade of ISG factor 3 (ISGF3) nuclear translocation, and mechanistically, this is due to ICP22-induced ubiquitination of STAT1, STAT2, and IRF9. HSV-2 ICP22 appears to interact with STAT1, STAT2, IRF9, and several other ubiquitinated proteins. Following further biochemical study, we show that HSV-2 ICP22 functions as an E3 ubiquitin protein ligase to induce the formation of polyubiquitin chains. Taken together, we demonstrate that HSV-2 interferes with type I IFN-mediated signaling by degrading the proteins of ISGF3, and we identify HSV-2 ICP22 as a novel E3 ubiquitin protein ligase to induce the degradation of ISGF3. Findings in this study highlight a new mechanism by which HSV-2 circumvents the host antiviral responses through a viral E3 ubiquitin protein ligase.

Interferon-γ Inhibits Ebola Virus Infection

Ebola virus outbreaks, such as the 2014 Makona epidemic in West Africa, are episodic and deadly. Filovirus antivirals are currently not clinically available. Our findings suggest interferon gamma, an FDA-approved drug, may serve as a novel and effective prophylactic or treatment option. Using mouse-adapted Ebola virus, we found that murine interferon gamma administered 24 hours before or after infection robustly protects lethally-challenged mice and reduces morbidity and serum viral titers. Furthermore, we demonstrated that interferon gamma profoundly inhibits Ebola virus infection of macrophages, an early cellular target of infection. As early as six hours following in vitro infection, Ebola virus RNA levels in interferon gamma-treated macrophages were lower than in infected, untreated cells. Addition of the protein synthesis inhibitor, cycloheximide, to interferon gamma-treated macrophages did not further reduce viral RNA levels, suggesting that interferon gamma blocks life cycle events that require protein synthesis such as virus replication. Microarray studies with interferon gamma-treated human macrophages identified more than 160 interferon-stimulated genes. Ectopic expression of a select group of these genes inhibited Ebola virus infection. These studies provide new potential avenues for antiviral targeting as these genes that have not previously appreciated to inhibit negative strand RNA viruses and specifically Ebola virus infection. As treatment of interferon gamma robustly protects mice from lethal Ebola virus infection, we propose that interferon gamma should be further evaluated for its efficacy as a prophylactic and/or therapeutic strategy against filoviruses. Use of this FDA-approved drug could rapidly be deployed during future outbreaks.

Filovirus outbreaks occur sporadically, but with increasing frequency. With no current approved filovirus therapeutics, the 2014 Makona Ebola virus epidemic in Guinea, Sierra Leone and Liberia emphasizes the need for effective treatments against this highly pathogenic family of viruses. The use of this FDA-approved drug to inhibit Ebola virus infection would allow rapid implementation of a novel antiviral therapy for future crises. Interferon gamma elicits an antiviral state in antigen-presenting cells and stimulates cellular immune responses. We demonstrate that interferon gamma profoundly inhibits Ebola virus infection of macrophages, which are early cellular targets of Ebola virus. We also identify novel interferon gamma-stimulated genes in human macrophage populations that have not been previously appreciated to inhibit filoviruses or other negative strand RNA viruses. Finally and most importantly, we show that interferon gamma given 24 hours prior to or after virus infection protects mice from lethal Ebola virus challenge, suggesting that this drug may serve as an effective prophylactic and/or therapeutic strategy against this deadly virus.

Interplay between innate immunity and negative-strand RNA viruses: towards a rational model

The discovery of a new class of cytosolic receptors recognizing viral RNA, called the RIG-like receptors (RLRs), has revolutionized our understanding of the interplay between viruses and host cells. A tremendous amount of work has been accumulating to decipher the RNA moieties required for an RLR agonist, the signal transduction pathway leading to activation of the innate immunity orchestrated by type I interferon (IFN), the cellular and viral regulators of this pathway, and the viral inhibitors of the innate immune response. Previous reviews have focused on the RLR signaling pathway and on the negative regulation of the interferon response by viral proteins. The focus of this review is to put this knowledge in the context of the virus replication cycle within a cell. Likewise, there has been an expansion of knowledge about the role of innate immunity in the pathophysiology of viral infection. As a consequence, some discrepancies have arisen between the current models of cell-intrinsic innate immunity and current knowledge of virus biology. This holds particularly true for the nonsegmented negative-strand viruses (Mononegavirales), which paradoxically have been largely used to build presently available models. The aim of this review is to bridge the gap between the virology and innate immunity to favor the rational building of a relevant model(s) describing the interplay between Mononegavirales and the innate immune system.

Antiviral effect of a synthetic brassinosteroid on the replication of vesicular stomatitis virus in Vero cells

The antiviral mode of action of the synthetic brassinosteroid (22S,23S)-3beta-bromo-5alpha,22,23-trihydroxystigmastan-6-one (6b) against replication of vesicular stomatitis virus (VSV) in Vero cells was investigated. Time-related experiments showed that 6b mainly affects a late event of the virus growth cycle. Virus adsorption, internalisation and early RNA synthesis are not the target of the inhibitory action. Results obtained indicate that the antiviral compound adversely affects virus protein synthesis and viral mature particle formation.

Herpes simplex virus ICP0 mutants are hypersensitive to interferon

Interferon (IFN) is an important immune system molecule capable of inducing an antiviral state within cells. Herpes simplex virus type 1 (HSV-1) replication is somewhat reduced in tissue culture in the presence of IFN, presumably due to decreased viral transcription. Here, we show mutations that inactivate immediate-early (IE) gene product ICP0 render HSV-1 exquisitely sensitive to IFN inhibition, resulting in greatly decreased levels of viral mRNA transcripts and the resulting polypeptides and a severe reduction in plaque formation ability. Mutations in other HSV-1 genes, including the genes coding for virion transactivator VP16 and the virion host shutoff protein vhs, IE gene ICP22, and the protein kinase UL13 gene, do not increase the IFN sensitivity of HSV-1. Interestingly, ICP0 mutants demonstrate the same level of sensitivity to IFN as wild-type virus on U2OS cells, an osteosarcoma cell line that is known to complement mutations in ICP0 and VP16. Thus, in some cell types, functional ICP0 is required for HSV-1 to efficiently bypass the inhibitory effects of IFN in order to ensure its replication. The significance of this link between ICP0 and IFN resistance is discussed.

Possible involvement of the double-stranded RNA-binding core protein sigmaA in the resistance of avian reovirus to interferon

Treatment of primary cultures of chicken embryo fibroblasts with a recombinant chicken alpha/beta interferon (rcIFN) induces an antiviral state that causes a strong inhibition of vaccinia virus and vesicular stomatitis virus replication but has no effect on avian reovirus S1133 replication. The fact that avian reovirus polypeptides are synthesized normally in rcIFN-treated cells prompted us to investigate whether this virus expresses factors that interfere with the activation and/or the activity of the IFN-induced, double-stranded RNA (dsRNA)-dependent enzymes. Our results demonstrate that extracts of avian-reovirus-infected cells, but not those of uninfected cells, are able to relieve the translation-inhibitory activity of dsRNA in reticulocyte lysates, by blocking the activation of the dsRNA-dependent enzymes. In addition, our results show that protein sigmaA, an S1133 core polypeptide, binds to dsRNA in an irreversible manner and that clearing this protein from extracts of infected cells abolishes their protranslational capacity. Taken together, our results raise the interesting possibility that protein sigmaA antagonizes the IFN-induced cellular response against avian reovirus by blocking the intracellular activation of enzyme pathways dependent on dsRNA, as has been suggested for several other viral dsRNA-binding proteins.

Effect of combined alpha IFN and prostaglandin A1 treatment on vesicular stomatitis virus replication and heat shock protein synthesis in epithelial cells

The antiviral activity of prostaglandin A (PGA) and interferons (IFNs) has been widely described. In the present report, we investigated the effect of combined alpha IFN and PGA1 treatment on vesicular stomatitis virus (VSV) replication and on heat shock protein (HSP) induction in monkey epithelia cells. In uninfected cells, PGA1 caused a dose-dependent induction of HSP70, HSP90 and HSP110, while alpha IFN did not affect HSP synthesis. Alpha-IFN suppressed VSV replication dose-dependently, even when cells were treated after virus infection. VSV protein synthesis was not affected by alpha IFN, indicating a block at the level of virus assembly or maturation. PGA1 caused a dose-dependent inhibition of VSV replication, and suppressed VSV protein synthesis at concentrations which induced the synthesis of high levels of HSP70. The combined treatment with low doses of alpha IFN or PGA1, which only moderately inhibited VSV replication when administered separately, was found to suppress VSV production by more than 95%, and resulted in a 3-fold increase of HSP70 synthesis as compared to PGA1 alone. These results demonstrate a co-operative effect of PGA1 and alpha IFN against VSV infection and suggest that alpha IFN can potentiate the cellular response to HSP induction in virus-infected cells.

Inhibition of human immunodeficiency virus type 1 and vaccinia virus infection by a dominant negative factor of the interferon regulatory factor family expressed in monocytic cells

ICSBP is a member of the interferon (IFN) regulatory factor (IRF) family that regulates expression of type I interferon (IFN) and IFN-regulated genes. To study the role of the IRF family in viral infection, a cDNA for the DNA-binding domain (DBD) of ICSBP was stably transfected into U937 human monocytic cells. Clones that expressed DBD exhibited a dominant negative phenotype and did not elicit antiviral activity against vesicular stomatitis virus (VSV) infection upon IFN treatment. Most notably, cells expressing DBD were refractory to infection by vaccinia virus (VV) and human immunodeficiency virus type 1 (HIV-1). The inhibition of VV infection was attributed to defective virion assembly, and that of HIV-1 to low CD4 expression and inhibition of viral transcription in DBD clones. HIV-1 and VV were found to have sequences in their regulatory regions similar to the IFN-stimulated response element (ISRE) to which IRF family proteins bind. Accordingly, these viral sequences and a cellular ISRE bound a shared factor(s) expressed in U937 cells. These observations suggest a novel host-virus relationship in which the productive infection of some viruses is regulated by the IRF-dependent transcription pathway through the ISRE.

Vesicular stomatitis virus infection induces a nuclear DNA-binding factor specific for the interferon-stimulated response element

Vesicular stomatitis virus (VSV) has a broad host range. It replicates in the cytoplasm and causes rapid cytopathic effects. We show that following VSV infection, a nuclear factor that binds to a select set of interferon-stimulated responsive elements (ISRE) is induced in many cell types. This factor, tentatively called VSV-induced binding protein (VIBP), was estimated to have an approximate molecular mass of 50 kDa and was distinct from known members of the interferon regulatory factor family, that are known to bind to the ISRE. Induction of VIBP required tyrosine kinase activity but did not require cellular transcription. Treatment of cells with cycloheximide, which inhibits translation, only partially inhibited induction of VIBP. However, type I interferons and staurosporine, both of which inhibit VSV transcription, inhibited VIBP induction. Moreover, a double-stranded RNA analog, poly(I)-poly(C) also induced a DNA-binding activity very similar to that of VIBP. These results indicate that a preexisting cellular protein is activated upon VSV infection and that this activation requires primary viral transcripts. The functional activity of VIBP was analyzed in cells stably transfected with a herpesvirus thymidine kinase-luciferase reporter gene that is under control of the ISRE. While activity of the control promoter without ISRE was strongly inhibited following VSV infection (as a result of virus-mediated transcriptional shutdown of the host cell), the inhibition was reversed by the ISRE-containing promoter, albeit partially, which suggests that VSV infection differentially affects transcription of host genes. Although VIBP was induced in all other cells tested, it was not induced in embryonal carcinoma cells after VSV infection, suggesting developmental regulation of VIBP inducibility.

Mechanisms of viral inhibition by interferons

Interferons (IFNs) are a family of related proteins grouped in four species (alpha, beta, gamma and omega) according to their cellular origin, inducing agents and antigenic and functional properties. Their binding to specific receptors leads to the activation of signal transduction pathways that stimulate a defined set of genes, whose products are eventually responsible for the IFN antiviral effects. Their action against viruses is a complex phenomenon. It has been reported that IFNs restrict virus growth at the levels of penetration, uncoating, synthesis of mRNA, protein synthesis and assembly. This review will attempt to evaluate evidence of the involvement of the IFN-inducible proteins in the expression of the antiviral state against RNA or DNA viruses.

Interferon treatment reduces endocytosis of virus and facultatively intracellular bacteria in various cell lines

Previous studies have shown that interferons (IFNs) specifically interact with a number of cells cultured in vitro and reduce the invasiveness of facultatively intracellular bacteria. IFN treatment also reduced the internalization of vesicular stomatitis virus (VSV) in cell cultures. Here we show that the anti-invasive effect of IFN on bacteria is eliminated in an L-cell variant where its effect on the uptake of vesicular stomatitis virus is lost. The data strongly suggest that the anti-invasive effect of IFN is mediated through inhibition of endocytosis.

Inhibition of vesicular stomatitis viral mRNA synthesis by interferons

Interferon (IFN) treatment inhibited the replication of vesicular stomatitis virus (VSV) in human GM2767 and mouse JLSV-11 cells. The replication of this virus in either human RD-114 or mouse A402 cells was insensitive to IFN treatment. We analyzed various steps in the VSV life cycle as they occurred under different conditions of IFN treatment to identify the point(s) at which IFN was exerting its inhibitory effect. IFN treatment led to strong inhibition of viral protein synthesis and accumulation of viral RNA in both lines of IFN-sensitive cells. No such effect was observed in the IFN-resistant cells. Using a temperature-sensitive mutant (tsG41) and wild-type VSV that were not undergoing protein synthesis, we determined that the major site of action of IFN against VSV replication in JLSV-11 and GM2767 cells was at the level of primary viral transcription. The accumulation of primary viral transcripts was strongly inhibited in these cells by IFN treatment. This effect was not a consequence of any effect of IFN on virus entry and uncoating. Thus, it appears that IFN exerts a direct effect on the VSV transcriptional process in GM2767 and JLSV-11 cells.

The mechanism of the antiviral effect of interferon differs in two strains of a rabbit kidney cell line

Two variant strains of a rabbit kidney cell line, RK-13, differ markedly in their interferon (IFN)-mediated antiviral mechanism. Both strains are permissive for the growth of vesicular stomatitis (VSV) and vaccinia viruses. Following treatment with 100 U/ml of rabbit IFN, both cell strains restrict VSV yield about a 1000-fold; vaccinia is not inhibited by IFN in either cell strain. However, vaccinia is able to rescue VSV from the inhibitory effects of IFN in one strain (RK-13), but not in the other strain of cells (RK-13-37). Investigation of the mechanism of this phenomenon reveals that VSV growth is blocked at different levels in the two cell strains. In the strain in which vaccinia can rescue VSV from the effects of IFN (RK-13), the major IFN-mediated restriction of VSV growth is at the level of protein synthesis; in the other strain in which vaccinia is unable to rescue VSV (RK-13-37), IFN restricts VSV at earlier steps, including penetration and primary transcription. The two cell strains provide useful models for studying the multifaceted nature of IFN-mediated antiviral effects.

The requirement of protein synthesis for VSV inhibition of host cell RNA synthesis

Published ultraviolet (uv) inactivation data and in vitro transcription studies have suggested that vesicular stomatitis virus (VSV) leader RNA was solely responsible for the inhibition of host cell RNA synthesis by this virus. Since no protein product is encoded in leader RNA, this conclusion implied that no protein synthesis should be required for this effect. Therefore, the inhibitory activity of VSV was examined in the presence of the protein synthesis inhibitors, cycloheximide, pactamycin, and emetine. Protein synthesis inhibitors are known not to interfere with VSV primary transcription, but in their presence viral replication and amplification of transcription do not take place. Although at 39 degrees the VSV mutant tsG22 could undergo only primary transcription, maximum inhibition of host cell RNA synthesis took place. However, in the presence of the protein synthesis inhibitors the VSV mutant was no longer able to interfere with host cell RNA synthesis. These results could not be explained by a change in the concentration of intracellular leader RNA which remained unaltered by the drugs. Similar results were also obtained with wild-type VSV in the presence of cycloheximide. Upon removal of the drug, inhibition of host cell RNA synthesis was reestablished in parallel with the restoration of protein synthesis. It is concluded that protein synthesis is required for the inhibitory activity of VSV, presumably because the active inhibitory complex is a nucleoprotein containing leader RNA and either a cellular protein or the viral N protein. The cellular protein would have to be in limiting supply since de novo protein synthesis was required for the inhibition to take place.

Interferon induction by viruses. XIV. Development of interferon inducibility and its inhibition in chick embryo cells "aged" in vitro

Studies with a number of viruses revealed a time-dependent acquisition of interferon (IFN) inducibility in primary chick embryo cells as they "aged" in vitro for 2-12 days at a confluent cell density without a medium change. The time-course for the development of IFN inducibility was established by generating and analyzing a family of dose (multiplicity)-response (IFN yield) curves, using Newcastle disease virus (NDV, strain LaSota) as the inducer. Cells produced little or no IFN for the first 4-5 days. Between 5 and 6 days the cells gradually developed the capacity to respond to NDV (and other viruses). Maximal yields of IFN were inducible by day 10. This time-dependent development of IFN inducibility was abrogated almost completely when "aging" was carried out in the presence of drugs that inhibited the synthesis of cyclic derivatives of C20 oxygenated unsaturated fatty acids, i.e., inhibitors of prostaglandin/leukotriene synthesis and the arachidonic acid cascade. Of the prostaglandin synthesis inhibitors, indomethacin was particularly effective. Cells treated on day 0 with 10 micrograms/ml of indomethacin produced 100- to 1000-fold less IFN than controls when induced on day 8. To prevent maximally the development of IFN inducibility, indomethacin must be added within the first 2 days of seeding. After about 2 days, the cells begin to escape the action of the drug. Indomethacin added at the time of induction had no effect on the yield of IFN. IFN inducibility was partially restored when indomethacin was removed during the aging process. "Aging" chick cells in low concentrations of cycloheximide (0.5 micrograms/ml) produced results comparable to incubation with indomethacin. Neither reagent had any marked effect on the rate of total protein or RNA synthesis, nor did their action prevent the induction of stress (heat shock) proteins. Cells "aged" in indomethacin were threefold less efficient in responding to the action of IFN, whereas aging in cycloheximide had no effect on IFN's action. Plaque formation on drug-treated cells was normal for viruses that were poor inducers of IFN. However, both the plaquing efficiency and plaque size of Sindbis virus (an excellent IFN inducer) were enhanced markedly on cells treated with indomethacin or low concentrations of cycloheximide during the aging process. These data implicate a family of fatty acid derivatives of arachadonic acid, including prostaglandins and leukotrienes, in the development of IFN inducibility in primary chick embryo cells "aged" in vitro.

Characterization of La Crosse virus small-genome transcripts

With restriction fragments from DNA clones of the La Crosse virus S genome segment, the 3' end of the S mRNA was located by S1 nuclease mapping near a polyuridine tract, approximately 100 nucleotides, from the end of the S genome. Genome replication in La Crosse virus-infected cells was abolished by the drug cycloheximide, similar to other negative-strand RNA viruses. However, the synthesis of S mRNA could not be detected in cells pretreated with cycloheximide, suggesting that ongoing protein synthesis is required for La Crosse virus genome transcription and replication. Primer extension experiments in the presence of chain-terminating nucleoside triphosphates demonstrated that the 5' end of the La Crosse virus S mRNA begins 10 to 14 nucleotides before the 3' end of the S genome segment, suggesting that the La Crosse virus S mRNA is initiated on a host primer. A hypothesis consistent with these unexpected findings is presented.

Vaccinia rescue of VSV from interferon-induced resistance: reversal of translation block and inhibition of protein kinase activity

Coinfection with vaccinia virus rescues vesicular stomatitis virus (VSV) from the inhibitory effects of interferon (IFN) in mouse L cells. While vaccinia infection does not significantly affect VSV RNA synthesis, coinfection with vaccinia dramatically increases VSV protein synthesis in IFN-treated cells. Evidence is provided that vaccinia inhibits the activity of the IFN-induced dsRNA-dependent protein kinase.

Identification of four complementary RNA species in Akabane virus-infected cells

The analysis of RNA extracted from purified Akabane virus demonstrated the presence of three size classes of single-stranded RNAs with sedimentation coefficients of 31S (large, L), 26S (medium, M), and 13S (small, S). Molecular weights of these RNA species were estimated to be 2.15 X 10(6), 1.5 X 10(6), and 0.48 X 10(6) for the L, M, and S RNAs, respectively. Hybridization analysis involving viral genomic RNA and RNA from virus-infected cells resulted in the identification of four virus-specific cRNA species in infected cells. These cRNAs were found to be nonpolyadenylated by their inability to bind to oligodeoxythymidylate-cellulose. Kinetic analysis of cRNA synthesis in infected cells at various times postinfection suggested that cRNA synthesis could be detected as early as 2 h postinfection and that maximal synthesis occurred at 4 to 6 h postinfection. The RNAs synthesized in infected cells could be partially resolved by sucrose density gradient centrifugation. The RNA fraction that cosedimented with the S segment of viral genomic RNA yielded two duplex RNA species when hybridized with viral genomic RNA, suggesting the presence of two small cRNA species. Specific hybridization with individual viral genomic RNAs confirmed that two species of cRNA are coded by the S RNA segment. Analysis of cRNA synthesis in the presence of the protein synthesis inhibitors cycloheximide and puromycin indicated that cycloheximide completely inhibited virus-specific RNA synthesis early and late in infection, whereas a very low level of synthesis occurred in the presence of puromycin. The inhibitory effects of these drugs were found to be reversible when the drugs were washed from the cells. It is concluded that continued protein synthesis is required for cRNA synthesis to proceed in Akabane virus-infected cells.

Interferon-mediated inhibition of virus penetration

Pretreatment of mouse L cells with mouse interferon (IFN) inhibits the penetration of vesicular stomatitis virus without affecting viral adsorption. The inhibition of virus uptake by IFN is dose dependent and, at the highest dose tested (1,000 units/ml), reaches 65%; 24 hr of treatment with IFN are required for maximal effect. A similar inhibition of uptake of virus occurs in human diploid fibroblasts and primary chicken embryo fibroblasts treated with homologous IFN. No significant inhibition occurs when cells are treated with heterologous IFN. These results document a previously unrecognized antiviral effect of IFN--namely, inhibition at the level of viral uptake.

Interference among defective interfering particles of vesicular stomatitis virus

Three defective interfering (DI) particles of vesicular stomatitis virus (VSV), all derived from the same parental standard San Juan strain (Indiana serotype), were used in various combinations to infect cells together with the parental virus. The replication of their RNA genomes in the presence of other competing genomes was described by the hierarchical sequence: DI 0.52 particles greater than DI 0.45 particles less than or equal to DI-T particles greater than standard VSV. The advantage of one DI particle over another was not due simply to multiplicity effects nor to the irreversible occupation of limited cellular sites. Interference, however, did correlate with a change in the ratio of plus and minus RNA templates that accumulated intracellularly and with the presence of new sequences at the 3' end of the DI genomes. DI 0.52 particles contained significantly more nucleotides at the 3' end that were complementary to those at the 5' end of its RNA than did DI-T or DI 0.45 particles. The first 45 nucleotides at the 3' ends of all of the DI RNAs were identical. VSV and its DI particles can be separated into three classes, depending on their terminal RNA sequences. These sequences suggest two mechanisms, one based on the affinity of polymerase binding and the other on the affinity of N-protein binding, that may account for interference by DI particles against standard VSV and among DI particles themselves.

Differential effect of interferon on DNA synthesis, 2-deoxyglucose uptake and ornithine decarboxylase activity in 3T3 cells stimulated by polypeptide growth factors and tumor promotors

Quiescent 3T3 cells can be stimulated to enter S by defined factors. When used in combination, three polypeptide hormones (EGF, vasopressin, and insulin), or a tumor promotor and insulin, are very effective in stimulating DNA synthesis. Like serum, the defined factors also stimulate deoxyglucose uptake and induce the synthesis of ornithine decarboxylase during G1. The second stage of deoxyglucose uptake and the induction of ornithine decarboxylase are protein synthesis-dependent events. When added with the growth factors, mouse interferon inhibits the synthesis of DNA and the induction of ornithine decarboxylase but has no effect on the uptake of deoxyglucose. Kinetic experiments comparing the effect of inhibitors of translation or transcription on induction of ornithine decarboxylase with the effect of interferon suggest that interferon may affect the synthesis of enzyme by inhibiting both transcription and translation of message. The findings provide further support for the proposition that interferon exerts a differential effect on mitogen-stimulated events events which are dependent on continuous protein synthesis.

Interferon-treated cells release vesicular stomatitis virus particles lacking glycoprotein spikes: correlation with biochemical data

Earlier we reported a reduction to 1/30th-1/100th of the original number of infectious particles in the infectious vesicular stomatitis virus (VSV) released from L cells treated with 10 or 30 reference units of interferon per ml. However, in these cultures virus particle production, as measured by VSV particle-associated viral RNA, virus nucleocapsid protein, and viral transcriptase, was inhibited by less than 10%. Data reported in this paper show that there was a significant reduction in glycoprotein and membrane protein of VSV particles released from interferon-treated cells. Evidence supporting the deficiency of glycoprotein in VSV released from interferon-treated cells was derived from electron microscopic studies. Under conditions where glycoprotein spikes or projections were clearly detectable on the surface of VSV released from cells not treated with interferon, very few spikes were observed on VSV released from interferon-treated cells. These results suggested that interferon-treated cells produced VSV particles with low infectivity and that this low infectivity may be related to the reduced amount of glycoprotein and membrane protein incorporated into such particles.

Selective inhibition of glycoprotein and membrane protein of vesicular stomatitis virus from interferon-treated cells

A 200-fold inhibition in the titer of infectious vesicular stomatitis virus (VSV) was produced in cultures of Ly cells treated with 30 reference units of interferon per milliliter. Virus particle production, as measured by VSV particle-associated transcriptase, or nucleocapsid protein was inhibited by a maximum of tenfold. The glycoprotein and membrane protein content was reduced in VSV derived from interferon-treated cells. Thus interferon-treated cells may have produced VSV particles with low infectivity, which may be related to the reduced amount of glycoprotein incorporated into such particles. These findings resemble those reported in interferon-treated cells infected with murine leukemia viruses.

The effect of interferon on de novo infection of Moloney murine leukemia virus

The mode of action of interferon in de novo Moloney murine leukemia virus (Mo-MuLV) infection of mouse bone marrow/thymus (TB) cells was studied. Our results indicate that in interferon-treated cells, there is approximately a 2000 fold decrease in the production of infectious MuLV, but only a 10-20 fold decrease in the level of viral specific extracellular reverse transcriptase activity, and only about a 2 fold difference in the number of virus particles observed on the cell membrane as determined by scanning electron microscopic (SEM) studies. Transmission electron microscopic (TEM) studies showed that the proportion of early budding virions, which have shallow crescent-shaped ribonucleoprotein cores (Figure 3A), to virions in later stages of assembly (Figures 3B-3D) is relatively higher in interferon-treated cells than in the untreated controls. From a temperature shift-down experiment on a temperature-sensitive mutant of MuLV, ts 3, which produces viral particles that fail to dissociate from the cell surface at the nonpermissive temperature, we demonstrated that ts 3 virions partially assembled on the cell membrane prior to the addition of interferon are able to complete assembly and to dissociate from the cell membrane on temperature shift-down in the presence of interferon action. Our data suggest that interferon neither inhibits the late stages of virion assembly at which ts 3 virions are arrested at the nonpermissive temperature nor prevents release of the virions. Our findings also indicate that in interferon-treated cells, most of the extracellular virions are noninfectious.