Virus-specific effects of interferon in embryonal carcinoma cells

Disinfection procedures for controlling microorganisms in the semen and embryos of humans and farm animals

Semen and embryos generated by assisted reproductive techniques (ARTs) may be contaminated with numerous microorganisms. Contamination may arise from systemic or local reproductive tract infections in donors or the inadvertent introduction of microorganisms during ARTs, and may lead to disease transmission. This review describes sanitary procedures which have been investigated to ascertain whether they are effective in rendering semen and embryos free of pathogenic microorganisms, including internationally adopted washing procedures, which can be supplemented by antibiotics and enzymatic treatments. Other methods include treatment with antibodies or ozone, photoinactivation, acidification, and the use of novel antiviral compounds. In conclusion, despite the wide range of antimicrobial procedures available, none can be recommended as a universal disinfection method for rendering semen and embryos free from all potentially pathogenic microorganisms. However, some procedures are unsuitable, as they can compromise the viability of semen or embryos. In humans, washing by the gradient centrifugation method appears to be effective for reducing the microbial population in semen and is harmless to the spermatozoa. A useful procedure for embryos involving multiple washes in sterile medium has much to commend it for the prevention of disease transmission; furthermore, it is recommended by the International Embryo Transfer Society (IETS).

Oncolytic viruses in cancer therapy

Oncolytic virotherapy is a promising form of gene therapy for cancer, employing nature’s own agents to find and destroy malignant cells. The purpose of this review is to provide an introduction to this very topical field of research and to point out some of the current observations, insights and ideas circulating in the literature. We have strived to acknowledge as many different oncolytic viruses as possible to give a broader picture of targeting cancer using viruses. Some of the newest additions to the panel of oncolytic viruses include the avian adenovirus, foamy virus, myxoma virus, yaba-like disease virus, echovirus type 1, bovine herpesvirus 4, Saimiri virus, feline panleukopenia virus, Sendai virus and the non-human coronaviruses. Although promising, virotherapy still faces many obstacles that need to be addressed, including the emergence of virus-resistant tumor cells.

The role of tumor necrosis factor in viral disease

Tumor Necrosis Factor (TNF) is one of the many cytokines that comprise a complex intertwined network of biological response modifiers that takes on extreme significance as the host response to infectious diseases. Soluble factors such as Interleukin-2 and Interferon-gamma released by T cells and Interleukin-1, Interleukin-6 and TNF released by monocytes have been shown to play key roles in proliferation, activation and differentiation of immune cells. It has also become evident that development of treatment modalities for infectious diseases is complicated by the complexity of this cytokine network. In the last decade numerous reports have presented data, often conflicting, which clearly demonstrate a role for TNF in the response to infections caused by viruses. This review summarizes this rapidly growing volume of data, discussing consistencies and discrepancies as appropriate. By better understanding the role of TNF in the host immune response, it may be possible to modulate this complex network for the benefit of the host in its battle against viral infection.

Differentiation-dependent activation of interferon-stimulated gene factors and transcription factor NF-kappa B in mouse embryonal carcinoma cells

We have recently shown that the adenovirus E1A gene products block interferon-alpha-induced signal transduction and transcription factor NF-kappa B-mediated gene induction. Here we report that the same responses are also blocked in undifferentiated F9 teratocarcinoma cells. The block was removed upon cellular differentiation and regained upon the introduction of viral E1A into the differentiated cells. In undifferentiated cells, interferon-beta failed to induce the transcription of interferon-responsive genes because of a lack of activation of the cognate trans-acting factors. As a result, in these cells, virus replication was not inhibited by interferon. Similarly, in undifferentiated but not in differentiated F9 cells, tumor necrosis factor alpha failed to stimulate NF-kappa B-mediated transcription of a reporter gene because of a failure in the activation of NF-kappa B trans-acting factor. These results suggest that a cellular E1A-like activity, present in undifferentiated F9 cells, and adenoviral E1A use similar mechanisms for repressing the expression of specific cellular genes.

Virus-specific effects of recombinant porcine interferon-gamma and the induction of Mx proteins in pig cells

Interferon-alpha (IFN-alpha) and -gamma differed in their action against influenza virus and vesicular stomatitis virus (VSV) on pig cells. Recombinant IFN-alpha severely impaired the cytopathic effect of VSV on PK-15 cells, whereas recombinant porcine IFN-gamma did not. IFN-alpha impaired also the replication of VSV and of influenza virus in primary pig kidney cells in contrast to IFN-gamma, which failed to induce an efficient antiviral state against both viruses. Otherwise, the IFN system seemed to work properly in pig cells since both IFN-alpha and IFN-gamma induced an efficient antiviral state to mengovirus. The establishment of the antiviral state to VSV and influenza virus correlated with the induction of two cytoplasmic proteins related to the murine Mx protein involved in the selective resistance of mice to influenza virus infection. The results are discussed in the context of the susceptibility of pigs to influenza virus strains that are in circulation in birds and in humans.

A full-length murine 2-5A synthetase cDNA transfected in NIH-3T3 cells impairs EMCV but not VSV replication

Treatment of cells with interferons (IFNs) induces resistance to virus infection. The 2'-5'oligo A (2-5A) synthetase/RNase L is one of the pathways leading to translation inhibition induced by IFN treatment. A murine cDNA encoding the 43-kDa 2-5A synthetase was cloned and sequenced. NIH-3T3 cell clones transfected with this cDNA expressed the enzymatic activity to various extents and exhibited resistance to encephalomyocarditis virus (EMCV) but not to vesicular stomatitis virus replication. The specific resistance to EMCV can be attributed to 2-5A synthetase.

Constitutive expression of a 2',5'-oligoadenylate synthetase cDNA results in increased antiviral activity and growth suppression

The interferon (IFN)-induced enzyme 2',5'-oligoadenylate (2-5A) synthetase has been implicated in the development of antiviral activity in human and animal cells. However, its role in IFN-mediated growth inhibition remains unclear. To elucidate the function of 2-5A synthetase, we have stably introduced a human 2-5A synthetase cDNA into a human glioblastoma cell line (T98G). Constitutive expression of the cDNA in these cells is associated with increased levels of resistance to infection by encephalomyocarditis virus. One transfected subclone, which expresses elevated levels of 2-5A synthetase enzyme activity, also shows a reduced rate of cellular proliferation.

Effect of natural human interferon-beta on the replication of human cytomegalovirus

The antiviral effect of natural human interferon-beta (HuIFN-beta) against human cytomegalovirus (CMV) was evaluated in human embryonic lung fibroblasts (HEL). Natural HuIFN-beta, like other HuIFNs, inhibited the replication of CMV. Pretreatment of the cells with natural HuIFN-beta inhibited the appearance of immediate-early antigen (IEA) or pre-early nuclear antigen (PENA) as well as the production of infectious CMV. After a single treatment with natural HuIFN-beta, intracellular 2', 5'-oligoadenylate (2-5A) synthetase activity was induced and maintained at a high level for several days. The anti-CMV effect of natural HuIFN-beta correlated with the intracellular 2-5A synthetase activity.

Effect of recombinant murine interferon-beta on the replication of murine cytomegalovirus

Pretreatment of mouse embryo fibroblasts (MEF) with recombinant murine interferon-beta (rMuIFN-beta) induced a high level of intracellular 2',5'-oligoadenylate (2-5A) synthetase activity. However, murine cytomegalovirus (MCMV) replicated under such condition, indicating that MCMV is relatively insensitive in vitro to rMuIFN-beta. Thus, there was a dissociation of 2-5A synthetase activity and antiviral activity against MCMV. In contrast to MCMV, the two parameters were closely associated in the case of vesicular stomatitis virus (VSV).

Studies on the role of the 2'-5'-oligoadenylate synthetase-RNase L pathway in beta interferon-mediated inhibition of encephalomyocarditis virus replication

Interferons inhibit the replication of vesicular stomatitis virus (VSV), but not of encephalomyocarditis virus (EMCV), in mouse JLSV-11 cells. We report the isolation of clonal derivatives from this cell line in which the replication of both viruses is impaired by interferons. These clones were selected from the parental line by virtue of their rescue by interferon treatment from the cytopathic effects of EMCV infection. In one such clone, RK8, the replication of VSV and EMCV and the production of resident murine leukemia virus were inhibited by interferon. On the other hand, in clone RK6, which was isolated without any selection, the replication of VSV, but not of EMCV, was impaired by interferons. The levels of 2'-5'-oligoadenylate synthetase mRNA and enzyme activity were similarly elevated upon interferon treatment in the two clones. However, the level of RNase L, as determined by binding and cross-linking of a radiolabeled 2'-5'-oligoadenylate derivative, was much lower in RK6 cells than in RK8 cells. In accord with this observation, the introduction of 2'-5'-oligoadenylates into cells inhibited protein synthesis much less strongly in RK6 cells than in RK8 cells. These results are consistent with the notion that the 2'-5'-oligoadenylate-dependent RNase L may be a mediator of the inhibition of EMCV replication by interferons.

Failure to induce an antiviral state in preimplantation bovine embryos treated with interferon

Bovine blastocysts hatched from their zonae pellucidae were cultured for 24 h in the presence or absence of interferon and then challenged with either vesicular stomatitis virus or bluetongue virus to assess the induction of an antiviral state. In contrast to its application to fetal bovine cells, where significant antiviral effects were induced, interferon treatment of embryos failed to reduce virus yield and had no effect on virus-induced cytopathology. This lack of biologic activity of interferon in bovine embryos is similar to that previously observed with undifferentiated murine embryonal carcinoma cells and is probably a manifestation of a more general mechanism regulating gene expression in the early mammalian embryo.

Interferon inducibility and sensitivity of human teratocarcinoma-derived cell lines

Three cell lines tera I, tera II, and PA1, derived from human teratocarcinomas were tested for their capacity to produce interferon (IFN) and for their sensitivity to both human IFN-alpha and IFN-beta. When treated with Newcastle disease virus or Sendai virus, or a synthetic polyribonucleotide, poly(rI):poly(rC), tera I cells produced no IFN and the 2',5'-oligoadenylate (2-5A) synthetase enzymatic pathway was not activated, although there was an increase in protein kinase. In contrast, tera II and PA1 cells produced IFN and both enzymatic activities were detected. IFN treatment has no effect on the growth of any of the cell lines. Tera I and PA1 cells did not develop resistance to challenge with vesicular stomatitis virus or encephalomyocarditis virus, but the growth of a type-C baboon retrovirus was inhibited. Tera II cells were protected against all three viruses. It appears that human teratocarcinoma cell lines can thus differ greatly in their ability to produce IFN and to respond to it.

Bovine interferon: its biology and application in veterinary medicine

Investigations of the production and potential use of bovine interferons against viral infections have occurred since the first descriptions of interferons in other systems. The recent advent of recombinant DNA-technology has facilitated such studies and furthered our knowledge about the bovine interferon system in general. This review gives an overview of the biology, antiviral and immunomodulatory activities of bovine interferons. Areas in which the interferons are now applied or have potential application in viral diseases in cattle are described. Finally, the value of studies of the bovine interferon system with respect to comparative interferon research is discussed.

Sensitivity of human germ-cell-tumor cell lines to human interferons

We examined the sensitivity of four human germ-cell-tumor cell lines exhibiting different stages of differentiation to human interferons (IFNs) in vitro. The cell lines were derived from two embryonal carcinomas (NEC 8 and NEC 14), a choriocarcinoma (IMa), and a yolk-sac tumor (HUOT). Treatment with poly I:C induced IFN production in IMa and HUOT cells, but not in NEC-8 and NEC-14 cells. In the two embryonal-carcinoma cell lines, the addition of IFN-alpha, IFN-beta, and IFN-gamma did not prevent infection by vesicular stomatitis virus and encephalomyocarditis virus. Also, in these two lines, 2-5A synthetase was not induced by the addition of IFN-alpha. In contrast, both IMa and HUOT showed sensitivity to the antiviral action of IFN-alpha and IFN-beta against the two viruses, and 2-5A synthetase was induced by IFN-alpha. IFNs added at doses of up to 1000 IU/ml had no antiproliferative effect on NEC 8, NEC 14, and HUOT, whereas colony formation by IMa cells was greatly suppressed by all three forms of IFN. These results indicate that the production of and sensitivity to IFN are developmentally regulated and are related to the level of differentiation of human germ-cell stem cells.

Loss of (2'-5')oligoadenylate synthetase activity by production of antisense RNA results in lack of protection by interferon from viral infections

An expression vector was constructed that carries part of the human BK papovavirus with 0.5 kilobases of (2'-5')oligoadenylate (2-5A) synthetase cDNA inserted in inverted orientation downstream from the virion proteins (VP) promoter and the neomycin-resistance gene neo under the control of a simian virus 40 promoter. Cells transfected with this vector and selected for resistance to the neomycin derivative G418 synthesized RNA complementary to 2-5A synthetase mRNA. These cells lacked 2-5A synthetase activity, and the enzyme was not inducible by interferon. In contrast, 2-5A synthetase was induced in cells transfected with a control vector without the cDNA insert. Such cells were protected by interferon from RNA viruses, whereas cells lacking 2-5A synthetase were not protected from encephalomyocarditis virus, vesicular stomatitis virus, and Sindbis virus but were fully protected from influenza virus. These findings show that a high level of 2-5A synthetase is required for interferon-induced protection from the cytoplasmic RNA viruses tested.

Vaccinia-mediated rescue of encephalomyocarditis virus from the inhibitory effects of interferon

Coinfection of mouse L cells with vaccinia virus rescues encephalomyocarditis virus (EMC) from the inhibitory effect of interferon (IFN). The vaccinia-mediated rescue of EMC growth increases the yield of EMC as much as 1000-fold and is optimum when vaccinia is used at a multiplicity of infection of 1. This rescue correlates with a vaccinia-dependent stimulation of EMC gene expression. Evidence is presented to indicate that the rescue by vaccinia does not involve a block of the 2'-5'A synthetase pathway. However, the vaccinia rescue function is correlated with a vaccinia-mediated inhibition of the IFN-induced protein kinase.

Interferon-induced gene expression in wild-type and interferon-resistant human lymphoblastoid (Daudi) cells

Interferon-induced gene expression was analyzed in wild-type and interferon-resistant Daudi cells. Two classes of alpha-interferon-induced mRNAs and proteins were observed: those that were similarly induced in both types of cell and those that were induced only in the wild-type cells. Furthermore, the level of c-myc mRNA decreased in the wild-type but not in the resistant cells. This differential control in the wild-type and resistant cells indicates that there must be either functionally distinct alpha-interferon receptors or more than one pathway leading to altered gene expression triggered by a single receptor.

Effect of human alpha A interferon on influenza virus replication in MDBK cells

To determine the molecular mechanism whereby interferon induces resistance to influenza virus, we began an investigation of influenza virus replication in MDBK cells treated with recombinant human alpha A interferon. Negative- and positive-strand virus-specific RNA accumulation was monitored by blot hybridization with cloned probes. Primary transcription (transcription of infecting viral negative strands by the virion-associated polymerase) was inhibited by interferon treatment of MDBK cells. At moderate levels of interferon treatment (10 U/ml), this inhibition was restricted to transcripts of polymerase genes, whereas at higher levels of interferon treatment (50 U/ml), accumulation of all primary transcripts was markedly inhibited. Secondary transcripts and viral negative strands did not accumulate to any significant extent in interferon-treated MDBK cells. These results suggest that interferon-induced mechanisms which inhibit influenza virus replication in MDBK cells act at the level of primary transcription.

Regulation of ppp(A2'p)nA-dependent RNase levels during interferon treatment and cell differentiation

The intracellular effector oligonucleotides ppp(A2'p)nA (n = 2- greater than or equal to 4) regulate the breakdown of RNA by activating ppp(A2'p)nA-dependent RNase. Cellular levels of this RNase were demonstrated to be regulated during differentiation of murine embryonal carcinoma cells. An induction of this RNase by interferon was demonstrated in each of three differentiated cell types (F9 clone 9, PYS, and PSA 5E) by analyzing rRNA breakdown following the introduction of ppp(A2'p)nA into the intact cells. In contrast, in three undifferentiated embryonal carcinoma cell lines (F9, PC13 clone 5, and Nulli 2A) there was little if any ppp(A2'p)nA-dependent RNase either with or without interferon pretreatment. These results were confirmed by affinity labeling of the RNase in cell-free systems. Addition of the proteinase inhibitor, leupeptin, to the cell lysis buffer was necessary to stabilize the RNase against cleavage to discrete breakdown products. Moreover, during differentiation of PC13 clone 5 cells by retinoic acid and N6,O2'-dibutyryl-adenosine 3',5'-monophosphate there was a gradual induction of ppp(A2'p)nA-dependent RNase. The expression of this RNase is, therefore, greatly enhanced during cell differentiation. In addition, the double-stranded-RNA-dependent protein kinase was investigated and was found to be interferon-inducible in all of the cell lines regardless of the state of cell differentiation.

Comparative studies on (2'-5')oligoadenylate-related enzyme systems and the antiviral effect of interferon in two mouse cell lines which differ in (2'-5')oligoadenylate sensitivity of their protein synthesizing system

Effect of (2'-5')oligoadenylate (2-5A) on cellular and viral protein and RNA syntheses was investigated with two mouse cell lines, L929 and Lz (a subclone of L929). The oligonucleotide was introduced into the cells either by using calcium phosphate coprecipitation technique or by microinjection method. In L929 cells protein and viral RNA syntheses were severely inhibited by 2-5A, whereas in Lz cells, both were only slightly inhibited. The activities of 2-5A synthetase and double-stranded (ds)RNA-dependent protein kinase were enhanced by interferon (IFN) treatment roughly to the same extent and there was no significant difference in the level of 2'-5' phosphodiesterase activity either. On the other hand, 2-5A-dependent RNase (RNase L) activity in Lz cells was low, being about 10-20% of that of L929 cells. It was increased twofold after IFN treatment, but protein synthesis of Lz cells was not as sensitive to 2-5A as that of L929 cells even after IFN treatment. L929 and Lz cells were sensitive to the antiviral effect of mouse IFN against vesicular stomatitis virus (VSV) and Mengovirus. In contrast, however, Lz cells were relatively insensitive to the antiviral effect of IFN on vaccinia virus, whereas L929 cells were sensitive.

Disparate response of encephalomyocarditis virus and MM virus to interferon in JLS-V9R cells

JLS-V9R cells, a Balb/c mouse bone marrow cell line chronically infected with Rauscher leukemia virus, were treated with mouse interferon and inoculated with several different lytic viruses. Relatively low interferon concentrations protected the cells against Sindbis virus, vesicular stomatitis virus and MM virus. In contrast, encephalomyocarditis virus replication was inhibited by less than 1 log even with an interferon concentration of 1000 U/ml. These findings provide further evidence that interferon-induced antiviral effects are mediated through multiple mechanisms and demonstrate that even viruses which are classified within the same family (MM and encephalomyocarditis virus) can exhibit differential interferon sensitivities.

Effects of interferon and encephalomyocarditis virus on in vitro development of preimplantation mouse embryos with and without the zona pellucida

Development of preimplantation mouse embryos, with or without the zona pellucida, in the presence of interferon (IFN) and mouse encephalomyocarditis (EMC) virus was studied using the in vitro culture method. The embryos (2- to 8-cell stages) were obtained from superovulated mice and cultured in modified Witten's medium under paraffin oil in 5% CO2 in air at 37 degrees C. Removal of the zona pellucida does not affect the subsequent development of the embryos: 90% of embryos with and 87% of embryos without the zona pellucida reached the morula-early blastocyst stages. Mouse IFN (10(4) units/ml) had no inhibitory effect on the developmental ability of the preimplantation embryos with or without the zona pellucida: 88 and 89% of the embryos in each group, respectively, reached the morula-early blastocyst stages. The preimplantation mouse embryos were sensitive to the embryotoxic effect of EMC virus: at a multiplicity of 20 infection particles per embryo the development of 43% of embryos was inhibited. The zona pellucida had no significant protective effect: Its removal changed only slightly the susceptibility of the preimplantation embryos to this virus. Pretreatment of embryos with IFN did not protect them from the embryotoxic effect of EMC virus. This work indicates that preimplantation mouse embryos appear to be resistant for both the antiviral and antiproliferative activities of IFN.

Antiviral and protein-inducing activities of recombinant human leukocyte interferons and their hybrids

The antiviral activities of recombinant human leukocyte interferons IFN-alpha A and IFN-alpha D as well as five hybrids of these interferons against retroviruses, vesicular stomatitis virus, and encephalomyocarditis virus were studied in feline, human, and murine cells. Although these interferon species had widely different potencies, their activities against these viruses were, in general, proportional. The IFN-alpha A/D (Bgl) hybrid was the most potent species, and the IFN-alpha D/A (Bgl) hybrid was the least potent. However, the latter species did not interfere with the action of the former species. Like natural human leukocyte interferon, each of the seven species of recombinant interferons induced the synthesis of at least five proteins in human fibroblasts, whereas induction of only one such protein was readily detected in a feline fibroblast line in which these interferon species inhibited the replication of all three viruses.

Resistance of vaccinia virus to interferon is related to an interference phenomenon between the virus and the interferon system

In this investigation the sensitivity of vaccinia virus to interferon (IFN) has been examined in cultured cells. In a variety of mouse and human cells of different origins vaccinia virus functions (RNA, protein, and virus yields) were found to be relatively resistant to IFN. In these systems, the levels of the IFN-mediated enzyme activities (2-5A synthetase and protein kinase) were severely impaired by the virus. This virus-mediated inhibitory effect developed with time after infection and was dependent on viral protein synthesis. Mixed infections between vaccinia virus and viruses (VSV or polio) which are sensitive to IFN showed that both protein synthesis and virus yields were not inhibited. These findings show that vaccinia virus can overcome the antiviral action of IFN and that viral gene functions appear to be involved in this interference phenomenon.

Inhibitory effect of mouse interferon on the growth of an embryonal carcinoma in mice

Embryonal carcinoma cells (F9) were resistant to the inhibitory effects of interferon (IFN) on viral multiplication and cell division in vitro. Nevertheless, daily administration of IFN resulted in a marked inhibition of the growth of this carcinoma injected intraperitoneally (ip) and increased mouse survival time. An incidental finding was that daily IFN treatment increased the serum level of alpha-fetoprotein in normal 129 mice.

Developmentally regulated expression of the interferon system during Syrian hamster embryogenesis

Expression of interferon (IFN) during embryogenesis of the Syrian hamster has been characterized with respect to (1) the antiviral activity to IFN; (2) the activity of the IFN-induced enzyme, 2',5'-oligo A synthetase; (3) the subpopulation of IFN producing cells, and (4) the molecular structure of the elaborated IFN. These components of the IFN system were examined in cell cultures derived from embryos excised at 8-13 days of gestation and determined as a function of both in utero gestation and in vitro passaging. The antiviral responsiveness of nine-day gestation cultures (9 dgc) was 1/4-1/6 of that of 13 dgc, but in vitro passaging increased the responsiveness as did in vivo development. IFN enhancement of the synthetase level in 9 dgc was only minimal when compared with that in 13 dgc. However, the 9 dgc contained an unusually high basal level of the enzyme. During in vivo development and in vitro passaging, the basal levels of the enzymes progressively declined while the IFN-induced levels progressively increased. IFN production in embryo cells following induction by Newcastle disease virus differs substantially, depending on the gestational age of the cells. Using an agarose-overlay "zone of protection" assay, 8 dgc were found to contain 10-12 times the number of cells producing zones of protection than 13 dgc. Passaging of 9 dgc cells reduced the number of zones to the level of the 13 dgc, but had no effect on 13 dgc. Chromatographic analysis of IFN produced by 9 dgc and 13 dgc revealed the presence of an additional, unique species of "embryonic" IFN in 9 dgc which was not observed in IFN from 13 dgc. These observations suggest that the expression of various components of the IFN system are under developmental control during embryogenesis.

Growth regulation of melanoma cells by interferon and (2'-5')oligoadenylate synthetase

We report that endogenous, as well as exogenous, interferon (IFN) regulates the growth of human melanoma cells in culture. When antibodies directed against human fibroblast IFN were incorporated into the media of high-density cells stimulated to proliferate with serum, the cells entered the cell cycle earlier than did the controls. In investigating the biochemical basis for this finding, we have found that there is an inverse relationship between the (2'-5')oligoadenylate synthetase levels and the percentage of cells in S in untreated cultures. Upon IFN treatment, the relationship is obliterated and (2'-5')oligoadenylate synthetase levels increase throughout all phases of the cell cycle. This increase in enzyme levels correlates well with the decreased probability of the IFN-treated cells to cycle. These findings suggest a biological role for IFN as a negative growth factor for cells in culture.

Effect of interferon on two human choriocarcinoma-derived cell lines

Two cell lines derived from human choriocarcinomas (HCCM-5 and BeWo) are resistant to several biological effects of human interferon such as inhibition of VSV multiplication and inhibition of cell growth, but they develop a normal antiviral activity against EMCV. Nevertheless, in both cell lines, 2-5A synthetase and protein kinase are induced by IFN. 2-5A-dependent endonuclease can be measured by two independent methods and 2-5A itself is detected at least in poly(rI):poly(rC)- and IFN-treated BeWo cells. This is another example of two cell lines that are partially, with respect to the antiviral effect toward VSV, and totally, with respect to the anticellular effect, refractory to IFN treatment, although all the known elements of the 2-5A system are present.

Growth regulation of melanoma cells by interferon and (2'-5')oligoadenylate synthetase

We report that endogenous, as well as exogenous, interferon (IFN) regulates the growth of human melanoma cells in culture. When antibodies directed against human fibroblast IFN were incorporated into the media of high-density cells stimulated to proliferate with serum, the cells entered the cell cycle earlier than did the controls. In investigating the biochemical basis for this finding, we have found that there is an inverse relationship between the (2'-5')oligoadenylate synthetase levels and the percentage of cells in S in untreated cultures. Upon IFN treatment, the relationship is obliterated and (2'-5')oligoadenylate synthetase levels increase throughout all phases of the cell cycle. This increase in enzyme levels correlates well with the decreased probability of the IFN-treated cells to cycle. These findings suggest a biological role for IFN as a negative growth factor for cells in culture.

Xyloadenosine analogue of (A2'p)2A inhibits replication of herpes simplex viruses 1 and 2

Molecules of the structure ppp(A2'p)2A containing a 2' leads to 5' phosphodiester bond, commonly abbreviated as 2-5A, are synthesized in interferon-treated virally-infected cells and have been implicated in several systems as contributing to interferon's antiviral activity. The 2-5A binds to and subsequently activates an endogenous endonuclease, ultimately resulting in degradation of RNA. We have been interested in the use of 2-5A analogues to achieve antiviral activity without the use of interferon. For this approach to be successful, analogues must be synthesized with an increased stability (native 2-5A is rapidly degraded by cellular phosphodiesterases) and with increased ability to enter intact cells. Removal of the highly-negative charged 5' terminal phosphates from ppp(A2'p)2A results in formation of the 'core' species, (A2'p)2A, which should be able to penetrate intact cells more readily. While Kimchi et al. have shown that 2-5A core has an antimitogenic effect in mouse spleen lymphocytes and 3T3 fibroblasts, Williams and Kerr have reported lack of antiviral activity against Semliki Forest virus or encephalomyocarditis virus by exogenously-administered 2-5A core. We have previously determined that (xyloA2'p)2xyloA (abbreviated as xylo 2-5A core), the xyloadenosine analogue of the 5'-terminally dephosphorylated 2-5A core, is over 100 times more stable than the parent 2-5A core species. We now report that this xylo 2-5A core inhibits replication of herpes simplex viruses 1 and 2 in vitro, with greater than 100 times the activity of the parent 2-5A core. The mechanism of antiviral action of the 2-5A core analogue appears to involve a pathway different from that activated by the parent 5' triphosphorylated 2-5A species.

Epidermal growth factor-urogastrone action: induction of 2',5'-oligoadenylate synthetase activity and enhancement of the mitogenic effect by anti-interferon antibody

Epidermal growth factor-urogastrone (EGF-URO), early in the course of stimulating DNA synthesis in quiescent human fibroblasts, also causes a three to five-fold elevation of the activity of intracellular 2',5'-oligoadenylate synthetase (2,5A synthetase), an enzyme that has been previously implicated in the antiproliferative effects of interferon. The increase in synthetase activity precedes DNA synthesis by approximately six hours, with maximal synthetase activity either preceding or coinciding with maximal DNA synthesis. EGF-URO stimulation does not result in the secretion of detectable amounts of interferon (IFN) into the growth medium and anti-human IFN-beta antibodies do not block the EGF-URO-mediated rise in 2,5A synthetase activity. Thus, the elevation of 2,5A synthetase can be attributed to the action of EGF-URO itself, and not to IFN. Nonetheless, in the presence of anti-human interferon-antibodies, the time course of EGF-URO-stimulated DNA synthesis is prolonged both in human and in Syrian hamster embryo fibroblasts; the effects of the antibody were reversed in both cell strains by the addition of human IFN-beta (HuIFN-beta). The data suggest a role for 2',5'-oligoadenylate synthetase in the process of EGF-URO-mediated mitogenesis and point to the possible production of interferon-related cell-associated regulators during the course of EGF-URO action.

Differential antiviral effects of interferon in three murine cell lines

Infectious leukemia virus production by two chronically infected NIH/MOL lines was strongly inhibited by interferon treatment of the cells. The corresponding degree of inhibition in JLSV-11 cells was much lower. Multiplication of encephalomyocarditis virus in all three cell lines was barely affected by interferon treatment. Replication of vesicular stomatitis virus, on the other hand, was highly sensitive to interferon in the JLSV-11 line and in one NIH/MOL line but was practically insensitive in the other NIH/MOL line. Anticellular actions of interferon were more pronounced in the JLSV-11 line than in the others. In response to interferon treatment, 2',5'-oligoadenylate synthetase activity was induced to a high level in JLSV-11 cells and to lower levels in the NIH/MOL lines. We failed to detect any 2',5'-oligoadenylate-dependent endonuclease activity in extracts of these cells. Double-stranded RNA-dependent protein kinase activity was present in extracts of interferon-treated NIH/MOL cells, but it was barely detectable in extracts of interferon-treated JLSV-11 cells. The above studies demonstrated that interferon could differentially affect the replication of three different viruses in three different cell lines, including two seemingly identical NIH/MOL lines, and that certain tentative conclusions can be drawn regarding the roles of different interferon-inducible enzyme markers in the different antiviral actions of interferons.

The mechanism of interferon production

Interferons are formed when most cells are treated with viruses or double-stranded RNA (to form IFN-alpha or beta, or both) or when lymphoid cells are treated with mitogens or the appropriate antigen (to form IFN-gamma). Interferon-alpha and beta are formed as a result of transcription of cellular genes--probably in response to double-stranded RNA in the cytoplasm. The process can be controlled at three levels. (1) In mouse teratocarcinoma stem cells or early mouse embryos the interferon system is inaccessible and only becomes inducible as differentiation proceeds. (2) The target(s) responding to double-stranded RNA probably involve sequences upstream from the 5' end of the interferon genes, sequences now becoming accessible by gene cloning. (3) Levels of interferon mRNA can be regulated either by an increased rate of transcription or by an increased half-life of the mRNA.

Analysis of antiviral state in RD114 and A204 cells after interferon treatment

Interferon exerts antiviral and various non-antiviral activities on cells. For the development of the antiviral state in cells against exogenous infection of cytolytic viruses such as vesicular stomatitis virus and encephalomyocarditis virus (EMCV), induction of 2'-5'-oligo(A) synthetase or double-stranded (ds)-RNA-dependent protein kinase, or both, has been shown to have a crucial role (Revel 1979). However, in some cases, the antiviral effects of interferon are virus-specific (Nilsen et al. 1980; Samuel & Knutson 1981). Recently, different effects of mouse interferon on retrovirus production and on EM CV replication in a clonal cell line from NIH / 3T3 cells were reported (Gzarniecki et al. 1981).

Interferon restriction of target organs for lymphocytic choriomeningitis virus-induced T lymphocytes may be lethal

It is generally held that interferons play a role in recovery from acute primary viral infections. One of the most direct ways that this can be demonstrated is by use of anti-interferon serum. Rapid evolution of lethal disease in a number of murine infections (encephalomyocarditis, herpes simplex, Newcastle disease, Semliki Forest viruses) was observed when interferon liberated from virus-infected cells was neutralized by injection of anti-interferon serum. The neutralization suppressed the normal interferon effect, allowing unchecked dissemination of virus (Gresser et al . 1976 b ). However, it appears to be precisely this antiviral property of interferon that causes death in adult mice infected intracerebrally (i.c.) with lymphocytic choriomeningitis (LCM) virus. We explain here how the rapid proliferation of LCM virus could spare these mice rather than kill them.

The antiviral action of interferon

On interferon treatment cells develop an antiviral state. This requires time and RNA and protein synthesis. At least six polypeptides and two enzymes have been reported to be synthesized in increased amounts in response to interferon and a multiplicity of effects have been attributed to it. Interferon has been reported to inhibit virus growth at the level of the uncoating of the virus, virus RNA and protein synthesis and virus maturation. This has led to the acceptance of a multisite model for interferon action. The evidence for this and for the role of two known interferon-mediated enzymes, the 2-5A synthetase and protein kinase, are reviewed.