Distinguishing characteristics of interferon induction with poly(I)-poly(C) and Newcastle disease virus in human cells

Enhancement by muramyldipeptides of the activities of early-type inducers of interferon

A synthetic muramyldipeptide (MDP) and two analogues, B30-MDP and MDP-Lys(L18), augmented serum interferon (IFN) production in mice by the inducers lipopolysaccharide (LPS) and polyinosinic acid:polycytidylic acid (poly I:C), and also augmented immune IFN production induced by purified protein derivative (PPD) in mycobacteria-sensitized mice. These compounds were most effective when administered to mice one day before the interferon inducer. By contrast, IFN production in mice by either oral tilorone or virus infection was not enhanced with these compounds. Since LPS and poly I:C are well known as early-type IFN inducers, and tilorone and virus infection are late-type inducers, we presume that MDP and its analogues are able to augment only early-type IFN production. This enhancing effect may be mediated by macrophage activation. In vivo antiviral activity of MDP and its analogues was further tested in mice infected with vaccinia virus (VV) using early-type inducers. When mice previously treated with MDP or its analogues were stimulated for IFN production with a low dose of LPS, protective activity against VV infection was markedly enhanced.

Control of biologically active interleukin 2 messenger RNA formation in induced human lymphocytes

The regulation of human interleukin 2 (IL-2) mRNA production in induced normal lymphocytes was studied by following the expression of isolated mRNA in microinjected oocytes of Xenopus laevis. Mitogenic stimulation results in the appearance of greatly increased levels of IL-2 mRNA activity. This process requires de novo transcription. Induction is followed promptly by a shutoff of active IL-2 mRNA formation. This shutoff requires the synthesis of a protein repressor and can be prevented by cycloheximide, an inhibitor of translation. The presence of cycloheximide leads to extensive superinduction of IL-2, concomitant with an increase in active IL-2 mRNA formation up to 30-fold over normal levels. The repressor appears to be short-lived, as the addition of cycloheximide after shutoff leads to an immediate resumption of active IL-2 mRNA formation. The shutoff mechanism is restored rapidly upon removal of cycloheximide. The repressed state is readily reversed also by reinduction of the cells, even soon after shutoff has occurred, without a refractory period. The accumulated active IL-2 mRNA decays with a half-life of about 20 hr. The net result is the generation of a relatively short wave of IL-2 mRNA activity, demonstrating the tight control of IL-2 gene expression.

Two levels of regulation of beta-interferon gene expression in human cells

We cloned alpha- and beta-interferon cDNA and used them as specific probes to determine the relative levels of interferon mRNA in human fibroblasts cells induced with poly(rI).poly(rC) or Newcastle disease virus to synthesize interferon. Both inducers activated only the beta-interferon gene; however, the half life of beta-interferon mRNA in cells induced with virus was substantially longer than in poly(rI).poly(rC)-induced cells. The transcription rate of beta-interferon RNA sequences was examined in nuclei isolated from poly(rI).poly(rC)-induced cells; it was found that the induction leads to transcriptional activation of the beta-interferon gene and that the shutoff period when no interferon synthesis or cytoplasmic betamRNA are detected. Thus, the synthesis of beta interferon in poly(rI).poly-(rC)-induced human fibroblasts is controlled both by activation of transcription of the beta-interferon gene and by alteration of the beta-interferon mRNA stability.

Effect of inhibitors of methylation on early and late interferon synthesis in bovine kidney cell cultures

In virus infected bovine kidney cell cultures mainly late interferon is produced starting at about 4 hr after infection. Poly rI:poly rC induced cells as well as interferon pretreated virus infected cells produce early interferon starting immediately after induction. In infected cells the proportion of early interferon increases with time of interferon pretreatment, while late interferon is decreasing. Production of late interferon is selectively inhibited by cycloleucine, an inhibitor of S-adenosylmethionine (SAM) biosynthesis, whereas early interferon synthesis is not affected by the drug. Likewise, late interferon production is reduced much stronger than early interferon production by a combination of adenosine, L-homocysteine thiolactone, and erythro-9[3-(2-hydroxynonyl)]-adenine (EHNA) inducing in cells an accumulation of S-adenosylhomocysteine which inhibits SAM mediated methylation reactions. Inhibition of late interferon synthesis by cycloleucine is time and dose dependent and partially reversible. Cycloheximide equally blocks both early and late interferon production. Inhibition of incorporation of methyl groups into cellular RNA by the methylation inhibitors used is demonstrated by labeling with [methyl-3H] methionine and 3H-uridine. The results indicate that the synthesis of functional mRNA for early and late interferon is differentially sensitive to inhibition of methylation. The data suggest that, if early and late interferon is coded by the same structural gene, two different pathways are available for the cell to synthesize one species of mRNA.

Enhanced production of virus-inhibiting factor (interferon) in human diploid cells by ultraviolet irradiation and temperature shift-down after stimulation with Newcastle disease virus

The production of the virus-inhibiting factor or interferon (IF) was highest in cells incubated at 37 C after inoculation with Newcastle disease (ND) virus and decreased as the incubation temperature was lowered. Shift-down of incubation temperature to 32 C or 34 C after incubation at 37 C for 4--7 hr enhanced IF production in cell cultures stimulated with ND virus, as compared with cultures incubated continuously at 37 C. Shift-down to 32 C after incubation at 37 C for 6 hr was optimal for this enhancement of IF yield. Enhanced IF production was also observed in cell cultures irradiated by ultraviolet light 4--7 hr after stimulation with ND virus.

Enhanced viral interferon induction by the mineral wollastonite

The in vitro activity of the fibrous mineral wollastonite (CaSiO3) on the interferon system was investigated. Wollastonite enhanced the induction of interferon by influenza virus in mammalian (LLC-MK2) cell monolayers but the mineral per se did not induce interferon. The magnitude of enhanced interferon induction was dependent on mineral concentration, particle size, and its time and sequence of addition onto cell monolayers. A "synergistic effect" on viral induction of interferon was noted when cell cultures were interferon-primed and then treated with wollastonite. Interferon yields were significantly higher than those obtained by the use of either the primer or wollastonite alone. That influenza virus multiplied in wollastonite-treated cells to a level that was sevenfold less than that in normal cells was associated with increased interferon production. The ability of interferon to confer antiviral cellular resistance was not impaired by wollastonite. The findings of this study suggest that the incorporation of wollastonite in appropriate interferon inducer-host cell systems may be useful for augmenting interferon production.

Interferon induction with Newcastle disease virus in FS-4 cells: effect of priming with interferon and of virus inactivating treatments

Inoculation of human FS-4 cells with Newcastle disease virus (NDV) resulted in the induction of two distinct interferon responses, one that peaked at about 5 hr (early response) and one that reached a maximum between 10 to 24 hr after inoculation (second response). The early interferon response was enhanced by previous treatment of the cells with interferon (priming), whereas the second response decreased after interferon treatment in a dose-dependent manner. The early response diminished with decreasing multiplicities of infection, the magnitude of the second response in unprimed cells was relatively independent of the dose of NDV employed. The early interferon response was sensitive to inhibition by actinomycin D for only 1 hr after inoculation. In marked contrast, the second response remained sensitive to inhibition by actinomycin D until 12 hr after inoculation. The ability of NDV to induce the second response was greatly diminished by irradiation of the virus with ultraviolet light or by its treatment with hydroxylamine, whereas the ability to stimulate the early response was relatively resistant to these virus-inactivating treatments. Treatment of NDV with hydroxylamine abolished the virus to induce the second response at the same rate as it destroyed infectivity. The results suggest the existence of at least two distinct mechanisms of interferon induction by NDV; the early response is triggered either by a virion component or by a product of primary transcription, whereas induction of the second response requires the expression of some functions of the virus not needed for triggering the early response.

Interferon induction with Newcastle disease virus in FS-4 cells: effect of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB)

DRB is an inhibitor of heterogeneous nuclear RNA (hnRNA) and messenger RNA (MRNA) synthesis. The effect of DRB on interferon production stimulated by Newcastle disease virus (NDV) in the human FS-4 cells was studied. Interferon production in cells primed by treatment with interferon was markedly enhanced (superinduced) in the presence of DRB. This superinduction was essentially due to an inhibition of the rapid decline (shutoff) of interferon production observed in primed cells not treated with DRB. Continuous presence of DRB was required for maximal superinduction. In this and other respects the interferon response induced by NDV in primed cells resembled poly(I). poly(C)-induced interferon production. In contrast interferon production in cells not primed with interferon was virtually abolished by DRB treatment. Since neither virus specific RNA synthesis nor virus replication were significantly affected by DRB, the inhibition of interferon production is likely to result from the inhibitory action of DRB on a cellular, rather than viral, function. Apparently some differences exist in the synthesis or processing of the mRNAs for interferons in primed and unprimed cells and these determine the different sensitivities of these two responses to DRB.

Fibroblast interferon in man is coded by two loci on separate chromosomes

We have examined viral and poly(rl):poly(rC) induction of interferon synthesis in several human, mouse and Chinese hamster cell lines, and in hybrids derived from the fusion of such cells. We observed species and cell-type differences in inducer effectiveness and in the kinetics of interferon production. In some cases, parental characteristics are preserved in somatic cell hybrids, and in other cases, the expression of the donor phenotype is modulated by the epigenetic state of the recipient cell. Mapping studies in human/mouse and human/Chinese hamster hybrids indicate that there are at least two structural genes for human fibroblast interferon. Chromosomes 2 and 5 each contain genetic information for the synthesis of fibroblast interferon. Gene dosage experiments indicate that one gene is on the long arm of chromosome 2 and another is on the short arm of chromosome 5. Leukocyte interferon genes could not be mapped to these chromosomes, but this negative result could be influenced by the epigenetic state of the hybrid cells.

Appearance of interferon inducibility and sensitivity during differentiation of murine teratocarcinoma cells in vitro

Pluripotential embryonal carcinoma (EC) cells do not produce interferon after treatment with a wide variety of inducers, nor are they sensitive to its action. Several differentiated lines derived from the EC cells, however, both produce and are sensitive to mouse interferon. Differentiation of EC cells in vitro is accompanied by development of interferon inducibility and sensitivity.

Studies on the enhancement of interferon production in human diploid (FS-4) cells by ultraviolet

Interferon production stimulated with Polyinosinate-Polycytidylate [Poly (I). Poly (C)] in cultures of human FS-4 cells was enhanced ('superinduced') by the irradiation of cells with UV at the time of induction. UV showed no additional enhancing action on interferon production in cultures already superinduced by the sequential treatment with cycloheximide and actinomycin D; UV doses above 1,000 erg/mm2 inhibited interferon synthesis. In UV-irradiated cells interferon production remained sensitive to inhibition by high concentrations of actinomycin D for at least 3 hr after exposure to Poly (I). Poly (C). Irradiation of induced cells at 4, 5 or 6 hr after stimulation with Poly (I). Poly (C) prevented the rapid decline (shutoff) of interferon synthesis seen in control cultures. All these results support the conclusion that the action of UV protects the interferon mRNA from inactivation. This effect, and the fact that interferon mRNA synthesis can occur after the irradiation of cells with superinducing doses of UV, form the basis of the enhancement of interferon production by UV.