Inhibition Of Interferon Synthesis Research Articles

Loss of Interferon Regulatory Factor 3 in Cells Infected with Classical Swine Fever Virus Involves the N-Terminal Protease, N pro

We show that cells infected with the pestivirus classical swine fever virus (CSFV) fail to produce alpha/beta interferon not only following treatment with double-stranded RNA but also after superinfection with a heterologous virus, the alphavirus Sindbis virus, a virus shown to normally induce interferon. We investigated whether the inhibition of interferon synthesis by CSFV involved a block in interferon regulatory factor 3 (IRF3) activity. Cells infected with CSFV exhibited a lack of translocation of green fluorescent protein-IRF3 to the nucleus; however, constitutive shuttling of IRF3 was not blocked, since it could still accumulate in the nucleus in the presence of leptomycin B. Interestingly subcellular fractionation analysis showed that IRF3 was lost from the cytoplasm of infected cells from 18 h postinfection onwards. Using IRF3 promoter-luciferase reporter constructs, we demonstrate that loss of IRF3 was due to an inhibition of transcription of the IRF3 gene in CSFV-infected cells. Further, we investigated which viral protein may be responsible for the inhibition of interferon and loss of IRF3. We used cell lines expressing the CSFV N-terminal protease (Npro) to show that this single viral protein, unique to pestiviruses, inhibited interferon production in response to Sindbis virus. In addition to being lost from CSFV-infected cells, IRF3 was lost from Npro-expressing cells. The results demonstrate a novel viral evasion of innate host defenses, where interferon synthesis is prevented by inhibiting transcription of IRF3 in CSFV-infected cells.

Theoretical analysis of the regulation of interferon expression during priming and blocking

Interferon superinduction, in the case of cell pretreatment with low doses of interferon (priming), may be explained by activation of 2′,5′-oligoadenylate synthetase and endonuclease L, since the latter, as expected, leads to a more rapid amplification of the standard scheme of interferon induction based on the antirepression mechanism. In the given case, endonuclease L will further increase the degradation rates for messages, which encode repressor proteins controlling interferon gene expression. Under ordinary induction, these messages are destroyed only by short-lived nuclease activated by double-stranded RNA. Cell pretreatment with high doses of interferon (blocking) considerably increases the concentrations of protein kinase and 2′,5′-oligoadenylate synthetase in the cell. However, it seems that during blocking protein kinase plays the main role in inhibition of interferon synthesis, and this leads to almost complete depression of translation in the cell. When protein kinase is not sufficiently activated, blocking does not occur since treatment of cells with high concentrations of interferon does not hinder priming induced by 2′,5′-oligoadenylate synthetase and endonuclease L. The proposed model is consistent with the findings that both interferon-treated primed and blocked cells are able to produce interferon more rapidly than normal cells. The analysis, based on a computer simulation model, suggests that priming and blocking of interferon may be based on processes controlling its induction and antiviral activity.

Blocking of interferon synthesis in murine macrophages by pretreatment with interferon

The influence of pretreatment with interferon (IFN) on subsequent IFN synthesis was investigated in macrophage cultures of DBA/2 and C57BL/6 mice. The doses of IFN α/β for pretreatment ranged from 10000 U/ml to 100 U/ml and the incubation time was between 18 and 2 h. No blocking effect was observed for chemical induction with poly I:polyC or CMA. However, for viral infection with NDV, blocking was observed. This inhibition of IFN synthesis was dependent on the dose and time of IFN pretreatment and of the titer of the inducing virus. Similarly in mouse fibroblast cultures no blocking activity was observed for induction with poly I:poly C/DEAE-dextran. Again, with NDV as inducer, pretreatment with IFN resulted in inhibition of interferon synthesis. Thus, our data show that blocking occurs only with a viral inducer and suggest that it is caused by an antiviral effect.

Coinhibition of viral interferon induction by benzo[ a]pyrene and chrysotile asbestos

Benzo[a]pyrene (B[a]P) and its noncarcinogenic analog, benzo[e]pyrene (B[e]P), each in combination with chrysotile, were studied for their inhibitory effects on interferon (IFN) induction by influenza virus in rhesus monkey kidney (LLC-MK2) cell monolayers. B[a]P alone had no adverse effect on IFN induction; however, from 60 to 70% inhibition of IFN production occurred when B[a]P was enzymatically activated by rat liver S9. Chrysotile's inhibitory effect on the IFN process was similar in magnitude to that of activated B[a]P. The combination of activated B[a]P with chrysotile resulted in coinhibition of IFN induction which significantly exceeded (P less than 0.05) the inhibitory activity of the reagents tested alone or in other combinations. B[e]P alone or with S9 neither affected IFN induction nor was it capable of further enhancing chrysotile's inhibition of IFN synthesis. These findings provide further evidence of enhanced deleterious action by the combination of asbestos and activated B[a]P on a biological defense mechanism and further support the discriminatory power and credibility of the inhibition IFN induction assay for evaluating potential carcinogens.

Carbaryl inhibition of interferon synthesis in cultured goldfish cells.

Carbaryl inhibition of interferon synthesis in cultured goldfish cells.

Electrophoretically pure mouse interferon has priming but no blocking activity in poly(I.C.)-induced cells

The effect of interferon on its own synthesis was examined by exposing cells to electrophoretically pure interferon prior to induction with poly(I.C.) In C-243 cells, pretreatment with pure interferon, at any dose, up to 160,000 units, resulted in a very pronounced priming effect and no blocking was observed. Crude interferon did not display any blocking effect either, but its priming effect was much less pronounced than that of pure interferon. In mouse embryo fibroblast cultures, low doses of pure interferon had a slight priming effect, whereas higher doses, from 500 up to 50,000 units, had neither priming nor blocking activity. At a dose of 50,000 units the crude interferon preparation had blocking activity. When NDV instead of poly(I.C.) was used as inducer, pretreatment with pure interferon of both C-243 and mouse embryo fibroblast cells resulted in inhibition of interferon synthesis.

Specific inhibition of interferon synthesis in mice immunized against Brucella and Newcastle disease virus

Specific inhibition of interferon synthesis in mice immunized against Brucella and Newcastle disease virus

Inhibition of interferon synthesis in phospholipase C treated primary chick embryo cells

Treatment of primary chick embryo (PCE) cells with subcytotoxic concentrations of phospholipase C (1–2 units/ml) makes them incapable of producing interferon primed by various inducers. The adsorption-penetration steps of viral inducers do not seem to be involved in the mechanism of the inhibition. The inhibitory effect of the enzyme treatment appears to be confined to the cellular mechanism related to interferon synthesis, because the following functions of PCE cells are found to remain intact after exposure to the enzyme which results in nearly complete suppression of interferon production: (1) synthesis of RNA and proteins, (2) capacity to support multiplications of Western equine encephalitis virus (WEE), vesicular stomatitis virus (VSV), Newcastle disease virus (NDV), and Semiki Forest virus (SFV). The potency of phospholipase C to suppress interferon production was found to be copurified with the enzyme activity after gel filtration through Sephadex G-100.

The influence of cortisone on experimental viral infection. VII. Kinetics of interferon formation and its inhibition with hydrocortisone in relation to viral strain and virulence.

A comparative study was undertaken of the pathogenesis of infection of the allantoic sac of the chick embryo with three influenza viruses of differing virulence, and of the influence of hydrocortisone on the course of infection. Judged on the basis of earlier onset and greater degree of inflammatory response and diminished survival time of infected embryos, Mel. and Lee viruses were markedly more virulent than PR8, despite the earlier appearance of virus in PR8-infected embryos. Interferon appeared first and in greater quantity in the allantoic fluid of Lee-infected embryos and latest with PR8 infection. Thus, there was no correlation of avirulence and better interferon production with the viruses under study in the present system. Furthermore, evidence obtained suggested that Lee virus ("virulent") was most susceptible to interferon action, and also that viral synthesis in the chorioallantoic membrane with PR8 ("avirulent") persisted after the appearance of interferon. The injection of hydrocortisone within 2 hr of the initiation of infection delayed the synthesis of all three viruses; had no significant effect upon the inflammatory response; and transiently inhibited the synthesis of interferon, while prolonging the survival of Lee- and Mel.-infected embryos. Late administration of hydrocortisone suppresses both the inflammatory response and the production of interferon. Only in the case of Lee virus infection did hydrocortisone administration lead to augmentation of final yields of virus with the low infection multiplicity employed in the present experiments. It is postulated that Lee virus is a better inducer of interferon because its infectivity in vivo is more rapidly inactivated. As a consequence synthesis of Lee virus is more under the control of endogenous interferon than is the case with PR8 or Mel. virus. Therefore, inhibition of interferon synthesis with hydrocortisone has a greater influence on final yields of Lee virus.

Inhibition of Interferon Synthesis and Stimulation of Virus Plaque Development in Mammalian Cell Cultures after Ultra-Violet Irradiation

Inhibition of Interferon Synthesis and Stimulation of Virus Plaque Development in Mammalian Cell Cultures after Ultra-Violet Irradiation