PKR acts early in infection to suppress Semliki Forest virus production and strongly enhances the type I interferon response

Abstract

The double-stranded RNA-activated protein kinase (PKR) is a key regulator of protein translation, interferon (IFN) expression and cell survival. Upon infection of vertebrate cells in continuous culture, the alphavirus Semliki Forest virus (SFV) initiates apoptosis and IFN synthesis. To determine the effect of PKR on SFV infection, we studied the course of infection in wild-type (wt) mice, mice with a genetic deletion of PKR (PKR−/−) and mouse embryo fibroblasts (MEFs) derived from these mice. In MEFs, PKR delayed virus protein synthesis, production of infectious virus and caspase-3-activated cell death and reduced the yield of infectious virus by 90 %. Small interfering RNA suppression of PKR levels in NIH-3T3 cells also reduced virus production and apoptosis. In MEFs, PKR was not required for initiation of IFN-β gene transcription, but contributed strongly to the magnitude of this response. Levels of IFN-β transcripts in PKR−/− MEFs at 8 h were 80 % lower than those in wt MEFs and levels of functional IFN at 24 h were 95 % lower. Following infection of wt and PKR−/− mice, SFV4 and SFV A7(74) were avirulent. PKR increased levels of serum IFN and the rate of clearance of infectious virus from the brain. In summary, in response to SFV, PKR exerts an early antiviral effect that delays virus protein production and release of infectious virus and, whilst PKR is not required for induction of apoptosis or activation of the type I IFN response, it strongly augments the type I IFN response and contributes to clearance of infectious virus from the mouse brain.

Active Infection of Human Blood Monocytes by Chikungunya Virus Triggers an Innate Immune Response

“…4D). This is not surprising as CHIKV is known to be cytopathic (22), similar to other alphaviruses with continual cell death in the in vitro cultures between 24 and 48 hpi (33,34). However, it is worth mentioning that a large fraction of human monocytes (up to 60%) in the mock-infected cultures also died over the 48-h period in culture conditions devoid of macrophage growth factors (35)(36)(37).…”

Functional Characterization of Interferon Regulation Element of Hepatitis B virus Genome In Vivo

“…Firstly, interferon regulates HBV DNA replication by both immunomodulatory [4] and directly antiviral mechamism. Furthermore, as far as direct antiviral mechamism is concerned, except for HBV IRE-dependant pathway, interferon has the potential to trigger the activation of other multiple noncytolytic intracellur antiviral pathways that can target many steps in the viral life [2,11,12,23]. In a word, multiple mechanisms might be involved in antiviral effect by interferon on HBV, and IRE-dependant mechanism investigated in our present study was one of them.…”

A Semliki Forest virus vector engineered to express IFNα induces efficient elimination of established tumors

“…Alphaviruses are very sensitive to the action of type I IFNs, and it would be reasonable to think that expression of these cytokines from such a recombinant vector could hinder its production and activity. 31,32 On the other hand, alphaviruses induce the release of type I IFNs in infected cells and expression of more IFNa from the vector may be redundant for therapeutic purposes. 31,32,36 In spite of these potential drawbacks, we have shown that it is possible to produce high titers of recombinant SFV vectors expressing IFNa in BHK cells.…”

“…31,32 On the other hand, alphaviruses induce the release of type I IFNs in infected cells and expression of more IFNa from the vector may be redundant for therapeutic purposes. 31,32,36 In spite of these potential drawbacks, we have shown that it is possible to produce high titers of recombinant SFV vectors expressing IFNa in BHK cells. The most likely explanation for achieving this high SFV-IFN production is the fact that BHK cells have been shown to be defective in type I IFN responses.…”

“…In this study, we developed a SFV vector expressing murine IFNa1 (SFV-IFN) and evaluated its antitumor effects in the TC-1 tumor model. As alphaviruses are strongly inhibited by type I IFN responses, 31,32 the in vitro production and the in vivo efficacy of a recombinant alphavirus vector expressing IFNa represented a technical challenge. In spite of this, we show that SFVIFNa can be produced to normal titers, and can infect the TC-1 cell line and produce IFNa.…”