The E3L and K3L vaccinia virus gene products stimulate translation through inhibition of the double-stranded RNA-dependent protein kinase by different mechanisms

Abstract

Vaccinia virus has evolved multiple mechanisms to counteract the interferon-induced antiviral host cell response. Recently, two vaccinia virus gene products were shown to interfere with the activity of the double-stranded RNA-dependent protein kinase (PKR): the K3L gene product and the E3L gene product. We have evaluated the efficiency by which these gene products inhibit PKR and whether they act in a synergistic manner. The effects of the two vaccinia virus gene products were compared in an in vivo system in which translation of a reporter gene (dihydrofolate reductase or eukaryotic translation initiation factor 2at [eIF-2a]) was inhibited because of the localized activation of PKR. In this system, the E3L gene product, and to a lesser extent the K3L gene product, potentiated translation of the reporter gene and inhibited eIF-2at phosphorylation. Analysis in vitro demonstrated that the E3L gene product inhibited PKR approximately 50to 100-fold more efficiently than the K3L gene product. However, further studies demonstrated that the mechanism of action of these two inhibitors was different. Whereas the E3L inhibitor interfered with the binding of the kinase to double-stranded RNA, the K3L inhibitor did not. We propose that the K3L inhibitor acts through its homology to eIF-2a to interfere with the interaction of eIF-2a with PKR. The two inhibitors did not display a synergistic effect on translation or eIF-2a phosphorylation. In addition, neither K3L nor E3L expression detectably altered cellular protein synthesis.

One time intranasal vaccination with a modified vaccinia Tiantan strain MVTTZCI protects animals against pathogenic viral challenge

“…Third, M2L is probably involved in the regulation of host NF-kB responses in virus infection which may potentially influence inflammation and the severity of vaccinia infection [40]. Fourth, K3L gene is an immunomodulatory and anti-apoptotic gene that inhibits IFN intracellular signaling pathway by preventing RNA-dependent protein kinase (PKR) activation [41][42][43]. Thus, deletion of K3L in vaccinia virus may render the virus sensitive to the antiviral effects of IFN and probably limit disease progression in vivo.…”

Influenza virus and cell signaling pathways

“…Therefore, in order to counteract the effects of host IFN response and PKR activation, viruses have developed multiple mechanisms to suppress PKR activation [71]. Several lines of evidence support the fact that viral genes (vaccinia virus, adenovirus and hepatitis C virus) encode proteins that inhibit the IFN pathway by targeting PKR [72,73]. For instance, non-structural 5A protein of hepatitis C virus (HCV) causes repression of PKR activation, eventually leading to suppression of host IFN response.…”

Chapter 9 Viral Strategies to Subvert the Mammalian Translation Machinery

“…Many viruses synthesize dsRNA-binding proteins that prevent activation of PKR by interacting with and sequestering any free dsRNA molecules. 228,229 The first such dsRNA-binding protein identified in this regard was reovirus sigma 3. 230 The reovirus sigma 3 protein does not have catalytic activity and it was shown that inhibition of PKR by this protein could be overcome by the addition of excess dsRNA, 229 suggesting that the protein acts as a competitive inhibitor by directly binding to dsRNA.…”