Non-replicating Vaccinia Virus TianTan Strain (NTV) Translation Arrest of Viral Late Protein Synthesis Associated With Anti-viral Host Factor SAMD9.

Ying Zhao,Peng Zhang,Li Zhao,Wenjie Tan,Jiao Ren,Panpan Huang,Houwen Tian

doi:10.3389/fcimb.2020.00116

Abstract

NTV is a highly attenuated virus that was created by genetically deleting 26 genes related to host range and virulence from TianTan strain. Since NTV is highly attenuated, it has been used widely as an optimizing viral vector. In this study, we explored the biological characteristics in vitro and the host restriction mechanism of NTV. Most cell lines do not support sufficient dissemination and replication of NTV, and in non-permissive cell line HeLa, the replication block of NTV occurred at the translation stage of viral late protein expression. Lack of PKR activity was not sufficient to rescue expression of viral late proteins and replication, even though the phosphorylation level of eIF2α increased in NTV-infected HeLa cells. Moreover, the translation inhibition of NTV in HeLa cells was dependent upon a SAMD9 signaling pathway, as demonstrated by silencing SAMD9 expression with siRNA and observing the colocalization of SAMD9 and AVGs. Reinserting C7L or K1L into NTV rescued the late viral protein expression and replication of NTV in HeLa cells. Among the genes deleted in NTV, C7L or/and K1L gene was mainly responsible for its replication defect. Protein C7 interacted with SAMD9, which antagonized the antiviral response of SAMD9 to ensure viral protein translation and replication of NTV in non-permissive cell lines. Our finding will serve as a baseline for modification of NTV in future application.

Highlights

Vaccinia virus (VACV), a double-stranded DNA virus of the poxvirus family, was used as the smallpox vaccine during the worldwide smallpox eradication campaign
modified vaccinia virus Ankara (MVA) was attenuated by growing the vaccinia virus Ankara strain in chicken embryo fibroblasts (CEF) for more than 500 generations, 15% of the parental viral genome was lost during the course of attenuation, including genes associated with immunologic escape and host range (Antoine et al, 1998)
Among the candidate genes deleted in non-replicating vaccinia virus TianTan (NTV), we found that loss of C7L or K1L gene was mainly responsible for the replication defect of NTV, which was associated with the antiviral factor Sterile Alpha Motif Domain 9 (SAMD9)

Summary

Introduction

Vaccinia virus (VACV), a double-stranded DNA virus of the poxvirus family, was used as the smallpox vaccine during the worldwide smallpox eradication campaign. VACV is currently being investigated as a viral vector for vaccines against various infectious diseases and in cancer therapy because of its efficacious expression of large foreign genes and its ability to induce specific long-term protective humoral and cellular immune responses (Gomez et al, 2011). The attenuated replication-deficient VACV strains widely studied as viral vectors are modified vaccinia virus Ankara (MVA) and NYVAC. MVA was attenuated by growing the vaccinia virus Ankara strain in chicken embryo fibroblasts (CEF) for more than 500 generations, 15% of the parental viral genome was lost during the course of attenuation, including genes associated with immunologic escape and host range (Antoine et al, 1998). MVA expressing heterologous antigens was shown to induce considerable specific T-cell immunogenicity in humans against infectious disorders such as AIDS, malaria, and human papillomavirus-associated cancer (Sutter and Staib, 2003). Present human clinical trials with NYVAC-based vectors have demonstrated quality, safety, and a high level of immunity against different antigens (Raengsakulrach et al, 1999; Hel et al, 2002)

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