Effects of the PA-X and PB1-F2 Proteins on the Virulence of the 2009 Pandemic H1N1 Influenza A Virus in Mice.

Jun Ma,Shun Li,Kangjian Li,Xiangbin Wang,Shoujun Li

doi:10.3389/fcimb.2019.00315

Abstract

There have been several previous reports showing that PA-X and PB1-F2 proteins can regulate innate immune responses and may play roles in the adaptation of influenza viruses to new hosts. In this research, we investigated, for the first time, the combined effects of PA-X and PB1-F2 proteins on viral virulence in mice. Based on the 2009 pH1N1 A/Guangdong/1057/2010 virus backbone, four viruses encoding different combinations of full-length or truncated PA-X and PB1-F2 proteins were rescued by a reverse genetic engineering system. We analyzed viral replication, host-shutoff activity, in vitro viral pathogenicity and in vivo host immune response. We found that simultaneously expressing the full-length PA-X and PB1-F2 proteins enhanced viral replication in vitro through increasing the accumulation of the RNP complex protein and enhanced viral pathogenicity in mice during the early stage of infection. Furthermore, PA-X and PB1-F2 simultaneously regulated the host innate response, and different forms of PB1-F2 proteins may have impacts on the host shutoff activity induced by the PA-X protein. Our results provide a better understanding of the mechanisms of PA-X and PB1-F2 proteins during viral replication, pathogenicity and host immune response.

Highlights

Influenza A virus circulates in multiple hosts ranging from aquatic or terricolous birds to diverse mammalian species, including humans
Since the PA-X protein was discovered in 2012, multiple characteristics of this protein have been described in detail, including its effects on viral pathogenicity and modulation of the host immune response and the host shutoff activity that suppresses host protein synthesis (Gao et al, 2015b; Hu et al, 2018)
In contrast to previous studies, we investigated the combined effects caused by different forms of the PA-X (232 or 252 aa) and PB1-F2 proteins (11 or 90 aa) in the 2009 pH1N1 virus in regard to viral replication, pathogenicity and host immune response

Summary

Introduction

Influenza A virus circulates in multiple hosts ranging from aquatic or terricolous birds to diverse mammalian species, including humans. In the past few years, seven new proteins encoded by the virus genome have been identified, including PB1-F2 (Chen et al, 2001), PB1-N40 (Wise et al, 2009), PA-X (Jagger et al, 2012), M42 (Wise et al, 2012), NS3 (Selman et al, 2012), PA-N155, and PA-N182 (Muramoto et al, 2013) Among these novel discovered proteins, PA-X and PB1-F2 proteins have been discovered to have functions in regulating the host immune response and are suspected to play roles in the adaptation of influenza to mammalian hosts. PA-X can selectively degrade mRNAs transcripts produced by the host RNA polymerase II, but it ignores the activity of RNA polymerase I and III (Khaperskyy et al, 2016)

Methods

Results

Conclusion