Viral RNA-binding ability conferred by SUMOylation at PB1 K612 of influenza A virus is essential for viral pathogenesis and transmission.

Junping Li,Yongping Jiang,Xia Wen,Qian Wang,Xianying Zeng,Guobin Tian,Qibing Li,Li Jiang,Chengjun Li,Liling Liu,Guohua Deng,Yaping Zhang,Hualan Chen,Guangwen Wang,Pengfei Cui,Libin Liang,Jianzhong Shi,Yuhui Zhao,Jacob S Yount

doi:10.1371/journal.ppat.1009336

Abstract

Posttranslational modifications, such as SUMOylation, play specific roles in the life cycle of invading pathogens. However, the effect of SUMOylation on the adaptation, pathogenesis, and transmission of influenza A virus (IAV) remains largely unknown. Here, we found that a conserved lysine residue at position 612 (K612) of the polymerase basic protein 1 (PB1) of IAV is a bona fide SUMOylation site. SUMOylation of PB1 at K612 had no effect on the stability or cellular localization of PB1, but was critical for viral ribonucleoprotein (vRNP) complex activity and virus replication in vitro. When tested in vivo, we found that the virulence of SUMOylation-defective PB1/K612R mutant IAVs was highly attenuated in mice. Moreover, the airborne transmission of a 2009 pandemic H1N1 PB1/K612R mutant virus was impaired in ferrets, resulting in reversion to wild-type PB1 K612. Mechanistically, SUMOylation at K612 was essential for PB1 to act as the enzymatic core of the viral polymerase by preserving its ability to bind viral RNA. Our study reveals an essential role for PB1 K612 SUMOylation in the pathogenesis and transmission of IAVs, which can be targeted for the design of anti-influenza therapies.

Highlights

Influenza A virus (IAV) is an important zoonotic pathogen that causes frequent epidemics and occasional pandemics in humans
The transcription and replication of IAV genome occur in the nucleus of infected cells, which is catalyzed by the RNA-dependent RNA polymerase (RdRp)
We demonstrated that PB1 protein from different subtypes of IAV is a target of SUMOylation in both transfected and infected cells, and identified K612 of PB1 as the key SUMOylation site

Summary

Introduction

Influenza A virus (IAV) is an important zoonotic pathogen that causes frequent epidemics and occasional pandemics in humans. Humans are constantly facing threats posed by avian influenza viruses (AIVs), with H5N1 and H7N9 human infections as two prime examples. The first human infection with H5N1 AIV occurred in Hong Kong in 1997 [3], and between 2003 and 2020, 861 human infection cases were reported, of which 455 were fatal [4]. The H7N9 low pathogenic AIVs identified in 2013 and the subsequently mutated H7N9 highly pathogenic AIVs in 2017 [5,6,7,8] led to 1568 human infections, including 615 fatal cases [9]. Continued efforts to elucidate the factors and mechanisms underlying the pathogenesis and transmission of IAVs remain critical for the development of novel anti-influenza therapies

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