Eukaryotic Translation Initiation Factor 4GI Is a Cellular Target for NS1 Protein, a Translational Activator of Influenza Virus

Abstract

Influenza virus NS1 protein is an RNA-binding protein whose expression alters several posttranscriptional regulatory processes, like polyadenylation, splicing, and nucleocytoplasmic transport of cellular mRNAs. In addition, NS1 protein enhances the translational rate of viral, but not cellular, mRNAs. To characterize this effect, we looked for targets of NS1 influenza virus protein among cellular translation factors. We found that NS1 coimmunoprecipitates with eukaryotic initiation factor 4GI (eIF4GI), the large subunit of the cap-binding complex eIF4F, either in influenza virus-infected cells or in cells transfected with NS1 cDNA. Affinity chromatography studies using a purified His-NS1 protein-containing matrix showed that the fusion protein pulls down endogenous eIF4GI from COS-1 cells and labeled eIF4GI translated in vitro, but not the eIF4E subunit of the eIF4F factor. Similar in vitro binding experiments with eIF4GI deletion mutants indicated that the NS1-binding domain of eIF4GI is located between residues 157 and 550, in a region where no other component of the translational machinery is known to interact. Moreover, using overlay assays and pull-down experiments, we showed that NS1 and eIF4GI proteins interact directly, in an RNA-independent manner. Mapping of the eIF4GI-binding domain in the NS1 protein indicated that the first 113 N-terminal amino acids of the protein, but not the first 81, are sufficient to bind eIF4GI. The first of these mutants has been previously shown to act as a translational enhancer, while the second is defective in this activity. Collectively, these and previously published data suggest a model where NS1 recruits eIF4GI specifically to the 5 untranslated region (5 UTR) of the viral mRNA, allowing for the preferential translation of the influenza virus messengers.

Role of MAPK/MNK1 signaling in virus replication

“…Most DNA viruses such as HSV-1, African swine fever virus (ASFV) (Castello et al, 2009), vaccinia virus (Walsh et al, 2008) as well as some RNA viruses such as chikungunya virus (CHIKV) (Walsh et al, 2013), SARS-CoV (Cencic et al, 2011), orthomyxoviruses (Aragon et al, 2000;Yanguez et al, 2012), rhabdoviruses (VSV, rabies virus) (Komarova et al, 2007), reoviruses (Chulu et al, 2010), hantavirus (Mir and Panganiban, 2008), and alphaviruses (Voss et al, 2014) contain a 5′ cap in their mRNA. Some of the viruses such as influenza virus steal the 5′ cap from the cellular mRNAs (Gu et al, 2015;Plotch et al, 1981) whereas several other viruses synthesize it by using hostencoded capping apparatus, for instance, vaccinia virus and reoviruses (Harwig et al, 2017).…”

Avian Immunosuppressive Diseases and Immunoevasion

“…Although expression of NS1 alone was reported to induce apoptosis in MDCK and HeLa cells [223], in the context of a viral infection of mammalian or avian cells, its IFNregulatory activity makes it anti-apoptotic [224]. NS1 selectively enhances translation of viral but not cellular mRNAs by binding eIF4GI, PABP1 and the 5' UTRs of vmRNAs [225,226].…”

Systems-based candidate genes for human response to influenza infection

“…Viral NS1 is also a major player in shutting down host protein synthesis by interacting with host proteins to interfere with the host machinery, such as CPSF4 (cleavage and polyadenylation specific factor 4, 30kDa) and PABN1 (poly(A) binding protein, nuclear 1) (Chen et al, 1999) in polyadenylation; IVNS1ABP (influenza virus NS1A binding protein) (Wolff et al, 1998) in splicing; and BAT1(HLA-B associated transcript 1) ( Momose et al, 2001) in nucleocytoplasmic transport of cellular mRNAs. NS1 also recruits the cellular initiation factor, EIF4G1 (eukaryotic translation initiation factor 4 gamma, 1), allowing for the preferential translation of the IAV messengers (Aragon et al, 2000). Viral M1 can interact with VPS28 (vacuolar protein-sorting 28 homolog), a component of endosomal complexes required for transport, and CDC42 (cell division cycle 42), a small G protein, playing an important role in budding of the IAV (Hui et al, 2006).…”