Uncovering the Potential Pan Proteomes Encoded by Genomic Strand RNAs of Influenza A Viruses.PLoS One. 2016;11:e0146936. [PMID: 26761196 DOI: 10.1371/journal.pone.0146936]

The Unique Genome of the Virus and Alternative Strategies for its Realization

Dedicated to the 130th anniversary of Dmitry Ivanovsky's discovery of the virus kingdom as a new form of biological life. The genome of some RNA-containing viruses comprises ambipolar genes that are arranged in stacks (one above the other) encoding proteins in opposite directions. Ambipolar genes provide a new approach for developing viral diversity when virions possessing an identical genome may differ in its expression scheme (strategy) and have distinct types of progeny virions varying in the genomic RNA polarity and the composition of proteins expressed by positive- or negative-sense genes, the so-called ambipolar virions. So far, this pathway of viral genome expression remains hypothetical and hidden from us, like the dark side of the Moon, and deserves a detailed study.

MicroRNAs affect GPCR and Ion channel genes needed for influenza replication

Influenza virus causes seasonal epidemics and sporadic pandemics resulting in morbidity, mortality, and economic losses worldwide. Understanding how to regulate influenza virus replication is important for developing vaccine and therapeutic strategies. Identifying microRNAs (miRs) that affect host genes used by influenza virus for replication can support an antiviral strategy. In this study, G-protein coupled receptor (GPCR) and ion channel (IC) host genes in human alveolar epithelial (A549) cells used by influenza virus for replication (Orr-Burks et al., 2021) were examined as miR target genes following A/CA/04/09- or B/Yamagata/16/1988 replication. Thirty-three miRs were predicted to target GPCR or IC genes and their miR mimics were evaluated for their ability to decrease influenza virus replication. Paired miR inhibitors were used as an ancillary measure to confirm or not the antiviral effects of a miR mimic. Fifteen miRs lowered influenza virus replication and four miRs were found to reduce replication irrespective of virus strain and type differences. These findings provide evidence for novel miR disease intervention strategies for influenza viruses.

Drug repositioning of Clopidogrel or Triamterene to inhibit influenza virus replication in vitro

Influenza viruses cause respiratory tract infections and substantial health concerns. Infection may result in mild to severe respiratory disease associated with morbidity and some mortality. Several anti-influenza drugs are available, but these agents target viral components and are susceptible to drug resistance. There is a need for new antiviral drug strategies that include repurposing of clinically approved drugs. Drugs that target cellular machinery necessary for influenza virus replication can provide a means for inhibiting influenza virus replication. We used RNA interference screening to identify key host cell genes required for influenza replication, and then FDA-approved drugs that could be repurposed for targeting host genes. We examined the effects of Clopidogrel and Triamterene to inhibit A/WSN/33 (EC50 5.84 uM and 31.48 uM, respectively), A/CA/04/09 (EC50 6.432 uM and 3.32 uM, respectively), and B/Yamagata/16/1988 (EC50 0.28 uM and 0.11 uM, respectively) replication. Clopidogrel and Triamterene provide a druggable approach to influenza treatment across multiple strains and subtypes.

Ambisense polarity of genome RNA of orthomyxoviruses and coronaviruses

Influenza viruses and coronaviruses have linear single-stranded RNA genomes with negative and positive sense polarities and genes encoded in viral genomes are expressed in these viruses as positive and negative genes, respectively. Here we consider a novel gene identified in viral genomes in opposite direction, as positive in influenza and negative in coronaviruses, suggesting an ambisense genome strategy for both virus families. Noteworthy, the identified novel genes colocolized in the same RNA regions of viral genomes, where the previously known opposite genes are encoded, a so-called ambisense stacking architecture of genes in virus genome. It seems likely, that ambisense gene stacking in influenza and coronavirus families significantly increases genetic potential and virus diversity to extend virus-host adaptation pathways in nature. These data imply that ambisense viruses may have a multivirion mechanism, like "a dark side of the Moon", allowing production of the heterogeneous population of virions expressed through positive and negative sense genome strategies.

G-Protein-Coupled Receptor and Ion Channel Genes Used by Influenza Virus for Replication

Influenza virus causes epidemics and sporadic pandemics resulting in morbidity, mortality, and economic losses. Influenza viruses require host genes to replicate. RNA interference (RNAi) screens can identify host genes coopted by influenza virus for replication. Targeting these proinfluenza genes can provide therapeutic strategies to reduce virus replication. Nineteen proinfluenza G-protein-coupled receptor (GPCR) and 13 proinfluenza ion channel genes were identified in human lung (A549) cells by use of small interfering RNAs (siRNAs). These proinfluenza genes were authenticated by testing influenza virus A/WSN/33-, A/CA/04/09-, and B/Yamagata/16/1988-infected A549 cells, resulting in the validation of 16 proinfluenza GPCR and 5 proinfluenza ion channel genes. These findings showed that several GPCR and ion channel genes are needed for the production of infectious influenza virus. These data provide potential targets for the development of host-directed therapeutic strategies to impede the influenza virus productive cycle so as to limit infection.IMPORTANCE Influenza epidemics result in morbidity and mortality each year. Vaccines are the most effective preventive measure but require annual reformulation, since a mismatch of vaccine strains can result in vaccine failure. Antiviral measures are desirable particularly when vaccines fail. In this study, we used RNAi screening to identify several GPCR and ion channel genes needed for influenza virus replication. Understanding the host genes usurped by influenza virus during viral replication can help identify host genes that can be targeted for drug repurposing or for the development of antiviral drugs. The targeting of host genes is refractory to drug resistance generated by viral mutations, as well as providing a platform for the development of broad-spectrum antiviral drugs.

Unique Bipolar Gene Architecture in the RNA Genome of Influenza A Virus

The genome of influenza A virus consists of eight single-stranded negative-polarity RNA segments. The eighth segment (NS) encodes the anti-interferon protein NS1 (27 kDa) and the nuclear export protein NEP (14 kDa) via the classic negative-sense strategy. It also contains an additional positive-sense open reading frame that can be directly translated into the negative strand protein 8 (NSP8; 18–25 kDa in different strains). The existence of three or more genes of the opposite polarity in the same locus of a single-stranded RNA appears to be a unique (“economical”) type of gene architecture in living organisms. In silico analysis of genomes of human and animal influenza A viruses revealed that the NSP8 gene had emerged in the influenza A virus population about 100 years ago (“young” gene) and is highly evolutionary variable. The obtained experimental data suggest that NSP8 gene is expressed in the infected animals, which strengthens the concept of bipolar (ambisense) strategy of the influenza A virus genome. The high variability of the NSP8 protein suggests that the “young” NSP8 gene is in the process of functional optimization. Further accumulation of mutations may alter the functions of mature NSP8 protein and lead to the emergence of mature bipolar influenza A virus with unexpected properties that would be threatening for humans and animals.

NSP Protein Encoded in Negative NS RNA Strand of Influenza A Virus Induces Cellular Immune Response in Infected Animals

Infection of mice with influenza A viruses led to the formation of clones of lymphocytes that specifically recognizes viral domains in the central zone of the NSP protein (amino acid positions 83-119). Computer analysis of the primary structure of the NSP protein showed the presence of T-cell epitopes in the central part of the NSP molecule. The findings indicate that the viral NSP gene is expressed in the infected animals and verify the concept of the bipolar strategy (ambisense strategy) of the influenza A virus genome.

Negative-sense virion RNA of segment 8 (NS) of influenza a virus is able to translate in vitro a new viral protein

It was shown that full-length virion RNA of segment 8 of influenza virus A/Aichi/2/68 (H3N2) can initiate the synthesis of two major polypeptides with molecular weights of 23 and 13 kD and a minor polypeptide with a molecular weight of 19 kDa, which specifically reacted with the antibodies to the 30-membered peptide of the central part of the NSP protein of influenza A virus. Thus, the genomic-polarity RNA of segment 8 of influenza virus A has a translational template function. These data provide further confirmation of the concept of the bipolar (ambisens) strategy of functioning of the influenza A virus genome.