Avian-derived NS gene segments alter pathogenicity of the A/Puerto Rico/8/34 virus

Annexin A2 (ANXA2) interacts with nonstructural protein 1 and promotes the replication of highly pathogenic H5N1 avian influenza virus

BACKGROUND

Non-structural protein 1 (NS1) is a multifunctional protein and a crucial regulatory factor in the replication and pathogenesis of avian influenza virus (AIV). Studies have shown that NS1 can interact with a variety of host proteins to modulate the viral life cycle. We previously generated a monoclonal antibody against NS1 protein; In the current research study, using this antibody, we immunoprecipitated host proteins that interact with NS1 to better understand the roles played by NS1 in communications between virus and host.

RESULTS

Co-immunoprecipitation experiments identified annexin A2 (ANXA2) as a target molecule interacting with NS1. Results from confocal laser scanning microscopy indicated that NS1 co-localized with ANXA2 in the cell cytoplasm. Overexpression of ANXA2 significantly increased the titer of H5N1 subtype HPAIV, whereas siRNA-mediated knockdown of ANXA2 markedly inhibited the expression of viral proteins and reduced the progeny virus titer.

CONCLUSIONS

Our results indicate that ANXA2 interacts with NS1 and ANXA2 expression increases HPAIV replication.

Development of a dual-protective live attenuated vaccine against H5N1 and H9N2 avian influenza viruses by modifying the NS1 gene

An increasing number of outbreaks of avian influenza H5N1 and H9N2 viruses in poultry have caused serious economic losses and raised concerns for human health due to the risk of zoonotic transmission. However, licensed H5N1 and H9N2 vaccines for animals and humans have not been developed. Thus, to develop a dual H5N1 and H9N2 live-attenuated influenza vaccine (LAIV), the HA and NA genes from a virulent mouse-adapted avian H5N2 (A/WB/Korea/ma81/06) virus and a recently isolated chicken H9N2 (A/CK/Korea/116/06) virus, respectively, were introduced into the A/Puerto Rico/8/34 backbone expressing truncated NS1 proteins (NS1-73, NS1-86, NS1-101, NS1-122) but still possessing a full-length NS gene. Two H5N2/NS1-LAIV viruses (H5N2/NS1-86 and H5N2/NS1-101) were highly attenuated compared with the full-length and remaining H5N2/NS-LAIV viruses in a mouse model. Furthermore, viruses containing NS1 modifications were found to induce more IFN-β activation than viruses with full-length NS1 proteins and were correspondingly attenuated in mice. Intranasal vaccination with a single dose (10(4.0) PFU/ml) of these viruses completely protected mice from a lethal challenge with the homologous A/WB/Korea/ma81/06 (H5N2), heterologous highly pathogenic A/EM/Korea/W149/06 (H5N1), and heterosubtypic highly virulent mouse-adapted H9N2 viruses. This study clearly demonstrates that the modified H5N2/NS1-LAIV viruses attenuated through the introduction of mutations in the NS1 coding region display characteristics that are desirable for live attenuated vaccines and hold potential as vaccine candidates for mammalian hosts.

Differential microRNA expression following infection with a mouse-adapted, highly virulent avian H5N2 virus

Background

MicroRNAs (miRNAs) are known to regulate various biological processes, including expression of cellular gene and virus-induced inflammation. Recently, studies have indicated that some miRNAs could regulate influenza virus replication. Due to differential sensitivities of influenza A virus strains to different species (avian and mammalian), variations in host responses may be observed. Therefore, we investigated and compared the differences in global host miRNA expression in mouse lungs infected with wild type low pathogenicity A/Aquatic bird/Korea/w81/2005 (H5N2) (w81) or mouse-adapted virulent A/Aquatic bird /Korea/ma81/2007 (H5N2) (ma81) virus.

Results

Although the mice infected with ma81 exhibited much greater mortality than w81-infected mice, the parental w81 virus induced a higher number of differentially expressed miRNAs compared to the ma81 virus. Between these 2 viruses, a total of 27 and 20 miRNAs were commonly expressed at 1 dpi and 3 dpi, respectively. It is noteworthy that only 9 miRNAs (miR-100-5p, miR-130a-5p, miR-146b-3p, miR-147-3p, miR-151-5p, miR-155-3p, miR-223-3p, miR-301a-3p, and miR-495-3p) were significantly upregulated in both lungs infected with either wild type w81 or the mouse-adapted ma81 strain at both time points. Notably, expression levels of miR-147-3p, miR-151-5p, miR-155-3p, and miR-223-3p were higher in the lungs of mice infected with the ma81 virus than those infected with the w81 virus. To identify potential roles of these miRNAs in regulating influenza virus replication, each group of mice was intranasally treated with each inhibitor of specifically targeting 4 miRNAs, and then challenged with 5 mouse lethal dose 50% (MLD₅₀) of the virulent ma81 virus on the following day. Although the specific miRNA inhibitors could not completely attenuate mortality or reduce viral replication, the miR-151-5p- and miR-223-3p-inhibitors reduced mortality of inoculated mice to 70% and substantially delayed death.

Conclusions

Our results suggest that the mammalian adaptation of avian influenza A virus results in a different miRNA expression pattern in lungs of virus-infected mice compared with its parental strain, and use of specific miRNA inhibitors to target genes associated with the immune response or cell death may affect virulence and virus replication.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-014-0252-0) contains supplementary material, which is available to authorized users.