Differential nucleocytoplasmic shuttling of the nucleoprotein of influenza a viruses and association with host tropism

Abstract

The nucleoprotein (NP) of influenza A virus plays a crucial role in virus replication, infectivity, and host adaptation. As a major component of the viral ribonucleoprotein complexes (vRNP), NP initiates vRNP shuttling between the nucleus and cytoplasm in the host cell. However, the characteristics of the nucleocytoplasmic shuttling of NP from H1N1 influenza A virus still remain unclear. In the present study, the subcellular localization and the related key residues of the H1N1 influenza virus NP were identified and evaluated. The NP of influenza virus A/WSN/33 (H1N1; WSN) displayed a more obvious nuclear accumulation than A/Anhui/1/2013 (H7N9; AH) and A/chicken/Shandong/lx1023/2007 (H9N2; SD). NP residue K4, located in NLS1, and residue F253, located in NES3, from WSN NP are not conserved in H7N9 and H9N2, which instead encode Q4 and I253, respectively. Crucially, these residues are involved in the regulation of NP nucleocytoplasmic shuttling through interactions with CRM1 and importin-α. Moreover, residues at position 253 also play important roles in the replication of the virus, resulting in an increase in vRNP polymerase activity and an alteration of the cell tropism and pathogenicity in mice. The present data revealed a pivotal role of the Q4 and I253 residues of NP from H7N9 in enhancing the cytoplasmic accumulation of NP and vRNP activity compared to the K4 and F253 residues in WSN-NP. In addition, an F253I substitution in the NP of WSN altered the survival ratio of infected mice and the growth curve in infected avian-origin cells (DF-1). The current data indicate that the F253I mutation results in attenuated pathogenicity of the virus in mice and altered cell tropism. The present study demonstrated the dissimilarity in subcellular NP transport processes between H1N1 virus WSN and other influenza A virus strains, as well as uncovered the mechanism responsible for this difference.

Conserved methionine 165 of matrix protein contributes to the nuclear import and is essential for influenza A virus replication

“…Still, there is many studies focusing on nuclear export but nuclear import is not fully explained yet. It was suggested that some still unknown viral and host nuclear factors must be involved in regulation transport of vRNP and viral proteins, and our findings support these suggestions [ 31 , 45 , 46 ].…”

Phosphorylation of Influenza A Virus Matrix Protein 1 at Threonine 108 Controls Its Multimerization State and Functional Association with the STRIPAK Complex

“…Six hours later, the NP protein reached the nuclear periphery and was then transported to the cytosol at later time points (24 and 36 h.p.t. ), as described previously ( 40 ). Cells expressing M1 T108A showed an enrichment of the NP protein in the nuclear periphery at 24 h.p.t., but its nuclear export at later time points was severely compromised ( Fig.…”

Influence of Novel Highly Pathogenic Avian Influenza A (H5N1) Virus Infection on Migrating Whooper Swans Fecal Microbiota

“…Influenza is an infectious respiratory disease affecting many bird and mammal species (Laver and Webster, 1979 ). There are lots of researches focused on the role of antiviral immune against influenza virus infections (Iwasaki and Pillai, 2014 ; Jiang et al, 2016 ; Li et al, 2017 ; Liu et al, 2017 ; Zheng et al, 2017 ). Clinically, influenza in humans is often accompanied by gastroenteritis-like symptoms such as diarrhea.…”