Prevalence of the C-terminal truncations of NS1 in avian influenza A viruses and effect on virulence and replication of a highly pathogenic H7N1 virus in chickens

Abstract

(2016) Prevalence of the C-terminal truncations of NS1 in avian influenza A viruses and effect on virulence and replication of a highly pathogenic H7N1 virus in chickens, Virulence, 7:5, 546-557, DOI: 10.1080/21505594.2016 protein sequences of all AIV subtypes in birds from 1902 to 2015 were analyzed to study the prevalence and distribution of CTE truncation (DCTE). Thirteen different DCTE forms were observed in NS1 proteins from 11 HA and 8 NA subtypes with high prevalences in H9, H7, H6 and H10 and N9, N2, N6 and N1 subtypes particularly in chickens and minor poultry species. With 88% NS217 lacking amino acids 218-230 was the most common DCTE form followed by NS224 (3.6%). NS217 was found in 10 and 8 different HA and NA subtypes, respectively, whereas NS224 was detected exclusively in the Italian HPAIV H7N1 suggesting relevance for virulence. To test this assumption, 3 recombinant HPAIV H7N1 were constructed carrying wild-type HP NS1 (Hp-NS224), NS1 with extended CTE (Hp-NS230) or NS1 from LPAIV H7N1 (Hp-NSLp), and tested in-vitro and in-vivo. Extension of CTE in Hp NS1 significantly decreased virus replication in chicken embryo kidney cells. Truncation in the NS1 decreased the tropism of Hp-NS224 to the endothelium, central nervous system and respiratory tract epithelium without significant difference in virulence in chickens. This study described the variable forms of DCTE in NS1 and indicated that CTE is not an essential virulence determinant particularly for the Italian HPAIV H7N1 but may be a host-adaptation marker required for efficient virus replication.

Phylogenetic and molecular analysis of highly pathogenic avian influenza H5N8 and H5N5 viruses detected in Poland in 2016-2017

“…Apart from a polybasic cleavage site in the HA protein, other molecular markers potentially influencing the virulence were identified. C‐Terminal truncation of NS1 has been observed previously in various subtypes of AI viruses, mainly those from gallinaceous poultry (Abdelwhab et al., ). Experimental studies revealed that the effect of NS1 truncation on virus replication depends on the host and virus strain (Abdelwhab et al., ; Zielecki et al., ).…”

“…C‐Terminal truncation of NS1 has been observed previously in various subtypes of AI viruses, mainly those from gallinaceous poultry (Abdelwhab et al., ). Experimental studies revealed that the effect of NS1 truncation on virus replication depends on the host and virus strain (Abdelwhab et al., ; Zielecki et al., ). Similarly, truncation of the PB1‐F2 protein has been found to occur in particular hosts (mainly in mammals) (Dundon, ).…”

Composition of the Hemagglutinin Polybasic Proteolytic Cleavage Motif Mediates Variable Virulence of H7N7 Avian Influenza Viruses

“…Immunohistochemical examination of consecutive sections was performed with the avidin–biotin–peroxidase complex method (Vector Laboratories) using a primary polyclonal rabbit anti-NP antibody (1:750) and a secondary biotinylated goat anti-rabbit IgG1 (Vector Laboratories) antibody (1:200) as described47. The concentration of nucleoprotein antigen was semi quantitatively assessed by scoring on a 0 to 4 severity scale for tissues: 0 = negative; 1 = single cells, 2 = scattered foci, 3 = numerous foci, 4 = coalescing foci or diffuse and on a scale of 0 to 3 for endothelium: 0 = negative; 1 = single blood vessel, 2 = multiple blood vessels, 3 = diffuse as done before48.…”

Stop-codon variations in non-structural protein NS1 of avian influenza viruses

“…1 Another approach consists in analyzing the thousands of sequences that were deposited at the Influenza Virus Resource (http://www.ncbi.nlm.nih.gov/genomes/FLU/FLU.html). In a recently published article in Virulence, Abdelwhab et al 2 carried out a systematic study of C-terminal truncations of the Non-structural protein NS1 in avian influenza A viruses (IAVs) since the beginning of the 20th century. Influenza A viruses are enveloped viruses of the Orthomyxoviridae family, whose genome consists of 8 negative-strand RNAs which collectively encode more than 10 viral proteins.…”