Multifunctional Adaptive NS1 Mutations Are Selected upon Human Influenza Virus Evolution in the MouseReport as inadecuate




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The role of the NS1 protein in modulating influenza A virulence and host range was assessed by adapting A-Hong Kong-1-1968 H3N2 HK-wt to increased virulence in the mouse. Sequencing the NS genome segment of mouse-adapted variants revealed 11 mutations in the NS1 gene and 4 in the overlapping NEP gene. Using the HK-wt virus and reverse genetics to incorporate mutant NS gene segments, we demonstrated that all NS1 mutations were adaptive and enhanced virus replication up to 100 fold in mouse cells and-or lungs. All but one NS1 mutant was associated with increased virulence measured by survival and weight loss in the mouse. Ten of twelve NS1 mutants significantly enhanced IFN-β antagonism to reduce the level of IFN β production relative to HK-wt in infected mouse lungs at 1 day post infection, where 9 mutants induced viral yields in the lung that were equivalent to or significantly greater than HK-wt up to 16 fold increase. Eight of 12 NS1 mutants had reduced or lost the ability to bind the 30 kDa cleavage and polyadenylation specificity factor CPSF30 thus demonstrating a lack of correlation with reduced IFN β production. Mutant NS1 genes resulted in increased viral mRNA transcription 10 of 12 mutants, and protein production 6 of 12 mutants in mouse cells. Increased transcription activity was demonstrated in the influenza mini-genome assay for 7 of 11 NS1 mutants. Although we have shown gain-of-function properties for all mutant NS genes, the contribution of the NEP mutations to phenotypic changes remains to be assessed. This study demonstrates that NS1 is a multifunctional virulence factor subject to adaptive evolution.



Author: Nicole E. Forbes, Jihui Ping, Samar K. Dankar, Jian-Jun Jia, Mohammed Selman, Liya Keleta, Yan Zhou, Earl G. Brown

Source: http://plos.srce.hr/



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