PB2 Residue 158 Is a Pathogenic Determinant of Pandemic-H1N1 and H5 Influenza A Viruses In Mice
J Virol. 2010 Oct 20;
Influenza A viruses are human and animal pathogens that cause morbidity and mortality, which ranges from mild-to-severe. The 2009-H1N1 pandemic was caused by the emergence of a reassortant H1N1 subtype (H1N1pdm) influenza A virus containing gene segments that originally circulated in human, avian, and swine virus reservoirs. The molecular determinants of replication and pathogenesis of H1N1pdm viruses in humans and other mammals are poorly understood. Therefore, we set out to elucidate viral determinants critical to the pathogenesis of this novel reassortant using a mouse model. We found that a glutamate to glycine substitution at residue 158 of the PB2 gene (PB2-E158G) increased the morbidity and mortality of the parental H1N1pdm virus. Results from mini-genome replication assays in human cells and virus titration in mouse tissues demonstrate that PB2-E158G is a pathogenic determinant because it significantly increases viral replication rates. The virus load in PB2-E158G infected mouse lungs was 1300-fold higher than the wild type virus. Our data also shows that PB2-E158G had a much stronger influence on RNA replication and pathogenesis of H1N1pdm viruses than PB2-E627K, which is a known pathogenic determinant. Remarkably, PB2-E158G substitutions also altered the pathotype of two avian H5 viruses in mice, indicating that this residue impacts genetically divergent influenza A viruses and suggests that this region of PB2 could be a new antiviral target. Collectively the data presented in this study demonstrates that PB2-E158G is a novel pathogenic determinant of influenza A viruses in the mouse model. We speculate that PB2-E158G may be important in the adaptation of avian PB2 genes to other mammals and BLAST sequence analysis identified a naturally occurring human H1N1pdm isolate that has this substitution. Therefore, future surveillance efforts should include scrutiny in this region of PB2 because of its potential impact on pathogenesis.