부산대학교 도서관

Influenza A virus adaptation to humans is a rare but recurrent event that can result in a pandemic. The influenza polymerase, composed of the viral proteins PB1, PB2 and PA, is responsible for transcription and replication of the viral genome. Typical avian-origin influenza polymerases are restricted in human cells and polymerase subunit PB2 is particularly involved in this restriction. Residue 627 of PB2 is a glutamic acid in almost all avian influenza viruses, and mutation to a lysine is a potent enhancer of avian polymerase function in human cells. However, the underlying molecular mechanism and the cellular factors modulating avian-origin influenza replication in mammals are not known. Using a cell based replication assay in heterokaryons formed between avian and human cells, we concluded that the restriction is not due to a dominant human inhibitory factor. We also showed that supply of avian factors to human cells stimulated the activity of an avian-origin influenza polymerase and a functional screen was set up to attempt to isolate such chicken co-factor(s). We hypothesised that PB2 E627K mutation enhances the viral polymerase activity by optimizing an interaction with a human co-factor. A biochemical approach was used to try to identify this factor. Pigs are thought to be more susceptible to avian influenza than other mammalian species and are a supposed “mixing vessel” for influenza A viruses. To compare the replicative capacity of different influenza polymerases in pig, human and avian cells, an influenza polymerase assay in pig cells was set up. This assay was also used to study the impact in pig cells of known PB2 mammalian adaptive mutations. No obvious difference in the capacity of pig and human cells to support influenza polymerase activity was found, questioning the suggested susceptibility of pigs to influenza. Viruses from the avian H9N2 G1 lineage have been responsible for some human infections. Despite having none of the known mammalian signatures, we found the H9N2 G1 polymerase was active in human and pig cells. This study identified H9N2 G1 PA protein as being particularly mammalian adapted, highlighting the role of PA in influenza mammalian adaptation.