Accumulation of segment 6 sgRNAs of influenza A viruses in the presence of neuraminidase inhibitors

Abstract

Background: RNA segment 6 of influenza A viruses only encodes neuraminidase (NA), whereas the same segment of influenza B viruses encodes an additional protein, NB. The NA activity is not required for virus replication but is necessary for virus release from infected cells. In contrast, the NB is an essential influenza B viral membrane protein with an ion channel function. Methods: Influenza A and B viruses were passaged in Madine–Darby canine kidney (MDCK) cells in the presence of NA inhibitors. The segment 6 sequences of the selected viruses were analyzed. Results: Accumulation of subgenomic (sg) RNAs of segment 6 in influenza A, but not influenza B viruses, was observed as a result of passage in the presence of NA inhibitors. Sequencing of sgRNAs revealed that there were internal deletions of the NA gene both in-frame and with a shift in reading frame. Additional passage of the virus without NA inhibitor resulted in a reduction in the amount of sgRNAs, suggesting that it is a reversible phenomenon. Conclusions: Accumulations of sgRNAs could serve as an indicator of reduced viral dependence on NA function during the release of influenza A virus from infected cells. We speculate that the coding capacity of RNA segment 6 of influenza B viruses is preserved because of the essential role of the NB protein and possibly NA in influenza B virus replication.