Expression of importin-α isoforms in human nasal mucosa: implication for adaptation of avian influenza A viruses to human host.

BACKGROUND: Transportation into the host cell nucleus is crucial for replication and transcription of influenza virus. The classical nuclear import is regulated by specific cellular factor, importin-α. Seven isoforms of importin-α have been identified in human. The preference of importin-α3 of avian influenza virus and -α7 isoform of human strains during replication in human cells was previously identified. In addition, both avian and human influenza viruses were shown to use importin-α1 isoform for their replication. FINDING: The mRNA levels of importin-α1, -α3, and -α7 isoforms in human respiratory tract was determined by real-time RT-PCR. The results indicate that mRNA level of importin-α7 was significantly higher than that of importin-α1 (p-value < 0.0001) and importin-α3 (p-value < 0.0001) isoforms in human nasal mucosa while importin-α1 was detected as the highest expression importin-α isoform in lung tissues. CONCLUSIONS: These results may explain the preference of importin-α7 isoforms in seasonal influenza viruses in human upper respiratory tract and may suggest a selective pressure toward importin-α7 in human respiratory tract infection of an avian virus.