Extracellular truncated influenza virus nucleoprotein

Area of Science:

• Virology
• Molecular Biology
• Cell Biology

Background:

• Influenza A virus infection involves the synthesis and assembly of viral components, including the nucleoprotein (NP).
• The behavior and fate of viral proteins during infection are crucial for understanding viral replication and pathogenesis.

Purpose of the Study:

• To investigate the characteristics and origins of two distinct influenza A virus nucleoprotein (NP) forms (56 kDa and 53 kDa) observed during MDCK cell infection.
• To elucidate the processing, localization, and secretion pathways of the truncated 53 kDa NP.

Main Methods:

• Infection of Madin-Darby canine kidney (MDCK) cells with influenza A/Duck/Ukraine/1/63 (H3N8) virus.
• Detection and characterization of viral nucleoproteins (NP) in infected cells and culture medium using techniques like pulse-chase analysis.
• Analysis of NP oligomerization state and association with ribonucleoprotein (RNP) complexes.

Main Results:

• Two NP forms, full-length 56 kDa and truncated 53 kDa, were detected in the culture medium of infected MDCK cells.
• The 53 kDa NP was transiently detected within infected cells but was found extracellularly in free RNP complexes, not within virions.
• Extracellular NPs (both 53 kDa and 56 kDa) were oligomerized, with the 56 kDa form showing high protease resistance in its oligomeric state.

Conclusions:

• The 53 kDa NP is likely formed intracellularly through proteolytic cleavage of the 56 kDa NP monomer before oligomerization.
• This truncated NP then oligomerizes, incorporates into RNPs, and is rapidly secreted from infected cells.
• The findings suggest a specific pathway for the processing and secretion of a fraction of influenza NP during infection.