Interaction of the Mouse Polyomavirus Capsid Proteins with Importins Is Required for Efficient Import of Viral DNA...

Area of Science:

• Virology
• Cell Biology
• Molecular Mechanisms

Background:

• The precise mechanism by which mouse polyomavirus (MPyV) navigates the crowded cytoplasm to reach the nucleus remains incompletely understood.
• Nuclear import is a critical step for viral replication and pathogenesis.

Purpose of the Study:

• To investigate the role of importin α/β1-mediated transport in the nuclear delivery of MPyV genomes.
• To elucidate the contribution of viral capsid proteins' nuclear localization signals (NLSs) to this process.

Main Methods:

• Co-immunoprecipitation and proximity ligation assays to study virus-importin β1 interactions.
• Infectivity and nuclear delivery assays using wild-type and mutated MPyV virions and capsid proteins.
• Analysis of mutations affecting nuclear localization signals (NLSs) in VP1 and VP2/3 proteins.

Main Results:

• MPyV virions demonstrated time-dependent binding to importin β1, peaking at 6 hours post-infection.
• Disruption of NLSs in both VP1 and VP2/3 significantly reduced importin β1 binding and viral infectivity by 80%.
• Co-expression of VP1 and VP2 enhanced nuclear targeting of capsid proteins, with individual NLSs (VP1 or VP2) sufficient for nuclear delivery.

Conclusions:

• MPyV virions utilize nuclear localization signals (NLSs) on capsid proteins VP1 and/or VP2/VP3 to engage importins.
• This importin-mediated pathway is essential for efficient nuclear delivery of MPyV genomes and infectivity.
• MPyV employs a flexible strategy, using NLSs individually or in concert for nuclear import.