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Ultrastructural aspects of BK virus uptake and replication in human fibroblasts
Abstract:
After exposure of human embryonic fibroblasts to BK virus, virus particles adsorbed to the plasma membrane were engulfed by pinocytosis or captured by vesicles, possibly originating from the endoplasmic reticulum, within 2 h after infection. Most of the virus particles were then transported into lysosomes or into the nucleus, while a small amount of virus was found free in the cytoplasm. Virus particles entered the nucleus between 2 and 12 h after infection, were still detectable in the nucleus at 24 h after infectionand becamse morphologically undiscernible at 30 h after infection, suggesting that a nuclear uncoating mechanism was active between 24 and 30 h after infection. Virus progeny started to appear in the nucleus of infected cells at 4 days after infection, but not until 7 to 8 days after infection did the virus escape into the cytoplasm and cell degeneration became evident. The possible explanations for the long replicative cycle of BK virus are discussed.
Insights
BK virus enters human cells via pinocytosis and reaches the nucleus within 12 hours. Viral replication and cell damage occur after a prolonged 7-8 day cycle, suggesting a slow uncoating mechanism.
Area of Science:
- Virology
- Cell Biology
Background:
- BK virus is a human polyomavirus that can cause disease in immunocompromised individuals.
- Understanding the early stages of BK virus infection is crucial for developing antiviral therapies.
Purpose of the Study:
- To elucidate the entry pathway and intracellular trafficking of BK virus in human embryonic fibroblasts.
- To characterize the kinetics of BK virus replication and its impact on host cells.
Main Methods:
- Infection of human embryonic fibroblasts with BK virus.
- Time-course analysis of viral particle localization using microscopy.
- Assessment of viral progeny production and cytopathic effects.
Main Results:
- BK virus enters cells through pinocytosis or vesicular transport within 2 hours.
- Virus particles are primarily trafficked to lysosomes or the nucleus.
- Nuclear entry occurs between 2-12 hours, with uncoating between 24-30 hours.
- Viral progeny appear in the nucleus at 4 days, with cell degeneration evident at 7-8 days.
Conclusions:
- BK virus exhibits a prolonged replication cycle in human cells.
- A nuclear uncoating mechanism appears to be a rate-limiting step.
- The findings provide insights into the pathogenesis of BK virus infection.