Differential pH-dependent cellular uptake pathways among foamy viruses elucidated using dual-colored fluorescent...

Area of Science:

• Virology
• Cell Biology
• Molecular Biology

Background:

• Foamy viruses (FVs) are generally believed to enter host cells via endocytosis due to pH-dependent fusion.
• Prototype foamy virus (PFV) glycoprotein exhibits neutral pH fusion activity, suggesting a potentially different uptake mechanism compared to other FVs.
• Understanding FV entry mechanisms is crucial for deciphering viral pathogenesis and developing antiviral strategies.

Purpose of the Study:

• To develop and utilize fluorescently labeled infectious FVs to investigate FV uptake and entry processes in live host cells.
• To compare the entry pathways of PFV and simian FV (SFVmac) using double-tagged virions.
• To gain mechanistic insights into the early steps of FV infection, including fusion and capsid trafficking.

Main Methods:

• Development of N-terminally fluorescent protein-tagged FVs (eGFP-Gag and mCherry-Env) that retain infectivity.
• Observation of double-tagged PFV and SFVmac virions during early infection stages in host cells.
• Analysis of syncytia formation, virion trafficking, capsid release, and fusion kinetics using advanced imaging techniques.

Main Results:

• PFV Env-containing particles induced significant syncytia formation, unlike SFVmac Env particles.
• Both PFV and SFVmac virions trafficked to the cell center, with capsids accumulating in the perinuclear region post-fusion.
• Fusion-defective virions were degraded, while PFV virions fused rapidly (minutes), and SFVmac virions showed slower, prolonged fusion (90 minutes).

Conclusions:

• Productive FV fusion occurs early after target cell attachment and uptake, with distinct kinetics for different FV species.
• The study reveals apparent differences in the uptake and entry pathways of PFV and SFVmac.
• Infectious double-labeled FVs are valuable tools for real-time analysis of viral fusion events and early infection dynamics.