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Mechanism of lymphocytic choriomeningitis virus entry into cells
1Department of Neuropharmacology, Scripps Research Institute, La Jolla, California 92037.
Abstract:
The path that the arenavirus lymphocytic choriomeningitis virus (LCMV) uses to enter rodent fibroblastic cell lines was dissected by infectivity and inhibition studies and immunoelectron microscopy. Lysosomotropic weak bases (chloroquine and ammonium chloride) and carboxylic ionophores (monensin and nigericin) inhibited virus entry, assessed as virus nucleoprotein expression at early times post-infection, indicating that the entry process involved a pH-dependent fusion step in intracellular vesicles. That entry occurred in vesicles rather than by direct fusion of virions with the plasma membrane was confirmed by immunoelectron microscopy. The vesicles involved were large (150-300 nm diameter), smooth-walled, and not associated with clathrin. Unlike classical phagocytosis, virus uptake in these vesicles was a microfilament-independent process, as it was not blocked by cytochalasins. LCMV entry into rodent fibroblast cell lines thus involves viropexis in large smooth-walled vesicles, followed by a pH-dependent fusion event inside the cell.
Insights
Lymphocytic choriomeningitis virus (LCMV) enters rodent cells via viropexis in large vesicles. This process involves pH-dependent fusion within the cell, not direct plasma membrane fusion.
Area of Science:
- Virology
- Cell Biology
Background:
- Lymphocytic choriomeningitis virus (LCMV) is an arenavirus with significant implications for public health.
- Understanding viral entry mechanisms is crucial for developing antiviral strategies.
Purpose of the Study:
- To elucidate the specific pathway LCMV utilizes for cellular entry into rodent fibroblast cell lines.
- To characterize the nature of the vesicles involved and the dependence of the entry process on cellular conditions.
Main Methods:
- Infectivity and inhibition studies using lysosomotropic weak bases and carboxylic ionophores.
- Immunoelectron microscopy to visualize virus-cell interactions.
- Assessment of virus nucleoprotein expression as an indicator of entry.
Main Results:
- LCMV entry was inhibited by agents that disrupt pH gradients within intracellular vesicles.
- Immunoelectron microscopy confirmed entry via large (150-300 nm), smooth-walled vesicles, distinct from clathrin-coated pits.
- The uptake process was independent of microfilaments, differentiating it from classical phagocytosis.
Conclusions:
- LCMV entry into rodent fibroblasts occurs through viropexis within large, smooth-walled vesicles.
- A pH-dependent fusion event within these intracellular vesicles mediates viral entry.
- The mechanism bypasses direct fusion with the plasma membrane and is independent of microfilament activity.