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Requirements for entry of poliovirus RNA into cells at low pH
Abstract:
HeLa S3 cells were protected against infection by poliovirus type I by the presence of monensin and N,N'-dicyclohexylcarbodiimide (DCCD), compounds elevating the pH of acidic intracellular compartments. The protection was fully overcome by exposing the cells to pH 5.5 and lower, and at approximately pH 6.1 it was reduced by half. Measurements of the ability of the virus to enter the detergent phase under conditions where Triton X-114 was separated from water indicated that the virus is hydrophilic at neutral pH, and that it exposes hydrophobic regions at low pH. When the cells were pretreated with acetic acid, which reduces the intracellular pH, virus entry was inhibited, indicating that a pH gradient across the membrane is necessary for infection. Under all conditions which induced infection, the virus particles were altered to more slowly sedimenting material. Also, virus bound to aldehyde-fixed cells was altered when exposed to low pH at 37 degrees C. The data indicate that poliovirus bound to receptors on cells exposes hydrophobic regions at low pH, and that at physiological temperature it undergoes alteration. This alteration may be a necessary, but not sufficient requirement for infection.
Insights
Poliovirus infection requires a pH gradient, as low pH exposes hydrophobic viral regions necessary for entry. Alterations in virus particles at low pH and physiological temperatures are critical for infection.
Area of Science:
- Virology
- Cell Biology
- Biochemistry
Background:
- Poliovirus infects host cells, and its entry mechanism is influenced by cellular pH.
- Intracellular compartments maintain acidic pH, which can be modulated by chemical agents.
Purpose of the Study:
- To investigate the role of pH in poliovirus infection and viral particle alterations.
- To determine the biophysical changes in poliovirus associated with infectivity.
Main Methods:
- Utilized monensin and N,N'-dicyclohexylcarbodiimide (DCCD) to alter intracellular pH in HeLa S3 cells.
- Assessed poliovirus infectivity at various external and internal pH levels.
- Employed Triton X-114 phase separation to analyze viral hydrophobicity.
- Observed virus particle alterations via sedimentation analysis.
Main Results:
- Elevating intracellular pH with monensin or DCCD protected cells from poliovirus infection.
- Low pH (≤5.5) overcame protection; pH 6.1 halved protection, indicating a pH-dependent entry process.
- Poliovirus transitions from hydrophilic to hydrophobic at low pH, facilitating membrane interaction.
- Acetic acid pretreatment inhibited infection, confirming the necessity of a pH gradient.
- Infected virus particles showed altered sedimentation, and bound virus altered at low pH and 37°C.
Conclusions:
- A pH gradient across the cell membrane is essential for poliovirus infection.
- Low pH induces conformational changes in poliovirus, exposing hydrophobic regions.
- These pH-dependent viral alterations are a necessary, though not sufficient, step for cellular infection.