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Induction of ferritin synthesis in cells infected with Mengo virus
M R Mulvey1, L C Kühn, D G Scraba
1Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada.
Abstract:
We have recently identified ferritin as a cellular protein particle whose synthesis is stimulated in mouse or human cells infected by the picornavirus Mengo. Immunoprecipitation of the particle from infected murine L929 cells showed a 4- and 6-fold increase in the intracellular concentrations of H and L apoferritin subunits, respectively. This differential expression altered the H/L subunit ratio from 3.0 in uninfected cells to 2.2 in Mengo virus-infected cells. The induction is not due to an increase in transcription of the apoferritin L and H genes, nor is it due to an increase in stability of the apoferritin mRNAs. At the level of translation, the iron regulatory protein (IRP) remained intact, with similar amounts being detected in uninfected and infected cells. The Mengo virus RNA genome does not compete with the iron regulatory element (IRE) for the binding of IRP, and sequence analysis confirmed that there are no IREs in the virus RNA. The IRE binding activity of IRP in infected cells decreased approximately 30% compared with uninfected cells. The decrease in binding activity could be overcome by the addition of Desferal (deferoxamine mesylate; CIBA) an intracellular iron chelator, which suggests that virus infection causes an increase in intracellular free iron. Electron paramagnetic resonance (EPR) studies have confirmed the increase in free iron in Mengo virus infected cells. The permeability of cells for iron does not change in virus infected cells, suggesting that the induction of ferritin by Mengo virus is due to a change in the form of intracellular iron from a bound to a free state.
Insights
Mengo virus infection increases cellular ferritin synthesis by altering intracellular iron levels, not by affecting iron regulatory protein binding. This suggests viral infection shifts iron from bound to free states, stimulating ferritin production.
Area of Science:
- Virology
- Cell Biology
- Biochemistry
Background:
- Ferritin synthesis is upregulated in cells infected with Mengo virus.
- This upregulation involves increased intracellular concentrations of H and L apoferritin subunits.
- The ratio of H/L subunits shifts in infected cells.
Purpose of the Study:
- To investigate the mechanism by which Mengo virus infection stimulates ferritin synthesis.
- To determine if changes in iron metabolism are involved in this stimulation.
- To elucidate the role of the iron regulatory protein (IRP) and iron regulatory element (IRE) in this process.
Main Methods:
- Immunoprecipitation to quantify apoferritin subunits in infected and uninfected cells.
- Analysis of apoferritin gene transcription and mRNA stability.
- Assessment of iron regulatory protein (IRP) binding activity to iron regulatory elements (IREs).
- Use of Desferal (deferoxamine mesylate) to chelate intracellular iron.
- Electron paramagnetic resonance (EPR) studies to confirm changes in free iron levels.
Main Results:
- Mengo virus infection significantly increased H and L apoferritin subunits, altering the H/L ratio.
- The induction was not due to increased gene transcription or mRNA stability.
- IRP binding activity decreased in infected cells, suggesting increased intracellular free iron.
- Desferal treatment reversed the IRP binding decrease, confirming increased free iron.
- EPR studies corroborated the rise in free intracellular iron.
Conclusions:
- Mengo virus infection induces ferritin synthesis through a mechanism involving increased intracellular free iron.
- The cellular response appears to be a shift from bound to free iron, rather than direct IRP-IRE interaction modulation.
- Ferritin induction is a host response to altered iron homeostasis during viral infection.