Differential localization and turnover of infectious bronchitis virus 3b protein in mammalian versus avian cells
Amanda R Pendleton1, Carolyn E Machamer
1Department of Cell Biology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205, USA.
Abstract:
Infectious bronchitis virus (IBV) 3b protein is highly conserved among group 3 coronaviruses, suggesting that it is important for infection. A previous report (Virology 2003, 311:16-27) indicated that transfected IBV 3b localized to the nucleus in mammalian cells using a vaccinia-virus expression system. Although we confirmed these findings, we observed cytoplasmic localization of IBV 3b with apparent exclusion from the nucleus in avian cells (IBV normally infects chickens). IBV 3b was virtually undetectable by microscopy in mammalian cells transfected without vaccinia virus and in IBV-infected mammalian cells because of a greatly reduced half-life in these cells. A proteasome inhibitor stabilized IBV 3b in mammalian cells, but had little effect on IBV 3b in avian cells, suggesting that rapid turnover of IBV 3b in mammalian cells is proteasome-dependent while turnover in avian cells may be proteasome-independent. Our results highlight the importance of using cells derived from the natural host when studying coronavirus non-structural proteins.
Insights
Infectious bronchitis virus (IBV) 3b protein behaves differently in chicken cells versus mammalian cells. Rapid protein breakdown in mammalian cells, dependent on proteasomes, differs from avian cells.
Area of Science:
- * Virology
- * Molecular Biology
- * Coronavirus Research
Background:
- * Infectious bronchitis virus (IBV) is a significant pathogen in poultry.
- * The IBV 3b protein is highly conserved in group 3 coronaviruses, indicating functional importance.
- * Previous studies suggested nuclear localization of IBV 3b in mammalian cells via vaccinia virus expression.
Purpose of the Study:
- * To investigate the cellular localization and stability of the IBV 3b protein.
- * To compare the behavior of IBV 3b in avian versus mammalian cell systems.
- * To elucidate the mechanisms regulating IBV 3b protein turnover.
Main Methods:
- * Transfection of mammalian and avian cells with IBV 3b expression constructs.
- * Microscopy to observe protein localization.
- * Use of proteasome inhibitors to assess protein stability.
- * Comparison of protein half-life in different cell types.
Main Results:
- * IBV 3b localized to the cytoplasm in avian cells, with apparent nuclear exclusion.
- * IBV 3b showed rapid degradation (reduced half-life) in mammalian cells, especially when infected with IBV.
- * Proteasome inhibitors stabilized IBV 3b in mammalian cells, suggesting proteasomal degradation.
- * Proteasome inhibition had minimal effect on IBV 3b stability in avian cells.
Conclusions:
- * The cellular localization and stability of IBV 3b protein are host-cell dependent.
- * Rapid proteasome-dependent turnover of IBV 3b occurs in mammalian cells.
- * Proteasome-independent mechanisms may contribute to IBV 3b turnover in avian cells.
- * Studying coronavirus non-structural proteins requires using cells from the natural host species.
