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The Rubella virus capsid is an anti-apoptotic protein that attenuates the pore-forming ability of Bax.

Ilkow CS, Goping IS, Hobman TC - PLoS Pathog. (2011)

Bottom Line: The main mechanism of action was specific for Bax as capsid bound Bax and prevented Bax-induced apoptosis but did not bind Bak nor inhibit Bak-induced apoptosis.Intriguingly, interaction with capsid protein resulted in activation of Bax in the absence of apoptotic stimuli, however, release of cytochrome c from mitochondria and concomitant activation of caspase 3 did not occur.Accordingly, we propose that binding of capsid to Bax induces the formation of hetero-oligomers that are incompetent for pore formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, University of Alberta, Edmonton, Canada.

ABSTRACT
Apoptosis is an important mechanism by which virus-infected cells are eliminated from the host. Accordingly, many viruses have evolved strategies to prevent or delay apoptosis in order to provide a window of opportunity in which virus replication, assembly and egress can take place. Interfering with apoptosis may also be important for establishment and/or maintenance of persistent infections. Whereas large DNA viruses have the luxury of encoding accessory proteins whose primary function is to undermine programmed cell death pathways, it is generally thought that most RNA viruses do not encode these types of proteins. Here we report that the multifunctional capsid protein of Rubella virus is a potent inhibitor of apoptosis. The main mechanism of action was specific for Bax as capsid bound Bax and prevented Bax-induced apoptosis but did not bind Bak nor inhibit Bak-induced apoptosis. Intriguingly, interaction with capsid protein resulted in activation of Bax in the absence of apoptotic stimuli, however, release of cytochrome c from mitochondria and concomitant activation of caspase 3 did not occur. Accordingly, we propose that binding of capsid to Bax induces the formation of hetero-oligomers that are incompetent for pore formation. Importantly, data from reverse genetic studies are consistent with a scenario in which the anti-apoptotic activity of capsid protein is important for virus replication. If so, this would be among the first demonstrations showing that blocking apoptosis is important for replication of an RNA virus. Finally, it is tempting to speculate that other slowly replicating RNA viruses employ similar mechanisms to avoid killing infected cells.

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Capsid expression prevents Bax-induced release of cytochrome c from mitochondria.A549 cells were co-transfected with plasmids encoding capsid or vector alone together with GFP-Bax (A) or GFP-Bak (B). After 24 hours, cells were stained with mouse anti-capsid and rabbit anti-cytochrome c. Primary antibodies were detected with chicken anti-mouse Alexa594 and donkey anti-rabbit Alexa637. Asterisks mark Bax or Bak expressing cells that have released their mitochondrial stores of cytochrome c into the cytoplasm. In part A, the arrows denote a cell expressing both capsid and Bax. In this cell, it can be seen that cytochrome c remains associated with mitochondria. In part B, the arrowheads denote a cell expressing both capsid and Bak. However, in this case, the cell has released its mitochondrial stores of cytochrome c into the cytoplasm. Images shown are representative of three independent experiments in which at least 100 cells were examined. Scale bar  = 10 µm.
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ppat-1001291-g007: Capsid expression prevents Bax-induced release of cytochrome c from mitochondria.A549 cells were co-transfected with plasmids encoding capsid or vector alone together with GFP-Bax (A) or GFP-Bak (B). After 24 hours, cells were stained with mouse anti-capsid and rabbit anti-cytochrome c. Primary antibodies were detected with chicken anti-mouse Alexa594 and donkey anti-rabbit Alexa637. Asterisks mark Bax or Bak expressing cells that have released their mitochondrial stores of cytochrome c into the cytoplasm. In part A, the arrows denote a cell expressing both capsid and Bax. In this cell, it can be seen that cytochrome c remains associated with mitochondria. In part B, the arrowheads denote a cell expressing both capsid and Bak. However, in this case, the cell has released its mitochondrial stores of cytochrome c into the cytoplasm. Images shown are representative of three independent experiments in which at least 100 cells were examined. Scale bar  = 10 µm.

Mentions: To further understand how capsid functions to block apoptosis, we determined whether expression of this viral protein inhibits Bax-induced release of cytochrome c. A549 cells were co-transfected with plasmids encoding GFP-Bax and capsid or empty vector. Localization of cytochrome c was monitored by fluorescence microscopy at 24 hours post-transfection. As expected, in cells expressing GFP-Bax and vector alone, there was marked loss of cytochrome c from mitochondria (Figure 7A, asterisks). In contrast, in cells that expressed both capsid protein and GFP-Bax, cytochrome c remained associated with this organelle (Figure 7A, arrows). However, consistent with data shown in Figures 5 and 6, capsid did not block GFP-Bak-induced loss of cytochrome c from mitochondria (Figure 7B arrows).


The Rubella virus capsid is an anti-apoptotic protein that attenuates the pore-forming ability of Bax.

Ilkow CS, Goping IS, Hobman TC - PLoS Pathog. (2011)

Capsid expression prevents Bax-induced release of cytochrome c from mitochondria.A549 cells were co-transfected with plasmids encoding capsid or vector alone together with GFP-Bax (A) or GFP-Bak (B). After 24 hours, cells were stained with mouse anti-capsid and rabbit anti-cytochrome c. Primary antibodies were detected with chicken anti-mouse Alexa594 and donkey anti-rabbit Alexa637. Asterisks mark Bax or Bak expressing cells that have released their mitochondrial stores of cytochrome c into the cytoplasm. In part A, the arrows denote a cell expressing both capsid and Bax. In this cell, it can be seen that cytochrome c remains associated with mitochondria. In part B, the arrowheads denote a cell expressing both capsid and Bak. However, in this case, the cell has released its mitochondrial stores of cytochrome c into the cytoplasm. Images shown are representative of three independent experiments in which at least 100 cells were examined. Scale bar  = 10 µm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3040668&req=5

ppat-1001291-g007: Capsid expression prevents Bax-induced release of cytochrome c from mitochondria.A549 cells were co-transfected with plasmids encoding capsid or vector alone together with GFP-Bax (A) or GFP-Bak (B). After 24 hours, cells were stained with mouse anti-capsid and rabbit anti-cytochrome c. Primary antibodies were detected with chicken anti-mouse Alexa594 and donkey anti-rabbit Alexa637. Asterisks mark Bax or Bak expressing cells that have released their mitochondrial stores of cytochrome c into the cytoplasm. In part A, the arrows denote a cell expressing both capsid and Bax. In this cell, it can be seen that cytochrome c remains associated with mitochondria. In part B, the arrowheads denote a cell expressing both capsid and Bak. However, in this case, the cell has released its mitochondrial stores of cytochrome c into the cytoplasm. Images shown are representative of three independent experiments in which at least 100 cells were examined. Scale bar  = 10 µm.
Mentions: To further understand how capsid functions to block apoptosis, we determined whether expression of this viral protein inhibits Bax-induced release of cytochrome c. A549 cells were co-transfected with plasmids encoding GFP-Bax and capsid or empty vector. Localization of cytochrome c was monitored by fluorescence microscopy at 24 hours post-transfection. As expected, in cells expressing GFP-Bax and vector alone, there was marked loss of cytochrome c from mitochondria (Figure 7A, asterisks). In contrast, in cells that expressed both capsid protein and GFP-Bax, cytochrome c remained associated with this organelle (Figure 7A, arrows). However, consistent with data shown in Figures 5 and 6, capsid did not block GFP-Bak-induced loss of cytochrome c from mitochondria (Figure 7B arrows).

Bottom Line: The main mechanism of action was specific for Bax as capsid bound Bax and prevented Bax-induced apoptosis but did not bind Bak nor inhibit Bak-induced apoptosis.Intriguingly, interaction with capsid protein resulted in activation of Bax in the absence of apoptotic stimuli, however, release of cytochrome c from mitochondria and concomitant activation of caspase 3 did not occur.Accordingly, we propose that binding of capsid to Bax induces the formation of hetero-oligomers that are incompetent for pore formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, University of Alberta, Edmonton, Canada.

ABSTRACT
Apoptosis is an important mechanism by which virus-infected cells are eliminated from the host. Accordingly, many viruses have evolved strategies to prevent or delay apoptosis in order to provide a window of opportunity in which virus replication, assembly and egress can take place. Interfering with apoptosis may also be important for establishment and/or maintenance of persistent infections. Whereas large DNA viruses have the luxury of encoding accessory proteins whose primary function is to undermine programmed cell death pathways, it is generally thought that most RNA viruses do not encode these types of proteins. Here we report that the multifunctional capsid protein of Rubella virus is a potent inhibitor of apoptosis. The main mechanism of action was specific for Bax as capsid bound Bax and prevented Bax-induced apoptosis but did not bind Bak nor inhibit Bak-induced apoptosis. Intriguingly, interaction with capsid protein resulted in activation of Bax in the absence of apoptotic stimuli, however, release of cytochrome c from mitochondria and concomitant activation of caspase 3 did not occur. Accordingly, we propose that binding of capsid to Bax induces the formation of hetero-oligomers that are incompetent for pore formation. Importantly, data from reverse genetic studies are consistent with a scenario in which the anti-apoptotic activity of capsid protein is important for virus replication. If so, this would be among the first demonstrations showing that blocking apoptosis is important for replication of an RNA virus. Finally, it is tempting to speculate that other slowly replicating RNA viruses employ similar mechanisms to avoid killing infected cells.

Show MeSH
Related in: MedlinePlus