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MCMV-mediated inhibition of the pro-apoptotic Bak protein is required for optimal in vivo replication.

Fleming P, Kvansakul M, Voigt V, Kile BT, Kluck RM, Huang DC, Degli-Esposti MA, Andoniou CE - PLoS Pathog. (2013)

Bottom Line: Here we show that m41.1 is critical for optimal MCMV replication in vivo.Growth of a m41.1 mutant was attenuated in multiple organs, a defect that was not apparent in Bak(-/-) mice.Thus, m41.1 promotes MCMV replication by inhibiting Bak-dependent apoptosis during in vivo infection.

View Article: PubMed Central - PubMed

Affiliation: Immunology and Virology Program, Centre for Ophthalmology and Visual Science, The University of Western Australia, Nedlands, Western Australia, Australia.

ABSTRACT
Successful replication and transmission of large DNA viruses such as the cytomegaloviruses (CMV) family of viruses depends on the ability to interfere with multiple aspects of the host immune response. Apoptosis functions as a host innate defence mechanism against viral infection, and the capacity to interfere with this process is essential for the replication of many viruses. The Bcl-2 family of proteins are the principle regulators of apoptosis, with two pro-apoptotic members, Bax and Bak, essential for apoptosis to proceed. The m38.5 protein encoded by murine CMV (MCMV) has been identified as Bax-specific inhibitor of apoptosis. Recently, m41.1, a protein product encoded by the m41 open reading frame (ORF) of MCMV, has been shown to inhibit Bak activity in vitro. Here we show that m41.1 is critical for optimal MCMV replication in vivo. Growth of a m41.1 mutant was attenuated in multiple organs, a defect that was not apparent in Bak(-/-) mice. Thus, m41.1 promotes MCMV replication by inhibiting Bak-dependent apoptosis during in vivo infection. The results show that Bax and Bak mediate non-redundant functions during MCMV infection and that the virus produces distinct inhibitors for each protein to counter the activity of these proteins.

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Loss of m41.1 or m41 impairs viral replication in vivo.(A) BALB/c mice were infected with WT MCMV (filled square), Rev (filled circle) or Δm41.1 mutant (open diamond), organs were removed at the indicated times pi and viral load determined by plaque assay, mean ± S.D. of 5–6 mice per time point is plotted. ** P<0.01, *** P<0.0001. Dotted line indicates the limit of detection of the assay. (B) BALB/c mice were infected with WT MCMV (filled square), Rev (filled circle) or the Δm41 mutant (cross), organs removed at the indicated times pi and viral load determined by plaque assay. Mean ± S.D. of 5–6 mice per time point is plotted. ** P<0.01. Dotted line indicates the limit of detection of the assay.
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ppat-1003192-g005: Loss of m41.1 or m41 impairs viral replication in vivo.(A) BALB/c mice were infected with WT MCMV (filled square), Rev (filled circle) or Δm41.1 mutant (open diamond), organs were removed at the indicated times pi and viral load determined by plaque assay, mean ± S.D. of 5–6 mice per time point is plotted. ** P<0.01, *** P<0.0001. Dotted line indicates the limit of detection of the assay. (B) BALB/c mice were infected with WT MCMV (filled square), Rev (filled circle) or the Δm41 mutant (cross), organs removed at the indicated times pi and viral load determined by plaque assay. Mean ± S.D. of 5–6 mice per time point is plotted. ** P<0.01. Dotted line indicates the limit of detection of the assay.

Mentions: The in vitro data suggested that m41.1 inhibits apoptosis, and that this is required for viral replication to proceed in some cell types. The specific contribution of m41.1 to the in vivo pathogenesis of MCMV was then assessed by infection of BALB/c mice. Replication of the Δm41.1 mutant in the spleen was indistinguishable from that of WT or Rev virus, and in the salivary gland replication was equivalent to that of the control viruses at all time points with the exception of day 10 pi (Fig. 5A). By comparison, growth of the Δm41.1 virus was significantly attenuated in both the liver and lungs at multiple time points. Thus, m41.1 is required for MCMV to replicate effectively in several target organs during in vivo infection.


MCMV-mediated inhibition of the pro-apoptotic Bak protein is required for optimal in vivo replication.

Fleming P, Kvansakul M, Voigt V, Kile BT, Kluck RM, Huang DC, Degli-Esposti MA, Andoniou CE - PLoS Pathog. (2013)

Loss of m41.1 or m41 impairs viral replication in vivo.(A) BALB/c mice were infected with WT MCMV (filled square), Rev (filled circle) or Δm41.1 mutant (open diamond), organs were removed at the indicated times pi and viral load determined by plaque assay, mean ± S.D. of 5–6 mice per time point is plotted. ** P<0.01, *** P<0.0001. Dotted line indicates the limit of detection of the assay. (B) BALB/c mice were infected with WT MCMV (filled square), Rev (filled circle) or the Δm41 mutant (cross), organs removed at the indicated times pi and viral load determined by plaque assay. Mean ± S.D. of 5–6 mice per time point is plotted. ** P<0.01. Dotted line indicates the limit of detection of the assay.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585157&req=5

ppat-1003192-g005: Loss of m41.1 or m41 impairs viral replication in vivo.(A) BALB/c mice were infected with WT MCMV (filled square), Rev (filled circle) or Δm41.1 mutant (open diamond), organs were removed at the indicated times pi and viral load determined by plaque assay, mean ± S.D. of 5–6 mice per time point is plotted. ** P<0.01, *** P<0.0001. Dotted line indicates the limit of detection of the assay. (B) BALB/c mice were infected with WT MCMV (filled square), Rev (filled circle) or the Δm41 mutant (cross), organs removed at the indicated times pi and viral load determined by plaque assay. Mean ± S.D. of 5–6 mice per time point is plotted. ** P<0.01. Dotted line indicates the limit of detection of the assay.
Mentions: The in vitro data suggested that m41.1 inhibits apoptosis, and that this is required for viral replication to proceed in some cell types. The specific contribution of m41.1 to the in vivo pathogenesis of MCMV was then assessed by infection of BALB/c mice. Replication of the Δm41.1 mutant in the spleen was indistinguishable from that of WT or Rev virus, and in the salivary gland replication was equivalent to that of the control viruses at all time points with the exception of day 10 pi (Fig. 5A). By comparison, growth of the Δm41.1 virus was significantly attenuated in both the liver and lungs at multiple time points. Thus, m41.1 is required for MCMV to replicate effectively in several target organs during in vivo infection.

Bottom Line: Here we show that m41.1 is critical for optimal MCMV replication in vivo.Growth of a m41.1 mutant was attenuated in multiple organs, a defect that was not apparent in Bak(-/-) mice.Thus, m41.1 promotes MCMV replication by inhibiting Bak-dependent apoptosis during in vivo infection.

View Article: PubMed Central - PubMed

Affiliation: Immunology and Virology Program, Centre for Ophthalmology and Visual Science, The University of Western Australia, Nedlands, Western Australia, Australia.

ABSTRACT
Successful replication and transmission of large DNA viruses such as the cytomegaloviruses (CMV) family of viruses depends on the ability to interfere with multiple aspects of the host immune response. Apoptosis functions as a host innate defence mechanism against viral infection, and the capacity to interfere with this process is essential for the replication of many viruses. The Bcl-2 family of proteins are the principle regulators of apoptosis, with two pro-apoptotic members, Bax and Bak, essential for apoptosis to proceed. The m38.5 protein encoded by murine CMV (MCMV) has been identified as Bax-specific inhibitor of apoptosis. Recently, m41.1, a protein product encoded by the m41 open reading frame (ORF) of MCMV, has been shown to inhibit Bak activity in vitro. Here we show that m41.1 is critical for optimal MCMV replication in vivo. Growth of a m41.1 mutant was attenuated in multiple organs, a defect that was not apparent in Bak(-/-) mice. Thus, m41.1 promotes MCMV replication by inhibiting Bak-dependent apoptosis during in vivo infection. The results show that Bax and Bak mediate non-redundant functions during MCMV infection and that the virus produces distinct inhibitors for each protein to counter the activity of these proteins.

Show MeSH
Related in: MedlinePlus