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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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m41.1 inhibits Bak in vivo.WT B6 or B6.Bak−/− mice were depleted of NK cells prior to infection with WT MCMV (filled columns) or the Δm41.1 mutant (open columns). Viral load in the indicated organs was quantified by plaque assay on (A) day 4 pi, or (B) day 8 pi. Mean ± S.D. of 6–8 mice per group is plotted.
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ppat-1003192-g006: m41.1 inhibits Bak in vivo.WT B6 or B6.Bak−/− mice were depleted of NK cells prior to infection with WT MCMV (filled columns) or the Δm41.1 mutant (open columns). Viral load in the indicated organs was quantified by plaque assay on (A) day 4 pi, or (B) day 8 pi. Mean ± S.D. of 6–8 mice per group is plotted.

Mentions: The in vitro data indicate that m41.1 functions by inhibiting the pro-apoptotic Bak protein. To determine if the role of m41.1 is to prevent Bak-dependent death during in vivo infection, mice genetically deficient for Bak were infected with the Δm41.1 mutant. The ability of m41.1 to inhibit Bak-dependent apoptosis was examined in C57BL/6 (B6) mice as Bak-deficient mice on the BALB/c background are not available. B6 mice, unlike the BALB/c strain, are genetically resistant to MCMV due to an effective NK cell response [24]. Therefore Bak-deficient mice, or WT B6 mice, were depleted of NK cells prior to infection with either the WT virus or Δm41.1 mutant. As was the case for BALB/c mice, titers of the Δm41.1 virus were significantly lower than those of the WT virus in the liver and lung at day 4 pi (Fig. 6A). By contrast, the titre of the Δm41.1 mutant was equivalent to that of WT MCMV in the spleen at day 4 pi, while, as expected, neither virus was detectable in the salivary gland at this time (Fig. 6Aand data not shown). Furthermore, titers of the Δm41.1 mutant were significantly lower than WT virus in the lung and salivary gland at day 8 pi (Fig. 6B). Importantly, replication of the Δm41.1 virus was equivalent to that of the WT virus in B6.Bak−/− mice in all organs tested at both day 4 (Fig. 6A) and 8 pi (Fig. 6B). These data establish that m41.1 promotes viral replication in vivo by inhibiting Bak-dependent killing.


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)

m41.1 inhibits Bak in vivo.WT B6 or B6.Bak−/− mice were depleted of NK cells prior to infection with WT MCMV (filled columns) or the Δm41.1 mutant (open columns). Viral load in the indicated organs was quantified by plaque assay on (A) day 4 pi, or (B) day 8 pi. Mean ± S.D. of 6–8 mice per group is plotted.
© Copyright Policy
Related In: Results  -  Collection

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

ppat-1003192-g006: m41.1 inhibits Bak in vivo.WT B6 or B6.Bak−/− mice were depleted of NK cells prior to infection with WT MCMV (filled columns) or the Δm41.1 mutant (open columns). Viral load in the indicated organs was quantified by plaque assay on (A) day 4 pi, or (B) day 8 pi. Mean ± S.D. of 6–8 mice per group is plotted.
Mentions: The in vitro data indicate that m41.1 functions by inhibiting the pro-apoptotic Bak protein. To determine if the role of m41.1 is to prevent Bak-dependent death during in vivo infection, mice genetically deficient for Bak were infected with the Δm41.1 mutant. The ability of m41.1 to inhibit Bak-dependent apoptosis was examined in C57BL/6 (B6) mice as Bak-deficient mice on the BALB/c background are not available. B6 mice, unlike the BALB/c strain, are genetically resistant to MCMV due to an effective NK cell response [24]. Therefore Bak-deficient mice, or WT B6 mice, were depleted of NK cells prior to infection with either the WT virus or Δm41.1 mutant. As was the case for BALB/c mice, titers of the Δm41.1 virus were significantly lower than those of the WT virus in the liver and lung at day 4 pi (Fig. 6A). By contrast, the titre of the Δm41.1 mutant was equivalent to that of WT MCMV in the spleen at day 4 pi, while, as expected, neither virus was detectable in the salivary gland at this time (Fig. 6Aand data not shown). Furthermore, titers of the Δm41.1 mutant were significantly lower than WT virus in the lung and salivary gland at day 8 pi (Fig. 6B). Importantly, replication of the Δm41.1 virus was equivalent to that of the WT virus in B6.Bak−/− mice in all organs tested at both day 4 (Fig. 6A) and 8 pi (Fig. 6B). These data establish that m41.1 promotes viral replication in vivo by inhibiting Bak-dependent killing.

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