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J Virol. 2016 Sep 21. pii: JVI.01213-16. [Epub ahead of print]
Influenza virus susceptibility of wild-derived CAST/EiJ mice results from two amino acid changes in the MX1 restriction factor.
N?rnberger C1, Zimmermann V2, Gerhardt M2, Staeheli P3.
Author information
Abstract
The interferon-regulated Mx1 gene of the A2G mouse strain confers a high degree of resistance against influenza A and Thogoto viruses. Most other laboratory inbred mouse strains carry truncated non-functional Mx1 alleles and, consequently, exhibit high virus susceptibility. Interestingly, CAST/EiJ mice derived from wild Mus musculus castaneus possess a seemingly intact Mx1 gene, but are highly susceptible to influenza A virus challenge. To determine whether enhanced influenza virus susceptibility is due to intrinsically reduced antiviral activity of the CAST-derived Mx1 allele, we generated a congenic C57BL/6J mouse line that carries the Mx locus of CAST/EiJ. Adults animals of this line were almost as susceptible to influenza virus challenge as standard C57BL/6J mice lacking functional Mx1 alleles but exhibited far more pronounced resistance to Thogoto virus. Sequencing revealed that CAST-derived MX1 differs from A2G-derived MX1 by two amino acids (G83R and A222V) in the GTPase domain. Especially the A222V mutation reduced GTPase activity of purified MX1 and diminished the inhibitory effect of MX1 in influenza A virus polymerase activity assays. Further, MX1 protein was substantially less abundant in organs of interferon-treated mice carrying the CAST Mx1 allele in comparison to mice carrying the A2G Mx1 allele. We found that the CAST-specific mutations reduced the metabolic stability of the MX1 protein although Mx1 mRNA levels were unchanged. Thus, enhanced influenza virus susceptibility of CAST/EiJ mice can be explained by minor alterations in the MX1 restriction factor that negatively affect its enzymatic activity and reduce its half-life.
IMPORTANCE:
Although the crystal structures of the prototypic human MXA protein is known, the importance of specific protein domains for antiviral activity is still incompletely understood. Novel insights might come from studying naturally occuring MX protein variants with altered antiviral activity. Here we identified two seemingly minor amino acid changes in the GTPase domain that negatively affect enzymatic activity and metabolic stability of murine MX1 and thus dramatically reduce influenza virus resistance of the respective mouse inbred strain. These observations highlight our current inability to predict the biological consequences of previously uncharacterized MX mutations in mice. Since this is probably also true for naturally occurring mutations in Mx genes of humans, careful experimental analysis of any natural MXA variants for altered activity is necessary in order to assess possible consequences of such mutations on innate antiviral immunity.
Copyright ? 2016, American Society for Microbiology. All Rights Reserved.
PMID: 27654285 DOI: 10.1128/JVI.01213-16
[PubMed - as supplied by publisher]
Influenza virus susceptibility of wild-derived CAST/EiJ mice results from two amino acid changes in the MX1 restriction factor.
N?rnberger C1, Zimmermann V2, Gerhardt M2, Staeheli P3.
Author information
Abstract
The interferon-regulated Mx1 gene of the A2G mouse strain confers a high degree of resistance against influenza A and Thogoto viruses. Most other laboratory inbred mouse strains carry truncated non-functional Mx1 alleles and, consequently, exhibit high virus susceptibility. Interestingly, CAST/EiJ mice derived from wild Mus musculus castaneus possess a seemingly intact Mx1 gene, but are highly susceptible to influenza A virus challenge. To determine whether enhanced influenza virus susceptibility is due to intrinsically reduced antiviral activity of the CAST-derived Mx1 allele, we generated a congenic C57BL/6J mouse line that carries the Mx locus of CAST/EiJ. Adults animals of this line were almost as susceptible to influenza virus challenge as standard C57BL/6J mice lacking functional Mx1 alleles but exhibited far more pronounced resistance to Thogoto virus. Sequencing revealed that CAST-derived MX1 differs from A2G-derived MX1 by two amino acids (G83R and A222V) in the GTPase domain. Especially the A222V mutation reduced GTPase activity of purified MX1 and diminished the inhibitory effect of MX1 in influenza A virus polymerase activity assays. Further, MX1 protein was substantially less abundant in organs of interferon-treated mice carrying the CAST Mx1 allele in comparison to mice carrying the A2G Mx1 allele. We found that the CAST-specific mutations reduced the metabolic stability of the MX1 protein although Mx1 mRNA levels were unchanged. Thus, enhanced influenza virus susceptibility of CAST/EiJ mice can be explained by minor alterations in the MX1 restriction factor that negatively affect its enzymatic activity and reduce its half-life.
IMPORTANCE:
Although the crystal structures of the prototypic human MXA protein is known, the importance of specific protein domains for antiviral activity is still incompletely understood. Novel insights might come from studying naturally occuring MX protein variants with altered antiviral activity. Here we identified two seemingly minor amino acid changes in the GTPase domain that negatively affect enzymatic activity and metabolic stability of murine MX1 and thus dramatically reduce influenza virus resistance of the respective mouse inbred strain. These observations highlight our current inability to predict the biological consequences of previously uncharacterized MX mutations in mice. Since this is probably also true for naturally occurring mutations in Mx genes of humans, careful experimental analysis of any natural MXA variants for altered activity is necessary in order to assess possible consequences of such mutations on innate antiviral immunity.
Copyright ? 2016, American Society for Microbiology. All Rights Reserved.
PMID: 27654285 DOI: 10.1128/JVI.01213-16
[PubMed - as supplied by publisher]