Tweet
J Virol. 2016 Jul 20. pii: JVI.01384-16. [Epub ahead of print]
The PB2 subunit of the influenza A virus RNA polymerase is imported into the mitochondrial matrix.
Long JC1, Fodor E2.
Author information
Abstract
The PB2 subunit of the RNA polymerase complex of seasonal human influenza A viruses has been shown to localise to the mitochondria. Various roles including the regulation of apoptosis and innate immune responses to viral infection have been proposed for mitochondrial PB2. In particular, PB2 has been shown to inhibit interferon expression by associating with the mitochondrial antiviral signalling (MAVS) protein, which acts downstream of RIG-I and MDA-5 in the interferon induction pathway. However, in spite of a growing body of literature on the potential roles of mitochondrial PB2, the exact location of PB2 in mitochondria has not been determined. Here, we use Enhanced Ascorbate Peroxidase (APEX) tagged PB2 proteins and electron microscopy to study the localisation of PB2 in mitochondria. We find that PB2 is imported into mitochondria where it localises to the mitochondrial matrix. We also demonstrate that MAVS is not required for the import of PB2 into mitochondria by showing that PB2 associates with mitochondria in MAVS knockout mouse embryo fibroblasts. Instead, we find that amino acid residue 9 in the N-terminal mitochondrial targeting sequence is a determinant of the mitochondrial import of PB2, differentiating the localisation of PB2 of human from that of avian influenza A virus strains. We also show that a virus encoding non-mitochondrial PB2 is attenuated in MEFs compared with an isogenic virus encoding mitochondrial PB2, in a MAVS-independent manner, suggesting a role for PB2 within the mitochondrial matrix. This work extends our understanding of the interplay between influenza virus and mitochondria.
IMPORTANCE:
The PB2 subunit of the influenza virus RNA polymerase is a major determinant of viral pathogenicity. However, the molecular mechanisms of how PB2 determines pathogenicity remain poorly understood. PB2 associates with mitochondria and inhibits the function of the mitochondrial antiviral signalling protein MAVS, implicating PB2 in the regulation of innate immune responses. We find that PB2 is imported into the mitochondrial matrix and show that amino acid residue 9 is a determinant of mitochondrial import. Asparagine or threonine that is present in over 99% of all human seasonal influenza virus pre-2009 H1N1, H2N2 and H3N2 strains is compatible with mitochondrial import while an aspartic acid that is present in over 95% of all avian influenza viruses is not, resulting in a clear distinction between human-adapted and avian influenza viruses. These findings provide insights into the interplay between influenza virus and mitochondria and suggest mechanisms by which PB2 could affect pathogenicity.
Copyright ? 2016 Long and Fodor.
PMID: 27440905 DOI: 10.1128/JVI.01384-16
[PubMed - as supplied by publisher]
The PB2 subunit of the influenza A virus RNA polymerase is imported into the mitochondrial matrix.
Long JC1, Fodor E2.
Author information
Abstract
The PB2 subunit of the RNA polymerase complex of seasonal human influenza A viruses has been shown to localise to the mitochondria. Various roles including the regulation of apoptosis and innate immune responses to viral infection have been proposed for mitochondrial PB2. In particular, PB2 has been shown to inhibit interferon expression by associating with the mitochondrial antiviral signalling (MAVS) protein, which acts downstream of RIG-I and MDA-5 in the interferon induction pathway. However, in spite of a growing body of literature on the potential roles of mitochondrial PB2, the exact location of PB2 in mitochondria has not been determined. Here, we use Enhanced Ascorbate Peroxidase (APEX) tagged PB2 proteins and electron microscopy to study the localisation of PB2 in mitochondria. We find that PB2 is imported into mitochondria where it localises to the mitochondrial matrix. We also demonstrate that MAVS is not required for the import of PB2 into mitochondria by showing that PB2 associates with mitochondria in MAVS knockout mouse embryo fibroblasts. Instead, we find that amino acid residue 9 in the N-terminal mitochondrial targeting sequence is a determinant of the mitochondrial import of PB2, differentiating the localisation of PB2 of human from that of avian influenza A virus strains. We also show that a virus encoding non-mitochondrial PB2 is attenuated in MEFs compared with an isogenic virus encoding mitochondrial PB2, in a MAVS-independent manner, suggesting a role for PB2 within the mitochondrial matrix. This work extends our understanding of the interplay between influenza virus and mitochondria.
IMPORTANCE:
The PB2 subunit of the influenza virus RNA polymerase is a major determinant of viral pathogenicity. However, the molecular mechanisms of how PB2 determines pathogenicity remain poorly understood. PB2 associates with mitochondria and inhibits the function of the mitochondrial antiviral signalling protein MAVS, implicating PB2 in the regulation of innate immune responses. We find that PB2 is imported into the mitochondrial matrix and show that amino acid residue 9 is a determinant of mitochondrial import. Asparagine or threonine that is present in over 99% of all human seasonal influenza virus pre-2009 H1N1, H2N2 and H3N2 strains is compatible with mitochondrial import while an aspartic acid that is present in over 95% of all avian influenza viruses is not, resulting in a clear distinction between human-adapted and avian influenza viruses. These findings provide insights into the interplay between influenza virus and mitochondria and suggest mechanisms by which PB2 could affect pathogenicity.
Copyright ? 2016 Long and Fodor.
PMID: 27440905 DOI: 10.1128/JVI.01384-16
[PubMed - as supplied by publisher]