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Differential use of importin-α isoforms governs cell tropism and host adaptation of influenza virus.

Gabriel G, Klingel K, Otte A, Thiele S, Hudjetz B, Arman-Kalcek G, Sauter M, Shmidt T, Rother F, Baumgarte S, Keiner B, Hartmann E, Bader M, Brownlee GG, Fodor E, Klenk HD - Nat Commun (2011)

Bottom Line: Influenza A viruses are a threat to humans due to their ability to cross species barriers, as illustrated by the 2009 H1N1v pandemic and sporadic H5N1 transmissions.In this study, we analysed replication, host specificity and pathogenicity of avian and mammalian influenza viruses, in importin-α-silenced cells and importin-α-knockout mice, to understand the role of individual importin-α isoforms in adaptation.Thus, differences in importin-α specificity are determinants of host range underlining the importance of the nuclear envelope in interspecies transmission.

View Article: PubMed Central - PubMed

Affiliation: 1] Heinrich-Pette-Institute, Leibniz Institute for Experimental Virology, Hamburg, Germany. [2] Sir William Dunn School of Pathology, University of Oxford, Oxford, UK. [3] Institute of Virology, Philipps-University Marburg, Marburg, Germany.

ABSTRACT
Influenza A viruses are a threat to humans due to their ability to cross species barriers, as illustrated by the 2009 H1N1v pandemic and sporadic H5N1 transmissions. Interspecies transmission requires adaptation of the viral polymerase to importin-α, a cellular protein that mediates transport into the nucleus where transcription and replication of the viral genome takes place. In this study, we analysed replication, host specificity and pathogenicity of avian and mammalian influenza viruses, in importin-α-silenced cells and importin-α-knockout mice, to understand the role of individual importin-α isoforms in adaptation. For efficient virus replication, the polymerase subunit PB2 and the nucleoprotein (NP) of avian viruses required importin-α3, whereas PB2 and NP of mammalian viruses showed importin-α7 specificity. H1N1v replication depended on both, importin-α3 and -α7, suggesting ongoing adaptation of this virus. Thus, differences in importin-α specificity are determinants of host range underlining the importance of the nuclear envelope in interspecies transmission.

No MeSH data available.


Related in: MedlinePlus

Pathogenicity of SC35M in WT and importin-α-knockout animals.WT (black square; n=18), α4−/− (black triangle; n=16), α5−/− (black cross; n=16), α7−/− (red triangle; n=16) and α7ΔIBB/ΔIBB (orange circle; n=18) animals were infected with 100-fold LD50 of SC35M. Control groups received PBS (black diamond). (a) Survival and (b) weight loss were monitored for 14 days. (c) Virus titres in the lung, brain and liver homogenates of controls (black columns) and infected WT (dark grey columns), α7−/− (light grey columns) and α7ΔIBB/ΔIBB (white columns) animals were determined by plaque assays. The error bars indicate the standard deviation of viral titres detected in three animals per time point. The detection limit was ≥30 p.f.u. (d) In situ hybridization (upper panels) shows severe infection of epithelial cells with classical signs of primary viral pneumonia with extensive infiltration and destruction of the alveolae in WT mice (upper left panel) in contrast to mostly intact lung tissues of α7−/− or α7ΔIBB/ΔIBB animals (upper middle and right panel). Double-labelling experiments (lower panels) demonstrate virus RNA-positive Mac-3+ macrophages in the lungs of WT mice (lower left panel, arrows and inset) but not in α7−/− or α7ΔIBB/ΔIBB animals infected for 3 days (lower middle and right panel), respectively. The statistical significance of differences in lung titres of WT and importin-knockout animals were assessed by Student's t-test (*P<0.05; **P<0.01).
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f2: Pathogenicity of SC35M in WT and importin-α-knockout animals.WT (black square; n=18), α4−/− (black triangle; n=16), α5−/− (black cross; n=16), α7−/− (red triangle; n=16) and α7ΔIBB/ΔIBB (orange circle; n=18) animals were infected with 100-fold LD50 of SC35M. Control groups received PBS (black diamond). (a) Survival and (b) weight loss were monitored for 14 days. (c) Virus titres in the lung, brain and liver homogenates of controls (black columns) and infected WT (dark grey columns), α7−/− (light grey columns) and α7ΔIBB/ΔIBB (white columns) animals were determined by plaque assays. The error bars indicate the standard deviation of viral titres detected in three animals per time point. The detection limit was ≥30 p.f.u. (d) In situ hybridization (upper panels) shows severe infection of epithelial cells with classical signs of primary viral pneumonia with extensive infiltration and destruction of the alveolae in WT mice (upper left panel) in contrast to mostly intact lung tissues of α7−/− or α7ΔIBB/ΔIBB animals (upper middle and right panel). Double-labelling experiments (lower panels) demonstrate virus RNA-positive Mac-3+ macrophages in the lungs of WT mice (lower left panel, arrows and inset) but not in α7−/− or α7ΔIBB/ΔIBB animals infected for 3 days (lower middle and right panel), respectively. The statistical significance of differences in lung titres of WT and importin-knockout animals were assessed by Student's t-test (*P<0.05; **P<0.01).

Mentions: We next analysed virus infection in various importin-α-knockout mice, specifically those lacking α4, α5 and α7. Two different constructs were used for the importin-α7 gene knockouts, that is, animals lacked the entire importin-α7 gene (α7−/−) or just the importin-β-binding domain (IBB) of importin-α7 essential for nuclear transport (α7ΔIBB/ΔIBB). After infection with SC35M (ref. 10), all wild-type (WT), importin-α4-deficient mice (α4−/−) and importin-α5-deficient mice (α5−/−) died (Fig. 2a). Interestingly, despite high infection doses, one-third of α7−/− and α7ΔIBB/ΔIBB animals survived and started to regain weight 8 days post-infection (p.i.) (Fig. 2a,b). These findings show that the mouse-adapted virus depends specifically on importin-α7 to develop its full pathogenic potential.


Differential use of importin-α isoforms governs cell tropism and host adaptation of influenza virus.

Gabriel G, Klingel K, Otte A, Thiele S, Hudjetz B, Arman-Kalcek G, Sauter M, Shmidt T, Rother F, Baumgarte S, Keiner B, Hartmann E, Bader M, Brownlee GG, Fodor E, Klenk HD - Nat Commun (2011)

Pathogenicity of SC35M in WT and importin-α-knockout animals.WT (black square; n=18), α4−/− (black triangle; n=16), α5−/− (black cross; n=16), α7−/− (red triangle; n=16) and α7ΔIBB/ΔIBB (orange circle; n=18) animals were infected with 100-fold LD50 of SC35M. Control groups received PBS (black diamond). (a) Survival and (b) weight loss were monitored for 14 days. (c) Virus titres in the lung, brain and liver homogenates of controls (black columns) and infected WT (dark grey columns), α7−/− (light grey columns) and α7ΔIBB/ΔIBB (white columns) animals were determined by plaque assays. The error bars indicate the standard deviation of viral titres detected in three animals per time point. The detection limit was ≥30 p.f.u. (d) In situ hybridization (upper panels) shows severe infection of epithelial cells with classical signs of primary viral pneumonia with extensive infiltration and destruction of the alveolae in WT mice (upper left panel) in contrast to mostly intact lung tissues of α7−/− or α7ΔIBB/ΔIBB animals (upper middle and right panel). Double-labelling experiments (lower panels) demonstrate virus RNA-positive Mac-3+ macrophages in the lungs of WT mice (lower left panel, arrows and inset) but not in α7−/− or α7ΔIBB/ΔIBB animals infected for 3 days (lower middle and right panel), respectively. The statistical significance of differences in lung titres of WT and importin-knockout animals were assessed by Student's t-test (*P<0.05; **P<0.01).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3105303&req=5

f2: Pathogenicity of SC35M in WT and importin-α-knockout animals.WT (black square; n=18), α4−/− (black triangle; n=16), α5−/− (black cross; n=16), α7−/− (red triangle; n=16) and α7ΔIBB/ΔIBB (orange circle; n=18) animals were infected with 100-fold LD50 of SC35M. Control groups received PBS (black diamond). (a) Survival and (b) weight loss were monitored for 14 days. (c) Virus titres in the lung, brain and liver homogenates of controls (black columns) and infected WT (dark grey columns), α7−/− (light grey columns) and α7ΔIBB/ΔIBB (white columns) animals were determined by plaque assays. The error bars indicate the standard deviation of viral titres detected in three animals per time point. The detection limit was ≥30 p.f.u. (d) In situ hybridization (upper panels) shows severe infection of epithelial cells with classical signs of primary viral pneumonia with extensive infiltration and destruction of the alveolae in WT mice (upper left panel) in contrast to mostly intact lung tissues of α7−/− or α7ΔIBB/ΔIBB animals (upper middle and right panel). Double-labelling experiments (lower panels) demonstrate virus RNA-positive Mac-3+ macrophages in the lungs of WT mice (lower left panel, arrows and inset) but not in α7−/− or α7ΔIBB/ΔIBB animals infected for 3 days (lower middle and right panel), respectively. The statistical significance of differences in lung titres of WT and importin-knockout animals were assessed by Student's t-test (*P<0.05; **P<0.01).
Mentions: We next analysed virus infection in various importin-α-knockout mice, specifically those lacking α4, α5 and α7. Two different constructs were used for the importin-α7 gene knockouts, that is, animals lacked the entire importin-α7 gene (α7−/−) or just the importin-β-binding domain (IBB) of importin-α7 essential for nuclear transport (α7ΔIBB/ΔIBB). After infection with SC35M (ref. 10), all wild-type (WT), importin-α4-deficient mice (α4−/−) and importin-α5-deficient mice (α5−/−) died (Fig. 2a). Interestingly, despite high infection doses, one-third of α7−/− and α7ΔIBB/ΔIBB animals survived and started to regain weight 8 days post-infection (p.i.) (Fig. 2a,b). These findings show that the mouse-adapted virus depends specifically on importin-α7 to develop its full pathogenic potential.

Bottom Line: Influenza A viruses are a threat to humans due to their ability to cross species barriers, as illustrated by the 2009 H1N1v pandemic and sporadic H5N1 transmissions.In this study, we analysed replication, host specificity and pathogenicity of avian and mammalian influenza viruses, in importin-α-silenced cells and importin-α-knockout mice, to understand the role of individual importin-α isoforms in adaptation.Thus, differences in importin-α specificity are determinants of host range underlining the importance of the nuclear envelope in interspecies transmission.

View Article: PubMed Central - PubMed

Affiliation: 1] Heinrich-Pette-Institute, Leibniz Institute for Experimental Virology, Hamburg, Germany. [2] Sir William Dunn School of Pathology, University of Oxford, Oxford, UK. [3] Institute of Virology, Philipps-University Marburg, Marburg, Germany.

ABSTRACT
Influenza A viruses are a threat to humans due to their ability to cross species barriers, as illustrated by the 2009 H1N1v pandemic and sporadic H5N1 transmissions. Interspecies transmission requires adaptation of the viral polymerase to importin-α, a cellular protein that mediates transport into the nucleus where transcription and replication of the viral genome takes place. In this study, we analysed replication, host specificity and pathogenicity of avian and mammalian influenza viruses, in importin-α-silenced cells and importin-α-knockout mice, to understand the role of individual importin-α isoforms in adaptation. For efficient virus replication, the polymerase subunit PB2 and the nucleoprotein (NP) of avian viruses required importin-α3, whereas PB2 and NP of mammalian viruses showed importin-α7 specificity. H1N1v replication depended on both, importin-α3 and -α7, suggesting ongoing adaptation of this virus. Thus, differences in importin-α specificity are determinants of host range underlining the importance of the nuclear envelope in interspecies transmission.

No MeSH data available.


Related in: MedlinePlus