title: Influenza virus-induced caspase-dependent enlargement of nuclear pores promotes nuclear export of viral ribonucleoprotein complexes.
abstract: Influenza A viruses (IAV) replicate their segmented RNA genome in the nucleus of infected cells and utilize caspase-dependent nucleocytoplasmic export mechanisms to transport newly formed ribonucleoprotein complexes (RNPs) to the site of infectious virion release at the plasma membrane. In this study, we obtained evidence that apoptotic caspase activation in IAV-infected cells is associated with the degradation of the nucleoporin Nup153, an integral subunit of the nuclear pore complex. Transmission electron microscopy studies revealed a distinct enlargement of nuclear pores in IAV-infected cells. Transient expression and subcellular accumulation studies of multimeric marker proteins in virus-infected cells provided additional evidence for increased nuclear pore diameters facilitating the translocation of large protein complexes across the nuclear membrane. Furthermore, caspase 3/7 inhibition data obtained in this study suggest that active, Crm1-dependent IAV RNP export mechanisms are increasingly complemented by passive, caspase-induced export mechanisms at later stages of infection.
  
  
  OBJECTIVE
  In contrast to the process seen with most other RNA viruses, influenza virus genome replication occurs in the nucleus (rather than the cytoplasm) of infected cells. Therefore, completion of the viral replication cycle critically depends on intracellular transport mechanisms that ensure the translocation of viral ribonucleoprotein (RNP) complexes across the nuclear membrane. Here, we demonstrate that virus-induced cellular caspase activities cause a widening of nuclear pores, thereby facilitating nucleocytoplasmic translocation processes and, possibly, promoting nuclear export of newly synthesized RNPs. These passive transport mechanisms are suggested to complement Crm1-dependent RNP export mechanisms known to occur at early stages of the replication cycle and may contribute to highly efficient production of infectious virus progeny at late stages of the viral replication cycle. The report provides an intriguing example of how influenza virus exploits cellular structures and regulatory pathways, including intracellular transport mechanisms, to complete its replication cycle and maximize the production of infectious virus progeny.
authors: Institute of Medical Virology, Justus Liebig University Giessen, Giessen, Germany.
authors: Dirk
authors: D
authors: Mühlbauer
authors: Institute of Medical Virology, Justus Liebig University Giessen, Giessen, Germany.
authors: Julia
authors: J
authors: Dzieciolowski
authors: Imaging Unit, Biomedical Research Center, Justus Liebig University Giessen, Giessen, Germany.
authors: Martin
authors: M
authors: Hardt
authors: Department of Internal Medicine/Infectious Diseases and Respiratory Medicine, Charité, Universitätsmedizin Berlin, Berlin, Germany.
authors: Andreas
authors: A
authors: Hocke
authors: Division of Influenza and Other Respiratory Viruses, Robert Koch Institute, Berlin, Germany.
authors: Kristina L
authors: KL
authors: Schierhorn
authors: Institute of Medical Virology, Justus Liebig University Giessen, Giessen, Germany Center of Scientific Excellence for Influenza Viruses, National Research Center (NRC), Dokki, Giza, Egypt.
authors: Ahmed
authors: A
authors: Mostafa
authors: Institute of Medical Virology, Justus Liebig University Giessen, Giessen, Germany.
authors: Christin
authors: C
authors: Müller
authors: Institute of Medical Virology, Justus Liebig University Giessen, Giessen, Germany.
authors: Christian
authors: C
authors: Wisskirchen
authors: Department of Internal Medicine (Pulmonology), Universities of Giessen and Marburg Lung Center, Giessen, Germany.
authors: Susanne
authors: S
authors: Herold
authors: Division of Influenza and Other Respiratory Viruses, Robert Koch Institute, Berlin, Germany.
authors: Thorsten
authors: T
authors: Wolff
authors: Institute of Medical Virology, Justus Liebig University Giessen, Giessen, Germany.
authors: John
authors: J
authors: Ziebuhr
authors: Institute of Medical Virology, Justus Liebig University Giessen, Giessen, Germany stephan.pleschka@viro.med.uni-giessen.de.
authors: Stephan
authors: S
authors: Pleschka
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D009980:Influenza A virus / Q000502:physiology*; D046529:Microscopy, Electron, Transmission; D022022:Nuclear Pore / Q000378:metabolism*; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism*; D014779:Virus Replication
chemical_list: C079377:NUP153 protein, human; D028861:Nuclear Pore Complex Proteins; D012261:Ribonucleoproteins; D020169:Caspases