Influenza virus-induced caspase-dependent enlargement of nuclear pores promotes nuclear export of viral ribonucleoprotein complexes

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.