Showing papers by "Paul Digard published in 2001"

Interaction of the influenza virus nucleoprotein with the cellular CRM1-mediated nuclear export pathway.

Abstract: Influenza virus transcription occurs in the nuclei of infected cells, where the viral genomic RNAs are complexed with a nucleoprotein (NP) to form ribonucleoprotein (RNP) structures. Prior to assembly into progeny virions, these RNPs exit the nucleus and accumulate in the cytoplasm. The mechanisms responsible for RNP export are only partially understood but have been proposed to involve the viral M1 and NS2 polypeptides. We found that the drug leptomycin B (LMB), which specifically inactivates the cellular CRM1 polypeptide, caused nuclear retention of NP in virus-infected cells, indicating a role for the CRM1 nuclear export pathway in RNP egress. However, no alteration was seen in the cellular distribution of M1 or NS2, even in the case of a mutant virus which synthesizes greatly reduced amounts of NS2. Furthermore, NP was distributed throughout the nuclei of infected cells at early times postinfection but, when retained in the nucleus at late times by LMB treatment, was redistributed to the periphery of the nucleoplasm. No such change was seen in the nuclear distribution of M1 or NS2 after drug treatment. Similar to the behavior of NP, M1 and NS2 in infected cells, LMB treatment of cells expressing each polypeptide in isolation caused nuclear retention of NP but not M1 or NS2. Conversely, overexpression of CRM1 caused increased cytoplasmic accumulation of NP but had little effect on M1 or NS2 distribution. Consistent with this, NP bound CRM1 in vitro. Overall, these data raise the possibility that RNP export is mediated by a direct interaction between NP and the cellular CRM1 export pathway.

Interaction of the influenza virus nucleoprotein with F-actin

Abstract: Introduction : The influenza virus genome is transcribed in the nucleus of infected cells but assembled into progeny virions in the cytoplasm. This is reflected in the cellular distribution of the virus nucleoprotein (NP), a protein which encapsidates genomic RNA to form ribonucleoprotein (RNP) structures: at the early stage post-infection, NP is found in the nucleus, but later it is found predominantly in the cytoplasm. The purpose of this study was to examine the possibility that cytoplasmic NP interacts with actin microfilaments. Methods : Bacterially expressed NP was tested for the ability to interact with filamentous (F)-actin in a variety of in vitro assays, and the localisation of actin and exogenously expressed NP in mammalian cells was examined microscopically. Results : Purified NP bound actin filaments in vitro and showed partial colocalisation with β-actin in vivo. Electron microscopy showed that NP induced bundling of actin fibres in vitro. In confirmation of this, NP caused a dramatic increase in the low-shear viscosity and light-scattering properties of F-actin suspensions. Conclusions : NP binds F-actin in vitro and can alter the mechanical properties of actin filaments. This raises the possibility that influenza virus may use the host-cell cytoskeleton during virus replication.