Nuclear export of influenza viral ribonucleoprotein is temperature-dependently inhibited by dissociation of viral matrix protein

Abstract

The influenza virus copies its genomic RNA in the nuclei of host cells, but the viral particles are formed at the plasma membrane. Thus, the export of new genome from the nucleus into the cytoplasm is essential for viral production. Several viral proteins, such as nucleoprotein (NP) and RNA polymerases, synthesized in the cytoplasm, are imported into the nucleus, and form viral ribonucleoprotein (vRNP) with new genomic RNA. vRNP is then exported into the cytoplasm from the nucleus to produce new viral particles. M1, a viral matrix protein, is suggested to participate in the nuclear export of vRNP. It was found unexpectedly that the production of influenza virus was suppressed in MDCK cells at 41 degrees C, although viral proteins were synthesized and the cytopathic effect was observed in host cells. Indirect immunofluorescent staining with anti-NP or M1 monoclonal antibody showed that NP and M1 remained in the nuclei of infected cells at 41 degrees C, suggesting that a suppression of viral production was caused by inhibition of the nuclear export of these proteins. The cellular machinery for nuclear export depending on CRM1, which mediates the nuclear export of influenza viral RNP, functioned normally at 41 degrees C. Glycerol-density gradient centrifugation demonstrated that vRNP also formed normally at 41 degrees C. However, an examination of the interaction between vRNP and M1 by immunoprecipitation indicated that M1 did not associate with vRNP at 41 degrees C, suggesting that the association is essential for the nuclear export of vRNP. Furthermore, when infected cells incubated at 41 degrees C were cultured at 37 degrees C, the interaction between vRNP and M1 was no longer detected even at 37 degrees C. The results suggest that M1 synthesized at 41 degrees C is unable to interact with vRNP and the dissociation of M1 from vRNP is one of the reasons that the transfer of vRNP into the cytoplasm from the nucleus is prevented at 41 degrees C.

Pretreatment with Recombinant Human Vascular Endothelial Growth Factor Reduces Virus Replication and Inflammation in a Perinatal Lamb Model of Respiratory Syncytial Virus Infection

“…It is recognized that elevated body temperature is a by-product of the innate immune system, often resulting from cytokine (e.g., interleukin [IL]-1, IL-6, and tumor necrosis factor [TNF]-α) expression (10). Increased temperature can inhibit in vitro replication of some viruses including influenza and feline immunodeficiency virus and temperature regulation is in part the foundational precept of RSV temperature-sensitive vaccines (2,7,34). The correlation of increased body temperature during the course of disease to decreased RSV replication is a novel finding for this perinatal RSV model.…”

RAB11A Is Essential for Transport of the Influenza Virus Genome to the Plasma Membrane

“…Individual vRNPs assemble in the nucleus and undergo nuclear export after M1-mediated release from the nuclear matrix (9,28,41). vRNP-M1 complexes are thought to associate with the viral nuclear export protein (NS2/NEP), which bridges an interaction with the cellular CRM1 nuclear export machinery, and vRNPs are transported to the cytoplasm through nuclear pore complexes in an NEP-dependent manner (33,37).…”

Heat Shock Protein 70 Is Related to Thermal Inhibition of Nuclear Export of the Influenza Virus Ribonucleoprotein Complex

“…Therefore, new vRNP must be exported from the nucleus into the cytoplasm for viral offspring production (16). Matrix protein 1 (M1) and nonstructural protein 2/nuclear export protein (NS2/NEP) are known to be necessary for the nuclear export of vRNP (4,19,20,21,24,30). Both proteins also migrate into the nucleus and associate with vRNP (10,19,28,32,33) for transportation via the cellular machinery for nuclear export, dependent on chromosome region maintenance 1 (CRM1) protein (9,18,21).…”