Nucleocytoplasmic Traffic Disorder Induced by Cardioviruses

Abstract

Some picornaviruses, for example, poliovirus, increase bidirectional permeability of the nuclear envelope and suppress active nucleocytoplasmic transport. These activities require the viral protease 2Apro . Here, we studied nucleocytoplasmic traffic in cells infected with encephalomyocarditis virus (EMCV; a cardiovirus), which lacks the poliovirus 2A pro -related protein. EMCV similarly enhanced bidirectional nucleocytoplasmic traffic. By using the fluorescent "Timer" protein, which contains a nuclear localization signal, we showed that the cytoplasmic accumulation of nuclear proteins in infected cells was largely due to the nuclear efflux of "old" proteins rather than impaired active nuclear import of newly synthesized molecules. The nuclear envelope of digitonin-treated EMCV-infected cells permitted rapid efflux of a nuclear marker protein. Inhibitors of poliovirus 2A pro did not prevent the EMCV-induced efflux. Extracts from EMCV-infected cells and products of in vitro translation of viral RNAs contained an activity increasing permeability of the nuclear envelope of uninfected cells. This activity depended on the expression of the viral leader protein. Mutations disrupting the zinc finger motif of this protein abolished its efflux-inducing ability. Inactivation of the L protein phosphorylation site (Thr473Ala) resulted in a delayed efflux, while a phosphorylation-mimicking (Thr473Asp) replacement did not significantly impair the efflux-inducing ability. Such activity of extracts from EMCV-infected cells was suppressed by the protein kinase inhibitor staurosporine. As evidenced by electron microscopy, cardiovirus infection resulted in alteration of the nuclear pores, but it did not trigger degradation of the nucleoporins known to be degraded in the poliovirus-infected cells. Thus, two groups of picornaviruses, enteroviruses and cardioviruses, similarly alter the nucleocytoplasmic traffic but achieve this by strikingly different mechanisms.Picornaviruses, small nonenveloped icosahedral animal viruses with a single-stranded RNA genome of positive (mRNA) polarity, encompass the Enterovirus, Rhinoviruses, Cardiovirus, Aphthovirus, Parechovirus, and some other genera (64). All essential steps of their reproduction, such as translation, RNA synthesis, and encapsidation, take place in the cytoplasm of infected cells. The nonessential role of the nucleus for their reproduction follows from their ability to fulfill the complete infectious cycle in nuclei-free cytoplasts (31, 60) or cytoplasmic extracts (7,52,71). This fact, however, does not mean that the nuclei are not involved in the infectious process. Indeed, virusspecific proteins have been detected in the nuclei of poliovirusinfected (11, 29) and encephalomyocarditis virus (EMCV)-infected (5, 6) cells. Poliovirus proteases 2A and 3C are known to target a variety of nuclear transcription factors and histones (66,78,79,80). The EMCV 2A protein enters the nucleoli and interacts there with a ribosome precursor, contributing thereby to alterations in the translation c...

Alteration of the nuclear pore complex in Ca2+-mediated cell death

“…Alteration of several nuclear-cytoplasmic pathways has been documented during viral infection and an increase in nuclear permeability is a general strategy adopted by several viruses such as poliovirus, 19,45 rhinovirus 46 and cardiovirus 47 to gain access to the cell genetic information. In this case, the increased redistribution of NLS and NES-containing EGFP has been attributed to a perturbation of the docking of receptor-cargo complexes to the NPC.…”

RNA nuclear export is blocked by poliovirus 2A protease and is concomitant with nucleoporin cleavage

“…These NPC extensions might function as initial cargo-docking sites during nuclear-cytoplasmic transport (Cullen, 2003;Kohler and Hurt, 2007). Some viruses severely damage NPC architecture, which leads to the inhibition of protein trafficking between the nucleus and the cytoplasm (Belov et al, 2004;Gustin and Sarnow, 2001;Gustin and Sarnow, 2002;Park et al, 2008;Porter and Palmenberg, 2009), inhibition of RNA export from the nucleus (Her et al, 1997;Satterly et al, 2007), and, in some instance, an increase of the nuclear membrane permeability at later times post-infection (Belov et al, 2004;Lidsky et al, 2006). Here, we report that PV 2A pro induces alterations in the NPC, which inhibits nuclear export of U snRNA, rRNA and mRNA but not that of tRNAs.…”

Encephalomyocarditis Virus Leader Is Phosphorylated by CK2 and Syk as a Requirement for Subsequent Phosphorylation of Cellular Nucleoporins

“…After release during infection, or as a recombinant protein, the L from EMCV-R (L E ; 67 amino acids [aa]) triggers a cellular phosphorylation cascade aimed at the nucleoporins (Nups), which form the hydrophobic core of nuclear pore complexes (NPC). The degree of Nup hyperphosphorylation is so extensive, and so unlike anything that happens during the normal cell cycle, that it completely disrupts all active host nucleocytoplasmic trafficking pathways (12)(13)(14) (J. Ciomperlik, unpublished results). The altered NPC become open to widespread passive diffusion, allowing essential components to leak from the nucleus and become available for cytoplasmic viral rep-lication.…”