Abstract
Picornaviruses are positive-stranded RNA viruses. Even though replication and translation of their genome take place in the cytoplasm, these viruses evolved different strategies to disturb nucleocytoplasmic trafficking of host proteins and RNA. The major targets of picornavirus are the phenylalanine-glycine (FG)-nucleoporins, which form a mesh in the central channel of the nuclear pore complex through which protein cargos and karyopherins are actively transported in both directions. Interestingly, while enteroviruses use the proteolytic activity of their 2A protein to degrade FG-nucleoporins, cardioviruses act by triggering phosphorylation of these proteins by cellular kinases. By targeting the nuclear pore complex, picornaviruses recruit nuclear proteins to the cytoplasm, where they increase viral genome translation and replication; they affect nuclear translocation of cytoplasmic proteins such as transcription factors that induce innate immune responses and retain host mRNA in the nucleus thereby preventing cell emergency responses and likely making the ribosomal machinery available for translation of viral RNAs.
Highlights
Nucleocytoplasmic Trafficking of Proteins and Picornavirus ReplicationNucleocytoplasmic transport of proteins and RNA occurs through the nuclear pore complexes (NPC)
By treating picornavirus-infected cells with the pan-caspase inhibitor z-VAD-fmk, Gustin and Sarnow showed that the influence of caspases on NUP153 and NUP62 cleavage was negligible in the case of poliovirus and very weak in the case of rhinovirus [26]
Picornaviruses belonging to different genera evolved different strategies to target the nuclear pore complex and to perturb nucleocytoplasmic trafficking of proteins and RNA
Summary
Nucleocytoplasmic transport of proteins and RNA occurs through the nuclear pore complexes (NPC). These complexes, localized in the nuclear envelope, are composed of two main elements: a stationary phase and a soluble phase. The soluble phase is mainly composed of proteins such as the small GTPase RAN and nuclear transport receptors (karyopherins, which include importins and exportins). The importin binds RAN-GTP and this interaction induces the release of the cargo protein (Figure 1 left). The NES of the nuclear cargo protein is bound by an exportin complexed with RAN-GTP. The cargo-exportin-RAN-GTP complex translocates to the cytoplasm through the interaction of the exportin with the FG-Nups. RAN-GTP is hydrolyzed into RAN-GDP, which induces the dissociation of the cargo-exportin complex.
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