Annexin A2 associates to feline calicivirus RNA in the replication complexes from infected cells and participates in an efficient viral replication

ANXA2 Facilitates Enterovirus 71 Infection by Interacting with 3D Polymerase and PI4KB to Assist the Assembly of Replication Organelles

Similar to that of other enteroviruses, the replication of enterovirus 71 (EV71) occurs on rearranged membranous structures called replication organelles (ROs). Phosphatidylinositol 4-kinase III (PI4KB), which is required by enteroviruses for RO formation, yields phosphatidylinositol-4-phosphate (PI4P) on ROs. PI4P then binds and induces conformational changes in the RNA-dependent RNA polymerase (RdRp) to modulate RdRp activity. Here, we targeted 3D polymerase, the core enzyme of EV71 ROs, and found that the host factor Annexin A2 (ANXA2) can interact with 3D polymerase and promote the replication of EV71. Then, an experiment showed that the annexin domain of ANXA2, which possesses membrane-binding capacity, mediates the interaction of ANXA2 with EV71 3D polymerase. Further research showed that ANXA2 is localized on ROs and interacts with PI4KB. Overexpression of ANXA2 stimulated the formation of PI4P, and the level of PI4P was decreased in ANXA2-knockout cells. Furthermore, ANXA2, PI4KB, and 3D were shown to be localized to the viral RNA replication site, where they form a higher-order protein complex, and the presence of ANXA2 promoted the PI4KB-3D interaction. Altogether, our data provide new insight into the role of ANXA2 in facilitating formation of the EV71 RNA replication complex.

RPS5 interacts with the rabbit hemorrhagic disease virus 3' extremities region and plays a role in virus replication

Rabbit hemorrhagic disease virus (RHDV), a member of Caliciviridae family, causes a highly contagious disease in rabbits. The RHDV replication mechanism is poorly understood due to the lack of a suitable culture system in vitro. This study identified RHDV 5' and 3' extremities (Ex) RNA binding proteins from the rabbit kidney cell line RK-13 based on a pull-down assay by applying a tRNA scaffold streptavidin aptamer. Using mass spectrometry (MS), several host proteins were discovered which interact with RHDV 5' and 3' Ex RNA. The ribosomal protein S5 (RPS5) was shown to interact with RHDV 3' Ex RNA directly by RNA-pulldown and confocal microscopy. To further investigate the role of RPS5 in RHDV replication, small interfering RNAs for RPS5 and RPS5 eukaryotic expression plasmids were used to change the expression level of RPS5 in RK-13 cells and the results showed that the RHDV replication and translation levels were positively correlated with the expression level of RPS5. It was also verified that RPS5 promoted RHDV replication by constructing RPS5 stable overexpression cell lines and RPS5 knockdown cell lines. In summary, it has been identified that RPS5 interacted with the RHDV 3' Ex RNA region and played a role in virus replication. These results will help to understand the mechanism of RHDV replication.

Annexin A2 gene interacting with viral matrix protein to promote bovine ephemeral fever virus release

Bovine ephemeral fever virus (BEFV) causes bovine ephemeral fever, which can produce considerable economic damage to the cattle industry. However, there is limited experimental evidence regarding the underlying mechanisms of BEFV. Annexin A2 (AnxA2) is a calcium and lipid-conjugated protein that binds phospholipids and the cytoskeleton in a Ca²⁺-dependent manner, and it participates in various cellular functions, including vesicular trafficking, organization of membrane domains, and virus proliferation. The role of the AnxA2 gene during virus infection has not yet been reported. In this study, we observed that AnxA2 gene expression was up-regulated in BHK-21 cells infected with the virus. Additionally, overexpression of the AnxA2 gene promoted the release of mature virus particles, whereas BEFV replication was remarkably inhibited after reducing AnxA2 gene expression by using the small interfering RNA (siRNA). For viral proteins, overexpression of the Matrix (M) gene promotes the release of mature virus particles. Moreover, the AnxA2 protein interaction with the M protein of BEFV was confirmed by GST pull-down and co-immunoprecipitation assays. Experimental results indicate that the C-terminal domain (268-334 aa) of AxnA2 contributes to this interaction. An additional mechanistic study showed that AnxA2 protein interacts with M protein and mediates the localization of the M protein at the plasma membrane. Furthermore, the absence of the AnxA2-V domain could attenuate the effect of AnxA2 on BEFV replication. These findings can contribute to elucidating the regulation of BEFV replication and may have implications for antiviral strategy development.

Host cell p53 associates with the feline calicivirus major viral capsid protein VP1, the protease-polymerase NS6/7, and the double-stranded RNA playing a role in virus replication

p53 is implicated in several cellular pathways such as induction of cell-cycle arrest, differentiation, senescence, and apoptosis. p53 is activated by a broad range of stress signals, including viral infections. While some viruses activate p53, others induce its inactivation, and occasionally p53 is differentially modulated during the replicative cycle. During calicivirus infections, apoptosis is required for virus exit and spread into the host; yet, the role of p53 during infection is unknown. By confocal microscopy, we found that p53 associates with FCV VP1, the protease-polymerase NS6/7, and the dsRNA. This interaction was further confirmed by proximity ligation assays, suggesting that p53 participates in the FCV replication. Knocked-down of p53 expression in CrFK cells before infection, resulted in a strong reduction of the non-structural protein levels and a decrease of the viral progeny production. These results indicate that p53 is associated with the viral replication complex and is required for an efficient FCV replication.

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Host cell p53 protein levels and subcellular localization do not change during FCV infection.

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Host cell p53 associates with FCV major viral capsid protein VP1, protease-polymerase NS6/7, and the dsRNA in FCV infected cells.

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Host cell p53 is required for a FCV replication.