Cytoskeletal dynamics: concepts in measles virus replication and immunomodulation

Screening of candidate genes associated with high titer production of oncolytic measles virus based on systems biology approach

The number of viral particles required for oncolytic activity of measles virus (MV) can be more than a million times greater than the reported amount for vaccination. The aim of the current study is to find potential genes and signaling pathways that may be involved in the high-titer production of MV. In this study, a systems biology approach was considered including collection of gene expression profiles from the Gene Expression Omnibus (GEO) database, obtaining differentially expressed genes (DEGs), performing gene ontology, functional enrichment analyses, and topological analyses on the protein-protein interaction (PPI) network. Then, to validate the in-silico data, total RNA was isolated from five cell lines, and full-length cDNA from template RNA was synthesized. Subsequently, quantitative reverse transcription-PCR (RT-qPCR) was employed. We identified five hub genes, including RAC1, HSP90AA1, DNM1, LTBP1, and FSTL1 associated with the enhancement in MV titer. Pathway analysis indicated enrichment in PI3K-Akt signaling pathway, axon guidance, proteoglycans in cancer, regulation of actin cytoskeleton, focal adhesion, and calcium signaling pathways. Upon verification by RT-qPCR, the relative expression of candidate genes was generally consistent with our bioinformatics analysis. Hub genes and signaling pathways may be involved in understanding the pathological mechanisms by which measles virus manipulates host factors in order to facilitate its replication. RAC1, HSP90AA1, DNM1, LTBP1, and FSTL1 genes, in combination with genetic engineering techniques, will allow the direct design of high-throughput cell lines to answer the required amounts for the oncolytic activity of MV.

Ceramide and Related Molecules in Viral Infections

Ceramide is a lipid messenger at the heart of sphingolipid metabolism. In concert with its metabolizing enzymes, particularly sphingomyelinases, it has key roles in regulating the physical properties of biological membranes, including the formation of membrane microdomains. Thus, ceramide and its related molecules have been attributed significant roles in nearly all steps of the viral life cycle: they may serve directly as receptors or co-receptors for viral entry, form microdomains that cluster entry receptors and/or enable them to adopt the required conformation or regulate their cell surface expression. Sphingolipids can regulate all forms of viral uptake, often through sphingomyelinase activation, and mediate endosomal escape and intracellular trafficking. Ceramide can be key for the formation of viral replication sites. Sphingomyelinases often mediate the release of new virions from infected cells. Moreover, sphingolipids can contribute to viral-induced apoptosis and morbidity in viral diseases, as well as virus immune evasion. Alpha-galactosylceramide, in particular, also plays a significant role in immune modulation in response to viral infections. This review will discuss the roles of ceramide and its related molecules in the different steps of the viral life cycle. We will also discuss how novel strategies could exploit these for therapeutic benefit.

Transmissible gastroenteritis virus and porcine epidemic diarrhoea virus infection induces dramatic changes in the tight junctions and microfilaments of polarized IPEC-J2 cells

Viral infection converts the normal constitution of a cell to optimise viral entry, replication, and virion production. These conversions contain alterations or disruptions of the tight and adherens junctions between cells as part of their pathogenesis, and reorganise cellular microfilaments that initiate, sustain and spread the viral infections and so on. Using porcine epidemic diarrhoea virus (PEDV), transmissible gastroenteritis virus (TGEV) and a model of normal intestinal epithelial cells (IPEC-J2), we researched the interaction between tight and adherens junctions and microfilaments of IPEC-J2 cells with these viruses. In our work, the results showed that IPEC-J2 cells were susceptible to TGEV and PEDV infection. And TGEV could impair the barrier integrity of IPEC-J2 cells at early stages of infection through down-regulating some proteins of tight and adherens junctions, while PEDV cloud cause a slight of damage in the integrity of epithelial barrier. In addition, they also could affect the microfilaments remodelling of IPEC-J2 cells, and the drug-interfered microfilaments could inhibit viral replication and release. Furthermore, PEDV+TGEV co-infection was more aggravating to damage of tight junctions and remodelling of microfilaments than their single infection. Finally, the PEDV and TGEV infection affected the MAPK pathway, and inhibition of MAPK pathway regulated the changes of tight junctions and microfilaments of cells. These studies provide a new insight from the perspective of the epithelial barrier and microfilaments into the pathogenesis of PEDV and TGEV.

Transmissible gastroenteritis virus and porcine epidemic diarrhoea virus infection induces dramatic changes in the tight junctions and microfilaments of polarized IPEC-J2 cells

Viral infection converts the normal constitution of a cell to optimise viral entry, replication, and virion production. These conversions contain alterations or disruptions of the tight and adherens junctions between cells as part of their pathogenesis, and reorganise cellular microfilaments that initiate, sustain and spread the viral infections and so on. Using porcine epidemic diarrhoea virus (PEDV), transmissible gastroenteritis virus (TGEV) and a model of normal intestinal epithelial cells (IPEC-J2), we researched the interaction between tight and adherens junctions and microfilaments of IPEC-J2 cells with these viruses. In our work, the results showed that IPEC-J2 cells were susceptible to TGEV and PEDV infection. And TGEV could impair the barrier integrity of IPEC-J2 cells at early stages of infection through down-regulating some proteins of tight and adherens junctions, while PEDV cloud cause a slight of damage in the integrity of epithelial barrier. In addition, they also could affect the microfilaments remodelling of IPEC-J2 cells, and the drug-interfered microfilaments could inhibit viral replication and release. Furthermore, PEDV+TGEV co-infection was more aggravating to damage of tight junctions and remodelling of microfilaments than their single infection. Finally, the PEDV and TGEV infection affected the MAPK pathway, and inhibition of MAPK pathway regulated the changes of tight junctions and microfilaments of cells. These studies provide a new insight from the perspective of the epithelial barrier and microfilaments into the pathogenesis of PEDV and TGEV.

Influenza A viral nucleoprotein interacts with cytoskeleton scaffolding protein α-actinin-4 for viral replication

Influenza A virus (IAV), similar to other viruses, exploits the machinery of human host cells for its survival and replication. We identified α‐actinin‐4, a host cytoskeletal protein, as an interacting partner of IAV nucleoprotein (NP). We confirmed this interaction using co‐immunoprecipitation studies, first in a coupled in vitro transcription‐translation assay and then in cells either transiently co‐expressing the two proteins or infected with whole IAV. Importantly, the NP–actinin‐4 interaction was observed in several IAV subtypes, including the 2009 H1N1 pandemic virus. Moreover, immunofluorescence studies revealed that both NP and actinin‐4 co‐localized largely around the nucleus and also in the cytoplasmic region of virus‐infected A549 cells. Silencing of actinin‐4 expression resulted in not only a significant decrease in NP, M2 and NS1 viral protein expression, but also a reduction of both NP mRNA and viral RNA levels, as well as viral titers, 24 h post‐infection with IAV, suggesting that actinin‐4 was critical for viral replication. Furthermore, actinin‐4 depletion reduced the amount of NP localized in the nucleus. Treatment of infected cells with wortmannin, a known inhibitor of actinin‐4, led to a decrease in NP mRNA levels and also caused the nuclear retention of NP, further strengthening our previous observations. Taken together, the results of the present study indicate that actinin‐4, a novel interacting partner of IAV NP, plays a crucial role in viral replication and this interaction may participate in nuclear localization of NP and/or viral ribonucleoproteins.

Structured digital abstract

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Actin filaments disruption and stabilization affect measles virus maturation by different mechanisms

Background

Cytoskeletal proteins are often involved in the virus life cycle, either at early steps during virus entry or at later steps during formation of new virus particles. Though actin filaments have been shown to play a role in the production of measles virus (MV), the importance of actin dynamics for virus assembly and budding steps is not known yet. Aim of this work was thus to analyze the distinctive consequences of F-actin stabilization or disruption for MV protein trafficking, particle assembly and virus release.

Results

MV infection studies in the presence of inhibitors differently affecting the actin cytoskeleton revealed that not only actin disruption but also stabilization of actin filaments interfered with MV particle release. While overall viral protein synthesis, surface expression levels of the MV glycoproteins, and cell-associated infectivity was not altered, cell-free virus titers were decreased. Interestingly, the underlying mechanisms of interference with late MV maturation steps differed principally after F-actin disruption by Cytochalasin D (CD) and F-actin stabilization by Jasplakinolide (Jaspla). While intact actin filaments were shown to be required for transport of nucleocapsids and matrix proteins (M-RNPs) from inclusions to the plasma membrane, actin dynamics at the cytocortex that are blocked by Jaspla are necessary for final steps in virus assembly, in particular for the formation of viral buds and the pinching-off at the plasma membrane. Supporting our finding that F-actin disruption blocks M-RNP transport to the plasma membrane, cell-to-cell spread of MV infection was enhanced upon CD treatment. Due to the lack of M-glycoprotein-interactions at the cell surface, M-mediated fusion downregulation was hindered and a more rapid syncytia formation was observed.

Conclusion

While stable actin filaments are needed for intracellular trafficking of viral RNPs to the plasma membrane, and consequently for assembly at the cell surface and prevention of an overexerted fusion by the viral surface glycoproteins, actin dynamics are required for the final steps of budding at the plasma membrane.

The potential role of microfilaments in host cells for infection with infectious spleen and kidney necrosis virus infection

Background

Infectious spleen and kidney necrosis virus (ISKNV) belongs to the genus Megalocytivirus from the family Iridoviridae. Megalocytivirus causes severe economic losses to tropical freshwater and marine culture industry in Asian countries and is devastating to the mandarin fish farm industry in China particularly.

Methods

We investigated the involvement of microfilaments in the early and late stages of ISKNV infection in MFF-1 cells by selectively perturbing their architecture using well-characterized inhibitors of actin dynamics. The effect of disruption of actin cytoskeleton on ISKNV infection was evaluated by indirect immunofluorescence analysis or real-time quantitative PCR.

Results

The depolymerization of the actin filaments with cytochalasin D, cytochalasin B, or latrunculin A reduced ISKNV infection. Furthermore, depolymerization of filamentous actin by inhibitors did not inhibit binding of the virus but affected virus internalization in the early stages of infection. In addition, the depolymerization of actin filaments reduced total ISKNV production in the late stages of ISKNV.

Conclusions

This study demonstrated that ISKNV required an intact actin network during infection. The findings will help us to better understand how iridoviruses exploit the cytoskeleton to facilitate their infection and subsequent disease.

Toward system-level understanding of baculovirus-host cell interactions: from molecular fundamental studies to large-scale proteomics approaches

Baculoviruses are insect viruses extensively exploited as eukaryotic protein expression vectors. Molecular biology studies have provided exciting discoveries on virus-host interactions, but the application of omic high-throughput techniques on the baculovirus-insect cell system has been hampered by the lack of host genome sequencing. While a broader, systems-level analysis of biological responses to infection is urgently needed, recent advances on proteomic studies have yielded new insights on the impact of infection on the host cell. These works are reviewed and critically assessed in the light of current biological knowledge of the molecular biology of baculoviruses and insect cells.

Legume lectins inhibit human parainfluenza virus type 2 infection by interfering with the entry

Three lectins with different sugar binding specificities were investigated for anti-viral activity against human parainfluenza virus type 2 (hPIV-2). The lectins, concanavalin A (Con A), lens culinaris agglutinin (LCA) and peanut agglutinin (PNA), inhibited cell fusion and hemadsorption induced by hPIV-2. Virus nucleoprotein (NP) gene synthesis was largely inhibited, but fusion (F) and hemagglutinin-neuraminidase (HN) gene syntheses were not. An indirect immunofluorescence study showed that Con A inhibited virus NP, F and HN protein syntheses, but LCA did not completely inhibit them, and that PNA inhibited only NP protein synthesis. Using a recombinant green fluorescence protein-expressing hPIV-2, without matrix protein (rghPIV-2ΔM), it was found that virus entry into the cells was not completely prevented. The lectins considerably reduced the number of viruses released compared with that of virus infected cells. The lectins bound to cell surface within 10 min, and many aggregates were observed at 30 min. Con A and LCA slightly disrupted actin microfilaments and microtubules, but PNA had almost no effect on them. These results indicated that the inhibitory effects of the lectins were caused mainly by the considerable prevention of virus adsorption to the cells by the lectin binding to their receptors.