Integrity of membrane lipid rafts is necessary for the ordered assembly and release of infectious Newcastle disease virus particles

The multifaceted interactions between Newcastle disease virus proteins and host proteins: a systematic review

Newcastle disease virus (NDV) typically induces severe illness in poultry and results in significant economic losses for the worldwide poultry sector. NDV, an RNA virus with a single-stranded negative-sense genome, is susceptible to mutation and immune evasion during viral transmission, thus imposing enormous challenges to avian health and poultry production. NDV is composed of six structural proteins and two nonstructural proteins that exert pivotal roles in viral infection and antiviral responses by interacting with host proteins. Nowadays, there is a particular focus on the mechanisms of virus-host protein interactions in NDV research, yet a comprehensive overview of such research is still lacking. Herein, we briefly summarize the mechanisms regarding the effects of virus-host protein interaction on viral infection, pathogenesis, and host immune responses. This review can not only enhance the present comprehension of the mechanism underlying NDV and host interplay, but also furnish a point of reference for the advancement of antiviral measures.

Multifunctionality of matrix protein in the replication and pathogenesis of Newcastle disease virus: A review

As an important structural protein in virion morphogenesis, the matrix (M) protein of Newcastle disease virus (NDV) is demonstrated to be a nuclear-cytoplasmic trafficking protein and plays essential roles in viral assembly and budding. In recent years, increasing lines of evidence have indicated that the M protein has obvious influence on the pathotypes of NDV, and the interaction of M protein with cellular proteins is also closely associated with the replication and pathogenicity of NDV. Although substantial progress has been made in the past 40 years towards understanding the structure and function of NDV M protein, the available information is scattered. Therefore, this review article summarizes and updates the research progress on the structural feature, virulence and pathotype correlation, and nucleocytoplasmic transport mechanism of NDV M protein, as well as the functions of M protein and cellular protein interactions in M's intracellular localization, viral RNA synthesis and transcription, viral protein synthesis, viral immune evasion, and viral budding and release, which will provide an in-depth understanding of the biological functions of M protein in the replication and pathogenesis of NDV, and also contribute to the development of effective antiviral strategies aiming at blocking the early or late steps of NDV lifecycles.

Cellular Lipids—Hijacked Victims of Viruses

Over the millions of years-long co-evolution with their hosts, viruses have evolved plenty of mechanisms through which they are able to escape cellular anti-viral defenses and utilize cellular pathways and organelles for replication and production of infectious virions. In recent years, it has become clear that lipids play an important role during viral replication. Viruses use cellular lipids in a variety of ways throughout their life cycle. They not only physically interact with cellular membranes but also alter cellular lipid metabolic pathways and lipid composition to create an optimal replication environment. This review focuses on examples of how different viruses exploit cellular lipids in different cellular compartments during their life cycles.

Intranasal vaccination with a Newcastle disease virus-vectored vaccine protects hamsters from SARS-CoV-2 infection and disease

The pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of coronavirus disease 2019 (COVID-19). Worldwide efforts are being made to develop vaccines to mitigate this pandemic. We engineered two recombinant Newcastle disease virus (NDV) vectors expressing either the full-length SARS-CoV-2 spike protein (NDV-FLS) or a version with a 19 amino acid deletion at the carboxy terminus (NDV-Δ19S). Hamsters receiving two doses (prime-boost) of NDV-FLS developed a robust SARS-CoV-2-neutralizing antibody response, with elimination of infectious virus in the lungs and minimal lung pathology at five days post-challenge. Single-dose vaccination with NDV-FLS significantly reduced SARS-CoV-2 replication in the lungs but only mildly decreased lung inflammation. NDV-Δ19S-treated hamsters had a moderate decrease in SARS-CoV-2 titers in lungs and presented with severe microscopic lesions, suggesting that truncation of the spike protein was a less effective strategy. In summary, NDV-vectored vaccines represent a viable option for protection against COVID-19.

Plasminogen-induced foam cell formation by macrophages occurs through a histone 2B (H2B)-PAR1 pathway and requires integrity of clathrin-coated pits

OBJECTIVE

Plasminogen/plasmin is a serine protease system primarily responsible for degrading fibrin within blood clots. Plasminogen mediates its functions by interacting with plasminogen receptors on the cell surface. H2B, one such plasminogen receptor, is found on the surface of several cell types including macrophages. Both basic and clinical studies support the role of plasminogen in the process of foam cell formation (FCF), a hallmark of atherosclerosis. Growing evidence also implicates serine protease-activated receptors (PARs) in atherosclerosis. These receptors are also found on macrophages, and plasmin is capable of activating PAR1 and PAR4. The goal of this study was to determine the extent of H2B's contribution to plasminogen-mediated FCF by macrophages and if PARs are involved in this process.

APPROACH AND RESULTS

Treating macrophages with plasminogen increases their oxidized low-density lipoprotein uptake and plasminogen-mediated foam cell formation (Plg-FCF) significantly. The magnitude of Plg-FCF correlates with cell-surface expression of the H2B level. H2B blockade or downregulation reduces Plg-FCF, whereas its overexpression or high endogenous levels increases Plg-FCF. Modulating PAR1 level in mouse macrophages affects Plg-FCF. Activation/overexpression of PAR1 increases and its blockade/knockdown reduces this response. Confocal imaging indicates that both H2B and PAR1 colocalize with clathrin coated pits on the surface of macrophages, and reducing expression of clathrin or interfering with the clathrin-coated pits integrity reduces Plg-FCF.

CONCLUSION

Our data indicate that the magnitude of Plg-FCF by macrophages is proportional to the H2B levels and demonstrate for the first time that PAR1 is involved in this process and that the integrity of clathrin-coated pits is required for the full effect of Plg-induced FCF.

Roles of Cholesterol in Early and Late Steps of the Nipah Virus Membrane Fusion Cascade

Cholesterol has been implicated in various viral life cycle steps for different enveloped viruses, including viral entry into host cells, cell-cell fusion, and viral budding from infected cells. Enveloped viruses acquire their membranes from their host cells. Although cholesterol has been associated with the binding and entry of various enveloped viruses into cells, cholesterol's exact function in the viral-cell membrane fusion process remains largely elusive, particularly for the paramyxoviruses. Furthermore, paramyxoviral fusion occurs at the host cell membrane and is essential for both virus entry (virus-cell fusion) and syncytium formation (cell-cell fusion), central to viral pathogenicity. Nipah virus (NiV) is a deadly member of the Paramyxoviridae family, which also includes Hendra, measles, mumps, human parainfluenza, and various veterinary viruses. The zoonotic NiV causes severe encephalitis, vasculopathy, and respiratory symptoms, leading to a high mortality rate in humans. We used NiV as a model to study the role of membrane cholesterol in paramyxoviral membrane fusion. We used a combination of methyl-beta cyclodextrin (MβCD), lovastatin, and cholesterol to deplete or enrich cell membrane cholesterol outside cytotoxic concentrations. We found that the levels of cellular membrane cholesterol directly correlated with the levels of cell-cell fusion induced. These phenotypes were paralleled using NiV/vesicular stomatitis virus (VSV)-pseudotyped viral infection assays. Remarkably, our mechanistic studies revealed that cholesterol reduces an early F-triggering step but enhances a late fusion pore formation step in the NiV membrane fusion cascade. Thus, our results expand our mechanistic understanding of the paramyxoviral/henipaviral entry and cell-cell fusion processes.IMPORTANCE Cholesterol has been implicated in various steps of the viral life cycle for different enveloped viruses. Nipah virus (NiV) is a highly pathogenic enveloped virus in the Henipavirus genus within the Paramyxoviridae family, capable of causing a high mortality rate in humans and high morbidity in domestic and agriculturally important animals. The role of cholesterol for NiV or the henipaviruses is unknown. Here, we show that the levels of cholesterol influence the levels of NiV-induced cell-cell membrane fusion during syncytium formation and virus-cell membrane fusion during viral entry. Furthermore, the specific role of cholesterol in membrane fusion is not well defined for the paramyxoviruses. We show that the levels of cholesterol affect an early F-triggering step and a late fusion pore formation step during the membrane fusion cascade. Thus, our results expand our mechanistic understanding of the viral entry and cell-cell fusion processes, which may aid the development of antivirals.

Cholesterol-Rich Lipid Rafts in the Cellular Membrane Play an Essential Role in Avian Reovirus Replication

Cholesterol is an essential component of lipid rafts in cellular plasma membranes. Although lipid rafts have been reported to have several functions in multiple stages of the life cycles of many different enveloped viruses, the mechanisms by which non-enveloped viruses, which lack outer lipid membranes, infect host cells remain unclear. In this study, to investigate the dependence of non-enveloped avian reovirus (ARV) infection on the integrity of cholesterol-rich membrane rafts, methyl-β-cyclodextrin (MβCD) was used to deplete cellular membrane cholesterol at the ARV attachment, entry, and post-entry stages. Treatment with MβCD significantly inhibited ARV replication at both the entry and post-entry stages in a dose-dependent manner, but MβCD had a statistically insignificant effect when it was added at the attachment stage. Moreover, MβCD treatment markedly reduced syncytium formation, which occurs at a relatively late stage of the ARV life cycle and is involved in cell-cell transmission and release. Furthermore, the addition of exogenous cholesterol reversed the effects mentioned above. Colocalization data also showed that the ARV proteins σC, μNS, and p10 prefer to localize to cholesterol-rich lipid raft regions during ARV infection. Altogether, these results suggest that cellular cholesterol in lipid rafts plays a critical role in ARV replication.

Caveolae as Potential Hijackable Gates in Cell Communication

Caveolae are membrane microdomains described in many cell types involved in endocytocis, transcytosis, cell signaling, mechanotransduction, and aging. They are found at the interface with the extracellular environment and are structured by caveolin and cavin proteins. Caveolae and caveolins mediate transduction of chemical messages via signaling pathways, as well as non-chemical messages, such as stretching or shear stress. Various pathogens or signals can hijack these gates, leading to infectious, oncogenic and even caveolin-related diseases named caveolinopathies. By contrast, preclinical and clinical research have fallen behind in their attempts to hijack caveolae and caveolins for therapeutic purposes. Caveolae involvement in human disease is not yet fully explored or understood and, of all their scaffold proteins, only caveolin-1 is being considered in clinical trials as a possible biomarker of disease. This review briefly summarizes current knowledge about caveolae cell signaling and raises the hypothesis whether these microdomains could serve as hijackable “gatekeepers” or “gateways” in cell communication. Furthermore, because cell signaling is one of the most dynamic domains in translating data from basic to clinical research, we pay special attention to translation of caveolae, caveolin, and cavin research into clinical practice.

Cholesterol-rich lipid rafts both in cellular and viral membrane are critical for caprine parainfluenza virus type3 entry and infection in host cells

Cholesterol-rich lipid rafts have been shown to play important roles in the life cycle of various non-enveloped and enveloped viruses. Deletion of cholesterol from lipid rafts could influence different steps of viral replication cycle including entry, infection, assembly and release. Caprine parainfluenza virus type3 (CPIV3) is a newly identified member of Paramyxoviridae family. CPIV3 is highly prevalence and threatened the goat industry in China. The infection mechanism of CPIV3 is under exploring and still not fully understood, the roles of cholesterol and lipid rafts for CPIV3 infection remains unclear. In this study, we investigated the association of cholesterol and lipid rafts with CPIV3 during the different viral replication stages (binding, entry and infection) in two cells [MDBK and goat bronchial epithelial (GBE) cells]. Methyl-β- cyclodextrin (MβCD) was used to deplete cholesterol from cell and viral membranes. The results showed that MβCD treatment significantly inhibited CPIV3 entry and infection in these two cells with a dose-dependent manner, but didn't impair the binding of CPIV3. Addition of exogenous cholesterol to the cells after MβCD treatment restored the viral infection. In addition, treatment of MβCD only before virus-entry showed inhibitory effect in MDBK cells. Depletion of cholesterol from virion envelop also decreased the entry and infection of CPIV3 in the two cells. Furthermore, lipid rafts isolation test indicated that viral proteins (HN and N) co-localized with lipid rafts during infection in MDBK and GBE cells. Viral N protein co-localized with caveolin-1 (the marker of lipid rafts) in these two cells both at the entry and infection steps, as detected by con-focal laser scanning microscopy test. In conclusion, the results presented here demonstrated that cholesterol rich lipid rafts play an important role in CPIV3 life cycle. The findings give new insights on understanding of the mechanism of CPIV3 infection and provide a new anti-CPIV3 strategy.

Inhibition of Cavin3 Degradation by the Human Parainfluenza Virus Type 2 V Protein Is Important for Efficient Viral Growth

Cavin proteins have important roles in the formation of caveolae in lipid raft microdomains. Pulse-chase experiments of cells infected with human parainfluenza virus type 2 (hPIV-2) showed decreased proteasomal degradation of Cavin3. Overexpression of hPIV-2 V protein alone was sufficient to inhibit Cavin3 degradation. Immunoprecipitation analysis revealed that V protein bound to Cavin3. Trp residues within C-terminal region of V protein, as well as the N-terminal region of Cavin3, are important for V–Cavin3 interaction. Cavin3 knockdown suppressed hPIV-2 growth without affecting its entry, replication, transcription, or translation. Higher amounts of Cavin3 were observed in V protein-overexpressing cells than in control cells in lipid raft microdomains. Our data collectively suggest that hPIV-2 V protein binds to and stabilizes Cavin3, which in turn facilitates assembly and budding of hPIV-2 in lipid raft microdomains.

Multifaceted Functions of Host Cell Caveolae/Caveolin-1 in Virus Infections

Virus infection has drawn extensive attention since it causes serious or even deadly diseases, consequently inducing a series of social and public health problems. Caveolin-1 is the most important structural protein of caveolae, a membrane invagination widely known for its role in endocytosis and subsequent cytoplasmic transportation. Caveolae/caveolin-1 is tightly associated with a wide range of biological processes, including cholesterol homeostasis, cell mechano-sensing, tumorigenesis, and signal transduction. Intriguingly, the versatile roles of caveolae/caveolin-1 in virus infections have increasingly been appreciated. Over the past few decades, more and more viruses have been identified to invade host cells via caveolae-mediated endocytosis, although other known pathways have been explored. The subsequent post-entry events, including trafficking, replication, assembly, and egress of a large number of viruses, are caveolae/caveolin-1-dependent. Deprivation of caveolae/caveolin-1 by drug application or gene editing leads to abnormalities in viral uptake, viral protein expression, or virion release, whereas the underlying mechanisms remain elusive and must be explored holistically to provide potential novel antiviral targets and strategies. This review recapitulates our current knowledge on how caveolae/caveolin-1 functions in every step of the viral infection cycle and various relevant signaling pathways, hoping to provide a new perspective for future viral cell biology research.

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

Virion-Associated Cholesterol Regulates the Infection of Human Parainfluenza Virus Type 3

The matrix (M) proteins of paramyxoviruses bind to the nucleocapsids and cytoplasmic tails of glycoproteins, thus mediating the assembly and budding of virions. We first determined the budding characterization of the HPIV3 Fusion (F) protein to investigate the assembly mechanism of human parainfluenza virus type 3 (HPIV3). Our results show that expression of the HPIV3 F protein alone is sufficient to initiate the release of virus-like particles (VLPs), and the F protein can regulate the VLP-forming ability of the M protein. Furthermore, HPIV3_F-Flag, which is a recombinant HPIV3 with a Flag tag at the C-terminus of the F protein, was constructed and recovered. We found that the M, F, and hemagglutinin-neuraminidase (HN) proteins and the viral genome can accumulate in lipid rafts in HPIV3_F-Flag-infected cells, and the F protein mainly exists in the form of F₁ in VLPs, lipid rafts, and purified virions. Furthermore, the function of cholesterol in the viral envelope and cell membrane was assessed via the elimination of cholesterol by methyl-β-cyclodextrin (MβCD). Our results suggest that the infectivity of HPIV3 was markedly reduced, due to defective internalization ability in the absence of cholesterol. These results reveal that HPIV3 might assemble in the lipid rafts to acquire cholesterol for the envelope of HPIV3, which suggests the that disruption of the cholesterol composition of HPIV3 virions might be a useful method for the design of anti-HPIV3 therapy.

BALB/c mice immunized with a combination of virus-like particles incorporating Kaposi sarcoma-associated herpesvirus (KSHV) envelope glycoproteins gpK8.1, gB, and gH/gL induced comparable serum neutralizing antibody activity to UV-inactivated KSHV

Infection with Kaposi sarcoma-associated herpesvirus (KSHV) is estimated to account for over 44,000 new cases of Kaposi sarcoma annually, with 84% occurring in Africa, where the virus is endemic. To date, there is no prophylactic vaccine against KSHV. KSHV gpK8.1, gB, and gH/gL glycoproteins, implicated in the virus entry into host cells, are attractive vaccine targets for eliciting potent neutralizing antibodies (nAbs) against virus infection. We incorporated gpK8.1, gB, or gH/gL on the surface of virus-like particles (VLPs) and characterized these VLPs for their composition, size, and functionality. To determine which viral glycoprotein(s) elicit the most effective serum-nAbs, we immunized BALB/c mice with gpK8.1, gB, or gH/gL VLPs individually or in combination. Neutralizing antibody assay revealed that sera from mice immunized with the VLPs inhibited KSHV infection of HEK-293 cells in a dose-dependent manner. As a single immunogen, gpK8.1 VLPs stimulated comparable nAb activity to that of UV-inactivated KSHV (UV-KSHV). In contrast, UV-KSHV stimulated higher titers of nAb compared to gB (p = 0.0316) or gH/gL (p = 0.0486). Mice immunized with the combination of gB and gH/gL VLPs had a better nAb response than those immunized with either gB (p = 0.0268), or gH/gL (p = 0.0397) as single VLP immunogens. Immunization with any VLP combination stimulated comparable nAb activity to UV-KSHV serum. Our data provide the first evidence that KSHV gpK8.1, gB, and gH/gL glycoproteins can be incorporated onto the surface of VLPs and used as prophylactic vaccine candidates, with potential to prevent KSHV infection.

Novel Epstein-Barr virus-like particles incorporating gH/gL-EBNA1 or gB-LMP2 induce high neutralizing antibody titers and EBV-specific T-cell responses in immunized mice

Previous Epstein-Barr virus (EBV) prophylactic vaccines based on the major surface glycoprotein gp350/220 as an immunogen have failed to block viral infection in humans, suggesting a need to target other viral envelope glycoproteins. In this study, we reasoned that incorporating gH/gL or gB, critical glycoproteins for viral fusion and entry, on the surface of a virus-like particle (VLP) would be more immunogenic than gp350/220 for generating effective neutralizing antibodies to prevent viral infection of both epithelial and B cell lines. To boost the humoral response and trigger cell-mediated immunity, EBV nuclear antigen 1 (EBNA1) and latent membrane protein 2 (LMP2), intracellular latency proteins expressed in all EBV-infected cells, were also included as critical components of the polyvalent EBV VLP. gH/gL-EBNA1 and gB-LMP2 VLPs were efficiently produced in Chinese hamster ovary cells, an FDA-approved vehicle for mass-production of biologics. Immunization with gH/gL-EBNA1 and gB-LMP2 VLPs without adjuvant generated both high neutralizing antibody titers in vitro and EBV-specific T-cell responses in BALB/c mice. These data demonstrate that EBV glycoprotein(s)-based VLPs have excellent immunogenicity, and represent a potentially safe vaccine that will be invaluable not only in preventing EBV infection, but importantly, in preventing and treating the 200,000 cases of EBV-associated cancers that occur globally every year.

Cholesterol-rich lipid rafts play a critical role in bovine parainfluenza virus type 3 (BPIV3) infection

Lipid rafts are specialized lipid domains enriched in cholesterol and sphingolipid, which can be utilized in the lifecycle of numerous enveloped viruses. Bovine parainfluenza virustype3 (BPIV3) entry to cell is mediated by receptor binding and membrane fusion, but how lipid rafts in host cell membrane and BPIV3 envelope affect virus infection remains unclear. In this study, we investigated the role of lipid rafts in the different stages of BPIV3 infection. The MDBK cells were treated by methyl-β-cyclodextrin (MβCD) to disrupt cellular lipid raft, and the virus infection was determined. The results showed that MβCD significantly inhibited BPIV3 infection in a dose-dependent manner, but didn't block the binding of virus to the cell membrane. Whereas, the MDBK cells treated by MβCD after virus-entry had no effects on the virus infection, to suggest that BPIV3 infection was associated with lipid rafts in cell membrane during viral entry stage. To further confirm lipid rafts in viral envelope also affected BPIV3 infection, we treated BPIV3 with MβCD to determine the virus titer. We found that disruption of the viral lipid raft caused a significant reduction of viral yield. Cholesterol reconstitution experiment showed that BPIV3 infection was successfully restored by cholesterol supplementation both in cellular membrane and viral envelope, which demonstrated that cholesterol-rich lipid rafts played a critical role in BPIV3 infection. These findings provide insights on our understanding of the mechanism of BPIV3 infection and imply that lipid raft might be a good potential therapeutic target to prevent virus infection.

Interactions between cyclodextrins and cellular components: Towards greener medical applications?

In the field of host-guest chemistry, some of the most widely used hosts are probably cyclodextrins (CDs). As CDs are able to increase the water solubility of numerous drugs by inclusion into their hydrophobic cavity, they have been widespread used to develop numerous pharmaceutical formulations. Nevertheless, CDs are also able to interact with endogenous substances that originate from an organism, tissue or cell. These interactions can be useful for a vast array of topics including cholesterol manipulation, treatment of Alzheimer's disease, control of pathogens, etc. In addition, the use of natural CDs offers the great advantage of avoiding or reducing the use of common petroleum-sourced drugs. In this paper, the general features and applications of CDs have been reviewed as well as their interactions with isolated biomolecules leading to the formation of inclusion or exclusion complexes. Finally, some potential medical applications are highlighted throughout several examples.

Cholesterol reducing agents inhibit assembly of type I parainfluenza viruses

Many enveloped RNA viruses utilize lipid rafts for the assembly of progeny virions, but the role of cholesterol, a major component of rafts, on paramyxovirus budding and virion formation is controversial. In this study, we analyzed the effects of FDA-approved cholesterol-reducing agents, gemfibrozil and lovastatin, on raft formation and assembly of human parainfluenza virus type 1 (hPIV1) and Sendai virus (SeV). Treatment of the human airway epithelial A549 cells with the agents, especially when combined, significantly decreased production of infectious hPIV1 and SeV. Mechanistic analysis indicated that depletion of cellular cholesterol reduced cell surface accumulation of envelope glycoproteins and association of viral matrix and nucleocapsids with raft membrane, which resulted in impaired virus budding and release from the cells. These results indicate that cellular cholesterol is required for assembly and formation of type 1 parainfluenza viruses and suggest that cholesterol could be an attractive target for antiviral agents against hPIV1.

Membrane associated protein flotillin-2 in Litopenaeus vannamei plays a role in WSSV infection

Flotillin-2, an important protein of vesicular endocytosis, plays an essential role in a large number of cellular processes, including viruses and pathogen infection. In the present study, a flotillin-2 homolog in Litopenaeus vannamei, designed as Lvflotillin-2, was cloned and characterized. To analyze the putative role of Lvflotillin-2 during white spot syndrome virus (WSSV) infection, real-time quantitative PCR was performed. The result showed that the transcriptional level of Lvflotillin-2 was up-regulated significantly after virus challenge. Furthermore, upon WSSV stimulation, Lvflotillin-2 in shrimp cells could translocate from the plasma membrane to intracellular compartments, and unexpectedly, also into nucleus. Additionally, depletion of Lvflotillin-2 inhibited WSSV gene ie1 transcription. It suggested that Lvflotillin-2 could be hijacked by WSSV. These observations indicated that Lvflotillin-2 was involved in WSSV infection, and presented here should be useful for gaining insight into shrimp immunity and WSSV pathogenesis.

The LXR ligand GW3965 inhibits Newcastle disease virus infection by affecting cholesterol homeostasis

Newcastle disease (ND) is a contagious disease that affects most species of birds. Its causative pathogen, Newcastle disease virus (NDV), also exhibits considerable oncolytic activity against mammalian cancers. A better understanding of the pathogenesis of NDV will help us design efficient vaccines and novel anticancer strategies. GW3965, a widely used synthetic ligand of liver X receptor (LXR), induces the expression of LXRs and its downstream genes, including ATP-binding cassette transporter A1 (ABCA1). ABCA1 regulates cellular cholesterol homeostasis. Here, we found that GW3965 inhibited NDV infection in DF-1 cells. It also inhibited NF-κB activation and reduced the upregulation of proinflammatory cytokines induced by the infection. Further studies showed that GW3965 exerted its inhibitory effects on virus entry and replication. NDV infection increased the mRNA levels of several lipogenic genes but decreased the ABCA1 mRNA level. Overexpression of ABCA1 inhibited NDV infection and reduced the cholesterol content in DF-1 cells, but when the cholesterol was replenished, NDV infection was restored. GW3965 treatment prevented cholesterol accumulation in the perinuclear area of the infected cells. In summary, our studies suggest that GW3965 inhibits NDV infection, probably by affecting cholesterol homeostasis.

CD55 is a key complement regulatory protein that counteracts complement-mediated inactivation of Newcastle Disease Virus

Newcastle disease virus (NDV) is being developed as an oncolytic virus for virotherapy. In this study we analysed the regulation of complement-mediated inactivation of a recombinant NDV in different host cells. NDV grown in human cells was less sensitive to complement-mediated virus inactivation than NDV grown in embryonated chicken eggs. Additionally, NDV produced from HeLa-S3 cells is more resistant to complement than NDV from 293F cells, which correlated with higher expression and incorporation of complement regulatory proteins (CD46, CD55 and CD59) into virions from HeLa-S3 cells. Further analysis of the recombinant NDVs individually expressing the three CD molecules showed that CD55 is the most potent in counteracting complement-mediated virus inactivation. The results provide important information on selecting NDV manufacture substrate to mitigate complement-mediated virus inactivation.

Lipid rafts both in cellular membrane and viral envelope are critical for PRRSV efficient infection

Porcine reproductive and respiratory syndrome virus (PRRSV) represents a significantly economical challenge to the swine industry worldwide. In this study, we investigated the importance of cellular and viral lipid rafts in PRRSV infection. First, we demonstrated that PRRSV glycoproteins, Gp3 and Gp4, were associated with lipid rafts during viral entry, and disruption of cellular lipid rafts inhibited PRRSV entry. We also showed the raft-location of CD163, which might contribute to the glycoproteins–raft association. Subsequently, raft disruption caused a significant reduction of viral RNA production. Moreover, Nsp9 was shown to be distributed in rafts, suggesting that rafts probably serve as a platform for PRRSV replication. Finally, we confirmed that disassembly of rafts on the virus envelope may affect the integrity of PRRSV particles and cause the leakage of viral proteins, which impaired PRRSV infectivity. These findings might provide insights on our understanding of the mechanism of PRRSV infection.

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PRRSV needs lipid rafts to establish successful infection.

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Cellular lipid rafts function in PRRSV entry, replication, and release.

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Disassembly of viral lipid rafts adversely affects PRRSV infectivity.

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Lipid rafts in both cellular and viral membrane are critical to PRRSV infection.

New host factors important for respiratory syncytial virus (RSV) replication revealed by a novel microfluidics screen for interactors of matrix (M) protein

Although human respiratory syncytial virus (RSV) is the most common cause of bronchiolitis and pneumonia in infants and elderly worldwide, there is no licensed RSV vaccine or effective drug treatment available. The RSV Matrix protein plays key roles in virus life cycle, being found in the nucleus early in infection in a transcriptional inhibitory role, and later localizing in viral inclusion bodies before coordinating viral assembly and budding at the plasma membrane. In this study, we used a novel, high throughput microfluidics platform and custom human open reading frame library to identify novel host cell binding partners of RSV matrix. Novel interactors identified included proteins involved in host transcription regulation, the innate immunity response, cytoskeletal regulation, membrane remodeling, and cellular trafficking. A number of these interactions were confirmed by immunoprecipitation and cellular colocalization approaches. Importantly, the physiological significance of matrix interaction with the actin-binding protein cofilin 1, caveolae protein Caveolin 2, and the zinc finger protein ZNF502 was confirmed. siRNA knockdown of the host protein levels resulted in reduced RSV virus production in infected cells. These results have important implications for future antiviral strategies aimed at targets of RSV matrix in the host cell.

Newcastle disease virus interaction in targeted therapy against proliferation and invasion pathways of glioblastoma multiforme

Glioblastoma multiforme (GBM), or grade IV glioma, is one of the most lethal forms of human brain cancer. Current bioscience has begun to depict more clearly the signalling pathways that are responsible for high-grade glioma initiation, migration, and invasion, opening the door for molecular-based targeted therapy. As such, the application of viruses such as Newcastle disease virus (NDV) as a novel biological bullet to specifically target aberrant signalling in GBM has brought new hope. The abnormal proliferation and aggressive invasion behaviour of GBM is reported to be associated with aberrant Rac1 protein signalling. NDV interacts with Rac1 upon viral entry, syncytium induction, and actin reorganization of the infected cell as part of the replication process. Ultimately, intracellular stress leads the infected glioma cell to undergo cell death. In this review, we describe the characteristics of malignant glioma and the aberrant genetics that drive its aggressive phenotype, and we focus on the use of oncolytic NDV in GBM-targeted therapy and the interaction of NDV in GBM signalling that leads to inhibition of GBM proliferation and invasion, and subsequently, cell death.

Modification of the respiratory syncytial virus f protein in virus-like particles impacts generation of B cell memory

Immunization with virus-like particles (VLPs) containing the Newcastle disease virus (NDV) core proteins, NP and M, and two chimera proteins (F/F and H/G) containing the respiratory syncytial virus (RSV) F- and G-protein ectodomains fused to the transmembrane and cytoplasmic domains of NDV F and HN proteins, respectively, stimulated durable RSV-neutralizing antibodies, F-protein-specific long-lived, bone marrow-associated plasma cells (LLPCs), and B cell memory, in striking contrast to RSV infection, which did not (M. R. Schmidt, L. W. McGinnes, S. A. Kenward, K. N. Willems, R. T. Woodland, and T. G. Morrison, J. Virol. 86:11654-11662, 2012). Here we report the characterization of a VLP with an RSV F-protein ectodomain fused to the NDV F-protein heptad repeat 2 (HR2), transmembrane, and cytoplasmic domain sequences, creating a chimera with two tandem HR2 domains, one from the RSV F protein and the other from the NDV F-protein ectodomain (F/HR2F). The F/HR2F chimera protein was efficiently assembled into VLPs along with the H/G chimera protein. This VLP (VLP-H/G+F/HR2F) stimulated anti-F-protein and anti-G-protein IgG, durable RSV-neutralizing antibodies, and anti-RSV F-protein-secreting LLPCs. However, the subtypes of anti-F-protein IgG induced were different from those elicited by VLPs containing the F/F chimera (VLP-H/G+F/F). Most importantly, VLP-H/G+F/HR2F did not induce RSV F-protein-specific B cell memory, as shown by the adoptive transfer of B cells from immunized animals to immunodeficient animals. The VLP did, however, induce B cell memory specific to the RSV G protein. Thus, the form of the F protein has a direct role in inducing anti-F-protein B cell memory.

IMPORTANCE

The development of vaccines for respiratory syncytial virus (RSV) is hampered by a lack of a clear understanding of the requirements for eliciting protective as well as durable human immune responses to virus antigens. The results of this study indicate that the form of the RSV F protein has a direct and significant impact on the type of anti-F-protein IgG antibodies induced and the generation of F-protein-specific memory. Identification of the conformation of the RSV F protein that most effectively stimulates not only LLPCs and but also memory B cells will be important in the future development of RSV vaccines.

Analytical use of multi-protein Fluorescence Resonance Energy Transfer to demonstrate membrane-facilitated interactions within cytokine receptor complexes

Experiments measuring Fluorescence Resonance Energy Transfer (FRET) between cytokine receptor chains and their associated proteins led to hypotheses describing their organization in intact cells. These interactions occur within a larger protein complex or within a given nano-environment. To illustrate this complexity empirically, we developed a protocol to analyze FRET among more than two fluorescent proteins (multi-FRET). In multi-FRET, we model FRET among more than two fluorophores as the sum of all possible pairwise interactions within the complex. We validated our assumption by demonstrating that FRET among pairs within a fluorescent triplet resembled FRET between each pair measured in the absence of the third fluorophore. FRET between two receptor chains increases with increasing FRET between the ligand-binding chain (e.g., IFN-γR1, IL-10R1 and IFN-λR1) and an acylated fluorescent protein that preferentially resides within subsections of the plasma membrane. The interaction of IL-10R2 with IFN-λR1 or IL-10R1 results in decreased FRET between IL-10R2 and the acylated fluorescent protein. Finally, we analyzed FRET among four fluorescent proteins to demonstrate that as FRET between IFN-γR1 and IFN-γR2 or between IFN-αR1 and IFN-αR2c increases, FRET among other pairs of proteins changes within each complex.

Assembly and budding of negative-strand RNA viruses

Assembly of negative-strand RNA viruses occurs by budding from host plasma membranes. The budding process involves association of the viral core or nucleocapsid with a region of cellular membrane that will become the virus budding site, which contains the envelope glycoproteins and matrix protein. This region of membrane then buds out and pinches off to become the virus envelope. This review will address the questions of what are the mechanisms that bring the nucleocapsid and envelope glycoproteins together to form the virus budding site, and how does this lead to release of progeny virions? Recent evidence supports the idea that viral envelope glycoproteins and matrix proteins are organized into membrane microdomains that coalesce to form virus budding sites. There has also been substantial progress in understanding the last step in virus release, referred to as the "late budding function," which often involves host proteins of the vacuolar protein sorting apparatus. Key questions are raised as to the mechanism of the initial steps in formation of virus budding sites: How are membrane microdomains brought together and how are nucleocapsids selected for incorporation into these budding sites, particularly in the case of viruses for which genome RNA sequences are important for envelopment of nucleocapsids?

Mandarin fish caveolin 1 interaction with major capsid protein of infectious spleen and kidney necrosis virus and its role in early stages of infection

Infectious spleen and kidney necrosis virus (ISKNV) is the type species of the genus Megalocytivirus from the family Iridoviridae. ISKNV is one of the major agents that cause mortality and economic losses to the freshwater fish culture industry in Asian countries, particularly for mandarin fish (Siniperca chuatsi). In the present study, we report that the interaction of mandarin fish caveolin 1 (mCav-1) with the ISKNV major capsid protein (MCP) was detected by using a virus overlay assay and confirmed by pulldown assay and coimmunoprecipitation. This interaction was independent of the classic caveolin 1 scaffolding domain (CSD), which is responsible for interacting with several signaling proteins and receptors. Confocal immunofluorescence microscopy showed that ISKNV MCP colocalized with mCav-1 in the perinuclear region of virus-infected mandarin fish fry (MFF-1) cells, which appeared as soon as 4 h postinfection. Subcellular fractionation analysis showed that ISKNV MCP was associated with caveolae in the early stages of viral infection. RNA interference silencing of mCav-1 did not change virus-cell binding but efficiently inhibited the entry of virions into the cell. Taken together, these results suggested that mCav-1 plays an important role in the early stages of ISKNV infection.

Cellular membrane cholesterol is required for porcine reproductive and respiratory syndrome virus entry and release in MARC-145 cells

Cholesterol represents one of the key constituents of small, dynamic, sterol- and sphingolipid-enriched domains on the plasma membrane. It has been reported that many viruses depend on plasma membrane cholesterol for efficient infection. In this study, the role of the plasma membrane cholesterol in porcine reproductive and respiratory syndrome virus (PRRSV) infection of MARC-145 cells was investigated. Pretreatment of MARC-145 cells with methyl-β-cyclodextrin (MβCD), a drug used to deplete cholesterol from cellular membrane, significantly reduced PRRSV infection in a dose-dependent manner. This inhibition was partially reversed by supplementing exogenous cholesterol following MβCD treatment, suggesting that the inhibition of PRRSV infection was specifically mediated by removal of cellular cholesterol. Further detailed studies showed that depletion of cellular membrane cholesterol significantly inhibited virus entry, especially virus attachment and release. These results indicate that the presence of cholesterol in the cellular membrane is a key component of PRRSV infection.

Cholesterol dependence of Newcastle Disease Virus entry

Lipid rafts are membrane microdomains enriched in cholesterol, sphingolipids, and glycolipids that have been implicated in many biological processes. Since cholesterol is known to play a key role in the entry of some other viruses, we investigated the role of cholesterol and lipid rafts in the host cell plasma membrane in Newcastle Disease Virus (NDV) entry. We used methyl-β-cyclodextrin (MβCD) to deplete cellular cholesterol and disrupt lipid rafts. Our results show that the removal of cellular cholesterol partially reduces viral binding, fusion and infectivity. MβCD had no effect on the expression of sialic acid containing molecule expression, the NDV receptors in the target cell. All the above-described effects were reversed by restoring cholesterol levels in the target cell membrane. The HN viral attachment protein partially localized to detergent-resistant membrane microdomains (DRMs) at 4°C and then shifted to detergent-soluble fractions at 37°C. These results indicate that cellular cholesterol may be required for optimal cell entry in NDV infection cycle.

Function of membrane rafts in viral lifecycles and host cellular response

Membrane rafts are small (10–200 nm) sterol- and sphingolipid-enriched domains that compartmentalize cellular processes. Membrane rafts play an important role in viral infection cycles and viral virulence. Viruses are divided into four main classes, enveloped DNA virus, enveloped RNA virus, nonenveloped DNA virus, and nonenveloped RNA virus. General virus infection cycle is also classified into two sections, the early stage (entry process) and the late stage (assembly, budding, and release processes of virus particles). In the viral cycle, membrane rafts act as a scaffold of many cellular signal transductions, which are associated with symptoms caused by viral infections. In this paper, we describe the functions of membrane rafts in viral lifecycles and host cellular response according to each virus classification, each stage of the virus lifecycle, and each virus-induced signal transduction.

Cholesterol-rich lipid rafts are required for release of infectious human respiratory syncytial virus particles

Cholesterol and sphingolipid enriched lipid raft micro-domains in the plasma membrane play an important role in the life-cycle of numerous enveloped viruses. Although human respiratory syncytial virus (RSV) proteins associate with the raft domains of infected cells and rafts are incorporated in RSV virion particles, the functional role of raft during RSV infection was unknown. In the current study we have identified rafts as an essential component of host cell that is required for RSV infection. Treatment of human lung epithelial cells with raft disrupting agent methyl-beta-cyclodextrin (MBCD) led to drastic loss of RSV infectivity due to diminished release of infectious progeny RSV virion particles from raft disrupted cells. RSV infection of raft deficient Niemann-Pick syndrome type C human fibroblasts and normal human embryonic lung fibroblasts revealed that during productive RSV infection, raft is required for release of infectious RSV particles.

The transmembrane domain sequence affects the structure and function of the Newcastle disease virus fusion protein

The role of specific sequences in the transmembrane (TM) domain of Newcastle disease virus (NDV) fusion (F) protein in the structure and function of this protein was assessed by replacing this domain with the F protein TM domains from two other paramyxoviruses, Sendai virus (SV) and measles virus (MV), or the TM domain of the unrelated glycoprotein (G) of vesicular stomatitis virus (VSV). Mutant proteins with the SV or MV F protein TM domains were expressed, transported to cell surfaces, and proteolytically cleaved at levels comparable to that of the wild-type protein, while mutant proteins with the VSV G protein TM domain were less efficiently expressed on cell surfaces and proteolytically cleaved. All mutant proteins were defective in all steps of membrane fusion, including hemifusion. In contrast to the wild-type protein, the mutant proteins did not form detectable complexes with the NDV hemagglutinin-neuraminidase (HN) protein. As determined by binding of conformation-sensitive antibodies, the conformations of the ectodomains of the mutant proteins were altered. These results show that the specific sequence of the TM domain of the NDV F protein is important for the conformation of the preactivation form of the ectodomain, the interactions of the protein with HN protein, and fusion activity.

Influence of lipids on the interfacial disposition of respiratory syncytical virus matrix protein

The propensity of a matrix protein from an enveloped virus of the Mononegavirales family to associate with lipids representative of the viral envelope has been determined using label-free methods, including tensiometry and Brewster angle microscopy on lipid films at the air-water interface and atomic force microscopy on monolayers transferred to OTS-treated silicon wafers. This has enabled factors that influence the disposition of the protein with respect to the lipid interface to be characterized. In the absence of sphingomyelin, respiratory syncytial virus matrix protein penetrates monolayers composed of mixtures of phosphocholines with phosphoethanolamines or cholesterol at the air-water interface. In ternary mixtures composed of sphingomyelin, 1,2-dioleoyl-sn-glycero-3-phosphocholine, and cholesterol, the protein exhibits two separate behaviors: (1) peripheral association with the surface of sphingomyelin-rich domains and (2) penetration of sphingomyelin-poor domains. Prolonged incubation of the protein with mixtures of phosphocholines and phosphoethanolamines leads to the formation of helical protein assemblies of uniform diameter that demonstrate an inherent propensity of the protein to assemble into a filamentous form.

Assembly and immunological properties of Newcastle disease virus-like particles containing the respiratory syncytial virus F and G proteins

Human respiratory syncytial virus (RSV) is a serious respiratory pathogen in infants and young children as well as elderly and immunocompromised populations. However, no RSV vaccines are available. We have explored the potential of virus-like particles (VLPs) as an RSV vaccine candidate. VLPs composed entirely of RSV proteins were produced at levels inadequate for their preparation as immunogens. However, VLPs composed of the Newcastle disease virus (NDV) nucleocapsid and membrane proteins and chimera proteins containing the ectodomains of RSV F and G proteins fused to the transmembrane and cytoplasmic domains of NDV F and HN proteins, respectively, were quantitatively prepared from avian cells. Immunization of mice with these VLPs, without adjuvant, stimulated robust, anti-RSV F and G protein antibody responses. IgG2a/IgG1 ratios were very high, suggesting predominantly T(H)1 responses. In contrast to infectious RSV immunization, neutralization antibody titers were robust and stable for 4 months. Immunization with a single dose of VLPs resulted in the complete protection of mice from RSV replication in lungs. Upon RSV intranasal challenge of VLP-immunized mice, no enhanced lung pathology was observed, in contrast to the pathology observed in mice immunized with formalin-inactivated RSV. These results suggest that these VLPs are effective RSV vaccines in mice, in contrast to other nonreplicating RSV vaccine candidates.

Lipid rafts are essential for peroxisome biogenesis in HepG2 cells

Peroxisomes are particularly abundant in the liver and are involved in bile salt synthesis and fatty acid metabolism. Peroxisomal membrane proteins (PMPs) are required for peroxisome biogenesis [e.g., the interacting peroxisomal biogenesis factors Pex13p and Pex14p] and its metabolic function [e.g., the adenosine triphosphate-binding cassette transporters adrenoleukodystrophy protein (ALDP) and PMP70]. Impaired function of PMPs is the underlying cause of Zellweger syndrome and X-linked adrenoleukodystrophy. Here we studied for the first time the putative association of PMPs with cholesterol-enriched lipid rafts and their function in peroxisome biogenesis. Lipid rafts were isolated from Triton X-100-lysed or Lubrol WX-lysed HepG2 cells and analyzed for the presence of various PMPs by western blotting. Lovastatin and methyl-beta-cyclodextrin were used to deplete cholesterol and disrupt lipid rafts in HepG2 cells, and this was followed by immunofluorescence microscopy to determine the subcellular location of catalase and PMPs. Cycloheximide was used to inhibit protein synthesis. Green fluorescent protein-tagged fragments of PMP70 and ALDP were analyzed for their lipid raft association. PMP70 and Pex14p were associated with Triton X-100-resistant rafts, ALDP was associated with Lubrol WX-resistant rafts, and Pex13p was not lipid raft-associated in HepG2 cells. The minimal peroxisomal targeting signals in ALDP and PMP70 were not sufficient for lipid raft association. Cholesterol depletion led to dissociation of PMPs from lipid rafts and impaired sorting of newly synthesized catalase and ALDP but not Pex14p and PMP70. Repletion of cholesterol to these cells efficiently reestablished the peroxisomal sorting of catalase but not ALDP.

CONCLUSION

Human PMPs are differentially associated with lipid rafts independently of the protein homology and/or their functional interaction. Cholesterol is required for peroxisomal lipid raft assembly and peroxisome biogenesis.

A role for caveolin 1 in assembly and budding of the paramyxovirus parainfluenza virus 5

Caveolin 1 (Cav-1) is an integral membrane protein that forms the coat structure of plasma membrane caveolae and regulates caveola-dependent functions. Caveolae are enriched in cholesterol and sphingolipids and are related to lipid rafts. Many studies implicate rafts as sites of assembly and budding of enveloped virus. We show that Cav-1 colocalizes with the paramyxovirus parainfluenza virus 5 (PIV-5) nucleocapsid (NP), matrix (M), and hemagglutinin-neuraminidase (HN) proteins. Moreover, electron microscopy shows that Cav-1 is clustered at sites of viral budding. HN, M, and F(1)/F(2) are associated with detergent-resistant membranes, and these proteins float on sucrose gradients with Cav-1-rich fractions. A complex containing Cav-1 with M, NP, and HN from virus-infected cells and a complex containing Cav-1 and M from M-transfected cells were found on coimmunoprecipitation. A role of Cav-1 in the PIV-5 life cycle was investigated by utilizing MCF-7 human breast cancer cells that stably express Cav-1 (MCF-7/Cav-1). PIV-5 entry into MCF-7 and MCF-7/Cav-1 was found to be Cav-1 independent. However, the interaction between HN and M proteins was dramatically reduced in the Cav-1 null MCF-7 cells, and PIV-5 grown in MCF-7 cells had a reduced infectivity. Similarly, when PIV-5 was grown in MDCK cells that stably expressed dominant negative Cav-1 (MDCK/P132LCav-1), the virus showed a reduced infectivity. Virions lacking Cav-1 were defective and contained high levels of host cellular proteins and reduced levels of HN and M. These data suggest that Cav-1 affects assembly and/or budding, and this is supported by the finding that Cav-1 is incorporated into mature viral particles.

Paramyxovirus assembly and budding: building particles that transmit infections

The paramyxoviruses define a diverse group of enveloped RNA viruses that includes a number of important human and animal pathogens. Examples include human respiratory syncytial virus and the human parainfluenza viruses, which cause respiratory illnesses in young children and the elderly; measles and mumps viruses, which have caused recent resurgences of disease in developed countries; the zoonotic Hendra and Nipah viruses, which have caused several outbreaks of fatal disease in Australia and Asia; and Newcastle disease virus, which infects chickens and other avian species. Like other enveloped viruses, paramyxoviruses form particles that assemble and bud from cellular membranes, allowing the transmission of infections to new cells and hosts. Here, we review recent advances that have improved our understanding of events involved in paramyxovirus particle formation. Contributions of viral matrix proteins, glycoproteins, nucleocapsid proteins, and accessory proteins to particle formation are discussed, as well as the importance of host factor recruitment for efficient virus budding. Trafficking of viral structural components within infected cells is described, together with mechanisms that allow for the selection of specific sites on cellular membranes for the coalescence of viral proteins in preparation of bud formation and virion release.

Implications for lipids during replication of enveloped viruses

Enveloped viruses, which include many medically important viruses such as human immunodeficiency virus, influenza virus and hepatitis C virus, are intracellular parasites that acquire lipid envelopes from their host cells. Success of replication is intimately linked to their ability to hijack host cell mechanisms, particularly those related to membrane dynamics and lipid metabolism. Despite recent progress, our knowledge of lipid mediated virus-host interactions remains highly incomplete. In addition, diverse experimental systems are used to study different stages of virus replication thus complicating comparisons. This review aims to present a unifying view of the widely diverse strategies used by enveloped viruses at distinct stages of their replication cycles.

Retroviral vector production under serum deprivation: The role of lipids

The use of retroviral vectors for gene therapy applications demands high titer preparations and stringent quality standards. However, the manufacturing of these vectors still represents a highly challenging task due to the low productivity of the cell lines and reduced stability of the vector infectivity, particularly under serum-free conditions. With the objective of understanding the major limitations of retroviral vector production under serum deprivation, a thorough study of viral production kinetics, vector characterization and cell growth and metabolic behavior was conducted, for 293 FLEX 18 and Te Fly Ga 18 producer cell lines using different serum concentrations. The reduction of serum supplementation in the culture medium resulted in pronounced decreases in cell productivity of infectious vector, up to ninefold in 293 FLEX 18 cells and sevenfold in Te Fly Ga 18 cells. Total particles productivity was maintained, as assessed by measuring viral RNA; therefore, the decrease in infectious vector production could be attributed to higher defective particles output. The absence of the serum lipid fraction was found to be the major cause for this decrease in cell viral productivity. The use of delipidated serum confirmed the requirement of serum lipids, particularly cholesterol, as its supplementation not only allowed the total recovery of viral titers as well as additional production increments in both cell lines when comparing with the standard 10% (v/v) FBS supplementation. This work identified lower production ratios of infectious particles/total particles as the main restraint of retroviral vector production under serum deprivation; this is of the utmost importance concerning the clinical efficacy of the viral preparations. Lipids were confirmed as the key serum component correlated with the production of infective retroviral vectors and this knowledge can be used to efficiently design medium supplementation strategies for serum-free production. Biotechnol. Bioeng. 2009; 104: 1171-1181. (c) 2009 Wiley Periodicals, Inc.

Newcastle disease virus-like particles containing respiratory syncytial virus G protein induced protection in BALB/c mice, with no evidence of immunopathology

Respiratory syncytial virus (RSV) is the leading cause of serious respiratory infections in children as well as a serious cause of disease in elderly and immunosuppressed populations. There are no licensed vaccines available to prevent RSV disease. We have developed a virus-like particle (VLP) vaccine candidate for protection from RSV. The VLP is composed of the NP and M proteins of Newcastle disease virus (NDV) and a chimeric protein containing the cytoplasmic and transmembrane domains of the NDV HN protein and the ectodomain of the human RSV G protein (H/G). Immunization of mice with 10 or 40 microg total VLP-H/G protein by intraperitoneal or intramuscular inoculation stimulated antibody responses to G protein which were as good as or better than those stimulated by comparable amounts of UV-inactivated RSV. Immunization of mice with two doses or even a single dose of these particles resulted in the complete protection of mice from RSV replication in the lungs. Immunization with these particles induced neutralizing antibodies with modest titers. Upon RSV challenge of VLP-H/G-immunized mice, no enhanced pathology in the lungs was observed, although lungs of mice immunized in parallel with formalin-inactivated RSV (FI-RSV) showed the significant pathology that has previously been documented after immunization with FI-RSV. Thus, the VLP-H/G candidate vaccine was immunogenic in BALB/c mice and prevented replication of RSV in murine lungs, with no evidence of immunopathology. These data support further development of virus-like particle vaccine candidates for protection against RSV.

y Human herpesvirus 6 envelope components enriched in lipid rafts: evidence for virion-associated lipid rafts

In general, enveloped viruses are highly dependent on their lipid envelope for entry into host cells. Here, we demonstrated that during the course of virus maturation, a significant proportion of human herpesvirus 6 (HHV-6) envelope proteins were selectively concentrated in the detergent-resistant glycosphingolipid- and cholesterol-rich membranes (rafts) in HHV-6-infected cells. In addition, the ganglioside GM1, which is known to partition preferentially into lipid rafts, was detected in purified virions, along with viral envelope glycoproteins, gH, gL, gB, gQ1, gQ2 and gO indicating that at least one raft component was included in the viral particle during the assembly process.

Cholesterol Supplementation During Production Increases the Infectivity of Retroviral and Lentiviral Vectors Pseudotyped with the Vesicular Stomatitis Virus Glycoprotein (VSV-G)

Cholesterol, a major component of plasma membrane lipid rafts, is important for assembly and budding of enveloped viruses, including influenza and HIV-1. Cholesterol depletion impairs virus assembly and infectivity. This study examined the effects of exogenous cholesterol addition (delivered as a complex with methyl beta cyclodextrin) on the production of Molony murine leukemia virus retroviral vector and HIV-1-based lentiviral vector pseudotyped with the vesicular stomatitis virus glycoprotein (VSV-G). Cholesterol supplementation before and during vector production enhanced the infectivity of retroviral and lentiviral vectors up to 4-fold and 6-fold, respectively. In contrast, the amount of retroviral vector produced was unchanged, and that of lentiviral vector was increased less than two-fold. Both free cholesterol and cholesterol ester content in 293-gag-pol producer cells increased with cholesterol addition. In contrast, the phospholipids headgroup composition was essentially unchanged by cholesterol supplementation in 293-gag-pol packaging cells. Based on these results, it is proposed that cholesterol supplementation increases the infectivity of VSV-G-pseudotyped retroviral and lentiviral vectors, possibly by altering the composition of the producer cell membrane where the viral vectors are assembled and bud, and/or by changing the lipid composition of the viral vectors.

Subproteome analysis of the neutrophil cytoskeleton

Neutrophils play a key role in the early host-defense mechanisms due to their capacity to migrate into inflamed tissues and phagocytose microorganisms. The cytoskeleton has an essential role in these neutrophil functions, however, its composition is still poorly understood. We separately analyzed different cytoskeletal compartments: cytosolic skeleton, phagosome membrane skeleton, and plasma membrane skeleton. Using a proteomic approach, 138 nonredundant proteins were identified. Proteins not previously known to associate with the skeleton were: n-acetylglucosamine kinase, phosphoglycerate mutase 1, prohibitin, ficolin-1, phosphogluconate dehydrogenase, glucosidase, transketolase, major vault protein, valosin-containing protein, aldehyde dehydrogenase, and lung cancer-related protein-8 (LCRP8). The majority of these proteins can be classified as energy metabolism enzymes. Such a finding was interesting because neutrophil energy metabolism is unusual, mainly relying on glycolysis. The enrichment of phosphoglycerate mutase in cytosolic skeleton was additionally indicated by the use of Western blotting. This is the broadest subcellular investigation to date of the neutrophil cytoskeletal proteome and the first proteomic analysis in any cell type of the phagosome skeleton. The association of metabolic enzymes with cytoskeleton is suggestive of the importance of their localized enrichment and macromolecular organization in neutrophils.

Newcastle disease virus: a promising vector for viral therapy, immune therapy, and gene therapy of cancer

This review deals with the avian paramyxovirus Newcastle disease virus (NDV) and describes properties that explain its oncolytic activity, its tumor-selective replication behavior, and its immune-stimulatory capacity with human cells. The strong interferon response of normal cells upon contact with NDV appears to be the basis for the good tolerability of the virus in cancer patients and for its immune stimulatory properties, whereas the weak interferon response of tumor cells explains the tumor selectivity of replication and oncolysis. Various concepts for the use of this virus for cancer treatment are pointed out and results from clinical studies are summarized. Reverse genetics technology has made it possible recently to clone the genome and to introduce new foreign genes thus generating new recombinant viruses. These can, in the future, be used to transfer new therapeutic genes into tumors and also to immunize against new emerging pathogens. The modular nature of gene transcription, the undetectable rate of recombination, and the lack of a DNA phase in the replication cycle make NDV a suitable candidate for the rational design of a safe and stable vaccine and gene therapy vector.