Emerging picture of host chaperone and cyclophilin roles in RNA virus replication

Characterization and functional analysis of the small heat shock protein HSP19.5 in Bombyx mori in response to Nosema bombycis infection

Small heat shock proteins (sHSPs) are molecular chaperones known for their role in maintaining cellular homeostasis and protecting cells from various environmental stresses. This study focuses on the silkworm small heat shock protein HSP19.5 and its potential functions in the context of Nosema bombycis infection, a microsporidian pathogen causing severe disease in the sericulture industry. We cloned and characterized HSP19.5 and revealed its expression patterns in different silkworm tissues and developmental stages. Our results indicate that HSP19.5 expression is significantly up-regulated in response to N. bombycis infection, suggesting a role in the host stress response. Through a series of experiments, including RNA interference and overexpression analyses, we demonstrated that HSP19.5 promotes N. bombycis proliferation, possibly by inhibiting host cell apoptosis and regulating intracellular ROS levels. The cytoplasmic localization of HSP19.5 in silkworm cells is consistent with its function as a molecular chaperone. The results enhance our understanding of the complex host-pathogen interactions between silkworms and N. bombycis, and provides insights that may inform the development of novel strategies to control the pebrine disease.

Cold suppresses virus accumulation and alters the host transcriptomic response in the turnip mosaic virus-Arabidopsis halleri system

Since plant viruses cause lifelong infections, virus-plant interactions are exposed to large temperature fluctuations in evergreen perennials. In such circumstances, virus-plant interactions are expected to change significantly between the warm and cold seasons. However, few studies have investigated the effects of cold temperatures on virus-plant interactions. Here, we show that in a persistent infection system of the turnip mosaic virus (TuMV)-Arabidopsis halleri, cold temperatures lead to slow viral replication/spreading within the host, attenuated host symptoms, and cold-specific transcriptomic responses. Many differentially expressed genes (DEGs) were detected between virus-inoculated and mock-inoculated plants under warm and cold conditions; however, the sets of DEGs and response timings were temperature-dependent. At cold temperatures, the expression of photosynthesis-related genes decreased in the early stages of infection. However, it recovered to the same level as that in uninfected plants in the later stages. In contrast, the transcriptomic changes under warm conditions suggest that viral infections cause auxin signaling disruption. These responses coincided with the inhibition of host growth. We identified 6 cold- and 38 warm-specific DEGs, which changed their expression in response to TuMV infection under more than half of the conditions for either cold or warm temperatures. Further validation of the putative relationships between transcriptomic and phenotypic responses of the host is required. Our findings on temperature-dependent host responses at both symptomatic and transcriptomic levels help us understand how warm and cold temperatures affect virus-plant interactions in seasonal environments.

Plant cell-cycle regulators control the nuclear environment for viral pathogenesis

The proper regulation of cell-cycle regulators is curial for both viral replication and host-plant adaptive growth during the viral pathogenesis. Mechanisms on reorchestrating RETINOBLASTOMA-RELATED 1 (RBR1), repressor of E2F transcription factor, and downstream genes in host-virus interactions are unclear. Here, we discover that anaphase-promoting complex/cyclosome (APC/C) E3 ligase activator cell division cycle 20 (CDC20) in tomato binds RBR1 or mediates cyclin D1 depletion to preserve RBR1-E2F complexes, while geminivirus or crinivirus repurposes APC/CCDC20 activities to liberate E2Fs in two ways: activating APC/CCDC20 to deplete RBR1 or blocking APC/CCDC20 to stimulate cyclin-D1-mediated RBR1 depletion. The liberated E2Fs activate DNA polymerase or heat shock protein 70 gene transcription to favor virus propagation. The improper disruption of RBR1-E2F complexes via hijacking APC/CCDC20 causes the host growth repression. We uncover a scenario in which the virus co-opts host APC/CCDC20 to reprogram RBR1-E2F complex to favor its propagation while dampening host vitality.

Exploring proteins within the coccolith matrix

Coccolithophores comprise a major component of the oceanic carbon cycle. These unicellular algae produce ornate structures made of calcium carbonate, termed coccoliths, representing ~ 50% of calcite production in the open ocean. The exact molecular mechanisms which direct and control coccolith formation are unknown. In this study, we report on the presence and functional features of proteins within the coccoliths produced by a range of model coccolithophore species including: the globally abundant and well-studied Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and related Gephyrocapsa oceanica, as well as the larger and more heavily calcified Coccolithus braarudii. Protein features were compared between species and against biomineralisation proteins previously identified in other marine calcifying organisms. Notably, several protein features were consistently seen across the examined coccolithophore species, including the cell signalling 14-3-3 domain, chromosome segregation SMC ATPase domain, as well as proteins involved in protein processing and protease inhibition. The copper-binding cupredoxin domain was observed in both Gephyrocapsa species, as well as other marine calcifiers, suggestive of a requirement of Cu in biomineralisation. Building consensus with existing work, we highlight the pentapeptide repeat as a feature which is associated with the coccolith matrix, being identified in all three examined species, and propose that this structural motif may play a role in controlling coccolith growth. This preliminary study provides insight towards the functional diversity of calcification machinery in coccolithophores and presents a number of candidates for future research towards understanding the biochemical controls which direct coccolithogenesis.

Modulators of the Hop-HSP90 Protein-Protein Interaction Disrupt KSHV Lytic Replication

The central role of the chaperome in maintaining cellular proteostasis has seen numerous viral families evolve to parasitically exploit host chaperones in their life cycle. The HSP90 chaperone protein and its cochaperone Hop have both individually been shown to be essential factors for Kaposi sarcoma-associated herpesvirus (KSHV) lytic replication. Given the fundamental regulatory role that protein-protein interactions (PPIs) play in cellular biology, we reasoned that disrupting the Hop-HSP90 PPI may provide a new host-based target for inhibiting KSHV lytic replication. This study expands upon a previous report of non-natural peptides, which were found to disrupt the association between the HopTPR2A domain and its interacting HSP90CTD. Here, in addition to providing insight into the structure-activity relationships of PPI inhibition, we show disruption of the full-length Hop-HSP90 PPI. The inhibitory peptides selectively engaged the HopTPR2A domain in cell lysates and when tethered to a cell-penetrating peptide acted as noncytotoxic inhibitors of KSHV lytic replication by lowering the viral load, preventing the production of infectious virions, and reducing the expression of KSHV lytic genes. In addition to tentative evidence of Hop-HSP90 PPI as a much-needed target for KSHV drug discovery, this study represents an important step in understanding viral interactions with the host proteostasis machinery.

Intervention strategies targeting virus and host factors against porcine reproductive and respiratory syndrome virus: A systematic review

Porcine reproductive and respiratory syndrome (PRRS) caused by porcine reproductive and respiratory syndrome virus (PRRSV) causes considerable economic losses to the global swine industry every year and seriously hinders the healthy development of this industry. Although tremendous efforts have been made over the past 30 years toward the development of prevention and control strategies against PRRSV infection, to date, treatments with proven efficacy have yet to be available due to our incomplete understanding of the molecular basis and complexity of the infection machinery. This review systematically discusses recent advances in the research and development of anti-PRRSV therapies targeting different stages of the viral life cycle. Furthermore, this review puts forward novel intervention targets and research approaches based on our in-depth exploration of virus-host interactions and the latest biological technologies, which have the potential to complement or transform current anti-PRRSV strategies and become breakthrough points for the control of PRRS in the future.

A viral p3a protein targets and inhibits TaDOF transcription factors to promote the expression of susceptibility genes and facilitate viral infection

The interactions among viruses and host plants are complex and fascinating because these organisms interact with and adapt to each other continuously. Many plant transcription factors play important roles in plant growth and development and in the resistance to viral infection. To facilitate the infection of plants, some viral proteins typically target and inhibit the function of plant transcription factors. In this study, we found an interesting phenomenon wherein the p3a protein of barley yellow dwarf virus (BYDV) can interact with the zinc finger domain of the TaDOF transcription factor in wheat; the zinc finger domain of TaDOF can interact with the promoter of TaHSP70 and inhibit the transcription of the TaHSP70 gene; and p3a interacts with the TaDOF zinc finger domain through competitive binding, alleviating TaDOF zinc finger domain-mediated inhibition of the TaHSP70 promoter, thereby promoting TaHSP70 expression and promoting infection by BYDV. This study demonstrates that BYDV p3a is an immunosuppressive factor and enriches our understanding of the pathogenesis of BYDV.

The Role of Plant Latex in Virus Biology

At least 20,000 plant species produce latex, a capacity that appears to have evolved independently on numerous occasions. With a few exceptions, latex is stored under pressure in specialized cells known as laticifers and is exuded upon injury, leading to the assumption that it has a role in securing the plant after mechanical injury. In addition, a defensive effect against insect herbivores and fungal infections has been well established. Latex also appears to have effects on viruses, and laticifers are a hostile environment for virus colonization. Only one example of successful colonization has been reported: papaya meleira virus (PMeV) and papaya meleira virus 2 (PMeV2) in Carica papaya. In this review, a summary of studies that support both the pro- and anti-viral effects of plant latex compounds is provided. The latex components represent a promising natural source for the discovery of new pro- and anti-viral molecules in the fields of agriculture and medicine.

Comparative RNA-seq analysis of resistant and susceptible banana genotypes reveals molecular mechanisms in response to banana bunchy top virus (BBTV) infection

Bananas hold significant economic importance as an agricultural commodity, serving as a primary livelihood source, a favorite fruit, and a staple crop in various regions across the world. However, Banana bunchy top disease (BBTD), which is caused by banana bunchy top virus (BBTV), poses a considerable threat to banana cultivation. To understand the resistance mechanism and the interplay of host suitability factors in the presence of BBTV, we conducted RNA-seq-based comparative transcriptomics analysis on mock-inoculated and BBTV-inoculated samples from resistant (wild Musa balbisiana) and susceptible (Musa acuminata 'Lakatan') genotypes. We observed common patterns of expression for 62 differentially expressed genes (DEGs) in both genotypes, which represent the typical defense response of bananas to BBTV. Furthermore, we identified 99 DEGs exclusive to the 'Lakatan' banana cultivar, offering insights into the host factors and susceptibility mechanisms that facilitate successful BBTV infection. In parallel, we identified 151 DEGs unique to the wild M. balbisiana, shedding light on the multifaceted mechanisms of BBTV resistance, involving processes such as secondary metabolite biosynthesis, cell wall modification, and pathogen perception. Notably, our validation efforts via RT-qPCR confirmed the up-regulation of the glucuronoxylan 4-O-methyltransferase gene (14.28 fold-change increase), implicated in xylan modification and degradation. Furthermore, our experiments highlighted the potential recruitment of host's substrate adaptor ADO (30.31 fold-change increase) by BBTV, which may play a role in enhancing banana susceptibility to the viral pathogen. The DEGs identified in this work can be used as basis in designing associated gene markers for the precise integration of resistance genes in marker-assisted breeding programs. Furthermore, the findings can be applied to develop genome-edited banana cultivars targeting the resistance and susceptibility genes, thus developing novel cultivars that are resilient to important diseases.

Maize heat shock proteins-prospection, validation, categorization and in silico analysis of the different ZmHSP families

Among the plant molecular mechanisms capable of effectively mitigating the effects of adverse weather conditions, the heat shock proteins (HSPs), a group of chaperones with multiple functions, stand out. At a time of full progress on the omic sciences, they look very promising in the genetic engineering field, especially in order to conceive superior genotypes, potentially tolerant to abiotic stresses (AbSts). Recently, some works concerning certain families of maize HSPs (ZmHSPs) were published. However, there was still a lack of a study that, with a high degree of criteria, would fully conglomerate them. Using distinct but complementary strategies, we have prospected as many ZmHSPs candidates as possible, gathering more than a thousand accessions. After detailed data mining, we accounted for 182 validated ones, belonging to seven families, which were subcategorized into classes with potential for functional parity. In them, we identified dozens of motifs with some degree of similarity with proteins from different kingdoms, which may help explain some of their still poorly understood means of action. Through in silico and in vitro approaches, we compared their expression levels after controlled exposure to several AbSts' sources, applied at diverse tissues, on varied phenological stages. Based on gene ontology concepts, we still analyzed them from different perspectives of term enrichment. We have also searched, in model plants and close species, for potentially orthologous genes. With all these new insights, which culminated in a plentiful supplementary material, rich in tables, we aim to constitute a fertile consultation source for those maize researchers attracted by these interesting stress proteins.

An Enhanced Dissolving Cyclosporin-A Inhalable Powder Efficiently Reduces SARS-CoV-2 Infection In Vitro

This work illustrates the development of a dry inhalation powder of cyclosporine-A for the prevention of rejection after lung transplantation and for the treatment of COVID-19. The influence of excipients on the spray-dried powder's critical quality attributes was explored. The best-performing powder in terms of dissolution time and respirability was obtained starting from a concentration of ethanol of 45% (v/v) in the feedstock solution and 20% (w/w) of mannitol. This powder showed a faster dissolution profile (Weibull dissolution time of 59.5 min) than the poorly soluble raw material (169.0 min). The powder exhibited a fine particle fraction of 66.5% and an MMAD of 2.97 µm. The inhalable powder, when tested on A549 and THP-1, did not show cytotoxic effects up to a concentration of 10 µg/mL. Furthermore, the CsA inhalation powder showed efficiency in reducing IL-6 when tested on A549/THP-1 co-culture. A reduction in the replication of SARS-CoV-2 on Vero E6 cells was observed when the CsA powder was tested adopting the post-infection or simultaneous treatment. This formulation could represent a therapeutic strategy for the prevention of lung rejection, but is also a viable approach for the inhibition of SARS-CoV-2 replication and the COVID-19 pulmonary inflammatory process.

Dissecting insect cell heterogeneity during influenza VLP production using single-cell transcriptomics

The insect cell-baculovirus expression vector system (IC-BEVS) has been widely used to produce recombinant protein at high titers, including complex virus-like particles (VPLs). However, cell-to-cell variability upon infection is yet one of the least understood phenomena in virology, and little is known about its impact on production of therapeutic proteins. This study aimed at dissecting insect cell population heterogeneity during production of influenza VLPs in IC-BEVS using single-cell RNA-seq (scRNA-seq). High Five cell population was shown to be heterogeneous even before infection, with cell cycle being one of the factors contributing for this variation. In addition, infected insect cells were clustered according to the timing and level of baculovirus genes expression, with each cluster reporting similar influenza VLPs transgenes (i.e., hemagglutinin and M1) transcript counts. Trajectory analysis enabled to track infection progression throughout pseudotime. Specific pathways such as translation machinery, protein folding, sorting and degradation, endocytosis and energy metabolism were identified as being those which vary the most during insect cell infection and production of Influenza VLPs. Overall, this study lays the ground for the application of scRNA-seq in IC-BEVS processes to isolate relevant biological mechanisms during recombinant protein expression towards its further optimization.

Liaisons dangereuses: Intrinsic Disorder in Cellular Proteins Recruited to Viral Infection-Related Biocondensates

Liquid-liquid phase separation (LLPS) is responsible for the formation of so-called membrane-less organelles (MLOs) that are essential for the spatio-temporal organization of the cell. Intrinsically disordered proteins (IDPs) or regions (IDRs), either alone or in conjunction with nucleic acids, are involved in the formation of these intracellular condensates. Notably, viruses exploit LLPS at their own benefit to form viral replication compartments. Beyond giving rise to biomolecular condensates, viral proteins are also known to partition into cellular MLOs, thus raising the question as to whether these cellular phase-separating proteins are drivers of LLPS or behave as clients/regulators. Here, we focus on a set of eukaryotic proteins that are either sequestered in viral factories or colocalize with viral proteins within cellular MLOs, with the primary goal of gathering organized, predicted, and experimental information on these proteins, which constitute promising targets for innovative antiviral strategies. Using various computational approaches, we thoroughly investigated their disorder content and inherent propensity to undergo LLPS, along with their biological functions and interactivity networks. Results show that these proteins are on average, though to varying degrees, enriched in disorder, with their propensity for phase separation being correlated, as expected, with their disorder content. A trend, which awaits further validation, tends to emerge whereby the most disordered proteins serve as drivers, while more ordered cellular proteins tend instead to be clients of viral factories. In light of their high disorder content and their annotated LLPS behavior, most proteins in our data set are drivers or co-drivers of molecular condensation, foreshadowing a key role of these cellular proteins in the scaffolding of viral infection-related MLOs.

Porcine Epidemic Diarrhea Virus: An Updated Overview of Virus Epidemiology, Virulence Variation Patterns and Virus-Host Interactions

The porcine epidemic diarrhea virus (PEDV) is a member of the coronavirus family, causing deadly watery diarrhea in newborn piglets. The global pandemic of PEDV, with significant morbidity and mortality, poses a huge threat to the swine industry. The currently developed vaccines and drugs are only effective against the classic GI strains that were prevalent before 2010, while there is no effective control against the GII variant strains that are currently a global pandemic. In this review, we summarize the latest progress in the biology of PEDV, including its transmission and origin, structure and function, evolution, and virus-host interaction, in an attempt to find the potential virulence factors influencing PEDV pathogenesis. We conclude with the mechanism by which PEDV components antagonize the immune responses of the virus, and the role of host factors in virus infection. Essentially, this review serves as a valuable reference for the development of attenuated virus vaccines and the potential of host factors as antiviral targets for the prevention and control of PEDV infection.

Modeling Kaempferol as a Potential Pharmacological Agent for COVID-19/PF Co-Occurrence Based on Bioinformatics and System Pharmacological Tools

Objective: People suffering from coronavirus disease 2019 (COVID-19) are prone to develop pulmonary fibrosis (PF), but there is currently no definitive treatment for COVID-19/PF co-occurrence. Kaempferol with promising antiviral and anti-fibrotic effects is expected to become a potential treatment for COVID-19 and PF comorbidities. Therefore, this study explored the targets and molecular mechanisms of kaempferol against COVID-19/PF co-occurrence by bioinformatics and network pharmacology.

Methods: Various open-source databases and Venn Diagram tool were applied to confirm the targets of kaempferol against COVID-19/PF co-occurrence. Protein-protein interaction (PPI), MCODE, key transcription factors, tissue-specific enrichment, molecular docking, Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to clarify the influential molecular mechanisms of kaempferol against COVID-19 and PF comorbidities.

Results: 290 targets and 203 transcription factors of kaempferol against COVID-19/PF co-occurrence were captured. Epidermal growth factor receptor (EGFR), proto-oncogene tyrosine-protein kinase SRC (SRC), mitogen-activated protein kinase 3 (MAPK3), mitogen-activated protein kinase 1 (MAPK1), mitogen-activated protein kinase 8 (MAPK8), RAC-alpha serine/threonine-protein kinase (AKT1), transcription factor p65 (RELA) and phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit alpha isoform (PIK3CA) were identified as the most critical targets, and kaempferol showed effective binding activities with the above critical eight targets. Further, anti-COVID-19/PF co-occurrence effects of kaempferol were associated with the regulation of inflammation, oxidative stress, immunity, virus infection, cell growth process and metabolism. EGFR, interleukin 17 (IL-17), tumor necrosis factor (TNF), hypoxia inducible factor 1 (HIF-1), phosphoinositide 3-kinase/AKT serine/threonine kinase (PI3K/AKT) and Toll-like receptor signaling pathways were identified as the key anti-COVID-19/PF co-occurrence pathways.

Conclusion: Kaempferol is a candidate treatment for COVID-19/PF co-occurrence. The underlying mechanisms may be related to the regulation of critical targets (EGFR, SRC, MAPK3, MAPK1, MAPK8, AKT1, RELA, PIK3CA and so on) and EGFR, IL-17, TNF, HIF-1, PI3K/AKT and Toll-like receptor signaling pathways. This study contributes to guiding development of new drugs for COVID-19 and PF comorbidities.

Multiple isoforms of HSP70 and HSP90 required for betanodavirus multiplication in medaka cells

Heat shock proteins (HSPs) are molecular chaperones that have recently been shown to function as host factors (HFs) for virus multiplication in fish as well as in mammals, plants, and insects. HSPs are classified into families, and each family has multiple isoforms. However, no comprehensive studies have been performed to clarify the biological importance of these multiple isoforms for fish virus multiplication. Betanodaviruses are the causative agents of viral nervous necrosis in cultured marine fish and cause very high mortality. Although the viral genome and encoded proteins have been characterized extensively, information on HFs for these viruses is limited. In this study, therefore, we focused on the HSP70 and HSP90 families to examine the importance of their isoforms for betanodavirus multiplication. We found that HSP inhibitors (17-AAG, radicicol, and quercetin) suppressed viral RNA replication and production of progeny virus in infected medaka (Oryzias latipes) cells. Thermal stress or virus infection resulted in increased expression of some isoform genes and facilitated virus multiplication. Furthermore, overexpression and knockdown of some isoform genes revealed that the isoforms HSP70-1, HSP70-2, HSP70-5, HSP90-α1, HSP90-α2, and HSP90-β play positive roles in virus multiplication in medaka. Collectively, these results suggest that multiple isoforms of fish HPSs serve as HFs for betanodavirus multiplication.

Race against Time between the Virus and Host: Actin-Assisted Rapid Biogenesis of Replication Organelles is Used by TBSV to Limit the Recruitment of Cellular Restriction Factors

Positive-strand RNA viruses build large viral replication organelles (VROs) with the help of coopted host factors. Previous works on tomato bushy stunt virus (TBSV) showed that the p33 replication protein subverts the actin cytoskeleton by sequestering the actin depolymerization factor, cofilin, to reduce actin filament disassembly and stabilize the actin filaments. Then, TBSV utilizes the stable actin filaments as "trafficking highways" to deliver proviral host factors into the protective VROs. In this work, we show that the cellular intrinsic restriction factors (CIRFs) also use the actin network to reach VROs and inhibit viral replication. Disruption of the actin filaments by expression of the Legionella RavK protease inhibited the recruitment of plant CIRFs, including the CypA-like Roc1 and Roc2 cyclophilins, and the antiviral DDX17-like RH30 DEAD box helicase into VROs. Conversely, temperature-sensitive actin and cofilin mutant yeasts with stabilized actin filaments reduced the levels of copurified CIRFs, including cyclophilins Cpr1, CypA, Cyp40-like Cpr7, cochaperones Sgt2, the Hop-like Sti1, and the RH30 helicase in viral replicase preparations. Dependence of the recruitment of both proviral and antiviral host factors into VROs on the actin network suggests that there is a race going on between TBSV and its host to exploit the actin network and ultimately to gain the upper hand during infection. We propose that, in the highly susceptible plants, tombusviruses efficiently subvert the actin network for rapid delivery of proviral host factors into VROs and ultimately overcome host restriction factors via winning the recruitment race and overwhelming cellular defenses. IMPORTANCE Replication of positive-strand RNA viruses is affected by the recruitment of host components, which provide either proviral or antiviral functions during virus invasion of infected cells. The delivery of these host factors into the viral replication organelles (VROs), which represent the sites of viral RNA replication, depends on the cellular actin network. Using TBSV, we uncover a race between the virus and its host with the actin network as the central player. We find that in susceptible plants, tombusviruses exploit the actin network for rapid delivery of proviral host factors into VROs and ultimately overcome host restriction factors. In summary, this work demonstrates that the actin network plays a major role in determining the outcome of viral infections in plants.

Zika Virus Neuropathogenesis: The Different Brain Cells, Host Factors and Mechanisms Involved

Zika virus (ZIKV), despite being discovered six decades earlier, became a major health concern only after an epidemic in French Polynesia and an increase in the number of microcephaly cases in Brazil. Substantial evidence has been found to support the link between ZIKV and neurological complications in infants. The virus targets various cells in the brain, including radial glial cells, neural progenitor cells (NPCs), astrocytes, microglial and glioblastoma stem cells. It affects the brain cells by exploiting different mechanisms, mainly through apoptosis and cell cycle dysregulation. The modulation of host immune response and the inflammatory process has also been demonstrated to play a critical role in ZIKV induced neurological complications. In addition to that, different ZIKV strains have exhibited specific neurotropism and unique molecular mechanisms. This review provides a comprehensive and up-to-date overview of ZIKV-induced neuroimmunopathogenesis by dissecting its main target cells in the brain, and the underlying cellular and molecular mechanisms. We highlighted the roles of the different ZIKV host factors and how they exploit specific host factors through various mechanisms. Overall, it covers key components for understanding the crosstalk between ZIKV and the brain.

The Large Nonstructural Protein (NS1) of Human Bocavirus 1 Directly Interacts with Ku70, Which Plays an Important Role in Virus Replication in Human Airway Epithelia

Human bocavirus 1 (HBoV1), an autonomous human parvovirus, causes acute respiratory tract infections in young children. HBoV1 infects well-differentiated (polarized) human airway epithelium cultured at an air-liquid interface (HAE-ALI). HBoV1 expresses a large nonstructural protein, NS1, that is essential for viral DNA replication. HBoV1 infection of polarized human airway epithelial cells induces a DNA damage response (DDR) that is critical to viral DNA replication involving DNA repair with error-free Y-family DNA polymerases. HBoV1 NS1 or the isoform NS1-70 per se induces a DDR. In this study, using the second-generation proximity-dependent biotin identification (BioID2) approach, we identified that Ku70 is associated with the NS1-BioID2 pulldown complex through a direct interaction with NS1. Biolayer interferometry (BLI) assay determined a high binding affinity of NS1 with Ku70, which has an equilibrium dissociation constant (KD) value of 0.16 μM and processes the strongest interaction at the C-terminal domain. The association of Ku70 with NS1 was also revealed during HBoV1 infection of HAE-ALI. Knockdown of Ku70 and overexpression of the C-terminal domain of Ku70 significantly decreased HBoV1 replication in HAE-ALI. Thus, our study provides, for the first time, a direct interaction of parvovirus large nonstructural protein NS1 with Ku70. IMPORTANCE Parvovirus infection induces a DNA damage response (DDR) that plays a pivotal role in viral DNA replication. The DDR includes activation of ATM (ataxia telangiectasia mutated), ATR (ATM- and RAD3-related), and DNA-PKcs (DNA-dependent protein kinase catalytic subunit). The large nonstructural protein (NS1) often plays a role in the induction of DDR; however, how the DDR is induced during parvovirus infection or simply by the NS1 is not well studied. Activation of DNA-PKcs has been shown as one of the key DDR pathways in DNA replication of HBoV1. We identified that HBoV1 NS1 directly interacts with Ku70, but not Ku80, of the Ku70/Ku80 heterodimer at high affinity. This interaction is also important for HBoV1 replication in HAE-ALI. We propose that the interaction of NS1 with Ku70 recruits the Ku70/Ku80 complex to the viral DNA replication center, which activates DNA-PKcs and facilitates viral DNA replication.

Safety of conventional immunosuppressive therapies for patients with dermatological conditions and coronavirus disease 2019: A review of current evidence

The effect of coronavirus disease 2019 (COVID-19) on patients receiving conventional immunosuppressive (IS) therapy has yet to be fully determined; however, research on using IS therapy for treating COVID-19 in acutely ill patients is increasing. While some believe that IS therapy may be protective, others argue that these agents may make patients more susceptible to COVID-19 infection and morbidity and advocate for a more cautious, individualized approach to determining continuation, reduction, or discontinuation of therapy. In this review, we aim to provide an overview of COVID-19 risk in dermatological patients who are receiving conventional IS therapies, including mycophenolate mofetil, methotrexate, cyclosporine, azathioprine, apremilast, JAK inhibitors, and systemic steroids. Additionally, we provide recommendations for management of these medications for dermatological patients during the COVID-19 pandemic. Treatment of dermatological disease during the COVID-19 pandemic should involve shared decision-making between the patient and provider, with consideration of each patient's comorbidities and the severity of the patient's dermatological disease.

Targeting conserved co-opted host factors to block virus replication: Using allosteric inhibitors of the cytosolic Hsp70s to interfere with tomato bushy stunt virus replication

To further our understanding of the pro-viral roles of the host cytosolic heat shock protein 70 (Hsp70) family, we chose the conserved Arabidopsis thaliana Hsp70-2 and the unique Erd2 (early response to dehydration 2), which contain Hsp70 domains. Based on in vitro studies with purified components, we show that AtHsp70-2 and AtErd2 perform pro-viral functions equivalent to that of the yeast Ssa1 Hsp70. These functions include activation of the tombusvirus RdRp, and stimulation of replicase assembly. Yeast-based complementation studies demonstrate that AtHsp70-2 or AtErd2 are present in the purified tombusvirus replicase. RNA silencing and over-expression studies in Nicotiana benthamiana suggest that both Hsp70-2 and Erd2 are co-opted by tomato bushy stunt virus (TBSV). Moreover, we used allosteric inhibitors of Hsp70s to inhibit replication of TBSV and related plant viruses in plants. Altogether, interfering with the functions of the co-opted Hsp70s could be an effective antiviral approach against tombusviruses in plants.

Bombyx mori cell division cycle protein 37 promotes the proliferation of BmNPV

Cell division cycle protein 37 (Cdc37) is a molecular chaperone that actively participates in many intracellular physiological and biochemical processes as well as pathogen infection. However, the function of Cdc37 in silkworm cells under Bombyx mori nucleopolyhedrovirus (BmNPV) infection is unknown. We cloned and identified BmCdc37, a Cdc37 gene from B. mori, which is highly conserved among other species. After BmNPV infection, the expression level of the BmCdc37 gene was up-regulated and showed an expression pattern similar to the BmHsp90 gene, which relies on Cdc37 to stabilize and activate specific protein kinases. The immunofluorescence, bimolecular fluorescence complementation (BiFC), and co-immunoprecipitation (Co-IP) assays all indicated that BmCdc37 interacts with BmHsp90 in silkworm cells. Both BmCdc37 and BmHsp90 promote the reproduction of BmNPV. Co-expression of BmCdc37 and BmHsp90 was better at promoting virus proliferation than overexpression alone. These findings all indicate that BmCdc37 plays an active role in the proliferation of BmNPV.

Radicicol Inhibits Chikungunya Virus Replication by Targeting Nonstructural Protein 2

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that causes a debilitating febrile illness characterized by persistent muscle and joint pain. The widespread distribution of transmission-competent vectors, Aedes species mosquitoes, indicates the potential risk of large-scale epidemics with high attack rates that can severely impact public health globally. Despite this, currently, there are no antivirals available for the treatment of CHIKV infections. Thus, we aimed to identify potential drug candidates by screening a chemical library using a cytopathic effect-based high-throughput screening assay. As a result, we identified radicicol, a heat shock protein 90 (Hsp90) inhibitor that effectively suppressed CHIKV replication by blocking the synthesis of both positive- and negative-strand viral RNA as well as expression of viral proteins. Interestingly, selection for viral drug-resistant variants and mutational studies revealed nonstructural protein 2 (nsP2) as a putative molecular target of radicicol. Moreover, coimmunoprecipitation and in silico modeling analyses determined that G641D mutation in the methyltransferase (MT)-like domain of nsP2 is essential for its interaction with cytoplasmic Hsp90β chaperone. Our findings collectively support the potential application of radicicol as an anti-CHIKV agent. The detailed study of the underlying mechanism of action further contributes to our understanding of virus-host interactions for novel therapeutics against CHIKV infection.

Enhancement of immune responses by co-stimulation of TLR3 - TLR7 agonists as a potential therapeutics against rabies in mouse model

Rabies is always fatal, when post-exposure prophylaxis is administered after the onset of clinical symptoms. To date, there is no effective treatment of rabies once clinical symptoms has initiated. Therefore, we aimed to provide evidences which indicate the promising effects of combination treatment with TLR agonists following rabies infection. Four groups of rabies infected-mice (10-mice/group) were treated with PolyI:C 50 μg (a TLR3 agonist), Imiquimod50 μg (a TLR7 agonist), (Poly + Imi)25 μg and (Poly + Imi)50 μg respectively. The immune responses in each experimental groups were investigated in the brain through evaluation of GFAP, MAP2, CD4, HSP70, TLR3, TLR7 and apoptotic cell expression as well as determination of IFN-γ, TNF-α and IL-4, levels. The treatment with combination of agonists (Poly + Imi)50 μg/mouse resulted a 75% decrease of mortality rate and better extended survival time following street rabies virus infection. Higher number of CD4⁺T cells, TLR3 and TLR7 expression in the brain parenchyma observed in the groups receiving both combined agonist therapies at the levels of 25 μg and 50 μg. In spite of decreased number of neuronal cell, significant higher number of astrocytes was shown in the group given (Poly + Imi)25 μg. The obtained results also pointed to the dramatic decrease of HSP70 expression in all groups of infected mice whereas higher number of apoptotic cells and Caspase 8 expression were recorded in (Poly + Imi)25 μg treated group. Furthermore, the cytokine profile consisting the increased levels of TNF-α, IFN-γ and IL-4 revealed that both humoral and cellular responses were highly modulated in combination therapy of 50 μg of Imiquimod and Poly I:C. Reduced viral load as quantified by real-time PCR of rabies N gene expression in the brain also correlated with the better survival of agonist-treated groups of mice. Based on obtained results, we have presented evidences of beneficial utilization of combined agonist therapy composed of TLR3/TLR7 ligands. This treatment regimen extended survival of infected mice and decreased significantly their mortality rate. We believe that the results of synergy-inducing protection of both TLR3/TLR7 agonists lead to the enhancement of innate immune responses cells residing in the CNS which warrant the studies to further understanding of crosstalk mechanisms in cellular immunity against rabies in the future.

Effects of heat treatment on metabolism of tobacco plants infected with Potato virus Y

Many factors affect successful virus propagation and plant defence responses. Heat shock protein (Hsp) expression after heat shock plays an ambiguous role in viral infection. On the one hand, Hsp70 participates in plant defence response; on the other hand, Hsp70 could interact with viral proteins and facilitate virus propagation. Here, we studied metabolic adaptations of Nicotiana tabacum L. subjected to heat shock (42 °C, 2 h) before or after inoculating the plants with Potato virus Y (potyvirus). RT-qPCR and ELISA were used for potyvirus quantification. Hsp70 and Hsp90 isoforms were analysed by Western blotting. Salicylic, quinic and chlorogenic acid content was determined by LC-MS. The activity of Hatch-Slack enzymes (as markers of potyviral infection in tobacco) and glycosidases was assayed. Application of heat shock before or after inoculation showed accelerated potyviral propagation in comparison with only inoculated plants. Plants exposed to heat shock and concurrently inoculated showed higher potyviral content, higher amount of Hsp70, together with late decline of quinic acid content and low chlorogenic acid content. Spread of potyviral infection correlated with enhanced salicylic acid content and activities of enzymes of the Hatch-Slack cycle, α- and β-galactosidase, α-mannosidase, α-glucosidase and β-N-acetylhexosaminidase. Heat shock proteins accelerate potyviral propagation. The lower weight cytosolic and mitochondrial Hsp70 (~50-75 kDa) persist throughout the viral infection. Also, the plant defense response results in increase of salicylic and chlorogenic acids but decrease of quinic acid content.

A plant reovirus hijacks endoplasmic reticulum-associated degradation machinery to promote efficient viral transmission by its planthopper vector under high temperature conditions

In the field, many insect-borne crop viral diseases are more suitable for maintenance and spread in hot-temperature areas, but the mechanism remains poorly understood. The epidemic of a planthopper (Sogatella furcifera)-transmitted rice reovirus (southern rice black-streaked dwarf virus, SRBSDV) is geographically restricted to southern China and northern Vietnam with year-round hot temperatures. Here, we reported that two factors of endoplasmic reticulum-associated degradation (ERAD) machinery, the heat shock protein DnaJB11 and ER membrane protein BAP31, were activated by viral infection to mediate the adaptation of S. furcifera to high temperatures. Infection and transmission efficiencies of SRBSDV by S. furcifera increased with the elevated temperatures. We observed that high temperature (35°C) was beneficial for the assembly of virus-containing tubular structures formed by nonstructural protein P7-1 of SRBSDV, which facilitates efficient viral transmission by S. furcifera. Both DnaJB11 and BAP31 competed to directly bind to the tubule protein P7-1 of SRBSDV; however, DnaJB11 promoted whereas BAP31 inhibited P7-1 tubule assembly at the ER membrane. Furthermore, the binding affinity of DnaJB11 with P7-1 was stronger than that of BAP31 with P7-1. We also revealed that BAP31 negatively regulated DnaJB11 expression through their direct interaction. High temperatures could significantly upregulate DnaJB11 expression but inhibit BAP31 expression, thereby strongly facilitating the assembly of abundant P7-1 tubules. Taken together, we showed that a new temperature-dependent protein quality control pathway in the ERAD machinery has evolved for strong activation of DnaJB11 for benefiting P7-1 tubules assembly to support efficient transmission of SRBSDV in high temperatures. We thus deduced that ERAD machinery has been hitchhiked by insect-borne crop viruses to enhance their transmission in tropical climates.

The importance of virion-incorporated cellular RNA-Binding Proteins in viral particle assembly and infectivity

RNA is a central molecule in RNA virus biology due to its dual function as messenger and genome. However, the small number of proteins encoded by viral genomes is insufficient to enable virus infection. Hence, viruses hijack cellular RNA-binding proteins (RBPs) to aid replication and spread. In this review we discuss the 'knowns' and 'unknowns' regarding the contribution of host RBPs to the formation of viral particles and the initial steps of infection in the newly infected cell. Through comparison of the virion proteomes of ten different human RNA viruses, we confirm that a pool of cellular RBPs are typically incorporated into viral particles. We describe here illustrative examples supporting the important functions of these RBPs in viral particle formation and infectivity and we propose that the role of host RBPs in these steps can be broader than previously anticipated. Understanding how cellular RBPs regulate virus infection can lead to the discovery of novel therapeutic targets against viruses.

Human coronavirus dependency on host heat shock protein 90 reveals an antiviral target

Rapid accumulation of viral proteins in host cells render viruses highly dependent on cellular chaperones including heat shock protein 90 (Hsp90). Three highly pathogenic human coronaviruses, including MERS-CoV, SARS-CoV and SARS-CoV-2, have emerged in the past 2 decades. However, there is no approved antiviral agent against these coronaviruses. We inspected the role of Hsp90 for coronavirus propagation. First, an Hsp90 inhibitor, 17-AAG, significantly suppressed MERS-CoV propagation in cell lines and physiological-relevant human intestinal organoids. Second, siRNA depletion of Hsp90β, but not Hsp90α, significantly restricted MERS-CoV replication and abolished virus spread. Third, Hsp90β interaction with MERS-CoV nucleoprotein (NP) was revealed in a co-immunoprecipitation assay. Hsp90β is required to maintain NP stability. Fourth, 17-AAG substantially inhibited the propagation of SARS-CoV and SARS-CoV-2. Collectively, Hsp90 is a host dependency factor for human coronavirus MERS-CoV, SARS-CoV and SARS-COV-2. Hsp90 inhibitors can be repurposed as a potent and broad-spectrum antiviral against human coronaviruses.

Cyclosporine and COVID-19: Risk or favorable?

The coronavirus disease 2019 (COVID-19) pandemic is declared a global health emergency. COVID-19 is triggered by a novel coronavirus: severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Baseline characteristics of admitted patients with COVID-19 show that adiposity, diabetes, and hypertension are risk factors for developing severe disease, but so far immunosuppressed patients who are listed as high-risk patients have not been more susceptible to severe COVID-19 than the rest of the population. Multiple clinical trials are currently being conducted, which may identify more drugs that can lower mortality, morbidity, and burden on the society. Several independent studies have convincingly shown that cyclosporine inhibit replication of several different coronaviruses in vitro. The cyclosporine-analog alisporivir has recently been shown to inhibit SARS-CoV-2 in vitro. These findings are intriguing, although there is no clinical evidence for a protective effect to reduce the likelihood of severe COVID-19 or to treat the immune storm or acute respiratory distress syndrome (ARDS) that often causes severe morbidity. Here, we review the putative link between COVID-19 and cyclosporine, while we await more robust clinical data.

The Role of Molecular Chaperones in Virus Infection and Implications for Understanding and Treating COVID-19

The COVID-19 pandemic made imperative the search for means to end it, which requires a knowledge of the mechanisms underpinning the multiplication and spread of its cause, the coronavirus SARS-CoV-2. Many viruses use members of the hosts’ chaperoning system to infect the target cells, replicate, and spread, and here we present illustrative examples. Unfortunately, the role of chaperones in the SARS-CoV-2 cycle is still poorly understood. In this review, we examine the interactions of various coronaviruses during their infectious cycle with chaperones in search of information useful for future research on SARS-CoV-2. We also call attention to the possible role of molecular mimicry in the development of autoimmunity and its widespread pathogenic impact in COVID-19 patients. Viral proteins share highly antigenic epitopes with human chaperones, eliciting anti-viral antibodies that crossreact with the chaperones. Both, the critical functions of chaperones in the infectious cycle of viruses and the possible role of these molecules in COVID-19 autoimmune phenomena, make clear that molecular chaperones are promising candidates for the development of antiviral strategies. These could consist of inhibiting-blocking those chaperones that are necessary for the infectious viral cycle, or those that act as autoantigens in the autoimmune reactions causing generalized destructive effects on human tissues.

Coronavirus: proteomics analysis of chicken kidney tissue infected with variant 2 (IS-1494)-like avian infectious bronchitis virus

Avian infectious bronchitis virus is one of the most important gammacoronaviruses, which causes a highly contagious disease. In this study, we investigated changes in the proteome of kidney tissue of specific-pathogen-free (SPF) chickens that were infected with an isolate of the nephrotropic variant 2 genotype (IS/1494/06) of avian coronavirus. Twenty 1-day-old SPF White Leghorn chickens were randomly divided into two groups, each comprising 10 chickens, which were kept in separate positive-pressure isolators. Chickens in group A served as a virus-free control group up to the end of the experiment, whereas chickens in group B were inoculated with 0.1 ml of 10^4.5 EID₅₀ of the IBV/chicken/Iran/UTIVO-C/2014 isolate of IBV, and kidney tissue samples were collected at 2 and 7 days post-inoculation (dpi) from both groups. Sequencing of five protein spots at 2 dpi and 22 spots at 7 dpi that showed differential expression by two-dimensional electrophoresis (2DE) along with fold change greater than 2 was done by MS-MALDI/TOF/TOF. Furthermore, the corresponding protein-protein interaction (PPI) networks at 2 and 7 dpi were identified to develop a detailed understanding of the mechanism of molecular pathogenesis. Topological graph analysis of this undirected PPI network revealed the effect of 10 genes in the 2 dpi PPI network and nine genes in the 7 dpi PPI network during virus pathogenesis. Proteins that were found by 2DE analysis and MS/TOF-TOF mass spectrometry to be down- or upregulated were subjected to PPI network analysis to identify interactions with other cellular components. The results show that cellular metabolism was altered due to viral infection. Additionally, multifunctional heat shock proteins with a significant role in host cell survival may be employed circuitously by the virus to reach its target. The data from this study suggest that the process of pathogenesis that occurs during avian coronavirus infection involves the regulation of vital cellular processes and the gradual disruption of critical cellular functions.

Host protein chaperones, RNA helicases and the ubiquitin network highlight the arms race for resources between tombusviruses and their hosts

Positive-strand RNA viruses need to arrogate many cellular resources to support their replication and infection cycles. These viruses co-opt host factors, lipids and subcellular membranes and exploit cellular metabolites to built viral replication organelles in infected cells. However, the host cells have their defensive arsenal of factors to protect themselves from easy exploitation by viruses. In this review, the author discusses an emerging arms race for cellular resources between viruses and hosts, which occur during the early events of virus-host interactions. Recent findings with tomato bushy stunt virus and its hosts revealed that the need of the virus to exploit and co-opt given members of protein families provides an opportunity for the host to deploy additional members of the same or associated protein family to interfere with virus replication. Three examples with well-established heat shock protein 70 and RNA helicase protein families and the ubiquitin network will be described to illustrate this model on the early arms race for cellular resources between tombusviruses and their hosts. We predict that arms race for resources with additional cellular protein families will be discovered with tombusviruses. These advances will fortify research on interactions among other plant and animal viruses and their hosts.

Cold Exposure-Induced Up-Regulation of Hsp70 Positively Regulates PEDV mRNA Synthesis and Protein Expression In Vitro

Porcine epidemic diarrhea (PED) is a highly contagious, intestinal infectious disease caused by porcine epidemic diarrhea virus (PEDV). PEDV as an emerging and re-emerging epizootic virus of swine causes substantial economic losses to the pig industry in China and other countries. In China, the occurrence of PED shows significant seasonal variations, usually outbreak during the winter season. The epidemic characteristics of PED may be highly correlated with the changes of ambient temperature. However, molecular mechanism on the seasonal occurrence of PED still remains unclear. It has been widely observed that low ambient temperature up-regulates the expression of host heat shock protein 70 (Hsp70). Here, we showed that nucleotide and protein levels of Hsp70 were up-regulated in the intestinal of cold exposed pig and cold exposed Vero E6 cells. We found that overexpression of Hsp70 could increase PEDV mRNA synthesis and protein expression in Vero E6 and IPEC-J2 cells, while the siRNAs mediated knockdown of Hsp70 and VER155008 mediated inhibition of Hsp70 resulted in inhibition of viral mRNA synthesis and protein expression in Vero E6 cells. These data suggested that Hsp70 positively regulated PEDV mRNA synthesis and protein expression, which being helpful for understanding the seasonality of PED epidemics and development of novel antiviral therapies in the future.

Novel combined biological antiviral agents Cytosinpeptidemycin and Chitosan oligosaccharide induced host resistance and changed movement protein subcellular localization of tobacco mosaic virus

Plant viral diseases cause severe economic losses in agricultural production. Development of microorganism-derived antiviral agents provides an alternative strategy to efficiently control plant viral diseases. In this study, the antiviral effect and mechanism of a combined biological agent Cytosinpeptidemycin and Chitosan oligosaccharide (CytPM-COS) were investigated. CytPM-COS effectively inhibited tobacco mosaic virus (TMV) in Nicotiana glutinosa, suppressed viral RNA and CP accumulation in BY-2 protoplast and affected the subcellular localization as well as punctate formation of TMV MP in N. benthamiana leaves. In addition, CytPM-COS triggered reactive oxygen species (ROS) production and induced up-regulation of various defense responsive genes including PR-1, PR-5, FLS2, Hsp70. Our results indicated that CytPM-COS can potentially act as a pesticide for integrated control of plant viruses in the future.

Effect of heat shock on murine norovirus replication in RAW264.7 cells

Murine norovirus (MNV), is a prevalent pathogen of laboratory mice closely related to human norovirus (HuNoV), a contagious pathogen known to cause gastroenteritis worldwide; however, the mechanism of norovirus replication remains poorly understood. Both heat shock protein 90 (Hsp90) and heat shock protein 70 (Hsp70) play an important role in viral genome replication and viral gene expression. In this study, we first found that heat stress exerted a positive effect on the replication of MNV in the murine macrophage RAW264.7 cell line. Inhibition of Hsp70 and Hsp90 by the specific inhibitors, KNK437 and 17-AGG, respectively showed that Hsp70 and Hsp90 enhanced MNV genome replication and virion production. In addition, we found that KNK437 and 17-AGG could decrease the level of IL-1β, IL-10, and TNF-α mRNA expression in MNV-infected cells. These data suggested that heat stress can positively regulate MNV replication, which advances our understanding of the molecular mechanism of MNV infection.

Stvb-i, a Rice Gene Conferring Durable Resistance to Rice stripe virus, Protects Plant Growth From Heat Stress

Disease resistance is affected by temperature. A rice gene, Stvb-i, is known to have conferred sustained resistance to Rice stripe virus (RSV) despite global warming. Stvb-i protects plants from growth stunting caused by RSV. The underlying resistance mechanism is unclear. Here, Stvb-i showed stable RSV resistance for 20 years in laboratory experiments. This gene encodes a protein distinct from well-studied plant disease-resistance proteins. It has a domain homologous to the histidine kinase/heat-shock protein 90-like ATPase superfamily. Rice has three paralogous genes including Stvb-i. The genes are expressed mainly in meristematic tissues. In the initial period after viral inoculation, RSV multiplication enhanced Stvb-i, whereas Stvb-i suppressed RSV multiplication. Stvb-i silencing inhibited plant growth regardless of viral infection, and silencing of the other paralogous gene that located closely to Stvb-i caused morphological abnormalities. The results suggested that the Stvb-i and its paralogs are related to plant development; especially, Stvb-i supports meristem growth, resulting in plant growth stabilizing. Growth stunting in the Stvb-i-silenced plants was more severe under repetitive heat stress, suggesting that Stvb-i contributed to the attenuation of heat damage in plant development. The symptoms of RSV infection (chlorosis, wilting, stunting, fewer tillers, and defective panicles) were similar to those of heat damage, suggesting that RSV multiplication induces heat-like stress in meristematic cells. Our findings suggest that the mechanism of meristem growth protection conferred by Stvb-i allows plants to withstand both heat stress and RSV multiplication. The suppression of RSV multiplication by the Stvb-i function in meristems results in durable resistance.

Molecular Plant-Plum Pox Virus Interactions

Plum pox virus, the agent that causes sharka disease, is among the most important plant viral pathogens, affecting Prunus trees across the globe. The fabric of interactions that the virus is able to establish with the plant regulates its life cycle, including RNA uncoating, translation, replication, virion assembly, and movement. In addition, plant-virus interactions are strongly conditioned by host specificities, which determine infection outcomes, including resistance. This review attempts to summarize the latest knowledge regarding Plum pox virus-host interactions, giving a comprehensive overview of their relevance for viral infection and plant survival, including the latest advances in genetic engineering of resistant species.

Dynamics of Protein Accumulation from the 3' End of Viral RNA Are Different from Those in the Rest of the Genome in Potato Virus A Infection

One large open reading frame (ORF) encodes 10 potyviral proteins. We compared the accumulation of cylindrical inclusion (CI) protein from the middle, coat protein (CP) from the 3'end, and Renilla luciferase (RLUC) from two distinct locations in potato virus A (PVA) RNA. 5' RLUC was expressed from an rluc gene inserted between the P1 and helper component proteinase (HCPro) cistrons, and 3' RLUC was expressed from the gene inserted between the RNA polymerase and CP cistrons. Viral protein and RNA accumulation were quantitated (i) when expressed from PVA RNA in the presence of ectopically expressed genome-linked viral protein (VPg) and auxiliary proteins and (ii) at different time points during natural infection. The rate and timing of 3' RLUC and CP accumulation were found to be different from those of 5' RLUC and CI. Ectopic expression of VPg boosted PVA RNA, 3' RLUC, and, together with HCPro, CP accumulation, whereas 5' RLUC and CI accumulation remained unaffected regardless of the increased viral RNA amount. In natural infection, the rate of the noteworthy minute early accumulation of 3' RLUC accelerated toward the end of infection. 5' RLUC accumulation, which was already pronounced at 2 days postinfection, increased moderately and stabilized to a constant level by day 5, whereas PVA RNA and CP levels continued to increase throughout the infection. We propose that these observations connect with the mechanisms by which potyvirus infection limits CP accumulation during early infection and specifically supports its accumulation late in infection, but follow-up studies are required to understand the mechanism of how this occurs.IMPORTANCE The results of this study suggest that the dynamics of potyviral protein accumulation are regulated differentially from the 3' end of viral RNA than from the rest of the genome, the significance of which would be to satisfy the needs of replication early and particle assembly late in infection.

Identification of the Novel Host Protein Interacting With the Structural Protein VP1 of Chinese Sacbrood Virus by Yeast Two-Hybrid Screening

Chinese sacbrood virus (CSBV) is the major cause and lead to the collapse of Apis cerana colonies. VP1, the structural protein of CSBV, shows the highest variation in the amino acid sequences among proteins from different CSBV strains as well as exhibits excellent immunogenicity. However, its function with host protein still remains unclear. To clarify its function with host protein, we screened out host cellular proteins that interact with VP1 using the membrane protein yeast two-hybrid system. In addition, we verified interactions between heat shock protein 70 cognate 5 (Hsp70-c5) and VP1 using glutathione S-transferase (GST) pull-down and co-immunoprecipitation assays. VP1 and Hsp70-c5 were colocalized in the cytoplasm and nucleus. Using western blot and real-time polymerase chain reaction (PCR), Hsp70-c5 expression in CSBV-infected larvae was upregulated compared with that in healthy larvae. We observed that when we silenced Hsp70-c5, VP1 expression was significantly downregulated. These results demonstrate that Hsp70-c5 is involved in at least one stage(s) of the viral life cycle.

Genome-Wide Analysis of HSP70 Family Protein in Vigna radiata and Coexpression Analysis Under Abiotic and Biotic Stress

Heat shock protein 70 (Hsp70), a 70-kDa protein, also known as a molecular chaperone, is highly conserved. It plays a major role in cellular functions such as protein folding, regulation of protein degradation, translocation of proteins across membranes, receptor signaling, and protein assembly or disassembly. Vigna radiata is an important legume crop with available whole-genome sequence, but no such study on the HSP70 family is reported. A total of 32 V. radiate HSP70s (Vr-HSP70s) were identified and described. They are phylogenetically clustered into four subgroups. Vr-HSP70s show variations in intron/exon organization. This indicates that introns may play an essential role in gene regulating. The coexpression analysis of Vr-HSP70s revealed that these genes were involved in both abiotic and biotic stresses. Three cytoplasmic hub genes namely Vr-HSP70-C-14, Vr-HSP70-C-29, and Vr-HSP70-C-30 were found common in both stresses. Our findings provide directions for future studies to dissect functional analysis of Vr-HSP70s in response to abiotic and biotic stresses.

A Novel Biological Agent Cytosinpeptidemycin Inhibited the Pathogenesis of Tobacco Mosaic Virus by Inducing Host Resistance and Stress Response

Cytosinpeptidemycin (CytPM) is a microbial pesticide that displayed broad-spectrum antiviral activity against various plant viruses. However, the molecular mechanism underlying antiviral activity of CytPM is poorly understood. In this study, the results demonstrated that CytPM could effectively delay the systemic infection of tobacco mosaic virus (TMV) in Nicotiana benthamiana and significantly inhibit the viral accumulation in tobacco BY-2 protoplasts. Results of RNA-seq indicated that 210 and 120 differential expressed genes (DEGs) were significantly up- and down-regulated after CytPM treatment in BY-2 protoplasts, respectively. In addition, KEGG analysis indicated that various DEGs were involved in endoplasmic reticulum (ER) protein processing, suggesting a possible correlation between ER homeostasis and virus resistance. RT-qPCR was performed to validate the gene expression of crucial DEGs related with defense, stress responses, signaling transduction, and phytohormone, which were consistent with results of RNA-seq. Our works provided valuable insights into the antiviral mechanism of CytPM that induced host resistance to viral infection.

High basal heat-shock protein expression in bats confers resistance to cellular heat/oxidative stress

Bats, unique among mammals with powered flight, have many species with the longest size-proportionate lifespan of all mammals. Evolutionary adaptations would have been required to survive the elevated body temperatures during flight. Heat shock protein (HSP), highly conserved master regulators of cell stress, expression was examined across tissues and various cell lines in bats. Basal expression level of major HSPs (HSP70 and HSP90) is significantly higher in two different bat species compared to other mammals. This HSP expression could be a bat-unique, key factor to modulate cellular stress and death. Consequently, bat cells survive prolonged heat treatment, along with other stress stimuli, in a HSP-dependent manner, whereas other mammalian cells succumbed. This suggests HSP expression in bats could be an important adaption to intrinsic metabolic stresses like flight and therefore an important model to study stress resilience and longevity in general.

Comparative proteomics of Tobacco mosaic virus-infected Nicotiana tabacum plants identified major host proteins involved in photosystems and plant defence

Tobacco mosaic virus (TMV) is a positive single-stranded RNA virus. Its 5' end ORF codes for the replicase proteins, namely 126 kDa and 183 kDa, respectively. These proteins interact with many host proteins to form a virus replication complex (VRC). This study aims to dissect the proteome profile of TMV-infected Nicotiana tabacum in host cellular and molecular pathways. We used the isobaric tags for relative and absolute quantification (iTRAQ) technique to analyse the differential global proteomic profile of TMV infected and mock infected plants. Out of 1897 total proteins, we identified 407 differentially abundant proteins and grouped them into three functional categories, namely metabolism, cellular processes and signalling processing. Our results showed that photosynthesis, carbon metabolism, plant defence, protein synthesis, and protein processing in the endoplasmic reticulum were significantly altered. Carbon metabolism and photosynthesis were present in very low abundance, whereas accumulation of reactive oxygen species and misfolded proteins lead to the accumulation of thioredoxin H-type 1. In conclusion, we identified several key host proteins that are involved in TMV infection/replication in N. tabacum plants. SIGNIFICANCE OF THE STUDY: TMV is one of the most widely studied plant virus. It is used as a tool to study host-virus interaction. There are several host proteins reported that facilitate VRC formation and replication of TMV. However, there is limited knowledge in the expression regulation of these host proteins upon TMV infection. This study is the first report that investigates the response of host protein expression involved in TMV infection through a quantitative proteomics technique iTRAQ, combined with LC-MS/MS analysis. We used TMV-infected Nicotiana tabacum plants to investigate the effects of TMV infection on host proteins. Our results revealed differential abundance of proteins involving various pathways in protein translation, protein processing, photosynthesis and plant defence. There was a high abundance of thioredoxin H-type 1, a protein that counters oxidative stress and accelerated regulation of fatty acid synthesis to provide additional lipid molecules for VRC formation. There was a significant reduction in abundance of psaA and psbB proteins in the photosynthetic pathways. Our results identified key candidate host proteins involved in TMV-infected N. tabacum for functional studies in future.

CRISPR/Cas9-Mediated Knockout of DNAJC14 Verifies This Chaperone as a Pivotal Host Factor for RNA Replication of Pestiviruses

Pestiviruses like bovine viral diarrhea virus (BVDV) are a threat to livestock. For pestiviruses, cytopathogenic (cp) and noncytopathogenic (noncp) strains are distinguished in cell culture. The noncp biotype of BVDV is capable of establishing persistent infections, which is a major problem in disease control. The noncp biotype rests on temporal control of viral RNA replication, mediated by regulated cleavage of nonstructural protein 2-3 (NS2-3). This cleavage is catalyzed by the autoprotease in NS2, the activity of which depends on its cellular cofactor, DNAJC14. Since this chaperone is available in small amounts and binds tightly to NS2, NS2-3 translated later in infection is no longer cleaved. As NS3 is an essential constituent of the viral replicase, this shift in polyprotein processing correlates with downregulation of RNA replication. In contrast, cp BVDV strains arising mostly by RNA recombination show highly variable genome structures and display unrestricted NS3 release. The functional importance of DNAJC14 for noncp pestiviruses has been established so far only for BVDV-1. It was therefore enigmatic whether replication of other noncp pestiviruses is also DNAJC14 dependent. By generating bovine and porcine DNAJC14 knockout cells, we could show that (i) replication of 6 distinct noncp pestivirus species (A to D, F, and G) depends on DNAJC14, (ii) the pestiviral replicase NS3-5B can assemble into functional complexes in the absence of DNAJC14, and (iii) all cp pestiviruses replicate their RNA and generate infectious progeny independent of host DNAJC14. Together, these findings confirm DNAJC14 as a pivotal cellular cofactor for the replication and maintenance of the noncp biotype of pestiviruses.IMPORTANCE Only noncp pestivirus strains are capable of establishing life-long persistent infections to generate the virus reservoir in the field. The molecular basis for this biotype is only partially understood and only investigated in depth for BVDV-1 strains. Temporal control of viral RNA replication correlates with the noncp biotype and is mediated by limiting amounts of cellular DNAJC14 that activate the viral NS2 protease to catalyze the release of the essential replicase component NS3. Here, we demonstrate that several species of noncp pestiviruses depend on DNAJC14 for their RNA replication. Moreover, all cp pestiviruses, in sharp contrast to their noncp counterparts, replicate independently of DNAJC14. The generation of a cp BVDV in the persistently infected animal is causative for onset of mucosal disease. Therefore, the observed strict biotype-specific difference in DNAJC14 dependency should be further examined for its role in cell type/tissue tropism and the pathogenesis of this lethal disease.

Inhibition of Hepatitis C Replication by Targeting the Molecular Chaperone Hsp90: Synthesis and Biological Evaluation of 4,5,6,7-Tetrahydrobenzo[1,2-d]thiazole Derivatives

Cellular chaperones that belong to the heat-shock protein 90 (Hsp90) family are a prerequisite for successful viral propagation for most viruses. The hepatitis C virus (HCV) uses Hsp90 for maturation, folding, and modification of viral proteins. Based on our previous discovery that marine alkaloid analogues with a 4,5,6,7-tetrahydrobenzo[1,2-d]thiazole-2-amine structure show inhibition of HCV replication and binding to Hsp90, a series of twelve novel compounds based on this scaffold was designed and synthesized. The aim was improved Hsp90 affinity and anti-HCV activity. Through structural optimization, improved binding to Hsp90 and specific HCV inhibition in genotype 1b and 2a replicon models was achieved for three compounds belonging to the newly synthesized series. Furthermore, these compounds efficiently inhibited replication of full-length HCV genotype 2a in a reporter virus RNA assay with IC₅₀ values ranging from 0.03 to 0.6 μm.

Antiviral and Anti-Inflammatory Activities of Pochonin D, a Heat Shock Protein 90 Inhibitor, against Rhinovirus Infection

Human rhinoviruses (HRV) are one of the major causes of common cold in humans and are also associated with acute asthma and bronchial illness. Heat-shock protein 90 (Hsp90), a molecular chaperone, is an important host factor for the replication of single-strand RNA viruses. In the current study, we examined the effect of the Hsp90 inhibitor pochonin D, in vitro and in vivo, using a murine model of human rhinovirus type 1B (HRV1B) infection. Our data suggested that Hsp90 inhibition significantly reduced the inflammatory cytokine production and lung damage caused by HRV1B infection. The viral titer was significantly lowered in HRV1B-infected lungs and in Hela cells upon treatment with pochonin D. Infiltration of innate immune cells including granulocytes and monocytes was also reduced in the bronchoalveolar lavage (BAL) by pochonin D treatment after HRV1B infection. Histological analysis of the lung and respiratory tract showed that pochonin D protected the mice from HRV1B infection. Collectively, our results suggest that the Hsp90 inhibitor, pochonin D, could be an attractive antiviral therapeutic for treating HRV infection.

Comparative Characterization of the Sindbis Virus Proteome from Mammalian and Invertebrate Hosts Identifies nsP2 as a Component of the Virion and Sorting Nexin 5 as a Significant Host Factor for Alphavirus Replication

Recent advances in mass spectrometry methods and instrumentation now allow for more accurate identification of proteins in low abundance. This technology was applied to Sindbis virus, the prototypical alphavirus, to investigate the viral proteome. To determine if host proteins are specifically packaged into alphavirus virions, Sindbis virus (SINV) was grown in multiple host cells representing vertebrate and mosquito hosts, and total protein content of purified virions was determined. This analysis identified host factors not previously associated with alphavirus entry, replication, or egress. One host protein, sorting nexin 5 (SNX5), was shown to be critical for the replication of three different alphaviruses, Sindbis, Mayaro, and Chikungunya viruses. The most significant finding was that in addition to the host proteins, SINV nonstructural protein 2 (nsP2) was detected within virions grown in all host cells examined. The protein and RNA-interacting capabilities of nsP2 coupled with its presence in the virion support a role for nsP2 during packaging and/or entry of progeny virus. This function has not been identified for this protein. Taken together, this strategy identified at least one host factor integrally involved in alphavirus replication. Identification of other host proteins provides insight into alphavirus-host interactions during viral replication in both vertebrate and invertebrate hosts. This method of virus proteome analysis may also be useful for the identification of protein candidates for host-based therapeutics.

IMPORTANCE Pathogenic alphaviruses, such as Chikungunya and Mayaro viruses, continue to plague public health in developing and developed countries alike. Alphaviruses belong to a group of viruses vectored in nature by hematophagous (blood-feeding) insects and are termed arboviruses (arthropod-borne viruses). This group of viruses contains many human pathogens, such as dengue fever, West Nile, and Yellow fever viruses. With few exceptions, there are no vaccines or prophylactics for these agents, leaving one-third of the world population at risk of infection. Identifying effective antivirals has been a long-term goal for combating these diseases not only because of the lack of vaccines but also because they are effective during an ongoing epidemic. Mass spectrometry-based analysis of the Sindbis virus proteome can be effective in identifying host genes involved in virus replication and novel functions for virus proteins. Identification of these factors is invaluable for the prophylaxis of this group of viruses.