Vaccinia virus infection induces a stress response that leads to association of Hsp70 with viral proteins

Viral Infections and Their Ability to Modulate Endoplasmic Reticulum Stress Response Pathways

In eukaryotic cells, the endoplasmic reticulum is particularly important in post-translational modification of proteins before they are released extracellularly or sent to another endomembrane system. The correct three-dimensional folding of most proteins occurs in the ER lumen, which has an oxidative environment that is essential for the formation of disulfide bridges, which are important in maintaining protein structure. The ER is a versatile organelle that ensures the correct structure of proteins and is essential in the synthesis of lipids and sterols, in addition to offering support in the maintenance of intracellular calcium. Consequently, the cells needed to respond to demands caused by physiological conditions and pathological disturbances in the organelle homeostasis, leading to proper functioning of the cell or even programmed cell death. Disturbances to the ER function trigger a response to the accumulation of unfolded or misfolded proteins, known as the unfolded protein response. Such disturbances include abiotic stress, pharmacological agents, and intracellular pathogens, such as viruses. When misfolded proteins accumulate in the ER, they can undergo ubiquitination and proteasomal degradation through components of the ER-associated degradation system. Once a prolonged activity of the UPR pathway occurs, indicating that homeostasis cannot be reestablished, components of this pathway induce cell death by apoptosis. Here, we discuss how viruses have evolved ways to counteract UPR responses to maximize replication. This evolutionary viral ability is important to understand cell pathology and should be taken into account when designing therapeutic interventions and vaccines.

Genotype-environment associations reveal genes potentially linked to avian malaria infection in populations of an endemic island bird

Patterns of pathogen prevalence are, at least partially, the result of coevolutionary host-pathogen interactions. Thus, exploring the distribution of host genetic variation in relation to infection by a pathogen within and across populations can provide important insights into mechanisms of host defence and adaptation. Here, we use a landscape genomics approach (Bayenv) in conjunction with genome-wide data (ddRADseq) to test for associations between avian malaria (Plasmodium) prevalence and host genetic variation across 13 populations of the island endemic Berthelot's pipit (Anthus berthelotii). Considerable and consistent spatial heterogeneity in malaria prevalence was observed among populations over a period of 15 years. The prevalence of malaria infection was also strongly positively correlated with pox (Avipoxvirus) prevalence. Multiple host loci showed significant associations with malaria prevalence after controlling for genome-wide neutral genetic structure. These sites were located near to or within genes linked to metabolism, stress response, transcriptional regulation, complement activity and the inflammatory response, many previously implicated in vertebrate responses to malarial infection. Our findings identify diverse genes - not just limited to the immune system - that may be involved in host protection against malaria and suggest that spatially variable pathogen pressure may be an important evolutionary driver of genetic divergence among wild animal populations, such as Berthelot's pipit. Furthermore, our data indicate that spatio-temporal variation in multiple different pathogens (e.g. malaria and pox in this case) may have to be studied together to develop a more holistic understanding of host pathogen-mediated evolution.

New Insights into the Role and Therapeutic Potential of Heat Shock Protein 70 in Bovine Viral Diarrhea Virus Infection

Bovine viral diarrhea virus (BVDV), a positive-strand RNA virus of the genus Pestivirus in the Flaviviridae family, is the causative agent of bovine viral diarrhea-mucosal disease (BVD-MD). BVDV's unique virion structure, genome, and replication mechanism in the Flaviviridae family render it a useful alternative model for evaluating the effectiveness of antiviral drugs used against the hepatitis C virus (HCV). As one of the most abundant and typical heat shock proteins, HSP70 plays an important role in viral infection caused by the family Flaviviridae and is considered a logical target of viral regulation in the context of immune escape. However, the mechanism of HSP70 in BVDV infection and the latest insights have not been reported in sufficient detail. In this review, we focus on the role and mechanisms of HSP70 in BVDV-infected animals/cells to further explore the possibility of targeting this protein for antiviral therapy during viral infection.

Mode of Action of Heat Shock Protein (HSP) Inhibitors against Viruses through Host HSP and Virus Interactions

Misfolded proteins after stress-induced denaturation can regain their functions through correct re-folding with the aid of molecular chaperones. As a molecular chaperone, heat shock proteins (HSPs) can help client proteins fold correctly. During viral infection, HSPs are involved with replication, movement, assembly, disassembly, subcellular localization, and transport of the virus via the formation of macromolecular protein complexes, such as the viral replicase complex. Recent studies have indicated that HSP inhibitors can inhibit viral replication by interfering with the interaction of the virus with the HSP. In this review, we describe the function and classification of HSPs, the transcriptional mechanism of HSPs promoted by heat shock factors (HSFs), discuss the interaction between HSPs and viruses, and the mode of action of HSP inhibitors at two aspects of inhibiting the expression of HSPs and targeting the HSPs, and elaborate their potential use as antiviral agents.

Tumor Temperature: Friend or Foe of Virus-Based Cancer Immunotherapy

The temperature of a solid tumor is often dissimilar to baseline body temperature and, compared to healthy tissues, may be elevated, reduced, or a mix of both. The temperature of a tumor is dependent on metabolic activity and vascularization and can change due to tumor progression, treatment, or cancer type. Despite the need to function optimally within temperature-variable tumors, oncolytic viruses (OVs) are primarily tested at 37 °C in vitro. Furthermore, animal species utilized to test oncolytic viruses, such as mice, dogs, cats, and non-human primates, poorly recapitulate the temperature profile of humans. In this review, we discuss the importance of temperature as a variable for OV immunotherapy of solid tumors. Accumulating evidence supports that the temperature sensitivity of OVs lies on a spectrum, with some OVs likely hindered but others enhanced by elevated temperatures. We suggest that in vitro temperature sensitivity screening be performed for all OVs destined for the clinic to identify potential hinderances or benefits with regard to elevated temperature. Furthermore, we provide recommendations for the clinical use of temperature and OVs.

Genomic associations with poxvirus across divergent island populations in Berthelot's pipit

Understanding the mechanisms and genes that enable animal populations to adapt to pathogens is important from an evolutionary, health and conservation perspective. Berthelot's pipit (Anthus berthelotii) experiences extensive and consistent spatial heterogeneity in avian pox infection pressure across its range of island populations, thus providing an excellent system with which to examine how pathogen-mediated selection drives spatial variation in immunogenetic diversity. Here we test for evidence of genetic variation associated with avian pox at both an individual and population-level. At the individual level, we find no evidence that variation in MHC class I and TLR4 (both known to be important in recognising viral infection) was associated with pox infection within two separate populations. However, using genotype-environment association (Bayenv) in conjunction with genome-wide (ddRAD-seq) data, we detected strong associations between population-level avian pox prevalence and allele frequencies of single nucleotide polymorphisms (SNPs) at a number of sites across the genome. These sites were located within genes involved in cellular stress signalling and immune responses, many of which have previously been associated with responses to viral infection in humans and other animals. Consequently, our analyses indicates that pathogen-mediated selection may play a role in shaping genomic variation among relatively recently colonised island bird populations and highlights the utility of genotype-environment associations for identifying candidate genes potentially involved in host-pathogen interactions.

Diversity in heat shock protein families: functional implications in virus infection with a comprehensive insight of their role in the HIV-1 life cycle

Heat shock proteins (HSPs) are a group of cellular proteins that are induced during stress conditions such as heat stress, cold shock, UV irradiation and even pathogenic insult. They are classified into families based on molecular size like HSP27, 40, 70 and 90 etc, and many of them act as cellular chaperones that regulate protein folding and determine the fate of mis-folded or unfolded proteins. Studies have also shown multiple other functions of these proteins such as in cell signalling, transcription and immune response. Deregulation of these proteins leads to devastating consequences, such as cancer, Alzheimer's disease and other life threatening diseases suggesting their potential importance in life processes. HSPs exist in multiple isoforms, and their biochemical and functional characterization still remains a subject of active investigation. In case of viral infections, several HSP isoforms have been documented to play important roles with few showing pro-viral activity whereas others seem to have an anti-viral role. Earlier studies have demonstrated that HSP40 plays a pro-viral role whereas HSP70 inhibits HIV-1 replication; however, clear isoform-specific functional roles remain to be established. A detailed functional characterization of all the HSP isoforms will uncover their role in cellular homeostasis and also may highlight some of them as potential targets for therapeutic strategies against various viral infections. In this review, we have tried to comprehend the details about cellular HSPs and their isoforms, their role in cellular physiology and their isoform-specific functions in case of virus infection with a specific focus on HIV-1 biology.

Kinetically distinct processing pathways diversify the CD8+ T cell response to a single viral epitope

The source proteins from which CD8⁺ T cell-activating peptides are derived remain enigmatic. Glycoproteins are particularly challenging in this regard owing to several potential trafficking routes within the cell. By engineering a glycoprotein-derived epitope to contain an N-linked glycosylation site, we determined that optimal CD8⁺ T cell expansion and function were induced by the peptides that are rapidly produced from the exceedingly minor fraction of protein mislocalized to the cytosol. In contrast, peptides derived from the much larger fraction that undergoes translocation and quality control are produced with delayed kinetics and induce suboptimal CD8⁺ T cell responses. This dual system of peptide generation enhances CD8⁺ T cell participation in diversifying both antigenicity and the kinetics of peptide display.

Comparison of Multiplexed Immunofluorescence Imaging to Chromogenic Immunohistochemistry of Skin Biomarkers in Response to Monkeypox Virus Infection

Over the last 15 years, advances in immunofluorescence-imaging based cycling methods, antibody conjugation methods, and automated image processing have facilitated the development of a high-resolution, multiplexed tissue immunofluorescence (MxIF) method with single cell-level quantitation termed Cell DIVETM. Originally developed for fixed oncology samples, here it was evaluated in highly fixed (up to 30 days), archived monkeypox virus-induced inflammatory skin lesions from a retrospective study in 11 rhesus monkeys to determine whether MxIF was comparable to manual H-scoring of chromogenic stains. Six protein markers related to immune and cellular response (CD68, CD3, Hsp70, Hsp90, ERK1/2, ERK1/2 pT202_pY204) were manually quantified (H-scores) by a pathologist from chromogenic IHC double stains on serial sections and compared to MxIF automated single cell quantification of the same markers that were multiplexed on a single tissue section. Overall, there was directional consistency between the H-score and the MxIF results for all markers except phosphorylated ERK1/2 (ERK1/2 pT202_pY204), which showed a decrease in the lesion compared to the adjacent non-lesioned skin by MxIF vs an increase via H-score. Improvements to automated segmentation using machine learning and adding additional cell markers for cell viability are future options for improvement. This method could be useful in infectious disease research as it conserves tissue, provides marker colocalization data on thousands of cells, allowing further cell level data mining as well as a reduction in user bias.

Induction of pro-viral grass carp Ctenopharyngodon idella Hsp70 instead of Hsc70 during infection of grass carp reovirus

Grass carp Ctenopharyngodon idella Hsp70 has been identified to play a functional role in viral attachment of type III grass carp reovirus, GCRV-104. However, it remains to be clarified whether Hsc70, sharing 86% identity with Hsp70, plays a similar role during viral infection. In this study, grass carp Hsp70 was shown to be induced by GCRV-104 in different grass carp cell lines, whereas Hsc70 was expressed in a relatively constant level during the infection. The expression patterns of Hsc70 and Hsp70 were similar to their homologs in mammals. Notably, both inhibitor and over-expression assays indicated that Hsp70 was required for efficient viral replication. Thus, our study supported a novel pro-viral property of Hsp70 besides its reported role in the viral attachment. Results herein presented also suggested that the heat shock response of grass carp might be manipulated by aquareovirus to facilitate its replication in fish cells.

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.

Shrimp miR-34 from Shrimp Stress Response to Virus Infection Suppresses Tumorigenesis of Breast Cancer

During host stress response against virus infection, some animal microRNAs (miRNAs) can be upregulated to restore the virus-caused metabolic disorder of host cells via suppressing the expressions of miRNAs' target genes. These antiviral miRNAs may have antitumor capacity, because tumorigenesis results from metabolic disorder of cells. However, this subject has not been explored. In this study, the results showed that shrimp miR-34, which was upregulated during white spot syndrome virus (WSSV) infection, had antiviral activity in shrimp. The expression of shrimp miR-34 in breast cancer cells and in mice suppressed the growth and metastasis of breast cancer by targeting human CCND1, CDK6, CCNE2, E2F3, FOSL1, and MET genes in a cross-phylum manner. The results of this study indicated that miRNAs with antiviral activities can be promising sources for antitumor drug discovery.

Protein Primary Structure of the Vaccinia Virion at Increased Resolution

Here we examine the protein covalent structure of the vaccinia virus virion. Within two virion preparations, >88% of the theoretical vaccinia virus-encoded proteome was detected with high confidence, including the first detection of products from 27 open reading frames (ORFs) previously designated "predicted," "uncharacterized," "inferred," or "hypothetical" polypeptides containing as few as 39 amino acids (aa) and six proteins whose detection required nontryptic proteolysis. We also detected the expression of four short ORFs, each of which was located within an ORF ("ORF-within-ORF"), including one not previously recognized or known to be expressed. Using quantitative mass spectrometry (MS), between 58 and 74 proteins were determined to be packaged. A total of 63 host proteins were also identified as candidates for packaging. Evidence is provided that some portion of virion proteins are "nicked" via a combination of endoproteolysis and concerted exoproteolysis in a manner, and at sites, independent of virus origin or laboratory procedures. The size of the characterized virion phosphoproteome was doubled from 189 (J. Matson, W. Chou, T. Ngo, and P. D. Gershon, Virology 452-453:310-323, 2014, doi:http://dx.doi.org/10.1016/j.virol.2014.01.012) to 396 confident, unique phosphorylation sites, 268 of which were within the packaged proteome. This included the unambiguous identification of phosphorylation "hot spots" within virion proteins. Using isotopically enriched ATP, 23 sites of intravirion kinase phosphorylation were detected within nine virion proteins, all at sites already partially occupied within the virion preparations. The clear phosphorylation of proteins RAP94 and RP19 was consistent with the roles of these proteins in intravirion early gene transcription. In a blind search for protein modifications, cysteine glutathionylation and O-linked glycosylation featured prominently. We provide evidence for the phosphoglycosylation of vaccinia virus proteins.

IMPORTANCE

Poxviruses are among the most complex and irregular virions, about whose internal structure little is known. To better understand poxvirus virion structure, imaging should be supplemented with other tools. Here, we provide a deep study of the covalent structure of the vaccinia virus virion using the various tools of contemporary mass spectrometry.

Stress Beyond Translation: Poxviruses and More

Poxviruses are large double-stranded DNA viruses that form viral factories in the cytoplasm of host cells. These viruses encode their own transcription machinery, but rely on host translation for protein synthesis. Thus, poxviruses have to cope with and, in most cases, reprogram host translation regulation. Granule structures, called antiviral granules (AVGs), have been observed surrounding poxvirus viral factories. AVG formation is associated with abortive poxvirus infection, and AVGs contain proteins that are typically found in stress granules (SGs). With certain mutant poxviruses lack of immunoregulatory factor(s), we can specifically examine the mechanisms that drive the formation of these structures. In fact, cytoplasmic macromolecular complexes form during many viral infections and contain sensing molecules that can help reprogram transcription. More importantly, the similarity between AVGs and cytoplasmic structures formed during RNA and DNA sensing events prompts us to reconsider the cause and consequence of these AVGs. In this review, we first summarize recent findings regarding how poxvirus manipulates host translation. Next, we compare and contrast SGs and AVGs. Finally, we review recent findings regarding RNA- and especially DNA-sensing bodies observed during viral infection.

The master regulator of the cellular stress response (HSF1) is critical for orthopoxvirus infection

The genus Orthopoxviridae contains a diverse group of human pathogens including monkeypox, smallpox and vaccinia. These viruses are presumed to be less dependent on host functions than other DNA viruses because they have large genomes and replicate in the cytoplasm, but a detailed understanding of the host factors required by orthopoxviruses is lacking. To address this topic, we performed an unbiased, genome-wide pooled RNAi screen targeting over 17,000 human genes to identify the host factors that support orthopoxvirus infection. We used secondary and tertiary assays to validate our screen results. One of the strongest hits was heat shock factor 1 (HSF1), the ancient master regulator of the cytoprotective heat-shock response. In investigating the behavior of HSF1 during vaccinia infection, we found that HSF1 was phosphorylated, translocated to the nucleus, and increased transcription of HSF1 target genes. Activation of HSF1 was supportive for virus replication, as RNAi knockdown and HSF1 small molecule inhibition prevented orthopoxvirus infection. Consistent with its role as a transcriptional activator, inhibition of several HSF1 targets also blocked vaccinia virus replication. These data show that orthopoxviruses co-opt host transcriptional responses for their own benefit, thereby effectively extending their functional genome to include genes residing within the host DNA. The dependence on HSF1 and its chaperone network offers multiple opportunities for antiviral drug development.

Inhibition of HSP90 attenuates porcine reproductive and respiratory syndrome virus production in vitro

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) infection leads to substantial economic losses to the swine industry worldwide. However, no effective countermeasures exist to combat this virus infection so far. The most common antiviral strategy relies on directly inhibiting viral proteins. However, this strategy invariably leads to the emergence of drug resistance due to the error-prone nature of viral ploymerase. Targeting cellular proteins required for viral infection for developing new generation of antivirals is gaining concern. Recently, heat shock protein 90 (HSP90) was found to be an important host factor for the replication of multiple viruses and the inhibition of HSP90 showed significant antiviral effects. It is thought that the inhibition of HSP90 could be a promising broad-range antiviral approach. However, the effects of HSP90 inhibition on PRRSV infection have not been evaluated. In the current research, we tried to inhibit HSP90 and test whether the inhibition affect PRRSV infection.

Methods

We inhibit the function of HSP90 with two inhibitors, geldanamycin (GA) and 17- allylamono-demethoxygeldanamycin (17-AAG), and down-regulated the expression of endogenous HSP90 with specific small-interfering RNAs (siRNAs). Cell viability was measured with alamarBlue. The protein level of viral N was determined by western blotting and indirect immunofluorescence (IFA). Besides, IFA was employed to examine the level of viral double-stranded RNA (dsRNA). The viral RNA copy number and the level of IFN-β mRNA were determined by quantitative real-time PCR (qRT-PCR).

Results

Our results indicated that both HSP90 inhibitors showed strong anti-PRRSV activity. They could reduce viral production by preventing the viral RNA synthesis. These inhibitory effects were not due to the activation of innate interferon response. In addition, we observed that individual knockdown targeting HSP90α or HSP90β did not show dramatic inhibitory effect. Combined knockdown of these two isoforms was required to reduce viral infection.

Conclusions

Our results shed light on the possibility of developing potential therapeutics targeting HSP90 against PRRSV infection.

The D10 decapping enzyme of vaccinia virus contributes to decay of cellular and viral mRNAs and to virulence in mice

Posttranscriptional mechanisms are important for regulation of cellular and viral gene expression. The presence of the 5' cap structure m(7)G(5')ppp(5')Nm is a general feature of mRNAs that provides protection from exoribonuclease digestion and enhances translation. Vaccinia virus and other poxviruses encode enzymes for both cap synthesis and decapping. Decapping is mediated by two related enzymes, D9 and D10, which are synthesized before and after viral DNA replication, respectively. The timing of D10 synthesis correlates better with the shutdown of host gene expression, and deletion of this gene has been shown to cause persistence of host and viral mRNAs in infected cells. Here, we constructed specific mutant viruses in which translation of D10 was prevented by stop codons or activity of D10 was abrogated by catalytic site mutations, without other genomic alterations. Both mutants formed plaques of normal size and replicated to similar extents as the parental virus in monkey epithelial cells and mouse embryonic fibroblasts. The synthesis of viral proteins was slightly delayed, and cellular and viral mRNAs persisted longer in cells infected with the mutants compared to either the parental virus or clonal revertant. Despite the mild effects in vitro, both mutants were more attenuated than the revertants in intranasal and intraperitoneal mouse models, and less infectious virus was recovered from organs. In addition, there was less lung histopathology following intranasal infection with mutant viruses. These data suggest that the D10 decapping enzyme may help restrict antiviral responses by accelerating host mRNA degradation during poxvirus infection.

Hsp70 positively regulates porcine circovirus type 2 replication in vitro

The Hsp70 chaperone plays a central role in multiple processes within cells. Porcine circovirus type 2 (PCV2) is the essential causal agent of post-weaning multisystemic wasting syndrome (PMWS), which has spread worldwide. But the mechanism of PCV2 replication remains poorly understood. In this study, we firstly found the positive effect of heat stress on the replication of PCV2 in the continuous porcine monocytic cell line 3D4/31. Downregulation of Hsp70 by the specific chaperone inhibitor Quercetin or RNA interference and upregulation of Hsp70 by expression from a recombinant adenovirus showed that Hsp70 enhanced PCV2 genome replication and virion production. A specific interaction between Hsp70 and PCV2 Cap was confirmed by colocalization by confocal microscopy and co-immunoprecipitation. Furthermore, the NF-κB pathway was activated and caspase-3 activity was reduced when Hsp70 was overexpressed in PCV2-infected 3D4/31 cells. These data suggested that Hsp70 positively regulated PCV2 replication, which being helpful for understanding the molecular mechanism of PCV2 infection.

Proteomic analysis of purified Newcastle disease virus particles

Background

Newcastle disease virus (NDV) is an enveloped RNA virus, bearing severe economic losses to the poultry industry worldwide. Previous virion proteomic studies have shown that enveloped viruses carry multiple host cellular proteins both internally and externally during their life cycle. To address whether it also occurred during NDV infection, we performed a comprehensive proteomic analysis of highly purified NDV La Sota strain particles.

Results

In addition to five viral structural proteins, we detected thirty cellular proteins associated with purified NDV La Sota particles. The identified cellular proteins comprised several functional categories, including cytoskeleton proteins, annexins, molecular chaperones, chromatin modifying proteins, enzymes-binding proteins, calcium-binding proteins and signal transduction-associated proteins. Among these, three host proteins have not been previously reported in virions of other virus families, including two signal transduction-associated proteins (syntenin and Ras small GTPase) and one tumor-associated protein (tumor protein D52). The presence of five selected cellular proteins (i.e., β-actin, tubulin, annexin A2, heat shock protein Hsp90 and ezrin) associated with the purified NDV particles was validated by Western blot or immunogold labeling assays.

Conclusions

The current study presented the first standard proteomic profile of NDV. The results demonstrated the incorporation of cellular proteins in NDV particles, which provides valuable information for elucidating viral infection and pathogenesis.

Hsp70 protein positively regulates rabies virus infection

The Hsp70 chaperone plays a central role in multiple processes within cells, including protein translation, folding, intracellular trafficking, and degradation. This protein is implicated in the replication of numerous viruses. We have shown that rabies virus infection induced the cellular expression of Hsp70, which accumulated in Negri body-like structures, where viral transcription and replication take place. In addition, Hsp70 is present in both nucleocapsids purified from infected cells and in purified virions. Hsp70 has been shown to interact with the nucleoprotein N. The downregulation of Hsp70, using specific chaperone inhibitors, such as quercetin or RNA interference, resulted in a significant decrease of the amount of viral mRNAs, viral proteins, and virus particles. These results indicate that Hsp70 has a proviral function during rabies virus infection and suggest that Hsp70 is involved in at least one stage(s) of the viral life cycle, such as viral transcription, translation, and/or production. The mechanism by which Hsp70 controls viral infection will be discussed.

Broad action of Hsp90 as a host chaperone required for viral replication

Viruses are intracellular pathogens responsible for a vast number of human diseases. Due to their small genome size, viruses rely primarily on the biosynthetic apparatus of the host for their replication. Recent work has shown that the molecular chaperone Hsp90 is nearly universally required for viral protein homeostasis. As observed for many endogenous cellular proteins, numerous different viral proteins have been shown to require Hsp90 for their folding, assembly, and maturation. Importantly, the unique characteristics of viral replication cause viruses to be hypersensitive to Hsp90 inhibition, thus providing a novel therapeutic avenue for the development of broad-spectrum antiviral drugs. The major developments in this emerging field are hereby discussed. This article is part of a Special Issue entitled: Heat Shock Protein 90 (HSP90).

Human immunodeficiency virus-1 Nef suppresses Hsp70-mediated Tat activation

The human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) contains binding sites for several host transcription factors that contribute to HIV-1 gene expression. Although previous reports have indicated that HIV-1 Nef positively or negatively regulates HIV-1 gene expression, the precise molecular mechanisms by which this occurs remain largely unknown. In this study, we report that Nef suppressed LTR-driven transcription only in the presence of HIV-1 Tat, which was localized to the cytoplasm and degraded by the proteasome. However, the depletion of Hsp70 was found to reduce the suppressive effect of Nef on HIV-1 gene expression. These results suggest that Nef suppresses Hsp70-mediated HIV-1 Tat activation.

Proteomic characterization of influenza H5N1 virus-like particles and their protective immunogenicity

Recombinant virus-like particles (VLPs) have been shown to induce protective immunity. Despite their potential significance as promising vaccine candidates, the protein composition of VLPs produced in insect cells has not been well characterized. Here we report a proteomic analysis of influenza VLPs containing hemagglutinin (HA) and matrix M1 proteins from a human isolate of avian influenza H5N1 virus (H5 VLPs) produced in insect cells using the recombinant baculovirus expression system. Comprehensive proteomic analysis of purified H5 VLPs identified viral proteins and 37 additional host-derived proteins, many of which are known to be present in other enveloped viruses. Proteins involved in different cellular structures and functions were found to be present in H5 VLPs including those from the cytoskeleton, translation, chaperone, and metabolism. Immunization with purified H5 VLPs induced protective immunity, which was comparable to the inactivated whole virus containing all viral components. Unpurified H5 VLPs containing excess amounts of noninfluenza soluble proteins also conferred 100% protection against lethal challenge although lower immune responses were induced. These results provide important implications consistent with the idea that VLP production in insect cells may involve similar cellular machinery as other RNA enveloped viruses during synthesis, assembly, trafficking, and budding processes.

An RNA symbiont enhances heat tolerance and secondary homothallism in the oomycete Phytophthora infestans

Some strains ofPhytophthora infestans,the potato late blight pathogen, harbour a small extrachromosomal RNA called PiERE1. A previous study reported that this RNA symbiont does not noticeably affect its host. Here it is revealed that PiERE1 exerts subtle effects onP. infestans, which result in greater thermotolerance during growth and an increase in secondary homothallism, i.e. oospore formation in the absence of the opposite mating type. The interaction can be considered mutualistic since these traits may increase the fitness ofP. infestansin nature. Assays of biomarkers for cellular stress revealed that an Hsp70 chaperone was upregulated by PiERE1. A genome-wide search for more members of the Hsp70 family identified ten belonging to the DnaK subfamily, one in the Hsp110/SSE subfamily, and pseudogenes. Four DnaK subfamily genes encoding predicted cytoplasmic or endoplasmic reticulum proteins were upregulated in strains harbouring PiERE1. This may explain the greater thermotolerance conferred by the RNA element, and suggests that Hsp70 may be a useful biomarker for testing organisms for the cellular effects of symbiotic elements.

Proteomic analysis of purified coronavirus infectious bronchitis virus particles

BACKGROUND

Infectious bronchitis virus (IBV) is the coronavirus of domestic chickens causing major economic losses to the poultry industry. Because of the complexity of the IBV life cycle and the small number of viral structural proteins, important virus-host relationships likely remain to be discovered. Toward this goal, we performed two-dimensional gel electrophoresis fractionation coupled to mass spectrometry identification approaches to perform a comprehensive proteomic analysis of purified IBV particles.

RESULTS

Apart from the virus-encoded structural proteins, we detected 60 host proteins in the purified virions which can be grouped into several functional categories including intracellular trafficking proteins (20%), molecular chaperone (18%), macromolcular biosynthesis proteins (17%), cytoskeletal proteins (15%), signal transport proteins (15%), protein degradation (8%), chromosome associated proteins (2%), ribosomal proteins (2%), and other function proteins (3%). Interestingly, 21 of the total host proteins have not been reported to be present in virions of other virus families, such as major vault protein, TENP protein, ovalbumin, and scavenger receptor protein. Following identification of the host proteins by proteomic methods, the presence of 4 proteins in the purified IBV preparation was verified by western blotting and immunogold labeling detection.

CONCLUSIONS

The results present the first standard proteomic profile of IBV and may facilitate the understanding of the pathogenic mechanisms.

Role of Heat Shock Proteins in Viral Infection

One of the most intriguing and less known aspects of the interaction between viruses and their host is the impact of the viral infection on the heat shock response (HSR). While both a positive and a negative role of different heat shock proteins (HSP) in the control of virus replication has been hypothesized, HSP function during the virus replication cycle is still not well understood. This chapter describes different aspects of the interactions between viruses and heat shock proteins during infection of mammalian cells: the first part focuses on the modulation of the heat shock response by human viral pathogens; the second describes the interactions of HSP and other chaperones with viral components, and their function during different steps of the virus replication cycle; the last part summarizes our knowledge on the effect of hyperthermia and HSR modulators on virus replication.

HSP70 induced by Hantavirus infection interacts with viral nucleocapsid protein and its overexpression suppresses virus infection in Vero E6 cells

Hantavirus (HTV) infection is known to induce innate cellular response, a more specified cellular response in the host cells. However, whether it stimulates synthesis of stress proteins, particularly associations of viral proteins, is entirely unknown. The primary focus of this research is using Vero E6 cells infected with Hantaan 76-118 (HTNV) as an in vitro infection model to examine the individual contribution of HTV infection to heat shock response. This study shows that HTNV infection rapidly induced HSP70 expression in Vero E6 cells, which underwent a nucleo-cytoplasmic shuttle that lasted for more than 3 d. The increased HSP70 was preceded by induction of HSP70 mRNA. The physical association of HSP70 with viral nucleocapsid protein (NP) in infected cells was demonstrated by co-localization and immunoprecipation. Vero E6 cells that constitutively overexpress HSP70 after stable transfection with HSP70 gene, when infected with HTNV, showed selectively reduced NP synthesis. These findings suggest HSP70 is actively involved in the control of the expression level of viral structural proteins and possibly involved in virus assembly by binding of NP to HSP70. Overexpression of HSP70 does not favor viral propagation.

Two-dimensional blue native/SDS-PAGE analysis reveals heat shock protein chaperone machinery involved in hepatitis B virus production in HepG2.2.15 cells

Hepatitis B virus (HBV) infection is a major health concern with more than two billion individuals currently infected worldwide. Despite the prevalence of infection, gaining a complete understanding of the molecular mechanisms of HBV infection has been difficult because HBV cannot infect common immortalized cell lines. HepG2.2.15, however, is a well established version of the HepG2 cell line that constitutively expresses HBV. Therefore, comparative proteomics analysis of HepG2.2.15 and HepG2 may provide valuable clues for understanding the HBV virus life cycle. In this study, two-dimensional blue native/SDS-PAGE was utilized to characterize different multiprotein complexes from whole cell lysates between HepG2.2.15 and HepG2. These results demonstrate that two unique protein complexes existed in HepG2.2.15 cells. When these complexes were excised from the gel and subjected to the second dimension separation and the proteins were sequenced by mass spectrometry, 20 non-redundant proteins were identified. Of these proteins, almost 20% corresponded to heat shock proteins, including HSP60, HSP70, and HSP90. Antibody-based supershift assays were used to verify the validity of the distinct protein complexes. Co-immunoprecipitation assays confirmed that HSP60, HSP70, and HSP90 proteins physically interacted in HepG2.2.15 but not HepG2 cells. We further demonstrated that down-regulation of HSP70 or HSP90 by small interfering RNA significantly inhibited HBV viral production but did not influence cellular proliferation or apoptosis. Consistent with these results, a significant reduction in HepG2.2.15 HBV secretion was observed when the HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin was used to treat HepG2.2.15 cells. Collectively these results suggest that the interaction of HSP90 with HSP70/HSP60 contributes to the HBV life cycle by forming a multichaperone machine that may constitute therapeutic targets for HBV-associated diseases.

The cold adapted and temperature sensitive influenza A/Ann Arbor/6/60 virus, the master donor virus for live attenuated influenza vaccines, has multiple defects in replication at the restrictive temperature

We have previously determined that the temperature sensitive (ts) and attenuated (att) phenotypes of the cold adapted influenza A/Ann Arbor/6/60 strain (MDV-A), the master donor virus for the live attenuated influenza A vaccines (FluMist), are specified by the five amino acids in the PB1, PB2 and NP gene segments. To understand how these loci control the ts phenotype of MDV-A, replication of MDV-A at the non-permissive temperature (39 degrees C) was compared with recombinant wild-type A/Ann Arbor/6/60 (rWt). The mRNA and protein synthesis of MDV-A in the infected MDCK cells were not significantly reduced at 39 degrees C during a single-step replication, however, vRNA synthesis was reduced and the nuclear-cytoplasmic export of viral RNP (vRNP) was blocked. In addition, the virions released from MDV-A infected cells at 39 degrees C exhibited irregular morphology and had a greatly reduced amount of the M1 protein incorporated. The reduced M1 protein incorporation and vRNP export blockage correlated well with the virus ts phenotype because these defects could be partially alleviated by removing the three ts loci from the PB1 gene. The virions and vRNPs isolated from the MDV-A infected cells contained a higher level of heat shock protein 70 (Hsp70) than those of rWt, however, whether Hsp70 is involved in thermal inhibition of MDV-A replication remains to be determined. Our studies demonstrate that restrictive replication of MDV-A at the non-permissive temperature occurs in multiple steps of the virus replication cycle.

Lytic infection with vaccinia virus activates caspases in a Bcl-2-inhibitable manner

Vaccinia virus (VV) is considered to cause lytic infection of most cells, with lysis being regarded equivalent to necrosis. Activation of caspases has not been associated with necrosis. However, we observed the activation and activity of caspases in epithelial cells HeLa G and BSC-40 lytically infected with VV. Using three different flow-cytometric approaches, we characterized the distinct stages of caspase cascade in VV-infected cells: a cleaved, activated form of caspases detected using a fluorescent pan-caspase inhibitor; caspase activity assayed by cleavage of a non-fluorescent substrate into a fluorescent product; caspase-specific cleavage of death substrates characterized by a fluorescent antibody detecting a neo-epitope in cytokeratin-18. All of these approaches yielded an increased fluorescent signal in VV-infected cells compared to mock-infected controls. Additionally, the signal was decreased by the expression of Bcl-2. The cleavage of cytokeratin-18 was confirmed by western blotting, but another key protein involved in apoptosis, PARP, was not cleaved in VV-infected lytic cells. The necrotic phenotype of the cells was confirmed by increased cell membrane permeability and/or decreased mitochondrial membrane potential. In conclusion, our data suggest that VV infection of the epithelial cells HeLa G and BSC-40 initiates the apoptotic program, however, apoptosis is not completed and switches into necrosis.

Vaccinia virus D10 protein has mRNA decapping activity, providing a mechanism for control of host and viral gene expression

Previous studies indicated that the vaccinia virus D10 protein, which is conserved in all sequenced poxviruses, participates in the rapid turnover of host and viral mRNAs. D10 contains a motif present in the family of Nudix/MutT enzymes, a subset of which has been shown to enhance mRNA turnover in eukaryotic cells through cleavage of the 5' cap (m7GpppNm-). Here, we demonstrate that a purified recombinant D10 fusion protein possesses an intrinsic activity that liberates m7GDP from capped RNA substrates. Furthermore, point mutations in the Nudix/MutT motif abolished decapping activity. D10 has a strong affinity for capped RNA substrates (Km approximately 3 nm). RNAs of 24-309 nt were decapped to comparable extents, whereas the cap of a 12-nt RNA was uncleaved. At large molar ratios relative to capped RNA substrate, competitor m7GpppG, m7GTP, or m7GDP inhibited decapping, whereas even higher concentrations of unmethylated analogs did not. High concentrations of uncapped RNA were also inhibitory, suggesting that D10 recognizes its substrate through interaction with both cap and RNA moieties. Thus far, poxviruses represent the only virus family shown to encode a Nudix hydrolase-decapping enzyme. Although it may seem self-destructive for a virus to encode a decapping and a capping enzyme, accelerated mRNA turnover helps eliminate competing host mRNAs and allows stage-specific synthesis of viral proteins.

Impact of protein kinase PKR in cell biology: from antiviral to antiproliferative action

The double-stranded RNA-dependent protein kinase PKR is a critical mediator of the antiproliferative and antiviral effects exerted by interferons. Not only is PKR an effector molecule on the cellular response to double-stranded RNA, but it also integrates signals in response to Toll-like receptor activation, growth factors, and diverse cellular stresses. In this review, we provide a detailed picture on how signaling downstream of PKR unfolds and what are the ultimate consequences for the cell fate. PKR activation affects both transcription and translation. PKR phosphorylation of the alpha subunit of eukaryotic initiation factor 2 results in a blockade on translation initiation. However, PKR cannot avoid the translation of some cellular and viral mRNAs bearing special features in their 5' untranslated regions. In addition, PKR affects diverse transcriptional factors such as interferon regulatory factor 1, STATs, p53, activating transcription factor 3, and NF-kappaB. In particular, how PKR triggers a cascade of events involving IKK phosphorylation of IkappaB and NF-kappaB nuclear translocation has been intensively studied. At the cellular and organism levels PKR exerts antiproliferative effects, and it is a key antiviral agent. A point of convergence in both effects is that PKR activation results in apoptosis induction. The extent and strength of the antiviral action of PKR are clearly understood by the findings that unrelated viral proteins of animal viruses have evolved to inhibit PKR action by using diverse strategies. The case for the pathological consequences of the antiproliferative action of PKR is less understood, but therapeutic strategies aimed at targeting PKR are beginning to offer promising results.

Hsp70 negatively controls rotavirus protein bioavailability in caco-2 cells infected by the rotavirus RF strain

Previous studies demonstrated that the induction of the heat shock protein Hsp70 in response to viral infection is highly specific and differs from one cell to another and for a given virus type. However, no clear consensus exists so far to explain the likely reasons for Hsp70 induction within host cells during viral infection. We show here that upon rotavirus infection of intestinal cells, Hsp70 is indeed rapidly, specifically, and transiently induced. Using small interfering RNA-Hsp70-transfected Caco-2 cells, we observed that Hsp70 silencing was associated with an increased virus protein level and enhanced progeny virus production. Upon Hsp70 silencing, we observed that the ubiquitination of the main rotavirus structural proteins was strongly reduced. In addition, the use of proteasome inhibitors in infected Caco-2 cells was shown to induce an accumulation of structural viral proteins. Together, these results are consistent with a role of Hsp70 in the control of the bioavailability of viral proteins within cells for virus morphogenesis.

Hop cleavage and function in granzyme B-induced apoptosis

Granzyme B (GzmB) is a cytotoxic protease found in the granules of natural killer cells and cytotoxic T lymphocytes. GzmB cleaves multiple intracellular protein substrates, leading to caspase activation, DNA fragmentation, cytoskeletal instability, and rapid induction of target cell apoptosis. However, no known individual substrate is required for GzmB to induce apoptosis. GzmB is therefore thought to initiate multiple cell death pathways simultaneously to ensure the death of target cells. We previously identified Hop (Hsp70/Hsp90-organizing protein) as a GzmB substrate in a proteomic survey (Bredemeyer, A. J., Lewis, R. M., Malone, J. P., Davis, A. E., Gross, J., Townsend, R. R., and Ley, T. J. (2004) Proc. Natl. Acad. Sci. U. S. A. 101, 11785-11790). Hop is a co-chaperone for Hsp70 and Hsp90, which have been implicated in the negative regulation of apoptosis. We therefore hypothesized that Hop may have an anti-apoptotic function that is abolished upon cleavage, lowering the threshold for GzmB-induced apoptosis. Here, we show that Hop was cleaved directly by GzmB in vitro and in cells undergoing GzmB-induced apoptosis. Expression of the two cleavage fragments of Hop did not induce cell death. Although cleavage of Hop by GzmB destroyed Hop function in vitro, both cells overexpressing GzmB-resistant Hop and cells with a 90-95% reduction in Hop levels exhibited unaltered susceptibility to GzmB-induced death. We conclude that Hop per se does not set the threshold for susceptibility to GzmB-induced apoptosis. Although it is possible that Hop may be cleaved by GzmB as an "innocent bystander" during the induction of apoptosis, it may also act to facilitate apoptosis in concert with other GzmB substrates.

Human Gene Profiling in Response to the Active Protein Kinase, Interferon-induced Serine/threonine Protein Kinase (PKR), in Infected Cells

The interferon-induced serine/threonine protein kinase (PKR) has an essential role in cell survival and cell death after viral infection and under stress conditions, but the host genes involved in these processes are not well defined. We used human cDNA microarrays to identify, in infected cells, genes differentially expressed after PKR expression and analyzed the requirement of catalytic activity of the enzyme. To express PKR, we used vaccinia virus (VV) recombinants producing wild type PKR (VV-PKR) and the catalytically inactive mutant K296R (VV-PKR-K296R). Most regulated genes were classified according to biological function, including apoptosis, stress, defense, and immune response. Transcriptional changes detected by microarray analysis were confirmed for selected genes by quantitative real time reverse transcription PCR. A total of 111 genes were regulated specifically by PKR catalytic activity. Of these, 97 were up-regulated, and 14 were down-regulated. The ATF-3 transcription factor, involved in stress-induced beta-cell apoptosis, was up-regulated. Activation of endogenous PKR with a VV mutant lacking the viral protein E3L (VVDeltaE3L), a PKR inhibitor, triggered an increase in ATF-3 expression that was not observed in PKR(-/-) cells. Using null cells for ATF-3 and for the p65 subunit of NF-kappaB, we showed that induction of apoptosis by PKR at late times of infection was dependent on ATF-3 expression and regulated by NF-kappaB activation. Here, we identified human genes selectively induced by expression of active PKR in infected cells and linked ATF-3 to a novel mechanism used by PKR to induce apoptosis.

The treatment of melanoma with an emphasis on immunotherapeutic strategies

Melanoma continues to be one of the most difficult to treat of all solid tumors. Many new advances have been made in the surgical management of melanoma, including new guidelines for margins of excision, as well as sentinel node biopsy for the diagnosis of lymph node micrometastases. The search continues for an effective adjuvant melanoma treatment that can prevent local and distant recurrences. Melanoma is one of the most immunogenic of all tumors, and several clinical trials testing the immunotherapy of melanoma have been conducted, including trials in interferon, interleukin-2, and melanoma vaccines. Here we discuss many of the recent clinical trials in the surgical management of melanoma, in addition to the advances that have been made in the field of immunotherapy. A new second-generation melanoma vaccine, DC-MelVac (patent # 11221/5), has recently been granted FDA approval for Phase I clinical trials and will be introduced in this review.

Characterization of a vaccinia virus mutant with a deletion of the D10R gene encoding a putative negative regulator of gene expression

The D9 and D10 proteins of vaccinia virus are 25% identical to each other, contain a mutT motif characteristic of nudix hydrolases, and are conserved in all sequenced poxviruses. Previous studies indicated that overexpression of D10 and, to a lesser extent, D9 decreased the levels of capped mRNAs and their translation products. Here, we further characterized the D10 protein and showed that only trace amounts are associated with purified virions and that it is expressed exclusively at late times after vaccinia virus infection. A viable deletion mutant (vdeltaD10) produced smaller plaques and lower virus yields than either wild-type virus or a D9R deletion mutant (vdeltaD9). Purified vdeltaD10 virions appeared normal by microscopic examination and biochemical analysis but produced 6- to 10-fold-fewer plaques at the same concentration as wild-type or vdeltaD9 virions. When 4 PFU per cell of wild-type or vdeltaD9 virions or equal numbers of vdeltaD10 virions were used for inoculation, nearly all cells were infected in each case, but viral early and late transcription was initiated more slowly in vdeltaD10-infected cells than in the others. However, viral early transcripts accumulated to higher levels in vdeltaD10-infected cells than in cells infected with the wild type or vdeltaD9. In addition, viral early and late mRNAs and cellular actin mRNA persisted longer in vdeltaD10-infected cells than in others. Furthermore, analysis of pulse-labeled proteins indicated prolonged synthesis of cellular and viral early proteins. These results are consistent with a role for D10 in regulating RNA levels in poxvirus-infected cells.

Heat shock protein and heat shock factor 1 expression and localization in vaccinia virus infected human monocyte derived macrophages

BACKGROUND

Viruses remain one of the inducers of the stress response in the infected cells. Heat shock response induced by vaccinia virus (VV) infection was studied in vitro in human blood monocyte derived macrophages (MDMs) as blood cells usually constitute the primary site of the infection.

METHODS

Human blood monocytes were cultured for 12-14 days. The transcripts of heat shock factor 1 (HSF1), heat shock protein 70 (HSP70), heat shock protein 90 (HSP90) and two viral genes (E3L and F17R) were assayed by reverse transcriptase-polymerase chain reaction (RT-PCR), and the corresponding proteins measured by Western blot. Heat shock factor 1 DNA binding activities were estimated by electrophoretic mobility shift assay (EMSA) and its subcellular localization analyzed by immunocytofluorescence.

RESULTS

It appeared that infection with vaccinia virus leads to activation of the heat shock factor 1. Activation of HSF1 causes increased synthesis of an inducible form of the HSP70 both at the mRNA and the protein level. Although HSP90 mRNA was enhanced in vaccinia virus infected cells, the HSP90 protein content remained unchanged. At the time of maximum vaccinia virus gene expression, an inhibitory effect of the infection on the heat shock protein and the heat shock factor 1 was most pronounced. Moreover, at the early phase of the infection translocation of HSP70 and HSP90 from the cytoplasm to the nucleus of the infected cells was observed.

CONCLUSION

Preferential nuclear accumulation of HSP70, the major stress-inducible chaperone protein, suggests that VV employs this particular mechanism of cytoprotection to protect the infected cell rather than to help viral replication. The results taken together with our previous data on monocytes or MDMs infected with VV or S. aureus strongly argue that VV employs multiple cellular antiapoptotic/cytoprotective mechanisms to prolong viability and proinflammatory activity of the cells of monocytic-macrophage lineage.

Inhibition of lytic infection of pseudorabies virus by arginine depletion

Pseudorabies virus (PRV) is a member of Alphahepesviruses; it is an enveloped virus with a double-stranded DNA genome. Polyamines (such as spermine and spermidine) are ubiquitous in animal cells and participate in cellular proliferation and differentiation. Previous results of our laboratory showed that the PRV can accomplish lytic infection either in the presence of exogenous spermine (or spermidine) or depletion of cellular polyamines. The amino acid arginine is a precursor of polyamine biosynthesis. In this work, we investigated the role of arginine in PRV infection. It was found that the plaque formation of PRV was inhibited by arginase (enzyme catalyzing the conversion of arginine into ornithine and urea) treatment whereas this inhibition can be reversed by exogenous arginine, suggesting that arginine is essential for PRV proliferation. Western blotting was conducted to study the effect of arginine depletion on the levels of structural proteins of PRV in virus-infected cells. Four PRV structural proteins (gB, gE, UL47, and UL48) were chosen for examination, and results revealed that the levels of viral proteins were obviously reduced in long time arginase treatment. However, the overall protein synthesis machinery was apparently not influenced by arginase treatment either in mock or PRV-infected cells. Analyzing with native gel, we found that arginase treatment affected the mobility of PRV structural proteins, suggesting the conformational change of viral proteins by arginine depletion. Heat shock proteins, acting as molecular chaperons, participate in protein folding and translocation. Our results demonstrated that long time arginase treatment could reduce the expression of cellular heat shock proteins 70 (hsc70 and hsp70), and transcriptional suppression of heat shock protein 70 gene promoter was one of the mechanisms involved in this reduced expression.

Antibodies against heat shock proteins and cholesterol in HIV infection

This review summarizes data on the presence and function of different heat shock proteins (Hsp) in the HIV virions and the infected cells. A 60 kD heat shock protein-like molecule is present in the envelope of the human immunodeficiency virus type 1 which can specifically interact with the transmembrane glycoprotein gp41. The role of cholesterol in the so-called cholesterol-rich lipid raft where HIV is budding from the infected cells as well as the consequential insertion of cholesterol into the envelope of HIV virion are also discussed. Natural antibodies against 60 kD (Hsp60) and 70 kD (Hsp70) families of Hsp and cholesterol can be detected in most healthy individuals. HIV infection results in a sharp increase in the serum concentration of anti-Hsp70 and cholesterol antibodies whereas no difference in the concentration of anti-Hsp60 antibodies can be detected. Highly active antiretroviral therapy leads to normalization of the levels of both anti-Hsp70 and anti-cholesterol antibodies.

Severity of viral infection is promoted by hyperthermic pretreatment

The aim of this study was to determine if prior heat shock and consequential heat shock protein (HSP) accumulation would inhibit viral infection. Confluent cultures of Madin-Darby bovine kidney cells were subjected to 30 mins of hyperthermia at 42 degrees C then allowed to recover at 37 micro C for six hrs. During the six hrs, HSP concentrations increased by 232% in heat-shocked cultures. Following the recovery period, six replicates of heat-shocked (HS) and six replicates of non-heat-shocked (CON) cultures were infected with Bovine Herpes virus 1. After 72 hours, severity of infection was assessed by counting formed viral plaques in cell cultures. CON cultures averaged 172.0+/-34.3 plaques per culture and HS cultures averaged 339.3+/-96.1 plaques per culture, representing a significant increase in infected cells (p=0.0044). These data provide evidence that physiological stressors related to extreme or exhaustive exercise, specifically hyperthermia, may increase risk of viral infection.

Recruitment of Hsp70 chaperones: a crucial part of viral survival strategies

Virus proliferation depends on the successful recruitment of host cellular components for their own replication, protein synthesis, and virion assembly. In the course of virus particle production a large number of proteins are synthesized in a relatively short time, whereby protein folding can become a limiting step. Most viruses therefore need cellular chaperones during their life cycle. In addition to their own protein folding problems viruses need to interfere with cellular processes such as signal transduction, cell cycle regulation and induction of apoptosis in order to create a favorable environment for their proliferation and to avoid premature cell death. Chaperones are involved in the control of these cellular processes and some viruses reprogram their host cell by interacting with them. Hsp70 chaperones, as central components of the cellular chaperone network, are frequently recruited by viruses. This review focuses on the function of Hsp70 chaperones at the different stages of the viral life cycle emphasizing mechanistic aspects.

Nuclear translocation of papillomavirus minor capsid protein L2 requires Hsc70

Minor capsid protein L2 of papillomaviruses plays an essential role in virus assembly by recruiting viral components to PML bodies, the proposed sites of virus morphogenesis. We demonstrate here that the function of L2 in virus assembly requires the chaperone Hsc70. Hsc70 was found dispersed in naturally infected keratinocytes and cultured cells. A dramatic relocation of Hsc70 from the cytoplasm to PML bodies was induced in these cells by L2 expression. Hsc70-L2 complex formation was confirmed by coimmunoprecipitation. The complex was modulated by the cochaperones Hip and Bag-1, which stabilize and destabilize Hsc70-substrate complexes, respectively. Cytoplasmic depletion of Hsc70 caused retention of wild-type and N-terminally truncated L2, but not of C-terminally truncated L2, in the cytoplasm. This retention was partially reversed by overexpression of Hsc70 fused to green fluorescent protein but not by ATPase-negative Hsc70. Hsc70 associated with L1-L2 virus-like particles (VLPs) but not with VLPs composed either of L1 alone or of L1 and C-terminally truncated L2. Moreover, displacement of Hsc70 from L1-L2 VLPs by encapsidation of DNA, generating pseudovirions, was found. These data indicate that Hsc70 transiently associates with viral capsids during the integration of L2, possibly via the L2 C terminus. Completion of virus assembly results in displacement of Hsc70 from virions.

Antigenic peptides complexed to phylogenically diverse Hsp70s induce differential immune responses

The Hsp70 class of heat shock proteins (Hsps) has been implicated at multiple points in the immune response, including initiation of proinflammatory cytokine production, antigen recognition and processing, and phenotypic maturation of antigen-presenting cells (APCs). This class of chaperones is highly conserved in both sequence and structure, from prokaryotes to higher eukaryotes. In all cases, these chaperones function to bind short segments of either peptides or proteins through an adenosine triphosphate-dependent process. In addition to a possible role in antigen presentation, these chaperones have also been proposed to function as a potent adjuvant. We compared 4 evolutionary diverse Hsp70s, E. coli DnaK, wheat cytosolic Hsc70, plant chloroplastic CCS1, and human Hsp70, for their ability to prime and augment a primary immune response against herpes simplex virus-1 (HSV1). We discovered that all 4 Hsp70s were highly effective as adjuvants displaying similar ability to lipopolysaccharides in upregulating cytokine gene expression. In addition, they were all capable of inducing phenotypic maturation of APCs, as measured by the display of various costimulatory molecules. However, only the human Hsp70 was able to mediate sufficient cross-priming activity to afford a protective immune response to HSV1, as judged by protection from a lethal viral challenge, in vitro proliferation, cytotoxicity, and intracellular interferon-gamma production. The difference in immune response generated by the various Hsp70s could possibly be due to their differential ability to interact productively with other coreceptors and different regulatory cochaperones.

Closterovirus bipolar virion: evidence for initiation of assembly by minor coat protein and its restriction to the genomic RNA 5' region

The long flexuous virions of the Closteroviridae have a unique bipolar architecture incorporating two coat proteins, with most of the helical nucleocapsid encapsidated by the major coat protein (CP) and a small portion of one end encapsidated by the minor coat protein (CPm). It is not known whether CPm encapsidates the genomic RNA and, if so, which end and what effects transition between the two coat proteins. Two other virus-encoded proteins, an HSP70 homolog (HSP70h) and an approximately 61-kDa protein, are required to augment virion assembly. In this work, we examine the in vivo encapsidation of Citrus tristeza virus by its CPm in the absence of CP. In the absence of other assembly-related proteins, CPm protected a family of 5' coterminal RNAs, apparently because of pausing at different locations along the genomic RNA. Most of the nucleocapsids formed by CPm were short, but a few were full-length and infectious. Mutations within the 5' nontranslated region demonstrated that the CPm origin of assembly overlaps the previously described conserved stem-and-loop structures that function as a cis-acting element required for RNA synthesis. Thus, in the absence of CP, the CPm encapsidation is initiated from the 5' end of the genomic RNA. Coexpression of HSP70h and the p61 protein with CPm in protoplasts restricted encapsidation to the 5' approximately 630 nucleotides, which is close to the normal boundary of the bipolar virion, whereas the presence of either HSP70h or the p61 protein alone did not limit encapsidation by CPm.

Microarray analysis of A549 cells infected with rabbitpox virus (RPV): a comparison of wild-type RPV and RPV deleted for the host range gene, SPI-1

A documented consequence of poxvirus infections is global inhibition of host protein synthesis and reduction in mRNA levels. We examined this mRNA decrease by infecting A549 cells, derived from a human lung carcinoma, with rabbitpox virus (RPV), or RPV deleted for the serine protease inhibitor SPI-1 (RPVDeltaSPI-1), which exhibits a growth defect on A549 cells. At various times postinfection, mRNA profiles were analyzed using Affymetrix U95AV2 microarrays. There was a decline in overall cellular mRNA levels beginning at 2.5 hpi, and by 5 hpi, mRNA levels were drastically reduced for the majority of genes. However, several mRNAs increased, including those of heat-shock genes. Finally, a comparison of host mRNA profiles of RPV- to RPVDeltaSPI-1-infected cells revealed subtle differences in mRNA levels at 5 and 12 hpi. In summary, while there was a global decrease of host mRNA levels, the induction of selected mRNAs may be required for a successful poxvirus infection.

Redistribution of cyclophilin A to viral factories during vaccinia virus infection and its incorporation into mature particles

Cyclophilins are peptidyl-prolyl cis-trans isomerases involved in catalyzing conformational changes and accelerating the rate of protein folding and refolding in several cellular systems. In the present study, we analyzed the expression pattern and intracellular distribution of the cellular isomerase cyclophilin A (CypA) during vaccinia virus (VV) infection. An impressive increase in CypA stability was observed, leading to a practically unchanged accumulation of CypA during infection, although its synthesis was completely inhibited at late times. By confocal microscopy, we observed that CypA went through an intense reorganization in the cell cytoplasm and colocalized with the virosomes late in infection. CypA relocation to viral factories required the synthesis of viral postreplicative proteins, and treatment of infected cells with cyclosporine (CsA) prevented CypA relocation, clearly excluding the virosomes from CypA staining. Immunoelectron microscopy of VV-infected cells showed that CypA was incorporated into VV particles during morphogenesis. Biochemical and electron microscopic assays with purified virions confirmed that CypA was encapsidated within the virus particle and localized specifically in the core. This work suggests that CypA may develop an important role in VV replication.