Analysis of the specificity and mechanism of transcriptional activation of the human hsp70 gene during infection by DNA viruses

Alternations of Fertility Parameters by Graded Dose of Inorganic Arsenic in Adult Male White Pekin Ducks

A significant health issue, reproductive toxicity is mostly linked to exposure to various environmental heavy metals. A pervasive toxin that occurs naturally in the environment is arsenic (As). This research was done to determine the effects of various doses of inorganic As supplements on the reproductive organs of adult male white Pekin ducks. A total of 240 numbers of 14-days-old male white Pekin ducks were weighed and randomly assigned into 4 experimental groups with six replicates (10 ducklings in each replicate). The experimental groups were as follows: (T-1) basal diet along with normal drinking water (control group); (T-2 to T-4) basal diet along with As in the form of sodium-meta-arsenite at 7, 14, and 28 ppm of drinking water respectively. The results showed reduction in body weight and testicular weight, disruption of spermatogenesis, reduction in follicular-stimulating hormone (FSH), leutinizing hormone (LH), and testosterone levels and histopathological alterations as compared to control. Additionally, there was not only a significant decrease in various antioxidant parameters in testis tissue, like catalase (CAT), reduced glutathione (GSH), super oxide dismutase (SOD), and ferric-reducing antioxidant power (FRAP), but also a significant increase in oxidative parameters of testis like lipid peroxidation (LPO), myloperoxidase (MPO), nitric oxide (NO), and super oxide anion radical (O2-) in As-treated groups, in comparison with T-1. A significantly higher level of As content in testis was observed in all the 3 As-treated groups, with highest level recorded in T-4 birds. Besides that, there was upregulation of nuclear factor kappa B (NF-κB), heat shock proteins (Hsps) and pro-inflammatory cytokines like interlukin (IL) series, i.e., IL-2, IL-6, IL-18, IL-1β and tumor necrosis factor- α (TNF-α) levels, whereas anti-inflammatory parameters like IL-4 and IL-10 levels showed downregulation in testis of As-treated groups. Together, these findings provide deeper understandings of the roles played by oxidative stress, NF-κB and Hsps in the progression of testicular injury, which may help to explain how the As induced male sterility, in ducks, due to exposure.

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.

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.

Heat Shock Protein A6 Is Especially Involved in Enterovirus 71 Infection

Hand foot and mouth disease (HFMD) caused by Enterovirus 71 (EV71) infection is still a major infectious disease threatening children’s life and health in the absence of effective antiviral drugs due to its high prevalence and neurovirulence. A study of EV71-specific host response might shed some light on the reason behind its unique epidemiologic features and help to find means to conquer EV71 infection. We reported that host heat shock protein A6 (HSPA6) was induced by EV71 infection and involved infection in both Rhabdomyosarcoma (RD) cells and neurogliocytes. Most importantly, we found that EV71 did not induce the expression of other heat shock proteins HSPA1, HSPA8, and HSPB1 under the same conditions, and other HFMD-associated viruses including CVA16, CVA6, CVA10, and CVB1-3 did not induce the upregulation of HSPA6. In addition, EV71 infection enhanced the cytoplasmic aggregation of HSPA6 and its colocalization with viral capsid protein VP1. These findings suggest that HSPA6 is a potential EV71-specific host factor worthy of further study.

ITRAQ-based quantitative proteomics reveals the proteome profiles of MDBK cells infected with bovine viral diarrhea virus

Background

Bovine viral diarrhea (BVD) which is caused by Bovine viral diarrhea virus (BVDV), is an acute, contagious disease. In spite of the use of vaccines and elimination projects, BVDV still causes severe economic losses to the cattle industry for the past few years. The current study presents a preliminary analysis of the pathogenic mechanisms from the perspective of protein expression levels in infected host cells at different points in time to elucidate the infection process associated with BVDV.

Methods

We used the isobaric tags for relative and absolute quantitation (iTRAQ) technology coupled with liquid chromatography-tandem mass spectrometric (LC–MS/MS) approach for a quantitative proteomics comparison of BVDV NADL-infected MDBK cells and non-infected cells. The functions of the proteins were deduced by functional annotation and their involvement in metabolic processes explored by KEGG pathway analysis to identify their interactions.

Results

There were 357 (47.6% downregulated, 52.4% upregulated infected vs. control), 101 (52.5% downregulated, 47.5% upregulated infected vs. control), and 66 (21.2% downregulated, 78.8% upregulated infected vs. control) proteins were differentially expressed (fold change > 1.5 or < 0.67) in the BVDV NADL-infected MDBK cells at 12, 24, and 48 h after infection. GO analysis showed that the differentially expressed proteins (DEPs) are mainly involved in metabolic processes, biological regulation and localization. KEGG enrichment analysis showed that some signaling pathways that involved in the regulation of BVDV NADL-infection and host resistance are significantly (P < 0.05) enriched at different stages of the BVDV NADL-infection, such as Endocytosis signaling pathway, FoxO signaling pathway, Homologous recombination signaling pathway and Lysosome pathway.

Conclusions

These results revealed that the DEPs in BVDV NADL-infected MDBK cells have a wide range of regulatory effects; in addition, they provide a lot of resources for the study of host cell proteomics after BVDV infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01592-2.

Aquareovirus NS31 protein serves as a specific inducer for host heat shock 70-kDa protein

Elevation of heat-shock protein expression, known as cellular heat-shock responses, occurs during infection of many viruses, which is involved in viral replication through various mechanisms. Herein, transcriptome analysis revealed that over-expression of non-structural protein NS31 of grass carp reovirus (GCRV) in grass carp Ctenopharyngodon idellus kidney (CIK) cells specifically induced expression of heat-shock response (HSR) genes HSP30 and HSP70. We further found that, among the HSR genes, only HSP70 protein were shown to be efficiently induced in fish cells following NS31 over-expression or GCRV infection. Employing a luciferase assay, we were able to show that the promoter of the HSP70 gene can be specifically activated by NS31. In addition, over-expressing HSP70 in grass carp CIK cells resulted in enhanced replication efficiency of GCRV, and an inhibitor for HSP70 resulted in the inhibition of GCRV replication, indicating that HSP70 should serve as a pro-viral factor. We also found that NS31 could activate HSP70 expression in cells of other vertebrate animals. Similar inducing effect on HSP70 expression was demonstrated for NS31-homologue proteins of other aquareoviruses including American grass carp reovirus (AGCRV) and GRCV (green river chinook virus). All these results indicated NS31 proteins in the Aquareovirus genus should play a key role for up-regulating specific HSP70 gene during viral replication.

Assessing the oncolytic potential of rotavirus on mouse myeloma cell line Sp2/0-Ag14

INTRODUCTION

Cancer is the second leading cause of death in the United States, surpassed only by cardiovascular disease. However, cancer has now overtaken cardiovascular disease as the main cause of death in 12 countries in Western Europe. The burden of cancer is posing a major challenge to health care systems worldwide and demanding improvements in methods for cancer prevention, diagnosis, and treatment. Alternative and complementary strategies for orthodox surgery, radiotherapy, and chemotherapy need to be developed.

OBJECTIVE

To determine the oncolytic potential of tumor cell-adapted rotavirus in terms of their ability to infect and lysate murine myeloma Sp2/0-Ag14 cells.

MATERIALS AND METHODS

We inoculated rotaviruses Wt1-5, WWM, TRUYO, ECwt-O, and WTEW in Sp2/0-Ag14 cells and we examined their infectious effects by immunocytochemistry, immunofluorescence, flow cytometry, and DNA fragmentation assays.

RESULTS

Rotavirus infection involved the participation of some heat shock proteins, of protein disulfide isomerase (PDI), and integrin β3. We detected the accumulation of viral antigens within the virus-inoculated cells and in the culture medium in all the rotavirus isolates examined. The rotavirus-induced cell death mechanism in Sp2/0-Ag14 cells involved changes in cell membrane permeability, chromatin condensation, and DNA fragmentation, which were compatible with cytotoxicity and apoptosis.

CONCLUSIONS

The ability of the rotavirus isolates Wt1-5, WWM, TRUYO, ECwt-O, and WTEW to infect and cause cell death of Sp2/0-Ag14 cells through mechanisms that are compatible with virus-induced apoptosis makes them potential candidates as oncolytic agents.

Comparison of two different host plant genera responding to grapevine leafroll-associated virus 3 infection

Grapevine leafroll-associated virus 3 (GLRaV-3) is one of the most important viruses of grapevine but, despite this, there remain several gaps in our understanding of its biology. Because of its narrow host range - limited to Vitis species - and because the virus is restricted to the phloem, most GLRaV-3 research has concentrated on epidemiology and the development of detection assays. The recent discovery that GLRaV-3 can infect Nicotiana benthamiana, a plant model organism, makes new opportunities available for research in this field. We used RNA-seq to compare both V. vinifera and P1/HC-Pro N. benthamiana host responses to GLRaV-3 infection. Our analysis revealed that the majority of DEGs observed between the two hosts were unique although responses between the two hosts also showed several shared gene expression results. When comparing gene expression patterns that were shared between the two hosts, we observed the downregulation of genes associated with stress chaperones, and the induction of gene families involved in primary plant physiological processes. This is the first analysis of gene expression profiles beyond Vitis to mealybug-transmitted GLRaV-3 and demonstrates that N. benthamiana could serve as a useful tool for future studies of GLRaV-3-host interactions.

Promyelocytic leukemia protein isoform II inhibits infection by human adenovirus type 5 through effects on HSP70 and the interferon response

Promyelocytic leukemia (PML) proteins have been implicated in antiviral responses but PML and associated proteins are also suggested to support virus replication. One isoform, PML-II, is required for efficient transcription of interferon and interferon-responsive genes. We therefore investigated the PML-II contribution to human adenovirus 5 (Ad5) infection, using shRNA-mediated knockdown. HelaΔII cells showed a 2-3-fold elevation in Ad5 yield, reflecting an increase in late gene expression. This increase was found to be due in part to the reduced innate immune response consequent upon PML-II depletion. However, the effect was minor because the viral E4 Orf3 protein targets and inactivates this PML-II function. The major benefit to Ad5 in HelaΔII cells was exerted via an increase in HSP70; depletion of HSP70 completely reversed this replicative advantage. Increased Ad5 late gene expression was not due either to the previously described inhibition of inflammatory responses by HSP70 or to effects of HSP70 on major late promoter or L4 promoter activity, but might be linked to an observed increase in E1B 55K, as this protein is known to be required for efficient late gene expression. The induction of HSP70 by PML-II removal was specific for the HSPA1B gene among the HSP70 gene family and thus was not the consequence of a general stress response. Taken together, these data show that PML-II, through its various actions, has an overall negative effect on the Ad5 lifecycle.

The heat shock response restricts virus infection in Drosophila

Innate immunity is the first line of defence against pathogens and is essential for survival of the infected host. The fruit fly Drosophila melanogaster is an emerging model to study viral pathogenesis, yet antiviral defence responses remain poorly understood. Here, we describe the heat shock response, a cellular mechanism that prevents proteotoxicity, as a component of the antiviral immune response in Drosophila. Transcriptome analyses of Drosophila S2 cells and adult flies revealed strong induction of the heat shock response upon RNA virus infection. Dynamic induction patterns of heat shock pathway components were characterized in vitro and in vivo following infection with different classes of viruses. The heat shock transcription factor (Hsf), as well as active viral replication, were necessary for the induction of the response. Hsf-deficient adult flies were hypersensitive to virus infection, indicating a role of the heat shock response in antiviral defence. In accordance, transgenic activation of the heat shock response prolonged survival time after infection and enabled long-term control of virus replication to undetectable levels. Together, our results establish the heat shock response as an important constituent of innate antiviral immunity in Drosophila.

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.

Herpes Simplex Virus UL14 Protein Blocks Apoptosis

We report that an HSV-2 UL14 protein expressing cell line (14/HEp-2) was more resistant to apoptosis induced by osmotic shock and certain drugs than its parental cell line. Furthermore, HSV-1 UL14 protein deletion virus (UL14D) showed weaker inhibition of apoptosis compared to the rescued virus UL14R. The protein's anti-apoptotic function may derive from its heat shock protein-like properties.

Formation of covalently modified folding intermediates of simian virus 40 Vp1 in large T antigen-expressing cells

The folding and pentamer assembly of the simian virus 40 (SV40) major capsid protein Vp1, which take place in the infected cytoplasm, have been shown to progress through disulfide-bonded Vp1 folding intermediates. In this report, we further demonstrate the existence of another category of Vp1 folding or assembly intermediates: the nonreducible, covalently modified mdVp1s. These species were present in COS-7 cells that expressed a recombinant SV40 Vp1, Vp1ΔC, through plasmid transfection. The mdVp1s persisted under cell and lysate treatment and SDS-PAGE conditions that are expected to have suppressed the formation of artifactual disulfide cross-links. As shown through a pulse-chase analysis, the mdVp1s were derived from the newly synthesized Vp1ΔC in the same time frame as Vp1's folding and oligomerization. The apparent covalent modifications occurred in the cytoplasm within the core region of Vp1 and depended on the coexpression of the SV40 large T antigen (LT) in the cells. Analogous covalently modified species were found with the expression of recombinant polyomavirus Vp1s and human papillomavirus L1s in COS-7 cells. Furthermore, the mdVp1s formed multiprotein complexes with LT, Hsp70, and Hsp40, and a fraction of the largest mdVp1, md4, was disulfide linked to the unmodified Vp1ΔC. Both mdVp1 formation and most of the multiprotein complex formation were blocked by a Vp1 folding mutation, C87A-C254A. Our observations are consistent with a role for LT in facilitating the folding process of SV40 Vp1 by stimulating certain covalent modifications of Vp1 or by recruiting certain cellular proteins.

Virus-heat shock protein interaction and a novel axis for innate antiviral immunity

Virus infections induce heat shock proteins that in turn enhance virus gene expression, a phenomenon that is particularly well characterized for the major inducible 70 kDa heat shock protein (hsp70). However, hsp70 is also readily induced by fever, a phylogenetically conserved response to microbial infections, and when released from cells, hsp70 can stimulate innate immune responses through toll like receptors 2 and 4 (TLR2 and 4). This review examines how the virus-hsp70 relationship can lead to host protective innate antiviral immunity, and the importance of hsp70 dependent stimulation of virus gene expression in this host response. Beginning with the well-characterized measles virus-hsp70 relationship and the mouse model of neuronal infection in brain, we examine data indicating that the innate immune response is not driven by intracellular sensors of pathogen associated molecular patterns, but rather by extracellular ligands signaling through TLR2 and 4. Specifically, we address the relationship between virus gene expression, extracellular release of hsp70 (as a damage associated molecular pattern), and hsp70-mediated induction of antigen presentation and type 1 interferons in uninfected macrophages as a novel axis of antiviral immunity. New data are discussed that examines the more broad relevance of this protective mechanism using vesicular stomatitis virus, and a review of the literature is presented that supports the probable relevance to both RNA and DNA viruses and for infections both within and outside of the central nervous system.

Cellular transcripts of chicken brain tissues in response to H5N1 and Newcastle disease virus infection

Background

Highly-pathogenic avian influenza (HPAI) H5N1 and Newcastle disease (ND) viruses are the two most important poultry viruses in the world, with the ability to cause classic central nervous system dysfunction in poultry and migratory birds. To elucidate the mechanisms of neurovirulence caused by these viruses, a preliminary study was design to analyze host's cellular responses during infections of these viruses.

Methods

An improved mRNA differential display technique (Gene Fishing™) was undertaken to analyze differentially expressed transcripts regulated during HPAI H5N1 and velogenic neurotropic NDV infections of whole brain of chickens. The identification of differentially expressed genes (DEGs) was made possible as this technique uses annealing control primers that generate reproducible, authentic and long PCR products that are detectable on agarose gels.

Results

Twenty-three genes were identified to be significantly regulated during infections with both viruses, where ten of the genes have been selected for validation using a TaqMan^® based real time quantitative PCR assay. Some of the identified genes demonstrated to be key factors involving the cytoskeletal system, neural signal transduction and protein folding during stress. Interestingly, Septin 5, one of the genes isolated from HPAI H5N1-infected brain tissues has been reported to participate in the pathogenic process of Parkinson's disease.

Conclusions

In this limited study, the differentially expressed genes of infected brain tissues regulated by the viruses were found not to be identical, thus suggesting that their neurovirulence and neuropathogenesis may not share similar mechanisms and pathways.

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.

The salivary secretome of the tsetse fly Glossina pallidipes (Diptera: Glossinidae) infected by salivary gland hypertrophy virus

BACKGROUND

The competence of the tsetse fly Glossina pallidipes (Diptera; Glossinidae) to acquire salivary gland hypertrophy virus (SGHV), to support virus replication and successfully transmit the virus depends on complex interactions between Glossina and SGHV macromolecules. Critical requisites to SGHV transmission are its replication and secretion of mature virions into the fly's salivary gland (SG) lumen. However, secretion of host proteins is of equal importance for successful transmission and requires cataloging of G. pallidipes secretome proteins from hypertrophied and non-hypertrophied SGs.

METHODOLOGY/PRINCIPAL FINDINGS

After electrophoretic profiling and in-gel trypsin digestion, saliva proteins were analyzed by nano-LC-MS/MS. MaxQuant/Andromeda search of the MS data against the non-redundant (nr) GenBank database and a G. morsitans morsitans SG EST database, yielded a total of 521 hits, 31 of which were SGHV-encoded. On a false discovery rate limit of 1% and detection threshold of least 2 unique peptides per protein, the analysis resulted in 292 Glossina and 25 SGHV MS-supported proteins. When annotated by the Blast2GO suite, at least one gene ontology (GO) term could be assigned to 89.9% (285/317) of the detected proteins. Five (∼1.8%) Glossina and three (∼12%) SGHV proteins remained without a predicted function after blast searches against the nr database. Sixty-five of the 292 detected Glossina proteins contained an N-terminal signal/secretion peptide sequence. Eight of the SGHV proteins were predicted to be non-structural (NS), and fourteen are known structural (VP) proteins.

CONCLUSIONS/SIGNIFICANCE

SGHV alters the protein expression pattern in Glossina. The G. pallidipes SG secretome encompasses a spectrum of proteins that may be required during the SGHV infection cycle. These detected proteins have putative interactions with at least 21 of the 25 SGHV-encoded proteins. Our findings opens venues for developing novel SGHV mitigation strategies to block SGHV infections in tsetse production facilities such as using SGHV-specific antibodies and phage display-selected gut epithelia-binding peptides.

Heat shock factor 1 protects against lung mycoplasma pneumoniae infection in mice

Heat shock factor 1 (HSF1) is a transcriptional factor that controls the induction of heat shock proteins (e.g. HSP70) in response to stress. Bacterial infections contribute to the pathobiology of chronic lung diseases such as chronic obstructive pulmonary disease and asthma. Whether HSF1 is critical to lung bacterial infection remains unknown. This study is aimed at investigating the impact of HSF1 deficiency on lung Mycoplasma pneumoniae (Mp) infection and elucidating the underlying molecular mechanisms, such as Toll-like receptor 2 (TLR2) signaling. HSF1(-/-) and HSF1(+/+) mice were intranasally infected with Mp or saline and sacrificed 4, 24 and 72 h after treatment. HSF1(-/-) mice had a higher lung Mp load than HSF1(+/+) mice. Mp-induced lung TLR2, nuclear factor-κB and associated inflammation [e.g. keratinocyte-derived chemokine (KC), neutrophils and histopathology] were delayed in HSF1(-/-) mice as compared to HSF1(+/+) mice. HSP70 protein levels in bronchoalveolar lavage fluid of HSF1(-/-) mice were decreased. Furthermore, in response to Mp infection, HSF1(-/-) alveolar macrophages had less TLR2 mRNA expression and KC production than HSF1(+/+) counterparts. Nuclear factor-κB activity and KC production in HSF1(-/-) macrophages could be rescued by addition of exogenous HSP70 protein. These data suggest that HSF1 is necessary to initiate host defense against bacterial infection partly through promoting early TLR2 signaling activation.

The role of aldehyde dehydrogenase and hsp70 in suppression of white spot syndrome virus replication at high temperature

High temperature (32 to 33°C) has been shown to reduce mortality in white spot syndrome virus (WSSV)-infected shrimps, but the mechanism still remains unclear. Here we show that in WSSV-infected shrimps cultured at 32°C, transcriptional levels of representative immediate-early, early, and late genes were initially higher than those at 25°C. However, neither the IE1 nor VP28 protein was detected at 32°C, suggesting that high temperature might inhibit WSSV protein synthesis. Two-dimensional gel electrophoresis analysis revealed two proteins, NAD-dependent aldehyde dehydrogenase (ALDH) and the proteasome alpha 4 subunit (proteasome α4), that were markedly upregulated in WSSV-infected shrimps at 32°C. Reverse transcription-PCR (RT-PCR) analysis of members of the heat shock protein family also showed that hsp70 was upregulated at 32°C. When aldh, proteasome α4, and hsp70 were knocked down by double-stranded RNA interference and shrimps were challenged with WSSV, the aldh and hsp70 knockdown shrimps became severely infected at 32°C, while the proteasome α4 knockdown shrimps remained uninfected. Our results therefore suggest that ALDH and Hsp70 both play an important role in the inhibition of WSSV replication at high temperature.

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.

Heterotrimerization of heat-shock factors 1 and 2 provides a transcriptional switch in response to distinct stimuli

Organisms respond to circumstances threatening the cellular protein homeostasis by activation of heat-shock transcription factors (HSFs), which play important roles in stress resistance, development, and longevity. Of the four HSFs in vertebrates (HSF1-4), HSF1 is activated by stress, whereas HSF2 lacks intrinsic stress responsiveness. The mechanism by which HSF2 is recruited to stress-inducible promoters and how HSF2 is activated is not known. However, changes in the HSF2 expression occur, coinciding with the functions of HSF2 in development. Here, we demonstrate that HSF1 and HSF2 form heterotrimers when bound to satellite III DNA in nuclear stress bodies, subnuclear structures in which HSF1 induces transcription. By depleting HSF2, we show that HSF1-HSF2 heterotrimerization is a mechanism regulating transcription. Upon stress, HSF2 DNA binding is HSF1 dependent. Intriguingly, when the elevated expression of HSF2 during development is mimicked, HSF2 binds to DNA and becomes transcriptionally competent. HSF2 activation leads to activation of also HSF1, revealing a functional interdependency that is mediated through the conserved trimerization domains of these factors. We propose that heterotrimerization of HSF1 and HSF2 integrates transcriptional activation in response to distinct stress and developmental stimuli.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

The varicella-zoster virus immediate-early 63 protein affects chromatin-controlled gene transcription in a cell-type dependent manner

Background

Varicella Zoster Virus Immediate Early 63 protein (IE63) has been shown to be essential for VZV replication, and critical for latency establishment. The activity of the protein as a transcriptional regulator is not fully clear yet. Using transient transfection assays, IE63 has been shown to repress viral and cellular promoters containing typical TATA boxes by interacting with general transcription factors.

Results

In this paper, IE63 regulation properties on endogenous gene expression were evaluated using an oligonucleotide-based micro-array approach. We found that IE63 modulates the transcription of only a few genes in HeLa cells including genes implicated in transcription or immunity. Furthermore, we showed that this effect is mediated by a modification of RNA POL II binding on the promoters tested and that IE63 phosphorylation was essential for these effects. In MeWo cells, the number of genes whose transcription was modified by IE63 was somewhat higher, including genes implicated in signal transduction, transcription, immunity, and heat-shock signalling. While IE63 did not modify the basal expression of several NF-κB dependent genes such as IL-8, ICAM-1, and IκBα, it modulates transcription of these genes upon TNFα induction. This effect was obviously correlated with the amount of p65 binding to the promoter of these genes and with histone H3 acetylation and HDAC-3 removal.

Conclusion

While IE63 only affected transcription of a small number of cellular genes, it interfered with the TNF-inducibility of several NF-κB dependent genes by the accelerated resynthesis of the inhibitor IκBα.

A double-stranded-RNA response program important for RNA interference efficiency

When recognized by the RNA interference (RNAi) pathway, double-stranded RNA (dsRNA) produced in eukaryotic cells results in posttranscriptional gene silencing. In addition, dsRNA can trigger the interferon response as part of the immune response in vertebrates. In this study, we show that dsRNA, but not short interfering RNA (siRNA), induces the expression of qde-2 (an Argonaute gene) and dcl-2 (a Dicer gene), two central components of the RNAi pathway in the filamentous fungus Neurospora crassa. The induction of QDE-2 by dsRNA is required for normal gene silencing, indicating that this is a regulatory mechanism that allows the optimal function of the RNAi pathway. In addition, we demonstrate that Dicer proteins (DCLs) regulate QDE-2 posttranscriptionally, suggesting a role for DCLs or siRNA in QDE-2 accumulation. Finally, a genome-wide search revealed that additional RNAi components and homologs of antiviral and interferon-stimulated genes are also dsRNA-activated genes in Neurospora. Together, our results suggest that the activation of the RNAi components is part of a broad ancient host defense response against viral and transposon infections.

Global impact: elucidating plant responses to viral infection

Viruses induce a variety of responses in host cells that are mediated by perturbation of different signaling pathways. Advances in our understanding of the functions of viral proteins, plant biology in general, as well as technologies for profiling gene expression have converged in recent years to provide new insight into the events occurring inside susceptible and resistant host cells in response to virus infection. These effects range from nonspecific changes in gene expression due to the general accumulation of viral proteins to those responses that are initiated by the specific interactions between virus and host proteins. Here, we discuss a variety of expression profiling methods and approaches that have been used to study the effects of viruses on host transcriptomes. These studies have identified distinct sets of genes that have altered expression profiles in response to viruses, including stress- and defense-related genes. The activities of viral RNA silencing suppressors and interference with hormone signaling or biogenesis also influence plant gene expression and lead to developmental abnormalities.

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.

Degenerate PCR method for identification of an antiapoptotic gene in BHV-1

To investigate on the hypothetical presence of an antiapoptotic gene, we utilized the CODEHOP (COnsensus-DEgenerate Hybrid Oligonucleotide Primers) strategy amplifying unknown sequences from a background of genomic (bovine herpesvirus type-1) BHV-1 DNA. An alignment of carboxyl-terminal domains belonging to three proteins encoded by gamma34.5, MyD116 and GADD34 genes, was carried out to design degenerate PCR primers in highly conserved regions. This allowed the amplification of a 110 bp fragment. This fragment was subjected to automatic sequencing and DNA sequence analysis revealed that its position resided between the nt 14363 and the nt 14438 in bovine herpesvirus type-1 (BHV-1) Cooper strain sharing an identity of 86% (UL14). Transient transfections showed that UL14 protein is efficient in protecting MDBK and K562 cells from sorbitol induced apoptosis. The protein's anti-apoptotic function may derive from its heat shock protein-like properties.

Cellular stress rather than stage of the cell cycle enhances the replication and plating efficiencies of herpes simplex virus type 1 ICP0- viruses

This lab reported previously that the plating efficiency of a herpes simplex virus type 1 ICP0-null mutant was enhanced upon release from an isoleucine block which synchronizes cells to G1 phase (W. Cai and P. A. Schaffer, J. Virol. 65:4078-4090, 1991). Peak plating efficiency occurred as cells cycled out of G1 and into S phase, suggesting that the enhanced plating efficiency was due to cellular activities present in late G1/early S phase. We have found, however, that the enhanced plating efficiency did not occur when cells were synchronized by alternative methods. We now report that the plating efficiency of ICP0- viruses is not enhanced at a particular stage of the cell cycle but rather is enhanced by specific cellular stresses. Both the plating and replication efficiencies of ICP0- viruses were enhanced as much as 25-fold to levels similar to that of wild-type virus when monolayers were heat shocked prior to infection. In addition to heat shock, UV-C irradiation but not cold shock of monolayers prior to infection resulted in enhanced plating efficiency. We further report that the effect of cellular stress is transient and that cell density rather than age of the monolayers is the primary determinant of ICP0- virus plating efficiency. As both cell stress and ICP0 are required for efficient reactivation from latency, the identification of cellular activities that complement ICP0- viruses may lead to the identification of cellular activities that are important for reactivation from neuronal latency.

Downregulation of varicella-zoster virus (VZV) immediate-early ORF62 transcription by VZV ORF63 correlates with virus replication in vitro and with latency

Varicella-zoster virus (VZV) open reading frame 63 (ORF63) protein is expressed during latency in human sensory ganglia. Deletion of ORF63 impairs virus replication in cell culture and establishment of latency in cotton rats. We found that cells infected with a VZV ORF63 deletion mutant yielded low titers of cell-free virus and produced very few enveloped virions detectable by electron microscopy compared with those infected with parental virus. Microarray analysis of cells infected with a recombinant adenovirus expressing ORF63 showed that transcription of few human genes was affected by ORF63; a heat shock 70-kDa protein gene was downregulated, and several histone genes were upregulated. In experiments using VZV transcription arrays, deletion of ORF63 from VZV resulted in a fourfold increase in expression of ORF62, the major viral transcriptional activator. A threefold increase in ORF62 protein was observed in cells infected with the ORF63 deletion mutant compared with those infected with parental virus. Cells infected with ORF63 mutants impaired for replication and latency (J. I. Cohen, T. Krogmann, S. Bontems, C. Sadzot-Delvaux, and L. Pesnicak, J. Virol. 79:5069-5077, 2005) showed an increase in ORF62 transcription compared with those infected with parental virus. In contrast, cells infected with an ORF63 mutant that is not impaired for replication or latency showed ORF62 RNA levels equivalent to those in cells infected with parental virus. The ability of ORF63 to downregulate ORF62 transcription may play an important role in virus replication and latency.

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.

Formation of aggresome-like structures in herpes simplex virus type 2-infected cells and a potential role in virus assembly

Herpes simplex virus (HSV) is a large, enveloped DNA virus that replicates in the nucleus and is assembled in the cytoplasm to the mature infectious virion. In this study, we present evidence that, in HSV-2-infected cells, some tegument proteins (UL46 and VP16) and newly synthesized nucleocapsids accumulate in a juxtanuclear domain sharing characteristics with aggresomes, cellular structures formed in response to misfolded proteins [J. Cell Biol. 146 (1999) 1239, J. Cell Biol. 143 (1998) 2010]. The juxtanuclear domains (aggresome-like structures) induced by HSV-2 infection localize to the microtubule organizing center (MTOC) where the clustering mitochondria, Golgi-derived vesicles, and cellular chaperones including heat shock protein (Hsp)40 and Hsp70 were recruited. Formation of aggresome-like structures was blocked by the presence of microtubule-disassembling drug nocodazole, indicating that microtubule-dependent transport may be involved in the accumulation of viral and cellular proteins at these sites in HSV-2-infected cells. These features are similar to those governing the formation of aggresomes. In contrast to aggresomes, however, the vimentin cage surrounding the MTOC was not observed with the aggresome-like structures in HSV-2-infected cells, and the maintenance of these structures required an intact microtubular network. Disruption of the aggresome-like structures by nocodazole treatment led to a low but consistent effect (10-fold decrease) on the production of intracellular infectious particles. These results suggest that aggresome-like structures do not play a critical but augmentary role in HSV-2 replication.

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.

Bacterial infection and tissue-specific Hsp72, -73 and -90 expression in western painted turtles

Heat shock proteins (Hsps) are molecular chaperones that assist intracellular folding, assembly and translocation of proteins in prokaryotic and eukaryotic cells. A variety of stresses including hyperthermia, radiation, heavy metals, ischemia, anoxia and reoxygenation have been shown to increase the expression of Hsps. Likewise, bacterial infection represents a stress for the host cell. In this study, expression of the constitutive (Hsp73) and inducible (Hsp72) isoforms of Hsp70 and Hsp90 was monitored in brain, heart, liver and skeletal muscle from the western painted turtle Chrysemys picta bellii diagnosed with Septicemic Cutaneous Ulcerative Dermatitis (SCUD). This disease is caused by a gram-negative bacterium probably belonging to the Citrobacter spp. The expression of Hsp73 increased 1.8-fold in brain and liver, 2.2-fold in heart but did not change in skeletal muscle; Hsp72 expression increased 5.5-fold in brain and 3-fold in liver but did not change in heart or skeletal muscle; Hsp90 expression increased 9-fold in brain, 2.7-fold in heart and 2.4-fold in skeletal muscle but did not change in liver. These results suggest a tissue-specific Hsp response during bacterial infection and a role for Hsps in immunopathological events in reptiles.

Elevated serum heat-shock protein 70 levels in patients with acute infection: use of an optimized enzyme-linked immunosorbent assay

Heat-shock proteins (Hsps) are highly conserved throughout evolution and evoke great interest both in basic biology and in medicine. They are expressed in small quantities under normal conditions, and their expression can be strongly induced by several stressors. Although their action is basically intracellular, it is now obvious that these proteins can be released into the extracellular environment from viable cells. In this study, the human Hsp 70 serum concentrations were determined using an optimized, cost-effective enzyme-linked immunosorbent assay (ELISA). The average intra-assay variation was 6%, whereas the average interassay variation was 9%. The sensitivity of the assay was 10 ng/ml, and spiking experiments showed recoveries between 101 and 109%. As an application of the technique, we have investigated the serum levels of human Hsp 70 in patients with infection and in healthy subjects. Our data show significantly higher levels of Hsp 70 (P = 0.003) in patients compared to control subjects. Positive correlations were noticed between the serum levels of Hsp 70 and various markers of inflammation (IL-6; r = 0.579, P = 0.009, TNF-alpha; r = 0.552, P = 0.012, IL-10; r = 0.361, P = 0.002). We conclude that Hsp 70 is involved in inflammation of infectious origin. The interindividual variation in the serum concentration of Hsp 70 precludes the use of serum Hsp 70 levels to distinguish patients from healthy subjects.

Role for heat shock proteins in the immune response to measles virus infection

Heat shock proteins (HSPs) are recognized for their support of protein metabolism. Interaction with viral proteins also enhances the development of innate and adaptive immune responses against the infecting agent. At the level of the infected cell, HSPs are uniquely expressed on the cell surface, where they represent targets of lymphokine activated killer cells. Necrosis of the infected cell releases complexes of HSP and viral protein, which, in turn, binds antigen-presenting cells (APCs). One effect of binding is to stimulate APC maturation and the release of proinflammatory cytokines, an adjuvant effect that prepares the way for adaptive immune responses. A second effect of binding is to direct the antigenic cargo of the HSP into endogenous MHC presentation pathways for priming of naive cytotoxic T cells (CTL) or activation of antigen-specific CTLs. This alternate pathway of antigen presentation is essential to CTL priming following primary brain infection. Using heat shock to elevate brain levels of HSP in a mouse model of measles virus (MV) persistent infection, we provide evidence supporting a role for HSPs in promoting cell-mediated viral clearance from brain. The findings highlight the probable relevance of HSPs to anti-MV immunity, suggesting novel routes of both therapeutic intervention and preventative measures.

The patterns of accumulation of cellular RNAs in cells infected with a wild-type and a mutant herpes simplex virus 1 lacking the virion host shutoff gene

Cellular RNA extracted from quiescent human foreskin fibroblasts harvested at 1, 3, 7, or 12 h after infection was profiled on Affymetrix HG-U95Av2 arrays designed to detect 12,626 unique human transcripts. We also profiled RNA extracted from cells harvested at 1 and 7 h after infection with a mutant lacking the gene (DeltaU(L)41) encoding a protein (vhs) brought into cells by the virus and responsible for nonselective degradation of RNA early in infection. We report the following: (i) of the 12 tested genes, up-regulated at least 3-fold relative to the values of mock infected cells, 9 were confirmed by real-time PCR. The microchip assays analyses indicate that there were 475 genes up-regulated > or =3-fold. The up-regulated genes were clustered into 15 groups with respect to temporal pattern of transcript accumulation, and classified into 20 groups on the basis of their function. The preponderance of cellular genes up-regulated early in infection play a predominant role in transcription, whereas those up-regulated at later times respond to intracellular stress or concern themselves with the cell cycle and apoptosis. (ii) The number of genes up-regulated early in infection was higher in cells infected with the DeltaU(L)41 mutant. Conversely, more genes were down-regulated late in infection with wild-type virus than with mutant viruses. Both observations are compatible with the known function of the U(L)41 gene product early in infection and with degradation of cellular RNAs in the absence of replenishment by de novo transcription of cellular genes.

Activation of the herpes simplex virus type-1 origin-binding protein (UL9) by heat shock proteins

Heat shock proteins participate in the initiation of DNA replication of different organisms by facilitating the assembly of initiation complexes. We have examined the effects of human heat shock proteins (Hsp40 and Hsp70) on the interaction of the herpes simplex virus type-1 initiator protein (UL9) with oriS, one of the viral origins of replication. Hsp40 and Hsp70 act substoichiometrically to increase the affinity of UL9 for oriS. The major contributor to this effect is Hsp40. Heat shock proteins also stimulate the ATPase activity of UL9 with oriS and increase opening of the origin. In contrast, heat shock proteins have no effect on the origin-independent activities of UL9 suggesting that their role is not merely in refolding denatured protein. These observations are consistent with a role for heat shock proteins in activating UL9 to efficiently initiate viral origin-dependent DNA replication. The action of heat shock proteins in this capacity is analogous to their role in activating the initiator proteins of other organisms.

Molecular chaperone Hsp90 is important for vaccinia virus growth in cells

Molecular chaperones assist protein folding, and some chaperones are induced by heat, nutrient depletion, or pathogen invasion. This study investigates the role played by Hsp90 in the life cycle of vaccinia virus. The titer of vaccinia intracellular mature virions (IMV) was reduced by 2 orders of magnitude in RK13 cells treated with geldanamycin (GA), which blocks the ATPase activity of Hsp90. GA does not affect expression from the viral early promoter, but treatment with GA delays DNA replication and intermediate gene transcription and reduces expression from the viral late promoter. Vaccinia virus infection does not induce Hsp90 expression; however, intracellular distribution of Hsp90 is altered in virus-infected cells. Hsp90 is restricted to the cytoplasm of mock-infected cells; in contrast, Hsp90 is transiently associated with virosomes in virus-infected cells although it is not incorporated into IMV. In addition, Hsp90 interacts with viral core protein 4a, the mature form of the A10L gene product, in virus-infected cells. In conclusion, these results suggest that a cellular chaperone protein, Hsp90, is important for vaccinia virus growth in cultured cells and that viral core protein 4a associates with Hsp90-containing complexes in the infected cells.

Cell-to-cell movement and assembly of a plant closterovirus: roles for the capsid proteins and Hsp70 homolog

Diverse animal and plant viruses are able to translocate their virions between neighboring cells via intercellular connections. In this work, we analyze the virion assembly and cell-to-cell movement of a plant closterovirus and reveal a strong correlation between these two processes. The filamentous virions of a closterovirus possess a long body formed by the major capsid protein (CP) and a short tail formed by the minor capsid protein (CPm). Genetic and biochemical analyses show that the functions of these virion components are distinct. A virion body is required primarily for genome protection, whereas a tail represents a specialized device for cell-to-cell movement. Furthermore, tail assembly is mediated by the viral Hsp70 homolog (Hsp70h) that becomes an integral part of the virion. Inactivation of the ATPase domain of Hsp70h results in assembly of tailless virions that are incapable of translocation. A dual role for the viral molecular chaperone Hsp70h in virion assembly and transport, combined with the previous finding of this protein in intercellular channels, allowed us to propose a model of closteroviral movement from cell to cell.

Activation of heat-shock response by an adenovirus is essential for virus replication

Successful viral infection requires viruses to redirect host biochemistry to replicate the viral genome, and produce and assemble progeny virions. Cellular heat-shock responses, which are characterized as elevation and relocalization of heat-shock proteins, occur during replication of many viruses. Such responses might be host reactions to the synthesis of foreign protein, or might be irrelevant consequences of the viral need to activate transcription. Alternatively, as heat-shock proteins can facilitate protein folding, activating a heat-shock response might be a specific virus function ensuring proper synthesis of viral proteins and virions. It is not possible to determine whether heat-shock response is essential for virus replication, because the implicated viral genes (such as Ad5 EIA, ref. 10) also control other essential replication steps. Here we report that expression of Gam1, a protein encoded by the avian virus CELO (ref. 11), elevates and relocalizes hsp70 and hsp40. Gam1-negative CELO is replication-defective; however, Gam1 function can be partially replaced by either heat shock or forced hsp40 expression. Thus, an essential function of Gam1 during virus replication is to activate host heat-shock responses with hsp40 as a primary target.

Recombinant adenoviral vectors have adjuvant activity and stimulate T cell responses against tumor cells

The host-immune response against adenoviruses forms a major obstacle for their use as gene therapy vectors for treatment of genetic defects. None the less, they are the preferred vectors for in vivo gene transfer in experimental gene therapy protocols for cancer. In this article we demonstrate the antitumor efficacy of adenovirus-mediated transfer of human interleukin-2 cDNA in the rat-CC531 model for hepatic metastases of colorectal cancer: intratumoral administration of 10 plaque-forming units of the hlL-2-expressing adenoviral vector, AdCAIL-2, resulted in a cessation of tumor growth in 80% of the injected tumors. In control groups receiving AdCnull, a vector with the same viral backbone, but lacking transgene expression, none of the tumors responded. However, intratumoral treatment with this vector significantly enhanced tumor regression induced by systemic IL-2 protein treatment, which was used as a positive control. In addition we show, by performing delayed-type of hypersensitivity assays, that AdCnull when injected intratumorally enhances recognition of tumor antigens by T lymphocytes to the same extent as intratumoral treatment with the IL-2-expressing vector. The replication-deficient adenoviruses appear to have a therapeutic advantage in cytokine-mediated immunotherapy: even adenovirus vectors that do not express a transgene, show adjuvant activity and stimulate an antitumor immune response.

Characterization by two-dimensional gel electrophoresis of host proteins whose synthesis is sustained or stimulated during the course of herpes simplex virus type 1 infection

Herpes simplex virus type 1 (HSV-1) gene expression is concomitant with a selective shutoff of host protein synthesis. While the synthesis of the vast majority of cellular proteins is inhibited immediately after infection, several cellular proteins continue to be synthesized, even during the late phase of infection. Because these cellular proteins may intervene in the life cycle of the virus, we undertook two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) analyses to evaluate the proportion of cellular proteins that is represented by these particular proteins. Human cells were infected with HSV-1. At different times after infection, proteins were labeled with 35S just prior to harvesting. The rate of synthesis of a set of 183 acidic host proteins, as well as that of ribosomal proteins, was measured during the course of infection, after separation by 2-D PAGE. As expected, HSV-1 induces a strong inhibition of host protein synthesis immediately after infection. However, the synthesis of basic ribosomal proteins and that of an unexpected high proportion of the sub-set of cellular proteins analyzed is sustained or stimulated during HSV-1 infection. A 2-D PAGE analysis outlining the expression patterns of these proteins at different times of infection is presented.

HSC70 interactions with SV40 viral proteins differ between permissive and nonpermissive mammalian cells

SV40 belongs to a group of DNA tumor viruses which induce the expression of the 70 Kd heat shock proteins, but the meaning of this induction remains unclear. Investigating the role of hsc70 in the SV40 life cycle, we found that the protein translocates to the nucleus late in infection of permissive CV1 cells, in contrast to infected nonpermissive BALB/3T3 and NIH/3T3 cells in which hsc70 remains cytoplasmic. Moreover, the pattern of hsc70 nuclear staining was diffused and clearly distinguishable from that observed after heat shock. In addition hsc70 late in infection coimmunoprecipitated with the viral capsid protein VP1, suggesting a role in the process of viral packaging. Interactions of hsc70 with the early viral oncoprotein T antigen were observed only in nonpermissive cells, indicating that the binding of the above proteins is specific to cells that do not support viral propagation. Finally, treatment of permissive CV1 cells with interferon gamma, a known antiviral cytokine, resulted in hsc70 binding to T antigen. Our results suggest that the role of hsc70 in the process of SV40 infection is directly related to the ability of the host cells to support viral propagation and is clearly different between permissive and nonpermissive cell lines.

Gene transfer into hippocampal slice cultures with an adenovirus vector driven by cytomegalovirus promoter: stable co-expression of green fluorescent protein and lacZ genes

Virus-mediated gene transfer into identified neurons of organotypic hippocampal slice cultures offers a great potential for studying the cellular and molecular mechanisms of synaptic plasticity. We describe here a new adenovirus vector Ad-GFP-lacZ carrying an early cytomegalovirus (CMV) gene promoter that efficiently co-transferred the beta-galactosidase (lacZ) and green fluorescent protein (GFP) genes in rat organotypic hippocampal slice cultures. Monitoring of GFP fluorescence and immuno-histochemical staining for beta-galactosidase showed that the expression of the transferred genes was widespread in the glial cells and neurons of CA1, CA3/4, and dentate gyrus regions. Immunoblot analyses showed that the expression of gamma-galactosidase and GFP was maximal about 48 h after infection of hippocampal slices with the adenovirus vector and the expression levels were maintained for several weeks. Also, immunoblot analyses showed no significant differences in the MAP-2 and glial fibrillary acidic protein levels in the adenovirus vector infected and uninfected hippocampal slices. In addition, we found that the infection of hippocampal slices with the adenovirus vector caused no significant increase in the induction of heat shock protein (HSP)-70 and showed no change in their electrophysiological properties as measured by stable field synaptic potentials in CA1 region and its reactivity to high frequency stimulation. Our data suggest that this adenovirus vector can be exploited to transfer multiple genes into neurons and may have implications for developing strategies for gene therapy.

HSP70 homolog functions in cell-to-cell movement of a plant virus

Plant closteroviruses encode a homolog of the HSP70 (heat shock protein, 70 kDa) family of cellular proteins. To facilitate studies of the function of HSP70 homolog (HSP70h) in viral infection, the beet yellows closterovirus (BYV) was modified to express green fluorescent protein. This tagged virus was competent in cell-to-cell movement, producing multicellular infection foci similar to those formed by the wild-type BYV. Inactivation of the HSP70h gene by replacement of the start codon or by deletion of 493 codons resulted in complete arrest of BYV translocation from cell to cell. Identical movement-deficient phenotypes were observed in BYV variants possessing HSP70h that lacked the computer-predicted ATPase domain or the C-terminal domain, or that harbored point mutations in the putative catalytic site of the ATPase. These results demonstrate that the virus-specific member of the HSP70 family of molecular chaperones functions in intercellular translocation and represents an additional type of a plant viral-movement protein.

Subcellular localization of the HSP70-homolog encoded by beet yellows closterovirus

Closteroviridae is the only viral family coding for a homolog of HSP70 (HSP70h). Polyclonal antiserum to recombinant beet yellows closterovirus (BYV) HSP70h was generated and used for immunogold labeling of the leaf samples derived from the infected Nicotiana benthamiana plants. Ultrastructural analysis revealed the preferential accumulation of BYV in phloem, although occasional infection of the leaf mesophyll cells was also observed. The strongest HSP70h-specific labeling was associated with virion aggregates and vesicles harboring scattered virions. HSP70h was also observed in close proximity of plasmodesmata and inside the plasmodesmatal channels. The possible role of the BYV HSP70h in RNA encapsidation was tested in tobacco protoplasts. A BYV mutant possessing an inactivated HSP70h gene exhibited no detectable encapsidation defects. Collectively, the obtained results suggested that closteroviral HSP70h escorts the virions to their destinations inside the infected cells and possibly participates in the intercellular translocation of BYV.