Does Japanese encephalitis virus share the same cellular receptor with other mosquito-borne flaviviruses on the C6/36 mosquito cells?

Mechanism and complex roles of HSC70/HSPA8 in viral entry

The process of viruses entering host cells is complex, involving multiple aspects of the molecular organization of the cell membrane, viral proteins, the interaction of receptor molecules, and cellular signaling. Most viruses depend on endocytosis for uptake, when viruses reach the appropriate location, they are released from the vesicles, undergo uncoating, and release their genomes. Heat shock cognate protein 70(HSC70): also known as HSPA8, a protein involved in mediating clathrin-mediated endocytosis (CME), is involved in various viral entry processes. In this mini-review, our goal is to provide a summary of the function of HSC70 in viral entry. Understanding the interaction networks of HSC70 with viral proteins helps to provide new directions for targeted therapeutic strategies against viral infections.

Single-cell RNA sequencing reveals the immune features and viral tropism in the central nervous system of mice infected with Japanese encephalitis virus

Japanese encephalitis virus (JEV) is a neurotropic pathogen that causes lethal encephalitis. The high susceptibility and massive proliferation of JEV in neurons lead to extensive neuronal damage and inflammation within the central nervous system. Despite extensive research on JEV pathogenesis, the effect of JEV on the cellular composition and viral tropism towards distinct neuronal subtypes in the brain is still not well comprehended. To address these issues, we performed single-cell RNA sequencing (scRNA-seq) on cells isolated from the JEV-highly infected regions of mouse brain. We obtained 88,000 single cells and identified 34 clusters representing 10 major cell types. The scRNA-seq results revealed an increasing amount of activated microglia cells and infiltrating immune cells, including monocytes & macrophages, T cells, and natural killer cells, which were associated with the severity of symptoms. Additionally, we observed enhanced communication between individual cells and significant ligand-receptor pairs related to tight junctions, chemokines and antigen-presenting molecules upon JEV infection, suggesting an upregulation of endothelial permeability, inflammation and antiviral response. Moreover, we identified that Baiap2-positive neurons were highly susceptible to JEV. Our findings provide valuable clues for understanding the mechanism of JEV induced neuro-damage and inflammation as well as developing therapies for Japanese encephalitis.

CD4 is an important host factor for Japanese encephalitis virus entry and replication in PK-15 cells

Japanese encephalitis virus (JEV) is a flavivirus that is spread through mosquito bites and is the leading cause of viral encephalitis in Asia. JEV can infect a variety of cell types; however, crucial receptor molecules remain unclear. The purpose of this study was to determine whether porcine CD4 protein is a receptor protein that impacts JEV entry into PK15 cells and subsequent viral replication. We confirmed the interaction between the JEV E protein and the CD4 protein through Co-IP, virus binding and internalization, antibody blocking, and overexpression and created a PK-15 cell line with CD4 gene knockdown by CRISPR/Cas9. The results show that CD4 interacts with JEV E and that CD4 knockdown cells altered virus adsorption and internalization, drastically reducing virus attachment. The level of viral transcription in CD4 antibody-blocked cells, vs. control cells, was decreased by 49.1%. Based on these results, we believe that CD4 is a receptor protein for JEVs. Furthermore, most viral receptors appear to be associated with lipid rafts, and colocalization studies demonstrate the presence of CD4 protein on lipid rafts. RT‒qPCR and WB results show that virus replication was suppressed in PK-15-CD4KD cells. The difference in viral titer between KD and WT PK-15 cells peaked at 24 h, and the viral titer in WT PK-15 cells was 5.6 × 106, whereas in PK-15-CD4KD cells, it was only 1.8 × 106, a 64% drop, demonstrating that CD4 deficiency has an effect on the process of viral replication. These findings suggest that JEV enters porcine kidney cells via lipid raft-colocalized CD4, and the proliferation process is positively correlated with CD4.

Cellular protein HSC70 promotes fowl adenovirus serotype 4 replication in LMH cells via interacting with viral 100K protein

Fowl adenovirus serotype 4 (FAdV-4), the predominant causative agent of hepatitis-hydropericardium syndrome (HHS), has caused severe economic losses to poultry industry since 2015. Although fiber2 and hexon have been confirmed to be the virulence-related factors, the roles of nonstructural viral proteins in pathogenicity of FAdV-4 remain poorly understood. Here, a tandem mass spectrometry (MS) was used to identify host factors interacted with 100K protein of hypervirulent FAdV-4 isolate (CH/HNJZ/2015), and 2595 cellular proteins associated with many biological processes and pathways were identified according to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses. Among the proteins, HSC70 was verified to interact with 100K through co-immunoprecipitation assay. Notably, overexpression of HSC70 promoted the replication of FAdV-4 in LMH cells, whereas blocking HSC70 with inhibitor ver-155008 markedly suppressed viral replication. Collectively, these findings suggested that many cellular proteins involved in FAdV-4 infection through interacting with 100K and HSC70 positively regulated virus replication.

αVβ3 Integrin Expression Is Essential for Replication of Mosquito and Tick-Borne Flaviviruses in Murine Fibroblast Cells

The Flavivirus genus includes a number of important viruses that are pathogenic to humans and animals and are responsible for outbreaks across the globe. Integrins, a family of heterodimeric transmembrane molecules expressed in all nucleated cells mediate critical functions of cell physiology and cell cycle. Integrins were previously postulated to be involved in flavivirus entry and to modulate flavivirus replication efficiency. In the present study, mouse embryonic fibroblasts (MEF), lacking the expression of αVβ3 integrin (MEF-αVβ3^−/−), were infected with four different flaviviruses, namely yellow fever virus (YFV), West Nile virus (WNV), Usutu virus (USUV) and Langat virus (LGTV). The effects of the αVβ3 integrin absence in double-knockout MEF-αVβ3^−/− on flavivirus binding, internalization and replication were compared to the respective wild-type cells. Binding to the cell surface for all four flaviviruses was not affected by the ablation of αVβ3 integrin, whereas internalization of USUV and WNV was slightly affected by the loss of αVβ3 integrin expression. Most interestingly, the deletion of αVβ3 integrin strongly impaired replication of all flaviviruses with a reduction of up to 99% on virus yields and a strong reduction on flavivirus anti-genome RNA synthesis. In conclusion, our results demonstrate that αVβ3 integrin expression in flavivirus-susceptible cell lines enhances the flavivirus replication.

Mechanism and Complex Roles of HSC70 in Viral Infections

Heat shock cognate 71-kDa protein (HSC70), a constitutively expressed molecular chaperon within the heat shock protein 70 family, plays crucial roles in maintaining cellular environmental homeostasis through implicating in a wide variety of physiological processes, such as ATP metabolism, protein folding and transporting, antigen processing and presentation, endocytosis, and autophagy. Notably, HSC70 also participates in multiple non-communicable diseases and some pathogen-caused infectious diseases. It is known that virus is an obligatory intracellular parasite and heavily relies on host machineries to self-replication. Undoubtedly, HSC70 is a striking target manipulated by virus to ensure the successful propagation. In this review, we summarize the recent advances of the regulatory mechanisms of HSC70 during viral infections, which will be conducive to further study viral pathogenesis.

Prohibitin 1/2 mediates Dengue-3 entry into human neuroblastoma (SH-SY5Y) and microglia (CHME-3) cells

Background

Very few studies have identified receptor molecules for dengue virus (DENV) on neural cells. This study was designed to identify putative receptor/(s) involved in entry of DENV-3 in human neural cells of various lineages; neuronal-SH-SY5Y, astroglial-U-87 MG and microglial-CHME-3 cells.

Result

Virus overlay protein binding assay, LC-MS/MS and SEQUEST identified prohibitin1/2 (PHB1/2) as interacting proteins on SH-SY5Y, CHME-3, and U-87 MG cells. Infection inhibition and siRNA assays confirmed the role of PHB1/2 in the entry of DENV-3 into SH-SY5Y and CHME-3 cells but not in U-87 MG cells. Indirect immunofluorescence and flow-cytometry demonstrated the presence of PHB1/2 on the surface of SH-SY5Y and CHME-3 cells. Co-immunoprecipitation and Western blot, as well as double labelling, reconfirmed the interaction between PHB1/2 and DENV-3 EDIII protein.

Conclusion

These observations together for the first time indicate that PHB1/2 may serve as a putative receptor for DENV-3 in SH-SY5Y and CHME-3 cells. The study provided insights into DENV-3 and neural cell interactions.

Hsp40 Protein DNAJB6 Interacts with Viral NS3 and Inhibits the Replication of the Japanese Encephalitis Virus

The Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus prevalent in east and southeast Asia, the Western Pacific, and northern Australia. Since viruses are obligatory intracellular pathogens, the dynamic processes of viral entry, replication, and assembly are dependent on numerous host-pathogen interactions. Efforts to identify JEV-interacting host factors are ongoing because their identification and characterization remain incomplete. Three enzymatic activities of flavivirus non-structural protein 3 (NS3), including serine protease, RNA helicase, and triphosphatase, play major roles in the flaviviruses lifecycle. To identify cellular factors that interact with NS3, we screened a human brain cDNA library using a yeast two-hybrid assay, and identified eight proteins that putatively interact with NS3: COPS5, FBLN5, PPP2CB, CRBN, DNAJB6, UBE2N, ZNF350, and GPR137B. We demonstrated that the DnaJ heat shock protein family (Hsp40) member B6 (DNAJB6) colocalizes and interacts with NS3, and has a negative regulatory function in JEV replication. We also show that loss of DNAJB6 function results in significantly increased viral replication, but does not affect viral binding or internalization. Moreover, the time-course of DNAJB6 disruption during JEV infection varies in a viral load-dependent manner, suggesting that JEV targets this host chaperone protein for viral benefit. Deciphering the modes of NS3-interacting host proteins functions in virion production will shed light on JEV pathogenic mechanisms and may also reveal new avenues for antiviral therapeutics.

Flavivirus Receptors: Diversity, Identity, and Cell Entry

Flaviviruses are emerging and re-emerging arthropod-borne pathogens responsible for significant mortality and morbidity worldwide. The genus comprises more than seventy small, positive-sense, single-stranded RNA viruses, which are responsible for a spectrum of human and animal diseases ranging in symptoms from mild, influenza-like infection to fatal encephalitis and haemorrhagic fever. Despite genomic and structural similarities across the genus, infections by different flaviviruses result in disparate clinical presentations. This review focusses on two haemorrhagic flaviviruses, dengue virus and yellow fever virus, and two neurotropic flaviviruses, Japanese encephalitis virus and Zika virus. We review current knowledge on host-pathogen interactions, virus entry strategies and tropism.

Early Events in Japanese Encephalitis Virus Infection: Viral Entry

Japanese encephalitis virus (JEV), a mosquito-borne zoonotic flavivirus, is an enveloped positive-strand RNA virus that can cause a spectrum of clinical manifestations, ranging from mild febrile illness to severe neuroinvasive disease. Today, several killed and live vaccines are available in different parts of the globe for use in humans to prevent JEV-induced diseases, yet no antivirals are available to treat JEV-associated diseases. Despite the progress made in vaccine research and development, JEV is still a major public health problem in southern, eastern, and southeastern Asia, as well as northern Oceania, with the potential to become an emerging global pathogen. In viral replication, the entry of JEV into the cell is the first step in a cascade of complex interactions between the virus and target cells that is required for the initiation, dissemination, and maintenance of infection. Because this step determines cell/tissue tropism and pathogenesis, it is a promising target for antiviral therapy. JEV entry is mediated by the viral glycoprotein E, which binds virions to the cell surface (attachment), delivers them to endosomes (endocytosis), and catalyzes the fusion between the viral and endosomal membranes (membrane fusion), followed by the release of the viral genome into the cytoplasm (uncoating). In this multistep process, a collection of host factors are involved. In this review, we summarize the current knowledge on the viral and cellular components involved in JEV entry into host cells, with an emphasis on the initial virus-host cell interactions on the cell surface.

Identification of Glucose-Regulated Protein 78 (GRP78) as a Receptor in BHK-21 Cells for Duck Tembusu Virus Infection

Since 2010, outbreak and spread of tembusu virus (TMUV) caused huge losses to the breeding industry of waterfowl in several provinces of China. In this study, we identify the glucose-regulated protein 78 (GRP78) as a receptor in BHK-21 cells for duck TMUV infection. Using cell membrane from BHK-21 cells, a TMUV-binding protein of approximately 70 kDa was observed by viral overlay protein binding assay (VOPBA). LC-MS/MS analysis and co-immunoprecipitation identified GRP78 as a protein interacting with TMUV. Antibody against GRP78 inhibited the binding of TMUV to the cell surface of BHK-21 cells. Indirect immunofluorescence studies showed the colocalization of GRP78 with TMUV in virus-infected BHK-21 cells. We found that GRP78 over-expression increased TMUV infection, whereas GRP78 knockdown by using a specific small interfering RNA inhibited TMUV infection in BHK-21 cells. Taken together, our results indicate that GRP78 is a novel host factor involved in TMUV entry.

mosGCTL-7, a C-Type Lectin Protein, Mediates Japanese Encephalitis Virus Infection in Mosquitoes

Japanese encephalitis virus (JEV) is an arthropod-borne flavivirus prevalent in Asia and the Western Pacific and is the leading cause of viral encephalitis. JEV is maintained in a transmission cycle between mosquitoes and vertebrate hosts, but the molecular mechanisms by which the mosquito vector participates in transmission are unclear. We investigated the expression of all C-type lectins during JEV infection in Aedes aegypti The C-type lectin mosquito galactose-specific C-type lectin 7 (mosGCTL-7) (VectorBase accession no. AAEL002524) was significantly upregulated by JEV infection and facilitated infection in vivo and in vitro mosGCTL-7 bound to the N-glycan at N154 on the JEV envelope protein. This recognition of viral N-glycan by mosGCTL-7 is required for JEV infection, and we found that this interaction was Ca²⁺ dependent. After mosGCTL-7 bound to the glycan, mosPTP-1 bound to mosGCTL-7, promoting JEV entry. The viral burden in vivo and in vitro was significantly decreased by mosPTP-1 double-stranded RNA (dsRNA) treatment, and infection was abolished by anti-mosGCTL-7 antibodies. Our results indicate that the mosGCTL-7/mosPTP-1 pathway plays a key role in JEV infection in mosquitoes. An improved understanding of the mechanisms underlying flavivirus infection in mosquitoes will provide further opportunities for developing new strategies to control viral dissemination in nature.IMPORTANCE Japanese encephalitis virus is a mosquito-borne flavivirus and is the primary cause of viral encephalitis in the Asia-Pacific region. Twenty-four countries in the WHO Southeast Asia and Western Pacific regions have endemic JEV transmission, which exposes >3 billion people to the risks of infection, although JEV primarily affects children. C-type lectins are host factors that play a role in flavivirus infection in humans, swine, and other mammals. In this study, we investigated C-type lectin functions in JEV-infected Aedes aegypti and Culex pipiens pallens mosquitoes and cultured cells. JEV infection changed the expression of almost all C-type lectins in vivo and in vitro, and mosGCTL-7 bound to the JEV envelope protein via an N-glycan at N154. Cell surface mosPTP-1 interacted with the mosGCTL-7-JEV complex to facilitate virus infection in vivo and in vitro Our findings provide further opportunities for developing new strategies to control arbovirus dissemination in nature.

GRP78 Is an Important Host Factor for Japanese Encephalitis Virus Entry and Replication in Mammalian Cells

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, is the leading cause of viral encephalitis in Southeast Asia with potential to become a global pathogen. Here, we identify glucose-regulated protein 78 (GRP78) as an important host protein for virus entry and replication. Using the plasma membrane fractions from mouse neuronal (Neuro2a) cells, mass spectroscopy analysis identified GRP78 as a protein interacting with recombinant JEV envelope protein domain III. GRP78 was found to be expressed on the plasma membranes of Neuro2a cells, mouse primary neurons, and human epithelial Huh-7 cells. Antibodies against GRP78 significantly inhibited JEV entry in all three cell types, suggesting an important role of the protein in virus entry. Depletion of GRP78 by small interfering RNA (siRNA) significantly blocked JEV entry into Neuro2a cells, further supporting its role in virus uptake. Immunofluorescence studies showed extensive colocalization of GRP78 with JEV envelope protein in virus-infected cells. This interaction was also confirmed by immunoprecipitation studies. Additionally, GRP78 was shown to have an important role in JEV replication, as treatment of cells post-virus entry with subtilase cytotoxin that specifically cleaved GRP78 led to a substantial reduction in viral RNA replication and protein synthesis, resulting in significantly reduced extracellular virus titers. Our results indicate that GRP78, an endoplasmic reticulum chaperon of the HSP70 family, is a novel host factor involved at multiple steps of the JEV life cycle and could be a potential therapeutic target.IMPORTANCE Recent years have seen a rapid spread of mosquito-borne diseases caused by flaviviruses. The flavivirus family includes West Nile, dengue, Japanese encephalitis, and Zika viruses, which are major threats to public health with potential to become global pathogens. JEV is the major cause of viral encephalitis in several parts of Southeast Asia, affecting a predominantly pediatric population with a high mortality rate. This study is focused on identification of crucial host factors that could be targeted to cripple virus infection and ultimately lead to development of effective antivirals. We have identified a cellular protein, GRP78, that plays a dual role in virus entry and virus replication, two crucial steps of the virus life cycle, and thus is a novel host factor that could be a potential therapeutic target.

Sphingomyelin generated by sphingomyelin synthase 1 is involved in attachment and infection with Japanese encephalitis virus

Japanese encephalitis virus (JEV) is a mosquito-borne RNA virus which infects target cells via the envelope protein JEV-E. However, its cellular targets are largely unknown. To investigate the role of sphingomyelin (SM) in JEV infection, we utilized SM-deficient immortalized mouse embryonic fibroblasts (tMEF) established from SM synthase 1 (SMS1)/SMS2 double knockout mice. SMS deficiency significantly reduced both intracellular and extracellular JEV levels at 48 h after infection. Furthermore, after 15 min treatment with JEV, the early steps of JEV infection such as attachment and cell entry were also diminished in SMS-deficient tMEFs. The inhibition of JEV attachment and infection were recovered by overexpression of SMS1 but not SMS2, suggesting SMS1 contributes to SM production for JEV attachment and infection. Finally, intraperitoneal injection of JEV into SMS1-deficient mice showed an obvious decrease of JEV infection and its associated pathologies, such as meningitis, lymphocyte infiltration, and elevation of interleukin 6, compared with wild type mice. These results suggest that SMS1-generated SM on the plasma membrane is related in JEV attachment and subsequent infection, and may be a target for inhibition of JEV infection.

Inflammatory and oxidative stress in rotavirus infection

Rotaviruses are the single leading cause of life-threatening diarrhea affecting children under 5 years of age. Rotavirus entry into the host cell seems to occur by sequential interactions between virion proteins and various cell surface molecules. The entry mechanisms seem to involve the contribution of cellular molecules having binding, chaperoning and oxido-reducing activities. It appears to be that the receptor usage and tropism of rotaviruses is determined by the species, cell line and rotavirus strain. Rotaviruses have evolved functions which can antagonize the host innate immune response, whereas are able to induce endoplasmic reticulum (ER) stress, oxidative stress and inflammatory signaling. A networking between ER stress, inflammation and oxidative stress is suggested, in which release of calcium from the ER increases the generation of mitochondrial reactive oxygen species (ROS) leading to toxic accumulation of ROS within ER and mitochondria. Sustained ER stress potentially stimulates inflammatory response through unfolded protein response pathways. However, the detailed characterization of the molecular mechanisms underpinning these rotavirus-induced stressful conditions is still lacking. The signaling events triggered by host recognition of virus-associated molecular patterns offers an opportunity for the development of novel therapeutic strategies aimed at interfering with rotavirus infection. The use of N-acetylcysteine, non-steroidal anti-inflammatory drugs and PPARγ agonists to inhibit rotavirus infection opens a new way for treating the rotavirus-induced diarrhea and complementing vaccines.

Japanese encephalitis virus invasion of cell: allies and alleys

The mosquito-borne flavivirus, Japanese encephalitis virus (JEV), is the leading cause of virus-induced encephalitis globally and a major public health concern of several countries in Southeast Asia, with the potential to become a global pathogen. The virus is neurotropic, and the disease ranges from mild fever to severe hemorrhagic and encephalitic manifestations and death. The early steps of the virus life cycle, binding, and entry into the cell are crucial determinants of infection and are potential targets for the development of antiviral therapies. JEV can infect multiple cell types; however, the key receptor molecule(s) still remains elusive. JEV also has the capacity to utilize multiple endocytic pathways for entry into cells of different lineages. This review not only gives a comprehensive update on what is known about the virus attachment and receptor system (allies) and the endocytic pathways (alleys) exploited by the virus to gain entry into the cell and establish infection but also discusses crucial unresolved issues. We also highlight common themes and key differences between JEV and other flaviviruses in these contexts.

Dengue virus models based on mice as experimental hosts

Dengue virus (DENV) causes dengue fever, a widely distributed endemic disease transmitted by mosquitoes. The complex interaction of DENV with the human immune system has complicated the development of an effective vaccine. This may be attributed, at least in part, to the lack of a suitable animal model capable to reproduce symptoms observed in humans. Mouse models are simple but usually rely on host-adapted virus strains or immunodeficient mouse lineages. Recent evidences indicated that some natural DENV strains are capable to infect immunocompetent mice. In addition, humanized mouse lineages can more faithfully reproduce some of the symptoms observed in humans. Such experimental models are valuable tools for the study of DENV biology.

Efficient production of Tymovirus like particles displaying immunodominant epitopes of Japanese Encephalitis Virus envelope protein

Japanese Encephalitis (JE) is a mosquito borne arboviral infection caused by Japanese Encephalitis Virus (JEV). It is a major cause of viral encephalitis in Asian countries including India. In the present study, we have used a Tymovirus [i.e. Physalis Mottle Virus (PhMV) coat protein (CP)], which forms virus like particles (VLPs) as a template to display immunodominant epitopes of JEV envelope (E) protein. The immunodominant epitopes of JEV were inserted at the N-terminus of the wild type PhMV CP, and these constructs were cloned and expressed in Escherichia coli. The chimeric proteins were purified from the inclusion bodies and evaluated for VLP formation. The purified protein was identified by Western blotting and VLP formation was studied and confirmed by transmission electron microscopy and dynamic light scattering. Finally, the immunogenicity was studied in mice. Our results indicate that the chimeric protein with JEV epitopes assembled efficiently to form VLPs generating neutralizing antibodies. Hence, we report the purified chimeric VLP would be a potent vaccine candidate, which needs to be evaluated in a mouse challenge model.

Viral RNA intermediates as targets for detection and discovery of novel and emerging mosquito-borne viruses

Mosquito-borne viruses encompass a range of virus families, comprising a number of significant human pathogens (e.g., dengue viruses, West Nile virus, Chikungunya virus). Virulent strains of these viruses are continually evolving and expanding their geographic range, thus rapid and sensitive screening assays are required to detect emerging viruses and monitor their prevalence and spread in mosquito populations. Double-stranded RNA (dsRNA) is produced during the replication of many of these viruses as either an intermediate in RNA replication (e.g., flaviviruses, togaviruses) or the double-stranded RNA genome (e.g., reoviruses). Detection and discovery of novel viruses from field and clinical samples usually relies on recognition of antigens or nucleotide sequences conserved within a virus genus or family. However, due to the wide antigenic and genetic variation within and between viral families, many novel or divergent species can be overlooked by these approaches. We have developed two monoclonal antibodies (mAbs) which show co-localised staining with proteins involved in viral RNA replication in immunofluorescence assay (IFA), suggesting specific reactivity to viral dsRNA. By assessing binding against a panel of synthetic dsRNA molecules, we have shown that these mAbs recognise dsRNA greater than 30 base pairs in length in a sequence-independent manner. IFA and enzyme-linked immunosorbent assay (ELISA) were employed to demonstrate detection of a panel of RNA viruses from several families, in a range of cell types. These mAbs, termed monoclonal antibodies to viral RNA intermediates in cells (MAVRIC), have now been incorporated into a high-throughput, economical ELISA-based screening system for the detection and discovery of viruses from mosquito populations. Our results have demonstrated that this simple system enables the efficient detection and isolation of a range of known and novel viruses in cells inoculated with field-caught mosquito samples, and represents a rapid, sequence-independent, and cost-effective approach to virus discovery.

Heat shock cognate protein 70 isoform D is required for clathrin-dependent endocytosis of Japanese encephalitis virus in C6/36 cells

Japanese encephalitis virus (JEV), one of encephalitic flaviviruses, is naturally transmitted by mosquitoes. During infection, JEV generally enters host cells via receptor-mediated clathrin-dependent endocytosis that requires the 70 kDa heat-shock protein (Hsp70). Heat-shock cognate protein 70 (Hsc70) is one member of the Hsp70 family and is constitutively expressed; thus, it may be expressed under physiological conditions. In C6/36 cells, Hsc70 is upregulated in response to JEV infection. Since Hsc70 shows no relationship with viruses attaching to the cell surface, it probably does not serve as the receptor according to our results in the present study. In contrast, Hsc70 is evidently associated with virus penetration into the cell and resultant acidification of intracellular vesicles. It suggests that Hsc70 is highly involved in clathrin-mediated endocytosis, particularly at the late stage of viral entry into host cells. Furthermore, we found that Hsc70 is composed of at least three isoforms, including B, C and D; of these, isoform D helps JEV to penetrate C6/36 cells via clathrin-mediated endocytosis. This study provides relevant evidence that sheds light on the regulatory mechanisms of JEV infection in host cells, especially on the process of clathrin-mediated endocytosis.

Voltage dependent anion channel is redistributed during Japanese encephalitis virus infection of insect cells

Despite the availability of an effective vaccine, Japanese encephalitis remains a significant cause of morbidity and mortality in many parts of Asia. Japanese encephalitis is caused by the Japanese encephalitis virus (JEV), a mosquito transmitted flavivirus. Many of the details of the virus replication cycle in mosquito cells remain unknown. This study sought to determine whether GRP78, a well-characterized flavivirus E protein interacting protein, interacted with JEV E protein in insect cells, and whether this interaction was mediated at the cell surface. GRP78 was shown to interact with JEV E protein by coimmunoprecipitation, and was additionally shown to interact with voltage dependent anion protein (VDAC) through the same methodology. Antibody inhibition experiments showed that neither GRP78 nor VDAC played a role in JEV internalization to insect cells. Interestingly, VDAC was shown to be significantly relocalized in response to JEV infection, and significant levels of colocalization between VDAC and GRP78 and VDAC and ribosomal L28 protein were seen in JEV infected but not uninfected cells. This is the first report of relocalization of VDAC in response to JEV infection and suggests that this may be a part of the JEV replication strategy in insect cells.

Characterization and binding analysis of a microneme adhesive repeat domain-containing protein from Toxoplasma gondii

The intracellular parasite Toxoplasma gondii invades almost all nucleated cells, and has infected approximately 34% of the world's population to date. In order to develop effective vaccines against T. gondii infection, understanding of the role of the molecules that are involved in the invasion process is important. For this purpose, we characterized T. gondii proteins that contain microneme adhesive repeats (MARs), which are common in moving junction proteins. T. gondii MAR domain-containing protein 4a (TgMCP4a), which contains repeats of 17-22 amino acid segments at the N-terminus and three putative MAR domains at the C-terminus, is localized near the rhoptry of extracellular parasites. Following infection, TgMCP4a was detected in the parasitophorous vacuole. The recombinant Fc-TgMCP4a N-terminus protein (rTgMCP4a-1/Fc) showed binding activity to the surface proteins of Vero, 293T, and CHO cells. The recombinant GST-TgMCP4a N-terminus protein (rTgMCP4a-1/GST), which exhibited binding activity, was used to pull down the interacting factors from 293T cell lysate, and subsequent mass spectrometry analysis revealed that three types of heat shock proteins (HSPs) interacted with TgMCP4a. Transfection of a FLAG fusion protein of TgMCP4a-1 (rTgMCP4a-1/FLAG) into 293T cell and the following immunoprecipitation with anti-FLAG antibody confirmed the interactions of HSC70 with TgMCP4a. The addition of rTgMCP4a-1/GST into the culture medium significantly affected the growth of the parasite. This study hints that T. gondii may employ HSP proteins of host cell to facilitate their growth.

Japanese encephalitis virus infects porcine kidney epithelial PK15 cells via clathrin- and cholesterol-dependent endocytosis

BACKGROUND

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that causes acute viral encephalitis in humans. Pigs are important amplifiers of JEV. The entry mechanism of JEV into porcine cells remains largely unknown. In this study, we present a study of the internalization mechanism of JEV in porcine kidney epithelial PK15 cells.

RESULTS

We demonstrated that the disruption of the lipid raft by cholesterol depletion with methyl-β-cyclodextrin (MβCD) reduced JEV infection. We also found that the knockdown of clathrin by small interfering RNA (siRNA) significantly reduced JEV-infected cells and JEV E-glycoprotein levels, suggesting that JEV utilizes clathrin-dependent endocytosis. In contrast, the knockdown of caveolin-1, a principal component of caveolae, had only a small (although statistically significant) effect on JEV infection, however, JEV entry was not affected by genistein. These results suggested that JEV entry was independent of caveolae.

CONCLUSIONS

Taken together, our results demonstrate that JEV enters porcine kidney epithelial PK15 cells through cholesterol- and clathrin-mediated endocytosis.

Monoclonal antibodies against NS3 and NS5 proteins of Japanese encephalitis virus

Non-structural proteins NS3 and NS5 of Japanese encephalitis virus (JEV) were expressed in Escherichia coli and purified by dialysis. Two monoclonal antibodies (MAbs) named 1H7 and 2D4 against NS3 protein and three MAbs named 3C4, 3H7, and 3F10 against NS5 protein were generated by fusing mouse myeloma cell line SP2/0 with spleen lymphocytes from NS3 or NS5 protein immunized mice. Then activity of MAbs was characterized by enzyme-linked immunosorbent assay (ELISA), Western blot analysis, and indirect immunofluorescent assays (IFA). Our results demonstrated that all the MAbs showed high specificity and sensitivity in IFA at 1:100 dilution and in Western blot analysis at 1:500 dilution, which indicated that these MAbs against NS3 and NS5 proteins of JEV may be used as valuable tools for analysis of the protein functions and pathogenesis of JEV.

Comprehensive review on the HSC70 functions, interactions with related molecules and involvement in clinical diseases and therapeutic potential

Heat shock cognate protein 70 (HSC70) is a constitutively expressed molecular chaperone which belongs to the heat shock protein 70 (HSP70) family. HSC70 shares some of the structural and functional similarity with HSP70. HSC70 also has different properties compared with HSP70 and other heat shock family members. HSC70 performs its full functions by the cooperation of co-chaperones. It interacts with many other molecules as well and regulates various cellular functions. It is also involved in various diseases and may become a biomarker for diagnosis and potential therapeutic targets for design, discovery, and development of novel drugs to treat various diseases. In this article, we provide a comprehensive review on HSC70 from the literatures including the basic general information such as classification, structure and cellular location, genetics and function, as well as its protein association and interaction with other proteins. In addition, we also discussed the relationship of HSC70 and related clinical diseases such as cancer, cardiovascular, neurological, hepatic and many other diseases and possible therapeutic potential and highlight the progress and prospects of research in this field. Understanding the functions of HSC70 and its interaction with other molecules will help us to reveal other novel properties of this protein. Scientists may be able to utilize this protein as a biomarker and therapeutic target to make significant advancement in scientific research and clinical setting in the future.

Inhibition of Japanese encephalitis virus infection by the sulfated polysaccharide extracts from Ulva lactuca

Japanese encephalitis virus (JEV), a neurotropic flavivirus, is one of the major causes of acute encephalitis in humans. After infection, inflammatory reactions and neurological diseases often develop. Still there are no effective drugs available against virus infection. Recently, extracts of algae have been shown to possess a broad range of biological activities including antivirus activity. In this study, we identified that the sulfated polysaccharide extracts from Ulva lactuca can inhibit JEV infection in Vero cells. Mechanistic studies further revealed that the Ulva sulfated polysaccharide extracts can block virus adsorption and thus make the virus unable to enter cells. The Ulva sulfated polysaccharide extracts also effectively decrease the production of pro-inflammatory cytokines in the JEV-infected primary mixed glia cells. In an animal study, the JEV-infected C3H/HeN mice appeared to have neurobehavioral abnormalities on the fifth day and died on the seventh day post infection. However, the JEV-infected mice pretreated with the Ulva sulfated polysaccharide extracts can delay the onset of hind limb paralysis and thereby prevent mice from death.

Characterization of putative Japanese encephalitis virus receptor molecules on microglial cells

Japanese encephalitis virus (JEV) a mosquito-borne flavivirus is a major cause of viral encephalitis in Asia. While the principle target cells for JEV in the central nervous system are believed to be neurons, microglia are activated in response to JEV and have been proposed to act as a long lasting virus reservoir. Viral attachment to a host cell is the first step of the viral entry process and is a critical mediator of tissue tropism. This study sought to identify molecules associated with JEV entry to microglial cells. Virus overlay protein-binding assay (VOPBA) and liquid chromatography-mass spectrometry (LC/MS/MS) identified the 37/67 kDa high-affinity laminin receptor protein and nucleolin as a potential JEV-binding proteins. These proteins were subsequently investigated for a contribution to JEV entry to mouse microglial BV-2 cells together with other possible candidate receptor molecules including Hsp70, Hsp90, GRP78, CD14, and CD4. In antibody mediated inhibition of infection experiments, both anti-laminin receptor and anti-CD4 antibodies significantly reduced virus entry while anti-Hsp70 and 90 antibodies produced a slight reduction. Significant inhibition of virus entry (up to 80%) was observed in the presence of lipopolysaccharide (LPS) which resulted in a complete down-regulation of CD4 and moderate down-regulation of CD14. These results suggest that multiple receptor proteins may mediate the entry of JEV to microglial cells, with CD4 playing a major role.

Development and Applications of VSV Vectors Based on Cell Tropism

Viral vectors have been available in various fields such as medical and biological research or gene therapy applications. Targeting vectors pseudotyped with distinct viral envelope proteins that influence cell tropism and transfection efficiency are useful tools not only for examining entry mechanisms or cell tropisms but also for vaccine vector development. Vesicular stomatitis virus (VSV) is an excellent candidate for development as a pseudotype vector. A recombinant VSV lacking its own envelope (G) gene has been used to produce a pseudotype or recombinant VSV possessing the envelope proteins of heterologous viruses. These viruses possess a reporter gene instead of a VSV G gene in their genome, and therefore it is easy to evaluate their infectivity in the study of viral entry, including identification of viral receptors. Furthermore, advantage can be taken of a property of the pseudotype VSV, which is competence for single-round infection, in handling many different viruses that are either difficult to amplify in cultured cells or animals or that require specialized containment facilities. Here we describe procedures for producing pseudotype or recombinant VSVs and a few of the more prominent examples from envelope viruses, such as hepatitis C virus, Japanese encephalitis virus, baculovirus, and hemorrhagic fever viruses.

DnaJ homolog Hdj2 facilitates Japanese encephalitis virus replication

Background

Japanese encephalitis virus (JEV) is a member of the mosquito-borne Flaviviridae family of viruses that causes human encephalitis. Upon infection of a new host, replication of viral RNA involves not only the viral RNA-dependent RNA polymerase (RdRp), but also host proteins. Host factors involved in JEV replication are not well characterized.

Results

We identified Hdj2, a heat-shock protein 40 (Hsp40)/DnaJ homolog, from a mouse brain cDNA library interacting with JEV nonstructural protein 5 (NS5) encoding viral RdRp using yeast two-hybrid system. Specific interaction of Hdj2 with NS5 was confirmed by coimmunoprecipitation and colocalization in JEV-infected cells. Overexpression of Hdj2 in JEV-infected cells led to an increase of RNA synthesis, and the virus titer was elevated approximately 4.5- to 10-fold. Knocking down of Hdj2 by siRNA reduced the virus production significantly.

Conclusions

We conclude that Hdj2 directly associates with JEV NS5 and facilitates viral replication. This study is the first to demonstrate Hdj2 involved in JEV replication, providing insight into a potential therapeutic target and cell-based vaccine development of JEV infection.

Association of heat-shock protein 70 with lipid rafts is required for Japanese encephalitis virus infection in Huh7 cells

Japanese encephalitis virus (JEV) is an enveloped flavivirus and the most common agent of viral encephalitis. It enters cells through receptor-mediated endocytosis and low pH-triggered membrane fusion. Although lipid rafts, cholesterol-enriched lipid-ordered membrane domains, have been shown to participate in JEV entry, the mechanisms of the early events of JEV infection, including the cellular receptors of JEV, remain largely unknown. In the current study, it was demonstrated that heat-shock protein 70 (HSP70), rather than other members of the HSP70 family, was required for JEV entry into a human cell line. Cell-surface expression of HSP70 and a direct interaction between JEV envelope (E) protein and HSP70 were observed. Biochemical fractionation showed that HSP70 clearly migrated into the raft fraction after virus infection and co-fractioned with E protein. Depletion of cholesterol shifted the E protein and HSP70 to a non-raft membrane and decreased JEV entry without affecting virus binding to host cells. Notably, recruitment of HSP70 into lipid rafts was required for activation of the phosphoinositide 3-kinase/Akt signalling pathway in the early stage of JEV infection. These results indicate that lipid rafts facilitate JEV entry, possibly by providing a convenient platform to concentrate JEV and its receptors on the host-cell membrane.

Mosquito-borne flaviviruses: overview of viral life-cycle and host–virus interactions

Mosquito-borne flaviviruses such as dengue virus, Japanese encephalitis virus and West Nile virus pose a threat to half of the world population and are a serious public health challenge in many developing countries. There are no effective vaccines or antivirals for most of these viruses. Viruses, being obligate parasites, hijack host pathways for efficient replication and therefore each step of viral life-cycle, namely entry into the host cell, genome replication, assembly and exit, requires the participation of host factors. Investigating the biology of mosquito-borne flaviviruses and the complex interplay of virus with its host will help in identifying drug targets and also in developing safer vaccines and antivirals. This article provides insights into the recent developments in our understanding of the virus–host interactions at various steps in the life-cycle of these viruses.

Inducible viral receptor, A possible concept to induce viral protection in primitive immune animals

A pseudolysogen (PL) is derived from the lysogenic Vibrio harveyi (VH) which is infected with the VHS1 (Vibrio harveyi Siphoviridae-like 1) bacteriophage. The lysogenic Vibrio harveyi undergoes an unequivalent division of the extra-chromosomal VHS1 phage genome and its VH host chromosome and produces a true lysogen (TL) and pseudolysogen (PL). The PL is tolerant to super-infection of VHS1, as is of the true lysogen (TL), but the PL does not contain the VHS1 phage genome while the TL does. However, the PL can become susceptible to VHS1 phage infection if the physiological state of the PL is changed. It is postulated that this is due to a phage receptor molecule which can be inducible to an on-and-off regulation influence by an alternating condition of the bacterial host cell. This characteristic of the PL leads to speculate that this phenomenon can also occur in high organisms with low immunity such as shrimp. This article proposes a hypothesis that the viral receptor molecule on the target cell can play a crucial role in which the invertebrate aquaculture animals can become tolerant to viral infection. A possible mechanism may be that the target cell disrupts the viral receptor molecule to prevent super infection. This concept can explain a mechanism for the prevention of viral infection in invertebrate animals which do not have acquired immunity in response to pathogens. It can guide us to develop a mechanism of immunity to viral infection in low-evolved-immune animals. Also, it can be an additional mechanism that exists in high immune organism, as in human for the prevention of viral infection

Identification of a mutated BHK-21 cell line that became less susceptible to Japanese encephalitis virus infection

The pathogenesis of Japanese encephalitis virus (JEV) is not definitely elucidated as the initial interaction between virus and host cell receptors required for JEV infection is not clearly defined yet. Here, in order to discover those membrane proteins that may be involved in JEV attachment to or entry into virus permissive BHK-21 cells, a chemically mutated cell line (designated 3A10-3F) that became less susceptible to JEV infection was preliminarily established and selected by repeated low moi JEV challenges and RT-PCR detection for viral RNA E gene fragment. The susceptibility to JEV of 3A10-3F cells was significantly weakened compared with parental BHK-21 cells, verified by indirect immunofluorescence assay, virus plague formation assay, and flow cytometry. Finally, two-dimensional electrophoresis (2-DE) coupled with LC-MS/MS was utilized to recognize the most differentially expressed proteins from membrane protein extracts of 3A10-3F and BHK-21 cells respectively. The noted discrepancy of membrane proteins included calcium binding proteins (annexin A1, annexin A2), and voltage-dependent anion channels proteins (VDAC 1, VDAC 2), suggesting that these molecules may affect JEV attachment to and/or entry into BHK-21 cells and worthy of further investigation.

Role of the vacuolar-ATPase in Sindbis virus infection

Bafilomycin A(1) is a specific inhibitor of the vacuolar-ATPase (V-ATPase), which is responsible for pH homeostasis of the cell and for the acidification of endosomes. Bafilomycin A(1) has been commonly used as a method of inhibition of infection by viruses known or suspected to follow the path of receptor-mediated endocytosis and low-pH-mediated membrane fusion. The exact method of entry for Sindbis virus, the prototype alphavirus, remains undetermined. To further investigate the role of the V-ATPase in Sindbis virus infection, the effects of bafilomycin A(1) on the infection of BHK and insect cells by Sindbis virus were studied. Bafilomycin A(1) was found to block the expression of a virus-encoded reporter gene in both infection and transfection of BHK cells. The inhibitory effects of bafilomycin A(1) were found to be reversible. The results suggest that in BHK cells in the presence of bafilomycin A(1), virus RNA enters the cell and is translated, but replication and proper folding of the product proteins requires the function of the V-ATPase. Bafilomycin A(1) had no significant effect on the outcome of infection in insect cells.

Molecular mechanisms involved in the early steps of flavivirus cell entry

Flaviviruses enter their host cells by receptor-mediated endocytosis, a well-orchestrated process of receptor recognition, penetration and uncoating. Recent findings on these early steps in the life cycle of flaviviruses are the focus of this review.

Recent developments in understanding dengue virus replication

Dengue is the most important cause of mosquito-borne virus diseases in tropical and subtropical regions in the world. Severe clinical outcomes such as dengue hemorrhagic fever and dengue shock syndrome are potentially fatal. The epidemiology of dengue has undergone profound changes in recent years, due to several factors such as expansion of the geographical distribution of the insect vector, increase in traveling, and demographic pressure. As a consequence, the incidence of dengue has increased dramatically. Since mosquito control has not been successful and since no vaccine or antiviral treatment is available, new approaches to this problem are needed. Consequently, an in-depth understanding of the molecular and cellular biology of the virus should be helpful to design efficient strategies for the control of dengue. Here, we review the recently acquired knowledge on the molecular and cell biology of the dengue virus life cycle based on newly developed molecular biology technologies.

Response of the mosquito protein interaction network to dengue infection

Background

Two fifths of the world's population is at risk from dengue. The absence of effective drugs and vaccines leaves vector control as the primary intervention tool. Understanding dengue virus (DENV) host interactions is essential for the development of novel control strategies. The availability of genome sequences for both human and mosquito host greatly facilitates genome-wide studies of DENV-host interactions.

Results

We developed the first draft of the mosquito protein interaction network using a computational approach. The weighted network includes 4,214 Aedes aegypti proteins with 10,209 interactions, among which 3,500 proteins are connected into an interconnected scale-free network. We demonstrated the application of this network for the further annotation of mosquito proteins and dissection of pathway crosstalk. Using three datasets based on physical interaction assays, genome-wide RNA interference (RNAi) screens and microarray assays, we identified 714 putative DENV-associated mosquito proteins. An integrated analysis of these proteins in the network highlighted four regions consisting of highly interconnected proteins with closely related functions in each of replication/transcription/translation (RTT), immunity, transport and metabolism. Putative DENV-associated proteins were further selected for validation by RNAi-mediated gene silencing, and dengue viral titer in mosquito midguts was significantly reduced for five out of ten (50.0%) randomly selected genes.

Conclusions

Our results indicate the presence of common host requirements for DENV in mosquitoes and humans. We discuss the significance of our findings for pharmacological intervention and genetic modification of mosquitoes for blocking dengue transmission.

Flavivirus encephalitis: pathological aspects of mouse and other animal models

Encephalitic flaviviruses are important arthropod-borne pathogens of humans and other animals. In particular, the recent emergence of the West Nile virus (WNV) and Japanese encephalitis virus (JEV) in new geographic areas has caused a considerable public health alert and international concern. Among the experimental in vivo models of WNV and JEV infection, mice and other laboratory rodents are the most thoroughly studied and well-characterized systems, having provided data that are important for understanding the infectious process in humans. Macaca monkeys have also been used as a model for WNV and JEV infection, mainly for the evaluation of vaccine efficacy, although a limited number of published studies have addressed pathomorphology. These animal models demonstrate the development of encephalitis with many similarities to the human disease; however, the histological events that occur during infection, especially in peripheral tissues, have not been fully characterized.

Involvement of ceramide in the propagation of Japanese encephalitis virus

Japanese encephalitis virus (JEV) is a mosquito-borne RNA virus and one of the most important flaviviruses in the medical and veterinary fields. Although cholesterol has been shown to participate in both the entry and replication steps of JEV, the mechanisms of infection, including the cellular receptors of JEV, remain largely unknown. To clarify the infection mechanisms of JEV, we generated pseudotype (JEVpv) and recombinant (JEVrv) vesicular stomatitis viruses bearing the JEV envelope protein. Both JEVpv and JEVrv exhibited high infectivity for the target cells, and JEVrv was able to propagate and form foci as did authentic JEV. Anti-JEV envelope antibodies neutralized infection of the viruses. Treatment of cells with inhibitors for vacuolar ATPase and clathrin-mediated endocytosis reduced the infectivity of JEVpv, suggesting that JEVpv enters cells via pH- and clathrin-dependent endocytic pathways. Although treatment of the particles of JEVpv, JEVrv, and JEV with cholesterol drastically reduced the infectivity as previously reported, depletion of cholesterol from the particles by treatment with methyl beta-cyclodextrin enhanced infectivity. Furthermore, treatment of cells with sphingomyelinase (SMase), which hydrolyzes membrane-bound sphingomyelin to ceramide, drastically enhanced infection with JEVpv and propagation of JEVrv, and these enhancements were inhibited by treatment with an SMase inhibitor or C(6)-ceramide. These results suggest that ceramide plays crucial roles in not only entry but also egress processes of JEV, and they should assist in the clarification of JEV propagation and the development of novel therapeutics against diseases caused by infection with flaviviruses.

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.

Role of antibodies in controlling dengue virus infection

The incidence and disease burden of arthropod-borne flavivirus infections have dramatically increased during the last decades due to major societal and economic changes, including massive urbanization, lack of vector control, travel, and international trade. Specifically, in the case of dengue virus (DENV), the geographical spread of all four serotypes throughout the subtropical regions of the world has led to larger and more severe outbreaks. Many studies have established that recovery from infection by one DENV serotype provides immunity against that serotype, whereas reinfection with another serotype may result in severe disease. Pre-existing antibodies thus play a critical role in controlling viral infection. Both neutralization and enhancement of DENV infection by antibodies are thought to be related to the natural route of viral entry into cells. In this review, we will describe the current knowlegde on the mechanisms involved in flavivirus cell entry and discuss how antibodies may influence the course of infection towards neutralization or enhancement of viral disease.

Heat shock protein 70 on Neuro2a cells is a putative receptor for Japanese encephalitis virus

Japanese encephalitis virus (JEV) envelope (E) protein has been shown to play a critical role in attachment to cells. However, the receptor interacting with envelope protein has not been conclusively identified. Using mouse neuroblastoma (Neuro2a) cells and purified JEV-E protein in 'Virus Overlay Protein Binding Assay' followed by MALDI-TOF analysis, we identified 'heat shock protein 70' (Hsp70) as a possible receptor for JEV. Indirect immunofluorescence and flow-cytometry analysis demonstrated localization of Hsp70 on Neuro2a cell surface. Co-immunoprecipitation followed by Western blot analysis reconfirmed the interaction between Hsp70 and JEV-E protein. Further, anti-Hsp70 polyclonal-antibodies were able to block JEV entry into Neuro2a cells. Additionally, using the bioinformatic tool - FTDOCK, docking between the proteins was performed. Amongst six interacting structural poses studied one pose involving RGD motif on JEV-E and leucine(539) on Hsp70 displayed stable interaction. These observations indicate that Hsp70 serves as putative receptor for JEV in Neuro2A cells.

Ex vivo promoter analysis of antiviral heat shock cognate 70B gene in Anopheles gambiae

Background

The Anopheles gambiae heat shock cognate gene (hsc70B) encodes a constitutively expressed protein in the hsp70 family and it functions as a molecular chaperone for protein folding. However, the expression of hsc70B can be further induced by certain stimuli such as heat shock and infection. We previously demonstrated that the An. gambiae hsc70B is induced during o'nyong-nyong virus (ONNV) infection and subsequently suppresses ONNV replication in the mosquito. To further characterize the inducibility of hsc70B by ONNV infection in An. gambiae, we cloned a 2.6-kb region immediately 5' upstream of the starting codon of hsc70B into a luciferase reporter vector (pGL3-Basic), and studied its promoter activity in transfected Vero cells during infection with o'nyong-nyong, West Nile and La Crosse viruses.

Results

Serial deletion analysis of the hsc70B upstream sequence revealed that the putative promoter is likely located in a region 1615–2150 bp upstream of the hsc70B starting codon. Sequence analysis of this region revealed transcriptional regulatory elements for heat shock element-binding protein (HSE-bind), nuclear factor κB (NF-κB), dorsal (Dl) and fushi-tarazu (Ftz). Arbovirus infection, regardless of virus type, significantly increased the hsc70B promoter activity in transfected Vero cells.

Conclusion

Our results further validate the transcriptional activation of hsc70B during arbovirus infection and support the role of specific putative regulatory elements. Induction by three taxonomically distinct arboviruses suggests that the HSC70B protein may be expressed to cope with cellular stress imposed during infection.