Hsp90 inhibitors block outgrowth of EBV-infected malignant cells in vitro and in vivo through an EBNA1-dependent mechanism

EBNA1 Targeted Ultra-Small Near-Infrared Persistent Luminescent Nano-Inhibitor for Theranostics of EBV-Associated Cancer

Epstein-Barr virus (EBV) is a well-recognized oncogenic virus that promotes several lymphoid and epithelial cancers. The Epstein-Barr nuclear antigen 1 (EBNA1), which is known to be expressed in all EBV-positive cancers, plays a vital role in viral genome replication and maintenance and is therefore emerged as an attractive target for clinical intervention. Several EBNA1 inhibitors have shown potency in the growth inhibition of EBV-positive cancers, yet low bioavailability and in vivo unmonitored nature hamper their further implementation. Here a novel EBNA1 nano-inhibitor based on EBNA1-specific peptide inhibitor (P4) functionalized ZnGa2O4:Cr3+ ultra-small near-infrared persistent luminescent (NIR-PL) nanoparticles (ZGOC-P4) is developed. Owing to the specific binding to EBNA1, ZGOC-P4 nano-inhibitor can quickly achieve nuclear internalization in EBV-positive nasopharyngeal carcinoma (NPC) cells (C666-1) and selectively inhibit their growth. In sharp contrast, ZGOC-P4 nano-inhibitor shows no inhibition effect on EBV-negative NPC cells (HK-1). Moreover, the results indicate that the well-designed nano-inhibitor enables efficient tumor-targeting accumulation in NPC xenograft model under the monitoring of autofluorescence interference-free NIR-PL imaging in vivo and suppresses EBV-associated tumor growth with an inhibition rate of 61.6%. This work highlights the potency of ZGOC-P4 on NPC treatment and may provide new sight into future research on EBV-associated diseases.

Epstein-Barr virus-infected nasopharyngeal carcinoma therapeutics: oncoprotein targets and clinical implications

Nasopharyngeal carcinoma (NPC) is a distinctive epithelial cancer closely associated with Epstein-Barr Virus (EBV) infection, posing significant challenges in diagnosis and treatment due to its resistance to conventional therapies and high recurrence rates. Current therapies, including radiotherapy and chemotherapy, exhibit limited efficacy, particularly in recurrent or metastatic cases, highlighting the urgent need for novel therapeutic strategies. Targeting EBV oncoproteins, such as Epstein-Barr Virus encoded Nuclear Antigen 1 (EBNA1), Latent Membrane Protein 1 (LMP1), and Latent Membrane Protein 2 (LMP2), presents a promising therapeutic avenue in NPC treatment. This review discusses the latest advancements in drug discovery targeting EBV oncoproteins, emphasizing the identification of inhibitors for specific functional regions of oncoproteins EBNA1, LMP1, and LMP2. Particular attention is given to the molecular mechanisms of these inhibitors and their preclinical or clinical potential in treating EBV-positive NPC. These developments highlight a promising future for targeted therapies in improving outcomes for NPC patients.

Curcumin derivative C210 induces Epstein-Barr virus lytic cycle and inhibits virion production by disrupting Hsp90 function

Lytic induction therapy was devised to selectively combat malignancies associated with Epstein-Barr virus (EBV) by triggering viral reactivation from latency. At present, the major challenges of lytic induction therapy are to maximize reactivating efficiencies and meanwhile minimize infectious virion production. C210, a novel curcumin derivative with potent Hsp90 inhibitory activity, was explored for EBV-reactivating and virion-producing effects in EBV-positive nasopharyngeal carcinoma (NPC) and gastric carcinoma (GC) cell lines. And the molecular mechanisms underlying these effects were determined. Follow C210 treatment, EBV lytic RNAs and proteins were upregulated, but infectious virions were not produced. Knockdown of heat shock protein 90 (Hsp90) induced expression of lytic RNAs and proteins, and diminished C210-driven EBV lytic induction. Pretreatment with an X box binding protein 1 (XBP1) inhibitor reduced C210-induced EBV lytic RNA. Furthermore, we demonstrated that C210 inhibited the binding of Hsp90 with its clients, signal transducer and activator of transcription 3 (STAT3) and xeroderma pigmentosum group B-complementing protein (XPB), which subsequently promoted their proteasomal degradation. Degradation of STAT3 by C210 enhanced the EBV-reactivating and anticancer capacity of suberoylanilide hydroxamic acid (SAHA). Depletion of XPB blocked SAHA-induced expression of late viral genes and production of infectious virions. These results elucidate a novel Hsp90 inhibitor targeting EBV lytic phase and extend the research on lytic induction strategy, which may offer reference value in the treatment of EBV-positive malignancies.

Treatment of Epstein-Barr Virus infection in immunocompromised patients

Epstein-Barr Virus (EBV), is a ubiquitous γ-Herpesvirus that infects over 95% of the human population and can establish a life-long infection without causing any clinical symptoms in healthy individuals by residing in memory B-cells. Primary infection occurs in childhood and is mostly asymptomatic, however in some young adults it can result in infectious mononucleosis (IM). In immunocompromised individuals however, EBV infection has been associated with many different malignancies. Since EBV can infect both epithelial and B-cells and very rarely NK cells and T-cells, it is associated with both epithelial cancers like nasopharyngeal carcinoma (NPC) and gastric carcinoma (GC), with lymphomas including Burkitt Lymphoma (BL) or Post-transplant Lymphoproliferative Disorder (PTLD) and rarely with NK/T-cell lymphomas. Currently there are no approved antivirals active in PTLD nor in any other malignancy. Moreover, lytic phase disease almost never requires antiviral treatment. Although many novel therapies against EBV have been described, the management and/or prevention of EBV primary infections or reactivations remains difficult. In this review, we discuss EBV infection, therapies targeting EBV in both lytic and latent state with novel therapeutics developed that show anti-EBV activity as well as EBV-associated malignancies both, epithelial and lymphoproliferative malignancies and emerging therapies targeting the EBV-infected cells.

Hsp90 β is critical for the infection of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS) caused by the SFTS virus (SFTSV) is an emerging disease in East Asia with a fatality rate of up to 30%. However, the viral-host interaction of SFTSV remains largely unknown. The heat-shock protein 90 (Hsp90) family consists of highly conserved chaperones that fold and remodel proteins and has a broad impact on the infection of many viruses. Here, we showed that Hsp90 is an important host factor involved in SFTSV infection. Hsp90 inhibitors significantly reduced SFTSV replication, viral protein expression, and the formation of inclusion bodies consisting of nonstructural proteins (NSs). Among viral proteins, NSs appeared to be the most reduced when Hsp90 inhibitors were used, and further analysis showed that their translation was affected. Co-immunoprecipitation of NSs with four isomers of Hsp90 showed that Hsp90 β specifically interacted with them. Knockdown of Hsp90 β expression also inhibited replication of SFTSV. These results suggest that Hsp90 β plays a critical role during SFTSV infection and could be a potential target for the development of drugs against SFTS.

TRIM26 restricts Epstein-Barr virus infection in nasopharyngeal epithelial cells through K48-linked ubiquitination of HSP-90β

The tripartite interaction motif (TRIM) family of proteins is known for their antiviral activity through different mechanisms, such as interfering with viral components, regulating immune responses, and participating in autophagy-mediated defense pathways. In this study, we investigated the role of tripartite interaction motif 26 (TRIM26), which is encoded by a major histocompatibility complex (MHC) gene, in regulating Epstein-Barr virus (EBV) infection of nasopharyngeal epithelial cells. We found that TRIM26 expression was induced upon EBV infection and that it indirectly targeted EphA2, a crucial epithelial receptor for EBV entry. Our results showed that TRIM26 interacted with heat shock protein 90-beta (HSP-90β) and promoted its polyubiquitination, which led to its degradation via the proteasome pathway. This, in turn, affected EphA2 integrity and suppressed EBV infection. These findings suggest that TRIM26 could be a valuable target for developing therapeutic interventions against EBV infection and its associated pathogenesis.

Regulation of EBNA1 protein stability and DNA replication activity by PLOD1 lysine hydroxylase

Epstein-Barr virus (EBV) is a ubiquitous human γ-herpesvirus that is causally associated with various malignancies and autoimmune disease. Epstein-Barr Nuclear Antigen 1 (EBNA1) is the viral-encoded DNA binding protein required for viral episome maintenance and DNA replication during latent infection in proliferating cells. EBNA1 is known to be a highly stable protein, but the mechanisms regulating protein stability and how this may be linked to EBNA1 function is not fully understood. Proteomic analysis of EBNA1 revealed interaction with Procollagen Lysine-2 Oxoglutarate 5 Dioxygenase (PLOD) family of proteins. Depletion of PLOD1 by shRNA or inhibition with small molecule inhibitors 2,-2' dipyridyl resulted in the loss of EBNA1 protein levels, along with a selective growth inhibition of EBV-positive lymphoid cells. PLOD1 depletion also caused a loss of EBV episomes from latently infected cells and inhibited oriP-dependent DNA replication. Mass spectrometry identified EBNA1 peptides with lysine hydroxylation at K460 or K461. Mutation of K460, but not K461 abrogates EBNA1-driven DNA replication of oriP, but did not significantly affect EBNA1 DNA binding. Mutations in both K460 and K461 perturbed interactions with PLOD1, as well as decreased EBNA1 protein stability. These findings suggest that PLOD1 is a novel interaction partner of EBNA1 that regulates EBNA1 protein stability and function in viral plasmid replication, episome maintenance and host cell survival.

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.

Virus-Mediated Inhibition of Apoptosis in the Context of EBV-Associated Diseases: Molecular Mechanisms and Therapeutic Perspectives

Epstein-Barr virus (EBV), the representative of the Herpesviridae family, is a pathogen extensively distributed in the human population. One of its most characteristic features is the capability to establish latent infection in the host. The infected cells serve as a sanctuary for the dormant virus, and therefore their desensitization to apoptotic stimuli is part of the viral strategy for long-term survival. For this reason, EBV encodes a set of anti-apoptotic products. They may increase the viability of infected cells and enhance their resistance to chemotherapy, thereby contributing to the development of EBV-associated diseases, including Burkitt’s lymphoma (BL), Hodgkin’s lymphoma (HL), gastric cancer (GC), nasopharyngeal carcinoma (NPC) and several other malignancies. In this paper, we have described the molecular mechanism of anti-apoptotic actions of a set of EBV proteins. Moreover, we have reviewed the pro-survival role of non-coding viral transcripts: EBV-encoded small RNAs (EBERs) and microRNAs (miRNAs), in EBV-carrying malignant cells. The influence of EBV on the expression, activity and/or intracellular distribution of B-cell lymphoma 2 (Bcl-2) protein family members, has been presented. Finally, we have also discussed therapeutic perspectives of targeting viral anti-apoptotic products or their molecular partners.

Role of Heat Shock Proteins (HSP70 and HSP90) in Viral Infection

Heat shock proteins (HSPs) are a large group of chaperones found in most eukaryotes and bacteria. They are responsible for the correct protein folding, protection of the cell against stressors, presenting immune and inflammatory cytokines; furthermore, they are important factors in regulating cell differentiation, survival and death. Although the biological function of HSPs is to maintain cell homeostasis, some of them can be used by viruses both to fold their proteins and increase the chances of survival in unfavorable host conditions. Folding viral proteins as well as replicating many different viruses are carried out by, among others, proteins from the HSP70 and HSP90 families. In some cases, the HSP70 family proteins directly interact with viral polymerase to enhance viral replication or they can facilitate the formation of a viral replication complex and/or maintain the stability of complex proteins. It is known that HSP90 is important for the expression of viral genes at both the transcriptional and the translational levels. Both of these HSPs can form a complex with HSP90 and, consequently, facilitate the entry of the virus into the cell. Current studies have shown the biological significance of HSPs in the course of infection SARS-CoV-2. A comprehensive understanding of chaperone use during viral infection will provide new insight into viral replication mechanisms and therapeutic potential. The aim of this study is to describe the molecular basis of HSP70 and HSP90 participation in some viral infections and the potential use of these proteins in antiviral therapy.

Discovering High Potent Hsp90 Inhibitors as Antinasopharyngeal Carcinoma Agents through Fragment Assembling Approach

Hsp90 is a new promising target for cancer treatment. Many inhibitors have been discovered as therapeutic agents, and some have passed Phase I and II. However, no one is approved by FDA yet. Novel and druggable Hsp90 inhibitors are still demanding. Here, we report a new way to discover high potent Hsp90 inhibitors as antinasopharyngeal carcinoma agents through assembling fragments. With chemotyping analysis, we extract seven chemotypes from 3482 known Hsp90 inhibitors, screen 500 fragments that are compatible with the chemotypes, and confirm 15 anti-Hsp90 fragments. Click chemistry is employed to construct 172 molecules and synthesize 21 compounds among them. The best inhibitor 3d was further optimized and resulted in more potent 4f (IC50 = 0.16 μM). In vitro and in vivo experiments confirmed that 4f is a promising agent against nasopharyngeal carcinoma. This study may provide a strategy in discovering new ligands against targets without well-understood structures.

Hsp90 is involved in pseudorabies virus virion assembly via stabilizing major capsid protein VP5

Many viruses utilize molecular chaperone heat shock protein 90 (Hsp90) for protein folding and stabilization, however, the role of Hsp90 in herpesvirus lifecycle is obscure. Here, we provide evidence that Hsp90 participates in pseudorabies virus (PRV) replication. Viral growth kinetics assays show that Hsp90 inhibitor geldanamycin (GA) abrogates PRV replication at the post-penetration step. Transmission electron microscopy demonstrates that dysfunction of Hsp90 diminishes the quantity of PRV nucleocapsids. Overexpression and knockdown of Hsp90 suggest that de novo Hsp90 is involved in PRV replication. Mechanismly, dysfunction of Hsp90 inhibits PRV major capsid protein VP5 expression. Co-immunoprecipitation and indirect immunofluorescence assays indicate that Hsp90 interacts with VP5. Interestingly, Hsp70, a collaborator of Hsp90, also interacts with VP5, but doesn't affect PRV growth. Finally, inhibition of Hsp90 results in PRV VP5 degradation in a proteasome-dependent manner. Collectively, our data suggest that Hsp90 contributes to PRV virion assembly and replication via stabilization of VP5.

Stress proteins: the biological functions in virus infection, present and challenges for target-based antiviral drug development

Stress proteins (SPs) including heat-shock proteins (HSPs), RNA chaperones, and ER associated stress proteins are molecular chaperones essential for cellular homeostasis. The major functions of HSPs include chaperoning misfolded or unfolded polypeptides, protecting cells from toxic stress, and presenting immune and inflammatory cytokines. Regarded as a double-edged sword, HSPs also cooperate with numerous viruses and cancer cells to promote their survival. RNA chaperones are a group of heterogeneous nuclear ribonucleoproteins (hnRNPs), which are essential factors for manipulating both the functions and metabolisms of pre-mRNAs/hnRNAs transcribed by RNA polymerase II. hnRNPs involve in a large number of cellular processes, including chromatin remodelling, transcription regulation, RNP assembly and stabilization, RNA export, virus replication, histone-like nucleoid structuring, and even intracellular immunity. Dysregulation of stress proteins is associated with many human diseases including human cancer, cardiovascular diseases, neurodegenerative diseases (e.g., Parkinson’s diseases, Alzheimer disease), stroke and infectious diseases. In this review, we summarized the biologic function of stress proteins, and current progress on their mechanisms related to virus reproduction and diseases caused by virus infections. As SPs also attract a great interest as potential antiviral targets (e.g., COVID-19), we also discuss the present progress and challenges in this area of HSP-based drug development, as well as with compounds already under clinical evaluation.

Proteostasis in Viral Infection: Unfolding the Complex Virus-Chaperone Interplay

Viruses are obligate intracellular parasites that rely on their hosts for protein synthesis, genome replication, and viral particle production. As such, they have evolved mechanisms to divert host resources, including molecular chaperones, facilitate folding and assembly of viral proteins, stabilize complex structures under constant mutational pressure, and modulate signaling pathways to dampen antiviral responses and prevent premature host death. Biogenesis of viral proteins often presents unique challenges to the proteostasis network, as it requires the rapid and orchestrated production of high levels of a limited number of multifunctional, multidomain, and aggregation-prone proteins. To overcome such challenges, viruses interact with the folding machinery not only as clients but also as regulators of chaperone expression, function, and subcellular localization. In this review, we summarize the main types of interactions between viral proteins and chaperones during infection, examine evolutionary aspects of this relationship, and discuss the potential of using chaperone inhibitors as broad-spectrum antivirals.

Reactivation of Epstein-Barr virus by a dual-responsive fluorescent EBNA1-targeting agent with Zn2+-chelating function

EBNA1 is the only Epstein–Barr virus (EBV) latent protein responsible for viral genome maintenance and is expressed in all EBV-infected cells. Zn²⁺ is essential for oligomerization of the functional EBNA1. We constructed an EBNA1 binding peptide with a Zn²⁺ chelator to create an EBNA1-specific inhibitor (ZRL₅P₄). ZRL₅P₄ by itself is sufficient to reactivate EBV from its latent infection. ZRL₅P₄ is able to emit unique responsive fluorescent signals once it binds with EBNA1 and a Zn²⁺ ion. ZRL₅P₄ can selectively disrupt the EBNA1 oligomerization and cause nasopharyngeal carcinoma (NPC) tumor shrinkage, possibly due to EBV lytic induction. Dicer1 seems essential for this lytic reactivation. As can been seen, EBNA1 is likely to maintain NPC cell survival by suppressing viral reactivation.

Epstein–Barr nuclear antigen 1 (EBNA1) plays a vital role in the maintenance of the viral genome and is the only viral protein expressed in nearly all forms of Epstein–Barr virus (EBV) latency and EBV-associated diseases, including numerous cancer types. To our knowledge, no specific agent against EBV genes or proteins has been established to target EBV lytic reactivation. Here we report an EBNA1- and Zn²⁺-responsive probe (ZRL₅P₄) which alone could reactivate the EBV lytic cycle through specific disruption of EBNA1. We have utilized the Zn²⁺ chelator to further interfere with the higher order of EBNA1 self-association. The bioprobe ZRL₅P₄ can respond independently to its interactions with Zn²⁺ and EBNA1 with different fluorescence changes. It can selectively enter the nuclei of EBV-positive cells and disrupt the oligomerization and oriP-enhanced transactivation of EBNA1. ZRL₅P₄ can also specifically enhance Dicer1 and PML expression, molecular events which had been reported to occur after the depletion of EBNA1 expression. Importantly, we found that treatment with ZRL₅P₄ alone could reactivate EBV lytic induction by expressing the early and late EBV lytic genes/proteins. Lytic induction is likely mediated by disruption of EBNA1 oligomerization and the subsequent change of Dicer1 expression. Our probe ZRL₅P₄ is an EBV protein-specific agent that potently reactivates EBV from latency, leading to the shrinkage of EBV-positive tumors, and our study also suggests the association of EBNA1 oligomerization with the maintenance of EBV latency.

Curcumin Inhibits Proliferation of Epstein-Barr Virus-Associated Human Nasopharyngeal Carcinoma Cells by Inhibiting EBV Nuclear Antigen 1 Expression

This investigation aims to study the effect of curcumin on the proliferation, cycle arrest, and apoptosis of Epstein-Barr virus- (EBV-) positive nasopharyngeal carcinoma (NPC) cells. EBV⁺ NPC cells were subjected to curcumin treatment. The cell viability was evaluated with the CCK-8. Cell cycle and apoptosis were analyzed by flow cytometry analysis. Expression (protein and mRNA) levels were detected with western blotting and quantitative real-time PCR, respectively. Curcumin efficiently reduced the viability of EBV⁺ NPC cells. Curcumin induced the cycle arrest of the HONE1 and HK1-EBV cells positive for EBV. Moreover, curcumin treatment promoted the NPC cell apoptosis, via the mitochondria- and death receptor-mediated pathways. Furthermore, curcumin decreased the expression of EBNA1 in the HONE1 and HK1-EBV cells and inhibited the transcriptional level of EBNA1 in the HeLa cells. Curcumin induced EBNA1 degradation via the proteasome-ubiquitin pathway. In addition, curcumin inhibited the proliferation of HONE1 and HK1-EBV cells positive for EBV, probably by decreasing the expression level of EBNA1. In both the HONE1 and HK1-EBV cells, curcumin inhibited the EBV latent and lytic replication. Curcumin could reduce the EBNA1 expression and exert antitumor effects against NPC in vitro.

GAP31 from an ancient medicinal plant exhibits anti-viral activity through targeting to Epstein-Barr virus nuclear antigen 1

Since it was discovered as the first human tumor virus in 1964, Epstein-Barr Virus (EBV) is now implicated in several types of malignancies. Accordingly, certain aspects of EBV pathobiology have shown promise in anti-cancer research in developing virus-targeting methods for EBV-associated cancers. The unique role of EBV nuclear antigen 1 (EBNA1) in triggering episome-dependent functions has made it as the only latent gene to be expressed in most EBV+ neoplasms. Dimeric EBNA1 binds to the replication origin (oriP) to display its biological impact on EBV-driven cell transformation and maintenance. Hence, EBNA1/oriP has been made an ideal drug target site for anti-EBV protocol development. GAP31 protein was originally isolated from the seeds of an ancient medicinal plant Gelonium multiflorum. Although GAP31 has been shown to exhibit both anti-viral and anti-tumor activity, current understanding of the mechanistic picture underlying GAP31 functioning is not clear. Herein, we identify the EBNA1 DNA-binding domain as a core for GAP31 binding by performing affinity pulldown assays. Recombinant GAP31 (rGAP31) was shown to impair EBNA1-induced dimerization; consequently, it abrogated both EBNA1/oriP-mediated binding and transcription. Importantly, the therapeutic effects of GAP31 showed its capability to abrogate EBV-driven cell transformation and proliferation, and EBV-dependent tumorigenesis in xenograft animal models. Notably, the EBNA1 binding-mutant rGAP31_R166A/R169A simply exhibits defective phenotypes in the above-mentioned studies. Our data suggest rGAP31 is a potential anti-viral drug which can be applied to the development of therapeutic strategies against EBV-related malignancies.

EBNA1-targeted inhibitors: Novel approaches for the treatment of Epstein-Barr virus-associated cancers

Epstein-Barr virus (EBV) infects more than 90% of humans worldwide and establishes lifelong latent infection in the hosts. It is closely associated with endemic forms of a wide range of human cancers and directly contributes to the formation of some. Despite its critical role in cancer development, no EBV- or EBV latent protein-targeted therapy is available. The EBV-encoded latent protein, Epstein-Barr nuclear antigen 1 (EBNA1), is expressed in all EBV-associated tumors and acts as the only latent protein in some of these tumors. This versatile protein functions in the maintenance, replication, and segregation of the EBV genome and can therefore serve as an attractive therapeutic target to treat EBV-associated cancers. In the last decades, efforts have been made for designing specific EBNA1 inhibitors to decrease EBNA1 expression or interfere with EBNA1-dependent functions. In this review, we will briefly introduce the salient features of EBNA1, summarize its functional domains, and focus on the recent developments in the identification and design of EBNA1 inhibitors related to various EBNA1 domains as well as discuss their comparative merits.

Responsive upconversion nanoprobe for monitoring and inhibition of EBV-associated cancers via targeting EBNA1

Non-responsive emission enhancement is the disadvantage of upconversion nanomaterials (UCNM) when compared with conventional organic based agents for molecular imaging. We herein show a new strategy by conjugating NaGdF4:Yb3+,Er3+@NaGdF4 (UCNP) with peptides to achieve responsive UC emission enhancement upon binding to a targeted protein - EBNA1. EBNA1 is a well-known viral latent protein for the EBV-associated cancer. Peptide-coating of the functionalized core-shell nanoparticle diminishes upconverted emission intensity drastically. However, the peptide-coated UCNP shows selective and responsive UC emission enhancement via aggregation with the targeted protein. This phenomenon paves a new way for UCNM in molecular imaging.

Triptolide inhibits Epstein-Barr nuclear antigen 1 expression by increasing sensitivity of mitochondria apoptosis of nasopharyngeal carcinoma cells

BACKGROUND

Epstein-Barr virus (EBV) is widely found in nasopharyngeal carcinoma (NPC) tissue and associated with poor prognosis of patients. EBV nuclear antigen 1 (EBNA1) is expressed in all NPC tumors and plays multiple biological roles in both virus and host cells. Triptolide is a natural product extracted from Tripterygium and shows anti-cancer activities. The goal of this work was to illustrate the anti-cancer effect of triptolide and elucidate a novel anti-apoptotic mechanism of EBNA1 in NPC cells encountered with triptolide.

METHODS

In the present study, a CCK-8 assay was used to analyze the proliferation of NPC cells treated with triptolide in a dose- and time-dependent ways. Effects of triptolide on NPC cell cycle and apoptosis were investigated by flow cytometric analysis. EBNA1 expression in mRNA and protein levels was determined by quantitative real-time PCR and Western blot, respectively.

RESULTS

Our results showed that triptolide effectively inhibited proliferation of NPC cells. Triptolide arrested NPC cell cycles in S phase and induced apoptosis through a caspase-9-dependent apoptosis pathway. Low-dose of triptolide reduced the half-life of EBNA1 and significantly decreased EBNA1 expression by promoting the process of proteasome-ubiquitin pathway. Over-expression of EBNA1, which was independent from EBV genome, effectively attenuated the apoptosis induced by triptolide. In addition, triptolide significantly inhibited proliferations of tumors induced by EBV-positive cells in vivo. Furthermore, EBNA1 were expressed in all NPC biopsies of Chinese patients.

CONCLUSIONS

In summary, our study provides the evidence that triptolide induces EBNA1 degradation and stimulates NPC apoptosis through mitochondria apoptotic pathway. In addition, EBNA1 assists NPC cells to resist triptolide-induced apoptosis through inhibiting caspase-9-dependent apoptotic pathway.

The Hsp70 inhibitor 2-phenylethynesulfonamide inhibits replication and carcinogenicity of Epstein-Barr virus by inhibiting the molecular chaperone function of Hsp70

Epstein–Barr virus (EBV) can infect cells in latent and lytic period and cause serious disease. Epstein–Barr virus nuclear antigen 1 (EBNA1) is essential for the maintenance of the EBV DNA episome, replication and transcription. 2-phenylethynesulfonamide (PES) is a small molecular inhibitor of Heat shock protein 70 (Hsp70), which can interact with Hsp70 and disrupts its association with co-chaperones and substrate proteins of Hsp70. In our study, we found that PES could decrease the expression of EBNA1, which is independent of effects on EBNA1 transcription or proteasomal degradation pathway. The central glycine–alanine repeats domain was not required for inhibition of EBNA1 expression by PES. Also, PES could reduce the amount of intracellular EBV genomic DNA. PES inhibited proliferation and migration but induced cell cycle arrest and apoptosis of EBV positive cells. In addition, silencing of Hsp70 decreased expression of EBNA1 and the amounts of intracellular EBV genomic DNA, and PES increased this effect on a dose-dependent manner. On the contrast, over-expression of Hsp70 enhanced the expression of EBNA1 and the amounts of intracellular EBV genomic DNA, but PES inhibited this effect on a dose-dependent manner. Furthermore, Hsp70 interacted with EBNA1 but PES interfered this interaction. Our results indicate that PES suppresses replication and carcinogenicity of Epstein–Barr virus via inhibiting the molecular chaperone function of Hsp70.

How I treat T-cell chronic active Epstein-Barr virus disease

T-cell chronic active Epstein-Barr virus (CAEBV) is a rare disease in which EBV is present predominantly in T cells that infiltrate the tissues; patients have high levels of EBV in the blood. If untreated, patients often develop liver failure, hemophagocytic lymphohistiocytosis, coronary artery aneurysms, EBV infiltrating T cells impairing organ function, or T-cell lymphomas refractory to treatment. At present, hematopoietic stem-cell transplantation is the only curative therapy, and it is critical to make a proper diagnosis and initiate transplantation before the disease progresses to an irreversible stage. Specific medications such as high-dose systemic corticosteroids or ganciclovir combined with either histone deacetylase inhibitors or bortezomib may temporarily reduce systemic toxicity associated with T-cell CAEBV and allow the patient time to receive a transplant. Relapses of the disease after transplantation have also occurred, and the use of donor-derived virus-specific T cells may help to treat these relapses.

EBNA1: Oncogenic Activity, Immune Evasion and Biochemical Functions Provide Targets for Novel Therapeutic Strategies against Epstein-Barr Virus- Associated Cancers

The presence of the Epstein-Barr virus (EBV)-encoded nuclear antigen-1 (EBNA1) protein in all EBV-carrying tumours constitutes a marker that distinguishes the virus-associated cancer cells from normal cells and thereby offers opportunities for targeted therapeutic intervention. EBNA1 is essential for viral genome maintenance and also for controlling viral gene expression and without EBNA1, the virus cannot persist. EBNA1 itself has been linked to cell transformation but the underlying mechanism of its oncogenic activity has been unclear. However, recent data are starting to shed light on its growth-promoting pathways, suggesting that targeting EBNA1 can have a direct growth suppressing effect. In order to carry out its tasks, EBNA1 interacts with cellular factors and these interactions are potential therapeutic targets, where the aim would be to cripple the virus and thereby rid the tumour cells of any oncogenic activity related to the virus. Another strategy to target EBNA1 is to interfere with its expression. Controlling the rate of EBNA1 synthesis is critical for the virus to maintain a sufficient level to support viral functions, while at the same time, restricting expression is equally important to prevent the immune system from detecting and destroying EBNA1-positive cells. To achieve this balance EBNA1 has evolved a unique repeat sequence of glycines and alanines that controls its own rate of mRNA translation. As the underlying molecular mechanisms for how this repeat suppresses its own rate of synthesis in cis are starting to be better understood, new therapeutic strategies are emerging that aim to modulate the translation of the EBNA1 mRNA. If translation is induced, it could increase the amount of EBNA1-derived antigenic peptides that are presented to the major histocompatibility (MHC) class I pathway and thus, make EBV-carrying cancers better targets for the immune system. If translation is further suppressed, this would provide another means to cripple the virus.

Baicalein inhibits growth of Epstein-Barr virus-positive nasopharyngeal carcinoma by repressing the activity of EBNA1 Q-promoter

Epstein-Barr virus (EBV) can establish a life-long latent infection in the host and is associated with various human malignancies, including nasopharyngeal carcinoma (NPC), the most common cancer originated from nasopharynx. EBV nuclear antigen 1 (EBNA1) is the only viral protein absolutely demanded for segregation, replication, transcription and maintenance of EBV viral genome in host cells. Baicalein, a bioactive flavonoid compound purified from the root of Scutellariae baicaleinsis, displays anti-inflammatory, immunosuppressive, and anti-tumor properties. In this study, the therapeutic effects and functional mechanism of baicalein on EBV-positive human NPC were determined. Cell Counting Kit-8 assays and cell formation colony were performed to investigate that baicalein can suppress proliferation of EBV-infected human NPC cells. Flow cytometric and hoechst 33258 staining results indicated that baicalein induced cell cycle arrest and apoptosis. Western blotting results demonstrated that baicalein down-regulates EBNA1 expression but not reduces the stability and half-life of EBNA1 in EBV-infected NPC cells. Additionally, the mRNA level of EBNA1 was examined by real time-PCR, the activity of EBNA1 Q promoter (Qp) was determined by dual luciferase reporter assay. Considering that transcription factor specificity protein 1 (Sp1) can maintain EBNA1 Qp active. Further analyses also elucidated that baicalein inhibits the expression of Sp1 while knock-down Sp1 by specific shRNAs decreases the expression and transcription levels of EBNA1. Therefore, the results suggested that baicalein may decrease EBNA1 expression level in EBV-positive NPC cells via inhibiting the activity of EBNA1 Q-promoter while over-expression of EBNA1 attenuate the inhibitory effect of baicalein. Finally, it was found that baicalein may strongly reduce growth of tumor in the mouse xenograft model of EBV-positive NPC. These results indicated that baicalein inhibits growth of EBV-positive NPC by repressing the activity of EBNA1 Q-promoter. Baicalein may be used as a therapeutic agent to treat EBV-positive NPC.

Clinical Evaluation and Biomarker Profiling of Hsp90 Inhibitors

Inhibitors of the molecular chaperone heat shock protein 90 (Hsp90) have been in clinical development as anticancer agents since 1998. There have been 18 Hsp90 inhibitors (Hsp90i) that have entered the clinic, all of which, though structurally distinct, target the ATP-binding Bergerat fold of the chaperone N-terminus. Currently, there are five Hsp90 inhibitors in clinical trial and no approved drug in this class. One impediment to development of a clinically efficacious Hsp90 inhibitor has been the very low percentage of clinical trials that have codeveloped a predictive or pharmacodynamic marker of the anticancer activity inherent in this class of drugs. Here, we provide an overview of the clinical development of Hsp90 inhibitors, review the pharmacodynamic assays that have been employed in the past, and highlight new approaches to Hsp90 inhibitor clinical development.

HSP90: a promising broad-spectrum antiviral drug target

The emergence of antiviral drug-resistant mutants is the most important issue in current antiviral therapy. As obligate parasites, viruses require host factors for efficient replication. An ideal therapeutic target to prevent drug-resistance development is represented by host factors that are crucial for the viral life cycle. Recent studies have indicated that heat shock protein 90 (HSP90) is a crucial host factor that is required by many viruses for multiple phases of their life cycle including viral entry, nuclear import, transcription, and replication. In this review, we summarize the most recent advances regarding HSP90 function, mechanisms of action, and molecular pathways that are associated with viral infection, and provide a comprehensive understanding of the role of HSP90 in the immune response and exosome-mediated viral transmission. In addition, several HSP90 inhibitors have entered clinical trials for specific cancers that are associated with viral infection, which further implies a crucial role for HSP90 in the malignant transformation of virus-infected cells; as such, HSP90 inhibitors exhibit excellent therapeutic potential. Finally, we describe the challenge of developing HSP90 inhibitors as anti-viral drugs.

Berberine inhibits the proliferation of human nasopharyngeal carcinoma cells via an Epstein-Barr virus nuclear antigen 1-dependent mechanism

Nasopharyngeal carcinoma (NPC) is a malignancy derived from the epithelial cells of the nasopharynx cavity, and is closely associated with Epstein-Barr virus (EBV) infection. In addition to NPC, EBV causes various human malignancies, such as gastric cancer, hematological tumors and lymphoepithelioma-like carcinomas. Epstein-Barr nuclear antigen 1 (EBNA1) encoded by EBV is indispensable for replication, partition, transcription and maintenance of viral genomes. Berberine, a naturally occurring isoquinoline alkaloid, shows anti-inflammatory, anticholinergic, antioxidative, and anticancer activities. In the present study, the antitumor effect of berberine was studied. Cell Counting Kit-8 (CCK-8) assays were performed to demonstrate whether the proliferation of EBV-positive NPC cells was inhibited by berberine. Flow cytometric results revealed that berberine induced cell cycle arrest and apoptosis. Quantitative-PCR and western blotting results indicated that berberine decreased the expression of EBNA1 at both the mRNA and protein levels in the EBV-positive NPC cells. The function of EBNA1 promoter Qp which is to drive EBNA1 transcription in type Ⅱ latent infection was strongly suppressed by berberine. Overexpression of EBNA1 attenuated this inhibitory effect. Berberine also suppressed the activity of signal transducer and activator of transcription 3 which is a new therapeutic target in a series of malignancies, including NPC. Viral titer experiments demonstrated that berberine decreased the production of virions in HONE1 and HK1-EBV cells. In a mouse xenograft model of NPC induced by HONE1 cells, berberine significantly inhibited tumor formation. Altogether, these results indicate that berberine decreases the expression of EBNA1 and exhibits an antitumor effect against NPC both in vitro and in vivo.

Regulation of Viral Replication, Apoptosis and Pro-Inflammatory Responses by 17-AAG during Chikungunya Virus Infection in Macrophages

Chikungunya virus (CHIKV) infection has re-emerged as a major public health concern due to its recent worldwide epidemics and lack of control measures. Although CHIKV is known to infect macrophages, regulation of CHIKV replication, apoptosis and immune responses towards macrophages are not well understood. Accordingly, the Raw264.7 cells, a mouse macrophage cell line, were infected with CHIKV and viral replication as well as new viral progeny release was assessed by flow cytometry and plaque assay, respectively. Moreover, host immune modulation and apoptosis were studied through flow cytometry, Western blot and ELISA. Our current findings suggest that expression of CHIKV proteins were maximum at 8 hpi and the release of new viral progenies were remarkably increased around 12 hpi. The induction of Annexin V binding, cleaved caspase-3, cleaved caspase-9 and cleaved caspase-8 in CHIKV infected macrophages suggests activation of apoptosis through both intrinsic and extrinsic pathways. The pro-inflammatory mediators (TNF and IL-6) MHC-I/II and B7.2 (CD86) were also up-regulated during infection over time. Further, 17-AAG, a potential HSP90 inhibitor, was found to regulate CHIKV infection, apoptosis and pro-inflammatory cytokine/chemokine productions of host macrophages significantly. Hence, the present findings might bring new insight into the therapeutic implication in CHIKV disease biology.

Inhibition of hepatitis C virus using siRNA targeted to the virus and Hsp90

Hepatitis C (HCV) is a viral disease affecting millions of people worldwide, and persistent HCV infection can lead to progressive liver disease with the development of liver cirrhosis and hepatocellular carcinoma. During treatment for hepatitis C, the occurrence of viral resistance is common. To reduce the occurrence of resistance, new viral treatments should target both viral and cellular factors. Many interactions occur between viral and host proteins during the HCV replication cycle and might be used for the development of new therapies against hepatitis C. Heat shock protein 90 (Hsp90) plays a role in the folding of cellular and viral proteins and also interacts with HCV proteins. In the present study, we knocked down the expression of the Hsp90 gene and inhibited viral replication using siRNA molecules. Reducing the expression of Hsp90 successfully decreased HCV replication. All siRNA molecules specific to the viral genome showed the efficient inhibition of viral replication, particularly siRNA targeted to the 5'UTR region. The combination of siRNAs targeting the viral genome and Hsp90 mRNA also successfully reduced HCV replication and reduced the occurrence of viral resistance. Moreover, these results suggest that an approach based on the combination of cellular and viral siRNAs can be used as an effective alternative for hepatitis C viral suppression.

Ganetespib, an HSP90 inhibitor, kills Epstein-Barr virus (EBV)-infected B and T cells and reduces the percentage of EBV-infected cells in the blood

HSP90 inhibitors have been shown to kill Epstein-Barr virus (EBV)-infected cells by reducing the level of EBV EBNA-1 and/or LMP1. We treated virus-infected cells with ganetespib, an HSP90 inhibitor currently being evaluated in multiple clinical trials for cancer and found that the drug killed EBV-positive B and T cells and reduced the level of both EBV EBNA-1 and LMP1. Treatment of cells with ganetespib also reduced the level of pAkt. Ganetespib delayed the onset of EBV-positive lymphomas and prolonged survival in SCID mice inoculated with one EBV-transformed B-cell line, but not another B-cell line. The former cell line showed lower levels of EBNA-1 after treatment with ganetespib in vitro. Treatment of a patient with T-cell chronic active EBV with ganetespib reduced the percentage of EBV-positive cells in the peripheral blood. These data indicate that HSP90 inhibitors may have a role in the therapy of certain EBV-associated diseases.

The co-chaperone Cdc37 regulates the rabies virus phosphoprotein stability by targeting to Hsp90AA1 machinery

Cdc37, as a kinase-specific co-chaperone of the chaperone Hsp90AA1 (Hsp90), actively aids with the maturation, stabilization and activation of the cellular or viral kinase/kinase-like targets. Phosphoprotein (P) of rabies virus (RABV) is a multifunctional, non-kinase protein involved in interferon antagonism, viral transcription and replication. Here, we demonstrated that the RABV non-kinase P is chaperoned by Cdc37 and Hsp90 during infection. We found that Cdc37 and Hsp90 affect the RABV life cycle directly. Activity inhibition and knockdown of Cdc37 and Hsp90 increased the instability of the viral P protein. Overexpression of Cdc37 and Hsp90 maintained P's stability but did not increase the yield of infectious RABV virions. We further demonstrated that the non-enzymatic polymerase cofactor P protein of all the genotypes of lyssaviruses is a target of the Cdc37/Hsp90 complex. Cdc37, phosphorylated or unphosphorylated on Ser13, aids the P protein to load onto the Hsp90 machinery, with or without Cdc37 binding to Hsp90. However, the interaction between Cdc37 and Hsp90 appears to have additional allosteric regulation of the conformational switch of Hsp90. Our study highlighted a novel mechanism in which Cdc37/Hsp90 chaperones a non-kinase target, which has significant implications for designing therapeutic targets against Rabies.

Transcriptional and Bioinformatic Analysis Provide a Relationship between Host Response Changes to Marek's Disease Viruses Infection and an Integrated Long Terminal Repeat

GX0101, Marek's disease virus (MDV) strain with a long terminal repeat (LTR) insert of reticuloendotheliosis virus (REV), was isolated from CVI988/Rispens vaccinated birds showing tumors. We have constructed a LTR deleted strain GX0101ΔLTR in our previous study. To compare the host responses to GX0101 and GX0101ΔLTR, chicken embryo fibroblasts (CEF) cells were infected with two MDV strains and a gene-chip containing chicken genome was employed to examine gene transcription changes in host cells in the present study. Of the 42,368 chicken transcripts on the chip, there were 2199 genes that differentially expressed in CEF infected with GX0101 compared to GX0101ΔLTR significantly. Differentially expressed genes were distributed to 25 possible gene networks according to their intermolecular connections and were annotated to 56 pathways. The insertion of REV LTR showed the greatest influence on cancer formation and metastasis, followed with immune changes, atherosclerosis, and nervous system disorders in MDV-infected CEF cells. Based on these bio functions, GX0101 infection was predicated with a greater growth and survival inhibition but lower oncogenicity in chickens than GX0101ΔLTR, at least in the acute phase of infection. In summary, the insertion of REV LTR altered the expression of host genes in response to MDV infection, possibly resulting in novel phenotypic properties in chickens. Our study has provided the evidence of retroviral insertional changes of host responses to herpesvirus infection for the first time, which will promote to elucidation of the possible relationship between the LTR insertion and the observed phenotypes.

Triptolide decreases expression of latency-associated nuclear antigen 1 and reduces viral titers in Kaposi's sarcoma-associated and herpesvirus-related primary effusion lymphoma cells

Kaposi's sarcoma-associated herpesvirus (KSHV) can establish a life-long persistence in the host after primary infection and is associated with certain malignancies, which are resistant to conventional chemotherapeutic agents with a poor prognosis. Latency-associated nuclear antigen 1 (LANA1) encoded by KSHV is essential for segregation, replication and maintenance of viral genome. In addition, LANA1 upregulates the transcriptional activity of signal transducer and activator of transcription 3 (STAT3), which plays an important role in promoting survival of KSHV-associated primary effusion lymphoma (PEL) cells. Furthermore, LANA1 mediates transcriptional modulation of KSHV and host genome in host cells. In the present study, the antitumor effect of triptolide was assessed. CCK-8 assays were performed to demonstrate that the proliferations of PEL cells were efficiently inhibited by triptolide in a dose- and time-dependent manner. Flow cytometric results indicated that triptolide induced cell cycle arrest and apoptosis. Western blot results suggested that triptolide downregulated LANA1 expression and reduced half-life of LANA1 in the KSHV-infected malignant cells. Viral titer experiments indicated that triptolide treatment impaired the number of viral DNA copies and the production of virions in BCBL-1 cells. Triptolide also suppressed STAT3 activity and inhibited secretion of IL-6 in PEL cells. In a mouse xenograft model of primary effusion lymphoma by BCBL-1 cells, triptolide treatment significantly inhibited ascites formation and diffused organ infiltration. These results indicate that triptolide impairs the expression of LANA1 and shows antitumor activity against PEL in vitro and in vivo. Triptolide may be a potential agent for treatment of PEL.

M1 of Murine Gamma-Herpesvirus 68 Induces Endoplasmic Reticulum Chaperone Production

Viruses rely on host chaperone network to support their infection. In particular, the endoplasmic reticulum (ER) resident chaperones play key roles in synthesizing and processing viral proteins. Influx of a large amount of foreign proteins exhausts the folding capacity in ER and triggers the unfolded protein response (UPR). A fully-executed UPR comprises signaling pathways that induce ER folding chaperones, increase protein degradation, block new protein synthesis and may eventually activate apoptosis, presenting both opportunities and threats to the virus. Here, we define a role of the MHV-68M1 gene in differential modulation of UPR pathways to enhance ER chaperone production. Ectopic expression of M1 markedly induces ER chaperone genes and expansion of ER. The M1 protein accumulates in ER during infection and this localization is indispensable for its function, suggesting M1 acts from the ER. We found that M1 protein selectively induces the chaperon-producing pathways (IRE1, ATF6) while, interestingly, sparing the translation-blocking arm (PERK). We identified, for the first time, a viral factor capable of selectively intervening the initiation of ER stress signaling to induce chaperon production. This finding provides a unique opportunity of using viral protein as a tool to define the activation mechanisms of individual UPR pathways.

The AT-hook DNA binding ability of the Epstein Barr virus EBNA1 protein is necessary for the maintenance of viral genomes in latently infected cells

Epstein Barr Virus (EBV) is a human tumor virus that is causally linked to malignancies such as Burkitt׳s lymphoma, and gastric and nasopharyngeal carcinomas. Tethering of EBV genomes to cellular chromosomes is required for the synthesis and persistence of viral plasmids in tumor cells. However, it is not established how EBV genomes are tethered to cellular chromosomes. We test the hypothesis that the viral protein EBNA1 tethers EBV genomes to chromosomes specifically through its N-terminal AT-hook DNA-binding domains by using a small molecule, netropsin, that has been shown to inhibit the AT-hook DNA-binding of EBNA1 in vitro. We show that netropsin forces the loss of EBV genomes from epithelial and lymphoid cells in an AT-hook dependent manner and that EBV-positive lymphoma cells are significantly more inhibited in their growth by netropsin than are corresponding EBV-negative cells.

The heat shock protein 90 inhibitor BIIB021 suppresses the growth of T and natural killer cell lymphomas

Epstein-Barr virus (EBV), which infects not only B cells but also T and natural killer (NK) cells, is associated with a variety of lymphoid malignancies. Because EBV-associated T and NK cell lymphomas are refractory and resistant to conventional chemotherapy, there is a continuing need for new effective therapies. EBV-encoded “latent membrane protein 1” (LMP1) is a major oncogene that activates nuclear factor kappa B (NF-κB), c-Jun N-terminal kinase (JNK), and phosphatidylinositol 3-kinase signaling pathways, thus promoting cell growth and inhibiting apoptosis. Recently, we screened a library of small-molecule inhibitors and isolated heat shock protein 90 (Hsp90) inhibitors as candidate suppressors of LMP1 expression. In this study, we evaluated the effects of BIIB021, a synthetic Hsp90 inhibitor, against EBV-positive and -negative T and NK lymphoma cell lines. BIIB021 decreased the expression of LMP1 and its downstream signaling proteins, NF-κB, JNK, and Akt, in EBV-positive cell lines. Treatment with BIIB021 suppressed proliferation in multiple cell lines, although there was no difference between the EBV-positive and -negative lines. BIIB021 also induced apoptosis and arrested the cell cycle at G1 or G2. Further, it down-regulated the protein levels of CDK1, CDK2, and cyclin D3. Finally, we evaluated the in vivo effects of the drug; BIIB021 inhibited the growth of EBV-positive NK cell lymphomas in a murine xenograft model. These results suggest that BIIB021 has suppressive effects against T and NK lymphoma cells through the induction of apoptosis or a cell cycle arrest. Moreover, BIIB021 might help to suppress EBV-positive T or NK cell lymphomas via the down-regulation of LMP1 expression.

Epstein-Barr virus-encoded EBNA1 and ZEBRA: targets for therapeutic strategies against EBV-carrying cancers

The EBV-encoded EBNA1 was first discovered 40 years ago, approximately 10 years after the presence of EBV had been demonstrated in Burkitt's lymphoma cells. It took another 10 years before the functions of EBNA1 in maintaining the viral genome were revealed, and it has since been shown to be an essential viral factor expressed in all EBV-carrying cells. Apart from serving to maintain the viral episome and to control viral replication and gene expression, EBNA1 also harbours a cis-acting mechanism that allows virus-carrying host cells to evade the immune system. This relates to a particular glycine-alanine repeat (GAr) within EBNA1 that has the capacity to suppress antigen presentation to the major histocompatibility complex (MHC) class I pathway. We discuss the role of the GAr sequence at the level of mRNA translation initiation, rather than at the protein level, as at least part of the mechanism to avoid MHC presentation. Interfering with this mechanism has become the focus of the development of immune-based therapies against EBV-carrying cancers, and some lead compounds that affect translation of GAr-carrying mRNAs have been identified. In addition, we describe the EBV-encoded ZEBRA factor and the switch from the latent to the lytic cycle as an alternative virus-specific target for treating EBV-carrying cancers. Understanding the molecular mechanisms of how EBNA1 and ZEBRA interfere with cellular pathways not only opens new therapeutic approaches but continues to reveal new cell-biological insights on the interplay between host and virus. This review is a tale of discoveries relating to how EBNA1 and ZEBRA have emerged as targets for specific cancer therapies against EBV-carrying diseases, and serves as an illustration of how mRNA translation can play roles in future immune-based strategies to target viral disease.

EBNA1

Epstein-Barr nuclear antigen 1 (EBNA1) plays multiple important roles in EBV latent infection and has also been shown to impact EBV lytic infection. EBNA1 is required for the stable persistence of the EBV genomes in latent infection and activates the expression of other EBV latency genes through interactions with specific DNA sequences in the viral episomes. EBNA1 also interacts with several cellular proteins to modulate the activities of multiple cellular pathways important for viral persistence and cell survival. These cellular effects are also implicated in oncogenesis, suggesting a direct role of EBNA1 in the development of EBV-associated tumors.

Triptolide inhibits proliferation of Epstein-Barr virus-positive B lymphocytes by down-regulating expression of a viral protein LMP1

Epstein-Barr virus (EBV) infects various types of cells and mainly establishes latent infection in B lymphocytes. The viral latent membrane protein 1 (LMP1) plays important roles in transformation and proliferation of B lymphocytes infected with EBV. Triptolide is a compound of Tripterygium extracts, showing anti-inflammatory, immunosuppressive, and anti-cancer activities. In this study, it is determined whether triptolide inhibits proliferation of Epstein-Barr virus-positive B lymphocytes. The CCK-8 assays were performed to examine cell viabilities of EBV-positive B95-8 and P3HR-1 cells treated by triptolide. The mRNA and protein levels of LMP1 were examined by real time-PCR and Western blotting, respectively. The activities of two LMP1 promoters (ED-L1 and TR-L1) were determined by Dual luciferase reportor assay. The results showed that triptolide inhibited the cell viability of EBV-positive B lymphocytes, and the over-expression of LMP1 attenuated this inhibitory effect. Triptolide decreased the LMP1 expression and transcriptional levels in EBV-positive B cells. The activity of LMP1 promoter ED-L1 in type III latent infection was strongly suppressed by triptolide treatment. In addition, triptolide strongly reduced growth of B95-8 induced B lymphoma in BALB/c nude mice. These results suggest that triptolide decreases proliferation of EBV-induced B lymphocytes possibly by a mechanism related to down-regulation of the LMP1 expression.

Utilising proteomic approaches to understand oncogenic human herpesviruses (Review)

The γ-herpesviruses Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus are successful pathogens, each infecting a large proportion of the human population. These viruses persist for the life of the host and may each contribute to a number of malignancies, for which there are currently no cures. Large-scale proteomic-based approaches provide an excellent means of increasing the collective understanding of the proteomes of these complex viruses and elucidating their numerous interactions within the infected host cell. These large-scale studies are important for the identification of the intricacies of viral infection and the development of novel therapeutics against these two important pathogens.

Identification of protein kinase inhibitors with a selective negative effect on the viability of Epstein-Barr virus infected B cell lines

Epstein-Barr virus (EBV) is a human herpesvirus, which is causally associated with the development of several B lymphocytic malignancies that include Burkitt's lymphomas, Hodgkin's disease, AIDS and posttransplant associated lymphomas. The transforming activity of EBV is orchestrated by several latent viral proteins that mimic and modulate cellular growth promoting and antiapoptotic signaling pathways, which involve among others the activity of protein kinases. In an effort to identify small molecule inhibitors of the growth of EBV-transformed B lymphocytes a library of 254 kinase inhibitors was screened. This effort identified two tyrosine kinase inhibitors and two MEK inhibitors that compromised preferentially the viability of EBV-infected human B lymphocytes. Our findings highlight the possible dependence of EBV-infected B lymphocytes on specific kinase-regulated pathways underlining the potential for the development of small molecule-based therapeutics that could target selectively EBV-associated human B lymphocyte malignancies.

Small molecule inhibition of Epstein-Barr virus nuclear antigen-1 DNA binding activity interferes with replication and persistence of the viral genome

The replication and persistence of extra chromosomal Epstein-Barr virus (EBV) episome in latently infected cells are primarily dependent on the binding of EBV-encoded nuclear antigen 1 (EBNA1) to the cognate EBV oriP element. In continuation of the previous study, herein we characterized EBNA1 small molecule inhibitors (H20, H31) and their underlying inhibitory mechanisms. In silico docking analyses predicted that H20 fits into a pocket in the EBNA1 DNA binding domain (DBD). However, H20 did not significantly affect EBNA1 binding to its cognate sequence. A limited structure-relationship study of H20 identified a hydrophobic compound H31, as an EBNA1 inhibitor. An in vitro EBNA1 EMSA and in vivo EGFP-EBNA1 confocal microscopy analysis showed that H31 inhibited EBNA1-dependent oriP sequence-specific DNA binding activity, but not sequence-nonspecific chromosomal association. Consistent with this, H31 repressed the EBNA1-dependent transcription, replication, and persistence of an EBV oriP plasmid. Furthermore, H31 induced progressive loss of EBV episome. In addition, H31 selectively retarded the growth of EBV-infected LCL or Burkitt's lymphoma cells. These data indicate that H31 inhibition of EBNA1-dependent DNA binding decreases transcription from and persistence of EBV episome in EBV-infected cells. These new compounds might be useful probes for dissecting EBNA1 functions in vitro and in vivo.

Targeting the Hsp90-associated viral oncoproteome in gammaherpesvirus-associated malignancies

PU-H71 is a purine-scaffold Hsp90 inhibitor that, in contrast to other Hsp90 inhibitors, displays unique selectivity for binding the fraction of Hsp90 that is preferentially associated with oncogenic client proteins and enriched in tumor cells (teHsp90). This property allows PU-H71 to potently suppress teHsp90 without inducing toxicity in normal cells. We found that lymphoma cells infected by Epstein-Barr virus or Kaposi sarcoma-associated herpes virus (KSHV) are exquisitely sensitive to this compound. Using PU-H71 affinity capture and proteomics, an unbiased approach to reveal oncogenic networks, we identified the teHsp90 interactome in KSHV(+) primary effusion lymphoma cells. Viral and cellular proteins were identified, including many involved in nuclear factor (NF)-κB signaling, apoptosis, and autophagy. KSHV vFLIP is a viral oncoprotein homologous to cFLIPs, with NF-κB-activating and antiapoptotic activities. We show that teHsp90 binds vFLIP but not cFLIPs. Treatment with PU-H71 induced degradation of vFLIP and IKKγ, NF-κB downregulation, apoptosis and autophagy in vitro, and more importantly, tumor responses in mice. Analysis of the interactome revealed apoptosis as a central pathway; therefore, we tested a BCL2 family inhibitor in primary effusion lymphoma cells. We found strong activity and synergy with PU-H71. Our findings demonstrate PU-H71 affinity capture identifies actionable networks that may help design rational combinations of effective therapies.

EBV-positive diffuse large B-cell lymphoma of the elderly

Epstein-Barr virus (EBV) positive diffuse large B-cell lymphoma (DLBCL) of the elderly, initially described in 2003, is a provisional entity in the 2008 World Health Organization classification system and is defined as an EBV-positive monoclonal large B-cell proliferation that occurs in patients >50 years of age and in whom there is no known immunodeficiency or history of lymphoma. These tumors are more common in Asia but also occur in North America and Europe at a low frequency. These neoplasms exhibit a morphologic continuum, from polymorphous to monomorphous, but morphologic features do not correlate with prognosis as all patients have a clinically aggressive course. Most EBV-positive DLBCL of the elderly patients have an activated B-cell immunophenotype and are characterized by prominent nuclear factor-κB activation. Cytogenetic complexity is usually low. In this review, we comprehensively delineate the data emerging from analyses of EBV latency program, microRNA-mediated EBV viral oncogenesis, functional genomics of EBV and its biology, and differential diagnosis challenge for EBV-positive DLBCL of the elderly. It is hoped that the improved understanding of these tumors will lead to the development of novel therapeutic approaches, enhance the effectiveness of clinical trials, and improve prognosis.

Hsp90 inhibitor 17-DMAG decreases expression of conserved herpesvirus protein kinases and reduces virus production in Epstein-Barr virus-infected cells

All eight human herpesviruses have a conserved herpesvirus protein kinase (CHPK) that is important for the lytic phase of the viral life cycle. In this study, we show that heat shock protein 90 (Hsp90) interacts directly with each of the eight CHPKs, and we demonstrate that an Hsp90 inhibitor drug, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), decreases expression of all eight CHPKs in transfected HeLa cells. 17-DMAG also decreases expression the of the endogenous Epstein-Barr virus protein kinase (EBV PK, encoded by the BGLF4 gene) in lytically infected EBV-positive cells and inhibits phosphorylation of several different known EBV PK target proteins. Furthermore, 17-DMAG treatment abrogates expression of the human cytomegalovirus (HCMV) kinase UL97 in HCMV-infected human fibroblasts. Importantly, 17-DMAG treatment decreased the EBV titer approximately 100-fold in lytically infected AGS-Akata cells without causing significant cellular toxicity during the same time frame. Increased EBV PK expression in 17-DMAG-treated AGS-Akata cells did not restore EBV titers, suggesting that 17-DMAG simultaneously targets multiple viral and/or cellular proteins required for efficient viral replication. These results suggest that Hsp90 inhibitors, including 17-DMAG, may be a promising group of drugs that could have profound antiviral effects on herpesviruses.

Heat shock protein-90-beta facilitates enterovirus 71 viral particles assembly

Molecular chaperones are reported to be crucial for virus propagation, but are not yet addressed in Human Enterovirus 71 (EV71). Here we describe the specific association of heat shock protein-90-beta (Hsp90β), but not alpha form (Hsp90α), with EV71 viral particles by the co-purification with virions using sucrose density gradient ultracentrifugation, and by the colocalization with viral particles, as assessed by immunogold electron microscopy. The reduction of the Hsp90β protein using RNA interference decreased the correct assembly of viral particles, without affecting EV71 replication levels. Tracking ectopically expressed Hsp90β protein associated with EV71 virions revealed that Hsp90β protein was transmitted to new host cells through its direct association with infectious viral particles. Our findings suggest a new antiviral strategy in which extracellular Hsp90β protein is targeted to decrease the infectivity of EV71 and other enteroviruses, without affecting the broader functions of this constitutively expressed molecular chaperone.

Heat shock protein 90 inhibitors repress latent membrane protein 1 (LMP1) expression and proliferation of Epstein-Barr virus-positive natural killer cell lymphoma

Epstein-Barr virus (EBV) LMP1 is a major oncoprotein expressed in latent infection. It functions as a TNFR family member and constitutively activates cellular signals, such as NFκB, MAPK, JAK/STAT and AKT. We here screened small molecule inhibitors and isolated HSP90 inhibitors, Radicicol and 17-AAG, as candidates that suppress LMP1 expression and cell proliferation not only in EBV-positive SNK6 Natural Killer (NK) cell lymphoma cells, but also in B and T cells. Tumor formation in immuno-defficient NOD/Shi-scid/IL-2Rγ^null (NOG) mice was also retarded. These results suggest that HSP90 inhibitors can be alternative treatments for patients with EBV-positive malignancies.