The Epstein-Barr virus immediate-early protein BZLF1 regulates p53 function through multiple mechanisms

Interplay between the DNA damage response and the life cycle of DNA tumor viruses

Approximately 20 % of human cancers are associated with virus infection. DNA tumor viruses can induce tumor formation in host cells by disrupting the cell's DNA replication and repair mechanisms. Specifically, these viruses interfere with the host cell's DNA damage response (DDR), which is a complex network of signaling pathways that is essential for maintaining the integrity of the genome. DNA tumor viruses can disrupt these pathways by expressing oncoproteins that mimic or inhibit various DDR components, thereby promoting genomic instability and tumorigenesis. Recent studies have highlighted the molecular mechanisms by which DNA tumor viruses interact with DDR components, as well as the ways in which these interactions contribute to viral replication and tumorigenesis. Understanding the interplay between DNA tumor viruses and the DDR pathway is critical for developing effective strategies to prevent and treat virally associated cancers. In this review, we discuss the current state of knowledge regarding the mechanisms by which human papillomavirus (HPV), merkel cell polyomavirus (MCPyV), Kaposi's sarcoma-associated herpesvirus (KSHV), and Epstein-Barr virus (EBV) interfere with DDR pathways to facilitate their respective life cycles, and the consequences of such interference on genomic stability and cancer development.

P63 and P73 Activation in Cancers with p53 Mutation

The members of the p53 family comprise p53, p63, and p73, and full-length isoforms of the p53 family have a tumor suppressor function. However, p53, but not p63 or p73, has a high mutation rate in cancers causing it to lose its tumor suppressor function. The top and second-most prevalent p53 mutations are missense and nonsense mutations, respectively. In this review, we discuss possible drug therapies for nonsense mutation and a missense mutation in p53. p63 and p73 activators may be able to replace mutant p53 and act as anti-cancer drugs. Herein, these p63 and p73 activators are summarized and how to improve these activator responses, particularly focusing on p53 gain-of-function mutants, is discussed.

SUMO and SUMOylation Pathway at the Forefront of Host Immune Response

Pathogens pose a continuous challenge for the survival of the host species. In response to the pathogens, the host immune system mounts orchestrated defense responses initiating various mechanisms both at the cellular and molecular levels, including multiple post-translational modifications (PTMs) leading to the initiation of signaling pathways. The network of such pathways results in the recruitment of various innate immune components and cells at the site of infection and activation of the adaptive immune cells, which work in synergy to combat the pathogens. Ubiquitination is one of the most commonly used PTMs. Host cells utilize ubiquitination for both temporal and spatial regulation of immune response pathways. Over the last decade, ubiquitin family proteins, particularly small ubiquitin-related modifiers (SUMO), have been widely implicated in host immune response. SUMOs are ubiquitin-like (Ubl) proteins transiently conjugated to a wide variety of proteins through SUMOylation. SUMOs primarily exert their effect on target proteins by covalently modifying them. However, SUMO also engages in a non-covalent interaction with the SUMO-interacting motif (SIM) in target proteins. Unlike ubiquitination, SUMOylation alters localization, interactions, functions, or stability of target proteins. This review provides an overview of the interplay of SUMOylation and immune signaling and development pathways in general. Additionally, we discuss in detail the regulation exerted by covalent SUMO modifications of target proteins, and SIM mediated non-covalent interactions with several effector proteins. In addition, we provide a comprehensive review of the literature on the importance of the SUMO pathway in the development and maintenance of a robust immune system network of the host. We also summarize how pathogens modulate the host SUMO cycle to sustain infectability. Studies dealing mainly with SUMO pathway proteins in the immune system are still in infancy. We anticipate that the field will see a thorough and more directed analysis of the SUMO pathway in regulating different cells and pathways of the immune system. Our current understanding of the importance of the SUMO pathway in the immune system necessitates an urgent need to synthesize specific inhibitors, bioactive regulatory molecules, as novel therapeutic targets.

Aberrant Splicing Events and Epigenetics in Viral Oncogenomics: Current Therapeutic Strategies

Global cancer incidence and mortality are on the rise. Although cancer is fundamentally a non-communicable disease, a large number of cancers are known to have a viral aetiology. A high burden of infectious agents (Human immunodeficiency virus (HIV), human papillomavirus (HPV), hepatitis B virus (HBV)) in certain Sub-Saharan African countries drives the rates of certain cancers. About one-third of all cancers in Africa are attributed to infection. Seven viruses have been identified with carcinogenic characteristics, namely the HPV, HBV, Hepatitis C virus (HCV), Epstein–Barr virus (EBV), Human T cell leukaemia virus 1 (HTLV-1), Kaposi’s Sarcoma Herpesvirus (KSHV), and HIV-1. The cellular splicing machinery is compromised upon infection, and the virus generates splicing variants that promote cell proliferation, suppress signalling pathways, inhibition of tumour suppressors, alter gene expression through epigenetic modification, and mechanisms to evade an immune response, promoting carcinogenesis. A number of these splice variants are specific to virally-induced cancers. Elucidating mechanisms underlying how the virus utilises these splice variants to maintain its latent and lytic phase will provide insights into novel targets for drug discovery. This review will focus on the splicing genomics, epigenetic modifications induced by and current therapeutic strategies against HPV, HBV, HCV, EBV, HTLV-1, KSHV and HIV-1.

Ubiquitin Modification of the Epstein-Barr Virus Immediate Early Transactivator Zta

The Epstein-Barr virus (EBV) immediate early transactivator Zta plays a key role in regulating the transition from latency to the lytic replication stages of EBV infection. Regulation of Zta is known to be controlled through a number of transcriptional and posttranscriptional events. Here, we show that Zta is targeted for ubiquitin modification and that this can occur in EBV-negative and in EBV-infected cells. Genetic studies show critical roles for both an amino-terminal region of Zta and the basic DNA binding domain of Zta in regulating Zta ubiquitination. Pulse-chase experiments demonstrate that the bulk population of Zta is relatively stable but that at least a subset of ubiquitinated Zta molecules are targeted for degradation in the cell. Mutation of four out of a total of nine lysine residues in Zta largely abrogates its ubiquitination, indicating that these are primary ubiquitination target sites. A Zta mutant carrying mutations at these four lysine residues (lysine 12, lysine 188, lysine 207, and lysine 219) cannot induce latently infected cells to produce and/or release infectious virions. Nevertheless, this mutant can induce early gene expression, suggesting a possible defect at the level of viral replication or later in the lytic cascade. As far as we know, this is the first study that has investigated the targeting of Zta by ubiquitination or its role in Zta function.IMPORTANCE Epstein-Barr virus (EBV) is a ubiquitous human pathogen and associated with various human diseases. EBV undergoes latency and lytic replication stages in its life cycle. The transition into the lytic replication stage, at which virus is produced, is mainly regulated by the viral gene product, Zta. Therefore, the regulation of Zta function becomes a central issue regarding viral biology and pathogenesis. Known modifications of Zta include phosphorylation and sumoylation. Here, we report the role of ubiquitination in regulating Zta function. We found that Zta is subjected to ubiquitination in both EBV-infected and EBV-negative cells. The ubiquitin modification targets 4 lysine residues on Zta, leading to both mono- and polyubiquitination of Zta. Ubiquitination of Zta affects the protein's stability and likely contributes to the progression of viral lytic replication. The function and fate of Zta may be determined by the specific lysine residue being modified.

The bZIP Proteins of Oncogenic Viruses

Basic leucine zipper (bZIP) transcription factors (TFs) govern diverse cellular processes and cell fate decisions. The hallmark of the leucine zipper domain is the heptad repeat, with leucine residues at every seventh position in the domain. These leucine residues enable homo- and heterodimerization between ZIP domain α-helices, generating coiled-coil structures that stabilize interactions between adjacent DNA-binding domains and target DNA substrates. Several cancer-causing viruses encode viral bZIP TFs, including human T-cell leukemia virus (HTLV), hepatitis C virus (HCV) and the herpesviruses Marek’s disease virus (MDV), Epstein–Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV). Here, we provide a comprehensive review of these viral bZIP TFs and their impact on viral replication, host cell responses and cell fate.

Oncogenic Properties of the EBV ZEBRA Protein

Epstein Barr Virus (EBV) is one of the most common human herpesviruses. After primary infection, it can persist in the host throughout their lifetime in a latent form, from which it can reactivate following specific stimuli. EBV reactivation is triggered by transcriptional transactivator proteins ZEBRA (also known as Z, EB-1, Zta or BZLF1) and RTA (also known as BRLF1). Here we discuss the structural and functional features of ZEBRA, its role in oncogenesis and its possible implication as a prognostic or diagnostic marker. Modulation of host gene expression by ZEBRA can deregulate the immune surveillance, allow the immune escape, and favor tumor progression. It also interacts with host proteins, thereby modifying their functions. ZEBRA is released into the bloodstream by infected cells and can potentially penetrate any cell through its cell-penetrating domain; therefore, it can also change the fate of non-infected cells. The features of ZEBRA described in this review outline its importance in EBV-related malignancies.

[Dynamic changes of cellular environment during Epstein-Barr virus productive replication]

Productive (lytic) replication of DNA viruses elicits host cell DNA damage responses, which cause both beneficial and detrimental effects on viral replication. Viruses utilize them and selectively cancel the 'noisy' downstream signaling pathways, leading to maintain high S-phase CDK activities required for viral replication. To achieve this fine tuning of cellular environment, herpesviruses encode many (>70) genes in their genome, which are expressed in a strictly regulated temporal cascade (immediate-early, early, and late). Here, I introduce and discuss how Epstein-Barr virus, an oncogenic herpesvirus, hijacks the cellular environment and adapt it for the progeny production.

A reliable Epstein-Barr Virus classification based on phylogenomic and population analyses

The Epstein-Barr virus (EBV) infects more than 90% of the human population, playing a key role in the origin and progression of malignant and non-malignant diseases. Many attempts have been made to classify EBV according to clinical or epidemiological information; however, these classifications show frequent incongruences. For instance, they use a small subset of genes for sorting strains but fail to consider the enormous genomic variability and abundant recombinant regions present in the EBV genome. These could lead to diversity overestimation, alter the tree topology and misinterpret viral types when classified, therefore, a reliable EBV phylogenetic classification is needed to minimize recombination signals. Recombination events occur 2.5-times more often than mutation events, suggesting that recombination has a much stronger impact than mutation in EBV genomic diversity, detected within common ancestral node positions. The Hierarchical Bayesian Analysis of Population Structure (hierBAPS) resulted in the differentiation of 12 EBV populations showed seven monophyletic and five paraphyletic. The populations identified were related to geographic location, of which three populations (EBV-p1/Asia/GC, EBV-p2/Asia II/Tumors and EBV-p4/China/NPC) were related to tumor development. Therefore, we proposed a new consistent and non-simplistic EBV classification, beneficial in minimizing the recombination signal in the phylogeny reconstruction, investigating geography relationship and even infer associations to human diseases. These EBV classifications could also be useful in developing diagnostic applications or defining which strains need epidemiological surveillance.

Arsenic trioxide inhibits EBV reactivation and promotes cell death in EBV-positive lymphoma cells

Background

Epstein-Barr Virus (EBV) is associated with hematopoietic malignancies, such as Burkitt’s lymphoma, post-transplantation lymphoproliferative disorder, and diffuse large B-cell lymphoma. The current approach for EBV-associated lymphoma involves chemotherapy to eradicate cancer cells, however, normal cells may be injured and organ dysfunction may occur with currently employed regimens. This research is focused on employing arsenic trioxide (ATO) as EBV-specific cancer therapy takes advantage of the fact the EBV resides within the malignant cells.

Methods and results

Our research reveals that low ATO inhibits EBV gene expression and genome replication. EBV spontaneous reactivation starts as early as 6 h after re-suspending EBV-positive Mutu cells in RPMI media in the absence of ATO, however this does not occur in Mutu cells cultured with ATO. ATO’s inhibition of EBV spontaneous reactivation is dose dependent. The expression of the EBV immediate early gene Zta and early gene BMRF1 is blocked with low concentrations of ATO (0.5 nM – 2 nM) in EBV latency type I cells and EBV-infected PBMC cells. The combination of ATO and ganciclovir further diminishes EBV gene expression. ATO-mediated reduction of EBV gene expression can be rescued by co-treatment with the proteasome inhibitor MG132, indicating that ATO promotes ubiquitin conjugation and proteasomal degradation of EBV genes. Co-immunoprecipitation assays with antibodies against Zta pulls down more ubiquitin in ATO treated cell lysates. Furthermore, MG132 reverses the inhibitory effect of ATO on anti-IgM-, PMA- and TGF-β-mediated EBV reactivation. Thus, mechanistically ATO’s inhibition of EBV gene expression occurs via the ubiquitin pathway. Moreover, ATO treatment results in increased cell death in EBV-positive cells compared to EBV-negative cells, as demonstrated by both MTT and trypan blue assays. ATO-induced cell death in EBV-positive cells is dose dependent. ATO and ganciclovir in combination further enhances cell death specifically in EBV-positive cells.

Conclusion

ATO-mediated inhibition of EBV lytic gene expression results in cell death selectively in EBV-positive lymphocytes, suggesting that ATO may potentially serve as a drug to treat EBV-related lymphomas in the clinical setting.

Computational discovery of Epstein-Barr virus targeted human genes and signalling pathways

Epstein-Barr virus (EBV) plays important roles in the origin and the progression of human carcinomas, e.g. diffuse large B cell tumors, T cell lymphomas, etc. Discovering EBV targeted human genes and signaling pathways is vital to understand EBV tumorigenesis. In this study we propose a noise-tolerant homolog knowledge transfer method to reconstruct functional protein-protein interactions (PPI) networks between Epstein-Barr virus and Homo sapiens. The training set is augmented via homolog instances and the homolog noise is counteracted by support vector machine (SVM). Additionally we propose two methods to define subcellular co-localization (i.e. stringent and relaxed), based on which to further derive physical PPI networks. Computational results show that the proposed method achieves sound performance of cross validation and independent test. In the space of 648,672 EBV-human protein pairs, we obtain 51,485 functional interactions (7.94%), 869 stringent physical PPIs and 46,050 relaxed physical PPIs. Fifty-eight evidences are found from the latest database and recent literature to validate the model. This study reveals that Epstein-Barr virus interferes with normal human cell life, such as cholesterol homeostasis, blood coagulation, EGFR binding, p53 binding, Notch signaling, Hedgehog signaling, etc. The proteome-wide predictions are provided in the supplementary file for further biomedical research.

Factors associated with onset, relapses or progression in multiple sclerosis: A systematic review

Multiple sclerosis (MS) is a chronic disease of the central nervous system with an unidentified etiology. We systematically reviewed the literature on the possible risk factors associated with MS disease onset, relapses and progression from 1960 to 2012 by accessing six databases and including relevant systematic reviews, meta-analyses, case-control or cohort studies. The focus was on identifying modifiable risk factors. Fifteen systematic reviews and 169 original articles were quality assessed and integrated into a descriptive review. Best evidence, which included one or more prospective studies, suggested that lower exposure to sunlight and/or lower serum vitamin D levels were associated with an increased risk of developing MS onset and subsequent relapses, but a similar quality of evidence was lacking for disease progression. Prospective studies indicated that cigarette smoking may increase the risk of MS as well as accelerate disease progression, but whether smoking altered the risk of a relapse was largely unknown. Infections were implicated in both risk of developing MS and relapses, but data for progression were lacking. Specifically, exposure to the Epstein-Barr virus, particularly if this manifested as infectious mononucleosis during adolescence, was associated with increased MS risk. Upper respiratory tract infections were most commonly associated with an increase in relapses. Relapse rates typically dropped during pregnancy, but there was no strong evidence to suggest that pregnancy itself altered the risk of MS or affected long-term progression. Emerging research with the greatest potential to impact public health was the suggestion that obesity during adolescence may increase the risk of MS; if confirmed, this would be of major significance.

EBV and not HPV sensitizes tobacco-associated head and neck cancer cell line FaDu to radiotherapy

Conclusion EBV radiosensitized the p53 mutant tobacco associated head and neck cell line, FaDu. Objectives In the head and neck, HPV is a major risk factor associated with tonsil and base of tongue cancers, while a majority of undifferentiated nasopharyngeal cancers are positive for EBV. Clinically, head and neck tumors positive for HPV or EBV are more radiosensitive than tumors associated with tobacco and alcohol. This study aimed to evaluate whether viral infections can sensitize tobacco-associated head and neck squamous cell carcinoma cell line that harbors multiple mutations, especially TP53, to radiotherapy. Method Four FaDu cell lines (vector control - FaDu-DN; FaDu expressing HPV16 E6/E7 - FaDu-HPV; FaDu infected with EBV - FaDu-EBV; and FaDu-HPV infected with EBV - FaDu-HE) were evaluated for their radiation sensitivity using clonogenic assay. Cell cycle, protein expression, apoptosis, and cellular senescence were analyzed. Results FaDu-EBV and FaDu-HE exhibited significantly increased radiosensitivity in comparison with the control cell line. Radiation-induced cell cycle arrest was altered in all cell lines expressing viral genes. The observed distribution of cells at G1 and S phases was associated with a significant increase in expression of p21 protein along with decreased levels of pAKT/AKT and pERK/ERK ratio (p < 0.05) and increased cellular senescence (p < 0.05).

Gammaherpesvirus Infection of Human Neuronal Cells

Gammaherpesviruses human herpesvirus 4 (HHV4) and HHV8 are two prominent members of the herpesvirus family associated with a number of human cancers. HHV4, also known as Epstein-Barr virus (EBV), a ubiquitous gammaherpesvirus prevalent in 90 to 95% of the human population, is clinically associated with various neurological diseases such as primary central nervous system lymphoma, multiple sclerosis, Alzheimer's disease, cerebellar ataxia, and encephalitis. However, the possibility that EBV and Kaposi's sarcoma-associated herpesvirus (KSHV) can directly infect neurons has been largely overlooked. This study has, for the first time, characterized EBV infection in neural cell backgrounds by using the Sh-Sy5y neuroblastoma cell line, teratocarcinoma Ntera2 neurons, and primary human fetal neurons. Furthermore, we also demonstrated KSHV infection of neural Sh-Sy5y cells. These neuronal cells were infected with green fluorescent protein-expressing recombinant EBV or KSHV. Microscopy, genetic analysis, immunofluorescence, and Western blot analyses for specific viral antigens supported and validated the infection of these cells by EBV and KSHV and showed that the infection was efficient and productive. Progeny virus produced from infected neuronal cells efficiently infected fresh neuronal cells, as well as peripheral blood mononuclear cells. Furthermore, acyclovir was effective at inhibiting the production of virus from neuronal cells similar to lymphoblastoid cell lines; this suggests active lytic replication in infected neurons in vitro. These studies represent a potentially new in vitro model of EBV- and KSHV-associated neuronal disease development and pathogenesis.

IMPORTANCE

To date, no in vitro study has demonstrated gammaherpesvirus infection of neuronal cells. Moreover, worldwide clinical findings have linked EBV to neuronal pathologies, including multiple sclerosis, primary central nervous system lymphoma, and Alzheimer's disease. In this study, for the first time, we have successfully demonstrated the in vitro infection of Sh-Sy5y and Ntera2 cells, as well as human primary neurons. We have also determined that the infection is predominately lytic. Additionally, we also report infection of neuronal cells by KSHV in vitro similar to that by EBV. These findings may open new avenues of consideration related to neuronal pathologies and infection with these viruses. Furthermore, their contribution to chronic infection linked to neuronal disease will provide new clues to potential new therapies.

Epstein-Barr virus BZLF1 protein impairs accumulation of host DNA damage proteins at damage sites in response to DNA damage

Epstein-Barr virus (EBV) infection is closely associated with several human malignancies including nasopharyngeal carcinoma (NPC). The EBV immediate-early protein BZLF1 is the key mediator that switches EBV infection from latent to lytic forms. The lytic form of EBV infection has been implicated in human carcinogenesis but its molecular mechanisms remain unclear. BZLF1 has been shown to be a binding partner of several DNA damage response (DDR) proteins. Its functions in host DDR remain unknown. Thus, we explore the effects of BZLF1 on cellular response to DNA damage in NPC cells. We found that expression of BZLF1 impaired the binding between RNF8 and MDC1 (mediator of DNA damage checkpoint 1), which in turn interfered with the localization of RNF8 and 53BP1 to the DNA damage sites. The RNF8-53BP1 pathway is important for repair of DNA double-strand breaks and DNA damage-induced G2/M checkpoint activation. Our results showed that, by impairing DNA damage repair as well as abrogating G2/M checkpoint, BZLF1 induced genomic instability and rendered cells more sensitive to ionizing radiation. Moreover, the blockage of 53BP1 and RNF8 foci formation was recapitulated in EBV-infected cells. Taken together, our study raises the possibility that, by causing mis-localization of important DDR proteins, BZLF1 may function as a link between lytic EBV infection and impaired DNA damage repair, thus contributing to the carcinogenesis of EBV-associated human epithelial malignancies.

The Putative Role of Viruses, Bacteria, and Chronic Fungal Biotoxin Exposure in the Genesis of Intractable Fatigue Accompanied by Cognitive and Physical Disability

Patients who present with severe intractable apparently idiopathic fatigue accompanied by profound physical and or cognitive disability present a significant therapeutic challenge. The effect of psychological counseling is limited, with significant but very slight improvements in psychometric measures of fatigue and disability but no improvement on scientific measures of physical impairment compared to controls. Similarly, exercise regimes either produce significant, but practically unimportant, benefit or provoke symptom exacerbation. Many such patients are afforded the exclusionary, non-specific diagnosis of chronic fatigue syndrome if rudimentary testing fails to discover the cause of their symptoms. More sophisticated investigations often reveal the presence of a range of pathogens capable of establishing life-long infections with sophisticated immune evasion strategies, including Parvoviruses, HHV6, variants of Epstein-Barr, Cytomegalovirus, Mycoplasma, and Borrelia burgdorferi. Other patients have a history of chronic fungal or other biotoxin exposure. Herein, we explain the epigenetic factors that may render such individuals susceptible to the chronic pathology induced by such agents, how such agents induce pathology, and, indeed, how such pathology can persist and even amplify even when infections have cleared or when biotoxin exposure has ceased. The presence of active, reactivated, or even latent Herpes virus could be a potential source of intractable fatigue accompanied by profound physical and or cognitive disability in some patients, and the same may be true of persistent Parvovirus B12 and mycoplasma infection. A history of chronic mold exposure is a feasible explanation for such symptoms, as is the presence of B. burgdorferi. The complex tropism, life cycles, genetic variability, and low titer of many of these pathogens makes their detection in blood a challenge. Examination of lymphoid tissue or CSF in such circumstances may be warranted.

Epstein Barr virus: a prime candidate of breast cancer aetiology in Sudanese patients

Breast cancer is the commonest cancer in Sudanese women. Reported genetic alterations in the form of mutations in tumor suppressors are low in frequencies and could not explain the peculiarities of the diseases including its focal nature. Potential contributors disease aetiology include oncogenic viruses such as Epstein-Barr virus (EBV), an established culprit of nasopharyngeal carcinoma, one of the most frequent cancers in Sudan.In this study, DNA was extracted from malignant tissue samples and healthy tumour-free tissue from the same breast. Polymerase chain Reaction (PCR) was used to amplify two genes encoding for EBV viral proteins. The presence of Epstein-Barr virus and its cellular localization was confirmed by in situ hybridization (ISH) for Epstein-Barr encoded small RNAs (EBERs). Given the reported low frequency of mutations in BRCA1 and BRCA2 in Sudanese breast cancer patients, the methylation status of six tumor suppressor genes was investigated using methylation specific PCR. EBV genome was detected in 55.5% (n = 90) of breast cancer tissues as compared to 23% in control tissue samples (p = 0.0001). Using ISH, EBV signal was detected in all 18 breast cancer biopsies examined while all five normal breast tissue biopsies tested were negative for EBV. Of six tumour suppressor genes investigated BRCA1, BRCA2, and p14 appeared to be under strong epigenetic silencing.In conclusion, we present evidence of a strong association between EBV and breast carcinoma in Sudanese patients, and considerable epigenetic silencing of tumor suppressors that may likely be an outcome or an association with viral oncogenesis.

Sequence analysis of EBV immediate-early gene BZLF1 and BRLF1 in lymphomas

The immediate-early (IE) genes, BZLF1 and BRLF1, play an important role in switching Epstein-Barr virus from the latent to the lytic state. The functions of the two IE genes and their respective proteins: ZEBRA and Rta have been well studied, but little is known about their DNA coding sequence variations and disease association. In order to investigate the sequence variation patterns and elucidate their association with lymphomas, BZLF1 and BRLF1 were analyzed in 26 and 33 lymphomas using PCR-direct sequencing method respectively. Three sequence variation types of BZLF1 gene were identified. The type BZLF1-A and BZLF1-B was detected in 34.6% (9/26) and 57.7% (15/26) of the tumor specimens, respectively. Among the three functional domains of ZEBRA, the transactivation domain had the most mutations. Three variation types were also identified in BRLF1 gene where type BR1-A and BR1-C were detected in 27.3% (9/33) and 69.7% (23/33) of specimens, respectively. Among the three functional domains of Rta, the dimerization domain was well conserved while multiple mutations were detected in both the DNA binding domain and the transactivation domain. The variation types BZLF1-B and BR1-C were more frequent in the lymphomas, compared with the throat washing samples from the healthy donors. These results suggest that the type BZLF1-B and BR1-C may be associated with the tumorigenesis of lymphoma.

Interplay between DNA tumor viruses and the host DNA damage response

Viruses encounter many challenges within host cells in order to replicate their nucleic acid. In the case of DNA viruses, one challenge that must be overcome is recognition of viral DNA structures by the host DNA damage response (DDR) machinery. This is accomplished in elegant and unique ways by different viruses as each has specific needs and sensitivities dependent on its life cycle. In this review, we focus on three DNA tumor viruses and their interactions with the DDR. The viruses Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpesvirus (KSHV), and human papillomavirus (HPV) account for nearly all of the virus-associated human cancers worldwide. These viruses have also been excellent models for the study of oncogenic virus-mediated cell transformation. In this review, we will discuss how each of these viruses engage and subvert aspects of the host DDR. The first level of DDR engagement is a result of the genetic linkage between the oncogenic potential of these viruses and their ability to replicate. Namely, the promotion of cells from quiescence into the cell cycle to facilitate virus replication can be sensed through aberrant cellular DNA replication structures which activate the DDR and hinder cell transformation. DNA tumor viruses subvert this growth-suppressive DDR through changes in viral oncoprotein expression which ultimately facilitate virus replication. An additional level of DDR engagement is through direct detection of replicating viral DNA. These interactions parallel those observed in other DNA virus systems in that the need to subvert these intrinsic sensors of aberrant DNA structure in order to replicate must be in place. DNA tumor viruses are no exception. This review will cover the molecular features of DNA tumor virus interactions with the host DDR and the consequences for virus replication.

p53 and Sp1 cooperate to regulate the expression of Epstein-Barr viral Zta protein

Epstein-Barr virus (EBV) belongs to the gammaherpesvirus family. To produce infectious progeny, EBV reactivates from latency into the lytic cycle by expressing the determinative lytic transactivator, Zta. In the presence of histone deacetylase inhibitor (HDACi), p53 is a prerequisite for the initiation of the EBV lytic cycle by facilitating the expression of Zta. In this study, a serial mutational analysis of Zta promoter (Zp) indicated an important role for the ZID element in responding to HDACi induction and p53 binds to this ZID element together with Sp1, a universal transcription factor. Abolition of the DNA-binding ability of Sp1 reduces the inducibility of ZID by HDACi and also reduces the amount of p53 binding to ZID. Finally, it was shown that EBV in p53-positive-lymphoblastoid cell lines (LCLs) can enter into the lytic cycle spontaneously; however, knockdown of p53 in LCLs leads to retardation of EBV reactivation.

Viral perturbations of host networks reflect disease etiology

Many human diseases, arising from mutations of disease susceptibility genes (genetic diseases), are also associated with viral infections (virally implicated diseases), either in a directly causal manner or by indirect associations. Here we examine whether viral perturbations of host interactome may underlie such virally implicated disease relationships. Using as models two different human viruses, Epstein-Barr virus (EBV) and human papillomavirus (HPV), we find that host targets of viral proteins reside in network proximity to products of disease susceptibility genes. Expression changes in virally implicated disease tissues and comorbidity patterns cluster significantly in the network vicinity of viral targets. The topological proximity found between cellular targets of viral proteins and disease genes was exploited to uncover a novel pathway linking HPV to Fanconi anemia.

Viral oncoprotein LMP1 disrupts p53-induced cell cycle arrest and apoptosis through modulating K63-linked ubiquitination of p53

Disruption of the gatekeeper p53 tumor suppressor is involved in various virus-associated tumorigeneses, with aberrant ubiquitination as the major cause of p53 abnormalities in virus-associated tumors. Of note, wild-type p53 is accumulated in Epstein-Barr virus (EBV)-associated tumors, especially in nasopharyngeal carcinoma (NPC). We have previously identified that p53 is accumulated and phosphorylated by EBV oncoprotein latent membrane protein 1 (LMP1) in NPC. Here, we further found that LMP1 promoted p53 accumulation via two distinct ubiquitin modifications. LMP1 promoted p53 stability and accumulation by suppressing K48-linked ubiquitination of p53 mediated by E3 ligase MDM2, which is associated with its phosphorylation at Ser20, while increasing the levels of total cellular ubiquitinated p53. LMP1 also induced K63-linked ubiquitination of p53 by interacting with tumor necrosis factor receptor-associated factor 2 (TRAF2), thus contributing to p53 accumulation. Furthermore, LMP1 rescued tumor cell apoptosis and cell cycle arrest mediated by K63-linked ubiquitination of p53. Collectively, these results demonstrate aberrant ubiquitin modifications of p53 and its biological functions by viral protein LMP1, which has broad implications to the pathogenesis of multiple EBV-associated tumors.

An Epstein-Barr Virus (EBV) mutant with enhanced BZLF1 expression causes lymphomas with abortive lytic EBV infection in a humanized mouse model

Immunosuppressed patients are at risk for developing Epstein-Barr Virus (EBV)-positive lymphomas that express the major EBV oncoprotein, LMP1. Although increasing evidence suggests that a small number of lytically infected cells may promote EBV-positive lymphomas, the impact of enhanced lytic gene expression on the ability of EBV to induce lymphomas is unclear. Here we have used immune-deficient mice, engrafted with human fetal hematopoietic stem cells and thymus and liver tissue, to compare lymphoma formation following infection with wild-type (WT) EBV versus infection with a "superlytic" (SL) mutant with enhanced BZLF1 (Z) expression. The same proportions (2/6) of the WT and SL virus-infected animals developed B-cell lymphomas by day 60 postinfection; the remainder of the animals had persistent tumor-free viral latency. In contrast, all WT and SL virus-infected animals treated with the OKT3 anti-CD3 antibody (which inhibits T-cell function) developed lymphomas by day 29. Lymphomas in OKT3-treated animals (in contrast to lymphomas in the untreated animals) contained many LMP1-expressing cells. The SL virus-infected lymphomas in both OKT3-treated and untreated animals contained many more Z-expressing cells (up to 30%) than the WT virus-infected lymphomas, but did not express late viral proteins and thus had an abortive lytic form of EBV infection. LMP1 and BMRF1 (an early lytic viral protein) were never coexpressed in the same cell, suggesting that LMP1 expression is incompatible with lytic viral reactivation. These results show that the SL mutant induces an "abortive" lytic infection in humanized mice that is compatible with continued cell growth and at least partially resistant to T-cell killing.

Activation of lytic cycle of Epstein-Barr virus by suberoylanilide hydroxamic acid leads to apoptosis and tumor growth suppression of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is strongly associated with Epstein-Barr virus (EBV). We reported that suberoylanilide hydroxamic acid (SAHA) induced EBV lytic cycle in EBV-positive gastric carcinoma cells and mediated enhanced cell death. However, expression of EBV lytic proteins was thought to exert antiapoptotic effect in EBV-infected cells. Here, we examined the in vitro and in vivo effects of SAHA on EBV lytic cycle induction in NPC cells and investigated the cellular consequences. Micromolar concentrations of SAHA significantly induced EBV lytic cycle in EBV-positive NPC cells. Increased apoptosis and proteolytic cleavage of poly(ADP-ribose) polymerase and caspase-3, -7 and -9 in EBV-positive versus EBV-negative NPC cells were observed. More than 85% of NPC cells expressing immediate-early (Zta), early (BMRF1) or late (gp350/220) lytic proteins coexpressed cleaved caspase-3. Tracking of expression of EBV lytic proteins and cleaved caspase-3 over time demonstrated that NPC cells proceeded to apoptosis following EBV lytic cycle induction. Inhibition of EBV DNA replication and late lytic protein expression by phosphonoformic acid did not impact on SAHA's induced cell death in NPC, indicating that early rather than late phase of EBV lytic cycle contributed to the apoptotic effect. In vivo effects of SAHA on EBV lytic cycle induction and tumor growth suppression were also observed in NPC xenografts in nude mice. Taken together, our data indicated that activation of lytic cycle from latent cycle of EBV by SAHA leads to apoptosis and tumor growth suppression of NPC thereby providing experimental evidence for virus-targeted therapy against EBV-positive cancer.

The B-cell specific transcription factor, Oct-2, promotes Epstein-Barr virus latency by inhibiting the viral immediate-early protein, BZLF1

The Epstein-Barr virus (EBV) latent-lytic switch is mediated by the BZLF1 immediate-early protein. EBV is normally latent in memory B cells, but cellular factors which promote viral latency specifically in B cells have not been identified. In this report, we demonstrate that the B-cell specific transcription factor, Oct-2, inhibits the function of the viral immediate-early protein, BZLF1, and prevents lytic viral reactivation. Co-transfected Oct-2 reduces the ability of BZLF1 to activate lytic gene expression in two different latently infected nasopharyngeal carcinoma cell lines. Furthermore, Oct-2 inhibits BZLF1 activation of lytic EBV promoters in reporter gene assays, and attenuates BZLF1 binding to lytic viral promoters in vivo. Oct-2 interacts directly with BZLF1, and this interaction requires the DNA-binding/dimerization domain of BZLF1 and the POU domain of Oct-2. An Oct-2 mutant (Δ262–302) deficient for interaction with BZLF1 is unable to inhibit BZLF1-mediated lytic reactivation. However, an Oct-2 mutant defective for DNA-binding (Q221A) retains the ability to inhibit BZLF1 transcriptional effects and DNA-binding. Importantly, shRNA-mediated knockdown of endogenous Oct-2 expression in several EBV-positive Burkitt lymphoma and lymphoblastoid cell lines increases the level of lytic EBV gene expression, while decreasing EBNA1 expression. Moreover, treatments which induce EBV lytic reactivation, such as anti-IgG cross-linking and chemical inducers, also decrease the level of Oct-2 protein expression at the transcriptional level. We conclude that Oct-2 potentiates establishment of EBV latency in B cells.

Epstein-Barr virus (EBV) is a human herpesvirus associated with B-cell malignancies. EBV infection of cells can result in either lytic replication or latency. Memory B cells are the primary site of EBV latency within the human host, while oropharyngeal epithelial cells support the lytic form of infection. However, the cellular mechanism(s) that enable EBV to establish viral latency in a B-cell specific manner are not currently understood. In this report, we show that the B-cell specific cellular transcription factor, Oct-2, promotes viral latency by inhibiting the lytic form of infection. We find that Oct-2 interacts directly with the EBV immediate-early protein, BZLF1, and abrogates its ability to activate lytic viral gene transcription through protein-protein interactions off the DNA. Furthermore, knockdown of endogenous Oct-2 expression in several latently-infected Burkitt lymphoma B-cell lines increases EBV lytic protein expression. In addition, we show that certain stimuli which can prompt lytic EBV reactivation in B cells also decrease expression of endogenous Oct-2. Our results suggest that the cellular transcription factor, Oct-2, promotes EBV latency in a B-cell dependent manner.

Analysis of an ankyrin-like region in Epstein Barr Virus encoded (EBV) BZLF-1 (ZEBRA) protein: implications for interactions with NF-κB and p53

Background

The carboxyl terminal of Epstein-Barr virus (EBV) ZEBRA protein (also termed BZLF-1 encoded replication protein Zta or ZEBRA) binds to both NF-κB and p53. The authors have previously suggested that this interaction results from an ankyrin-like region of the ZEBRA protein since ankyrin proteins such as IκB interact with NF-κB and p53 proteins. These interactions may play a role in immunopathology and viral carcinogenesis in B lymphocytes as well as other cell types transiently infected by EBV such as T lymphocytes, macrophages and epithelial cells.

Methods

Randomization of the ZEBRA terminal amino acid sequence followed by statistical analysis suggest that the ZEBRA carboxyl terminus is most closely related to ankyrins of the invertebrate cactus IκB-like protein. This observation is consistent with an ancient origin of ZEBRA resulting from a recombination event between an ankyrin regulatory protein and a fos/jun DNA binding factor. In silico modeling of the partially solved ZEBRA carboxyl terminus structure using PyMOL software demonstrate that the carboxyl terminus region of ZEBRA can form a polymorphic structure termed ZANK (ZEBRA ANKyrin-like region) similar to two adjacent IκB ankyrin domains.

Conclusions

Viral capture of an ankyrin-like domain provides a mechanism for ZEBRA binding to proteins in the NF-κB and p53 transcription factor families, and also provides support for a process termed "Ping-Pong Evolution" in which DNA viruses such as EBV are formed by exchange of information with the host genome. An amino acid polymorphism in the ZANK region is identified in ZEBRA from tumor cell lines including Akata that could alter binding of Akata ZEBRA to the p53 tumor suppressor and other ankyrin binding protein, and a novel model of antagonistic binding interactions between ZANK and the DNA binding regions of ZEBRA is suggested that may be explored in further biochemical and molecular biological models of viral replication.

At a crossroads: human DNA tumor viruses and the host DNA damage response

Human DNA tumor viruses induce host cell proliferation in order to establish the necessary cellular milieu to replicate viral DNA. The consequence of such viral-programmed induction of proliferation coupled with the introduction of foreign replicating DNA structures makes these viruses particularly sensitive to the host DNA damage response machinery. In fact, sensors of DNA damage are often activated and modulated by DNA tumor viruses in both latent and lytic infection. This article focuses on the role of the DNA damage response during the life cycle of human DNA tumor viruses, with a particular emphasis on recent advances in our understanding of the role of the DNA damage response in EBV, Kaposi's sarcoma-associated herpesvirus and human papillomavirus infection.

Interference with p53 functions in human viral infections, a target for novel antiviral strategies?

Viral infections cause a major stress in host cells. The cellular responses to stress are mediated by p53, which by deregulation of cell cycle and apoptosis, may also be part of the host cell reaction to fight infections. Therefore, during evolutionary viral adaptation to host organisms, viruses have developed strategies to manipulate host cell p53 dependent pathways to facilitate their viral life cycles. Thus, interference with p53 function is an important component in viral pathogenesis. Many viruses have proteins that directly affect p53, whereas others alter the regulation of p53 in an indirect manner, mediated by Hdm2 or Akt, or induction of interferon. Rescue of p53 activity is becoming an area of therapeutic development in oncology. It might be feasible that manipulation of p53 mediated responses can become a therapeutic option to limit viral replication or dissemination. In this report, the mechanisms by which viral proteins manipulate p53 responses are reviewed, and it is proposed that a pharmacological rescue of p53 functions might help to control viral infections.

Cellular transcriptional profiling in human lung epithelial cells infected by different subtypes of influenza A viruses reveals an overall down-regulation of the host p53 pathway

Background

Influenza viruses can modulate and hijack several cellular signalling pathways to efficiently support their replication. We recently investigated and compared the cellular gene expression profiles of human lung A549 cells infected by five different subtypes of human and avian influenza viruses (Josset et al. Plos One 2010). Using these transcriptomic data, we have focused our analysis on the modulation of the p53 pathway in response to influenza infection.

Results

Our results were supported by both RT-qPCR and western blot analyses and reveal multiple alterations of the p53 pathway during infection. A down-regulation of mRNA expression was observed for the main regulators of p53 protein stability during infection by the complete set of viruses tested, and a significant decrease in p53 mRNA expression was also observed in H5N1 infected cells. In addition, several p53 target genes were also down-regulated by these influenza viruses and the expression of their product reduced.

Conclusions

Our data reveal that influenza viruses cause an overall down-regulation of the host p53 pathway and highlight this pathway and p53 protein itself as important viral targets in the altering of apoptotic processes and in cell-cycle regulation.

An ATM/Chk2-mediated DNA damage-responsive signaling pathway suppresses Epstein-Barr virus transformation of primary human B cells

Epstein-Barr virus (EBV), an oncogenic herpesvirus that causes human malignancies, infects and immortalizes primary human B cells in vitro into indefinitely proliferating lymphoblastoid cell lines, which represent a model for EBV-induced tumorigenesis. The immortalization efficiency is very low suggesting that an innate tumor suppressor mechanism is operative. We identify the DNA damage response (DDR) as a major component of the underlying tumor suppressor mechanism. EBV-induced DDR activation was not due to lytic viral replication nor did the DDR marks co-localize with latent episomes. Rather, a transient period of EBV-induced hyper-proliferation correlated with DDR activation. Inhibition of the DDR kinases ATM and Chk2 markedly increased transformation efficiency of primary B cells. Further, the viral latent oncoproteins EBNA3C was required to attenuate the EBV-induced DNA damage response We propose that heightened oncogenic activity in early cell divisions activates a growth-suppressive DDR which is attenuated by viral latency products to induce cell immortalization.

Human papillomavirus detection in moroccan patients with nasopharyngeal carcinoma

BACKGROUND

Nasopharyngeal carcinoma (NPC) is a malignant tumor which arises in surface epithelium of the posterior wall of the nasopharynx. There's is evidence that Epstein Barr virus (EBV) is associated to NPC development. However, many epidemiologic studies point to a connection between viral infections by the human papillomavirus (HPV) and NPC.

METHOD

Seventy Moroccan patients with NPC were screened for EBV and HPV. EBV detection was performed by PCR amplification of BZLF1 gene, encoding the ZEBRA (Z Epstein-Barr Virus Replication Activator) protein, and HPV infection was screened by PCR amplification with subsequent typing by hybridization with specific oligonucleotides for HPV types 16, 18, 31, 33, 35, 45 and 59.

RESULTS

The age distribution of our patients revealed a bimodal pattern. Sixty two cases (88.9%) were classified as type 3 (undifferentiated carcinoma), 6 (8.6%) as type 2 (non keratinizing NPC) and only 2 (2.9%) cases were classified as type 1 (keratinizing NPC). EBV was detected in all NPC tumors, whereas HPV DNA was revealed in 34% of cases (24/70). Molecular analysis showed that 20.8% (5/24) were infected with HPV31, and the remaining were infected with other oncogenic types (i.e., HPV59, 16, 18, 33, 35 and 45). In addition, statistical analysis showed that there's no association between sex or age and HPV infection (P > 0.1).

CONCLUSION

Our data indicated that EBV is commonly associated with NPC in Moroccan patients and show for the first time that NPC tumours from Moroccan patients harbour high risk HPV genotypes.

The Epstein-Barr virus BRRF1 protein, Na, induces lytic infection in a TRAF2- and p53-dependent manner

The Epstein-Barr virus (EBV) BRRF1 lytic gene product (Na) is encoded within the same immediate-early region as the BZLF1 (Z) and BRLF1(R) gene products, but its role during EBV infection has not been well defined. We previously showed that Na cooperates with the R protein to induce lytic gene expression in latently infected EBV-positive 293 cells, and in some EBV-negative cell lines it can activate the Z promoter in reporter gene assays. Here we show that overexpression of Na alone is sufficient to induce lytic gene expression in several different latently infected epithelial cell lines (Hone-Akata, CNE2-Akata, and AGS-Akata), while knockdown of endogenous Na expression reduces lytic gene expression. Consistent with its ability to interact with tumor necrosis factor receptor-associated factor 2 (TRAF2) in a yeast two-hybrid assay, we demonstrate that Na interacts with TRAF2 in cells. Furthermore, we show that TRAF2 is required for Na induction of lytic gene expression, that Na induces Jun N-terminal protein kinase (JNK) activation in a TRAF2-dependent manner, and that a JNK inhibitor abolishes the ability of Na to disrupt viral latency. Additionally, we show that Na and the tumor suppressor protein p53 cooperate to induce lytic gene expression in epithelial cells (including the C666-1 nasopharyngeal carcinoma cell line), although Na does not appear to affect p53 function. Together these data suggest that Na plays an important role in regulating the switch between latent and lytic infection in epithelial cells and that this effect requires both the TRAF2 and p53 cellular proteins.

Getting the message direct manipulation of host mRNA accumulation during gammaherpesvirus lytic infection

The Gammaherpesvirinae subfamily of herpesviruses comprises lymphotropic viruses, including the oncogenic human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus. During lytic infection, gammaherpesviruses manipulate host gene expression to optimize the cellular environment for viral replication and to evade the immune response. Additionally, although a lytically infected cell will itself be killed in the process of viral replication, lytic infection can contribute to pathogenesis by inducing the secretion of paracrine factors with functions in cell survival and proliferation, and angiogenesis. The mechanisms by which these viruses manipulate host gene expression are varied and target the accumulation of cellular mRNAs and their translation, signaling pathways, and protein stability. Here, we discuss how gammaherpesviral proteins directly influence host mRNA biogenesis and stability, either selectively or globally, in order to fine-tune the cellular environment to the advantage of the virus. Appreciation of the mechanisms by which these viruses interface with and adapt normal cellular processes continues to inform our understanding of gammaherpesviral biology and the regulation of mRNA accumulation and turnover in our own cells.

Human genetic variants of homologous recombination repair genes first found to be associated with Epstein-Barr virus antibody titers in healthy Cantonese

Epstein-Barr virus (EBV) infection is a major risk factor for nasopharyngeal carcinoma (NPC). Despite high prevalence of infection among the general population worldwide, only a small proportion of infected individuals presents with seropositivity for EBV-specific IgA antibodies. This seropositive subgroup of EBV carriers has an elevated cumulative risk for NPC during their lifetime. Previous studies reported that the host homologous recombination repair (HRR) system participates in EBV lytic replication, suggesting a potential mechanism to influence EBV reactivation status and thus seropositivity. To investigate whether genetic variants of HRR genes are associated with the serostatus in a healthy population, we investigated the association between seropositivity for anti-VCA-IgA and 156 tagging SNPs in 35 genes connected with HRR in an observational study among 755 healthy Cantonese speakers in southern China. Six variant alleles of MDC1, RAD54L, TP53BP1, RPA1, LIG3 and RFC1 exhibited associations with seropositivity (p(trend) from 0.0085 to 0.00027). Our study provides evidence that genetic variation within the HRR might affect an individual's propensity for EBV seropositive status of anti-VCA IgA antibody.

Noise cancellation: viral fine tuning of the cellular environment for its own genome replication

Productive replication of DNA viruses elicits host cell DNA damage responses, which cause both beneficial and detrimental effects on viral replication. In response to the viral productive replication, host cells attempt to attenuate the S-phase cyclin-dependent kinase (CDK) activities to inhibit viral replication. However, accumulating evidence regarding interactions between viral factors and cellular signaling molecules indicate that viruses utilize them and selectively block the downstream signaling pathways that lead to attenuation of the high S-phase CDK activities required for viral replication. In this review, we describe the sophisticated strategy of Epstein-Barr virus to cancel such “noisy” host defense signals in order to hijack the cellular environment.

Modulation of lung inflammation by the Epstein-Barr virus protein Zta

Several studies have implicated gamma-herpesviruses, particularly Epstein-Barr virus (EBV), in the progression of idiopathic pulmonary fibrosis. The data presented here examine the possible role that EBV plays in the potentiation of this disease by evaluating the pulmonary response to expression of the EBV lytic transactivator protein Zta. Expression of Zta in the lungs of mice via adenovirus-mediated delivery (Adv-Zta) produced profibrogenic inflammation that appeared most pronounced by day 7 postexposure. Relative to mice exposed to control GFP-expressing adenovirus (Adv-GFP), mice exposed to Adv-Zta displayed evidence of lung injury and a large increase in inflammatory cells, predominantly neutrophils, recovered by bronchoalveolar lavage (BAL). Cytokine and mRNA profiling of the BAL fluid and cells recovered from Adv-Zta-treated mice revealed a Th2 and Th17 bias. mRNA profiles from Adv-Zta-infected lung epithelial cells revealed consistent induction of mRNAs encoding Th2 cytokines. Coexpression in transient assays of wild-type Zta, but not a DNA-binding-defective mutant Zta, activated expression of the IL-13 promoter in lung epithelial cells, and detection of IL-13 in Adv-Zta-treated mice correlated with expression of Zta. Induction of Th2 cytokines in Zta-expressing mice corresponded with alternative activation of macrophages. In cell culture and in mice, Zta repressed lung epithelial cell markers. Despite the profibrogenic character at day 7, the inflammation resolves by 28 days postexposure to Adv-Zta without evidence of fibrosis. These observations indicate that the EBV lytic transactivator protein Zta displays activity consistent with a pathogenic role in pulmonary fibrosis associated with herpesvirus infection.

Regulation of p53 tumor suppressor by Helicobacter pylori in gastric epithelial cells

BACKGROUND & AIMS

Infection with the gastric mucosal pathogen Helicobacter pylori is the strongest identified risk factor for distal gastric cancer. These bacteria colonize a significant part of the world's population. We investigated the molecular mechanisms of p53 regulation in H pylori-infected cells.

METHODS

Mongolian gerbils were challenged with H pylori and their gastric tissues were analyzed by immunohistochemistry and immunoblotting with p53 antibodies. Gastric epithelial cells were co-cultured with H pylori and the regulation of p53 was assessed by real-time polymerase chain reaction, immunoblotting, immunofluorescence, and cell survival assays. Short hairpin RNA and dominant-negative mutants were used to inhibit activities of Human Double Minute 2 (HDM2) and AKT1 proteins.

RESULTS

We found that in addition to previously reported up-regulation of p53, H pylori can also negatively regulate p53 by increasing ubiquitination and proteasomal degradation via activation of the serine/threonine kinase AKT1, which phosphorylates and activates the ubiquitin ligase HDM2. These effects were mediated by the bacterial virulence factor CagA; ectopic expression of CagA in gastric epithelial cells increased phosphorylation of HDM2 along with the ubiquitination and proteasomal degradation of p53. The decrease in p53 levels increased survival of gastric epithelial cells that had sustained DNA damage.

CONCLUSIONS

H pylori is able to inhibit the tumor suppressor p53. H pylori activates AKT1, resulting in phosphorylation and activation of HDM2 and subsequent degradation of p53 in gastric epithelial cells. H pylori-induced dysregulation of p53 is a potential mechanism by which the microorganism increases the risk of gastric cancer in infected individuals.

The Epstein-Barr virus BZLF1 protein inhibits tumor necrosis factor receptor 1 expression through effects on cellular C/EBP proteins

The Epstein-Barr virus immediate-early protein, BZLF1 (Z), initiates the switch between latent and lytic infection and plays an essential role in mediating viral replication. Z also inhibits expression of the major receptor for tumor necrosis factor (TNF), TNFR1, thus repressing TNF cytokine signaling, but the mechanism for this effect is unknown. Here, we demonstrate that Z prevents both C/EBPα- and C/EBPβ-mediated activation of the TNFR1 promoter (TNFR1p) by interacting directly with both C/EBP family members. We show that Z interacts directly with C/EBPα and C/EBPβ in vivo and that a Z mutant altered at alanine residue 204 in the bZIP domain is impaired for the ability to interact with both C/EBP proteins. Furthermore, we find that the Z(A204D) mutant is attenuated in the ability to inhibit the TNFR1p but mediates lytic viral reactivation and replication in vitro in 293 cells as well as wild-type Z. Although Z does not bind directly to the TNFR1p in EMSA studies, chromatin immunoprecipitation studies indicate that Z is complexed with this promoter in vivo. The Z(A204D) mutant has reduced interaction with the TNFR1p in vivo but is similar to wild-type Z in its ability to complex with the IL-8 promoter. Finally, we show that the effect of Z on C/EBPα- and C/EBPβ-mediated activation is promoter dependent. These results indicate that Z modulates the effects of C/EBPα and C/EBPβ in a promoter-specific manner and that in some cases (including that of the TNFR1p), Z inhibits C/EBPα- and C/EBPβ-mediated activation.

Hypothesis: could Epstein-Barr virus play a role in the development of gastroschisis?

BACKGROUND

The strong inverse association between maternal age and risk of gastroschisis in offspring has spurred many investigators to hypothesize that behaviors among younger females are the cause. Examples include cigarette smoking, illicit drugs, genitourinary infections, and sexually transmitted diseases, each of which has been reported to be associated with gastroschisis. Although these exposures are more common in young women, recent studies have shown that cigarette smoking, genitourinary infections, and sexually transmitted diseases are most strongly associated with gastroschisis in older women. There is both anecdotal and published evidence showing that gastroschisis sometimes (but not always) occurs in clusters, raising the possibility that an infectious agent might be involved in its pathogenesis.

RESULTS

One such agent whose epidemiologic characteristics parallel those of gastroschisis is Epstein-Barr virus (EBV). Primary EBV infection in early childhood has been decreasing over time, leaving a greater proportion of adolescents at risk, as reflected by increased rates of infectious mononucleosis over time. During the childbearing years, risk of primary EBV infection decreases dramatically, as does risk of gastroschisis. The stronger risks of gastroschisis associated with cigarette smoking, genitourinary infections, and sexually transmitted diseases in older women might be explained by EBV reactivation resulting from multiple challenges to immune response such as pregnancy, age, toxic exposures, and genitourinary and sexually transmitted infections.

CONCLUSION

EBV and other herpes viruses should be added to the research agenda for gastroschisis.

Salmonella typhimurium infection increases p53 acetylation in intestinal epithelial cells

The ability of Salmonella typhimurium to enter intestinal epithelial cells constitutes a crucial step in pathogenesis. Salmonella invasion of the intestinal epithelium requires bacterial type three secretion system. Type three secretion system is a transport device that injects virulence proteins, called effectors, to paralyze or reprogram the eukaryotic cells. Avirulence factor for Salmonella (AvrA) is a Salmonella effector that inhibits the host's inflammatory responses. The mechanism by which AvrA modulates host cell signaling is not entirely clear. p53 is situated at the crossroads of a network of signaling pathways that are essential for genotoxic and nongenotoxic stress responses. We hypothesized that Salmonella infection activates the p53 pathway. We demonstrated that Salmonella infection increased p53 acetylation. Cells infected with AvrA-sufficient Salmonella have increased p53 acetylation, whereas cells infected with AvrA-deficient Salmonella have less p53 acetylation. In a cell-free system, AvrA possessed acetyltransferase activity and used p53 as a substrate. AvrA expression increased p53 transcriptional activity and induced cell cycle arrest. HCT116 p53-/- cells had less inflammatory responses. In a mouse model of Salmonella infection, intestinal epithelial p53 acetylation was increased by AvrA expression. Our studies provide novel mechanistic evidence that Salmonella modulates the p53 pathway during intestinal inflammation and infection.

Transactivators Zta and Rta of Epstein-Barr virus promote G0/G1 to S transition in Raji cells: a novel relationship between lytic virus and cell cycle

In the present study, we show that the treatment of Epstein-Barr virus (EBV) latently infected Raji cells with TPA/SB caused the cell growth arrest. The Zta-positive cells were predominantly enriched in G0/G1 phase of cell cycle. When Zta expression reached a maximal level, a fraction of Zta expressing cell population reentered S phase. Analysis of the expression pattern of a key set of cell cycle regulators revealed that the expression of Zta and Rta substantially interfered with the cell cycle regulatory machinery in Raji cells, strongly inhibiting the expression of Rb and p53 and inducing the expression of E2F1. Down-regulation of Rb was further demonstrated to be mediated by proteasomal degradation, and p53 and p21 affected at transcription level. The data indicate that both Zta and Rta promote entry into S phase of Raji cells. The important roles of Zta and Rta in EBV lytic reactivation were also demonstrated. Our finding suggests that these two transcriptional activators may act synergistically to govern the expression of downstream early and late genes as well as cellular genes and initiation of lytic cycle and manipulation of cell cycle regulatory mechanisms require the joint and interactive contributions of Rta and Zta.

Human cytomegalovirus IE1-72 protein interacts with p53 and inhibits p53-dependent transactivation by a mechanism different from that of IE2-86 protein

Infection of host cells with human cytomegalovirus (HCMV) induces cell cycle dysregulation. Two HCMV immediate-early (IE) proteins, IE1-72 and IE2-86, are promiscuous transactivators that have been implicated in the dysregulatory events. Cellular p53 protein is accumulated to high levels in HCMV-infected cells, but the indicative marker of p53 transcriptional activity, p21, is markedly decreased. Both IE1-72 and IE2-86 were able to transactivate the p53 promoter and interact with p53 protein in DNA-transfected or HCMV-infected cells. HCMV UL84, a multiregulatory protein expressed in early periods of HCMV infection, also interacted with p53. HCMV IE1-72 prevented or disrupted p53 binding to p53-specific DNA sequences, while IE2-86 and/or UL84 enhanced p53 binding and induced supershift of this DNA-protein complex. Both HCMV IE1-72 and IE2-86 were able to inhibit p53-dependent transcriptional activation in plasmid-transfected cells. IE1-72, rather than IE2-86, was found to be responsible for p21 downregulation in HCMV-infected HEL cells. DNA transfection analysis using IE1-72 mutants revealed that exon 2/3 and the zinc finger region of IE1-72 are essential for IE1-72's effect on the repression of p53-dependent transcriptional activation. These data suggest that HCMV IE1-72 and/or IE2-86 transactivates the p53 promoter and induces p53 accumulation, but HCMV IE1-72 represses the p53 transactivation activity by a unique binding hindrance mechanism different from that of IE2-86. Thus, various modes of viral IE proteins and p53 interactions might result in multiple outcomes, such as stimulation of cellular DNA synthesis, cell cycle progression and cell cycle arrest, and prevention of program cell death.

Functional interaction between Epstein-Barr virus replication protein Zta and host DNA damage response protein 53BP1

Epstein-Barr virus (EBV; human herpesvirus 4) poses major clinical problems worldwide. Following primary infection, EBV enters a form of long-lived latency in B lymphocytes, expressing few viral genes, and it persists for the lifetime of the host with sporadic bursts of viral replication. The switch between latency and replication is governed by the action of a multifunctional viral protein Zta (also called BZLF1, ZEBRA, and Z). Using a global proteomic approach, we identified a host DNA damage repair protein that specifically interacts with Zta: 53BP1. 53BP1 is intimately connected with the ATM signal transduction pathway, which is activated during EBV replication. The interaction of 53BP1 with Zta requires the C-terminal ends of both proteins. A series of Zta mutants that show a wild-type ability to perform basic functions of Zta, such as dimer formation, interaction with DNA, and the transactivation of viral genes, were shown to have lost the ability to induce the viral lytic cycle. Each of these mutants also is compromised in the C-terminal region for interaction with 53BP1. In addition, the knockdown of 53BP1 expression reduced viral replication, suggesting that the association between Zta and 53BP1 is involved in the viral replication cycle.

Gene expression profiling by microarray analysis reveals an important role for caspase-1 in dengue virus-induced p53-mediated apoptosis

Recently, a dengue virus-induced apoptosis p53- and mitochondria-mediated were reported in human and animal cells. To understand further the underlying mechanisms, a p53-deficient cell line, H1299, and a p53-knockin cell line, H273, were infected with dengue type 1 virus and the cellular gene expression profiles at the mRNA level were analyzed by affymetrix array analysis. The results showed 183 genes with at least twofold increase at mRNA expression level in dengue virus-infected cells. Among the 183 genes, 68 genes were up-regulated in both H1299 and H273 cells and 78 genes were found to be up-regulated in only H273 cells. Eleven selected genes, mainly involved in IFN-pathway, cell cycle, signal transduction, and ubiquitin-proteasome pathways were confirmed using qualitative and quantitative PCR. Interestingly, an approximately 32-fold increase in caspase-1 expression was observed in the p53-knockin cell line, H273. Gene silencing of caspase-1 or inhibition of caspase-1 activity led to reduction in dengue virus-induced apoptosis with minimal effect on virus replication.

EBV Zta protein induces the expression of interleukin-13, promoting the proliferation of EBV-infected B cells and lymphoblastoid cell lines

Epstein-Barr virus (EBV) infection can modify the cytokine expression profiles of host cells and determine the fate of those cells. Of note, expression of interleukin-13 (IL-13) may be detected in EBV-associated Hodgkin lymphoma and the natural killer (NK) cells of chronic active EBV-infected patients, but its biologic role and regulatory mechanisms are not understood. Using cytokine antibody arrays, we found that IL-13 production is induced in B cells early during EBV infection. Furthermore, the EBV lytic protein, Zta (also known as the BZLF-1 product), which is a transcriptional activator, was found to induce IL-13 expression following transfection. Mechanistically, induction of IL-13 expression by Zta is mediated directly through its binding to the IL-13 promoter, via a consensus AP-1 binding site. Blockade of IL-13 by antibody neutralization showed that IL-13 is required at an early stage of EBV-induced proliferation and for long-term maintenance of the growth of EBV immortalized lymphoblastoid cell lines (LCLs). Thus, Zta-induced IL-13 production facilitates B-cell proliferation and may contribute to the pathogenesis of EBV-associated lymphoproliferative disorders, such as posttransplantation lymphoproliferative disease (PTLD) and Hodgkin lymphoma.

Epstein-Barr virus nuclear antigen 3C targets p53 and modulates its transcriptional and apoptotic activities

The p53 tumor suppressor gene is one of the most commonly mutated genes in human cancers and the corresponding encoded protein induces apoptosis or cell-cycle arrest at the G1/S checkpoint in response to DNA damage. To date, previous studies have shown that antigens encoded by human tumor viruses such as SV40 large T antigen, adenovirus E1A and HPV E6 interact with p53 and disrupt its functional activity. In a similar fashion, we now show that EBNA3C, one of the EBV latent antigens essential for the B-cell immortalization in vitro, interacts directly with p53. Additionally, we mapped the interaction of EBNA3C with p53 to the C-terminal DNA-binding and the tetramerization domain of p53, and the region of EBNA3C responsible for binding to p53 was mapped to the N-terminal domain of EBNA3C (residues 130-190), previously shown to interact with a number of important cell-cycle components, specifically SCF(Skp2), cyclin A, and cMyc. Furthermore, we demonstrate that EBNA3C substantially represses the transcriptional activity of p53 in luciferase based reporter assays, and rescues apoptosis induced by ectopic p53 expression in SAOS-2 (p53(-/-)) cells. Interestingly, we also show that the DNA-binding ability of p53 is diminished in the presence of EBNA3C. Thus, the interaction between the p53 and EBNA3C provides new insights into the mechanism(s) by which the EBNA3C oncoprotein can alter cellular gene expression in EBV associated human cancers.

Critical role of p53 in histone deacetylase inhibitor-induced Epstein-Barr virus Zta expression

The tumor suppressor gene p53 plays a central role in the maintenance of normal cell growth and genetic integrity, while its impact on the Epstein-Barr virus (EBV) life cycle remains elusive. We found that p53 is important for histone deacetylase inhibitor-induced EBV lytic gene expression in nasopharyngeal carcinoma cells. Restoration of p53 in p53-null, EBV-infected H1299 cells augments the potential for viral lytic cycle initiation. Evidence from reporter assays demonstrated that p53 contributes to the expression of the immediate-early viral Zta gene. Further analysis indicated that the DNA-binding ability of p53 and phosphorylation of Ser392 may be critical. This study provides the first evidence that p53 is involved in the regulation of EBV lytic cycle initiation.