Latent membrane protein 1 regulates STAT1 through NF-kappaB-dependent interferon secretion in Epstein-Barr virus-immortalized B cells

Induction of the antiviral factors APOBEC3A and RSAD2 upon CCL2 neutralization in primary human macrophages involves NF-κB, JAK/STAT, and gp130 signaling

The CCL2/CC chemokine receptor 2 axis plays key roles in the pathogenesis of HIV-1 infection. We previously reported that exposure of monocyte-derived macrophages to CCL2 neutralizing antibody (αCCL2 Ab) restricted HIV-1 replication at postentry steps of the viral life cycle. This effect was associated with induction of transcripts coding for innate antiviral proteins, including APOBEC3A and RSAD2. This study aimed at identifying the signaling pathways involved in induction of these factors by CCL2 blocking in monocyte-derived macrophages. Through a combination of pharmacologic inhibition, quantitative reverse transcription polymerase chain reaction, Western blotting, and confocal laser-scanning microscopy, we demonstrated that CCL2 neutralization activates the canonical NF-κB and JAK/STAT pathways, as assessed by time-dependent phosphorylation of IκB, STAT1, and STAT3 and p65 nuclear translocation. Furthermore, pharmacologic inhibition of IκB kinase and JAKs strongly reduced APOBEC3A and RSAD2 transcript accumulation elicited by αCCL2 Ab treatment. Interestingly, exposure of monocyte-derived macrophages to αCCL2 Ab resulted in induction of IL-6 family cytokines, and interference with glycoprotein 130, the common signal-transducing receptor subunit shared by these cytokines, inhibited APOBEC3A and RSAD2 upregulation triggered by CCL2 neutralization. These results provide novel insights into the signal transduction pathways underlying the activation of innate responses triggered by CCL2 neutralization in macrophages. Since this response was found to be associated with protective antiviral effects, the new findings may help design innovative therapeutic approaches targeting CCL2 to strengthen host innate immunity.

Global transcriptomic network analysis of the crosstalk between microbiota and cancer-related cells in the oral-gut-lung axis

Background

The diagnosis and treatment of lung, colon, and gastric cancer through the histologic characteristics and genomic biomarkers have not had a strong impact on the mortality rates of the top three global causes of death by cancer.

Methods

Twenty-five transcriptomic analyses (10 lung cancer, 10 gastric cancer, and 5 colon cancer datasets) followed our own bioinformatic pipeline based on the utilization of specialized libraries from the R language and DAVID´s gene enrichment analyses to identify a regulatory metafirm network of transcription factors and target genes common in every type of cancer, with experimental evidence that supports its relationship with the unlocking of cell phenotypic plasticity for the acquisition of the hallmarks of cancer during the tumoral process. The network's regulatory functional and signaling pathways might depend on the constant crosstalk with the microbiome network established in the oral-gut-lung axis.

Results

The global transcriptomic network analysis highlighted the impact of transcription factors (SOX4, TCF3, TEAD4, ETV4, and FOXM1) that might be related to stem cell programming and cancer progression through the regulation of the expression of genes, such as cancer-cell membrane receptors, that interact with several microorganisms, including human T-cell leukemia virus 1 (HTLV-1), the human papilloma virus (HPV), the Epstein-Barr virus (EBV), and SARS-CoV-2. These interactions can trigger the MAPK, non-canonical WNT, and IFN signaling pathways, which regulate key transcription factor overexpression during the establishment and progression of lung, colon, and gastric cancer, respectively, along with the formation of the microbiome network.

Conclusion

The global transcriptomic network analysis highlights the important interaction between key transcription factors in lung, colon, and gastric cancer, which regulates the expression of cancer-cell membrane receptors for the interaction with the microbiome network during the tumorigenic process.

Epstein-Barr virus lytic gene BNRF1 promotes B-cell lymphomagenesis via IFI27 upregulation

Epstein-Barr virus (EBV) is a ubiquitous human lymphotropic herpesvirus that is causally associated with several malignancies. In addition to latent factors, lytic replication contributes to cancer development. In this study, we examined whether the lytic gene BNRF1, which is conserved among gamma-herpesviruses, has an important role in lymphomagenesis. We found that lymphoblastoid cell lines (LCLs) established by BNRF1-knockout EBV exhibited remarkably lower pathogenicity in a mice xenograft model than LCLs produced by wild-type EBV (LCLs-WT). RNA-seq analyses revealed that BNRF1 elicited the expression of interferon-inducible protein 27 (IFI27), which promotes cell proliferation. IFI27 knockdown in LCLs-WT resulted in excessive production of reactive oxygen species, leading to cell death and significantly decreased their pathogenicity in vivo. We also confirmed that IFI27 was upregulated during primary infection in B-cells. Our findings revealed that BNRF1 promoted robust proliferation of the B-cells that were transformed by EBV latent infection via IFI27 upregulation both in vitro and in vivo.

Therapeutic strategy for oncovirus-mediated oral cancer: A comprehensive review

Oral cancer is a neoplastic disorder of the oral cavities, including the lips, tongue, buccal mucosa, and lower and upper gums. Oral cancer assessment entails a multistep process that requires deep knowledge of the molecular networks involved in its progression and development. Preventive measures including public awareness of risk factors and improving public behaviors are necessary, and screening techniques should be encouraged to enable early detection of malignant lesions. Herpes simplex virus (HSV), human papillomavirus (HPV), Epstein-Barr virus (EBV), and Kaposi sarcoma-associated herpesvirus (KSHV) are associated with other premalignant and carcinogenic conditions leading to oral cancer. Oncogenic viruses induce chromosomal rearrangements; activate signal transduction pathways via growth factor receptors, cytoplasmic protein kinases, and DNA binding transcription factors; modulate cell cycle proteins, and inhibit apoptotic pathways. In this review, we present an up-to-date overview on the use of nanomaterials for regulating viral proteins and oral cancer as well as the role of phytocompounds on oral cancer. The targets linking oncoviral proteins and oral carcinogenesis were also discussed.

Comprehensive insight into altered host cell-signaling cascades upon Helicobacter pylori and Epstein-Barr virus infections in cancer

Cancer is characterized by mutagenic events that lead to disrupted cell signaling and cellular functions. It is one of the leading causes of death worldwide. Literature suggests that pathogens, mainly Helicobacter pylori and Epstein-Barr virus (EBV), have been associated with the etiology of human cancer. Notably, their co-infection may lead to gastric cancer. Pathogen-mediated DNA damage could be the first and crucial step in the carcinogenesis process that modulates numerous cellular signaling pathways. Altogether, it dysregulates the metabolic pathways linked with cell growth, apoptosis, and DNA repair. Modulation in these pathways leads to abnormal growth and proliferation. Several signaling pathways such RTK, RAS/MAPK, PI3K/Akt, NFκB, JAK/STAT, HIF1α, and Wnt/β-catenin are known to be altered in cancer. Therefore, this review focuses on the oncogenic roles of H. pylori, EBV, and its associated signaling cascades in various cancers. Scrutinizing these signaling pathways is crucial and may provide new insights and targets for preventing and treating H. pylori and EBV-associated cancers.

NF-kappa-B essential modulator (NEMO) gene polymorphism in an adult woman with systemic lupus erythematosus and recurrent non-tuberculous mycobacterial disseminated infections

Infections are among the most serious complications in patients with systemic lupus erythematosus (SLE), with bacterial and viral infections being the most common. Non-tuberculous mycobacterial (NTM) infections are quite rare and are typically seen in older patients with SLE with longstanding disease duration treated with corticosteroids. Here, we describe a 39-year-old woman with SLE and an unusual pattern of recurrent NTM disseminated infections. After excluding the presence of autoantibodies against interferon-γ, whole exome sequencing revealed a homozygous polymorphism in the NF-kappa-B essential modulator (NEMO) gene. Primary immunodeficiencies should be included in the differential diagnosis of patients with recurrent opportunistic infections, even in those with iatrogenic immunosuppression.

When AHR signaling pathways meet viral infections

Aryl hydrocarbon receptor (AHR) is a ligand-dependent transcriptional factor widely expressed among immune, epithelial, endothelial and stromal cells in barrier tissues. It can be activated by small molecules provided by pollutants, microorganisms, food, and metabolism. It has been demonstrated that AHR plays an important role in modulating the response to many microbial pathogens, and the abnormal expression of AHR signaling pathways may disrupt endocrine, cause immunotoxicity, and even lead to the occurrence of cancer. Most humans are infected with at least one known human cancer virus. While the initial infection with these viruses does not cause major disease, the metabolic activity of infected cells changes, thus affecting the activation of oncogenic signaling pathways. In the past few years, lots of studies have shown that viral infections can affect disease progression by regulating the transmission of multiple signaling pathways. This review aims to discuss the potential effects of virus infections on AHR signaling pathways so that we may find a new strategy to minimize the adverse effects of the AHR pathway on diseases. Video Abstract.

Strategies of Epstein-Barr virus to evade innate antiviral immunity of its human host

Epstein-Barr virus (EBV) is a double-stranded DNA virus of the Herpesviridae family. This virus preferentially infects human primary B cells and persists in the human B cell compartment for a lifetime. Latent EBV infection can lead to the development of different types of lymphomas as well as carcinomas such as nasopharyngeal and gastric carcinoma in immunocompetent and immunocompromised patients. The early phase of viral infection is crucial for EBV to establish latency, but different viral components are sensed by cellular sensors called pattern recognition receptors (PRRs) as the first line of host defense. The efficacy of innate immunity, in particular the interferon-mediated response, is critical to control viral infection initially and to trigger a broad spectrum of specific adaptive immune responses against EBV later. Despite these restrictions, the virus has developed various strategies to evade the immune reaction of its host and to establish its lifelong latency. In its different phases of infection, EBV expresses up to 44 different viral miRNAs. Some act as viral immunoevasins because they have been shown to counteract innate as well as adaptive immune responses. Similarly, certain virally encoded proteins also control antiviral immunity. In this review, we discuss how the virus governs innate immune responses of its host and exploits them to its advantage.

Extranodal NK/T-Cell Lymphoma, Nasal Type: Genetic, Biologic, and Clinical Aspects with a Central Focus on Epstein-Barr Virus Relation

Extranodal NK/T-Cell Lymphoma, nasal type (ENKTL-NT) has some salient aspects. The lymphoma is commonly seen in Eastern Asia, has progressive necrotic lesions in the nasal cavity, makes midfacial destructive lesions, and shows poor prognosis. The lymphoma cell is originated from either NK- or γδ T-cells, which express CD56. Since the authors first demonstrated the existence of Epstein–Barr virus (EBV) DNA and EBV oncogenic proteins in lymphoma cells, ENKTL-NT has been recognized as an EBV-associated malignancy. Because the angiocentric and polymorphous lymphoma cells are mixed with inflammatory cells on a necrotic background, the diagnosis of ENKTL-NT requires CD56 immunostaining and EBER in situ hybridization. In addition, serum the EBV DNA level is useful for the diagnosis and monitoring of ENKTL-NT. Although ENKTL-NT is refractory lymphoma, the prognosis is improved by the development of therapies such as concomitant chemoradiotherapy. The basic research reveals that a wide variety of intracellular/cell surface molecules, cytokines, chemokines, and micro RNAs are involved in lymphomagenesis, and some of them are related to EBV. Understanding lymphoma behavior introduces new therapeutic strategies, such as the usage of immune checkpoint inhibitors, peptide vaccines, and molecular targeting therapy. This review addresses recent advances in basic and clinical aspects of ENKTL-NT, especially its relation to EBV features.

Patients With Natural Killer (NK) Cell Chronic Active Epstein-Barr Virus Have Immature NK Cells and Hyperactivation of PI3K/Akt/mTOR and STAT1 Pathways

BACKGROUND

Chronic active Epstein-Barr virus (CAEBV) presents with high levels of viral genomes in blood and tissue infiltration with Epstein-Barr virus (EBV)-positive lymphocytes. The pathogenesis of CAEBV is poorly understood.

METHODS

We evaluated 2 patients with natural killer (NK) cell CAEBV and studied their NK cell phenotype and signaling pathways in cells.

RESULTS

Both patients had increased numbers of NK cells, EBV predominantly in NK cells, and immature NK cells in the blood. Both patients had increased phosphorylation of Akt, S6, and STAT1 in NK cells, and increased total STAT1. Treatment of 1 patient with sirolimus reduced phosphorylation of S6 in T and B cells, but not in NK cells and did not reduce levels of NK cells or EBV DNA in the blood. Treatment of both patients' cells with JAK inhibitors in vitro reduced phosphorylated STAT1 to normal. Patients with T- or B-cell CAEBV had increased phosphorylation of Akt and S6 in NK cells, but no increase in total STAT1.

CONCLUSIONS

The increase in phosphorylated Akt, S6, and STAT1, as well as immature NK cells describe a new phenotype for NK cell CAEBV. The reduction of STAT1 phosphorylation in their NK cells with JAK inhibitors suggests a novel approach to therapy.

Inhibitory effects of cynaropicrin and related sesquiterpene lactones from leaves of artichoke (Cynara scolymus L.) on induction of iNOS in RAW264.7 cells and its high-affinity proteins

The methanolic extract of the leaves of artichoke (Cynara scolymus L.) was found to inhibit nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Among the constituents of the extract, six sesquiterpene lactones (cynaropicrin, grosheimin, 11β,13-dihydrocynaropicrin, 3β-hydroxy-8α-[(S)-3-hydroxy-2-methylpropionyloxy]guaia-4(15),10(14),11(13)-trien-1α,5α,6βH-12,6-olide, 3β-hydroxy-8α-[2-methoxymethyl-2-propenoyloxy]guaia-4(15),10(14),11(13)-trien-1α,5α,6βH-12,6-olide, and deacylcynaropicrin) inhibited NO production and/or inducible nitric oxide synthase (iNOS) induction. The acyl group having an α,β-unsaturated carbonyl group at the 8-position and the α-methylene-γ-butyrolactone moiety were important for the strong inhibitory activity. Our results suggested that these sesquiterpene lactones inhibited the LPS-induced iNOS expression via the suppression of the JAK-STAT signaling pathway in addition to the κNF-κB signaling pathway. With regard to the target molecules of the sesquiterpene lactones, high-affinity proteins of cynaropicrin were purified from the cell extract. ATP/ADP translocase 2 and tubulin were identified and suggested to be involved in the cytotoxic effects of cynaropicrin, although the target molecules for the inhibition of iNOS expression were not clarified.

Epstein-Barr Virus (EBV) Tegument Protein BGLF2 Suppresses Type I Interferon Signaling To Promote EBV Reactivation

Interferon alpha (IFN-α) and IFN-β are type I IFNs that are induced by virus infection and are important in the host's innate antiviral response. EBV infection activates multiple cell signaling pathways, resulting in the production of type I IFN which inhibits EBV infection and virus-induced B-cell transformation. We reported previously that EBV tegument protein BGLF2 activates p38 and enhances EBV reactivation. To further understand the role of BGLF2 in EBV infection, we used mass spectrometry to identify cellular proteins that interact with BGLF2. We found that BGLF2 binds to Tyk2 and confirmed this interaction by coimmunoprecipitation. BGLF2 blocked type I IFN-induced Tyk2, STAT1, and STAT3 phosphorylation and the expression of IFN-stimulated genes (ISGs) IRF1, IRF7, and MxA. In contrast, BGLF2 did not inhibit STAT1 phosphorylation induced by IFN-γ. Deletion of the carboxyl-terminal 66 amino acids of BGLF2 reduced the ability of the protein to repress type I IFN signaling. Treatment of gastric carcinoma and Raji cells with IFN-α blocked BZLF1 expression and EBV reactivation; however, expression of BGLF2 reduced the ability of IFN-α to inhibit BZLF1 expression and enhanced EBV reactivation. In summary, EBV BGLF2 interacts with Tyk2, inhibiting Tyk2, STAT1, and STAT3 phosphorylation and impairs type I IFN signaling; BGLF2 also counteracts the ability of IFN-α to suppress EBV reactivation.IMPORTANCE Type I interferons are important for controlling virus infection. We have found that the Epstein-Barr virus (EBV) BGLF2 tegument protein binds to a protein in the type I interferon signaling pathway Tyk2 and inhibits the expression of genes induced by type I interferons. Treatment of EBV-infected cells with type I interferon inhibits reactivation of the virus, while expression of EBV BGLF2 reduces the ability of type I interferon to inhibit virus reactivation. Thus, a tegument protein delivered to cells during virus infection inhibits the host's antiviral response and promotes virus reactivation of latently infected cells. Therefore, EBV BGLF2 might protect virus-infected cells from the type I interferon response in cells undergoing lytic virus replication.

Regulation of cGAS-Mediated Immune Responses and Immunotherapy

Early detection of infectious nucleic acids released from invading pathogens by the innate immune system is critical for immune defense. Detection of these nucleic acids by host immune sensors and regulation of DNA sensing pathways have been significant interests in the past years. Here, current understandings of evolutionarily conserved DNA sensing cyclic GMP-AMP (cGAMP) synthase (cGAS) are highlighted. Precise activation and tight regulation of cGAS are vital in appropriate innate immune responses, senescence, tumorigenesis and immunotherapy, and autoimmunity. Hence, substantial insights into cytosolic DNA sensing and immunotherapy of indispensable cytosolic sensors have been detailed to extend limited knowledge available thus far. This Review offers a critical, in-depth understanding of cGAS regulation, cytosolic DNA sensing, and currently established therapeutic approaches of essential cytosolic immune agents for improved human health.

PD-1 immunobiology in systemic lupus erythematosus

Programmed death (PD)-1 receptors and their ligands have been identified in the pathogenesis and development of systemic lupus erythematosus (SLE). Two key pathways, toll-like receptor and type I interferon, are significant to SLE pathogenesis and modulate the expression of PD-1 and the ligands (PD-L1, PD-L2) through activation of NF-κB and/or STAT1. These cell signals are regulated by tyrosine kinase (Tyro, Axl, Mer) receptors (TAMs) that are aberrantly activated in SLE. STAT1 and NF-κB also exhibit crosstalk with the aryl hydrocarbon receptor (AHR). Ligands to AHR are identified in SLE etiology and pathogenesis. These ligands also regulate the activity of the Epstein-Barr virus (EBV), which is an identified factor in SLE and PD-1 immunobiology. AHR is important in the maintenance of immune tolerance and the development of distinct immune subsets, highlighting a potential role of AHR in PD-1 immunobiology. Understanding the functions of AHR ligands as well as AHR crosstalk with STAT1, NF-κB, and EBV may provide insight into disease development, the PD-1 axis and immunotherapies that target PD-1 and its ligand, PD-L1.

The regulatory role of protein phosphorylation in human gammaherpesvirus associated cancers

Activation of specific sets of protein kinases by intracellular signal molecules has become more and more apparent in the past decade. Phosphorylation, one of key posttranslational modification events, is activated by kinase or regulatory protein and is vital for controlling many physiological functions of eukaryotic cells such as cell proliferation, differentiation, malignant transformation, and signal transduction mediated by external stimuli. Moreovers, the reversible modification of phosphorylation and dephosphorylation can result in different features of the target substrate molecules including DNA binding, protein-protein interaction, subcellular location and enzymatic activity, and is often hijacked by viral infection. Epstein-Barr virus (EBV) and Kaposi’s sarcomaassociated herpesvirus (KSHV), two human oncogenic gamma-herpesviruses, are shown to tightly associate with many malignancies. In this review, we summarize the recent progresses on understanding of molecular properties and regulatory modes of cellular and viral proteins phosphorylation influenced by these two tumor viruses, and highlight the potential therapeutic targets and strategies against their related cancers.

Epstein-Barr virus latent membrane protein-1 up-regulates cytokines and correlates with older age and poorer prognosis in Hodgkin lymphoma

AIMS

Previously, we reported an association between Epstein-Barr virus (EBV)-positive Hodgkin lymphoma (HL), older age, and poorer prognosis. The aim of this study was to investigate the mechanisms underlying this association.

METHODS AND RESULTS

Transfection of HL cell lines with EBV latent membrane protein-1 (LMP1) resulted in up-regulation of many cytokine genes as assessed by the use of oligonucleotide microarrays. The up-regulation of cytokines was validated by using an inflammatory cytokine protein array: macrophage inflammatory protein (MIP)-1α, MIP-1β, and interleukin (IL)-13. Immunostaining of HL samples (n = 104) showed that expression of MIP-1α, MIP-1β and IL-13 correlated with EBV infection and LMP1 expression. Combined expression of these cytokines was more common in patients aged >60 years (P < 0.001), and was associated with a poorer prognosis (P = 0.042). In another cohort, serum levels of MIP-1α, MIP-1β and IL-13 were increased in HL patients (n = 53) and highest in EBV-positive HL patients as compared with healthy controls (n = 40). Xenograft mice injected with EBV-positive HL cells had higher serum levels of MIP-1α, MIP-1β and IL-13 than mice injected with EBV-negative HL cells, although there was no difference in growth.

CONCLUSIONS

EBV infection appears to promote the release of cytokines in HL patients, and negatively impacts on patient survival. Physiological immunosenescence probably explains the association between EBV infection and older age. Cytokine modulation is a potential therapeutic target for EBV-positive HL patients.

The translation inhibitor silvestrol exhibits direct anti-tumor activity while preserving innate and adaptive immunity against EBV-driven lymphoproliferative disease

Treatment options for patients with Epstein-Barr Virus-driven lymphoproliferative diseases (EBV-LPD) are limited. Chemo-immunotherapeutic approaches often lead to immune suppression, risk of lethal infection and EBV reactivation, thus it is essential to identify agents that can deliver direct anti-tumor activity while preserving innate and adaptive host immune surveillance. Silvestrol possesses direct anti-tumor activity in multiple hematologic malignancies while causing minimal toxicity to normal mononuclear cells. However, the effects of silvestrol on immune function have not been described. We utilized in vitro and in vivo models of EBV-LPD to simultaneously examine the impact of silvestrol on both tumor and normal immune function. We show that silvestrol induces direct anti-tumor activity against EBV-transformed lymphoblastoid cell lines (LCL), with growth inhibition, decreased expression of the EBV oncogene latent membrane protein-1, and inhibition of the downstream AKT, STAT1 and STAT3 signaling pathways. Silvestrol promoted potent indirect anti-tumor effects by preserving expansion of innate and EBV antigen-specific adaptive immune effector subsets capable of effective clearance of LCL tumor targets in autologous co-cultures. In an animal model of spontaneous EBV-LPD, silvestrol demonstrated significant therapeutic activity dependent on the presence of CD8-positive T-cells. These findings establish a novel immune-sparing activity of silvestrol, justifying further exploration in patients with EBV-positive malignancies.

Immune Evasion by Epstein-Barr Virus

Epstein-Bar virus (EBV) is widespread within the human population with over 90% of adults being infected. In response to primary EBV infection, the host mounts an antiviral immune response comprising both innate and adaptive effector functions. Although the immune system can control EBV infection to a large extent, the virus is not cleared. Instead, EBV establishes a latent infection in B lymphocytes characterized by limited viral gene expression. For the production of new viral progeny, EBV reactivates from these latently infected cells. During the productive phase of infection, a repertoire of over 80 EBV gene products is expressed, presenting a vast number of viral antigens to the primed immune system. In particular the EBV-specific CD4+ and CD8+ memory T lymphocytes can respond within hours, potentially destroying the virus-producing cells before viral replication is completed and viral particles have been released. Preceding the adaptive immune response, potent innate immune mechanisms provide a first line of defense during primary and recurrent infections. In spite of this broad range of antiviral immune effector mechanisms, EBV persists for life and continues to replicate. Studies performed over the past decades have revealed a wide array of viral gene products interfering with both innate and adaptive immunity. These include EBV-encoded proteins as well as small noncoding RNAs with immune-evasive properties. The current review presents an overview of the evasion strategies that are employed by EBV to facilitate immune escape during latency and productive infection. These evasion mechanisms may also compromise the elimination of EBV-transformed cells, and thus contribute to malignancies associated with EBV infection.

Difference in cytokine production and cell cycle progression induced by Epstein-Barr virus Lmp1 deletion variants in Kmh2, a Hodgkin lymphoma cell line

Background

Epstein-Barr virus (EBV) is associated with 20-40% of Hodgkin’s Lymphoma (HL) cases. EBV-encoded latent membrane protein 1 (LMP1) is a well-known oncogenic protein and two C-terminal deletion variants, del30-LMP1 and del69-LMP1, have been described in animal models to be more tumorigenic than the wild-type form. This work aims to detail the implication of LMP1 in the development of HL and to characterize the particular effects of these variants.

Methods

We established HL-derived cell lines stably transfected with the pRT-LMP1 vector coding for the EBNA1 gene and allowing expression of the different LMP1 variants under the control of a doxycyclin-inducible promoter. Communication between cells was assessed by measuring the expression of various pro-inflammatory cytokines by flow cytometry after intracellular LMP1 and cytokine double staining. Proliferative properties of LMP1 variants were also compared by studying the repartition of cells in the different phases of the cell cycle after EdU incorporation combined to LMP1 and DAPI staining.

Results

All LMP1 proteins induced the expression of several pro-inflammatory cytokines such as TNF-α, TNF-β, IL-6, RANTES/CCL5 and IFN-γ. However, the del30-LMP1 variant induced cytokine expression at a lower level than the other variants, especially IFN-γ, while the del69-LMP1 variant stimulated greater cytokine expression. In addition, we measured that all LMP1 proteins greatly impacted the cell cycle progression, triggering a reduction in the number of cells in S-phase and an accumulation of cells in the G2/M phase compared to the HL-non induced cells. Interestingly, the del30-LMP1 variant reduced the number of cells in S-phase in a significantly greater manner and also increased the number of cells in the G0/G1 phase of the cell cycle.

Conclusion

Weak IFN-γ expression and specific alteration of the cell cycle might be a way for del30-LMP1 infected cells to escape the immune anti-viral response and to promote the development of cancer. The differences observed between the LMP1 variants reflect their own oncogenic properties and eventually impact the development of HL.

TLR3-triggered reactive oxygen species contribute to inflammatory responses by activating signal transducer and activator of transcription-1

Intracellular reactive oxygen species (ROS) are essential secondary messengers in many signaling cascades governing innate immunity and cellular functions. TLR3 signaling is crucially involved in antiviral innate and inflammatory responses; however, the roles of ROS in TLR3 signaling remain largely unknown. In this study, we show that TLR3-induced ROS generation is required for the activation of NF-κB, IFN-regulatory factor 3, and STAT1-mediated innate immune responses in macrophages. TLR3 induction led to a rapid increase in ROS generation and a physical association between components of the NADPH oxidase (NOX) enzyme complex (NOX2 and p47(phox)) and TLR3 via a Ca(2+)-c-Src tyrosine kinase-dependent pathway. TLR3-induced ROS generation, NOX2, and p47(phox) were required for the phosphorylation and nuclear translocation of STAT1 and STAT2. TLR3-induced activation of STAT1 contributed to the generation of inflammatory mediators, which was significantly attenuated in NOX2- and p47(phox)-deficient macrophages, suggesting a role for ROS-STAT1 in TLR3-mediated innate immune responses. Collectively, these results provide a novel insight into the crucial role that TLR3-ROS signaling plays in innate immune responses by activating STAT1.

Soluble ICAM-1 secretion and its functional role as an autocrine growth factor in nasal NK/T cell lymphoma cells

Nasal natural killer-T cell lymphoma (NNKTL) is associated with the Epstein-Barr virus and has distinct histologic features, such as angiocentric and polymorphous lymphoreticular infiltrates that contain too many cell types, including tumor and inflammatory cells. We have shown previously that intercellular adhesion molecule (ICAM)-1 is expressed in NNKTL cells, and that soluble ICAM-1 (sICAM-1) is significantly increased in patients' sera. However, the functional role of sICAM-1 remains unknown. In this study, we found that Epstein-Barr virus-positive NNKTL cell line SNK6 secreted sICAM-1 in a time-dependent manner. Moreover, exogenous sICAM-1 enhanced the growth of SNK6 cells in a dose-dependent manner. In comparison, neutralizing ICAM-1 and LFA-1 antibodies, as well as the LFA-1 blocker simvastatin, caused a dose-dependent reduction in the number of viable SNK6 cells. Double immunohistologic staining of NNKTL tissues confirmed that CD56 positive lymphoma cells coexpressed LFA-1. Moreover, serum sICAM-1 levels in NNKTL patients decreased after treatment, suggesting that the levels reflected disease progression. We conclude that NNKTL cells secrete sICAM-1 that acts as an autocrine factor for lymphoma progression, and suggest that simvastatin could be a potential candidate to treat NNKTL.

In vitro studies on the influence of dexamethasone and meloxicam on bovine WC1+ γδ T cells

In view of the lack of data on the effect of meloxicam (non-steroidal anti-inflammatory drug) on bovine γδ T cells (WC1(+) cells) and very poorly recognized effects of dexamethasone (steroidal anti-inflammatory drug) on these cells, the purpose of the present study has been to determine the in vitro influence of these drugs on CD25(high)WC1(+), CD25(low)WC1(+) and CD25(-)WC1(+) lymphocytes of the peripheral blood of cattle. Peripheral blood mononuclear cells were treated with the drugs in concentrations reflecting their plasma levels achieved in vivo at therapeutic doses (dexamethasone 10(-7)M; meloxicam 5×10(-6)M) and at ten-fold lower concentrations. It was found out that percentages and absolute counts of CD25(high)WC1(+) and CD25(low)WC1(+) cells increased in the presence of dexamethasone, and this effect was at least partly attributable to lower mortality of these cells, whose apoptosis was depressed by exposure to dexamethasone. It seems certain that this effect was not a result of increased multiplication of CD25(high)WC1(+) and CD25(low)WC1(+) cells because their proliferation was reduced in the presence of dexamethasone. Exposure to this drug caused a rapidly occurring and lasting depletion of CD25(-)WC1(+), which was at least partly due to their higher apoptosis. The results seem to suggest that impaired proliferation of these cells was responsible for a more profound expression of this disorder. Paradoxically, the percentage of cells producing IFN-γ, a proinflammatory cytokine, increased in the presence of dexamethasone, whereas the count of cells secreting the key anti-inflammatory and immunosuppressive cytokine, i.e. IL-10, declined. This effect was observed in all analyzed subpopulations of cells. Meloxicam did not interfere so drastically as dexamethasone with the functioning of WC1(+) lymphocytes because it did not affect their apoptosis, proliferation, percentage or absolute count. With respect to the effect of meloxicam on counts of particular WC1(+) lymphocyte subpopulations, it was only demonstrated that exposure to the drug was correlated with a transient and very weakly expressed decrease in the relative and absolute counts of CD25(high)WC1(+) and CD25(low)WC1(+) cells, which was most probably a result of a temporary down-regulation of the expression of the CD25 molecule. In the presence of meloxicam, percentages of IFN-γ(+)CD25(-)WC1(+) cells as well as cells producing IL-10 declined, an effect observed in all analyzed cell populations. These results suggest that care should be taken when administering this medication to animals with bacterial or viral infections, and we should avoid giving it to patients suffering from allergic or autoimmune disorders.

B7-H1, which represses EBV-immortalized B cell killing by autologous T and NK cells, is oppositely regulated by c-Myc and EBV latency III program at both mRNA and secretory lysosome levels

EBV-immortalized B cells induce a complex immune response such that the virus persists as a clinically silent infection for the lifetime of the infected host. B7-H1, also called PD-L1, is a cosignaling molecule of the B7 family that can inhibit activated T cell effectors by interaction with its receptor PD-1. In this work, we have studied the dependence of B7-H1 on NF-κB and c-Myc, the two main transcription factors in EBV latency III proliferating B cells, on various lymphoblastoid and Burkitt lymphoma cell lines, some of them being inducible or not for the EBV latency III program and/or for c-Myc. We found that B7-H1 repressed killing of EBV-immortalized B cells by their autologous T and NK cells. At the mRNA level, NF-κB was a weak inducer whereas c-Myc was a strong repressor of B7-H1 expression, an effect mediated by STAT1 inhibition. At the protein level, B7-H1 molecules were stored in both degradative and unconventional secretory lysosomes. Surface membrane B7-H1 molecules were constitutively internalized and proteolyzed in lysosomes. The EBV latency III program increased the amounts of B7-H1-containing secretory lysosomes and their export to the surface membrane. By repressing actin polymerization, c-Myc blocked secretory lysosome migration and B7-H1 surface membrane export. In addition to B7-H1, various immunoregulatory molecules participating in the immunological synapse are stored in secretory lysosomes. By playing on actin polymerization, c-Myc could thus globally regulate the immunogenicity of transformed B cells, acting on export of secretory lysosomes to plasma membrane.

rhPLD2 suppresses chronic inflammation reactions in a guinea pig asthma model

BACKGROUND

Asthma is a complex inflammatory disorder of the airways, and research on alternative therapeutic strategies has attracted attention. This study aimed at hypersusceptibility and toxicity of recombinant human phospholipase D2 (rhPLD2) in guinea pigs. We determined the behavioral responses in the model of immediate hypersensitivity animals and changes of eosinophil levels following use of the drugs. Special attention was given to the effects of rhPLD2 in vivo on the guinea pig with chronic persistent asthma and the mechanism involved.

METHODS

To investigate the effect of rhPLD2 on the expression of protein kinase C (PKC), and to examine the activity of signal transducer and activator of transcription 1 and 5a in the lung of the guinea pig with chronic asthma. Guinea pigs with chronic asthma were divided into five groups: a saline group, a dexamethasone 5.0 mg group, and rhPLD2 (1.5, 2, or 3 mg) groups. Non-sensitized animals were as normal control group. PKC expression was measured by immunohistochemistry, alterations of STAT1 and STAT5a were detected by TransAM transcription factor assay kits.

RESULTS

rhPLD2 (3.0 mg) decreased PKC expression to baseline and inhibited STAT1 activity compared with that of the saline group (p < 0.01).

CONCLUSION

The rhPLD2 may suppress the chronic inflammatory reaction through down-regulating PKC expression and STAT1/STAT5a activity in the lung. The rhPLD2 may be a suitable therapeutic target for asthma.

9p21 DNA variants associated with coronary artery disease impair interferon-γ signalling response

Genome wide association studies (GWAS) have identified SNPs in the 9p21 gene desert associated with coronary artery disease (CAD)1–4 and Type 2 diabetes (T2D)5–7. Despite evidence for a role of the associated interval in neighboring gene regulation8–10, the biological underpinnings of these genetic associations to CAD or T2D have not yet been explained. Here we identify 33 enhancers in 9p21; the interval is the second densest gene-desert for predicted enhancers and 6 times denser than the whole genome (p<6.55 10⁻³³). The CAD risk alleles of SNPs rs10811656/rs10757278 are located in one of these enhancers and disrupt a binding site for STAT1. Lymphoblastoid cell lines (LCL) homozygous for the CAD risk haplotype exhibit no binding of STAT1, and in LCL homozygous for the CAD non-risk haplotype binding of STAT1 inhibits CDKN2BAS expression, which is reversed by siRNA knock-down of STAT1. Using a new, open-ended approach to detect long-distance interactions (3D-DSL), we find that in human vascular endothelium cells (HUVEC) the enhancer interval containing the CAD locus physically interacts with the CDKN2A/B locus, the MTAP gene and an interval downstream of INFA21. In HUVEC, IFNγ activation strongly affects the structure of the chromatin and the transcriptional regulation in the 9p21 locus, including STAT1 binding, long-range enhancer interactions and altered expression of neighboring genes. Our findings establish a link between CAD genetic susceptibility and the response to inflammatory signaling in a vascular cell type and thus demonstrate the utility of GWAS findings to direct studies to novel genomic loci and biological processes important for disease etiology.

Innate immune modulation in EBV infection

Epstein-Barr Virus (EBV) belongs to the gammaherpesvirus family, members of which are oncogenic. Compared with other closely related herpesviruses, EBV has developed much more elaborate and sophisticated strategies for subverting host immune system, which may account for its high prevalence in immune competent hosts. Thus, study of EBV-specific immune dysregulation is important for understanding EBV latency and oncogenesis, and will identify potential molecular targets for immunotherapeutic interventions. Here I summarize the recent findings of individual EBV products in regulating host immune responses, with emphasis on the innate immune modulation.

Epstein-Barr virus latent membrane protein 1 increases chemo-resistance of cancer cells via cytoplasmic sequestration of Pim-1

Improved treatment of EBV positive lymphoma depends on the identification of molecular mechanism underlying chemo-resistance. LMP1 is an essential transmembrane protein for EBV-induced immortalization of hematopoietic cells. Herein, we show that an oncogenic Pim-1 is translocated to the cytoplasm by LMP1. Three lines of evidence indicate that cytoplasmic sequestration of Pim-1 may be required for LMP1-induced cancer cell survival. First, Pim-1 enhanced the survival of LMP1-overexpressing cells treated with doxorubicin. Second, nuclear export of Pim-1 was sufficient to increase the survival. Third, knockdown of Pim-1 effectively suppressed LMP-1-induced survival of cancer cells. Collectively, these data suggest that Pim-1 is a downstream target of LMP1, and that it contributes to the chemo-resistance of cancer cells.

Epstein-Barr virus interferes with the amplification of IFNalpha secretion by activating suppressor of cytokine signaling 3 in primary human monocytes

Background

Epstein-Barr virus is recognized to cause lymphoproliferative disorders and is also associated with cancer. Evidence suggests that monocytes are likely to be involved in EBV pathogenesis, especially due to a number of cellular functions altered in EBV-infected monocytes, a process that may affect efficient host defense. Because type I interferons (IFNs) are crucial mediators of host defense against viruses, we investigated the effect of EBV infection on the IFNα pathway in primary human monocytes.

Methodology/Principal Findings

Infection of monocytes with EBV induced IFNα secretion but inhibited the positive feedback loop for the amplification of IFNα. We showed that EBV infection induced the expression of suppressor of cytokine signaling 3 (SOCS3) and, to a lesser extent, SOCS1, two proteins known to interfere with the amplification of IFNα secretion mediated by the JAK/STAT signal transduction pathway. EBV infection correlated with a blockage in the activation of JAK/STAT pathway members and affected the level of phosphorylated IFN regulatory factor 7 (IRF7). Depletion of SOCS3, but not SOCS1, by small interfering RNA (siRNA) abrogated the inhibitory effect of EBV on JAK/STAT pathway activation and significantly restored IFNα secretion. Finally, transfection of monocytes with the viral protein Zta caused the upregulation of SOCS3, an event that could not be recapitulated with mutated Zta.

Conclusions/Significance

We propose that EBV protein Zta activates SOCS3 protein as an immune escape mechanism that both suppresses optimal IFNα secretion by human monocytes and favors a state of type I IFN irresponsiveness in these cells. This immunomodulatory effect is important to better understand the aspects of the immune response to EBV.

Interleukin-2 induces NF-kappaB activation through BCL10 and affects its subcellular localization in natural killer lymphoma cells

Deregulation of nuclear factor (NF)-kappaB signalling is common in cancers and is essential for tumourigenesis. Constitutive NF-kappaB activation in extranodal natural killer (NK)-cell lymphoma, nasal type (ENKL) is known to be associated with aberrant nuclear translocation of BCL10. Here we investigated the mechanisms leading to NF-kappaB activation and BCL10 nuclear localization in ENKLs. Given that ENKLs are dependent on T-cell-derived interleukin-2 (IL2) for cytotoxicity and proliferation, we investigated whether IL2 modulates NF-kappaB activation and BCL10 subcellular localization in ENKLs. In the present study, IL2-activated NK lymphoma cells were found to induce NF-kappaB activation via the PI3K/Akt pathway, leading to an increase in the entry of G(2)/M phase and concomitant transcription of NF-kappaB-responsive genes. We also found that BCL10, a key mediator of NF-kappaB signalling, participates in the cytokine receptor-induced activation of NF-kappaB. Knockdown of BCL10 expression resulted in deficient NF-kappaB signalling, whereas Akt activation was unaffected. Our results suggest that BCL10 plays a role downstream of Akt in the IL2-triggered NF-kappaB signalling pathway. Moreover, the addition of IL2 to NK cells led to aberrant nuclear translocation of BCL10, which is a pathological feature of ENKLs. We further show that BCL10 can bind to BCL3, a transcriptional co-activator and nuclear protein. Up-regulation of BCL3 expression was observed in response to IL2. Similar to BCL10, the expression and nuclear translocation of BCL3 were induced by IL2 in an Akt-dependent manner. The nuclear translocation of BCL10 was also dependent on BCL3 because silencing BCL3 by RNA interference abrogated this translocation. We identified a critical role for BCL10 in the cytokine receptor-induced NF-kappaB signalling pathway, which is essential for NK cell activation. We also revealed the underlying mechanism that controls BCL10 nuclear translocation in NK cells. Our findings provide insight into a molecular network within the NF-kappaB signalling pathway that promotes the pathogenesis of NK cell lymphomas.

STAT1-dependent IgG cell-surface expression in a human B cell line derived from a STAT1-deficient patient

STAT1 is a key effector of cytokines involved in the resistance to pathogens; its identified transcriptional targets mediate the innate immune response involved in the defense against viruses and bacteria. Little is known about the role of STAT1 in adaptive immunity, including its impact on BCR or surface Ig expression. Analysis of this point is difficult in humans, as STAT1 deficiency is extremely rare. SD patients die early in childhood from a severe immunodeficiency. Herein, a SD B cell line obtained from a SD patient was compared with a B cell line from a STAT1-proficient subject in search of differences in surface Ig expression. In this SD B cell line, a complete absence of surface IgG was noted. The mRNA encoding the surface form of IgG was detected only in STAT1-proficient B cells; the mRNAs encoding the secreted and the surface forms were detected in SD and STAT1-proficient B cells. Re-expression of STAT1 in SD B cells restored surface IgG expression and a functional BCR. Conversely, shRNA silencing of STAT1 in B cells reduced considerably the expression of the surface IgG. Although limited to one B cell line, these results suggest that STAT1 may play an essential role in surface IgG expression in human B cells. Possible mechanisms involve regulation of mRNA splicing, transcription, or both. These observations extend the role of STAT1 further in adaptive immunity, including the regulation of BCR expression.

STAT1 and pathogens, not a friendly relationship

STAT1 belongs to the STAT family of transcription factors, which comprises seven factors: STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B and STAT6. STAT1 is a 91 kDa protein originally identified as the mediator of the cellular response to interferon (IFN) α, and thereafter found to be a major component of the cellular response to IFNγ. STAT1 is, in fact, involved in the response to several cytokines and to growth factors. It is activated by cytokine receptors via kinases of the JAK family. STAT1 becomes phosphorylated and forms a dimer which enters the nucleus and triggers the transcription of its targets. Although not lethal at birth, selective gene deletion of STAT1 in mice leads to rapid death from severe infections, demonstrating its major role in the response to pathogens. Similarly, in humans who do not express STAT1, there is a lack of resistance to pathogens leading to premature death. This indicates a key, non-redundant function of STAT1 in the defence against pathogens. Thus, to successfully infect organisms, bacterial, viral or parasitic pathogens must overcome the activity of STAT1, and almost all the steps of this pathway can be blocked or inhibited by proteins produced in infected cells. Interestingly, some pathogens, like the oncogenic Epstein–Barr virus, have evolved a strategy which uses STAT1 activation.

Protein kinase C zeta mediates cigarette smoke/aldehyde- and lipopolysaccharide-induced lung inflammation and histone modifications

Atypical protein kinase C (PKC) zeta is an important regulator of inflammation through activation of the nuclear factor-kappaB (NF-kappaB) pathway. Chromatin remodeling on pro-inflammatory genes plays a pivotal role in cigarette smoke (CS)- and lipopolysaccharide (LPS)-induced abnormal lung inflammation. However, the signaling mechanism whereby chromatin remodeling occurs in CS- and LPS-induced lung inflammation is not known. We hypothesized that PKCzeta is an important regulator of chromatin remodeling, and down-regulation of PKCzeta ameliorates lung inflammation by CS and LPS exposures. We determined the role and molecular mechanism of PKCzeta in abnormal lung inflammatory response to CS and LPS exposures in PKCzeta-deficient (PKCzeta(-/-)) and wild-type mice. Lung inflammatory response was decreased in PKCzeta(-/-) mice compared with WT mice exposed to CS and LPS. Moreover, inhibition of PKCzeta by a specific pharmacological PKCzeta inhibitor attenuated CS extract-, reactive aldehydes (present in CS)-, and LPS-mediated pro-inflammatory mediator release from macrophages. The mechanism underlying these findings is associated with decreased RelA/p65 phosphorylation (Ser(311)) and translocation of the RelA/p65 subunit of NF-kappaB into the nucleus. Furthermore, CS/reactive aldehydes and LPS exposures led to activation and translocation of PKCzeta into the nucleus where it forms a complex with CREB-binding protein (CBP) and acetylated RelA/p65 causing histone phosphorylation and acetylation on promoters of pro-inflammatory genes. Taken together, these data suggest that PKCzeta plays an important role in CS/aldehyde- and LPS-induced lung inflammation through acetylation of RelA/p65 and histone modifications via CBP. These data provide new insights into the molecular mechanisms underlying the pathogenesis of chronic inflammatory lung diseases.

Activation of the JAK/STAT pathway in Epstein Barr virus+-associated posttransplant lymphoproliferative disease: role of interferon-gamma

Epstein Barr virus (EBV) is associated with B-cell lymphomas in posttransplant lymphoproliferative disease (PTLD). Latent membrane protein 1 (LMP1), the major oncogenic protein of EBV, promotes tumorigenesis through activation of NF-kappaB, Erk, p38, JNK and Akt. The Jak/STAT signal transduction pathway is also constitutively active in PTLD-associated EBV(+) B-cell lymphomas. Here we determine the mechanism of Jak/STAT activation in EBV(+) B-cell lymphomas and the role of LMP1 in this process. Immunoprecipitation studies revealed no direct interaction of LMP1 and JAK3, but known associations between JAK3 and common gamma chain, and between LMP1 and TRAF3, were readily detected in EBV(+) B cell lines from patients with PTLD. An inducible LMP1 molecule expressed in EBV(-) BL41 Burkitt's cells demonstrated STAT activation only after prolonged LMP1 signaling. While LMP1 induced IFN-gamma production in BL41 cells, IFN-gamma receptor blockade and IFN-gamma neutralization prior to LMP1 activation markedly decreased STAT1 activation and expression of LMP1-driven IFN-gamma inducible genes. Understanding the mechanisms by which EBV induces cellular signal transduction pathways may facilitate development of new treatments for PTLD.

Activation of the JAK/STAT pathway in Epstein Barr virus+-associated posttransplant lymphoproliferative disease: role of interferon-gamma

Epstein Barr virus (EBV) is associated with B-cell lymphomas in posttransplant lymphoproliferative disease (PTLD). Latent membrane protein 1 (LMP1), the major oncogenic protein of EBV, promotes tumorigenesis through activation of NF-kappaB, Erk, p38, JNK and Akt. The Jak/STAT signal transduction pathway is also constitutively active in PTLD-associated EBV(+) B-cell lymphomas. Here we determine the mechanism of Jak/STAT activation in EBV(+) B-cell lymphomas and the role of LMP1 in this process. Immunoprecipitation studies revealed no direct interaction of LMP1 and JAK3, but known associations between JAK3 and common gamma chain, and between LMP1 and TRAF3, were readily detected in EBV(+) B cell lines from patients with PTLD. An inducible LMP1 molecule expressed in EBV(-) BL41 Burkitt's cells demonstrated STAT activation only after prolonged LMP1 signaling. While LMP1 induced IFN-gamma production in BL41 cells, IFN-gamma receptor blockade and IFN-gamma neutralization prior to LMP1 activation markedly decreased STAT1 activation and expression of LMP1-driven IFN-gamma inducible genes. Understanding the mechanisms by which EBV induces cellular signal transduction pathways may facilitate development of new treatments for PTLD.

c-Myc and Rel/NF-kappaB are the two master transcriptional systems activated in the latency III program of Epstein-Barr virus-immortalized B cells

The Epstein-Barr virus (EBV) latency III program imposed by EBNA2 and LMP1 is directly responsible for immortalization of B cells in vitro and is thought to mediate most immunodeficiency-related posttransplant lymphoproliferative diseases in vivo. To answer the question whether and how this proliferation program is related to c-Myc, we have established the transcriptome of both c-Myc and EBV latency III proliferation programs using a Lymphochip specialized microarray. In addition to EBV-positive latency I Burkitt lymphoma lines and lymphoblastoid cell lines (LCLs), we used an LCL expressing an estrogen-regulatable EBNA2 fusion protein (EREB2-5) and derivative B-cell lines expressing a constitutively active or tetracycline-regulatable c-myc gene. A total of 897 genes were found to be fourfold or more up- or downregulated in either one or both proliferation programs compared to the expression profile of resting EREB2-5 cells. A total of 661 (74%) of these were regulated similarly in both programs. Numerous repressed genes were known targets of STAT1, and most induced genes were known to be upregulated by c-Myc and to be involved in cell proliferation. In keeping with the gene expression patterns, inactivation of c-Myc by a chemical inhibitor or by conditional expression of dominant-negative c-Myc and Max mutants led to proliferation arrest of LCLs. Most genes differently regulated in both proliferation programs corresponded to genes induced by NF-kappaB in LCLs, and many of them coded for immunoregulatory and/or antiapoptotic molecules. Thus, c-Myc and NF-kappaB are the two main transcription factors responsible for the phenotype, growth pattern, and biological properties of cells driven into proliferation by EBV.

Epstein-Barr virus induces a distinct form of DNA-bound STAT1 compared with that found in interferon-stimulated B lymphocytes

Since 'constitutive activation' of STAT1 was first described in Epstein-Barr virus (EBV)-immortalized lymphoblastoid cell lines (LCLs), there has been controversy regarding the molecular identity of the STAT1 DNA-binding complex found in these cells. The post-translational modifications of STAT1 in LCLs have been analysed and an LMP1-induced STAT1 DNA-binding complex, different from that generated by alpha interferon (IFN) stimulation and not involving tyrosine phosphorylation, is demonstrated. STAT1 is serine-phosphorylated downstream of PI3K and MEK in LCLs and this modification restricts IFN-stimulated STAT1-DNA binding. These data suggest that EBV induces a distinct form of DNA-bound STAT1 in virus-infected cells.

C-myc activation impairs the NF-kappaB and the interferon response: implications for the pathogenesis of Burkitt's lymphoma

Deregulation of the proto-oncogene c-myc is a key event in the pathogenesis of many tumors. A paradigm is the activation of the c-myc gene by chromosomal translocations in Burkitt lymphoma (BL). Despite expression of a restricted set of Epstein-Barr viral (EBV) antigens, BL cells are not recognized by antigen-specific cytotoxic T cells (CTLs) because of their inability to process and present HLA class I-restricted antigens. In contrast, cells of EBV-driven posttransplant lymphoproliferative disease (PTLD) are recognized and rejected by EBV-specific CTLs. It is not known whether the poor immunogenicity of BL cells is due to nonexpression of viral antigens, overexpression of c-myc, or both. To understand the basis for immune recognition and escape, we have compared the mRNA expression profiles of BL and EBV-immortalized cells (as PTLD model). Among the genes expressed at low level in BL cells, we have identified many genes involved in the NF-kappaB and interferon response that play a pivotal role in antigen presentation and immune recognition. Using a cell line in which EBNA2 and c-myc can be regulated at will, we show that c-MYC negatively regulates STAT1, the central player linking the Type-I and Type-II interferon response. Switching off c-myc expression leads to STAT1 induction through a direct and indirect mechanism involving induction of Type-I interferons. c-MYC thus masks an interferon-inducing activity in these cells. Our findings imply that immune escape of tumor cells is not only a matter of in vivo selection but may be additionally promoted by activation of a cellular oncogene.

Egr-1, a new downstream molecule of Epstein-Barr virus latent membrane protein 1

To investigate the effect of Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) on human cancer cells, we sought to identify and analyze potential target genes that were differentially expressed in the presence and absence of LMP1. Our cDNA microarray analysis revealed that expression of early growth response gene-1 (Egr-1) was increased by LMP1 expression in MCF7 and Jurkat cells. An NFkappaB inhibitor (SN50) antagonized LMP1-induced enhancement of Egr-1 expression, indicating that LMP1 induced Egr-1 via NFkappaB. Furthermore, three lines of evidence indicated that Egr-1 was required for LMP1-induced cancer cell survival. First, Egr-1 expression enhanced the survival of doxorubicin-treated MCF7 cells. Second, inhibition of Egr-1 expression by siRNA (siEgr-1) effectively suppressed LMP-1-induced survival of MCF7 cells. Third, Egr-1 knockdown decreased LMP1-induced expression of Bfl-1. Similar relationships among EBV infection, Egr-1 and drug resistance were also observed in tissues of peripheral T-cell lymphoma-unspecified (PTCL-u) patients.

Bmi-1 is induced by the Epstein-Barr virus oncogene LMP1 and regulates the expression of viral target genes in Hodgkin lymphoma cells

Polycomb group (PcG) proteins are chromatin modifiers that are necessary for the maintenance and renewal of embryonic and adult stem cells. However, overexpression of the PcG protein, Bmi-1, causes lymphoma in transgenic mice. We show that Bmi-1 is up-regulated in Hodgkin lymphoma (HL) cells by the Epstein-Barr virus (EBV) oncogene latent membrane protein-1 (LMP1) and that this up-regulation is mediated by NF-κB signaling. We also show that Bmi-1 is up-regulated by NF-κB in EBV-negative HL cells. Down-regulation of LMP1 and Bmi-1 decreased the survival of HL cells, suggesting that Bmi-1 may mediate the prosurvival effects of LMP1-induced NF-κB signaling in HL cells. Transcriptional targets of Bmi-1 were identified after its knockdown in an HL cell line. We show here that Bmi-1 and LMP1 down-regulate the ataxia telangiectasia–mutated (ATM) tumor suppressor and conclude that Bmi-1 contributes to LMP1-induced oncogenesis in HL.

The Epstein-Barr virus-encoded LMP-1 oncoprotein negatively affects Tyk2 phosphorylation and interferon signaling in human B cells

Epstein-Barr virus (EBV) establishes a persistent infection in the human host and is associated with a variety of human cancers. Persistent infection results from a balance between the host immune response and viral immune evasion mechanisms. EBV infection is controlled initially by the innate immune response and later by T-cell-mediated adaptive immunity. EBV has evolved mechanisms to evade the host immune response so that it can persist for the lifetime of the host. Latent membrane protein 1 (LMP-1) is the EBV oncoprotein essential for B-cell immortalization by EBV. We show here that LMP-1 interacts with Tyk2, a signaling intermediate in the alpha interferon (IFN-alpha) signaling pathway, via a previously uncharacterized LMP-1 signaling domain. LMP-1 prevents Tyk2 phosphorylation and inhibits IFN-alpha-stimulated STAT2 nuclear translocation and interferon-stimulated response element transcriptional activity. Long-term culture of EBV+ lymphoblastoid cells in IFN-alpha is associated with outgrowth of a population expressing elevated LMP-1 protein levels, suggesting that cells expressing higher levels of LMP-1 survive the antiproliferative selective pressure imposed by IFN-alpha. These results show that LMP-1 can protect EBV+ cells from the IFN-alpha-stimulated antiviral/antiproliferative response and suggest that chronic IFN-alpha treatment may encourage the outgrowth of cells expressing elevated, and therefore potentially oncogenic, LMP-1 levels in EBV+ individuals.

Autoactivation of the Epstein-Barr virus oncogenic protein LMP1 during type II latency through opposite roles of the NF-kappaB and JNK signaling pathways

Epstein-Barr virus (EBV) is associated with several human malignancies where it expresses limited subsets of latent proteins. Of the latent proteins, latent membrane protein 1 (LMP1) is a potent transforming protein that constitutively induces multiple cell signaling pathways and contributes to EBV-associated oncogenesis. Regulation of LMP1 expression has been extensively described during the type III latency of EBV. Nevertheless, in the majority of EBV-associated tumors, the virus is commonly found to display a type II latency program in which it is still unknown which viral or cellular protein is really involved in maintaining LMP1 expression. Here, we demonstrate that LMP1 activates its own promoter pLMP1 through the JNK signaling pathway emerging from the TES2 domain. Our results also reveal that this activation is tightly controlled by LMP1, since pLMP1 is inhibited by LMP1-activated NF-kappaB signaling pathway. By using our physiological models of EBV-infected cells displaying type II latency as well as lymphoblastoid cell lines expressing a type III latency, we also demonstrate that this balanced autoregulation of LMP1 is shared by both latency programs. Finally, we show that this autoactivation is the most important mechanism to maintain LMP1 expression during the type II latency program of EBV.

Identification of a new in vivo phosphorylation site in the cytoplasmic carboxyl terminus of EBV-LMP1 by tandem mass spectrometry

Latent membrane protein 1 (LMP1), an oncogenic protein encoded by Epstein-Barr virus (EBV), has been verified to be phosphorylated in vitro by protein casein kinase 2 (CK2). In this study, we characterized the phosphorylation of the carboxyl terminus of LMP1 fused with glutathione-S-transferase (GST-LMP1c) and the FLAG-epitope-tagged LMP1 (F-LMP1) proteins expressed in HEK293T cells. Using a combination of chemical modification and tandem mass spectrometry, we detected the phosphorylation of a tryptic peptide, 191-223 amino acids, in both GST-LMP1c catalysed by CK2 and F-LMP1-expressing cell lines. Serine residues at positions 211 and 215 were determined to be the substrates of CK2 in vitro. Most importantly, the S215 phosphorylation was also detected in F-LMP1-expressing human cell lines. The phosphorylation of S215, which is located in the carboxyl-terminus activation region 1 of LMP1, provides a new insight for investigating the role and modulation of the phosphorylation of LMP1.

Update on the therapy of highly aggressive non-Hodgkin’s lymphoma

This review focuses on the current understanding of the biology of highly aggressive non-Hodgkin's lymphomas, such as Burkitt's lymphoma, lymphoblastic lymphoma and adult T cell lymphoma/leukaemia. Specifically, this review will examine how our increased understanding of the pathophysiology of these diseases can be used to develop new therapies.