The Epstein-Barr virus LMP1 amino acid sequence that engages tumor necrosis factor receptor associated factors is critical for primary B lymphocyte growth transformation

Epstein-Barr virus latent membrane protein 1 subverts IMPDH pathways to drive B-cell oncometabolism

Epstein-Barr virus (EBV) is associated with multiple types of cancers, many of which express the viral oncoprotein Latent Membrane Protein 1 (LMP1). LMP1 contributes to both epithelial and B-cell transformation. Although metabolism reprogramming is a cancer hallmark, much remains to be learned about how LMP1 alters lymphocyte oncometabolism. To gain insights into key B-cell metabolic pathways subverted by LMP1, we performed systematic metabolomic analyses on B cells with conditional LMP1 expression. This approach highlighted that LMP highly induces de novo purine biosynthesis, with xanthosine-5-P (XMP) as one of the most highly LMP1-upregulated metabolites. Consequently, IMPDH inhibition by mycophenolic acid (MPA) triggered death of LMP1-expressing EBV-transformed lymphoblastoid cell lines (LCL), a key model for EBV-driven immunoblastic lymphomas. Whereas MPA instead caused growth arrest of Burkitt lymphoma cells with the EBV latency I program, conditional LMP1 expression triggered their death, and this phenotype was rescuable by guanosine triphosphate (GTP) supplementation, implicating LMP1 as a key driver of B-cell GTP biosynthesis. Although both IMPDH isozymes are expressed in LCLs, only IMPDH2 was critical for LCL survival, whereas both contributed to proliferation of Burkitt cells with the EBV latency I program. Both LMP1 C-terminal cytoplasmic tail domains critical for primary human B-cell transformation were important for XMP production, and each contributed to LMP1-driven Burkitt cell sensitivity to MPA. Metabolomic analyses further highlighted roles of NF-kB, mitogen activated kinase, and protein kinase C downstream of LMP1 in support of XMP abundance. Of these, only protein kinase C activity was important for supporting GTP levels in LMP1 expressing Burkitt cells. MPA also de-repressed EBV lytic antigens, including LMP1 itself in latency I Burkitt cells, highlighting crosstalk between the purine biosynthesis pathway and the EBV epigenome. These results suggest novel oncometabolism-based therapeutic approaches to LMP1-driven lymphomas.

Epstein-Barr Infection, Hodgkin's Lymphoma, and the Immune System: Insights into the Molecular Mechanisms Facilitating Immune Evasion

Epstein-Barr virus (EBV) constitutes a very common pathogen and a well-characterized carcinogen. EBV has the ability to establish a chronic latent infection, during which only a subset of the viral genes is expressed. EBV is implicated in multiple malignancies, including Hodgkin's lymphoma (HL). HL mainly affects adolescents and young adults and has an overall favorable prognosis. However, relapsed or refractory disease still poses a therapeutic challenge. EBV does not only induce malignant transformation but also hinders the detection and clearance of the neoplastic cells by the immune system. The proteins and non-coding RNAs expressed in latency IIa, which is associated with HL, employ a variety of mechanisms to target different steps of innate and adaptive immunity, to take advantage of the immunosuppressant effect of immune checkpoints, and to shape the microenvironment to support the survival and proliferation of malignant cells. They suppress the expression or promote the degradation of pattern-recognition receptors, interfere with type I interferon and proinflammatory cytokine mediated signaling, and hinder the effector function of natural killer cells. The processing and presentation of peptides to CD4 and CD8 T cells are also hampered. EBV induces the expression of immune checkpoints, the secretion of immunosuppressive cytokines, and the efflux of regulatory T cells in the tumor microenvironment. The current review provides a comprehensive overview of the molecular mechanisms underlying this complex interplay between EBV and the immune system in HL with focus on clinical data from the pediatric population, which is the key for developing novel, effective therapeutic interventions.

Epstein-Barr Virus Latent Membrane Protein 1 Subverts IMPDH pathways to drive B-cell oncometabolism

Epstein-Barr virus (EBV) is associated with multiple types of cancers, many of which express the key viral oncoprotein Latent Membrane Protein 1 (LMP1). LMP1 is the only EBV-encoded protein whose expression is sufficient to transform both epithelial and B-cells. Although metabolism reprogramming is a cancer hallmark, much remains to be learned about how LMP1 alters lymphocyte oncometabolism. To gain insights into key B-cell metabolic pathways subverted by LMP1, we performed systematic metabolomic analyses on B cells with conditional LMP1 expression. This approach highlighted that LMP highly induces de novo purine biosynthesis, with xanthosine-5-P (XMP) as one of the most highly LMP1-upregulated metabolites. Consequently, IMPDH inhibition by mycophenolic acid (MPA) triggered apoptosis of LMP1-expressing EBV-transformed lymphoblastoid cell lines (LCL), a key model for EBV-driven immunoblastic lymphomas. Whereas MPA instead caused growth arrest of Burkitt lymphoma cells with the EBV latency I program, conditional LMP1 expression triggered their apoptosis. Although both IMPDH isozymes are expressed in LCLs, only IMPDH2 was critical for LCL survival, whereas both contributed to proliferation of Burkitt cells with the EBV latency I program. Both LMP1 C-terminal cytoplasmic tail domains critical for primary human B-cell transformation were important for XMP production, and each contributed to LMP1-driven Burkitt cell sensitivity to MPA. MPA also de-repressed EBV lytic antigens including LMP1 in latency I Burkitt cells, highlighting crosstalk between the purine biosynthesis pathway and the EBV epigenome. These results suggest novel oncometabolism-based therapeutic approaches to LMP1-driven lymphomas.

IMPORTANCE

Altered metabolism is a hallmark of cancer, yet much remains to be learned about how EBV rewires host cell metabolism to support multiple malignancies. While the oncogene LMP1 is the only EBV-encoded gene that is sufficient to transform murine B-cells and rodent fibroblasts, knowledge has remained incomplete about how LMP1 alters host cell oncometabolism to aberrantly drive infected B-cell growth and survival. Likewise, it has remained unknown whether LMP1 expression creates metabolic vulnerabilities that can be targeted by small molecule approaches to trigger EBV-transformed B-cell programmed cell death. We therefore used metabolomic profiling to define how LMP1 signaling remodels the B-cell metabolome. We found that LMP1 upregulated purine nucleotide biosynthesis, likely to meet increased demand. Consequently, LMP1 expression sensitized Burkitt B-cells to growth arrest upon inosine monophosphate dehydrogenase blockade. Thus, while LMP1 itself may not be a therapeutic target, its signaling induces dependence on downstream druggable host cell nucleotide metabolism enzymes, suggesting rational therapeutic approaches.

Aberrant non-canonical NF-κB signalling reprograms the epigenome landscape to drive oncogenic transcriptomes in multiple myeloma

In multiple myeloma, abnormal plasma cells establish oncogenic niches within the bone marrow by engaging the NF-κB pathway to nurture their survival while they accumulate pro-proliferative mutations. Under these conditions, many cases eventually develop genetic abnormalities endowing them with constitutive NF-κB activation. Here, we find that sustained NF-κB/p52 levels resulting from such mutations favours the recruitment of enhancers beyond the normal B-cell repertoire. Furthermore, through targeted disruption of p52, we characterise how such enhancers are complicit in the formation of super-enhancers and the establishment of cis-regulatory interactions with myeloma dependencies during constitutive activation of p52. Finally, we functionally validate the pathological impact of these cis-regulatory modules on cell and tumour phenotypes using in vitro and in vivo models, confirming RGS1 as a p52-dependent myeloma driver. We conclude that the divergent epigenomic reprogramming enforced by aberrant non-canonical NF-κB signalling potentiates transcriptional programs beneficial for multiple myeloma progression.

Characterization of target gene regulation by the two Epstein-Barr virus oncogene LMP1 domains essential for B-cell transformation

IMPORTANCE

Epstein-Barr virus (EBV) causes multiple human cancers, including B-cell lymphomas. In cell culture, EBV converts healthy human B-cells into immortalized ones that grow continuously, which model post-transplant lymphomas. Constitutive signaling from two cytoplasmic tail domains of the EBV oncogene latent membrane protein 1 (LMP1) is required for this transformation, yet there has not been systematic analysis of their host gene targets. We identified that only signaling from the membrane proximal domain is required for survival of these EBV-immortalized cells and that its loss triggers apoptosis. We identified key LMP1 target genes, whose abundance changed significantly with loss of LMP1 signals, or that were instead upregulated in response to switching on signaling by one or both LMP1 domains in an EBV-uninfected human B-cell model. These included major anti-apoptotic factors necessary for EBV-infected B-cell survival. Bioinformatics analyses identified clusters of B-cell genes that respond differently to signaling by either or both domains.

Role of Virus-Induced EGFR Trafficking in Proviral Functions

Since its discovery in the early 1980s, the epidermal growth factor receptor (EGFR) has emerged as a pivotal and multifaceted player in elucidating the intricate mechanisms underlying various human diseases and their associations with cell survival, proliferation, and cellular homeostasis. Recent advancements in research have underscored the profound and multifaceted role of EGFR in viral infections, highlighting its involvement in viral entry, replication, and the subversion of host immune responses. In this regard, the importance of EGFR trafficking has also been highlighted in recent studies. The dynamic relocation of EGFR to diverse intracellular organelles, including endosomes, lysosomes, mitochondria, and even the nucleus, is a central feature of its functionality in diverse contexts. This dynamic intracellular trafficking is not merely a passive process but an orchestrated symphony, facilitating EGFR involvement in various cellular pathways and interactions with viral components. Furthermore, EGFR, which is initially anchored on the plasma membrane, serves as a linchpin orchestrating viral entry processes, a crucial early step in the viral life cycle. The role of EGFR in this context is highly context-dependent and varies among viruses. Here, we present a comprehensive summary of the current state of knowledge regarding the intricate interactions between EGFR and viruses. These interactions are fundamental for successful propagation of a wide array of viral species and affect viral pathogenesis and host responses. Understanding EGFR significance in both normal cellular processes and viral infections may not only help develop innovative antiviral therapies but also provide a deeper understanding of the intricate roles of EGFR signaling in infectious diseases.

Characterization of Target Gene Regulation by the Two Epstein-Barr Virus Oncogene LMP1 Domains Essential for B-cell Transformation

The Epstein-Barr virus (EBV) oncogene latent membrane protein 1 (LMP1) mimics CD40 signaling and is expressed by multiple malignancies. Two LMP1 C-terminal cytoplasmic tail regions, termed transformation essential sites (TES) 1 and 2, are critical for EBV transformation of B lymphocytes into immortalized lymphoblastoid cell lines (LCL). However, TES1 versus TES2 B-cell target genes have remained incompletely characterized, and whether both are required for LCL survival has remained unknown. To define LCL LMP1 target genes, we profiled transcriptome-wide effects of acute LMP1 CRISPR knockout (KO) prior to cell death. To then characterize specific LCL TES1 and TES2 roles, we conditionally expressed wildtype, TES1 null, TES2 null or double TES1/TES2 null LMP1 alleles upon endogenous LMP1 KO. Unexpectedly, TES1 but not TES2 signaling was critical for LCL survival. The LCL dependency factor cFLIP, which plays obligatory roles in blockade of LCL apoptosis, was highly downmodulated by loss of TES1 signaling. To further characterize TES1 vs TES2 roles, we conditionally expressed wildtype, TES1 and/or TES2 null LMP1 alleles in two Burkitt models. Systematic RNAseq analyses revealed gene clusters that responded more strongly to TES1 versus TES2, that respond strongly to both or that are oppositely regulated. Robust TES1 effects on cFLIP induction were again noted. TES1 and 2 effects on expression of additional LCL dependency factors, including BATF and IRF4, and on EBV super-enhancers were identified. Collectively, these studies suggest a model by which LMP1 TES1 and TES2 jointly remodel the B-cell transcriptome and highlight TES1 as a key therapeutic target.

EBV infection mediated BDNF expression is associated with bladder inflammation in interstitial cystitis/bladder pain syndrome with Hunner's lesion

Interstitial cystitis/bladder pain syndrome with Hunner's lesion (HIC) is characterized by chronic inflammation and nerve hyperplasia; however, the pathogenesis of HIC remains a mystery. In this study, we detected both Epstein-Barr virus (EBV) latency infection genes EBNA-1 and LMP-1 and EBV lytic infection BZLF-1 and BRLF-1 expression in the HIC bladders, indicating the coexistence of EBV persistence and reactivation in the B cells in HIC bladders. Upregulation of EBV-associated inflammatory genes in HIC bladders, such as TNF-α and IL-6, suggests EBV infection is implicated in the pathogenesis of bladder inflammation. Nerve hyperplasia and upregulation of brain-derived neurotrophic factor (BDNF) were noted in the HIC bladders. Double immunochemical staining and flow cytometry revealed the origin of BDNF to be EBV-infected B cells. Inducible BDNF expression was noted in B cells upon EBV infection, but not in the T cells. A chromatin immunoprecipitation study revealed BDNF transcription could be promoted by cooperation between EBV nuclear antigens, chromatin modifiers, and B-cell-specific transcription. Knockdown of BDNF in EBV-infected B cells resulted in the inhibition of cell proliferation and viability. Downregulation of phosphorylated SMAD2 and STAT3 after BDNF knockdown may play a role in the mechanism. Implantation of latent EBV-infected B cells into rat bladder walls resulted in a higher expression level of CD45 and PGP9.5, suggesting tissue inflammation and nerve hyperplasia. In contrast, implantation of BDNF depleted EBV-infected B cells abrogated these effects. This is the first study to provide insights into the mechanisms underlying the involvement of EBV-infected B cells in HIC pathogenesis. © 2022 The Pathological Society of Great Britain and Ireland.

Insights into intricacies of the Latent Membrane Protein-1 (LMP-1) in EBV-associated cancers

Numerous lymphomas, carcinomas, and other disorders have been associated with Epstein-Barr Virus (EBV) infection. EBV's carcinogenic potential can be correlated to latent membrane protein 1 (LMP1), which is essential for fibroblast and primary lymphocyte transformation. LMP1, a transmembrane protein with constitutive activity, belongs to the tumour necrosis factor receptor (TNFR) superfamily. LMP1 performs number of role in the life cycle of EBV and the pathogenesis by interfering with, reprogramming, and influencing a vast range of host cellular activities and functions that are getting well-known but still poorly understood. LMP1, pleiotropically perturbs, reprograms and balances a wide range of various processes of cell such as extracellular vesicles, epigenetics, ubiquitin machinery, metabolism, cell proliferation and survival, and also promotes oncogenic transformation, angiogenesis, anchorage-independent cell growth, metastasis and invasion, tumour microenvironment. By the help of various experiments, it is proven that EBV-encoded LMP1 activates multiple cell signalling pathways which affect antigen presentation, cell-cell interactions, chemokine and cytokine production. Therefore, it is assumed that LMP1 may perform majorly in EBV associated malignancies. For the development of novel techniques toward targeted therapeutic applications, it is essential to have a complete understanding of the LMP1 signalling landscape in order to identify potential targets. The focus of this review is on LMP1-interacting proteins and related signalling processes. We further discuss tactics for using the LMP1 protein as a potential therapeutic for cancers caused by the EBV.

TNF Receptor Associated Factor 2 (TRAF2) Signaling in Cancer

Simple Summary

Tumor necrosis factor (TNF) receptor associated factor-2 (TRAF2) is an intracellular adapter protein with E3 ligase activity, which interacts with a plethora of other signaling proteins, including plasma membrane receptors, kinases, phosphatases, other E3 ligases, and deubiquitinases. TRAF2 is involved in various cancer-relevant cellular processes, such as the activation of transcription factors of the NFκB family, stimulation of mitogen-activated protein (MAP) kinase cascades, endoplasmic reticulum (ER) stress signaling, autophagy, and the control of cell death programs. In a context-dependent manner, TRAF2 promotes tumor development but it can also act as a tumor suppressor. Based on a general description, how TRAF2 in concert with TRAF2-interacting proteins and other TRAF proteins act at the molecular level is discussed for its importance for tumor development and its potential usefulness as a therapeutic target in cancer therapy.

Abstract

Tumor necrosis factor (TNF) receptor associated factor-2 (TRAF2) has been originally identified as a protein interacting with TNF receptor 2 (TNFR2) but also binds to several other receptors of the TNF receptor superfamily (TNFRSF). TRAF2, often in concert with other members of the TRAF protein family, is involved in the activation of the classical NFκB pathway and the stimulation of various mitogen-activated protein (MAP) kinase cascades by TNFRSF receptors (TNFRs), but is also required to inhibit the alternative NFκB pathway. TRAF2 has also been implicated in endoplasmic reticulum (ER) stress signaling, the regulation of autophagy, and the control of cell death programs. TRAF2 fulfills its functions by acting as a scaffold, bringing together the E3 ligase cellular inhibitor of apoptosis-1 (cIAP1) and cIAP2 with their substrates and various regulatory proteins, e.g., deubiquitinases. Furthermore, TRAF2 can act as an E3 ligase by help of its N-terminal really interesting new gene (RING) domain. The finding that TRAF2 (but also several other members of the TRAF family) interacts with the latent membrane protein 1 (LMP1) oncogene of the Epstein–Barr virus (EBV) indicated early on that TRAF2 could play a role in the oncogenesis of B-cell malignancies and EBV-associated non-keratinizing nasopharyngeal carcinoma (NPC). TRAF2 can also act as an oncogene in solid tumors, e.g., in colon cancer by promoting Wnt/β-catenin signaling. Moreover, tumor cell-expressed TRAF2 has been identified as a major factor-limiting cancer cell killing by cytotoxic T-cells after immune checkpoint blockade. However, TRAF2 can also be context-dependent as a tumor suppressor, presumably by virtue of its inhibitory effect on the alternative NFκB pathway. For example, inactivating mutations of TRAF2 have been associated with tumor development, e.g., in multiple myeloma and mantle cell lymphoma. In this review, we summarize the various TRAF2-related signaling pathways and their relevance for the oncogenic and tumor suppressive activities of TRAF2. Particularly, we discuss currently emerging concepts to target TRAF2 for therapeutic purposes.

IKKα-Mediated Noncanonical NF-κB Signaling Is Required To Support Murine Gammaherpesvirus 68 Latency In Vivo

Noncanonical NF-κB signaling is activated in B cells via the tumor necrosis factor (TNF) receptor superfamily members CD40, lymphotoxin β receptor (LTβR), and B-cell-activating factor receptor (BAFF-R). The noncanonical pathway is required at multiple stages of B cell maturation and differentiation, including the germinal center reaction. However, the role of this pathway in gammaherpesvirus latency is not well understood. Murine gammaherpesvirus 68 (MHV68) is a genetically tractable system used to define pathogenic determinants. Mice lacking the BAFF-R exhibit defects in splenic follicle formation and are greatly reduced for MHV68 latency. We report a novel approach to disrupt noncanonical NF-κB signaling exclusively in cells infected with MHV68. We engineered a recombinant virus that expresses a dominant negative form of IκB kinase α (IKKα), named IKKα-SA, with S176A and S180A mutations that prevent phosphorylation by NF-κB-inducing kinase (NIK). We controlled for the transgene insertion by introducing two all-frame stop codons into the IKKα-SA gene. The IKKα-SA mutant but not the IKKα-SA.STOP control virus impaired LTβR-mediated activation of NF-κB p52 upon fibroblast infection. IKKα-SA expression did not impact replication in primary fibroblasts or in the lungs of mice following intranasal inoculation. However, the IKKα-SA mutant was severely defective in the colonization of the spleen and in the establishment of latency compared to the IKKα-SA.STOP control and wild-type (WT) MHV68 at 16 days postinfection (dpi). Reactivation was undetectable in splenocytes infected with the IKKα-SA mutant, but reactivation in peritoneal cells was not impacted by IKKα-SA. Taken together, the noncanonical NF-κB signaling pathway is essential for the establishment of latency in the secondary lymphoid organs of mice infected with the murine gammaherpesvirus pathogen MHV68. IMPORTANCE The latency programs of the human gammaherpesviruses Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) are associated with B cell lymphomas. It is critical to understand the signaling pathways that are used by gammaherpesviruses to establish and maintain latency in primary B cells. We used a novel approach to block noncanonical NF-κB signaling only in the infected cells of mice. We generated a recombinant virus that expresses a dominant negative mutant of IKKα that is nonresponsive to upstream activation. Latency was reduced in a route- and cell type-dependent manner in mice infected with this recombinant virus. These findings identify a significant role for the noncanonical NF-κB signaling pathway that might provide a novel target to prevent latent infection of B cells with oncogenic gammaherpesviruses.

Potential Role of Epstein-Barr Virus in Oral Potentially Malignant Disorders and Oral Squamous Cell Carcinoma: A Scoping Review

Though the oral cavity is anatomically proximate to the nasal cavity and acts as a key reservoir of EBV habitation and transmission, it is still unclear whether EBV plays a significant role in oral carcinogenesis. Many studies have detected EBV DNA in tissues and exfoliated cells from OSCC patients. However, very few studies have investigated the expression of functional EBV proteins implicated in its oncogenicity. The most studied are latent membrane protein 1 (LMP-1), a protein associated with the activation of signalling pathways; EBV determined nuclear antigen (EBNA)-1, a protein involved in the regulation of gene expression; and EBV-encoded small non-polyadenylated RNA (EBER)-2. LMP-1 is considered the major oncoprotein, and overexpression of LMP-1 observed in OSCC indicates that this molecule might play a significant role in oral carcinogenesis. Although numerous studies have detected EBV DNA and proteins from OSCC and oral potentially malignant disorders, heterogeneity in methodologies has led to discrepant results, hindering interpretation. Elucidating the exact functions of EBV and its proteins when expressed is vital in establishing the role of viruses in oral oncogenesis. This review summarises the current evidence on the potential role of EBV in oral oncogenesis and discusses the implications as well as recommendations for future research.

EBV Genome Mutations and Malignant Proliferations

The Epstein-Barr virus (EBV) is a DNA virus with a relatively stable genome. Indeed, genomic variability is reported to be around 0.002%. However, some regions are more variable such as those carrying latency genes and specially EBNA1, -2, -LP, and LMP1. Tegument genes, particularly BNRF1, BPLF1, and BKRF3, are also quite mutated. For a long time, it has been considered for this ubiquitous virus, which infects a very large part of the population, that particular strains could be the cause of certain diseases. However, the mutations found, in some cases, are more geographically restricted rather than associated with proliferation. In other cases, they appear to be involved in oncogenesis. The objective of this chapter is to provide an update on changes in viral genome sequences in malignancies associated with EBV. We focused on describing the structure and function of the proteins corresponding to the genes mentioned above in order to understand how certain mutations of these proteins could increase the tumorigenic character of this virus. Mutations described in the literature for these proteins were identified by reporting viral and/or cellular functional changes as they were described.

Monocarboxylate transporter antagonism reveals metabolic vulnerabilities of viral-driven lymphomas

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus that typically causes asymptomatic infection but can promote B lymphoid tumors in the immune suppressed. In vitro, EBV infection of primary B cells stimulates glycolysis during immortalization into lymphoblastoid cell lines (LCLs). Lactate export during glycolysis is crucial for continued proliferation of many cancer cells-part of a phenomenon known as the "Warburg effect"- and is mediated by monocarboxylate transporters (MCTs). However, the role of MCTs has yet to be studied in EBV-associated malignancies, which display Warburg-like metabolism in vitro. Here, we show that EBV infection of B lymphocytes directly promotes temporal induction of MCT1 and MCT4 through the viral proteins EBNA2 and LMP1, respectively. Functionally, MCT1 was required for early B cell proliferation, and MCT4 up-regulation promoted acquired resistance to MCT1 antagonism in LCLs. However, dual MCT1/4 inhibition led to LCL growth arrest and lactate buildup. Metabolic profiling in LCLs revealed significantly reduced oxygen consumption rates (OCRs) and NAD+/NADH ratios, contrary to previous observations of increased OCR and unaltered NAD+/NADH ratios in MCT1/4-inhibited cancer cells. Furthermore, U-¹³C₆-glucose labeling of MCT1/4-inhibited LCLs revealed depleted glutathione pools that correlated with elevated reactive oxygen species. Finally, we found that dual MCT1/4 inhibition also sensitized LCLs to killing by the electron transport chain complex I inhibitors phenformin and metformin. These findings were extended to viral lymphomas associated with EBV and the related gammaherpesvirus KSHV, pointing at a therapeutic approach for targeting both viral lymphomas.

Molecular characterization of Epstein-Barr virus variants detected in the oral cavity of adolescents in Cali, Colombia

Introduction: The Epstein-Barr virus (EBV) is an ubiquitous and oncogenic virus associated with the development of diseases such as infectious mononucleosis, Burkitt’s lymphoma, nasopharyngeal carcinoma, and other neoplasms. Currently, two types are recognized: EBV-1 and EBV-2, which have genetic differences with their EBNA nuclear antigens. Likewise, due to the high degree of heterogeneity and variability found in the LMP1 protein of the virus, variants associated with pathogenesis or specific geographic regions have been described. Objective: To identify and characterize molecularly EBV variants detected in the oral cavity of 84 adolescents in Cali, Colombia. Materials and methods: Conventional PCR amplification, purification, and sequencing of the gen EBNA3C were carried out to typify the virus and the C-ter domain of the LMP1 protein to identify variants. We also conducted a phylogenetic and nucleotide variant analysis of the obtained sequences versus pathogenic or geographic variants reported in GenBank-NCBI. Results: The predominant viral subtype was EBV-1 (79%); 72.6% was grouped with the pathogenic variant Raji, derived from B lymphocytes of a patient with Burkitt›s lymphoma, 13.7% was related to a variant of Mediterranean origin, and 13.7% was not grouped with any of the reference variants. Conclusions: This is the first time that variants of LMP1-EBV have been identified in Cali, Colombia. Additional studies are necessary to characterize the unidentified variant and to determine if it is pathogenic or if it is just an isolate present in the city of Cali.

The interplay between Epstein-Bar virus (EBV) with the p53 and its homologs during EBV associated malignancies

p53, p63, and p73, the members of the p53 family of proteins, are structurally similar proteins that play central roles regulating cell cycle and apoptotic cell death. Alternative splicing at the carboxyl terminus and the utilization of different promoters further categorizes these proteins as having different isoforms for each. Among such isoforms, TA and ΔN versions of each protein serve as the pro and the anti-apoptotic proteins, respectively. Changes in the expression patterns of these isoforms are noted in many human cancers. Proteins of certain human herpesviruses, like Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV), interact with p53 family members and alter their expressions in many malignancies. Upon infections in the B cells and epithelial cells, EBV expresses different lytic or latent proteins during viral replication and latency respectively to preserve viral copy number, chromosomal integrity and viral persistence inside the host. In this review, we have surveyed and summarised the interactions of EBV gene products, known so far, with the p53 family proteins. The interactions between P53 and EBV oncoproteins are observed in stomach cancer, non-Hodgkin's lymphoma (NHL) of the head and neck, Nasopharyngeal Cancer (NPC), Gastric carcinoma (GC) and Burkitt's lymphoma (BL). EBV latent protein EBNA1, EBNA3C, LMP-1, and lytic proteins BZLF-1 can alter p53 expressions in many cancer cell lines. Interactions of p63 with EBNA-1, 2, 5, LMP-2A and BARF-1 have also been investigated in several cancers. Similarly, associations of p73 isoform with EBV latent proteins EBNA3C and LMP-1 have been reported. Methylation and single nucleotide polymorphisms in p53 have also been found to be correlated with EBV infection. Therefore, interactions and altered expression strategies of the isoforms of p53 family proteins in EBV associated cancers propose an important field for further molecular research.

The Epstein-Barr virus LMP1 interactome: biological implications and therapeutic targets

The oncogenic potential of Epstein-Barr virus (EBV) is mostly attributed to latent membrane protein 1 (LMP1), which is essential and sufficient for transformation of fibroblast and primary lymphocytes. LMP1 expression results in the activation of multiple signaling cascades like NF-ΚB and MAP kinases that trigger cell survival and proliferative pathways. LMP1 specific signaling events are mediated through the recruitment of a number of interacting proteins to various signaling domains. Based on these properties, LMP1 is an attractive target to develop effective therapeutics to treat EBV-related malignancies. In this review, we focus on LMP1 interacting proteins, associated signaling events, and potential targets that could be exploited for therapeutic strategies.

Epstein-Barr Virus-Associated Malignancies: Roles of Viral Oncoproteins in Carcinogenesis

The Epstein–Barr virus (EBV) is the first herpesvirus identified to be associated with human cancers known to infect the majority of the world population. EBV-associated malignancies are associated with a latent form of infection, and several of the EBV-encoded latent proteins are known to mediate cellular transformation. These include six nuclear antigens and three latent membrane proteins (LMPs). In lymphoid and epithelial tumors, viral latent gene expressions have distinct pattern. In both primary and metastatic tumors, the constant expression of latent membrane protein 2A (LMP2A) at the RNA level suggests that this protein is the key player in the EBV-associated tumorigenesis. While LMP2A contributing to the malignant transformation possibly by cooperating with the aberrant host genome. This can be done in part by dysregulating signaling pathways at multiple points, notably in the cell cycle and apoptotic pathways. Recent studies also have confirmed that LMP1 and LMP2 contribute to carcinoma progression and that this may reflect the combined effects of these proteins on activation of multiple signaling pathways. This review article aims to investigate the aforementioned EBV-encoded proteins that reveal established roles in tumor formation, with a greater emphasis on the oncogenic LMPs (LMP1 and LMP2A) and their roles in dysregulating signaling pathways. It also aims to provide a quick look on the six members of the EBV nuclear antigens and their roles in dysregulating apoptosis.

Frequency of EBV LMP-1 Promoter and Coding Variations in Burkitt Lymphoma Samples in Africa and South America and Peripheral Blood in Uganda

Epstein-Barr virus (EBV) is linked to several cancers, including endemic Burkitt lymphoma (eBL), but causal variants are unknown. We recently reported novel sequence variants in the LMP-1 gene and promoter in EBV genomes sequenced from 13 of 14 BL biopsies. Alignments of the novel sequence variants for 114 published EBV genomes, including 27 from BL cases, revealed four LMP-1 variant patterns, designated A to D. Pattern A variant was found in 48% of BL EBV genomes. Here, we used PCR-Sanger sequencing to evaluate 50 additional BL biopsies from Ghana, Brazil, and Argentina, and peripheral blood samples from 113 eBL cases and 115 controls in Uganda. Pattern A was found in 60.9% of 64 BL biopsies evaluated. Compared to PCR-negative subjects in Uganda, detection of Pattern A in peripheral blood was associated with eBL case status (odds ratio [OR] 31.7, 95% confidence interval: 6.8⁻149), controlling for relevant confounders. Variant Pattern A and Pattern D were associated with eBL case status, but with lower ORs (9.7 and 13.6, respectively). Our results support the hypothesis that EBV LMP-1 Pattern A may be associated with eBL, but it is not the sole associated variant. Further research is needed to replicate and elucidate our findings.

The interactome of EBV LMP1 evaluated by proximity-based BioID approach

Epstein-Barr virus LMP1 is an oncoprotein required for immortalizing B lymphocytes and also plays important roles in transforming non-lymphoid tissue. The discovery of LMP1 protein interactions will likely generate targets to treat EBV-associated cancers. Here, we define the broader LMP1 interactome using the recently developed BioID method. Combined with mass spectrometry, we identified over 1000 proteins across seven independent experiments with direct or indirect relationships to LMP1. Pathway analysis suggests that a significant number of the proteins identified are involved in signal transduction and protein or vesicle trafficking. Interestingly, a large number of proteins thought to be important in the formation of exosomes and protein targeting were recognized as probable LMP1 interacting partners, including CD63, syntenin-1, ALIX, TSG101, HRS, CHMPs, and sorting nexins. Therefore, it is likely that LMP1 modifies protein trafficking and exosome biogenesis pathways. In support of this, knock-down of syntenin-1 and ALIX resulted in reduced exosomal LMP1.

EBV and Apoptosis: The Viral Master Regulator of Cell Fate?

Epstein-Barr virus (EBV) was first discovered in cells from a patient with Burkitt lymphoma (BL), and is now known to be a contributory factor in 1-2% of all cancers, for which there are as yet, no EBV-targeted therapies available. Like other herpesviruses, EBV adopts a persistent latent infection in vivo and only rarely reactivates into replicative lytic cycle. Although latency is associated with restricted patterns of gene expression, genes are never expressed in isolation; always in groups. Here, we discuss (1) the ways in which the latent genes of EBV are known to modulate cell death, (2) how these mechanisms relate to growth transformation and lymphomagenesis, and (3) how EBV genes cooperate to coordinately regulate key cell death pathways in BL and lymphoblastoid cell lines (LCLs). Since manipulation of the cell death machinery is critical in EBV pathogenesis, understanding the mechanisms that underpin EBV regulation of apoptosis therefore provides opportunities for novel therapeutic interventions.

Epstein-Barr Virus LMP1-Mediated Oncogenicity

Epstein-Barr virus latent membrane protein 1 (LMP1) is expressed in multiple human malignancies, including nasopharyngeal carcinoma and Hodgkin and immunosuppression-associated lymphomas. LMP1 mimics CD40 signaling to activate multiple growth and survival pathways, in particular, NF-κB. LMP1 has critical roles in Epstein-Barr virus (EBV)-driven B-cell transformation, and its expression causes fatal lymphoproliferative disease in immunosuppressed mice. Here, we review recent developments in studies of LMP1 signaling, LMP1-induced host dependency factors, mouse models of LMP1 lymphomagenesis, and anti-LMP1 immunotherapy approaches.

Tumor Suppressor p53 Stimulates the Expression of Epstein-Barr Virus Latent Membrane Protein 1

Epstein-Barr virus (EBV) is associated with multiple human malignancies. EBV latent membrane protein 1 (LMP1) is required for the efficient transformation of primary B lymphocytes in vitro and possibly in vivo The tumor suppressor p53 plays a seminal role in cancer development. In some EBV-associated cancers, p53 tends to be wild type and overly expressed; however, the effects of p53 on LMP1 expression is not clear. We find LMP1 expression to be associated with p53 expression in EBV-transformed cells under physiological and DNA damaging conditions. DNA damage stimulates LMP1 expression, and p53 is required for the stimulation. Ectopic p53 stimulates endogenous LMP1 expression. Moreover, endogenous LMP1 blocks DNA damage-mediated apoptosis. Regarding the mechanism of p53-mediated LMP1 expression, we find that interferon regulatory factor 5 (IRF5), a direct target of p53, is associated with both p53 and LMP1. IRF5 binds to and activates a LMP1 promoter reporter construct. Ectopic IRF5 increases the expression of LMP1, while knockdown of IRF5 leads to reduction of LMP1. Furthermore, LMP1 blocks IRF5-mediated apoptosis in EBV-infected cells. All of the data suggest that cellular p53 stimulates viral LMP1 expression, and IRF5 may be one of the factors for p53-mediated LMP1 stimulation. LMP1 may subsequently block DNA damage- and IRF5-mediated apoptosis for the benefits of EBV. The mutual regulation between p53 and LMP1 may play an important role in EBV infection and latency and its related cancers.IMPORTANCE The tumor suppressor p53 is a critical cellular protein in response to various stresses and dictates cells for various responses, including apoptosis. This work suggests that an Epstein-Bar virus (EBV) principal viral oncogene is activated by cellular p53. The viral oncogene blocks p53-mediated adverse effects during viral infection and transformation. Therefore, the induction of the viral oncogene by p53 provides a means for the virus to cope with infection and DNA damage-mediated cellular stresses. This seems to be the first report that p53 activates a viral oncogene; therefore, the discovery would be interesting to a broad readership from the fields of oncology to virology.

Manipulation of the host cell membrane by human γ-herpesviruses EBV and KSHV for pathogenesis

The cell membrane regulates many physiological processes including cellular communication, homing and metabolism. It is therefore not surprising that the composition of the host cell membrane is manipulated by intracellular pathogens. Among these, the human oncogenic herpesviruses Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) exploit the host cell membrane to avoid immune surveillance and promote viral replication. Accumulating evidence has shown that both EBV and KSHV directly encode several similar membrane-associated proteins, including receptors and receptor-specific ligands (cytokines and chemokines), to increase virus fitness in spite of host antiviral immune responses. These proteins are expressed individually at different phases of the EBV/KSHV life cycle and employ various mechanisms to manipulate the host cell membrane. In recent decades, much effort has been made to address how these membrane-based signals contribute to viral tumorigenesis. In this review, we summarize and highlight the recent understanding of how EBV and KSHV similarly manipulate host cell membrane signals, particularly how remodeling of the cell membrane allows EBV and KSHV to avoid host antiviral immune responses and favors their latent and lytic infection.

Utility of Lymphoblastoid Cell Lines for Induced Pluripotent Stem Cell Generation

A large number of EBV immortalized LCLs have been generated and maintained in genetic/epidemiological studies as a perpetual source of DNA and as a surrogate in vitro cell model. Recent successes in reprograming LCLs into iPSCs have paved the way for generating more relevant in vitro disease models using this existing bioresource. However, the overall reprogramming efficiency and success rate remain poor and very little is known about the mechanistic changes that take place at the transcriptome and cellular functional level during LCL-to-iPSC reprogramming. Here, we report a new optimized LCL-to-iPSC reprogramming protocol using episomal plasmids encoding pluripotency transcription factors and mouse p53DD (p53 carboxy-terminal dominant-negative fragment) and commercially available reprogramming media. We achieved a consistently high reprogramming efficiency and 100% success rate using this optimized protocol. Further, we investigated the transcriptional changes in mRNA and miRNA levels, using FC-abs ≥ 2.0 and FDR ≤ 0.05 cutoffs; 5,228 mRNAs and 77 miRNAs were differentially expressed during LCL-to-iPSC reprogramming. The functional enrichment analysis of the upregulated genes and activation of human pluripotency pathways in the reprogrammed iPSCs showed that the generated iPSCs possess transcriptional and functional profiles very similar to those of human ESCs.

The Latent Membrane Protein 1 (LMP1)

Almost exactly twenty years after the discovery of Epstein-Barr virus (EBV), the latent membrane protein 1 (LMP1) entered the EBV stage, and soon thereafter, it was recognized as the primary transforming gene product of the virus. LMP1 is expressed in most EBV-associated lymphoproliferative diseases and malignancies, and it critically contributes to pathogenesis and disease phenotypes. Thirty years of LMP1 research revealed its high potential as a deregulator of cellular signal transduction pathways leading to target cell proliferation and the simultaneous subversion of cell death programs. However, LMP1 has multiple roles beyond cell transformation and immortalization, ranging from cytokine and chemokine induction, immune modulation, the global alteration of gene and microRNA expression patterns to the regulation of tumor angiogenesis, cell-cell contact, cell migration, and invasive growth of tumor cells. By acting like a constitutively active receptor, LMP1 recruits cellular signaling molecules associated with tumor necrosis factor receptors such as tumor necrosis factor receptor-associated factor (TRAF) proteins and TRADD to mimic signals of the costimulatory CD40 receptor in the EBV-infected B lymphocyte. LMP1 activates NF-κB, mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3-K), IRF7, and STAT pathways. Here, we review LMP1's molecular and biological functions, highlighting the interface between LMP1 and the cellular signal transduction network as an important factor of virus-host interaction and a potential therapeutic target.

Characterization of the rapamycin-inducible EBV LMP1 activation system

Epstein-Barr virus (EBV) latent infection membrane protein 1 (LMP1) is required for EBV-mediated B lymphocyte transformation into proliferating lymphoblastoid cell lines (LCL). LMP1 oligomerizes spontaneously in membrane lipid rafts via its transmembrane domain and constitutively activates signal transduction pathways, including NF-κB, p38 Mitogen-Activated Protein Kinase (MAPK), and c-Jun N-terminal Kinase (JNK). Since LMP1 mimics the tumor necrosis factor receptor (TNFR), CD40, it may be effectively utilized to study the effects of constitutive activation of signal transduction pathways on cellular physiology. On the other hand, LMP1 presents a disadvantage in terms of determining the sequential events and factors involved in signaling pathways. A CD40-LMP1 chimeric molecule has been generated to overcome this limitation but does not represent the authentic and physiological nature of LMP1. In the current study, a ligand-dependent activation system for LMP1 using rapamycin-inducible dimerization was generated to delineate the LMP1 signaling pathway.

TRAF1 Coordinates Polyubiquitin Signaling to Enhance Epstein-Barr Virus LMP1-Mediated Growth and Survival Pathway Activation

The Epstein-Barr virus (EBV) encoded oncoprotein Latent Membrane Protein 1 (LMP1) signals through two C-terminal tail domains to drive cell growth, survival and transformation. The LMP1 membrane-proximal TES1/CTAR1 domain recruits TRAFs to activate MAP kinase, non-canonical and canonical NF-kB pathways, and is critical for EBV-mediated B-cell transformation. TRAF1 is amongst the most highly TES1-induced target genes and is abundantly expressed in EBV-associated lymphoproliferative disorders. We found that TRAF1 expression enhanced LMP1 TES1 domain-mediated activation of the p38, JNK, ERK and canonical NF-kB pathways, but not non-canonical NF-kB pathway activity. To gain insights into how TRAF1 amplifies LMP1 TES1 MAP kinase and canonical NF-kB pathways, we performed proteomic analysis of TRAF1 complexes immuno-purified from cells uninduced or induced for LMP1 TES1 signaling. Unexpectedly, we found that LMP1 TES1 domain signaling induced an association between TRAF1 and the linear ubiquitin chain assembly complex (LUBAC), and stimulated linear (M1)-linked polyubiquitin chain attachment to TRAF1 complexes. LMP1 or TRAF1 complexes isolated from EBV-transformed lymphoblastoid B cell lines (LCLs) were highly modified by M1-linked polyubiqutin chains. The M1-ubiquitin binding proteins IKK-gamma/NEMO, A20 and ABIN1 each associate with TRAF1 in cells that express LMP1. TRAF2, but not the cIAP1 or cIAP2 ubiquitin ligases, plays a key role in LUBAC recruitment and M1-chain attachment to TRAF1 complexes, implicating the TRAF1:TRAF2 heterotrimer in LMP1 TES1-dependent LUBAC activation. Depletion of either TRAF1, or the LUBAC ubiquitin E3 ligase subunit HOIP, markedly impaired LCL growth. Likewise, LMP1 or TRAF1 complexes purified from LCLs were decorated by lysine 63 (K63)-linked polyubiqutin chains. LMP1 TES1 signaling induced K63-polyubiquitin chain attachment to TRAF1 complexes, and TRAF2 was identified as K63-Ub chain target. Co-localization of M1- and K63-linked polyubiquitin chains on LMP1 complexes may facilitate downstream canonical NF-kB pathway activation. Our results highlight LUBAC as a novel potential therapeutic target in EBV-associated lymphoproliferative disorders.

The linear ubiquitin assembly complex (LUBAC) plays crucial roles in immune receptor-mediated NF-kB and MAP kinase pathway activation. Comparatively little is known about the extent to which microbial pathogens use LUBAC to activate downstream pathways. We demonstrate that TRAF1 enhances EBV oncoprotein LMP1 TES1/CTAR1 domain mediated MAP kinase and canonical NF-kB activation. LMP1 TES1 signaling induces association between TRAF1 and LUBAC, and triggers M1-polyubiquitin chain attachment to TRAF1 complexes. TRAF1 and LMP1 complexes are decorated by M1-polyubiquitin chains in LCL extracts. TRAF2 plays a key role in LMP1-induced LUBAC recruitment and M1-chain attachment to TRAF1 complexes. TRAF1 and LMP1 complexes are modified by lysine 63-linked polyubiquitin chains in LCL extracts, and TRAF2 is a target of LMP1-induced K63-ubiquitin chain attachment. Thus, the TRAF1:TRAF2 heterotrimer may coordinate ubiquitin signaling downstream of TES1. Depletion of TRAF1 or the LUBAC subunit HOIP impairs LCL growth and survival. Thus, although TRAF1 is the only TRAF without a RING finger ubiquitin ligase domain, TRAF1 nonetheless has important roles in ubiqutin-mediated signal transduction downstream of LMP1. Our work suggests that LUBAC is important for EBV-driven B-cell proliferation, and suggests that LUBAC may be a novel therapeutic target in EBV-associated lymphoproliferative disorders.

Epstein-Barr virus latent genes

Latent Epstein–Barr virus (EBV) infection has a substantial role in causing many human disorders. The persistence of these viral genomes in all malignant cells, yet with the expression of limited latent genes, is consistent with the notion that EBV latent genes are important for malignant cell growth. While the EBV-encoded nuclear antigen-1 (EBNA-1) and latent membrane protein-2A (LMP-2A) are critical, the EBNA-leader proteins, EBNA-2, EBNA-3A, EBNA-3C and LMP-1, are individually essential for in vitro transformation of primary B cells to lymphoblastoid cell lines. EBV-encoded RNAs and EBNA-3Bs are dispensable. In this review, the roles of EBV latent genes are summarized.

Regulation and dysregulation of tumor necrosis factor receptor-1

TNF is an essential regulator of the immune system. Dysregulation of TNF plays a role in the pathology of many auto-immune diseases. TNF-blocking agents have proven successful in the treatment of such diseases. Development of novel, safer or more effective drugs requires a deeper understanding of the regulation of the pro-inflammatory activities of TNF and its receptors. The ubiquitously expressed TNFR1 is responsible for most TNF effects, while TNFR2 has a limited expression pattern and performs immune-regulatory functions. Despite extensive knowledge of TNFR1 signaling, the regulation of TNFR1 expression, its modifications, localization and processing are less clear and the data are scattered. Here we review the current knowledge of TNFR1 regulation and discuss the impact this has on the host.

Role of Ca2+/calmodulin-dependent kinase II-IRAK1 interaction in LMP1-induced NF-κB activation

We have previously reported that interleukin-1 (IL-1) receptor-associated kinase (IRAK1) is essential for Epstein-Barr virus (EBV) latent infection membrane protein 1 (LMP1)-induced p65/RelA serine 536 phosphorylation and NF-κB activation but not for IκB kinase α (IKKα) or IKKβ activation (Y. J. Song, K. Y. Jen, V. Soni, E. Kieff, and E. Cahir-McFarland, Proc. Natl. Acad. Sci. U. S. A. 103:2689-2694, 2006, doi:10.1073/pnas.0511096103). Since the kinase activity of IRAK1 is not required for LMP1-induced NF-κB activation, IRAK1 is proposed to function as a scaffold protein to recruit a p65/RelA serine 536 kinase(s) to enhance NF-κB-dependent transcriptional activity. We now report that Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) interacts with IRAK1 and is critical for LMP1-induced p65/RelA serine 536 phosphorylation and NF-κB activation. CaMKII bound the death domain of IRAK1 and directly phosphorylated p65/RelA at serine 536 in vitro. Downregulation of CaMKII activity or expression significantly reduced LMP1-induced p65/RelA serine 536 phosphorylation and NF-κB activation. Furthermore, LMP1-induced CaMKII activation and p65/RelA serine 536 phosphorylation were significantly reduced in IRAK1 knockout (KO) mouse embryonic fibroblasts (MEFs). Thus, IRAK1 may recruit and activate CaMKII, which phosphorylates p65/RelA serine 536 to enhance the transactivation potential of NF-κB in LMP1-induced NF-κB activation pathway.

Genetic diversity of EBV-encoded LMP1 in the Swiss HIV Cohort Study and implication for NF-Κb activation

Epstein-Barr virus (EBV) is associated with several types of cancers including Hodgkin's lymphoma (HL) and nasopharyngeal carcinoma (NPC). EBV-encoded latent membrane protein 1 (LMP1), a multifunctional oncoprotein, is a powerful activator of the transcription factor NF-κB, a property that is essential for EBV-transformed lymphoblastoid cell survival. Previous studies reported LMP1 sequence variations and induction of higher NF-κB activation levels compared to the prototype B95-8 LMP1 by some variants. Here we used biopsies of EBV-associated cancers and blood of individuals included in the Swiss HIV Cohort Study (SHCS) to analyze LMP1 genetic diversity and impact of sequence variations on LMP1-mediated NF-κB activation potential. We found that a number of variants mediate higher NF-κB activation levels when compared to B95-8 LMP1 and mapped three single polymorphisms responsible for this phenotype: F106Y, I124V and F144I. F106Y was present in all LMP1 isolated in this study and its effect was variant dependent, suggesting that it was modulated by other polymorphisms. The two polymorphisms I124V and F144I were present in distinct phylogenetic groups and were linked with other specific polymorphisms nearby, I152L and D150A/L151I, respectively. The two sets of polymorphisms, I124V/I152L and F144I/D150A/L151I, which were markers of increased NF-κB activation in vitro, were not associated with EBV-associated HL in the SHCS. Taken together these results highlighted the importance of single polymorphisms for the modulation of LMP1 signaling activity and demonstrated that several groups of LMP1 variants, through distinct mutational paths, mediated enhanced NF-κB activation levels compared to B95-8 LMP1.

Inhibition of latent membrane protein 1 impairs the growth and tumorigenesis of latency II Epstein-Barr virus-transformed T cells

Epstein-Barr virus (EBV) is a common human herpesvirus. Infection with EBV is associated with several human malignancies in which the virus expresses a set of latent proteins, among which is latent membrane protein 1 (LMP1). LMP1 is able to transform numerous cell types and is considered the main oncogenic protein of EBV. The mechanism of action is based on mimicry of activated members of the tumor necrosis factor (TNF) receptor superfamily, through the ability of LMP1 to bind similar adapters and to activate signaling pathways. We previously generated two unique models: a monocytic cell line and a lymphocytic (NC5) cell line immortalized by EBV that expresses the type II latency program. Here we generated LMP1 dominant negative forms (DNs), based on fusion between green fluorescent protein (GFP) and transformation effector site 1 (TES1) or TES2 of LMP1. Then we generated cell lines conditionally expressing these DNs. These DNs inhibit NF-κB and Akt pathways, resulting in the impairment of survival processes and increased apoptosis in these cell lines. This proapoptotic effect is due to reduced interaction of LMP1 with specific adapters and the recruitment of these adapters to DNs, which enable the generation of an apoptotic complex involving TRADD, FADD, and caspase 8. Similar results were obtained with cell lines displaying a latency III program in which LMP1-DNs decrease cell viability. Finally, we prove that synthetic peptides display similar inhibitory effects in EBV-infected cells. DNs derived from LMP1 could be used to develop therapeutic approaches for malignant diseases associated with EBV.

Recent Advances on the Possible Neuroprotective Activities of Epstein-Barr Virus Oncogene BARF1 Protein in Chronic Inflammatory Disorders of Central Nervous System

Multiple sclerosis and neurodegenerative diseases in which cells of the central nervous system (CNS) are lost or damaged are rapidly increasing in frequency, and there is neither effective treatment nor cure to impede or arrest their destructive course. The Epstein-Barr virus is a human gamma-herpesvirus that infects more than 90% of the human population worldwide and persisting for the lifetime of the host. It is associated with numerous epithelial cancers, principally undifferentiated nasopharyngeal carcinoma and gastric carcinoma. Individuals with a history of symptomatic primary EBV infection, called infectious mononucleosis, carry a moderately higher risk of developing multiple sclerosis (MS). It is not known how EBV infection potentially promotes autoimmunity and central nervous system (CNS) tissue damage in MS. Recently it has been found that EBV isolates from different geographic regions have highly conserved BARF1 epitopes. BARF1 protein has the neuroprotective and mitogenic activity, thus may be useful to combat and overcome neurodegenerative disease. BARF1 protein therapy can potentially be used to enhance the neuroprotective activities by combinational treatment with anti-inflammatory antagonists and neuroprotectors in neural disorders.

Canonical NF-kappaB activation is essential for Epstein-Barr virus latent membrane protein 1 TES2/CTAR2 gene regulation

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) transforms rodent fibroblasts and is expressed in most EBV-associated malignancies. LMP1 (transformation effector site 2 [TES2]/C-terminal activation region 2 [CTAR2]) activates NF-κB, p38, Jun N-terminal protein kinase (JNK), extracellular signal-regulated kinase (ERK), and interferon regulatory factor 7 (IRF7) pathways. We have investigated LMP1 TES2 genome-wide RNA effects at 4 time points after LMP1 TES2 expression in HEK-293 cells. By using a false discovery rate (FDR) of <0.001 after correction for multiple hypotheses, LMP1 TES2 caused >2-fold changes in 1,916 mRNAs; 1,479 RNAs were upregulated and 437 were downregulated. In contrast to tumor necrosis factor alpha (TNF-α) stimulation, which transiently upregulates many target genes, LMP1 TES2 maintained most RNA effects through the time course, despite robust and sustained induction of negative feedback regulators, such as IκBα and A20. LMP1 TES2-regulated RNAs encode many NF-κB signaling proteins and secondary interacting proteins. Consequently, many LMP1 TES2-regulated RNAs encode proteins that form an extensive interactome. Gene set enrichment analyses found LMP1 TES2-upregulated genes to be significantly enriched for pathways in cancer, B- and T-cell receptor signaling, and Toll-like receptor signaling. Surprisingly, LMP1 TES2 and IκBα superrepressor coexpression decreased LMP1 TES2 RNA effects to only 5 RNAs, with FDRs of <0.001-fold and >2-fold changes. Thus, canonical NF-κB activation is critical for almost all LMP1 TES2 RNA effects in HEK-293 cells and a more significant therapeutic target than previously appreciated.

Malignancy after renal transplantation: the role of immunosuppression

Outcomes of kidney transplantation, in terms of graft and patient survival, have improved over the past few decades, partly as a result of the introduction of new immunosuppressive drugs. Many immunosuppressive agents are associated with an increased risk of cardiovascular events and an increased risk of cancer, however, which can compromise patient survival. Cancer is more common among solid-organ transplant recipients than it is in the general population or in patients on dialysis. In fact, malignancy is the third most common cause of death in renal transplant recipients. Immunosuppressive treatments used in renal transplant recipients can cause malignancy by supporting oncogenesis caused by certain viruses or by impairing immune surveillance thereby enabling faster tumor growth. In this Review, we describe the epidemiological and clinical characteristics of common tumor types occurring after kidney transplantation, and the etiopathogenetic factors that lead to their appearance, with a particular focus on the relationship between immunosuppressive treatment and malignancy. Immunosuppressive drugs associated with an increased risk of malignancy after transplantation are also discussed, as are immunosuppressive drugs that seem to have antioncogenic properties.

EBV-encoded LMP1 increases nuclear β-catenin accumulation and its transcriptional activity in nasopharyngeal carcinoma

This paper aimed to study whether Epstein-Barr virus-encoded latent membrane protein 1 (LMP1) regulates β-catenin signaling pathway in nasopharyngeal carcinoma (NPC). Western blotting, immunofluorescence, luciferase reporter assay, co-immunoprecipitation assay, and immunohistochemistry staining were used. LMP1 increased β-catenin transcriptional activity in NPC cell lines. The upregulation of β-catenin transcriptional activity induced by LMP1 was much higher in poorly differentiated NPC cell line CNE2 than that in well-differentiated NPC cell line CNE1. Immunofluorescence staining and Western blotting also showed that LMP1 increased nuclear β-catenin accumulation in NPC cell lines. Moreover, LMP1 expression was closely related to abnormal β-catenin expression in NPC tissues by immunohistochemistry. LMP1 may be involved in nasopharyngeal carcinogenesis via β-catenin signaling pathway.

Epstein-Barr virus LMP1 activates EGFR, STAT3, and ERK through effects on PKCdelta

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus that infects more than 90% of the world's adult population and is linked to multiple malignancies, including Burkitt lymphoma, Hodgkin disease, and nasopharyngeal carcinoma (NPC). The EBV oncoprotein LMP1 induces transcription of the epidermal growth factor receptor (EGFR), which is expressed at high levels in NPC. EGFR transcription is induced by LMP1 through a p50 NFκB1-Bcl-3 complex, and Bcl-3 is induced by LMP1-mediated activation of STAT3. This study reveals that LMP1, through its carboxyl-terminal activation domain 1 (LMP1-CTAR1), activates both STAT3 and EGFR in a serum-independent manner with constitutive serine phosphorylation of STAT3. Upon treatment with EGF, the LMP1-CTAR1-induced EGFR was additionally phosphorylated and STAT3 became phosphorylated on tyrosine, concomitant with upregulation of a subset of STAT3 target genes. The kinase responsible for LMP1-CTAR1-mediated serine phosphorylation of STAT3 was identified to be PKCδ using specific RNAi, a dominant negative PKCδ, and the PKCδ inhibitor rottlerin. Interestingly, inhibition of PKCδ also inhibited constitutive phosphorylation of EGFR and LMP1-CTAR1-induced phosphorylation of ERK. Inhibition of PKCδ blocked LMP1-CTAR1-mediated transformation of Rat-1 cells, likely through the inhibition of ERK activation. These findings indicate that LMP1 activates multiple distinct signaling pathways and suggest that PKCδ functions as a master regulator of EGFR, STAT3, and ERK activation by LMP1-CTAR1.

Differential B-lymphocyte regulation by CD40 and its viral mimic, latent membrane protein 1

CD40 plays a vital role in humoral immunity, via its potent and multifaceted function as an activating receptor of various immune cells, most notably B lymphocytes. The Epstein-Barr virus-encoded transforming protein latent membrane protein 1 (LMP1) serves as a functional mimic of CD40 signals to B cells but lacks key regulatory controls that restrain CD40 signaling. This allows LMP1 to activate B cells in an abnormal manner that can contribute to the pathogenesis of human B-cell lymphoma and autoimmune disease. This review focuses upon a comparative analysis of CD40 versus LMP1 functions and mechanisms of action in B lymphocytes, discussing how this comparison can provide valuable information on both how CD40 signaling is normally regulated and how LMP1 disrupts the normal CD40 pathways, which can provide information of value to therapeutic design.

Epstein-Barr latent membrane protein 1 transformation site 2 activates NF-kappaB in the absence of NF-kappaB essential modifier residues 133-224 or 373-419

Epstein Barr virus latent membrane protein 1 (LMP1) induces NF-κB activation through transformation effector sites (TES) 1 and 2, both of which are critical for B-lymphocyte transformation. TES2 principally activates canonical NF-κB, which we confirm is NF-κB essential modifier (NEMO)-dependent and requires an intact ubiquitin binding in A20 binding inhibitor of NF-κB and NEMO (UBAN) domain. LMP1 TES2 activated NF-κB in Jurkat cell lines harboring NEMO truncated at 372 (A45) or NEMO with an in-frame deletion of 133-224 (2C), whereas TNFα, 12-O-Tetradecanoylphorbol-13-acetate, human T-cell leukemia virus 1 Tax, and CD40 did not. In both A45 and 2C Jurkat cell lines, LMP1 TES2-mediated NF-κB activation was blocked by siRNAs to TNFα receptor-associated factor 6 and NEMO, by IκB kinase inhibitors, and by the IκBα superrepressor, indicating that the NEMO mutants function to support canonical NF-κB activation. Expression of A45 or 2C mutants in NEMO-deficient murine embryonic fibroblasts reproduced the Jurkat phenotypes: LMP1 TES2 activated NF-κB in fibroblasts lacking NEMO amino acids 133-224 or 373-419, but TNFα and Tax did not. Further analysis indicated that TES2 did not activate NF-κB in cells expressing the double deletion mutant Δ133-224/Δ372-419. These data provide further evidence of the essential role for NEMO in LMP1 TES2 NF-κB activation and highlight the importance of unique domains within NEMO for sensing distinct NF-κB stimuli.

Viral latency and its regulation: lessons from the gamma-herpesviruses

Latency is a state of cryptic viral infection associated with genomic persistence and highly restricted gene expression. Its hallmark is reversibility: under appropriate circumstances, expression of the entire viral genome can be induced, resulting in the production of infectious progeny. Among the small number of virus families capable of authentic latency, the herpesviruses stand out for their ability to produce such infections in every infected individual and for being completely dependent upon latency as a mode of persistence. Here, we review the molecular basis of latency, with special attention to the gamma-herpesviruses, in which the understanding of this process is most advanced.

Dual functions of interferon regulatory factors 7C in Epstein-Barr virus-mediated transformation of human B lymphocytes

Epstein-Barr virus (EBV) infection is associated with several human malignancies. Interferon (IFN) regulatory factor 7 (IRF-7) has several splicing variants, and at least the major splicing variant (IRF-7A) has oncogenic potential and is associated with EBV transformation processes. IRF-7C is an alternative splicing variant with only the DNA-binding domain of IRF-7. Whether IRF-7C is present under physiological conditions and its functions in viral transformation are unknown. In this report, we prove the existence of IRF-7C protein and RNA in certain cells under physiological conditions, and find that high levels of IRF-7C are associated with EBV transformation of human primary B cells in vitro as well as EBV type III latency. EBV latent membrane protein 1 (LMP-1) stimulates IRF-7C expression in B lymphocytes. IRF-7C has oncogenic potential in rodent cells and partially restores the growth properties of EBV-transformed cells under a growth-inhibition condition. A tumor array experiment has identified six primary tumor specimens with high levels of IRF-7C protein—all of them are lymphomas. Furthermore, we show that the expression of IRF-7C is apparently closely associated with other IRF-7 splicing variants. IRF-7C inhibits the function of IRF-7 in transcriptional regulation of IFN genes. These data suggest that EBV may use splicing variants of IRF-7 for its transformation process in two strategies: to use oncogenic properties of various IRF-7 splicing variants, but use one of its splicing variants (IRF-7C) to block the IFN-induction function of IRF-7 that is detrimental for viral transformation. The work provides a novel relation of host/virus interactions, and has expanded our knowledge about IRFs in EBV transformation.

EBV and HIV-Related Lymphoma

HIV-associated lymphoproliferative disorders represent a heterogeneous group of diseases, arising in the presence of HIV-associated immunodeficiency. The overall prevalence of HIV-associated lymphoma is significantly higher compared to that of the general population and it continues to be relevant even after the wide availability of highly active antiretroviral therapy (HAART) (1). Moreover, they still represent one of the most frequent cause of death in HIV-infected patients. Epstein-Barr virus (EBV), a γ-Herpesviruses, is involved in human lymphomagenesis, particularly in HIV immunocompromised patients. It has been largely implicated in the development of B-cell lymphoproliferative disorders as Burkitt lymphoma (BL), Hodgkin disease (HD), systemic non Hodgkin lymphoma (NHL), primary central nervous system lymphoma (PCNSL), nasopharyngeal carcinoma (NC). Virus-associated lymphomas are becoming of significant concern for the mortality of long-lived HIV immunocompromised patients, and therefore, research of advanced strategies for AIDS-related lymphomas is an important field in cancer chemotherapy. Detailed understanding of the EBV lifecycle and related cancers at the molecular level is required for novel strategies of molecular-targeted cancer chemotherapy The linkage of HIV-related lymphoma with EBV infection of the tumor clone has several pathogenetic, prognostic and possibly therapeutic implications which are reviewed herein.

Cutaneous presentation of post-renal transplant lymphoproliferative disorder: a series of four cases

We report detailed histological and molecular characteristics of four post transplant lymphoproliferative disorders (PTLD) presenting in the skin of renal transplant patients, and their clinical outcome. Three had B-cell lymphomas (cases 1-3), and one had a T-cell lymphoma (case 4). All B-cell lymphomas showed Epstein-Barr virus (EBV) by immunohistochemistry (IHC) or in situ hybridization (ISH). Cases 1 and 2 were large cell lymphomas, and case 3 a plasmacytoma. Case 1 showed light chain restriction and heavy chain gene rearrangement by polymerase chain reaction (PCR). The patient was then diagnosed with an abdominal lymphoma and died of sepsis. Case 2 had no recoverable DNA. Case 3 had a plasmacytoma that showed monoclonal light chain restriction on IHC and an oligoclonal heavy chain rearrangement by PCR. In cases 2 and 3, the lesions regressed following reduction of immunosuppression, and died 1.5 and 8 years later from unrelated medical causes. Case 4 was a CD 30+ anaplastic large T-cell lymphoma with no EBV detected by IHC, ISH and PCR, and died of heart failure 2 years later. Cutaneous manifestations of PTLD are rare, show wide array of clinical and pathological features, and generally have a favorable prognosis. EBV appears to be associated only with B-cell cutaneous lymphomas.

Transcriptional downregulation of p27KIP1 through regulation of E2F function during LMP1-mediated transformation

LMP1 induces the phenotypic transformation of fibroblasts and affects regulators of the cell cycle during this process. LMP1 decreases expression of the cyclin-dependent kinase inhibitor p27 and increases the levels and phosphorylation of cyclin-dependent kinase 2 and the retinoblastoma protein. In the present study, the effects of LMP1 on cell cycle progression and the mechanism of p27 downregulation by LMP1 were determined. Although p27 is frequently regulated at the posttranscriptional level during cell cycle progression and in cancer, LMP1 did not decrease ectopically expressed p27. However, LMP1 did decrease p27 RNA levels and inhibited the activity of p27 promoter reporters. The LMP1-regulated promoter element was mapped to a region containing two E2F sites. Electrophoretic mobility shift assays determined that the regulated cis element bound an inhibitory E2F complex containing E2F4 and p130. These findings indicate that LMP1 decreases p27 transcription through effects on E2F family transcription factors. This property likely contributes to the ability of LMP1 to stimulate cell cycle progression.

Inhibition of tumor necrosis factor-induced phenotypes by short intracellular versions of latent membrane protein-1

Tumor necrosis factor (TNF) is a potent multi-functional cytokine with a homeostatic role in host defence. In case of deregulation, TNF is implicated in numerous pathologies. The latent membrane protein-1 (LMP1) is expressed by Epstein-Barr virus during viral latency and displaying properties of a constitutively activated member of the TNF receptor family. Both TNFR1 and LMP1 share a similar set of proximal adapters and signalling pathways although they display different biological responses. We previously demonstrated that the intracellular part of LMP1, LMP1-CT, a dominant-negative form of LMP1, inhibits LMP1 signalling. Here, we developed shorter versions derived from C-terminal part of LMP1 to investigate their roles on LMP1 and TNF signalling. We constructed several mutants of LMP1 containing a part of cytoplasmic signalling region fused to the green fluorescent protein. These mutants selectively impair signalling by LMP1 and TNF but not by IL-1beta which uses other adapters. Dominant-negative effect was due to binding and sequestration of LMP1 adapters RIP, TRAF2 and TRADD as assessed by coimmunoprecipitation experiments and confocal analysis. Expression of these mutants impairs the recruitment of these adapters by TNFR1 and TNF-associated phenotypes. These mutants did not display cytostatic properties but were able to modulate TNF-induced phenotypes, apoptosis or cell survival, depending on the cell context. Interestingly, these mutants are able to inhibit a pro-inflammatory response in endothelial cells. These data demonstrate that LMP1 derived molecules can be used to design compounds with potential therapeutic roles in diseases due to TNF overactivation.

Discerning regulation of cis- and trans-presentation of CD8+ T-cell epitopes by EBV-encoded oncogene LMP-1 through self-aggregation

Activation of the nuclear factor–κB pathway by Epstein-Barr virus–encoded latent membrane protein-1 (LMP-1) leads to an up-regulation of the major histocompatibility complex class I antigen–processing pathway. Paradoxically, LMP-1 itself induces a subdominant CD8+ T-cell response and appears to have evolved to avoid immune recognition. Here we show that, although expression of LMP-1 in human cells dramatically enhanced the trans-presentation of CD8+ T-cell epitopes, cis-presentation of LMP-1–derived epitopes was severely impaired. Testing of a series of LMP-1 mutants revealed that deletion of the first transmembrane domain of LMP-1, which prevented self-aggregation, significantly enhanced cis-presentation of T-cell epitopes from this protein, whereas it lost its ability to up-regulate trans-presentation. Interestingly, we also found that cis-presentation of LMP-1 epitopes was rescued by blocking the proteasome function. Taken together, these results delineate a novel mechanism of immune evasion, which renders a virally encoded oncogene inaccessible to the conventional major histocompatibility complex class I pathway limiting its cis-presentation to effector cells.