The truncated form of the Epstein-Barr virus latent-infection membrane protein expressed in virus replication does not transform rodent fibroblasts

Assembly and activation of EBV latent membrane protein 1

Latent membrane protein 1 (LMP1) is the primary oncoprotein of Epstein-Barr virus (EBV) and plays versatile roles in the EBV life cycle and pathogenesis. Despite decades of extensive research, the molecular basis for LMP1 folding, assembly, and activation remains unclear. Here, we report cryo-electron microscopy structures of LMP1 in two unexpected assemblies: a symmetric homodimer and a higher-order filamentous oligomer. LMP1 adopts a non-canonical and unpredicted fold that supports the formation of a stable homodimer through tight and antiparallel intermolecular packing. LMP1 dimers further assemble side-by-side into higher-order filamentous oligomers, thereby allowing the accumulation and specific organization of the flexible cytoplasmic tails for efficient recruitment of downstream factors. Super-resolution microscopy and cellular functional assays demonstrate that mutations at both dimeric and oligomeric interfaces disrupt LMP1 higher-order assembly and block multiple LMP1-mediated signaling pathways. Our research provides a framework for understanding the mechanism of LMP1 and for developing potential therapies targeting EBV-associated diseases.

(-)-Epigallocatechin-3-gallate inhibition of Epstein-Barr virus spontaneous lytic infection involves downregulation of latent membrane protein 1

The Epstein-Barr virus (EBV) lytic cycle contributes to the development of EBV-associated diseases. EBV-encoded latent membrane protein 1 (LMP1) is key to EBV lytic replication, and our previous work indicated that epigallocatechin-3-gallate (EGCG) inhibited constitutive EBV lytic infection through the suppression of LMP1-activated phosphoinositide 3-kinase/Akt and mitogen-activated protein kinase kinase/extracellular signal-related protein kinase 1/2 signaling. The present study demonstrated that LMP1 in CNE-LMP1 constructed cells significantly induced the expression of the EBV lytic proteins BZLF1 (P<0.001) and BMRF1 (P<0.05) compared with CNE1 cells. Following treatment with a specific DNAzyme that targets LMP1, significantly reduced protein expression levels of BZLF1 and BMRF1 in EBV-associated epithelial carcinoma CNE1-LMP1 cells (P<0.001 and P<0.01, respectively) and lymphoma B95.8 cells (both P<0.01) were observed. Furthermore, EGCG significantly inhibited the mRNA and protein expression levels of LMP1 (P<0.05) in an apparent dose-dependent manner in CNE1-LMP1 and B95.8 cells. Thus, the present findings indicated that the molecular mechanism underlying EGCG inhibition of EBV lytic infection involves downregulation of LMP1.

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.

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.

The tumor marker Fascin is induced by the Epstein-Barr virus-encoded oncoprotein LMP1 via NF-κB in lymphocytes and contributes to their invasive migration

Background

The actin-bundling protein Fascin (FSCN1) is a tumor marker that is highly expressed in numerous types of cancer including lymphomas and is important for migration and metastasis of tumor cells. Fascin has also been detected in B lymphocytes that are freshly-infected with Epstein-Barr virus (EBV), however, both the inducers and the mechanisms of Fascin upregulation are still unclear.

Results

Here we show that the EBV-encoded oncoprotein latent membrane protein 1 (LMP1), a potent regulator of cellular signaling and transformation, is sufficient to induce both Fascin mRNA and protein in lymphocytes. Fascin expression is mainly regulated by LMP1 via the C-terminal activation region 2 (CTAR2). Block of canonical NF-κB signaling using a chemical inhibitor of IκB kinase β (IKKβ) or cotransfection of a dominant-negative inhibitor of IκBα (NFKBIA) reduced not only expression of p100, a classical target of the canonical NF-κB-pathway, but also LMP1-induced Fascin expression. Furthermore, chemical inhibition of IKKβ reduced both Fascin mRNA and protein levels in EBV-transformed lymphoblastoid cell lines, indicating that canonical NF-κB signaling is required for LMP1-mediated regulation of Fascin both in transfected and transformed lymphocytes. Beyond that, chemical inhibition of IKKβ significantly reduced invasive migration of EBV-transformed lymphoblastoid cells through extracellular matrix. Transient transfection experiments revealed that Fascin contributed to LMP1-mediated enhancement of invasive migration through extracellular matrix. While LMP1 enhanced the number of invaded cells, functional knockdown of Fascin by two different small hairpin RNAs resulted in significant reduction of invaded, non-attached cells.

Conclusions

Thus, our data show that LMP1-mediated upregulation of Fascin depends on NF-κB and both NF-κB and Fascin contribute to invasive migration of LMP1-expressing lymphocytes.

Latent membrane protein 1 is dispensable for Epstein-Barr virus replication in human embryonic kidney 293 cells

Epstein Barr Virus (EBV) replicates in oral epithelial cells and gains entry to B-lymphocytes. In B-lymphocytes, EBV expresses a restricted subset of genes, the Latency III program, which converts B-lymphocytes to proliferating lymphoblasts. Latent Membrane Protein 1 (LMP1) and the other Latency III associated proteins are also expressed during virus replication. LMP1 is essential for virus replication and egress from Akata Burkitt Lymphoma cells, but a role in epithelial cell replication has not been established. Therefore, we have investigated whether LMP1 enhances EBV replication and egress from HEK293 cells, a model epithelial cell line used for EBV recombinant molecular genetics. We compared wild type (wt) and LMP1-deleted (LMP1Δ) EBV bacterial artificial chromosome (BAC) based virus replication and egress from HEK293. Following EBV immediate early Zta protein induction of EBV replication in HEK293 cells, similar levels of EBV proteins were expressed in wt- and LMP1Δ-infected HEK293 cells. LMP1 deletion did not impair EBV replication associated DNA replication, DNA encapsidation, or mature virus release. Indeed, virus from LMP1Δ-infected HEK293 cells was as infectious as EBV from wt EBV infected HEK cells. Trans-complementation with LMP1 reduced Rta expression and subsequent virus production. These data indicate that LMP1 is not required for EBV replication and egress from HEK293 cells.

Identification of a sub-population of B cells that proliferates after infection with Epstein-Barr virus

Background

Epstein-Barr virus (EBV)-driven B cell proliferation is critical to its subsequent persistence in the host and is a key event in the development of EBV-associated B cell diseases. Thus, inquiry into early cellular events that precede EBV-driven proliferation of B cells is essential for understanding the processes that can lead to EBV-associated B cell diseases.

Methods

Infection with high titers of EBV of mixed, primary B cells in different stages of differentiation occurs during primary EBV infection and in the setting of T cell-immunocompromise that predisposes to development of EBV-lymphoproliferative diseases. Using an ex vivo system that recapitulates these conditions of infection, we correlated expression of selected B cell-surface markers and intracellular cytokines with expression of EBV latency genes and cell proliferation.

Results

We identified CD23, CD58, and IL6, as molecules expressed at early times after EBV-infection. EBV differentially infected B cells into two distinct sub-populations of latently infected CD23⁺ cells: one fraction, marked as CD23^hiCD58⁺IL6^- by day 3, subsequently proliferated; another fraction, marked as CD23^loCD58⁺, expressed IL6, a B cell growth factor, but failed to proliferate. High levels of LMP1, a critical viral oncoprotein, were expressed in individual CD23^hiCD58⁺ and CD23^loCD58⁺ cells, demonstrating that reduced levels of LMP1 did not explain the lack of proliferation of CD23^loCD58⁺ cells. Differentiation stage of B cells did not appear to govern this dichotomy in outcome either. Memory or naïve B cells did not exclusively give rise to either CD23^hi or IL6-expressing cells; rather memory B cells gave rise to both sub-populations of cells.

Conclusions

B cells are differentially susceptible to EBV-mediated proliferation despite expression of viral gene products known to be critical for continuous B cell growth. Cellular events, in addition to viral gene expression, likely play a critical role in determining the outcome of EBV infection. By indentifying cells predicted to undergo EBV-mediated proliferation, our study provides new avenues of investigation into EBV pathogenesis.

Viral oncogenes, noncoding RNAs, and RNA splicing in human tumor viruses

Viral oncogenes are responsible for oncogenesis resulting from persistent virus infection. Although different human tumor viruses express different viral oncogenes and induce different tumors, their oncoproteins often target similar sets of cellular tumor suppressors or signal pathways to immortalize and/or transform infected cells. Expression of the viral E6 and E7 oncogenes in papillomavirus, E1A and E1B oncogenes in adenovirus, large T and small t antigen in polyomavirus, and Tax oncogene in HTLV-1 are regulated by alternative RNA splicing. However, this regulation is only partially understood. DNA tumor viruses also encode noncoding RNAs, including viral microRNAs, that disturb normal cell functions. Among the determined viral microRNA precursors, EBV encodes 25 from two major clusters (BART and BHRF1), KSHV encodes 12 from a latent region, human polyomavirus MCV produce only one microRNA from the late region antisense to early transcripts, but HPVs appears to produce no viral microRNAs.

Epstein-Barr virus-encoded LMP1 regulates epithelial cell motility and invasion via the ERK-MAPK pathway

The Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) is an oncogenic protein which has previously been shown to engage the NF-kappaB, stress-activated MAP kinase, phosphatidylinositol 3-kinase (PI 3-kinase), and extracellular-regulated kinase (ERK)-MAPK pathways. In this study, we demonstrate that LMP1 activates ERK-MAPK in epithelial cells via the canonical Raf-MEK-ERK-MAPK pathway but in a Ras-independent manner. In agreement with the results of a previous study (B. A. Mainou, D. N. Everly, Jr., and N. Raab-Traub, J. Virol. 81:9680-9692, 2007), we show that the ability of LMP1 to activate ERK-MAPK mapped to its CTAR1 domain, the TRAF binding domain previously implicated in PI 3-kinase activation. A role for ERK-MAPK in LMP1-induced epithelial cell motility was identified, as LMP1-expressing cells displayed increased rates of haptotactic migration compared to those of LMP1-negative cells. These data implicate the ERK-MAPK pathway in LMP1-induced effects associated with transformation, suggesting that this pathway may contribute to the oncogenicity of LMP1 through its ability to promote cell motility and to enhance the invasive properties of epithelial cells.

LMP1 TRAFficking Activates Growth and Survival pathways

Epstein-Barr Virus (EBV) Latent Infection Membrane Protein 1 (LMP1) is expressed in all the EBV related malignancies. LMP1 expression is critical for transformation of human B-cells by EBV. LMP1 expression in human B cells induces activation and adhesion molecule expression and cell dumping, which are characteristic of CD40 activated B lymphocytes. In immortalized fibroblasts, LMP1 mimics aspects of activated ras in enabling serum, contact, and anchorage independent growth. Reverse genetic analyses implicate six transmembrane domains (TM), TM1-6, and two C-terminal cytosolic domains, transformation effector sites 1 and 2 (TES1 and 2) or C-terminal activation regions 1 and 2 (CTAR1 and 2) as the essential domains for LMP1 effects. The 6 transmembrane domains cause intermolecular interaction, whereas the C-terminal domains signal through tumor necrosis factor receptor (TNFR) associated factors (TRAFs) or TNFR associated death domain proteins (TRADD) and activate NF-kappaB, JNK, and p38. LMP1 TES1/CTAR1 directly recruits TRAFs 1, 2, 3 and 5 whereas LMP1 TES2/CTAR2 indirectly recruits TRAF6 via BS69. LMP1 TES1/CTAR1 activates TRAF2, NIK, IKKalpha and p52 mediated noncanonical NF-KB pathway and LMP1 TES2/CTAR2 activates TRAF6, TAB1, TAK1, IKKalpha/ IKKbeta/ IKKgamma mediated canonical NF-KB pathway. Interestingly, TRAF3 is a negative regulator of noncanonical NF-kappaB activation, although a positive role in LMP1 signaling has also been described. LMP1 mediated JNK activation is predominantly TES2/CTAR2 dependent and requires TRAF6. LMP1 specifically increases TRAF3 partitioning into lipid rafts and interestingly does not induce degradation of any of the TRAFs upon NF-kappaB activation. Studies of the chemistry and biology of LMP1-TRAF interaction mediated activation of signaling pathways are important for controlling EBV infected cell survival and growth.

Epstein-barr virus latent membrane protein 2B (LMP2B) modulates LMP2A activity

Latent membrane protein 2A (LMP2A) and LMP2B are viral proteins expressed during Epstein-Barr virus (EBV) latency in EBV-infected B cells both in cell culture and in vivo. LMP2A has important roles in modulating B-cell receptor (BCR) signal transduction by associating with the cellular tyrosine kinases Lyn and Syk via specific phosphotyrosine motifs found within the LMP2A N-terminal tail domain. LMP2A has been shown to alter normal BCR signal transduction in B cells by reducing levels of Lyn and by blocking tyrosine phosphorylation and calcium mobilization following BCR cross-linking. Although little is currently known about the function of LMP2B in B cells, the similarity in structure between LMP2A and LMP2B suggests that they may localize to the same cellular compartments. To investigate the function of LMP2B, B-cell lines expressing LMP2A, LMP2B, LMP2A/LMP2B, and the relevant vector controls were analyzed. As was previously shown, cells expressing LMP2A had a dramatic block in normal BCR signal transduction as measured by calcium mobilization and tyrosine phosphorylation. There was no effect on BCR signal transduction in cells expressing LMP2B. Interestingly, when LMP2B was expressed in conjunction with LMP2A, there was a restoration of normal BCR signal transduction upon BCR cross-linking. The expression of LMP2B did not alter the cellular localization of LMP2A but did bind to and prevent the phosphorylation of LMP2A. A restoration of Lyn levels, but not a change in LMP2A levels, was also observed in cells coexpressing LMP2B with LMP2A. From these results, we conclude that LMP2B modulates LMP2A activity.

Oncogenic activity of Epstein-Barr virus latent membrane protein 1 (LMP-1) is down-regulated by lytic LMP-1

The Epstein-Barr virus (EBV) is an oncogenic human herpesvirus. EBV latent membrane protein 1 (LMP-1) is a viral oncogene that manifests its oncogenic phenotype through activation of cellular signaling pathways involved in cell growth, survival, differentiation, and transformation. Lytic LMP-1 (lyLMP-1) is a related EBV gene without oncogenic properties. The lyLMP-1 gene is found in 60% of the EBV strains circulating in nature, but it is not found in EBV strains associated with nasopharyngeal carcinoma. We recently demonstrated that lyLMP-1 down-regulates the half-life of LMP-1 in epithelial cells. Therefore in this study, we tested the hypothesis that lyLMP-1 concomitantly down-regulates LMP-1 oncogenic activity. The results demonstrated that lyLMP-1 inhibits LMP-1-mediated intracellular signaling activation, epithelial cell growth and survival, and fibroblast cell transformation in a dose-dependent manner. Lytic LMP-1 manifested this effect through the promotion of LMP-1 degradation and a reduction in the expressed quantity of LMP-1. Thus, lyLMP-1 functions as a posttranslational negative regulator of LMP-1 oncogenesis. These results support a model of EBV-associated epithelial oncogenesis in which lyLMP-1 may act in vivo to reduce the risk of LMP-1-mediated transformation and is therefore subjected to negative selection in nasopharyngeal carcinoma pathogenesis.

Regulation of intracellular signalling by the terminal membrane proteins of members of the Gammaherpesvirinae

The human gamma(1)-herpesvirus Epstein-Barr virus (EBV) and the gamma(2)-herpesviruses Kaposi's sarcoma-associated herpesvirus (KSHV), rhesus rhadinovirus (RRV), herpesvirus saimiri (HVS) and herpesvirus ateles (HVA) all contain genes located adjacent to the terminal-repeat region of their genomes, encoding membrane proteins involved in signal transduction. Designated 'terminal membrane proteins' (TMPs) because of their localization in the viral genome, they interact with a variety of cellular signalling molecules, such as non-receptor protein tyrosine kinases, tumour-necrosis factor receptor-associated factors, Ras and Janus kinase (JAK), thereby initiating further downstream signalling cascades, such as the MAPK, PI3K/Akt, NF-kappaB and JAK/STAT pathways. In the case of TMPs expressed during latent persistence of EBV and HVS (LMP1, LMP2A, Stp and Tip), their modulation of intracellular signalling pathways has been linked to the provision of survival signals to latently infected cells and, hence, a contribution to occasional cellular transformation. In contrast, activation of similar pathways by TMPs of KSHV (K1 and K15) and RRV (R1), expressed during lytic replication, may extend the lifespan of virus-producing cells, alter their migration and/or modulate antiviral immune responses. Whether R1 and K1 contribute to the oncogenic properties of KSHV and RRV has not been established satisfactorily, despite their transforming qualities in experimental settings.

Epstein-Barr virus transforming protein LMP1 plays a critical role in virus production

The Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1), which is critical for EBV-induced B-cell transformation, is also abundantly expressed during the lytic cycle of viral replication. However, the biological significance of this strong LMP1 induction remains unknown. We engineered a bacterial artificial chromosome clone containing the entire genome of Akata strain EBV to specifically disrupt the LMP1 gene. Akata cell clones harboring the episomes of LMP1-deleted EBV were established, and the effect of LMP1 loss on virus production was investigated. We found that the degree of viral DNA amplification and the expression levels of viral late gene products were unaffected by LMP1 loss, demonstrating that the LMP1-deleted EBV entered the lytic replication cycle as efficiently as the wild-type counterpart. This was confirmed by our electron microscopic observation that nucleocapsid formation inside nuclei occurred even in the absence of LMP1. By contrast, loss of LMP1 severely impaired virus release into culture supernatants, resulting in poor infection efficiency. The expression of truncated LMP1 in Akata cells harboring LMP1-deleted EBV rescued the virus release into the culture supernatant and the infectivity, and full-length LMP1 partially rescued the infectivity. These results indicate that inducible expression of LMP1 during the viral lytic cycle plays a critical role in virus production.

Interferon regulatory factor 7 is associated with Epstein-Barr virus-transformed central nervous system lymphoma and has oncogenic properties

Interferon regulatory factor 7 (IRF-7) is implicated in the regulation of Epstein-Barr virus (EBV) latency. EBV transforms primary B cells, and the major EBV oncoprotein, latent membrane protein 1 (LMP-1), is required for the process. LMP-1 both induces the expression of IRF-7 and activates the IRF-7 protein by phosphorylation and nuclear translocation. Here we report that the expression of IRF-7 is increased in EBV-immortalized B lymphocytes compared with that in primary B cells. IRF-7 was phosphorylated and predominantly localized in the nucleus in the immortalized cells. The expression of IRF-7 was detected in 19 of 27 specimens of primary lymphomas of the human central nervous system by immunohistochemical analysis. The association between LMP-1 and IRF-7 was statistically highly significant for these specimens. An appreciable amount of the IRF-7 expressed in lymphoma cells was localized in the nucleus. Furthermore, IRF-7 promoted the anchorage-independent growth of NIH 3T3 cells. LMP-1 and IRF-7 showed additive effects on the growth transformation of NIH 3T3 cells. IRF-7-expressing NIH 3T3 cells formed tumors in athymic mice. Thus, IRF-7 has oncogenic properties and, along with LMP-1, may mediate or potentiate the EBV transformation process in the pathogenesis of EBV-associated lymphomas.

Epstein-Barr virus latent membrane protein 1 (LMP-1) half-life in epithelial cells is down-regulated by lytic LMP-1

This study examined the effect of naturally occurring Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1) gene sequence variation on the LMP-1 half-life in epithelial cells. The LMP-1 half-life was not influenced by sequence variation in amino acids 250 to 307 or amino acids 343 to 352. The LMP-1 half-life was short when the amino acid encoded at position 129 was methionine, the initiation codon product of lytic LMP-1 (lyLMP-1). The mutation of amino acid 129 to isoleucine greatly increased the LMP-1 half-life. Expression of lyLMP-1 in trans down-regulated the LMP-1 half-life in a dose-dependent manner and restored a short-half-life phenotype to the mutated LMP-1 construct lacking the cis ability to express lyLMP-1. This observed dominant negative effect of lyLMP-1 expression on the LMP-1 half-life in epithelial cells in vitro may have implications for EBV epithelial oncogenesis in vivo.

Construction and characterization of monoclonal antibodies specific to Epstein-Barr virus latent membrane protein 1

Epstein-Barr virus (EBV) has been implicated in the development of many human neoplasias including B lymphomas and nasopharyngeal carcinoma (NPC). The EBV latent membrane protein 1 (LMP-1) has been found to participate in diverse cellular signaling pathways and is essential for virus-induced B-cell immortalization. In order to determine quantitatively the amount of LMP-1 in cells, five monoclonal antibodies (Mabs) specific to LMP-1 were generated. The epitopes recognized by these Mabs were found to cluster within the repeat region between the CTAR1 and CTAR2 domains, corresponding to amino acid positions 254-319 of LMP-1. These Mabs were capable of recognizing LMP-1 proteins of both lymphoid and epithelial origin as revealed by immunoblot, enzyme-linked immunosorbent assay (ELISA) and immunocytofluorescence analysis. A sandwich ELISA for the quantification of LMP-1 has been established using these Mabs. Taken together, our results indicate that the Mabs generated in this study are suitable for the detection of LMP-1 in biomedical research.

Epstein-Barr Virus and Breast Cancer: State of the Evidence for Viral Carcinogenesis

As the etiology and progression of breast cancer remain incompletely understood, novel routes of disease pathogenesis are important to consider. Viral pathogens have not been much explored, but recent interest has focused on Epstein-Barr virus (EBV). Studies of an association of this ubiquitous herpesvirus with breast cancer have had notably inconsistent results, marked by varying EBV presence (from 0% to 50% of tumors) and the absence of certain viral characteristics found in other EBV-related malignancies. The research has been plagued by the technical challenges of localizing EBV to tumor cells and by a tendency to overlook epidemiological cofactors, shown in all other EBV-related cancers to impact the EBV association. Breast cancer studies to date have used several viral detection methods of varying or uncertain sensitivity and specificity; most have involved small and/or poorly characterized case series and paid insufficient attention to epidemiological cofactors relevant to breast cancer and to EBV-related malignancies. Given these limitations and the established complexity of the connection of EBV with other cancers, a definitive judgment regarding the presence of this virus in breast cancer cannot yet be rendered. Recent advances in laboratory methodologies should help overcome the challenges of EBV detection in breast cancers. Further research is warranted, given the potential for an EBV association to inform not only breast cancer etiology but also early detection, treatment, and prevention.

Latent infection membrane protein transmembrane FWLY is critical for intermolecular interaction, raft localization, and signaling

Relatively little is known about the biochemical mechanisms through which the Epstein-Barr virus latent infection integral membrane protein 1 (LMP1) transmembrane domains cause constitutive LMP1 aggregation and continuous cytoplasmic C terminus-mediated signal transduction. We now evaluate the role of the three consecutive LMP1 hydrophobic transmembrane pairs, transmembrane domains (TM)1-2, TM3-4, and TM5-6, in intermolecular aggregation and NF-kappaB activation. LMP1TM1-2 enabled approximately 40% of wild-type LMP1 cytoplasmic domain-mediated NF-kappaB activation, whereas TM3-4 or TM5-6 assayed in parallel had almost no effect independent of LMP1TM1-2. Alanine mutagenesis of conserved residues in LMP1TM1-2 identified FWLY(38-41) to be critical for LMP1TM1-2 intermolecular association with LMP1TM3-6. Further, in contrast to wild-type LMP1, LMP1 with FWLY(38-41) mutated to AALA(38-41) did not (i). significantly partition to lipid Rafts or Barges and effectively intermolecularly associate, (ii). enable cytoplasmic C terminus engagement of tumor necrosis factor receptor-associated factor 3, (iii). activate NF-kappaB, and thereby (iv). induce tumor necrosis factor receptor-associated factor 1 expression. Other LMP1 intermolecular associations were observed that involved LMP1TM1-2/LMP1TM1-2 or LMP1TM3-4/LMP1TM3-6 interactions; these probably also contribute to LMP1 aggregation. Because FWLY(38-41) was essential for LMP1-mediated signal transduction, and LMP1 activation of NF-kappaB is essential for proliferating B lymphocyte survival, inhibition of LMP1FWLY(41)-mediated LMP1/LMP1 intermolecular interactions is an attractive therapeutic target.

Epstein-Barr virus latent membrane protein 1 activation of NF-kappaB through IRAK1 and TRAF6

Epstein-Barr virus latent membrane protein 1 (LMP1) activation of NF-kappaB is critical for Epstein-Barr virus-infected B lymphocyte survival. LMP1 activates the IkappaB kinase complex and NF-kappaB through two cytoplasmic signaling domains that engage tumor necrosis factor receptor-associated factor (TRAF)1/2/3/5 or TRADD and RIP. We now use cells lacking expression of TRAF2, TRAF5, TRAF6, IKKalpha, IKKbeta, IKKgamma, TAB2, IL-1 receptor-associated kinase (IRAK)1, or IRAK4 to assess their roles in LMP1-mediated NF-kappaB activation. LMP1-induced RelA nuclear translocation was similar in IKKalpha knockout (KO) and WT murine embryo fibroblasts (MEFs) but substantially deficient in IKKbeta KO MEFs. NF-kappaB-dependent promoter responses were also substantially deficient in IKKbeta KO MEFs but were hyperactive in IKKalpha KO MEFs. More surprisingly, NF-kappaB responses were near normal in TRAF2 and TRAF5 double-KO MEFs, IKKgamma KO MEFs, TAB2 KO MEFs, and IRAK4 KO MEFs but were highly deficient in TRAF6 KO MEFs and IRAK1 KO HEK293 cells. Consistent with the importance of TRAF6, LMP1-induced NF-kappaB activation in HEK293 cells was inhibited by expression of dominant-negative TAB2 and Ubc13 alleles. These data extend a role for IKKalpha in IKKbeta regulation, identify an unusual IKKbeta-dependent and IKKgamma-independent NF-kappaB activation, and indicate that IRAK1 and TRAF6 are essential for LMP1-induced NF-kappaB activation.

Epstein-Barr virus latent membrane protein-1 (LMP-1) and lytic LMP-1 localization in plasma membrane-derived extracellular vesicles and intracellular virions

Epstein-Barr virus (EBV) is a human herpesvirus associated with a number of malignancies. EBV establishes a latent infection in human B cells in vitro, and infected lymphoblastoid cells proliferate indefinitely as a result of virus activation of cellular signalling pathways. Latently infected cells express a viral oncoprotein called the latent membrane protein-1 (LMP-1). LMP-1 signals both proliferative and survival signals to the infected B cell. The switch from latency to lytic replication is associated with upregulation of an N-terminally truncated LMP-1, called lytic LMP-1 (lyLMP-1). To understand better the relationship between LMP-1 protein function and the virus life cycle, LMP-1 and lyLMP-1 were precisely localized in infected B cells. Immunoelectron microscopy of latently infected cells revealed LMP-1 localized in discrete patches in the plasma membrane. Unexpectedly, immunogold-labelled LMP-1 was found in vesicles budding from the plasma membrane into the extracellular space and in small membrane vesicles accumulating in conditioned medium from infected cells. LyLMP-1 immunolabelling was observed only in B95-8 cells harbouring detectable intracellular virus particles and was abundant in the nuclear membrane early, and in the plasma membrane late, following lytic cycle induction. LyLMP-1 immunoreactivity was also observed at sites of virus budding and associated with intracellular virions, suggesting that lyLMP-1 might be incorporated into cytoplasmic virions when budding through the nuclear membrane.

Unexpected absence of the Epstein-Barr virus (EBV) lyLMP-1 open reading frame in tumor virus isolates: lack of correlation between Met129 status and EBV strain identity

The lytic cycle-associated lytic latent membrane protein-1 (lyLMP-1) of Epstein-Barr virus (EBV) is an amino-terminally truncated form of the oncogenic LMP-1. Although lyLMP-1 shares none of LMP-1's transforming and signal transducing activities, we recently reported that lyLMP-1 can negatively regulate LMP-1-stimulated NF-kappaB activation. The lyLMP-1 protein encoded by the B95-8 strain of EBV initiates from methionine 129 (Met129) of the LMP-1 open reading frame (ORF). The recent report that Met129 in the B95-8 LMP-1 ORF is not conserved in the Akata strain of EBV prompted us to screen a panel of EBV-positive cell lines for conservation of Met129 and lyLMP-1 expression. We found that 15 out of 16 tumor-associated virus isolates sequenced encoded an ATT or ACC codon in place of ATG in the LMP-1 ORF at position 129, and tumor cell lines harboring isolates lacking an ATG at codon 129 did not express the lyLMP-1 protein. In contrast, we found that EBV DNA from 22 out of 37 healthy seropositive donors retained the Met129 codon. Finally, the lyLMP-1 initiator occurs variably within distinct EBV strains and its presence cannot be predicted by EBV strain identity. Thus, Met129 is not peculiar to the B95-8 strain of EBV, but rather can be found in the background of several evolutionarily distinct EBV strains. Its absence from EBV isolates from tumors raises the possibility of selective pressure on Met129 in EBV-dependent tumors.

Epstein-Barr virus in gastric adenocarcinomas: association with ethnicity and CDKN2A promoter methylation

AIMS

It has been shown previously (by immunohistochemistry) that gastric adenocarcinomas harbouring Epstein-Barr virus (EBV) frequently lose p16 protein. This study aimed to examine the mechanisms of inactivation of the CDKN2A gene and correlate the results with clinicopathological features.

METHODS

Methylation specific polymerase chain reaction was used to detect CDKN2A promoter methylation in gastric adenocarcinomas from American patients. In addition, immunohistochemistry was used to detect the loss of the p16 protein and in situ hybridisation was used to detect the presence of EBV. The tumours were also analysed for the presence of microsatellite instability.

RESULTS

Eleven (10%) of 107 tumours harboured EBV in the malignant cells. In gastric cancers without EBV, 32% exhibited CDKN2A promoter methylation and 26% had p16 protein loss. In contrast, 91% of the tumours containing EBV had CDKN2A promoter methylation (p = 0.0003) and 90% showed p16 protein loss (p = 0.0001). The presence of EBV was also associated with male sex (p = 0.03) and was more common in tumours from Texas Hispanics than from non-Hispanic whites or African-Americans (p = 0.01). EBV was not associated with microsatellite instability, histological subtype, stage, or grade of the tumour, or age or survival time of the patient.

CONCLUSIONS

The presence of EBV in gastric adenocarcinomas is strongly associated with CDKN2A inactivation by promoter methylation. In addition, these findings suggest that there are ethnic differences in tumour virology and pathogenesis.

Preferential localization of the Epstein-Barr virus (EBV) oncoprotein LMP-1 to nuclei in human T cells: implications for its role in the development of EBV genome-positive T-cell lymphomas

The Epstein-Barr virus (EBV)-encoded latent membrane protein-1 (LMP-1) is thought to play a role in the EBV-induced B-cell transformation and immortalization. EBV has also been implicated in certain human T-cell lymphomas; however, the phenotypic effects of the expression of this oncoprotein in T cells are not known. To learn whether LMP-1 also induces phenotypic changes in T cells, we stably expressed it in human cell lines of T and B lineages and 25 LMP-1-expressing T-cell clones and 7 B-cell clones were examined. Our results show for the first time that, in sharp contrast to B cells, LMP-1 preferentially localizes to nuclei in T cells and does not induce the phenotypic changes in these cells that it induces in B cells, does not associate with TRAF proteins, and does not arrest the cell cycle in the G2/M phase. A computer-assisted analysis revealed that LMP-1 lacks the canonical nuclear localization signal. Our results suggest that this oncoprotein may not play the same role in the lymphomagenesis of T cells as it does in B cells.

LMP1 structure and signal transduction

The oncogenic Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) has structural features and functions reminiscent of a constitutively active TNF family receptor. LMP1 aggregates at the plasma membrane and initiates the activation of signalling pathways, such as NF- kappa B, the mitogen-activated protein kinases JNK and p38, the small GTPase Cdc42 and the JAK/STAT cascade. The constitutive engagement of these signals and the characteristic molecular interactions that regulate them provide the basis for the molecular explanation of the transforming properties of this key EBV protein.

Frequent expression of the tumor necrosis factor receptor-associated factor 1 in latent membrane protein 1-positive posttransplant lymphoproliferative disease and HIV-associated lymphomas

The tumor necrosis factor receptor-associated factor 1 (TRAF1) participates in the signal transduction of various members of the tumor necrosis factor receptor (TNFR) family, including TNFR2, CD40, CD30, and the Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1). In vitro, TRAF1 is induced by LMP1, and previous studies have suggested that expression of TRAF1 is higher in EBV-associated tumors than in their EBV-negative counterparts. To determine whether this was the case in posttransplant lymphoproliferative disease (PTLD) and related disorders, we used immunohistochemistry to analyze expression of TRAF1 in a total of 42 such lesions arising in a variety of immunosuppressive states. The specimens consisted of 22 PTLD lesions, 18 acquired immunodeficiency syndrome-associated lymphomas, including 6 primary central nervous system lymphomas, and 2 cases of Hodgkin disease. The presence of latent EBV infection was determined by EBER in situ hybridization, and expression of EBV-LMP1 was detected by immunohistochemistry. Latent EBV infection, as determined by a positive EBER signal, was detected in 36 of 42 tumors. Of the EBER-positive specimens, 30 of 36 also expressed LMP1. Twenty-four of 30 LMP1-positive tumors, including both Hodgkin disease specimens, expressed TRAF1, compared with only 3 of 12 LMP1-negative tumors. This difference was statistically significant (P <.005). These results show frequent expression of TRAF1 at the protein level in LMP1-positive PTLD and related disorders and suggest an important role for LMP1-mediated TRAF1 signaling in the pathogenesis of EBV-positive tumors arising in immunosuppressive states.

The cytoplasmic amino-terminus of the Latent Membrane Protein-1 of Epstein-Barr Virus: relationship between transmembrane orientation and effector functions of the carboxy-terminus and transmembrane domain

The Latent Membrane Protein 1 (LMP-1) protein of Epstein-Barr virus (EBV) is localized in the plasma membrane of the infected cell. LMP-1 possesses a hydrophobic membrane spanning domain, and charged, intracellular amino- and carboxy-termini. Two models have been proposed for the contribution of the amino-terminus to LMP-1's function: (i) as an effector domain, interacting with cellular proteins, or (ii) as a structural domain dictating the correct orientation of transmembrane domains and thereby positioning LMP-1's critical effector domains (i.e. the carboxy-terminus). However, no studies to date have addressed directly the structural contributions of LMP-1's cytoplasmic amino-terminus to function. This study was designed to determine if LMP-1's cytoplasmic amino-terminus (N-terminus) encodes information required solely for maintenance of proper topological orientation. We have constructed LMP-1 chimeras in which the cytoplasmic N-terminus of LMP-1 is replaced with an unrelated domain of similar size and charge, but of different primary sequence. Retention of the charged amino-terminal (N-terminal) cytoplasmic domain and first predicted transmembrane domain was required for correct transmembrane topology. The absolute primary sequence of the cytoplasmic N-terminus was not critical for LMP-1's cytoskeletal association, turnover, plasma membrane patching, oligomerization, Tumor Necrosis Factor Receptor-associated factor (TRAF) binding, NF-kappaB activation, rodent cell transformation and cytostatic activity. Furthermore, our results point to the hydrophobic transmembrane domain, independent of the cytoplasmic domains, as the primary LMP-1 domain mediating oligomerization, patching and cytoskeletal association. The cytoplasmic amino-terminus provides the structural information whereby proper transmembrane orientation is achieved.

Expression of the tumour necrosis factor receptor-associated factors 1 and 2 in Hodgkin's disease

The tumour necrosis factor receptor-associated factors (TRAFs) 1 and 2 participate in the signal transduction of various members of the tumour necrosis factor receptor (TNFR) family, including TNFR1, TNFR2, CD40, CD30, and the Epstein-Barr virus (EBV)-encoded latent membrane protein-1 (LMP1). Previous in situ hybridization studies have demonstrated TRAF1 transcripts in the malignant cells of the majority of Hodgkin's disease (HD) tumours, where the expression of TRAF1 was higher in EBV-associated tumours than in their EBV-negative counterparts. In order to determine whether TRAF1 and also TRAF2 were expressed at the protein level in HD and whether there was any relationship to EBV status, immunohistochemistry has been used to detect these proteins in a series of HD specimens. TRAF1 protein was detected more frequently in Hodgkin/Reed-Sternberg (HRS) cells from EBV-positive tumours than in their EBV-negative counterparts. This difference was statistically significant (p=0.01). In contrast, TRAF2 expression by HRS cells appeared to be independent of EBV status. Using a sequential labelling approach, co-localization of LMP1 with either TRAF1 or TRAF2 was also demonstrated in HRS cells from EBV-positive tumours.

Cytokine signaling and Epstein-Barr virus-mediated cell transformation

Epstein-Barr virus (EBV) latent infection is tightly associated with the development of lymphoid and epithelial human malignancies. The disruption of cell-growth checkpoints is mediated by a limited number of viral proteins that interfere with signal transduction mechanisms and transcription control in the infected cell. Genetic and biochemical evidence supports the notion that EBV-mediated transformation relies extensively on interference with cytokine signaling networks. This is achieved through direct modulation of cytokine receptor signaling mechanisms as well as alterations in the expression levels of various cytokines. The principal effector of these interventions is the EBV latent membrane protein 1 (LMP1) which plays a central role in the transformation process. This viral protein mimics activated receptors of the tumor necrosis factor receptor superfamily to promote cell growth and antiapoptotic mechanisms. LMP1 and other EBV latent proteins upregulate cytokines and growth factors which participate in autocrine and paracrine loops that are likely to promote cell transformation and modulate immune responses. This report will review the molecular mechanisms that underlie the disruption of cytokine signaling mechanisms in EBV-mediated transformation with a particular emphasis on the LMP1 mechanism of function.

Epstein-Barr virus latent-infection membrane proteins are palmitoylated and raft-associated: protein 1 binds to the cytoskeleton through TNF receptor cytoplasmic factors

Epstein-Barr virus encodes integral membrane proteins LMP1 and LMP2A in transformed lymphoblastoid cell lines. We now find that LMP1 associates with the cell cytoskeleton through a tumor necrosis factor receptor-associated factor-interacting domain, most likely mediated by tumor necrosis factor receptor-associated factor 3. LMP1 is palmitoylated, and the transmembrane domains associate with lipid rafts. Mutation of LMP1 cysteine-78 abrogates palmitoylation but does not affect raft association or NF-kappaB or c-Jun N-terminal kinase activation. LMP2A also associates with rafts and is palmitoylated but does not associate with the cell cytoskeleton. The associations of LMP1 and LMP2A with rafts and of LMP1 with the cell cytoskeleton are likely to effect interactions with cell proteins involved in shape, motility, signal transduction, growth, and survival.

N-terminal domain of BARF1 gene encoded by Epstein-Barr virus is essential for malignant transformation of rodent fibroblasts and activation of BCL-2

The BARF1 gene encoded by the Epstein-Barr virus induces morphological changes, loss of contact inhibition and anchorage independence in established rodent Balb/c3T3 fibroblast. BARF1 gene was also capable of inducing malignant transformation in a human Louckes B cell line. Our recent study showed that BARF1 gene had an ability to immortalize primary epithelial cells. However we do not know which region(s) of BARF1 protein is(are) responsible for inducing malignant transformation in established rodent cells. Using the deletion mutants, we now localized a malignant transforming region in N-terminal of BARF1 protein. The mutants lacking this region were unable to transform the cells in malignant state. Furthermore, we demonstrated that only the mutants containing this region rendered the cells resistant to apoptosis induced by serum deprivation. Surprisingly, the BARF1 gene was capable of activating anti-apoptotic Bcl-2 expression and this activation was due to the N-terminal transforming region. These data suggest that the cooperation of BARF1 with Bcl-2 is essential for the induction of malignant transformation.

Epstein-barr virus-associated malignancies: epidemiologic patterns and etiologic implications

Epstein-Barr virus (EBV), a ubiquitous B-lymphotrophic herpesvirus, has been found in the tumor cells of a heterogeneous group of malignancies (Burkitt's lymphoma, lymphomas associated with immunosuppression, other non-Hodgkin's lymphomas, Hodgkin's disease, nasopharyngeal carcinoma, gastric adenocarcinoma, lymphoepithelioma-like carcinomas, and immunodeficiency-related leiomyosarcoma). As the epidemiologic characteristics of these cancers have not been considered together, this review seeks to relate their incidence patterns and risk factors to EBV biology and virus-host interaction in an attempt to help elucidate factors involved in EBV-related carcinogenesis. We include a brief review of EBV virology and primary infection to provide a biologic context for considering the epidemiology, summarize the most salient epidemiologic features of each malignancy, synthesize epidemiologic data by risk factor to uncover commonalities and informative contrasts across the diseases, and propose hypotheses regarding etiologic mechanisms, based on the possible effect of the risk factors at various stages in the viral life cycle.

The late lytic LMP-1 protein of Epstein-Barr virus can negatively regulate LMP-1 signaling

The BNLF-1 open reading frame of Epstein-Barr virus (EBV) encodes two related proteins, latent membrane protein-1 (LMP-1) and lytic LMP-1 (lyLMP-1). LMP-1 is a latent protein required for immortalization of human B cells by EBV, whereas lyLMP-1 is expressed during the lytic cycle and is found in the EBV virion. We show here that, in contrast to LMP-1, lyLMP-1 is stable, with a half-life of >20 h in tetradecanoyl phorbol acetate- and butyrate-treated B95-8 cells. Although lyLMP-1 itself has negligible effects on NF-kappaB activity, it inhibits NF-kappaB activation by LMP-1 in a dose-dependent manner. The lyLMP-1 protein does not oligomerize with LMP-1, and the negative effect of lyLMP-1 on NF-kappaB activation by LMP-1 does not result from lyLMP-1-mediated disruption of LMP-1 oligomers. Modulation of LMP-1-activated signaling pathways is the first identified biological activity associated with lyLMP-1, and this activity may contribute to the progression of EBV's lytic cycle.

The residues between the two transformation effector sites of Epstein-Barr virus latent membrane protein 1 are not critical for B-lymphocyte growth transformation

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) is essential for EBV-mediated transformation of primary B lymphocytes. LMP1 spontaneously aggregates in the plasma membrane and enables two transformation effector sites (TES1 and TES2) within the 200-amino-acid cytoplasmic carboxyl terminus to constitutively engage the tumor necrosis factor receptor (TNFR)-associated factors TRAF1, TRAF2, TRAF3, and TRAF5 and the TNFR-associated death domain proteins TRADD and RIP, thereby activating NF-kappaB and c-Jun N-terminal kinase (JNK). To investigate the importance of the 60% of the LMP1 carboxyl terminus that lies between the TES1-TRAF and TES2-TRADD and -RIP binding sites, an EBV recombinant was made that contains a specific deletion of LMP1 codons 232 to 351. Surprisingly, the deletion mutant was similar to wild-type (wt) LMP1 EBV recombinants in its efficiency in transforming primary B lymphocytes into lymphoblastoid cell lines (LCLs). Mutant and wt EBV-transformed LCLs were similarly efficient in long-term outgrowth and in regrowth after endpoint dilution. Mutant and wt LMP1 proteins were also similar in their constitutive association with TRAF1, TRAF2, TRAF3, TRADD, and RIP. Mutant and wt EBV-transformed LCLs were similar in steady-state levels of Bcl2, JNK, and activated JNK proteins. The wt phenotype of recombinants with LMP1 codons 232 to 351 deleted further demarcates TES1 and TES2, underscores their central importance in B-lymphocyte growth transformation, and provides a new perspective on LMP1 sequence variation between TES1 and TES2.

Effect of Epstein-Barr Virus Infection on Response to Chemotherapy and Survival in Hodgkin’s Disease

We have analyzed paraffin sections from 190 patients with histologically confirmed Hodgkin’s disease (HD) for the presence of Epstein-Barr virus (EBV) using in situ hybridization to detect the EBV-encoded Epstein-Barr virus early RNAs (EBERs) and immunohistochemistry to identify latent membrane protein-1 (LMP1) expression. EBV was present in the tumor cells in 51 HD cases (27%) and was mainly confined to the mixed cellularity and nodular sclerosis subtypes. There was no difference between EBV-positive and EBV-negative HD patients with regard to age, clinical stage, presentation, and the number of alternating chemotherapy cycles of ChIVPP and PABIOE received. The complete remission rate after study chemotherapy was 80% in EBV-positive patients versus 69% in EBV-negative patients (P = .05). The 2-year failure-free survival rate was significantly better for EBV-positive patients when compared with the EBV-negative HD group (P = .02). Although 2-year and 5-year overall survival rates were better for EBV-positive HD patients, the differences were not statistically significant (P = .18 andP = .40, respectively). In conclusion, the results confirm the favorable prognostic value of EBV in the tumor cells of HD patients and suggest important differences in response to chemotherapy between EBV-positive and EBV-negative patients.

Effect of Epstein-Barr Virus Infection on Response to Chemotherapy and Survival in Hodgkin’s Disease

We have analyzed paraffin sections from 190 patients with histologically confirmed Hodgkin’s disease (HD) for the presence of Epstein-Barr virus (EBV) using in situ hybridization to detect the EBV-encoded Epstein-Barr virus early RNAs (EBERs) and immunohistochemistry to identify latent membrane protein-1 (LMP1) expression. EBV was present in the tumor cells in 51 HD cases (27%) and was mainly confined to the mixed cellularity and nodular sclerosis subtypes. There was no difference between EBV-positive and EBV-negative HD patients with regard to age, clinical stage, presentation, and the number of alternating chemotherapy cycles of ChIVPP and PABIOE received. The complete remission rate after study chemotherapy was 80% in EBV-positive patients versus 69% in EBV-negative patients (P = .05). The 2-year failure-free survival rate was significantly better for EBV-positive patients when compared with the EBV-negative HD group (P = .02). Although 2-year and 5-year overall survival rates were better for EBV-positive HD patients, the differences were not statistically significant (P = .18 andP = .40, respectively). In conclusion, the results confirm the favorable prognostic value of EBV in the tumor cells of HD patients and suggest important differences in response to chemotherapy between EBV-positive and EBV-negative patients.

Epstein-Barr virus-transforming protein latent infection membrane protein 1 activates transcription factor NF-kappaB through a pathway that includes the NF-kappaB-inducing kinase and the IkappaB kinases IKKalpha and IKKbeta

The Epstein-Barr virus oncoprotein latent infection membrane protein 1 (LMP1) is a constitutively aggregated pseudo-tumor necrosis factor receptor (TNFR) that activates transcription factor NF-kappaB through two sites in its C-terminal cytoplasmic domain. One site is similar to activated TNFRII in associating with TNFR-associated factors TRAF1 and TRAF2, and the second site is similar to TNFRI in associating with the TNFRI death domain interacting protein TRADD. TNFRI has been recently shown to activate NF-kappaB through association with TRADD, RIP, and TRAF2; activation of the NF-kappaB-inducing kinase (NIK); activation of the IkappaB alpha kinases (IKKalpha and IKKbeta); and phosphorylation of IkappaB alpha. IkappaB alpha phosphorylation on Ser-32 and Ser-36 is followed by its degradation and NF-kappaB activation. In this report, we show that NF-kappaB activation by LMP1 or by each of its effector sites is mediated by a pathway that includes NIK, IKKalpha, and IKKbeta. Dominant negative mutants of NIK, IKKalpha, or IKKbeta substantially inhibited NF-kappaB activation by LMP1 or by each of its effector sites.

Epstein-Barr virus and a cellular signaling pathway in lymphomas from immunosuppressed patients

BACKGROUND

Epstein-Barr virus (EBV) is associated with various malignant and benign lymphoproliferative disorders. It also efficiently transforms human B lymphocytes in vitro. The latent membrane protein 1 (LMP1) of EBV-infected cells plays a central part in this process by mimicking members of the family of tumor necrosis factor (TNF) receptors, thereby transmitting growth signals from the cell membrane to the nucleus through cytoplasmic TNF-receptor-associated factors (TRAFs). I sought evidence of LMP1-mediated signal transduction through TRAFs in tumor tissue from patients with post-transplantation lymphoproliferative disease and non-Hodgkin's lymphomas related to the acquired immunodeficiency syndrome (AIDS).

METHODS

The association of LMP1 with TRAF-1 or TRAF-3 in tumor tissue was studied with double-immunofluorescence microscopy and immunoprecipitation assays. Evidence of LMP1-TRAF signaling was sought with an electrophoretic mobility shift assay for the nuclear factor-kappaB (NF-kappaB) transcription factor.

RESULTS

Tumors from eight patients with post-transplantation lymphoproliferative disease, two patients with AIDS-associated non-Hodgkin's lymphoma, and three patients with endemic Burkitt's lymphoma were analyzed. Tumors from six of the patients with post-transplantation lymphoproliferative disease were positive for EBV and expressed LMP1; two samples were EBV-negative. Tumors from both patients with AIDS-associated non-Hodgkin's lymphoma were EBV-positive and expressed LMP1, whereas tumors from all three patients with Burkitt's tumors were positive for EBV but negative for LMP1. Double-immunofluorescence microscopy showed that LMP1 localized with and immunoprecipitated with TRAF-1 and TRAF-3 in all eight of the EBV-positive, LMP1-positive samples. An electrophoretic mobility shift assay revealed activated NF-kappaB in all eight EBV-positive, LMP1-positive samples as well, but not in either of the EBV-negative, LMP1-negative samples or in the three EBV-positive, LMP1-negative samples.

CONCLUSIONS

LMP1-mediated signaling through the TRAF system has a role in the pathogenesis of the EBV-positive lymphomas that arise in immunosuppressed patients.

Interaction of tumor necrosis factor receptor-associated factor signaling proteins with the latent membrane protein 1 PXQXT motif is essential for induction of epidermal growth factor receptor expression

The Epstein-Barr virus latent membrane protein 1 (LMP1) oncoprotein causes multiple cellular changes, including induction of epidermal growth factor receptor (EGFR) expression and activation of the NF-kappaB transcription factor. LMP1 and the cellular protein CD40, which also induces EGFR expression, interact with the tumor necrosis factor receptor-associated factor (TRAF) proteins. The LMP1 carboxy-terminal activation region 1 signaling domain interacts specifically with the TRAFs and is essential for EGFR induction through a mechanism independent of NF-kappaB alone. LMP1 and CD40 share a common TRAF binding motif, PXQXT. In this study, the PXQXT motifs in both LMP1 and CD40 were altered and mutant proteins were analyzed for induction of EGFR expression. Replacement of the T residue with A in CD40 completely blocked induction of the EGFR, while the same mutation in LMP1 did not affect EGFR induction. Replacement of both P and Q residues with A's in LMP1 reduced EGFR induction by >75%, while deletion of PXQXT blocked EGFR induction. These results genetically link EGFR induction by LMP1 to the TRAF signaling pathway. Overexpression of TRAF2 potently activates NF-kappaB, although TRAF2 did not induce expression of the EGFR either alone or in combination with TRAF1 and TRAF3. In vivo analyses of the interaction of the TRAFs with LMP1 variants mutated in the PXQXT domain indicate that high-level induction of EGFR expression requires interaction with TRAF1, -2, and -3. However, exogenous expression of TRAF3 decreased EGFR induction mediated by either LMP1 or CD40. These data suggest that TRAF-mediated activation of EGFR expression requires assembly of a complex containing the appropriate stoichiometry of TRAF proteins clustered at the cell membrane with LMP1.

A Fusion of the EBV Latent Membrane Protein-1 (LMP1) Transmembrane Domains to the CD40 Cytoplasmic Domain Is Similar to LMP1 in Constitutive Activation of Epidermal Growth Factor Receptor Expression, Nuclear Factor-κB, and Stress-Activated Protein Kinase

The EBV latent infection transforming protein, LMP1, has six hydrophobic transmembrane domains that enable it to aggregate in the plasma membrane and a 200-amino acid carboxyl-terminal cytoplasmic domain (CT) that activates nuclear factor-κB and induces many of the phenotypic changes in B lymphocytes that accompany CD40 activation. Since the phenotypic effects of LMP1 are similar to those of activated CD40, we now compare signaling from the LMP1 CT with that from the CD40 CT fused to the LMP1 transmembrane domains. The LMPCD40 chimera was similar to LMP1 in nuclear factor-κB activation and in up-regulation of epidermal growth factor receptor expression. CD40 ligation was known to activate the stress-activated protein kinase, and both LMPCD40 and LMP1 are now shown to induce stress-activated protein kinase activity in the absence of ligand. Deletion of the first four transmembrane domains of LMP1 abrogated LMP1 aggregation in the plasma membrane and nearly abolished signaling from LMP1 or the LMPCD40 chimera. These results highlight the role of LMP1 as a constitutively active receptor similar to CD40 and provide a novel approach for the generation of ligand-independent receptors.

Identification of cytotoxic T cell epitopes within Epstein-Barr virus (EBV) oncogene latent membrane protein 1 (LMP1): evidence for HLA A2 supertype-restricted immune recognition of EBV-infected cells by LMP1-specific cytotoxic T lymphocytes

Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) and latent membrane proteins (LMP) are the only antigens consistently expressed in malignancies such as nasopharyngeal carcinoma (NPC) and Hodgkin's disease (HD). Since EBNA1 is not recognized by EBV-specific cytotoxic T lymphocytes (CTL), there is increasing interest in the identification of the potential target epitopes within LMP1. Although LMP1-specific CTL have been isolated from seropositive individuals, earlier attempts to identify the peptide epitopes recognized by these T cells have been unsuccessful. In the present report we used a novel protocol to identify CTL epitopes within LMP1 which can be recognized by both polyclonal and clonal CTL. Firstly, a computer-based program was employed to identify the potential HLA-binding peptides within LMP1. Polyclonal CD8+ CTL were then isolated from seropositive donors that recognized the peptide epitopes YLLEMLWRL and YLQQNWWTL from LMP1 in association with HLA A2. Limiting dilution analysis of the memory CTL response revealed that the LMP1-specific CTL response constitutes a minor component of the CTL response in healthy virus carriers. Interestingly, analysis of YLLEMLWRL-specific CTL revealed that these CTL were able to lyse EBV-infected B cells expressing different HLA A2 supertype alleles including A*0201, A*0202, A*0203, A*0204, A*0206, A*6802 and A*6901. These data strongly support the notion that HLA class I supertype-restricted CTL may be of significant use in the development of peptide-based immunotherapeutics against EBV-associated malignancies in different ethnic populations.

Sequence variations between two Epstein-Barr virus LMP 1 variants have no effect on the activation of NF-kappaB activity

Previously, we reported that the LMP 1 gene of Epstein-Barr virus (EBV) derived from nasopharyngeal carcinoma (NPC) tissues (i.e., NLMP 1 gene) was able to transform BALB/c3T3 cells. On the other hand, LMP 1 gene of B95-8 strain (i.e., BLMP 1 gene) was not able to transform these cells (Chen et aL, 1992). Further studies indicated that a 10-amino-acid deletion in the carboxyl terminus of NLMP 1 played an important role in transformation (Li et al., 1996). In this study, we tested if this 10-amino-acid deletion affected the induction of NF-kappaB activity by LMP 1. The long terminal repeat of the human immunodeficiency virus type 1 (HIV-1 LTR) contained two copies of NF-kappaB sites and was used to construct the Luc gene-based reporter plasmid, p kappaB-Luc. Plasmid p kappaB-Luc was co-transfected with plasmids containing the NLMP 1 gene, BLMP 1 gene, and their chimeric or deletion constructs, respectively, into C-33A and BALB/c3T3 cells. The activation was then measured by the luciferase activity. Results showed that the full-length proteins induced a similar level of NF-kappaB activity, the two 3' mutants (R15delta and D4delta) still induced a relatively high level of activity, and the two 5' deletion mutants (delta3058 and delta3243) of NLMP 1 gene did not show any significant activation in C-33A cells. However, none of these LMP 1 proteins induced NF-kappaB activity in BALB/c3T3 cells. Using subcellular fractionation analysis and an immunocytostaining method, the truncated proteins of delta3058 and delta3243 were detected in the cytoplasm of the cells whereas the full-length NLMP 1 protein was located at the cytoplasmic membrane. Stable BALB/c3T3 cell clones that expressed both truncated proteins were established and then their ability to induce tumors in nude mice was examined. Data showed that both truncated NLMP 1 proteins still maintained partial transformation activity. Our results suggested that there was no direct correlation between NF-kappaB activation and transformation activity of LMP 1 in BALB/c3T3 cell transformation and that the amino-terminal membrane-spanning domain was important for maintaining both functions of LMP 1.

Early detection of the lytic LMP-1 protein in EBV-infected B-cells suggests its presence in the virion

The Epstein-Barr virus (EBV)-positive B958 cell line expresses two related membrane proteins encoded by BNLF-1 open reading frames. One protein (LMP-1) has been shown to be essential for the growth transforming properties of EBV. The second protein (the lytic LMP-1) is an amino-terminally truncated form of LMP-1 whose expression is associated with induction of EBV's lytic cycle. We have investigated the expression of full-length and lytic forms of LMP-1 immediately after infection of the EBV-negative, B-lymphoma cell line BJAB. Only the lytic LMP-1 protein is present in BJAB cells early (within minutes following addition of virus) after infection with virus derived from either uninduced or tetradecanoyl phorbol acetate and sodium butyrate-induced B958 cells. Lytic LMP-1 protein levels begin to decline by 48 hr after infection, whereas levels of full-length LMP-1 increase between 24 and 48 hr after infection and then remain constant. The presence of the lytic LMP-1 protein in infected cells is independent of both protein synthesis and virus internalization. We also find the lytic LMP-1 protein in BJAB cells early after infection (within 3 hr of addition of virus) with the HH514 strain of EBV, and HH514 cells treated with tetradecanoyl phorbol acetate and sodium butyrate, express high levels of both the lytic LMP-1 and full-length LMP-1 proteins. The lytic LMP-1 protein is enriched in purified virion preparations, and immunoelectron microscopic analysis indicates that EBV virions can be specifically labeled with anti-LMP-1 antisera. Together, these results are consistent with a model in which the lytic LMP-1 protein is present in the EBV virion and is carried into the B-cell upon infection and suggest a role for this protein in early infection events and/or in EBV's lytic cycle.

Epstein-Barr virus LMP1 induction of the epidermal growth factor receptor is mediated through a TRAF signaling pathway distinct from NF-kappaB activation

The Epstein-Barr virus (EBV)-encoded LMP1 protein induces several cellular changes including induction of epidermal growth factor receptor (EGFR) expression and activation of the NF-kappaB transcription factor. Two domains within the carboxy terminus have been identified that activate NF-kappaB. In this study, mutational analysis of the LMP1 protein indicated that the proximal NF-kappaB activation domain, which is identical to the TRAF interaction domain (amino acids 187 to 231), is essential for induction of the EGFR. The distal NF-kappaB activation domain (amino acids 352 to 386) did not induce expression of the EGFR. In contrast, the two domains both independently activated a kappaB-CAT reporter gene and induced expression of the NF-kappaB-regulated A20 gene in C33A epithelial cells. These results indicate that induction of the EGFR by LMP1 involves the TRAF interaction domain and that activation of NF-kappaB alone is not sufficient. Northern blot analysis revealed that induction of EGFR and A20 expression is likely to be at the transcriptional level. Interestingly expression of CD40 in the C33A cells also induced expression of the EGFR. Overexpression of either TRAF3 or an amino-terminal-truncated form of TRAF3 (TRAF3-C) inhibited signaling from the LMP1 TRAF interaction domain but did not affect signaling from the distal NF-kappaB activation domain. These data further define the mechanism by which LMP1 induces expression of the EGFR and indicate that TRAF signaling from LMP1 and CD40 activates a downstream transcription pathway distinct from NF-kappaB that induces expression of the EGFR.

Tumor necrosis factor receptor associated factor 2 is a mediator of NF-kappa B activation by latent infection membrane protein 1, the Epstein-Barr virus transforming protein

Latent infection membrane protein 1 (LMP1), the Epstein-Barr virus transforming protein, associates with tumor necrosis factor receptor (TNFR) associated factor 1 (TRAF1) and TRAF3. Since TRAF2 has been implicated in TNFR-mediated NF-kappa B activation, we have evaluated the role of TRAF2 in LMP1-mediated NF-kappa B activation. TRAF2 binds in vitro to the LMP1 carboxyl-terminal cytoplasmic domain (CT), coprecipitates with LMP1 in B lymphoblasts, and relocalizes to LMP1 plasma membrane patches. A dominant negative TRAF2 deletion mutant that lacks amino acids 6-86 (TRAF/ delta 6-86) inhibits NF-kappa B activation from the LMP1 CT and competes with TRAF2 for LMP1 binding. TRAF2 delta 6-86 inhibits NF-kappa B activation mediated by the first 45 amino acids of the LMP1 CT by more than 75% but inhibits NF-kappa B activation through the last 55 amino acids of the CT by less than 40%. A TRAF interacting protein, TANK, inhibits NF-kappa B activation by more than 70% from both LMP1 CT domains. These data implicate TRAF2 aggregation in NF-kappa B activation by the first 45 amino acids of the LMP1 CT and suggest that a different TRAF-related pathway may be involved in NF-kappa B activation by the last 55 amino acids of the LMP1 CT.

Promotion of IL8, IL10, TNF alpha and TNF beta production by EBV infection

Burkitt's lymphoma (BL) represents a high malignant B cell tumour. It has been proposed that cytokines are responsible for some of the characteristics of BL. We have analysed a panel of different BL and lymphoblastoid cell lines (LCLs) for the expression of cytokines, including: IL 1 alpha, IL 1 beta, IL2, IL3, IL4, IL6, IL8, IL10, TNF alpha and TNF beta and for the soluble cytokine receptor for IL2 (slL2R). Our results show that expression of IL8, IL10, TNF alpha or TNF beta was detected frequently in several of the Burkitt or lymphoblastoid cell lines. There was a correlation between Epstein-Barr virus (EBV) infection and cytokine protein production. Our results suggest that EBV promote the expression of IL8, IL10, TNF alpha and TNF beta.

Interactions involving cyclosporine A, interleukin-6, and Epstein-Barr virus lead to the promotion of B-cell lymphoproliferative disease

Post-transplant patients undergoing prolonged Cyclosporine A (CsA) immunosuppressive therapy were reported to have an increased incidence of Epstein-Barr virus (EBV)-associated lymphoproliferative disorders. EBV-infected B cells cultured with CsA demonstrated increased EBV B-cell out-growth as compared to those cultured without CsA. Peripheral blood mononuclear cells (PBMC), following infection with EBV and CsA treatment, demonstrated increased IL-6 activity in the culture supernatant. The induction of IL-6 appeared to differ within the various lymphocyte populations. In monocytes and B cells, IL-6 expression was preferentially induced by EBV, and initiated by the binding of the two major virion glycoproteins, gp350 and gp220, to CD21, or a CD21-like receptor. Expression of IL-6 in T cells appeared to be due mainly to CsA. B cells also expressed IL-6 following EBV exposure, but not following CsA treatment. EBY-immortalized B-cell lines cultured with CsA exhibited both an increased number of cells expressing viral lytic-cycle antigens and increased amounts of lytic-cycle proteins. IL-6, which was induced by CsA in PBMC, was also capable of inducing the lytic viral cycle in several EBV-immortalized cells. When IL-6 was expressed, it was shown to act as an autocrine growth factor for B cells and to inhibit the immune system allowing for the promotion of B-cell tumors by impairing lymphokine-activated killer cells. Thus CsA treatment, in promoting both increased numbers of lytic EBV B cells and expression of the EBV paracrine growth factor, IL-6, within the microenvironment of EBV B:T cell and EBV B:monocyte interactions, may lead to increased EBV B-cell immortalization and ultimately result in the promotion of B-cell lymphomas in immunosuppressed patients.

The ecology and pathology of Epstein-Barr virus

Epstein-Barr virus achieves its ubiquitous and uniform epidemiological distribution by a dual strategy of latency to guarantee lifelong persistence and intermittent replication to guarantee transmission. These two functions appear to dictate residence in different cell types: latency in B lymphocytes and replication in epithelial cells. Both of these cell compartments are potential sites for EBV-associated malignancies.

Characterization of 5'-upstream sequence of the latent membrane protein 1 (LMP-1) gene of an Epstein-Barr virus identified in nasopharyngeal carcinoma tissues

Sequence variations of the 5'-upstream region of latent membrane protein 1 (LMP-1) in two Epstein-Barr virus (EBV) strains have been reported before (Chen et al., 1992). To investigate the effect of these variations on gene expression, we constructed a series of deletion plasmids encompassing positions -950 to +20 of the LMP-1 promoter region and tested for the ability to drive chloramphenicol acetyltransferase (CAT) gene expression in C33A cells. Results showed that the promoter activities of constructs from NPC strain were 3-fold lower than the corresponding constructs from the B95-8 strain. In addition, the region between -54 and +20 contained the basic, constitutive promoter activity for both strains. Sequence analysis of this region indicated that an activating transcription factor (ATF) binding site, TGACGTAG, which is present in B95-8 strain was changed to TCTCGTAG in NPC strain. A chimeric plasmid study suggested that these sequence variations in the ATF binding site may contribute to the 3-fold increase of CAT activity observed for B95-8 strain. Furthermore, the activity of the promoter constructs was not activated by EBV-encoded nuclear antigen 2 (EBNA-2) in C33A cells. However, the promoter activities were upregulated in B-lymphocyte cells such as CG3 and CA46 cells. The biological significance of this difference in promoter activity of LMP-1 gene between two strains and the involvement of the cellular factors were discussed.

Induction of CD44 expression by the Epstein-Barr virus latent membrane protein LMP1 is associated with lymphoma dissemination

Epstein-Barr Virus (EBV) is implicated in the pathogenesis of endemic Burkitt's lymphoma (BL), B-cell lymphomas occurring under immunosuppression, nasopharyngeal carcinoma and Hodgkin's disease. Two distinct patterns of latent EBV gene expression occur in EBV-associated lymphomas. BLs typically display expression of the nuclear antigen EBNAI only, whereas EBV-associated, non-Burkitt B-cell lymphomas express at least 9 latent viral genes (6 EBNAs and 3 latent membrane proteins), reminiscent of in vitro EBV-immortalized lymphoblastoid cell lines (LCL). BLs are characterized by local, extra-nodal growth, whereas EBV-associated B-cell lymphomas often disseminate to peripheral lymphoid tissue. We show here that BL cells forming local tumors after xenotransplantation into SCID mice disseminate to lymphoid tissue following introduction of the latent membrane protein I (LMP 1) gene. Introduction of LMP 1 into BL cells induced expression of CD44 on the cell surface, a molecule implicated in enhanced lymphoid tumor growth and dissemination. Introduction of CD44 into LMP 1-/CD44-BL cells was observed to confer the disseminated tumor growth pattern associated with LMP 1 expression. Taken together our results show that expression of LMP 1 may regulate expression of CD44 and play an important role in the behavior of EBV-based lymphomas.