Induction of inducible nitric oxide synthase by Epstein-Barr virus B95-8-derived LMP1 in Balb/3T3 cells promotes stress-induced cell death and impairs LMP1-mediated transformation

Increased production of nitric oxide correlates with tumor growth in Algerian patients with nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is thought to arise because of chronic inflammation. The correlation between nitric oxide (NO) production, a biomarker of inflammation and NPC development remains unexplored. To investigate this question, we performed a profile analysis on plasma collected from untreated, treated, remissive, cured and relapsing patients. Nitrites were measured to assess NO activity. We observed that increased nitrites concentrations in untreated and relapsing patients associated with tumor development. Moreover, nitrites levels were similar in remissive, cured and healthy individuals. Altogether, our results suggest that NO might be an interesting blood biomarker to monitor tumor growth in NPC patients.

Role of nitrative and oxidative DNA damage in inflammation-related carcinogenesis

Chronic inflammation induced by biological, chemical, and physical factors has been found to be associated with the increased risk of cancer in various organs. We revealed that infectious agents including liver fluke, Helicobacter pylori, and human papilloma virus and noninfectious agents such as asbestos fiber induced iNOS-dependent formation of 8-nitroguanine and 8-oxo-7, 8-dihydro-2′-deoxyguanosine (8-oxodG) in cancer tissues and precancerous regions. Our results with the colocalization of phosphorylated ATM and γ-H2AX with 8-oxodG and 8-nitroguanine in inflammation-related cancer tissues suggest that DNA base damage leads to double-stranded breaks. It is interesting from the aspect of genetic instability. We also demonstrated IL-6-modulated iNOS expression via STAT3 and EGFR in Epstein-Barr-virus-associated nasopharyngeal carcinoma and found promoter hypermethylation in several tumor suppressor genes. Such epigenetic alteration may occur by controlling the DNA methylation through IL-6-mediated JAK/STAT3 pathways. Collectively, 8-nitroguanine would be a useful biomarker for predicting the risk of inflammation-related cancers.

Functional interaction of Ugene and EBV infection mediates tumorigenic effects

Epstein-Barr virus (EBV) infection is associated with many human neoplasms, in which EBV-derived latent membrane protein-1 (LMP1) appears to be critical, but its exact oncogenic mechanism remains to be defined. To this end, our initial microarray analyses identified a LMP1-inducible gene, Ugene, originally characterized as a binding partner for uracil DNA glycosylase 2, which is highly expressed in malignant colon cancer. In this report, it was found that Ugene, designated herein as LMP1-induced protein (LMPIP), was induced, in a time-dependent manner, in EBV-infected peripheral blood mononuclear cells and LMP1-transfected 293 cells. Functionally, when compared with mock-transfected cells, overexpression of LMPIP in nasopharyngeal carcinoma (NPC) cell lines resulted in a decrease in reactive oxygen species production and maintained mitochondria membrane potential (Δψ) loss induced by H(2)O(2). The NPC cells transfected with LMPIP also showed a decrease in G1 population and an increase in the cell population in sub-G1 and multiploid phase, concomitant with increased levels of cell cycle activators, including cyclin D1 and CDK4. In contrast, silencing of LMPIP expression in the NPC tumor cell lines with short hairpin RNA interference revealed significantly decreased cell population at G1/S phase, while the number of cells in multiploid phase increased. Significantly, NPC cells with LMPIP knock-down also showed a decrease in tumorigenic and transforming activity induced by ectopic LMP1 expression, as determined by analyses of soft agar foci and tumor size in nude mice. Further, elevated LMPIP expression was also noted in cytoplasm and nuclei in EBV-infected NPC tumor cell mass and non-EBV-infected tumor cell lines. These results suggested that LMPIP may have an important mediator role in EBV-mediated neoplasm and may serve as a new target for therapy of tumors induced by EBV infection.

Functional analysis of epstein-barr virus latent membrane proteins (LMP1) in patients with limphoproliferative disorders

Latent membrane protein1 (LMP1) encoded by the LMP1 gene of the Epstein-Barr virus (EBV) is a transmembrane protein, which can activate a number of cellular signal cascades and transcriptional factors leading to cell transformation. In the present study the sequencing of full-length LMP1 variants isolated from Russian patients with Hodgkin's lymphoma (HL), non-Hodgkin's lymphomaе (NHL) and infectious mononucleosis (IM) has been carried out. The phylogenetic analysis of obtained sequences revealed dominance of the LMP1 variants belonging to proteins of low-divergent group LMP1-B95.8b characterized by minimal set of mutations. Investigation of biological properties in the Russian representatives of this group revealed that expression of studied LMP1 variants in embryonic kidney 293 cells was accompanied by insignificant increase in transcriptional factor NF-κB activation and had minor influence on activation of transcriptional factor AP-1. It was also detected that all investigated low-divergent LMP1 variants expressed in Rat-1 cells induced activation of inducible NO-synthase (iNOS) and intracellular production of nitric oxide (NO). At the same time the level of NO accumulation was lower than that induced by the low-transforming prototype variant LMP1-B95.8. The data obtained indicate that the LMP1 variants, which are the most common among Russian patients with EBV-associated lymphoproliferative diseases, are characterized by minimum number of mutations and rather low ability to activate basic cellular signaling pathways regardless the nature of pathological process, benign (IM) or malignant (HL, NHL). It is suggested that in addition to the modest activation of NF-κB and iNOS induction by LMP1 other factors are involved in the cell transformation process.

Functionally significant mutations in the Epstein-Barr virus LMP1 gene and their role in activation of cell signaling pathways

Latent membrane protein 1 (LMP1) of the Epstein-Barr virus is a constitutively activated analog of the tumor necrosis factor receptor TNF-R1. LMP1 serves as a viral oncogene able to transform human B-lymphocytes and rodent fibroblasts via activation of numerous cellular signal cascades. Two specific motifs within LMP1 are responsible for interaction of this viral protein with the receptor protein beta-TrCP/HOS SCF of the ubiquitin ligase E3 complex, playing an important role in degradation of numerous cellular proteins including NF-kappaB inhibitor IkappaBalpha. In this study, we demonstrate for the first time the importance of point mutations affecting HOS-recognizing motifs of LMP1 for activation of NF-kappaB, AP1, and PI3K/Akt signaling pathways. It has also been shown that rat fibroblast cell lines (Rat-1) expressing different HOS mutants of LMP1 produce different amounts of reactive nitrogen species. Our data confirm the hypothesis that point mutations in the C-terminal region of the LMP1 cytoplasmic domain can influence the transforming potential of the Epstein-Barr virus.

A simplified tumour model established via Epstein-Barr virus-encoded, nasopharyngeal carcinoma-derived oncogene latent membrane protein 1 in immunocompetent mice

The expression and immune modulation of Epstein-Barr virus-encoded oncogene latent membrane protein 1 (N-LMP1) is essential in the pathogenesis of nasopharyngeal carcinoma. In previous studies, cell transformation has been induced by the expression of EBV-encoded N-LMP1 in non-tumour BALB/c-3T3 cells and these cells have then been used to form tumours in T-cell-deficient nude mice. However, studies using this model have been limited by the lack of a competent immune system. To facilitate the study of immune components in N-LMP1-driven oncogenesis, we herein developed a simplified N-LMP1-derived tumour model in immunocompetent mice. Cell transformation was induced by the expression of N-LMP1 in BALB/c-3T3 cells, and these transformants were used to induce oncogenesis in BALB/c mice. In contrast to the 100% successful tumour-induction rate in nude mice treated with monodispersed transformed cells, the tumour incidence in BALB/c mice was only 5-36%. However, the transplantation of tumour fragments into BALB/c mice yielded a reproducible tumour-induction rate of >85%, which is acceptable for most of the research needs. This novel model of N-LMP1-directed oncogenesis in an immunocompetent environment may serve as an important platform for the future assessment of N-LMP1-targeted tumour therapies.

Reactive nitrogen species-dependent DNA damage in EBV-associated nasopharyngeal carcinoma: the relation to STAT3 activation and EGFR expression

Nasopharyngeal carcinoma (NPC) is strongly associated with Epstein-Barr virus (EBV) infection. Recently, reactive nitrogen and oxygen species are considered to participate in inflammation-related carcinogenesis through DNA damage. In our study, we obtained biopsy and surgical specimens of nasopharyngeal tissues from NPC patients in southern China, and performed double immunofluorescent staining to examine the formation of 8-nitroguanine, a nitrative DNA lesion and 8-oxo-7,8-dihydro-2'-deoxyguanosine, an oxidative DNA lesion, in these specimens. Strong DNA lesions were observed in cancer cells and inflammatory cells in stroma of NPC patients. Intensive immunoreactivity of iNOS was detected in the cytoplasm of 8-nitroguanine-positive cancer cells. DNA lesions and iNOS expression were also observed in epithelial cells of EBV-positive patients with chronic nasopharyngitis, although their intensities were significantly weaker than those in NPC patients. In EBV-negative subjects, no or little DNA lesions and iNOS expression were observed. EGFR and phosphorylated STAT3 were strongly expressed in cancer cells of NPC patients, but NF-kappaB was not expressed, suggesting that STAT3-dependent mechanism is important for NPC carcinogenesis. IL-6 was expressed mainly in inflammatory cells of nasopharyngeal tissues of EBV-infected patients. EBV-encoded RNAs (EBERs) and latent membrane protein 1 (LMP1) were detected in cancer cells from all EBV-infected patients. In vitro cell system, nuclear accumulation of EGFR was observed in LMP1-expressing cells, and IL-6 induced phosphorylated STAT3 and iNOS. These data suggest that nuclear accumulation of EGFR and STAT3 activation by IL-6 play the key role in iNOS expression and resultant DNA damage, leading to EBV-mediated NPC.

Oncogenic virus-associated neoplasia: a role for cyclin D1 genotypes influencing the age of onset of disease?

Cyclin D1 (CCND1) is a key regulatory protein at the G1/S checkpoint of the cell cycle. The purpose of our study was to assess the role of CCND1 genotypes influencing the age of onset of oncogenic virus-associated neoplasia. We conducted a hospital-based case-control study of 581 individuals, including 247 controls and 334 cases (108 nasopharyngeal and 226 cervical cancer cases). The polymorphism analysis was performed in blood samples by PCR-RFLP methodology. Age-adjusted logistic regression analysis indicates that individuals carrying two G-alleles have an increased genetic susceptibility for the development of oncogenic virus-associated cancers (aOR=2.02, 95% CI 1.30-3.14, P=0.002). Moreover, our results indicate that the waiting time for onset of oncogenic virus-associated neoplasia in patients homozygous (GG) for CCND1 genotypes (52 years) was 12 years earlier in comparison with patients carrying AG or AA genotypes (60 years) (log-rank test: P=0.0003). Our results may be important in contributing to a more extensive knowledge of the mechanisms involved in oncogenic virus-associated carcinogenesis, as CCND1 may be an important target for the development of new strategies for cancer treatment and prevention.

siRNA targeting LMP1-induced apoptosis in EBV-positive lymphoma cells is associated with inhibition of telomerase activity and expression

Epstein-Barr Virus (EBV) is closely associated with B cell malignancies. However, whether EBV appears to be absolutely required for cell proliferation and survival in lymphoma cells is still unknown. In this study, small interfering RNA (siRNA) targeting LMP1 was employed to investigate the effect of LMP1 on cell proliferation in EBV-positive lymphoblastoid B-cell line. A plasmid stable encoding 21-nt small RNA specifically and efficiently interfering LMP1 was constructed, resulting in a substantial loss of LMP1 mRNA and a significantly decreased LMP1 protein expression. Our data demonstrated that cell proliferation was completely inhibited and apoptosis was induced after knockdown of LMP1 gene in lymphoblastoid B-cell line. Also, we found that suppression of LMP1 caused downregulation of telomerase protein expression and decreased telomerase activity in lymphoma cells. In EBV-negative NPC cell line, transfection of plasmid expressing LMP1 greatly enhanced telomerase protein expression. Our results suggested that siRNA targeting LMP1 can induce apoptosis in EBV-positive lymphoma cells and is associated with inhibition of telomerase activity and expression. siRNA-directed LMP1 silencing may be of the therapeutic value for preventing and treating those EBV-associated tumors.

Human gingival mucosal keratinocytes exhibiting anchorage-independent growth express increased inducible nitric oxide synthase: regulation by MAP kinases

Inducible nitric oxide synthase (iNOS) has been implicated in cancer formation because of its vast presence cancer tissues. Studies to support such a role during transformation of human cells are very limited. We have developed a cell culture system, which renders a more transformed epithelial phenotype. The model cells generated from immortalized human gingival mucosal (GM) keratinocytes are consisted of less transformed epithelial-like (EPI) cells and more transformed fibroblast-like (FIB) cells. The latter exhibit anchorage independent growth (AIG). Our data showed that iNOS at mRNA and protein levels was up-regulated in more transformed FIB cells in comparison with less transformed EPI cells. FIB cells at low passages (p<22) were unstable being able to morphologically and functionally revert back to EPI phenotype, while no reversion was observed in FIB cells at high passages (p>43). The morphological reversion of FIB cells was associated with the reversal of vimentin expression as well as AIG. More importantly, these revertants showed reduced levels of iNOS mRNA as well as MAP kinase ERK and phospho-ERK protein expression, while FIB cells without reversion maintained the expression. Furthermore, the MEK1/2 inhibitor U0126 could reduce detectable iNOS mRNA levels suggesting that MAP kinases were upstream regulators of iNOS transcription. U0126 caused both morphological and functional reversion of FIB cells indicating involvement of MAP kinases in these functions. Taken together, we provide evidence for an up-regulation of iNOS in cultured human keratinocytes which exhibit AIG. This up-regulation may reflect progressive transformation which still requires further changes to reach tumorigenic conversion.

Actinodaphnine induces apoptosis through increased nitric oxide, reactive oxygen species and down-regulation of NF-kappaB signaling in human hepatoma Mahlavu cells

Actinodaphnine, extracted from Cinnamomum insularimontanum (Lauraceae), possesses cytotoxicity in some cancers, but the mechanism by which actinodaphnine induces apoptosis in human hepatoma cells remains poorly understood. In this study, we investigated the mechanisms of apoptosis induced by actinodaphnine in human hepatoma Mahlavu cells. Treatment with actinodaphnine dose-dependently induced apoptosis in Mahlavu cells that correlated with increased intracellular nitric oxide (NO) and reactive oxygen species (ROS), disruptive mitochondrial transmembrane potential (DeltaPsi(m)), and activation of caspase 3/7. Our data also demonstrated that actinodaphnine down-regulated activity of nuclear factor kappaB (NF-kappaB). The apoptotic response to actinodaphnine was markedly decreased in Mahlavu cells pretreated with dexsamethasone, a NO inhibitor, N-acetylcysteine (NAC), an antioxidant, and Boc-Asp(OMe)-fmk, a broad caspases inhibitor. These results suggested that actinodaphnine-induced apoptosis is initially mediated through the NO and/or ROS increase and caspases-dependent pathway. In conclusion, our results indicate that an increase of ROS and/or NO is the initial essential event that results in the decrease of DeltaPsi(m) and the activation of caspases that commits the cells to the apoptotic pathway in actinodaphnine-treated hepatoma Mahlavu cells.

Tetrahydrobiopterin deficiency exaggerates intimal hyperplasia after vascular injury

Decreased levels of tetrahydrobiopterin (BH4), an absolute cofactor for nitric oxide synthase (NOS), lead to uncoupling of NOS into a superoxide v. nitric oxide producing enzyme, and it is this uncoupling that links it to the development of vascular disease. However, the effects of in vivo deficiency of BH4 on neointimal formation after vascular injury have not been previously investigated. Hph-1 mice, which display 90% deficiency in guanine triphosphate cyclohydrolase I, the rate limiting enzyme in BH4 synthesis, were used. Hph-1 and wild-type mice, treated with either vehicle or BH4 (n = 15 per group), were subjected to wire-induced femoral artery injury, and NOS expression and activity, inflammation, cell proliferation, superoxide production, and neointimal formation were assessed. The major form of NOS expressed over vessel wall after vascular injury was endothelial NOS. Hph-1 mice exhibited lower NOS activity (2.8 +/- 0.3 vs. 4.5 +/- 0.4 pmol/min/mg protein, P < 0.01), and higher aortic superoxide content (5.2 +/- 2.0 x 10(5) cpm vs. 1.6 +/- 0.7 x 10(5) cpm, P < 0.01) compared with wild-type controls, indicating uncoupling of NOS. Treatment of hph-1 mice with BH4 significantly increased NOS activity (from 2.8 +/- 0.3 to 4.1 +/- 0.4 pmol.min(-1).mg protein(-1), P < 0.05), and attenuated superoxide production (from 5.2 +/- 2.0 x 10(5) cpm to 0.8 +/- 0.7 x 10(5) cpm, P < 0.05). Hph-1 mice also had higher inflammatory reactions and more cell proliferation after vascular injury. Furthermore, hph-1 mice responded by a marked increase in neointimal formation at 4 wk after vascular injury, compared with wild-type controls (intima:media ratio: 4.5 +/- 0.5 vs. wild-type 0.7 +/- 0.1, P < 0.001). Treatment of hph-1 mice with BH4 prevented vascular injury-induced increase in neointimal formation (intima:media ratio: 1.4 +/- 0.1 vs. hph-1, P < 0.001). Treatment had no effect on wild-type controls. In summary, we describe, for the first time, that in vivo BH4 deficiency facilitates neointimal formation after vascular injury. Modulation of BH4 bioavailability is an important therapeutic target for restenosis.

Nasal NK/T cell lymphoma in Taiwan: a clinicopathologic study of 22 cases, with analysis of histologic subtypes, Epstein-Barr virus LMP-1 gene association, and treatment modalities

Nasal NK/T cell lymphoma is a distinctive type of extranodal lymphoma with an unique immunophenotype and a strong association with Epstein-Barr virus (EBV). It is one of the common extranodal lymphomas in Taiwan. We studied 22 cases of nasal NK/T cell lymphoma to characterize their clinicopathologic features and to explore the possible differences between histologic subtypes and their clinical behavior as well as the prevalence of 30-base pair (bp) deleted latent membrane protein-1 (LMP-1) gene of the EBV. They consisted of 5 cases of small cell type (SC), 6 cases of medium-sized cell type (MC), 6 cases of large cell type (LC), and 5 cases of pleomorphic cell type (PC). Twelve patients were men and 10 were women (1.2 to 1), and their ages ranged from 34 to 75 years with a median age of 55.5 years. The median ages of the LC type and PC type were older than the other 2 types. No other clinical features differed significantly among the 4 subtypes. Nasal obstruction was the most common initial presenting symptom. All but 1 case had stage IE disease at the time of diagnosis. Five cases developed extranasal involvement and skin was the most common site. No bone marrow involvement was detected. The majority of patients received local radiotherapy and chemotherapy. Local irradiation was more effective than chemotherapy alone. We achieved an overall survival of 63.6% at 5 years as estimated by the Kaplan-Meier analysis, which was better than other series. All cases displayed an immunophenotypic profile of CD3(epsilon)+, CD20-, CD56+, and TIA-1+ except that 1 case was CD3(epsilon)-. Fourteen of 22 cases (64%) expressed LMP-1. Nine cases of various cell types (41%) were also CD30+. Among the 4 histologic subtypes, the SC type differed from the other types by the absence of angiodestruction and necrosis, although angioinvasive growth was seen in 2 of them. Pseudoepitheliomatous hyperplasia was seen in only 3 cases of the SC type, and all 5 cases of the SC type were CD30-. No statistical difference in survival was found among the 4 histologic subtypes or between CD30+ and CD30- cases. All 22 cases were positive for EBV by polymerase chain reaction and Epstein-Barr virus early RNA (EBER) in-situ hybridization. A high prevalence rate of 86% (19/22) of the 30-base pair (bp) deleted LMP-1 gene was found, but 81.5% (22/27) of the EBV-positive control reactive lymphoid tissues also had the 30-bp deleted LMP-1 gene. Therefore, the high prevalence of the 30-bp deleted LMP-1 gene found in NK/T cell lymphoma could be due to the high prevalence of the deleted variant in this geographic region. However, it remains possible that the high prevalence of the deleted LMP-1 gene contributed to the increased incidence of EBV-associated nasal NK/T cell lymphoma in Taiwan.

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.

Epstein-Barr virus latent membrane protein 1: structure and functions

The Epstein-Barr virus latent membrane protein (LMP) 1 is a versatile protein that has profound effects on target cells through its effect on constitutive cellular proteins, e.g. TRAFs, TRADD, RIP, JAK3, BRAM1, and p85. LMP1 can stimulate or inhibit signaling pathways, resulting in transformation of rodent fibroblast cell lines, blockade of differentiation in epithelial cells, upregulation of anti-apoptotic proteins, production of cytokines, upregulation of cell surface markers, upregulation of DNA methyltransferase activity, and downregulation of cell adhesion molecules and cyclin-dependent kinases. Overall, this results in greater transformation and survival in LMP1-expressing cells. Within nasopharyngeal carcinoma biopsy tissues, a naturally occurring LMP1 variant has been identified as having a 10-amino acid deletion in the C-terminus that seems to confer greater transformation potential than non-deleted LMP1. The role of LMP1 as a viral oncogene and its interaction with cellular factors are discussed.