Pathology and molecular pathology of Epstein-Barr virus-associated gastric carcinoma

Hyperactivation of mTOR/eIF4E Signaling Pathway Promotes the Production of Tryptophan-To-Phenylalanine Substitutants in EBV-Positive Gastric Cancer

Although messenger RNA translation is tightly regulated to preserve protein synthesis and cellular homeostasis, chronic exposure to interferon-γ (IFN-γ) in several cancers can lead to tryptophan (Trp) shortage via the indoleamine-2,3-dioxygenase (IDO)- kynurenine pathway and therefore promotes the production of aberrant peptides by ribosomal frameshifting and tryptophan-to-phenylalanine (W>F) codon reassignment events (substitutants) specifically at Trp codons. However, the effect of Trp depletion on the generation of aberrant peptides by ribosomal mistranslation in gastric cancer (GC) is still obscure. Here, it is shows that the abundant infiltrating lymphocytes in EBV-positive GC continuously secreted IFN-γ, upregulated IDO1 expression, leading to Trp shortage and the induction of W>F substitutants. Intriguingly, the production of W>F substitutants in EBV-positive GC is linked to antigen presentation and the activation of the mTOR/eIF4E signaling pathway. Inhibiting either the mTOR/eIF4E pathway or EIF4E expression counteracted the production and antigen presentation of W>F substitutants. Thus, the mTOR/eIF4E pathway exposed the vulnerability of gastric cancer by accelerating the production of aberrant peptides and boosting immune activation through W>F substitutant events. This work proposes that EBV-positive GC patients with mTOR/eIF4E hyperactivation may benefit from anti-tumor immunotherapy.

Exploring the role and diversity of mucins in health and disease with special insight into non-communicable diseases

Mucins are major glycoprotein components of the mucus that coats the surfaces of cells lining the respiratory, digestive, gastrointestinal and urogenital tracts. They function to protect epithelial cells from infection, dehydration and physical or chemical injury, as well as to aid the passage of materials through a tract i.e., lubrication. They are also implicated in the pathogenesis of benign and malignant diseases of secretory epithelial cells. In Human there are two types of mucins, membrane-bound and secreted that are originated from mucous producing goblet cells localized in the epithelial cell layer or in mucous producing glands and encoded by MUC gene. Mucins belong to a heterogeneous family of high molecular weight proteins composed of a long peptidic chain with a large number of tandem repeats that form the so-called mucin domain. The molecular weight is generally high, ranging between 0.2 and 10 million Dalton and all mucins contain one or more domains which are highly glycosylated. The size and number of repeats vary between mucins and the genetic polymorphism represents number of repeats (VNTR polymorphisms), which means the size of individual mucins can differ substantially between individuals which can be used as markers. In human it is only MUC1 and MUC7 that have mucin domains with less than 40% serine and threonine which in turn could reduce number of PTS domains. Mucins can be considered as powerful two-edged sword, as its normal function protects from unwanted substances and organisms at an arm's length while, malfunction of mucus may be an important factor in human diseases. In this review we have unearthed the current status of different mucin proteins in understanding its role and function in various non-communicable diseases in human with special reference to its organ specific locations. The findings described in this review may be of direct relevance to the major research area in biomedicine with reference to mucin and mucin associated diseases.

MicroRNA in gastrointestinal cancer: a step closer to reality

Despite significant strides in understanding molecular pathogenesis of cancer, gastrointestinal malignancy (gastric, colorectal, pancreatic, and liver) still ranks among the leading causes of cancer-related mortality and morbidity worldwide. One of the key clinical challenges in effectively reducing disease burden associated with gastrointestinal neoplasia stems from late diagnosis, underscoring the need for early detection, risk assessment, and intervention. Currently available screening approaches are inadequate, and the development of accurate noninvasive molecular biomarkers is very much needed, microRNAs (miRNAs) are short (20-24 nucleotides in length) noncoding RNAs that have emerged as important translational gene regulators in cancer cells. In contrast to genetic markers, miRNAs have a cancer-specific expression pattern. They are present in a remarkably stable form and can be detected in a wide variety of body fluids including blood and feces. These properties make them attractive cancer biomarker targets. Although development of miRNA biomarkers is still in its early stages, burgeoning evidence supports their potential use for development as markers for early detection, prognosis, and prediction of disease recurrence and therapeutic outcome in gastrointestinal cancers. In the future, it is likely that miRNA biomarkers will revolutionize personalized medicine and mitigate disease burden associated with gastrointestinal cancers.

Enrichment of stem-like cell population comprises transformation ability of Epstein-Barr virus latent membrane protein 2A for non-transformed cells

Epstein-Barr virus (EBV) is a representative human oncogenic virus that causes malignancies of various cell lineages. LMP2A, an EBV-encoded latent membrane protein, is expressed in EBV-associated malignancies of various cell lineages. LMP2A caused visible tumor formation transplanted in nude mice when transferred to immortalized non-transformed fibroblasts, NIH3T3. LMP2A-expressing cells showed higher ability of colony formation in soft agar than empty vector-transfected control cells, although the expression of LMP2A did not cause focus transformation in low serum concentrations. LMP2A expression increased the size of Hoechst 33,342 dye excreting side population (SP), in which cancer-initiating cells or cancer stem-like cells were enriched. SP increase by LMP2A was also responsible for colony formation in soft agar. The LMP2A-mediated SP increase depended on the activations of Stat3, MEK/ERK, and PI3K pathways, and on upregulation of HMGA2. Enrichment of SP, stem-like cells, by LMP2A promoted the transformation capability of LMP2A from non-transformed cells. The enrichment of stem-like cell population by a virus-encoded factor might explain the oncogenic functions of oncogenic viruses.

Epstein-Barr virus infection is common in inflamed gastrointestinal mucosa

BACKGROUND AND AIMS

Epstein-Barr virus (EBV) is present in the malignant epithelial cells of 10% of all gastric adenocarcinomas; however, localization of the virus in normal gastrointestinal mucosa is largely unexplored. In the present study, we measured EBV DNA and localized viral gene products in gastritis specimens (n = 89), normal gastric and colonic mucosa (n = 14), Crohn's disease (n = 9), and ulcerative colitis (n = 11) tissues.

METHODS

A battery of sensitive and specific quantitative polymerase chain reactions targeted six disparate regions of the EBV genome: BamH1 W, EBNA1, LMP1, LMP2, BZLF1, and EBER1. EBV infection was localized by EBV-encoded RNA (EBER) in situ hybridization and by immunohistochemical stains for viral latent proteins LMP1 and LMP2 and for viral lytic proteins BMRF1 and BZLF1. B lymphocytes were identified using CD20 immunostains.

RESULTS

EBV DNA was essentially undetectable in normal gastric mucosa but was present in 46% of gastritis lesions, 44% of normal colonic mucosa, 55% of Crohn's disease, and 64% of ulcerative colitis samples. Levels of EBV DNA exceeded what would be expected based on the numbers of B lymphocytes in inflamed tissues, suggesting that EBV is preferentially localized to inflammatory gastrointestinal lesions. Histochemical staining revealed EBER expression in lymphoid cells of some PCR-positive lesions. The viral lytic viral proteins, BMRF1 and BZLF1, were expressed in lymphoid cells of two ulcerative colitis tissues, both of which had relatively high viral loads by quantitative PCR.

CONCLUSION

EBV-infected lymphocytes are frequently present in inflamed gastric and colonic mucosa. Active viral replication in some lesions raises the possibility of virus-related perpetuation of gastrointestinal inflammation.

Epstein-Barr virus-specific methylation of human genes in gastric cancer cells

Background

Epstein-Barr Virus (EBV) is found in 10% of all gastric adenocarcinomas but its role in tumor development and maintenance remains unclear. The objective of this study was to examine EBV-mediated dysregulation of cellular factors implicated in gastric carcinogenesis.

Methods

Gene expression patterns were examined in EBV-negative and EBV-positive AGS gastric epithelial cells using a low density microarray, reverse transcription PCR, histochemical stains, and methylation-specific DNA sequencing. Expression of PTGS2 (COX2) was measured in AGS cells and in primary gastric adenocarcinoma tissues.

Results

In array studies, nearly half of the 96 human genes tested, representing 15 different cancer-related signal transduction pathways, were dysregulated after EBV infection. Reverse transcription PCR confirmed significant impact on factors having diverse functions such as cell cycle regulation (IGFBP3, CDKN2A, CCND1, HSP70, ID2, ID4), DNA repair (BRCA1, TFF1), cell adhesion (ICAM1), inflammation (COX2), and angiogenesis (HIF1A). Demethylation using 5-aza-2'-deoxycytidine reversed the EBV-mediated dysregulation for all 11 genes listed here. For some promoter sequences, CpG island methylation and demethylation occurred in an EBV-specific pattern as shown by bisulfite DNA sequencing. Immunohistochemistry was less sensitive than was western blot for detecting downregulation of COX2 upon EBV infection. Virus-related dysregulation of COX2 levels in vitro was not recapitulated in vivo among naturally infected gastric cancer tissues.

Conclusions

EBV alters human gene expression in ways that could contribute to the unique pathobiology of virus-associated cancer. Furthermore, the frequency and reversability of methylation-related transcriptional alterations suggest that demethylating agents have therapeutic potential for managing EBV-related carcinoma.

Activation of DNA methyltransferase 1 by EBV latent membrane protein 2A leads to promoter hypermethylation of PTEN gene in gastric carcinoma

CpG island promoter methylation of tumor suppressor genes is one of the most characteristic abnormalities in EBV-associated gastric carcinoma (GC). Aberrant promoter methylation and expression loss of PTEN were evaluated in cancer tissues of GC by methylation-specific PCR and immunohistochemistry, respectively, showing that both abnormalities occurred concurrently in EBV-associated GC. PTEN abnormalities were reiterated in GC cell lines MKN-1 and MKN-7 infected with recombinant EBV, and DNA methyltransferase 1 (DNMT1) was commonly overexpressed in both cell lines. Stable and transient transfection systems in MKN-1 similarly showed that viral latent membrane protein 2A (LMP2A) up-regulated DNMT1, leading to an increase in methylation of the PTEN promoter. Importantly, the level of phosphorylated signal transducer and activator of transcription 3 (pSTAT3) increased in the nuclei of LMP2A-expressing GC cells, and knockdown of STAT3 counteracted LMP2A-mediated DNMT1 overexpression. Immunohistochemistry for both pSTAT3 and DNMT1 showed diffuse labeling in the nuclei of the cancer cells in GC tissues, especially in EBV-associated GC. Taken together, LMP2A induces the phosphorylation of STAT3, which activates DNMT1 transcription and causes PTEN expression loss through CpG island methylation of the PTEN promoter in EBV-associated GC. LMP2A plays an essential role in the epigenetic abnormalities in host stomach cells and in the development and maintenance of EBV-associated cancer.

Spectrum of Epstein-Barr virus-related diseases: a pictorial review

Epstein-Barr virus (EBV) prevails among more than 90% of the adult population worldwide. Most primary infections occur during young childhood and cause no or only nonspecific symptoms; then the virus becomes latent and resides in lymphocytes in the peripheral blood. Inactive latent EBV usually causes no serious consequences, but once it becomes active it can cause a wide spectrum of malignancies: epithelial tumors such as nasopharyngeal and gastric carcinomas; mesenchymal tumors such as follicular dendritic cell tumor/sarcoma; and lymphoid malignancies such as Burkitt lymphoma, lymphomatoid granulomatosis, pyothorax-associated lymphoma, immunodeficiency-associated lymphoproliferative disorders, extranodal natural killer (NK) cell/T-cell lymphoma, and Hodgkin's lymphoma. The purpose of this article is to describe the spectrum of EBV-related diseases and their key imaging findings. EBV-related lymphoproliferative disorders and lymphomas are especially common in immunocompromised patients. Awareness of their clinical settings and imaging spectrum contributes to early detection and early treatment of possibly life-threatening disorders.

The role of viral and bacterial pathogens in gastrointestinal cancer

The association of Helicobacter pylori (H. pylori) with gastric cancer is thus far the best understood model to comprehend the causal relationship between a microbial pathogen and cancer in the human gastrointestinal tract. Besides H. pylori, a variety of other pathogens are now being recognized as potential carcinogens in different settings of human cancer. In this context, viral causes of human cancers are central to the issue since these account for 10-20% of cancers worldwide. In the case of H. pylori and gastric cancer, as well as the human papillomavirus and anal cancer, the causal relationship between the infectious agent and the related cancer in the gastrointestinal tract has been clearly confirmed by epidemiological and experimental studies. Similarly, Epstein-Barr virus and the oncogenic JC virus are being suggested as possible causative agents for cancers in the upper and lower gastrointestinal tract. This review discusses various viral and microbial pathogens and their oncogenic properties in the evolution of gastrointestinal carcinogenesis and summarizes the available experimental data make a convincing agreement favoring the associations between infectious agents and specific human cancers.

Survival advantage of EBV-associated gastric carcinoma: survivin up-regulation by viral latent membrane protein 2A

EBV-associated gastric carcinoma is a distinct subset of gastric carcinoma infected with EBV, which shows latency I type expression of EBV latent genes (EBNA1, EBER, BARF0, and LMP2A). To clarify the role of EBV in this type of gastric carcinoma, the cell biological characteristics (growth, apoptosis, and migration) were evaluated in gastric carcinoma cell lines (MKN-1, TMK1, MKN-74 and MKN-7) with and without infection of recombinant EBV harboring the neomycin resistance gene. The infection reiterated the latency I type infection, and the only difference observed in EBV-infected gastric carcinoma cell lines was the resistance to serum deprivation-induced apoptosis. Comparative analyses of transcripts of apoptosis-associated genes in MKN-1 and EBV-MKN-1 and subsequent quantitative reverse transcription-PCR analysis showed up-regulation of the cellular survivin gene in EBV-infected gastric carcinoma cell lines. Small interfering RNA-mediated knockdown of survivin increased apoptosis in EBV-MKN-1 to the level of the original MKN-1 cells. Transfection of EBV-latent genes into MKN-1 showed that LMP2A, but not EBNA1, EBER, or BARF0, up-regulated survivin gene expression. LMP2A-mediated survivin up-regulation in gastric carcinoma cells was inhibited with a nuclear factor-kappaB (NF-kappaB) inhibitor, Bay 11-7082. In parallel with these findings in vitro, survivin expression was frequent in carcinoma tissues of gastric carcinoma by immunohistochemistry, and significantly more in EBV-associated gastric carcinoma (12 of 13) than in EBV-negative gastric carcinoma in the advanced stage (P = 0.0307). Thus, EBV uses its latent protein, LMP2A, to activate the NF-kappaB-survivin pathway to rescue EBV-infected epithelial cells from serum deprivation, and up-regulation of survivin may play a role in the progression of this specific type of gastric carcinoma infected with EBV.

Expression of viral microRNAs in Epstein-Barr virus-associated gastric carcinoma

Epstein-Barr virus (EBV) is associated with about 6 to 16% of gastric carcinoma cases worldwide. Expression of the EBV microRNAs (miRNAs) was observed in B cells and nasopharyngeal carcinoma cells infected with EBV. However, it is not clear if the EBV miRNAs are expressed in EBV-associated gastric carcinomas (EBVaGCs). We found that BART miRNAs but not BHRF1 miRNAs were expressed in EBV-infected gastric carcinoma cell lines and the tumor tissues from patients as well as the animal model. The expression of viral miRNAs in EBVaGCs suggests that these EBV miRNAs may play important roles in the tumorigenesis of EBVaGCs.

Establishment and characterization of an in vivo model for Epstein–Barr virus positive gastric carcinoma

Research regarding the role of the Epstein-Barr virus (EBV) in gastric carcinogenesis has been hampered by the absence of a suitable model system. SNU-719 is a gastric carcinoma cell line naturally infected with EBV. This cell line developed tumors in nude mice approximately 40-56 days after inoculation. SNU-719 also showed low serum dependency and anchorage independent growth in vitro. The developed tumors expressed EBERs, EBNA1, and LMP2A but not other EBV latent genes. Additionally, Qp was active and either mono- or bi-clonal EBV genome was observed in the tumor tissues. Because the developed tumors retained characteristics of EBV-associated gastric cancer, this cell line could serve as a useful in vivo system to investigate the tumorigenesis mechanism and treatment methods for this type of tumor.

Phenotype analysis by MUC2, MUC5AC, MUC6, and CD10 expression in Epstein-Barr virus-associated gastric carcinoma

BACKGROUND

Gastric marker mucins (MUC5AC and MUC6) and intestinal marker molecules (MUC2 and CD10) have been used to determine the cell lineage of epithelial cell of gastric carcinoma (GC).

METHODS

To clarify the characteristics of Epstein-Barr virus (EBV)-associated GC, 18 cases were immunohistochemically evaluated along with 56 cases of EBV-negative GC.

RESULTS

MUC2 expression was lower in EBV-associated GC: immunostaining grades 0, 1, 2, 3, and 4 were observed in 10, 6, 1, 1, and 0 cases of EBV-associated GC, respectively, and in 18, 11, 15, 6, and 6 cases of EBV-negative GC, respectively (P = 0.013). CD10 positivity (grades 2-4) in EBV-associated GC was 6%, significantly lower than in EBV-negative GC (34%) (P = 0.030). When phenotypes of GC were categorized by the combined positivities of gastric markers (either MUC5AC or MUC6) and intestinal markers (either MUC2 or CD10), EBV-associated GC included primarily null (44%) and gastric (39%) types, but EBV-negative GC comprised null (7%), gastric (30%), intestinal (27%), and mixed (36%) types. The age of patients with gastric types was significantly younger for both EBV-associated GC and EBV-negative GC cases.

CONCLUSIONS

Neoplastic epithelial cells of EBV-associated GC did not express MUC2 or CD10, and most of them were categorized as null or gastric types. EBV infection may occur in the epithelial cells of null or gastric phenotypes, which may be devoid of transdifferentiation potential toward intestinal phenotypes.

CpG island methylation status in gastric carcinoma with and without infection of Epstein-Barr virus

PURPOSE

EBV-associated gastric carcinoma shows global CpG island methylation of the promoter region of various cancer-related genes. To further clarify the significance of CpG island methylator phenotype (CIMP) status in gastric carcinoma, we investigated methylation profile and clinicopathologic features including overall survival in four subgroups defined by EBV infection and CIMP status: EBV-associated gastric carcinoma and EBV-negative/CIMP-high (H), EBV-intermediate (I), and EBV-negative (N) gastric carcinoma.

EXPERIMENTAL DESIGN

Methylation-specific PCR was applied to 106 gastric carcinoma cases. CIMP-N, CIMP-I, and CIMP-H status was determined by the number (0, 1-3, and 4-5, respectively) of methylated marker genes (LOX, HRASLS, FLNc, HAND1, and TM), that were newly identified as highly methylated in gastric cancer cell lines. The methylation status of 10 other cancer-related genes (p14, p15, p16, p73, TIMP-3, E-cadherin, DAPK, GSTP1, hMLH1, and MGMT) was also evaluated.

RESULTS

Nearly all (14 of 15) of EBV-associated gastric carcinoma exhibited CIMP-H, constituting a homogenous group (14%). EBV-negative gastric carcinoma consisted of CIMP-H (24%), CIMP-I (38%), and CIMP-N (24%). EBV-associated gastric carcinoma showed significantly higher frequencies of methylation of cancer-related genes (mean number +/- SD = 6.9 +/- 1.5) even if compared with EBV-negative/CIMP-H gastric carcinoma (3.5 +/- 1.8). Among EBV-negative gastric carcinoma subgroups, CIMP-H gastric carcinoma showed comparatively higher frequency of methylation than CIMP-I or CIMP-N, especially of p16 and hMLH1. CIMP-N gastric carcinoma predominantly consisted of advanced carcinoma with significantly higher frequency of lymph node metastasis. The prognosis of the patients of CIMP-N was significantly worse compared with other groups overall by univariate analysis (P = 0.0313).

CONCLUSION

The methylation profile of five representative genes is useful to stratify gastric carcinomas into biologically different subgroups. EBV-associated gastric carcinoma showed global CpG island methylation, comprising a pathogenetically distinct subgroup in CIMP-H gastric carcinoma.

No association of primary adenocarcinomas of the small bowel with Epstein-Barr virus infection

Epstein-Barr Virus (EBV) infection is considered to play an etiologic role in human malignancies, including a subset of gastric and cardiac cancers. Adenocarcinomas of the small bowel comprise a very rare entity, with little knowledge about molecular properties and etiological aspects. We have investigated the prevalence of EBER expression (EBV-encoded small RNAs) in a series of small bowel adenocarcinomas (n=56) utilizing RNA in situ hybridization (EBER-RISH). The patients had undergone primary surgical resection at either the Technical University of Munich or at the University of Graz. A surgical series of 82 primary resected gastric (n=36) or cardiac (n=46) adenocarcinomas (TU Munich) was used as control group. None of the 56 small bowel carcinomas exhibited EBER expression whereas in the control group the rate of EBER expression accounted for 4.4% in the group of cardia carcinomas and 8.6% in the group of gastric cancers. These results indicate that EBV infection plays no etiologic role in primary small bowel adenocarcinomas.

Cancer risk to the gastric corpus in Japanese, its correlation with interleukin-1beta gene polymorphism (+3953*T) and Epstein-Barr virus infection

Polymorphisms of interleukin-1 (IL-1) genes have been reported to modify the risk of gastric carcinoma (GC) in Caucasians. The significance of IL-1beta gene polymorphisms was evaluated in Japanese GC patients with or without infection of Helicobacter pylori and Epstein Barr virus (EBV) with special reference to the topographic features of GC. IL-1beta gene polymorphisms at positions -511 and +3953 were evaluated by PCR-RFLP and a penta-allelic polymorphism of IL-1RA by PCR in healthy controls (n = 103) and GC (n =140; corpus 95, antrum 45). EBV-infection was determined in the neoplastic tissues by EBER1 in situ hybridization, and H. pylori infection in nonneoplastic gastric mucosa by PCR targeting of the H. pylori urease A gene. GC consisted of EBV-associated (n = 24) and EBV-negative (n = 116) patients, whereas H. pylori infection was positive in 130 cases. Among IL-1beta gene polymorphisms, genotype IL-1beta+3953 C/T was more frequent in the EBV-negative (21%) and corpus GC (23%) patients, compared to the controls (10%), respectively, although there was no genotype IL-1beta+3953 T/T in either group. Thus, the effect of IL-1beta+3953 T was statistically significant in logistic regression models adjusted for age in EBV negativity (odds ratio [OR] 2.27, 95% confidence interval [CI] 1.02-5.05) and in the corpus GC (2.70, 1.19-6.12) with highest OR 3.55 (1.54-8.23) in EBV-negative corpus GC. There was no significant influence of IL-1 gene polymorphism in EBV-associated GC, but it occurred predominantly in the corpus (24/24) compared to EBV-negative GC (71/116) (p = 0.00002). There was no correlation between H. pylori infection and IL-1 gene polymorphism in GC. The cancer risk of the gastric corpus in Japanese is influenced by IL-1beta+3953 polymorphisms. On the other hand, the risk of EBV-associated GC, which occurs predominantly in the corpus, is not influenced by this pro-inflammatory polymorphism.

High-density methylation of p14ARF and p16INK4A in Epstein-Barr virus-associated gastric carcinoma

Promoter hypermethylation of various tumor-related genes is extremely frequent in gastric carcinoma (GC) associated with Epstein-Barr virus (EBV). To investigate the significance of the promoter methylation in this type of GC, we examined the methylation densities of the promoter regions of p14ARF and p16INK4A in EBV-associated (n=7) and EBV-negative (n=14) GC. Bisulfite sequencing demonstrated a high frequency of concurrent methylation of p14ARF and p16INK4A promoter regions in EBVaGC. Methylation was observed in all 29 CpG sites of p14ARF and all 16 sites of p16INK4A with equally high densities. In EBV-negative GC, the methylation profiles differed between the 2 genes. Promoter methylation was sporadic and variable in p14ARF, and only the last position of CpG in p14ARF was methylated at high frequency. High-density methylation in p16INK4A was observed in a subset of GC, but the first position of CpG was never methylated in EBV-negative GC. These findings suggest the presence of mechanisms of de novo and maintenance methylation specific to EBVaGC that might be associated with EBV infection.

Promoter hypermethylation of E-cadherin and its abnormal expression in Epstein-Barr virus-associated gastric carcinoma

Promoter hypermethylation of various tumor-related genes is extremely frequent in Epstein-Barr virus (EBV)-associated gastric carcinoma (EBVaGC). To investigate the significance of the promoter methylation in EBVaGC, we focused on one of the important proteins in the carcinogenesis of the stomach, E-cadherin. Methylation-specific PCR analysis (MSP) was applied to surgically resected gastric carcinomas, together with immunohistochemistry, PCR-based analysis of mutations and allelic loss, and site-specific MSP of E-cadherin gene. By MSP, nearly all of the carcinomas showed aberrant methylation of E-cadherin promoter in EBVaGC (21/22), and the frequency of this aberration was significantly higher than that in EBV-negative gastric carcinoma (GC; 45/81; p = 0.0003). According to immunohistochemistry of E-cadherin, the frequency of abnormal staining pattern in EBVaGC (87%) was comparable to that in the diffuse type (80%), but higher than that in the intestinal type of EBV-negative GC (47%). Promoter methylation was well correlated with abnormal staining pattern in EBVaGC, but not in EBV-negative GC. Neither mutation nor allelic loss of E-cadherin was observed in EBVaGC. Methylation status of E-cadherin within each carcinoma was heterogeneous as far as examined. Thus, in addition to the known association involving p16, we determined that promoter methylation-mediated silencing of E-cadherin gene was also closely associated with the development of EBVaGC, although it becomes heterogeneous within a given tumor along its progression.

Reduced expression and promoter methylation of p16 gene in Epstein-Barr virus-associated gastric carcinoma

Epstein-Barr virus (EBV)-associated gastric carcinoma (EBVaGC) is a unique type of gastric carcinoma (GC), which is considered to develop in a different pathway from EBV-negative GC. To evaluate a possible role of p16, an inhibitor of G1/S transition of the cell cycle, in the carcinogenesis of EBVaGC, p16-immunohistochemistry and methylation-specific PCR analysis (MSP) were applied to surgically resected gastric carcinomas. When the percentage of p16-positive cells in more than 1000 carcinoma cells was expressed as p16 labeling index (p16-LI), it ranged from 2.5 to 88.1 (mean 42.9+/-24.4) in 70 gastric carcinomas. EBVaGC showed significantly lower values (n=15, 26.1+/ -22.1) than EBV-negative GC (n=55, 47.5+/-23.2) (P=0.0036). Fresh frozen tissues of 55 gastric carcinomas (16 EBVaGC and 39 EBV-negative GC) were further subjected to MSP, to evaluate abnormal methylation of the promoter region of the p16 gene. The frequency of methylation was significantly higher in EBVaGC (14/16) than in EBV-negative GC (9/39) (<0.0001). The methylation-positive carcinomas showed significantly lower p16-LI (35.9+/-21.6) than the unmethylated ones (55.2+/-22.7) (P=0.0014). Thus, a marked decrease of p16 expression, caused by the aberrant methylation of the p16 gene promoter, is closely associated with the development of EBVaGC.