Gastritis-Infection-Cancer Sequence of Epstein-Barr Virus-Associated Gastric Cancer

The Role of LMP1 in Epstein-Barr Virus-associated Gastric Cancer

EBV promotes many cancers such as lymphoma, nasopharyngeal carcinoma, and gastric; Latent Membrane Protein 1 (LMP1) is considered to be a major oncogenic protein encoded by Epstein- Barr virus (EBV). LMP1 functions as a carcinogen in lymphoma and nasopharyngeal carcinoma, and LMP1 may also promote gastric cancer. The expression level of LMP1 in host cells is a key determinant in tumorigenesis and maintenance of virus specificity. By promoting cell immortalization and cell transformation, promoting cell proliferation, affecting immunity, and regulating cell apoptosis, LMP1 plays a crucial tumorigenic role in epithelial cancers. However, very little is currently known about LMP1 in Epstein-Barr virus-associated gastric cancer (EBVaGC); the main reason is that the expression level of LMP1 in EBVaGC is comparatively lower than other EBV-encoded proteins, such as The Latent Membrane Protein 2A (LMP2A), Epstein-Barr nuclear antigen 1 (EBNA1) and BamHI-A rightward frame 1 (BARF1), to date, there are few studies related to LMP1 in EBVaGC. Recent studies have demonstrated that LMP1 promotes EBVaGC by affecting The phosphatidylinositol 3-kinase- Akt (PI3K-Akt), Nuclear factor-kappa B (NF-κB), and other signaling pathways to regulate many downstream targets such as Forkhead box class O (FOXO), C-X-C-motif chemokine receptor (CXCR), COX-2 (Cyclooxygenase-2); moreover, the gene methylation induced by LMP1 in EBVaGC has become one of the characteristics that distinguish this gastric cancer (GC) from other types of gastric cancer and LMP1 also promotes the formation of the tumor microenvironment (TME) of EBVaGC in several ways. This review synthesizes previous relevant literature, aiming to highlight the latest findings on the mechanism of action of LMP1 in EBVaGC, summarize the function of LMP1 in EBVaGC, lay the theoretical foundation for subsequent new research on LMP1 in EBVaGC, and contribute to the development of novel LMP1-targeted drugs.

Endoscopic Diagnosis and Therapy for Epstein-Barr Virus-Associated Gastric Cancer

Epstein-Barr-virus-associated gastric cancer (EBVaGC) represents almost 7% of all GC and is a distinct subtype of GC with extreme DNA hypermethylation. EBVaGC is a tumor-infiltrating lymphocyte-rich tumor with little lymph-node metastasis in its early stage and with a relatively favorable prognosis in its advanced stage. Using upper gastrointestinal endoscopy, we recognize EBVaGC as a mainly depressed type with SMT-like protrusion in the upper part of the stomach near the gastric mucosal atrophic border or remnant stomach. The EBVaGC recognition rate of 21.4% with the endoscopic motif is not high, and further progress in endoscopic diagnosis of EBVaGC is needed. As less invasive endoscopic therapy, the extension of the criteria of endoscopic submucosal dissection (ESD) for early EBVaGC with little lymph-node metastasis should be discussed. Endoscopic diagnosis of EBVaGC may be relevant for the selection of patients who could benefit from endoscopic treatment or chemotherapy.

Prognostic roles of leptin-signaling proteins, PD-L1, and tumor-infiltrating lymphocytes in surgically-resected biliary tract cancers

BACKGROUND

Biliary tract cancers are rare, with a poor patient prognosis. Leptin and programmed death-ligand 1 (PD-L1) influence CD8⁺ and forkhead box P3 (FOXP3)⁺ lymphocytes, and thus, cancer cell growth. We aimed to define the prognostic implications of these variables and the clinicopathological features of biliary tract cancers.

METHODS

Immunohistochemistry for leptin signaling-related proteins (leptin, leptin receptor, pSTAT3, extracellular-regulated kinase, mammalian target of rapamycin), PD-L1, CD8, and FOXP3 and in situ hybridization for Epstein-Barr virus-encoded small RNAs were performed in 147 cases of surgically-resected biliary tract cancers.

RESULTS

Immune cell PD-L1-positivity, tumor size < 3 cm, adjuvant chemotherapy, no recurrence, and early-stage tumors were correlated with better 5-year survival in the tumoral PD-L1^(-) and leptin^(-) subgroups, and extrahepatic cholangiocarcinoma through multivariate analysis (all p < 0.05). Immune cell PD-L1 and adjuvant chemotherapy lost its prognostic significance in the tumoral PD-L1⁺ and leptin⁺ subgroups.

CONCLUSIONS

The prognostic implication of the variables may depend upon tumoral protein expression and the anatomical site. Immune cell PD-L1-positivity and the administration of adjuvant chemotherapy may indicate the favorable survival of patients with surgically-resected biliary tract cancers, specifically, in the tumoral PD-L1^(-) or tumor leptin^(-) subgroups and extrahepatic cholangiocarcinoma. PD-L1- or leptin-targeted therapy combined with conventional chemotherapy may benefit the tumoral PD-L1⁺ or leptin⁺ subgroups.

EBV persistence in gastric cancer cases conventionally classified as EBER-ISH negative

Background

The Epstein-Barr virus (EBV) causes various B-cell lymphomas and epithelial malignancies, including gastric cancer (GC) at frequencies ranging from 5 to 10% in adenocarcinomas (ADK) to 80% in GC with lymphoid stroma (GCLS). Using high-sensitivity methods, we recently detected EBV traces in a large cohort of EBV-negative B-cell lymphomas, suggesting a hit-and-run mechanism.

Methods

Here, we used routine and higher-sensitivity methods [droplet digital PCR (ddPCR) for EBV segments on microdissected tumour cells and RNAscope for EBNA1 mRNA] to assess EBV infection in a cohort of 40 GCs (28 ADK and 12 GCLS).

Results

ddPCR documented the presence of EBV nucleic acids in rare tumour cells of several cases conventionally classified as EBV-negative (ADK, 8/26; GCLS, 6/7). Similarly, RNAscope confirmed EBNA1 expression in rare tumour cells (ADK, 4/26; GCLS, 3/7). Finally, since EBV induces epigenetic changes that are heritable and retained after complete loss of the virus from the host cell, we studied the methylation pattern of EBV-specifically methylated genes (Timp2, Eya1) as a mark of previous EBV infection. Cases with EBV traces showed a considerable level of methylation in Timp2 and Eya1 genes that was similar to that observed in EBER-ISH positive cases and greater than cases not featuring any EBV traces.

Conclusions

These findings suggest that: (a) EBV may contribute to gastric pathogenesis more widely than currently acknowledged and (b) indicate the methylation changes as a mechanistic framework for how EBV can act in a hit-and-run manner. Finally, we found that the viral state was of prognostic significance in univariate and multivariate analyses.

Immunosuppressive Tumor Microenvironment and Immunotherapy of Epstein–Barr Virus-Associated Malignancies

The Epstein–Barr virus (EBV) can cause different types of cancer in human beings when the virus infects different cell types with various latent patterns. EBV shapes a distinct and immunosuppressive tumor microenvironment (TME) to its benefit by influencing and interacting with different components in the TME. Different EBV-associated malignancies adopt similar but slightly specific immunosuppressive mechanisms by encoding different EBV products to escape both innate and adaptive immune responses. Strategies reversing the immunosuppressive TME of EBV-associated malignancies have been under evaluation in clinical practice. As the interactions among EBV, tumor cells, and TME are intricate, in this review, we mainly discuss the epidemiology of EBV, the life cycle of EBV, the cellular and molecular composition of TME, and a landscape of different EBV-associated malignancies and immunotherapy by targeting the TME.

Gastric Carcinoma with Lymphoid Stroma: A Combination of Mismatch Repair Deficient Medullary Type and Epstein-Barr Virus-associated Gastric Carcinomas

Gastric carcinomas consist of a heterogeneous group of neoplasms with broad cytological and architectural variations. Gastric carcinomas with lymphoid stroma show poor correlation between their histomorphology and biological behavior. This contrast causes a need for more detailed analysis and molecular exploration of lymphoid stroma-rich gastric carcinomas with medullary like features and lack of glandular differentiation. In this study, we performed a detailed retrospective analysis of 53 gastric carcinomas among 654 gastric tumors from surgical resection specimens, all of which had no prominent glandular differentiation. Morphological and clinical data were compared with immunohistochemistry (MLH1, PMS2, MSH2 and MSH6 for mismatch repair mechanism deficiency; CD2, CD8 and CD163 for immune infiltration; and PD-1, PD-L1, LMP-1, ERBB2 and ki-67) besides EBER in situ hybridization and molecular studies (PCR based microsatellite instability and BRAF V600E mutation analysis). Morphological, immunohistochemical and molecular findings lead us to classify lymphoid stroma-rich advanced gastric carcinomas (n = 40/53) into two distinct entities originating from two different pathogenetic pathway: one is gastric carcinomas revealing predominantly medullary type morphology with defective DNA mismatch repair mechanism (n = 30/53) and the other is EBV associated carcinomas (n = 10/53). In addition, we suggest that biomarker based classification algorithms besides morphological evaluation are necessary to identify these two entities. Distinguishing these entities is crucial to apply different treatment strategies, including alternative treatments such as immunotherapy.

Bacterial-Viral Interactions in Human Orodigestive and Female Genital Tract Cancers: A Summary of Epidemiologic and Laboratory Evidence

Infectious agents, including viruses, bacteria, fungi, and parasites, have been linked to pathogenesis of human cancers, whereas viruses and bacteria account for more than 99% of infection associated cancers. The human microbiome consists of not only bacteria, but also viruses and fungi. The microbiome co-residing in specific anatomic niches may modulate oncologic potentials of infectious agents in carcinogenesis. In this review, we focused on interactions between viruses and bacteria for cancers arising from the orodigestive tract and the female genital tract. We examined the interactions of these two different biological entities in the context of human carcinogenesis in the following three fashions: (1) direct interactions, (2) indirect interactions, and (3) no interaction between the two groups, but both acting on the same host carcinogenic pathways, yielding synergistic or additive effects in human cancers, e.g., head and neck cancer, liver cancer, colon cancer, gastric cancer, and cervical cancer. We discuss the progress in the current literature and summarize the mechanisms of host-viral-bacterial interactions in various human cancers. Our goal was to evaluate existing evidence and identify gaps in the knowledge for future directions in infection and cancer.

Virus-host interactions in carcinogenesis of Epstein-Barr virus-associated gastric carcinoma: Potential roles of lost ARID1A expression in its early stage

Epstein-Barr virus (EBV)-associated gastric carcinoma (EBVaGC) is a distinct molecular subtype of gastric cancer characterized by viral infection and cellular abnormalities, including loss of AT-rich interaction domain 1A (ARID1A) expression (lost ARID1A). To evaluate the significance of lost ARID1A in the development of EBVaGC, we performed in situ hybridization of EBV-encoded RNA (EBER) and immunohistochemistry of ARID1A in the non-neoplastic gastric mucosa and intramucosal cancer tissue of EBVaGC with in vitro infection analysis of ARID1A-knockdown and -knockout gastric cells. Screening of EBER by in situ hybridization revealed a frequency of approximately 0.2% EBER-positive epithelial cells in non-neoplastic gastric mucosa tissue samples. Six small foci of EBV-infected epithelial cells showed two types of histology: degenerated (n = 3) and metaplastic (n = 3) epithelial cells. ARID1A was lost in the former type. In intramucosal EBVaGC, there were ARID1A-lost (n = 5) and -preserved tumors (n = 7), suggesting that ARID1A-lost carcinomas are derived from ARID1A-lost precursor cells in the non-neoplastic mucosa. Lost ARID1A was also observed in non-neoplastic mucosa adjacent to an ARID1A-lost EBVaGC. In vitro experiments using siRNA knockdown and the CRISPR/Cas9-knockout system demonstrated that transient reduction or permanent loss of ARID1A expression markedly increased the efficiency of EBV infection to stomach epithelial cells. Taken together, lost ARID1A plays a role in initiating EBV-driven carcinogenesis in stomach epithelial cells, which develop to a distinct subtype of EBVaGC within the proper mucosal layer. Lost ARID1A is one of the constituents of virus-host interactions in the carcinogenesis of EBVaGC.

Chromatin remodeler ARID1A binds IRF3 to selectively induce antiviral interferon production in macrophages

Transcription factor IRF3 is critical for the induction of antiviral type I interferon (IFN-I). The epigenetic regulation of IFN-I production in antiviral innate immunity needs to be further identified. Here, we reported that epigenetic remodeler ARID1A, a critical component of the mSWI/SNF complex, could bind IRF3 and then was recruited to the Ifn-I promoter by IRF3, thus selectively promoting IFN-I but not TNF-α, IL-6 production in macrophages upon viral infection. Myeloid cell-specific deficiency of Arid1a rendered mice more susceptible to viral infection, accompanied with less IFN-I production. Mechanistically, ARID1A facilitates chromatin accessibility of IRF3 at the Ifn-I promoters by interacting with histone methyltransferase NSD2, which methylates H3K4 and H3K36 of the promoter regions. Our findings demonstrated the new roles of ARID1A and NSD2 in innate immunity, providing insight into the crosstalks of chromatin remodeling, histone modification, and transcription factors in the epigenetic regulation of antiviral innate immunity.

Insights Into Exosomal Non-Coding RNAs Sorting Mechanism and Clinical Application

Exosomes are natural nanoscale bilayer phospholipid vesicles that can be secreted by almost all types of cells and are detected in almost all types of body fluids. Exosomes are effective mediators of cell–cell signaling communication because of their ability to carry and transfer a variety of bioactive molecules, including non-coding RNAs. Non-coding RNAs have also been found to exert strong effects on a variety of biological processes, including tumorigenesis. Many researchers have established that exosomes encapsulate bioactive non-coding RNAs that alter the biological phenotype of specific target cells in an autocrine or a paracrine manner. However, the mechanism by which the producer cells package non-coding RNAs into exosomes is not well understood. This review focuses on the current research on exosomal non-coding RNAs, including the biogenesis of exosomes, the possible mechanism of sorting non-coding RNAs, their biological functions, and their potential for clinical application in the future.

Cancer stem cells in Epstein-Barr virus-associated gastric carcinoma

Cancer stem cells (CSCs) play a decisive role in the development and progression of cancer. To investigate CSCs in Epstein-Barr virus (EBV)-associated carcinoma (EBVaGC), we screened previously reported stem cell markers of gastric cancer in EBV-infected gastric cancer cell lines (TMK1 and NUGC3) and identified CD44v6v9 double positive cells as candidate CSCs. CD44v6/v9^+/+ cells were sorted from EBVaGC cell line (SNU719) cells and EBV-infected TMK1 cells and these cell populations showed high spheroid-forming ability and tumor formation in SCID mice compared with the respective CD44v6/v9^-/- cells. Sphere-forming ability was dependent on the nuclear factor-κB (NF-κB) signaling pathway, which was confirmed by decrease of sphere formation ability under BAY 11-7082. Small interfering RNA knockdown of latent membrane protein 2A (LMP2A), one of the latent gene products of EBV infection, decreased spheroid formation in SNU719 cells. Transfection of the LMP2A gene increased the sphere-forming ability of TMK1 cells, which was mediated through NF-κB signaling. Together, these results indicate that CD44v6v9^+/+ cells are CSCs in EBVaGC that are maintained through the LMP2A/NF-κB pathway. Future studies should investigate CD44v6/v9^+/+ cells in normal and neoplastic gastric epithelium to prevent and treat this specific subtype of gastric cancer infected with EBV.

Potential prognostic impact of EBV RNA-seq reads in gastric cancer: a reanalysis of The Cancer Genome Atlas cohort

Epstein-Barr virus (EBV)-associated gastric cancer (EBVaGC), whose prognosis remains controversial, is diagnosed by in situ hybridization of EBV-derived EBER1/2 small RNAs. In The Cancer Genome Atlas (TCGA) Stomach Adenocarcinoma (STAD) project, the EBV molecular subtype was determined through a combination of multiple next-generation sequencing methods, but not by the gold standard in situ hybridization method. This leaves unanswered questions regarding the discordance of EBV positivity detected by different approaches and the threshold of sequencing reads. Therefore, we reanalyzed the TCGA-STAD RNA sequencing (RNA-seq) dataset including 375 tumor and 32 normal samples, using our analysis pipeline. We defined a reliable threshold for EBV-derived next-generation sequencing reads by mapping them to the EBV genome with three different random arbitrary alignments. We analyzed the prognostic impact of EBV status on the histopathological subtypes of gastric cancer. EBV-positive cases identified by reanalysis comprised nearly half of the cases (49.6%) independent from infiltrating lymphocyte signatures, and showed significantly longer overall survival for adenocarcinomas of the 'not-otherwise-specified' type [P = 0.016 (log-rank test); hazard ratios (HR): 0.476; 95% CI: 0.260-0.870, P = 0.016 (Cox univariate analysis)], but shorter overall survival for the tubular adenocarcinoma type [P = 0.005 (log-rank test); HR: 3.329; 95% CI: 1.406-7.885, P = 0.006 (Cox univariate analysis)]. These results demonstrate that the EBV positivity rates were higher when determined by RNA-seq than when determined by EBER1/2 in situ hybridization. The RNA-seq-based EBV positivity demonstrated distinct results for gastric cancer prognosis depending on the histopathological subtype, suggesting its potential to be used in clinical prognoses.

The impact of EBV on the epigenetics of gastric carcinoma

EBV is an important human tumor virus and is closely related to the occurrence of a variety of tumors, involving 10% of gastric cancer. In EBV-associated gastric carcinoma (EBVaGC), EBV expresses restrict viral genes including EBV nuclear antigen 1, EBV encoded small RNAs, Bam HI-A rightward transcripts, latent membrane protein 2A and miRNAs. The role of EBV in gastric carcinogenesis has received increasing attention and is considered to be another pathogenic factor in addition to Helicobacter pylori. A typical characteristic of EBVaGC is the extensive methylation of viral and host genome. Combined with other epigenetic mechanisms, EBV infection acts as an epigenetic driver of EBVaGC oncogenesis. In this review we discuss recent findings of EBV effect on host epigenetic alterations in EBVaGC and its role in oncogenic process.

Epstein-Barr Virus and Helicobacter Pylori Co-Infection in Non-Malignant Gastroduodenal Disorders

Epstein–Barr virus (EBV) and Helicobacter pylori (H. pylori) are two pathogens associated with the development of various human cancers. The coexistence of both microorganisms in gastric cancer specimens has been increasingly reported, suggesting that crosstalk of both pathogens may be implicated in the carcinogenesis process. Considering that chronic inflammation is an initial step in the development of several cancers, including gastric cancer, we conducted a systematic review to comprehensively evaluate publications in which EBV and H. pylori co-infection has been documented in patients with non-malignant gastroduodenal disorders (NMGDs), including gastritis, peptic ulcer disease (PUD), and dyspepsia. We searched the PubMed database up to August 2019, as well as publication references and, among the nine studies that met the inclusion criteria, we identified six studies assessing EBV infection directly in gastric tissues (total 949 patients) and three studies in which EBV infection status was determined by serological methods (total 662 patients). Due to the substantial methodological and clinical heterogeneity among studies identified, we could not conduct a meta-analysis. The overall prevalence of EBV + H. pylori co-infection in NMGDs was 34% (range 1.8% to 60%). A higher co-infection rate (EBV + H. pylori) was reported in studies in which EBV was documented by serological methods in comparison with studies in which EBV infection was directly assessed in gastric specimens. The majority of these studies were conducted in Latin-America and India, with most of them comparing NMGDs with gastric cancer, but there were no studies comparing the co-infection rate in NMGDs with that in asymptomatic individuals. In comparison with gastritis caused by only one of these pathogens, EBV + H. pylori co-infection was associated with increased severity of gastric inflammation. In conclusion, only relatively small studies testing EBV and H. pylori co-infection in NMGDs have been published to date and the variable report results are likely influenced by geographic factors and detection methods.

Thirty years of Epstein-Barr virus-associated gastric carcinoma

Thirty years have passed since a possible association of Epstein-Barr virus (EBV) with gastric carcinoma was reported. We now know EBV-associated gastric carcinoma to be a specific subtype of gastric carcinoma. Global epigenetic methylation and counteraction of the antitumour microenvironment are two major characteristics of this subtype of gastric carcinoma. Recent development of therapeutic modalities for gastric carcinoma, such as endoscopic mucosal dissection and immune checkpoint inhibitor therapy, has made the presence of EBV infection a biomarker for the treatment of gastric carcinoma. This review presents a portrait of EBV-associated gastric carcinoma from initiation to maturity that we define as the 'gastritis-infection-cancer sequence', followed by its molecular abnormalities and interactions with immune checkpoint molecules and the microenvironment. EBV non-coding RNAs (microRNA and circular RNA) and exosomes derived from EBV-infected cells that were previously behind the scenes are now recognized for their roles in EBV-associated gastric carcinoma. The virus utilizes cellular machinery skilfully to control infected cells and their microenvironment. We should thus strive to understand virus-host interactions more fully in the following years to overcome this virus-driven subtype of gastric carcinoma.

Proposal for an Organ-Specific Chronic Inflammation–Remodeling–Carcinoma Sequence

An organ-specific chronic inflammation–remodeling–carcinoma sequence has been proposed, mainly for the alimentary tract. As representative diseases, gastroesophageal reflux disease, chronic gastritis and inflammatory bowel disease (ulcerative colitis and Crohn’s disease of the colitis type) were adopted for this discussion. Tissue remodeling is such an important part of tumorigenesis in this sequence that an organ-specific chronic inflammation–remodeling–carcinoma sequence has been proposed in detail. Chronic inflammation accelerates the cycle of tissue injury and regeneration; in other words, cell necrosis (or apoptosis) and proliferation result in tissue remodeling in long-standing cases of inflammation. Remodeling encompasses epithelial cell metaplasia and stromal fibrosis, and modifies epithelial–stromal cell interactions. Further, the accumulation of genetic, epigenetic and molecular changes—as well as morphologic disorganization—also occurs during tissue remodeling. The expression of mucosal tissue adapted to chronic inflammatory injury is thought to occur at an early stage. Subsequently, dysplasia and carcinoma develop on a background of remodeling due to continuous, active inflammation. Accordingly, organ-specific chronic inflammation should be ameliorated or well controlled with appropriate monitoring if complete healing is unachievable.

Epstein-Barr virus strain variation and cancer

Epstein-Barr virus (EBV) is a human tumor virus and is etiologically linked to various malignancies. Certain EBV-associated diseases, such as Burkitt lymphomas and nasopharyngeal carcinomas, are endemic and exhibit biased geographic distribution worldwide. Recent advances in deep sequencing technology enabled high-throughput sequencing of the EBV genome from clinical samples. Rapid cloning and sequencing of cancer-derived EBV genomes, followed by reconstitution of infectious virus, have also become possible. These developments have revealed that various EBV strains are differentially distributed throughout the world, and that the behavior of cancer-derived EBV strains is different from that of the prototype EBV strain of non-cancerous origin. In this review, we summarize recent progress and future perspectives regarding the association between EBV strain variation and cancer.

Molecular features and translational outlook for Epstein-Barr virus-associated gastric cancer

Epstein-Barr Virus (EBV) was the first discovered human tumor virus and is the etiological agent of B cell lymphomas and also epithelial cancers. Indeed, nearly 10% of gastric cancers worldwide are EBV-positive and display unique molecular, epigenetic, and clinicopathological features. EBV-positive gastric cancers display the highest rate of host genome methylation of all tumor types studied and harbor recurrent mutations activating PI3Kα, silencing ARID1A, and amplifying PD-L1. While EBV infection of B cells can be studied efficiently, de novo epithelial cell infection is much more difficult. We propose that new culture models including 3D-based gastric organoids and xenografts can bring new insight into EBV-induced gastric carcinogenesis and will lead to improved precision medicine-based therapies for patients with EBV-positive gastric cancer.