Update on Epstein-Barr virus and gastric cancer (review)

Expression and prognostic roles of PIK3CA, JAK2, PD-L1, and PD-L2 in Epstein-Barr virus-associated gastric carcinoma

As a special subtype of gastric carcinoma, Epstein-Barr virus (EBV)-associated gastric carcinoma (EBVaGC) has distinct clinicopathological features. The Cancer Genome Atlas Research Network revealed that EBVaGC also has distinct molecular features: PIK3CA mutations, DNA hypermethylation, and JAK2, PD-L1, and PD-L2 amplification. Here, we evaluated PIK3CA, JAK2, PD-L1, and PD-L2 expression in 59 EBVaGC and 796 EBV-negative gastric carcinoma (EBVnGC) cases using immunohistochemistry and found that PIK3CA, JAK2, PD-L1, and PD-L2 were highly expressed in 75.9% and 48.8% (P<.001), 81.8% and 71.1% (P=.091), 92.5% and 84.8% (P=.132), and 98.1% and 89.7% (P=.049) of the EBVaGC and EBVnGC cases, respectively. However, the expression of PIK3CA, JAK2, PD-L1, or PD-L2 was not significantly associated with clinicopathological features or patient outcomes in EBVaGC. In contrast, in EBVnGC, high PIK3CA expression was significantly associated with indolent clinicopathological features and independently predicted better 5-year overall survival (57.8% versus 33.4%, P<.001). Our study indicated that the protein expression of the 4 characteristic molecules of EBVaGC was basically consistent with their genetic alterations, making them potential characteristic protein biomarkers and therapeutic targets of EBVaGC. The favorable impact of PIK3CA overexpression on survival found in this study gives us new insight into the clinical significance of PIK3CA in EBVnGC.

Epstein-Barr Virus and Gastric Cancer Risk: A Meta-analysis With Meta-regression of Case-control Studies

Objectives:

Research on how the risk of gastric cancer increases with Epstein-Barr virus (EBV) infection is lacking. In a systematic review that investigated studies published until September 2014, the authors did not calculate the summary odds ratio (SOR) due to heterogeneity across studies. Therefore, we include here additional studies published until October 2015 and conduct a meta-analysis with meta-regression that controls for the heterogeneity among studies.

Methods:

Using the studies selected in the previously published systematic review, we formulated lists of references, cited articles, and related articles provided by PubMed. From the lists, only case-control studies that detected EBV in tissue samples were selected. In order to control for the heterogeneity among studies, subgroup analysis and meta-regression were performed.

Results:

In the 33 case-control results with adjacent non-cancer tissue, the total number of test samples in the case and control groups was 5280 and 4962, respectively. In the 14 case-control results with normal tissue, the total number of test samples in case and control groups was 1393 and 945, respectively. Upon meta-regression, the type of control tissue was found to be a statistically significant variable with regard to heterogeneity. When the control tissue was normal tissue of healthy individuals, the SOR was 3.41 (95% CI, 1.78 to 6.51; I-squared, 65.5%).

Conclusions:

The results of the present study support the argument that EBV infection increases the risk of gastric cancer. In the future, age-matched and sex-matched case-control studies should be conducted.

Role of Viral miRNAs and Epigenetic Modifications in Epstein-Barr Virus-Associated Gastric Carcinogenesis

MicroRNAs are short (21–23 nucleotides), noncoding RNAs that typically silence posttranscriptional gene expression through interaction with target messenger RNAs. Currently, miRNAs have been identified in almost all studied multicellular eukaryotes in the plant and animal kingdoms. Additionally, recent studies reported that miRNAs can also be encoded by certain single-cell eukaryotes and by viruses. The vast majority of viral miRNAs are encoded by the herpesviruses family. These DNA viruses including Epstein-Barr virus encode their own miRNAs and/or manipulate the expression of cellular miRNAs to facilitate respective infection cycles. Modulation of the control pathways of miRNAs expression is often involved in the promotion of tumorigenesis through a specific cascade of transduction signals. Notably, latent infection with Epstein-Barr virus is considered liable of causing several types of malignancies, including the majority of gastric carcinoma cases detected worldwide. In this review, we describe the role of the Epstein-Barr virus in gastric carcinogenesis, summarizing the functions of the Epstein-Barr virus-encoded viral proteins and related epigenetic alterations as well as the roles of Epstein-Barr virus-encoded and virally modulated cellular miRNAs.

Identification of Epstein-Barr Virus Replication Proteins in Burkitt's Lymphoma Cells

The working model to describe the mechanisms used to replicate the cancer-associated virus Epstein-Barr virus (EBV) is partly derived from comparisons with other members of the Herpes virus family. Many genes within the EBV genome are homologous across the herpes virus family. Published transcriptome data for the EBV genome during its lytic replication cycle show extensive transcription, but the identification of the proteins is limited. We have taken a global proteomics approach to identify viral proteins that are expressed during the EBV lytic replication cycle. We combined an enrichment method to isolate cells undergoing EBV lytic replication with SILAC-labeling coupled to mass-spectrometry and identified viral and host proteins expressed during the EBV lytic replication cycle. Amongst the most frequently identified viral proteins are two components of the DNA replication machinery, the single strand DNA binding protein BALF2, DNA polymerase accessory protein BMRF1 and both subunits of the viral ribonucleoside-diphosphate reductase enzyme (BORF2 and BaRF1). An additional 42 EBV lytic cycle proteins were also detected. This provides proteomic identification for many EBV lytic replication cycle proteins and also identifies post-translational modifications.

Pathogenesis of Gastric Cancer

Gastric cancer (GC) is the fifth most common malignancy and the third leading cause of cancer-related death worldwide. GC is a heterogeneous disease and the endpoint of a long multistep process largely influenced by Helicobacter pylori infection, genetic susceptibility, and environmental factors. In a subset of GC cases, infection with the Epstein-Barr virus (EBV) may also be involved. The development of GC is the consequence of the accumulation of multiple epi/genetic changes during the patient's lifetime that will result in oncogenic activation and/or tumor suppressor pathways' inactivation. This review will focus on the most recent updates on the characterization of the molecular phenotypes of sporadic and hereditary GC. This article will also update the most recent findings on the relationship between H. pylori infection and stem cells at the origin of GC. The understanding of the molecular genetics underlying gastric carcinogenesis is of paramount importance to identify novel potential targets for the development of screening and prognostic markers that can be clinically valuable for the management of GC patients and for the design of clinical trials.

Epstein-Barr Virus-Associated Gastric Carcinoma: Use of Host Cell Machineries and Somatic Gene Mutations

Epstein-Barr virus (EBV)-associated gastric carcinoma (EBVaGC) is a distinct subtype of gastric carcinoma, consisting of clonal growth of EBV-infected epithelial cells. Its unique characteristics have been demonstrated by epidemiological, clinical and pathological studies using in situ hybridization for EBV-encoded small RNAs. An oncogenic process for EBVaGC has also been revealed. EBV uses various host-cell machineries, including cell division machinery to propagate clonal virus genomes, DNA-methylation machinery to epigenetically control infected cells, and microRNA and exosome machineries to modify the behavior and microenvironment of infected cells. Recent comprehensive molecular analyses from The Cancer Genome Atlas project demonstrate that EBVaGC is a representative molecular subtype that is distinct from microsatellite unstable, genomically stable and chromosome unstable subtypes. In addition to having the highest level of DNA methylation in CpG islands of promoter regions, EBVaGC harbors particular gene alterations, including a high frequency of mutations in PIK3CA and ARID1A, mutation in BCOR, and amplification of PD-L1 and PD-L2. Although currently undetermined, the virus might use the altered cellular functions that are induced by these somatic mutations. Further investigation of virus-driven oncogenesis will enable hitherto unknown functions of stomach epithelial cell machineries to be elucidated, which may reveal potential therapeutic targets for EBVaGC.