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Epstein–Barr virus (EBV) is associated with various human malignancies. An association between EBV infection and oral squamous cell carcinoma (OSCC) has recently been reported. We established EBV-positive OSCC cells and demonstrated that EBV infection promoted OSCC progression. However, the mechanisms by which EBV promotes OSCC progression remain poorly understood. Therefore, we performed metabolic analyses of EBV-positive OSCC cells and established a xenograft model to investigate the viral contribution to OSCC progression. Here, we demonstrated that EBV infection induced mitochondrial stress by reducing the number of mitochondrial DNA (mtDNA) copies. Microarray data from EBV-positive OSCC cells showed altered expression of glycolysis-related genes, particularly the upregulation of key genes involved in the Warburg effect, including LDHA, GLUT1, and PDK1. Furthermore, lactate production and LDH activity were elevated in EBV-positive OSCC cells. EBV infection significantly upregulated the expression levels of cancer stem cell (CSC) markers such as CD44 and CD133 in the xenograft model. In this model, tumor growth was significantly increased in EBV-positive SCC25 cells compared with that in uninfected cells. Furthermore, tumorigenicity increased after serial passages of EBV-positive SCC25 tumors. This study revealed the oncogenic role of EBV in OSCC progression by inducing the Warburg effect and cancer stemness. [ABSTRACT FROM AUTHOR]

Epstein-Barr virus (EBV) encodes BamHIA rightward transcript (BART) microRNAs (miRNAs). These miRNAs are expressed at high levels in epithelial tumors, such as nasopharyngeal carcinoma (NPC). BART miRNAs play important roles in EBV-associated malignancies, however, the reason for their high expression in NPC is unclear. We performed multiple sequence alignment of six completely sequenced EBV strains: Akata, YCCEL1, SNU719, C666-1, Mutu I, and M81. A single-nucleotide deletion was identified at the promoter region of BART. The luciferase assay suggested that this single-nucleotide polymorphism (SNP) significantly increased BART promoter activity. In addition to deletion, substitution at the same site also increased BART promoter activity. Analysis of the 170 EBV genome sequences from NPC and EBV-associated gastric cancers revealed that the frequency of this SNP was associated with NPC incidence and this SNP was found to be accumulated in the BART promoter region. Overall, our results suggested that this SNP should enhance BART promoter activity and thus, might contribute to the development of EBV-associated epithelial malignancies. • EBV encoded BART miRNAs are highly expressed in epithelial tumors. • A SNP in the EBV miRNA promoter is prevalent in NPC cells. • The SNP significantly increased BART promoter activity. [ABSTRACT FROM AUTHOR]

The etiology of oral carcinogenesis appears to be multifactorial. There is emerging evidence of the presence of Epstein-Barr virus (EBV) in epithelial oral squamous cell carcinoma (OSCC), but an association of EBV with oral carcinogenesis has not yet been established. Although epigenetic alterations, such as aberrant DNA methylation, are known to contribute to the pathogenesis of oral cancer, the relationship of such alterations with EBV infection is little known. This study aimed to investigate the association between EBV infection and promoter methylation patterns of tumor-associated genes in OSCC tissues. A total of 165 of formalin-fixed paraffin-embedded OSCC tissues were studied (68 of EBV positive and 97 of EBV negative). The promoter methylation patterns were investigated for four tumor-associated genes, E-cadherin, p16 INK4a , p14 ARF , and MGMT, by using methylation-specific polymerase chain reaction (MSP). The frequencies of gene promoter hypermethylation in all cases were 47.3% for E-cadherin, 92.7% for p16 INK4a , 74.5% for p14 ARF , and 35.8% for MGMT. Interestingly, most of the analyzed gene promoters were more frequently hypermethylated in EBV-positive than EBV-negative cases, in particular the E-cadherin (56/22) and MGMT (38/21) gene promoters (p < 0.05). Concomitantly, hypermethylation of multiple gene promoters (≥3) was encountered more frequently in EBV-positive samples. Hypermethylation of the E-cadherin promoter associated with EBV was more frequently observed in moderately and poorly differentiated OSCC tissues. These results indicate that epigenetic changes frequently occur in OSCCs and may partly be induced by EBV infection, therefore, EBV may involve in development and progression of the OSCCs. [ABSTRACT FROM AUTHOR]

The Epstein–Barr virus (EBV) is a human herpesvirus associated with various cancers. The number of reports that describe infection of EBV in oral squamous carcinoma cells is increasing. However, there is no available in vitro model to study the possible role of EBV in the development of oral squamous cell carcinoma. Herein, we report establishment of a latent EBV infection of well-differentiated HSC1 cells and poorly differentiated SCC25 cells. Viral copy numbers per cell in EBV-infected HSC1 and SCC25 cells are 2 and 5, respectively. Although the EBV copy number was small, spontaneous viral replication was observed in EBV-infected HSC1 cells. Contrarily, infectious viral production was not observed in EBV-infected SCC25 cells, despite containing larger number of EBV genomes. Chemical activation of cells induced expression of viral lytic BZLF1 gene in EBV-infected HSC1 cells, but not in EBV-infected SCC25 cells. EBV infection activated proliferation and migration of HSC1 cells. However, EBV-infection activated migration but not proliferation in SCC25 cells. In conclusion, EBV can infect squamous cells and establish latent infection, but promotion of cell proliferation and of lytic EBV replication may vary depending on stages of cell differentiation. Our model can be used to study the role of EBV in the development of EBV-associated oral squamous cell carcinoma. [ABSTRACT FROM AUTHOR]