Downregulation of EB virus miR-BART4 inhibits proliferation and aggressiveness while promoting radiosensitivity of nasopharyngeal carcinoma.

Objective: This study aims to explore the role of Epstein-Barr virus (EBV) miR-BART4 in occurrence and progression of nasopharyngeal carcinoma (NPC) and its effect on radiosensitivity.

Method: The expressions of EBV and miR-BART4 in 108 cases of NPC tissues and 97 cases of chronic nasopharyngeal inflammation tissues were determined by real time quantitative polymerase chain reaction (PCR), and the relationship between the expression of miR-BART4 and the clinicopathological features of NPC was analyzed. Cell lines, HONEl, CNEl, CNE2, C666-1, 6-10B, and NP-69 were used to compare the expression of miR-BART4, in which the CNE2 cells were selected for further experiments. CNE2 cells were grouped into blank group, negative control (NC) group, miR-BART4 inhibitors group and miR-BART4 mimics group. Cells in above groups were under radiation of 6 Gy X ray for 12 h before grouped into control group, 6 Gy group, NC + 6 Gy group, miR-BART4 inhibitors + 6 Gy group and miR-BART4 mimics + 6 Gy group. Cell proliferation, clone formation ability, cell apoptosis, invasion and migration ability were measured by MTT assay, clone formation assay, flow cytometry (FCM), Transwell assay and scratch test, respectively. Western blot analysis was used to detect the expression of apoptosis-related proteins (cleaved caspase-3, Bax and Bcl-2) and epithelial-mesenchymal transition (EMT) marker protein E-cadherin and Vimentin. mRNA and protein expression of PTEN were detected by qRT-PCR and western blot. Bioinformatics software and luciferase activity experiments were used to verify the targeting relationship between miR-BART4 and PTEN.

Results: Positive rate of EBV in NPC tissues (93.5%) was remarkably higher than that in chronic nasopharyngeal inflammation tissues (21.6%). miR-BART4 was highly expressed and mRNA and protein expression of PTEN was lowly expressed in EBV positive NPC tissues compared with EBV negative NPC tissues and chronic nasopharyngeal inflammation tissues. The expression of miR-BART4 was related to the clinical stage, lymph node metastasis and differentiation degree of NPC. Expression of miR-BART4 in CNE2, CNEl, HONEl, C666-1, 6-10B, 5-8F cells was higher than that in NP-69 cells. In CNE2 and C666-1 cell experiments, compared with blank group and NC group, miR-BART4 inhibitors group had decreased miR-BART4 expression, increased mRNA and protein expression of PTEN, cell survival rate, invasion and migration ability and increased cell apoptosis rate, which is totally contrary to the observation in miR-BART4 mimics group. The radiosensitive NPC tissues had higher miR-BART4 expression than that in radio-resistance NPC tissues. In comparison to 6 Gy group and NC + 6 Gy group, cell survival rate and clone number was inhibited, but the cell apoptosis rate was increased in miR-BART4 inhibitors +6 G group, in contrary to the observation in miR-BART4 inhibitors + 6 Gy group. Bioinformatics software and luciferase activity experiments confirmed that miR-BART4 could inhibit the expression of PTEN.

Conclusion: EBV may promote development and progression of NPC by up-regulating miR-BART4 expressions, consequently inhibiting its radiosensitivity, whose effect may be related to the targeting inhibition of PTEN expression.