Epstein-Barr Virus-Encoded MicroRNA BART15-3p Promotes Cell Apoptosis Partially by Targeting BRUCE

Epstein-Barr Virus (EBV) generates a variety of viral microRNAs (miRNAs) by processing the BHRF1 and BamHI A rightward (BART) transcripts. BART miRNAs are expressed in all cells latently infected with EBV, but the functions of most BART miRNAs remain unknown. The results of a cell proliferation assay revealed that miR-BART15-3p inhibited cell proliferation. Fluorescence-activated cell sorting following staining with annexin V or propidium iodide showed that miR-BART15-3p promoted apoptosis. Furthermore, the inhibitor for miR-BART15-3p increased cell growth and reduced apoptosis in EBV-infected cells. Using bioinformatic analyses, we predicted that miR-BART15-3p may target the antiapoptotic B-cell lymphoma 2 (BCL2), BCL2L2, DEAD (Asp-Glu-Ala-Asp) box polypeptide 42 (DDX42), and baculovirus inhibitor of apoptosis repeat-containing ubiquitin-conjugating enzyme (BRUCE) mRNAs. The luciferase reporter assay showed that only the 3' untranslated region (UTR) of BRUCE was affected by miR-BART15-3p. Two putative seed-matched sites for miR-BART15-3p were evident on the BRUCE 3' UTR. The results of a mutation study indicated that miR-BART15-3p hybridized only with the first seed-matched site on the BRUCE 3' UTR. miR-BART15-3p downregulated the BRUCE protein in EBV-negative cells, while the inhibitor for miR-BART15-3p upregulated the BRUCE protein in EBV-infected cells without affecting the BRUCE mRNA level. miR-BART15-3p was secreted from EBV-infected gastric carcinoma cells, and the level of miR-BART15-3p was 2- to 16-fold higher in exosomes than in the corresponding cells. Our data suggest that miR-BART15-3p can induce apoptosis partially by inhibiting the translation of the apoptosis inhibitor BRUCE. Further study is warranted to understand the role of miR-BART15-3p in the EBV life cycle.