miR-BART5 is an anti-apoptotic miRNA encoded by EBV and inhibits PUMA to promote host cell survival

Abstract

Epstein-Barr virus (EBV) is a herpesvirus associated with nasopharyngeal carcinoma (NPC) and other types of epithelial and lymphoid malignancies. EBV is the first human virus found to express microRNAs (miRNAs), but the functions of these viral miRNAs are largely unknown. Here, we identified and characterized a cellular target of an EBV miRNA known as miR-BART5, which is conserved with rhesus lymphocryptovirus miR-rL1-8 and abundantly expressed in NPC cells. By in silico analysis and functional screening with luciferase reporter assays, we showed that miR-BART5 targets the 3-untranslated region of a cellular mRNA transcript encoding p53 upregulated modulator of apoptosis (PUMA), a mediator of p53-dependent and –independent apoptosis. The target site of miR-BART5 was identified and characterized. Regulation of the endogenous PUMA expression was verified by overexpressing miR-BART5. In addition, a synthetic anti-miR-BART5 oligonucleotide inhibitor was used to confirm that reduction of endogenous miR-BART5 in NPC cells led to alteration in PUMA expression. Consistent with a role in the development of NPC, PUMA was found to be significantly underexpressed in about 60% of human NPC tissues constitutively harboring EBV. More importantly, miR-BART5-expressing NPC cells were less sensitive to proapoptotic agents adriamycin and etoposide. In addition, apoptosis can be induced in these cells by inhibiting miR-BART5 activity. Taken together, our findings suggest a model for viral promotion of tumor cell survival in which EBV encodes an miRNA to repress the expression of PUNA and consequently facilitate the establishment of stable latent infection and the development of epithelial carcinoma.