EBV BART MicroRNAs Target Multiple Pro-apoptotic Cellular Genes to Promote Epithelial Cell Survival

Epstein-barr virus (ebv) is a ubiquitous human γ-herpesvirus that can give rise to cancers of both b-cell and epithelial cell origin. in ebv-induced cancers of epithelial origin,including nasopharyngeal carcinomas (npcs) and gastric carcinomas,the latent ebv genome expresses very high levels of a cluster of 22 viral pre-mirnas,called the mir-barts,and these have previously been shown to confer a degree of resistance to pro-apoptotic drugs. here,we present an analysis of the ability of individual mir-bart pre-mirnas to confer an anti-apoptotic phenotype and report that five of the 22 mir-barts demonstrate this ability. we next used photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (par-clip) to globally identify the mrna targets bound by these mir-barts in latently infected epithelial cells. this led to the identification of ten mrnas encoding pro-apoptotic mrna targets,all of which could be confirmed as valid targets for the five anti-apoptotic mir-barts by indicator assays and by demonstrating that ectopic expression of physiological levels of the relevant mir-bart in the epithelial cell line ags resulted in a significant repression of the target mrna as well as the encoded protein product. using rna interference,we further demonstrated that knockdown of at least seven of these cellular mir-bart target transcripts phenocopies the anti-apoptotic activity seen upon expression of the relevant ebv mir-bart mirna. together,these observations validate previously published reports arguing that the mir-barts can exert an anti-apoptotic effect in ebv-infected epithelial cells and provide a mechanistic explanation for this activity. moreover,these results identify and validate a substantial number of novel mrna targets for the anti-apoptotic mir-barts. © 2015 kang et al.