Epstein-Barr Virus miR-BHRF1-3 Targets the BZLF1 3'UTR and Regulates the Lytic Cycle.

Suppression of lytic viral gene expression is a key aspect of the Epstein-Barr virus (EBV) life cycle to facilitate the establishment of latent infection. Molecular mechanisms regulating transitions between EBV lytic replication and latency are not fully understood. Here, we investigated the impact of viral microRNAs on the EBV lytic cycle. Through functional assays, we found that miR-BHRF1-3 attenuates EBV lytic gene expression following reactivation. To understand the miRNA targets contributing to this activity, we performed Ago PAR-CLIP analysis on EBV-positive, reactivated Burkitt's lymphoma cells and identified multiple miR-BHRF1-3 interactions with viral transcripts. Using luciferase reporter assays, we confirmed a miRNA interaction site within the 3'UTR of BZLF1 which encodes the essential immediate early (IE) transactivator Zta. Comparison of >850 published EBV genomes identified sequence polymorphisms within the miR-BHRF1-3 locus that deleteriously affect miRNA expression and function. Molecular interactions between the homologous viral miRNA, miR-rL1-17, and IE transcripts encoded by rhesus lymphocryptovirus were further identified. Our data demonstrate that regulation of IE gene expression by a BHRF1 miRNA is conserved among lymphocryptoviruses, and further reveal virally-encoded genetic elements that orchestrate viral antigen expression during the lytic cycle. IMPORTANCE Epstein-Barr virus infection is predominantly latent in healthy individuals, while periodic cycles of reactivation are thought to facilitate persistent lifelong infection. Lytic infection has been linked to development of certain EBV-associated diseases. Here, we demonstrate that EBV miR-BHRF1-3 can suppress lytic replication by directly inhibiting Zta expression. Moreover, we identify nucleotide variants that impact the function of miR-BHRF1-3, which may contribute to specific EBV pathologies.