B Cell Receptor-Responsive miR-141 and viral miR-BART9 promote Epstein-Barr Virus Reactivation Through FOXO3 Inhibition

Antigen recognition by the B cell receptor (BCR) is a physiological trigger for reactivation of Epstein-Barr virus (EBV) and can be recapitulated in vitro by cross-linking of surface immunoglobulins. Previously, we identified a subset of EBV microRNAs (miRNAs) that attenuate BCR signal transduction and subsequently, dampen lytic replication in B cells. The roles of host miRNAs in virus reactivation are not completely understood. To investigate this process, we profiled the small RNAs in latently infected and reactivated Burkitt’s lymphoma cells, and identified several miRNAs, such as miR-141, that are induced upon BCR cross-linking. Notably, EBV encodes a viral miRNA, miR-BART9, with sequence homology to miR-141. To better understand the functions of these two miRNAs, we examined their molecular targets and experimentally validated multiple candidates commonly regulated by both miRNAs. Targets included transcriptional regulators of the EBV immediate early promoters and B cell transcription factors, leading us to hypothesize that these miRNAs modulate kinetics of the latent to lytic switch in B cells. Through functional assays, we identified roles for miR-141 and EBV miR-BART9 and one specific target, FOXO3, in lytic reactivation. Our data support a model whereby EBV exploits BCR-responsive miR-141 and further mimics activity of this miRNA family via a viral miRNA to promote productive virus replication.