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

Abstract

6Antigen recognition by the B cell receptor (BCR) is a physiological trigger for reactivation of Epstein-Barr virus 7(EBV) and can be recapitulated in vitro by cross-linking of surface immunoglobulins. Previously, we identified a 8 subset of EBV microRNAs (miRNAs) that attenuate BCR signal transduction and subsequently, dampen lytic 9replication in B cells. The roles of host miRNAs in virus reactivation are not completely understood. To 10 investigate this process, we profiled the small RNAs in latently infected and reactivated Burkitt's lymphoma 11 cells, and identified several miRNAs, such as miR-141, that are induced upon BCR cross-linking. Notably, EBV 12 encodes a viral miRNA, miR-BART9, with sequence homology to miR-141. To better understand the functions 13 of these two miRNAs, we examined their molecular targets and experimentally validated multiple candidates 14 commonly regulated by both miRNAs. Targets included transcriptional regulators of the EBV immediate early 15promoters and B cell transcription factors, leading us to hypothesize that these miRNAs modulate kinetics of 16 the latent to lytic switch in B cells. Through functional assays, we identified roles for miR-141 and EBV miR-17 BART9 and one specific target, FOXO3, in lytic reactivation. Our data support a model whereby EBV exploits 18BCR-responsive miR-141 and further mimics activity of this miRNA family via a viral miRNA to promote 19 productive virus replication. 20 Importance 21EBV is a human pathogen associated with several malignancies. A key aspect of lifelong virus persistence is 22 the ability to switch between latent and lytic replication modes. Mechanisms governing latency and lytic 23 reactivation are only partly understood, and how the EBV latent to lytic switch is post-transcriptionally regulated 24remains an outstanding question. This study sheds light on how miR-141 expression is regulated in Burkitt's 25 lymphoma cells, and identifies a role for FOXO3, a common target of both miR-141 and viral miR-BART9, in 26 modulating EBV reactivation. 27 28

Epstein-Barr virus miR-BARTs 7 and 9 modulate viral cycle, cell proliferation and proteomic profiles in Burkitt lymphoma

“…In addition, we also found that both BART7 and BART9 mutants display an increased expression of the viral genes encoding the lytic proteins ZTA and gp350 (BLZF1 and BLLF1, respectively). EBV BART9 was reported to attenuate and regulate the EBV lytic cycle via transcriptional inhibition of several components of the BCR and FOXO3 signaling pathway, showing striking sequence homology to the human miRNA miR-141 (hsa-miR-141) [27,28]. Our results support the hypothesis that the expression of BART7 and BART9 are associated with regulating cell proliferation, apoptosis and maintaining the viral latency in B-cells.…”