Epstein-Barr virus microRNAs regulate B cell receptor signal transduction and lytic reactivation.

Yan Chen,Nikita S Ivanov,Rebecca L Skalsky,Devin Fachko,Camille M Skinner,Zhen Lin

doi:10.1371/journal.ppat.1007535

Abstract

MicroRNAs (miRNAs) are post-transcriptional regulatory RNAs that can modulate cell signaling and play key roles in cell state transitions. Epstein-Barr virus (EBV) expresses >40 viral miRNAs that manipulate both viral and cellular gene expression patterns and contribute to reprogramming of the host environment during infection. Here, we identified a subset of EBV miRNAs that desensitize cells to B cell receptor (BCR) stimuli, and attenuate the downstream activation of NF-kappaB or AP1-dependent transcription. Bioinformatics and pathway analysis of Ago PAR-CLIP datasets identified multiple EBV miRNA targets related to BCR signal transduction, including GRB2, SOS1, MALT1, RAC1, and INPP5D, which we validated in reporter assays. BCR signaling is critical for B cell activation, proliferation, and differentiation, and for EBV, is linked to reactivation. In functional assays, we demonstrate that EBV miR-BHRF1-2-5p contributes to the growth of latently infected B cells through GRB2 regulation. We further determined that activities of EBV miR-BHRF1-2-5p, EBV miR-BART2-5p, and a cellular miRNA, miR-17-5p, directly regulate virus reactivation triggered by BCR engagement. Our findings provide mechanistic insight into some of the key miRNA interactions impacting the proliferation of latently infected B cells and importantly, governing the latent to lytic switch.

Highlights

Epstein Barr virus (EBV) is a human gamma-herpesvirus that infects >90% of adults worldwide
In addition to IL1R1, we recently reported that the EBV BHRF1-2 miRNAs target other IL-1 signaling components such as SOS1, a Ras GDP/GTP exchange factor, and PLCG1, encoding phospholipase C gamma 1 that contributes to receptor-mediated tyrosine kinase signal transduction [11]
As BJAB cells are not infected with EBV, these results further show that desensitization to B cell receptor (BCR) stimuli occurs through viral miRNA actions on the host cell, presumably through the partial inhibition or complete silencing of cellular targets

Summary

Introduction

Epstein Barr virus (EBV) is a human gamma-herpesvirus that infects >90% of adults worldwide. Following EBV transmission through the oral cavity and subsequent infection of naïve B cells, EBV co-opts multiple aspects of normal B cell activation that induces cell proliferation, initiates differentiation programs, and can drive infected B cells through germinal center (GC) reactions to establish latency in the memory B cell compartment [3,4,5]. Periodic virus reactivation can occur throughout life-long infection of the host and is thought to help maintain the pool of latently infected cells [5,6]. EBV has both latent and lytic replication phases, and key to the success of long-term persistence is the ability to navigate between these phases

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Conclusion