Dissecting the regulation of EBV's BART miRNAs in carcinomas

Ya-Chun Yang,Amy Liem,Paul F Lambert,Bill Sugden

doi:10.1016/j.virol.2017.02.013

Abstract

Epstein-Barr virus (EBV) encodes multiple miRNAs known to contribute to its pathogenicity. Previous studies have found that the levels of some EBV miRNAs are 10–100 fold higher in biopsies and in tumor xenografts than in cells grown in culture. We have asked if these increased levels reflect transcriptional enhancement resulting from the tumor microenvironment, selection for increased levels of the EBV genome, or both. We measured the levels of BART miRNAs and their DNA templates in tumor xenografts induced from EBV-positive gastric carcinoma cells and EBV-negative gastric carcinoma cells expressing plasmid replicons encoding these miRNAs. We focused on BART miRNAs which are expressed in all tumors and found that they provide tumors selective growth advantages as xenografts. Stem-loop PCR and real-time PCR revealed that the xenografts expressed both higher levels of some miRNAs and viral DNA templates than did the corresponding cells in culture.

Highlights

Epstein-Barr virus (EBV) is a human herpesvirus that successfully infects more than 90% of the human population (Williams and Crawford, 2006)
EBV’s BART miRNAs have been shown to provide the virus selective advantages on infecting primary B-cells, to normal and tumor cells grown in culture, and to tumors grown as xenografts in immuno-compromised mice
We have analyzed multiple cell types grown both in culture and as tumor xenografts in nude mice to elucidate the mechanism underlying the higher level of expression of BART miRNAs found in tumors

Summary

Introduction

Epstein-Barr virus (EBV) is a human herpesvirus that successfully infects more than 90% of the human population (Williams and Crawford, 2006). Infection with EBV is associated with several human cancers, including Burkitt’s lymphoma (BL), Hodgkin’s disease, post transplant lymphoproliferative disease, and both gastric and nasopharyngeal carcinoma (NPC) (Brady et al, 2007; Hammerschmidt and Sugden, 2004; Raab-Traub, 2002, 2015; Sugden, 2014; Tse and Kwong, 2015). This tumor virus infects quiescent B cells, induces their proliferation, and is maintained in them in a latent state where its genome exists as a circular plasmid. BART miRNAs are transcribed from a single primary transcript, the expression patterns of BART miRNAs vary dramatically among different EBV-positive cell lines (Hooykaas et al, 2016; Pratt et al, 2009; Yang et al, 2013)

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