The Epstein–Barr virus M81 strain, isolated from a nasopharyngeal carcinoma, induces potent spontaneous virus production in infected B cells. We found that the M81 non-coding Epstein–Barr-encoded RNA EBER2, which carries polymorphisms that are mainly restricted to viruses found in endemic nasopharyngeal carcinomas, markedly stimulated this process. M81 EBER2 increased CXCL8 expression, and this chemokine enhanced spontaneous lytic replication levels in M81-infected B cells. Both events resulted from the endocytosis of extracellular vesicles containing EBER2 that were generated by neighbouring M81-infected B cells, thereby generating a paracrine loop. These effects were strictly dependent on a functional Toll-like receptor 7 (TLR7), a sensor of single-stranded RNA located in the endosome of these cells. These unique properties of M81 EBER2 could be ascribed to its unusually high expression level and to the ability of its single-stranded region to activate TLR7; both of these properties were dependent on M81-specific polymorphisms. Thus, M81 induced chronic inflammation in its target cells and this resulted in increased virus production. These observations provide a mechanistic molecular link between M81 virus replication—a central viral function and a cancer risk factor—and the production of a chemokine involved in inflammation and carcinogenesis.
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The data that support the findings of this study are available within the article and its Supplementary Information files, or from the corresponding author upon request. The raw microarray data that support the findings of this study have been deposited at ArrayExpress, with accession no. E-MTAB-8102.
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We thank the staff of the animal facility at DKFZ for their assistance with the animal experiments; the microarray unit of the DKFZ Genomics and Proteomics Core Facility for providing the Illumina Whole-Genome Expression Beadchips and related services; and J. M. Middeldorp (VU -University Medical Center, Amsterdam, Netherlands), for the OT6 antibody. This study was supported by German Cancer Research Center (F100), Institut National de la Santé et de la Recherche Médicale (U1074). Z.L. is supported by a stipend from the Chinese Scientific Council (CSC).
The authors declare no competing interests.
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