Epstein-Barr virus co-opts ADAR1 to evade PKR activation of the integrated stress response in nasopharyngeal carcinoma

Abstract

Viruses generate immunogenic double-stranded RNA (dsRNA) during their life cycle, necessitating mechanisms to evade host innate immune detection. Protein kinase R (PKR) is a pattern recognition receptor (PRR) that senses viral dsRNA and activates the host integrated stress response (ISR) by phosphorylating eukaryotic initiation factor 2 (eIF2) on its alpha subunit, causing global mRNA translation arrest. Viruses evade activation of the ISR and translation shut-down to facilitate replication. Adenosine deaminase acting on RNA 1 (ADAR1) is uniquely positioned to support viral replication due to its ability to convert adenosine (A) into inosine (I) inside dsRNA, thereby disrupting base-pair matching and preventing PKR activation. Here, we discovered that Epstein-Barr virus (EBV), the oncogenic driver of nasopharyngeal carcinoma (NPC), requires ADAR1 both to maintain latent infection and for lytic reactivation by preventing PKR-mediated ISR activation. EBV lytic reactivation stimulated viral protein expression, which was attenuated in the absence of ADAR1. Importantly, lytic reactivation or treatment of synthetic dsRNA in the absence of ADAR1 induced phosphorylation of eIF2 by PKR, stress granule formation, and caused cancer cell lethality without the production of virion progeny. Together these findings support a strategy for EBV lytic induction therapy in NPC without viral dissemination by exposing EBV to endogenous PRRs through ADAR1 inhibition.