The herpesvirus accessory protein γ134.5 facilitates viral replication by disabling mitochondrial translocation of RIG-I

RIG-I and MDA5 are cytoplasmic RNA sensors that mediate cell intrinsic immunity against viral pathogens. While it has been well-established that RIG-I and MDA5 recognize RNA viruses, their interactive network with DNA viruses, including herpes simplex virus 1 (HSV-1), remains less clear. Using a combination of RNA-deep sequencing and genetic studies, we show that the gamma(1)34.5 gene product, a virus-encoded virulence factor, enables HSV growth by neutralization of RIG-I dependent restriction. When expressed in mammalian cells, HSV-1 gamma(1)34.5 targets RIG-I, which cripples cytosolic RNA sensing and subsequently suppresses antiviral gene expression. Rather than inhibition of RIG-I K63-linked ubiquitination, the gamma(1)34.5 protein precludes the assembly of RIG-I and cellular chaperone 14-3-3 epsilon into an active complex for mitochondrial translocation. The gamma(1)34.5-mediated inhibition of RIG-I-14-3-3 epsilon binding abrogates the access of RIG-I to mitochondrial antiviral-signaling protein (MAVS) and activation of interferon regulatory factor 3. As such, unlike wild type virus HSV-1, a recombinant HSV-1 in which gamma(1)34.5 is deleted elicits efficient cytokine induction and replicates poorly, while genetic ablation of RIG-I expression, but not of MDA5 expression, rescues viral growth. Collectively, these findings suggest that viral suppression of cytosolic RNA sensing is a key determinant in the evolutionary arms race of a large DNA virus and its host. Author summary Host cytosolic RNA sensing has been implicated in the recognition of herpesvirus infection. As such, herpesviruses likely have evolved strategies to escape this host surveillance mechanism; however, molecular insight into antagonism of RNA sensors by herpesviruses remains largely elusive. We show that the gamma(1)34.5 protein encoded by herpes simplex virus 1 inactivates the helicase RIG-I that serves as an RNA receptor. Viral gamma(1)34.5 hijacks RIG-I and selectively inhibits its engagement with the chaperone protein 14-3-3 epsilon in the cytoplasm of infected cells. Targeting of RIG-I by gamma(1)34.5 blocks the cytosol-to-mitochondrial translocation of RIG-I, which ultimately dampens antiviral innate immunity. Finally, depletion of RIG-I enhances the growth of a recombinant HSV-1 in which gamma(1)34.5 was deleted. Our work provides insights into viral modulation of intracellular RNA recognition in herpesvirus infection, which in turn may guide the rational development of therapeutic agents.

Automated summary

This study demonstrates that the HSV-1-encoded γ(1)34.5 protein inactivates RIG-I, a key RNA sensor in host cells, to dampen antiviral innate immunity. By targeting RIG-I, HSV-1 inhibits its interaction with the chaperone protein 14-3-3 epsilon, ultimately blocking the cytosol-to-mitochondrial translocation of RIG-I. The viral evasion of cytosolic RNA sensing is highlighted as a crucial factor in the evolutionary arms race between a large DNA virus and its host.