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

Abstract

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 γ134.5 gene product, a virus-encoded virulence factor, enables HSV growth by neutralization of RIG-I dependent restriction. When expressed in mammalian cells, HSV-1 γ134.5 targets RIG-I, which cripples cytosolic RNA sensing and subsequently suppresses antiviral gene expression. Rather than inhibition of RIG-I K63-linked ubiquitination, the γ134.5 protein precludes the assembly of RIG-I and cellular chaperone 14-3-3ε into an active complex for mitochondrial translocation. The γ134.5-mediated inhibition of RIG-I-14-3-3ε 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 γ134.5 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.

Integrative Interactome and Ubiquitinome Analyses Reveal Multiple Regulatory Pathways Targeted by ICP0 in HSV-1 Infected Neuronal Cells

“…Our results showing that OTUD4 was induced by HSV-1 to enhance type I IFN production were consistent with a recent report that OTUD4 was induced by RNA viruses and targeted MAVS for deubiquitination thereby promoting signaling leading to type I interferon production [61]. The RIG-I like receptor RNA sensing pathway through MAVS is known to function during HSV-1 infection too [62]. Therefore it is possible that OTUD4 functions by a similar mechanism during HSV-1 infection although this hypothesis needs to be tested.…”

Oncolytic HSV: Underpinnings of Tumor Susceptibility

“…HSV γ 1 34.5 is present in two copies per viral genome within the inverted repeat regions [ 10 ]. The γ 1 34.5 protein is multifunctional, with roles regulating protein synthesis, autophagy, nucleic acid sensing, and viral egress [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. Importantly, these roles map to two functionally distinct domains, an amino-terminal domain and a carboxyl-terminal domain, which are connected by a triplet amino acid repeat linker region (Ala-Thr-Pro) ( Figure 1 ).…”

“…As such, studies over the last decade have drawn light on how γ 1 34.5 overcomes IFN restriction at multiple levels of the immune response. At the level of nucleic acid sensing, γ 1 34.5 has been shown to directly bind and inhibit RIG-I [ 15 ]. Concurrently, γ 1 34.5 inhibits downstream adaptors, TBK-1 and STING, which are critical for innate immune signaling and IFN production [ 14 , 16 ].…”

“…These studies have also indicated that activity of dsRNA sensing for the most part remains intact within these malignant cell lines [ 76 , 77 , 92 ]. Active PKR, TBK-1, cGAS/STING, and RIG-I all have the potential to restrict Δγ 1 34.5 replication [ 14 , 15 , 16 , 41 ], and the heterogenous inhibition of these pathways across cancer types provides a possible explanation for the replication variability observed with first-generation Δγ 1 34.5 oncolytics. Thus, several strategies have evolved from first-generation oHSV to enhance oncolytic replication and ultimately improve therapeutic efficacy ( Table 1 ).…”

“…Since their discovery, several functional overlaps between γ 1 34.5 and Us11 have been identified. Both exhibit inhibitory activity toward PKR [ 12 , 106 ], autophagy [ 13 , 107 ], RIG-I [ 15 , 108 ], and both contribute to full IFN resistance in late stages of HSV infection [ 109 ]. In hindsight, these overlaps make it clear why the serial evolution of Δγ 1 34.5 HSV in non-permissive glioma can select for α expression of Us11 [ 110 , 111 ].…”