Herpes simplex virus (HSV) establishes latent infection in long‐lived neurons. During initial infection, neurons are exposed to multiple inflammatory cytokines but the effects of immune signaling on the nature of HSV latency are unknown. We show that initial infection of primary murine neurons in the presence of type I interferon (IFN) results in a form of latency that is restricted for reactivation. We also find that the subnuclear condensates, promyelocytic leukemia nuclear bodies (PML‐NBs), are absent from primary sympathetic and sensory neurons but form with type I IFN treatment and persist even when IFN signaling resolves. HSV‐1 genomes colocalize with PML‐NBs throughout a latent infection of neurons only when type I IFN is present during initial infection. Depletion of PML prior to or following infection does not impact the establishment latency; however, it does rescue the ability of HSV to reactivate from IFN‐treated neurons. This study demonstrates that viral genomes possess a memory of the IFN response during de novo infection, which results in differential subnuclear positioning and ultimately restricts the ability of genomes to reactivate.

Herpes simplex virus-1 (HSV-1) enters a latent infection in neurons and periodically reactivates. Reactivation manifests as a variety of clinical symptoms.

Herpes simplex virus (HSV) establishes latent infection in long-lived neurons. During initial infection, neurons are exposed to multiple inflammatory cytokines but the effects of immune signaling on the nature of HSV latency is unknown. We show that initial infection of primary murine neurons in the presence of type I interferon (IFN) results in a form of latency that is restricted for reactivation. We also found that the subnuclear condensates, promyelocytic leukemia-nuclear bodies (PML-NBs), are absent from primary sympathetic and sensory neurons but form with type I IFN treatment and persist even when IFN signaling resolves. HSV-1 genomes colocalized with PML-NBs throughout a latent infection of neurons only when type I IFN was present during initial infection. Depletion of PML prior to or following infection did not impact the establishment latency; however, it did rescue the ability of HSV to reactivate from IFN-treated neurons. This study demonstrates that viral genomes possess a memory of the IFN response during de novo infection, which ultimately results in differential subnuclear positioning that restricts the ability of genomes to reactivate.

Viruses pose substantial challenges for society, economy, healthcare systems, and research. Their distinctive pathologies are based on specific interactions with cellular factors. In order to develop new antiviral treatments, it is of central importance to understand how viruses interact with their host and how infected cells react to the virus on a molecular level. Invading viruses are commonly sensed by components of the innate immune system, which is composed of a highly effective yet complex network of proteins that, in most cases, mediate efficient virus inhibition. Central to this process is the activity of interferons and other cytokines that coordinate the antiviral response. So far, numerous methods have been used to identify how viruses interact with cellular processes and revealed that the innate immune response is highly complex and involves interferon-stimulated genes and their binding partners as functional factors. Novel approaches and careful experimental design, combined with large-scale, high-throughput methods and cutting-edge analysis pipelines, have to be utilized to delineate the antiviral innate immune landscape at a global level. In this review, we describe different currently used screening approaches, how they contributed to our knowledge on virus–host interactions, and essential considerations that have to be taken into account when planning such experiments.

A notable signaling mechanism employed by mammalian innate immune signaling pathways uses nucleotide based second messengers such as 2'-3'-cGAMP and 2'-5'-oligoadenylates (2'-5' OA), which bind and activate STING and RNase L, respectively. Interestingly, the involvement of nucleotide second messengers to activate antiviral responses is evolutionary conserved, evidenced by the identification of an antiviral cGAMP-dependent pathway in Drosophila. RNase L is the only characterized downstream receptor of 2'-5' OA and is activated by 2'-5' OA greater than three linked adenine bases in length. Active oligoadenylate synthase (OAS) genes are present in organisms as old as sponges, while RNase L is present beginning in jawed vertebrates. No structural or functional conservation of RNase L activity exists in more ancient organisms, suggesting that alternate receptors of 2'-5' OA evolved in organisms lacking RNase L that may be conserved. Using a mass spectrometry approach, we identified several members of the ABCF family in human, mouse, and Drosophila cell lysates as 2'-5' OA binding proteins, suggesting an evolutionary conserved function. Biochemical characterization of these interactions demonstrates high-affinity binding of 2'-5' OA to ABCF1, which depended on phosphorylated 2'-5' OA and an intact Walker A/B motif of the ABC cassette of ABCF1. As further support for species-specific interactions with 2'-5' OA, we additionally identified that the metabolism enzyme Decr1 from mouse, but not human or Drosophila cells forms a high-affinity complex with 2'-5' OA. A 1.4 Angstrom co-crystal structure of the mouse Decr1-2'-5' OA complex explains high-affinity recognition of 2'-5' OA and the mechanism of species-specificity. Despite clear evidence of physical interactions, we could not identify profound antiviral functions of ABCF1, ABCF3 or Decr1 or 2'-5' OA-dependent regulation of cellular translation rates as suggested by the engagement of ABCF proteins. Thus, although the biological consequences of the here identified interactions need to be identified, our data suggests that 2'-5' OA can serve as signaling hub to distribute a signal to different recipient proteins.