HSV-1 ICP0: An E3 Ubiquitin Ligase That Counteracts Host Intrinsic and Innate Immunity

A key player in the intrinsic resistance against human cytomegalovirus (HCMV) is the interferon-␥-inducible protein 16 (IFI16), which behaves as a viral DNA sensor in the first hours postinfection and as a repressor of viral gene transcription in the later stages. Previous studies on HCMV replication demonstrated that IFI16 binds to the viral protein kinase pUL97, undergoes phosphorylation, and relocalizes to the cytoplasm of infected cells. In this study, we demonstrate that the tegument protein pp65 (pUL83) recruits IFI16 to the promoter of the UL54 gene and downregulates viral replication, as shown by use of the HCMV mutant v65Stop, which lacks pp65 expression. Interestingly, at late time points of HCMV infection, IFI16 is stabilized by its interaction with pp65, which stood in contrast to IFI16 degradation, observed in herpes simplex virus 1 (HSV-1)-infected cells. Moreover, we found that its translocation to the cytoplasm, in addition to pUL97, strictly depends on pp65, as demonstrated with the HCMV mutant RV-VM1, which expresses a form of pp65 unable to translocate into the cytoplasm. Thus, these data reveal a dual role for pp65: during early infection, it modulates IFI16 activity at the promoter of immediate-early and early genes; subsequently, it delocalizes IFI16 from the nucleus into the cytoplasm, thereby stabilizing and protecting it from degradation. Overall, these data identify a novel activity of the pp65/IFI16 interactome involved in the regulation of UL54 gene expression and IFI16 stability during early and late phases of HCMV replication. IMPORTANCEThe DNA sensor IFI16, a member of the PYHIN proteins, restricts HCMV replication by impairing viral DNA synthesis. Using a mutant virus lacking the tegument protein pp65 (v65Stop), we demonstrate that pp65 recruits IFI16 to the early UL54 gene promoter. As a putative counteraction to its restriction activity, pp65 supports the nucleocytoplasmic export of IFI16, which was demonstrated with the viral mutant RV-VM1 expressing a nuclearly retained pp65. These data reveal a dual role of pp65 in IFI16 regulation: in the early phase of HCMV infection, it contributes to viral evasion from IFI16 restriction activity, while at later time points, it promotes the nuclear delocalization of IFI16, thereby stabilizing and protecting it from degradation. In the present work, we further clarify the mechanisms HCMV relies on to overcome intracellular innate immune restriction and provide new insights into the relevance of DNA-sensing restriction factor IFI16 during HCMV infection. Human cytomegalovirus (HCMV) is a member of the Betaherpesvirinae subfamily of Herpesviridae. It is a widespread pathogen that infects the majority of the world's population by early adulthood (1). The virus establishes a lifelong infection with some cells being latently infected, a state in which the virus resides in a nonproductive form, while other cells show a low-level persistent productive infection in which the virus is not cleared from the organism and is periodically reactiv...

contrasting

confidence: 38%

Regulatory Interaction between the Cellular Restriction Factor IFI16 and Viral pp65 (pUL83) Modulates Viral Gene Expression and IFI16 Protein Stability

Biolatti

Dell’Oste

Pautasso

et al. 2016

“…By degrading host restrictive factors with its E3 ubiquitin ligase or by directly interacting with host regulatory complexes, ICP0 plays a vital role in disarming host antiviral responses (13,32,33). Because of ICP0's complex biochemical properties, the cooperativity of its functional domains is not clearly understood.…”

Section: Discussionmentioning

confidence: 99%

A Tale of Two PMLs: Elements Regulating a Differential Substrate Recognition by the ICP0 E3 Ubiquitin Ligase of Herpes Simplex Virus 1

Zheng

Samrat

2016

Infected cell protein 0 (ICP0) of herpes simplex virus 1 (HSV-1) is an ␣ gene product required for viral replication at low multiplicities of infection. Upon entry, nuclear domain 10 (ND10) converges at the incoming DNA and represses viral gene expression. ICP0 contains a RING-type E3 ubiquitin ligase that degrades the ND10 organizer PML and disperses ND10 to alleviate the repression. In the present study, we focused on understanding the regulation of ICP0 E3 ligase activity in the degradation of different ICP0 substrates. We report the following. (i) A SUMO interaction motif located at ICP0 residues 362 to 364 is required for the degradation of PML isoforms II, IV, and VI but not isoform I. This differentiation mechanism exists in both HEp-2 and U2OS cells, regardless of the cell's permissiveness to the ICP0-null virus. (ii) Physical interaction between SIM 362-364 and PML II is necessary but not sufficient for PML II degradation. Both proximal sequences surrounding SIM 362-364 and distal sequences located at the ICP0 C terminus enhance the degradation of PML II. (iii) The ICP0 C terminus is dispensable for PML I degradation. Instead, bipartite PML I binding domains located in the N-terminal half of ICP0 coordinate to promote the degradation of PML I. (iv) The stability of ICP0, but not its ND10 fusion ability, affects the rate of PML I degradation. Taken together, our results show that ICP0 uses at least two regulatory mechanisms to differentiate its substrates. The disparate recognition of the ICP0 E3 substrates may be related to the different roles these substrates may play in HSV-1 infection. IMPORTANCEViruses have a limited genetic coding capacity but must encounter a multilayered comprehensive host defense. To establish a successful infection, viruses usually produce multifunctional proteins to coordinate the counteractions. Here we report that an HSV-1 protein, ICP0, can recognize individual host factors and target them differently for destruction. We identified elements that are important for the ICP0 E3 ubiquitin ligase to differentially recognize two of its substrates, PML I and PML II. This is the first study that has systematically investigated how ICP0 discriminates two similar molecules by very different mechanisms. This work lays the foundation for understanding the role of host defensive factors and the mechanisms viruses use to take advantage of some host proteins while destroying others. Herpes simplex virus (HSV) causes a wide range of mild to severe herpetic diseases, including cold sores, genital lesions, stromal keratitis, and encephalitis. Following infection, HSV establishes a lifelong latency in ganglion neurons. Its sporadic and sometimes asymptomatic reactivation nourishes a wide spread of the virus, making it one of the most prevalent opportunistic pathogens that cause severe problems in immunocompromised individuals (1).Upon HSV-1 infection, the incoming viral DNA encounters various host restrictive factors, namely, the intrinsic and innate antiviral responses. To establish ...

“…Innate immune responses are critical in controlling virulence of HSV-1 and many other viruses through a variety of antiviral pathways (4)(5)(6)(7)(8)(9)(10)(11)(12), and viruses have coevolved to counter these host responses (13)(14)(15)(16)(17)(18)(19)(20). Cells detect the presence of incoming virus through pattern recognition receptors (21,22) that, in turn, lead to the activation of pivotal transcription factors such as IRF (5,23) and NF-B (24).…”

mentioning

confidence: 99%

“…Virions then travel in a retrograde direction to the soma, where they may replicate or immediately establish latency, depending partly on the infected neuronal subtype (3). Virions resulting from periodic reactivation events travel in an anterograde direction along the axon, allowing reinfection of the oral epithelium, thereby facilitating viral shedding and host-to-host transmission (2).Innate immune responses are critical in controlling virulence of HSV-1 and many other viruses through a variety of antiviral pathways (4-12), and viruses have coevolved to counter these host responses (13)(14)(15)(16)(17)(18)(19)(20). Cells detect the presence of incoming virus through pattern recognition receptors (21, 22) that, in turn, lead to the activation of pivotal transcription factors such as IRF (5, 23) and NF-B (24).…”

mentioning

confidence: 99%

Herpes Simplex Virus and Interferon Signaling Induce Novel Autophagic Clusters in Sensory Neurons

Katzenell

Leib

2016

IMPORTANCEHerpes simplex virus type 1 (HSV-1) is a ubiquitous virus and a significant cause of morbidity and some mortality. It is the causative agent of benign cold sores, but it can also cause blindness and life-threatening encephalitis. The success of HSV-1 is largely due to its ability to establish lifelong latent infections in neurons and to occasionally reactivate. The exact mechanisms by which neurons defend against virus infection is poorly understood, but such defense is at least partially mediated by autophagy, an intracellular pathway by which pathogens and other unwanted cargoes are degraded. The study demonstrates and investigates a new autophagic structure that appears to be specific to the interaction between neurotropic herpesviruses and murine primary sensory neurons. This work may therefore have important implications for our understanding of latency and reactivation. Herpes simplex virus 1 (HSV-1) is a highly prevalent human pathogen that establishes lifelong infection in the neurons of sensory and autonomic ganglia (1, 2). Initial infection and lytic replication at mucosal sites are followed by infection of innervating axonal termini of sensory neurons. Virions then travel in a retrograde direction to the soma, where they may replicate or immediately establish latency, depending partly on the infected neuronal subtype (3). Virions resulting from periodic reactivation events travel in an anterograde direction along the axon, allowing reinfection of the oral epithelium, thereby facilitating viral shedding and host-to-host transmission (2).Innate immune responses are critical in controlling virulence of HSV-1 and many other viruses through a variety of antiviral pathways (4-12), and viruses have coevolved to counter these host responses (13)(14)(15)(16)(17)(18)(19)(20). Cells detect the presence of incoming virus through pattern recognition receptors (21, 22) that, in turn, lead to the activation of pivotal transcription factors such as IRF (5, 23) and NF-B (24). These factors subsequently induce the production of type I interferon (IFN), which drives IFN-stimulated gene (ISG) expression (25) through a JAK-STAT-dependent pathway (26,27). This further stimulates production of type I IFN and ISGs to establish an antiviral state that consists of transcriptional and translational arrest, cytokine production, and apoptosis (28,29).Defects in innate immunity are often associated with increased susceptibility to HSV infection in both mice and humans, with frequent neurological sequelae (8,12,(30)(31)(32). That said, the IFNdriven responses of neurons themselves are muted and atypical (12,33). Nondestructive clearance is especially critical for postmitotic adult neurons, a population of irreplaceable cells that is essential for both the success and survival of the host. Indeed, there is mounting evidence that neurons depend on autophagy rather than inflammatory or cell-destructive responses for the control of intracellular pathogens (34-37). Autophagy is a highly conserved response to starvation, during...