Activation of NF-κB in CD8+ dendritic cells Ex Vivo by the γ134.5 null mutant correlates with immunity against herpes simplex virus 1

An Insight into Current Treatment Strategies, Their Limitations, and Ongoing Developments in Vaccine Technologies against Herpes Simplex Infections

Herpes simplex virus (HSV) infection, the most prevalent viral infection that typically lasts for a lifetime, is associated with frequent outbreaks of oral and genital lesions. Oral herpes infection is mainly associated with HSV-1 through oral contact, while genital herpes originates due to HSV-2 and is categorized under sexually transmitted diseases. Immunocompromised patients and children are more prone to HSV infection. Over the years, various attempts have been made to find potential targets for the prevention of HSV infection. Despite the global distress caused by HSV infections, there are no licensed prophylactic and therapeutic vaccines available on the market against HSV. Nevertheless, there are numerous promising candidates in the pre-clinical and clinical stages of study. The present review gives an overview of two herpes viruses, their history, and life cycle, and different treatments adopted presently against HSV infections and their associated limitations. Majorly, the review covers the recent investigations being carried out globally regarding various vaccine strategies against oral and genital herpes virus infections, together with the recent and advanced nanotechnological approaches for vaccine development. Consequently, it gives an insight to researchers as well as people from the health sector about the challenges and upcoming solutions associated with treatment and vaccine development against HSV infections.

Herpes simplex virus interference with immunity: Focus on dendritic cells

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) are highly prevalent in the human population. These viruses cause lifelong infections by establishing latency in neurons and undergo sporadic reactivations that promote recurrent disease and new infections. The success of HSVs in persisting in infected individuals is likely due to their multiple molecular determinants involved in escaping the host antiviral and immune responses. Importantly, HSVs infect and negatively modulate the function of dendritic cells (DCs), key immune cells that are involved in establishing effective and balanced immunity against viruses. Here, we review and discuss several molecular and cellular processes modulated by HSVs in DCs, such as autophagy, apoptosis, and the unfolded protein response. Given the central role of DCs in establishing optimal antiviral immunity, particular emphasis should be given to the outcome of the interactions occurring between HSVs and DCs.

Immune Response to Herpes Simplex Virus Infection and Vaccine Development

Herpes simplex virus (HSV) infections are among the most common viral infections and usually last for a lifetime. The virus can potentially be controlled with vaccines since humans are the only known host. However, despite the development and trial of many vaccines, this has not yet been possible. This is normally attributed to the high latency potential of the virus. Numerous immune cells, particularly the natural killer cells and interferon gamma and pathways that are used by the body to fight HSV infections have been identified. On the other hand, the virus has developed different mechanisms, including using different microRNAs to inhibit apoptosis and autophagy to avoid clearance and aid latency induction. Both traditional and new methods of vaccine development, including the use of live attenuated vaccines, replication incompetent vaccines, subunit vaccines and recombinant DNA vaccines are now being employed to develop an effective vaccine against the virus. We conclude that this review has contributed to a better understanding of the interplay between the immune system and the virus, which is necessary for the development of an effective vaccine against HSV.

Pseudorabies Virus UL24 Abrogates Tumor Necrosis Factor Alpha-Induced NF-κB Activation by Degrading P65

The transcription factor NF-κB plays a critical role in diverse biological processes. The NF-κB pathway can be activated by incoming pathogens and then stimulates both innate and adaptive immunity. However, many viruses have evolved corresponding strategies to balance NF-κB activation to benefit their replication. Pseudorabies virus (PRV) is an economically important pathogen that belongs to the alphaherpesvirus group. There is little information about PRV infection and NF-κB regulation. This study demonstrates for the first time that the UL24 protein could abrogate tumor necrosis factor alpha (TNF-α)-mediated NF-κB activation. An overexpression assay indicated that UL24 inhibits this pathway at or downstream of P65. Furthermore, co-immunoprecipitation analysis demonstrated that UL24 selectively interacts with P65. We demonstrated that UL24 could significantly degrade P65 by the proteasome pathway. For the first time, PRV UL24 was shown to play an important role in NF-κB evasion during PRV infection. This study expands our understanding that PRV can utilize its encoded protein UL24 to evade NF-κB signaling.

Herpes Simplex Virus 1 Induces Phosphorylation and Reorganization of Lamin A/C through the γ134.5 Protein That Facilitates Nuclear Egress

Herpes simplex virus 1 (HSV-1) remodels nuclear membranes during virus egress. Although the UL31 and UL34 proteins control nucleocapsid transit in infected cells, the molecular interactions required for their function are unclear. Here we report that the γ₁34.5 gene product of HSV-1 facilitates nucleocapsid release to the cytoplasm through bridging the UL31/UL34 complex, cellular p32, and protein kinase C. Unlike wild-type virus, an HSV mutant devoid of γ₁34.5 or its amino terminus is crippled for viral growth and release. This is attributable to a defect in virus nuclear egress. In infected cells, wild-type virus recruits protein kinase C to the nuclear membrane and triggers its activation, whereas the γ₁34.5 mutants fail to exert such an effect. Accordingly, the γ₁34.5 mutants are unable to induce phosphorylation and reorganization of lamin A/C. When expressed in host cells γ₁34.5 targets p32 and protein kinase C. Meanwhile, it communicates with the UL31/UL34 complex through UL31. Deletion of the amino terminus from γ₁34.5 disrupts its activity. These results suggest that disintegration of the nuclear lamina mediated by γ₁34.5 promotes HSV replication.

IMPORTANCE

HSV nuclear egress is a key step that determines the outcome of viral infection. While the nuclear egress complex mediates capsid transit across the nuclear membrane, the regulatory components are not clearly defined in virus-infected cells. We report that the γ₁34.5 gene product, a virulence factor of HSV-1, facilitates nuclear egress cooperatively with cellular p32, protein kinase C, and the nuclear egress complex. This work highlights a viral mechanism that may contribute to the pathogenesis of HSV infection.

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

The herpes simplex virus type 1 (HSV-1) encoded E3 ubiquitin ligase, infected cell protein 0 (ICP0), is required for efficient lytic viral replication and regulates the switch between the lytic and latent states of HSV-1. As an E3 ubiquitin ligase, ICP0 directs the proteasomal degradation of several cellular targets, allowing the virus to counteract different cellular intrinsic and innate immune responses. In this review, we will focus on how ICP0’s E3 ubiquitin ligase activity inactivates the host intrinsic defenses, such as nuclear domain 10 (ND10), SUMO, and the DNA damage response to HSV-1 infection. In addition, we will examine ICP0’s capacity to impair the activation of interferon (innate) regulatory mediators that include IFI16 (IFN γ-inducible protein 16), MyD88 (myeloid differentiation factor 88), and Mal (MyD88 adaptor-like protein). We will also consider how ICP0 allows HSV-1 to evade activation of the NF-κB (nuclear factor kappa B) inflammatory signaling pathway. Finally, ICP0’s paradoxical relationship with USP7 (ubiquitin specific protease 7) and its roles in intrinsic and innate immune responses to HSV-1 infection will be discussed.

Herpes simplex virus 1 protein kinase US3 hyperphosphorylates p65/RelA and dampens NF-κB activation

Nuclear factor κB (NF-κB) plays important roles in innate immune responses by regulating the expression of a large number of target genes involved in the immune and inflammatory response, apoptosis, cell proliferation, differentiation, and survival. To survive in the host cells, viruses have evolved multiple strategies to evade and subvert the host immune response. Herpes simplex virus 1 (HSV-1) bears a large DNA genome, with the capacity to encode many different viral proteins to counteract the host immune responses. In the present study, we demonstrated that HSV-1 protein kinase US3 significantly inhibited NF-κB activation and decreased the expression of inflammatory chemokine interleukin-8 (IL-8). US3 was also shown to hyperphosphorylate p65 at serine 75 and block its nuclear translocation. Two US3 mutants, K220M and D305A, still interacted with p65; however, they could not hyperphosphorylate p65, indicating that the kinase activity of US3 was indispensable for the function. The attenuation of NF-κB activation by HSV-1 US3 protein kinase may represent a critical adaptation to enable virus persistence within the host. Importance: This study demonstrated that HSV-1 protein kinase US3 significantly inhibited NF-κB activation and decreased the expression of inflammatory chemokine interleukin-8 (IL-8). US3 hyperphosphorylated p65 at serine 75 to inhibit NF-κB activation. The kinase activity of US3 was indispensable for its hyperphosphorylation of p65 and abrogation of the nuclear translocation of p65. The present study elaborated a novel mechanism of HSV-1 US3 to evade the host innate immunity.

Type I interferon and NF-κB activation elicited by herpes simplex virus gH/gL via αvβ3 integrin in epithelial and neuronal cell lines

αvβ3 integrin represents a novel sensing system which detects herpes simplex virus (HSV) and bacterial constituents. In cooperation with Toll-like receptor 2 (TLR2), it elicits an innate response that leads to activation of type I interferon (IFN), NF-κB, and a specific set of cytokines. We report that this defensive branch is functional in cells which represent experimental models of epithelial, including keratinocytic, and neuronal cells. These are the major targets of HSV in vivo. HSV entered the three cell lines via distinct routes. Hence, the defensive response was independent of the route of virus entry. Soluble gH/gL sufficed to elicit type I IFN and NF-κB activation and represents the viral pathogen-associated molecular pattern (PAMP) of this defense system.

Herpes simplex virus 1 E3 ubiquitin ligase ICP0 protein inhibits tumor necrosis factor alpha-induced NF-κB activation by interacting with p65/RelA and p50/NF-κB1

NF-κB plays central roles in regulation of diverse biological processes, including innate and adaptive immunity and inflammation. HSV-1 is the archetypal member of the alphaherpesviruses, with a large genome encoding over 80 viral proteins, many of which are involved in virus-host interactions and show immune modulatory capabilities. In this study, we demonstrated that the HSV-1 ICP0 protein, a viral E3 ubiquitin ligase, was shown to significantly suppress tumor necrosis factor alpha (TNF-α)-mediated NF-κB activation. ICP0 was demonstrated to bind to the NF-κB subunits p65 and p50 by coimmunoprecipitation analysis. ICP0 bound to the Rel homology domain (RHD) of p65. Fluorescence microscopy demonstrated that ICP0 abolished nuclear translocation of p65 upon TNF-α stimulation. Also, ICP0 degraded p50 via its E3 ubiquitin ligase activity. The RING finger (RF) domain mutant ICP0 (ICP0-RF) lost its ability to inhibit TNF-α-mediated NF-κB activation and p65 nuclear translocation and degrade p50. Notably, the RF domain of ICP0 was sufficient to interact with p50 and abolish NF-κB reporter gene activity. Here, it is for the first time shown that HSV-1 ICP0 interacts with p65 and p50, degrades p50 through the ubiquitin-proteasome pathway, and prevents NF-κB-dependent gene expression, which may contribute to immune evasion and pathogenesis of HSV-1.

Herpes simplex virus 1 DNA polymerase processivity factor UL42 inhibits TNF-α-induced NF-κB activation by interacting with p65/RelA and p50/NF-κB1

Herpes simplex virus 1 (HSV-1) is the archetypal member of the alphaherpesvirus with a large genome encoding over 80 viral proteins, many of which are involved in virus-host interactions and show immune modulatory capabilities. In this study, we demonstrated that the HSV-1 UL42 protein, a DNA polymerase processivity factor, was a novel antagonism of the canonical NF-κB signaling pathway. UL42 was shown to significantly suppress TNF-α mediated NF-κB activation. Co-immunoprecipitation experiment revealed that UL42 bound to the NF-κB subunits p65 and p50. Fluorescence microscopy demonstrated that UL42 abolished nuclear translocation of p65 and p50 upon TNF-α-stimulation. But the inhibiting capacity of UL42 2R/2A (R279A, R280A) and UL42 3R/3A (R113A, R279A and R280A) mutants were less than wild type UL42. Also UL42 bound to the Rel homology domain of the NF-κB subunit p65 and p50. Notably, the N-terminal of UL42 was sufficient to interact with p65 and p50 and abolished NF-κB reporter gene activity. Thus, it was first time we demonstrated that HSV-1 UL42 appeared to prevent NF-κB-dependent gene expression by retaining p65 and p50 in the cytoplasm, and UL42-dependent transcriptional activation were inherently coupled to promote HSV-1 lytic replication, which also may contribute to immune evasion and pathogenesis of HSV-1.