Prevention of fatal equine herpesvirus type 1 encephalitis in mice by immunization with a limited-replication cycle virus

Equine herpesvirus type 1 (EHV-1) is a devastating pathogen of horses, their natural hosts, and causes fatal encephalitis in non-natural hosts. We previously demonstrated that acylation of the tegument protein UL11 is required for viral replication in cultured cells. We created a mutant virus (EHV-1 UL12 trunc UL11 G2AC7AC9A), in which glycyl and cysteinyl residues at positions 2, 7 and 9 of UL11 that are normally acylated were replaced with alanyl residues. This virus, designated the 2/7/9 mutant, has a limited-replication cycle (LRC), in which replication stops after just a few cycles. Here, we tested whether the 2/7/9 mutant could be used as a vaccine against fatal encephalitis in a mouse model. A virulence test showed that the 2/7/9 mutant was not pathogenic in mice and elicited an antibody response. We also attempted to use the 2/7/9 mutant to immunize mice against a zebra-borne EHV-1, 94-137. Two trials were conducted, each with five immunized mice, five non-immunized and five control mice. In both trials, clinical signs and fatalities were much lower in the immunized mice than in the non-immunized mice. In addition, none of the mice in either trial developed neutralizing antibodies, indicating that the immunity induced by the 2/7/9 mutant was not due to neutralizing activity. The results indicate that the 2/7/9 LRC mutant has promise as a vaccine against EHV-1 infection non-natural hosts.

The N-terminal glycine of EHV-1 UL11 is essential for the localization of UL11 and EHV-1 replication in cultured cells

Equine herpesvirus type 1 (EHV-1) UL11 is a 74-amino-acid (aa) protein encoded by ORF51. UL11 is modified by acylation including myristoylation and palmitoylation. Myristoylation of EHV-1 UL11 is assumed to occur on the N-terminal glycine, while palmitoylation is assumed to occur on the seventh and ninth cysteines. ORF51, which encodes the first 24 aa, overlaps ORF50 encoding UL12. We previously demonstrated that UL11 was essential for EHV-1 replication in cultured cells and that UL11 was localized at the Golgi apparatus where herpesviruses obtain their final envelope. It is unclear whether the acylation is related to the localization of EHV-1 UL11 and viral replication. In this study, we investigated the role of UL11 acylation in the intracellular localization and viral growth and replication of EHV-1. We constructed seven UL11 acylation mutant plasmids and seven UL11 acylation mutant BAC DNAs; then, we analysed the localizations of the mutant UL11s and attempted virus rescue. We found that both the N-terminal glycine and the seventh or ninth cysteine, especially N-terminal glycine, were involved in the localization of UL11 and viral replication. Taken together, these results suggest that EHV-1 viral growth requires that UL11 is modified by myristoylation of an N-terminal glycine and by palmitoylation of at least one of the cysteines, and that UL11 is localized at the Golgi apparatus. This study shows that a single amino acid in EHV-1 can determine the fate of viral replication.

UL11 Protein Is a Key Participant of the Duck Plague Virus in Its Life Cycle

Tegument protein UL11 plays a critical role in the life cycle of herpesviruses. The UL11 protein of herpesviruses is important for viral particle entry, release, assembly, and secondary envelopment. Lipid raft is cholesterol-rich functional microdomains in cell membranes, which plays an important role in signal transduction and substance transport. Flotillin and prohibition, which are considered to be specific markers of lipid raft. However, little is known about the function of duck plague virus (DPV) UL11 in the life cycle of the viruses and the relationship between the lipid raft and UL11. In this study, an interference plasmid shRNA126 for UL11 was used. Results showed that UL11 is involved in the replication, cell to cell spread, viral particle assembly, and release processes. Furthermore, UL11 was verified that it could interact with the lipid raft through sucrose density gradient centrifugation and that function correlates with the second glycine of the UL11. When the lipid raft was depleted using the methyl-β-cyclodextrin, the release of the DPV was decreased. Moreover, UL11 can decrease several relative viral genes mRNA levels by qRT-PCR and Western blot test. Altogether, these results highlight an important role for UL11 protein in the viral replication cycle.

Functional hierarchy of herpes simplex virus type-1 membrane proteins in corneal infection and virus transmission to ganglionic neurons

PURPOSE

To determine the relative importance of viral glycoproteins gK, gM, gE and the membrane protein UL11 in infection of mouse corneas and ganglionic neurons.

METHODS

Mouse eyes were scarified and infected with herpes simplex virus (HSV)-1(F), gE-null, gM-null, gK-null, or UL11-null viruses. Clinical signs of ocular disease were monitored daily. Virus shedding was determined at 24, 48 and 72 h post infection. Viral DNA within trigeminal ganglia (TG) was quantified by quantitative PCR at 30 d post infection.

RESULTS

The gE-null virus replicated as efficiently as the parental virus and formed viral plaques approximately half-the-size in comparison with the HSV-1(F) wild-type virus. The UL11-null and gM-null viruses replicated approximately one log less efficiently than the wild-type virus, and formed plaques that were on average one-third the size and one-half the size of the wild-type virus, respectively. The gK-null virus replicated more than 3-logs less efficiently than the wild-type virus and formed very small plaques (5-10 cells). Mice infected with the wild-type virus exhibited mild clinical ocular symptoms, while mice infected with the mutant viruses did not show any significant ocular changes. The wild-type virus produced the highest virus shedding post infection followed by the gM-null, gE-null and UL11-null viruses, while no gK-null virus was detected at any time point. All TG collected from mice infected with the wild-type virus and 6-of-10 of TG retrieved from mice infected with the UL11-null virus contained high numbers of viral genomes. The gE-null and gM-null-infected ganglia contained moderate-to-low number of viral genomes in 4-of-10 and 2-of-10 mice, respectively. No viral genomes were detected in ganglionic tissues obtained from gK-null eye infections.

CONCLUSIONS

The results show that gK plays the most important role among gM, gE and UL11 in corneal and ganglionic infection in the mouse eye model.