Herpes simplex virus 1 (HSV-1) strain HSZP glycoprotein B gene: comparison of mutations among strains differing in virulence

Ophthalmic Solutions with a Broad Antiviral Action: Evaluation of Their Potential against Ocular Herpetic Infections

HSV-1 can be associated with severe and recurrent eye infections characterized by a strong inflammatory response that leads to blepharoconjunctivitis, epithelial and stromal keratitis, and retinal necrosis. The incidence of HSV-1 keratitis is 1.5 million every year worldwide, including more than 40,000 new cases exhibiting serious visual failures. Generally, the therapy uses antiviral drugs to promote healing; however, there are currently no compounds that are able to completely eradicate the virus. In addition, the phenomenon of resistance is rapidly spreading among HSV-1 strains, creating mutants developing resistance to the common antiviral drugs; therefore, deep research on this issue is warranted. The efficacy of different ophthalmic solutions already on the market was evaluated for reducing HSV-1 infection. Different plaque assays were set up on epithelial cells, revealing that two ophthalmic solutions were able to inhibit viral replication in the early stages of infection. The data were further confirmed by molecular tests analyzing the expression levels of the principal genes involved in HSV-1 infection, and a strong reduction was observed after only 1 min of eye-drop treatment. Collectively, these results suggested the use of ophthalmic solutions as potential antiviral options for the treatment of ocular herpetic infection.

Evolution and diversity in human herpes simplex virus genomes

Herpes simplex virus 1 (HSV-1) causes a chronic, lifelong infection in >60% of adults. Multiple recent vaccine trials have failed, with viral diversity likely contributing to these failures. To understand HSV-1 diversity better, we comprehensively compared 20 newly sequenced viral genomes from China, Japan, Kenya, and South Korea with six previously sequenced genomes from the United States, Europe, and Japan. In this diverse collection of passaged strains, we found that one-fifth of the newly sequenced members share a gene deletion and one-third exhibit homopolymeric frameshift mutations (HFMs). Individual strains exhibit genotypic and potential phenotypic variation via HFMs, deletions, short sequence repeats, and single-nucleotide polymorphisms, although the protein sequence identity between strains exceeds 90% on average. In the first genome-scale analysis of positive selection in HSV-1, we found signs of selection in specific proteins and residues, including the fusion protein glycoprotein H. We also confirmed previous results suggesting that recombination has occurred with high frequency throughout the HSV-1 genome. Despite this, the HSV-1 strains analyzed clustered by geographic origin during whole-genome distance analysis. These data shed light on likely routes of HSV-1 adaptation to changing environments and will aid in the selection of vaccine antigens that are invariant worldwide.

Amino acid differences in glycoproteins B (gB), C (gC), H (gH) and L (gL) are associated with enhanced herpes simplex virus type-1 (McKrae) entry via the paired immunoglobulin-like type-2 receptor α

BACKGROUND

Herpes simplex virus type-1 (HSV-1) enters into cells via membrane fusion of the viral envelope with plasma or endosomal membranes mediated by viral glycoproteins. HSV-1 virions attach to cell surfaces by binding of viral glycoproteins gC, gD and gB to specific cellular receptors. Here we show that the human ocular and highly neurovirulent HSV-1 strain McKrae enters substantially more efficiently into cells via the gB-specific human paired immunoglobulin-like type-2 receptor-α (hPILR-α). Comparison of the predicted amino acid sequences between HSV-1(F) and McKrae strains indicates that amino acid changes within gB, gC, gH and gL may cause increased entry via the hPILR- α receptor.

RESULTS

HSV-1 (McKrae) entered substantially more efficiently than viral strain F in Chinese hamster ovary (CHO) cells expressing hPIRL-α but not within CHO-human nectin-1, -(CHO-hNectin-1), CHO-human HVEM (CHO-hHVEM) or Vero cells. The McKrae genes encoding viral glycoproteins gB, gC, gD, gH, gL, gK and the membrane protein UL20 were sequenced and their predicted amino acid (aa) sequences were compared with virulent strains F, H129, and the attenuated laboratory strain KOS. Most aa differences between McKrae and F were located at their gB amino termini known to bind with the PILRα receptor. These aa changes included a C10R change, also seen in the neurovirulent strain ANG, as well as redistribution and increase of proline residues. Comparison of gC aa sequences revealed multiple aa changes including an L132P change within the 129-247 aa region known to bind to heparan sulfate (HS) receptors. Two aa changes were located within the H1 domain of gH that binds gL. Multiple aa changes were located within the McKrae gL sequence, which were preserved in the H129 isolate, but differed for the F strain. Viral glycoproteins gD and gK and the membrane protein UL20 were conserved between McKrae and F strains.

CONCLUSIONS

The results indicate that the observed entry phenotype of the McKrae strain is most likely due to a combination of increased binding to heparan sulfate receptors and enhanced virus entry via gB-mediated fusion of the viral envelope with plasma membranes.

Evaluation of the T-REx transcription switch for conditional expression and regulation of HSV-1 vectors

Herpes simplex virus 1 (HSV-1) strain ANG and ANGpath were cloned as bacterial artificial chromosome (BAC). Two different types of BAC genomes were obtained. BAC genomes of type I contained the BAC replicon at the intended target region between the genes of UL48 and UL49. In BAC genomes of type II, the BAC sequences were found to be aberrantly fused between the termini of the HSV-1 genome. Both the BAC types were used to establish a conditional gene expression system for HSV-1 by Flp recombinase-mediated insertion of expression vectors that were modified to respond to the T-REx tetracycline (Tet)-inducible transcription switch. During BAC cloning and mutagenesis in E. coli, not only deletions but also defined mutations of the HSV-1 genome were observed. Successful virus reconstitution from BACs with large inserts demonstrated that HSV-1 has a packaging capacity for foreign sequences of at least 8.1% of its genome size. Targets for Tet-regulated gene expression were the viral DNA polymerase gene (pol) and a reporter gene of glycoprotein B fused to enhanced green fluorescent protein (gBGFP). Results with the pol gene as target showed that virus plaque production could not be significantly controlled by the T-REx gene switch using vectors encoding one copy of the tetR gene. In contrast, an efficient Tet-response was achieved with the gBGFP reporter, which was optimal in a Tet repressor (TetR)-producing cell line, demonstrating that the TetR concentration provided by the virus was not sufficient for a tight control of Tet-regulated gene expression.

Molecular basis for resistance of herpes simplex virus type 1 mutants to the sulfated oligosaccharide inhibitor PI-88

Herpes simplex virus type 1 variants selected by virus propagation in cultured cells in the presence of the sulfated oligosaccharide PI-88 were analyzed. Many of these variants were substantially resistant to the presence of PI-88 during their initial infection of cells and/or their cell-to-cell spread. Nucleotide sequence analysis revealed that the deletion of amino acids 33-116 of gC but not lack of gC expression provided the virus with selective advantage to infect cells in the presence of PI-88. Purified gC (Delta33-116) was more resistant to PI-88 than unaltered protein in its binding to cells. Alterations that partly contributed to the virus resistance to PI-88 in its cell-to-cell spread activity were amino acid substitutions Q27R in gD and R770W in gB. These results suggest that PI-88 targets several distinct viral glycoproteins during the course of initial virus infection and cell-to-cell spread.

Herpes simplex virus type 1 targets the MHC class II processing pathway for immune evasion

HSV type 1 (HSV-1) has evolved numerous strategies for modifying immune responses that protect against infection. Important targets of HSV-1 infection are the MHC-encoded peptide receptors. Previous studies have shown that a helper T cell response and Ab production play important roles in controlling HSV-1 infection. The reduced capacity of infected B cells to stimulate CD4(+) T cells is beneficial for HSV-1 to evade immune defenses. We investigated the impact of HSV-1 infection on the MHCII processing pathway, which is critical to generate CD4(+) T cell help. HSV-1 infection targets the molecular coplayers of MHC class II processing, HLA-DR (DR), HLA-DM (DM), and invariant chain (Ii). HSV-1 infection strongly reduces expression of Ii, which impairs formation of SDS-resistant DR-peptide complexes. Residual activity of the MHC class II processing pathway is diminished by viral envelope glycoprotein B (gB). Binding of gB to DR competes with binding to Ii. In addition, we found gB associated with DM molecules. Both, gB-associated DR and DM heterodimers are exported from the endoplasmic reticulum, as indicated by carbohydrate maturation. Evaluation of DR, DM, and gB subcellular localization revealed abundant changes in intracellular distribution. DR-gB complexes are localized in subcellular vesicles and restrained from cell surface expression.

Herpes simplex virus type 1 mutants containing the KOS strain ICP34.5 gene in place of the McKrae ICP34.5 gene have McKrae-like spontaneous reactivation but non-McKrae-like virulence

Herpes simplex virus type 1 (HSV-1) strain McKrae is neurovirulent in rabbits infected by the ocular route, causing fatal encephalitis in approximately 50% of the animals, and has a high-level spontaneous reactivation phenotype, with 10% of rabbit eyes containing reactivated virus at any given time. In contrast, HSV-1 strain KOS is completely avirulent (no rabbits die) and has a completely negative spontaneous reactivation phenotype. Mutations of the ICP34.5 gene can reduce the neurovirulence of HSV-1 strains McKrae and 17syn(+) by up to 100000-fold. ICP34.5 mutants also have reduced spontaneous reactivation phenotypes. To determine whether differences in the ICP34.5 gene might be involved in the reduced neurovirulence and spontaneous reactivation phenotypes of KOS compared with McKrae, we constructed chimeric viruses containing the KOS ICP34.5 gene in place of the McKrae ICP34.5 gene. Rabbits ocularly infected with the chimeric viruses had a high spontaneous reactivation phenotype indistinguishable from McKrae. In contrast, neurovirulence of the chimeric viruses was decreased compared with McKrae. Thus, one or more 'defects' in the KOS ICP34.5 gene appeared to be at least partially responsible for the reduced neurovirulence of KOS compared with McKrae. However, there appeared to be no 'defect' in the KOS ICP34.5 function required for efficient spontaneous reactivation.