Stable attachment for herpes simplex virus penetration into human cells requires glycoprotein D in the virion and cell receptors that are missing for entry-defective porcine cells

HSV usurps eukaryotic initiation factor 3 subunit M for viral protein translation: novel prevention target

Prevention of genital herpes is a global health priority. B5, a recently identified ubiquitous human protein, was proposed as a candidate HSV entry receptor. The current studies explored its role in HSV infection. Viral plaque formation was reduced by ∼90% in human cells transfected with small interfering RNA targeting B5 or nectin-1, an established entry receptor. However, the mechanisms were distinct. Silencing of nectin-1 prevented intracellular delivery of viral capsids, nuclear transport of a viral tegument protein, and release of calcium stores required for entry. In contrast, B5 silencing had no effect on these markers of entry, but inhibited viral protein translation. Specifically, viral immediate early genes, ICP0 and ICP4, were transcribed, polyadenylated and transported from the nucleus to the cytoplasm, but the viral transcripts did not associate with ribosomes or polysomes in B5-silenced cells. In contrast, immediate early gene viral transcripts were detected in polysome fractions isolated from control cells. These findings are consistent with sequencing studies demonstrating that B5 is eukaryotic initiation factor 3 subunit m (eIF3m). Although B5 silencing altered the polysome profile of cells, silencing had little effect on cellular RNA or protein expression and was not cytotoxic, suggesting that this subunit is not essential for host cellular protein synthesis. Together these results demonstrate that B5 plays a major role in the initiation of HSV protein translation and could provide a novel target for strategies to prevent primary and recurrent herpetic disease.

Soluble V domain of Nectin-1/HveC enables entry of herpes simplex virus type 1 (HSV-1) into HSV-resistant cells by binding to viral glycoprotein D

Interaction of herpes simplex virus (HSV) glycoprotein D (gD) with specific cellular receptors is essential for HSV infection of susceptible cells. Virus mutants that lack gD can bind to the cell surface (attachment) but do not enter, implying that interaction of gD with its receptor(s) initiates the postattachment (entry) phase of HSV infection. In this report, we have studied HSV entry in the presence of the gD-binding variable (V) domain of the common gD receptor nectin-1/HveC to determine whether cell association of the gD receptor is required for HSV infection. In the presence of increasing amounts of the soluble nectin-1 V domain (sNec1(123)), increasing viral entry into HSV-resistant CHO-K1 cells was observed. At a multiplicity of 3 in the presence of optimal amounts of sNec1(123), approximately 90% of the cells were infected. The soluble V domain of nectin-2, a strain-specific HSV entry receptor, promoted entry of the HSV type 1 (HSV-1) Rid-1 mutant strain, but not of wild-type HSV-1. Preincubation and immunofluorescence studies indicated that free or gD-bound sNec1(123) did not associate with the cell surface. sNec1(123)-mediated entry was highly impaired by interference with the cell-binding activities of viral glycoproteins B and C. While gD has at least two functions, virus attachment to the cell and initiation of the virus entry process, our results demonstrate that the attachment function of gD is dispensable for entry provided that other means of attachment are available, such as gB and gC binding to cell surface glycosaminoglycans.

The C terminus of the B5 receptor for herpes simplex virus contains a functional region important for infection

The expression of a previously uncharacterized human hfl-B5 cDNA confers susceptibility for herpes simplex virus (HSV) to porcine cells and fulfills criteria as an HSV entry receptor (A. Perez, Q.-X. Li, P. Perez-Romero, G. DeLassus, S. R. Lopez, S. Sutter, N. McLaren, and A. Oveta Fuller, J. Virol. 79:7419-7430, 2005). Heptad repeats found in the B5 C terminus are predicted to form an alpha-helix for coiled coil structure. We used mutagenesis and synthetic peptides with wild-type and mutant sequences to examine the function of the heptad repeat motif in HSV binding and entry into porcine cells that express B5 and for infection of naturally susceptible human HEp-2 cells. B5 with point mutations predicted to disrupt the putative C-terminal coiled coil failed to mediate HSV binding and entry into porcine cells. Synthetic peptides that contain the single amino acid changes lose the blocking activity of HSV entry. We concluded that the C terminus of B5 contains a functional region that is important for the B5 receptor to mediate events in HSV entry. Structural evidence that this functional region forms coiled coil structures is under investigation. Blocking of HSV interaction with the C-terminal region of the B5 receptor is a new potential target site to intervene in the virus infection of human cells.

A new class of receptor for herpes simplex virus has heptad repeat motifs that are common to membrane fusion proteins

We isolated a human cDNA by expression cloning and characterized its gene product as a new human protein that enables entry and infection of herpes simplex virus (HSV). The gene, designated hfl-B5, encodes a type II cell surface membrane protein, B5, that is broadly expressed in human primary tissue and cell lines. It contains a high-scoring heptad repeat at the extracellular C terminus that is predicted to form an alpha-helix for coiled coils like those in cellular SNAREs or in some viral fusion proteins. A synthetic 30-mer peptide that has the same sequence as the heptad repeat alpha-helix blocks HSV infection of B5-expressing porcine cells and human HEp-2 cells. Transient expression of human B5 in HEp-2 cells results in increased polykarocyte formation even in the absence of viral proteins. The B5 protein fulfills all criteria as a receptor or coreceptor for HSV entry. Use by HSV of a human cellular receptor, such as B5, that contains putative membrane fusion domains provides an example where a pathogenic virus with broad tropism has usurped a widely expressed cellular protein to function in infection at events that lead to membrane fusion.

Herpes simplex virus entry mediator associates in infected cells in a complex with viral proteins gD and at least gH

We examined herpes simplex virus (HSV)-infected human HEp-2 cells or porcine cells that express herpes virus entry mediator (HVEM) for virus and receptor protein interactions. Antibody to HVEM, or its viral ligand gD, coimmunoprecipitated several similar proteins. A prominent 110-kDa protein that coprecipitated was identified as gH. The HVEM/gD/gH complex was detected with mild or stringent cell lysis conditions. It did not form in cells infected with HSV-1(KOS)Rid1 virus or with null virus lacking gD, gH, or gL. Thus, in cells a complex forms through physical associations of HVEM, gD, and at least gH.

Herpes Simplex Virus Targeting to the EGF Receptor by a gD-Specific Soluble Bridging Molecule

Herpes simplex virus 1 (HSV-1) enters cells via initial binding of envelope glycoproteins (g) C and B to cell-surface glycosaminoglycans (GAGs) and subsequent membrane fusion involving envelope gD, gB, and gH/gL. Current insights suggest that the fusion process is initiated by interaction of gD with a cognate cellular receptor, such as the widely distributed cell adhesion molecule nectin-1. To redirect the tropism of HSV-1, we have generated a soluble adapter protein (P-V528LH) comprising the gD-binding variable domain of nectin-1 fused to a single-chain antibody (528LH) recognizing the EGF receptor. The adapter molecule enabled HSV-1 entry into naturally nonpermissive CHO cells expressing the human EGF receptor, but not into CHO cells lacking the receptor, and entry was not observed when the antibody portion of the adapter was replaced with an antibody of different specificity. Adapter-mediated entry increased with the viral dose and was nearly as efficient as direct viral entry into nectin-1-bearing CHO cells. Entry depended on viral gD and was diminished in the absence of cellular GAGs. These experiments represent the first demonstration that a soluble molecule can direct HSV infection via a new receptor, supporting the possible utility of this approach for HSV retargeting.

Truncated forms of glycoprotein D of herpes simplex virus 1 capable of blocking apoptosis and of low-efficiency entry into cells form a heterodimer dependent on the presence of a cysteine located in the shared transmembrane domains

Earlier studies have shown that herpes simplex virus 1 (HSV-1) virions of mutant lacking glycoprotein D (gD) and made in either complementing (gD(-/+) stocks) or noncomplementing cells (gD(-/-) stocks) induce apoptosis. Subsequent studies have shown that apoptosis induced by gD(-/-) mutant virus stocks can be blocked by in trans delivery of viral genes that encode either intact gD or a mixture of two genes encoding the glycoprotein ectodomain plus transmembrane domain (gD-B) and transmembrane domain plus the cytoplasmic carboxyl terminus of the protein (gD-D), respectively. Since the presence of the transmembrane domains was critical for precluding apoptosis in the bipartite system, the question arose whether the two components, gD-B and gD-D, form a heterodimer mediated by an unpaired cysteine located in the transmembrane domain. We report the following. (i) The substitution of the unpaired cysteine with serine in either gD-B or gD-D truncated forms of gD disabled the ability of gD-D and gD-B to block apoptosis. (ii) Immunoprecipitation of gD-D coprecipitated gD-B only from lysates of cells transduced with gD-D and gD-B containing the cysteine in the transmembrane domains. Replacement of cysteine with serine ablated coprecipitation of the components. (ii) The mixture of gD-D and gD-B complemented at a low level gD(-/+) virions. We conclude that the gD-B and gD-D can form a heterodimer dependent on the presence of cysteines in the transmembrane domain and the heterodimer can substitute for intact gD but at a much reduced efficiency.

Defective infection of bovine herpesvirus 1 in non-permissive murine cells

The defective growth of bovine herpesvirus I (BHV-1) was analyzed in non-permissive murine embryo fibroblast, BALB/3T3 A31-1-1 (A31) cells. BHV-1 was able to attach and penetrate into A31 cells at similar levels that were seen in semi-permissive cells. Once penetrated into A31 cells, BHV-1 was efficiently transported to nuclei, but the onset of expression of immediate early (IE) protein and viral DNA replication was not observed. These data suggest that the viral replication of BHV-1 in A31 cells is arrested at the point prior to the expression of IE proteins.

Porcine HveC, a member of the highly conserved HveC/nectin 1 family, is a functional alphaherpesvirus receptor

Human herpesvirus entry mediator C (HveC) is an alphaherpesvirus receptor which binds to virion glycoprotein D (gD). We identified porcine HveC and studied its interaction with pseudorabies virus (PrV) and herpes simplex virus type 1 (HSV-1) gD. Porcine and human HveC have 96% amino acid identity and HveC from African green monkey, mouse, hamster, and cow are similarly conserved. Porcine HveC mediates entry of HSV-1, HSV-2, PrV, and bovine herpesvirus type 1. Truncated soluble forms of HSV-1 and PrV gD bind competitively to porcine HveC. Biosensor analysis shows that PrV gD binds with a 10-fold higher affinity than HSV-1 gD. Monoclonal antibodies against human HveC recognize the porcine homologue and can block gD binding and entry of HSV-1 and PrV. Porcine HveC is functionally indistinguishable from human HveC. Our results are consistent with the suggestion that HveC is a pan-alphaherpesvirus receptor that interacts with a conserved structural domain of gD.

Attachment and penetration of canine herpesvirus 1 in non-permissive cells

Canine herpesvirus 1 (CHV-1) has a relatively narrow host cell range when compared to other alphaherpesviruses. The early events of CHV-1 infection in a permissive Madin-Darby canine kidney (MDCK) and non-permissive cell lines. In order to quantify attachment and penetration, were investigated quantitative competitive PCR (QCPCR) method was established for quantitation of CHV-1 DNA. In all non-permissive cells tested, no significant decrease in viral attachment was observed. When CHV-1 was treated with heparin, viral attachment to MDCK cells was reduced by 25% of the input CHV-1 attached to MDCK cells even in the presence of 50 microg/ml heparin. However, the attachment of CHV-1 to non-permissive cells was severely impaired by heparin treatment. In permissive MDCK cells, about 80% of attached CHV-1 penetrated into cells. However, only 4-10% of CHV-1 attached to non-permissive cells penetrated into cells. Our data indicated that CHV-1, like other herpesviruses, attached to permissive MDCK cells through two mechanisms: the first one is through the interaction mediated by heparan sulfate (HS) on the cell surface and the second involves unidentified viral component and the cellular receptor. In contrast, the non-permissive cells lacked the cellular receptor for the second attachment mechanism and the defect in viral penetration into non-permissive cell might be related to the lack of the cellular receptor.