Patricia G. Spear

Herpes Simplex Virus-1 Entry into Cells Mediated by a Novel Member of the TNF/NGF Receptor Family

We identified and cloned a cellular mediator of herpes simplex virus (HSV) entry. Hamster and swine cells resistant to viral entry became susceptible upon expression of a human cDNA encoding this protein, designated HVEM (for herpesvirus entry mediator). HVEM was shown to mediate the entry of several wild-type HSV strains of both serotypes. Anti-HVEM antibodies and a soluble hybrid protein containing the HVEM ectodomain inhibited HVEM-dependent infection but not virus binding to cells. Mutations in the HSV envelope glycoprotein gD significantly reduced HVEM-mediated entry. The contribution of HVEM to HSV entry into human cells was demonstrable in activated T cells. HVEM, the first identified mediator of HSV entry, is a new member of the TNF/NGF receptor family.

A novel role for 3-O-sulfated heparan sulfate in herpes simplex virus 1 entry

Herpes simplex virus type 1 (HSV-1) binds to cells through interactions of viral glycoproteins gB and gC with heparan sulfate chains on cell surface proteoglycans. This binding is not sufficient for viral entry, which requires fusion between the viral envelope and cell membrane. Here, we show that heparan sulfate modified by a subset of the multiple D-glucosaminyl 3-O-sulfotransferase isoforms provides sites for the binding of a third viral glycoprotein, gD, and for initiation of HSV-1 entry. We conclude that susceptibility of cells to HSV-1 entry depends on (1) presence of heparan sulfate chains to which virus can bind and (2) 3-O-sulfation of specific glucosamine residues in heparan sulfate to generate gD-binding sites or the expression of other previously identified gD-binding receptors.

LIGHT, a New Member of the TNF Superfamily, and Lymphotoxin α Are Ligands for Herpesvirus Entry Mediator

Herpes simplex virus (HSV) 1 and 2 infect activated T lymphocytes by attachment of the HSV envelope glycoprotein D (gD) to the cellular herpesvirus entry mediator (HVEM), an orphan member of the tumor necrosis factor receptor superfamily. Here, we demonstrate that HVEM binds two cellular ligands, secreted lymphotoxin alpha (LTalpha) and LIGHT, a new member of the TNF superfamily. LIGHT is a 29 kDa type II transmembrane protein produced by activated T cells that also engages the receptor for the LTalphabeta heterotrimer but does not form complexes with either LTalpha or LTbeta. HSV1 gD inhibits the interaction of HVEM with LIGHT, and LIGHT and gD interfere with HVEM-dependent cell entry by HSV1. This characterizes herpesvirus gD as a membrane-bound viokine and establishes LIGHT-HVEM as integral components of the lymphotoxin cytokine-receptor system.

Herpesvirus entry: An update

Herpesviruses engage multiple receptors during viral entry. Some are considered binding receptors only, in that engagement with these receptors may be reversible and may serve to concentrate virus on the cell surface without triggering changes required for membrane fusion. Others are considered entry receptors, binding to which triggers events required for membrane fusion. Most herpesviruses probably recognize multiple entry receptors, any one of which may be sufficient for viral entry. The purpose of this review is to summarize recent findings on the entry of alpha- and gammaherpesviruses and on structure-function studies of their entry receptors and viral ligands. Members of the Herpesviridae form a large and diverse family comprised of three subfamilies designated alpha-, beta-, and gammaherpesviruses. Virions are composed of a large DNA genome encased in an icosahedral capsid, which is in turn coated with a layer of proteins called the tegument and an envelope composed of about a dozen viral proteins and glycoproteins in a lipid bilayer. At least three, sometimes four, of these envelope glycoproteins are absolutely essential for viral entry. The three glycoproteins thought to be essential for the entry of all herpesviruses are designated gB, gH, and gL. The genes for these glycoproteins are conserved, with gB exhibiting the highest degree of sequence similarity. For at least some herpesviruses, gB is a homodimer or homotrimer displayed as a prominent spike. Heterodimerization of gH and gL is a conserved feature, with the addition of another viral protein subunit for some viruses. Common features of herpesvirus biology include a high incidence of asymptomatic infections and the establishment of latent infections which can be reactivated to cause recurrent or new episodes of disease. The human herpesviruses exhibit these common features as well as diversity in biology and pathogenesis. They include the alphaherpesviruses, herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) and varicellazoster virus (VZV); the betaherpesviruses, cytomegalovirus (CMV) and human herpesviruses 6 and 7; and the gammaherpesviruses, Epstein-Barr virus (EBV) and human herpesvirus 8 (HHV-8). HSV-1 and HSV-2 are responsible for localized mucocutaneous lesions, most commonly, but can also cause meningitis and encephalitis. VZV causes systemic disease with skin lesions during primary infection (chicken pox) and zoster. All three viruses establish latent infections in neurons and can be reactivated from neurons. The betaherpesviruses cause mostly asymptomatic infections in immunocompetent individuals and can establish latent infections in several cell types, including leukocytes of various lineages. EBV is the major cause of infectious mononucleosis and is causally associated with various malignancies, including Burkitt’s lymphoma, Hodgkin’s disease, other lymphomas, and nasopharyngeal carcinoma. HHV-8 is associated with Kaposi’s sarcoma, multicentric Castleman’s disease, and primary effusion lymphoma.

Herpes simplex virus: receptors and ligands for cell entry.

Entry of herpes simplex virus (HSV) into cells depends upon multiple cell surface receptors and multiple proteins on the surface of the virion. The cell surface receptors include heparan sulphate chains on cell surface proteoglycans, a member of the tumor necrosis factor (TNF) receptor family and two members of the immunoglobulin superfamily related to the poliovirus receptor. The HSV ligands for these receptors are the envelope glycoproteins gB and gC for heparan sulphate and gD for the protein receptors and specific sites in heparan sulphate generated by certain 3‐O‐sulfotransferases. HSV gC also binds to the C3b component of complement and can block complement‐mediated neutralization of virus. The purposes of this review are to summarize available information about these cell surface receptors and the viral ligands, gC and gD, and to discuss roles of these viral glycoproteins in immune evasion and cellular responses as well as in viral entry.

Herpesviruses and heparan sulfate: an intimate relationship in aid of viral entry

Glycosaminoglycan chains on cell surface proteoglycans provide initial docking sites for the binding to eukaryotic cells of various viruses and other microorganisms. The ubiquitously expressed glycosaminoglycan heparan sulfate is particularly important in this regard, at least for viruses. Often, binding of a viral protein to heparan sulfate is only the first step in a cascade of interactions between virus and cell that is required for viral entry into the cell and the initiation of infection. The steps that occur after binding of virus to heparan sulfate may require the interaction of other

Glycoprotein C-independent binding of herpes simplex virus to cells requires cell surface heparan sulphate and glycoprotein B

Previous studies have shown that the initial interaction of herpes simplex virus (HSV) with cells is binding to heparan sulphate and that HSV-1 glycoprotein C (gC) is principally responsible for this binding. Although gC-negative viral mutants are impaired for binding and entry, they retain significant infectivity. The purpose of the studies reported here was to explore the requirements for infectivity of gC-negative HSV-1 mutants. We found that absence or alteration of cell surface heparan sulphate significantly reduced the binding of gC-negative mutant virus and rendered cells resistant to infection, as shown previously for the wild-type virus. We isolated a recombinant double-mutated HSV strain that produces virions devoid of both of the known heparin-binding glycoproteins, gB and gC. The drastically impaired binding of these mutant virions to cells, relative to gC-negative and wild-type virions, indicates that gB mediates the binding of gC-negative virions to cells. Thus at least two HSV glycoproteins can independently mediate the binding of HSV to cell surface heparan sulphate to start the process of viral entry into cells.

Glycoproteins Specified by Herpes Simplex Viruses

Membrane glycoproteins specified by enveloped viruses are important determinants of viral pathogenecity. They are exposed on the surfaces of virions and on the surfaces of infected cells. They mediate entry of the virus into cells and cell-to-cell spread of infection and also influence tissue tropism and host range. As a consequence of the foregoing, viral membrane glycoproteins are also probably the most important elicitors of protective immune responses.

PILRα Is a Herpes Simplex Virus-1 Entry Coreceptor That Associates with Glycoprotein B

Glycoprotein B (gB) is one of the essential components for infection by herpes simplex virus-1 (HSV-1). Although several cellular receptors that associate with glycoprotein D (gD), such as herpes virus entry mediator (HVEM) and Nectin-1, have been identified, specific molecules that mediate HSV-1 infection by associating with gB have not been elucidated. Here, we found that paired immunoglobulin-like type 2 receptor (PILR) alpha associates with gB, and cells transduced with PILRalpha become susceptible to HSV-1 infection. Furthermore, HSV-1 infection of human primary cells expressing both HVEM and PILRalpha was blocked by either anti-PILRalpha or anti-HVEM antibody. Our results demonstrate that cellular receptors for both gB and gD are required for HSV-1 infection and that PILRalpha plays an important role in HSV-1 infection as a coreceptor that associates with gB. These findings uncover a crucial aspect of the mechanism underlying HSV-1 infection.

O-linked oligosaccharides are acquired by herpes simplex virus glycoproteins in the Golgi apparatus

Abstract The O-linked oligosaccharides on mature forms of herpes simplex virus type 1 (HSV1) glycoproteins were characterized, and were found to account largely for the lower electrophoretic mobilities of these forms relative to the mobilities of immature forms. Other posttranslational modifications of HSV1 glycoproteins (designated gB, gC, gD and gE) were related temporally to the discrete shifts in electrophoretic mobilities that signal acquisition of the O-linked oligosaccharides. Fatty acid acylation (principally of gE) could be detected just prior to the shifts, whereas conversion of high-mannosetype N-linked oligosaccharides to the complex type occurred coincident with the shifts. The addition of O-linked oligosaccharides did not occur in cells treated with the ionophore monensin or in a ricinresistant cell line defective in the processing of N-linked oligosaccharides. We conclude that extension of O-linked oligosaccharide chains on HSV1 glycoproteins, and probably also attachment of the first O-linked sugars, occurs as a late posttranslational modification in the Golgi apparatus.