Deepak Shukla

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.

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

Viral entry mechanisms: cellular and viral mediators of herpes simplex virus entry

Herpes simplex virus type‐1 and type‐2 are highly prevalent human pathogens causing life‐long infections. The process of infection begins when the virions bind heparan sulfate moieties present on host cell surfaces. This initial attachment then triggers a cascade of molecular interactions involving multiple viral and host cell proteins and receptors, leading to penetration of the viral nucleocapsid and tegument proteins into the cytoplasm. The nucleocapsid is then transported to the nuclear membrane and the viral DNA is released for replication in the nucleus. Recent studies have revealed that herpes simplex virus entry or penetration into cells may be a highly complex process and the mechanism of entry may demonstrate unique cell‐type specificities. Although specificities clearly exist, past and ongoing studies demonstrate that herpes simplex virus may share certain common receptors and pathways that are also used by many other human viruses. This minireview helps to shed light on recent revelations on the herpes simplex virus entry process.

Heparan sulfate 3-O-sulfotransferase isoform 5 generates both an antithrombin-binding site and an entry receptor for herpes simplex virus, type 1.

Heparan sulfate 3-O-sulfotransferase transfers sulfate to the 3-OH position of a glucosamine residue of heparan sulfate (HS) to form 3-O-sulfated HS. The 3-O-sulfated glucosamine residue contributes to two important biological functions of HS: binding to antithrombin and thereby carrying anticoagulant activity, and binding to herpes simplex viral envelope glycoprotein D to serve as an entry receptor for herpes simplex virus 1. A total of five HS 3-O-sulfotransferase isoforms were reported previously. Here we report the isolation and characterization of a novel HS 3-O-sulfotransferase isoform, designated as HS 3-O-sulfotransferase isoform 5 (3-OST-5). 3-OST-5 cDNA was isolated from a human placenta cDNA library and expressed in COS-7 cells. The disaccharide analysis of 3-OST-5-modified HS revealed that 3-OST-5 generated at least three 3-O-sulfated disaccharides as follows: IdoUA2S-AnMan3S, GlcUA-AnMan3S6S, and IdoUA2S-AnMan3S6S. Transfection of the plasmid expressing 3-OST-5 rendered wild type Chinese hamster ovary cells susceptible to the infection by herpes simplex virus 1, suggesting that 3-OST-5-modified HS serves as an entry receptor for herpes simplex virus 1. In addition, 3-OST-5-modified HS bound to herpes simplex viral envelope protein glycoprotein D. Furthermore, we found that 3-OST-5-modified HS also bound to antithrombin, suggesting that 3-OST-5 also produces anticoagulant HS. In summary, our results indicate that a new member of 3-OST family generates both anticoagulant HS and an entry receptor for herpes simplex virus 1. These results provide a new insight regarding the mechanism for the biosynthesis of biologically active HS.

Herpes Simplex Epithelial and Stromal Keratitis: An Epidemiologic Update

Herpes simplex virus (HSV) is associated with a variety of ocular diseases, including epithelial and stromal keratitis. HSV can cause stromal opacification and is believed to be the leading cause of infectious blindness in the developed world. An improved understanding of the global burden of HSV keratitis, including the incidence of severe vision loss, could have a significant effect on prevention and treatment and place it in perspective among causes of corneal ulceration. We found that the global incidence of HSV keratitis is roughly 1.5 million, including 40,000 new cases of severe monocular visual impairment or blindness each year. We also discuss relevant epidemiologic issues regarding HSV epithelial and stromal disease.

Mutations in the N Termini of Herpes Simplex Virus Type 1 and 2 gDs Alter Functional Interactions with the Entry/Fusion Receptors HVEM, Nectin-2, and 3-O-Sulfated Heparan Sulfate but Not with Nectin-1

ABSTRACT Multiple cell surface molecules (herpesvirus entry mediator [HVEM], nectin-1, nectin-2, and 3-O-sulfated heparan sulfate) can serve as entry receptors for herpes simplex virus type 1 (HSV-1) or HSV-2 and also as receptors for virus-induced cell fusion. Viral glycoprotein D (gD) is the ligand for these receptors. A previous study showed that HVEM makes contact with HSV-1 gD at regions within amino acids 7 to 15 and 24 to 32 at the N terminus of gD. In the present study, amino acid substitutions and deletions were introduced into the N termini of HSV-1 and HSV-2 gDs to determine the effects on interactions with all of the known human and mouse entry/fusion receptors, including mouse HVEM, for which data on HSV entry or cell fusion were not previously reported. A cell fusion assay was used to assess functional activity of the gD mutants with each entry/fusion receptor. Soluble gD:Fc hybrids carrying each mutation were tested for the ability to bind to cells expressing the entry/fusion receptors. We found that deletions overlapping either or both of the HVEM contact regions, in either HSV-1 or HSV-2 gD, severely reduced cell fusion and binding activity with all of the human and mouse receptors except nectin-1. Amino acid substitutions described previously for HSV-1 (L25P, Q27P, and Q27R) were individually introduced into HSV-2 gD and, for both serotypes, were found to be without effect on cell fusion and the binding activity for nectin-1. Each of these three substitutions in HSV-1 gD enhanced fusion with cells expressing human nectin-2 (ordinarily low for wild-type HSV-1 gD), but the same substitutions in HSV-2 gD were without effect on the already high level of cell fusion observed with the wild-type protein. The Q27P or Q27R substitution in either HSV-1 and HSV-2 gD, but not the L25P substitution, significantly reduced cell fusion and binding activity for both human and mouse HVEM. Each of the three substitutions in HSV-1 gD, as well as the deletions mentioned above, reduced fusion with cells bearing 3-O-sulfated heparan sulfate. Thus, the N terminus of HSV-1 or HSV-2 gD is not necessary for functional interactions with nectin-1 but is necessary for all of the other receptors tested here. The sequence of the N terminus determines whether nectin-2 or 3-O-sulfated heparan sulfate, as well as HVEM, can serve as entry/fusion receptors.

Virostatic potential of micro–nano filopodia-like ZnO structures against herpes simplex virus-1

Herpes simplex virus type-1 (HSV-1) entry into target cell is initiated by the ionic interactions between positively charged viral envelop glycoproteins and a negatively charged cell surface heparan sulfate (HS). This first step involves the induction of HS-rich filopodia-like structures on the cell surface that facilitate viral transport during cell entry. Targeting this initial first step in HSV-1 pathogenesis, we generated different zinc oxide (ZnO) micro-nano structures (MNSs) that were capped with multiple nanoscopic spikes mimicking cell induced filopodia. These MNSs were predicted to target the virus to compete for its binding to cellular HS through their partially negatively charged oxygen vacancies on their nanoscopic spikes, to affect viral entry and subsequent spread. Our results demonstrate that the partially negatively charged ZnO-MNSs efficiently trap the virions via a novel virostatic mechanism rendering them unable to enter into human corneal fibroblasts - a natural target cell for HSV-1 infection. The anti-HSV-1 activity of ZnO MNSs was drastically enhanced after creating additional oxygen vacancies under UV-light illumination. Our results provide a novel insight into the significance of ZnO MNSs as the potent HSV-1 inhibitor and rationalize their development as a novel topical agent for the prevention of HSV-1 infection.

Characterization of heparan sulphate 3-O-sulphotransferase isoform 6 and its role in assisting the entry of herpes simplex virus type 1

Heparan sulphate (HS) 3-O-sulphotransferase transfers sulphate to the 3-OH position of the glucosamine residue of HS to form 3-O-sulphated HS. The HS modified by 3-O-sulphotransferase isoform 3 binds to HSV-1 (herpes simplex virus type 1) gD (envelope glycoprotein D), and the resultant 3-O-sulphated HS serves as an entry receptor for HSV-1. In the present paper, we report the isolation and characterization of a novel HS 3-O-sulphotransferase isoform, designated HS 3-O-sulphotransferase isoform 6 (3-OST-6). Mouse 3-OST-6 gene was identified in the EST (expressed sequence tag) database and cloned into pcDNA3.1/Myc-His vector. A CHO (Chinese-hamster ovary) cell line that stably expresses 3-OST-6 (3OST6/CHO cells) was prepared. The disaccharide analysis of the HS isolated from 3OST6/CHO cells revealed that 3-OST-6 exhibits HS 3-O-sulphotransferase activity. Furthermore, 3OST6/CHO cells were susceptible to infection by HSV-1, but not by other alphaherpesviruses examined, suggesting that 3-OST-6 produces a specific entry receptor for HSV-1. Our results indicate that a new member of 3-OST family generates an entry receptor for HSV-1. The findings add to the growing body of evidence that HSV-1 entry is mediated by 3-O-sulphated HS generated by multiple members of 3-O-sulphotransferases.

Using a 3-O-sulfated heparin octasaccharide to inhibit the entry of herpes simplex virus type 1.

Heparan sulfate (HS) is a highly sulfated polysaccharide and is present in large quantities on the cell surface and in the extracellular matrix. Herpes simplex virus type 1 (HSV-1) utilizes a specialized cell surface HS, known as 3-O-sulfated HS, as an entry receptor to establish infection. Here, we exploit an approach to inhibiting HSV-1 infection by using a 3-O-sulfated octasaccharide, mimicking the active domain of the entry receptor. The 3-O-sulfated octasaccharide was synthesized by incubating a heparin octasaccharide (3-OH octasaccharide) with HS 3-O-sulfotransferase isoform 3. The resultant 3-O-sulfated octasaccharide has a structure of Delta UA2S-GlcNS6S-IdoUA2S-GlcNS6S-IdoUA2S-GlcNS3S6S-IdoUA2S-GlcNS6S (where Delta UA is 4-deoxy-alpha-L-threo-hex-4-enopyranosyluronic acid, GlcN is D-glucosamine, and IdoUA is L-iduronic acid). Results from cell-based assays revealed that the 3-O-sulfated octasaccharide has stronger activity in blocking HSV-1 infection than that of the 3-OH octasaccharide, suggesting that the inhibition of HSV-1 infection requires a unique sulfation moiety. Our results suggest the feasibility of inhibiting HSV-1 infection by blocking viral entry with a specific oligosaccharide.

Prophylactic, therapeutic and neutralizing effects of zinc oxide tetrapod structures against herpes simplex virus type-2 infection

The attachment of Herpes simplex virus type-2 (HSV-2) to a target cell requires ionic interactions between negatively charged cell surface co-receptor heparan sulfate (HS) and positively charged residues on viral envelop glycoproteins, gB and gC. Effective blocking of this first step of HSV-2 pathogenesis demonstrates significant prophylactic effects against the viral disease; any in vitro therapeutic effects of blocking this interaction, however, are not clear. Here, we provide new evidence that zinc oxide tetrapod micro-nanostructures synthesized by flame transport approach significantly block HSV-2 entry into target cells and, in addition, demonstrate the potential to stop the spread of the virus among already infected cells. The zinc oxide tetrapods (ZnOTs) also exhibit the ability to neutralize HSV-2 virions. Natural target cells such as human vaginal epithelial and HeLa cells showed highly reduced infectivity when infected with HSV-2 virions that were pre-incubated with the ZnOTs. The mechanism behind the ability of ZnOTs to prevent, neutralize or reduce HSV-2 infection relies on their ability to bind the HSV-2 virions. We used fluorescently labeled ZnOTs and GFP-expressing HSV-2 virions to demonstrate the binding of the ZnOTs with HSV-2. We also show that the binding and hence, the antiviral effects of ZnOTs can be enhanced by illuminating the ZnOTs with UV light. Our results provide new insights into the anti-HSV-2 effects of ZnOT and rationalize their development as a HSV-2 trapping agent for the prevention and/or treatment of infection. The observed results also demonstrate that blocking HSV-2 attachment can have prophylactic as well as therapeutic applications.