Herpes simplex virus type I (HSV-1)-induced cell fusion: Influence of viral glycoprotein D alleles and cell surface expression of glycosaminoglycans on cell fusion mediated by HSV entry receptors HveA, HveB and HveC

Cell surface glycosaminoglycans (GAGs) serve as the initial point of attachment for HSV and positively influence cell-cell fusion. HveA, HveB and HveC are cell surface co-receptors of HSV entry. HveC mediates the entry of all HSV strains tested, whereas HveA and HveB mediate entry for subsets of HSV-1 expressing wild-type or mutant (Rid1) gD, respectively. The aims of this study were to determine (1) whether HveA, HveB, and HveC served as co-receptors for HSV-1-induced cell fusion; (2) whether the allele of gD expressed by the virus influenced cell fusion mediated by these receptors; (3) whether cell surface GAGs influenced cell fusion mediated by these receptors; and (4) whether monoclonal antibodies specific for viral glycoproteins or receptors could inhibit cell fusion mediated by HveA.;Using HSV-1 syncytial strains expressing either the Rid1 or wild-type form of gD, it was determined that all three receptors were efficient mediators of HSV-1 induced cell fusion. Each receptor's ability to mediate fusion paralleled its action in entry. HveA mediated fusion when the virus expressed wild-type, but not Rid1, gD. The converse was true for HveB: it mediated fusion when the virus expressed Rid1gD but not wild-type gD. HveC mediated the fusion of both viruses, but the syncytia were larger when the virus expressed Rid1 gD.;Maintenance of receptor-expressing cell lines in medium containing chlorate, a potent inhibitor of GAG sulfation, HSV binding and ultimately infection, inhibited viral entry mediated by all three receptors, but impaired only the ability of HveB, not HveA or HveC, to mediate cell fusion. Furthermore, HveA mediated equivalent levels of fusion in both mutant GAG-negative and wild-type GAG-positive CHO cells, suggesting that GAGs influence cell fusion in a receptor-dependent fashion and are more important for entry than cell fusion.;Antibodies specific for HveA or for gD inhibited HveA-dependent fusion consistent with the ability of these antibodies to block viral entry. Antibodies unable to block the binding of soluble HveA to virions (anti-gH and certain anti-gD monoclonal antibodies) blocked HveA-dependent cell fusion, indicating that they probably interfere with functional domains of gH and gD which do not directly interact with HveA.