Human Herpesvirus 8 Envelope Glycoprotein K8.1A Interaction with the Target Cells Involves Heparan Sulfate

Human herpesvirus-8 (HHV-8) or Kaposi's sarcoma-associated herpesvirus K8.1 gene encodes for two immunogenic glycoproteins, gpK8.1A and gpK8.1B, originating from spliced messages. The 228-amino-acid (aa) gpK8.1A is the predominant form associated with the virion envelope, consisting of a 167-aa region identical to gpK8.1B and a 61-aa unique region (L. Zhu, V. Puri, and B. Chandran, Virology 262:237-249, 1999). HHV-8 has a broad in vivo and in vitro cellular tropism, and our studies showed that this may be in part due to HHV-8's interaction with the ubiquitous host cell surface molecule, heparan sulfate (HS). Since HHV-8 K8.1 gene is positionally colinear to the Epstein-Barr virus (EBV) gene encoding the gp350/gp220 protein involved in EBV binding to the target cells, gpK8.1A's ability to interact with the target cells was examined. The gpK8.1A without the transmembrane and carboxyl domains (DeltaTMgpK8.1A) was expressed in a baculovirus system and purified. Radiolabeled purified DeltaTMgpK8.1A protein bound to the target cells, which was blocked by unlabeled DeltaTMgpK8.1A. Unlabeled DeltaTMgpK8.1A blocked the binding of [(3)H]thymidine-labeled purified HHV-8 to the target cells. Binding of radiolabeled DeltaTMgpK8.1A to the target cells was inhibited in a dose-dependent manner by soluble heparin, a glycosaminoglycan (GAG) closely related to HS, but not by other GAGs such as chondroitin sulfate A and C, N-acetyl heparin and de-N-sulfated heparin. Cell surface absorbed DeltaTMgpK8.1A was displaced by soluble heparin. Radiolabeled DeltaTMgpK8.1A also bound to HS expressing Chinese hamster ovary (CHO-K1) cells, and binding to mutant CHO cell lines deficient in HS was significantly reduced. The DeltaTMgpK8.1A specifically bound to heparin-agarose beads, which was inhibited by HS and heparin, but not by other GAGs. Virion envelope-associated gpK8.1A was specifically precipitated by heparin-agarose beads. These findings suggest that gpK8.1A interaction with target cells involves cell surface HS-like moieties, and HHV-8 interaction with HS could be in part mediated by virion envelope-associated gpK8.1A.