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, origi nating from spliced messages. The 228-amino-acid (aa) gpK8.1A is the predom inant form associated with the virion envelope, consisting of a 167-aa regi on 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 vit ro 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, hepara n sulfate (HS). Since HHV-8 K8.1 gene is positionally colinear to the Epste in-Barr virus (EBV) gene encoding the gp350/gp220 protein involved in EBV b inding to the target cells, gpK8.1A's ability to interact with the target c ells was examined. The gpK8.1A without the transmembrane and carboxyl domai ns (Delta TMgpK8.1A) was expressed in a baculovirus system and purified. Ra diolabeled purified Delta TMgpK8.1A protein bound to the target cells, whic h was blocked by unlabeled Delta TMgpK8.1A. Unlabeled Delta TMgpK8.1-A bloc ked the binding of [H-3]thymidine-labeled purified HHV-8 to the target cell s. Binding of radiolabeled Delta TMgpK8.1A to the target cells was inhibite d 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 De lta TMgpK8.1A was displaced by soluble heparin. Radiolabeled Delta TMgpK8.1 A also bound to HS expressing Chinese hamster ovary (CHO-K1) cells, and bin ding to mutant CHO cell lines deficient in HS was significantly reduced. Th e Delta TMgpK8.1A specifically bound to heparin-agarose beads, which was in hibited by HS and heparin, but not by other GAGs. Virion envelope- associat ed gpK8.1A was specifically precipitated by heparin-agarose beads. These fi ndings suggest that gpK8.1A interaction with target cells involves cell sur face HS-like moieties, and HHV-8 interaction with HS could be in part media ted by virion envelope-associated gpK8.1A.