Human herpesvirus (HHV)-7 infection is associated with persistence of viral genomes in salivary gland (SG) tissues, and chronic expression of viral antigens in these sites. The virus is generally thought to be spread by a salivary route, and there is lifelong shedding of large amounts of infectious virions in saliva. These observations suggest the following hypothesis: that HHV-7 has evolved specific mechanisms to gain entry to SG cells and to evade host immune responses in SG tissues. In this proposal, we will examine the role of specific viral proteins in virus attachment and entry to SG epithelial cells. In the first two specific aims, the unique viral glycoprotein, gp65, will be studied. Gp65 is a component of the virus particle, and polyclonal antisera directed against gp65 neutralize virus infectivity; HHV-7 gp65 also binds to heparan sulfate proteoglycans (HSPGs). These data strongly suggest that gp65 plays a role in cellular attachment and entry by HHV-7; this hypothesis will be tested experimentally. First, we will examine the interaction of purified recombinant HHV-7 gp65 with cell surface HSPGs found on cultured human SG cells. Second, a gp65- deleted recombinant virus will be constructed, and its ability to attach to and enter cultured SG cells will be examined. Third, the molecular architecture of gp65, and its interaction with host macromolecules will be studied. In the third aim, we will study two putative 7-transmembrane (7- tm) receptors encoded by HHV-7, U12 and U51. Homologous genes encoded by rat and mouse cytomegalovirus (CMV) are essential for efficient viral replication in salivary glands, and a related gene in human CMV has been shown to contribute to membrane fusion events that may be involved in virus entry or spread. Experiments will therefore be conducted, to determine whether HHV-7 U12 and U51 can enhance membrane fusion events mediated by different viral proteins in cultured SG cells. It is expected that a greater understanding of the molecular pathways exploited by HHV-7 will contribute to the future design of enhanced gene delivery vehicles for SG gene therapy; such vector systems may incorporate components of HHV-7.
