The Role of ORF10 in Gammaherpesvirus Pathogenesis

Gammaherpesviruses comprise the human Kaposi’s Sarcoma-associated herpesvirus and Epstein-Barr virus, as well as the rodent virus, murine gammaherpesvirus-68 (MHV-68). Since KSHV lacks a small, immunocompetent animal model due to the restricted host range, MHV-68, which resembles human gammaherpesviruses at the genetic and pathological level, is used to investigate viral-host interaction. Gammaherpesvirus ORF10 is known to inhibit host transcript export selectively through its interaction with the cellular export factor, Rae1. The ORF10-Rae1 interaction is conserved across KSHV and MHV-68 ORF10s. However, the impact of cellular transcript manipulation by ORF10 on both the host and the virus remains unclear. Therefore, we aimed to investigate the role of ORF10 in gammaherpesvirus pathogenesis through three angles.The first angle involved an investigation on the molecular mechanism by which the KSHV ORF10-Rae1 complex performs its function in selective host transcript export inhibition. The second angle involved the possibility that the absence of ORF10 leads to an accelerated expression of other KSHV viral genes, implying that KSHV ORF10 could hold a role in controlling the tightly timed and sequential expression of KSHV genes required during lytic replication. The main study of the dissertation is the third angle, which involves MHV-68 ORF10 as studied within an in vivo system. The initial direction was to verify the potential antagonistic role of MHV-68 ORF10 against host type I interferon signaling, a first-line of defense against viral infection by the mammalian host. Despite the finding that ORF10 is not required for host interferon response evasion, the in vivo study yielded a surprising phenotype that became the center point of this dissertation. We followed-up on these phenotypes with in vitro experiments to confirm the role of ORF10 in cell-to-cell spread and viral dissemination within peripheral organs. Complementary investigations in vitro determined that MHV-68 infection without ORF10 was more significantly impacted when cell-free viral dissemination was impaired. Despite the ambiguous results from MHV-68 ORF10 complementation, we demonstrated that KSHV ORF10 complementation was capable of rescuing the MHV-68 ORF10S viral infection in a forced cell-to-cell spread setting, highlighting the conserved nature and importance of ORF10’s role in cell-to-cell spread and viral dissemination