| Herpes simplex virus glycoprotein D (gD) is required, along with gB and gH/gL, for virus entry. Entry is initiated by gD binding to a cellular receptor, mainly nectin-1, which is expressed on epithelial cells and neurons, or HVEM, which is found on immune cells. Part 1 and 2 of this thesis identify what happens to nectin-1 in response to gD binding and virus infection. To accomplish this, a co-culture system was established using cells engineered to express gD. I found that co-culturing these cells with nectin-1 expressing cells resulted in nectin-1 internalization and degradation. Nectin-1 internalization occurred in the same cells that HSV enters by endocytosis, but did not occur in cells that HSV enters by fusion at the plasma membrane. Moreover, the kinetics of virus entry and gD-induced nectin-1 internalization were the same. After virus and nectin-1 endocytosis, both co-localized inside the cell. Normally, nectin-1 accumulates at cell contacts by trans-interacting with another nectin. The interaction with gD on cells or virions has a very different outcome by inducing endocytosis. Thus, gD hijacks nectin-1 to achieve internalization of the virus.;In part 3 of this thesis, I focused on HVEM. This receptor is expressed mainly on cells of the immune system, which are not the primary targets of HSV infection in its host. Nevertheless, since the virus survives in an immune host, it is likely that this interaction is beneficial to the virus. HVEM has four natural ligands that either stimulate (LIGHT, Lia) or inhibit (BTLA, CD 160) the immune response. Therefore, I investigated the effect gD has on the interaction between HVEM and its natural ligands. I found that although gD had the lowest binding affinity for HVEM, it still competed with the other ligands for HVEM binding. As with nectin-1, binding of gD to HVEM induced down-regulation of this receptor. Interestingly, LIGHT and BTLA also caused HVEM down-regulation. Thus, receptor down-regulation may be a natural mechanism for modulating HVEM signaling. I propose that HSV may use receptor internalization to alter the immune response to ensure its survival in the host. |
