KSHV is a relatively new gamma-herpesvirus that has been linked to KS, primary effusion lymphoma, and the plasmablastic variant of Castleman's disease. Although KSHV is considered essential for development of all forms of KS, the mechanisms of how KSHV contributes to KS tumor cell growth and the elucidation of co-factors that may be involved in KS pathogenesis are poorly understood. Over the last several years, we have pursued projects that have centered on understanding the molecular mechanisms involved in reactivation (latent-to-lytic switching) of KSHV. Viral reactivation occurs prior to onset of KS lesions and is a potential target for blocking KS development. After developing a novel assay to detect and quantify viral reactivation within single cells, we studied a variety of drugs (e.g., ganciclovir, cidofovir), signal transduction inhibitors (e.g., cyclosporine), and conditions (e.g., hypoxia) that either induced or inhibited virus reactivation. While studying the ability of histone deacetylase inhibitors to induce viral replication, we discovered that these compounds were potent inducers of apoptosis in KSHV-infected cells. We are now exploring the anti-tumor effects of these drugs in mouse models in vivo and the possibility of clinically using them in patients with KS. All KS tumor cells are latently infected with KSHV. These cells are known to express the KSHV latent genes LANA, k-cyclin, and v-FLIP. To begin to understand how these latent genes contribute to KS tumorigenesis, we have studied their function in both in vitro and in vivo models. We recently reported that LANA, but not k-cyclin, induced prolonged life span in primary endothelial cells that expressed this gene. To study in vivo function of these genes, we have created transgenic mice that express either k-cyclin or LANA within lymphatic endothelial cells (now believed to be the cell of origin of KS tumor cells). To create tissue-specific expression, we first cloned, sequenced, and characterized the murine VEGFR-3 promoter, a gene specifically expressed in lymphatics. Interestingly, VEGFR-3/k-cyclin mice demonstrated lymphatic dysfunction as characterized by pleural effusions and the inability to drain fluid from peripheral tissues. We are now planning to breed k-cyclin mice with p53 knockout mice, a model that is likely to induce lymphatic tumors. Lastly, generation of transgenic mice that simultaneously express all 3 latent genes, a situation that would mimic gene expression in KS tumors, is underway. In summary, these studies should be critical in understanding how KSHV induces the development of KS and may aid in the design of novel therapeutic approaches that target KS-specific markers. 100% AIDS-RELATED
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