Kaposi's sarcoma (KS), caused by the oncogenic Kaposi's sarcoma herpesvirus (KSHV), is an angiogenic tumor characterized by intense angiogenesis, inflammation and proliferation of KSHV-infected spindle cells. We describe the characterization of a mouse model of KS by transfection of a KSHV bacterial artificial chromosome (KSHVBac36) into mouse bone marrow endothelial-lineage cells which generated a cell (mECK36) that forms KS-like tumors in mice. Our results define mECK36 as a biologically sensitive animal model of KSHV-dependent KS with the following characteristics: (1) the pathological phenotype is a consequence of KSHV gene expression in normal progenitor cells subjected to in vivo growth conditions, (2) the histopathologic phenotype of the tumors resembles KS lesions, and (3) the model is suitable for analysis of vGPCR-driven tumorigenesis in the context of the whole KSHV genome. The mechanism by which vGPCR promotes tumorigenesis is not fully understood. The characterization of a Rac1 transgenic mouse model that produces KS-like lesions that highly resemble human KS has helped us to identify the potential role of Rac1, which is activated by vGPCR, in the pathogenesis of KS. The results from the RacCA transgenic mouse suggest that viral and host genes triggering Rac1 and ROS production may play an important role in KS tumorigenesis. We set out to determine how vGPCR physiologically activates Rac1 in KSHV-infected cells in the KS model mECK36. We found that KSHV oncogenesis in mECK36 is promoted by vGPCR activation of a paracrine oncogenic mechanism through PDGF-BB, which requires a Rac1- and ROS-mediated loop, leading to STAT3 transcriptional activation of c-Myc, VEGF and KSHV latent viral gene expression. We also found that the latency-associated nuclear antigen (LANA) upregulates the PDGFR in vivo, priming latently-infected cells to the PDGF signaling pathway. This oncogenic mechanism can be targeted with the antioxidant N-acetylcysteine (NAC) and FDA-approved PDGF receptor inhibitors to control KSHV-induced tumorigenesis. Our results highlight a ROS-dependent axis whereby Rac1 activating oncogenes and inflammatory signaling drive paracrine stimulation of neoplastic growth and angiogenesis in neighboring cells, defining this axis and its components as attractive anti-tumor targets in KS pathogenesis.

There are eight described human herpesviruses. All share the ability to achieve latency in their host following primary infection and may subsequently reactivate later in life. In immunocompetent individuals herpesvirus infections, especially those caused by reactivating virus, are usually mild however in patients with impaired cellular immune function they may cause significant morbidity and mortality. In this thesis molecular and serological techniques were used to define the prevalence of the human herpesviruses in a variety of immunocompromised groups as these individuals are at greatest risk of severe herpesviral disease. Human herpesvirus 8 (HHV8) is the most recently discovered of the human herpesviruses. A nested polymerase chain reaction (PCR) for detecting HHV8 genome was designed and used to examine the association between infection with HHV8 and FIIV-associated Kaposi's sarcoma (KS). The prevalence of HHV8 genome carriage in the general UK population was defined, as were potential routes of HHV8 transmission. Novel treatments for HIV-KS were investigated. The value of herpesviral genome detection in predicting associated disease was evaluated, together with the genome load response of cytomegalovirus (CMV), a significant herpesviral pathogen, to a novel chemotherapeutic protocol for immunosuppressed patients receiving allogenic bone marrow transplantation. The prevalence and epidemiology of HHV8 were found to be compatible with that predicted for a causal agent of KS, but not the haematological malignancy multiple myeloma. Apart from 1-IHV8, Epstein-Barr virus and CMV were found to be the most significant herpesvirus pathogens in the immunocompromised host. The use of molecular detection techniques, such as PCR, were shown to be of great value in the diagnostic and epidemiological determination of herpesviral infection in immunocompromised patients.