Investigating the Effect of Caspases and Anti-Viral Responses on KSHV Tumorigeniesis

PROJECT SUMMARY Kaposi's sarcoma, caused by Kaposi's sarcoma-associated herpesvirus (KSHV), remains a major health challenge for people living with HIV and other immunocompromised patients. While research has historically focused on the latent cycle of KSHV infection, recent evidence demonstrates that viral reactivation to the lytic cycle is crucial for tumor development through growth factor secretion and maintenance of latently infected cells. This central role of the lytic cycle offers a new therapeutic opportunity. Therefore, there is a need to discover strategies to block KSHV reactivation and its associated pro-tumor activities, as a starting point to develop new targeted therapies. Type I interferons (IFNs) potently block KSHV replication at early stages of the lytic cycle. However, direct IFN administration causes severe systemic side effects in patients, limiting its use. We recently discovered that KSHV hijacks cellular caspase enzymes to suppress IFN responses. This finding suggests that caspase inhibition could restore antiviral IFN responses in infected cells and serve as an alternative approach to leveraging IFN response for therapy. However, we do not yet know whether manipulating caspase activity and type I IFNs can block the pro-tumor activities of lytic replication. This is because IFN responses have been studied in conventional 2D cell culture infection models that poorly mimic KSHV infection in tumors. To address this gap, we will use a recently developed 3D primary human endothelial cell organoid model. These organoids better recapitulate characteristics of Kaposi’s sarcoma tumors, including stable maintenance of the latently infected cell mass through spontaneous viral reactivation and changes in cell morphology and differentiation. We will use this new model to test the hypothesis that activation of the IFN pathway, either through direct IFN administration or caspase inhibition, disrupts two key tumorigenic processes due to lytic reactivation: growth factor secretion and maintenance of the latently infected cell population. We will first dissect type I IFN and caspase signaling during KSHV infection in organoids and compare it to IFN and caspase activation in Kaposi’s sarcoma tumor tissue (Aim 1). We will then test how inducing IFN responses through direct IFN administration or caspase inhibition affects growth factor secretion and maintenance of the latently infected cell population (Aim 2). This study will thus evaluate the potential for modulation of caspases and IFN responses in blocking KSHV tumorigenic activities and as therapeutic strategy against Kaposi’s sarcoma. Success could lead to new targeted treatments for Kaposi’s sarcoma while providing a foundation for future mechanistic studies of KSHV pathogenesis.