Deciphering the mechanisms of nucleolar stress response during MCPyV infection - PROJECT SUMMARY Merkel Cell Polyomavirus (MCPyV) is a double-stranded DNA human tumor virus that is the main causative agent of Merkel Cell Carcinoma (MCC), a rare, but extremely aggressive skin cancer. MCC predominantly affects elderly or immunosuppressed patients. Currently, there is a lack of durable and effective treatment options to treat this cancer, thereby necessitating the need to identify new therapeutic options as rates of MCC are steadily increasing. Before the onset of MCC, MCPyV establishes a latent infection and therefore, must have its own mechanisms to promote long term survival within its host to cause MCC later in life. It is known that other human tumor viruses, such as Human Papilloma Virus (HPV), induce cell cycle arrest in infected cells to promote viral persistence. My previous results showed that MCPyV induces host cell cycle arrest and cellular senescence by expressing the large tumor antigen (LT) as a mechanism to promote viral genome maintenance in human fibroblast cells. When investigating how MCPyV LT might induce cellular senescence, we observed that this viral oncoprotein induces the nucleolar stress response (NSR), a host stress response that functions to cause cell cycle arrest and/or cellular senescence, usually in a p53-dependent manner. The NSR is canonically activated upon factors that can inhibit ribosomal biogenesis and often results in disruption of the nucleolar structure and activation of p53. Though this stress response has been characterized in response to nutrient starvation, chemotherapeutic drugs, or other stressors, it has not been sufficiently defined in the context of viral infections. The goal of this proposal is to determine how the NSR is regulated by MCPyV infection and how this stress response might impact MCPyV replication. Specifically, my preliminary data indicated that MCPyV LT downregulates processes that regulate ribosomal RNA (rRNA) expression and processing, or dysregulates ribosomal assembly and/or protein synthesis seen by a lack of phospho-ribosomal protein S6 (p-RPS6) expression, implicating a potential role of LT in modulating ribosomal biogenesis on the RNA and protein level. Accordingly, the central hypothesis of this proposal is that MCPyV LT can inhibit ribosomal biogenesis to induce the NSR, which is required for MCPyV viral persistence. To address this hypothesis, Specific Aim 1 will characterize the NSR phenotypes and elucidate the mechanism and processes of ribosomal biogenesis that are directly disrupted by MCPyV LT. Specific Aim 2 will investigate the mechanism by which MCPyV LT promotes p53 activation and how the p53-dependent NSR regulates MCPyV genome replication and persistence. Taken altogether, the findings from this proposal will significantly expand our understanding on the role of the NSR as a critical viral sensor and identify host factors that are essential for MCPyV pathogenesis.
