The role of the Merkel cell polyomavirus small T antigen in virus replication and MCC pathogenesis

Merkel cell carcinoma (MCC) is a highly aggressive human cancer and its incidence is increasing worldwide. In 2008 a novel human polyomavirus named Merkel cell polyomavirus (MeV) was isolated from MCC tumours. MCV is monoclonally integrated into the genomic DNA of 80% of these tumours and is now recognised as a causative factor in MCC pathogenesis. The Small Tumour (ST) antigens of mammalian polyomaviruses have been demonstrated to regulate viral promoter activation and contribute to cellular transformation. Mechanisms central to these putative functions are typically dependent on an interaction between ST and the major cellular phosphatase: protein phosphatase 2A (PP2A). In contrast, MCC ST alone transforms rat fibroblast cells in a PP2A-independent manner. Therefore, elucidation of novel mechanisms regarding the putative functions of MCV ST is required. Results in Chapter 3 describe the generation of various MCV ST reagents produced from an MCC tumour section. Initial characterisation indicated that MCV ST is involved in activating the early viral promoter and contributes to increased cell invasiveness/motility. Subsequent work in Chapter 4 demonstrated that MCV ST specifically downregulates NF-kB-driven transcription. Moreover, a novel protein-protein interaction between MCV ST and NF-KB Essential Modulator (NEMO) was observed. Further analysis showed that tumour necrosis factor (TN F)-induced phosphorylation of the inhibitor of KB (IKB) protein and nuclear translocation of NF-KB are down regulated upon MCV 5T expression. Together, these findings suggest that MCV 5T-mediated NFKB inhibition is dependent on NEMO binding. Additional novel interacting partners of MCV ST were identified in Chapter 5; including the PP2Aβ scaffolding subunit and the protein phosphatase 4 catalytic subunit (PP4C). Results indicated that (i) these phosphatases are involved in NF-KB inhibition by MCV 5T and (ii) the PP4C interaction is required for MCV 5T-mediated microtubule destabilisation. Overall, data presented herein will increase our understanding of this oncogenic viral protein and provide new routes of therapeutic intervention for MCC.EThOS - Electronic Theses Online ServiceGBUnited Kingdo