Abstract
Viruses can inhibit host autophagy through multiple mechanisms, and evasion of autophagy plays an important role in immune suppression and viral oncogenesis. Merkel cell polyomavirus (MCPyV) T-antigens are expressed and involved in the pathogenesis of a large proportion of Merkel cell carcinoma (MCC). Yet, how MCPyV induces tumorigenesis is not fully understood. Herein, we show that MCPyV T-antigens induce miR-375, miR-30a-3p and miR-30a-5p expressions, which target multiple key genes involved in autophagy, including ATG7, SQSTM1 (p62) and BECN1. In MCC tumors, low expression of ATG7 and p62 are associated with MCPyV-positive tumors. Ectopic expression of MCPyV small T-antigen and truncated large T-antigen (LT), but not the wild-type LT, resulted in autophagy suppression, suggesting the importance of autophagy evasion in MCPyV-mediated tumorigenesis. Torin-1 treatment induced cell death, which was attenuated by autophagy inhibitor, but not pan-caspase inhibitor, suggesting a potential role of autophagy in promoting cell death in MCC. Conceptually, our study shows that MCPyV oncoproteins suppress autophagy to protect cancer cells from cell death, which contribute to a better understanding of MCPyV-mediated tumorigenesis and potential MCC treatment.