Yes / Virus-encoded miRNAs are emerging as key regulators of persistent infection and host-cell immune evasion. Merkel cell polyomavirus (MCPyV), the predominant aetiological agent of Merkel cell carcinoma (MCC), encodes a single miRNA, MCV-miR-M1, which targets the oncogenic MCPyV large T antigen (LT). MCV-miR-M1 has previously been shown to play an important role in establishment of long-term infection, however, the underlying mechanism is not fully understood. A key unanswered question is whether, in addition to auto-regulating LT, MCV-miR-M1 also targets cellular transcripts to orchestrate an environment conducive for persistent infection. To address this, we adopted an RNA-Seq-based approach to identify cellular targets of MCV-miR-M1. Intriguingly, bioinformatics analysis of transcripts that are differentially expressed in cells expressing MCV-miR-M1 revealed several genes implicated in immune evasion. Subsequent target validation led to the identification of the innate immunity protein, SP100, as a direct target of MCV-miR-M1. Moreover, MCV-miR-M1-mediated modulation of SP100 was associated with a significant decrease in CXCL8 secretion, resulting in the attenuation of neutrophil chemotaxis towards Merkel cells harbouring synthetic MCPyV. Based on these observations we propose that MCV-miR-M1 targets key immune response regulators to help facilitate persistent infection, which is a pre-requisite for cellular transformation in MCC. / Funded in part by a University of Bradford studentship to PA and a Royal Society research award to JRB.

yes / Merkel cell carcinoma (MCC) is an aggressive skin cancer with a high propensity for recurrence and metastasis. Merkel cell polyomavirus (MCPyV) is recognised as the causative factor in the majority of MCC cases. The MCPyV small tumour antigen (ST) is considered to be the main viral transforming factor, however potential mechanisms linking ST expression to the highly metastatic nature of MCC are yet to be fully elucidated. Metastasis is a complex process, with several discrete steps required for the formation of secondary tumour sites. One essential trait that underpins the ability of cancer cells to metastasise is how they interact with adjoining tumour cells and the surrounding extracellular matrix. Here we demonstrate that MCPyV ST expression disrupts the integrity of cell-cell junctions, thereby enhancing cell dissociation and implicate the cellular sheddases, A disintegrin and metalloproteinase (ADAM) 10 and 17 proteins in this process. Inhibition of ADAM 10 and 17 activity reduced MCPyV ST-induced cell dissociation and motility, attributing their function as critical to the MCPyV-induced metastatic processes. Consistent with these data, we confirm that ADAM 10 and 17 are upregulated in MCPyV-positive primary MCC tumours. These novel findings implicate cellular sheddases as key host cell factors contributing to virus-mediated cellular transformation and metastasis. Notably, ADAM protein expression may be a novel biomarker of MCC prognosis and given the current interest in cellular sheddase inhibitors for cancer therapeutics, it highlights ADAM 10 and 17 activity as a novel opportunity for targeted interventions for disseminated MCC. / In parts by the Medical Research Council (95505126) to AW, Royal Society (UF100419) to JM and Biotechnology and Biological Sciences Research Council (BB/R000352/1) to GEB and AW.