The oncogenic potential of BK‐polyomavirus is linked to viral integration into the human genome

It has been suggested that BK‐polyomavirus is linked to oncogenesis via high expression levels of large T‐antigen in some urothelial neoplasms arising following kidney transplantation. However, a causal association between BK‐polyomavirus, large T‐antigen expression and oncogenesis has never been demonstrated in humans. Here we describe an investigation using high‐throughput sequencing of tumour DNA obtained from an urothelial carcinoma arising in a renal allograft. We show that a novel BK‐polyomavirus strain, named CH‐1, is integrated into exon 26 of the myosin‐binding protein C1 gene (MYBPC1) on chromosome 12 in tumour cells but not in normal renal cells. Integration of the BK‐polyomavirus results in a number of discrete alterations in viral gene expression, including: (a) disruption of VP1 protein expression and robust expression of large T‐antigen; (b) preclusion of viral replication; and (c) deletions in the non‐coding control region (NCCR), with presumed alterations in promoter feedback loops. Viral integration disrupts one MYBPC1 gene copy and likely alters its expression. Circular episomal BK‐polyomavirus gene sequences are not found, and the renal allograft shows no productive polyomavirus infection or polyomavirus nephropathy. These findings support the hypothesis that integration of polyomaviruses is essential to tumourigenesis. It is likely that dysregulation of large T‐antigen, with persistent over‐expression in non‐lytic cells, promotes cell growth, genetic instability and neoplastic transformation. © 2015 Authors. Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.