Persistence of BK virus in human foetal pancreas cells

The case for BK polyomavirus as a cause of bladder cancer

In 2014, the International Agency for Research on Cancer judged Merkel cell polyomavirus (MCPyV) to be a probable human carcinogen. BK polyomavirus (BKPyV, a distant cousin of MCPyV) was ruled a possible carcinogen. In this review, we argue that it has recently become reasonable to view both of these viruses as known human carcinogens. In particular, several complementary lines of evidence support a causal role for BKPyV in the development of bladder carcinomas affecting organ transplant patients. The expansion of inexpensive deep sequencing has opened new approaches to investigating the important question of whether BKPyV causes urinary tract cancers in the general population.

Human polyomavirus BKV infection of endothelial cells results in interferon pathway induction and persistence

Polyomavirus BKV is highly prevalent among humans. The virus establishes an asymptomatic persistent infection in the urinary system in healthy people, but uncontrolled productive infection of the virus in immunocompromised patients can lead to serious diseases. In spite of its high prevalence, our knowledge regarding key aspects of BKV polyomavirus infection remains incomplete. To determine tissue and cell type tropism of the virus, primary human epithelial cells, endothelial cells and fibroblasts isolated from the respiratory and urinary systems were tested. Results from this study demonstrated that all 9 different types of human cells were infectable by BKV polyomavirus but showed differential cellular responses. In microvascular endothelial cells from the lung and the bladder, BKV persistent infection led to prolonged viral protein expression, low yield of infectious progeny and delayed cell death, in contrast with infection in renal proximal tubular epithelial cells, a widely used cell culture model for studying productive infection of this virus. Transcriptomic profiling revealed the activation of interferon signaling and induction of multiple interferon stimulated genes in infected microvascular endothelial cells. Further investigation demonstrated production of IFNβ and secretion of chemokine CXCL10 by infected endothelial cells. Activation of IRF3 and STAT1 in infected endothelial cells was also confirmed. In contrast, renal proximal tubular epithelial cells failed to mount an interferon response and underwent progressive cell death. These results demonstrated that microvascular endothelial cells are able to activate interferon signaling in response to polyomavirus BKV infection. This raises the possibility that endothelial cells might provide initial immune defense against BKV infection. Our results shed light on the persistence of and immunity against infection by BKV polyomavirus.

BK nephropathy in the native kidneys of patients with organ transplants: Clinical spectrum of BK infection

Nephropathy secondary to BK virus, a member of the Papoviridae family of viruses, has been recognized for some time as an important cause of allograft dysfunction in renal transplant recipients. In recent times, BK nephropathy (BKN) of the native kidneys has being increasingly recognized as a cause of chronic kidney disease in patients with solid organ transplants, bone marrow transplants and in patients with other clinical entities associated with immunosuppression. In such patients renal dysfunction is often attributed to other factors including nephrotoxicity of medications used to prevent rejection of the transplanted organs. Renal biopsy is required for the diagnosis of BKN. Quantitation of the BK viral load in blood and urine are surrogate diagnostic methods. The treatment of BKN is based on reduction of the immunosuppressive medications. Several compounds have shown antiviral activity, but have not consistently shown to have beneficial effects in BKN. In addition to BKN, BK viral infection can cause severe urinary bladder cystitis, ureteritis and urinary tract obstruction as well as manifestations in other organ systems including the central nervous system, the respiratory system, the gastrointestinal system and the hematopoietic system. BK viral infection has also been implicated in tumorigenesis. The spectrum of clinical manifestations from BK infection and infection from other members of the Papoviridae family is widening. Prevention and treatment of BK infection and infections from other Papovaviruses are subjects of intense research.

Oncogenic transformation by BK virus and association with human tumors

BK virus (BKV), a human polyomavirus closely related to JC virus and Simian Virus 40, is ubiquitous in human populations worldwide. After primary infection, BKV establishes a lifelong latent infection in many organs. BKV transforms rodent cells to the neoplastic phenotype and is highly oncogenic in rodents. This review considers the oncogenic potential of BKV in humans and its possible involvement in human tumors. BKV sequences and T antigen (Tag) are detected in several types of human neoplasms, although the viral load is generally low, with less than one copy of the viral genome per cell. The possible causative role of BKV in human oncogenesis rests on the ability of BKV Tag to inactivate the functions of tumor suppressor proteins p53 and pRB family as well as on its ability to induce chromosomal aberrations in human cells. A 'hit and run' mechanism and secretion of paracrine growth factors by BKV Tag-positive cells, recruiting into proliferation neighboring and distant cells, are discussed as possible BKV pathogenic elements in human oncogenesis.