Role of cellular ion channels in the BK polyomavirus life cycle

BK polyomavirus (BKPyV) is a human pathogen that infects the majority of the population, worldwide, establishing a lifelong infection. Immunocompromised patients following renal transplantation, are likely to suffer from severe clinical complications, including polyomavirus-associated nephropathy (PVAN), which can ultimately lead to kidney graft failure. Currently, there are no direct acting anti-viral compounds targeting BKPyV and the number of renal transplants is increasing significantly. Therefore, there is an urgent need to understand the viral life cycle in order to identify potential targets that can be exploited for therapeutic development. Ion channels play a critical role in kidney physiology by controlling several processes, implicating them as candidate proteins required for BKPyV infection. A pharmacological analysis was performed in which human primary renal epithelial cells were treated with a range of pharmacological modulators of host ion channels and the effect on BKPyV production assayed using a fluorescence-based technique. From this approach, it was identified that the clinically available drug, Glibenclamide is a potent inhibitor of BKPyV infection. Biochemical analysis and molecular-based techniques revealed that the cystic fibrosis transmembrane conductance regulator (CFTR) was the target of Glibenclamide and time-of-addition experiments indicated that CFTR might be required during the entry and trafficking of BKPyV through the cytoplasm. These studies provide the first reported requirement for host ion channels in the BKPyV life cycle. Studies on other related polyomaviruses, including JCPyV, SV40 and Merkel cell polyomavirus determined a cell type-dependent requirement of CFTR in the viruses’ life cycle, highlighting the importance of understanding the role of host ion channels in polyomaviruses’ life cycle. Ion channels are an emerging target for many medical conditions and such compounds that target these may represent a novel strategy for developing therapeutics to treat PVAN and/or other polyomavirus-associated clinical complications

Agnoprotein Is an Essential Egress Factor during BK Polyomavirus Infection.

BK polyomavirus (BKPyV; hereafter referred to as BK) causes a lifelong chronic infection and is associated with debilitating disease in kidney transplant recipients. Despite its importance, aspects of the virus life cycle remain poorly understood. In addition to the structural proteins, the late region of the BK genome encodes for an auxiliary protein called agnoprotein. Studies on other polyomavirus agnoproteins have suggested that the protein may contribute to virion infectivity. Here, we demonstrate an essential role for agnoprotein in BK virus release. Viruses lacking agnoprotein fail to release from host cells and do not propagate to wild-type levels. Despite this, agnoprotein is not essential for virion infectivity or morphogenesis. Instead, agnoprotein expression correlates with nuclear egress of BK virions. We demonstrate that the agnoprotein binding partner α-soluble N-ethylmaleimide sensitive fusion (NSF) attachment protein (α-SNAP) is necessary for BK virion release, and siRNA knockdown of α-SNAP prevents nuclear release of wild-type BK virions. These data highlight a novel role for agnoprotein and begin to reveal the mechanism by which polyomaviruses leave an infected cell