BKV Agnoprotein Interacts with α-Soluble N-Ethylmaleimide-Sensitive Fusion Attachment Protein, and Negatively Influences Transport of VSVG-EGFP

Abstract

BackgroundThe human polyomavirus BK (BKV) infects humans worldwide and establishes a persistent infection in the kidney. The BK virus genome encodes three regulatory proteins, large and small tumor-antigen and the agnoprotein, as well as the capsid proteins VP1 to VP3. Agnoprotein is conserved among BKV, JC virus (JCV) and SV40, and agnoprotein-deficient mutants reveal reduced viral propagation. Studies with JCV and SV40 indicate that their agnoproteins may be involved in transcription, replication and/or nuclear and cellular release of the virus. However, the exact function(s) of agnoprotein of BK virus remains elusive.Principal FindingsAs a strategy of exploring the functions of BKV agnoprotein, we decided to look for cellular interaction partners for the viral protein. Several partners were identified by yeast two-hybrid assay, among them α-SNAP which is involved in disassembly of vesicles during secretion. BKV agnoprotein and α-SNAP were found to partially co-localize in cells, and a complex consisting of agnoprotein and α-SNAP could be co-immunoprecipitated from cells ectopically expressing the proteins as well as from BKV-transfected cells. The N-terminal part of the agnoprotein was sufficient for the interaction with α-SNAP. Finally, we could show that BKV agnoprotein negatively interferes with secretion of VSVG-EGFP reporter suggesting that agnoprotein may modulate exocytosis.ConclusionsWe have identified the first cellular interaction partner for BKV agnoprotein. The most N-terminal part of BKV agnoprotein is involved in the interaction with α-SNAP. Presence of BKV agnoprotein negatively interferes with secretion of VSVG-EGFP reporter.

Nuclear Magnetic Resonance Structure Revealed that the Human Polyomavirus JC Virus Agnoprotein Contains an α-Helix Encompassing the Leu/Ile/Phe-Rich Domain

“…JCV agnoprotein was previously shown to interact with a number of cellular and viral proteins, including YB-1 (11), p53 (12), FEZ1 and HP1-␣ (13), adaptor protein complex 3 (14), JCV small t antigen (Sm t-Ag) (15), and JCV large T antigen (LT-Ag) (16), and has been implicated in various aspects of the JCV life cycle, including viral replication (4,17), viral transcription (11), functioning as a viroporin (14,18), encapsidation (19), and interfering with exocytosis (20). In addition, this protein deregulates cell cycle progression, where cells stably expressing agnoprotein largely accumulate at the G 2 /M phase of the cell cycle (12).…”

Agnoprotein of mammalian polyomaviruses

“…Binding of these agnoproteins to caveolin has not been reported, but the motif overlaps with the region required for co-localization of BKPyV agnoprotein with lipid droplets (Unterstab et al, 2010). a-soluble N-ethylmaleimide-sensitive fusion attachment protein (a-SNAP), another interaction partner of BKPyV agnoprotein, is found in lipids and may explain the presence of agnoprotein in lipid droplets (Johannessen et al, 2011).…”

“…In addition to its viroporin function, the viroporins Vpu of HIV-1 and M2 of influenza virus impair the secretory pathway (Henkel et al, 2000;Tokarev and Guatelli, 2011). Similarly, BKPyV agnoprotein also interferes with secretion through its interaction with a-SNAP (Johannessen et al, 2011).…”

Essential roles of Leu/Ile/Phe-rich domain of JC virus agnoprotein in dimer/oligomer formation, protein stability and splicing of viral transcripts

“…It has been implicated in many different aspects of the JCV life cycle, including viral transcription (Safak and Khalili, 2001), replication (Safak and Khalili, 2001), functioning as viroporin (Suzuki et al, 2010), encapsidation (Sariyer et al, 2006) and interfering with the process of exocytosis (Johannessen et al, 2011). In addition, this protein was found to deregulate cell cycle progression, where cells that stably express agnoprotein largely accumulate at the G2/M phase of the cell cycle (Darbinyan et al, 2002).…”