Infection of Vero Cells by BK Virus Is Dependent on Caveolae

Abstract

Polyomavirus-associated nephropathy occurs in ϳ5% of renal transplant recipients and results in loss of graft function in 50 to 70% of these patients. The disease is caused by reactivation of the common human polyomavirus BK (BKV) in the transplanted kidney. The early events in productive BKV infection are unknown. In this report, we focus on elucidating the mechanisms of BKV internalization in its target cell. Our data reveal that BKV entry into permissive Vero cells is slow, is independent of clathrin-coated-pit assembly, is dependent on an intact caveolin-1 scaffolding domain, is sensitive to tyrosine kinase inhibition, and requires cholesterol. BKV colocalizes with the caveola-mediated endocytic marker cholera toxin subunit B but not with the clathrin-dependent endocytic marker transferrin. In addition, BKV infectious entry is sensitive to elevation in intracellular pH. These findings indicate that BKV entry into Vero cells occurs by caveola-mediated endocytosis involving a pH-dependent step.Humans are the natural host species for two members of the polyomavirus family, BK virus (BKV) and JC virus (JCV) (22). Both viruses establish persistent subclinical infections in the kidneys and peripheral blood in 85% of the population worldwide (10, 36). The urotheliotropic nature of BKV is characterized by infection of the epithelial lining of the collective ducts, the transitional epithelial cells of the renal calyces, the parietal epithelium of the Bowman's capsule, and the transitional epithelium of the renal pelvis and the urinary tract (11, 56). Sporadic reactivation of BKV resulting in limited viral replication is seen in 0.5 to 20% of healthy seropositive individuals, yet renal function is left unaffected (20,23,62). A dramatic increase in viral activity leading to disease progression occurs predominantly in the context of greatly impaired T-cell-mediated immunity (26,27).Kidney transplant recipients are subjected to a potent immunosuppressive therapy and are thus at a high risk for exacerbated BKV replication (1). Active BKV infection in the renal allograft, known as polyomavirus nephropathy, has been linked to progressive graft dysfunction and ultimate graft loss (13). Sustained high levels of viral replication result in lytic destruction of the host tubular cells and release of BKV progeny to perpetuate the infection (1, 33, 34). BKV, the causative agent of polyomavirus nephropathy, is drawing increasing attention as a significant factor in the failure of renal transplants (48).Similar to those of the other polyomaviruses, BK virions are small (40.5 to 45 nm in diameter) and consist of a superhelical circular double-stranded DNA genome contained within a nonenveloped icosahedral capsid (18). Though the exact identity of the BK receptor(s) is unknown, evidence suggests that gangliosides type II, GD1a, and GT play important roles in the initial interaction between BKV and the permissive monkey kidney (Vero) cell line, as well as in BKV hemagglutination of human type O red blood cells (54,59,60). Following pen...

Late-Onset BK Viral Nephropathy in a Kidney Transplant Recipient

“…The virus, which has renal tropism, enters the cell via caveolin-1emediated endocytosis and integrates with the host DNA [9]. The latter contributes to the dormant stage of the infection.…”

Role of Membrane Rafts in Viral Infection

“…Although SV40 receptor MHC-I is not localized in membrane rafts, MHC-1 induces association of viral particles with caveola [4][5][6][7][8], or GM1 ganglioside, which is enriched in membrane rafts and known to be one of receptors for SV40 and murine polyoma virus [10,11]. Other polyomaviruses, including BK virus and JC virus, have been reported to utilize caveola-mediated endocytosis in virus entry [13][14][15][16]47]. BK virus, which is a causative agent of an infectious complication termed polyomavirusassociated nephropathy in renal transplant recipients, enters cells by slow caveola-mediated endocytosis dependent on pH in Vero cells and human renal proximal tubular epithelial cells [13][14][15].…”

“…Other polyomaviruses, including BK virus and JC virus, have been reported to utilize caveola-mediated endocytosis in virus entry [13][14][15][16]47]. BK virus, which is a causative agent of an infectious complication termed polyomavirusassociated nephropathy in renal transplant recipients, enters cells by slow caveola-mediated endocytosis dependent on pH in Vero cells and human renal proximal tubular epithelial cells [13][14][15]. JC virus and bovine papillomavirus are transported to early endosomes and caveolae by clathrindependent endocytosis and then carried by the slow caveoladependent pathway [16,17] [48].…”

“…The role of membrane rafts in entry of nonenveloped viruses has been investigated for simian virus 40 (SV40; Papovaviridae) [4][5][6][7][8][9][10][11][12], BK virus (Papovaviridae) [13][14][15], JC virus (Papovaviridae) [16], bovine papillomavirus (Papovaviridae) [17], human papillomavirus (HPV; Papovaviridae) [18][19][20][21][22][23][24][25][26], rotavirus (Reoviridae) [27][28][29], echovirus type 1 [30] and 11 (Picornaviridae) [31][32][33][34][35], enterovirus (Picornaviridae) [31], rhinovirus (Picornaviridae) [36], Coxsackievirus A9 and B4 (CAV; Picornaviridae) [37][38][39], and species C human adenovirus (HAdV; Adenoviridae) [40,41].…”

How Viruses Use the Endoplasmic Reticulum for Entry, Replication, and Assembly

“…After internalization, the virus is transferred first to the endolysosome (Eash et al 2004;Querbes et al 2006;Qian et al 2009;Engel et al 2011) and then the ER Gilbert and Benjamin 2004;Qian et al 2009). Py transport to the ER, a phenomenon documented over 20 years ago by Helenius and coworkers using electron microscopy (EM) (Kartenbeck et al 1989), is unique as most extracellular ligands do not reach the ER after endocytosis.…”