Propagation and assay of the JC virus

The Oxindole GW-5074 Inhibits JC Polyomavirus Infection and Spread by Antagonizing the MAPK-ERK Signaling Pathway

JC polyomavirus (JCPyV) is a ubiquitous, double-stranded DNA virus that causes the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML) in immunocompromised patients. Current treatments for PML are limited to immune reconstitution, and no effective antivirals exist. In this report, we show that the oxindole GW-5074 (3-(3,5-dibromo-4-hydroxybenzylidene)-5-iodoindolin-2-one) reduces JCPyV infection in primary and immortalized cells. This compound potently inhibits virus spread, which suggests that it could control infection in PML patients. We demonstrate that GW-5074 inhibits endogenous ERK phosphorylation, and that JCPyV infection in GW-5074-treated cells cannot be rescued with ERK agonists, which indicates that the antiviral mechanism may involve its antagonistic effects on MAPK-ERK signaling. Importantly, GW-5074 exceeds thresholds of common pharmacological parameters that identify promising compounds for further development. This MAPK-ERK antagonist warrants further investigation as a potential treatment for PML. IMPORTANCE Human polyomaviruses, such as JCPyV and BKPyV, cause significant morbidity and mortality in immunocompromised or immunomodulated patients. There are no treatments for polyomavirus-induced diseases other than restoration of immune function. We discovered that the oxindole GW-5074 potently inhibits infection by both JCPyV and BKPyV. Further optimization of this compound could result in the development of antiviral therapies for polyomavirus-induced diseases.

Biogenesis of JC polyomavirus associated extracellular vesicles

JC polyomavirus (JCPyV) is a small, non-enveloped virus that persists in the kidney in about half the adult population. In severely immune-compromised individuals JCPyV causes the neurodegenerative disease progressive multifocal leukoencephalopathy (PML) in the brain. JCPyV has been shown to infect cells by both direct and indirect mechanisms, the latter involving extracellular vesicle (EV) mediated infection. While direct mechanisms of infection are well studied indirect EV mediated mechanisms are poorly understood. Using a combination of chemical and genetic approaches we show that several overlapping intracellular pathways are responsible for the biogenesis of virus containing EV. Here we show that targeting neutral sphingomyelinase 2 (nSMase2) with the drug cambinol decreased the spread of JCPyV over several viral life cycles. Genetic depletion of nSMase2 by either shRNA or CRISPR/Cas9 reduced EV-mediated infection. Individual knockdown of seven ESCRT-related proteins including HGS, ALIX, TSG101, VPS25, VPS20, CHMP4A, and VPS4A did not significantly reduce JCPyV associated EV (JCPyV(+) EV) infectivity, whereas knockdown of the tetraspanins CD9 and CD81 or trafficking and/or secretory autophagy-related proteins RAB8A, RAB27A, and GRASP65 all significantly reduced the spread of JCPyV and decreased EV-mediated infection. These findings point to a role for exosomes and secretory autophagosomes in the biogenesis of JCPyV associated EVs with specific roles for nSMase2, CD9, CD81, RAB8A, RAB27A, and GRASP65 proteins.

Teriflunomide Inhibits JCPyV Infection and Spread in Glial Cells and Choroid Plexus Epithelial Cells

Several classes of immunomodulators are used for treating relapsing-remitting multiple sclerosis (RRMS). Most of these disease-modifying therapies, except teriflunomide, carry the risk of progressive multifocal leukoencephalopathy (PML), a severely debilitating, often fatal virus-induced demyelinating disease. Because teriflunomide has been shown to have antiviral activity against DNA viruses, we investigated whether treatment of cells with teriflunomide inhibits infection and spread of JC polyomavirus (JCPyV), the causative agent of PML. Treatment of choroid plexus epithelial cells and astrocytes with teriflunomide reduced JCPyV infection and spread. We also used droplet digital PCR to quantify JCPyV DNA associated with extracellular vesicles isolated from RRMS patients. We detected JCPyV DNA in all patients with confirmed PML diagnosis (n = 2), and in six natalizumab-treated (n = 12), two teriflunomide-treated (n = 7), and two nonimmunomodulated (n = 2) patients. Of the 21 patients, 12 (57%) had detectable JCPyV in either plasma or serum. CSF was uniformly negative for JCPyV. Isolation of extracellular vesicles did not increase the level of detection of JCPyV DNA versus bulk unprocessed biofluid. Overall, our study demonstrated an effect of teriflunomide inhibiting JCPyV infection and spread in glial and choroid plexus epithelial cells. Larger studies using patient samples are needed to correlate these in vitro findings with patient data.

Phosphoinositide 3'-Kinase γ Facilitates Polyomavirus Infection

Polyomaviruses are small, non-enveloped DNA tumor viruses that cause serious disease in immunosuppressed people, including progressive multifocal leukoencephalopathy (PML) in patients infected with JC polyomavirus, but the molecular events mediating polyomavirus entry are poorly understood. Through genetic knockdown approaches, we identified phosphoinositide 3′-kinase γ (PI3Kγ) and its regulatory subunit PIK3R5 as cellular proteins that facilitate infection of human SVG-A glial cells by JCPyV. PI3Kα appears less important for polyomavirus infection than PI3Kγ. CRISPR/Cas9-mediated knockout of PIK3R5 or PI3Kγ inhibited infection by authentic JCPyV and by JC pseudovirus. PI3Kγ knockout also inhibited infection by BK and Merkel Cell pseudoviruses, other pathogenic human polyomaviruses, and SV40, an important model polyomavirus. Reintroduction of the wild-type PI3Kγ gene into the PI3Kγ knock-out SVG-A cells rescued the JCPyV infection defect. Disruption of the PI3Kγ pathway did not block binding of JCPyV to cells or virus internalization, implying that PI3Kγ facilitates some intracellular step(s) of infection. These results imply that agents that inhibit PI3Kγ signaling may have a role in managing polyomavirus infections.

Genetic and Functional Dissection of the Role of Individual 5-HT2 Receptors as Entry Receptors for JC Polyomavirus

JC polyomavirus (JCPyV) is a ubiquitous human pathogen that causes progressive multifocal leukoencephalopathy (PML). The entry receptors for JCPyV belong to the 5-hydroxytryptamine 2 receptor (5-HT₂R) family, but how individual members of the family function to facilitate infection is not known. We used proximity ligation assay (PLA) to determine that JCPyV interacts with each of the 5-HT₂ receptors (5-HT₂Rs) in a narrow window of time during entry. We used CRISPR-Cas9 to randomly introduce stop codons in the gene for each receptor and discovered that the second intracellular loop of each was necessary for infection. This loop contains a motif possibly involved in receptor internalization by β-arrestin. Mutation of this motif and small interfering RNA (siRNA) knockdown of β-arrestin recapitulated the results of our CRISPR-Cas9 screen, showing that this motif is critical. Our results have implications for the role these receptors play in virus infection and for their normal functioning as receptors for serotonin.

5-HT₂ receptors are important for infection of cells by JC virus (JCPyV). Assetta et al. show that JCPyV interacts transiently with each of three 5-HT₂ receptors during entry and pinpoint a critical role for a proline in the second intracellular loop of each receptor in facilitating virus infection.

Adipocyte Plasma Membrane Protein (APMAP) promotes JC Virus (JCPyV) infection in human glial cells

The demyelinating disease progressive multifocal leukoencephalopathy (PML) is caused by the human polyomavirus, JCPyV, under conditions of prolonged immunosuppression. Initial infection is asymptomatic, and the virus establishes lifelong persistence in the host. Following the loss of immune surveillance, the virus can traffic to the central nervous system and infect oligodendrocytes to cause demyelination and PML. The mechanisms involved in glial cell infection are not completely understood. In a screen for N-glycosylated proteins that influence JCPyV pathology, we identified Adipocyte Plasma Membrane Associated Protein (APMAP) as a host cell modulator of JCPyV infection. The removal of APMAP by small interfering siRNA as well as by CRISPR-Cas9 gene editing resulted in a significant decrease in JCPyV infection. Exogenous expression of APMAP in APMAP knockout cell lines rescued susceptibility to infection. These data suggest that virus infection of glial cells is dependent on APMAP.

JC Virus infected choroid plexus epithelial cells produce extracellular vesicles that infect glial cells independently of the virus attachment receptor

The human polyomavirus, JCPyV, is the causative agent of progressive multifocal leukoencephalopathy (PML) in immunosuppressed and immunomodulated patients. Initial infection with JCPyV is common and the virus establishes a long-term persistent infection in the urogenital system of 50-70% of the human population worldwide. A major gap in the field is that we do not know how the virus traffics from the periphery to the brain to cause disease. Our recent discovery that human choroid plexus epithelial cells are fully susceptible to virus infection together with reports of JCPyV infection of choroid plexus in vivo has led us to hypothesize that the choroid plexus plays a fundamental role in this process. The choroid plexus is known to relay information between the blood and the brain by the release of extracellular vesicles. This is particularly important because human macroglia (oligodendrocytes and astrocytes), the major targets of virus infection in the central nervous system (CNS), do not express the known attachment receptors for the virus and do not bind virus in human tissue sections. In this report we show that JCPyV infected choroid plexus epithelial cells produce extracellular vesicles that contain JCPyV and readily transmit the infection to human glial cells. Transmission of the virus by extracellular vesicles is independent of the known virus attachment receptors and is not neutralized by antisera directed at the virus. We also show that extracellular vesicles containing virus are taken into target glial cells by both clathrin dependent endocytosis and macropinocytosis. Our data support the hypothesis that the choroid plexus plays a fundamental role in the dissemination of virus to brain parenchyma.

JC Polyomavirus Uses Extracellular Vesicles To Infect Target Cells

The endemic human JC polyomavirus (JCPyV) causes progressive multifocal leukoencephalopathy in immune-suppressed patients. The mechanisms of virus infection in vivo are not understood because the major target cells for virus in the brain do not express virus receptors and do not bind virus. We found that JCPyV associates with extracellular vesicles (EVs) and can infect target cells independently of virus receptors. Virus particles were found packaged inside extracellular vesicles and attached to the outer side of vesicles. Anti-JCPyV antisera reduced infection by purified virus but had no effect on infection by EV-associated virus. Treatment of cells with the receptor-destroying enzyme neuraminidase inhibited infection with purified virus but did not inhibit infection by EV-associated virus. Mutant pseudoviruses defective in sialic acid receptor binding could not transduce cells as purified pseudovirions but could do so when associated with EVs. This alternative mechanism of infection likely plays a critical role in the dissemination and spread of JCPyV both to and within the central nervous system.IMPORTANCE JC polyomavirus (JCPyV) is a ubiquitous human pathogen that causes progressive multifocal leukoencephalopathy (PML), a severe and often fatal neurodegenerative disease in immunocompromised or immunomodulated patients. The mechanisms responsible for initiating infection in susceptible cells are not completely known. The major attachment receptor for the virus, lactoseries tetrasaccharide c (LSTc), is paradoxically not expressed on oligodendrocytes or astrocytes in human brain, and virus does not bind to these cells. Because these are the major cell types targeted by the virus in the brain, we hypothesized that alternative mechanisms of infection must be responsible. Here we provide evidence that JCPyV is packaged in extracellular vesicles from infected cells. Infection of target cells by vesicle-associated virus is not dependent on LSTc and is not neutralized by antisera directed against the virus. This is the first demonstration of a polyomavirus using extracellular vesicles as a means of transmission.

JC Polyomavirus Infection of Primary Human Renal Epithelial Cells Is Controlled by a Type I IFN-Induced Response

The JC and BK human polyomaviruses (JCPyV and BKPyV, respectively) establish lifelong persistent infections in the kidney. In immunosuppressed individuals, JCPyV causes progressive multifocal leukoencephalopathy (PML), a fatal neurodegenerative disease, and BKPyV causes polyomavirus-associated nephropathy (PVN). In this study, we compared JCPyV and BKPyV infections in primary human renal proximal tubule epithelial (HRPTE) cells. JCPyV established a persistent infection, but BKPyV killed the cells in 15 days. To identify the cellular factors responsible for controlling JCPyV infection and promoting viral persistence, we profiled the transcriptomes of JCPyV- and BKPyV-infected cells at several time points postinfection. We found that infection with both viruses induced interferon production but that interferon-stimulated genes (ISGs) were only activated in the JCPyV-infected cells. Phosphorylated STAT1 and IRF9, which are responsible for inducing ISGs, translocated to the nucleus of JCPyV-infected cells but did not in BKPyV-infected cells. In BKPyV-infected cells, two critical suppressors of cytokine signaling, SOCS3 and SOCS1, were induced. Infection with BKPyV but not JCPyV caused reorganization of PML bodies that are associated with inactivating antiviral responses. Blockade of the interferon receptor and neutralization of soluble interferon alpha (IFN-α) and IFN-β partially alleviated the block to JCPyV infection, leading to enhanced infectivity. Our results show that a type I IFN response contributes to the establishment of persistent infection by JCPyV in HRPTE cells.

The human polyomaviruses JCPyV and BKPyV both establish lifelong persistent infection in the kidneys. In immunosuppressed patients, BKPyV causes significant pathology in the kidney, but JCPyV is only rarely associated with disease in this organ. The reasons behind this striking difference in kidney pathology are unknown. In this study, we show that infection of primary human renal tubule epithelial cells with JCPyV and BKPyV results in divergent innate immune responses that control JCPyV but fail to control BKPyV. This is the first study that directly compares JCPyV and BKPyV infection in vitro in the same cell type they naturally infect, and the significant differences that have been uncovered could in part explain the distinct disease outcomes.

Human polyomavirus receptor distribution in brain parenchyma contrasts with receptor distribution in kidney and choroid plexus

The human polyomavirus, JCPyV, is the causative agent of progressive multifocal leukoencephalopathy, a rare demyelinating disease that occurs in the setting of prolonged immunosuppression. After initial asymptomatic infection, the virus establishes lifelong persistence in the kidney and possibly other extraneural sites. In rare instances, the virus traffics to the central nervous system, where oligodendrocytes, astrocytes, and glial precursors are susceptible to lytic infection, resulting in progressive multifocal leukoencephalopathy. The mechanisms by which the virus traffics to the central nervous system from peripheral sites remain unknown. Lactoseries tetrasaccharide c (LSTc), a pentasaccharide containing a terminal α2,6-linked sialic acid, is the major attachment receptor for polyomavirus. In addition to LSTc, type 2 serotonin receptors are required for facilitating virus entry into susceptible cells. We studied the distribution of virus receptors in kidney and brain using lectins, antibodies, and labeled virus. The distribution of LSTc, serotonin receptors, and virus binding sites overlapped in kidney and in the choroid plexus. In brain parenchyma, serotonin receptors were expressed on oligodendrocytes and astrocytes, but these cells were negative for LSTc and did not bind virus. LSTc was instead found on microglia and vascular endothelium, to which virus bound abundantly. Receptor distribution was not changed in the brains of patients with progressive multifocal leukoencephalopathy. Virus infection of oligodendrocytes and astrocytes during disease progression is LSTc independent.

5-HT2 receptors facilitate JC polyomavirus entry

The human JC polyomavirus (JCPyV) causes the rapidly progressing demyelinating disease progressive multifocal leukoencephalopathy (PML). The disease occurs most often in individuals with AIDS but also occurs in individuals receiving immunomodulatory therapies for immune-related diseases such as multiple sclerosis. JCPyV infection of host cells requires the pentasaccharide lactoseries tetrasaccharide c (LSTc) and the serotonin receptor 5-hydroxytryptamine (5-HT) receptor 5-HT2AR. While LSTc is involved in the initial attachment of virus to cells via interactions with VP1, the mechanism by which 5-HT2AR contributes to infection is not clear. To further define the roles of serotonin receptors in infection, HEK293A cells, which are poorly permissive to JCPyV, were transfected with 14 different isoforms of serotonin receptor. Only 5-HT2 receptors were found to support infection by JCPyV. None of the other 11 isoforms of serotonin receptor supported JCPyV infection. Expression of 5-HT2 receptors did not increase binding of JCPyV to cells, but this was not unexpected, given that the cells uniformly expressed the major attachment receptor, LSTc. Infection of these cells remained sensitive to inhibition with soluble LSTc, confirming that LSTc recognition is required for JCPyV infection. Virus internalization into HEK293A cells was significantly and specifically enhanced when 5HT2 receptors were expressed. Taken together, these data confirm that the carbohydrate LSTc is the attachment receptor for JCPyV and that the type 2 serotonin receptors contribute to JCPyV infection by facilitating entry.

Role of N-linked glycosylation of the 5-HT2A receptor in JC virus infection

JC virus (JCV) is a human polyomavirus and the causative agent of the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). JCV infection of host cells is dependent on interactions with cell surface asparagine (N)-linked sialic acids and the serotonin 5-hydroxytryptamine(2A) receptor (5-HT(2A)R). The 5-HT(2A)R contains five potential N-linked glycosylation sites on the extracellular N terminus. Glycosylation of other serotonin receptors is essential for expression, ligand binding, and receptor function. Also, glycosylation of cellular receptors has been reported to be important for JCV infection. Therefore, we hypothesized that the 5-HT(2A)R N-linked glycosylation sites are required for JCV infection. Treatment of 5-HT(2A)R-expressing cells with tunicamycin, an inhibitor of N-linked glycosylation, reduced JCV infection. Individual mutation of each of the five N-linked glycosylation sites did not affect the capacity of 5-HT(2A)R to support JCV infection and did not alter the cell surface expression of the receptor. However, mutation of all five N-linked glycosylation sites simultaneously reduced the capacity of 5-HT(2A)R to support infection and altered the cell surface expression. Similarly, tunicamycin treatment reduced the cell surface expression of 5-HT(2A)R. Mutation of all five N-linked glycosylation sites or tunicamycin treatment of cells expressing wild-type 5-HT(2A)R resulted in an altered electrophoretic mobility profile of the receptor. Treatment of cells with PNGase F, to remove N-linked oligosaccharides from the cell surface, did not affect JCV infection in 5-HT(2A)R-expressing cells. These data affirm the importance of 5-HT(2A)R as a JCV receptor and demonstrate that the sialic acid component of the receptor is not directly linked to 5-HT(2A)R.

Modulation of PML protein expression regulates JCV infection

JC virus (JCV) is a human polyomavirus that infects the majority of the human population worldwide. It is responsible for the fatal demyelinating disease Progressive Multifocal Leukoencephalopathy. JCV binds to cells using the serotonin receptor 5-HT(2A)R and alpha(2-6)- or alpha(2-3)-linked sialic acid. It enters cells using clathrin-dependent endocytosis and traffics to the early endosome and possibly to the endoplasmic reticulum. Viral DNA is then delivered to the nucleus where transcription, replication, and assembly of progeny occur. We found that the early regulatory protein large T antigen accumulates in microdomains in the nucleus adjacent to ND-10 or PML domains. This observation prompted us to explore the role of these domains in JCV infection. We found that a reduction of nuclear PML enhanced virus infection and that an increase in nuclear PML reduced infection. Infection with JCV did not directly modulate nuclear levels of PML but our data indicate that a host response involving interferon beta is likely to restrict virus infection by increasing nuclear PML.

BK virus (BKV): infection, propagation, quantitation, purification, labeling, and analysis of cell entry

BK virus (BKV) can cause BKV nephritis in renal transplant patients and has become a significant reason for graft loss in this decade. BKV is latent in the urogenital tract and most likely is transported with the donor kidney to recipients. BKV replication occurs in the nucleus of human renal proximal tubular cells (HRPTEC) and daughter viruses are delivered to other cells to spread infection. A few in vitro studies have been reported about the mechanism and kinetics of BKV infection. However, there are still a lot of unknown factors regarding BKV infection. This unit describes the handling of BKV, BKV propagation, determination of titer and ability to infect cells, as well as purification and labeling of BKV in order to analyze BKV cell entry.

BK virus (BKV): infection, propagation, quantitation, purification, labeling, and analysis of cell entry

BK virus (BKV) can cause BKV nephritis in renal transplant patients and has become a significant reason for graft loss in this decade. BKV is latent in the urogenital tract and most likely is transported with the donor kidney to recipients. BKV replication occurs in the nucleus of human renal proximal tubular cells (HRPTEC) and daughter viruses are delivered to other cells to spread infection. A few in vitro studies have been reported about the mechanism and kinetics of BKV infection. However, there are still a lot of unknown factors regarding BKV infection. This unit describes the handling of BKV, BKV propagation, determination of titer and ability to infect cells, as well as purification and labeling of BKV in order to analyze BKV cell entry.

Interferon beta1-a and selective anti-5HT(2a) receptor antagonists inhibit infection of human glial cells by JC virus

JC virus (JCV) is the causative agent of progressive multifocal leukoenchaphalopathy (PML). The disease develops when JCV gains access to the central nervous system, infects and destroys oligodendrocytes. The disease is rapidly progressing, typically fatal and no effective therapies exist to treat or prevent PML. The recent occurrence of PML in multiple sclerosis patients being treated with Avonex (IFNbeta1-a) and Tysabri (Natalizumab) and the recent reports linking JCV infection to the 5HT(2a) serotonin receptor led us to evaluate the effects of IFNbeta1-a and a panel of 5HT(2a) receptor antagonists for their ability to modulate virus infection. IFNbeta1-a was found to be a potent inhibitor of both virus infection and viral early and late gene expression. In addition, several 5HT(2a) receptor antagonists inhibited initial infection of cells by JCV but were less effective at reducing viral loads in an already established infection.

Nuclear factor of activated T-cells (NFAT) plays a role in SV40 infection

Recent evidence highlighted a role for the transcription factor, nuclear factor of activated T-cells (NFAT), in the transcription of the human polyomavirus JCV. Here we show that NFAT is also important in the transcriptional control of the related polyomavirus, Simian Virus 40 (SV40). Inhibition of NFAT activity reduced SV40 infection of Vero, 293A, and HeLa cells, and this block occurred at the stage of viral transcription. Both NFAT3 and NFAT4 bound to the SV40 promoter through kappaB sites located within the 72 bp repeated enhancer region. In Vero cells, NFAT was involved in late transcription, but in HeLa and 293A cells both early and late viral transcription required NFAT activity. SV40 large T-Ag was found to increase NFAT activity and provided a positive feedback loop to transactivate the SV40 promoter.

Caveolar endocytosis is critical for BK virus infection of human renal proximal tubular epithelial cells

In recent years, BK virus (BKV) nephritis after renal transplantation has become a severe problem. The exact mechanisms of BKV cell entry and subsequent intracellular trafficking remain unknown. Since human renal proximal tubular epithelial cells (HRPTEC) represent a main natural target of BKV nephritis, analysis of BKV infection of HRPTEC is necessary to obtain additional insights into BKV biology and to develop novel strategies for the treatment of BKV nephritis. We coincubated HRPTEC with BKV and the cholesterol-depleting agents methyl beta cyclodextrin (MBCD) and nystatin (Nys), drugs inhibiting caveolar endocytosis. The percentage of infected cells (detected by immunofluorescence) and the cellular levels of BKV large T antigen expression (detected by Western blot analysis) were significantly decreased in both MBCD- and Nys-treated HPRTEC compared to the level in HRPTEC incubated with BKV alone. HRPTEC infection by BKV was also tested after small interfering RNA (siRNA)-dependent depletion of either the caveolar structural protein caveolin-1 (Cav-1) or clathrin, the major structural protein of clathrin-coated pits. BKV infection was inhibited in HRPTEC transfected with Cav-1 siRNA but not in HRPTEC transfected with clathrin siRNA. The colocalization of labeled BKV particles with either Cav-1 or clathrin was investigated by using fluorescent microscopy and image cross-correlation spectroscopy. The rate of colocalization of BKV with Cav-1 peaked at 4 h after incubation. Colocalization with clathrin was insignificant at all time points. These results suggest that BKV entered into HRPTEC via caveolae, not clathrin-coated pits, and that BKV is maximally associated with caveolae at 4 h after infection, prior to relocation to a different intracellular compartment.

Microarray analysis of glial cells resistant to JCV infection suggests a correlation between viral infection and inflammatory cytokine gene expression

The human polyomavirus, JCV, has a highly restricted tropism and primarily infects glial cells. The mechanisms restricting infection of cells by JCV are poorly understood. Previously we developed and described a glial cell line that was resistant to JCV infection with the aim of using these cells to identify factors that determine JCV tropism. Gene expression profiling of susceptible and resistant glial cells revealed a direct correlation between the expression of inflammatory cytokines and susceptibility to JCV infection. This correlation manifested at the level of viral gene transcription. Previous studies have suggested a link between an increase in cytokine gene expression in HIV patients and the development of PML and these data supports this hypothesis.

Invasion of host cells by JC virus identifies a novel role for caveolae in endosomal sorting of noncaveolar ligands

Invasion of glial cells by the human polyomavirus, JC virus (JCV), leads to a rapidly progressing and uniformly fatal demyelinating disease known as progressive multifocal leukoencephalopathy. The endocytic trafficking steps used by JCV to invade cells and initiate infection are not known. We demonstrated that JCV infection was inhibited by dominant defective and constitutively active Rab5-GTPase mutants that acted at distinct steps in endosomal sorting. We also found that labeled JCV colocalized with labeled cholera toxin B and with caveolin-1 (cav-1) on early endosomes following internalization by clathrin-dependent endocytosis. JCV entry and infection were both inhibited by dominant defective mutants of eps15 and Rab5-GTPase. Expression of a dominant-negative scaffolding mutant of cav-1 did not inhibit entry or infection by JCV. A single-cell knockdown experiment using cav-1 shRNA did not inhibit JCV entry but interfered with a downstream trafficking event important for infection. These data show that JCV enters cells by clathrin-dependent endocytosis, is transported immediately to early endosomes, and is then sorted to a caveolin-1-positive endosomal compartment. This latter step is dependent on Rab5-GTPase, cholesterol, caveolin-1, and pH. This is the first example of a ligand that enters cells by clathrin-dependent endocytosis and is then sorted from early endosomes to caveosomes, indicating that caveolae-derived vesicles play a more important role than previously realized in sorting cargo from early endosomes.

NFAT4 is required for JC virus infection of glial cells

The human polyomavirus JC virus (JCV) infects 70% of the population worldwide. In immunosuppressed patients, JCV infection can lead to progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system (CNS). The majority of PML cases occur in the setting of human immunodeficiency virus (HIV) infection, and it has been suggested that the link between HIV and the development of PML is in part related to the production of numerous cytokines in the CNS during HIV infection. To examine the link between the expression of inflammatory cytokines and JCV infection, we tested an anti-inflammatory compound, cyclosporine A (CsA), for its ability to block JCV infection of glial cells. We found that CsA inhibited JCV infection by preventing the activation of the transcription factor nuclear factor of activated T cells 4 (NFAT4). Luciferase reporter assays and chromatin immunoprecipitation assays revealed that NFAT4 directly bound the JCV promoter during infection and was important for the activation of both early and late transcription. In addition, the expression of the JCV early viral gene products increased NFAT activity to further aid viral transcription. The necessity of NFAT for JCV infection suggests that calcium signaling and the activation of NFAT in glial cells are required for JCV infection of the CNS.

Contrasting roles of endosomal pH and the cytoskeleton in infection of human glial cells by JC virus and simian virus 40

Infection of eukaryotic cells by pathogens requires the efficient use of host cell endocytic and cytoplasmic transport mechanisms. Understanding how these cellular functions are exploited by microorganisms allows us to better define the basic biology of pathogenesis while providing better insight into normal cellular functions. In this report we compare and contrast intracellular transport and trafficking of the human polyomavirus JC virus (JCV) with that of simian virus 40 (SV40). We have previously shown that infection of human glial cells by JCV requires clathrin-dependent endocytosis. In contrast, infection of cells by SV40 proceeds by caveola-dependent endocytosis. We now examine the roles of endosomal pH and the cellular cytoskeleton during infection of glial cells by both viruses. Our results demonstrate that JCV infection is sensitive to disruption of endosomal pH, whereas SV40 infection is pH independent. Infection by JCV is inhibited by treatment of glial cells with cytochalasin D, nocodazole, and acrylamide, whereas SV40 infection is affected only by nocodazole. These data point to critical differences between JCV and SV40 in terms of endocytosis and intracellular trafficking of their DNA genomes to the nucleus. These data also suggest a unique sequential involvement of cytoskeletal elements during infection of glial cells by JCV.