Interaction of a Nuclear Factor-1-like Protein with the Regulatory Region of the Human Polyomavirus JC Virus

Replication of JC Virus DNA in the G144 Oligodendrocyte Cell Line Is Dependent Upon Akt

Progressive multifocal leukoencephalopathy (PML) is an often-fatal demyelinating disease of the central nervous system. PML results when oligodendrocytes within immunocompromised individuals are infected with the human JC virus (JCV). We have identified an oligodendrocyte precursor cell line, termed G144, that supports robust levels of JCV DNA replication, a central part of the JCV life cycle. In addition, we have determined that JC virus readily infects G144 cells. Furthermore, we have determined that JCV DNA replication in G144 cells is stimulated by myristoylated (i.e., constitutively active) Akt and reduced by the Akt-specific inhibitor MK2206. Thus, this oligodendrocyte-based model system will be useful for a number of purposes, such as studies of JCV infection, establishing key pathways needed for the regulation of JCV DNA replication, and identifying inhibitors of this process.IMPORTANCE The disease progressive multifocal leukoencephalopathy (PML) is caused by the infection of particular brain cells, termed oligodendrocytes, by the JC virus. Studies of PML, however, have been hampered by the lack of an immortalized human cell line derived from oligodendrocytes. Here, we report that the G144 oligodendrocyte cell line supports both infection by JC virus and robust levels of JCV DNA replication. Moreover, we have established that the Akt pathway regulates JCV DNA replication and that JCV DNA replication can be inhibited by MK2206, a compound that is specific for Akt. These and related findings suggest that we have established a powerful oligodendrocyte-based model system for studies of JCV-dependent PML.

The biology of JC polyomavirus

JC polyomavirus (JCPyV) is the causative agent of a fatal central nervous system demyelinating disease known as progressive multifocal leukoencephalopathy (PML). PML occurs in people with underlying immunodeficiency or in individuals being treated with potent immunomodulatory therapies. JCPyV is a DNA tumor virus with a double-stranded DNA genome and encodes a well-studied oncogene, large T antigen. Its host range is highly restricted to humans and only a few cell types support lytic infection in vivo or in vitro. Its oncogenic potential in humans has not been firmly established and the international committee on oncogenic viruses lists JCPyV as possibly carcinogenic. Significant progress has been made in understanding the biology of JCPyV and here we present an overview of the field and discuss some important questions that remain unanswered.

Analysis of JC virus DNA replication using a quantitative and high-throughput assay

Progressive Multifocal Leukoencephalopathy (PML) is caused by lytic replication of JC virus (JCV) in specific cells of the central nervous system. Like other polyomaviruses, JCV encodes a large T-antigen helicase needed for replication of the viral DNA. Here, we report the development of a luciferase-based, quantitative and high-throughput assay of JCV DNA replication in C33A cells, which, unlike the glial cell lines Hs 683 and U87, accumulate high levels of nuclear T-ag needed for robust replication. Using this assay, we investigated the requirement for different domains of T-ag, and for specific sequences within and flanking the viral origin, in JCV DNA replication. Beyond providing validation of the assay, these studies revealed an important stimulatory role of the transcription factor NF1 in JCV DNA replication. Finally, we show that the assay can be used for inhibitor testing, highlighting its value for the identification of antiviral drugs targeting JCV DNA replication.

Lymphocyte gene expression and JC virus noncoding control region sequences are linked with the risk of progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML)-derived noncoding control region (NCCR) sequences permitted greater early viral gene expression than kidney-associated NCCR sequences. This was driven in part by binding of the transcription factor Spi-B to unique PML-associated Spi-B binding sites. Spi-B is upregulated in developing B cells in response to natalizumab therapy, a known risk factor for PML. Naturally occurring JCV sequence variation, together with drug treatment-induced cellular changes, may synergize to create an environment leading to an increased risk of PML.

Early magnetic resonance detection of natalizumab-related progressive multifocal leukoencephalopathy in a patient with multiple sclerosis

Diagnosis of progressive multifocal leukoencephalopathy is usually based on the clinical presentation, on the demonstration of the brain lesions at the magnetic resonance imaging examination, and on the detection of the JC virus DNA in the cerebrospinal fluid with high sensitive polymerase chain reaction. The role of magnetic resonance imaging specifically in natalizumab-associated progressive multifocal leukoencephalopathy is strengthening, and it is gaining importance not only as an irreplaceable diagnostic tool but also as a surveillance and risk stratifying tool in treated patients. While other imaging techniques such as computed tomography lack sensitivity and specificity, magnetic resonance performed with morphological and functional sequences offers clinicians the possibility to early identify the stage of the disease and the emergence of an immune reconstitution inflammatory syndrome after natalizumab blood removal plasmapheresis.

Molecular biology, epidemiology, and pathogenesis of progressive multifocal leukoencephalopathy, the JC virus-induced demyelinating disease of the human brain

Progressive multifocal leukoencephalopathy (PML) is a debilitating and frequently fatal central nervous system (CNS) demyelinating disease caused by JC virus (JCV), for which there is currently no effective treatment. Lytic infection of oligodendrocytes in the brain leads to their eventual destruction and progressive demyelination, resulting in multiple foci of lesions in the white matter of the brain. Before the mid-1980s, PML was a relatively rare disease, reported to occur primarily in those with underlying neoplastic conditions affecting immune function and, more rarely, in allograft recipients receiving immunosuppressive drugs. However, with the onset of the AIDS pandemic, the incidence of PML has increased dramatically. Approximately 3 to 5% of HIV-infected individuals will develop PML, which is classified as an AIDS-defining illness. In addition, the recent advent of humanized monoclonal antibody therapy for the treatment of autoimmune inflammatory diseases such as multiple sclerosis (MS) and Crohn's disease has also led to an increased risk of PML as a side effect of immunotherapy. Thus, the study of JCV and the elucidation of the underlying causes of PML are important and active areas of research that may lead to new insights into immune function and host antiviral defense, as well as to potential new therapies.

JC virus promoter/enhancers contain TATA box-associated Spi-B-binding sites that support early viral gene expression in primary astrocytes

JC virus (JCV) is the aetiological agent of the demyelinating disease progressive multifocal leukoencephalopathy, an AIDS defining illness and serious complication of mAb therapies. Initial infection probably occurs in childhood. In the working model of dissemination, virus persists in the kidney and lymphoid tissues until immune suppression/modulation causes reactivation and trafficking to the brain where JCV replicates in oligodendrocytes. JCV infection is regulated through binding of host factors such as Spi-B to, and sequence variation in the non-coding control region (NCCR). Although NCCR sequences differ between sites of persistence and pathogenesis, evidence suggests that the virus that initiates infection in the brain disseminates via B-cells derived from latently infected haematopoietic precursors in the bone marrow. Spi-B binds adjacent to TATA boxes in the promoter/enhancer of the PML-associated JCV Mad-1 and Mad-4 viruses but not the non-pathogenic, kidney-associated archetype. The Spi-B-binding site of Mad-1/Mad-4 differs from that of archetype by a single nucleotide, AAAAGGGAAGGGA to AAAAGGGAAGGTA. Point mutation of the Mad-1 Spi-B site reduced early viral protein large T-antigen expression by up to fourfold. Strikingly, the reverse mutation in the archetype NCCR increased large T-antigen expression by 10-fold. Interestingly, Spi-B protein binds the NCCR sequence flanking the viral promoter/enhancer, but these sites are not essential for early viral gene expression. The effect of mutating Spi-B-binding sites within the JCV promoter/enhancer on early viral gene expression strongly suggests a role for Spi-B binding to the viral promoter/enhancer in the activation of early viral gene expression.

Transcription factor Spi-B binds unique sequences present in the tandem repeat promoter/enhancer of JC virus and supports viral activity

Progressive multifocal leukoencephalopathy (PML) is an often fatal demyelinating disease caused by lytic infection of oligodendrocytes with JC virus (JCV). The development of PML in non-immunosuppressed individuals is a growing concern with reports of mortality in patients treated with mAb therapies. JCV can persist in the kidneys, lymphoid tissue and bone marrow. JCV gene expression is restricted by non-coding viral regulatory region sequence variation and cellular transcription factors. Because JCV latency has been associated with cells undergoing haematopoietic development, transcription factors previously reported as lymphoid specific may regulate JCV gene expression. This study demonstrates that one such transcription factor, Spi-B, binds to sequences present in the JCV promoter/enhancer and may affect early virus gene expression in cells obtained from human brain tissue. We identified four potential Spi-B-binding sites present in the promoter/enhancer elements of JCV sequences from PML variants and the non-pathogenic archetype. Spi-B sites present in the promoter/enhancers of PML variants alone bound protein expressed in JCV susceptible brain and lymphoid-derived cell lines by electromobility shift assays. Expression of exogenous Spi-B in semi- and non-permissive cells increased early viral gene expression. Strikingly, mutation of the Spi-B core in a binding site unique to the Mad-4 variant was sufficient to abrogate viral activity in progenitor-derived astrocytes. These results suggest that Spi-B could regulate JCV gene expression in susceptible cells, and may play an important role in JCV activity in the immune and nervous systems.

Molecular regulation of JC virus tropism: insights into potential therapeutic targets for progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a growing concern for patients undergoing immune modulatory therapies for treatment of autoimmune diseases such as multiple sclerosis. Currently, there are no drugs approved for the treatment of PML that have been demonstrated in the patient to effectively and reproducibly alter the course of disease progression. The human polyoma virus JC is the causative agent of PML. JC virus (JCV) dissemination is tightly controlled by regulation of viral gene expression from the promoter by cellular transcription factors expressed in cells permissive for infection. JCV infection likely occurs during childhood, and latent virus containing PML-associated promoter sequences is maintained in lymphoid cells within the bone marrow. Because development of PML is tightly linked to suppression and or modulation of the immune system as in development of hematological malignancies, AIDS, and monoclonal antibody treatments, further scrutiny of the course of JCV infection in immune cells will be essential to our understanding of development of PML and identification of new therapeutic targets.

Role of Tat protein in HIV neuropathogenesis

The Tat protein of the human immunodeficiency virus (HIV) has been implicated in the pathophysiology of the neurocognitive deficits associated with HIV infection. This is the earliest protein to be produced by the proviral DNA in the infected cell. The protein not only drives the regulatory regions of the virus but may also be actively released from the cell and then interact with the cell surface receptors of other uninfected cells in the brain leading to cellular dysfunction. It may also be taken up by these cells and can then activate a number of host genes. The Tat protein is highly potent and has the unique ability to travel along neuronal pathways. Importantly, its production is not impacted by the use of antiretroviral drugs once the proviral DNA has been formed. This article reviews the pleomorphic actions of Tat protein and the evidence supporting its central role in the neuropathogenesis of the HIV infection.

JC virus: an oncogenic virus in animals and humans?

JC virus (JCV) is a human polyomavirus of the Polyomaviridae family, which also includes BK virus and simian vacuolating virus 40 (SV40). JC virus was first isolated in 1971 from the brain of a patient with Progressive Multifocal Leukoencephalopathy (PML). Like other polyomaviruses, JCV has a restricted host range. The virus infects the majority of the human population with seroconversion occurring during adolescence. JCV has a limited and specific tissue tropism infecting the kidney and oligodendrocytes and astrocytes in the central nervous system (CNS). Initial JCV infection is generally asymptomatic in immunocompetent hosts, and it establishes a persistent infection in the kidney and possibly bone marrow. In immunocompromised individuals JCV can cause a lytic infection in the CNS and lead to development of the fatal, demyelinating disease PML. The name polyoma is derived from the Greek terms: poly, meaning many, and oma, meaning tumors, owing to the capacity of this group of viruses to cause tumors. JCV inoculation of small animal models and non-human primates, which are not permissive to a productive JCV infection, leads to tumor formation. Given the ubiquitous nature of the virus and its strong association with cancer in animal models, it is hypothesized that JCV plays a role in human cancers. However, the role for JCV in human cancers and tumor formation is not clear. Some researchers have reported an association of JCV with human cancers including brain tumors, colorectal cancers, and cancers of the gastrointestinal tract, while other groups report no correlation. Here, we review the role of JCV in cancers in animal models and present the findings on JCV in human cancers.

DNA-binding transcription factor NF-1A negatively regulates JC virus multiplication

JC virus (JCV) DNA replication occurs in the nuclei of infected cells. The level of JCV genome expression depends on nucleotide sequences in the viral regulatory region and their interaction with host-cell nuclear transcription factors. Our previous studies showed a higher level of NF-1X in JCV-permissive cells compared with the other members of the NF-1 family, NF-1A, B and C, which suggests that NF-1X plays a positive role in JCV multiplication. It remained unclear whether a reduction in the level of NF-1A, which is expressed abundantly in JCV-non-permissive cell types, leads to an increase in JCV multiplication. In this study, we show that downregulation of NF-1A expression in JCV-non-susceptible progenitor and HeLa cells results in a reversion to susceptibility for JCV multiplication. These data demonstrate that a higher level of NF-1A protein in JCV-non-permissive cell types, compared with the level of NF-1X, may be acting as a negative regulator at the JCV promoter to control JCV multiplication.

Pharmacological cdk inhibitor R-Roscovitine suppresses JC virus proliferation

The human Polyomavirus JC virus (JCV) utilizes cellular proteins for viral replication and transcription in the host cell nucleus. These cellular proteins represent potential targets for antiviral drugs against the JCV. In this study, we examined the antiviral effects of the pharmacological cyclin-dependent kinase (cdk) inhibitor R-Roscovitine, which has been shown to have antiviral activity against other viruses. We found that Roscovitine significantly inhibited the viral production and cytopathic effects of the JCV in a JCV-infected cell line. Roscovitine attenuated the transcriptional activity of JCV late genes, but not early genes, and also prevented viral replication via inhibiting phosphorylation of the viral early protein, large T antigen. These data suggest that the JCV requires cdks to transcribe late genes and to replicate its own DNA. That Roscovitine exhibited antiviral activity in JCV-infected cells suggests that Roscovitine might have therapeutic utility in the treatment of progressive multifocal leukoencephalopathy (PML).

Transforming Activities of JC Virus Early Proteins

Polyomaviruses, as their name indicates, are viruses capable of inducing a variety of tumors in vivo. Members of this family, including the human JC and BK viruses (JCV, BKV), and the better characterized mouse polyomavirus and simian virus 40 (SV40), are small DNA viruses that commandeer a cell's molecular machinery to reproduce themselves. Studies of these virus-host interactions have greatly enhanced our understanding of a wide range of phenomena from cellular processes (e.g., DNA replication and transcription) to viral oncogenesis. The current chapter will focus upon the five known JCV early proteins and the contributions each makes to the oncogenic process (transformation) when expressed in cultured cells. Where appropriate, gaps in our understanding of JCV protein function will be supplanted with information obtained from the study of SV40 and BKV.

JC Virus Can Infect Human Immune and Nervous System Progenitor Cells

Recent advances in stem cell biology have called attention to the role these cells may play in the pathogenesis of systemic and nervous system diseases. Although not capable of indefinite self renewal and pluripotentiality as stem cells are, progenitor cells can give rise to cells of different lineages. It is infection of these differentiated cells that has traditionally been associated with the pathology and symptoms of viral-induced disease. However, neural progenitor cells have been shown, in vitro, to be susceptible to infection by neurotropic viruses such as the human polyomavirus, JCV, and the lentivirus, HIV-1. These progenitor cells, which exist during development as well as in the fully developed adult brain, could therefore be involved in neuropathogenesis. Morever, JCV can also infect progenitor cells of the hematopoietic system, derivatives of which have been implicated in the trafficking of virus from the periphery to the brain. Interestingly, susceptibility to and molecular regulation of JCV infection in hematopoietic cells closely parallels what has been observed in glial cells. The biological interaction between the immune and nervous systems that exists in the dissemination of virus from periphery to nervous system and the susceptibility of both systems to JCV infection provide potential for hematopoietic and neural progenitor cell involvement in JCV pathogenesis.

Viral proteomics: a promising approach for understanding JC virus tropism

The human polyomavirus JC virus (JCV) is responsible for the CNS demyelination observed in cases of progressive multifocal leukoencephalopathy. The JCV regulatory region (promoter) is a hypervariable, noncoding, nucleotide sequence positioned between the early and late protein-coding regions in the viral genome. Selective binding of cellular transcription factors to this promoter region participates in the control of viral tropism. Hence, further study of these proteins might provide new insights into JCV tropism and associated pathogenesis. This review gives an overview of viral proteomics - the study of all proteins expressed from the viral gene transcripts, and all the cellular proteins that play a role in JCV tropism. It also describes a new biochemical approach for studying relevant JCV promoter-binding proteins, which is an anchored-JCV transcriptional promoter (ATP) assay. An ATP assay utilizes the product of PCR-amplified JCV promoter sequences coupled with Sepharose beads in order to capture and isolate cellular nuclear proteins with specific promoter-binding affinity for analysis. Proteins that bind to JCV-ATPs can be eluted and subjected to proteomic analysis. Insights from this approach may improve the understanding of viral and cellular parameters that control JCV tropism.

Management of infections by the human polyomavirus JC: past, present and future

Progressive multifocal leukoencephalopathy is a fatal demyelinating disease caused by infection of oligodendrocytes by the human polyomavirus known as JC virus. Over the past 10 years, the disease has been documented almost exclusively in AIDS patients, who constitute a rapidly growing population of immunosuppressed individuals. More recently, progressive multifocal leukoencephalopathy has also been described in patients undergoing solid organ or cell transplant, as a result of immunosuppressive therapy to avoid graft rejection. Although there are several reports of successful treatment of progressive multifocal leukoencephalopathy, large-scale prospective trials have been few, and with mixed results. As more is discovered about the biology of JC virus infection and advances are made in targeted parenchymal delivery of therapeutic agents, there is hope for the development of an effective therapy for progressive multifocal leukoencephalopathy.

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.

Interactions between c-Jun, nuclear factor 1, and JC virus promoter sequences: implications for viral tropism

The infectious cycle of the human polyomavirus JC (JCV) is ultimately regulated in cellular nuclei at the level of viral protein expression and genomic replication. Such activity is prompted by interactions between variant nucleotide sequences within the JCV regulatory region (promoter) and cellular transcription factors that bind specific DNA consensus sites. In previous work we identified an NF-1 class member, NF-1X, as a critical transcription factor affecting the JCV cellular host range. Within variant JCV promoters, as well as other viral and cellular promoters, adjacently located NF-1 and AP-1 consensus sites are often found. The close proximity of these two binding sites suggests the opportunity for interaction between NF-1 and AP-1 proteins. Here, by electrophoretic mobility shift assays, we show temporal and dose-dependent interference by an AP-1 family member, c-Jun, upon NF-1 proteins binding an NF-1 consensus site derived from JCV promoter sequence. Moreover, as demonstrated by protein-protein interaction assays, we identify specific binding affinity independent of DNA binding between NF-1X and c-Jun. Finally, to compare the binding profiles of NF-1X and c-Jun on JCV promoter sequence in parallel with in vivo detection of viral activity levels, we developed an anchored transcriptional promoter (ATP) assay. With use of extracts from JCV-infected cells transfected to overexpress either NF-1X or c-Jun, ATP assays showed concurrent increases in NF-1X binding and viral protein expression. Conversely, increased c-Jun binding accompanied decreases in both NF-1X binding and viral protein expression. Therefore, inhibition of NF-1X binding by c-Jun appears to play a role in regulating levels of JCV activity.

Human polyomavirus JCV late leader peptide region contains important regulatory elements

Transcription is a complex process that relies on the cooperative interaction between sequence-specific factors and the basal transcription machinery. The strength of a promoter depends on upstream or downstream cis-acting DNA elements, which bind transcription factors. In this study, we investigated whether DNA elements located downstream of the JCV late promoter, encompassing the late leader peptide region, which encodes agnoprotein, play regulatory roles in the JCV lytic cycle. For this purpose, the entire coding region of the leader peptide was deleted and the functional consequences of this deletion were analyzed. We found that viral gene expression and replication were drastically reduced. Gene expression also decreased from a leader peptide point mutant but to a lesser extent. This suggested that the leader peptide region of JCV might contain critical cis-acting DNA elements to which transcription factors bind and regulate viral gene expression and replication. We analyzed the entire coding region of the late leader peptide by a footprinting assay and identified three major regions (region I, II and III) that were protected by nuclear proteins. Further investigation of the first two protected regions by band shift assays revealed a new band that appeared in new infection cycles, suggesting that viral infection induces new factors that interact with the late leader peptide region of JCV. Analysis of the effect of the leader peptide region on the promoter activity of JCV by transfection assays demonstrated that this region has a positive and negative effect on the large T antigen (LT-Ag)-mediated activation of the viral early and late promoters, respectively. Furthermore, a partial deletion analysis of the leader peptide region encompassing the protected regions I and II demonstrated a significant down-regulation of viral gene expression and replication. More importantly, these results were similar to that obtained from a complete deletion of the late leader peptide region, indicating the critical importance of these two protected regions in JCV regulation. Altogether, these findings suggest that the late leader peptide region contains important regulatory elements to which transcription factors bind and contribute to the JCV gene regulation and replication.

Lineage pathway of human brain progenitor cells identified by JC virus susceptibility

Multipotential human central nervous system progenitor cells, isolated from human fetal brain tissue by selective growth conditions, were cultured as undifferentiated, attached cell layers. Selective differentiation yielded highly purified populations of neurons or astrocytes. This report describes the novel use of this cell culture model to study cell type-specific recognition of a human neurotropic virus, JC virus. Infection by either JC virions or a plasmid encoding the JC genome demonstrated susceptibility in astrocytes and, to a lesser degree, progenitor cells, whereas neurons remained nonpermissive. JC virus susceptibility correlated with significantly higher expression of the NFI-X transcription factor in astrocytes than in neurons. Furthermore, transfection of an NFI-X expression vector into progenitor-derived neuronal cells before infection resulted in viral protein production. These results indicate that susceptibility to JC virus infection occurs at the molecular level and also suggest that differential recognition of the viral promoter sequences can predict lineage pathways of multipotential progenitor cells in the human central nervous system.

Members of the AP-1 family, c-Jun and c-Fos, functionally interact with JC virus early regulatory protein large T antigen

The activating protein 1 (AP-1) family of regulatory proteins is characterized as immediate-early inducible transcription factors which were shown to be activated by a variety of stress-related stimuli and to be involved in numerous biological processes, including cellular and viral gene expression, cell proliferation, differentiation, and tumorigenesis. We have recently demonstrated the involvement of the AP-1 family members c-Jun and c-Fos in transcriptional regulation of the human polyomavirus, JC virus (JCV), genome. Here, we further examined their role in JCV gene regulation and replication through their physical and functional interaction with JCV early regulatory protein large T antigen (T-Ag). Transfection and replication studies indicated that c-Jun and c-Fos can significantly diminish T-Ag-mediated JCV gene transcription and replication. Affinity chromatography and coimmunoprecipitation assays demonstrated that c-Jun and T-Ag physically interact with each other. Results from band shift assays showed that the binding efficiency of c-Jun to the AP-1 site was reduced in the presence of T-Ag. In addition, we have mapped, through the use of a series of deletion mutants, the regions of these proteins which are important for their interaction. While the c-Jun interaction domain of T-Ag is localized to the middle portion of the protein, the T-Ag interacting domain of c-Jun maps to its basic-DNA binding region. Results of transient-transfection assays with various c-Jun mutants and T-Ag expression constructs further confirm the specificity of the functional interaction between c-Jun and T-Ag. Taken together, these data demonstrate that immediate-early inducible transcription factors c-Jun and c-Fos physically and functionally interact with JCV major early regulatory protein large T-Ag and that this interaction modulates JCV transcription and replication in glial cells.

Traffic of JC virus from sites of initial infection to the brain: the path to progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disorder of the human brain caused by infection with the human polyomavirus, JC. Up to 80% of humans express serum antibodies to JC virus (JCV), yet considerably fewer people develop PML-predominantly those under immunosuppressive conditions. Recent research showed JCV infection in multiple tissues throughout the body, suggesting sites for viral latency. These observations allow the proposal of pathways that JCV may use from sites of initial infection to the brain. Results from investigations into cell-surface receptors, intracellular DNA-binding proteins, and variant viral regulatory regions also suggest mechanisms that may regulate cellular susceptibility to JCV infection. Together, these data elucidate how JCV may establish infection in various cell types, persist latently or become reactivated, and ultimately reach the brain to cause PML.

Functional interaction between JC virus late regulatory agnoprotein and cellular Y-box binding transcription factor, YB-1

Human polyomavirus JC virus (JCV) is a causative agent of progressive multifocal leukoencephalopathy which results from lytic infection of glial cells. Although significant progress has been made in understanding the regulation of JCV gene transcription, the mechanism(s) underlying the viral lytic cycle remains largely unknown. We recently reported that the JCV late auxiliary Agnoprotein may have a regulatory role in JCV gene transcription and replication. Here, we investigated its regulatory function in viral gene transcription through its physical and functional interaction with YB-1, a cellular transcription factor which contributes to JCV gene expression in glial cells. Time course studies revealed that Agnoprotein is first detected at day 3 postinfection and that its level increased during the late stage of the infection cycle. Agnoprotein is mainly localized to the cytoplasmic compartment of the infected cell, with high concentrations found in the perinuclear region. While the position of Agnoprotein throughout the infection cycle remained relatively unaltered, the subcellular distribution of YB-1 between the cytoplasm and nucleus changed. Results from coimmunoprecipitation and glutathione S-transferase pull-down experiments revealed that Agnoprotein physically interacts with YB-1 and that the amino-terminal region of Agnoprotein, between residues 1 and 36, is critical for this association. Further investigation of this interaction by functional assays demonstrated that Agnoprotein negatively regulates YB-1-mediated gene transcription and that the region corresponding to residues 1 to 36 of Agnoprotein is important for the observed regulatory event. Taken together, these data demonstrate that the interaction of the viral late regulatory Agnoprotein and cellular Y-box binding factor YB-1 modulates transcriptional activity of JCV promoters.

JC virus multiplication in human hematopoietic progenitor cells requires the NF-1 class D transcription factor

JCV, a small DNA virus of the polyomavirus family, has been shown to infect glial cells of the central nervous system, hematopoietic progenitor cells, and immune system lymphocytes. A family of DNA binding proteins called nuclear factor-1 (NF-1) has been linked with site-coding specific transcription of cellular and viral genes and replication of some viruses, including JC virus (JCV). It is unclear which NF-1 gene product must be expressed by cells to promote JCV multiplication. Previously, it was shown that elevated levels of NF-1 class D mRNA were expressed by human brain cells that are highly susceptible to JCV infection but not by JCV nonpermissive HeLa cells. Recently, we reported that CD34(+) precursor cells of the KG-1 line, when treated with the phorbol ester phorbol 12-myristate 13-acetate (PMA), differentiated to cells with macrophage-like characteristics and lost susceptibility to JCV infection. These studies have now been extended by asking whether loss of JCV susceptibility by PMA-treated KG-1 cells is linked with alterations in levels of NF-1 class D expression. Using reverse transcription-PCR, we have found that PMA-treated KG-1 cells express mRNA that codes for all four classes of NF-1 proteins, although different levels of RNA expression were observed in the hematopoietic cells differentiated into macrophages. Northern hybridization confirms that the expression of NF-1 class D gene is lower in JCV nonpermissive PMA-treated KG-1 cells compared with non-PMA-treated cells. Further, using gel mobility shift assays, we were able to show the induction of specific NF-1-DNA complexes in KG-1 cells undergoing PMA treatment. The binding increases in direct relation to the duration of PMA treatment. These results suggest that the binding pattern of NF-1 class members may change in hematopoietic precursor cells, such as KG-1, as they undergo differentiation to macrophage-like cells. Transfection of PMA-treated KG-1 cells with an NF-1 class D expression vector restored the susceptibility of these cells to JCV infection, while the transfection of PMA-treated KG-1 cells with NF-1 class A, B, and C vectors was not able to restore JCV susceptibility. These data collectively suggest that selective expression of NF-1 class D has a regulatory role in JCV multiplication.

Transcriptional control in myelinating glia: flavors and spices

Transcriptional control in myelinating glia is often described in terms of a handful of trans-acting proteins with preferential expression in these cells. An equally valid approach is the identification of cis-acting elements in genes, which are specifically transcribed in myelinating glia. Regulatory regions of several myelin genes have been analyzed in transgenic animals, transient transfections and in vitro. In some cases, these studies have identified regions responsible for glial expression within the promoters or immediate upstream regions. Other myelin genes possess promoters, which simply secure basal levels of transcription, but do not contain glia-specific cis-acting elements. Promoters of myelin genes also differ strongly in other respects. They either contain a TATA-box or are TATA-less and GC-rich. They exhibit multiple transcription initiation sites or a single strong one. Binding sites for general transcription factors, such as NF-I, Sp1, and CAAT-box binding proteins, and for downstream effectors of major signaling pathways are found in them in abundance. In agreement, members of the AP-1, CREB, STAT, and NF-kappaB families are well-described components of the transcription machinery in myelinating glia. Together with several members of the nuclear receptor family, they are an intrinsic part of the transcriptional control in myelinating glia.

Roles of the NFI/CTF gene family in transcription and development

The Nuclear Factor I (NFI) family of site-specific DNA-binding proteins (also known as CTF or CAAT box transcription factor) functions both in viral DNA replication and in the regulation of gene expression. The classes of genes whose expression is modulated by NFI include those that are ubiquitously expressed, as well as those that are hormonally, nutritionally, and developmentally regulated. The NFI family is composed of four members in vertebrates (NFI-A, NFI-B, NFI-C and NFI-X), and the four NFI genes are expressed in unique, but overlapping, patterns during mouse embryogenesis and in the adult. Transcripts of each NFI gene are differentially spliced, yielding as many as nine distinct proteins from a single gene. Products of the four NFI genes differ in their abilities to either activate or repress transcription, likely through fundamentally different mechanisms. Here, we will review the properties of the NFI genes and proteins and their known functions in gene expression and development.

Glial cell-specific regulation of the JC virus early promoter by large T antigen

Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disease that results from an oligodendrocyte infection caused by JC virus. The JC virus early promoter directs cell-specific expression of the viral replication factor large T antigen, and thus transcriptional regulation constitutes a major mechanism of glial tropism in PML. We have previously demonstrated that T antigen controls the JC virus basal promoter in a glial cell-specific manner, since T antigen repressed the JC virus and simian virus 40 (SV40) early promoters in glioma cells but induced strong activation of the JC virus early promoter in nonglial cells. To further analyze these findings, T antigen and nuclear extracts from glial and nonglial cells were used to examine DNase I footprints on the proximal promoter. T-antigen binding to site II was more extensive than expected based on sequence homology with SV40, and nuclear proteins protected several regions of the proximal promoter in a cell-specific manner. Multiple Sp1 binding domains were identified. Site-directed mutagenesis revealed that T-antigen-mediated activation required a TATA box sequence, a pentanucleotide repeat immediately upstream of the TATA box, and an Sp1 binding site downstream of the TATA box. When footprints were obtained with mutant promoters which blocked T-antigen-induced transactivation, no change in T-antigen binding was observed. These results suggest that T antigen activates the JC virus basal promoter in nonglial cells by interaction with the transcription initiation complex.

Comparison of antibody titers determined by hemagglutination inhibition and enzyme immunoassay for JC virus and BK virus

A comparison of antibody titers to JC virus (JCV) or BK virus (BKV) was made by hemagglutination inhibition (HI) and enzyme immunoassay (EIA) with 114 human plasma samples. Antibody titers to JCV or BKV determined by HI were lower than those determined by EIA. Nevertheless, as HI titers increased so did EIA titers. When antibody data were compared by the Spearman rank correlation test, highly significant correlations were found between HI and EIA titers. Results obtained by plotting EIA antibody titers for JCV against those for BKV generally showed a reciprocal relationship, i.e., samples with high antibody titers to JCV had lower antibody titers to BKV and vice versa. Some samples, however, had antibody titers to both viruses. Of the samples tested, 25.4% (25 of 114) had HI and EIA antibody titers to JCV and BKV which were identical or closely related. This is not the scenario one would expect for cross-reactive epitopes shared by the two viruses, but one suggesting that these samples were from individuals who had experienced infections by both viruses. Adsorption with concentrated JCV or BKV antigen of sera with high antibody titers to both JCV and BKV and testing by JCV and BKV EIA gave results which support this conclusion. Although 52.6% (51 of 97) of the samples from the Japanese population tested had very high antibody titers (>/=40,960) to either JCV or BKV, none of the samples were found by a dot blot immunoassay to have antibodies which cross-reacted with simian virus 40. The results from this study, in agreement with those of others, suggest that humans infected by JCV or BKV produce antibodies to species-specific epitopes on their VP1 capsid protein, which is associated with hemagglutination and cellular binding.

Propagation of the human polyomavirus, JCV, in human neuroblastoma cell lines

Susceptibility to infection by the human polyomavirus, JCV, is determined by intracellular mechanisms which control transcription and replication. Originally thought to propagate well only in human cells of oligodendroglial lineage, JCV has recently been shown to infect astrocytes, astrogliomas, and a neuroblastoma cell line. The data reported here describe two cell types that have been subcultured from a human neuroblastoma cell line, SK-N-SH. The SH-SY5Y subclone displays neuronal phenotypes and is not susceptible to JCV infection, while the SH-EP subclone displays glial cell phenotypes and is susceptible to infection. Binding of nuclear proteins from the permissive SH-EP cells to the nuclear factor-1 (NF-1) site in the JCV regulatory DNA sequences results in a gel shift pattern that is different from the nonpermissive SH-SY5Y cell proteins. Northern analysis of mRNA for the four classes of NF-1 proteins showed a predominance of the NF-1/X class in SH-EP cells similar to the highly permissive human fetal glial cells. Very low levels of mRNA for NF-1/X were seen in the nonpermissive SH-SY5Y cells, similar to that seen for the nonpermissive HeLa cells. Several other cell lines tested that were permissive for JCV infection also showed synthesis of the NF-1/X class of proteins. SH-EP cells represent a cell line in a glial cell lineage which is susceptible to JCV multiplication. These cells may be a useful cell culture system for the investigation of DNA binding factors which correlates with viral susceptibility.

BK virus and a new type of JC virus excreted by HIV-1 positive patients in rural Tanzania

HIV-1 positive patients from Tanzanian villages near Shirati were examined for urinary excretion of the human polyomaviruses JC and BK using the polymerase chain reaction (PCR). BK virus (BKV) was detected in 11 of 23 individuals tested. The BKV DNA sequences were all closely related to prototype Gardner strain and BKV (DUN). In contrast, a new type of JCV, termed Type 3 [or JCV (Shi)], was identified in seven of these same 23 individuals by comparison with Type 1 and Type 2 sequences of the VP1/intergenic/T antigen region of U.S., European and Asian strains. This suggests that JCV and BKV, although closely related, have different evolutionary histories within the African population. The six BKV regulatory regions amplified all showed the archetypal configuration. However, two of the seven JCV regulatory regions showed rearrangements: a small deletion and an inverted repeat. JCV causes a fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML), in about 5% of AIDS patients in Europe and the U.S.A., but only one case has been reported in Africa. Our results suggest that this rarity of PML is not due to the absence of JCV in the African population.

Transcriptional regulation of human JC polyomavirus promoters by cellular proteins YB-1 and Pur alpha in glial cells

Transcription of the human polyomavirus (JCV) genome is regulated by host cell proteins and the viral early protein, T antigen. A region called the lytic control element (LCE), located within the enhancer of JCV, is important for transcription of JCV early and late promoters. Earlier studies have led to the identification of two single-stranded DNA-binding proteins, YB-1 and Pur alpha, with the ability to interact with nucleotides on the early and late strands of LCE, respectively. Of particular interest is the notion that the unique interplay between these two cellular proteins and JCVT antigen determines their binding activities with the LCE. In this study, we employed a series of cotransfection experiments to evaluate the levels of transcription from JCV early and late promoters in the presence of YB-1, Pur alpha, and T antigen. Results from these studies indicated that Pur alpha stimulates JCV early and has little effect on the late promoter. Moreover, T antigen was able to decrease the induced level of early gene transcription by Pur alpha. On the other hand, the extent of transactivation of the viral late promoter by T antigen was reduced upon overexpression of Pur alpha in the transfected cells. These observations suggest that Pur alpha and T antigen exert an antagonistic effect on each other's regulatory action upon their responsive promoters. Of particular interest was the observation that YB-1 liberated T-antigen-induced late promoter activity from repression imposed by overexpression of pur alpha. Under similar conditions, overexpression of YB-1 showed no effect on the transcriptional activity of the early promoter in cells transfected with T-antigen- and Pur alpha-producing plasmids. On the basis of the data presented here and the previous binding results, a model is proposed which describes the potential role of Pur alpha, YB-1, and T antigen in differential expression of the viral genome during the lytic cycle.

The role of a pentanucleotide repeat sequence, AGGGAAGGGA, in the regulation of JC virus DNA replication

The human polyomavirus JCV differs from other papovaviruses in its narrow host range and tissue tropism for human glial cells. It is believed that the cell-specific tropism of JCV to glial cells rests, at least in part, in transcription of the viral early gene that encodes the large tumor antigen (T-antigen). The secondary stage, however, which restricts the replication cycle of JCV to primate cells, is controlled at the level of viral DNA replication. In this study, we demonstrate that a cis-acting transcription regulatory element encompassing the pentanucleotide repeat sequence AGGGAAGGGA (penta), which is located in close proximity to the origin of DNA replication, plays an important role in the replication of viral DNA mediated by the JCV T-antigen, but not T-antigen derived from SV40. Analysis of DNA structure by diethyl pyrocarbonate (DEPC) has revealed that mutations within the penta which affect DNA replication also alter the structure of the neighboring A+T-rich region. These results suggest that, in addition to the regulatory role in viral gene expression, the penta may function as a DNA structural element which is important for JCV DNA replication mediated by the JCV T-antigen.

Stimulation of HIV type 1 gene expression and induction of NF-kappa B (p50/p65)-binding activity in tumor necrosis factor alpha-treated human fetal glial cells

In vitro, HIV-1 infection of human fetal glial cells initiates a noncytopathic, productive infection that results in a long-term persistence during which the viral genome remains latent. The cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1 beta) reactivate HIV-1 gene expression in these cells, leading to production of infectious virus. Here we show that treatment of human fetal glial cells with TNF-alpha and IL-1 beta increase expression of the reporter gene chloramphenicol acetyltransferase (CAT) when placed under the control of the HIV-1 5' LTR. We also show that treatment of human fetal glial cells with TNF-alpha leads to increased binding of the nuclear transcription factor NF-kappa B (p50/p65) to a consensus kappa B-binding site present in the HIV-1 5'LTR. Our results suggest that TNF-alpha stimulation of HIV-1 gene expression in primary cultures of human fetal glial cells is mediated by an increase in binding of NF-kappa B (p50/p65) to the HIV-1 LTR. This is the first report documenting NF-kappa B-binding activity in primary cultures of human fetal glial cells.

Complex functional interactions at the early enhancer of the PQ strain of BK virus

BK virus is a human papovavirus that latently infects a majority of the world's population. There are more than 30 strains of the virus, most of which differ in the structure of the early enhancer region. The enhancer of the progenitor strain, WW, from which the other strains can be derived, consists of four conserved DNA domains, P, Q, R, and S. Rearrangement of the enhancer occurs upon passage in tissue culture and is thought to occur during virus replication. The strain under study, PQ, was selected upon passage of the Gardner strain (PPPQS) in the permissive cell line, Vero. Mutational analysis of the entire enhancer region demonstrates the importance of five cis-acting sequences: DNA sites B, C, and F, which have homology to the NF-1 protein binding sequence; one purine-rich motif designated A; and site D, which is similar to an SP-1 protein binding site. Two sites, B and C, appear to have a negative influence on gene activity. To study the functional interactions in more detail, promoter-enhancer constructions that contain different combinations of the five DNA sites linked to the chloramphenicol acetyltransferase gene were tested for early gene activity. The results reveal that the proteins binding to the enhancer functionally cooperate with each other. The effects of making mutations at the DNA sites are very similar to the effects of using excess enhancer DNA sequences to titrate the proteins that bind to the cis-acting DNA sites (in vivo competition). Moreover, the effects of changing the spacing between the DNA sites also demonstrate that there are cooperative interactions among the proteins that bind to the PQ strain enhancer. DNA sites B, C, and F are clearly protected from DNase I digestion by Vero cell nuclear proteins. In addition, mutation of each DNA site alters its sensitivity to DNase I in the presence of Vero cell proteins. Interestingly, mutation of site B affects protein binding to site B as well as to sites A, C, D, and F. These results suggest that cooperative functional and physical interactions occur at the early enhancer of the PQ strain.

Nuclear factor I and epithelial cell-specific transcription of human papillomavirus type 16

The transcription of human papillomavirus type 16 (HPV-16) is mediated by the viral enhancer. Epithelial cell-specific activation is achieved by the cooperative interaction of apparently ubiquitous transcriptional factors. One of them, nuclear factor I (NFI), binds seven sites within the HPV-16 enhancer. Point mutations on enhancer fragments, which retain epithelial cell specificity, verify the functional contribution of NFI. In band shift experiments, the epithelial cell-derived NFI proteins CTF-1, CTF-2, and CTF-3 form a characteristic pattern of heterodimeric complexes which are observed in all epithelial cells tested. Divergence from this pattern in fibroblasts, liver cells, and lymphoid cells correlates with the lack of HPV-16 enhancer activation. The HPV-16 enhancer can be activated by CTF-1 in SL-2 cells, which lack NFI-like proteins. However, exogenous CTF-1 fails to overcome the inactivity of the viral enhancer in fibroblasts. Western immunoblot and supershift analysis shows that exogenously introduced CTF-1 proteins form different heterodimer complexes with the given subset of endogenous NFI proteins in epithelial or fibroblast cells. Polymerase chain reaction analysis and cDNA library screens identified the endogenous fibroblast type NFI as NFI-X, an NFI family member originally cloned from hamster liver cells. The strict correlation between the activation or lack of activation of the HPV-16 enhancer and cell-specific subsets of NFI proteins argues for the pivotal role of NFI binding sites in the epithelial cell-specific function of the viral enhancer.

Human JC virus perfect palindromic nuclear factor 1-binding sequences important for glial cell-specific expression in differentiating embryonal carcinoma cells

The brain cell specificity of the human papovavirus JC virus was examined by site-directed mutagenesis of the nuclear factor 1 (NF1) motifs within the viral regulatory region. The NF1 motif sites, located within the 98-bp tandem repeats that contain 6-bp perfect inverted palindromic sequences, were important for glial cell-specific expression of JC virus in differentiated embryonal carcinoma cells in vivo. The NF1 site on the late side of the repeats was not important, a fact confirmed by in vitro transcription studies. These observations were correlated with in vitro DNase I footprinting and mobility shift assays, which demonstrated specific interactions of factors in glial cell nuclear extracts with NF1 sites.

Interaction of the human polyomavirus, JCV, with human B-lymphocytes

The human polyomavirus, JCV, is the causative agent of the central nervous system demyelinating disease progressive multifocal leukoencephalopathy (PML). The principal target of JCV infection in the central nervous system (CNS) is the myelinating oligodendrocyte. However, the site of JCV multiplication outside of the CNS and the mechanism by which virus gains access to the brain are not known. Recently, JCV infected B-lymphocytes have been demonstrated in PML patients in several lymphoid organs, in circulating peripheral lymphocytes, and in brain, suggesting a possible role of B-lymphocytes in the dissemination of virus to the brain. The experiments reported here were undertaken to understand more about the interactions of JCV with human B-lymphocytes. The data show that JCV is able to multiply in either Epstein-Barr virus transformed (EBV) or EBV negative human B cell lines resulting in production of infectious, progeny virions. In addition, nuclear proteins extracted from these B cells bind to similar nucleotides within the JCV regulatory region that are bound by nuclear proteins extracted from human fetal glial cells, the most susceptible host and principal target cell for JCV infection in vitro. It is not known, however, whether these DNA binding proteins from susceptible B cells and glial cells are similar.

Novel DNA binding proteins participate in the regulation of human neurofilament H gene expression

By a combination of DNase I footprinting, methylation interference, and gel shift analyses we have identified multiple binding sites for nuclear proteins within the promoter region of the human neurofilament H gene. Two sites likely bind the transcription factor Sp1 while two others may be targets for previously unrecognized DNA binding proteins. One site, PAL, occurs within the 10 bp sequence GGGGAGGAGG. Two copies of the PAL sequence form an interrupted palindrome around one of the Sp1 sites. A second site, PROX, is found within the sequence GGTTGGACC. Nuclear extracts prepared from both neural and non-neural cell lines, mouse brain, and mouse liver contain proteins that recognize and bind to the PROX and PAL sequences indicating that proteins which bind to these target sequences are widespread. The appearance of these target sequences in the 5' upstream region of several neuron specific genes suggests that they play key roles in the transcription of neuron specific genes. The functional activity of these target DNA sequences was demonstrated by transfection assays using a reporter gene fused to nested deletions of the NF(H) promoter region. Interestingly, these assays revealed that maximal transient expression was obtained with DNA fusion genes containing the PAL, PROX and TATA sequences. Inclusion of the Sp1 sites into the fusion genes failed to enhance the expression of the reporter gene. To determine if the NF(H) promoter can be activated in a tissue specific manner during development transgenic mice containing the promoter region linked to a beta-galactosidase reporter gene were generated. In one line sporadic expression of the transgene occurred in the CNS and testis while in four other lines no expression occurred. Collectively these results suggest that the NF(H) gene promoter is active in a tissue specific manner only by interactions with regulatory elements that lie further upstream or downstream of the start site of initiation.

Enhancer/promoter activities of regulatory regions of representative JC virus isolates

The enhancer/promoter activities of JC virus isolates MAD1, MAD8, and MAD11 in HeLa cells and in human glial cells expressing either SV40 or JCV(MAD1) tumor antigens were significantly different from one another in each cell line.