JC virus induces altered patterns of cellular gene expression: interferon-inducible genes as major transcriptional targets

Human polyomavirus JC (JCV) infects 80% of the population worldwide. Primary infection, typically occurring during childhood, is asymptomatic in immunocompetent individuals and results in lifelong latency and persistent infection. However, among the severely immunocompromised, JCV may cause a fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). Virus-host interactions influencing persistence and pathogenicity are not well understood, although significant regulation of JCV activity is thought to occur at the level of transcription. Regulation of the JCV early and late promoters during the lytic cycle is a complex event that requires participation of both viral and cellular factors. We have used cDNA microarray technology to analyze global alterations in gene expression in JCV-permissive primary human fetal glial cells (PHFG). Expression of more than 400 cellular genes was altered, including many that influence cell proliferation, cell communication and interferon (IFN)-mediated host defense responses. Genes in the latter category included signal transducer and activator of transcription 1 (STAT1), interferon stimulating gene 56 (ISG56), myxovirus resistance 1 (MxA), 2'5'-oligoadenylate synthetase (OAS), and cig5. The expression of these genes was further confirmed in JCV-infected PHFG cells and the human glioblastoma cell line U87MG to ensure the specificity of JCV in inducing this strong antiviral response. Results obtained by real-time RT-PCR and Western blot analyses supported the microarray data and provide temporal information related to virus-induced changes in the IFN response pathway. Our data indicate that the induction of an antiviral response may be one of the cellular factors regulating/controlling JCV replication in immunocompetent hosts and therefore constraining the development of PML.

Assessment of JC polyoma virus in colon neoplasms

PURPOSE

Research data have recently emphasized an intriguing association of JC polyoma virus with colon carcinogenesis. Tumorigenicity of JC virus is attributed to the T-antigen of its Mad-1 variant. Controversy arose when another research group did not confirm this association. The purpose of this study was to detect JC virus in a series of colon neoplasms from Greek patients.

METHODS

A nested polymerase chain reaction assay was used to detect JC virus in 80 cancerous, 25 adenomatous specimens of large bowel, and 20 colonoscopic biopsy samples from normal patients without colorectal neoplasia. Quantitation of JC virus DNA was performed by real-time polymerase chain reaction.

RESULTS

JC polyoma virus nucleotide sequence was detected in 61 percent of colon adenocarcinomas and in 60 percent of adenomas, at a viral load of 9 x 10(3) to 20 x 10(3) copies/microg DNA. Adjacent normal mucosa in 35 positive colon adenocarcinoma specimens, and normal mucosa from six patients of the control group, had low viral loads (50-450 copies/microg DNA).

CONCLUSIONS

JC polyoma virus genome is present in colon neoplasms. JC virus detection in adenomas at comparable viral loads to malignant tumors suggests its implication at early steps of colonic carcinogenesis. Taking into consideration other published data, infection of colonic epithelium with JC virus might be a prime candidate for a role in chromosomal and genomic instability.

JC virus and colorectal cancer: a possible trigger in the chromosomal instability pathways

PURPOSE OF REVIEW

Most colorectal cancers (CRCs) have deletions, duplications, and rearrangements of their chromosomes that reflect a destabilizing process called chromosomal instability (CIN). The cause of CIN is controversial, but no intrinsic mutation in cancer cells has been reported that can reasonably account for this in CRC. This review explores the new hypothesis that JC virus (JCV) may be the cause of CIN.

RECENT FINDINGS

A polyomavirus has been found in most colon cancers that encodes a T-antigen gene, which can induce CIN in several laboratory models. This virus, JCV, infects virtually every human population that has been investigated, and evidence for the virus has been found in the gastrointestinal tracts of most healthy adults. It is hypothesized that the virus infects the gut in childhood and remains there in a latent form for most people. In people who develop colorectal neoplasia, it is proposed that the virus is activated, and expression of the oncogene-T-antigen-leads to CIN. This form of genomic instability is necessary to explain the losses of tumor suppressor genes that occur in the context of the multistep carcinogenesis pathway. Furthermore, it is proposed that once neoplastic colonic epithelial cells have experienced biallelic inactivation of a critical number of tissue-specific tumor suppressor genes-including APC and p53-the ongoing effect of the transforming virus may be relatively deleterious to a neoplastic cell, and selective pressure may lead to loss of viral infection.

SUMMARY

This review summarizes the experimental data that have led to the hypothesis that JCV is a common cause of CIN in CRC.

Role of JC virus agnoprotein in DNA repair

The late region of human neurotropic JC virus encodes a small 71-amino-acid agnoprotein that is also found in the polyomaviruses simian virus 40 and BK virus. Several functions of agnoprotein have been identified, including roles in regulating viral transcription and virion maturation. Earlier studies showed that agnoprotein expressed alone induced p21/WAF-1 expression and caused cells to accumulate in the G(2)/M stage of the cell cycle. Here we report that agnoprotein expression sensitized cells to the cytotoxic effects of the DNA-damaging agent cisplatin. Agnoprotein reduced the viability of cisplatin-treated cells and increased chromosome fragmentation and micronucleus formation. Whereas cisplatin-treated control cells accumulated in S phase, cells expressing agnoprotein did not, instead becoming aneuploid. Agnoprotein expression correlated with impaired double-strand-break repair activity in cellular extracts and reduced expression of the Ku70 and Ku80 DNA repair proteins. After agnoprotein expression, much of the Ku70 protein was located in the perinuclear space, where agnoprotein was also found. Results from binding studies showed an interaction of agnoprotein with Ku70 which was mediated by the N terminus. The ability of agnoprotein to inhibit double-strand break repair activity when it was added to cellular extracts was also mediated by the N terminus. We conclude that agnoprotein inhibits DNA repair after DNA damage and interferes with DNA damage-induced cell cycle regulation. Since Ku70 is a subunit of the DNA-dependent protein kinase that is responsible both for double-strand break repair and for signaling damage-induced cell cycle arrest, the modulation of Ku70 and/or Ku80 by agnoprotein may represent an important event in the polyomavirus life cycle and in cell transformation.

Detection of JC virus-specific cytotoxic T lymphocytes in healthy individuals

The polyomavirus JC (JCV) infects 85% of healthy individuals, and its reactivation in a limited number of immunosuppressed people causes progressive multifocal leukoencephalopathy (PML), a severe demyelinating disease of the central nervous system. We hypothesized that JCV-specific cytotoxic T lymphocytes (CTLs) might control JCV replication in healthy individuals, blocking the evolution of PML. Using 51Cr release and tetramer staining assays, we show that 8 of 11 HLA-A*0201+ healthy subjects (73%) harbor detectable JCV-specific CD8+ CTLs that recognize one or two epitopes of JCV VP1 protein, the HLA-A*0201-restricted VP1p36 and VPp1100 epitopes. We determined that the frequency of JCV VP1 epitope-specific CTLs varied from less than 1/100,000 to 1/2,494 peripheral blood mononuclear cells. More individuals had JCV VP1-specific than cytomegalovirus-specific CTLs (8 of 11 subjects [73%] versus 2 of 10 subjects [20%], respectively). These results show that a CD8+-T-cell response against JCV is commonly found in immunocompetent people and suggest that these cells might protect against the development of PML.

Inhibition of virus production in JC virus-infected cells by postinfection RNA interference

RNA interference has been applied for the prevention of virus infections in mammalian cells but has not succeeded in eliminating infections from already infected cells. We now show that the transfection of JC virus-infected SVG-A human glial cells with small interfering RNAs that target late viral proteins, including agnoprotein and VP1, results in a marked inhibition both of viral protein expression and of virus production. RNA interference directed against JC virus genes may thus provide a basis for the development of new strategies to control infections with this polyomavirus.

Intracellular approach for blocking JC virus gene expression by using RNA interference during viral infection

The human polyomavirus, JC virus (JCV), encodes two regulatory proteins at the early (T antigen) and the late (agnoprotein) phases of viral infection whose activities are important for the production of the viral capsid proteins and the dysregulation of several host factors and their functions. For this study, we designed and utilized an RNA interference strategy via small interfering RNAs (siRNAs) that targeted the expression of T antigen and agnoprotein in human astrocytic cells. The treatment of cells with specific siRNA oligonucleotides targeting a conserved region of T antigen, nucleotides (nt) 4256 to 4276 (Mad-1 strain), caused a >50% decline in the level of T antigen and in its transcriptional activity upon the viral capsid genes as well as a significant reduction in viral DNA replication in infected cells. Similarly, a single siRNA that aimed at nt 324 to 342 of agnoprotein noticeably reduced early and late viral protein production. A combined treatment of the infected cells with both T-antigen and agnoprotein siRNAs completely abolished viral capsid protein production, indicative of the ability of the siRNAs to effectively halt multiplication of the virus in infected cells. These observations provide a new avenue for possible treatments of patients with the JCV-induced demyelinating disease progressive multifocal leukoencephalopathy.

Meningoencephalitis and Demyelination Are Pathologic Manifestations of Primary Polyomavirus Infection in Immunosuppressed Rhesus Monkeys

The human polyomavirus JC (JCV) is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a demyelinating disease of the CNS that occurs in immunosuppressed individuals. Because polyomavirus-induced CNS pathology usually occurs as a result of the reactivation of latent virus, little is known about the disease manifestations of a primary polyomavirus-induced disease in man. To model such a primary infection, SV40-negative rhesus monkeys were immunosuppressed by infection with the virus SHIV-89.6P and then superinfected with the polyomavirus SV40. The animals developed CNS pathology characterized by both demyelination and meningoencephalitis. This observation suggests that a primary polyomavirus infection can be associated with an inflammatory CNS process. These data shed new light on the pathogenic mechanisms of primate polyomaviruses in the immunocompromised host.

JC virus induces nonapoptotic cell death of human central nervous system progenitor cell-derived astrocytes

JC virus (JCV), a human neurotropic polyomavirus, demonstrates a selective glial cell tropism that causes cell death through lytic infection. Whether these cells die via apoptosis or necrosis following infection with JCV remains unclear. To investigate the mechanism of virus-induced cell death, we used a human central nervous system progenitor-derived astrocyte cell culture model developed in our laboratory. Using in situ DNA hybridization, immunocytochemistry, electron microscopy, and an RNase protection assay, we observed that astrocytes support a progressive JCV infection, which eventually leads to nonapoptotic cell death. Infected astrocyte cell cultures showed no difference from noninfected cells in mRNA expression of the caspase family genes or in any ultrastructural features associated with apoptosis. Infected cells demonstrated striking necrotic features such as cytoplasmic vacuolization, watery cytoplasm, and dissolution of organelles. Furthermore, staining for caspase-3 and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling were not detected in infected astrocyte cultures. Our findings suggest that JCV-induced cell death of these progenitor cell-derived astrocytes does not utilize an apoptosis pathway but exhibits a pattern of cell destruction consistent with necrotic cell death.

Differential distribution of the JC virus receptor-type sialic acid in normal human tissues

JC virus (JCV), a member of the polyomavirus family, causes a demyelinating disease of the central nervous system (CNS) in humans known as progressive multifocal leukoencephalopathy. Although glial cells are the principal target of JCV productive infection in progressive multifocal leukoencephalopathy patients, little is known regarding the site of JCV persistence and the mechanisms by which the virus spreads to the CNS to cause disease. Previous work has demonstrated the presence of replicating JCV DNA in B lymphocytes from peripheral blood, tonsil, and spleen and it has been hypothesized that lymphocytes may be one site of JCV persistence. Detection of viral gene products in renal tubules and excretion of JC virions in the urine suggests JCV persistence in the kidney. A respiratory route of viral transmission has also been hypothesized implicating the lung as another possible site of persistent JCV infection. Earlier studies from our laboratory have shown that terminal alpha 2,6-linked sialic acid is a critical component of the JCV receptor. In this report we examined the tissue distribution of this JCV receptor-type sialic acid in a panel of normal human tissues. Our results demonstrate that in normal brain JCV receptor-type sialic acids are expressed on oligodendrocytes and astrocytes, but not on cortical neurons. The receptor-type sialic acid is also more highly expressed on B lymphocytes than on T lymphocytes in normal human spleen and tonsil. In addition, both the kidney and lung express abundant levels of alpha 2-6-linked sialic acids. Our data show a striking correlation between the expression of the JCV receptor-type sialic acid on cells and their susceptibility to infection by the virus. These findings also support the hypothesis of JCV persistence in lymphoid tissue and B-cell-facilitated viral dissemination to the CNS.

A JC virus-induced signal is required for infection of glial cells by a clathrin- and eps15-dependent pathway

Infectious entry of JC virus (JCV) into human glial cells occurs by receptor-mediated clathrin-dependent endocytosis. In this report we demonstrate that the tyrosine kinase inhibitor genistein blocks virus entry and inhibits infection. Transient expression of dominant-negative eps15 mutants, including a phosphorylation-defective mutant, inhibited both virus entry and infection. We also show that the JCV-induced signal activates the mitogen-activated protein kinases ERK1 and ERK2. These data demonstrate that JC virus binding to human glial cells induces an intracellular signal that is critical for entry and infection by a ligand-inducible clathrin-dependent mechanism.

Viruses and cancer: lessons from the human polyomavirus, JCV

The possible role of eucaryotic viruses in the development of cancer has been the subject of intense investigation during the past 50 years. Thus far, a strong link between some RNA and DNA viruses and various cancers in humans has been established and the transforming activity of several of the viruses in cell culture and their oncogenecity in experimental animals has been well documented. Perhaps, one of the most common themes among the oncogenic viruses rests in the ability of one or more of the viral proteins to deregulate pathways involved in the control of cell proliferation. For example, inactivation of tumor suppressors through their association with viral transforming proteins, and/or impairment of signal transduction pathways upon viral infection and expression of viral proteins are among the key biological events that can either trigger and/or contribute to the process of cancer. In recent years, more attention has been paid to human polyomaviruses, particularly JC virus (JCV), which infects greater than 80% of the human population, due to the ability of this virus to induce a fatal demyelinating disease in the brain, its presence in various tumors of central nervous system (CNS) and non-CNS origin, and the oncogenic potential of this virus in several laboratory animal models. Here, we will focus our attention on JCV and describe several pathways employed by the virus to contribute to and/or accelerate cancer development.

JC virus-induced changes in cellular gene expression in primary human astrocytes

Cell-type-specific transcription of the JC virus (JCV) promoter in glial cells initiates a series of events leading to viral replication in the brain and the development of the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML) in patients with neurologic complications due to infection with human immunodeficiency virus type 1. Here we employed an in vitro infection of primary cultures of human astrocytes to compare the transcriptional profile of cellular genes after JCV infection by using an oligonucleotide-based microarray of 12600 genes. Transcription of nearly 355 genes was enhanced and expression of 130 genes was decreased to various degrees. Many transcripts that were increased upon JCV infection were found to encode proteins with properties that suggest their involvement in cell proliferation, including cyclin A and cyclin B1; signaling pathways, such as transforming growth factor beta receptor 1, platelet-derived growth factor receptor and fibroblast growth factor family receptor; and other regulatory events, such as inflammatory responses, including cyclo-oxygenase-2 (Cox-2). Microarray-based data for several cell cycle-regulatory genes were further examined by using Western blot analysis of in vitro infected astrocytes harvested early and late during the infection. Results demonstrate that protein levels of all upregulated genes were found to increase at some point during the infection time course. In parallel, immunohistochemical assessment of cell cycle proteins, including cyclins A, B1, E, and Cdk2, showed positive staining of astrocytes within PML lesions of brain tissue from patients with neuro-AIDS. Microarray analysis was found to be a useful predictor of gene expression in infected cells; however, it may not directly correlate with protein levels during infection with JCV.

Propagation of archetype and nonarchetype JC virus variants in human fetal brain cultures: demonstration of interference activity by archetype JC virus

In immunologically normal individuals, the polyomavirus, JC virus (JCV), produces an asymptomatic primary infection followed by lifelong persistence of the virus in renal tubular epithelial cells. In some immunocompromised patients, however, in particular acquired immunodeficiency syndrome (AIDS) patients, JCV causes an opportunistic central nervous system (CNS) disorder, progressive multifocal leukoencephalopathy (PML). JCV DNA as it persists in kidneys (archetypal JCV) and JCV DNA isolated from PML lesions show differences in their regulatory regions in which transcription and replication are controlled. Archetypal JCV DNA has a single enhancer and no rearrangements or deletions in the regulatory region. In contrast, JCV DNA from PML isolates is characterized by alterations in the regulatory region. Some PML-associated JCVs can be grown in cultures of human fetal brain (HFB) cells. Growth of archetypal JCV in cultured cells has not been reported, however. Here we demonstrate successful propagation of the archetypal JCV, strain GS/K, in HFB cells. Growth occurred more slowly and to lower titers than is seen with the prototypical PML JCV strain Mad-1, with relatively few cells containing viral T antigen (T-Ag) or viral capsid protein, Vp1. Interestingly, GS/K growth could be enhanced, with a large increase in viral DNA and cytopathic effect, by coinfection with GS/B, a nonarchetypal brain-derived JCV variant isolated from the same PML patient as GS/K. The amount of GS/K DNA was also greatly enhanced when it was cotransfected with Mad-1 JCV DNA, the prototypical PML isolate. In contrast to GS/K plus GS/B-cotransfected cells, in GS/K plus Mad-1-infected cells, cytopathic effect was not increased. On subsequent passage of culture lysates to naïve cells, however, the infection produced by either combination of viral DNAs slowed, no cytopathic effect (CPE) was present, and the amount of GS/B or Mad-1 viral DNA was greatly reduced as compared to that of GS/K DNA. These data suggest that GS/K was able to use either GS/B or Mad-1 as a helper and that GS/K was in turn able to interfere with the growth of either helper virus. Archetype JCV can be successfully propagated in HFB cells, although infection develops much more slowly than that caused by the PML JCV variant Mad-1. The ability of archetypal and variant JCVs to enhance or retard each other's replication may have implications in vivo for the maintenance of JCV persistence and the growth of JCV variants.

Derivation of a JC virus-resistant human glial cell line: implications for the identification of host cell factors that determine viral tropism

JC virus (JCV) is a common human polyomavirus that infects 70-80% of the population worldwide. In immunosuppressed individuals, JCV infects oligodendrocytes and causes a fatal demyelinating disease known as progressive multifocal leukoencephalopathy (PML). The tropism of JCV is restricted to oligodendrocytes, astrocytes, and B lymphocytes. Several mechanisms may contribute to the restricted tropism of JCV, including the presence or absence of cell-type-specific transcription and replication factors and the presence or absence of cell-type-specific receptors. We have established a system to investigate cellular factors that influence viral tropism by selecting JCV-resistant cells from a susceptible glial cell line (SVG-A). SVG-A cells were subjected to several rounds of viral infection using JC virus (M1/SVE Delta). A population of resistant cells emerged (SVGR2) that were refractory to infection with the Mad-4 strain of JCV, the hybrid virus M1/SVE Delta, as well as to the related polyomavirus SV40. SVGR2 cells were as susceptible as the SVG-A cells to infection with an unrelated amphotropic retrovirus. The stage at which these cells are resistant to infection was investigated and the block appears to be at early viral gene transcription. This system should ultimately allow us to identify glial specific factors that influence the tropism of JCV.

Human neurotropic polyomavirus, JCV, and its role in carcinogenesis

A number of recent studies have reported the detection of the ubiquitous human polyomavirus, JC virus (JCV), in samples derived from several types of neural as well as non-neural human tumors. The human neurotropic JCV was first identified as the etiologic agent of the fatal demyelinating disease, progressive multifocal leukoencephalopathy, which usually occurs in individuals with defects in cell-mediated immunity, including AIDS. However, upon mounting evidence of the oncogenic potential of the viral regulatory protein, T-antigen, and JCV's oncogenecity in a broad range of animal models, studies were initiated to determine its potential involvement in human carcinogenesis. Initially, the most frequently observed tumors in rodent models, including medulloblastoma, astrocytoma, glioblastoma, and other neural-origin tumors were analysed. These studies were followed by analysis of non-neural tumors such as colorectal carcinomas. In a subset of each tumor type examined, JC viral genomic DNA sequences could be detected by PCR and confirmed by Southern blot hybridization or direct sequencing. In a smaller subset of the tumors, the expression of T-antigen was observed by immunohistochemical analysis. Owing to the established functions of T-antigen including its ability to interact with tumor suppressor proteins such as Rb and p53, and its ability to influence chromosomal stability, potential mechanisms of JCV T-antigen-mediated cellular dysregulation are discussed. Further, as increasing evidence suggests that T-antigen is not required for maintenance of a transformed phenotype, a hit-and-run model for T-antigen-induced transformation is proposed.

[Virological, epidemiological and pathogenic aspects of human polyomaviruses]

VIROLOGICAL ASPECTS: Human polyomaviruses (BK virus and JC virus), together with simian polyomaviruses (SV40 virus) share 75% of genomic homology. Their in vivo and in vitro genomes vary. Molecular analyses have identified several genotypes, some of which appear related to the development of viral diseases. Genomic modifications of the regulation area might provide the BKv with a pathogenic aspect thus enhancing the induction of tubulo-interstitial nephropathies in renal transplant recipients.

EPIDEMIOLOGY

Human polyomaviruses are ubiquitous and exhibit a sero-prevalence of 60 to 80% in adults. Following a primary infection via the respiratory tract in childhood, these viruses are diffused in the blood using the B-lymphocytes during their latent stage in the urogenital tract. The reactivation that occurs after several years is asymptomatic and urinary excretion of BKv is observed in 4 to 6% of immunocompetent patients.

PATHOGENIC POTENTIAL

Human polyomaviruses have a cytopathogenic effect on the urothelium and epithelium of renal transplant recipients. Infection by BKv may provoke hemorrhagic cystitis or urethral stenosis. The JCv is the cause of progressive multifocal leuko-encephalitis. The BKv (and less frequently the JCv) is responsible for tubulo-interstitial nephritis possible leading to renal transplant loss. They also have an oncogenic effect and their implication in the origin of tumours is the subject of many studies.

[Therapeutic possibilities for polyomavirus infections in renal transplantation]

TO IMPROVE THERAPEUTIC MANAGEMENT: The aim is the early detection of polyomavirus infection, before the onset of tubulo-interstitial nephritic lesions, and to reduce viral replication. AT THE STAGE OF POLYOMAVIRUS INFECTION: Treatment relies on the reduction of immunosuppression. Efficacy is controlled by monitoring the decoy cells in the urine and the detection and quantification of the DNA of polyomaviruses in the plasma and urine. AT THE STAGE OF POLYOMAVIRUS DISEASE: The aim is to reduce the viral replication by further decreasing immunosuppression to stabilize renal function and avoid graft rejection. When signs of rejection and viral infection co-exist, cidofovir could be a therapeutic alternative. However, the use of cidofovir remains in the field of clinical research and requires the further development of therapeutic protocols.

[Clinical aspects of human polyomaviruses in renal transplantation]

A THREAT FOR RENAL ALLOGRAFT: Human polyomavirus infections (BK virus, JC virus), known for the past 30 years, were considered as common in renal transplantation until the recently reported studies describing the responsibility of BKv (and less JCv) in the occurrence of tubulo-interstitial nephritis in around 5% of renal transplant recipients, with worsening of the renal function leading to graft failure in 10 to 45% of infected patients. Their description coincided with the use of new immunosuppressors (tacrolimus and mycophenolate mofetil) without, however, their responsibility clearly incriminated. EARLY DIAGNOSIS FOR EFFICIENT TREATMENT: The presence of cells infected by the polyomavirus ("decoy cells") in the urine and the detection of BKv or JCv DNA by PCR in the plasma and urine are viral replication markers which strongly suggest the possibility of a polyomavirus nephropathy. TWO CLINICAL VARYING FORMS: Polyomavirus infection is frequent and often asymptomatic. The diagnosis requires the detection of large nucleus "decoy cells" in fresh urine. Polyomavirus renal allograft disease is characterised by the association of decoy cells and renal failure related to a tubulo-interstitial nephropathy and the presence of DNA of the virus in the plasma. The diagnosis requires identification of intra-nuclear viral inclusions in epithelial cells using immunohistochemistry, in situ hybridisation, or electron microscopy techniques. A DIFFICULT DIAGNOSIS: Confusion between interstitial nephritis and acute cellular rejection is the major risk leading to therapeutic error. Risk factors include over-immunosuppression and/or treatment of rejection episodes which could increase viral replication as well as the emergence of mutant BKv strains at the origin of tubulo-interstitial nephritis, leading to acute and chronic dysfunction of the renal transplantation.

Human polyomavirus DNA is not detected in Guthrie cards (dried blood spots) from children who developed acute lymphoblastic leukemia

BACKGROUND

Epidemiological evidence has suggested that some childhood acute lymphoblastic leukemia (ALL) may be initiated in utero and may have an infectious etiology. The human polyomavirus JC virus (JCV) has been discussed as a candidate virus, but its presence has not been demonstrated in leukemia cells from children with ALL. The aim of this study was, therefore, to investigate if prenatal human polyomavirus infection could still indirectly be correlated to the development of childhood ALL.

PROCEDURE

Fifty-four Guthrie cards (stored, dried blood spots filter papers, routinely collected from newborns for different screening analyses), collected at 3-5 days of age, from Swedish children who subsequently developed ALL, as well as from 37 healthy controls, were investigated by nested PCR for the presence of human polyomaviruses JCV and BK virus (BKV).

RESULTS

JCV and BKV DNA were not detected in any of the Guthrie cards from ALL patients or from healthy controls, although all tested samples had amplifiable DNA as confirmed by an HLA DQ PCR.

CONCLUSIONS

JCV or BKV were not found in any of the dried blood spots of children who later developed ALL or in the healthy controls. These findings suggest that it is unlikely that childhood ALL is associated with an in utero infection with JCV or BKV, although it is not possible to exclude an association with an in utero infection that has become latent in the kidneys with very low levels of circulating virus at birth.

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.

Insulin-like growth factor-I receptor - a potential therapeutic target in medulloblastomas

Medulloblastomas represent nearly 25% of all paediatric intracranial neoplasms. These highly malignant tumours arise from the cerebellum and affect predominantly children between the ages of 5 and 15. Although the aetiology of medulloblastomas has not been elucidated, several reports show that the insulin-like growth factor-I (IGF-I) signalling system is highly activated in medulloblastoma cell lines, medulloblastoma animal models and medulloblastoma biopsies, suggesting its contribution to the development and/or progression of these tumours. In addition, reports from multiple laboratories confirm a critical role for the IGF-I receptor (IGF-IR) in the process of cellular transformation. Taken together, these observations prompt the investigation of different strategies to impair the function of IGF-IR as a potential therapeutic tool, which by compromising growth and survival of medulloblastoma cells could supplement conventional therapeutic regiments against these malignant neoplasms of childhood.

Progressive myoclonic ataxia and JC virus encephalitis in an AIDS patient

A case of progressive myoclonic ataxia in an AIDS patient is described, which evolved over a 13 month period. The ataxia persisted as the only clinical finding for several months before the appearance of a severe tetraparesis and cachexia. Throughout the clinical progression, magnetic resonance imaging (MRI) revealed the presence of bilateral, progressive, isolated, and symmetrical lesions involving the red nuclei, subthalami, thalami, lenticular nuclei, and primary motor cortices. Neuropathological examination, supplemented by in situ hybridisation for JC virus DNA, confirmed that the lesions were those of progressive multifocal leucoencephalopathy (PML). The exceptional clinical presentation of PML in this case is the first report of progressive myoclonic ataxia caused by PML. The selective nature of the lesions confirms the role of the dentato-rubral-thalamo-cortical tract in the pathogenesis of progressive myoclonic ataxia. The atypical MRI findings further emphasise the need for expanded diagnostic criteria for PML in AIDS patients and support the use of more aggressive diagnostic methods as new treatments become available.

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.

[Progressive multifocal leukoencephalopathy. Demyelinating viral disease--common complication of AIDS]

PML is a chronic, progressive, fatal disease in the CNS of humans. Characteristic pathologic features are spotty demyelination, enlarged oligodendrocytes with nuclear inclusions, and transformed astrocytes. It is caused by the polyoma virus JCV, which has worldwide distribution and usually is harmless. In some individuals with impaired cell-mediated immunity, most commonly in aids, virus changes into a pathogenic form. Hence, PML is a slow, viral, opportunistic infection. The infection is productive in astrocytes and destructive in oligodendrocytes. Lysis of the latter causes demyelination. The discovery of PML in 1958 opened the door to extensive research in several fields of biomedicine.

Predicted amino acid sequences for 100 JCV strains

DNA sequence variation between JCV genotypes is confined largely to noncoding intergenic regions and introns. Nevertheless, evidence suggests that the amino acid sequence variations among the 8 genotypes of JCV can influence the potential for neurovirulence of the virus. In the current study, the amino acid sequences for 100 JCV genomes were translated and grouped into genotype families. Subtype consensus sequences were determined and the type-specific amino acid sequence variants were identified.

Detection of human herpesvirus 6 and JC virus in progressive multifocal leukoencephalopathy complicating follicular lymphoma

Progressive multifocal leukoencephalopathy (PML), a demyelinating infectious disease caused by JC virus (JCV), occurs almost exclusively in immunocompromised patients usually with malignant diseases. We report here a Japanese female with follicular lymphoma who subsequently developed PML. In addition to JCV, human herpesvirus 6 (HHV-6) was detected in the affected brain lesions of the patient by polymerase chain reaction and by in situ hybridization. HHV-6, recognized as a neurotropic virus, is known to be reactivated during immunosuppression and can cause fatal complications such as encephalitis/encephalopathy. It is likely that impaired immunity associated with lymphoma and the additional immunosuppression following cytopenia-inducing chemotherapies predisposed the patient to reactivated HHV-6 infection. Although it remains to be clarified whether HHV-6 plays an important role as a co-agent with JCV in causing demyelination of the brain, our observation alerts physicians to the possible association of HHV-6 with the pathogenesis of PML.

Progressive multifocal leukoencephalopathy in human immunodeficiency virus type 1-infected patients: absence of correlation between JC virus neurovirulence and polymorphisms in the transcriptional control region and the major capsid protein loci

Progressive multifocal leukoencephalopathy (PML) is a rapidly fatal demyelinating disease of the central nervous system related to JC polyomavirus (JCV) replication in oligodendrocytes. PML usually occurs in immunocompromised individuals, especially in the setting of AIDS. Administration of highly active anti-retroviral therapy (HAART) may improve survival prognosis in some, but not all, patients with AIDS-related PML. This observation might be explained by the outgrowth of some JCV variants of increased fitness. To evaluate this hypothesis, two subgroups of five patients with AIDS-related PML, started on HAART after PML diagnosis, were analysed. The non-responder (NR) patients died rapidly despite HAART, while responders (R) had a positive outcome and were still alive. JCV DNA was extracted from cerebrospinal fluid biopsies and two regions of the genome were analysed, the transcriptional control region (TCR) and the major capsid protein gene (VP1). Both regions show different degrees of polymorphism and are recognized as evolving independently. Sequence analysis demonstrated that (i) extensive TCR rearrangements were present in both subgroups of patients, (ii) VP1 sequence polymorphisms could be identified in the BC loop, suggesting the absence of immune selection, and (iii) no genomic marker for JCV specific neurovirulence could be identified in the TCR and VP1 loci.

Oncogenic potential of human neurotropic virus: laboratory and clinical observations

Cancer is a multi-step disease involving a series of genetic alterations that result in the loss of control of cell proliferation and differentiation. Such genetic alterations could emerge from the activation of oncogenes and the loss or malfunctioning of tumor suppressor gene activity. Our understanding of cancer has greatly increased through the use of DNA tumor viruses and their transforming proteins as a biological tool to decipher a cascade of events that lead to deregulation of cell proliferation and subsequent tumor formation. For the past ten years our laboratory has focused on the molecular biology of the human neurotropic papovavirus, JCV. This virus causes progressive multifocal leukoencephalopathy, a fatal neurodegenerative disease of the central nervous system in immunocompromised patients. JCV is a common human virus that infects more than 80% of humans but does not induce any obvious clinical symptoms. The increased incidence of acquired immune deficiency syndrome and the use of immunosuppressive chemotherapy have dramatically raised the incidence of PML. The coincidental occurrence of malignant astrocytes and oligodendrocytes in PML patients, coupled with the induction of glioblastoma in JCV-infected nonhuman primates, provides intriguing speculation on the association between JCV and CNS malignancies. In this report we discuss clinical data and laboratory observations pointing to the direct involvement of JCV in cancer.

JC virus genotypes in France: molecular epidemiology and potential significance for progressive multifocal leukoencephalopathy

JC virus (JCV) induces progressive multifocal leukoencephalopathy (PML), especially in human immunodeficiency virus (HIV)-infected patients. Although JCV genotypes have primarily been associated with geographic patterns, a distinctive neuropathogenicity was recently attributed to genotype 2. A multicenter study was conducted to describe the distribution of JCV genotypes in France and to investigate correlations between genotypes and PML. Genotypes were determined by sequencing 494 bp in the VP1 capsid gene. Peripheral JCV was studied in 65 urine samples from 43 HIV-infected patients and from 22 control subjects. Genotypes 1, 4, 2, and 3 were detected in 52.3%, 30.8%, 12.3%, and 4.6% of the samples, respectively. In 56 brain or cerebrospinal fluid samples, PML-associated JCV of genotypes 1, 2, 4, and 3 was found in 66%, 19.7%, 8.9%, and 5.4%, respectively. Infection with JCV genotypes 1 or 2 was correlated with PML (odds ratio, 3.29). On the other hand, infection with JCV genotype 4 could represent a lower risk for PML.

Pituitary neoplasia induced by expression of human neurotropic polyomavirus, JCV, early genome in transgenic mice

In recent years, there has been mounting evidence pointing to the association of polyomaviruses with a wide range of human cancers. The human neurotropic polyomavirus, JCV, infecting greater than 75% of the human population produces a regulatory protein named T-antigen which is expressed at the early phase of viral lytic infection and plays a critical role in completion of the viral life cycle. Furthermore, this protein has the ability to transform neural cells in vitro and its expression has been detected in several human neural-origin tumors. To further investigate the oncogenic potential of the JCV early protein in vivo, transgenic mice expressing JCV T-antigen under the control of its own promoter were generated. Nearly 50% of the animals developed large, solid masses within the base of the skull by 1 year of age. Evaluation of the location as well as histological and immunohistochemical data suggest that the tumors arise from the pituitary gland. As T-antigen is known to interact with several cell cycle regulators, the neoplasms were analysed for the presence of the tumor suppressor protein, p53. Immunoprecipitation/Western blot analysis demonstrated overexpression of wild-type, but not mutant p53 within tumor tissue. In addition, co-immunoprecipitation established an interaction between p53 and T-antigen and overexpression of p53 downstream target protein, p21/WAF1. This report describes the analysis of inheritable pituitary adenomas induced by expression of the human polyomavirus, JCV T-antigen in transgenic mice where T-antigen disrupts the p53 pathway by binding to and sequestering wild-type p53. This animal model may serve as a useful tool to further evaluate mechanisms of tumorigenesis by JCV T-antigen.

Expression of Bax, Bcl-2, and P53 in progressive multifocal leukoencephalopathy

It has been shown in vitro that JC viral protein can form a complex with wild-type p53 protein, which is a key regulator of both cell proliferation and cell death. Cellular factors, Bax and Bcl-2, are two essential downstream elements involved in p53-dependent apoptosis. To determine whether association of JC virus with p53 protein affects the expression of Bax and Bcl-2 in viral-infected cells in progressive multifocal leukoencephalopathy (PML), we studied the expression of Bax, Bcl-2, and p53 in 14 cases from 13 PML patients by using paraffin immunohistochemistry. Seven of 13 patients were known to be HIV positive. Overexpression of p53 was found in viral-infected oligodendrocytes and some astrocytes in all 14 cases. Intense immunostaining of Bax was strongly expressed in viral-infected oligodendrocytes and astrocytes. Bax immunostaining was also found in macrophages in the demyelinating lesions. Bcl-2 was not detected in viral-infected glial cells. The expression pattern of Bax positive/Bcl-2 negative in viral-infected glial cells suggests that the oligodendrocyte may be undergoing apoptosis which may in turn contribute to the demyelinating process in PML. The coexpression of p53 and Bax in the infected glial cells suggests that p53 detected by immunohistochemistry may still maintain its wild-type function.

Is JC polyoma virus the cause of ulcerative colitis and multiple sclerosis?

JC polyoma virus (JCV) is known to be the cause of the degenerative central nervous system white matter disease progressive multifocal leucoencephalopathy. Recently, JCV DNA has unexpectedly been found in significant quantity in normal colon mucosa and in tissue from colonic carcinomas, with increased quantities in the cancerous tissues. The yield of JCV DNA was increased by use of topoisomerase I, possibly because the JCV DNA was negatively supercoiled. The causes of ulcerative colitis (in which colon cancer is common) and multiple sclerosis are not known. Here I suggest that JCV may play a role in the pathogenesis of these diseases, and discuss methods for testing this hypothesis.

JC virus enters human glial cells by clathrin-dependent receptor-mediated endocytosis

The human polyomavirus JC virus (JCV) is the etiologic agent of a fatal central nervous system (CNS) demyelinating disease known as progressive multifocal leukoencephalopathy (PML). PML occurs predominantly in immunosuppressed patients and has increased dramatically as a result of the AIDS pandemic. The major target cell of JCV infection and lytic replication in the CNS is the oligodendrocyte. The mechanisms by which JCV initiates and establishes infection of these glial cells are not understood. The initial interaction between JCV and glial cells involves virus binding to N-linked glycoproteins containing terminal alpha(2-6)-linked sialic acids. The subsequent steps of entry and targeting of the viral genome to the nucleus have not been described. In this report, we compare the kinetics and mechanisms of infectious entry of JCV into human glial cells with that of the related polyomavirus, simian virus 40 (SV40). We demonstrate that JCV, unlike SV40, enters glial cells by receptor-mediated clathrin-dependent endocytosis.

BAG-1, a novel Bcl-2-interacting protein, activates expression of human JC virus

Transcription of the human polyomavirus JC virus (JCV) genome is regulated by cellular proteins and the large tumour (T) antigen. Earlier studies led to the identification of nuclear factor-1 (NF-1)-binding sites in the JCV enhancer by DNase I protection assays of extracts from retinoic acid (RA)-differentiated P19 embryonal carcinoma (EC) cells. In this study, a cDNA clone that encodes a protein capable of binding to the JCV NF-1 sites was isolated from an RA-differentiated EC cell cDNA library. Sequence analysis revealed that the cDNA isolated was identical to the previously described Bcl-2-interacting protein BAG-1 (Bcl-2-associated athano gene-1). Results from RNA studies indicated that BAG-1 is expressed in several cell types. Co-transfection of a recombinant BAG-1 expression plasmid with JCV promoters indicated that BAG-1 stimulates transcription of the JCV(E) promoter and to a lesser extent the JCV(L) promoter. Mutations in the NF-1 sites in the JCV(E) promoter eliminated the activation by BAG-1. Thus, BAG-1 is a novel transcription factor that may play a role in JCV expression.

Viral variant nucleotide sequences help expose leukocytic positioning in the JC virus pathway to the CNS

The human polyomavirus JCV lytically infects oligodendrocytes of immunosuppressed individuals leading to the fatal demyelinating disease termed progressive multifocal leukoencephalopathy (PML). Dementia, hemiparesis, and hemianopsia are the predominant presenting signs of PML. Asymptomatic JCV infection is common worldwide with approximately 80% of adults testing positive for JCV antibodies. In addition to the brain, JCV has been shown to infect tonsil, lymphoid, bone marrow, and kidney tissues. Viral variants, classified according to the nucleotide sequences of their regulatory regions, are being mapped in human tissues and cell types to help trace the pathway of JCV from a site of initial infection to target oligodendrocytes. In most literature, a dichotomy of the JCV regulatory region structure exists by tissue. B lymphocytes, however, have demonstrated the capacity to harbor JCV of diverse regulatory regions, which helps position their interaction with virus amid every stage of infection and implicates a lymphocytic role in latency.

Detection of JC virus DNA in human tonsil tissue: evidence for site of initial viral infection

Progressive multifocal leukoencephalopathy is a demyelinating disease of the human central nervous system that results from lytic infection of oligodendrocytes by the polyomavirus JC (JCV). Originally, JCV was thought to replicate exclusively in human glial cells, specifically oligodendrocytes. However, we have recently shown that JCV can replicate in cells of lymphoid origin such as hematopoietic precursor cells, B lymphocytes, and tonsillar stromal cells. To determine whether tonsils harbor JCV, we tested a total of 54 tonsils, 38 from children and 16 from adult donors. Nested PCRs with primer sets specific for the viral T protein and regulatory regions were used for the detection of JCV DNA. JCV DNA was detected in 21 of 54 tonsil tissues, or 39% (15 of 38 children and 6 of 16 adults) by using regulatory-region primers and in 19 of 54 tonsil tissues, or 35% (13 of 38 children and 6 of 16 adults) by using the T-protein primers. The DNA extracted from children's nondissected tonsil tissue, isolated tonsillar lymphocytes, and isolated stromal cells that demonstrated PCR amplification of the JCV regulatory region underwent cloning and nucleotide sequencing. Of the regulatory-region sequences obtained, nearly all contained tandem repeat arrangements. Clones originating from nondissected tonsil tissue and tonsillar lymphocytes were found to have sequences predominantly of the Mad-1 prototype strain, whereas the majority of clones from the DNA of tonsillar stromal cells had sequences characteristic of the Mad-8br strain of JCV. A few clones demonstrated structures other than tandem repeats but were isolated only from tonsillar lymphocytes. These data provide the first evidence of the JCV genome in tonsil tissue and suggest that tonsils may serve as an initial site of viral infection.