Role of cell cycle regulators in tumor formation in transgenic mice expressing the human neurotropic virus, JCV, early protein

Revisiting JC virus and progressive multifocal leukoencephalopathy

Since its definition 65 years ago, progressive multifocal leukoencephalopathy (PML) has continued to devastate a growing population of immunosuppressed patients despite major advances in our understanding of the causative JC virus (JCV). Unless contained by the immune system, JCV lyses host oligodendrocytes collateral to its life cycle, leading to demyelination, neurodegeneration, and death. Novel treatments have stagnated in the absence of an animal model while current antiviral agents fail to address the now ubiquitous polyomavirus. In this review, we highlight the established pathogenesis by which JCV infection progresses to PML, highlighting major challenges that must be overcome to eliminate the underlying virus and, therefore, the debilitating disease.

The oncogenic roles of JC polyomavirus in cancer

JC polyomavirus (JCPyV) belongs to the human polyomavirus family. Based on alternative splicing, the early region encodes the large and small T antigens, while the late region encodes the capsid structural proteins (VP1, VP2, and VP3) and the agnoprotein. The regulatory transcription factors for JCPyV include Sp1, TCF-4, DDX1, YB-1, LCP-1, Purα, GF-1, and NF-1. JCPyV enters tonsillar tissue through the intake of raw sewage, inhalation of air droplets, or parent-to-child transmission. It persists quiescently in lymphoid and renal tissues during latency. Both TGF-β1 and TNF-α stimulates JCPyV multiplication, while interferon-γ suppresses the process. The distinct distribution of caspid receptors (α-2, 6-linked sialic acid, non-sialylated glycosaminoglycans, and serotonin) determines the infection capabilities of JCPyV virions, and JCPyV entry is mediated by clathrin-mediated endocytosis. In permissive cells, JCPyV undergoes lytic proliferation and causes progressive multifocal leukoencephalopathy, while its DNA is inserted into genomic DNA and leads to carcinogenesis in non-permissive cells. T antigen targets p53, β-catenin, IRS, Rb, TGF-β1, PI3K/Akt and AMPK signal pathways in cancer cells. Intracranial injection of T antigen into animals results in neural tumors, and transgenic mice develop neural tumors, lens tumor, breast cancer, gastric, Vater’s, colorectal and pancreatic cancers, insulinoma, and hepatocellular carcinoma. Additionally, JCPyV DNA and its encoded products can be detected in the brain tissues of PML patients and brain, oral, esophageal, gastric, colorectal, breast, cervical, pancreatic, and hepatocellular cancer tissues. Therefore, JCPyV might represent an etiological risk factor for carcinogenesis and should be evaluated for early prevention, diagnosis, and treatment of cancers.

[The phenomenon of pseudotumorous cross immunohistochemical reactivity of glia in progressive multifocal leukoencephalopathy]

Progressive multifocal leukoencephalopathy (PML) is a subacute demyelinating brain damage caused by infection of oligodendrocytes and astrocytes with the lytic JC virus on the background of immunosuppression. A case report of PML with a tumor-like course is presented. Morphological diagnostics revealed non-specific staining of antibodies to Ki-67, p53, IDH1, NF and Vim in the nuclei of gliocytes affected by the JC virus. Histological examination and microscopic evaluation of the changes in the brain for the diagnosis of PML is a priority. The recommended intravital biopsy does not always help in clear verification of PML due to the limited volume of tissue fragments presented for research. For the correct interpretation of changes during an intravital pathological examination and verification of PML, it is important to take material during a stereotaxic biopsy, not only from the center, but from the edges and perifocal zone of the altered tissues for the possibility of a spatial histological assessment of the pathological process.

Induction of Brain Tumors by the Archetype Strain of Human Neurotropic JCPyV in a Transgenic Mouse Model

JC Virus (JCPyV), a member of the Polyomaviridiæ family, is a human neurotropic virus with world-wide distribution. JCPyV is the established opportunistic infectious agent of progressive multifocal leukoencephalopathy, a fatal demyelinating disease, which results from the cytolytic infection of oligodendrocytes. Mutations in the regulatory region of JCPyV determine the different viral strains. Mad-1 the strain associated with PML contains two 98 base pair repeats, whereas the archetype strain (CY), which is the transmissible form of JCPyV, contains only one 98 tandem with two insertions of 62 and 23 base pairs respectively. The oncogenicity of JCPyV has been suspected since direct inoculation into the brain of rodents and primates resulted in the development of brain tumors and has been attributed to the viral protein, T-Antigen. To further understand the oncogenicity of JCPyV, a transgenic mouse colony containing the early region of the archetype strain (CY), under the regulation of its own promoter was generated. These transgenic animals developed tumors of neural crest origin, including: primitive neuroectodermal tumors, medulloblastomas, adrenal neuroblastomas, pituitary tumors, malignant peripheral nerve sheath tumors, and glioblastomas. Neoplastic cells from all different phenotypes express T-Antigen. The close parallels between the tumors developed by these transgenic animals and human CNS tumors make this animal model an excellent tool for the study of viral oncogenesis.

PAM (PIK3/AKT/mTOR) signaling in glia: potential contributions to brain tumors in aging

Despite a growing proportion of aged individuals at risk for developing cancer in the brain, the prognosis for these conditions remains abnormally poor due to limited knowledge of underlying mechanisms and minimal treatment options. While cancer metabolism in other organs is commonly associated with upregulated glycolysis (i.e. Warburg effect) and hyperactivation of PIK3/AKT/mTOR (PAM) pathways, the unique bioenergetic demands of the central nervous system may interact with these oncogenic processes to promote tumor progression in aging. Specifically, constitutive glycolysis and PIK3/AKT/mTOR signaling in glia may be dysregulated by age-dependent alterations in neurometabolic demands, ultimately contributing to pathological processes otherwise associated with PIK3/AKT/mTOR induction (e.g. cell cycle entry, impaired autophagy, dysregulated inflammation). Although several limitations to this theoretical model exist, the consideration of aberrant PIK3/AKT/mTOR signaling in glia during aging elucidates several therapeutic opportunities for brain tumors, including non-pharmacological interventions.

JCPyV T-Antigen Activation of the Anti-Apoptotic Survivin Promoter-Its Role in the Development of Progressive Multifocal Leukoencephalopathy

Progressive Multifocal Leukoencephalopathy (PML) is a fatal demyelinating disease of the CNS, resulting from the lytic infection of oligodendrocytes by the human neurotropic polyomavirus JC (JCPyV), typically associated with severe immunocompromised states and, in recent years, with the use of immunotherapies. Apoptosis is a homeostatic mechanism to dispose of senescent or damaged cells, including virally infected cells, triggered in the vast majority of viral infections of the brain. Previously, we showed upregulation of the normally dormant anti-apoptotic protein Survivin in cases of PML, which—in vitro—resulted in protection from apoptosis in JCPyV-infected primary cultures of astrocytes and oligodendrocytes. In the present study, we first demonstrate the absence of apoptotic DNA fragmentation and the lack of caspase activity in 16 cases of PML. We also identified the viral protein large T-Antigen as being responsible for the activation of the Survivin promoter. Chromatin Immunoprecipitation assay shows a direct binding between T-Antigen and the Survivin promoter DNA. Finally, we have identified the specific region of T-Antigen, spanning from amino acids 266 and 688, which binds to Survivin and translocates it to the nucleus, providing evidence of a mechanism that results in the efficient replication of JCPyV and a potential target for novel therapies.

A Comprehensive Proteomics Analysis of the JC Virus (JCV) Large and Small Tumor Antigen Interacting Proteins: Large T Primarily Targets the Host Protein Complexes with V-ATPase and Ubiquitin Ligase Activities While Small t Mostly Associates with Those Having Phosphatase and Chromatin-Remodeling Functions

The oncogenic potential of both the polyomavirus large (LT-Ag) and small (Sm t-Ag) tumor antigens has been previously demonstrated in both tissue culture and animal models. Even the contribution of the MCPyV tumor antigens to the development of an aggressive human skin cancer, Merkel cell carcinoma, has been recently established. To date, the known primary targets of these tumor antigens include several tumor suppressors such as pRb, p53, and PP2A. However, a comprehensive list of the host proteins targeted by these proteins remains largely unknown. Here, we report the first interactome of JCV LT-Ag and Sm t-Ag by employing two independent “affinity purification/mass spectroscopy” (AP/MS) assays. The proteomics data identified novel targets for both tumor antigens while confirming some of the previously reported interactions. LT-Ag was found to primarily target the protein complexes with ATPase (v-ATPase and Smc5/6 complex), phosphatase (PP4 and PP1), and ligase (E3-ubiquitin) activities. In contrast, the major targets of Sm t-Ag were identified as Smarca1/6, AIFM1, SdhA/B, PP2A, and p53. The interactions between “LT-Ag and SdhB”, “Sm t-Ag and Smarca5”, and “Sm t-Ag and SDH” were further validated by biochemical assays. Interestingly, perturbations in some of the LT-Ag and Sm t-Ag targets identified in this study were previously shown to be associated with oncogenesis, suggesting new roles for both tumor antigens in novel oncogenic pathways. This comprehensive data establishes new foundations to further unravel the new roles for JCV tumor antigens in oncogenesis and the viral life cycle.

The Role of the JC Virus in Central Nervous System Tumorigenesis

Cancer is the second leading cause of mortality worldwide. The study of DNA tumor-inducing viruses and their oncoproteins as a causative agent in cancer initiation and tumor progression has greatly enhanced our understanding of cancer cell biology. The initiation of oncogenesis is a complex process. Specific gene mutations cause functional changes in the cell that ultimately result in the inability to regulate cell differentiation and proliferation effectively. The human neurotropic Polyomavirus JC (JCV) belongs to the family Polyomaviridae and it is the causative agent of progressive multifocal leukoencephalopathy (PML), which is a fatal neurodegenerative disease in an immunosuppressed state. Sero-epidemiological studies have indicated JCV infection is prevalent in the population (85%) and that initial infection usually occurs during childhood. The JC virus has small circular, double-stranded DNA that includes coding sequences for viral early and late proteins. Persistence of the virus in the brain and other tissues, as well as its potential to transform cells, has made it a subject of study for its role in brain tumor development. Earlier observation of malignant astrocytes and oligodendrocytes in PML, as well as glioblastoma formation in non-human primates inoculated with JCV, led to the hypothesis that JCV plays a role in central nervous system (CNS) tumorigenesis. Some studies have reported the presence of both JC viral DNA and its proteins in several primary brain tumor specimens. The discovery of new Polyomaviruses such as the Merkel cell Polyomavirus, which is associated with Merkel cell carcinomas in humans, ignited our interest in the role of the JC virus in CNS tumors. The current evidence known about JCV and its effects, which are sufficient to produce tumors in animal models, suggest it can be a causative factor in central nervous system tumorigenesis. However, there is no clear association between JCV presence in CNS and its ability to initiate CNS cancer and tumor formation in humans. In this review, we will discuss the correlation between JCV and tumorigenesis of CNS in animal models, and we will give an overview of the current evidence for the JC virus’s role in brain tumor formation.

Association between JC virus and colorectal cancer: systematic review and meta-analysis

Objective: Given the probable role of JC virus in associate with increasing the odds of colorectal cancer, this study was conducted systematically to evaluate the association between JC virus and colorectal cancer.Materials and methods: Systematic reviews of the articles published prior to January 1, 2019 without time and place limitations were done independently through the PubMed, ISI, EMBASE and Medline main databases. The heterogeneity rate was assessed through I2, Chi2 and Tau2, and the sensitivity analysis and meta-regression were used to investigate the source of heterogeneity among the studies.Results: 24 studies with a sample size of 2576 were finally entered into the meta-analysis. The results showed that the prevalence of JC virus in colorectal cancer tissues was about 43% (95% CI: 29% -58%). The meta-analysis results also showed that the presence of JCV in colorectal tissues increased the odds of colorectal cancer 4.70 times as much (OR Pooled = 4.70; 95% CI: 2.95-7.50). Also, the results of the sub-group analysis indicated that the presence of JC virus, compared with the tissues adjacent to the tumour and the healthy control tissues, increased the odds of colorectal cancer (OR Pooled = 4.50, 95% CI: 2.09-9.65 and OR Pooled = 4.70, 95% CI: 2.95-7.50) respectively.Conclusion: The meta-analysis showed that as an oncogene virus, JC could increase the odds of colorectal cancer, reinforcing the hypothesis on the role of viral factors in the pathogenesis of cancers.

The RB tumor suppressor at the intersection of proliferation and immunity: relevance to disease immune evasion and immunotherapy

The retinoblastoma tumor suppressor (RB) was the first identified tumor suppressor based on germline predisposition to the pediatric eye tumor. Since these early studies, it has become apparent that the functional inactivation of RB is a common event in nearly all human malignancy. A great deal of research has gone into understanding how the loss of RB promotes tumor etiology and progression. Since malignant tumors are characterized by aberrant cell division, much of this research has focused upon the ability of RB to regulate the cell cycle by repression of proliferation-related genes. However, it is progressively understood that RB is an important mediator of multiple functions. One area that is gaining progressive interest is the emerging role for RB in regulating diverse features of immune function. These findings suggest that RB is more than simply a regulator of cellular proliferation; it is at the crossroads of proliferation and the immune response. Here we review the data related to the functional roles of RB on the immune system, relevance to immune evasion, and potential significance to the response to immune-therapy.

Human glial chimeric mice reveal astrocytic dependence of JC virus infection

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease triggered by infection with the human gliotropic JC virus (JCV). Due to the human-selective nature of the virus, there are no animal models available to investigate JCV pathogenesis. To address this issue, we developed mice with humanized white matter by engrafting human glial progenitor cells (GPCs) into neonatal immunodeficient and myelin-deficient mice. Intracerebral delivery of JCV resulted in infection and subsequent demyelination of these chimeric mice. Human GPCs and astrocytes were infected more readily than oligodendrocytes, and viral replication was noted primarily in human astrocytes and GPCs rather than oligodendrocytes, which instead expressed early viral T antigens and exhibited apoptotic death. Engraftment of human GPCs in normally myelinated and immunodeficient mice resulted in humanized white matter that was chimeric for human astrocytes and GPCs. JCV effectively propagated in these mice, which indicates that astroglial infection is sufficient for JCV spread. Sequencing revealed progressive mutation of the JCV capsid protein VP1 after infection, suggesting that PML may evolve with active infection. These results indicate that the principal CNS targets for JCV infection are astrocytes and GPCs and that infection is associated with progressive mutation, while demyelination is a secondary occurrence, following T antigen-triggered oligodendroglial apoptosis. More broadly, this study provides a model by which to further assess the biology and treatment of human-specific gliotropic viruses.

Prevalence of JC polyomavirus large T antigen sequences among Iranian patients with central nervous system tumors

The human neurotropic JC virus (JCV) is of significant interest due to its experimental neuro- oncogenic potential. In clinical samples from human central nervous system (CNS) tumors, detection of JCV sequences suggests a possible association with CNS neoplasms, but the results are discrepant worldwide. To assess the prevalence of JCV sequences in Iranian patients with primary and metastatic CNS malignancies, a total of 58 fresh CNS tumors were examined by quantitative real-time PCR targeting the JCV large T antigen (LT-Ag) gene, and JCV DNA load was determined as viral copy number per cell. All patients were immunocompetent, and none of them had received immunosuppressive therapy before surgical operation. JC virus LT-Ag sequences were found in a total of 15 (25.9 %) out of the 58 tested samples. In primary CNS tumors, JCV sequences were identified more frequently in meningiomas (50.0 %) and schwannomas (35.7 %). In metastatic CNS tumors, JCV LT-Ag was identified in one case with brain adenocarcinoma originating from lung cancer. No statistically significant association between JCV positivity and various types of CNS malignancies was observed (P = 0.565). The mean JCV LT-Ag copy number in 15 positive cases was 1.8 × 10(-4) ± 4.5 × 10(-4) copies per cell (range 1.0 × 10(-5)-1.78 × 10(-3) copies per cell). An inverse correlation between white blood cell (WBC) count and JCV copy number was observed, but this correlation was not statistically significant (R = -0.198, P = 0.480). This study provides the first data on the prevalence of JCV in primary and metastatic CNS tumors from Iranian patients.

Immune surveillance and response to JC virus infection and PML

The ubiquitous human polyomavirus JC virus (JCV) is the established etiological agent of the debilitating and often fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). Most healthy individuals have been infected with JCV and generate an immune response to the virus, yet remain persistently infected at subclinical levels. The onset of PML is rare in the general population, but has become an increasing concern in immunocompromised patients, where reactivation of JCV leads to uncontrolled replication in the CNS. Understanding viral persistence and the normal immune response to JCV provides insight into the circumstances which could lead to viral resurgence. Further, clues on the potential mechanisms of reactivation may be gleaned from the crosstalk among JCV and HIV-1, as well as the impact of monoclonal antibody therapies used for the treatment of autoimmune disorders, including multiple sclerosis, on the development of PML. In this review, we will discuss what is known about viral persistence and the immune response to JCV replication in immunocompromised individuals to elucidate the deficiencies in viral containment that permit viral reactivation and spread.

Human polyoma JC virus minor capsid proteins, VP2 and VP3, enhance large T antigen binding to the origin of viral DNA replication: evidence for their involvement in regulation of the viral DNA replication

JC virus (JCV) lytically infects the oligodendrocytes in the central nervous system in a subset of immunocompromized patients and causes the demyelinating disease, progressive multifocal leukoencephalopathy. JCV replicates and assembles into infectious virions in the nucleus. However, understanding the molecular mechanisms of its virion biogenesis remains elusive. In this report, we have attempted to shed more light on this process by investigating molecular interactions between large T antigen (LT-Ag), Hsp70 and minor capsid proteins, VP2/VP3. We demonstrated that Hsp70 interacts with VP2/VP3 and LT-Ag; and accumulates heavily in the nucleus of the infected cells. We also showed that VP2/VP3 associates with LT-Ag through their DNA binding domains resulting in enhancement in LT-Ag DNA binding to Ori and induction in viral DNA replication. Altogether, our results suggest that VP2/VP3 and Hsp70 actively participate in JCV DNA replication and may play critical roles in coupling of viral DNA replication to virion encapsidation.

Pulmonary tumors associated with the JC virus T-antigen in a transgenic mouse model

Many attempts to demonstrate the oncogenic role of the JC virus (JCV) have been partially successful in producing brain tumors, either by direct inoculation of JCV into the brain or in transgenic models in rodents. We previously reported the presence of JCV DNA with a relatively high incidence in pulmonary and digestive organs. However, we could not prove the oncogenic role of JCV. We prepared a transgene composed of the K19 promoter, specific to bronchial epithelium with the JCV T-antigen and established transgenic (TG) mice. Pulmonary tumors were detected without any metastasis in 2 out of 15 (13.3%) 16-month-old K19/JCV T-antigen TG mice. Using immunohistochemistry (IHC), these tumors showed JCV T-antigen, p53 and CK 19 expression, but not expression of nuclear and cytoplasmic β-catenin and insulin receptor substrate 1 (IRS1). IHC revealed the same expression pattern as in the bronchial epithelium of the TG mice. One tumor, which was examined with laser capture microdissection and molecular biological tools, demonstrated an EGFR mutation but not a K-ras mutation. We propose that the pulmonary tumors were derived from the JCV T-antigen in a TG mouse model. These findings shed light on pulmonary carcinogenesis.

Neurofibromatosis type 2 tumor suppressor protein, NF2, induces proteasome-mediated degradation of JC virus T-antigen in human glioblastoma

Neurofibromatosis type 2 protein (NF2) has been shown to act as tumor suppressor primarily through its functions as a cytoskeletal scaffold. However, NF2 can also be found in the nucleus, where its role is less clear. Previously, our group has identified JC virus (JCV) tumor antigen (T-antigen) as a nuclear binding partner for NF2 in tumors derived from JCV T-antigen transgenic mice. The association of NF2 with T-antigen in neuronal origin tumors suggests a potential role for NF2 in regulating the expression of the JCV T-antigen. Here, we report that NF2 suppresses T-antigen protein expression in U-87 MG human glioblastoma cells, which subsequently reduces T-antigen-mediated regulation of the JCV promoter. When T-antigen mRNA was quantified, it was determined that increasing expression of NF2 correlated with an accumulation of T-antigen mRNA; however, a decrease in T-antigen at the protein level was observed. NF2 was found to promote degradation of ubiquitin bound T-antigen protein via a proteasome dependent pathway concomitant with the accumulation of the JCV early mRNA encoding T-antigen. The interaction between T-antigen and NF2 maps to the FERM domain of NF2, which has been shown previously to be responsible for its tumor suppressor activity. Co-immunoprecipitation assays revealed a ternary complex among NF2, T-antigen, and the tumor suppressor protein, p53 within a glioblastoma cell line. Further, these proteins were detected in various degrees in patient tumor tissue, suggesting that these associations may occur in vivo. Collectively, these results demonstrate that NF2 negatively regulates JCV T-antigen expression by proteasome-mediated degradation, and suggest a novel role for NF2 as a suppressor of JCV T-antigen-induced cell cycle regulation.

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.

Nuclear IRS-1 and cancer

The family of insulin receptor substrates (IRS) consists of four proteins (IRS-1-IRS-4), which were initially characterized as typical cytosolic adaptor proteins involved in insulin receptor (IR) and insulin-like growth factor I receptor (IGF-IR) signaling. The first cloned and characterized member of the IRS family, IRS-1, has a predicted molecular weight of 132 kDa, however, as a result of its extensive serine phosphorylation it separates on a SDS gel as a band of approximately 160-185 kDa. In addition to its metabolic and growth-promoting functions, IRS-1 is also suspected to play a role in malignant transformation. The mechanism by which IRS-1 supports tumor growth is not fully understood, and the argument that IRS-1 merely amplifies the signal from the IGF-1R and/or IR requires further investigation. Almost a decade ago, we reported the presence of nuclear IRS-1 in medulloblastoma clinical samples, which express viral oncoprotein, large T-antigen of human polyomavirus JC (JCV T-antigen). This first demonstration of nuclear IRS-1 was confirmed by several other laboratories. Nuclear IRS-1 was also detected by cells expressing the SV40 T-antigen, v-Src, in immortalized fibroblasts stimulated with IGF-I, in hepatocytes, 32D cells, and in an osteosarcoma cell line. More recently, nuclear IRS-1 was detected in breast cancer cells in association with estrogen receptor alpha (ERα), and in JC virus negative medulloblastoma cells expressing estrogen receptor beta (ERβ), further implicating nuclear IRS-1 in cellular transformation. Here, we discuss how nuclear IRS-1 acting on DNA repair fidelity, transcriptional activity, and cell growth can support tumor development and progression.

JC virus T-antigen regulates glucose metabolic pathways in brain tumor cells

Recent studies have reported the detection of the human neurotropic virus, JCV, in a significant population of brain tumors, including medulloblastomas. Accordingly, expression of the JCV early protein, T-antigen, which has transforming activity in cell culture and in transgenic mice, results in the development of a broad range of tumors of neural crest and glial origin. Evidently, the association of T-antigen with a range of tumor-suppressor proteins, including p53 and pRb, and signaling molecules, such as β-catenin and IRS-1, plays a role in the oncogenic function of JCV T-antigen. We demonstrate that T-antigen expression is suppressed by glucose deprivation in medulloblastoma cells and in glioblastoma xenografts that both endogenously express T-antigen. Mechanistic studies indicate that glucose deprivation-mediated suppression of T-antigen is partly influenced by 5′-activated AMP kinase (AMPK), an important sensor of the AMP/ATP ratio in cells. In addition, glucose deprivation-induced cell cycle arrest in the G1 phase is blocked with AMPK inhibition, which also prevents T-antigen downregulation. Furthermore, T-antigen prevents G1 arrest and sustains cells in the G2 phase during glucose deprivation. On a functional level, T-antigen downregulation is partially dependent on reactive oxygen species (ROS) production during glucose deprivation, and T-antigen prevents ROS induction, loss of ATP production, and cytotoxicity induced by glucose deprivation. Additionally, we have found that T-antigen is downregulated by the glycolytic inhibitor, 2-deoxy-D-glucose (2-DG), and the pentose phosphate inhibitors, 6-aminonicotinamide and oxythiamine, and that T-antigen modulates expression of the glycolytic enzyme, hexokinase 2 (HK2), and the pentose phosphate enzyme, transaldolase-1 (TALDO1), indicating a potential link between T-antigen and metabolic regulation. These studies point to the possible involvement of JCV T-antigen in medulloblastoma proliferation and the metabolic phenotype and may enhance our understanding of the role of viral proteins in glycolytic tumor metabolism, thus providing useful targets for the treatment of virus-induced tumors.

Detection of human polyomavirus proteins, T-antigen and agnoprotein, in human tumor tissue arrays

Expression of the human polyomavirus JCV genome in several experimental animals induces a variety of neural origin tumors. The viral proteins, T-antigen and Agnoprotein, contribute to the oncogenesis of JCV by associating with several tumor suppressor proteins and dysregulating signaling pathways, which results in uncontrolled cell proliferation. In addition, T-antigen and Agnoprotein have been associated with DNA damage and interfering with DNA repair mechanisms. In this study, we have utilized commercially available tissue arrays of human tumors of various origins and demonstrated the expression of both T-antigen and Agnoprotein in some, but not all, tumors of neural and non-neural origin. Most notably, more than 40% of human glioblastomas and greater than 30% of colon adenocarcinomas express viral proteins. The detection of viral transforming proteins, T-antigen and Agnoprotein in the absence of viral capsid proteins suggests a role for JCV in the development and/or progression of human tumors. These results invite further large-scale investigation on the role of polyomaviruses, particularly JCV in the pathogenesis of human cancer.

JC virus in the pathogenesis of colorectal cancer, an etiological agent or another component in a multistep process?

JCV infection occurs early in childhood and last throughout life. JCV has been associated to colorectal cancer and might contribute to the cancer phenotype by several mechanisms. Among JCV proteins, particularly two of them, large T-antigen and agnoprotein, can interfere with cell cycle control and genomic instability mechanisms, but other viral proteins might also contribute to the process. Part of viral DNA sequences are detected in carcinoma lesions, but less frequently in adenomas, and not in the normal surrounding tissue, suggesting they are integrated in the host cell genome and these integrations have been selected; in addition viral integration can cause a gene, or chromosomal damage. The inflammatory infiltration caused by a local chronic viral infection in the intestine can contribute to the selection and expansion of a tumor prone cell in a cytokine rich microenvironment. JCV may not be the cause of colorectal cancer, but it can be a relevant risk factor and able to facilitate progression at one or several stages in tumor progression. JCV transient effects might lead to selective expansion of tumor cells. Since there is not a direct cause and effect relationship, JCV infection may be an alternative to low frequency cancer predisposition genes.

Human polyoma viruses and disease with emphasis on clinical BK and JC

Polyoma viruses are ubiquitous infecting many different mammalian species including humans. There are five known human polyoma viruses. JC virus and BK virus are two polyoma viruses identified nearly three decades ago. Recently WU, KI and Merkel cell polyoma viruses have been isolated from humans. The exact role of these three newly discovered viruses in human disease is not known. Most human polyoma disease is caused by BK and JC viruses which are usually acquired in childhood. Approximately 50-80% of humans have seropositivity to these viruses. Clinically apparent diseases in immunocompetent hosts are extremely rare. These viruses remain latent possibly in the lymphoid organs, neuronal tissue, and kidney and under the circumstances of severe immunosuppression both these viruses reactivate. Neurotropic JC virus reaches the brain and causes progressive multifocal leukoencephalopathy, a demyelinating disease of the central nervous system with a high mortality rate. BK virus is urotheliotropic and its reactivation causes a form of interstitial nephritis, known as BK or polyoma virus associated nephropathy which is associated with high graft loss if not recognized early. There are no known effective antiviral agents for any of the polyoma viruses.

IGF-IR-dependent expression of Survivin is required for T-antigen-mediated protection from apoptosis and proliferation of neural progenitors

The Insulin-like Growth Factor-1 Receptor (IGF-IR) and the human polyomavirus JCV protein, T-Antigen cooperate in the transformation of neuronal precursors in the cerebellum, which may be a contributing factor in the development of brain tumors. Since it is not clear why T-Antigen requires IGF-IR for transformation, we investigated this process in neural progenitors from IGF-IR knockout embryos (ko-IGF-IR) and from their wild type non-transgenic littermates (wt-IGF-IR). In contrast to wt-IGF-IR, the brain and dorsal root ganglia of ko-IGF-IR embryos showed low levels of the anti-apoptotic protein Survivin, accompanied by elevated numbers of apoptotic neurons and an earlier differentiation phenotype. In wt-IGF-IR neural progenitors in vitro, induction of T-Antigen expression tripled the expression of Survivin, and accelerated cell proliferation. In ko-IGF-IR progenitors induction of T-Antigen failed to increase Survivin, resulting in massive apoptosis. Importantly, ectopic expression of Survivin protected ko-IGF-IR progenitor cells from apoptosis and siRNA inhibition of Survivin activated apoptosis in wt-IGF-IR progenitors expressing T-Antigen. Our results indicate that reactivation of the anti-apoptotic Survivin may be a critical step in JCV T-Antigen induced transformation, which in neural progenitors requires IGF-IR.

Modulation of PML protein expression regulates JCV infection

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

Evidence for modulation of BAG3 by polyomavirus JC early protein

Polyomavirus JC (JCV) infects oligodendrocytes and astrocytes in the brain and is the cause of the demyelinating disease progressive multifocal leukoencephalopathy (PML). In cell culture, JCV infection is characterized by severe damage to cellular DNA, which begins early in infection, and a viral cytopathic effect, which is observed late in infection. Nevertheless, these JCV-infected cells show a low level of apoptosis, at both the early and late stages of infection. This suggests that there is conflicting interplay between viral anti-apoptotic pathways that seek to optimize virus production, e.g. through T antigen (T-Ag)-p53 interaction, and cellular pro-apoptotic pathways that seek to eliminate virally infected cells. The apoptosis regulatory protein BAG3 is a member of the human Bcl-2-associated athanogene (BAG) family of proteins, which function as molecular co-chaperones through their interaction with Hsc70/Hsp70 and function in the regulation of the cellular stress response, proliferation and apoptosis. This study showed that BAG3 protein is downregulated upon JCV infection and that this effect is mediated by JCV T-Ag via repression of the BAG3 promoter. The site of action of T-Ag was mapped to an AP2 site in the BAG3 promoter, and gel shift and chromatin immunoprecipitation assays showed that T-Ag inhibited AP2 binding to this site, resulting in downregulation of BAG3 promoter expression. Using BAG3 and T-Ag expression and BAG3 siRNA, it was found that BAG3 and T-Ag had antagonistic effects on the induction of apoptosis, being anti-apoptotic and pro-apoptotic, respectively. The significance of these interactions to the JCV life cycle is discussed.

JC virus infection in colorectal neoplasia that develops after liver transplantation

PURPOSE

Liver transplant recepients (LTRs) have an increased risk of colorectal neoplasia. The mechanism responsible for this is unknown. JCV encodes for TAg and has been implicated in colorectal carcinogenesis. We hypothesized that the use of immunosuppression in LTRs facilitates activation of JCV and is responsible for the increased risk of neoplasia.

EXPERIMENTAL DESIGN

JCV TAg DNA and protein expression were determined in normal colonic epithelium (n = 15) and adenomatous polyps (n = 26) from LTRs and compared with tissue samples from control patients (normal colon, n = 21; adenomas, n = 40). Apoptosis and proliferation were determined by M30 and Ki-67 immunoreactivity, respectively.

RESULTS

JCV TAg DNA was found in 10 of 15 (67%) of normal colonic mucosa from LTRs compared with 5 of 21 (24%) of control normal mucosa (P = 0.025). JCV TAg DNA was detected in 16 of 26 (62%) of the adenomas from LTRs and in 20 of 40 (50%) of control adenomas. JCV TAg protein was expressed in 13 of 26 (50%) adenomas from LTRs versus 2 of 40 (5%) of adenomas from controls (P < 0.001). In adenomas from LTRs, the mean proliferative activity was higher compared with controls (60.3 +/- 3.2% versus 42.7 +/- 2.8%, P < 0.001), whereas mean apoptotic indices were lower in LTRs (0.29 +/- 0.08% versus 0.39 +/- 0.06%, P = 0.05).

CONCLUSIONS

The presence of JCV in the colorectal mucosa and adenomas from LTRs, in concert with the use of immunosuppressive agents, suggests that JCV may undergo reactivation, and the subsequent TAg protein expression might explain the increased risk of colorectal neoplasia in LTRs.

Potential mechanisms of the human polyomavirus JC in neural oncogenesis

The human polyomavirus JC (JCV) is a small DNA tumor virus and the etiologic agent of the progressive multifocal leukoencephalopathy. In progressive multifocal leukoencephalopathy, active JCV replication causes the lytic destruction of oligodendrocytes. The normal immune system prevents JCV replication and suppresses the virus into a state of latency so that expression of viral proteins cannot be detected. In a cellular context that is nonpermissive for viral replication, JCV can affect oncogenic transformation. For example, JCV is highly tumorigenic when inoculated into experimental animals, including rodents and monkeys. In these animal tumors, there is expression of early T-antigen but not of late capsid proteins, nor is there viral replication. Moreover, mice transgenic for JCV T-antigen alone develop tumors of neural tube origin. Detection of JCV genomic sequences and expression of viral T-antigen and agnoprotein suggest a possible association of this virus with a variety of human brain and non-CNS tumors. Here, we discuss the mechanisms involved in JCV oncogenesis, briefly review studies that do and do not support a causative role for this virus in human CNS tumors, and identify key issues for future research.

The role of viral and bacterial pathogens in gastrointestinal cancer

The association of Helicobacter pylori (H. pylori) with gastric cancer is thus far the best understood model to comprehend the causal relationship between a microbial pathogen and cancer in the human gastrointestinal tract. Besides H. pylori, a variety of other pathogens are now being recognized as potential carcinogens in different settings of human cancer. In this context, viral causes of human cancers are central to the issue since these account for 10-20% of cancers worldwide. In the case of H. pylori and gastric cancer, as well as the human papillomavirus and anal cancer, the causal relationship between the infectious agent and the related cancer in the gastrointestinal tract has been clearly confirmed by epidemiological and experimental studies. Similarly, Epstein-Barr virus and the oncogenic JC virus are being suggested as possible causative agents for cancers in the upper and lower gastrointestinal tract. This review discusses various viral and microbial pathogens and their oncogenic properties in the evolution of gastrointestinal carcinogenesis and summarizes the available experimental data make a convincing agreement favoring the associations between infectious agents and specific human cancers.

High JC virus load in tongue carcinomas may be a risk factor for tongue tumorigenesis

The John Cunningham virus (JCV) asymptomatically infects a large proportion (approximately 90%) of the population worldwide but may be activated in immunodeficient patients, resulting in progressive multifocal leukoencephalopathy. Recent reports demonstrated its oncogenic role in malignancies. In this paper, the presence of JCV-targeting T antigen was investigated in tongue carcinoma (TC, n = 39), dysplastic tongue epithelium (DTE, n = 15) and glossitis (n = 15) using real-time polymerase chain reaction (PCR) and in situ PCR and immunohistochemistry, and JCV copies were analyzed with the clinicopathological parameters of TCs. The results demonstrated that glossitis and DTEs had significantly lower copies of JCV (410.5 +/- 44.3 and 658.3 +/- 53.3 copies/mug DNA respectively) than TCs (981.5 +/- 14.0, p < 0.05). When they were divided into three groups with 0-200 copies/mug DNA (low), 201-1,000 (moderate) and more than 1001 (high), TCs showed 3 (7.6%) in the low group, 21 (53.8%) in the moderate group and 15 (38.4%) in the high group and glossitis showed 11 (73.3%) in the low group, 0 (0%) in the moderate group and 4 (26.6%) in the high group. The DTEs occupied an intermediate position between them (p < 0.001). In situ PCR demonstrated that the nuclei of TC and DTE cells are sporadically T-antigen positive but not in nasal turbinate epithelial cells. Immunohistochemistry for T-antigen protein revealed four positive cases only in TCs. The existence of JCV T-antigen DNA was not associated with the clinicopathological variables of TCs. In conclusion, the presence of JCV may be a risk factor of tongue carcinogenesis.

Detection of the JC virus genome in lung cancers: possible role of the T-antigen in lung oncogenesis

The JC virus (JCV) infects a large proportion of the population worldwide and 80% to 90% of adults are seropositive and it may be activated in immunodeficient patients, resulting in progressive multifocal leukoencephalopathy. Recent reports described the possibility of its oncogenetic role in several malignancies. To clarify whether JCV might have a potential role in the genesis of lung cancers, we investigated the presence of its genome in 62 tumors, along with 23 samples of normal lung tissue, targeting the T-antigen, VP, and Agnoprotein by nested polymerase chain reaction/Southern blotting followed by direct DNA sequencing. Immunohistochemistry was performed to assess links between p53 and beta-catenin in lung cancers and the presence of T-antigen. The T-antigen was detected in 25 of 62 lung cancers but only 4 of 23 normal lung samples (P=0.048). In total, the JCV genome was present in 33 of the lung cancers and 10 of the normal samples. Furthermore, T-antigen was found in cancer cells in metastatic lymph nodes in 3 of 4 cases (P=0.042) and was more frequently detected in adenocarcinomas than in squamous cell carcinomas (P=0.038). Immunohistochemistry showed significant correlations between T-antigen and p53 (P=0.022) and also nuclear detection of beta-catenin (P=0.021). It is concluded that the JCV genome might be present in cancer cells in approximately half of all Japanese lung cancer cases, and that the T-antigen may play a role in oncogenesis of lung cancers through inactivation of p53 and dysregulation of the Wnt signaling pathway.

Alterations of DNA damage repair pathways resulting from JCV infection

Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disorder of the CNS caused by infection of glial cells with the polyomavirus, JCV. Here we report that genomic stability and DNA repair are significantly dysregulated by JCV infection of human astrocytes. Metaphase spreads exhibited increased ploidy correlating with duration of infection. Increased micronuclei formation and phospho-Histone2AX expression also indicated DNA damage. Western blot analysis revealed perturbation in expression of some DNA repair proteins including a large elevation of Rad51. Immunohistochemistry on clinical samples of PML showed robust labeling for Rad51 in nuclei of bizarre astrocytes and inclusion body-bearing oligodendrocytes that are characteristic of JCV infection. Finally, in vitro end-joining DNA repair was altered in extracts prepared from JCV-infected human astrocytes. Alterations in DNA repair pathways may be important for the life cycle of JCV and the pathogenesis of PML.

Human retinoblastoma is not caused by known pRb-inactivating human DNA tumor viruses

Retinoblastomas occur as the consequence of inactivation of the tumor suppressor retinoblastoma protein (pRb), classically upon biallelic inactivation of the RB1 gene locus. Recently, human papillomavirus (HPV) genomic DNA has been detected in retinoblastomas. To investigate the possibility that oncoproteins encoded by pRb-inactivating DNA tumor viruses play a role in the pathogenesis of human retinoblastoma, 40 fresh-frozen tumors were analyzed for the presence of HPV, adenovirus (HAdV) and polyomavirus (BKV, JCV and SV40) genomic DNA sequences by real-time polymerase chain reaction (PCR). Tumors were screened for genetic and epigenetic alterations in all 27 exons of the RB1 gene locus and promoter by exonic copy number detection, sequencing and methylation-specific PCR of the promoter region. Retinoblastoma tumors from children with bilateral familial (n=1), bilateral nonfamilial (n=1) and unilateral nonfamilial (n=38) disease were analyzed. Inactivating modifications to the RB1 gene locus were identified on both the alleles in 27 tumors, one allele in 8, and neither allele in 5 cases. A median of over 107,000 tumor cells were analyzed for viral genomic DNA in each PCR reaction. All tumor samples were negative for 37 HPV types, 51 HAdV types, BKV and JCV genomic sequences. Very low copy number (0.2-260 copies per 100,000 tumor cells) SV40 genomic DNA detected in 8 of 39 samples was demonstrated to be consistent with an artifact of plasmid-derived SV40. In contrast to recent reports, we obtained substantial quantitative evidence indicating that neither HPV nor any other pRb-inactivating human DNA tumor viruses play a role in the development of retinoblastoma, regardless of RB1 genotype.

High JC virus load in gastric cancer and adjacent non-cancerous mucosa

The JC virus (JCV) infects a large proportion of the worldwide population and approximately 90% of adults are seropositive. Recent reports have described the possibility of its oncogenetic role in several malignancies. The aim of the present study was to assess the oncogenetic significance of JCV for gastric cancer. Twenty-two sample pairs of fresh tumor and adjacent non-cancerous tissue (ANCT) as well as 10 normal gastric mucosa specimens were investigated on the basis of nested polymerase chain reaction (PCR) followed by Southern blotting, DNA direct sequencing, real-time PCR, in situ PCR and immunohistochemistry. The T antigen sequence was detected in 86.4% of gastric cancers and ANCT, and in 100% of the normal mucosa samples, as for virus capsid protein, 54.1%, 68.1% and 70%, respectively. A generally low incidence was noted for agnoprotein. The JCV DNA load was approximately 10-fold higher in both gastric cancers and paired ANCT (4784 +/- 759 and 5394 +/- 1466 copies/microg DNA, respectively) than in normal gastric tissue (542.4 +/- 476.0 copies/microg DNA, P < 0.0001). In situ PCR revealed sporadic JCV genome-positive cancer cells and foveolar epithelial cells. T antigen protein expression assessed by immunohistochemistry was detected only in one case (1/22; 4.5%), probably because the half life of T antigen might be short. It was concluded that the gastric epithelium in most Japanese people is infected with JCV at a low rate but levels of infection are increased markedly in both cancer cells and ANCT, indicating that multiplication of JCV copies might be a risk factor and a background for gastric carcinogenesis.

Interaction of retinoblastoma protein family members with large T-antigen of primate polyomaviruses

The retinoblastoma gene product pRb and other members of the Rb family of pocket proteins have a central role in the regulation of cell cycle progression. Soon after its discovery, pRb was found to interact with the transforming oncoproteins of DNA tumor viruses and this led to rapid advances in our understanding of the mechanisms of viral transformation and cell cycle progression. DNA viruses of the polyomavirus family have small, circular, double-stranded DNA genomes contained within non-enveloped icosahedral capsids and are highly tumorigenic in experimental animals. At least three types of polyomavirus infect humans: JC virus (JCV), BK virus (BKV) and Simian Vacuolating virus-40. The early region of these viruses encodes the transforming proteins large T-antigen and small t-antigen, which are involved in viral replication and also promote transformation of cells in culture and oncogenesis in vivo. Binding of T-antigen to pRb promotes the activation of the E2F family of transcription factors, which induce the expression of cellular genes required for S phase. In the context of lytic infection, this cell cycle progression is necessary for viral replication because polyomaviruses rely on S phase-specific host factors for their DNA synthesis. In the context of cellular transformation and tumorigenesis, T-antigen/pRB interaction is an indispensable event.

The polyomavirus, JCV and its involvement in human disease

The human neurotropic polyomavirus, JC virus (JCV), is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system that occurs mainly in immunosuppressed patients. JCV has also been found to be associated with human tumors of the brain and other organs. In this chapter, we describe JC virus and its role in human diseases.

Characterization and application of polyclonal antibodies that specifically recognize JC virus large T antigen

Polyomavirus JC virus (JCV) is the causative agent of progressive multifocal leukoencephalopathy, a fatal demyelinating disease of the central nervous system. Similar to other polyomaviruses, such as simian vacuolating virus 40 (SV40) and BK virus (BKV), JCV is also associated with human tumours. The Polyomavirus early protein large T antigen (TAg) plays a crucial role in tumour pathogenesis. An antibody to SV40 TAg (PAb416), which cross-reacts with TAgs of both JCV and BKV, has been used widely for the detection of JCV and BKV TAgs. As a consequence, it is difficult to discriminate between the TAgs of SV40, BKV and JCV by immunohistochemical analyses. In the present study, we generated JCV TAg-specific polyclonal antibodies (JCT629 and JCT652) by immunization of New Zealand white rabbits with synthetic peptides reproducing the JCV TAg carboxyl-terminal region as immunogens. Immunoblotting analyses indicated that the new antibodies bind specifically to JCV TAg, and not to those of SV40 or BKV. We also demonstrated that these antibodies can be used for immunoprecipitation, immunocytochemical analyses and immunohistochemical staining of routinely processed specimens. In conclusion, the newly generated JCV-specific TAg antibodies may be useful both in the investigation of the pathophysiological function of JCV TAg and in discriminating between Polyomavirus-related clinical samples.

Expression of JC virus regulatory proteins in human cancer: potential mechanisms for tumourigenesis

JC virus (JCV) is a human polyomavirus that is the etiologic agent of the fatal demyelinating disease of the central nervous system known as progressive multifocal leukoencephalopathy (PML). JCV is also linked to some tumours of the brain and other organs as evidenced by the presence of JCV DNA sequences and the expression of viral proteins in clinical samples. Since JCV is highly oncogenic in experimental animals and transforms cells in culture, it is possible that JCV contributes to the malignant phenotype of human tumours with which it is associated. JCV encodes three non-capsid regulatory proteins: large T-antigen, small t-antigen and agnoprotein that interact with a number of cellular target proteins and interfere with certain normal cellular functions. In this review, we discuss how JCV proteins deregulate signalling pathways especially ones pertaining to transcriptional regulation and cell cycle control. These effects may be involved in the progression of JCV-associated tumours and may represent potential therapeutic targets.

Detection of JC virus DNA sequences in colorectal cancers in Japan

JC virus (JCV), a ubiquitous polyoma virus that commonly infects humans, was first identified as the etiologic agent for the fetal demyelinating disease, progressive multifocal leukoencephalopathy. Recently, a number of reports have documented detection of JCV in samples derived from several types of neural as well as non-neural human tumors. It has been suggested that oncogenicity of JCV depends on a T antigen having a strict structural homology to the T antigen of simian virus 40. To clarify whether JCV might have a potential role with regard to colorectal cancers, we investigated the presence of its genome in a series of cases along with colorectal adenomas and normal colonic mucosa, targeting T antigen, VP and agnoprotein by nested polymerase chain reaction and Southern blotting and T antigen by immunohistochemistry. While VP and agnoprotein were not found in any of the samples examined, T antigen was detected in 6 of 23 colorectal cancers (26.1%) and 1 of 21 adenomas (4.8%), but none of 20 samples of normal colonic mucosa. No clear and diffuse staining with anti-T-antigen antibodies (1:100) could be detected, and there was no correlation with CD20-positive cells, which might have indicated JCV latent infection of B lymphocytes. Presence of T antigen did not influence clinicopathological variables, including survival. In one colonic cancer case positive for T antigen together with lymph node metastasis, DNA extracted from cancer cells in the lymph node revealed no detection of T antigen. Our results are in the intermediate position between the high T antigen rate (81%) in one report and the lack of it (0%) in another focused on colon cancers. It was concluded that T antigen might be integrated in cancer cells in approximately one fourth of Japanese colon cancer cases without clear and diffuse expression of the protein, suggesting a possible role in oncogenesis which might involve a hit-and-run mechanism.

Human polyomaviruses and brain tumors

Polyomaviruses are DNA tumor viruses with small circular genomes. Three polyomaviruses have captured attention with regard to their potential role in the development of human brain tumors: JC virus (JCV), BK virus (BKV), and simian vacuolating virus 40 (SV40). JCV is a neurotropic polyomavirus that is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system occurring mainly in AIDS patients. BKV is the causative agent of polyomavirus-associated nephropathy (PVN) which occurs after renal transplantation when BKV reactivates from a latent state during immunosuppressive therapy to cause allograft failure. SV40, originating in rhesus monkeys, gained notoriety when it entered the human population via contaminated polio vaccines. All three viruses are highly oncogenic when injected into the brain of experimental animals. Reports indicate that these viruses, especially JCV, are associated with brain tumors and other cancers in humans as evidenced from the analysis of clinical samples for the presence of viral DNA sequences and expression of viral proteins. Human polyomaviruses encode three non-capsid regulatory proteins: large T-antigen, small t-antigen, and agnoprotein. These proteins interact with a number of cellular target proteins to exert effects that dysregulate pathways involved in the control of various host cell functions including the cell cycle, DNA repair, and others. In this review, we describe the three polyomaviruses, their abilities to cause brain and other tumors in experimental animals, the evidence for an association with human brain tumors, and the latest findings on the molecular mechanisms of their actions.

Detection of JC virus DNA sequences and expression of viral T antigen and agnoprotein in esophageal carcinoma

BACKGROUND

The human polyomavirus JC virus (JCV) causes progressive multifocal leukoencephalopathy. Subclinical infection with JCV occurs in 85-90% of the population worldwide. The virus usually remains latent but can reactivate under immunosuppressive conditions, resulting in progressive multifocal leukoencephalopathy. JCV is oncogenic in experimental animals and is associated with human brain tumors. JCV is found in normal mucosa of the gastrointestinal tract, and some colon carcinomas express the oncogenic JCV T-antigen protein. The objective of this study was to examine the presence of JCV DNA sequences and JCV protein expression in normal and malignant human esophageal tissues.

METHODS

The authors examined the presence of JCV DNA sequences and protein expression in normal and malignant human esophageal tissues. Seventy well characterized biopsy specimens from patients with a spectrum of esophageal disorders were studied by immunohistochemistry, and 18 specimens were analyzed further by polymerase chain reaction amplification.

RESULTS

JC viral DNA was isolated from 11 of 13 normal esophageal biopsy specimens (85%) and from 5 of 5 esophageal carcinomas (100%). Using immunohistochemistry, JCV T antigen was detected in 10 of 19 carcinomas (53%), agnoprotein was detected in 8 carcinomas (42%), p53 tumor suppressor was detected in 11 carcinomas (58%), and beta-catenin was detected in 4 carcinomas (21%). Zero of 51 normal, benign, and premalignant esophageal samples expressed viral proteins. Laser-capture microdissection verified the presence and specificity of JCV DNA sequences. beta-Catenin and p53 were colocalized with JCV T-antigen in the nuclei of neoplastic cells.

CONCLUSIONS

The results provide evidence for infection of gastrointestinal tract cells by JCV and suggest a potential role of JCV in the development of upper digestive tract carcinomas.

Polyomaviruses and human cancer: molecular mechanisms underlying patterns of tumorigenesis

Polyomaviruses are DNA tumor viruses with small circular genomes encoding only six proteins including three structural capsid proteins. Despite this simplicity, our understanding of the mechanisms of polyomavirus-mediated tumorigenesis is far from complete. The archetypal primate polyomavirus, SV40, was isolated more than 40 years ago and has been used extensively as a model system for the study of basic eukaryotic cellular processes such as DNA replication and transcription. Two human polyomaviruses have been isolated from clinical samples: JC virus (JCV) and BK virus (BKV). In this review, SV40, JCV, and BKV will be compared based on what is known about their molecular biology from experiments performed in vitro, in cell culture and in laboratory animals. The association of these viruses with clinical tumors is discussed along with the possible roles of these polyomaviruses in the etiology of human malignant disease.

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.

Molecular characterisation of JC virus strains detected in human brain tumours

AIMS

The aim of this study was to evaluate the presence and significance of JC virus (JCV) in human brain tumours.

METHODS

Histology, immunohistochemistry (IHC) and molecular biology techniques were employed to examine specimens of tumour tissue, peripheral blood and cerebrospinal fluid taken from 22 patients with primary neuro-epithelial tumours. Furthermore, the coding viral protein (VP1) region and non-coding transcription control region (TCR) of JCV genome isolated from the tumours were submitted to sequence analysis in order to detect viral rearrangements or mutations.

RESULTS

JCV genome was found in nine of the 22 tumour specimens (40.9%), including eight astrocyte-derived tumours (seven glioblastomas and one astrocytoma) and one oligodendroglioma, and in two of the 15 cerebrospinal fluid specimens (13.3%) with positive tumour tissue (one glioblastoma and one astrocytoma). Sequence analysis of JCV VP1, which was amplified in seven tissue samples and the two cerebrospinal fluid samples, revealed only genotype 1 (four 1a and three 1b), whereas TCR was amplified in six tissue samples and only one cerebrospinal fluid sample. TCR sequence analysis was possible in four cases and identified three Mad-4 and one type II sequences; the TCR genomic structures of JCV isolated from cerebrospinal fluid were the same as those sequenced from corresponding tumour tissue, thus indicating a possible cerebrospinal fluid dissemination of neoplastic cells carrying viral DNA.

CONCLUSIONS

Our results suggest a possible role of JCV in the induction of brain tumours, especially in those originating from brain cells normally targeted by JCV infection.

Evidence for dysregulation of cell cycle by human polyomavirus, JCV, late auxiliary protein

The late region of the human neurotropic JC virus encodes a 71 amino acid protein, named Agnoprotein, whose biological function remains elusive. Here we demonstrate that in the absence of other viral proteins, expression of Agnoprotein can inhibit cell growth by deregulating cell progression through the cell cycle stages. Cells with constitutive expression of Agnoprotein were largely accumulated at the G2/M stage and that decline in the activity of cyclins A and B is observed in these cells. Agnoprotein showed the ability to augment p21 promoter activity in transient transfection assay and a noticeable increase in the level of p21 is detected in cells continuously expressing Agnoprotein. Results from binding studies revealed the interaction of Agnoprotein with p53 through the N-terminal of the Agnoprotein spanning residues 1-36. Co-expression of p53 and Agnoprotein further stimulated transcription of the p21 promoter. Thus, the interaction of p53 and Agnoprotein can lead to a higher level of p21 expression and suppression of cell cycle progression during the cell cycle.

Expression of a human polyomavirus oncoprotein and tumour suppressor proteins in medulloblastomas

AIMS

Although the aetiology of medulloblastoma remains elusive, several lines of evidence suggest an association with the human neurotropic polyomavirus JC and its oncoprotein T antigen. The tumour forming properties of JC virus T antigen are the result, at least in part, of its ability to bind and inactivate tumour suppressor/cell cycle regulatory proteins, such as p53 and the retinoblastoma family of proteins.

METHODS

To examine potential relations between these factors, immunohistochemistry was used to determine associations between the T antigen and the expression of p53 and the retinoblastoma proteins pRb, p107, and Rb2/p130 in eight medulloblastomas.

RESULTS

Only the three medulloblastomas with T antigen expression also showed nuclear positivity with antibodies to p53. Although immunohistochemistry detected nuclear labelling for pRb in five of the cases, the three that were positive for T antigen showed the highest pRb labelling. The retinoblastoma related proteins p107 and Rb2/p130 were also immunopositive in most T antigen positive medulloblastomas. Double label immunohistochemistry also demonstrated p53 and pRb positivity in the same cells that were T antigen positive.

CONCLUSIONS

These correlations suggest that associations between T antigen and p53 and/or T antigen and pRb occur in some of these tumours. These data provide indirect evidence that JC virus, acting through T antigen, might be involved in the formation and progression of medulloblastoma.