Small tumor antigen of polyomaviruses: role in viral life cycle and cell transformation

The regulatory proteins of polyomaviruses, including small and large T antigens, play important roles, not only in the viral life cycle but also in virus-induced cell transformation. Unlike many other tumor viruses, the transforming proteins of polyomaviruses have no cellular homologs but rather exert their effects mostly by interacting with cellular proteins that control fundamental processes in the regulation of cell proliferation and the cell cycle. Thus, they have proven to be valuable tools to identify specific signaling pathways involved in tumor progression. Elucidation of these pathways using polyomavirus transforming proteins as tools is critically important in understanding fundamental regulatory mechanisms and hence to develop effective therapeutic strategies against cancer. In this short review, we will focus on the structural and functional features of one polyomavirus transforming protein, that is, the small t-antigen of the human neurotropic JC virus (JCV) and the simian virus, SV40.

Diagnostic value of JC/BK virus antibody immunohistochemistry staining in urine samples from posttransplant immunosuppressed patients in relation to polyomavirus reactivation

OBJECTIVE

To compare the diagnostic value of cytology and immunohistochemistry staining (IHS) of urine samples for polyomavirus reactivation diagnosis.

STUDY DESIGN

Sixty-eight urine samples collected from 18 immunosuppressed patients were analyzed by Papanicolaou and IHS with a JC/BK virus-specific monoclonal antibody.

RESULTS

Overall, polyomavirus BK (BKV) was positive in 11 of 18 patients (61.1%) (3 of whom developed hemorrhagic cystitis) and in 23 of 68 urine samples (28%). Of 23 samples, 4 (17%) were positive by 1 of the 2 techniques, only. Of 23 samples, 19 (83%) were positive by both methods. In matching urine samples from the same patient, the number of BKV-infected positive cells detected by IHS in urine slides was higher than those detected by Papanicolaou staining (71.3%).

CONCLUSION

The main advantage of LHS is that it allowed confirmation of BKV infection diagnosis in urine samples. IHS detected more BKV-infected cells in samples with few positive urothelial cells, which would have gone undetected if only Papanicolaou staining had been used as the BKV screening method. Urine samples testing for BKV by both techniques will improve diagnosis in asymptomatic patients, allowing early therapeutic intervention and a better clinical outcome.

Progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) was a rare disease until the advent of the HIV/AIDS pandemic. Recent interest in the disorder has been spurred by its appearance in patients treated with the monoclonal antibodies natalizumab and rituximab. Unless the accompanying underlying immune deficit can be reversed, PML typically progresses to death fairly rapidly. Treatment directed against the JC virus has been unhelpful, but an increased understanding of disease pathogenesis may result in effective therapeutic strategies.

Induction of experimental autoimmune encephalomyelitis in Lewis rats by a viral peptide with limited homology to myelin basic protein

Viral infections are thought to play an important role in the pathogenesis of multiple sclerosis potentially through molecular mimicry, but direct evidence from humans and animal models remains inadequate. Based on the fact that amino acid homology has been found between viral and host encephalitogenic protein, we designed four viral peptides (peptides of HBV polymerase protein, large T protein of JC virus, EB virus DNA polymerase and alkaline exonuclease of Human herpesvirus 6) with limited homology to myelin basic protein and explored their clinical, immunological and histological characteristics in Lewis rats. The immunization with JC virus peptide induced slight clinical signs of EAE in Lewis rats. Immunological examination indicated that rats immunized with JC virus peptide triggered T-cell cross-reactivity against MBP68-86, but failed to induce antibody cross-reactivity with MBP68-86. Histological staining exhibited the infiltration of inflammatory T cells and the activation of microglia in spinal cords of rats immunized with MBP68-86 and JC virus peptide. Other three peptides had negative findings in Lewis rats. These results suggested that molecular mimicry could be an important factor in the pathogenesis of EAE induced with JC virus peptide by expanding a population of reactive T cells that recognize MBP68-86 in Lewis rats inferring a possible pathogenesis for molecular mimicry in MS.

Chimeric immune receptors (CIRs) specific to JC virus for immunotherapy in progressive multifocal leukoencephalopathy (PML)

Progressive multifocal leukoencephalopathy (PML) is a deadly brain disease caused by the polyomavirus JC (JCV). The aim of this study is to develop 'designer T cells' armed with anti-JCV TCR-based chimeric immune receptors (CIRs) by gene modification for PML immunotherapy. Two T cell lines specific to two dominant CTL epitopes derived from JCV VP1 protein (termed p36 and p100) from an HLA-A0201+ PML survivor were generated for TCR cloning. Two distinct dominant TCR alpha chains (Valpha6 and Valpha12) and a unique TCR beta chain (Vbeta5.1) were cloned from the p36-specific cell line, while only one alpha (Valpha8.6) and one beta (Vbeta2) chains were dominant in the p100-specific line. Retroviral constructs encoding CIRs were created with the extracellular domains of TCR alpha and beta chains fused to the transmembrane and cytoplasmic portions of CD3zeta (ValphaCalphaCD3zeta or VbetaCbetaCD3zeta). Cellular expression and screening for binding specific peptide-HLA-A0201 tetramer confirmed the reactivity of the p100 TCRalphabeta and of one of the two pairs of p36 TCRalphabeta (Valpha12 and Vbeta5.1). Functional tests confirmed CIR-expressing T cells secreted cytokines and expressed potent cytotoxicity on contact with A0201+ B-lymphoblastoid line loaded with peptides and/or with HLA-A0201+ cells expressing native JCV VP1 protein. In conclusion, anti-JCV designer T cells were generated.

Discovery and epidemiology of the human polyomaviruses BK virus (BKV) and JC virus (JCV)

Although discovered over thirty years ago, many aspects of the epidemiology of BKV and JCV in the general population, such as the source of infectious virus and the mode of transmission, are still unknown. Primary infection with both BKV and JCV is usually asymptomatic, and so age seroprevalence studies have been used to indicate infection. BKV commonly infects young children in all parts of the world, with the exception of a few very isolated communities, adult seroprevalence rates of 65-90% being reached by the age of ten years. In contrast, the pattern of JCV infection appears to vary between populations; in some anti-JCV antibody is acquired early as for BKV, but in others anti-JCV antibody prevalence continues to rise throughout life. This indicates that the two viruses are probably transmitted independently and by different routes. Whilst BKV DNA is found infrequently in the urine of healthy adults, JCV viruria occurs universally, increasing with age, with adult prevalence rates often between 20% and 60%. Four antigenic subtypes have been described for BKV and eight genotypes are currently recognized for JCV. The latter have been used to trace population movements and to reconstruct the population history in various communities.

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

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

Improvement of progressive multifocal leukoencephalopathy after cidofovir therapy in a patient with a destructive polyarthritis

The human neurotropic JC virus (JCV) is responsible for progressive multifocal leukoencephalopathy (PML), an infectious demyelinating brain disease with major morbidity and mortality, usually refractory to treatment. We describe a PML in a 67-year-old woman with a destructive polyarthritis associated with anti-JO1 antibodies treated with corticosteroids. Although glucocorticoid therapy was maintained, administration of cidofovir improved the neurological condition. Our observation demonstrates the expanding clinical importance of JCV in systemic rheumatic diseases, particularly when immunosuppressive agents are used, and neurological symptoms or white matter changes on central nervous system imaging should arouse the suspicion of PML.

Reactivation of JC virus and development of PML in patients with multiple sclerosis

The attention of researchers and clinicians specializing in both multiple sclerosis (MS) and JC virus (JCV), the etiologic agent of progressive multifocal leukoencephalopathy (PML), was rekindled by the development of PML in two patients with MS enrolled in a clinical trial of combination therapy with natalizumab (Tysabri) and interferon beta-1A (Avonex) in recent years. PML had not been previously reported with either MS or treatment with interferon beta alone. This occurrence of PML with alpha4beta1-integrin inhibition in MS raised a number of issues in terms both of the scientific understanding of these diseases and for the future of immunomodulatory treatment for MS. In this review, we examine the current status of knowledge of the virus, its molecular biology, life cycle, and pathogenetic mechanisms, and how this relates to the basic science and clinical perspectives of MS. A better understanding of the specific steps from JCV infection to the development of PML is key to this issue. Other critical issues for further investigation include the role of alpha4beta1-integrin inhibition by natalizumab in the re-expression of JCV from latent sites and in the inhibition of entry into the brain and peripheral sites.

Oncogenic role of JC virus in lung cancer

The JC virus (JCV) infects a large proportion of the population world wide and can cause progressive multifocal leucoencephalopathy in the context of immunodeficiency. Recent reports provide evidence that it may also be oncogenic. Here, JCV was examined by targeting its T-antigen in lung carcinomas (n=103) and normal lung tissues (n=18) by nested-PCR followed by Southern blot, real-time PCR, immunohistochemistry, in situ hybridization and in situ PCR. Additionally, expression of Ki-67, caspase-3, beta-catenin, p53, and Rb was analysed by immunohistochemistry on tissue microarrays of lung carcinomas. Copy numbers of JCV were compared with clinicopathological features. Normal lung tissue was positive significantly less frequently, and contained a lower copy number of JCV than lung carcinomas (p<0.05), and copies were lower in lung adenocarcinomas than in squamous, small or large cell carcinomas (p<0.05). In situ PCR and immunolabelling revealed JCV positivity in the nuclei of lung carcinoma cells. The JCV copy number correlated closely with sex, and expression of Ki-67 and membrane beta-catenin (p<0.05), but not with age, tumour size, pleural invasion, lymph node metastasis, expression of caspase-3, cytoplasmic beta-catenin, p53 or Rb, prognosis, smoking or cancer family history (p>0.05). Age and UICC staging were independent prognostic factors for lung carcinoma patients. These data suggest that JCV may be involved in lung carcinogenesis, especially in tumour types other than adenocarcinoma. Lung carcinomas with higher JCV copy numbers display high proliferation and down-regulation of cell adhesion mediated by membrane beta-catenin.

Immune reconstitution inflammatory syndrome associated with PML in AIDS: A treatable disorder

An HIV-1-infected patient with progressive multifocal leukoencephalopathy presented clinical deterioration and contrast-enhancing lesions on brain nuclear MR after the initiation of highly active antiretroviral therapy (HAART). Brain biopsy identified an inflammatory reaction compatible with immune reconstitution inflammatory syndrome. Treatment with corticosteroids and transient suppression of HAART led to marked neurologic improvement.

T-cell responses to peptide fragments of the BK virus T antigen: implications for cross-reactivity of immune response to JC virus

Infection with BK virus (BKV) induces both humoral and cellular immunity, but the viral antigens of T-antigen (T-ag) stimulating T-cell responses are largely unknown. To identify BKV-specific T cells in healthy individuals, peripheral blood lymphocytes were cultured with autologous dendritic cells (DCs) loaded with BKV lysate and T cells were screened for intracellular gamma interferon production after stimulation with an overlapping 15mer peptide library of the BKV T-ag. Among many immunogenic peptides identified, four T-ag peptides were identified as candidate major histocompatibility complex class I and II T-cell epitopes, restricted to human leukocyte antigen (HLA)-B*0702, -B*08, -DRB1*0301 and -DRB1*0901. Further, a candidate 9mer peptide, LPLMRKAYL, was confirmed to be restricted to HLA-B*0702 and -B*08. Because the polyomaviruses BKV, JC virus (JCV) and Simian virus 40 (SV40) share extensive sequence similarity in the immunogenic proteins T-ag and VP1, it was hypothesized that, in humans, these proteins contain conserved cytotoxic T-lymphocyte (CTL) target epitopes. Four HLA-restricted conserved epitopes of BKV, JCV and SV40 were identified: HLA-B*07, -B*08 and -DRB1*0901 for T-ag and -A*0201 for VP1. T cells cultured in vitro that were specific for one viral antigen recognized other conserved epitopes. CTLs generated from BKV T-ag and VP1 peptide were cytotoxic to DC targets pulsed with either BKV or JCV. Therefore, infection by one of the two viruses (BKV and JCV) could establish cross-immunity against the other. Although cross-cytotoxicity experiments were not performed with SV40, cross-recognition data from conserved antigen epitopes of polyomaviruses suggest strongly that cross-immunity might also exist among the three viruses.

Oncogenic T-antigen of JC virus is present frequently in human gastric cancers

BACKGROUND

JC virus (JCV) is a polyomavirus that commonly infects humans and is the causative agent of progressive multifocal leukoencephalopathy in immune-compromised patients. An association between JCV and human cancers long has been suspected, because this virus induces brain tumors in several animal models. The oncogenic potential of JCV is mediated by a transforming protein, the T-antigen (T-Ag), which is a multifunctional protein that transforms cells through interactions with various growth-regulatory genes, including p53 and pRb, and by stabilizing beta-catenin. Previously, the laboratory at the authors' institution demonstrated that JCV is present frequently in the human gastrointestinal tract and may play a role in colorectal carcinogenesis. However, to date, no studies have determined whether JCV sequences are present specifically in gastric cancers. The current study was designed to investigate whether JCV sequences and expression are found in human gastric cancers.

METHODS

DNA was extracted from 23 paraffin embedded and 14 frozen gastric cancer specimens. For the detection of JCV gene sequences, polymerase chain reaction amplifications were performed using gene-specific primers for T-Ag, VP-1 (a JCV capsid gene), and the viral regulatory region (or transcriptional control region). Immunohistochemical staining was performed with an anti-T-Ag monoclonal antibody to detect protein expression.

RESULTS

Twenty-one of 37 gastric cancers (57%) harbored JCV T-Ag sequences, and 13 of 37 gastric cancers (30%) contained VP-1 sequences. T-Ag sequences also were found in adjacent nonneoplastic mucosa. In addition, JCV regulatory region sequences were present frequently in gastric cancers and adjacent nonneoplastic mucosa. T-Ag protein expression was found in 9 of 23 gastric cancers (39%), whereas no expression was observed in any of the nonneoplastic tissues.

CONCLUSIONS

To the authors' knowledge, this is the first demonstration of the presence of JCV T-Ag expression in human gastric cancers. These findings suggest a possible role for this polyomavirus in gastric carcinogenesis.

JC virus induces a vigorous CD8+ cytotoxic T cell response in multiple sclerosis patients

We sought to compare the ongoing CD8+ cytotoxic T lymphocytes (CTL) immune response of MS patients to self and viral antigens. Using 51Cr release and tetramer staining assays, we found that the CTL response against VP1, the major capsid protein of the polyomavirus JC (JCV), was significantly higher than the one against epitopes of MBP and PLP. The JCV-specific CTL response was also significantly stronger in MS patients than healthy control subjects. These findings may shed a new light on the recent events related to the development of progressive multifocal leukoencephalopathy in three natalizumab-treated patients.

Association of JC virus T-antigen expression with the methylator phenotype in sporadic colorectal cancers

BACKGROUND & AIMS

JC virus (JCV) is a polyomavirus that ubiquitously infects humans and has been implicated in various human cancers. JCV encodes a "transforming" gene, T-antigen (T-Ag), which is believed to mediate the oncogenic potential of the virus. We have previously shown that JCV DNA sequences are usually present in human colorectal cancers (CRCs), and we have provided in vitro evidence that JCV can induce chromosomal instability (CIN) in CRC cells. This study tests the hypothesis that JCV T-Ag expression correlates with one or more forms of genomic or epigenetic instability in sporadic CRCs.

METHODS

We characterized 100 sporadic CRCs for microsatellite instability (MSI) and CIN. PCR amplifications were performed for T-Ag sequences, and immunohistochemical (IHC) staining was performed to detect T-Ag expression. De novo methylation of the promoter regions of nine putative tumor suppressor genes thought to play a role in colorectal carcinogenesis was studied by methylation-specific PCR.

RESULTS

JCV T-Ag DNA sequences were found in 77% of the CRCs and 56% of these cancers (or 43% of the total) expressed T-Ag by IHC. Significant associations were observed between T-Ag expression and CIN in CRCs (P = .017) and between T-Ag expression and promoter methylation of multiple genes (P = .01).

CONCLUSIONS

The association between T-Ag expression and promoter methylation in CRC suggests that this viral oncogene may induce methylator phenotype and that JCV may be involved in CRC through multiple mechanisms of genetic and epigenetic instability.

Cross-reactive CTL recognizing two HLA-A*02-restricted epitopes within the BK virus and JC virus VP1 polypeptides are frequent in immunocompetent individuals

Two HLA-A*02-restricted epitopes have been identified within the VP1 polypeptide of a human polyomavirus, BK virus, which is associated with polyomavirus-associated nephropathy in kidney transplant patients. Immunization of transgenic mice with recombinant modified vaccinia Ankara expressing BKV VP1 (rMVA-BKV VP1) elicited functional CTL populations recognizing the sequences LLMWEAVTV (amino acids residues 108-116, BKV VP1p108) and AITEVECFL (residues 44-52, BKV VP1p44) and cross-reactive to the previously described JC virus VP1 homologs. Flow-based analyses of PBMC from a panel of thirty healthy HLA-A*02 human volunteers indicated that the majority of these subjects harbored functional CTL populations recognizing the BKV epitopes and cross-reactive with the JCV homologs. CTL recognizing the JCV VP1p100 and JCV VP1p36 epitopes have previously been associated with prolonged survival in progressive multifocal leukoencephalopathy patients. These findings suggest that infection with BKV or JCV could potentially induce cross-protective T-cell immunity against diseases associated with these viruses.

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.

Prediagnostic Circulating Antibodies to JC and BK Human Polyomaviruses and Risk of Non-Hodgkin Lymphoma

Viral infections have been associated with increased risk of non-Hodgkin's lymphoma (NHL). We conducted a nested case-control study to investigate the association between prediagnostic serum antibodies to the human polyomaviruses, JC (JCV) and BK (BKV), and subsequent risk of NHL. Two research serum banks were established in Washington County, Maryland, in 1974 and 1989, with the collection of blood samples from >45,000 volunteers. Incident NHL cases diagnosed through 2002 (n = 170) were identified among participants by linkage to population-based cancer registries. Two controls were matched to each case (n = 340) on age, sex, and blood draw date. Prediagnostic IgG antibodies to JCV and BKV were measured using virus-like particle ELISA. Associations between JCV and BKV antibody seropositivity and NHL were estimated using conditional logistic regression. Overall, neither antibodies to JCV [odds ratio (OR), 0.83; 95% confidence interval (95% CI), 0.56-1.23] nor BKV (OR, 0.98; 95% CI, 0.64-1.48) were associated with an increased risk of NHL. Results were similar after stratification by NHL subtype or induction period and adjustment for EBV seropositivity. Among those who donated blood in both 1974 and 1989, an increase in JCV antibody levels over time was associated with a 4-fold increased risk of NHL compared with a steep decline in antibody levels (OR, 4.59; 95% CI, 1.30-16.25; P(trend) = 0.02). Whereas JCV seropositivity was not associated with NHL overall, the finding of an increased risk of NHL associated with increasing antibody levels among those who were seropositive at baseline warrants further research into factors influencing reactivation of JCV infection.

Regulation of human neurotropic JCV in colon cancer cells

BACKGROUND

Recently, the genome of the human polyomavirus, JC (JCV), and expression of its early and late regulatory proteins (T-antigen and agnoprotein) have been demonstrated in neoplastic cells of colonic cancer cases.

MATERIALS AND METHODS

Regulation of JCV was investigated in a human colon cancer cell line (SW480) and compared to a human glioblastoma cell line (U87-MG) that is permissive for JCV replication.

RESULTS

SW480 cells supported basal transcription of both early and late JCV promoters. The expression of TCF-4, a component of Wnt signaling, modulated JCV transcription in a cell type-specific manner. Both TCF-4 and T-antigen bound to the JCV promoter region and bound to each other. In addition, the expression of TCF-4 caused a decrease in the ability of the T-antigen to stimulate viral DNA replication in U87-MG cells.

CONCLUSION

Wnt pathway signaling proteins and T-antigen interact to regulate JCV in colonic epithelial cells.