Molecular biology and pathogenesis of human polyomavirus infections

The two human polyomaviruses JC and BK are ubiquitous in the human population. Primary infection leads to lifelong persistence in the kidney, the CNS and in lymphoid cells. Virus is shed into the urine and is transmitted at least in part by the oral route. Under limited changes of the immunological state persistent polyomavirus infection is activated to an asymptomatic virus production. However, in severe long-lasting immunosuppression, highly effective virus multiplication can be accompanied by extended cytolytic damage of viral target cells leading to fatal disease. Whereas BKV is associated with severe urogenital disorders, JCV affects the CNS, leading to progressive multifocal leukoencephalopathy (PML). Although the number of PML cases is steadily increasing because of the AIDS epidemic, the mechanisms responsible for the change from asymptomatic-activated to the diseased state are not yet understood. As a possible pathogenic factor, the role of genomic heterogeneity of the transcriptional control region in the induction of disease is discussed.

Oncogenic potential of human neurotropic papovavirus, JCV, in CNS

The human polyomavirus, JCV, is the causative agent of Progressive Multifocal Leukoencephalopathy (PML), a fatal human demyelinating disease. PML results from the cytolytic destruction of oligodendrocytes, the myelin-producing cells of the nervous system. JCV has also been shown to be tumorigenic in several animal models. Transgenic mice expressing the JCV early protein, T-antigen, develop poorly differentiated neural crest origin tumours. Intracerebral inoculation of JCV into newborn hamsters induces medulloblastomas, astrocytomas, and primitive neuroectodermal tumours. Further, inoculation of the virus into the brains of non-human primates, owl and squirrel monkeys, results in astrocytomas and glioblastoma multiforme. Several case reports have associated JCV with human CNS tumours in patients with concomitant PML, and one such report has detected JCV in a glial tumour in the absence of PML. The induction of neural origin tumours by JCV has been studied in transgenic mice harbouring the early genome of the virus. Alterations in the level and function of tumour suppressor proteins p53 and Rb, as well as associated cell cycle regulators, have been detected in tumour tissue from JCV T-antigen transgenic mice. Possible mechanisms by which JCV may exert its oncogenic potential by alteration of cellular growth control pathways in both humans and experimental animals are discussed.

JC virus infection in cells from lymphoid tissue

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease characterized by infection of oligodendrocytes by JC virus. The exact nature of the pathogenesis of PML is not known. The nature of the primary infection, the site of viral latency, and the route by which JCV enters the brain remain to be elucidated. Different laboratories have shown the presence of JCV in peripheral lymphocytes from immunosuppressed individuals, suggesting these cells as possible carriers of JCV to the brain. To examine this observation, we tested the susceptibility to JCV infection of cells from lymphoid organs, focusing our attention on CD34+ haematopoietic precursor cells and B lymphocytes. The results demonstrate that both these cell types are susceptible to JCV infection and, moreover, that JCV can infect only those cells that differentiate into lymphocytic lineage.

T-antigen-dependent transcriptional initiation and its role in the regulation of human neurotropic JC virus late gene expression

The multifunctional protein of papovaviruses, T-antigen, regulates the virus lytic cycle partly by exerting transcriptional control over viral and cellular gene expression. In this study, the ability of the T-antigen of human neurotropic JC virus (JCV) to enhance expression from the virus late promoter has been further examined. By deletion analysis, a T-antigen-responsive region was mapped within the JCV 98 bp enhancer/promoter between nucleotides 139 and 168. Interestingly, T-antigen appears to mediate transactivation by increasing expression from a basal transcriptional initiation site and through a novel T-antigen-dependent initiation site (TADI). The TADI element contains a region homologous to initiator (Inr) sequences and is sufficient to confer T-antigen responsiveness to a heterologous minimal promoter. Electrophoretic mobility shift and UV crosslinking analyses demonstrate that multiple cellular proteins interact with both single- and double-stranded forms of this sequence. Mutations within the TADI element which abolish T-antigen-mediated transcriptional activation also prevent the formation of specific nucleoprotein complexes. These data suggest that the ability of JCV T-antigen to regulate JCV late gene expression may be partly due to the formation of specific nucleoprotein complexes and transcriptional initiation from the TADI site on the viral promoter.

Tumor pathogenesis of human neurotropic JC virus in the CNS

In the last several years, studies have reported the detection of sequences similar to the polyomavirus, Simian Virus 40 (SV40) in human tumors including choroid plexus papillomas and ependymomas. Taken together with well-established evidence that SV40, as well as the human polyomaviruses JC virus (JCV) and BK virus (BKV), are oncogenic in several animal models, new interest has resurfaced regarding a possible role for these viruses in human tumors. In particular, a strong case can be made for re-evaluating the oncogenic potential of JCV in a neurotropic polyomavirus which is the causative agent of the fatal human demyelinating disease, Progressive Multifocal Leukoencephalopathy (PML). In this review, we discuss the transforming capability of JCV in vitro, JCV's ability to induce neural origin tumors in non-human primates as well as in rodents, and several case reports which suggest a possible role for JCV in tumor pathogenesis in the central nervous system.

Human polyomavirus JC control region variants in persistently infected CNS and kidney tissue

The question of a possible role for JC virus (JCV) genomic rearrangements in the pathogenesis of progressive multifocal leukoencephalopathy (PML) was addressed by analysis of the genomic complexity and the transcriptional control region (TCR) of the JCV DNA population in persistently infected CNS and kidney tissue. After cloning of full-length viral DNA, no extensive changes were detected in the coding regions of the JCV genome by restriction analysis suggesting an intact JCV DNA population. For further analysis of the distribution of JCV subtypes, the non-coding region was amplified by PCR. Molecular analysis revealed homogeneous JCV TCR populations in almost 50% of the individuals. Heterogeneity was found in two CNS samples with three and five different JCV subtypes, respectively, and in four kidney specimens with two TCR subtypes. Altogether, seven TCR subtypes were identified. One in each group represented single promoter element TCRs without duplication of sequences. The TCR of the major variant JCV-W1 was comparable in sequence and structure to that of the PML prototype JCV Mad-1 DNA. The identification of dominant PML-derived JCV TCR subtypes in most persistently infected individuals suggests that rearrangements of the JCV TCR can be associated with the persistent state of infection. However, it appears unlikely that PML-associated JCV subtypes are generated anew in each individual host in the course of persistence. The findings rather suggest that a limited number of stable JCV subtypes circulate in different geographical regions of the world.

The human polyomavirus, JCV, and neurological diseases (review)

JC virus, a human neurotropic polyomavirus, is the established etiologic agent of the fatal demyelinating disease, progressive multifocal leukoencephalopathy, which usually affects individuals with defects in cell-mediated immunity. Cytolytic destruction of oligodendrocytes, the myelin-producing cells of the central nervous system is attributed as the mechanism by which JCV induces demyelination. PML was at one time a rare complication however it is now a much more common disease affecting patients of all ages due to the prevalence of AIDS. Of interest, in vitro evidence points to a cooperative interaction between JCV and HIV-1, via the HIV-1 regulatory protein, Tat. In addition, JCV has been demonstrated to induce tumors of neural origin in several animal models, including rodents and non-human primates, and several clinical reports have suggested a possible association between JCV and glial-origin tumors in humans. The viral regulatory protein, T-antigen, which has been shown to play a key role in orchestrating the events of the viral lytic cycle, is also capable of altering cellular functions, by nature of its direct interaction with cellular regulatory proteins and by its effect on cellular transcription. In this review, we discuss clinical aspects of PML, the ability of JCV to induce tumors in animal models, and the ability of JCV T-antigen to alter cellular function in vitro.

Overexpression of Ki-67 and cyclins A and B1 in JC virus-infected cells of progressive multifocal leukoencephalopathy

Both SV40 and JC virus (JCV) appropriate the host cell replicative machinery to attend to their own reproductive needs. SV40 large T antigen is able to induce the expression of cyclins A, B1, and E (but not of cylin D1) in transfected diploid cells. Whether JCV infection influences cyclin expression in a similar fashion in the setting of progressive multifocal leukoencephalopathy (PML) remains unknown. Brain lesions from 7 PML cases (4 autopsies and 3 biopsies) were immunohistochemically investigated for the expression of Ki-67 and cyclins A, B1, and D1. All 7 cases showed strong positivity for Ki-67 and cyclins A and B1 in JCV-infected oligodendrocytes and astrocytes, the nuclear immunolocalization of cyclin A being in strong contrast to the cytoplasmic distribution of cyclin B1. No immunostaining for cyclin D1 was obtained in any of the 7 cases. These findings suggest that JCV infection is associated with overexpression of Ki-67 and cyclins A and B1 in PML host glial cells. Since cyclin changes in JCV-infected cells recapitulate SV40 T antigen-associated cyclin fluctuations, it appears reasonable to think that JCV T antigen shares some of the previously described capabilities of SV40 T antigen to alter cyclin expression for the sake of viral replication.

The human polyomavirus, JCV, does not share receptor specificity with SV40 on human glial cells

The initial event in the life cycle of a virus is its interaction with specific receptors present on the surface of a cell. Understanding these interactions is important to our understanding of viral tropism and tissue specific pathology associated with viral disease. The human polyomavirus, JCV, is the etiological agent of the fatal central nervous system (CNS) demyelinating disease, progressive multifocal leukoencephalopathy (PML). PML is the direct result of JCV infection of oligodendrocytes, the myelin producing cell in the CNS. In vivo, JCV can be detected in oligodendrocytes, astrocytes, lymphoid tissue, and peripheral blood of PML patients. In vitro, JCV infects human glial cells, tonsilar stromal cells, and, to a limited extent, human B lymphocytes. The initial step in infection of cells by JCV is at the level of attachment and entry. A specific cell surface receptor for JCV on human glial cells has not been identified. To begin to understand the nature of JCV receptors on human glial cells, large quantities of a previously characterized hybrid JC virus (Mad-1/SVEdelta) were purified. A direct virus binding assay demonstrated that these highly purified and labeled JCV virions bound to a finite number of cellular receptors on human glial cells. A competitive virus binding assay demonstrated that an excess of unlabeled JCV competed with labeled JCV more efficiently than did an excess of purified SV40. Furthermore, anti-class I antibodies which inhibited infection of glial cells by SV40 had no significant effect on infection by JCV. These results imply that JCV does not share receptor specificity with the related polyomavirus, SV40.

Review: JC virus infection of lymphocytes--revisited

JC virus (JCV), the causative agent of the fatal human demyelinating disease progressive multifocal leukoencephalopathy (PML), is an opportunistic papovavirus that infects and destroys oligodendrocytes, the myelin-producing cells of the central nervous system. Since its isolation from the brain of a PML patient, JCV has long been classed as a neurotropic virus. Many studies, however, have demonstrated that JCV can infect various other cell types, including immune system cells. Moreover, several recent studies have focused specifically on lymphocytes as a target of JCV. This review chronicles the association of JCV with lymphocytes, including cell type localization, molecular regulation, and viral sequences, and discusses clinical implications of these findings.

JCV-DNA and BKV-DNA in the CNS tissue and CSF of AIDS patients and normal subjects. Study of 41 cases and review of the literature

SUMMARY

We studied the distribution and localization of the human papova-viruses JCV and BKV in the central nervous system (CNS) and cerebrospinal fluid (CSF) of HIV-positive patients with and without progressive multifocal leukoencephalopathy (PML) as compared with HIV-seronegative patients. The presence of JCV-DNA and BKV-DNA was evaluated by nested polymerase chain reaction (PCR) and in situ hybridization (ISH) on CNS autopsy tissues of AIDS patients with (group A, n = 13) and without (group B, n = 16) PML and of HIV-negative patients (group C, n = 12). PCR for JCV-DNA and BKV-DNA was also performed on CSF samples collected 7-420 days before death in all the 29 AIDS patients. Tissue PCR for JCV-DNA was positive in all the cases in group A, in 44 percent of the patients in group B, and in 33 percent of the patients in group C. ISH was positive in all the cases with PML and in three AIDS cases without PML (12 percent), but negative in all the HIV-negative cases. BKV-DNA was detected in two cases from group A and in one case from group B. CSF was PCR-positive for JCV-DNA in 8 of 13 (62 percent) AIDS patients with PML, but in none of the HIV patients without PML, irrespective of the presence of JCV-DNA in CNS tissues. No CSF sample was positive for BKV-DNA. Our data demonstrates that JCV-DNA and, rarely, BKV-DNA can be detected in the CNS of immunocompromised patients with and without PML and also in the CNS of HIV-negative subjects. However, only HIV-positive patients with clinically evident PML and JCV-DNA in the brain have PCR-detectable JCV-DNA in their CSF.

Presence of human polyomavirus DNA in the peripheral circulation of bone marrow transplant patients with and without hemorrhagic cystitis

In BMT patients, shedding of BK virus (BKV) in the urine has been strongly but not absolutely correlated to hemorrhagic cystitis (HC). The possible presence of human polyomaviruses in peripheral blood leukocytes (PBLs), plasma, serum and urine in BMT patients and an association with HC was investigated by a nested PCR assay. Samples from allogeneic BMT patients with and without HC as well as from autologous BMT patients were analyzed. Human polyomaviruses were detected in urine and blood samples of both allogeneic and autologous BMT patients with and without HC. An association between the presence of a specific human polyomavirus in blood and HC was thus not observed.

Sequences within the early and late promoters of archetype JC virus restrict viral DNA replication and infectivity

Two forms of JC virus (JCV) have been isolated from its human host, an archetype found in kidney tissue and urine of nonimmunocompromised individuals and a rearranged type detected in lymphocytes and brain tissue of patients with and without progressive multifocal leukoencephalopathy. To investigate the hypothesis that alterations to the archetype transcriptional control region yield rearranged forms of the virus exhibiting new tissue tropic and pathogenic potentials, attempts were made to propagate archetype JCV in human renal and glial cell cultures. Although rearranged forms of JCV multiplied in these cells, archetype JCV failed to do so. Through the use of chimeric and mutant viral genomes, and a cell line that constitutively expresses viral T protein, we demonstrated that archetype's inactivity relative to that of rearranged forms was due to differences in the promoter-enhancer and not in the protein coding regions or origin of DNA replication. Additional analyses revealed that the absence of a large tandem duplication and the presence of a 23- and a 66-base pair sequence in the archetype transcriptional control region were responsible for this restricted lytic behavior. We discuss the possibility that deletion and duplication events within the archetype promoter-enhancer might yield more active viral variants via the loss of a negative, or the creation of a positive, transcriptional control signal(s).

Converting the JCV T antigen Rb binding domain to that of SV40 does not alter JCV's limited transforming activity but does eliminate viral viability

Two sets of mutations were introduced into a region of the JC virus (JCV) large tumor (T) antigen involved in binding the retinoblastoma susceptibility gene product (Rb). The first set converted the JCV sequences to those found in the corresponding region of the simian virus 40 (SV40) T antigen. The second set contained sequence changes predicted to abolish Rb binding. Each of these mutations was also inserted into a chimeric T antigen (MSTn) composed of JCV and SV40 sequences at its amino- and carboxy termini, respectively. The JCV T antigen is less efficient than its SV40 counterpart at transforming Rat2 cells and at binding Rb and viral DNA. These activities were altered in the two sets of mutants generated in this study. A JCV T antigen mutant having an SV40-like Rb-binding domain exhibited increased DNA binding activity while, unexpectedly, displaying decreased Rb binding and wild-type transforming behavior. A mutant T antigen that was unable to bind Rb exhibited decreased DNA binding and failed to transform Rat2 cells. Both mutants were defective for DNA replication and did not produce infectious virions. Additional phenotypic changes were observed when each mutation was introduced into the chimeric MSTn T antigen. As the oligomerization state of SV40 T antigen is known to influence several of its activities, including Rb binding, the quaternary structure of the T proteins used in this study was assessed by sucrose gradient sedimentation. The SV40 and chimeric MSTn T antigen sedimented as a mixture of monomers/dimers and higher oligomers, whereas the JCV T antigen sedimented predominantly as monomers/dimers; neither mutation in the T antigen Rb-binding motif affected the sedimentation profiles of the parental T proteins. Restricted biochemical activity of the JCV T protein relative to that of SV40 supports the suggestion that this regulatory protein contributes to the attenuation of the JCV lytic cycle.

Progressive multifocal leucoencephalopathy

Progressive multifocal leucoencephalopathy (PML) is a progressive, usually fatal, demyelinating disease of the CNS that is associated with infection of oligodendrocytes by the papovavirus JC. The incidence of PML is rising as a consequence of the AIDS epidemic.

JC virus and multiple sclerosis: a refutation?

Polyomavirus JC (JCV) has been implicated in the etiology of multiple sclerosis (MS), because it causes progressive multifocal leukoencephalopathy (PML), a multifocal demyelinating disease with many microscopical similarities to MS. During childhood, the virus establishes a latent infection in the kidneys, which can be reactivated in immunocompromised patients. During reactivation, the virus is shed in the urine. The kidney is the only known site of latent infection and reactivation. Therefore, excretion of the virus in the urine of MS patients is to be expected, if reactivated JCV is involved in the etiology of MS. We studied urine samples of 53 patients with definitive MS and of 53 controls matched for age and sex. We found no evidence of active JCV infection in MS. The hypothesis of a polyomaviral etiology of MS is not supported by the results of this study.

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

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

Pathogenesis and molecular biology of progressive multifocal leukoencephalopathy, the JC virus-induced demyelinating disease of the human brain

Studies of the pathogenesis and molecular biology of JC virus infection over the last two decades have significantly changed our understanding of progressive multifocal leukoencephalopathy, which can be described as a subacute viral infection of neuroglial cells that probably follows reactivation of latent infection rather than being the consequence of prolonged JC virus replication in the brain. There is now sufficient evidence to suggest that JC virus latency occurs in kidney and B cells. However, JC virus isolates from brain or kidney differ in the regulatory regions of their viral genomes which are controlled by host cell factors for viral gene expression and replication. DNA sequences of noncoding regions of the viral genome display a certain heterogeneity among isolates from brain and kidney. These data suggest that an archetypal strain of JC virus exists whose sequence is altered during replication in different cell types. The JC virus regulatory region likely plays a significant role in establishing viral latency and must be acted upon for reactivation of the virus. A developing hypothesis is that reactivation takes place from latently infected B lymphocytes that are activated as a result of immune suppression. JC virus enters the brain in the activated B cell. Evidence for this mechanism is the detection of JC virus DNA in peripheral blood lymphocytes and infected B cells in the brains of patients with progressive multifocal leukoencephalopathy. Once virus enters the brain, astrocytes as well as oligodendrocytes support JC virus multiplication. Therefore, JC virus infection of neuroglial cells may impair other neuroglial functions besides the production and maintenance of myelin. Consequently our increased understanding of the pathogenesis of progressive multifocal leukoencephalopathy suggests new ways to intervene in JC virus infection with immunomodulation therapies. Perhaps along with trials of nucleoside analogs or interferon administration, this fatal disease, for which no consensus of antiviral therapy exists, may yield to innovative treatment protocols.

Implications of progressive multifocal leukoencephalopathy and JC virus for the etiology of MS

JCV infects oligodendrocytes and, to a lesser extent, astrocytes in the brain and spinal cord and causes the demyelinating disease known as progressive multifocal leukoencephalopathy (PML) in immunocompromised individuals. The possibility exists that this opportunistic infection reactivates from a latent state in the brain. It is proposed that the pathogenetic immune response in a multiple sclerosis (MS) brain may be directed predominantly toward antigens of a DNA virus, such as JCV, which is latent in glial cells. The target antigens could be synthesized only during transient viral reactivation or could persist, thus explaining the two basic patterns of neurological symptoms in MS. It is further proposed that the viral genome as a minichromosome becomes focally distributed in glial cells following vertical passage in dividing progenitor cells after infection early in life. The concept that the host response to a single agent can evoke two distinct pathologies (PML and MS) derives from a chronic mycobacterial infection of peripheral nerves-leprosy.

JC virus-simian virus 40 genomes containing heterologous regulatory signals and chimeric early regions: identification of regions restricting transformation by JC virus

The papovavirus JC virus (JCV) is highly oncogenic in experimental animals but, unlike simian virus 40 (SV40), is severely restricted in its ability to transform cells in culture. We exploited the close genetic relatedness of these two viruses to delimit region(s) of the T protein which can restrict transforming activity. Novel chimeric genomes were produced by exchanging various segments of the JCV and SV40 T-protein-coding regions. These DNA constructs specified early proteins with in-frame substitutions of analogous amino acid sequences. A second set of genomes was prepared which, in addition to chimeric early proteins, contained substituted regulatory regions. The transformation efficiencies of these chimeric genomes were intermediate between those of SV40 and JCV, with the source of T protein exerting a greater effect than that of the regulatory region. The ability of certain constructs to induce efficient transformation required the presence of an SV40 regulatory region or specific sequences within the SV40 early coding region. Cloned cell lines prepared from representative transformants were characterized; the ability to form colonies in soft agarose was investigated, and the presence of viral T and cellular p53 proteins was determined. The various T proteins differed in amount, stability, and the ability to form stable complexes with p53.

Genetic characterization of JC virus Tokyo-1 strain, a variant oncogenic in rodents

The genome DNA of JC virus Tokyo-1 strain [JCV(Tokyo-1)], a variant oncogenic in rodents, was molecularly cloned directly from the brain of a Japanese patient with progressive multifocal leukoencephalopathy and from tissue culture, and the restriction enzyme cleavage pattern and regulatory sequences were determined. The restriction pattern of the cloned JCV(Tokyo-1) DNA was different from those of JCVs previously reported in the United States and Germany. Also, the arrangement of the regulatory sequence was unique to this strain. Thus JCV(Tokyo-1) can be classified as a new subtype. The relationship between the restriction pattern and the regulatory sequence of JCV(Tokyo-1), and its characteristic oncogenicity, is discussed.

Early regions of JC virus and BK virus induce distinct and tissue-specific tumors in transgenic mice

JC virus and BK virus are ubiquitous human viruses that share sequence and structural homology with simian virus 40. To characterize tissue-specific expression of these viruses and to establish model systems for the study of human viral-induced disease, transgenic mice containing early regions of each of the viruses were produced. The viral sequences induced tumors in a distinct and tissue-specific manner that was similar to their tissue tropism in humans. Ten JC virus-containing founder mice were produced, of which 5 survived to maturity. Four of them developed adrenal neuroblastomas, which metastasized to several other tissues. JC virus tumor-antigen RNA was detected at high levels in the tumor tissues and at low levels in the normal tissues of these mice. One of the three BK virus-containing mice was abnormally shaped and died at 2 weeks of age. The other two BK virus-containing mice developed primary hepatocellular carcinomas and renal tumors and died at 8-10 months of age. BK virus tumor-antigen RNA was expressed in tumor tissues of both mice. Since each of the viruses retained the general tissue tropism that it exhibits in humans, these data suggest that transgenic mice harboring human viruses will be useful as animal models for viral-induced diseases.

The early region of human papovavirus JC induces dysmyelination in transgenic mice

Transgenic mice containing the early region of human papovavirus JC were produced. Some of these mice exhibited a shaking disorder similar to the previously described mutant mice jimpy or quaking. Neuropathological analysis indicated a dysmyelination in the central nervous system, but not the peripheral nervous system. A high level of JCV T-antigen mRNA was present in the brains of the mice exhibiting the myelin disorder. JC virus is associated in humans with a degenerative demyelinating disease: progressive multifocal leukoencephalopathy. The JCV-containing transgenic mice may therefore provide an animal model for studying this disease.