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

Concomitant progressive multifocal leucoencephalopathy and primary central nervous system lymphoma expressing JC virus oncogenic protein, large T antigen

This report describes the concomitant occurrence of the JC virus (JCV) induced demyelinating disease progressive multifocal leucoencephalopathy (PML) and a primary central nervous system lymphoma (PCNS-L) in a patient with AIDS. Postmortem neuropathological examination revealed characteristic features of PML including multiple lesions of demyelination, enlarged oligodendrocytes with hyperchromatic nuclei (many containing eosinophilic intranuclear inclusions), and enlarged astrocytes with bizarre hyperchromatic nuclei. Immunohistochemical analysis demonstrated the expression of the JCV capsid protein VP-1 in the nuclei of infected oligodendrocytes and astrocytes. The PCNS-L lesion located in the basal ganglia was highly cellular, distributed perivascularly, and consisted of large atypical plasmacytoid lymphocytes. Immunohistochemical examination of this neoplasm identified it to be of B cell origin. Moreover, expression of the JCV oncogenic protein, T antigen, was detected in the nuclei of the neoplastic lymphocytes. This study provides the first evidence for a possible association between JCV and PCNS-L.

Molecular characterization and sequence analysis of polyomavirus strains isolated from needle biopsy specimens of kidney allograft recipients

We retrospectively examined 29 renal allograft biopsy specimens from 42 kidney transplant recipients by means of molecular biologic techniques (nested polymerase chain reaction), immunohistochemical analysis (anti-SV40 antibody), and histologic examination to evaluate the presence of polyomaviruses (PVs), viral genotypes, genomic mutations, and their pathologic significance. PV genomes were found in six cases (21%); restriction fragment length polymorphism analysis characterized 4 as JC virus (JCV) and 2 as BK virus (BKV). The latter also were positively stained immunohistochemically and showed histologically typical intranuclear viral inclusions; JCV cases were negative. DNA sequence analysis revealed only minor changes in the 4 JCV cases (3 archetypes and 1 JCV type 3, not associated with a known pathogenic genotype) but identified 2 specific variants in the BKV isolates (AS and WW strains). Given the different histologic findings (mixed inflammatory infiltration in the AS and no inflammation in the WW strain), we speculate that different BKV strains may cause differential damage in transplanted kidneys. Finally, the negative histologic and immunohistochemical JCV results, as well as the absence of viral mutations, indicate that JCV renal infection is latent in transplant recipients.

Single-stranded nucleic acid-binding protein, Pur alpha, interacts with RNA homologous to 18S ribosomal RNA and inhibits translation in vitro

Pur alpha is a highly conserved, eukaryotic sequence-specific DNA- and RNA-binding protein involved in diverse cellular and viral functions including transcription, replication, and cell growth. Pur alpha exerts its activity in part by interacting with other viral and cellular proteins. One such protein is the human immunodeficiency virus (HIV) type I regulatory protein Tat. Earlier studies have demonstrated that this interaction is mediated by Pur alpha-associated RNA (PARNA) and that RNA immunopurified from mammalian expressed Pur alpha was capable of reconstituting the interaction between these two proteins. In the current study, we characterize four RNA species which were immunopurified with Pur alpha. Northern blot analysis with one of the PARNAs revealed a highly abundant signal of approximately 2.0 kilobases (kb) present in all cell lines tested. Sequence analysis of each of the four PARNA clones revealed a high homology to different regions of the human 18S ribosomal RNA sequence. Based on this homology, we investigated the influence of Pur alpha on translation. Luciferase assays were performed after coupled in vitro transcription/translation reactions with a vector containing a luciferase reporter construct and increasing concentrations of BSA, GST, and GST-Pur alpha. Inclusion of GST-Pur alpha in these reactions resulted in a dose-dependent inhibition of luciferase activity. Similar inhibition was observed with in vitro translation reactions performed with in vitro transcribed luciferase RNA and increasing concentrations of GST-Pur alpha. In control experiments, inclusion of increasing concentrations of GST-Pur alpha with luciferase protein resulted in no effect on luciferase activity. Taken together, these data demonstrate that Pur alpha inhibits translation reactions in vitro. Moreover, this Pur alpha-mediated inhibition of translation can be abrogated by HIV-1 Tat protein.

Involvement of Wnt signaling pathway in murine medulloblastoma induced by human neurotropic JC virus

By using the early genome of the human neurotropic polyomavirus, JCV, we have created transgenic animals that develop cerebellar primitive neuroectodermal tumors which model human medulloblastoma. Expression of T-antigen was found in some, but not all, tumor cells, and examination of the clonal cell lines derived from the tumor population showed enhanced tumorigenicity of cells expressing T-antigen in comparison to T-antigen negative cells. Considering the earlier notion on the potential involvement of beta-catenin with human medulloblastoma, we investigated various components of the Wnt signaling pathway including beta-catenin, its partner transcription factor, LEF-1, and their downstream target gene c-myc in these two cell populations. Immunohistochemical staining of the cells revealed enhanced nuclear appearance of beta-catenin in T-antigen positive cells. Results from Western blot showed higher levels of beta-catenin and LEF-1 in T-antigen positive cells in comparison to those in T-antigen negative cells. The enhanced level of LEF-1 expression correlated with the increase in DNA binding activity of this protein in nuclear extracts of T-antigen positive cells. Results from Northern and Western blot analyses revealed that the level of c-myc expression is augmented both at the RNA and protein levels in T-antigen positive cells. These observations corroborated results from transfection studies indicating the ability of JCV T-antigen to stimulate c-myc promoter activity. Further, co-transfection experiments revealed that the amount of c-myc and T-antigen protein in tumor cells may dictate the activity of JCV early promoter in these cells. These observations are interesting in light of recent discoveries on the association of JCV with human medulloblastoma and suggest that communication between JCV and the Wnt pathway may be an important event in the genesis of these tumors.

A classification scheme for human polyomavirus JCV variants based on the nucleotide sequence of the noncoding regulatory region

The human polyomavirus JCV is responsible for the central nervous system (CNS) demyelination observed in cases of progressive multifocal leukoencephalopathy (PML). Lytic infection of oligodendrocytes, the cells that constitute the basis of myelin in the CNS, is established by JCV in conjunction with immunosuppressive conditions. Beyond this, however, many questions related to JCV pathogenesis remain unanswered. The JCV regulatory region is a hypervariable noncoding sequence positioned between the early and late protein-coding regions. The particular nucleotide sequence of a JCV regulatory region affects levels of viral transcription and replication. Modifications to this promoter/enhancer structure can alter the cellular host range and may be responsible for switching JCV between states of lytic and latent infection. The regulatory region structure has, therefore, been used to distinguish JCV variants. Nucleotide sequencing studies have uncovered numerous variations of regulatory region structure. Until now, however, no inclusive nomenclature existed that linked variants by regulatory region structure and/or activity. We have arranged all known variant JCV regulatory regions into quadrants according to the integration of particular sequence sections and repetition of sequence section groups. This arrangement of regulatory regions results in an updated nomenclature that is well-suited for describing the relationships between JCV variants. Four distinct structural forms (I-S, I-R, II-S, and II-R) are defined along with tissue tropisms. This design provides logical connections between the variant regulatory regions and may be useful for elucidating crucial steps in JCV pathogenesis.

Analysis of minimal sequences on JC virus VP1 required for capsid assembly

Human JC virus (JCV) belongs to the family of Polyomaviridae. The viral capsid is composed of 72 capsomeres. Five VP1 molecules make up a capsomere structure. To investigate the minimal sequences on JCV VP1 polypeptide required for capsid assembly, the first 12 (Delta N12) and 19 (Delta N19) amino acids at the N-terminus and the last 16 (Delta C16), 17 (Delta C17), and 31 (Delta C31) amino acids at the C-terminus of VP1 were truncated and expressed in E. coli. The VP1 proteins of Delta N12 and Delta C16 were able to self-assemble into a virus-like particle similar to that of wild-type (WT) VP1. However, the mutant proteins of Delta N19, Delta C17, and Delta C31 formed a pentameric capsomere structure as demonstrated by a 10-50% sucrose gradient centrifugation and electron microscopy. These results suggest that the 12 amino-terminal and 16 carboxy-terminal amino acids of VP1 are dispensable for the formation of virus-like particles, and further truncation at either end of VP1 leads to the loss of this property.

Immune response in progressive multifocal leukoencephalopathy: an overview

Progressive multifocal leukoencephalopathy (PML) is a disease usually occurring in immunosuppressed patients. By far the most common underlying immunosuppressive illness is the acquired immune deficiency syndrome, accounting for about 85% of PML cases currently seen in clinical practice. PML may occur in patients with deficits in the humoral and/or cellular immune response such as lymphoproliferative diseases, myeloproliferative diseases, carcinomatous diseases and acquired immunodeficiency due to autoimmune diseases and immunosuppressive therapy. The humoral immune response in PML is indicative of a persistent, reactivated infection with a prominent immunoglobulin (lgG) G synthesis to virus protein 1 (VP1). An lgM synthesis in serum is rarely found. In about 76% of PML cases, an intrathecal humoral immune response to recombinant VP1 can be found as compared to only 3.2% in healthy controls. The detection of intrathecally synthesized lgG antibodies to VP1 can be used as an additional diagnostic test for the diagnosis of PML. The magnitude of the intrathecal humoral immune response appears to rise over time and may be associated with a decrease of viral load in cerebrospinal fluid (CSF) and possibly the central nervous system (CNS). Compared to healthy controls, proliferation of peripheral blood mononuclear cells (PBMC) is reduced in PML patients. Immunological studies suggest a general impairment of the Th1-type T-helper cell function of cell-mediated immunity. Furthermore, the appearance of JCV-specific cytotoxic T-lymphocytes appears to be associated with a favorable clinical outcome.

Broad distribution of the JC virus receptor contrasts with a marked cellular restriction of virus replication

To investigate the early events of JC virus (JCV) infection, including attachment, penetration, transport to the nuclei, and replication of the virus, we analyzed the susceptibility of 15 different cell lines to infection using a semiquantitative polymerase chain reaction (PCR) assay, in situ hybridization, laser scanning confocal microscopy, and a viral replication assay. The cell lines examined were human permissive and nonpermissive cells as well as cells of monkey and mouse origin. JCV entry into the nuclei of the all cell lines was observed within 10 min after inoculation, demonstrating that the virus receptor is widely distributed among mammalian cells. Inhibition of viral entry by an anti-JCV VP1 antibody and sialidase treatment to remove sialic acid residues, which are considered a candidate for the JCV receptor, suggested that VP1 may interact with the cellular surface sialic acid. In addition, chlorpromazine, a clathrin-dependent pathway inhibitor, significantly suppressed entry of JCV into nuclei. In spite of the broad spectrum of cells susceptible to JCV entry, replication of the virus occurred exclusively in human neuroblastoma cell lines. These results suggest that whereas JCV can enter a wide variety of cell types and localize to the nuclei, cell-specific intranuclear mechanisms are required for virus replication.

Bk virus: a clinical review

We present a review of the clinically oriented literature about BK virus, a relative of JC virus, which is the etiologic agent of progressive multifocal leukoencephalopathy (PML). The kidney, lung, eye, liver, and brain have been proposed as sites of BK virus-associated disease, both primary and reactivated. BK virus has also been detected in tissue specimens from a variety of neoplasms. We believe that BK virus is most often permissively present in sites of disease in immunosuppressed patients, rather than being an etiologic agent that causes symptoms or pathologic findings. There is, however, strong evidence for BK virus-associated hemorrhagic cystitis and nephritis, especially in recipients of solid organ or bone marrow transplants. Now that BK virus can be identified by use of specific and sensitive techniques, careful evaluation of the clinical and pathologic presentations of patients with BK virus will allow us to form a clearer picture of viral-associated pathophysiology in many organ systems.

Disulfide bonds stabilize JC virus capsid-like structure by protecting calcium ions from chelation

To investigate the role of disulfide bonds in the capsid structure, a recombinant JC virus-like particle (VLP) was used. The major capsid protein, VP1, of the JC virus was expressed in yeast cells. The yeast-expressed VP1 was self-assembled into a VLP. Disulfide bonds were found in the VLP which caused dimeric and trimeric VP1 linkages as demonstrated by non-reducing SDS-PAGE. The VLP remained intact when disulfide bonds were reduced by dithiothreitol. The VLP without disulfide bonds could be disassembled into capsomeres by EGTA alone, but those with disulfide bonds could not be disassembled by EGTA. Capsomeres were reassembled into VLPs in the presence of calcium ions. Capsomeres formed irregular aggregations instead of VLPs when treated with diamide to reconstitute the disulfide bonds. These results indicate that disulfide bonds play an important role in maintaining the integrity of the JC VLP by protecting calcium ions from chelation.

Coordinate effects of human immunodeficiency virus type 1 protein Tat and cellular protein Puralpha on DNA replication initiated at the JC virus origin

JC virus (JCV) causes progressive multifocal leukoencephalopathy, a demyelinating disease in brains of individuals with AIDS. Previous work has shown that the Tat protein, encoded by human immunodeficiency virus type 1 (HIV-1), can interact with cellular protein Puralpha to enhance both TAR-dependent HIV-1 transcription and JCV late gene transcription. Tat has been shown to activate JCV transcription through interaction with Puralpha, which binds to promoter sequence elements near the JCV origin of replication. DNA footprinting has shown that Puralpha and large T-antigen cooperatively interact at several binding sites in the origin and transcriptional control region. Overexpression of Puralpha inhibits replication initiated at the JCV origin by T-antigen. In transfected glial cells Tat reversed this inhibition and enhanced DNA replication. In an in vitro replication system maximal activation by Tat, more than sixfold the levels achieved with T-antigen alone, was achieved in the presence of Puralpha. Effects of mutant Tat proteins on both activation of replication and binding to Puralpha have revealed that Cys22 exerts a conformational effect that affects both activities. The origin of an archetypal strain of JCV was less susceptible to activation of replication by Tat relative to the rearranged Mad-1 strain. These results have revealed a previously undocumented role for Tat in DNA replication and have indicated a regulatory role for JCV origin auxiliary sequences in replication and activation by Tat.

Identification of a DNA encapsidation sequence for human polyomavirus pseudovirion formation

Human polyomavirus is a naked capsid virus containing a closed circular double-stranded DNA genome. The mechanism of DNA encapsidation for the viral progeny formation is not fully understood. In this study, DNA encapsidation domain of the major capsid protein, VP1, of the human polyomavirus JCV was investigated. When the first 12 amino acids were deleted, the E. coli expressed VP1 (Delta N12VP1) failed to encapsidate the host DNA although the integrity of the capsid-like structure was maintained. In addition, capsid-like particles of Delta N12VP1 did not package exogenous DNA in vitro, which is in contrast to that of the full-length VP1 protein. These findings suggest that the N-terminal of the first 12 amino acids of VP1 were responsible for DNA encapsidation. The importance of amino acids in the DNA encapsidation domain was determined further using site-directed mutagenesis. All of the positively charged amino acids at the N-terminal region of VP1 were essential for DNA encapsidation. The results indicate that the N-terminal region of the human polyomavirus major capsid protein VP1 may be involved in viral genome encapsidation during progeny maturation.

Molecular characterization and sequence analysis of polyomavirus BKV-strain in a renal-allograft recipient

The significance of polyomavirus (PV) infection was investigated in a 53-year-old patient who underwent renal transplantation and was treated with triple immunosuppressive therapy (tacrolimus, prednisone, and azathioprine). A renal biopsy taken because of the suspicion of acute rejection showed focal inflammatory interstitial infiltration, tubulitis, and tubular cell nuclear changes consistent with the hypothesis of viral infection. Both the tubular and decoy cells identified by means of urinalysis positively stained for anti-SV40 antibody. Polymerase chain reaction performed on the DNA extracted from renal tissue and isolated from urine showed the presence of an antigenic variant (AS) of the BKV archetype after sequence analysis of the transcription control region (TCR). On the basis of the diagnosis of BKV infection, immunosuppressive therapy was reduced. The patient's renal function improved and was still stable 8 months later when urinalysis showed only a few decoy cells, which were found to be infected by JC but not BK virus. These data suggest that only the BKV, probably favoured by immunosuppressive therapy (tacrolimus), causes renal damage. It is worth underlining that even small and sporadic viral genome mutations may lead to pathologic effects.

JC virus regulatory region tandem repeats in plasma and central nervous system isolates correlate with poor clinical outcome in patients with progressive multifocal leukoencephalopathy

JC virus (JCV), the causative agent of progressive multifocal leukoencephalopathy (PML), has a hypervariable regulatory region (JCV RR). A conserved archetype form is found in the urines of healthy and immunocompromised individuals, whereas forms with tandem repeats and deletions are found in the brains of PML patients. Type I JCV RR, seen in MAD-1, the first sequenced strain of JCV, contains two 98-bp tandem repeats each containing a TATA box. Type II JCV RR has additional 23-bp and 66-bp inserts or fragments thereof and only one TATA box. We cloned and sequenced JCV RR from different anatomic compartments of PML patients and controls and correlated our findings with the patients' clinical outcome. Twenty-three different sequences were defined in 198 clones obtained from 16 patients. All 104 clones with tandem repeats were type II JCV RR. Patients with poor clinical outcome had high proportions of JCV RR clones with both tandem repeats in plasma (54%) and brain or cerebrospinal fluid (85%). In those who became survivors of PML, archetype sequences predominated in these anatomic compartments (75 and 100%, respectively). In patients with advanced human immunodeficiency virus infection without PML, only 8% of JCV RR clones obtained in the plasma contained tandem repeats. These data suggest that the presence of tandem repeats in plasma and CNS JCV RR clones is associated with poor clinical outcome in patients with PML.

Virus receptors in the human central nervous system

The initial event in the life cycle of a virus is its interaction with receptors present on the surface of a cell. Understanding these interactions is important to our understanding of viral tropism, spread, and pathogenesis. This is particularly true of viruses that target the central nervous system as these viruses must maintain a tropism for both the nervous system and for peripheral organs that allow for viral replication and spread to new susceptible hosts. These viruses therefore interact with a diverse set of cells and tissues, interactions that are likely mediated by both common and unique receptors present on each target tissue. In addition, physiological changes in the host can lead to increased or decreased expression of virus receptors, which influence virus trafficking, spread, and tissue specific pathology. This review will focus on the relatively few virus receptor systems that have been described in some level of detail for viruses that target the human central nervous system.

Increased frequency of JC virus type 2 and of dual infection with JC virus type 1 and 2 in Italian progressive multifocal leukoencephalopathy patients

To verify the possibility of different role of JC virus genotypes in the etiology of progressive multifocal leukoencephalopathy, we analysed several JC virus isolates amplified from AIDS patients with and without progressive multifocal leukoencephalopathy and healthy controls by nucleotide sequencing. Cerebrospinal fluid (CSF), peripheral blood mononuclear cells (PBMCs) and urine from 52 AIDS patients suffering from various neurological diseases including 21 cases of progressive multifocal leukoencephalopathy, and PBMCs and urine from healthy subjects were evaluated by nested polymerase chain reaction (PCR) for the presence of DNA belonging to the highly conserved large T antigen (LT) of JC virus. The different JC virus subtypes were identified by nucleotide sequence analysis of the virion protein (VP1) genomic region. JC virus DNA was detected in all the CSF samples from the progressive multifocal leukoencephalopathy patients, but not in the CSF from non-progressive multifocal leukoencephalopathy cases, while the frequency of JC virus DNA detection in the PBMCs and urine did not differ among the three groups studied. JC virus type 2 was detected only in progressive multifocal leukoencephalopathy patients, and in particular in 52.4% of their CSF samples. Moreover, in the CSF of 19.0% of the progressive multifocal leukoencephalopathy cases, dual infection with both JC virus types 1 and 2 was found. The data obtained in this study indicate that the unexpected involvement of JC virus type 2, a strain not common in Italy, and the high frequency of dual infection with both JC virus types 1 and 2 in progressive multifocal leukoencephalopathy CSF, can be indications of risk factors for progressive multifocal leukoencephalopathy development.

Interaction of JC virus agno protein with T antigen modulates transcription and replication of the viral genome in glial cells

In addition to encoding the structural and regulatory proteins, many viruses encode auxiliary proteins, some of which have been shown to play important roles in lytic and latent states of the viruses. The human neurotropic JC virus (JCV) genome encodes an auxiliary protein called Agno whose function remains unknown. Here, we investigated the functional role of JCV Agno protein on transcription and replication of the viral genome in glial cells. Results from transfection of human glial cells showed that Agno protein suppresses both T-antigen-mediated transcription of the viral late gene promoter and T-antigen-induced replication of viral DNA. Affinity chromatography and coimmunoprecipitation assays demonstrated that the Agno protein and T antigen physically interact with each other. Through the use of a series of deletion mutants, we demonstrated that the T-antigen-interacting region of Agno protein is localized to its amino-terminal half and the Agno-interacting domain of T antigen maps to its central portion. Furthermore, utilizing various Agno deletion mutants in functional studies, we confirmed the importance of the Agno-T antigen interaction in the observed down-modulation of T antigen function upon viral gene transcription and DNA replication by Agno protein. Taken together these data suggest that the Agno protein of JCV, which is produced late during the late phase of the lytic cycle, can physically and functionally interact with the viral early protein, T antigen, and downregulate viral gene expression and DNA replication. The importance of these observations in the lytic cycle of JCV is discussed.

JC virus DNA sequences are frequently present in the human upper and lower gastrointestinal tract

BACKGROUND & AIMS

JC virus (JCV), a human polyomavirus, has been found in a limited number of normal human tissues and cancers. The oncogenic potential of this virus is mediated by a transforming protein, the T antigen (TAg). We have previously demonstrated the presence of JCV-TAg in colorectal cancers, in adjacent normal colonic mucosa from these patients, and in the human colon cancer cell line SW480. The mode of transmission of this virus is unclear, and we hypothesized that the gastrointestinal (GI) tract may be a reservoir for the virus.

METHODS

DNA was extracted from 129 normal GI tissue samples collected from 33 patients. Topoisomerase I-assisted polymerase chain reaction (PCR) was used to detect the virus using exact and degenerate primers. Nested PCR and Southern blot analysis confirmed the identity of the PCR products. Single-stranded conformation polymorphism (SSCP) analysis and sequencing were used to evaluate the presence of viral quasispecies.

RESULTS

JCV sequences were found in 75.8% of patients (70.6% of upper GI and 81.2% of colonic samples); no significant differences in rates of infection were found by site. The use of degenerate primers combined with topoisomerase I treatment led to viral detection in 58.9% of samples, compared with 27.9% of samples using exact primers and topoisomerase I (P < 0.01). SSCP and sequencing analysis confirmed the amplification of viral quasispecies and the authenticity of TAg sequences.

CONCLUSIONS

The results show that JCV DNA sequences are highly prevalent in the human upper and lower gastrointestinal tract of immunocompetent individuals.

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

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

Infection with JC virus and possible dysplastic ganglion-like transformation of the cerebral cortical neurons in a case of progressive multifocal leukoencephalopathy

Infection of the cerebral cortical neurons with JC virus (JCV) with possible dysplastic ganglion-like alteration of the infected neurons found in a case of progressive multifocal leukoencephalopathy (PML) is described. The patient was a 21-year-old man with common variable immunodeficiency who died of PML after a 9-month clinical course. At autopsy, the white matter of the cerebrum, brainstem, cerebellum, and spinal cord exhibited extensive demyelination and necrosis. Numerous inclusion-bearing oligodendrocytes and bizarre astrocytes were found. In the occipital and temporal cortex, thick band-like aggregates of dysplastic ganglion-like cells (DGLCs) were found. These DGLCs showed immunohistochemical properties of neurons, and nuclei of some DGLCs were immunoreactive for large T antigen of SV40/JCV and p53, but not for capsid protein JCV VP1. In situ hybridization for mRNA of JCV large T antigen revealed positive signals in the nuclei of some DGLCs. These results indicate that JCV infected neurons and it is suggested that binding of the large T antigen with cellular proteins could have resulted in the dysplastic, ganglion cell-like change of the infected neurons, although the possibility that the aggregates of DGLCs represent a pre-existent malformative lesion of the cortex cannot be excluded completely.

Human cytomegalovirus immediate-early gene 2 expression leads to JCV replication in nonpermissive cells via transcriptional activation of JCV T antigen

Human papovavirus JCV is the causative agent of the demyelinating brain disease progressive multifocal leukoencephalopathy (PML) that typically develops as a complication of impaired immunocompetence. JCV displays a strong tropism for glial cells which is correlated by glial-specific transcriptional regulation of viral gene expression. In a previous report HCMV was shown to overcome the restricted cell specificity of JCV by inducing DNA replication of a PML-derived JCV strain in human fibroblasts which are nonpermissive for the replication of JCV alone. Here we show that productive JCV replication is induced by HCMV in human glioblastoma cells. Both in fibroblasts and in glioblastoma cells, the HCMV immediate-early transactivator 2 (IE2) is sufficient to mediate JCV replication. Furthermore, IE2 induces DNA replication of several structurally different brain- or kidney-derived JCV variants. IE2-induced JCV DNA replication is accompanied by the induction of JCV T antigen expression due to stimulation of the JCV early promoter. Our results indicate that stimulation of JCV early gene expression by HCMV-IE2 is sufficient to overcome the restricted cell specificity of JCV.

Transcriptional control in myelinating glia: flavors and spices

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

Progressive multifocal leukoencephalopathy with concurrent Richter's syndrome

Progressive multifocal leukoencephalopathy (PML) is a demyelinating infectious disease caused by the JC virus. It was originally described in patients with chronic lymphocytic leukemia (CLL). Richter's syndrome, or transformation to large cell Lymphoma, occurs in approximately 3% of patients with CLL, and carries a poor prognosis. We report a patient with documented PML and concurrent Richter's transformation outside the central nervous system. Before establishing a definitive diagnosis of PML, radiation therapy to the presumed lymphomatous brain lesion had been considered, raising the issue of whether stereotactic brain biopsy should be considered in every patient in a similar situation. Although this is likely a rare occurrence, patients with Richter's transformation documented at an extra-neural site and a brain lesion may benefit from the establishment of an infectious diagnosis which would influence therapy.

The HHV6 paradox: ubiquitous commensal or insidious pathogen? A two-step in situ PCR approach

BACKGROUND

Progressive multifocal leukoencephalopathy (PML) and multiple sclerosis (MS) are demyelinative diseases of the central nervous system (CNS). PML occurs mostly in individuals with AIDS-impaired immunity and is thought to be caused by JC polyoma virus (JCV). In MS a neurotrophic virus trigger is suspected, but the precise etiology remains unknown. Human herpesvirus 6 (HHV6) is a ubiquitous, commensal and usually benign beta-herpesvirus. Some researchers have found evidence for HHV6 infection in MS plaques and sera. We recently demonstrated a high frequency of cells containing HHV6 genome in PML lesions, as well as co-infection of oligodendrocytes by JCV and HHV6. This suggests that HHV6 may be a co-factor in the etiology of PML, and raises questions about its role in other demyelinative diseases.

OBJECTIVES

To determine the prevalence and cellular localization of HHV6, JCV and HIV-1 infected cells in PML, MS, AIDS and control CNS tissues, and their potential relationship with disease.

STUDY DESIGN

An unconventional, sensitive two-step in situ polymerase chain reaction (ISPCR) procedure was used to amplify and detect HHV6, JCV and HIV-1 genomic DNAs in formalin fixed, paraffin-embedded archival CNS tissues. HHV6, JCV and HIV-1 gene expression was detected by ICC for HHV6 p41 and gp101, JCV large T, and HIV-1 p24 gag and NEF proteins.

RESULTS

A high frequency of HHV6 genome was consistently detected in both PML and MS white matter lesional cells; a peri-lesional concentration was notable. HHV6 was found mainly in oligodendrocytes, but neurons were also infected. HHV6 was present in larger amounts than JCV in PML lesions, while more HIV-1 than HHV6 was present in AIDS. Variable amounts of HHV6 genome were detected in normal, AIDS and other control brains; the frequency of infected cells tended to increase with patient age.

CONCLUSIONS

High concentrations of HHV6 genome in association with PML and MS lesions, open the possibility that HHV6 activation may play a role in the pathogenesis of these demyelinative diseases.

Central Nervous System Opportunistic Infections in HIV-1 Infection

Neurologic disease is commonly encountered in the population infected with human immunodeficiency virus type 1 (HIV-1). Although HIV-1 is responsible for many of these neurologic complications, other organisms will affect the nervous system as the immune deficiency state progresses. With the wide use of potent antiretroviral therapy, the mortality from and incidence of opportunistic infections (OIs) among persons with advanced HIV-1 infection has decreased. Nevertheless, these diseases are still seen frequently, especially among those with limited access to new antiretroviral therapies. Therefore, it remains important to recognize the most common OIs of the central nervous system (CNS) as well as primary CNS lymphoma, which will be the focus of this review.

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

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

Comparison of cytosine arabinoside delivery to rat brain by intravenous, intrathecal, intraventricular and intraparenchymal routes of administration

We evaluated the delivery of 14C-cytosine arabinoside (AraC) to rat brain by: 1) intravenous (IV) bolus, by 2) intrathecal (IT) and 3) intraventricular (IVT) infusion, and by 4) convection-enhanced delivery (CED) into the caudate nucleus. Plasma and brain AraC metabolites were measured with HPLC, and distribution and concentration of 14C-AraC in brain sections were measured by quantitative autoradiography. After IV administration, the alpha and beta plasma half-lives were 1.9 and 46.5 min, respectively. The blood-to-brain transfer constant of AraC was 2.5+/-1.4 microliter g(-1) min(-1), compatible with high water solubility. After IT and IVT administration, tissue levels were high at the brain and ventricular surfaces, but declined exponentially into brain. After CED, maximum brain levels were up to 10,000 times higher than the IV group, and the distribution pattern was one of high 14C-AraC concentration in the convective component, with exponentially declining concentrations outside this region. The rate loss constant from brain was 0.002+/-0.0004 min(-1), suggesting that AraC was accumulating in brain cells. AraC was metabolized into uracil arabinoside within the brain. 14C-AraC was infused into 1 dog and distributed widely in the ipsilateral hemisphere. These studies suggest that delivery of AraC to brain parenchyma by the IV, IT or IVT routes will be subtherapeutic. Delivery by CED can achieve, and maintain, therapeutic levels of AraC in the brain, and should be further evaluated as a potential method of drug delivery.

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

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

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

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

Highly active antiretroviral therapy and progressive multifocal leukoencephalopathy: effects on cerebrospinal fluid markers of JC virus replication and immune response

Cerebrospinal fluid (CSF) samples were examined from 7 patients infected with human immunodeficiency virus type 1 (HIV-1) who had progressive multifocal leukoencephalopathy (PML). Samples were obtained both before and after 35-365 days of highly active antiretroviral therapy (HAART). By polymerase chain reaction, JC virus (JCV) DNA was found in 6 of 7 patients at baseline but in only 1 patient after HAART. In contrast, in 25 historical control patients from whom sequential CSF specimens were obtained, no reversion from detectable to undetectable JCV DNA was observed. By use of enzyme-linked immunosorbent assay, intrathecal production of antibody to JCV-VP1 was shown in only 1 of 4 HAART recipients at baseline but in 5 of 5 patients after treatment. The neuroradiological picture improved or had stabilized in all patients after 12 months of HAART, and all were alive after a median of 646 days (range, 505-775 days). Prolonged survival after HAART for PML is associated with JCV clearance from CSF. JCV-specific humoral intrathecal immunity may play a role in this response.

Polyomaviruria in renal transplant patients is not correlated to the cold ischemia period or to rejection episodes

Polyomaviruria was observed in one-third of all renal transplant patients, irrespective of whether their renal grafts came from a living or cadaver donor, and was not correlated to graft rejection episodes. This suggests that the renal graft ischemia period is not the major cause of polyomavirus reactivation and that reactivation of polyomavirus is not a dominant cause of graft rejection.

Oligodendrocyte programmed cell death and central myelination deficiency induced in transgenic mice by synergism between c-Myc and Oct-6

The basic helix-loop-helix transcription factor c-Myc is a potent trigger of programmed cell death when overexpressed during late oligodendrocyte development in transgenic mice. Here we provide evidence that c-Myc can act synergistically with the Pit, Oct, Unc homeodomain transcription factor Oct-6 to produce myelin disease pathogenesis in transgenic mice. More than 70% of c-myc/Oct-6 bitransgenic mice, obtained from crosses between phenotypically normal heterozygous mice of various My (c-Myc) and Oc (Oct-6) transgenic strains that express c-myc and oct-6 transgenes under transcriptional control of the myelin basic protein gene, developed severe neurological disturbances characterized by action tremors, recurrent seizures, and premature death. Affected bitransgenic mice exhibited multiple hypomyelinated lesions in the white matter that did not stain with myelin-specific antibodies against myelin basic protein, proteolipid protein, CNPase, and myelin-associated glycoprotein. The mice also exhibited a larger number of terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling positive cells in the white matter as well as ultrastructural evidence of glial cell death and astrogliosis. These observations indicate that the myelin lesions observed in the c-myc/oct-6 bitransgenic mice result from the untimely programmed cell death of oligodendroglia and that the c-myc and oct-6 transgenes act synergistically in producing the lesions.

A 23-bp sequence element from human neurotropic JC virus is responsive to NF-kappa B subunits

The regulatory region of the human neurotropic JC virus (JCV) is composed of several cis-acting motifs that confer cell type specificity to viral gene transcription and enable the viral promoters to respond to extracellular stimuli. For example, the bidirectional 98-bp tandem repeat sequences, positioned between the JCV early and late genes, were shown to be responsible for basal and activated levels of viral gene transcription in central nervous system (CNS) cells. Additionally, the NF-kappaB site located approximately 75 bp from the repeats on the early side of the viral genome was also found to influence both levels of viral transcription. Recently, we isolated a novel JCV variant, JCV(Phila-1), from a clinical specimen that contains a 23-bp sequence element (23-bpse) within its promoter-enhancer region. Here we demonstrate that this element is responsive to an extracellular stimulatory factor, such as phorbol 12-myristate 13-acetate (PMA), and can augment the basal levels of the viral early and to a lesser degree late promoter activities in cells derived from the CNS. The 23-bpse, by associating with nuclear proteins present in uninduced cells, forms a 40-kDa DNA-protein complex. Although no direct correlation between transcriptional enhancement of the JCV promoter by PMA treatment and the level of the 40-kDa DNA-protein complex was observed, results from site-directed mutagenesis indicated that formation of this complex is critical for the transcriptional activation of the viral promoter by PMA. These observations suggested that transcriptional enhancement of the JCV promoter activity upon PMA treatment may be an indirect event and mediated by an intermediary factor(s). In this respect, we demonstrated that overexpression of the inducible NF-kappaB subunits, p50 and p65, enhanced transcriptional activity of the JCV promoter through the 23-bp region with no evidence for their direct association with the 23-bpse DNA. Of importance, the p50/p65-induced JCV promoter activity requires the nucleotide sequences within the 23-bpse that are critical for the assembly of the 40-kDa DNA-protein complex. Thus, it is likely that the NF-kappaB subunits, by recruiting the cellular factors such as those associated with the 40-kDa DNA-protein complex, influence the basal level of the viral gene transcription. The implications of these findings with respect to regulation of viral and cellular genomes by extracellular stimuli and NF-kappaB pathway are discussed.

Reduced concentrations of HIV-RNA and TNF-alpha coexist in CSF of AIDS patients with progressive multifocal leukoencephalopathy

OBJECTIVES

To confirm reduced human immunodeficiency virus type-1 (HIV-1) burden in the CSF of patients with progressive multifocal leukoencephalopathy (PML) and to verify whether this viral load coincides with the absence of inflammatory changes in the CSF.

METHODS

Paired CSF and plasma samples from 17 patients with PML, 26 with non-PML cerebral opportunistic infections, nine with HIV-1 leukoencephalopathy (HIVE), and 12 neurologically asymptomatic AIDS patients were subjected to HIV-RNA titration. Tumour necrosis factor (TNF)-alpha was also measured and the CSF albumin: serum albumin ratio (Q(Alb)) was calculated.

RESULTS

The CSF HIV-1 burden of patients with PML did not differ from that of neurologically asymptomatic patients (p=0.21), but was significantly lower than CSF burden of the remaining patients (non-PML opportunistic infections, p<0.001; HIVE, p<0.001). Q(Alb) was normal for all neurologically asymptomatic patients, for 86.6% patients with PML, and 62.5% patients with HIVE (p=0.09). Q(Alb) was altered in 91.6% patients with non-PML opportunistic infections. TNF-alpha in CSF was higher in patients with non-PML opportunistic infections (p<0.001) and those with HIVE (p<0.001) than in patients with PML who consistently had TNF-alpha concentrations<10 pg/ml.

CONCLUSIONS

These results, while indicating a reduced HIV replication in CSF of patients with PML which might serve as a disease marker, emphasise the increased CSF HIV-RNA concentration in patients with HIVE and patients with non-PML opportunistic infections. Low concentrations of HIV-RNA in CSF coincide with reduced TNF-alpha concentrations, possibly due to particular features of PML compared with other opportunistic infections as it develops without detectable inflammatory changes in the CSF.

Human polyomavirus JC latency and reactivation status in blood of HIV-1-positive immunocompromised patients with and without progressive multifocal leukoencephalopathy

BACKGROUND

Human polyomavirus JC (JCV) induces human progressive multifocal leukoencephalopathy (PML) in patients with AIDS. Peripheral blood mononuclear cells (PBMC) of HIV-1-positive immunocompetent and immunocompromised patients can harbour JCV genome, but their precise role in JCV latency or reactivation status before the onset of PML remains hypothetical.

OBJECTIVES

To assess JCV latency or reactivation status in PBMC of HIV-1-positive immunocompromised patients without PML.

DESIGN

A group of 82 HIV-1-positive immunocompromised patients who did not have PML were compared with 10 patients with AIDS and PML and with 69 HIV-1-positive immunocompetent patients without PML.

METHODS

DNA and total RNA were extracted from PBMC. The presence of JCV DNA was demonstrated by a semi-nested polymerase chain reaction (PCR). By using primer pairs specific for an early gene,T, and a late gene, VP1, the expression of both early and late gene mRNA in PBMC could be identified using reverse transcriptase (RT) PCR.

RESULTS

JCV DNA was detected by PCR in 17.4% of 69 HIV-1-positive immunocompetent patients, in 23.2% of 82 HIV-1-positive immunocompromised patients, and in 60% of 10 patients with AIDS and PML. No correlation could be drawn between the detection of JCV DNA in the PBMC and the clinical or biological status of the HIV-1-positive patients. By using RT-PCR procedures, no expression of JCV early and late mRNA in PBMC was found in any patients.

CONCLUSIONS

JCV DNA is detectable in the PBMC of 20.5% of 151 HIV-1-infected patients independently of the CDC (Centers for Disease Control and Prevention) stages of the infection. Moreover, our results suggest that active replication of JCV in PBMC appears to be absent or at least a very rare event in HIV-1-positive immunocompromised patients with and without PML.

JC virus DNA is present in the mucosa of the human colon and in colorectal cancers

JC virus (JCV) is a polyoma virus that commonly infects humans. We have found T antigen DNA sequences of JCV in the mucosa of normal human colons, colorectal cancers, colorectal cancer xenografts raised in nude mice, and in the human colon cancer cell line SW480. A larger number of viral copies is present in cancer cells than in non-neoplastic colon cells, and sequence microheterogeneity occurs within individual colonic mucosal specimens. The improved yield of detection after treatment with topoisomerase I suggests that the viral DNA is negatively supercoiled in the human tissues. These results indicate that JCV DNA can be found in colonic tissues, which raises the possibility that this virus may play a role in the chromosomal instability observed in colorectal carcinogenesis.

Differential sialylation of cell surface glycoconjugates in a human B lymphoma cell line regulates susceptibility for CD95 (APO-1/Fas)-mediated apoptosis and for infection by a lymphotropic virus

Sialic acid, as a terminal saccharide residue on cell surface glycoconjugates, plays an important role in a variety of biological processes. In this study, we investigated subclones of the human B lymphoma cell line BJA-B for differences in the glycosylation of cell surface glycoconjugates, and studied the functional implications of such differences. With respect to the expression level of most of the tested B cell-associated antigens, as well as the presence of penultimate saccharide moieties on oligosaccharide chains, subclones were phenotypically indistinguishable. Marked differences among subclones, however, were found in the overall level of glycoconjugate sialylation, involving both alpha-2,6 and alpha-2,3-linked sialic acid residues. Accordingly, subclones were classified as highly- (group I) or hyposialylated (group II). The function of two sialic acid-dependent receptor-mediated processes is correlated with the sialylation status of BJA-B subclones. Susceptibility to and binding of the B lymphotropic papovavirus (LPV) was dependent on a high sialylation status of host cells, suggesting that differential sialylation in BJA-B cells can modulate LPV infection via its alpha-2,6-sialylated glycoprotein receptor. CD95-mediated apoptosis, induced by either the human CD95 ligand or a cytotoxic anti-CD95 monoclonal antibody, was drastically enhanced in hyposialylated group II cells. An increase in endogenous sialylation may be one antiapoptotic mechanism that converts tumor cells to a more malignant phenotype. To our knowledge, this is the first report demonstrating that differential sialylation in a clonal cell line may regulate the function of virus and signal-transducing receptors.

[Progressive multifocal leukoencephalopathy]

PATHOGENESIS

Progressive multifocal leukoencephalopathy is a demyelinating disease of the central nervous system caused by infection and reactivation of JC-virus. About 5% of all HIV-infected patients develop this fatal disease. Although pathogenesis is not completely understood, progressive multifocal leukoencephalopathy is thought to be a persistent infection. The kidneys, bone marrow, peripheral blood lymphocytes and the brain itself are candidates for latency sites of JC-virus. Loss of T-helper-cells in the course of HIV-infection or other immunosuppressive states result in reactivation of JC-virus.

DIAGNOSIS

Progressive multifocal leukoencephalopathy can be diagnosed by focal neurological symptoms, radiographic signs in magnetic resonance imaging and detection of JC-virus in brain tissue or cerebrospinal fluid.

TREATMENT

A specific therapy is not yet available or established. Highly active antiretroviral therapy (HAART) and cidofovir are promising and may prove useful in the near future.

Molecular cloning and expression of major structural protein VP1 of the human polyomavirus JC virus: formation of virus-like particles useful for immunological and therapeutic studies

The major structural viral protein, VP1, of the human polyomavirus JC virus (JCV), the causative agent of progressive multifocal leukoencephalopathy (PML), was expressed by using recombinant baculoviruses. Recombinant VP1 formed virus-like particles (VLP) with the typical morphology of empty JCV capsids. Purified VP1 VLP bind to SVG, B, and T cells, as well as to monkey kidney cells. After binding, VP1 VLP were also internalized with high efficiency and transported to the nucleus. Immunization studies revealed these particles as highly immunogenic when administered with adjuvant, while immunization without adjuvant induced no immune response. VP1 VLP hyperimmune serum inhibits binding to SVG cells and neutralizes natural JCV. Furthermore, the potential of VP1 VLP as an efficient transporter system for gene therapy was demonstrated. Exogenous DNA could be efficiently packaged into VP1 VLP, and the packaged DNA was transferred into COS-7 cells as shown by the expression of a marker gene. Thus, VP1 VLP are useful for PML vaccine development and represent a potential new transporter system for human gene therapy.

The J domain of papovaviral large tumor antigen is required for synergistic interaction with the POU-domain protein Tst-1/Oct6/SCIP

Large T antigens from polyomaviruses are multifunctional proteins with roles in transcriptional regulation, viral DNA replication, and cellular transformation. They have been shown to enhance the activity of various cellular transcription factors. In the case of the POU protein Tst-1/Oct6/SCIP, this enhancement involves a direct physical interaction between the POU domain of the transcription factor and the amino-terminal region of large T antigen. Here we have analyzed the structural requirements for synergistic interaction between the two proteins in greater detail. Tst-1/Oct6/SCIP and the related POU protein Brn-1 were both capable of direct physical interaction with large T antigen. Nevertheless, only Tst-1/Oct6/SCIP functioned synergistically with large T antigen. This differential behavior was due to differences in the amino-terminal regions of the proteins, as evident from chimeras between Tst-1/Oct6/SCIP and Brn-1. Synergy was specifically observed for constructs containing the amino-terminal region of Tst-1/Oct6/SCIP. Large T antigen, on the other hand, functioned synergistically with Tst-1/Oct6/SCIP only when the integrity of its J-domain-containing amino terminus was maintained. Mutations that disrupted the J domain concomitantly abolished the ability to enhance the function of Tst-1/Oct6/SCIP. The J domain of T antigen was also responsible for the physical interaction with Tst-1/Oct6/SCIP and could be replaced in this property by other J domains. Intriguingly, a heterologous J domain from a human DnaJ protein partially substituted for the amino terminus of T antigen even with regard to the synergistic enhancement of Tst-1/Oct6/SCIP function. Given the general role of J domains, we propose chaperone activity as the underlying mechanism for synergy between Tst-1/Oct6/SCIP and large T antigens.

Reciprocal interaction between two cellular proteins, Puralpha and YB-1, modulates transcriptional activity of JCVCY in glial cells

Cross communication between regulatory proteins is an important event in the control of eukaryotic gene transcription. Here we have examined the structural and functional interaction between two cellular regulatory proteins, YB-1 and Puralpha, on the 23-bp sequence element derived from the enhancer-promoter of the human polyomavirus JCV. YB-1 and Puralpha are single-stranded DNA binding proteins which recognize C/T- and GC/GA-rich sequences, respectively. Results from band shift studies demonstrated that while both proteins interact directly with their DNA target sequences within the 23-bp motif, each protein can regulate the association of the other one with the DNA. Affinity chromatography and coimmunoprecipitation provide evidence for a direct interaction between Puralpha and YB-1 in the absence of the DNA sequence. Ectopic expression of YB-1 and Puralpha in glial cells synergistically stimulated viral promoter activity via the 23-bp sequence element. Results from mutational studies revealed that residues between amino acids 75 and 203 of YB-1 and between amino acids 85 and 215 of Puralpha are important for the interaction between these two proteins. Functional studies with glial cells indicated that the region within Puralpha which mediates its association with YB-1 and binding to the 23-bp sequence is important for the observed activation of the JCV promoter by the Puralpha and YB-1 proteins. The results of this study suggest that the cooperative interaction between YB-1 and Puralpha mediates the synergistic activation of the human polyomavirus JCV genome by these cellular proteins. The importance of these findings for cellular and viral genes which are regulated by Puralpha and YB-1 is discussed.

Human neurotropic JC virus early protein deregulates glial cell cycle pathway and impairs cell differentiation

Progressive multifocal leukoencephalopathy (PML), a human demyelinating disease of the central nervous system (CNS), is induced upon replication of the human neurotropic virus, JCV, in glial cells. Similar to other polyomaviruses, replication of JCV is initiated and orchestrated by the viral early protein, T-antigen, and results in the cytolytic destruction of oligodendrocytes, the subset of glial cells responsible for myelin production, and the appearance of bizarre astrocytic glial cells in affected individuals. Earlier results from studies in transgenic animals have suggested that in the absence of viral replication, expression of JCV T-antigen induces pathology consistent with hypomyelination of the brain. These observations suggest that JCV T-antigen has the ability to deregulate oligodendrocyte and perhaps astrocyte function in the CNS. Here we demonstrate that expression of JCV T-antigen in the bipotential glial cell line, CG-4, severely affects the ability of these cells to differentiate toward oligodendrocyte and astrocyte lineages as evidenced by their distinct morphological changes. Examination of the activity of cell cycle regulatory proteins including cyclins and their associated kinases reveals that in the absence of T-antigen, differentiation of CG-4 cells toward astrocytes and oligodendrocytes is accompanied by a decline in cyclin E, cdk2, cyclin A, and cyclin B activity. In contrast, cdc2 activity increased upon CG-4 differentiation. In T-antigen-producing cells, distinct variations in the activity of several cyclins was observed. For example, while the activity of cdk2 and cyclin E was enhanced in T-antigen expressing astrocytes compared to their levels in control cells, the activity of cdc2 was decreased in this cell type. In oligodendrocytes, expression of T-antigen decreased the activity of several cyclins and cdks including cyclin E and cdc2. On the other hand, the level of expression and activity of cyclin A was increased. Thus, it is evident that JCV T-antigen deregulates several important cell cycle regulators during CG-4 differentiation, and these alterations may contribute to the process of cell growth and differentiation in glial cells. The importance of our findings with regard to the neuropathogenesis of PML is discussed.

Human anti-JC virus serum reacts with native but not denatured JC virus major capsid protein VP1

The immunoreactivity of human anti-JC virus (JCV) serum against the major capsid protein VP1 of JCV was analyzed by Western blot, dot blot, and hemagglutination inhibition (HAI) assays. JCV-positive human serum reacted with native but not denatured JCV major capsid protein VP1, as demonstrated by dot blot and Western blot. Rabbit antiserum raised against native JCV capsid had immunoreactivities similar to those of human anti-JCV serum. These results indicate that the antigenecity of native and denatured JCV VP1 is different. In addition, both JCV-positive human serum and rabbit antiserum raised against native JCV capsid protein inhibited the hemagglutination activity of JCV capsid particles. In contrast, rabbit antiserum raised against denatured JCV VP1 did not inhibit hemagglutination. These findings reveal that denaturation may alter the antigenic epitopes of JCV VP1. Therefore, keeping the JCV capsid protein native appears to be essential for serological or other immunological analyses of the virus.

Progressive multifocal leukoencephalopathy and human immunodeficiency virus-associated white matter lesions in AIDS: magnetization transfer MR imaging

PURPOSE

To determine the magnetization transfer features of progressive multifocal leukoencephalopathy (PML) and human immunodeficiency virus (HIV)-associated white matter lesions (WML) (hereafter, HIV-WML) on magnetic resonance (MR) images obtained in patients with acquired immunodeficiency syndrome (AIDS).

MATERIALS AND METHODS

Conventional MR imaging and magnetization transfer MR imaging were performed in 21 AIDS patients with 42 areas of white matter hyperintensity on MR images (13 patients had 25 PML lesions, eight patients had 17 WML). The magnetization transfer ratio was calculated for each lesion.

RESULTS

Compared with normal-appearing white matter (magnetization transfer ratio = 47.9%), both PML and HIV-WML showed reduced magnetization transfer ratio. The magnetization transfer ratio was significantly lower in PML lesions (magnetization transfer ratio = 26.1%) than in HIV-WML (magnetization transfer ratio = 38.0%, P < .0001), and there was no overlap in the magnetization transfer ratio between PML lesions and HIV-WML. The separation in magnetization transfer ratio between the two lesion types was valid for lesion as small as 0.5 cm2.

CONCLUSION

The larger reduction in magnetization transfer ratio for PML lesions is most likely due to demyelination, whereas the reduction in HIV-WML may be associated primarily with gliosis. PML lesions appear to cause strong reductions in magnetization transfer ratio early in the course of disease. Magnetization transfer MR imaging is a noninvasive tool that improves the differentiation between PML and HIV-WML in patients with AIDS.