JC virus multiplication in human hematopoietic progenitor cells requires the NF-1 class D transcription factor

Insights into the genetic characteristics, clustering patterns, and phylogeographic dynamics of the JC polyomavirus, 1993 to 2023

The human JC polyomavirus (JCV) is a widespread, neurotropic, opportunistic pathogen responsible for progressive multifocal leukoencephalopathy (PML) as well as other diseases in immunosuppressed individuals, including granule cell neuronopathy, JCV-associated nephropathy, encephalitis, and meningitis in rare cases. JCV classification is still unclear, where the ICTV (International Committee on Taxonomy of Viruses) has grouped all the strains into human polyomavirus 2, with no classification on clade and subclade levels. Therefore, JCV strains were previously classified using different genomic regions, e.g., full-length, VP1, and the V-T intergenic region etc., and the strains were grouped into several types related to various geographic locations and human ethnicities. However, neither of these classifications and nomenclature contemplates all the groups described so far. Herein, we evaluated all the available full-length coding genomes, VP1, and large T antigen nucleotide sequences of JCV reported during 1993-2023 and classified them into four major phylogenetic clades, i.e., GI-GIV, where GI is further grouped into two types GI.1 and GI.2 with five sub-clades each (GI.1/GI.2 a-e), GII into three (GII a-c), GIII as a separate clade, and GIV into seven sub-clades (GIV a-g). Similarly, the phylogeographic network analysis indicated four major clusters corresponding to GI-GIV clades, each with multiple subclusters and mutational sub-branches corresponding to the subclades. GI and GIV clusters are connected via GI.1-e reported from Europe and America, GII, GIII and GIV clusters are connected by GII-b and GII-c strains reported from Africa, while GIV cluster strains are connected to the Russia-Italy JCV haplotype. Furthermore, we identified JCV-variant-GS/B-Germany-1997 (GenBank ID: AF004350.1) as an inter-genotype recombinant having major and minor parents in the GI.1-e and GII-a clades, respectively. Additionally, the amino acid variability analysis revealed high entropy across all proteins. The large T antigen exhibited the highest variability, while the small t antigen showed the lowest variability. Our phylogenetic and phylogeographic analyses provide a new approach to genotyping and sub-genotyping and present a comprehensive classification system of JCV strains based on their genetic characteristics and geographic distribution, while the genetic recombination and amino acid variability can help identify pathogenicity and develop effective preventive and control measures against JCV infections.

Detection Analysis and Study of Genomic Region Variability of JCPyV, BKPyV, MCPyV, HPyV6, HPyV7 and QPyV in the Urine and Plasma of HIV-1-Infected Patients

Since it was clearly established that HIV/AIDS predisposes to the infection, persistence or reactivation of latent viruses, the prevalence of human polyomaviruses (HPyVs) among HIV-1-infected patients and a possible correlation between HPyVs and HIV sero-status were investigated. PCR was performed to detect and quantify JCPyV, BKPyV, MCPyV, HPyV6, HPyV7 and QPyV DNA in the urine and plasma samples of 103 HIV-1-infected patients. Subsequently, NCCR, VP1 and MCPyV LT sequences were examined. In addition, for MCPyV, the expression of transcripts for the LT gene was investigated. JCPyV, BKPyV and MCPyV's presence was reported, whereas HPyV6, HPyV7 and QPyV were not detected in any sample. Co-infection patterns of JCPyV, BKPyV and MCPyV were found. Archetype-like NCCRs were observed with some point mutations in plasma samples positive for JCPyV and BKPyV. The VP1 region was found to be highly conserved among these subjects. LT did not show mutations causing stop codons, and LT transcripts were expressed in MCPyV positive samples. A significant correlation between HPyVs' detection and a low level of CD4+ was reported. In conclusion, HPyV6, HPyV7 and QPyV seem to not have a clinical relevance in HIV-1 patients, whereas further studies are warranted to define the clinical importance of JCPyV, BKPyV and MCPyV DNA detection in these subjects.

Progressive multifocal leukoencephalopathy and the spectrum of JC virus-related disease

Progressive multifocal leukoencephalopathy (PML) is a devastating CNS infection caused by JC virus (JCV), a polyomavirus that commonly establishes persistent, asymptomatic infection in the general population. Emerging evidence that PML can be ameliorated with novel immunotherapeutic approaches calls for reassessment of PML pathophysiology and clinical course. PML results from JCV reactivation in the setting of impaired cellular immunity, and no antiviral therapies are available, so survival depends on reversal of the underlying immunosuppression. Antiretroviral therapies greatly reduce the risk of HIV-related PML, but many modern treatments for cancers, organ transplantation and chronic inflammatory disease cause immunosuppression that can be difficult to reverse. These treatments — most notably natalizumab for multiple sclerosis — have led to a surge of iatrogenic PML. The spectrum of presentations of JCV-related disease has evolved over time and may challenge current diagnostic criteria. Immunotherapeutic interventions, such as use of checkpoint inhibitors and adoptive T cell transfer, have shown promise but caution is needed in the management of immune reconstitution inflammatory syndrome, an exuberant immune response that can contribute to morbidity and death. Many people who survive PML are left with neurological sequelae and some with persistent, low-level viral replication in the CNS. As the number of people who survive PML increases, this lack of viral clearance could create challenges in the subsequent management of some underlying diseases.

In this Review, Cortese et al. provide an overview of the pathobiology and evolving presentations of progressive multifocal leukoencephalopathy and other diseases caused by JC virus, and discuss emerging immunotherapeutic approaches that could increase survival.

Progressive multifocal leukoencephalopathy (PML) is a rare, debilitating and often fatal disease of the CNS caused by JC virus (JCV).

JCV establishes asymptomatic, lifelong persistent or latent infection in immune competent hosts, but impairment of cellular immunity can lead to reactivation of JCV and PML.

PML most commonly occurs in patients with HIV infection or lymphoproliferative disease and in patients who are receiving natalizumab for treatment of multiple sclerosis.

The clinical phenotype of PML varies and is shaped primarily by the host immune response; changes in the treatment of underlying diseases associated with PML have changed phenotypes over time.

Other clinical manifestations of JCV infection have been described, including granule cell neuronopathy.

Survival of PML depends on reversal of the underlying immunosuppression; emerging immunotherapeutic strategies include use of checkpoint inhibitors and adoptive T cell transfer.

High mobility group nucleosomal binding 2 reduces integrin α5/β1-mediated adhesion of Klebsiella pneumoniae on human pulmonary epithelial cells via nuclear factor I

It has been reported that high mobility group nucleosomal binding domain 2 (HMGN2) is a nucleus-related protein that regulates gene transcription and plays a critical role in bacterial clearance. An elevated level of HMGN2 reduced integrin α5/β1 expression of human pulmonary epithelial A549 cells was demonstrated during Klebsiella pneumoniae infection, thus weakening bacterial adhesion and invasion. However, the mechanism by which HMGN2 regulates integrin expression remains unclear. This study found that a transcription factor-nuclear factor I (NFI), which serves as the potential target of HMGN2 regulated integrin expression. The results showed that HMGN2 was able to promote NFIA and NFIB expression by increasing H3K27 acetylation of NFIA/B promoter regions. The integrin α5/β1 expression was significantly enhanced by knockdown of NFIA/B via a siRNA approach. Meanwhile, NFIA/B silence could also compromise the inhibition effect of HMGN2 on the integrin α5/β1 expression. Mechanistically, it was demonstrated that HMGN2 facilitated the recruitment of NFI on the promoter regions of integrin α5/β1 according to the chromatin immunoprecipitation assay. In addition, it was further demonstrated that the knockdown of NFIA/B induced more adhesion of Klebsiella pneumoniae on pulmonary epithelial A549 cells, which could be reversed by the application of an integrin inhibitor RGD. The results revealed a regulatory role of HMGN2 on the transcription level of integrin α5/β1, indicating a potential treatment strategy against Klebsiella pneumoniae-induced infectious lung diseases.

BK virus infection in allogeneic hematopoietic cell transplantation: An update on pathogenesis, immune responses, diagnosis and treatments

In hematopoietic cell transplantation (HCT) patients, BK polyomavirus (BKPyV) infection results in significant morbidity mainly due to hemorrhagic cystitis (HC). Despite increased knowledge acquired over recent decades, no treatment has shown effectiveness in the management of organ damage in HCT allografts. This review summarizes the current knowledge on BKPyV, from the virus constitution to the pathophysiology and immune-related mechanisms. We next focus on BKPyV-induced HC in HCT to discuss the benefit of monitoring BKPyV viruria and viremia in the management of patients. At last, we review currently used therapeutics, along with future promising therapies to propose clinical and practical guidelines and further interesting research areas.

JC Polyomavirus Infection Reveals Delayed Progression of the Infectious Cycle in Normal Human Astrocytes

JC polyomavirus (JCPyV) infects 50 to 80% of the population and is the causative agent of a fatal demyelinating disease of the central nervous system (CNS). JCPyV presents initially as a persistent infection in the kidneys of healthy people, but during immunosuppression, the virus can reactivate and cause progressive multifocal leukoencephalopathy (PML). Within the CNS, JCPyV predominately targets two cell types, oligodendrocytes and astrocytes. Until recently, the role of astrocytes has been masked by the pathology in the myelin-producing oligodendrocytes, which are lytically destroyed by the virus. To better understand how astrocytes are impacted during JCPyV infection, the temporal regulation and infectious cycle of JCPyV were analyzed in primary normal human astrocytes (NHAs). Previous research to define the molecular mechanisms underlying JCPyV infection has mostly relied on the use of cell culture models, such as SVG-A cells (SVGAs), an immortalized, mixed population of glial cells transformed with simian virus 40 (SV40) T antigen. However, SVGAs present several limitations due to their immortalized characteristics, and NHAs represent an innovative approach to study JCPyV infection in vitro Using infectivity assays, quantitative PCR, and immunofluorescence assay approaches, we have further characterized JCPyV infectivity in NHAs. The JCPyV infectious cycle is significantly delayed in NHAs, and the expression of SV40 T antigen alters the cellular environment, which impacts viral infection in immortalized cells. This research establishes a foundation for the use of primary NHAs in future studies and will help unravel the role of astrocytes in PML pathogenesis.IMPORTANCE Animal models are crucial in advancing biomedical research and defining the pathogenesis of human disease. Unfortunately, not all diseases can be easily modeled in a nonhuman host or such models are cost prohibitive to generate, including models for the human-specific virus JC polyomavirus (JCPyV). JCPyV infects most of the population but can cause a rare, fatal disease, progressive multifocal leukoencephalopathy (PML). There have been considerable advancements in understanding the molecular mechanisms of JCPyV infection, but this has mostly been limited to immortalized cell culture models. In contrast, PML pathogenesis research has been greatly hindered because of the lack of an animal model. We have further characterized JCPyV infection in primary human astrocytes to better define the infectious process in a primary cell type. Albeit a cell culture model, primary astrocytes may better recapitulate human disease, are easier to maintain than other primary cells, and are less expensive than using an animal model.

Reduced expression of L-selectin in T-cells correlates with relative lymphocyte increase in patients with RRMS treated with natalizumab - functional implication towards PML risk

Objectives: Natalizumab (NTZ), a treatment indicated for patients with highly active Relapsing - Remitting Multiple Sclerosis (RRMS), is known to induce increased relative frequency of lymphocytes. Progressive Multifocal Leukoencephalitis (PML) is a rare but serious adverse event related to NTZ. Moreover, reduced L-selectin (CD62L) expression in T-cells in cryopreserved samples of patients with RRMS under NTZ has been proposed as a biomarker of pre-PML state. We explore the association between L-selectin expression in T-cells and hematological parameters in freshly processed samples of patients with RRMS under NTZ.Methods: We studied L-selectin expression in patients with: RRMS under NTZ (n=34), fingolimod (FTY, n=14), interferon-beta (IFNβ, n=22), glatiramer acetate (GA, N=17); in 9 patients with secondary progressive (SP) MS and in 6 healthy controls. Twenty-two patients under NTZ and 6 patients under FTY were followed for 18 months. One NTZ-treated patient developed PML during the study.Results: Patients under NTZ exhibited increased relative frequency of lymphocytes (40.02±1.45) compared to patients under first-line treatment (30.57±1.68, p<0.001) and to patients with SPMS (29±1.56, p=0.02), and a lower mean L-selectin expression in (69.39±1.73) compared to patients under first-line treatment (79.1±1.17, p=0.003). A negative correlation between the relative frequency of CD4+CD62L+ T-cells and the absolute lymphocyte counts (Pearson's r=0.367, p=0.033) was observed.Discussion: We hereby provide mechanistic insight in a possible pathway implicated in NTZ-related PML risk. These results further underline the need for thorough validation of L-selectin expression in T-cells as a potential pre-PML biomarker.

JCPyV-Induced MAPK Signaling Activates Transcription Factors during Infection

JC polyomavirus (JCPyV), a ubiquitous human pathogen, is the etiological agent of the fatal neurodegenerative disease progressive multifocal leukoencephalopathy (PML). Like most viruses, JCPyV infection requires the activation of host-cell signaling pathways in order to promote viral replication processes. Previous works have established the necessity of the extracellular signal-regulated kinase (ERK), the terminal core kinase of the mitogen-activated protein kinase (MAPK) cascade (MAPK-ERK) for facilitating transcription of the JCPyV genome. However, the underlying mechanisms by which the MAPK-ERK pathway becomes activated and induces viral transcription are poorly understood. Treatment of cells with siRNAs specific for Raf and MAP kinase kinase (MEK) targets proteins in the MAPK-ERK cascade, significantly reducing JCPyV infection. MEK, the dual-specificity kinase responsible for the phosphorylation of ERK, is phosphorylated at times congruent with early events in the virus infectious cycle. Moreover, a MAPK-specific signaling array revealed that transcription factors downstream of the MAPK cascade, including cMyc and SMAD4, are upregulated within infected cells. Confocal microscopy analysis demonstrated that cMyc and SMAD4 shuttle to the nucleus during infection, and nuclear localization is reduced when ERK is inhibited. These findings suggest that JCPyV induction of the MAPK-ERK pathway is mediated by Raf and MEK and leads to the activation of downstream transcription factors during infection. This study further defines the role of the MAPK cascade during JCPyV infection and the downstream signaling consequences, illuminating kinases as potential therapeutic targets for viral infection.

Infections with DNA Viruses, Adenovirus, Polyomaviruses, and Parvovirus B19 in Hematopoietic Stem Cell Transplant Recipients and Patients with Hematologic Malignancies

Infections due to adenovirus, polyomaviruses (BK and JC viruses), and parvovirus B19 may not be as common as infections due to other DNA viruses, such as cytomegalovirus in patients with hematological malignancies and the recipients of hematopoietic stem cell transplantation. However, these infections may result in life-threatening diseases that significantly impact patients' recovery, morbidity, and mortality. Treating physicians should be aware of the diseases associated with these viruses, the patient populations at increased risk for complications due to these infections, and the available diagnostic and therapeutic approaches.

Replication of JC Virus DNA in the G144 Oligodendrocyte Cell Line Is Dependent Upon Akt

Progressive multifocal leukoencephalopathy (PML) is an often-fatal demyelinating disease of the central nervous system. PML results when oligodendrocytes within immunocompromised individuals are infected with the human JC virus (JCV). We have identified an oligodendrocyte precursor cell line, termed G144, that supports robust levels of JCV DNA replication, a central part of the JCV life cycle. In addition, we have determined that JC virus readily infects G144 cells. Furthermore, we have determined that JCV DNA replication in G144 cells is stimulated by myristoylated (i.e., constitutively active) Akt and reduced by the Akt-specific inhibitor MK2206. Thus, this oligodendrocyte-based model system will be useful for a number of purposes, such as studies of JCV infection, establishing key pathways needed for the regulation of JCV DNA replication, and identifying inhibitors of this process.IMPORTANCE The disease progressive multifocal leukoencephalopathy (PML) is caused by the infection of particular brain cells, termed oligodendrocytes, by the JC virus. Studies of PML, however, have been hampered by the lack of an immortalized human cell line derived from oligodendrocytes. Here, we report that the G144 oligodendrocyte cell line supports both infection by JC virus and robust levels of JCV DNA replication. Moreover, we have established that the Akt pathway regulates JCV DNA replication and that JCV DNA replication can be inhibited by MK2206, a compound that is specific for Akt. These and related findings suggest that we have established a powerful oligodendrocyte-based model system for studies of JCV-dependent PML.

Efficient propagation of archetype JC polyomavirus in COS-7 cells: evaluation of rearrangements within the NCCR structural organization after transfection

John Cunningham virus (JCPyV) is an ubiquitous human pathogen that causes disease in immunocompromised patients. The JCPyV genome is composed of an early region and a late region, which are physically separated by the non-coding control region (NCCR). The DNA sequence of the NCCR distinguishes two forms of JCPyV, the designated archetype and the prototype, which resulted from a rearrangement of the archetype sequence. To date, the cell culture systems for propagating JCPyV archetype have been very limited in their availability and robustness. Prior to this study, it was demonstrated that JCPyV archetype DNA replicates in COS-7 simian kidney cells expressing SV40 TAg and COS-7 cells expressing HIV-1 Tat. Based on these observations, the present study was conducted to reproduce an in vitro model in COS-7 cells transfected with the JCPyV archetype strain in order to study JCPyV DNA replication and analyze NCCR rearrangements during the viral life cycle. The efficiency of JCPyV replication was evaluated by quantitative PCR (Q-PCR) and by hemagglutination (HA) assay after transfection. In parallel, sequence analysis of JCPyV NCCR was performed. JCPyV efficiently replicated in kidney-derived COS-7 cells, as demonstrated by a progressive increase in viral load and virion particle production after transfection. The archetypal structure of NCCR was maintained during the viral cycle, but two characteristic point mutations were detected 28 days after transfection. This model is a useful tool for analyzing NCCR rearrangements during in vitro replication in cells that are sites of viral persistence, such as tubular epithelial cells of the kidney.

The biology of JC polyomavirus

JC polyomavirus (JCPyV) is the causative agent of a fatal central nervous system demyelinating disease known as progressive multifocal leukoencephalopathy (PML). PML occurs in people with underlying immunodeficiency or in individuals being treated with potent immunomodulatory therapies. JCPyV is a DNA tumor virus with a double-stranded DNA genome and encodes a well-studied oncogene, large T antigen. Its host range is highly restricted to humans and only a few cell types support lytic infection in vivo or in vitro. Its oncogenic potential in humans has not been firmly established and the international committee on oncogenic viruses lists JCPyV as possibly carcinogenic. Significant progress has been made in understanding the biology of JCPyV and here we present an overview of the field and discuss some important questions that remain unanswered.

Polyomavirus JC microRNA expression after infection in vitro

The in vitro expression of the Polyomavirus JC (JCPyV) microRNAs, JC-miRNA-3p and -5p, at early time points post-infection was investigated. The expression of the JCPyV microRNAs was monitored in hematopoietic progenitor KG-1 cells and in kidney fibroblast-like COS-7 cells transformed with SV40 after infection with a JCPyV CY archetype viral clone. The JCPyV DNA viral load was low in KG-1 cells compared with that in COS-7 cells, which showed productive viral replication. The expression of the JCPyV microRNAs was observed from 12h after the viral infection of both cell types and in the exosomes present in their cell supernatant. Additionally, this study verified that the JCPyV microRNAs in the exosomes present in the supernatants produced by the infected cells might be carried into uninfected cells. These findings suggest that additional investigations of the expression of JCPyV microRNAs and their presence in exosomes are necessary to shed light on their regulatory role during viral reactivation.

Animal Models for Progressive Multifocal Leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a severe demyelinating disease of the CNS caused by the human polyomavirus JC (JCV). JCV replication occurs only in human cells and investigation of PML has been severely hampered by the lack of an animal model. The common feature of PML is impairment of the immune system. The key to understanding PML is working out the complex mechanisms that underlie viral entry and replication within the CNS and the immunosurveillance that suppresses the virus or allows it to reactivate. Early models involved the simple inoculation of JCV into animals such as monkeys, hamsters, and mice. More recently, mouse models transgenic for the gene encoding the JCV early protein, T-antigen, a protein thought to be involved in the disruption of myelin seen in PML, have been employed. These animal models resulted in tumorigenesis rather than demyelination. Another approach is to use animal polyomaviruses that are closely related to JCV but able to replicate in the animal such as mouse polyomavirus and SV40. More recently, novel models have been developed that involve the engraftment of human cells into the animal. Here, we review progress that has been made to establish an animal model for PML, the advances and limitations of different models and weigh future prospects.

B cells and progressive multifocal leukoencephalopathy: search for the missing link

Progressive multifocal leukoencephalopathy (PML) is a deadly demyelinating disease due to JC virus (JCV) replication in the brain. PML classically occurs in patients with severe immunodepression, and cases have recently been linked to therapeutic monoclonal antibodies such as natalizumab and also rituximab, which depletes B cells. B cells appear to play a complex role in the pathogenesis of PML. They may act as a viral reservoir and as a vector for viral dissemination in the central nervous system. Anti-JCV antibody responses appear to have a limited effect on JCV replication in the brain. However, accumulating evidence suggests that B cells may considerably influence T cell responses through their cytokine secretion. This immunomodulatory function of B cells may play an important role in the control of JCV infection and in the pathogenesis of PML, including rituximab-induced PML.

Human polyomavirus JC replication and non-coding control region analysis in multiple sclerosis patients under natalizumab treatment

In the last years, the treatment of multiple sclerosis (MS) patients with natalizumab has been associated with the occurrence of progressive multifocal leukoencephalopathy (PML) caused by human polyomavirus JC (JCV). Here, we have shown a significant correlation between patients with JC viruria and positive JC-specific antibody response and patients without JCV-specific antibodies after 1 year of natalizumab (p = 0.0006). Furthermore, JCV-specific quantitative PCR on urine and plasma samples, collected at the enrollment (t0) and every 4 months (t1, t2, t3) in the first year and at two time points (t4 and t5) in the second year of natalizumab treatment, indicated the prevalence of JC viremia rather than JC viruria only in the second year of treatment (p = 0.04). Moreover, the analysis of JCV non-coding control region (NCCR) sequences in peripheral blood mononuclear cells of patients with JC-specific antibodies after 12 natalizumab infusions (t3) revealed the presence of rearranged sequences, whereas the prevalence of genotypes 1A, 1B, and 4 was detected in these patients by VP1 sequence analysis. In summary, JC viruria evaluation seems to be useful to identify early those patients who do not already develop a humoral immune response against JCV. It may also be interesting to study the JCV NCCR rearrangements since they could give us new insights on the onset of neuro-invasive viral variants.

Persistence and pathogenesis of the neurotropic polyomavirus JC

Many neurological diseases of the central nervous system (CNS) are underpinned by malfunctions of the immune system, including disorders involving opportunistic infections. Progressive multifocal leukoencephalopathy (PML) is a lethal CNS demyelinating disease caused by the human neurotropic polyomavirus JC (JCV) and is found almost exclusively in individuals with immune disruption, including patients with human immunodeficiency virus/acquired immunodeficiency syndrome, patients receiving therapeutic immunomodulatory monoclonal antibodies to treat conditions such as multiple sclerosis, and transplant recipients. Thus, the public health significance of this disease is high, because of the number of individuals constituting the at-risk population. The incidence of PML is very low, whereas seroprevalence for the virus is high, suggesting infection by the virus is very common, and so it is thought that the virus is restrained but it persists in an asymptomatic state that can only occasionally be disrupted to lead to viral reactivation and PML. When JCV actively replicates in oligodendrocytes and astrocytes of the CNS, it produces cytolysis, leading to formation of demyelinated lesions with devastating consequences. Defining the molecular nature of persistence and events leading to reactivation of the virus to cause PML has proved to be elusive. In this review, we examine the current state of knowledge of the JCV life cycle and mechanisms of pathogenesis. We will discuss the normal course of the JCV life cycle including transmission, primary infection, viremia, and establishment of asymptomatic persistence as well as pathogenic events including migration of the virus to the brain, reactivation from persistence, viral infection, and replication in the glial cells of the CNS and escape from immunosurveillance.

Analysis of JC virus DNA replication using a quantitative and high-throughput assay

Progressive Multifocal Leukoencephalopathy (PML) is caused by lytic replication of JC virus (JCV) in specific cells of the central nervous system. Like other polyomaviruses, JCV encodes a large T-antigen helicase needed for replication of the viral DNA. Here, we report the development of a luciferase-based, quantitative and high-throughput assay of JCV DNA replication in C33A cells, which, unlike the glial cell lines Hs 683 and U87, accumulate high levels of nuclear T-ag needed for robust replication. Using this assay, we investigated the requirement for different domains of T-ag, and for specific sequences within and flanking the viral origin, in JCV DNA replication. Beyond providing validation of the assay, these studies revealed an important stimulatory role of the transcription factor NF1 in JCV DNA replication. Finally, we show that the assay can be used for inhibitor testing, highlighting its value for the identification of antiviral drugs targeting JCV DNA replication.

JC virus reactivation during prolonged natalizumab monotherapy for multiple sclerosis

OBJECTIVE

To determine the prevalence of JC virus (JCV) reactivation and JCV-specific cellular immune response during prolonged natalizumab treatment for multiple sclerosis (MS).

METHODS

We enrolled 43 JCV-seropositive MS patients, including 32 on natalizumab monotherapy >18 months, 6 on interferon β-1a monotherapy >36 months, and 5 untreated controls. We performed quantitative real-time polymerase chain reaction in cerebrospinal fluid (CSF), blood, and urine for JCV DNA, and we determined JCV-specific T-cell responses using enzyme-linked immunosorbent spot (ELISpot) and intracellular cytokine staining (ICS) assays, ex vivo and after in vitro stimulation with JCV peptides.

RESULTS

JCV DNA was detected in the CSF of 2 of 27 (7.4%) natalizumab-treated MS patients who had no symptoms or magnetic resonance imaging-detected lesions consistent with progressive multifocal leukoencephalopathy. JCV DNA was detected in blood of 12 of 43 (27.9%) and in urine of 11 of 43 (25.6%) subjects without a difference between natalizumab-treated patients and controls. JC viral load was higher in CD34(+) cells and in monocytes compared to other subpopulations. ICS was more sensitive than ELISpot. JCV-specific T-cell responses, mediated by both CD4(+) and CD8(+) T lymphocytes, were detected more frequently after in vitro stimulation. JCV-specific CD4(+) T cells were detected ex vivo more frequently in MS patients with JCV DNA in CD34(+) (p = 0.05) and B cells (p = 0.03).

INTERPRETATION

Asymptomatic JCV reactivation may occur in CSF of natalizumab-treated MS patients. JCV DNA load is higher in circulating CD34(+) cells and monocytes compared to other mononuclear cells, and JCV in blood might trigger a JCV-specific CD4(+) T-cell response. JCV-specific cellular immune response is highly prevalent in all JCV-seropositive MS patients, regardless of treatment.

Lymphocyte gene expression and JC virus noncoding control region sequences are linked with the risk of progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML)-derived noncoding control region (NCCR) sequences permitted greater early viral gene expression than kidney-associated NCCR sequences. This was driven in part by binding of the transcription factor Spi-B to unique PML-associated Spi-B binding sites. Spi-B is upregulated in developing B cells in response to natalizumab therapy, a known risk factor for PML. Naturally occurring JCV sequence variation, together with drug treatment-induced cellular changes, may synergize to create an environment leading to an increased risk of PML.

Human Polyomavirus JC monitoring and noncoding control region analysis in dynamic cohorts of individuals affected by immune-mediated diseases under treatment with biologics: an observational study

BACKGROUND

Progressive multifocal leukoencephalopathy (PML) onset, caused by Polyomavirus JC (JCPyV) in patients affected by immune-mediated diseases during biological treatment, raised concerns about the safety profile of these agents. Therefore, the aims of this study were the JCPyV reactivation monitoring and the noncoding control region (NCCR) and viral protein 1 (VP1) analysis in patients affected by different immune-mediated diseases and treated with biologics.

METHODS

We performed JCPyV-specific quantitative PCR of biological samples collected at moment of recruitment (t0) and every 4 months (t1, t2, t3, t4). Subsequently, rearrangements' analysis of NCCR and VP1 was carried out. Data were analyzed using χ2 test.

RESULTS

Results showed that at t0 patients with chronic inflammatory rheumatic diseases presented a JCPyV load in the urine significantly higher (p≤0.05) than in patients with multiple sclerosis (MS) and Crohn's disease (CD). It can also be observed a significant association between JC viruria and JCPyV antibodies after 1 year of natalizumab (p=0.04) in MS patients. Finally, NCCR analysis showed the presence of an archetype-like sequence in all urine samples, whereas a rearranged NCCR Type IR was found in colon-rectal biopsies collected from 2 CD patients after 16 months of infliximab. Furthermore, sequences isolated from peripheral blood mononuclear cells (PBMCs) of 2 MS patients with JCPyV antibody at t0 and t3, showed a NCCR Type IIR with a duplication of a 98 bp unit and a 66 bp insert, resulting in a boxB deletion and 37 T to G transversion into the Spi-B binding site. In all patients, a prevalence of genotypes 1A and 1B, the predominant JCPyV genotypes in Europe, was observed.

CONCLUSIONS

It has been important to understand whether the specific inflammatory scenario in different immune-mediated diseases could affect JCPyV reactivation from latency, in particular from kidneys. Moreover, for a more accurate PML risk stratification, testing JC viruria seems to be useful to identify patients who harbor JCPyV but with an undetectable JCPyV-specific humoral immune response. In these patients, it may also be important to study the JCPyV NCCR rearrangement: in particular, Spi-B expression in PBMCs could play a crucial role in JCPyV replication and NCCR rearrangement.

Human polyomavirus reactivation: disease pathogenesis and treatment approaches

JC and BK polyomaviruses were discovered over 40 years ago and have become increasingly prevalent causes of morbidity and mortality in a variety of distinct, immunocompromised patient cohorts. The recent discoveries of eight new members of the Polyomaviridae family that are capable of infecting humans suggest that there are more to be discovered and raise the possibility that they may play a more significant role in human disease than previously understood. In spite of this, there remains a dearth of specific therapeutic options for human polyomavirus infections and an incomplete understanding of the relationship between the virus and the host immune system. This review summarises the human polyomaviruses with particular emphasis on pathogenesis in those directly implicated in disease aetiology and the therapeutic options available for treatment in the immunocompromised host.

New insights on human polyomavirus JC and pathogenesis of progressive multifocal leukoencephalopathy

John Cunningham virus (JCV) is a member of the Polyomaviridae family. It was first isolated from the brain of a patient with Hodgkin disease in 1971, and since then the etiological agent of the progressive multifocal leukoencephalopathy (PML) was considered. Until the human immunodeficiency virus (HIV) pandemic, PML was rare: in fact HIV-induced immunodeficiency is the most common predisposing factor accounting for 85% of all instances of PML. This data led to intense research on JCV infection and resulted in better understanding of epidemiology and clinic-pathologic spectrum. Recently, cases of PML have been observed after the introduction of monoclonal antibodies, such as natalizumab, rituximab, efalizumab, and infliximab, in the treatment of autoimmune disease, underlining the important role of host immunity in PML pathogenesis. In this review current understanding of the JCV infection and the new findings relating to the pathogenesis of PML has been comprehensively revised, focusing our attention on the interaction between the cellular and viral molecular pathways implicated in the JCV infection and the modulating role of host immune surveillance in the viral reactivation from a latent state.

Differentiation of human fetal multipotential neural progenitor cells to astrocytes reveals susceptibility factors for JC virus

Viral infections of the central nervous system (CNS) are of increasing concern, especially among immunocompromised populations. Rodent models are often inappropriate for studies of CNS infection, as many viruses, including JC virus (JCV) and HIV, cannot replicate in rodent cells. Consequently, human fetal brain-derived multipotential CNS progenitor cells (NPCs) that can be differentiated into neurons, oligodendrocytes, or astrocytes have served as a model in CNS studies. NPCs can be nonproductively infected by JCV, while infection of progenitor-derived astrocytes (PDAs) is robust. We profiled cellular gene expression at multiple times during differentiation of NPCs to PDAs. Several activated transcription factors show commonality between cells of the brain, in which JCV replicates, and lymphocytes, in which JCV is likely latent. Bioinformatic analysis determined transcription factors that may influence the favorable transcriptional environment for JCV in PDAs. This study attempts to provide a framework for understanding the functional transcriptional profile necessary for productive JCV infection.

Molecular biology, epidemiology, and pathogenesis of progressive multifocal leukoencephalopathy, the JC virus-induced demyelinating disease of the human brain

Progressive multifocal leukoencephalopathy (PML) is a debilitating and frequently fatal central nervous system (CNS) demyelinating disease caused by JC virus (JCV), for which there is currently no effective treatment. Lytic infection of oligodendrocytes in the brain leads to their eventual destruction and progressive demyelination, resulting in multiple foci of lesions in the white matter of the brain. Before the mid-1980s, PML was a relatively rare disease, reported to occur primarily in those with underlying neoplastic conditions affecting immune function and, more rarely, in allograft recipients receiving immunosuppressive drugs. However, with the onset of the AIDS pandemic, the incidence of PML has increased dramatically. Approximately 3 to 5% of HIV-infected individuals will develop PML, which is classified as an AIDS-defining illness. In addition, the recent advent of humanized monoclonal antibody therapy for the treatment of autoimmune inflammatory diseases such as multiple sclerosis (MS) and Crohn's disease has also led to an increased risk of PML as a side effect of immunotherapy. Thus, the study of JCV and the elucidation of the underlying causes of PML are important and active areas of research that may lead to new insights into immune function and host antiviral defense, as well as to potential new therapies.

Stimulation of BK virus DNA replication by NFI family transcription factors

BK polyomavirus (BKV) establishes persistent, low-level, and asymptomatic infections in most humans and causes polyomavirus-associated nephropathy (PVAN) and other pathologies in some individuals. The activation of BKV replication following kidney transplantation, leading to viruria, viremia, and, ultimately, PVAN, is associated with immune suppression as well as inflammation and stress from ischemia-reperfusion injury of the allograft, but the stimuli and molecular mechanisms leading to these pathologies are not well defined. The replication of BKV DNA in cell cultures is regulated by the viral noncoding control region (NCCR) comprising the core origin and flanking sequences, to which BKV T antigen (Tag), cellular proteins, and small regulatory RNAs bind. Six nuclear factor I (NFI) binding sites occur in sequences flanking the late side of the core origin (the enhancer) of the archetype virus, and their mutation, either individually or in toto, reduces BKV DNA replication when placed in competition with templates containing intact BKV NCCRs. NFI family members interacted with the helicase domain of BKV Tag in pulldown assays, suggesting that NFI helps recruit Tag to the viral core origin and may modulate its function. However, Tag may not be the sole target of the replication-modulatory activities of NFI: the NFIC/CTF1 isotype stimulates BKV template replication in vitro at low concentrations of DNA polymerase-α primase (Pol-primase), and the p58 subunit of Pol-primase associates with NFIC/CTF1, suggesting that NFI also recruits Pol-primase to the NCCR. These results suggest that NFI proteins (and the signaling pathways that target them) activate BKV replication and contribute to the consequent pathologies caused by acute infection.

JC virus promoter/enhancers contain TATA box-associated Spi-B-binding sites that support early viral gene expression in primary astrocytes

JC virus (JCV) is the aetiological agent of the demyelinating disease progressive multifocal leukoencephalopathy, an AIDS defining illness and serious complication of mAb therapies. Initial infection probably occurs in childhood. In the working model of dissemination, virus persists in the kidney and lymphoid tissues until immune suppression/modulation causes reactivation and trafficking to the brain where JCV replicates in oligodendrocytes. JCV infection is regulated through binding of host factors such as Spi-B to, and sequence variation in the non-coding control region (NCCR). Although NCCR sequences differ between sites of persistence and pathogenesis, evidence suggests that the virus that initiates infection in the brain disseminates via B-cells derived from latently infected haematopoietic precursors in the bone marrow. Spi-B binds adjacent to TATA boxes in the promoter/enhancer of the PML-associated JCV Mad-1 and Mad-4 viruses but not the non-pathogenic, kidney-associated archetype. The Spi-B-binding site of Mad-1/Mad-4 differs from that of archetype by a single nucleotide, AAAAGGGAAGGGA to AAAAGGGAAGGTA. Point mutation of the Mad-1 Spi-B site reduced early viral protein large T-antigen expression by up to fourfold. Strikingly, the reverse mutation in the archetype NCCR increased large T-antigen expression by 10-fold. Interestingly, Spi-B protein binds the NCCR sequence flanking the viral promoter/enhancer, but these sites are not essential for early viral gene expression. The effect of mutating Spi-B-binding sites within the JCV promoter/enhancer on early viral gene expression strongly suggests a role for Spi-B binding to the viral promoter/enhancer in the activation of early viral gene expression.

Transcription factor Spi-B binds unique sequences present in the tandem repeat promoter/enhancer of JC virus and supports viral activity

Progressive multifocal leukoencephalopathy (PML) is an often fatal demyelinating disease caused by lytic infection of oligodendrocytes with JC virus (JCV). The development of PML in non-immunosuppressed individuals is a growing concern with reports of mortality in patients treated with mAb therapies. JCV can persist in the kidneys, lymphoid tissue and bone marrow. JCV gene expression is restricted by non-coding viral regulatory region sequence variation and cellular transcription factors. Because JCV latency has been associated with cells undergoing haematopoietic development, transcription factors previously reported as lymphoid specific may regulate JCV gene expression. This study demonstrates that one such transcription factor, Spi-B, binds to sequences present in the JCV promoter/enhancer and may affect early virus gene expression in cells obtained from human brain tissue. We identified four potential Spi-B-binding sites present in the promoter/enhancer elements of JCV sequences from PML variants and the non-pathogenic archetype. Spi-B sites present in the promoter/enhancers of PML variants alone bound protein expressed in JCV susceptible brain and lymphoid-derived cell lines by electromobility shift assays. Expression of exogenous Spi-B in semi- and non-permissive cells increased early viral gene expression. Strikingly, mutation of the Spi-B core in a binding site unique to the Mad-4 variant was sufficient to abrogate viral activity in progenitor-derived astrocytes. These results suggest that Spi-B could regulate JCV gene expression in susceptible cells, and may play an important role in JCV activity in the immune and nervous systems.

JC virus-induced Progressive Multifocal Leukoencephalopathy

Progressive multifocal encephalopathy (PML) is a fatal demyelinating disease of the central nervous system (CNS), caused by the lytic infection of oligodendrocytes by a human polyomavirus, JC virus (JCV). PML is rare disease but mostly develops in patients with underlying immunosuppressive conditions, including Hodgkin's lymphoma, lymphoproliferative diseases, in those undergoing antineoplastic therapy and AIDS. However, consistent with the occurrence of PML under immunocompromised conditions, this disease seems to be also steadily increasing among autoimmune disease patients (multiple sclerosis and Crohn's disease), who are treated with antibody-based regimens (natalizumab, efalizumab and rituximab). This unexpected occurrence of the disease among such a patient population reconfirms the existence of a strong link between the underlying immunosuppressive conditions and development of PML. These recent observations have generated a new interest among investigators to further examine the unique biology of JCV.

Molecular regulation of JC virus tropism: insights into potential therapeutic targets for progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a growing concern for patients undergoing immune modulatory therapies for treatment of autoimmune diseases such as multiple sclerosis. Currently, there are no drugs approved for the treatment of PML that have been demonstrated in the patient to effectively and reproducibly alter the course of disease progression. The human polyoma virus JC is the causative agent of PML. JC virus (JCV) dissemination is tightly controlled by regulation of viral gene expression from the promoter by cellular transcription factors expressed in cells permissive for infection. JCV infection likely occurs during childhood, and latent virus containing PML-associated promoter sequences is maintained in lymphoid cells within the bone marrow. Because development of PML is tightly linked to suppression and or modulation of the immune system as in development of hematological malignancies, AIDS, and monoclonal antibody treatments, further scrutiny of the course of JCV infection in immune cells will be essential to our understanding of development of PML and identification of new therapeutic targets.

[Progressive multifocal leukoencephalopathy. Undesirable side effect of immunotherapy]

As new cases arise of progressive multifocal leukoencephalopathy (PML) in patients with multiple sclerosis (MS) treated with the monoclonal antibody natalizumab, a critical discussion about risks and advantages of this specific kind of immunotherapy appears necessary. Practical consequences and treatment options are addressed based on current concepts of PML's pathogenesis in patients treated with natalizumab. Critical patient selection based on risk:benefit considerations, limited therapy regimens, early diagnosis of PML by clinical and paraclinical criteria, and therapeutic perspectives for treating PML are discussed. The risk of PML in patients with MS needs to be continually monitored and should be reduced with all means available to ensure optimal outcome.

Restriction of human polyomavirus BK virus DNA replication in murine cells and extracts

BK virus (BKV) causes persistent and asymptomatic infections in most humans and is the etiologic agent of polyomavirus-associated nephropathy (PVAN) and other pathologies. Unfortunately, there are no animal models with which to study activation of BKV replication in the human kidney and the accompanying PVAN. Here we report studies of the restriction of BKV replication in murine cells and extracts and the cause(s) of this restriction. Upon infection of murine cells, BKV expressed large T antigen (TAg), but viral DNA replication and progeny were not detected. Transfection of murine cells with BKV TAg expression vectors also caused TAg expression without accompanying DNA replication. Analysis of the replication of DNAs containing chimeric BKV and murine polyomavirus origins revealed the importance of BKV core origin sequences and TAg for DNA replication. A sensitive assay was developed with purified BKV TAg that supported TAg-dependent BKV DNA replication with human but not with murine cell extracts. Addition of human replication proteins, DNA polymerase alpha-primase, replication protein A, or topoisomerase I to the murine extracts with BKV TAg did not rescue viral DNA replication. Notably, addition of murine extracts to human extracts inhibited BKV TAg-dependent DNA replication at a step prior to or during unwinding of the viral origin. These findings and differences in replication specificity between BKV TAg and the TAgs of simian virus 40 (SV40) and JC virus (JCV) and their respective origins implicate features of the BKV TAg and origin distinct from SV40 and JCV in restriction of BKV replication in murine cells.

Virus receptors and tropism

Polyomaviruses are small, tumorigenic, nonenveloped viruses that infect several different species. Interaction of these viruses with cell surface receptors represents the initial step during infection of host cells. This interaction can be a major determinant of viral host and tissue tropism. This chapter reviews what is currently known about the cellular receptors for each of five polyomavirus family members: Mouse polyomavirus (PyV), JC virus (JCV), BK virus (BKV), Lymphotropic papovavirus (LPV) and Simian virus 40 (SV40). These polyomaviruses serve to illustrate the enormous diversity of virus-cell surface interactions and allow us to closely evaluate the role of receptors in their life cycles. The contribution of other factors such as transcriptional regulators and signaling pathways are also summarized.

Human polyomavirus JC and BK persistent infection

Primary contact with the human polyomaviruses (HPV) is followed by lifelong persistence of viral DNA in its host. The most prominent organs affected are the kidney, the Central Nervous System (CNS)and the hematopoietic system. Under impairment of immune competence limited activation of virus infection can be followed by prolonged virus multiplication, severe destruction of tissue and disease. The mechanisms responsible for activation episodes of the asymptomatic persistent infection are not understood and questions on cellular localization, routes of dissemination of HPV infection and its activation are controversially discussed. The type of interaction of HPVs with target organs and patients groups is highly differentiated. Organ-specific activation above basic level argues for strong dependence on the respective immune states of risk group patients. However, since immune impairment generally plays an important role in the activation of polyomavirus infection, amplification of virus deoxyribonucleic acid (DNA) and activation of virus replication is also a normal event that is probably subject to immunomodulation in the healthy individual. It also becomes clear that BKV and JCV infection is differentially regulated by mechanisms depending on the balance of immune control as well as on organ-specific signalling.

JC Virus Can Infect Human Immune and Nervous System Progenitor Cells

Recent advances in stem cell biology have called attention to the role these cells may play in the pathogenesis of systemic and nervous system diseases. Although not capable of indefinite self renewal and pluripotentiality as stem cells are, progenitor cells can give rise to cells of different lineages. It is infection of these differentiated cells that has traditionally been associated with the pathology and symptoms of viral-induced disease. However, neural progenitor cells have been shown, in vitro, to be susceptible to infection by neurotropic viruses such as the human polyomavirus, JCV, and the lentivirus, HIV-1. These progenitor cells, which exist during development as well as in the fully developed adult brain, could therefore be involved in neuropathogenesis. Morever, JCV can also infect progenitor cells of the hematopoietic system, derivatives of which have been implicated in the trafficking of virus from the periphery to the brain. Interestingly, susceptibility to and molecular regulation of JCV infection in hematopoietic cells closely parallels what has been observed in glial cells. The biological interaction between the immune and nervous systems that exists in the dissemination of virus from periphery to nervous system and the susceptibility of both systems to JCV infection provide potential for hematopoietic and neural progenitor cell involvement in JCV pathogenesis.

Viral proteomics: a promising approach for understanding JC virus tropism

The human polyomavirus JC virus (JCV) is responsible for the CNS demyelination observed in cases of progressive multifocal leukoencephalopathy. The JCV regulatory region (promoter) is a hypervariable, noncoding, nucleotide sequence positioned between the early and late protein-coding regions in the viral genome. Selective binding of cellular transcription factors to this promoter region participates in the control of viral tropism. Hence, further study of these proteins might provide new insights into JCV tropism and associated pathogenesis. This review gives an overview of viral proteomics - the study of all proteins expressed from the viral gene transcripts, and all the cellular proteins that play a role in JCV tropism. It also describes a new biochemical approach for studying relevant JCV promoter-binding proteins, which is an anchored-JCV transcriptional promoter (ATP) assay. An ATP assay utilizes the product of PCR-amplified JCV promoter sequences coupled with Sepharose beads in order to capture and isolate cellular nuclear proteins with specific promoter-binding affinity for analysis. Proteins that bind to JCV-ATPs can be eluted and subjected to proteomic analysis. Insights from this approach may improve the understanding of viral and cellular parameters that control JCV tropism.

The role of sialic acid in human polyomavirus infections

JC virus (JCV) and BK virus (BKV) are human polyomaviruses that infect approximately 85% of the population worldwide [1,2]. JCV is the underlying cause of the fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML), a condition resulting from JCV induced lytic destruction of myelin producing oligodendrocytes in the brain [3]. BKV infection of kidneys in renal transplant recipients results in a gradual loss of graft function known as polyomavirus associated nephropathy (PVN) [4]. Following the identification of these viruses as the etiological agents of disease, there has been greater interest in understanding the basic biology of these human pathogens [5,6]. Recent advances in the field have shown that viral entry of both JCV and BKV is dependent on the ability to interact with sialic acid. This review focuses on what is known about the human polyomaviruses and the role that sialic acid plays in determining viral tropism.

JC virus minor capsid proteins Vp2 and Vp3 are essential for virus propagation

Virus-encoded capsid proteins play a major role in the life cycles of all viruses. The JC virus capsid is composed of 72 pentamers of the major capsid protein Vp1, with one of the minor coat proteins Vp2 or Vp3 in the center of each pentamer. Vp3 is identical to two-thirds of Vp2, and these proteins share a DNA binding domain, a nuclear localization signal, and a Vp1-interacting domain. We demonstrate here that both the minor proteins and the myristylation site on Vp2 are essential for the viral life cycle, including the proper packaging of its genome.

Interactions between c-Jun, nuclear factor 1, and JC virus promoter sequences: implications for viral tropism

The infectious cycle of the human polyomavirus JC (JCV) is ultimately regulated in cellular nuclei at the level of viral protein expression and genomic replication. Such activity is prompted by interactions between variant nucleotide sequences within the JCV regulatory region (promoter) and cellular transcription factors that bind specific DNA consensus sites. In previous work we identified an NF-1 class member, NF-1X, as a critical transcription factor affecting the JCV cellular host range. Within variant JCV promoters, as well as other viral and cellular promoters, adjacently located NF-1 and AP-1 consensus sites are often found. The close proximity of these two binding sites suggests the opportunity for interaction between NF-1 and AP-1 proteins. Here, by electrophoretic mobility shift assays, we show temporal and dose-dependent interference by an AP-1 family member, c-Jun, upon NF-1 proteins binding an NF-1 consensus site derived from JCV promoter sequence. Moreover, as demonstrated by protein-protein interaction assays, we identify specific binding affinity independent of DNA binding between NF-1X and c-Jun. Finally, to compare the binding profiles of NF-1X and c-Jun on JCV promoter sequence in parallel with in vivo detection of viral activity levels, we developed an anchored transcriptional promoter (ATP) assay. With use of extracts from JCV-infected cells transfected to overexpress either NF-1X or c-Jun, ATP assays showed concurrent increases in NF-1X binding and viral protein expression. Conversely, increased c-Jun binding accompanied decreases in both NF-1X binding and viral protein expression. Therefore, inhibition of NF-1X binding by c-Jun appears to play a role in regulating levels of JCV activity.

Nuclear factor-1-X regulates astrocyte-specific expression of the alpha1-antichymotrypsin and glial fibrillary acidic protein genes

Discrete tissue-specific changes in chromatin structure of the distal serpin subcluster on human chromosome 14q32.1 allow a single gene encoding alpha1-antichymotrypsin (ACT) to be expressed in astrocytes and glioma cells. This astrocyte-specific regulation involves activatory protein-1 (AP-1) because overexpression of dominant-negative c-jun(TAM67) abolishes ACT expression in glioma cells. Here we identify a new regulatory element, located within the -13-kb enhancer of the ACT gene, that binds nuclear factor-1 (NFI) and is indispensable for the full basal transcriptional activity of the ACT gene. Furthermore, down-regulation of NFI expression by siRNA abolishes basal ACT expression in glioma cells. However, NFI does not mediate astrocyte-specific expression by itself, but likely cooperates with AP-1. A detailed analysis of the 14-kb long 5'-flanking region of the ACT gene indicated the presence of adjacent NFI and AP-1 elements that colocalized with DNase I-hypersensitive sites found in astrocytes and glioma cells. Interestingly, knock-down of NFI expression also specifically abrogates the expression of glial acidic fibrillary protein (GFAP), which is an astrocyte-specific marker protein. Mutations introduced into putative NFI and AP-1 elements within the 5'-flanking region of the GFAP gene also diminished basal expression of the reporter. In addition, we found, using isoform-specific siRNAs, that NFI-X regulates the astrocyte-specific expression of ACT and GFAP. We propose that NFI-X cooperates with AP-1 by an unknown mechanism in astrocytes, which results in the expression of a subset of astrocyte-specific genes.

Sp1/3 and NF-1 mediate basal transcription of the human P2X1 gene in megakaryoblastic MEG-01 cells

BACKGROUND

P2X1 receptors play an important role in platelet function as they can induce shape change, granule centralization and are also involved in thrombus formation. As platelets have no nuclei, the level of P2X1 expression depends on transcriptional regulation in megakaryocytes, the platelet precursor cell. Since nothing is known about the molecular mechanisms regulating megakaryocytic P2X1 expression, this study aimed to identify and functionally characterize the P2X1 core promoter utilized in the human megakaryoblastic cell line MEG-01.

RESULTS

In order to identify cis-acting elements involved in the transcriptional regulation of P2X1 expression, the ability of 4.7 kb P2X1 upstream sequence to drive luciferase reporter gene expression was tested. Low promoter activity was detected in proliferating MEG-01 cells. This activity increased 20-fold after phorbol-12-myristate-13-acetate (PMA) induced differentiation. A transcription start site was detected 365 bp upstream of the start codon by primer extension. Deletion analysis of reporter constructs indicated a core promoter located within the region -68 to +149 bp that contained two Sp1 sites (named Sp1a and Sp1b) and an NF-1 site. Individual mutations of Sp1b or NF-1 binding sites severely reduced promoter activity whereas triple mutation of Sp1a, Sp1b and NF-1 sites completely abolished promoter activity in both untreated and PMA treated cells. Sp1/3 and NF-1 proteins were shown to bind their respective sites by EMSA and interaction of Sp1/3, NF-1 and TFIIB with the endogenous P2X1 core promoter in MEG-01 cells was demonstrated by chromatin immunoprecipitation. Alignment of P2X1 genes from human, chimp, rat, mouse and dog revealed consensus Sp1a, Sp1b and NF-1 binding sites in equivalent positions thereby demonstrating evolutionary conservation of these functionally important sites.

CONCLUSION

This study has identified and characterized the P2X1 promoter utilized in MEG-01 cells and shown that binding of Sp1/3 and NF-1 to elements in the direct vicinity of the transcription start site is essential for basal transcription. Targeting the function of these transcription factors in megakaryocytes may therefore provide a basis for the future therapeutic manipulation of platelet P2X1 function.

Investigation on the role of cell transcriptional factor Sp1 and HIV-1 TAT protein in PML onset or development

JC virus (JCV) causes progressive multifocal leukoencephalopathy (PML), characterized by multiple areas of demyelination and attendant loss of brain function. PML is often associated with immunodepression and it is significantly frequent in AIDS patients. The viral genome is divided into early and late genes, between which lies a non-coding control region (NCCR) that regulates JCV replication and presents a great genetic variability. The NCCR of JCV archetype (CY strain) is divided into six regions: A-F containing binding sites for cell factors involved in viral transcription. Deletions and enhancements of these binding sites characterize JCV variants, which could promote viral gene expression and could be more suitable for the onset or development of PML. Therefore, we evaluated by means of polymerase chain reaction (PCR) the presence of JCV genome in cerebrospinal fluid (CSF) of HIV positive and negative subjects both with PML and after sequencing, we analyzed the viral variants found focusing on Sp1 binding sites (box B and D) and up-TAR sequence (box C). It is known that Sp1 activates JCV early promoter and can contribute in maintaining methylation-free CpG islands in active genes, while up-TAR sequence is important for HIV-1 Tat stimulation of JCV late promoter. Our results showed that in HIV-positive subjects all NCCR structures presented enhancements of up-TAR element, whereas in HIV-negative subjects both Sp1 binding sites were always retained. Therefore, we can support the synergism HIV-1/JCV in CNS and we can hypothesize that both Sp1 binding sites could be important to complete JCV replication cycle in absence of HIV-coinfection.

Internalization of exogenous human immunodeficiency virus-1 protein, Tat, by KG-1 oligodendroglioma cells followed by stimulation of DNA replication initiated at the JC virus origin

JC virus (JCV) is the etiological agent of an opportunistic brain infection, progressive multifocal leukoencephalopathy (PML), in AIDS. PML is fatal in approximately 4% of HIV-infected individuals, and although the overall incidence has fallen due to highly aggressive antiretroviral therapy (HAART), this percent has remained steady. It has been shown that the Tat protein of human immunodeficiency virus-1 (HIV-1) interacts in cells with cellular protein Puralpha. This interaction can stimulate transcription of both HIV-1 and JCV genes. HIV-1, however, infects primarily microglia and astrocytes in the brain, whereas JCV infects primarily oligodendrocytes. Although HIV-1 has been shown capable of infecting oligodendrocytes in vitro (Albright et al., 1996), no instance of viral coinfection of such cells with JCV has been reported. Tat is known to be secreted from cells in which it is made. Here we ask whether such exogenous Tat can influence JCV replication in oligodendrocytes. We find that glial cells infected with either HIV-1 or JCV are in proximity at the outer edge of PML lesions. Exogenous Tat is avidly incorporated into cultured KG-1 oligodendroglioma cells over a 72-h period and is colocalized with endogenous Puralpha both nuclear and juxtanuclear. At concentrations in the medium well below the pM range, Tat stimulates several-fold the replication in vivo of DNA initiated at the JCV origin. These results define a pathway by which a protein made by HIV-1 can directly affect the course of infection by another disease-causing virus.

Astrocyte differentiation selectively upregulates CCL2/monocyte chemoattractant protein-1 in cultured human brain-derived progenitor cells

Chemokines (chemoattractant cytokines) and their receptors are present in the brain and may play roles in both neurodevelopment and neuropathology. Increased brain levels of monocyte chemoattractant protein-1 (MCP-1), also known as CCL2, are found in patients with human immunodeficiency virus type 1 (HIV-1)-associated dementia and other acute and chronic neurologic diseases. Although the function of CCL2 in the brain is unclear, it is believed that upregulation of this chemokine during neuropathologic or neuroinflammatory conditions leads to recruitment of activated monocytes into the brain, where they differentiate into macrophages producing neurotoxic and inflammatory molecules. We recently showed that human fetal brain-derived progenitor cells are susceptible to HIV-1 and JC virus infection, and that differentiation toward an astrocyte phenotype increased virus production from these cells. In the current study, we found that in the absence of infection, progenitors produced moderate levels of CCL2 (5.6 ng per million cells). Astrocyte differentiation over 3 weeks increased CCL2 protein levels 30-fold in a biphasic manner, whereas neuronal differentiation decreased production 20-fold. Electromobility shift assays (EMSAs) demonstrated increased nuclear NF-kappaB levels within 2 h of initiating astrocyte differentiation, and inhibitors of NF-kappaB activation partially blocked the CCL2 increase in differentiating astrocytes. Transfection of progenitors with mutated CCL2 promoter/CAT reporter constructs showed that the distal promoter region, containing NF-kappaB and NF-I binding sites, is important for differentiation-induced CCL2 upregulation. Together these results suggest that the transcription factor NF-kappaB, and possibly NF-I, contribute to the upregulation of CCL2 chemokine production during the differentiation of human progenitor cells toward an astrocyte phenotype.

Transcriptional activation of JC virus early promoter by phorbol ester and interleukin-1β: critical role of nuclear factor-1

JC virus causes the fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML) under immunosuppressive states such as AIDS. During the pathogenesis of AIDS, HIV-infected microglia secrete cytokines including interleukin-1 and tumor necrosis factor-alpha (TNF-alpha), which affect neuronal cells resulting in dysfunction of the CNS. We hypothesized that extracellular stimuli released from HIV-infected microglia may reactivate JC virus by affecting neighboring oligodendrocytes. In the present study, we found that phorbol myristate acetate (PMA) and interleukin-1beta (IL-1beta) dramatically increased JC virus transcription in glial cells. Site-directed mutagenesis and gel shift analyses revealed that PMA and IL-1beta strongly induced nuclear factor-1 (NF-1) binding to the JC virus enhancer region, increasing transcriptional activity of the viral early promoter. Additionally, we demonstrated that protein kinase C (PKC) pathways were involved in the PMA/IL-1beta-mediated up-regulation of the JC virus early promoter. These findings may represent one of the possible mechanisms for higher incidence of PML among AIDS patients.

Stromal cell-derived factor 1-mediated CXCR4 signaling in rat and human cortical neural progenitor cells

Stromal cell-derived factor 1 (SDF-1) and the chemokine receptor CXCR4 are highly expressed in the nervous system. Knockout studies have suggested that both SDF-1 and CXCR4 play essential roles in cerebellar, hippocampal, and neocortical neural cell migration during embryogenesis. To extend these observations, CXCR4 signaling events in rat and human neural progenitor cells (NPCs) were examined. Our results show that CXCR4 is expressed in abundance on rat and human NPCs. Moreover, SDF-1alpha induced increased NPCs levels of inositol 1,4,5-triphosphate, extracellular signal-regulated kinases 1/2, Akt, c-Jun N-terminal kinase, and intracellular calcium whereas it diminished cyclic adenosine monophosphate. Finally, SDF-1alpha can induce human NPC chemotaxis in vitro, suggesting that CXCR4 plays a functional role in NPC migration. Both T140, a CXCR4 antagonist, and pertussis toxin (PTX), an inactivator of G protein-coupled receptors, abrogated these events. Ultimately, this study suggested that SDF-1alpha can influence NPC function through CXCR4 and that CXCR4 is functional on NPC.