A novel role of Rac1 GTPase in JCV T-antigen-mediated beta-catenin stabilization

Crosstalk between the Intestinal Virome and Other Components of the Microbiota, and Its Effect on Intestinal Mucosal Response and Diseases

In recent years, there has been ample evidence illustrating the effect of microbiota on gut immunity, homeostasis, and disease. Most of these studies have engaged more efforts in understanding the role of the bacteriome in gut mucosal immunity and disease. However, studies on the virome and its influence on gut mucosal immunity and pathology are still at infancy owing to limited metagenomic tools. Nonetheless, the existing studies on the virome have largely been focused on the bacteriophages as these represent the main component of the virome with little information on endogenous retroviruses (ERVs) and eukaryotic viruses. In this review, we describe the gut virome, and its role in gut mucosal response and disease progression. We also explore the crosstalk between the virome and other microorganisms in the gut mucosa and elaborate on how these interactions shape the gut mucosal immunity going from bacteriophages through ERVs to eukaryotic viruses. Finally, we elucidate the potential contribution of this crosstalk in the pathogenesis of inflammatory bowel diseases and colon cancer.

The oncogenic roles of JC polyomavirus in cancer

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

The Oncogenic Effects, Pathways, and Target Molecules of JC Polyoma Virus T Antigen in Cancer Cells

JC polyoma virus (JCPyV) is a ubiquitous polyoma virus that infects the individual to cause progressive multifocal leukoencephalopathy and malignancies. Here, we found that T-antigen knockdown suppressed proliferation, glycolysis, mitochondrial respiration, migration, and invasion, and induced apoptosis and G₂ arrest. The reverse was true for T-antigen overexpression, with overexpression of Akt, survivin, retinoblastoma protein, β-catenin, β-transducin repeat-containing protein (TRCP), and inhibitor of growth (ING)1, and the underexpression of mammalian target of rapamycin (mTOR), phosphorylated (p)-mTOR, p-p38, Cyclin D1, p21, vascular endothelial growth factor (VEGF), ING2, and ING4 in hepatocellular and pancreatic cancer cells and tissues. In lens tumor cells, T antigen transcriptionally targeted viral carcinogenesis, microRNAs in cancer, focal adhesion, p53, VEGF, phosphoinositide 3 kinase-Akt, and Forkhead box O signaling pathways, fructose and mannose metabolism, ribosome biosynthesis, and choline and pyrimidine metabolism. At a metabolomics level, it targeted protein digestion and absorption, aminoacryl-tRNA biosynthesis, biosynthesis of amino acids, and the AMPK signal pathway. At a proteomic level, it targeted ribosome biogenesis in eukaryotes, citrate cycle, carbon metabolism, protein digestion and absorption, aminoacryl-tRNA biosynthesis, extracellular-matrix-receptor interaction, and biosynthesis of amino acids. In lens tumor cells, T antigen might interact with various keratins, ribosomal proteins, apolipoproteins, G proteins, ubiquitin-related proteins, RPL19, β-catenin, β-TRCP, p53, and CCAAT-enhancer-binding proteins in lens tumor cells. T antigen induced a more aggressive phenotype in mouse and human cancer cells due to oncogene activation, inactivation of tumor suppressors, and disruption of metabolism, cell adhesion, and long noncoding RNA-microRNA-target axes.

Higher detection of JC polyomavirus in colorectal cancerous tissue after pretreatment with topoisomerase I enzyme; colorectal tissue serves as a JCPyV persistence site

BACKGROUND

The JC polyomavirus has been blamed to contribute in colorectal cancer (CRC), however, the topic is still controversial. Varying detection rate of JCPyV genome has been reported mainly due to technical reasons. Here, we provide summative data on the topic, with emphasize on technical issues.

METHODS

Formalin-fixed paraffin-embedded tissue samples from 50 patients with CRC, consisting of tumoral and non-cancerous marginal tissue (totally 100 samples) were included in the study. After DNA extraction, specific JCPyV T-Ag sequences were targeted using Real-time PCR. To unwind the supercoiled JCPyV genome, pretreatment with topoisomerase I, was applied. Immunohistochemical (IHC) staining was performed using an anti-T-Ag monoclonal antibody.

RESULTS

In the first attempts, no samples were found to be positive in Real-time PCR assays. However, JCPyV sequences were found in 60% of CRC tissues and 38% of non-cancerous colorectal mucosa after application of pre-treatment step with topoisomerase I enzyme (P = 0.028). T-Ag protein was found in the nuclear compartment of the stained cells in IHC assays.

CONCLUSIONS

The presence of JCPyV in CRC tissues, as well as T-Ag localization in the nucleolus, where its oncogenic effect takes place, may provide supporting evidence for JCPyV involvement in CRC development. The study highlights the importance of using topoisomerase I to enhance JCPyV genome detection. Also, colorectal tissue is one of the permissive human tissue for JC resistance after preliminary infection.

Viruses in colorectal cancer

Increasing evidence suggests that microorganisms might represent at least highly interesting cofactors in colorectal cancer (CRC) oncogenesis and progression. Still, associated mechanisms, specifically in colonocytes and their microenvironmental interactions, are still poorly understood. Although, currently, at least seven viruses are being recognized as human carcinogens, only three of these – Epstein–Barr virus (EBV), human papillomavirus (HPV) and John Cunningham virus (JCV) – have been described, with varying levels of evidence, in CRC. In addition, cytomegalovirus (CMV) has been associated with CRC in some publications, albeit not being a fully acknowledged oncovirus. Moreover, recent microbiome studies set increasing grounds for new hypotheses on bacteriophages as interesting additional modulators in CRC carcinogenesis and progression. The present Review summarizes how particular groups of viruses, including bacteriophages, affect cells and the cellular and microbial microenvironment, thereby putatively contributing to foster CRC. This could be achieved, for example, by promoting several processes – such as DNA damage, chromosomal instability, or molecular aspects of cell proliferation, CRC progression and metastasis – not necessarily by direct infection of epithelial cells only, but also by interaction with the microenvironment of infected cells. In this context, there are striking common features of EBV, CMV, HPV and JCV that are able to promote oncogenesis, in terms of establishing latent infections and affecting p53‐/pRb‐driven, epithelial–mesenchymal transition (EMT)‐/EGFR‐associated and especially Wnt/β‐catenin‐driven pathways. We speculate that, at least in part, such viral impacts on particular pathways might be reflected in lasting (e.g. mutational or further genomic) fingerprints of viruses in cells. Also, the complex interplay between several species within the intestinal microbiome, involving a direct or indirect impact on colorectal and microenvironmental cells but also between, for example, phages and bacterial and viral pathogens, and further novel species certainly might, in part, explain ongoing difficulties to establish unequivocal monocausal links between specific viral infections and CRC.

Trio cooperates with Myh9 to regulate neural crest-derived craniofacial development

Trio is a unique member of the Rho-GEF family that has three catalytic domains and is vital for various cellular processes in both physiological and developmental settings. TRIO mutations in humans are involved in craniofacial abnormalities, in which patients present with mandibular retrusion. However, little is known about the molecular mechanisms of Trio in neural crest cell (NCC)-derived craniofacial development, and there is still a lack of direct evidence to assign a functional role to Trio in NCC-induced craniofacial abnormalities. Methods: In vivo, we used zebrafish and NCC-specific knockout mouse models to investigate the phenotype and dynamics of NCC development in Trio morphants. In vitro, iTRAQ, GST pull-down assays, and proximity ligation assay (PLA) were used to explore the role of Trio and its potential downstream mediators in NCC migration and differentiation. Results: In zebrafish and mouse models, disruption of Trio elicited a migration deficit and impaired the differentiation of NCC derivatives, leading to craniofacial growth deficiency and mandibular retrusion. Moreover, Trio positively regulated Myh9 expression and directly interacted with Myh9 to coregulate downstream cellular signaling in NCCs. We further demonstrated that disruption of Trio or Myh9 inhibited Rac1 and Cdc42 activity, specifically affecting the nuclear export of β-catenin and NCC polarization. Remarkably, craniofacial abnormalities caused by trio deficiency in zebrafish could be partially rescued by the injection of mRNA encoding myh9, ca-Rac1, or ca-Cdc42. Conclusions: Here, we identified that Trio, interacting mostly with Myh9, acts as a key regulator of NCC migration and differentiation during craniofacial development. Our results indicate that trio morphant zebrafish and Wnt1-cre;Trio^fl/fl mice offer potential model systems to facilitate the study of the pathogenic mechanisms of Trio mutations causing craniofacial abnormalities.

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

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

The Role of the JC Virus in Central Nervous System Tumorigenesis

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

Effect of the Large and Small T-Antigens of Human Polyomaviruses on Signaling Pathways

Viruses are intracellular parasites that require a permissive host cell to express the viral genome and to produce new progeny virus particles. However, not all viral infections are productive and some viruses can induce carcinogenesis. Irrespective of the type of infection (productive or neoplastic), viruses hijack the host cell machinery to permit optimal viral replication or to transform the infected cell into a tumor cell. One mechanism viruses employ to reprogram the host cell is through interference with signaling pathways. Polyomaviruses are naked, double-stranded DNA viruses whose genome encodes the regulatory proteins large T-antigen and small t-antigen, and structural proteins that form the capsid. The large T-antigens and small t-antigens can interfere with several host signaling pathways. In this case, we review the interplay between the large T-antigens and small t-antigens with host signaling pathways and the biological consequences of these interactions.

Human Polyomavirus JCPyV and Its Role in Progressive Multifocal Leukoencephalopathy and Oncogenesis

The human neurotropic virus JCPyV, a member of the Polyomaviridiae family, is the opportunistic infectious agent of Progressive Multifocal Leukoencephalopathy (PML), a fatal disease seen in severe immunosuppressive conditions and, during the last decade, in patients undergoing immunotherapy. JCPyV is a ubiquitous pathogen with up to 85% of the adult population word-wide exhibiting antibodies against it. Early experiments demonstrated that direct inoculation of JCPyV into the brain of different species resulted in the development of brain tumors and other neuroectodermal-derived neoplasias. Later, several reports showed the detection of viral sequences in medulloblastomas and glial tumors, as well as expression of the viral protein T-Antigen. Few oncogenic viruses, however, have caused so much controversy regarding their role in the pathogenesis of brain tumors, but the discovery of new Polyomaviruses that cause Merkel cell carcinomas in humans and brain tumors in racoons, in addition to the role of JCPyV in colon cancer and multiple mechanistic studies have shed much needed light on the role of JCPyV in cancer. The pathways affected by the viral protein T-Antigen include cell cycle regulators, like p53 and pRb, and transcription factors that activate pro-proliferative genes, like c-Myc. In addition, infection with JCPyV causes chromosomal damage and T-Antigen inhibits homologous recombination, and activates anti-apoptotic proteins, such as Survivin. Here we review the different aspects of the biology and physiopathology of JCPyV.

Human Polyomaviruses: The Battle of Large and Small Tumor Antigens

About 40 years ago, the large and small tumor antigens (LT-Ag and sT-Ag) of the polyomavirus (PyVs) simian vacuolating virus 40 have been identified and characterized. To date, it is well known that all the discovered human PyVs (HPyVs) encode these 2 multifunctional and tumorigenic proteins, expressed at viral replication early stage. The 2 T-Ags are able to transform cells both in vitro and in vivo and seem to play a distinct role in the pathogenesis of some tumors in humans. In addition, they are involved in viral DNA replication, transcription, and virion assembly. This short review focuses on the structural and functional features of the HPyVs’ LT-Ag and sT-Ag, with special attention to their transforming properties.

The Wnt pathway: a key network in cell signalling dysregulated by viruses

Viruses are obligate parasites dependent on host cells for survival. Viral infection of a cell activates a panel of pattern recognition receptors that mediate antiviral host responses to inhibit viral replication and dissemination. Viruses have evolved mechanisms to evade and subvert this antiviral host response, including encoding proteins that hijack, mimic and/or manipulate cellular processes such as the cell cycle, DNA damage repair, cellular metabolism and the host immune response. Currently, there is an increasing interest whether viral modulation of these cellular processes, including the cell cycle, contributes to cancer development. One cellular pathway related to cell cycle signalling is the Wnt pathway. This review focuses on the modulation of this pathway by human viruses, known to cause (or associated with) cancer development. The main mechanisms where viruses interact with the Wnt pathway appear to be through (i) epigenetic modification of Wnt genes; (ii) cellular or viral miRNAs targeting Wnt genes; (iii) altering specific Wnt pathway members, often leading to (iv) nuclear translocation of β-catenin and activation of Wnt signalling. Given that diverse viruses affect this signalling pathway, modulating Wnt signalling could be a generalised critical process for the initiation or maintenance of viral pathogenesis, with resultant dysregulation contributing to virus-induced cancers. Further study of this virus-host interaction may identify options for targeted therapy against Wnt signalling molecules as a means to reduce virus-induced pathogenesis and the downstream consequences of infection. Copyright © 2016 John Wiley & Sons, Ltd.

Pur-Alpha Induces JCV Gene Expression and Viral Replication by Suppressing SRSF1 in Glial Cells

Objective

PML is a rare and fatal demyelinating disease of the CNS caused by the human polyomavirus, JC virus (JCV), which occurs in AIDS patients and those on immunosuppressive monoclonal antibody therapies (mAbs). We sought to identify mechanisms that could stimulate reactivation of JCV in a cell culture model system and targeted pathways which could affect early gene transcription and JCV T-antigen production, which are key steps of the viral life cycle for blocking reactivation of JCV. Two important regulatory partners we have previously identified for T-antigen include Pur-alpha and SRSF1 (SF2/ASF). SRSF1, an alternative splicing factor, is a potential regulator of JCV whose overexpression in glial cells strongly suppresses viral gene expression and replication. Pur-alpha has been most extensively characterized as a sequence-specific DNA- and RNA-binding protein which directs both viral gene transcription and mRNA translation, and is a potent inducer of the JCV early promoter through binding to T-antigen.

Methods and Results

Pur-alpha and SRSF1 both act directly as transcriptional regulators of the JCV promoter and here we have observed that Pur-alpha is capable of ameliorating SRSF1-mediated suppression of JCV gene expression and viral replication. Interestingly, Pur-alpha exerted its effect by suppressing SRSF1 at both the protein and mRNA levels in glial cells suggesting this effect can occur independent of T-antigen. Pur-alpha and SRSF1 were both localized to oligodendrocyte inclusion bodies by immunohistochemistry in brain sections from patients with HIV-1 associated PML. Interestingly, inclusion bodies were typically positive for either Pur-alpha or SRSF1, though some cells appeared to be positive for both proteins.

Conclusions

Taken together, these results indicate the presence of an antagonistic interaction between these two proteins in regulating of JCV gene expression and viral replication and suggests that they play an important role during viral reactivation leading to development of PML.

The oncogenic role of JC virus T antigen in lens tumors without cell specificity of alternative splicing of its intron

JC virus (JCV), a ubiquitous polyoma virus that commonly infects the human, is identified as the etiologic agent for progressive multifocal leukoencephalopathy and some malignancies. To clarify the oncogenic role of JCV T antigen, we established two transgenic mice of T antigen using either α-crystallin A (αAT) or cytokeratin 19(KT) promoter. Lens tumors were found in high-copy αAT mice with the immunopositivity of T antigen, p53, β-catenin and N-cadherin. Enlarged eyeballs were observed and tumor invaded into the brain by magnetic resonance imaging and hematoxylin-and-eosin staining. The overall survival time of homozygous mice was shorter than that of hemizygous mice (p<0.01), the latter than wild-type mice (p<0.01). The spontaneous salivary tumor and hepatocellular carcinoma were seen in αAT5 transgenic mice with no positivity of T antigen. KT7 mice suffered from lung tumor although JCV T antigen was strongly expressed in gastric epithelial cells. The alternative splicing of T antigen intron was detectable in the lens tumor of αAT mice, gastric mucosa of KT mice, and various cells transfected with pEGFP-N1-T antigen. It was suggested that JCV T antigen might induce carcinogenesis at a manner of cell specificity, which is not linked to alternative splicing of its intron. Both spontaneous lens and lung tumor models provide good tools to investigate the oncogenic role of JCV T antigen.

IFN-Gamma Inhibits JC Virus Replication in Glial Cells by Suppressing T-Antigen Expression

Objective

Patients undergoing immune modulatory therapies for the treatment of autoimmune diseases such as multiple sclerosis, and individuals with an impaired-immune system, most notably AIDS patients, are in the high risk group of developing progressive multifocal leukoencephalopathy (PML), an often lethal disease of the brain characterized by lytic infection of oligodendrocytes in the central nervous system (CNS) with JC virus (JCV). The immune system plays an important regulatory role in controlling JCV reactivation from latent sites by limiting viral gene expression and replication. However, little is known regarding the molecular mechanisms responsible for this regulation.

Methods and Results

Here, we investigated the impact of soluble immune mediators secreted by activated PBMCs on viral replication and gene expression by cell culture models and molecular virology techniques. Our data revealed that viral gene expression and viral replication were suppressed by soluble immune mediators. Further studies demonstrated that soluble immune mediators secreted by activated PBMCs inhibit viral replication induced by T-antigen, the major viral regulatory protein, by suppressing its expression in glial cells. This unexpected suppression of T-antigen was mainly associated with the suppression of translational initiation. Cytokine/chemokine array studies using conditioned media from activated PBMCs revealed several candidate cytokines with possible roles in this regulation. Among them, only IFN-γ showed a robust inhibition of T-antigen expression. While potential roles for IFN-β, and to a lesser extent IFN-α have been described for JCV, IFN-γ has not been previously implicated. Further analysis of IFN-γ signaling pathway revealed a novel role of Jak1 signaling in control of viral T-antigen expression. Furthermore, IFN-γ suppressed JCV replication and viral propagation in primary human fetal glial cells, and showed a strong anti-JCV activity.

Conclusions

Our results suggest a novel role for IFN-γ in the regulation of JCV gene expression via downregulation of the major viral regulatory protein, T-antigen, and provide a new avenue of research to understand molecular mechanisms for downregulation of viral reactivation that may lead to development of novel strategies for the treatment of PML.

Activation of c-Myc and Cyclin D1 by JCV T-Antigen and β-catenin in colon cancer

During the last decade, mounting evidence has implicated the human neurotropic virus JC virus in the pathology of colon cancer. However, the mechanisms of JC virus-mediated oncogenesis are still not fully determined. One candidate to mediate these effects is the viral early transcriptional product T-Antigen, which has the ability to inactivate cell cycle regulatory proteins such as p53. In medulloblastomas, T-Antigen has been shown to bind the Wnt signaling pathway protein β-catenin; however, the effects of this interaction on downstream cell cycle regulatory proteins remain unknown. In light of these observations, we investigated the association of T-Antigen and nuclear β-catenin in colon cancer cases and the effects of this complex in the activation of the transcription and cell cycle regulators c-Myc and Cyclin D1 in vitro. Gene amplification demonstrated the presence of viral sequences in 82.4% of cases and we detected expression of T-Antigen in 64.6% of cases by immunohistochemistry. Further, we found that T-Antigen and β-catenin co-localized in the nuclei of tumor cells and we confirmed the physical binding between these two proteins in vitro. The nuclear presence of T-Antigen and β-catenin resulted in the significant enhancement of TCF-dependent promoter activity and activation of the β-catenin downstream targets, c-Myc and Cyclin D1. These observations provide further evidence for a role of JCV T-Antigen in the dysregulation of the Wnt signaling pathway and in the pathogenesis of colon cancer.

Dock-family exchange factors in cell migration and disease

Dock family proteins are evolutionary conserved exchange factors for the Rho GTPases Rac and Cdc42. There are 11 Dock proteins in mammals, named Dock1 (or Dock180) to Dock11 that play different cellular functions. In particular, Dock proteins regulate actin cytoskeleton, cell adhesion and migration. Not surprisingly, members of the Dock family have been involved in various pathologies, including cancer and defects in the central nervous and immune systems. This review proposes an update of the recent findings regarding the function of Dock proteins, focusing on their role in the control of cell migration and invasion and the consequences in human diseases.

Immune surveillance and response to JC virus infection and PML

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

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

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

Human polyomavirus JC reactivation and pathogenetic mechanisms of progressive multifocal leukoencephalopathy and cancer in the era of monoclonal antibody therapies

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease of the central nervous system caused by the neurotropic human polyomavirus JC (JCV) lytic infection of oligodendrocytes. PML was first described as a complication of lymphoproliferative disorders more than 50 years ago and emerged as a major complication of human immunodeficiency virus (HIV) infection in the 1980s. Despite the ubiquity of this virus, PML is rare and always seen in association with underlying immunosuppressive condition, such as HIV infection, autoimmune diseases, cancer, and organ transplantation. JCV remains quiescent in the kidneys, where it displays a stable archetypal non-coding control region (NCCR). Conversely, rearranged JCV NCCR, including tandem repeat patterns found in the brain of PML patients, have been associated with neurovirulence. The specific site and mechanism of JCV NCCR transformation is unknown. According to one model, during the course of immunosuppression, JCV departs from its latent state and after entering the brain, productively infects and destroys oligodendrocytes. Although the majority of PML cases occur in severely immunesuppressed individuals, PML has been increasingly diagnosed in patients treated with biological therapies such as monoclonal antibodies (mAbs) that modulate immune system functions: in fact, CD4+ and CD8+ T lymphopenia, resulting from this immunomodulatory therapy, are the primary risk factor. Furthermore, JCV reactivation in nonpermissive cells after treatment with mAbs, such as intestinal epithelial cells in Crohn's disease patients, in association with other host tumor-inducing factors, could provide valid information on the role of JCV in several malignancies, such as colorectal cancer.

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

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

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

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

Does JC virus have a role in the etiology and prognosis of Egyptian colorectal carcinoma?

John Cunningham virus (JCV) encodes an oncogenic T-antigen, which is capable of interacting with key growth regulatory pathways. JCV definite role as causal agent of human cancer, still awaits final confirmation. The present study was conducted to assess the possible role of JCV in Egyptian colorectal carcinoma (CRC) and correlate the expression with the clinicopathological features and survival. JCV in situ hybridization (ISH) signals and large T antigen immunoreactivity were examined in 87 colonic specimens. Positive glandular JCV ISH signals were detected in 20%, 25% and 40% of normal, adenoma and CRC cases respectively. Stromal JCV ISH signals were identified in 26% of CRC cases and 5% of adenoma however, normal mucosa did not show stromal positivity with significant difference (p = 0.03). Glandular JCV expression was significantly associated with high grade (p = 0.03), high mitotic index (p=0.02) and low apoptotic index (p = 0.00). Positive stromal signals were significantly associated with low apoptosis (p = 0.00). No positive nuclear immunostaining of JCV large T antigen was detected in all specimens. JCV stromal expression was the 2nd most powerful indicator of short survival and bad prognosis (p = 0.03) in CRC patients. JCV might play an etiological role in CRC tumorogenesis and short survival in Egyptian CRC patients.

Interaction and co-localization of JC virus large T antigen and the F-box protein β-transducin-repeat containing protein

Lytic infection and transformation of cultured cells by JC virus (JCV) require five tumor proteins, which interact with factors regulating critical cellular processes. We demonstrate that JCV large T antigen (TAg) binds the F-box proteins β-transducin-repeat containing protein-1 and 2 (βTrCP1/2). These interactions involve a phosphodegron (DpSGX(2-4)pS) found in βTrCP substrates. TAg stability is unaltered, suggesting TAg is a pseudo-substrate. βTrCP and TAg co-localize in the cytoplasm, and a functional SCF complex is required. We examined whether TAg influences the levels of β-catenin, a βTrCP substrate. We were unable to demonstrate that TAg elevates β-catenin as previously reported, and a mutant TAg unable to bind βTrCP also had no detectable effect on β-catenin stability. Results presented in this study link JCV TAg to the cellular degradation complex, SCF(βTrCP1/2). Proteasomal degradation is essential for proper regulation of cellular functions, and interference with proteasomal pathways highlights possible JCV pathogenic and oncogenic mechanisms.

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

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

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

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

Genetic and epigenetic characteristics of gastric cancers with JC virus T-antigen

AIM: To clarify the significance of JC virus (JCV) T-antigen (T-Ag) expression in human gastric cancer.

METHODS: We investigated the relationship between T-Ag detected by immunohistochemistry and Epstein-Barr virus (EBV) infection, microsatellite instability (MSI), and genetic and epigenetic alterations in gastric cancers. Mutations in the p53, β-catenin, KRAS, BRAF, PIK3CA genes were analyzed by polymerase chain reaction (PCR)-single strand conformation polymorphism and DNA sequencing. Allelic losses were determined by PCR at 7 microsatellite loci. Aberrant DNA methylation was analyzed by MethyLight assay.

RESULTS: JCV T-Ag protein expression was found in 49% of 90 gastric cancer tissues. T-Ag positivity was not correlated with clinicopathological characteristics. T-Ag expression was detected in a similar percentage of EBV positive cancers (4 of 9, 44%) and EBV negative cancers (35 of 73, 48%). T-Ag expression was detected in a significantly lower percentage of MSI-H cancers (14%) than in non MSI-H cancers (55%, P = 0.005). T-Ag expression was detected in a significantly higher percentage of cancers with nuclear/cytoplasmic localization of β-catenin (15 of 21, 71%) than in cancers without (42%, P = 0.018). p53 mutations were detected in a significantly lower percentage of T-Ag positive cancers (32%) than in T-Ag negative cancers (57%, P = 0.018). T-Ag positive gastric cancers showed a significant increase in the allelic losses and aberrant methylation compared with T-Ag negative gastric cancers (P = 0.008 and P = 0.003).

CONCLUSION: The results suggest that JCV T-Ag is involved in gastric carcinogenesis through multiple mechanisms of genetic and epigenetic alterations.

Potential mechanisms of the human polyomavirus JC in neural oncogenesis

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

Molecular association between beta-catenin degradation complex and Rac guanine exchange factor DOCK4 is essential for Wnt/beta-catenin signaling

The canonical Wnt/beta-catenin pathway is a highly conserved signaling cascade that is involved in development and stem cell renewal. The deregulation of this pathway is often associated with increased cell growth and neoplasia. The small GTPase Rac has been shown to influence canonical Wnt signaling by regulating beta-catenin stability through an unknown mechanism. We report that DOCK4, a guanine nucleotide exchange factor (GEF) for Rac and a member of the CDM family of unconventional GEFs, mediates Wnt-induced Rac activation in the canonical Wnt/beta-catenin pathway. DOCK4 expression regulates cellular beta-catenin levels in response to the Wnt signal, in vitro. Biochemical studies demonstrate that DOCK4 interacts with the beta-catenin degradation complex, consisting of the proteins adenomatosis polyposis coli, Axin and glycogen synthase kinase 3beta (GSK3beta). This molecular interaction enhances beta-catenin stability and Axin degradation. Furthermore, we observe that DOCK4 is phosphorylated by GSK3beta, which enhances Wnt-induced Rac activation. Using a T-cell factor reporter zebrafish we confirm that DOCK4 is required for Wnt/beta-catenin activity, in vivo. These results elucidate a novel intracellular signaling mechanism in which a Rac GEF, DOCK4 acts as a scaffold protein in the Wnt/beta-catenin pathway.