Role of JC virus agnoprotein in DNA repair

Nuclear antiviral innate responses at the intersection of DNA sensing and DNA repair

The coevolution of vertebrate and mammalian hosts with DNA viruses has driven the ability of host cells to distinguish viral from cellular DNA in the nucleus to induce intrinsic immune responses. Concomitant viral mechanisms have arisen to inhibit DNA sensing. At this virus-host interface, emerging evidence links cytokine responses and cellular homeostasis pathways, particularly the DNA damage response (DDR). Nuclear DNA sensors, such as the interferon (IFN)-γ inducible protein 16 (IFI16), functionally intersect with the DDR regulators ataxia telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNA-PK). Here, we discuss accumulating knowledge for the DDR-innate immunity signaling axis. Through the lens of this infection-driven signaling axis, we present host and viral molecular strategies acquired to regulate autoinflammation and antiviral responses.

Lactate drives cellular DNA repair capacity: Role of lactate and related short-chain fatty acids in cervical cancer chemoresistance and viral infection

The characteristic feature of a cancer microenvironment is the presence of a highly elevated concentration of L-lactate in the tumor niche. The lactate-rich environment is also maintained by commensal mucosal microbiota, which has immense potential for affecting cancer cells through its receptoric and epigenetic modes of action. Some of these lactate activities might be associated with the failure of anticancer therapy as a consequence of the drug resistance acquired by cancer cells. Upregulation of cellular DNA repair capacity and enhanced drug efflux are the most important cellular mechanisms that account for ineffective radiotherapy and drug-based therapies. Here, we present the recent scientific knowledge on the role of the HCA1 receptor for lactate and lactate intrinsic activity as an HDAC inhibitor in the development of an anticancer therapy-resistant tumor phenotype, with special focus on cervical cancer cells. In addition, a recent study highlighted the viable role of interactions between mammalian cells and microorganisms in the female reproductive tract and demonstrated an interesting mechanism regulating the efficacy of retroviral transduction through lactate-driven modulation of DNA-PKcs cellular localization. To date, very few studies have focused on the mechanisms of lactate-driven enhancement of DNA repair and upregulation of particular multidrug-resistance proteins in cancer cells with respect to their intracellular regulatory mechanisms triggered by lactate. This review presents the main achievements in the field of lactate impact on cell biology that may promote undesirable alterations in cancer physiology and mitigate retroviral infections.

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.

Unravelling the Immunomodulatory Effects of Viral Ion Channels, towards the Treatment of Disease

The current COVID-19 pandemic has highlighted the need for the research community to develop a better understanding of viruses, in particular their modes of infection and replicative lifecycles, to aid in the development of novel vaccines and much needed anti-viral therapeutics. Several viruses express proteins capable of forming pores in host cellular membranes, termed "Viroporins". They are a family of small hydrophobic proteins, with at least one amphipathic domain, which characteristically form oligomeric structures with central hydrophilic domains. Consequently, they can facilitate the transport of ions through the hydrophilic core. Viroporins localise to host membranes such as the endoplasmic reticulum and regulate ion homeostasis creating a favourable environment for viral infection. Viroporins also contribute to viral immune evasion via several mechanisms. Given that viroporins are often essential for virion assembly and egress, and as their structural features tend to be evolutionarily conserved, they are attractive targets for anti-viral therapeutics. This review discusses the current knowledge of several viroporins, namely Influenza A virus (IAV) M2, Human Immunodeficiency Virus (HIV)-1 Viral protein U (Vpu), Hepatitis C Virus (HCV) p7, Human Papillomavirus (HPV)-16 E5, Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) Open Reading Frame (ORF)3a and Polyomavirus agnoprotein. We highlight the intricate but broad immunomodulatory effects of these viroporins and discuss the current antiviral therapies that target them; continually highlighting the need for future investigations to focus on novel therapeutics in the treatment of existing and future emergent viruses.

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.

Nuku, a family of primate retrocopies derived from KU70

The gene encoding the ubiquitous DNA repair protein, Ku70p, has undergone extensive copy number expansion during primate evolution. Gene duplications of KU70 have the hallmark of long interspersed element-1 mediated retrotransposition with evidence of target-site duplications, the poly-A tails, and the absence of introns. Evolutionary analysis of this expanded family of KU70-derived "NUKU" retrocopies reveals that these genes are both ancient and also actively being created in extant primate species. NUKU retrocopies show evidence of functional divergence away from KU70, as evinced by their altered pattern of tissue expression and possible tissue-specific translation. Molecular modeling predicted that amino acid changes in Nuku2p at the interaction interface with Ku80p would prevent the assembly of the Ku heterodimer. The lack of Nuku2p-Ku80p interaction was confirmed by yeast two-hybrid assay, which contrasts the robust interaction of Ku70p-Ku80p. While several NUKU retrocopies appear to have been degraded by mutation, NUKU2 shows evidence of positive natural selection, suggesting that this retrocopy is undergoing neofunctionalization. Although Nuku proteins do not appear to antagonize retrovirus transduction in cell culture, the observed expansion and rapid evolution of NUKUs could be being driven by alternative selective pressures related to infectious disease or an undefined role in primate physiology.

CC and CXC chemokines play key roles in the development of polyomaviruses related pathological conditions

It has been reported that polyomaviruses are the microbes which can be a cause of several human pathological conditions including cancers, nephropathy, progressive multifocal leukoencephalopathy and gynaecological disease. Although investigators proposed some mechanisms used by the viruses to induce the disorders, the roles played by chemokines in the pathogenesis of polyomaviruses infections are yet to be clarified. This review article investigated recent studies regarding the roles played by chemokines in the pathogenesis of the polyomaviruses infections. The research in the literature revealed that CXC chemokines, including CXCL1, CXCL5, CXCL8, CXCL9, CXCL10, CXCL11, CXCL12 and CXCL16, significantly participate in the pathogenesis of polyomaviruses. CC chemokines, such as CCL2, CCL5 and CCL20 also participate in the induction of the pathological conditions. Therefore, it appears that CXC chemokines may be considered as the strategic factors involved in the pathogenesis of polyomaviruses.

Viral interactions with non-homologous end-joining: a game of hide-and-seek

There are extensive interactions between viruses and the host DNA damage response (DDR) machinery. The outcome of these interactions includes not only direct effects on viral nucleic acids and genome replication, but also the activation of host stress response signalling pathways that can have further, indirect effects on viral life cycles. The non-homologous end-joining (NHEJ) pathway is responsible for the rapid and imprecise repair of DNA double-stranded breaks in the nucleus that would otherwise be highly toxic. Whilst directly repairing DNA, components of the NHEJ machinery, in particular the DNA-dependent protein kinase (DNA-PK), can activate a raft of downstream signalling events that activate antiviral, cell cycle checkpoint and apoptosis pathways. This combination of possible outcomes results in NHEJ being pro- or antiviral depending on the infection. In this review we will describe the broad range of interactions between NHEJ components and viruses and their consequences for both host and pathogen.

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.

High-grade urothelial carcinoma in a kidney transplant recipient after JC virus nephropathy: The first evidence of JC virus as a potential oncovirus in bladder cancer

Kidney transplant (KT) recipients have an increased risk for urothelial carcinoma. A role for JC virus (JCV) in human cancers is not yet proved but there is an increasingly reported association between BK virus (BKV) nephropathy and renourinary neoplasms. We report a KT recipient who developed a high-grade urothelial carcinoma 5 years after a diagnosis of JCV nephropathy and 9 years after kidney transplantation. Neoplastic tissue was positive for JCV DNA by real-time polymerase chain reaction (PCR). Immunochemical staining showed strong positivity for cell cycle markers (p16, p53, and Ki67) and for early viral protein JCV large T antigen (JCV LTag; using a broad polyomavirus antibody); however, late viral protein (VP1) stained negative. In contrast, in non-neoplastic urothelium, JCV DNA and all immunochemical markers were negative. These facts suggest that malignancy was induced by JCV. To the best of our knowledge, this is the first report of urothelial high-grade carcinoma associated with JCV nephropathy in a KT recipient.

Human BK and JC polyomaviruses: Molecular insights and prevalence in Asia

Polyomaviridae family consists of small circular dsDNA viruses. Out of the 14 human polyomaviruses described so far, BKPyV and JCPyV have been studied extensively since their discovery in 1971. Reportedly, both BKPyV and JCPyV are widely distributed across the globe with the frequency of 80-90 % in different populations. The primary infection of these viruses is usually asymptomatic and latent which is activated as a consequence of immunosuppression. Activated BKPyV and JCPyV viruses lead to the development of BK Virus Associated Nephropathy and Progressive Multifocal Leukoencephalopathy, respectively. Immense progress has been made during the last few decades regarding the molecular understanding of polyomaviruses. Epidemiology of polyomaviruses has also been studied extensively. However, most of the epidemiological studies have focused on European and American populations. Therefore, limited data is available regarding the geographical distribution of these potentially oncogenic viruses in Asian countries. In this article, we have presented a compendium of latest advances in the molecular understanding of polyomaviruses and their pathobiology. We also present a comprehensive review of published literature regarding the epidemiology and prevalence of BKPyV and JCPyV in Asian regions. For this purpose, a thorough search of available online resources was performed. As a result, we retrieved 24 studies for BKPyV and 22 studies for JCPyV, that describe their prevalence in Asia. These studies unanimously report high occurrence of both BKPyV and JCPyV in Asian populations. The available data from these studies was categorized into two groups: on the basis of prevalence (low, medium and high) and disease development (healthy and diseased). Altogether, Korean population hasbeen evidenced to possess highest frequency of BKPyV (66.7 %), while JCPyV was found to be most prevalent in Taiwan (88 %). Due to high and ubiquitous distribution of these viruses, frequent studies are required to develop a better understanding regarding the epidemiology and pathobiology of these viruses in Asia.

Human polyomavirus modulation of the host DNA damage response

The human DNA damage response (DDR) is a complex signaling network constituting many factors responsible for the preservation of genomic integrity. Human polyomaviruses (HPyVs) are able to harness the DDR machinery during their infectious cycle by expressing an array of tumor (T) antigens. These molecular interactions between human polyomavirus T antigens and the DDR create conditions that promote viral replication at the expense of host genomic stability to cause disease as well as carcinogenesis in the cases of the Merkel cell polyomavirus and BK polyomavirus. This review focuses on the six HPyVs with disease association, emphasizing strain-dependent differences in their selective manipulation of the DDR. Appreciation of the HPyV-DDR interface at a molecular scale is conducive to the development of novel therapeutic approaches.

A comprehensive proteomics analysis of JC virus Agnoprotein-interacting proteins: Agnoprotein primarily targets the host proteins with coiled-coil motifs

JC virus (JCV) Agnoprotein (Agno) plays critical roles in successful completion of the viral replication cycle. Understanding its regulatory roles requires a complete map of JCV-host protein interactions. Here, we report the first Agno interactome with host cellular targets utilizing "Two-Strep-Tag" affinity purification system coupled with mass spectroscopy (AP/MS). Proteomics data revealed that Agno primarily targets 501 cellular proteins, most of which contain "coiled-coil" motifs. Agno-host interactions occur in several cellular networks including those involved in protein synthesis and degradation; and cellular transport; and in organelles, including mitochondria, nucleus and ER-Golgi network. Among the Agno interactions, Rab11B, Importin and Crm-1 were first validated biochemically and further characterization was done for Crm-1, using a HIV-1 Rev-M10-like Agno mutant (L33D + E34L), revealing the critical roles of L33 and E34 residues in Crm-1 interaction. This comprehensive proteomics data provides new foundations to unravel the critical regulatory roles of Agno during the JCV life cycle.

Expression of novel proteins by polyomaviruses and recent advances in the structural and functional features of agnoprotein of JC virus, BK virus, and simian virus 40

Polyomavirus family consists of a highly diverse group of small DNA viruses. The founding family member (MPyV) was first discovered in the newborn mouse in the late 1950s, which induces solid tumors in a wide variety of tissue types that are the epithelial and mesenchymal origin. Later, other family members were also isolated from a number of mammalian, avian and fish species. Some of these viruses significantly contributed to our current understanding of the fundamentals of modern biology such as transcription, replication, splicing, RNA editing, and cell transformation. After the discovery of first two human polyomaviruses (JC virus [JCV] and BK virus [BKV]) in the early 1970s, there has been a rapid expansion in the number of human polyomaviruses in recent years due to the availability of the new technologies and brought the present number to 14. Some of the human polyomaviruses cause considerably serious human diseases, including progressive multifocal leukoencephalopathy, polyomavirus-associated nephropathy, Merkel cell carcinoma, and trichodysplasia spinulosa. Emerging evidence suggests that the expression of the polyomavirus genome is more complex than previously thought. In addition to encoding universally expressed regulatory and structural proteins (LT-Ag, Sm t-Ag, VP1, VP2, and VP3), some polyomaviruses express additional virus-specific regulatory proteins and microRNAs. This review summarizes the recent advances in polyomavirus genome expression with respect to the new viral proteins and microRNAs other than the universally expressed ones. In addition, a special emphasis is devoted to the recent structural and functional discoveries in the field of polyomavirus agnoprotein which is expressed only by JCV, BKV, and simian virus 40 genomes.

An unusually high substitution rate in transplant-associated BK polyomavirus in vivo is further concentrated in HLA-C-bound viral peptides

Infection with human BK polyomavirus, a small double-stranded DNA virus, potentially results in severe complications in immunocompromised patients. Here, we describe the in vivo variability and evolution of the BK polyomavirus by deep sequencing. Our data reveal the highest genomic evolutionary rate described in double-stranded DNA viruses, i.e., 10⁻³–10⁻⁵ substitutions per nucleotide site per year. High mutation rates in viruses allow their escape from immune surveillance and adaptation to new hosts. By combining mutational landscapes across viral genomes with in silico prediction of viral peptides, we demonstrate the presence of significantly more coding substitutions within predicted cognate HLA-C-bound viral peptides than outside. This finding suggests a role for HLA-C in antiviral immunity, perhaps through the action of killer cell immunoglobulin-like receptors. The present study provides a comprehensive view of viral evolution and immune escape in a DNA virus.

Little is known about the mechanisms of evolution and viral immune escape in double-stranded DNA (dsDNA) viruses. Here, we study the evolution of BK polyomavirus and observe the highest genomic evolutionary rate described so far for a dsDNA virus, in the range of RNA viruses, which usually evolve rapidly. Furthermore, the prediction of viral peptides to determine immune escape suggests a specific role of HLA-C in antiviral immunity. These findings are helpful for future advances in antiviral therapies and provide a step forward in our understanding of in vivo viral evolution in humans.

In vitro toxicity and efficacy of verdinexor, an exportin 1 inhibitor, on opportunistic viruses affecting immunocompromised individuals

Infection of immunocompromised individuals with normally benign opportunistic viruses is a major health burden globally. Infections with viruses such as Epstein-Barr virus (EBV), human cytomegalovirus (HCMV), Kaposi's sarcoma virus (KSHV), adenoviruses (AdV), BK virus (BKPyV), John Cunningham virus (JCPyV), and human papillomavirus (HPV) are significant concerns for the immunocompromised, including when these viruses exist as a co-infection with human immunodeficiency virus (HIV). These viral infections are more complicated in patients with a weakened immune system, and often manifest as malignancies resulting in significant morbidity and mortality. Vaccination is not an attractive option for these immune compromised individuals due to defects in their adaptive immune response. Verdinexor is part of a novel class of small molecules known as SINE (Selective Inhibitor of Nuclear Export) compounds. These small molecules demonstrate specificity for the nuclear export protein XPO1, to which they bind and block function, resulting in sequestration of XPO1-dependent proteins in the nucleus of the cell. In antiviral screening, verdinexor demonstrated varying levels of efficacy against all of the aforementioned viruses including previously with HIV. Studies by other labs have discussed likely mechanisms of action for verdinexor (ie. XPO1-dependence) against each virus. GLP toxicology studies suggest that anti-viral activity can be achieved at a tolerable dose range, based on the safety profile of a previous phase 1 clinical trial of verdinexor in healthy human volunteers. Taken together, these results indicate verdinexor has the potential to be a broad spectrum antiviral for immunocompromised subjects for which vaccination is a poor option.

Beyond Channel Activity: Protein-Protein Interactions Involving Viroporins

Viroporins are short polypeptides encoded by viruses. These small membrane proteins assemble into oligomers that can permeabilize cellular lipid bilayers, disrupting the physiology of the host to the advantage of the virus. Consequently, efforts during the last few decades have been focused towards the discovery of viroporin channel inhibitors, but in general these have not been successful to produce licensed drugs. Viroporins are also involved in viral pathogenesis by engaging in critical interactions with viral proteins, or disrupting normal host cellular pathways through coordinated interactions with host proteins. These protein-protein interactions (PPIs) may become alternative attractive drug targets for the development of antivirals. In this sense, while thus far most antiviral molecules have targeted viral proteins, focus is moving towards targeting host proteins that are essential for virus replication. In principle, this largely would overcome the problem of resistance, with the possibility of using repositioned existing drugs. The precise role of these PPIs, their strain- and host- specificities, and the structural determination of the complexes involved, are areas that will keep the fields of virology and structural biology occupied for years to come. In the present review, we provide an update of the efforts in the characterization of the main PPIs for most viroporins, as well as the role of viroporins in these PPIs interactions.

Biology of the BKPyV: An Update

The BK virus (BKPyV) is a member of the Polyomaviridae family first isolated in 1971. BKPyV causes frequent infections during childhood and establishes persistent infections with minimal clinical implications within renal tubular cells and the urothelium. However, reactivation of BKPyV in immunocompromised individuals may cause serious complications. In particular, with the implementation of more potent immunosuppressive drugs in the last decade, BKPyV has become an emerging pathogen in kidney and bone marrow transplant recipients where it often causes associated nephropathy and haemorrhagic cystitis, respectively. Unfortunately, no specific antiviral against BKPyV has been approved yet and the only therapeutic option is a modulation of the immunosuppressive drug regimen to improve immune control though it may increase the risk of rejection. A better understanding of the BKPyV life cycle is thus needed to develop efficient treatment against this virus. In this review, we provide an update on recent advances in understanding the biology of BKPyV.

Review on the role of the human Polyomavirus JC in the development of tumors

Almost one fifth of human cancers worldwide are associated with infectious agents, either bacteria or viruses, and this makes the possible association between infections and tumors a relevant research issue. We focused our attention on the human Polyomavirus JC (JCPyV), that is a small, naked DNA virus, belonging to the Polyomaviridae family. It is the recognized etiological agent of the Progressive Multifocal Leukoencephalopathy (PML), a fatal demyelinating disease, occurring in immunosuppressed individuals.

JCPyV is able to induce cell transformation in vitro when infecting non-permissive cells, that do not support viral replication and JCPyV inoculation into small animal models and non human primates drives to tumor formation. The molecular mechanisms involved in JCPyV oncogenesis have been extensively studied: the main oncogenic viral protein is the large tumor antigen (T-Ag), that is able to bind, among other cellular factors, both Retinoblastoma protein (pRb) and p53 and to dysregulate the cell cycle, but also the early proteins small tumor antigen (t-Ag) and Agnoprotein appear to cooperate in the process of cell transformation.

Consequently, it is not surprising that JCPyV genomic sequences and protein expression have been detected in Central Nervous System (CNS) tumors and colon cancer and an association between this virus and several brain and non CNS-tumors has been proposed. However, the significances of these findings are under debate because there is still insufficient evidence of a casual association between JCPyV and solid cancer development.

In this paper we summarized and critically analyzed the published literature, in order to describe the current knowledge on the possible role of JCPyV in the development of human tumors.

Expression of Signaling Molecules in Progressive Multifocal Leukoencephalopathy

INTRODUCTION

Progressive multifocal leukoencephalopathy (PML) is a debilitating demyelinating disease of the CNS caused by the infection and destruction of glial cells by JC virus (JCV) and is an AIDS-defining disease. Infection with JCV is common and most people acquire antibodies early in life. After initial infection, JCV remains in an asymptomatic persistent state and can be detected by PCR in many tissues including brain. A major question in PML pathogenesis is how the virus reactivates from persistence in HIV-1/AIDS. Our studies with primary cultures of glial cells have implicated transcription factors NF-κB and NFAT4, which bind to a unique site in the JCV noncoding control region and stimulate viral gene expression. Furthermore, these transcription factors are controlled by pathways downstream of proinflammatory cytokines, e.g., TNF-α activates NF-κB and stimulates JCV transcription.

OBJECTIVES

We hypothesize that HIV-1/PML initiation may involve reactivation of JCV by cytokine disturbances in the brain such as occur in HIV-1/AIDS. In this study, the objective was to evaluate HIV-1/PML clinical samples for expression of TNF-α and its receptors and subcellular localization of NF-κB p65 and NFAT4 compared to non-PML controls.

METHODS

We evaluated HIV-1/PML clinical samples and non-PML controls for expression of TNF-α and its receptors and subcellular localization of NF-κB p65 and NFAT4 using Western blot and immunohistochemistry.

RESULTS

Consistent with our hypothesis, compared to non-PML controls, HIV-1/PML tissue has high levels of TNF-α and TNFR1 expression and NF-κB and NFAT4 were preferentially localized to the nucleus.

CONCLUSION

The involvement of TNF-α/NF-κB/NFAT4 signaling in JCV regulation that we reported from experiments in cultured human glial cells may be clinically relevant in PML.

Emerging From the Unknown: Structural and Functional Features of Agnoprotein of Polyomaviruses

Agnoprotein is an important regulatory protein of polyomaviruses, including JCV, BKV, and SV40. In the absence of its expression, these viruses are unable to sustain their productive life cycle. It is a highly basic phosphoprotein that localizes mostly to the perinuclear area of infected cells, although a small amount of the protein is also found in nucleus. Much has been learned about the structure and function of this important regulatory protein in recent years. It forms highly stable dimers/oligomers in vitro and in vivo through its Leu/Ile/Phe-rich domain. Structural NMR studies revealed that this domain adopts an alpha-helix conformation and plays a critical role in the stability of the protein. It associates with cellular proteins, including YB-1, p53, Ku70, FEZ1, HP1α, PP2A, AP-3, PCNA, and α-SNAP; and viral proteins, including small t antigen, large T antigen, HIV-1 Tat, and JCV VP1; and significantly contributes the viral transcription and replication. This review summarizes the recent advances in the structural and functional properties of this important regulatory protein. J. Cell. Physiol. 231: 2115-2127, 2016. © 2016 Wiley Periodicals, Inc.

Molecular characterization of BK virus in patients infected with human immunodeficiency virus

Immunosuppression seems to be the most important cause of BKPyV reactivation. Recently, a spectrum of diseases associated with BKPyV infection has been reported in HIV-infected patients. BKPyV isolates can be classified into four subtypes based on nucleotide polymorphisms within VP1 coding region. Mutations within the BC loop of the VP1 may be associated with an increase in the viral pathogenicity. The aims of this study were to determine prevalence and distribution of BKPyV subtypes, sequence variation and mutations within VP1 among HIV-infected patients and healthy donors. Urine samples from 114 HIV-infected patients and 120 healthy donors were collected. PCR followed by sequence analysis was carried out using primers specific for VP1 and NCRR of the virus genome. The predominant BKPyV subtype was I, followed by IV. In isolates from HIV-infected patients, the majority of non-synonymous alterations were located within the BC loop. BKV sequences from healthy donors showed non-synonymous alterations outside of the receptor loops in the β-sheets. The higher frequency of mutations in the BC loop of VP1 protein was detected among HIV-infected patients. The most frequent mutation was E82D. All HIV-infected patients who harbored mutations had CD4(+) cell counts less than 200 cell/mm(3). It seems that immunosuppression is a very important factor for BKPyV reactivation that can increase viral replication rate and leads to higher frequency of mutations in the BC loop of the VP1. These mutations may change receptor specificity, and further studies are needed to determine the effect of these mutations on the biological properties of the BKPyV.

Viroporins: structure, function and potential as antiviral targets

The channel-forming activity of a family of small, hydrophobic integral membrane proteins termed 'viroporins' is essential to the life cycles of an increasingly diverse range of RNA and DNA viruses, generating significant interest in targeting these proteins for antiviral development. Viroporins vary greatly in terms of their atomic structure and can perform multiple functions during the virus life cycle, including those distinct from their role as oligomeric membrane channels. Recent progress has seen an explosion in both the identification and understanding of many such proteins encoded by highly significant pathogens, yet the prototypic M2 proton channel of influenza A virus remains the only example of a viroporin with provenance as an antiviral drug target. This review attempts to summarize our current understanding of the channel-forming functions for key members of this growing family, including recent progress in structural studies and drug discovery research, as well as novel insights into the life cycles of many viruses revealed by a requirement for viroporin activity. Ultimately, given the successes of drugs targeting ion channels in other areas of medicine, unlocking the therapeutic potential of viroporins represents a valuable goal for many of the most significant viral challenges to human and animal health.

Human JC virus small tumour antigen inhibits nucleotide excision repair and sensitises cells to DNA-damaging agents

The human JC virus (JCV) is potentially carcinogenic to humans as a Group 2B carcinogen, and it is ubiquitous in human populations. To investigate whether the small tumour (ST) antigen of the JCV contributes to genomic instability, we established cell lines stably expressing the JCV ST and examined its role in DNA repair. Results from host cell reactivation (HCR) assay revealed that the established cell lines exhibited lower nucleotide excision repair (NER) activity than the vector control cells did. The presence of γ-H2AX, a marker of DNA damage, indicated that the established cell line contained more DNA damage foci compared with vector control cells. Furthermore, the results of clonogenic analyses indicated that the JCV ST-expressing cells were more sensitive than the vector control cells to ultraviolet (UV) irradiation and cisplatin treatment. Micronuclei formation assay revealed that the JCV ST-positive cells presented more chromosomal breakages than did the JCV ST-negative cells, particularly after exposure to DNA-damaging agents. The xeroderma pigmentosum Group D protein, a DNA helicase involved in NER, was downregulated in the JCV ST-positive cells in response to UV irradiation. The effect of the protein phosphatase 2A (PP2A) inhibitor okadaic acid on NER was similar to that of the ST, which is a PP2A-binding protein. Therefore, the deactivation of the PP2A might underlie ST-mediated NER inhibition. The results of this study indicate that exposing JCV ST-positive cells to DNA-damaging agents causes genomic instability, which contributes to carcinogenesis. Our data provide further evidence on the association between the JCV ST and human cancer.

Manipulation of cellular DNA damage repair machinery facilitates propagation of human papillomaviruses

In general, the interplay among viruses and DNA damage repair (DDR) pathways can be divided based on whether the interaction promotes or inhibits the viral lifecycle. The propagation of human papillomaviruses is both promoted and inhibited by DDR proteins. As a result, HPV proteins both activate repair pathways, such as the ATM and ATR pathways, and inhibit other pathways, most notably the p53 signaling pathway. Indeed, the role of HPV proteins, with regard to the DDR pathways, can be divided into two broad categories. The first set of viral proteins, HPV E1 and E2 activate a DNA damage response and recruit repair proteins to viral replication centers, where these proteins are likely usurped to replicate the viral genome. Because the activation of the DDR response typically elicits a cell cycle arrest that would impeded the viral lifecycle, the second set of HPV proteins, HPV E6 and E7, prevents the DDR response from pausing cell cycle progression or inducing apoptosis. This review provides a detailed account of the interactions among HPV proteins and DDR proteins that facilitate HPV propagation.

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.

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.

DNA viruses and the cellular DNA-damage response

It is clear that a number of host-cell factors facilitate virus replication and, conversely, a number of other factors possess inherent antiviral activity. Research, particularly over the last decade or so, has revealed that there is a complex inter-relationship between viral infection and the host-cell DNA-damage response and repair pathways. There is now a realization that viruses can selectively activate and/or repress specific components of these host-cell pathways in a temporally coordinated manner, in order to promote virus replication. Thus, some viruses, such as simian virus 40, require active DNA-repair pathways for optimal virus replication, whereas others, such as adenovirus, go to considerable lengths to inactivate some pathways. Although there is ever-increasing molecular insight into how viruses interact with host-cell damage pathways, the precise molecular roles of these pathways in virus life cycles is not well understood. The object of this review is to consider how DNA viruses have evolved to manage the function of three principal DNA damage-response pathways controlled by the three phosphoinositide 3-kinase (PI3K)-related protein kinases ATM, ATR and DNA-PK and to explore further how virus interactions with these pathways promote virus replication.

JCV agnoprotein-induced reduction in CXCL5/LIX secretion by oligodendrocytes is associated with activation of apoptotic signaling in neurons

An indispensable role for oligodendrocytes in the protection of axon function and promotion of neuronal survival is strongly supported by the finding of progressive neuron/axon degeneration in human neurological diseases that affect oligodendrocytes. Imaging and pathological studies of the CNS have shown the presence of neuroaxonal injury in progressive multifocal leukoencephalopathy (PML), a demyelinating disease of the CNS, resulting from destruction of oligodendrocytes upon productive replication of the pathogenic neurotropic polyomavirus JC. Here, we examined the extracellular factors involved in communication between oligodendrocytes and neurons. Culturing cortical neurons with conditioned medium (CM) from rat CG4 oligodendrocytic cells that express the JCV agnoprotein showed that CXCL5/LIX, which is a chemokine closely related to the human CXCL5/ENA78 and CXCL6/GCP-2 chemokines, is essential for neuronal cell survival. We found that in CM from agnoprotein-producing CG-4 cells level of CXC5/LIX is decreased compared to control cells. We also demonstrated that a reduced expression of CXCL5/LIX by CG4 GFP-Agno cells triggered a cascade of signaling events in cortical neurons. Analysis of mitogen-activated protein kinases (MAPK) and glycogen synthase kinase (GSK3) pathways showed that they are involved in mechanisms of neuronal apoptosis in response to the depletion of CXCL5/LIX signaling. These data suggest that agnoprotein-induced dysregulation of chemokine production by oligodendrocytes may contribute to neuronal/axonal injury in the pathogenesis of PML lesions.

Agnoprotein of mammalian polyomaviruses

Polyomaviruses are naked viruses with an icosahedral capsid that surrounds a circular double-stranded DNA molecule of about 5000 base-pairs. Their genome encodes at least five proteins: large and small tumor antigens and the capsid proteins VP1, VP2 and VP3. The tumor antigens are expressed during early stages of the viral life cycle and are implicated in the regulation of viral transcription and DNA replication, while the capsid proteins are produced later during infection. Members of the Polyomaviridae family have been isolated in birds (Avipolyomavirus) and mammals (Orthopolyomavirus and Wukipolyomavirus). Some mammalian polyomaviruses encode an additional protein, referred to as agnoprotein, which is a relatively small polypeptide that exerts multiple functions. This review discusses the structure, post-translational modifications, and functions of agnoprotein, and speculates why not all polyomaviruses express this protein.

Design stars: how small DNA viruses remodel the host nucleus

Numerous host components are encountered by viruses during the infection process. While some of these host structures are left unchanged, others may go through dramatic remodeling processes. In this review, we summarize these host changes that occur during small DNA virus infections, with a focus on host nuclear components and pathways. Although these viruses differ significantly in their genome structures and infectious pathways, there are common nuclear targets that are altered by various viral factors. Accumulating evidence suggests that these nuclear remodeling processes are often essential for productive viral infections and/or viral-induced transformation. Understanding the complex interactions between viruses and these host structures and pathways will help to build a more integrated network of how the virus completes its life cycle and point toward the design of novel therapeutic regimens that either prevent harmful viral infections or employ viruses as nontraditional treatment options or molecular tools.

JC virus intranuclear inclusions associated with PML-NBs: analysis by electron microscopy and structured illumination microscopy

Progressive multifocal leukoencephalopathy is a fatal demyelinating disorder caused by JC virus infection. JC virus was recently found to target promyelocytic leukemia nuclear bodies (PML-NBs), punctuate domains in the nuclei. Thus, the virus progenies cluster in dots as intranuclear inclusions (ie, as dot-shaped inclusions). In the present study, both the viral major and minor capsid proteins were expressed from polycistronic expression vectors with a powerful promoter, and formation into virus-like particles (VLPs) was examined by electron microscopy. When the upstream regulatory sequence including the agnogene (nt 275 to 490) was present, capsid protein expression was suppressed, but numerous VLPs were efficiently formed with restricted accumulation to PML-NBs. VLPs were uniform, and the cells were severely degraded. In contrast, when the 5' terminus of the agnogene (nt 275 to 409; 135 bp) was deleted, capsid protein expression was markedly enhanced, but VLPs were more randomly produced in the nucleus outside of PML-NBs. VLPs were pleomorphic, and cell degradation was minimal. JC virus association with PML-NBs was confirmed in human brain tissues by structured illumination microscopy. PML-NBs were shaped in spherical shells, with viral capsid proteins circumscribing the surface. These findings indicate that PML-NBs are intranuclear locations for pathogenic JC virus proliferation. Either the agnogene or its product likely supports efficient progeny production at PML-NBs, leading to subsequent degeneration of host glial cells.

VP-1 quasispecies in human infection with polyomavirus BK

Polyomavirus BK is a recognized cause of nephropathy and hemorrhagic cystitis in kidney or allogeneic hematopoietic stem cell transplant recipients. This study explored a role of genetic variations in capsid protein VP-1 gene as a factor in viral pathogenesis. VP-1 was amplified from 7 healthy subjects with viruria, 7 transplant patients with viruria, and 11 patients with viremia or nephropathy. PCR products were cloned and a total of 558 clonal sequences were subjected to phylogenetic analysis using standard methods. VP-1 quasispecies were found in 25/25 and coinfection with different genotypes in 12/25 subjects. Genotype II was found as an unexpected minority species in 5/25 individuals. Recombinant strains of uncertain biologic significance, which frequently contained genotype II and IV sequences were identified in 9/25 subjects. Viremia/nephropathy group was characterized by (a) greater sequence complexity in whole VP-1 versus BC loop and BC loop compared to the HI loop, (b) greater intra-strain genetic diversity in the BC loop compared to whole VP-1 protein and HI loop, (c) more non-synonymous substitutions (dN) in the BC loop compared to whole VP-1 and HI loop, (e) fewer synonymous substitutions (dS) compared to healthy-viruria group, and (f) selection pressure (dN/dS >1.0) exerted on VP-1. In conclusion, this study documents frequent occurrence of quasispecies in a host DNA polymerase dependent virus, which is theoretically expected to show high replication fidelity. Quasispecies occur even in healthy subjects with viruria, but evolutionary selection pressure directed at the viral capsid protein (VP-1) is seen only in patients with viremia or nephropathy.

VP-1 quasispecies in human infection with polyomavirus BK

Polyomavirus BK is a recognized cause of nephropathy and hemorrhagic cystitis in kidney or allogeneic hematopoietic stem cell transplant recipients. This study explored a role of genetic variations in capsid protein VP-1 gene as a factor in viral pathogenesis. VP-1 was amplified from 7 healthy subjects with viruria, 7 transplant patients with viruria, and 11 patients with viremia or nephropathy. PCR products were cloned and a total of 558 clonal sequences were subjected to phylogenetic analysis using standard methods. VP-1 quasispecies were found in 25/25 and coinfection with different genotypes in 12/25 subjects. Genotype II was found as an unexpected minority species in 5/25 individuals. Recombinant strains of uncertain biologic significance, which frequently contained genotype II and IV sequences were identified in 9/25 subjects. Viremia/nephropathy group was characterized by (a) greater sequence complexity in whole VP-1 versus BC loop and BC loop compared to the HI loop, (b) greater intra-strain genetic diversity in the BC loop compared to whole VP-1 protein and HI loop, (c) more non-synonymous substitutions (dN) in the BC loop compared to whole VP-1 and HI loop, (e) fewer synonymous substitutions (dS) compared to healthy-viruria group, and (f) selection pressure (dN/dS >1.0) exerted on VP-1. In conclusion, this study documents frequent occurrence of quasispecies in a host DNA polymerase dependent virus, which is theoretically expected to show high replication fidelity. Quasispecies occur even in healthy subjects with viruria, but evolutionary selection pressure directed at the viral capsid protein (VP-1) is seen only in patients with viremia or nephropathy.

Activation of HIV-1 LTR by Rad51 in microglial cells

Infection with HIV-1 induces a variety of biological alterations to the host that are beneficial to the life cycle of the virus but may have adverse effects on the host cell. Here we demonstrate that expression of Rad51, a major component of the homologous recombination-directed DNA repair (HRR) pathway, is induced upon HIV-1 infection of microglial cells. Activation of Rad51 expression positively impacts on HIV-1 LTR transcription through a region of the viral promoter known for binding the inducible transcription factor NFκB. Rad51 showed the ability to form a complex with the p65 subunit of NFκB and regulate the level of p65 interaction with LTR DNA encompassing the κB motif. This study provides evidence for reciprocal interaction of HIV-1 and a host DNA repair protein that impacts on expression of the viral genome. These results also point to the ability of HIV-1 to recruit proteins involved in DNA repair that are necessary for retroviral DNA integration, efficient replication and prevention of viral-induced cell death.

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.

High frequency and diversity of rearrangements in polyomavirus bk noncoding regulatory regions cloned from urine and plasma of Israeli renal transplant patients and evidence for a new genetic subtype

Polyomavirus BK (BKV) establishes latent infection in various human tissues, including the kidney. Reactivation following renal transplantation (RT) may cause BKV-associated nephropathy, leading to graft loss. BKV reactivation is often associated with extensive rearrangements in the BKV noncoding regulatory region (NCRR). We explored the formation and predominance of the rearrangements versus the diversity of the rearrangements by cloning and characterizing PCR-amplified NCRR sequences from six Israeli RT patients. We found a high frequency and a high degree of diversity of rearrangements: NCRRs that contained major rearrangements (mrNCRRs), including large insertions and deletions, were detected in 0 to 100% of the clones from individual samples (mean, 50% and 67% in plasma and urine, respectively). In addition, we found a high frequency of mrNCRRs that contained single-nucleotide variations (snvNCRRs) among identical mrNCRRs and archetype clones. mrNCRRs were present in plasma and in concomitantly collected urine samples, but for each patient, only a subset of the mrNCRRs and snvNCRRs were present in both compartments at the same time and/or in subsequent samples from the same compartment. Some mrNCRRs were observed over several months, indicating the continuous replication of the viral genomes carrying them. Phylogenetic analysis based on the snvNCRR in the archetype clones grouped isolates from four of the patients into a new subgroup of genotype IV. Genotypes Ib-1 and Ib-2 were also found. Isolates from two patients had NCRRs from two genotypes, one concurrently with a RT and one after a second RT. Our study prompts further investigation of the functional consequences of NCRR rearrangements to assess their biological significance and their putative role in disease progression and prognosis.

Protective role of Puralpha to cisplatin

BACKGROUND

The nucleic acid-binding protein Puralpha is involved at stalled DNA replication forks, in double-strand break (DSB) DNA repair and the cellular response to DNA replication stress. Puralpha also regulates homologous recombination-directed DNA repair (HRR).

RESULTS

Cells lacking Puralpha showed enhanced sensitivity to cisplatin as evaluated by assays for cell viability and cell clonogenicity. This was seen both in Puralpha-negative MEFs and in human glioblastoma cells treated with siRNA directed against Puralpha. MEFs lacking Puralpha also showed enhanced H2AX phosphorylation in response to cisplatin. Repair of a reporter plasmid that had been treated with cisplatin was decreased in a reactivation assay using Puralpha-negative MEFs and the capacity of nuclear extracts from Puralpha-negative MEFs to perform non-homologous end-joining in vitro was also impaired.

METHODS

We investigated the effects of the DNA damage-inducing cancer chemotherapeutic agent cisplatin on mouse embryo fibroblasts (MEFs) from PURA(-/-) knockout mice that lack Puralpha.

CONCLUSIONS

Puralpha has a role in the cellular response to cisplatin-induced DNA damage and may provide new therapeutic modalities for cisplatin-resistant tumors.

Progressive multifocal leukoencephalopathy – the importance of early diagnosis illustrated in four cases

Progressive multifocal leukoencephalopathy (PML) is a rare, deadly demyelinating disease of the central nervous system, which is caused by a reactivation of the DNA polyomavirus JC and occurs in immunosuppressed individuals. So far, only 25 cases have been described in patients with SLE and none survived without antiviral therapy and only two cases in RA. We present four additional cases from a defined area, three in SLE, of which one survived without antiviral therapy, and one case in RA, also surviving after reduction of immunosuppressive treatment. In three of these cases, diagnosis could only be confirmed by stereotactical brain biopsy, including the two surviving cases. Thus, this article illustrates the difficulty in diagnosing progressive multifocal leukoencephalopathy, the need for brain biopsy in many cases, the importance of reduced immunosuppression as early as possible and the severe damage progressive multifocal leukoencephalopathy can cause. Furthermore, progressive multifocal leukoencephalopathy might be much more common in SLE than expected with 1 case in 800 patient-years.

Detection of JC virus DNA fragments but not proteins in normal brain tissue

OBJECTIVE

Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disease of the white matter affecting immunocompromised patients that results from the cytolytic destruction of glial cells by the human neurotropic JC virus (JCV). According to one model, during the course of immunosuppression, JCV departs from its latent state in the kidney and after entering the brain, productively infects and destroys oligodendrocytes. The goal of this study was to test the hypothesis that JCV may reside in a latent state in a specific region of the brains of immunocompetent (non-PML) individuals without any neurological conditions.

METHODS

Gene amplification was performed together with immunohistochemistry to examine the presence of JCV DNA sequences and expression of its genome in five distinct regions of the brain from seven immunocompetent non-PML individuals.

RESULTS

Although no viral proteins were expressed in any of these cases, fragments of the viral DNA were present in various regions of normal brain. Laser-capture microdissection showed the presence of JCV DNA in oligodendrocytes and astrocytes, but not in neurons.

INTERPRETATION

The detection of fragments of viral DNA in non-PML brain suggests that JCV has full access to all regions of the brain in immunocompetent individuals. Thus, should the immune system become impaired, the passing and/or the resident virus may gain the opportunity to express its genome and initiate its lytic cycle in oligodendrocytes. The brain as a site of JCV latency is a possibility.

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.

JC virus agnoprotein inhibits in vitro differentiation of oligodendrocytes and promotes apoptosis

Productive infection of oligodendrocytes, which are responsible for the formation of myelin sheath in the central nervous system, with the human neurotropic virus JC virus (JCV) causes the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). In addition to encoding T antigen and the capsid proteins, which are produced at the early and late phases of the infection cycle, respectively, JCV encodes a small regulatory protein named agnoprotein that is important for successful completion of the virus life cycle. Here we used bipotential CG-4 cells to examine the impact of agnoprotein on oligodendrocyte differentiation and survival in the absence of JCV lytic infection. We demonstrate that the expression of agnoprotein delayed the formation of complex outgrowth networks of the cells during oligodendrocyte differentiation. These alterations were accompanied by high levels of DNA damage, induction of proapoptotic proteins, and suppression of prosurvival signaling. Accordingly, apoptosis was significantly increased upon the induction of CG-4 cells toward differentiation in cells expressing agnoprotein. These observations provide the first evidence for the possible involvement of agnoprotein, independent from its role in viral replication, in a series of biological events that may contribute to the pathological features seen in PML lesions.

Alterations of DNA damage repair pathways resulting from JCV infection

Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disorder of the CNS caused by infection of glial cells with the polyomavirus, JCV. Here we report that genomic stability and DNA repair are significantly dysregulated by JCV infection of human astrocytes. Metaphase spreads exhibited increased ploidy correlating with duration of infection. Increased micronuclei formation and phospho-Histone2AX expression also indicated DNA damage. Western blot analysis revealed perturbation in expression of some DNA repair proteins including a large elevation of Rad51. Immunohistochemistry on clinical samples of PML showed robust labeling for Rad51 in nuclei of bizarre astrocytes and inclusion body-bearing oligodendrocytes that are characteristic of JCV infection. Finally, in vitro end-joining DNA repair was altered in extracts prepared from JCV-infected human astrocytes. Alterations in DNA repair pathways may be important for the life cycle of JCV and the pathogenesis of PML.

Using or abusing: viruses and the cellular DNA damage response

During infection, viruses attempt to hijack the cell while the host responds with various defense systems. Traditional defenses include the interferon response and apoptosis, but recent work suggests that this antiviral arsenal also includes the cellular DNA damage response machinery. The observation of interactions between viruses and cellular DNA repair proteins has not only uncovered new complexities of the virus-host interaction but is also reinforcing the view that viruses can reveal key regulators of cellular pathways through the proteins they target.