Identification and characterization of a novel GGA/C-binding protein, GBP-i, that is rapidly inducible by cytokines

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.

Cytokine-mediated reversal of multidrug resistance

The occurrence of the multidrug resistance phenotype still represents a limiting factor for successful cancer chemotherapy. Numerous efforts have been made to develop strategies for reversal and/or modulation of this major therapy obstacle through targeting at different levels of intervention. The phenomenon of MDR is often associated with overexpression of resistance-associated genes. Since the classical type of MDR in human cancers is mainly mediated by the P-glycoprotein encoded by the multidrug resistance gene 1, mdr1, the majority of reversal approaches target the expression and/or function of the mdr1 gene/P-glycoprotein. Due to the fact that the multidrug phenotype always represents the net effect of a panel of resistance-associated genes/gene products, other resistance genes, e.g. those encoding the multidrug resistance-associated protein MRP or the lung resistance protein LRP, were included in the studies. Cytokines such as tumor necrosis factor alpha and interleukin-2 have been shown to modulate the MDR phenotype in different experimental settings in vitro and in vivo. Several studies have been performed to evaluate their potential as chemosensitizers of tumor cells in the context of a combined application of MDR-associated anticancer drugs like doxorubicin and vincristine with cytokines. Moreover, the capability of cytokines to modulate the expression of MDR-associated genes was demonstrated, either by external addition or by transduction of the respective cytokine gene. Knowledge of the combination effects of cytokines and cytostatics and its link to their MDR-modulating capacity may contribute to a more efficient and to a more individualized immuno-chemotherapy of human malignancies.

Transforming growth factor beta-induced reactivation of Epstein-Barr virus involves multiple Smad-binding elements cooperatively activating expression of the latent-lytic switch BZLF1 gene

Transforming growth factor β (TGF-β) physiologically induces Epstein-Barr virus (EBV) lytic infection by activating the expression of EBV's latent-lytic switch BZLF1 gene. Liang et al. (J. Biol. Chem. 277:23345-23357, 2002) previously identified a Smad-binding element (SBE) within the BZLF1 promoter, Zp; however, it accounts for only 20 to 30% of TGF-β-mediated activation of transcription from Zp. Here, we identified additional factors responsible for the rest of this activation. The incubation of EBV-positive MutuI cells with a TGF-β neutralizing antibody or inhibitors of the TGF-β type I receptor (TβRI) or Smad3 eliminated the TGF-β-induced reactivation of EBV. The coexpression of Smad2, Smad3, and Smad4 together with a constitutively active form of TβRI induced 15- to 25-fold transcription from Zp in gastric carcinoma AGS cells. By electrophoretic mobility shift assays, we identified four additional Smad-binding elements, named SBE2 to SBE5. Substitution mutations in individual SBEs reduced Smad-mediated activation of Zp by 20 to 60%; together, these mutations essentially eliminated it. Chromatin immunoprecipitation assays confirmed that Smad4 newly bound the Zp region of the EBV genome following the incubation of MutuI cells with TGF-β. SBE2 overlaps the ZEB-binding ZV silencing element of Zp. Depending upon posttranslational modifications, Smad4 either competed with ZEB1 for binding or formed a complex with ZEB1 on the Zp ZV element in a cell-free assay system. In transiently transfected cells, exogenously expressed ZEB1 inhibited Smad-mediated transcriptional activation from Zp. We conclude that TGF-β induces EBV lytic reactivation via the canonical Smad pathway by activating BZLF1 gene expression through multiple SBEs acting in concert.

Modulation of JC virus transcription by C/EBPbeta

The polyomavirus JC (JCV) causes the demyelinating disease progressive multifocal leukoencephalopathy (PML). Infection by JCV is very common in childhood after which the virus enters a latent state, which is poorly understood. Under conditions of severe immunosuppression, especially AIDS, JCV may reactivate to cause PML. Expression of JC viral proteins is regulated by the JCV non-coding control region (NCCR), which contains an NF-kappaB binding site previously shown to activate transcription. We now report that C/EBPbeta inhibits basal and NF-kappaB-stimulated JCV transcription via the same site. Gel shift analysis showed C/EBPbeta bound to this region in vitro and ChIP assays confirmed this binding in vivo. Further, a ternary complex of NF-kappaB/p65, C/EBPbeta-LIP and JCV DNA could be detected in co-immunoprecipitation experiments. Mutagenesis analysis of the JCV NCCR indicated p65 and C/EBPbeta-LIP bound to adjacent but distinct sites and that both sites regulate basal and p65-stimulated transcription. Thus C/EBPbeta negatively regulates JCV, which together with NF-kappaB activation, may control the balance between JCV latency and activation leading to PML. This balance may be regulated by proinflammatory cytokines in the brain.

Regulation of gene expression in primate polyomaviruses

Polyomaviruses are a growing family of small DNA viruses with a narrow tropism for both the host species and the cell type in which they productively replicate. Species host range may be constrained by requirements for precise molecular interactions between the viral T antigen, host replication proteins, including DNA polymerase, and the viral origin of replication, which are required for viral DNA replication. Cell type specificity involves, at least in part, transcription factors that are necessary for viral gene expression and restricted in their tissue distribution. In the case of the human polyomaviruses, BK virus (BKV) replication occurs in the tubular epithelial cells of the kidney, causing nephropathy in kidney allograft recipients, while JC virus (JCV) replication occurs in the glial cells of the central nervous system, where it causes progressive multifocal leukoencephalopathy. Three new human polyomaviruses have recently been discovered: MCV was found in Merkel cell carcinoma samples, while Karolinska Institute Virus and Washington University Virus were isolated from the respiratory tract. We discuss control mechanisms for gene expression in primate polyomaviruses, including simian vacuolating virus 40, BKV, and JCV. These mechanisms include not only modulation of promoter activities by transcription factor binding but also enhancer rearrangements, restriction of DNA methylation, alternate early mRNA splicing, cis-acting elements in the late mRNA leader sequence, and the production of viral microRNA.

Interferon beta1-a and selective anti-5HT(2a) receptor antagonists inhibit infection of human glial cells by JC virus

JC virus (JCV) is the causative agent of progressive multifocal leukoenchaphalopathy (PML). The disease develops when JCV gains access to the central nervous system, infects and destroys oligodendrocytes. The disease is rapidly progressing, typically fatal and no effective therapies exist to treat or prevent PML. The recent occurrence of PML in multiple sclerosis patients being treated with Avonex (IFNbeta1-a) and Tysabri (Natalizumab) and the recent reports linking JCV infection to the 5HT(2a) serotonin receptor led us to evaluate the effects of IFNbeta1-a and a panel of 5HT(2a) receptor antagonists for their ability to modulate virus infection. IFNbeta1-a was found to be a potent inhibitor of both virus infection and viral early and late gene expression. In addition, several 5HT(2a) receptor antagonists inhibited initial infection of cells by JCV but were less effective at reducing viral loads in an already established infection.

Early growth response-1 protein is induced by JC virus infection and binds and regulates the JC virus promoter

JC virus (JCV) is a human polyomavirus that can emerge from a latent state to cause the cytolytic destruction of oligodendrocytes in the brain resulting in the fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). Previous studies described a cis-acting transcriptional regulatory element in the JCV non-coding control region (NCCR) that is involved in the response of JCV to cytokines. This consists of a 23 base pair GGA/C rich sequence (GRS) near the replication origin (5112 to +4) that contains potential binding sites for Sp1 and Egr-1. Gel shift analysis showed that Egr-1, but not Sp1, bound to GRS. Evidence is presented that the GRS gel shift seen on cellular stimulation is due to Egr-1. Thus, TPA-induced GRS gel shift could be blocked by antibody to Egr-1. Further, the TPA-induced GRS DNA/protein complex was isolated and found to contain Egr-1 by Western blot. No other Egr-1 sites were found in the JCV NCCR. Functionally, Egr-1 was found to stimulate transcription of JCV late promoter but not early promoter reporter constructs. Mutation of the Egr-1 site abrogated Egr-1 binding and virus with the mutated Egr-1 site showed markedly reduced VP1 expression and DNA replication. Infection of primary astrocytes by wild-type JCV induced Egr-1 nuclear expression that was maximal at 5-10 days post-infection. Finally, upregulation of Egr-1 was detected in PML by immunohistochemistry. These data suggest that Egr-1 induction may be important in the life cycle of JCV and PML pathogenesis.

An overview: Human polyomavirus JC virus and its associated disorders

JC virus (JCV) is a polyomavirus infecting greater than 80% of the human population early in life. Replication of this virus in oligodendrocytes and astrocytes results in the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML) in immunocompromised individuals, most notably acquired immunodeficiency syndrome (AIDS) patients. Moreover, recent studies have pointed to the association of JCV with a variety of brain tumors, including medulloblastoma. The JCV genome encodes for viral early protein, including large and small T antigens and the newly discovered isoform T', at the early phase of infection and the structural proteins VP1, VP2, and VP3 at the late stage of the lytic cycle. In addition, the late gene is responsible for the production of a small nonstructural protein, agnoprotein, whose function is not fully understood. Here, we have summarized some aspects of the JCV genome structure and function, and its associated diseases, including PML and brain tumors.

Members of the AP-1 family, c-Jun and c-Fos, functionally interact with JC virus early regulatory protein large T antigen

The activating protein 1 (AP-1) family of regulatory proteins is characterized as immediate-early inducible transcription factors which were shown to be activated by a variety of stress-related stimuli and to be involved in numerous biological processes, including cellular and viral gene expression, cell proliferation, differentiation, and tumorigenesis. We have recently demonstrated the involvement of the AP-1 family members c-Jun and c-Fos in transcriptional regulation of the human polyomavirus, JC virus (JCV), genome. Here, we further examined their role in JCV gene regulation and replication through their physical and functional interaction with JCV early regulatory protein large T antigen (T-Ag). Transfection and replication studies indicated that c-Jun and c-Fos can significantly diminish T-Ag-mediated JCV gene transcription and replication. Affinity chromatography and coimmunoprecipitation assays demonstrated that c-Jun and T-Ag physically interact with each other. Results from band shift assays showed that the binding efficiency of c-Jun to the AP-1 site was reduced in the presence of T-Ag. In addition, we have mapped, through the use of a series of deletion mutants, the regions of these proteins which are important for their interaction. While the c-Jun interaction domain of T-Ag is localized to the middle portion of the protein, the T-Ag interacting domain of c-Jun maps to its basic-DNA binding region. Results of transient-transfection assays with various c-Jun mutants and T-Ag expression constructs further confirm the specificity of the functional interaction between c-Jun and T-Ag. Taken together, these data demonstrate that immediate-early inducible transcription factors c-Jun and c-Fos physically and functionally interact with JCV major early regulatory protein large T-Ag and that this interaction modulates JCV transcription and replication in glial cells.

Functional interaction between JC virus late regulatory agnoprotein and cellular Y-box binding transcription factor, YB-1

Human polyomavirus JC virus (JCV) is a causative agent of progressive multifocal leukoencephalopathy which results from lytic infection of glial cells. Although significant progress has been made in understanding the regulation of JCV gene transcription, the mechanism(s) underlying the viral lytic cycle remains largely unknown. We recently reported that the JCV late auxiliary Agnoprotein may have a regulatory role in JCV gene transcription and replication. Here, we investigated its regulatory function in viral gene transcription through its physical and functional interaction with YB-1, a cellular transcription factor which contributes to JCV gene expression in glial cells. Time course studies revealed that Agnoprotein is first detected at day 3 postinfection and that its level increased during the late stage of the infection cycle. Agnoprotein is mainly localized to the cytoplasmic compartment of the infected cell, with high concentrations found in the perinuclear region. While the position of Agnoprotein throughout the infection cycle remained relatively unaltered, the subcellular distribution of YB-1 between the cytoplasm and nucleus changed. Results from coimmunoprecipitation and glutathione S-transferase pull-down experiments revealed that Agnoprotein physically interacts with YB-1 and that the amino-terminal region of Agnoprotein, between residues 1 and 36, is critical for this association. Further investigation of this interaction by functional assays demonstrated that Agnoprotein negatively regulates YB-1-mediated gene transcription and that the region corresponding to residues 1 to 36 of Agnoprotein is important for the observed regulatory event. Taken together, these data demonstrate that the interaction of the viral late regulatory Agnoprotein and cellular Y-box binding factor YB-1 modulates transcriptional activity of JCV promoters.

Physical and functional interaction between viral and cellular proteins modulate JCV gene transcription

The lytic phase of JC virus (JCV) appears to be highly complex and remains elusive. A growing body of experimental evidence suggests that the regulation of JCV gene expression and replication requires, in addition to the presence of specific transcription factors, cooperativity between viral and cellular regulatory proteins. This cooperativity may be accomplished by physical interaction of the participant proteins on and/or off the viral DNA sequence. Here, we present evidence of specific physical and functional interaction between a cellular factor, YB-1, and the JCV early protein, T-antigen, and showed that both proteins play important roles in JCV gene transcription. Additionally, our data indicate that YB-1 also functionally interact with another viral protein, designated agnoprotein, which is expressed late during the course of infection, adding further complexity to the currently known picture on JCV gene regulation.

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

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

Regulation of Epstein-Barr virus promoters in oral epithelial cells and lymphocytes

Hairy leukoplakia (HL) is a proliferative lesion of the tongue that supports abundant Epstein-Barr virus (EBV) replication. Previous work showed high-level expression of the EBV BMRF2 gene in HL. To characterize the regulation of BMRF2 expression in HL, we mapped the 5' ends of the BMRF1 and BMRF2 transcripts and showed that BMRF2 is expressed from a novel internal promoter within the BMRF1 coding region. Mechanisms of BMRF2 regulation were compared in oral epithelial cells and B lymphocytes, as were those of BMRF1 and BDLF3, early and late EBV transcripts, respectively, that are also known to be expressed in HL. Basal activity of the putative BMRF2 promoter was 10-fold higher in HSC-3 epithelial cells than in B lymphocytes. The BMRF2 and the BDLF3 promoters were responsive to induction by phorbol ester, but unlike the BMRF1 promoter, they were not responsive to BZLF1 transactivation. By mutational analysis, the major activity of the BMRF2 promoter mapped to a 50-bp region, which includes a TATA-like element and a GC box. The BMRF2 promoter may be regulated differentially from the BMRF1 promoter and more closely resembles that of BDLF3. This novel BMRF2 promoter likely belongs to a class of viral promoters that is more responsive to mechanisms known to induce epithelial cell differentiation, consistent with its high level of expression in HL.

[Progressive multifocal leukoencephalopathy]

PATHOGENESIS

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

DIAGNOSIS

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

TREATMENT

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

Transcriptional regulation of human polyomavirus JC: evidence for a functional interaction between RelA (p65) and the Y-box-binding protein, YB-1

The transcriptional control region of the human neurotropic polyomavirus JC virus contains a consensus NF-kappa B site which has been shown to enhance both basal and extracellular stimulus-induced levels of transcription of JC promoters. Here, we show that the expression of JC late promoter constructs containing the NF-kappa B site is decreased by cotransfection with the NF-kappa B/rel subunits, p50 and p52, but enhanced by the p65 subunit. However, JC promoter constructs lacking the NF-kappa B site were activated by p52 and p50 and repressed by p65. This antithetical response of the JC promoter mapped specifically to the D domain, which is a target site for the cellular transcription factor, YB-1. Band shift studies indicated that YB-1 and p65 modulate each other's binding to DNA: YB-1 augments the affinity of p65 for the NF-kappa B site, while p65 reduces the binding of YB-1 to the D domain. Results from coimmunoprecipitation followed by Western blot (immunoblot) analysis suggest an in vivo interaction between p65 and YB-1 in glial cells. Functionally, YB-1 appears to act synergistically with p65 to control transcription from the NF-kappa B site. A converse pattern is seen with the D domain, in which YB-1 acts synergistically with p50 and p52 to regulate transcription. p50 and p52 may function as transcriptional activators on the D domain by removing the repressive effect of p65 on YB-1 binding to the D domain. On the basis of these data, we propose a model in which NF-kappa B/rel subunits functionally interact with consensus NF-kappa B sites or YB-1-binding sites, with disparate effects on eukaryotic gene expression.

Transcription of the JC virus archetype late genome: importance of the kappa B and the 23-base-pair motifs in late promoter activity in glial cells

The transcription control region of the archetype strain of the human polyomavirus JC virus (JCV(Cy)), unlike its neurotropic counterpart (JCV(Mad-1)), contains only one copy of the 98-bp enhancer/promoter repeat with the 23-bp and the 66-bp insertion blocks. Early studies by us and others have indicated that the structural organization of JCV(Mad-1) is critical for glial cell-specific transcription of the viral genome. In addition, the kappa B regulatory motif found in the JCV(Mad-1) genome, which also exists in JCV(Cy), confers inducibility to the JCV(Mad-1) early and late promoters in response to extracellular stimuli. In this study, we have investigated the regulatory role of the 23- and the 66-bp blocks and their functional relationship to the kappa B motif in stimulating transcription of the Cy early and late promoters in glial cells. We demonstrate that mutations in the kappa B motif reduce the basal activity of the Cy early promoter and decrease the levels of its induction by phorbol myristate acetate or factors derived from activated T cells. Under similar circumstances, mutation in the kappa B motif completely abrogated the basal and the induced levels of transcription of the viral late promoter. Using deletion and hybrid promoter constructs, we have demonstrated that the 23-bp block of the Cy promoter plays a critical role in the observed inactivation of Cy late promoter transcription in glial cells. Results from DNA binding studies have indicated the formation of a common nucleoprotein complex with the 23-bp sequence, mutant kappa B (kappa B(mut)), and wild-type kappa B (kappa B(wt)). Analysis of this complex by UV cross-linking has identified a 40-kDa protein which binds to the 23-bp sequence and the kappa B motif. The importance of these findings for the activation of JCV(Cy) under various physiological conditions is discussed.

Transcriptional regulation of human JC polyomavirus promoters by cellular proteins YB-1 and Pur alpha in glial cells

Transcription of the human polyomavirus (JCV) genome is regulated by host cell proteins and the viral early protein, T antigen. A region called the lytic control element (LCE), located within the enhancer of JCV, is important for transcription of JCV early and late promoters. Earlier studies have led to the identification of two single-stranded DNA-binding proteins, YB-1 and Pur alpha, with the ability to interact with nucleotides on the early and late strands of LCE, respectively. Of particular interest is the notion that the unique interplay between these two cellular proteins and JCVT antigen determines their binding activities with the LCE. In this study, we employed a series of cotransfection experiments to evaluate the levels of transcription from JCV early and late promoters in the presence of YB-1, Pur alpha, and T antigen. Results from these studies indicated that Pur alpha stimulates JCV early and has little effect on the late promoter. Moreover, T antigen was able to decrease the induced level of early gene transcription by Pur alpha. On the other hand, the extent of transactivation of the viral late promoter by T antigen was reduced upon overexpression of Pur alpha in the transfected cells. These observations suggest that Pur alpha and T antigen exert an antagonistic effect on each other's regulatory action upon their responsive promoters. Of particular interest was the observation that YB-1 liberated T-antigen-induced late promoter activity from repression imposed by overexpression of pur alpha. Under similar conditions, overexpression of YB-1 showed no effect on the transcriptional activity of the early promoter in cells transfected with T-antigen- and Pur alpha-producing plasmids. On the basis of the data presented here and the previous binding results, a model is proposed which describes the potential role of Pur alpha, YB-1, and T antigen in differential expression of the viral genome during the lytic cycle.