A 53 kDa protein binds to the negative regulatory region of JC virus early promoter

Human polyomaviruses JCPyV and MCPyV in urothelial cell carcinoma: a single institution experience

Objective

Urothelial cell carcinoma (UCC) is the most common type of urinary bladder. JCPyV and BKPyV have been detected in the urine and tissue of urothelial cell carcinomas (UCC) in immunocompetent patients. Here, we investigated the presence of several HPyVs in UCC samples using diverse molecular techniques to study the prevalence of HPyVs in UCC.

Methods

A large single-institution database of urine cytology specimens (UCS; n = 22.867 UCS) has previously been searched for decoy cells (n = 30), suggesting polyomavirus infection. The available urine sediments and formalin-fixed paraffin-embedded (FFPE) tissue samples of UCC patients were tested for the presence of JCPyV-LTAg expression by immunohistochemistry (IHC) labeled with SV40-LTAg antibody (clone: PAb416) and subsequent PCR followed by sequencing. In addition, the presence of the oncogenic Merkel cell polyomavirus (MCPyV) and the presence of human polyomavirus 6 (HPyV6) and 7 (HPyV7) DNA were tested with DNA PCR or IHC.

Results

Of the 30 patients harboring decoy cells, 14 were diagnosed with UCC of the urinary bladder (14/30; 46.6%) before presenting with decoy cells in the urine. The SV40-LTAg IHC was positive in all 14 UCC urine sediments and negative in the FFPE tissues. JCPyV-DNA was identified in all five available UCS and in three FFPE samples of UCC (three of 14; 21.4%). Two UCC cases were positive for MCPyV-DNA (two of 14; 14.3%), and one of them showed protein expression by IHC (one of 14; 7.1%). All specimens were HPyV6 and HPyV7 negative.

Conclusion

Our findings show the presence of JCPyV in the urine and UCC of immunocompetent patients. Moreover, MCPyV was detected in two UCC cases. In total, five UCC cases showed the presence of either JCPyV or MCPyV. The evidence here supports the hypothesis that these viruses might sporadically be associated with UCC. Further studies are needed to confirm the relevance of JCPyV or MCPyV as a possible risk factor for UCC development.

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.

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

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

JC virus: an oncogenic virus in animals and humans?

JC virus (JCV) is a human polyomavirus of the Polyomaviridae family, which also includes BK virus and simian vacuolating virus 40 (SV40). JC virus was first isolated in 1971 from the brain of a patient with Progressive Multifocal Leukoencephalopathy (PML). Like other polyomaviruses, JCV has a restricted host range. The virus infects the majority of the human population with seroconversion occurring during adolescence. JCV has a limited and specific tissue tropism infecting the kidney and oligodendrocytes and astrocytes in the central nervous system (CNS). Initial JCV infection is generally asymptomatic in immunocompetent hosts, and it establishes a persistent infection in the kidney and possibly bone marrow. In immunocompromised individuals JCV can cause a lytic infection in the CNS and lead to development of the fatal, demyelinating disease PML. The name polyoma is derived from the Greek terms: poly, meaning many, and oma, meaning tumors, owing to the capacity of this group of viruses to cause tumors. JCV inoculation of small animal models and non-human primates, which are not permissive to a productive JCV infection, leads to tumor formation. Given the ubiquitous nature of the virus and its strong association with cancer in animal models, it is hypothesized that JCV plays a role in human cancers. However, the role for JCV in human cancers and tumor formation is not clear. Some researchers have reported an association of JCV with human cancers including brain tumors, colorectal cancers, and cancers of the gastrointestinal tract, while other groups report no correlation. Here, we review the role of JCV in cancers in animal models and present the findings on JCV in human cancers.

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

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

Identification and characterization of a JC virus pentanucleotide repeat element binding protein: cellular nucleic acid binding protein

The JC virus (JCV) control region contains AGGGAAGGGA, the tandem pentanucleotide repeat element (Pnt2). Several proteins specifically interacted via Pnt2 to regulate the expression of JCV early promoter-enhancer (JCV(E)) or late promoter-enhancer (JCV(L)). In this study, a JCV Pnt2 oligonucleotide probe was used to screen a cDNA expression library from glial P19 mouse embryonal carcinoma cells. A cDNA clone was isolated by Southwestern blot assay and it produced a protein that reproducibly and specifically bound to Pnt2. This cDNA had 100% homology to one of three previously identified mouse cDNAs called cellular nucleic acid binding proteins (Cnbps). Cnbps are a highly homologous family of eukaryotic genes implicated in functional interactions with cytoplasmic RNA and regulatory DNA elements. An mRNA of 2.2 kb of Pnt2-interacting Cnbp (PCnbp) was seen in undifferentiated, muscle or glial P19 cells. When expressed from a cDNA expression vector as a fusion protein that also contained 115 kDa from beta-galactosidase, a Pnt2 binding protein (PCNBP) specifically bound to Pnt2 in Southwestern blots as a 30 kDa component of the 145 kDa fusion protein. Furthermore, JCV(E) expression was negatively regulated by PCnbp produced in vivo from the cDNA expression vector. Regulation of JCV(L) was unaffected. We suggest a novel role for CNBP as a PCNBP that interacts with Pnt2 in the negative transcriptional regulation of JCV(E).

Cell-specific activation of the glial-specific JC virus early promoter by large T antigen

JC virus causes the human demyelinating disease progressive multifocal leukoencephalopathy by selective infection of glial cells. This cell specificity results from glial-specific expression of viral early genes (large and small T antigens). Analysis of transcriptional regulation by the MH1 JC virus early promoter demonstrates that glial specificity is directed by the basal promoter. Because T antigen regulates the basal region of several viral and cellular promoters, we investigated whether it controls the JC virus basal promoter in a glial-specific manner. A JC virus T antigen expression plasmid generated a 95-kDa protein which exhibited nuclear localization and physical association with p53. T antigen repressed the JC virus and SV40 early promoters 4- to 5-fold in glioma cells. Conversely, T antigen induced 100- to 200-fold activation of the JC virus early promoter in nonglial cells, whereas the SV40 promoter was repressed. Activation required the JC virus TATA box sequence and a pentanucleotide repeat immediately upstream of the TATA box, but was independent of the upstream enhancer region. These data demonstrate that the JC virus basal promoter is responsible for glial-specific gene expression and suggest a mechanism for this regulation.

The JC virus minimal core promoter is glial cell specific in vivo

The glial cell specificity of the human papovavirus JC (JCV), an etiologic agent for progressive multifocal leukoencephalopathy, is thought to be due to the presence of both positive and negative regulatory elements upstream of the TATA region within the JCV promoter. Here we report that the JCV minimal core promoter, containing only the TATA box and an 8-bp poly(T) region immediately upstream, is sufficient to initiate transcription of an attached gene in glial cells and functions as an autonomously active initiator. We further define the sequences required for this core promoter's glial cell specificity by appropriate substitution and point mutation analysis. Ectopic expression of Tst-1, a POU domain transcription factor that has been implicated in the regulation of oligodendrocyte development, leads to higher activation of the JCV minimal core promoter in Tst-1-deficient glial cells than in non-glial HeLa cells. These results suggest a requirement for a glial cell coactivator(s) for the optimum activation of the JCV minimal core promoter by Tst-1. A discrete affinity of Tst-1 for the JCV core promoter (Kd, 1.4 x 10(-8) M) is also shown to be optimal for its promoter strength. Mutations within the core promoter that maintain this affinity for Tst-1 show maintenance of promoter strength, whereas mutants carrying a change that results in an increased affinity for Tst-1 show reduced transcriptional activity. These results suggest that moderate affinity of Tst-1 for the JCV TATA region may allow the interaction of some glial cell-specific coactivator(s) along with the basal transcription machinery to direct glial cell-specific transcription from the JCV core promoter.

Localization of adjacent binding domains for cellular proteins over the minute virus of mice P4 promoter by site-specific photoaffinity labelling

A photoaffinity labelling (PHL) procedure was used to localize the specific binding sites for A92L fibroblast nuclear proteins on the minute virus of mice (MVM) P4 promoter. We describe a chemical and biochemical method for the construction of precisely modified photoreactive (phr) DNA probes. In this method, a phenylazide group is attached to the DNA fragment by coupling SASD [sulfosuccinimidyl-2-(p-azidosalicyl-amido)ethyl-1,3'-dithiopro pio nate] to the primary amino group of the linker arm present at any predetermined position. These phr probes would identify, upon photocrosslinking, only those proteins which bind to the location of the phr group. Specifically, two phr probes representing the 139-172 bp region of the MVM P4 promoter were constructed in which the highly phr phenylazide group was attached with a linker at nucleotide 168, towards the side of the GC box proximal to the TATA box. The PHL studies with these photoprobes revealed that although the proteins of 95 and 120-kDa bind near nt 168 of the P4 promoter, the 120-kDa protein requires the region between the TATA box and the GC box for binding to the MVM P4 promoter.

A novel sequence-specific DNA-binding protein, LCP-1, interacts with single-stranded DNA and differentially regulates early gene expression of the human neurotropic JC virus

We have identified a novel brain-derived single-stranded-DNA-binding protein that interacts with a region of the human neurotropic JC virus enhancer designated the lytic control element (LCE). This nuclear factor, LCP-1 (for lytic control element-binding protein 1), specifically recognizes the LCE, as determined by gel retardation assays. Alkylation interference showed that specific nucleotides within the LCE were contacted by LCP-1. Subsequent experiments revealed that point mutations within the LCE differentially affected LCP-1 binding. UV cross-linking and competition analysis suggested that the LCP-1 DNA-protein complexes were 50 to 52 and 100 to 120 kDa in size. Promoter mutations that affected LCP-1 binding reduced early mRNA transcription during the early phase of the lytic cycle. However, upon DNA replication in the presence of JC virus T antigen, when early mRNA initiation shifts to new locations indicative of the late phase, the LCP-1 mutations had no effect. We suggest that the JC virus early transcription unit is differentially regulated by LCP-1 prior to but not after DNA replication, suggesting a novel mechanism by which DNA structure regulates eukaryotic gene expression.