The genome of simian virus 40

An Elusive Target: Inhibitors of JC Polyomavirus Infection and Their Development as Therapeutics for the Treatment of Progressive Multifocal Leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a rare demyelinating disease caused by infection with JC Polyomavirus (JCPyV). Despite the identification of the disease and isolation of the causative pathogen over fifty years ago, no antiviral treatments or prophylactic vaccines exist. Disease onset is usually associated with immunosuppression, and current treatment guidelines are limited to restoring immune function. This review summarizes the drugs and small molecules that have been shown to inhibit JCPyV infection and spread. Paying attention to historical developments in the field, we discuss key steps of the virus lifecycle and antivirals known to inhibit each event. We review current obstacles in PML drug discovery, including the difficulties associated with compound penetrance into the central nervous system. We also summarize recent findings in our laboratory regarding the potent anti-JCPyV activity of a novel compound that antagonizes the virus-induced signaling events necessary to establish a productive infection. Understanding the current panel of antiviral compounds will help center the field for future drug discovery efforts.

Novel Polyomaviruses in Mammals from Multiple Orders and Reassessment of Polyomavirus Evolution and Taxonomy

As the phylogenetic organization of mammalian polyomaviruses is complex and currently incompletely resolved, we aimed at a deeper insight into their evolution by identifying polyomaviruses in host orders and families that have either rarely or not been studied. Sixteen unknown and two known polyomaviruses were identified in animals that belong to 5 orders, 16 genera, and 16 species. From 11 novel polyomaviruses, full genomes could be determined. Splice sites were predicted for large and small T antigen (LTAg, STAg) coding sequences (CDS) and examined experimentally in transfected cell culture. In addition, splice sites of seven published polyomaviruses were analyzed. Based on these data, LTAg and STAg annotations were corrected for 10/86 and 74/86 published polyomaviruses, respectively. For 25 polyomaviruses, a spliced middle T CDS was observed or predicted. Splice sites that likely indicate expression of additional, alternative T antigens, were experimentally detected for six polyomaviruses. In contrast to all other mammalian polyomaviruses, three closely related cetartiodactyl polyomaviruses display two introns within their LTAg CDS. In addition, the VP2 of Glis glis (edible dormouse) polyomavirus 1 was observed to be encoded by a spliced transcript, a unique experimental finding within the Polyomaviridae family. Co-phylogenetic analyses based on LTAg CDS revealed a measurable signal of codivergence when considering all mammalian polyomaviruses, most likely driven by relatively recent codivergence events. Lineage duplication was the only other process whose influence on polyomavirus evolution was unambiguous. Finally, our analyses suggest that an update of the taxonomy of the family is required, including the creation of novel genera of mammalian and non-mammalian polyomaviruses.

Small size, big impact: how studies of small DNA tumour viruses revolutionized biology

Intense study of three families of small tumour viruses with double-stranded DNA genomes, carried out over 50 years, has had a profound impact on biology. The polyomaviruses and papillomaviruses have circular DNA genomes of approximately 5000 and approximately 8000 base-pairs, respectively, and thus encode only a handful of proteins. Adenoviruses have a 32 000-base-pair linear DNA genome, still far smaller than the three billion-base-pair human genome. Members of all three virus families can transform cultured cells to tumorigenicity and cause tumours in experimental animals. Several human papillomaviruses (HPV) and at least one polyomavirus are oncogenic in humans. Early analysis of these viruses, particularly the polyomavirus SV40, led to the development of many powerful experimental tools, including restriction mapping, site-directed mutagenesis, gene transfer, genome-wide sequencing and recombinant DNA. These tools have since been refined and used to study cellular genes, revolutionizing our understanding of biology. These tools were also applied to the viruses themselves. Analysis of the virus life cycle and the effect of these viruses on cells yielded important new insights into many aspects of gene expression, DNA replication, cell biology and carcinogenesis. These studies have also led to vaccination strategies to prevent infection and cancer in humans. This article is part of the theme issue 'Silent cancer agents: multi-disciplinary modelling of human DNA oncoviruses'.

DNA Tumor Viruses and Their Contributions to Molecular Biology

This summer marks the 51st anniversary of the DNA tumor virus meetings. Scientists from around the world will gather in Trieste, Italy, to report their latest results and to agree or disagree on the current concepts that define our understanding of this diverse class of viruses. This article offers a brief history of the impact the study of these viruses has had on molecular and cancer biology and discusses obstacles and opportunities for future progress.

Cre Recombinase Mediates the Removal of Bacterial Backbone to Efficiently Generate rSV40

Gene therapy has been shown to be a feasible approach to treat inherited disorders in vivo. Among the currently used viral vector systems, adeno-associated virus (AAV) vectors are the most advanced and have been applied in patients successfully. An important drawback of non-integrating AAV vectors is their loss of expression upon cell division, while repeating systemic administration lacks efficacy due to the induction of neutralizing antibodies. In addition, a significant percentage of the general population is not eligible for AAV-mediated gene therapy due to pre-existing immunity. Development of additional viral vectors may overcome this hurdle. Simian virus 40 (SV40)-derived vectors have been reported to transduce different tissues, including the liver, and prevalence of neutralizing antibodies in the general population is very low. This renders recombinant SV40 (rSV40) vector an interesting candidate for effective (re-)administration. Clinical use of SV40 vectors is in part hampered by less advanced production methods compared to AAVs. To optimize the production of rSV40 and make it better suitable for clinical practice, we developed a production system that relies on Cre recombinase-mediated removal of the bacterial plasmid backbone.

Human Polyomaviruses: The Battle of Large and Small Tumor Antigens

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

Viral Carcinogenesis

Cancer has been recognized for thousands of years. Egyptians believed that cancer occurred at the will of the gods. Hippocrates believed human disease resulted from an imbalance of the four humors: blood, phlegm, yellow bile, and black bile with cancer being caused by excess black bile. The lymph theory of cancer replaced the humoral theory and the blastema theory replaced the lymph theory. Rudolph Virchow was the first to recognize that cancer cells like all cells came from other cells and believed chronic irritation caused cancer. At the same time there was a belief that trauma caused cancer, though it never evolved after many experiments inducing trauma. The birth of virology occurred in 1892 when Dimitri Ivanofsky demonstrated that diseased tobacco plants remained infective after filtering their sap through a filter that trapped bacteria. Martinus Beijerinck would call the tiny infective agent a virus and both Dimitri Ivanofsky and Marinus Beijerinck would become the fathers of virology. Not to long thereafter, Payton Rous founded the field of tumor virology in 1911 with his discovery of a transmittable sarcoma of chickens by what would come to be called Rous sarcoma virus or RSV for short. The first identified human tumor virus was the Epstein-Barr virus (EBV), named after Tony Epstein and Yvonne Barr who visualized the virus particles in Burkitt's lymphoma cells by electron microscopy in 1965. Since that time, many viruses have been associated with carcinogenesis including the most studied, human papilloma virus associated with cervical carcinoma, many other anogenital carcinomas, and oropharyngeal carcinoma. The World Health Organization currently estimates that approximately 22% of worldwide cancers are attributable to infectious etiologies, of which viral etiologies is estimated at 15-20%. The field of tumor virology/viral carcinogenesis has not only identified viruses as etiologic agents of human cancers, but has also given molecular insights to all human cancers including the oncogene activation and tumor suppressor gene inactivation.

Transcription enhancers as major determinants of SV40 polyomavirus growth efficiency and host cell tropism

The non-coding control region (NCCR) of polyomaviruses includes the promoters for early and late genes, a transcription enhancer and the origin of DNA replication. Particularly virulent variants of the human pathogens BKPyV and JCPyV, as well as of simian virus 40 (SV40), occur in vitro and in vivo. These strains often harbour rearrangements in their NCCR, typically deletions of some DNA segment(s) and/or duplications of others. Using an SV40-based model system we provide evidence that duplications of enhancer elements, whether from SV40 itself or from the related BKPyV and JCPyV, increase early gene transcription and replicative capacity. SV40 harbouring subsegments of the strong cytomegalovirus (HCMV) enhancer replicated better than the common 'wild-type' SV40 in the human cell lines HEK293 and U2OS. In conclusion, replacing the SV40 enhancer with heterologous enhancers can profoundly influence SV40's infective capacity, underscoring the potential of small DNA viruses to overcome cell type and species barriers.

Interaction between Simian Virus 40 Major Capsid Protein VP1 and Cell Surface Ganglioside GM1 Triggers Vacuole Formation

Simian virus 40 (SV40), a polyomavirus that has served as an important model to understand many aspects of biology, induces dramatic cytoplasmic vacuolization late during productive infection of monkey host cells. Although this activity led to the discovery of the virus in 1960, the mechanism of vacuolization is still not known. Pentamers of the major SV40 capsid protein VP1 bind to the ganglioside GM1, which serves as the cellular receptor for the virus. In this report, we show that binding of VP1 to cell surface GM1 plays a key role in SV40 infection-induced vacuolization. We previously showed that SV40 VP1 mutants defective for GM1 binding fail to induce vacuolization, even though they replicate efficiently. Here, we show that interfering with GM1-VP1 binding by knockdown of GM1 after infection is established abrogates vacuolization by wild-type SV40. Vacuole formation during permissive infection requires efficient virus release, and conditioned medium harvested late during SV40 infection rapidly induces vacuoles in a VP1- and GM1-dependent fashion. Furthermore, vacuolization can also be induced by a nonreplicating SV40 pseudovirus in a GM1-dependent manner, and a mutation in BK pseudovirus VP1 that generates GM1 binding confers vacuole-inducing activity. Vacuolization can also be triggered by purified pentamers of wild-type SV40 VP1, but not by GM1 binding-defective pentamers or by intracellular expression of VP1. These results demonstrate that SV40 infection-induced vacuolization is caused by the binding of released progeny viruses to GM1, thereby identifying the molecular trigger for the activity that led to the discovery of SV40.

IMPORTANCE

The DNA tumor virus SV40 was discovered more than a half century ago as a contaminant of poliovirus vaccine stocks, because it caused dramatic cytoplasmic vacuolization of permissive host cells. Although SV40 played a historically important role in the development of molecular and cellular biology, restriction mapping, molecular cloning, and whole-genome sequencing, the basis of this vacuolization phenotype was unknown. Here, we show that SV40-induced vacuolization is triggered by the binding of the major viral capsid protein, VP1, to a cell surface ganglioside receptor, GM1. No other viral proteins or virus replication is required for vacuole formation. Other polyomaviruses utilize different ganglioside receptors, but they do not induce vacuolization. This work identifies the molecular trigger for the phenotype that led to the discovery of this important virus and provides the first molecular insight into an unusual and enigmatic cytopathic effect due to virus infection.

Ribosome Profiling as a Tool to Decipher Viral Complexity

Viral genomes harbor a variety of unusual translational phenomena that allow them to pack coding information more densely and evade host restriction mechanisms imposed by the cellular translational apparatus. Annotating translated sequences within these genomes thus poses particular challenges, but identifying the full complement of proteins encoded by a virus is critical for understanding its life cycle and defining the epitopes it presents for immune surveillance. Ribosome profiling is an emerging technique for global analysis of translation that offers direct and experimental annotation of viral genomes. Ribosome profiling has been applied to two herpesvirus genomes, those of human cytomegalovirus and Kaposi's sarcoma-associated herpesvirus, revealing translated sequences within presumptive long noncoding RNAs and identifying other micropeptides. Synthesis of these proteins has been confirmed by mass spectrometry and by identifying T cell responses following infection. Ribosome profiling in other viruses will likely expand further our understanding of viral gene regulation and the proteome.

Potential pitfalls and solutions for use of fluorescent fusion proteins to study the lysosome

Use of fusion protein tags to investigate lysosomal proteins can be complicated by the acidic, protease-rich environment of the lysosome. Potential artifacts include degradation or release of the tag and acid quenching of fluorescence. Tagging can also affect protein folding, glycosylation and/or trafficking. To specifically investigate the use of fluorescent tags to reveal lysosomal localization, we tested mCherry derivatives as C-terminal tags for Niemann-Pick disease type C protein 2 (NPC2), a luminal lysosomal protein. Full-length mCherry was released from the NPC2 chimera while deletion of the 11 N-terminal residues of mCherry generated a cleavage-resistant (cr) fluorescent variant. Insertion of proline linkers between NPC2 and crmCherry had little effect while Gly-Ser linkers promoted cleavage. The NPC2-crmCherry fusion was targeted to the lysosome and restored function in NPC2-deficient cells. Fusion of crmCherry to known and candidate lysosomal proteins revealed that the linkers had different effects on lysosomal localization. Direct fusion of crmCherry impaired mannose 6-phosphorylation and lysosomal targeting of the lysosomal protease tripeptidyl peptidase I (TPP1), while insertion of linkers corrected the defects. Molecular modeling suggested structural bases for the effects of different linkers on NPC2 and TPP1 fusion proteins. While mCherry fusion proteins can be useful tools for studying the lysosome and related organelles, our findings underscore the potential artifacts associated with such applications.

Immortalization of neuronal progenitors using SV40 large T antigen and differentiation towards dopaminergic neurons

Transplantation is common in clinical practice where there is availability of the tissue and organ. In the case of neurodegenerative disease such as Parkinson's disease (PD), transplantation is not possible as a result of the non-availability of tissue or organ and therefore, cell therapy is an innovation in clinical practice. However, the availability of neuronal cells for transplantation is very limited. Alternatively, immortalized neuronal progenitors could be used in treating PD. The neuronal progenitor cells can be differentiated into dopaminergic phenotype. Here in this article, the current understanding of the molecular mechanisms involved in the differentiation of dopaminergic phenotype from the neuronal progenitors immortalized with SV40 LT antigen is discussed. In addition, the methods of generating dopaminergic neurons from progenitor cells and the factors that govern their differentiation are elaborated. Recent advances in cell-therapy based transplantation in PD patients and future prospects are discussed.

Gene expression profiling of lens tumors, liver and spleen in α-crystallin/SV40 T antigen transgenic mice treated with Juzen-taiho-to

The autogenic lens tumors induced by the Simian vacuolating virus 40 (SV40) T antigen in α-crystallin/SV40 T antigen transgenic (TG) mice, provide a tool to screen anti-tumor reagents in vivo and to clarify the underlying mechanisms. Juzen-taiho-to, a Chinese medicine composed of 10 herbs, was frequently used as an alternative medicine for cancer patients by clinicians and occasionally it was demonstrated to have beneficial effects on the prognosis and general condition of cancer patients. However, it was not scientifically verified. In the present study, the anti-tumor effects and underlying mechanisms of Juzen-taiho-to in the TG mice model was examined using cDNA microarray analysis and the results were confirmed by real-time PCR. The TG mice demonstrated a higher cumulative survival rate after treatment with the drug compared with the control group (P<0.05). Gene chip profiles demonstrated that cell functions involving the membrane, glycoprotein, cell membrane, signal and ionic channel for the lens tumor, the cell cycle, DNA replication, homeobox, mitosis and cell division for the spleen and the acetylation, mitochondrion, ribosomal protein, ribonucleoprotein for the liver, were altered by the administration of Juzen‑taiho-to. The important canonical pathways were those of the mitogen-activated protein kinase (MAPK), the cell cycle and the ribosome for the altered genes of the lens tumor, spleen and liver after drug administration, respectively. From real-time PCR, in the eyeball, epidermal growth factor receptor (Egfr), Rasgrf1 and heat shock protein 1B (Hspa1b) mRNAs were found to be significantly lower in treated lenses than in those not exposed to the drug, while Rps25 mRNA demonstrated the opposite association in the liver. It was suggested that Juzen-taiho-to may prolong the survival time of SV40 T antigen TG mice by improving their nutritional condition, inhibiting the MAPK pathway and strengthening the immune system without causing hepatic toxicity.

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.

The rapidly expanding family of human polyomaviruses: recent developments in understanding their life cycle and role in human pathology

Since their discovery in 1971, the polyomaviruses JC (JCPyV) and BK (BKPyV), isolated from patients with progressive multifocal leukoencephalopathy and polyomavirus-associated nephropathy, respectively, remained for decades as the only known members of the Polyomaviridae family of viruses of human origin. Over the past five years, the application of new genomic amplification technologies has facilitated the discovery of several novel human polyomaviruses (HPyVs), bringing the present number to 10. These HPyVs share many fundamental features in common such as genome size and organization. Infection by all HPyVs is widespread in the human population, but they show important differences in their tissue tropism and association with disease. Much remains unknown about these new viruses. In this review, we discuss the problems associated with studying HPyVs, such as the lack of culture systems for the new viruses and the gaps in our basic understanding of their biology. We summarize what is known so far about their distribution, life cycle, tissue tropism, their associated pathologies (if any), and future research directions in the field.

The viroporin activity of the minor structural proteins VP2 and VP3 is required for SV40 propagation

For nonenveloped viruses such as Simian Virus 40, the mechanism used to translocate viral components across membranes is poorly understood. Previous results indicated that the minor structural proteins, VP2 and VP3, might act as membrane proteins during infection. Here, purified VP2 and VP3 were found to form pores in host cell membranes. To identify possible membrane domains, individual hydrophobic domains from VP2 and VP3 were expressed in a model protein and tested for their ability to integrate into membranes. Several domains from the late proteins supported endoplasmic reticulum membrane insertion as transmembrane domains. Mutations in VP2 and VP3 were engineered that inhibited membrane insertion and pore formation. When these mutations were introduced into the viral genome, viral propagation was inhibited. This comprehensive approach revealed that the viroporin activity of VP2 and VP3 was inhibited by targeted disruptions of individual hydrophobic domains and the loss of membrane disruption activity impaired viral infection.

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

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

Structure-based mutational analysis of the highly conserved domain IV of glycoprotein H of pseudorabies virus

Glycoprotein H (gH) is an envelope protein conserved in the Herpesviridae. Together with glycoprotein B (gB), the heterodimeric complex of gH and glycoprotein L (gL) mediates penetration and direct viral cell-to-cell spread. In herpes simplex and pseudorabies virus (PrV), coexpression of gH/gL, gB, and gD induces membrane fusion to form polykaryocytes. The recently determined crystal structure of a core fragment of PrV gH revealed marked structural similarity to other gH proteins (M. Backovic et al., Proc. Natl. Acad. Sci. U. S. A. 107:22635-22640, 2010). Within the membrane-proximal part (domain IV), a conserved negatively charged surface loop (flap) is flanked by intramolecular disulfide bonds. Together with an N-linked carbohydrate moiety, this flap covers an underlying patch of hydrophobic residues. To investigate the functional relevance of these structures, nonconservative amino acid substitutions were introduced by site-directed mutagenesis. The mutated proteins were tested for correct expression, fusion activity, and functional complementation of gH-deleted PrV. Several single amino acid changes within the flap and the hydrophobic patch were tolerated, and deletion of the glycosylation site had only minor effects. However, multiple alanine substitutions within the flap or the hydrophobic patch led to significant defects. gH function was also severely affected by disruption of the disulfide bond at the C terminus of the flap and after introduction of cysteine pairs designed to bridge the central part of the flap with the hydrophobic patch. Interestingly, all mutated gH proteins were able to complement gH-deleted PrV, but fusion-deficient gH mutants resulted in a pronounced delay in virus entry.

Evaluation of stable and highly productive gene amplified CHO cell line based on the location of amplified genes

In order to establish an easy and quick construction method for obtaining a stable and highly productive gene-amplified recombinant Chinese Hamster Ovary (CHO) cell line, variouskinds of stepwise methotrexate (MTX) selection were carriedout. The specific growth and production rates of the cell were compared with each other, and the distribution of the amplified gene location was determined using fluorescence in situ hybridization (FISH). The specific growth andproduction rates of the cell pool reached the highest levels under the selection condition in which the stepwise increase in the MTX concentration was most gradual; about 82% of amplified genes were observed near the telomeric region. During long-term cultivation without MTX, the percentage ofamplified genes near the telomeric region hardly changed, butthat of amplified genes at other regions decreased. Based on these results, stable and highly productive cell pools could be easily and quickly constructed and amplified and gradual stepwise increase of the MTX concentration. In addition, the FISH technique was powerful tool to evaluate highly productiveand stable gene-amplified cells based on the chromosomal location of the amplified gene.

The SV40 late protein VP4 is a viroporin that forms pores to disrupt membranes for viral release

Nonenveloped viruses are generally released by the timely lysis of the host cell by a poorly understood process. For the nonenveloped virus SV40, virions assemble in the nucleus and then must be released from the host cell without being encapsulated by cellular membranes. This process appears to involve the well-controlled insertion of viral proteins into host cellular membranes rendering them permeable to large molecules. VP4 is a newly identified SV40 gene product that is expressed at late times during the viral life cycle that corresponds to the time of cell lysis. To investigate the role of this late expressed protein in viral release, water-soluble VP4 was expressed and purified as a GST fusion protein from bacteria. Purified VP4 was found to efficiently bind biological membranes and support their disruption. VP4 perforated membranes by directly interacting with the membrane bilayer as demonstrated by flotation assays and the release of fluorescent markers encapsulated into large unilamellar vesicles or liposomes. The central hydrophobic domain of VP4 was essential for membrane binding and disruption. VP4 displayed a preference for membranes comprised of lipids that replicated the composition of the plasma membranes over that of nuclear membranes. Phosphatidylethanolamine, a lipid found at high levels in bacterial membranes, was inhibitory against the membrane perforation activity of VP4. The disruption of membranes by VP4 involved the formation of pores of ∼3 nm inner diameter in mammalian cells including permissive SV40 host cells. Altogether, these results support a central role of VP4 acting as a viroporin in the perforation of cellular membranes to trigger SV40 viral release.

Viruses exploit host cells for their propagation. Once an adequate number of viral particles have been assembled within the cell through the aid of cellular machinery of the host cell, the virus must be released from the cell for the virus to spread. For nonenveloped viruses or viruses that are solely encapsulated by a protein shell, this step most commonly involves the perforation of cellular membranes resulting in the lysis or death of the host cell. The mechanism for how this key terminal step in the viral life cycle is performed is poorly understood. We demonstrated that for the model nonenveloped virus SV40, the newly discovered virally encoded protein, termed VP4, perforates membranes by forming pores with a diameter of ∼3 nm in host cell membranes. While these pores are not of a sufficient size to provide a conduit that permits the movement of the virus through the membrane, they support membrane destabilization that leads to the disintegration of the membrane of the host cell and viral release.

Infectious Disease Genomics

The history and development of infectious disease genomics are discussed in this chapter. HGP must not be restricted to the human genome and should include model organisms including mouse, bacteria, yeast, fruit fly, and worm. The completed or ongoing genome projects will provide enormous opportunities for the discovery of novel vaccines and drug targets against human pathogens as well as the improvement of diagnosis and discovery of infectious agents and the development of new strategies for invertebrate vector control. The polysaccharide capsule is important for meningococci to escape from complement-mediated killing. With the completion of the genome sequence of a virulent MenB strain, a “reverse vaccinology” approach was applied for the development of a universal MenB vaccine by Novartis. The indispensable fatty acid synthase (FAS) pathway in bacteria has been regarded as a promising target for the development of antimicrobial agents. Through a systematic screening of 250,000 natural product extracts, a Merck team identified a potent and broad-spectrum antibiotic, platensimycin, which is derived from Streptomyces platensis. Vector Biology Network was formed to achieve three goals (1) to develop basic tools for the stable transformation of anopheline mosquitoes by the year 2000; (2) to engineer a mosquito incapable of carrying the malaria parasite by 2005; and (3) to run controlled experiments to test how to drive the engineered genotype into wild mosquito populations by 2010. The most immediate impact of a completely sequenced pathogen genome is for infectious disease diagnosis.

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.

Conformational rearrangements of SV40 large T antigen during early replication events

The Simian virus 40 (SV40) large tumor antigen (LTag) functions as the replicative helicase and initiator for viral DNA replication. For SV40 replication, the first essential step is the assembly of an LTag double hexamer at the origin DNA that will subsequently melt the origin DNA to initiate fork unwinding. In this study, we used three-dimensional cryo-electron microscopy to visualize early events in the activation of DNA replication in the SV40 model system. We obtained structures of wild-type double-hexamer complexes of LTag bound to SV40 origin DNA, to which atomic structures have been fitted. Wild-type LTag was observed in two distinct conformations: In one conformation, the central module containing the J-domains and the origin binding domains of both hexamers is a compact closed ring. In the other conformation, the central module is an open ring with a gap formed by rearrangement of the N-terminal regions of the two hexamers, potentially allowing for the passage of single-stranded DNA generated from the melted origin DNA. Double-hexamer complexes containing mutant LTag that lacks the N-terminal J-domain show the central module predominantly in the closed-ring state. Analyses of the LTag C-terminal regions reveal that the LTag hexamers bound to the A/T-rich tract origin of replication and early palindrome origin of replication elements are structurally distinct. Lastly, visualization of DNA density protruding from the LTag C-terminal domains suggests that oligomerization of the LTag complex takes place on double-stranded DNA.

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.

SV40 T antigen disrupted the cell metabolism and the balance between proliferation and apoptosis in lens tumors of transgenic mice

PURPOSE

Simian Vacuolating Virus 40 (SV40) T antigen perturbed p53 and RB to cause cell malignant transformation. The purpose of this study was to identify the molecular changes during lens carcinogenesis and cancer progression induced by SV40 T antigen.

METHODS

The different lens lesions of alpha A-crystallin/SV40 T antigen transgenic mice were examined using cDNA microarray, immunohistochemistry and TUNEL to scan the influenced molecules and signal pathways.

RESULTS

There appeared dysplasia, carcinoma in situ, followed by invasion inside or outside eyeball, and final metastasis into lymph node or lung. Cell functions largely changed from such many aspects as cell cycle, cell morphology, cell development, cell-to-cell signaling and so forth since lens carcinogenesis. The significant differences were observed in such signaling pathways as metabolism about carbohydrate, amino acid, nucleotides, Xenobiotics and nitrogen (P < 0.05).The remarkable distinction of cell proliferation and cell death was found after carcinoma began to invade. There was significant alteration in cell growth, cell cycle, cell-to-cell signaling and metabolism since carcinoma invasion outside the eyeball happened. Parafibromin, Stat 1alpha, Mek kinase-1, CK2alpha, GRP78, Arp2 and Apr3 were not expressed in wild-type mice lens, but in others. The proliferative levels of dysplasia, carcinoma in situ and invasive carcinoma inside eyeballs were statistically higher than other groups (P < 0.05). The apoptotic levels of dysplasia were significantly higher than wild-type control (P < 0.05), but lower than the others (P < 0.05).

CONCLUSION

SV40 T antigen remarkably targeted the cell metabolism and disrupted the balance between proliferation and apoptosis during the lens carcinogenesis and following progression.

Expression of a transgene encoding mutant p193/CUL7 preserves cardiac function and limits infarct expansion after myocardial infarction

BACKGROUND

Transgenic mice expressing the dominant interfering p193 protein in cardiomyocytes (MHC-1152stop mice) exhibit an induction of cell cycle activity and altered remodelling after experimental myocardial infarction (MI).

OBJECTIVE

To determine whether the altered remodelling results in improved cardiac function in the MHC-1152stop mice after MI, as compared with non-transgenic mice.

METHODS

MHC-1152stop mice and non-transgenic littermates were subjected to experimental MI via permanent occlusion of the coronary artery. Infarct size was determined at 24 h and at 4 weeks after MI, and left ventricular pressure-volume measurements were performed at 4 weeks after MI in infarcted and sham-operated animals.

RESULTS

Infarct size in MHC-1152stop mice and non-transgenic littermates was not statistically different at 24 h after MI, as measured by tetrazolium staining. Morphometric analysis showed that infarct scar expansion at 4 weeks after MI was reduced by 10% in the MHC-1152stop mice (p<0.05). No differences in cardiac function were detected between sham-operated MHC-1152stop mice and their non-transgenic littermates. However, at 4 weeks after MI, the ventricular isovolumic relaxation time constant (tau) was decreased by 19% (p<0.05), and the slope of the dP/dt(max)-EDV relationship was increased 99% (p<0.05), in infarcted MHC-1152stop mice as compared with infarcted non-transgenic littermates.

CONCLUSION

Expression of the dominant interfering p193 transgene results in a decrease in infarct scar expansion and preservation of myocardial function at 4 weeks after MI. Antagonism of p193 activity may represent an important strategy for the treatment of MI.

Small DNA tumor viruses: large contributors to biomedical sciences

Studies of the small DNA tumor viruses (the polyomaviruses, the adenoviruses and the papillomaviruses) have led to fundamental discoveries that have advanced our understanding of basic mammalian cell molecular biology processes such as transcription and DNA replication, uncovered pathways and genes often perturbed in human cancer, and identified bona fide human cancer viruses. In this article we examine the many contributions that have come from the small DNA tumor virus field and provide a recounting of some of the major landmark discoveries.

SV40 DNA replication: from the A gene to a nanomachine

Duplication of the simian virus 40 (SV40) genome is the best understood eukaryotic DNA replication process to date. Like most prokaryotic genomes, the SV40 genome is a circular duplex DNA organized in a single replicon. This small viral genome, its association with host histones in nucleosomes, and its dependence on the host cell milieu for replication factors and precursors led to its adoption as a simple and powerful model. The steps in replication, the viral initiator, the host proteins, and their mechanisms of action were initially defined using a cell-free SV40 replication reaction. Although our understanding of the vastly more complex host replication fork is advancing, no eukaryotic replisome has yet been reconstituted and the SV40 paradigm remains a point of reference. This article reviews some of the milestones in the development of this paradigm and speculates on its potential utility to address unsolved questions in eukaryotic genome maintenance.

SV40: Cell transformation and tumorigenesis

The story of SV40-induced tumorigenesis and cellular transformation is intimately entwined with the development of modern molecular biology. Because SV40 and other viruses have small genomes and are relatively easy to manipulate in the laboratory, they offered tractable systems for molecular analysis. Thus, many of the early efforts to understand how eukaryotes replicate their DNA, regulate expression of their genes, and translate mRNA were focused on viral systems. The discovery that SV40 induces tumors in certain laboratory animals and transforms many types of cultured cells offered the first opportunity to explore the molecular basis for cancer. The goal of this article is to highlight some of the experiments that have led to our current view of SV40-induced transformation and to provide some context as to how they contributed to basic research in molecular biology and to our understanding of cancer.

Small DNA tumour viruses and their contributions to our understanding of transcription control

The study of small DNA tumour viruses like SV40 and polyoma was one of the major entry points for the study of eukaryotes. It opened fields like gene structure, transcription or replication control, chromatin structure and cell transformation. This review outlines the breakthroughs that occurred at the end of the 1970s and during the 1980s in our understanding of gene structure and the basic processes involved in control of gene expression starting with DNA tumour viruses and reaching their cellular hosts. These developments were made possible by concomitant advances in the isolation of restriction enzymes, developing DNA sequencing protocols, DNA cloning, DNA transfections, in vitro transcription systems and isolation of sequence specific DNA binding protein among others. The conceptual and methodological advances that resulted from the studies of small DNA tumour viruses opened the era for the study of host genomes far more complex, culminating with the establishment of the sequence and a functional map of the human genome.

SV40 vectors carrying minimal sequence of viral origin with exchangeable capsids

Polyomaviral vectors are generated by transfecting 293T cells with three sets of DNAs: DNA for the expression of simian virus 40 (SV40) T antigen; DNA for the expression of SV40 capsid proteins, and vector DNA harboring a reporter gene expression cassette carrying a SV40 origin. The vector DNA harbors a minimal sequence originating from SV40, and thus can carry a longer transgene. Moreover, the viable recombinants are not detectable in the vector preparation, and the vectors can transduce the DNA with efficiency similar to that of virions. Vector particles bearing capsid proteins of BK virus, JC virus, and B-lymphotropic papovavirus instead of SV40 were prepared, and they exhibited differential efficiency of gene transduction to the target cells. This method can be used to develop a surrogate system to study the functions of capsid proteins of polyomaviruses and to generate a set of polyomaviral vectors targeted at specific cell types.

A very late viral protein triggers the lytic release of SV40

How nonenveloped viruses such as simian virus 40 (SV40) trigger the lytic release of their progeny is poorly understood. Here, we demonstrate that SV40 expresses a novel later protein termed VP4 that triggers the timely lytic release of its progeny. Like VP3, VP4 synthesis initiates from a downstream AUG start codon within the VP2 transcript and localizes to the nucleus. However, VP4 expression occurs approximately 24 h later at a time that coincides with cell lysis, and it is not incorporated into mature virions. Mutation of the VP4 initiation codon from the SV40 genome delayed lysis by 2 d and reduced infectious particle release. Furthermore, the co-expression of VP4 and VP3, but not their individual expression, recapitulated cell lysis in bacteria. Thus, SV40 regulates its life cycle by the later temporal expression of VP4, which results in cell lysis and enables the 50-nm virus to exit the cell. This study also demonstrates how viruses can generate multiple proteins with diverse functions and localizations from a single reading frame.

Evidence that SV40 VP1-DNA interactions contribute to the assembly of 40-nm spherical viral particles

The simian virus 40 (SV40) particle is mainly composed of the major capsid protein termed VP1. VP1 self-assembles into virus-like particles (VLPs) of approximately 40 nm in diameter when over-expressed in bacteria or in insect cells, but purified VP1 does not form such a structure under physiological conditions, and thus, the mechanism of VP1 assembly is not well understood. Using a highly purified VP1 assembly/disassembly system in vitro, here we provide evidence that DNA is a factor that contributes to VP1 assembly into 40-nm spherical particles. At pH 5, for example, VP1 preferentially assembles into 40-nm particles in the presence of DNA, whereas VP1 assembles into tubular structures in the absence of DNA. Electron microscopic observations revealed that the concentration of DNA and its length are important for the formation of 40-nm particles. In addition, sucrose gradient sedimentation analysis and DNase I-sensitivity assays indicated that DNA of up to 2,000 bp is packaged into the 40-nm particles under the conditions examined. We propose that DNA may facilitate the formation of 40-nm spherical particles by acting as a scaffold that increases the local concentration of VP1 and/or by acting as an allosteric effector that alters the structure of VP1.

Analysis and development of the computer methods of nucleosome localization on DNA fragments with different AT-content

Trinucleotide parameter sets published previously were used for the development of the predictive method for the determining the nucleosome positions along the DNA. The choice of the type of parameter sets used depends upon AT-content of the fragment. Some limitations are imposed on these predictions due to the presence of A(n), T(n) tracts (in our case n>5 or =5) within the 145 bp fragment leading to the displacement or even the prohibition for the corresponding site to be occupied by nucleosomes. The predicted nucleosome positioning site with the large potential may influence on the choice of the proximal nucleosome positions with the weaker bending potentials as is revealed by the comparison with the micrococcal nuclease digestion map. Trinucleotide methods may be considered as advantageous in the comparison with the dinucleotide ones.

SV40 VP2 and VP3 Insertion into ER Membranes Is Controlled by the Capsid Protein VP1: Implications for DNA Translocation out of the ER

Nonenveloped viruses such as Simian Virus 40 (SV40) exploit established cellular pathways for internalization and transport to their site of penetration. By analyzing mutant SV40 genomes that do not express VP2 or VP3, we found that these structural proteins perform essential functions that are regulated by VP1. VP2 significantly enhanced SV40 particle association with the host cell, while VP3 functioned downstream. VP2 and VP3 both integrated posttranslationally into the endoplasmic reticulum (ER) membrane. Association with VP1 pentamers prevented their ER membrane integration, indicating that VP1 controls the function of VP2 and VP3 by directing their localization between the particle and the ER membrane. These findings suggest a model in which VP2 aids in cell binding. After capsid disassembly within the ER lumen, VP3, and perhaps VP2, oligomerizes and integrates into the ER membrane, potentially creating a viroporin that aids in viral DNA transport out of the ER.

Is there a role for SV40 in human cancer?

The question of whether Simian Virus 40 (SV40) can cause human tumors has been one of the most highly controversial topics in cancer research during the last 50 years. The longstanding debate began with the discovery of SV40 as a contaminant in poliovirus vaccine stocks that were used to inoculate approximately 100 million children and adults in the United States between 1955 and 1963, and countless more throughout the world. Concerns regarding the potential health risk of SV40 exposure were reinforced by studies demonstrating SV40's potential to transform human cells and promote tumor growth in animal models. Many studies have attempted to assess the relationship between the potential exposure of humans to SV40 and cancer incidence. Reports of the detection of SV40 DNA in a variety of cancers have raised serious concerns as to whether the inadvertent inoculation with SV40 has led to the development of cancer in humans. However, inconsistent reports linking SV40 with various tumor types has led to conflicting views regarding the potential of SV40 as a human cancer virus. Several recent studies suggest that older detection methodologies were flawed, and the limitations of these methods could account for most, if not all, of the positive correlations of SV40 in human tumors to date. Although many people may have been exposed to SV40 by polio vaccination, there is inadequate evidence to support widespread SV40 infection in the population, increased tumor incidence in those individuals who received contaminated vaccine, or a direct role for SV40 in human cancer.

Simian virus 40 late proteins possess lytic properties that render them capable of permeabilizing cellular membranes

Many nonenveloped viruses have evolved an infectious cycle that culminates in the lysis or permeabilization of the host to enable viral release. How these viruses initiate the lytic event is largely unknown. Here, we demonstrated that the simian virus 40 progeny accumulated at the nuclear envelope prior to the permeabilization of the nuclear, endoplasmic reticulum, and plasma membranes at a time which corresponded with the release of the progeny. The permeabilization of these cellular membranes temporally correlated with late protein expression and was not observed upon the inhibition of their synthesis. To address whether one or more of the late proteins possessed an inherent capacity to induce membrane permeabilization, we examined the permeability of Escherichia coli that separately expressed the late proteins. VP2 and VP3, but not VP1, caused the permeabilization of bacterial membranes. Additionally, VP3 expression resulted in bacterial cell lysis. These findings demonstrate that VP3 possesses an inherent lytic property that is independent of eukaryotic signaling or cell death pathways.

Targeted expression of cyclin D2 results in cardiomyocyte DNA synthesis and infarct regression in transgenic mice

Restriction point transit and commitment to a new round of cell division is regulated by the activity of cyclin-dependent kinase 4 and its obligate activating partners, the D-type cyclins. In this study, we examined the ability of D-type cyclins to promote cardiomyocyte cell cycle activity. Adult transgenic mice expressing cyclin D1, D2, or D3 under the regulation of the alpha cardiac myosin heavy chain promoter exhibited high rates of cardiomyocyte DNA synthesis under baseline conditions. Cardiac injury in mice expressing cyclin D1 or D3 resulted in cytoplasmic cyclin D accumulation, with a concomitant reduction in the level of cardiomyocyte DNA synthesis. In contrast, cardiac injury in mice expressing cyclin D2 did not alter subcellular cyclin localization. Consequently, cardiomyocyte cell cycle activity persisted in injured hearts expressing cyclin D2, ultimately resulting in infarct regression. These data suggested that modulation of D-type cyclins could be exploited to promote regenerative growth in injured hearts.

The agnoprotein of polyomaviruses: a multifunctional auxiliary protein

The late region of the three primate polyomaviruses (JCV, BKV, and SV40) encodes a small, highly basic protein known as agnoprotein. While much attention during the last two decades has focused on the transforming proteins encoded by the early region (small and large T-antigens), it has become increasingly evident that agnoprotein has a critical role in the regulation of viral gene expression and replication, and in the modulation of certain important host cell functions including cell cycle progression and DNA repair. The importance of agnoprotein is underscored by its expression during lytic infection of glial cells by JCV that occurs in progressive multifocal leukoencephalopathy (PML), and also in some JCV-associated human neural tumors particularly medulloblastoma. In this review, we will discuss the structure and function of agnoprotein in the viral life cycle during the course of lytic infection and the consequences of agnoprotein expression for the host cell.

Expression of Mutant p193 and p53 Permits Cardiomyocyte Cell Cycle Reentry After Myocardial Infarction in Transgenic Mice

Previous studies have demonstrated that expression of p193 and p53 mutants with dominant-interfering activities renders embryonic stem cell-derived cardiomyocytes responsive to the growth promoting activities of the E1A viral oncoproteins. In this study, the effects of p53 and p193 antagonization on cardiomyocyte cell cycle activity in normal and infarcted hearts were examined. Transgenic mice expressing the p193 and/or the p53 dominant-interfering mutants in the heart were generated. Transgene expression had no effect on cardiomyocyte cell cycle activity in uninjured adult hearts. In contrast expression of either transgene resulted in a marked induction of cardiomyocyte cell cycle activity at the infarct border zone at 4 weeks after permanent coronary artery occlusion. Expression of the p193 dominant-interfering mutant was also associated with an induction of cardiomyocyte DNA synthesis in the interventricular septa of infarcted hearts. A concomitant and marked reduction in hypertrophic cardiomyocyte growth was observed in the septa of hearts expressing the p193 dominant-interfering transgene, suggesting that cell cycle activation might partially counteract the adverse ventricular remodeling that occurs after infarction. Collectively these data suggest that antagonization of p193 and p53 activity relaxes the otherwise stringent regulation of cardiomyocyte cell cycle reentry in the injured adult heart.