The hamster polyomavirus--a brief review of recent knowledge

Hamster polyomavirus-associated T-cell lymphomas in Syrian hamsters (Mesocricetus auratus)

Hamster polyomavirus (HaPyV) infection has been associated with lymphomas in Syrian hamsters. In the present study, 14 cases of lymphoma in pet Syrian hamsters were pathologically examined and the involvement of HaPyV was investigated. Among 14 cases, 11 were abdominal and 3 were cutaneous lymphomas. The average ages of hamsters with abdominal lymphoma and cutaneous lymphoma were 7 months (range: 4-12 months) and 14 months (range: 6-23 months), respectively. Histologically, abdominal lymphomas were characterized by the diffuse growth of tumor cells with intermediate or large nuclei, low mitotic rates, the presence of tingible body macrophages, and the T-cell immunophenotype. Furthermore, 4/11 abdominal lymphomas were immunopositive for T-cell intracellular antigen-1, suggesting cytotoxic T-cell lymphomas. Cutaneous lymphomas were diagnosed as nonepitheliotropic T-cell lymphoma. Polymerase chain reaction (PCR) detected HaPyV DNA in 12/14 samples, and a sequence analysis of PCR amplicons confirmed >99% nucleotide identity to the published HaPyV sequences. In situ hybridization (ISH) for HaPyV DNA resulted in diffuse nuclear signals within tumor cells in 10/14 cases. Consistent with previous findings, all HaPyV-associated lymphomas were observed in the abdominal cavity of young hamsters. Polymerase chain reaction and ISH were useful for identifying the involvement of HaPyV in lymphomas, and ISH results indicated the presence of episomal HaPyV in neoplastic lymphocytes. The present study suggests that HaPyV infection is highly involved in abdominal lymphomas in young pet Syrian hamsters in Japan and provides diagnostic information on HaPyV-associated lymphoma.

Survey for zoonotic pathogens in Norway rat populations from Europe

BACKGROUND

The Norway rat Rattus norvegicus is an important reservoir of various zoonotic pathogens, such as cowpox virus and Leptospira, but also for agents of no or unknown zoonotic potential. We describe a survey of 426 Norway rats originating from five European countries and different habitats for Leptospira spp., rickettsiae, orthopoxvirus (OPV), avian metapneumovirus subtypes A and B (aMPV) and rat polyomavirus (rat PyV).

RESULTS

Leptospira DNA was detected in 60 out of 420 (14.3%) rats, and Rickettsia DNA was found in three out of 369 (0.8%) rats investigated. PCR-based typing resulted in the identification of L. interrogans sequence type 17, which corresponds to the serogroup Icterohaemorrhagiae, and Rickettsia helvetica respectively. Rat PyV DNA was detected in 103 out of 421 (24.5%) rats. OPV DNA and aMPV RNA were detected in none of the rats, but OPV-specific antibodies were detected in three out of 388 (0.8%) rats. The frequency of single Leptospira and rat PyV infections and coinfections was, independent of sex, greater for adults compared with juveniles/subadults and greater at rural sites compared with urban areas.

CONCLUSIONS

Study results indicate a broad geographical distribution of Leptospira DNA in rats within Europe, underlining the need to investigate further the potential mechanisms leading to increased prevalence in rural habitats and to assess the relevance to public health. In contrast, rickettsia and OPV infections rarely occurred in wild rat populations. The potential influence of rat PyV on the susceptibility to infections with other pathogens should be investigated in future studies. © 2016 Society of Chemical Industry.

Identification of Two Novel Members of the Tentative Genus Wukipolyomavirus in Wild Rodents

Two novel polyomaviruses (PyVs) were identified in kidney and chest-cavity fluid samples of wild bank voles (Myodes glareolus) and common voles (Microtus arvalis) collected in Germany. All cloned and sequenced genomes had the typical PyV genome organization, including putative open reading frames for early regulatory proteins large T antigen and small T antigen on one strand and for structural late proteins (VP1, VP2 and VP3) on the other strand. Virus-like particles (VLPs) were generated by yeast expression of the VP1 protein of both PyVs. VLP-based ELISA and large T-antigen sequence-targeted polymerase-chain reaction investigations demonstrated signs of infection of these novel PyVs in about 42% of bank voles and 18% of common voles. In most cases only viral DNA, but not VP1-specific antibodies were detected. In additional animals exclusively VP1-specific antibodies, but no viral DNA was detected, indicative for virus clearance. Phylogenetic and clustering analysis including all known PyV genomes placed novel bank vole and common vole PyVs amongst members of the tentative Wukipolymavirus genus. The other known four rodent PyVs, Murine PyV and Hamster PyV, and Murine pneumotropic virus and Mastomys PyV belong to different phylogenetic clades, tentatively named Orthopolyomavirus I and Orthopolyomavirus II, respectively. In conclusion, the finding of novel vole-borne PyVs may suggest an evolutionary origin of ancient wukipolyomaviruses in rodents and may offer the possibility to develop a vole-based animal model for human wukipolyomaviruses.

Genome Sequences of a Rat Polyomavirus Related to Murine Polyomavirus, Rattus norvegicus Polyomavirus 1

We amplified and sequenced six complete genomes of a polyomavirus from feral Norway rats (Rattus norvegicus) and from a long-term breeding colony derived from Norway rats. This virus, which is closely related to hamster polyomavirus and murine polyomavirus, may contribute to understanding the evolutionary history of rodent polyomaviruses.

STAT2 Knockout Syrian Hamsters Support Enhanced Replication and Pathogenicity of Human Adenovirus, Revealing an Important Role of Type I Interferon Response in Viral Control

Human adenoviruses have been studied extensively in cell culture and have been a model for studies in molecular, cellular, and medical biology. However, much less is known about adenovirus replication and pathogenesis in vivo in a permissive host because of the lack of an adequate animal model. Presently, the most frequently used permissive immunocompetent animal model for human adenovirus infection is the Syrian hamster. Species C human adenoviruses replicate in these animals and cause pathology that is similar to that seen with humans. Here, we report findings with a new Syrian hamster strain in which the STAT2 gene was functionally knocked out by site-specific gene targeting. Adenovirus-infected STAT2 knockout hamsters demonstrated an accentuated pathology compared to the wild-type control animals, and the virus load in the organs of STAT2 knockout animals was 100- to 1000-fold higher than that in wild-type hamsters. Notably, the adaptive immune response to adenovirus is not adversely affected in STAT2 knockout hamsters, and surviving hamsters cleared the infection by 7 to 10 days post challenge. We show that the Type I interferon pathway is disrupted in these hamsters, revealing the critical role of interferon-stimulated genes in controlling adenovirus infection. This is the first study to report findings with a genetically modified Syrian hamster infected with a virus. Further, this is the first study to show that the Type I interferon pathway plays a role in inhibiting human adenovirus replication in a permissive animal model. Besides providing an insight into adenovirus infection in humans, our results are also interesting from the perspective of the animal model: STAT2 knockout Syrian hamster may also be an important animal model for studying other viral infections, including Ebola-, hanta-, and dengue viruses, where Type I interferon-mediated innate immunity prevents wild type hamsters from being effectively infected to be used as animal models.

Lymphoma outbreak in a GASH:Sal hamster colony

We have detected a high incidence of lymphomas in a colony of GASH:Sal Syrian golden hamsters (Mesocricetus auratus). This strain is characterised by its ability to present convulsive crises of audiogenic origin. Almost 16 % (90 males and 60 females) of the 975 animals were affected during a 5-year period by the development of a progressing lymphoid tumour and exhibited similar clinical profiles characterised by lethargy, anorexia, evident abdominal distension, and a rapid disease progression resulting in mortality within 1 to 2 weeks. A TaqMan® probe-based real-time PCR analysis of genomic DNA from different tissue samples of the affected animals revealed the presence of a DNA sequence encoding the hamster polyomavirus (HaPyV) VP1 capsid protein. Additionally, immunohistochemical analysis using HaPyV-VP1-specific monoclonal antibodies confirmed the presence of viral proteins in all hamster tumour tissues analysed within the colony. An indirect ELISA and western blot analysis confirmed the presence of antibodies against the VP1 capsid protein in sera, not only from affected and non-affected GASH:Sal hamsters but also from control hamsters from the same breeding area. The HaPyV genome that accumulated in tumour tissues typically contained deletions affecting the noncoding regulatory region and adjacent sequences coding for the N-terminal part of the capsid protein VP2.

DNA-tumor virus entry--from plasma membrane to the nucleus

DNA-tumor viruses comprise enveloped and non-enveloped agents that cause malignancies in a large variety of cell types and tissues by interfering with cell cycle control and immortalization. Those DNA-tumor viruses that replicate in the nucleus use cellular mechanisms to transport their genome and newly synthesized viral proteins into the nucleus. This requires cytoplasmic transport and nuclear import of their genome. Agents that employ this strategy include adenoviruses, hepadnaviruses, herpesviruses, and likely also papillomaviruses, and polyomaviruses, but not poxviruses which replicate in the cytoplasm. Here, we discuss how DNA-tumor viruses enter cells, take advantage of cytoplasmic transport, and import their DNA genome through the nuclear pore complex into the nucleus. Remarkably, nuclear import of incoming genomes does not necessarily follow the same pathways used by the structural proteins of the viruses during the replication and assembly phases of the viral life cycle. Understanding the mechanisms of DNA nuclear import can identify new pathways of cell regulation and anti-viral therapies.

Cutaneous papillomatosis and carcinomatosis in the Western barred bandicoot (Perameles bougainville)

A progressive wart-like syndrome in both captive and wild populations of the Western barred bandicoot (WBB) is hindering conservation efforts to prevent the extinction of this endangered marsupial. In this study, 42 WBBs exhibiting the papillomatosis and carcinomatosis syndrome were examined. The disease was characterized by multicentric proliferative lesions involving cutaneous and mucosal surfaces, which were seen clinically to increase in size with time. Grossly and histologically the smaller skin lesions resembled papillomas, whereas the larger lesions were most commonly observed to be squamous cell carcinomas. Large amphophilic intranuclear inclusion bodies were observed in hyperplastic conjunctival lesions of 8 WBBs under light microscopy. Conjunctival lesions from 2 WBBs examined using transmission electron microscopy contained a crystalline array of spherical electron-dense particles of 45-nm diameter, within the nucleus of conjunctival epithelial cells, consistent with a papillomavirus or polyomavirus. Conjunctival samples from 3 bandicoots that contained intranuclear inclusion bodies also demonstrated a positive immunohistochemical reaction after indirect immunohistochemistry for papillomavirus structural antigens. Ultrastructural and/or immunohistochemical evidence of an etiologic agent was not identified in the nonconjunctival lesions examined. Here we describe the gross, histopathologic, ultrastructural, and immunohistochemical findings of a papillomatosis and carcinomatosis syndrome recently identified in the WBB.

A novel virus detected in papillomas and carcinomas of the endangered western barred bandicoot (Perameles bougainville) exhibits genomic features of both the Papillomaviridae and Polyomaviridae

Conservation efforts to prevent the extinction of the endangered western barred bandicoot (Perameles bougainville) are currently hindered by a progressively debilitating cutaneous and mucocutaneous papillomatosis and carcinomatosis syndrome observed in captive and wild populations. In this study, we detected a novel virus, designated the bandicoot papillomatosis carcinomatosis virus type 1 (BPCV1), in lesional tissue from affected western barred bandicoots using multiply primed rolling-circle amplification and PCR with the cutaneotropic papillomavirus primer pairs FAP59/FAP64 and AR-L1F8/AR-L1R9. Sequencing of the BPCV1 genome revealed a novel prototype virus exhibiting genomic properties of both the Papillomaviridae and the Polyomaviridae. Papillomaviral properties included a large genome size ( approximately 7.3 kb) and the presence of open reading frames (ORFs) encoding canonical L1 and L2 structural proteins. The genomic organization in which structural and nonstructural proteins were encoded on different strands of the double-stranded genome and the presence of ORFs encoding the nonstructural proteins large T and small t antigens were, on the other hand, typical polyomaviral features. BPCV1 may represent the first member of a novel virus family, descended from a common ancestor of the papillomaviruses and polyomaviruses recognized today. Alternatively, it may represent the product of ancient recombination between members of these two virus families. The discovery of this virus could have implications for the current taxonomic classification of Papillomaviridae and Polyomaviridae and can provide further insight into the evolution of these ancient virus families.

Hamster polyomavirus-derived virus-like particles are able to transfer in vitro encapsidated plasmid DNA to mammalian cells

The authentic major capsid protein 1 (VP1) of hamster polyomavirus (HaPyV) consists of 384 amino acid (aa) residues (42 kDa). Expression from an additional in-frame initiation codon located upstream from the authentic VP1 open reading frame (at position -4) might result in the synthesis of a 388 aa-long, amino-terminally extended VP1 (aa -4 to aa 384; VP1(ext)). In a plasmid-mediated Drosophila Schneider (S2) cell expression system, both VP1 derivatives as well as a VP1(ext) variant with an amino acid exchange of the authentic Met1Gly (VP1(ext-M1)) were expressed to a similar high level. Although all three proteins were detected in nuclear as well as cytoplasmic fractions, formation of virus-like particles (VLPs) was observed exclusively in the nucleus as confirmed by negative staining electron microscopy. The use of a tryptophan promoter-driven Escherichia coli expression system resulted in the efficient synthesis of VP1 and VP1(ext) and formation of VLPs. In addition, establishment of an in vitro disassembly/reassembly system allowed the encapsidation of plasmid DNA into VLPs. Encapsidated DNA was found to be protected against the action of DNase I. Mammalian COS-7 and CHO cells were transfected with HaPyV-VP1-VLPs carrying a plasmid encoding enhanced green fluorescent protein (eGFP). In both cell lines eGFP expression was detected indicating successful transfer of the plasmid into the cells, though at a still low level. Cesium chloride gradient centrifugation allowed the separation of VLPs with encapsidated DNA from "empty" VLPs, which might be useful for further optimization of transfection. Therefore, heterologously expressed HaPyV-VP1 may represent a promising alternative carrier for foreign DNA in gene transfer applications.

Virus-like particles derived from major capsid protein VP1 of different polyomaviruses differ in their ability to induce maturation in human dendritic cells

As polyomavirus major capsid protein VP1-derived virus-like particles (VLPs) have been demonstrated to be highly immunogenic, we studied their interaction with human dendritic cells (hDCs). Exposure of hDCs to VLPs originating from murine (MPyV) or hamster polyomavirus (HaPyV) induced hDC maturation. In contrast, exposure of hDCs to VLPs derived from human polyomaviruses (BK and JC) and simian virus 40 (SV40) only marginally induced DC maturation. The hDCs stimulated by HaPyV- or MPyV-derived VLPs readily produced interleukin-12 and stimulated CD8-positive T-cell responses in vitro. The highest frequencies of activated T cells were again observed after pulsing with HaPyV- and MPyV-derived VLPs. Monocyte-derived hDCs both bound and internalized the various tested polyomavirus VP1-derived VLPs with different levels of efficiency, partially explaining their individual maturation potentials. In conclusion, our data suggest a high variability in uptake of polyomavirus-derived VLPs and potency to induce hDC maturation.

Comparing phylogenetic codivergence between polyomaviruses and their hosts

Seventy-two full genomes corresponding to nine mammalian (67 strains) and two avian (5 strains) polyomavirus species were analyzed using maximum likelihood and Bayesian methods of phylogenetic inference. Our fully resolved and well-supported (bootstrap proportions > 90%; posterior probabilities = 1.0) trees separate the bird polyomaviruses (avian polyomavirus and goose hemorrhagic polyomavirus) from the mammalian polyomaviruses, which supports the idea of spitting the genus into two subgenera. Such a split is also consistent with the different viral life strategies of each group. Simian (simian virus 40, simian agent 12 [Sa12], and lymphotropic polyomavirus) and rodent (hamster polyomavirus, mouse polyomavirus, and murine pneumotropic polyomavirus [MPtV]) polyomaviruses did not form monophyletic groups. Using our best hypothesis of polyomavirus evolutionary relationships and established host phylogenies, we performed a cophylogenetic reconciliation analysis of codivergence. Our analyses generated six optimal cophylogenetic scenarios of coevolution, including 12 codivergence events (P < 0.01), suggesting that Polyomaviridae coevolved with their avian and mammal hosts. As individual lineages, our analyses showed evidence of host switching in four terminal branches leading to MPtV, bovine polyomavirus, Sa12, and BK virus, suggesting a combination of vertical and horizontal transfer in the evolutionary history of the polyomaviruses.

Size and position of truncations in the carboxy-terminal region of major capsid protein VP1 of hamster polyomavirus expressed in yeast determine its assembly capacity

The hamster polyomavirus major capsid protein VP1 was modified in its carboxy-terminal region by consecutive truncations and single amino acid exchanges. The ability of yeast-expressed VP1 variants to form virus-like particles (VLPs) strongly depended on the size and position of the truncation. VP1 variants lacking 21, 69, and 79 amino acid (aa) residues in their carboxy-terminal region efficiently formed VLPs similar to those formed by the unmodified VP1 (diameter 40-45 nm). In contrast, VP1 derivatives with carboxy-terminal truncations of 35 to 56 aa residues failed to form VLPs. VP1 mutants with a single A336G aa exchange or internal deletions of aa 335 to aa 346 and aa 335 to aa 363 resulted in the formation of VLPs of a smaller size (diameter 20 nm). These data indicate that certain parts of the carboxy-terminal region of VP1 are not essential for pentamer-pentamer interactions in the capsid, at least in the yeast expression system used.

Segments of Puumala Hantavirus Nucleocapsid Protein Inserted into Chimeric Polyomavirus-Derived Virus-Like Particles Induce a Strong Immune Response in Mice

Insertion of a short-sized epitope at four different sites of yeast-expressed hamster polyomavirus major capsid protein VP1 has been found to result in the formation of chimeric virus-like particles. Here, we demonstrate that the insertion of 45 or 120 amino acid-long segments from the N-terminus of Puumala hantavirus nucleocapsid protein into sites 1 (amino acids 80-89) and 4 (amino acids 288-295) of VP1 allowed the highly efficient formation of virus-like particles. In contrast, expression level and assembly capacity of fusions to sites 2 (amino acids 222-225) and 3 (amino acids 243-247) were drastically reduced. Immunization of BALB/c mice with chimeric virus-like particles induced a high-titered antibody response against the hantavirus nucleocapsid protein, even in the absence of any adjuvant. The strongest response was observed in mice immunized with virus-like particles harboring 120 amino acids of hantavirus nucleocapsid protein. According to the immunoglobulin subclass distribution of nucleocapsid protein-specific antibodies a mixed Th1/Th2 response was detected. The VP1 carrier itself also induced a mixed Th1/Th2 response, which was found to be reduced in mice immunized with virus-like particles harboring 120 amino acid-long inserts. In conclusion, hamster polyomavirus VP1 represents a promising carrier moiety for future vaccine development.

Generation of recombinant virus-like particles of human and non-human polyomaviruses in yeast Saccharomyces cerevisiae

OBJECTIVES

Non-viral methods of gene transfer have been preferred in gene therapy approaches for several reasons, particularly for their safety, simplicity and convenience in introducing heterologous DNA into cells. Polyomavirus virus-like particles (VLPs) represent a promising carrier for encapsidation of foreign nucleic acids for gene therapy. For the development of such gene delivery systems as well as for providing reagents for improving virus diagnostics, an efficient yeast expression system for the generation of different polyomavirus VLPs was established.

METHODS

A galactose-inducible Saccharomyces cerevisiae yeast expression system was used. Formation of empty VLPs was confirmed by cesium chloride ultracentrifugation, agarose gel electrophoresis and electron microscopy. Cross-reactivity of the major capsid proteins (VP1) of different polyomaviruses was analyzed by Western blot using rabbit and mice sera raised against the VP1 proteins.

RESULTS

VP1 of polyomaviruses from humans (JC polyomavirus and serotypes AS and SB of BK polyomavirus), rhesus monkeys (simian virus 40), hamsters (hamster polyomavirus), mice (murine polyomavirus) and birds (budgerigar fledgling disease virus) were expressed at high levels in yeast. Empty VLPs formed by all yeast-expressed VP1 proteins were dissociated into pentamers and reassociated into VLPs by defined ion and pH conditions. Different patterns of cross-reactivity of the VP1 proteins with heterologous mice and rabbit sera were observed.

CONCLUSION

The developed heterologous yeast expression system is suitable for high-level production of polyomavirus VLPs. Yeast-derived VLPs are generally free of toxins, host cell DNA and proteins. These VLPs might be useful for the generation of new diagnostical tools, gene delivery systems and antiviral vaccines.

Chimeric bacteriophage fr virus-like particles harboring the immunodominant C-terminal region of hamster polyomavirus VP1 induce a strong VP1-specific antibody response in rabbits and mice

The late region of the hamster polyomavirus (HaPyV, former HaPV) genome encodes three structural proteins VP1, VP2, and VP3, where VP1 represents the major capsid protein of 384 amino acids. Screening of sera from HaPyV-infected papilloma-bearing and papilloma-free hamsters demonstrated the immunodominant features of all three capsid proteins. For both groups of hamsters in the C-terminal region of VP1 immunodominant B-cell epitopes were identified in the regions between amino acids 305 and 351 and amino acids 351 and 384. The high flexibility of the C-terminal region of VP1 was confirmed by the formation of chimeric virus-like particles based on the coat protein of the RNA bacteriophage fr which was previously found to tolerate only very short-sized foreign insertions. Phage fr coat protein-derived virus-like particles tolerated the N-terminal fusion of amino acids 333-384, 351-384, 351-374, and 364-384, respectively, of VP1. The induction of VP1-specific antibodies in rabbits and mice by immunization with chimeric virus-like particles harboring amino acids 333-384, 351-384, and 364-384, respectively, of VP1 suggested the immunodominant nature of the C-terminal region of VP1.

Induction and bypass of p53 during productive infection by polyomavirus

Lytic infection by polyomavirus leads to elevated levels of p53 and induction of p53 target genes p21Cip1/WAF1 (p21) and BAX. This is seen both in polyomavirus-infected primary mouse cell cultures and in kidney tissue of infected mice. Stabilization of p53 and induction of a p53 response are accompanied by phosphorylation of p53 on serine 18, mimicking a DNA damage response. Stabilization of p53 does not depend on p19Arf interaction with mdm2. Cells infected by a mutant virus defective in binding pRb and in inducing G(1)-to-S progression show a greatly diminished p53 response. However, cells infected by wild-type virus and blocked from entering S phase by addition of mimosine still show a p53 response. These results suggest a role of E2F target genes in inducing a p53 response. Polyomavirus large T antigen coprecipitates with p53 phosphorylated on serine 18 and also with p21Cip1/WAF1. Implications of these and other findings on possible mechanisms of induction and override of p53 functions during productive infection by polyomavirus are discussed.

Polyomavirus infection in hamsters and trichoepitheliomas/cutaneous adnexal tumours

Multiple skin nodules, with histological features of adnexal tumours consistent with trichoepithelioma, were observed on the head and trunk of Syrian hamsters. Skin biopsies from 20 hamsters from five different colonies were affected, and two of the affected hamsters also had lymphoma. Two owners reported that 16 of 70 hamsters and 50 of 100 hamsters in their colonies had similar skin lesions. These tumours have previously been associated in laboratory colonies with hamster polyomavirus (HaPV) infection. Examination of skin tissues by electron microscopy failed to reveal intranuclear virus particles. Using recombinant major capsid protein VP1 of HaPV, VP1-specific antibodies were detected in sera from 12 of 12 affected hamsters and in four of four unaffected in-contact hamsters, by ELISA. The ELISA data were verified by immunoblot analysis. Eleven of 13 serum samples contained antibodies which reacted with at least one recombinant structural HaPV protein (VP2), including samples from three in-contact unaffected hamsters. Nine of the 11 anti-VP2-positive samples also reacted with recombinant VP3 of HaPV, and six reacted with VP1. Amplification by PCR and sequencing detected VP1 -encoding sequences showing a high degree of homology with HaPV. The findings suggest a possible infection by HaPV or a HaPV-like virus and it is likely that such an infection was enzootic within the affected colonies.