Search

Hamster polyomavirus (Mesocricetus auratus polyomavirus 1, HaPyV) was discovered as one of the first rodent polyomaviruses at the end of the 1960s in a colony of Syrian hamsters ( Mesocricetus auratus ) affected by skin tumors. Natural HaPyV infections have been recorded in Syrian hamster colonies due to the occurrence of skin tumors and lymphomas. HaPyV infections of Syrian hamsters represent an important and pioneering tumor model. Experimental infections of Syrian hamsters of different colonies are still serving as model systems (e.g., mesothelioma). The observed phylogenetic relationship of HaPyV to murine polyomaviruses within the genus Alphapolyomavirus, and the exclusive detection of other cricetid polyomaviruses, i.e., common vole (Microtus arvalis polyomavirus 1) and bank vole (Myodes glareolus polyomavirus 1) polyomaviruses, in the genus Betapolyomavirus , must be considered with caution, as knowledge of rodent-associated polyomaviruses is still limited. The genome of HaPyV shows the typical organization of polyomaviruses with an early and a late transcriptional region. The early region encodes three tumor (T) antigens including a middle T antigen; the late region encodes three capsid proteins. The major capsid protein VP1 of HaPyV was established as a carrier for the generation of autologous, chimeric, and mosaic virus-like particles (VLPs) with a broad range of applications, e.g., for the production of epitope-specific antibodies. Autologous VLPs have been applied for entry and maturation studies of dendritic cells. The generation of chimeric and mosaic VLPs indicated the high flexibility of the VP1 carrier protein for the insertion of foreign sequences. The generation of pseudotype VLPs of original VP1 and VP2-foreign protein fusion can further enhance the applicability of this system. Future investigations should evaluate the evolutionary origin of HaPyV, monitor its occurrence in wildlife and Syrian hamster breeding, and prove its value for the generation of potential vaccine candidates and as a gene therapy vehicle.

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.

We inserted the sequence of the carcinoembryonic antigen-derived T cell epitope CAP-1-6D (CEA) into different positions of the hamster polyomavirus major capsid protein VP1. Independently from additional flanking linkers, yeast-expressed VP1 proteins harboring the CEA insertion between VP1 amino acid residues 80 and 89 (site 1) or 288 and 295 (site 4) or simultaneously at both positions assembled to chimeric virus-like particles (VLPs). BALB/c mice immunized with adjuvant-free VLPs developed VP1- and epitope-specific antibodies. The level of the CEA-specific antibody response was determined by the insertion site, the number of inserts, and the flanking linker. The strongest CEA-specific antibody response was observed in mice immunized with VP1 proteins harboring the CEA insert at site 1. Moreover, the CEA-specific antibodies in these mice were still detectable 6 mo after the final booster immunization. Our results indicate that hamster polyomavirus-derived VLPs represent a highly immunogenic carrier for foreign insertions that might be useful for clinical and therapeutic applications.

We generated highly immunogenic virus-like particles that are based on the capsid protein VP1 of the hamster polyomavirus (HaPV-VP1) and harbor inserted foreign epitopes. The HaPV-VP1 regions spanning amino acids 81-88 (position 1), 222/223 (2), 244-246 (3), and 289-294 (4) were predicted to be surface exposed. An epitope of the pre-S1 region of the hepatitis B virus (designated S1; amino acid sequence DPAFR) was introduced into the predicted positions of VP1. All VP1/S1 fusion proteins were expressed in yeast and generated virus-like particles. Immunoassays using the S1-specific monoclonal antibody MA18/7 and immunization of C57Bl6 mice with different VP1/S1 constructs showed a pronounced reactivity and a strong S1-specific antibody response for particles carrying the insert in position 1, 2, 1+2, and 1+3. Our results suggest that HaPV-VP1 represents a highly flexible carrier moiety for the insertion of foreign sequences offering a broad range of potential uses, especially in vaccine development., (Copyright 2000 Academic Press.)

Polyomavirus-derived virus-like particles (VLPs) have been described as potential carriers for encapsidation of nucleic acids in gene therapy. Although VLPs can be generated in E. coli or insect cells, the yeast expression system should be advantageous as it is well established for the biotechnological generation of products for human use, especially because they are free of toxins hazardous for humans. We selected the yeast Saccharomyces cerevisiae for expression of the major capsid protein VP1 of a non-human polyomavirus, the hamster polyomavirus (HaPV). Two entire HaPV VP1-coding sequences, starting with the authentic and a second upstream ATG, respectively, were subcloned and expressed to high levels in Saccharomyces cerevisiae. The expressed VP1 assembled spontaneously into VLPs with a structure resembling that of the native HaPV capsid. Determination of the subcellular localization revealed a nuclear localization of some particles formed by the N-terminally extended VP1, whereas particles formed by the authentic VP1 were found mainly in the cytoplasmic compartment.

On the basis of its genome organization the hamster polyomavirus (HaPV) is closely related to the murine polyomavirus Py. But HaPV infection, in contrast to Py infection, gives rise to two different tumor types; depending on the hamster strain used for infection, HaPV induces either epitheliomas or lymphomas. Although the HaPV virions were shown to be similar to those of Py and SV40, more precise information about the structure and protein composition of the HaPV capsid was still missing. Here we describe the primary structure of the capsid protein-encoding HaPV genes and the structure and protein composition of the HaPV capsid. Virions isolated from epitheliomas in HaPV-infected hamsters were shown by electron microscopy to be spherical particles with the typical icosahedral structure of polyomaviruses. However, in contrast to the capsids of SV40 and Py, a T = 7 laevo symmetry of HaPV capsids was observed. Separation of HaPV virions in SDS polyacrylamide gels and Western blotting with VP1-specific antisera identified VP1 as the major capsid protein species corresponding in its molecular weight to the predicted value of 41.8 kDa. Because of the presence of two potential translational initiation sites in the VP1 gene, the N-terminal amino acid sequence of virion VP1 was determined and found to start at the second initiation site. The amino acid homologies of HaPV capsid proteins shared with Py varied between 65.5% (VP1), 45.4% (VP3) and 44.6% (VP2), whereas the homologies to the relevant proteins of other polyomaviruses were found to range between 49.6-57.9% for VP1 and 28.9-41% for VP2/VP3.

The hamster polyomavirus (HaPV) induces either hair follicle epitheliomas or lymphomas in either Z3 or HaP respectively. Syrian hamsters. In the lymphomas specifically deleted "lymphoma-type" (lt) HaPV genomes are accumulated. In the present study the temporal pattern of generation of HaPV (lt) DNA was investigated in context of the development of lymphomas in neonatally infected HaP hamsters. The generation of HaPV (lt) DNA was first detectable during the postnatal phase of high level replication of viral DNA in hemopoietic organs (at 7 days post infection), thus clearly preceding the development of overt lymphoma. A variety of HaPV (lt) DNA species is generated in lymphoid cells, but usually only one of them is accumulated to high amounts in lymphoma cells. Furthermore, the pattern of HaPV (lt) and wild-type (wt) DNA was studied in normal and tumor tissues of tumor-bearing hamsters as well as in tumor-free hamsters. In tumor-bearing hamsters predominantly HaPV (lt) DNA species were found in the infected tissues, while HaPV (wt) DNA was detected rarely and only in tumor-free tissues. In contrast, in tissues of tumor-free hamsters HaPV (wt) DNA prevailed over HaPV (lt) DNA species.