European elk papillomavirus: characterization of the genome, induction of tumors in animals, and transformation in vitro

Infection and cancer in multicellular organisms

Evolutionary considerations suggest that oncogenic infections should be pervasive among animal species. Infection-associated cancers are well documented in humans and domestic animals, less commonly reported in undomesticated captive animals, and rarely documented in nature. In this paper, we review the literature associating infectious agents with cancer to evaluate the reasons for this pattern. Non-malignant infectious neoplasms occur pervasively in multicellular life, but oncogenic progression to malignancy is often uncertain. Evidence from humans and domestic animals shows that non-malignant infectious neoplasms can develop into cancer, although generally with low frequency. Malignant neoplasms could be difficult to find in nature because of a low frequency of oncogenic transformation, short survival after malignancy and reduced survival prior to malignancy. Moreover, the evaluation of malignancy can be ambiguous in nature, because criteria for malignancy may be difficult to apply consistently across species. The information available in the literature therefore does not allow for a definitive assessment of the pervasiveness of infectious cancers in nature, but the presence of infectious neoplasias and knowledge about the progression of benign neoplasias to cancer is consistent with a widespread but largely undetected occurrence.

Papillomavirus-associated fibropapillomas of red deer ( Cervus elaphus )

Oval, firm, cutaneous tumours with a rough, hairless, pigmented surface, exhibiting a moderately pronounced papillary structure were detected on the abdominal skin of two young red deer ( Cervus elaphus ). One animal was shot in Lower Austria in 2004, the other at a deer farm in Hungary in 2007. Histological examination of both samples classified the tumours as fibropapillomas, showing marked proliferation of fibroblasts and connective tissue, accompanied by hyperkeratosis, parakeratosis and acanthosis of the overlaying epidermis, and occasional foci of inflammation. The distribution of cytokeratin and vimentin was characterised in the lesion. The presence of papillomavirus (PV) antigen was demonstrated by immunohistochemistry in both cases. Papillomavirus-specific DNA was successfully amplified by PCR from one sample. The obtained partial nucleotide sequence of the L2 ORF exhibited the highest critical identity values with the homologous regions of Delta-papillomaviruses, especially the Roe deer papillomavirus (93%). Phylogenetic analysis of the partial L2 ORF sequence alignment of 10 papillomaviruses by both neighbour-joining and maximum parsimony method confirmed that the Red deer PV is very closely related to the Western roe deer papillomavirus (CcPV1).

Endemic papillomavirus infection of roe deer (Capreolus capreolus)

Roe deer papillomavirus (CcPV1) infection has been identified as an endemic disease in roe deer populations of the Carpathian basin in Central Europe (Hungary, Austria and Croatia). The disease is characterised by easily recognizable skin tumours similar to deer papillomavirus infection of North American deer species. In 2006, a questionnaire study was conducted among all Hungarian game management units (GMUs) in order to assess the distribution of the disease and its major epidemiological features. Categorical information was collected about disease occurrence, trend and frequency of detection, on primarily affected age classes in both sexes, and association of lesions with mortality. Replies were received from 539 GMUs representing 50.9% of total GMU territory and disease presence was reported by 295 (54.7%) GMUs. Older age classes of both sexes were found to be more affected. Association of various environmental factors with disease occurrence was evaluated and data were collected on the occurrence of similar skin lesions in other European countries. Pathological features of CcPV1 infection were described and the localisation of both CcPV1 antigen and DNA was characterised by immunohistochemistry and in situ DNA hybridisation in skin lesions. Virus presence was also demonstrated by PCR and PCR product sequencing.

Characterisation of the first complete genome sequence of the roe deer (Capreolus capreolus) papillomavirus

The complete genomic DNA of a novel roe deer (Capreolus capreolus) papillomavirus (CcPV1) was amplified and sequenced from fibropapillomatous skin lesions of a Hungarian roe deer. Viral DNA was detected by a pair of degenerate primers and the remaining genomic sequence was amplified by a long-template high-fidelity PCR and sequenced. The CcPV1 genome was 8032 bp long and contained open reading frames (ORFs) typical for Delta-papillomaviruses (E6, E7, E1, E2, E4, E5, E9, L2, and L1) and a 799 bp long untranslated regulatory region (URR). Phylogenetic analysis based on the 3861 bp long concatenated sequence of the E1-E2-L2-L1 ORFs and on separate alignments of all major ORFs using both neighbour-joining and maximum parsimony methods placed CcPV1 on a distinct branch between Ovine papillomavirus 1 and the other deer papillomaviruses within the Delta-papillomavirus genus, although pairwise nucleotide alignments of L1 ORF sequences determined highest identities with European Elk Papillomavirus (71.2%) and Reindeer Papillomavirus (70.3%).

Bovine papillomavirus E7 oncoprotein inhibits anoikis

The bovine papillomavirus type 1 (BPV-1) E7 oncoprotein is required for the full transformation activity of the virus. Although BPV-1 E7 by itself is not sufficient to induce cellular transformation, it enhances the abilities of the other BPV-1 oncogenes to induce anchorage independence. We have been exploring the mechanisms by which E7 might affect the transformation efficiency of other viral oncoproteins and in particular whether it might protect cells from apoptosis. We report here that BPV-1 E6 and E7 can each independently inhibit anoikis, a type of apoptosis that is induced upon cell detachment. Using site-directed mutagenesis, we determined regions of the E7 protein that were essential for its antiapoptotic activity. The ability of E7 to inhibit anoikis did partially correlate with an ability to enhance anchorage independence of BPV-1 E6-transformed cells. In addition, the antiapoptotic activity of E7 also only partially correlated with its ability to bind p600, a cellular protein that has previously been reported to play a role in anoikis. We conclude that the contribution of E7 to BPV-induced cellular transformation may involve its ability to inhibit anoikis but that additional functional activities must also be involved.

Bovine papillomavirus E7 transformation function correlates with cellular p600 protein binding

The E7 oncoprotein of bovine papillomavirus type 1 (BPV-1) is required for the full transformation activity of the virus. However, the mechanism by which E7 contributes to cellular transformation is unknown. To address this question, we used the proteomic approach of tandem affinity purification to identify cellular proteins that are in complex with E7, and identified the 600-kDa protein, p600, as a binding partner of E7. The ability of E7 to complex with p600 correlated with its ability to enhance anchorage independence of BPV-1 E6-expressing cells. Furthermore, E7 mutant proteins impaired in their ability to bind p600 were transformation defective. Additionally, knockdown of p600 reduced transformation of cells expressing both BPV-1 E6 and E7, as well as E6 alone, suggesting that the ability of E7 to transformed cells is mediated, at least in part, through its ability to bind p600. These data complement work that shows that HPV16 E7 also interacts with p600, and that this interaction correlates with the ability of HPV16 E7 to transform cells. These studies thus identify p600 as a shared target of the E7 proteins of multiple papillomaviruses.

The genomes of the animal papillomaviruses European elk papillomavirus, deer papillomavirus, and reindeer papillomavirus contain a novel transforming gene (E9) near the early polyadenylation site

We report that the genomes of reindeer papillomavirus (RPV), European elk papillomavirus (EEPV), and deer papillomavirus (DPV) contain a short conserved translational open reading frame (ORF), E9, which is located between the E5 ORF and the early polyadenylation site. In RPV, DPV, and EEPV, E9 ORFs have the potential to encode extremely hydrophobic polypeptides of approximately 40 amino acids. In mouse C127 cells transformed by EEPV and RPV, there exists a unique, abundant mRNA species of approximately 700 nucleotides which has the capacity to encode an E9 polypeptide. This mRNA is transcribed from a previously unrecognized promoter at position 4030 in the EEPV genome. The EEPV E9 ORF exhibits weak transforming activity in C127 cells and primary rat embryo fibroblasts. We also show that EEPV E5 is the major oncogene in the EEPV genome when assayed in C127 cells, although it is less efficient in transformation than the E5 genes of bovine papillomavirus type 1, DPV, and RPV.

Viruses and oral cancer

Oral cancer is a disease with a complex etiology. There is evidence for important roles of smoking, drinking, and genetic susceptibility, as well as strong indications that DNA viruses could be involved. The herpes simplex virus type 1 has been associated with oral cancer by serological studies, and animal models and in vitro systems have demonstrated that it is capable of inducing oral cancer. Papillomaviruses are found in many oral cancers and are also capable of transforming cells to a malignant phenotype. However, both virus groups depend on co-factors for their carcinogenic effects. Future research on viruses and oral cancer is expected to clarify the role of these viruses, and this will lead to improvements in diagnosis and treatment of the disease.

Genome of the European elk papillomavirus (EEPV)

The genome of the European elk papillomavirus (EEPV) was found to be 8,095 base pairs (bp) long and its genetic organization was similar to that of other papillomaviruses. Ten open reading frames (ORFs), designated E1-E7 and L1-L3, were identified in the genome, all located on one strand. The presence of the L3 ORF is rare among the papillomaviruses and to date has only been identified in the genomes of EEPV, the deer papillomavirus (DPV) and the Cottontail papillomavirus (CRPV). The ORF is well conserved between DPV and EEPV with regard to both length and sequence. Potential promoter regions were identified at the 5'-end of the E6 ORF, at the 3'-end of the E1 ORF and downstream of the L1 ORF. Furthermore, two potential polyadenylation signals were found, one located in the long control region (LCR), downstream of the L1 ORF, and another preceding the L2 ORF. The EEVP genome is closely related to the genome of the DPV, the most highly conserved regions being ORFs E1 (70%), E5 (69%), and L1 (74%).

Cloning and characterization of a papillomavirus associated with papillomas and carcinomas in the European harvest mouse (Micromys minutus)

Individuals in a colony of European harvest mice (Micromys minutus) were diagnosed with a variety of skin tumors including papillomas, trichoepitheliomas, and sebaceous carcinomas. Papillomavirus group-specific antigens and viruslike particles were detected in the papillomas. A 7.6-kilobase supercoiled circular DNA, which was cleaved once by EcoRI, was visualized in papilloma extracts by low-stringency Southern blot hybridization with a bovine papillomavirus type 2 probe. The molecule was cloned in pUC18, and a restriction map was generated. The molecule was shown to be colinear with the genome of human papillomavirus type 1a by partial sequence analysis. The DNA hybridized to human papillomavirus type 1a, rabbit oral papillomavirus, and the genome of Mastomys natalensis papillomavirus at Tm - 33 degrees C but not to the DNAs of 13 other papillomaviruses. Transformation of NIH 3T3 or C127I cells by tail papilloma extracts or transfected viral DNA was not observed. All 17 tumors examined contained large amounts of viral DNA in a supercoiled, unintegrated form as revealed by Southern blot hybridization. Furthermore, many extracts (25 of 35) from normal organs and skin of individuals with lesions elsewhere on their bodies contained viral DNA. This represents the first reported molecular cloning of a papillomavirus genome from a mouse species.

Reindeer papillomavirus transforming properties correlate with a highly conserved E5 region

A papillomavirus was isolated from the epithelial layer of a cutaneous fibropapilloma on a Swedish reindeer (Rangifer tarandus). Reindeer papillomavirus (RPV) is morphologically indistinguishable from other papillomaviruses, but the restriction enzyme cleavage pattern of its genome is different. No sequence homology was detected between RPV DNA and the DNAs of bovine papillomavirus type 1 (BPV-1) and avian papillomavirus when hybridization was performed under stringent conditions. However, the RPV genome hybridized to the genome of the European elk papillomavirus and the deer papillomavirus under stringent conditions. A physical map of the RPV genome was constructed, and selected regions of the genome, covering the open translational reading frame (ORF) E5 and part of the E1 and L1 ORFs, were studied by nucleotide sequence analysis. The results made it possible to align the RPV genome with the genome of BPV-1. The E5 ORF of RPV has the potential to encode a 44-amino-acid, exceptionally hydrophobic polypeptide which is very similar to the E5 polypeptides of BPV-1 and deer and European elk papillomaviruses. RPV is oncogenic for hamsters and transforms C127 mouse cells in vitro. Several virus-specific mRNAs were detected in RPV-transformed C127 cells.

Promoters and processing sites within the transforming region of bovine papillomavirus type 1

The mRNAs present in bovine papillomavirus type 1 (BPV-1)-transformed C127 cells were studied by primer extension. The results show that two internal promoters are present in the E region of BPV-1 in addition to the previously identified promoter at coordinate 1 (H. Ahola, A. Stenlund, J. Moreno-López, and U. Pettersson, Nucleic Acids Res. 11:2639-2650, 1983). One, located at coordinate 31, generated a set of mRNAs with heterogeneous 5' ends, which may encode the major transforming protein of BPV-1, the E5 protein. The second promoter, which is located at coordinate 39, generates colinear mRNAs which encode either the E4 protein or a truncated form of the E2 protein. Unlike the cottontail rabbit papillomavirus (O. Danos, E. Georges, G. Orth, and M. Yaniv, J. Virol. 53:735-741, 1985), BPV-1 appears to lack a separate promoter for expression of the E7 protein. The major splice sites in the transforming region (E region) of the BPV-1 genome were also identified by nucleotide sequence analysis.

Papillomavirus DNA associated with pulmonary fibromatosis in European elks

Multiple beadlike fibromas have been observed in the lungs of European elks bearing cutaneous fibromas and fibropapillomas. DNA extracted from the lung fibromas was found to contain multiple copies of unintegrated European elk papillomavirus DNA, indicating an association between pulmonary fibromatosis and papillomavirus. No virus particles were observed in the tumor tissue by electron microscopy. Histological examination revealed that the lung fibromas had a morphology similar to that of cutaneous fibromas.

Organization and expression of the transforming region from the European elk papillomavirus (EEPV)

The nucleotide sequence of the early (transforming) region from the European elk papillomavirus (EEPV) double-stranded DNA has been determined together with flanking regions. The established sequence, which is 5732 bp long, shows that the genome of EEPV is closely related to the previously sequenced bovine papillomavirus type 1 (BPV-1) and deer papillomavirus (DPV) genomes. Seven open reading frames (ORFs), designated E1-E7, were identified in similar positions as in the BPV-1 genome. The E1 and E5 regions were best conserved. The strong homology between the E5 ORFs of EEPV, BPV-1 and DPV is interesting in the light of the recent proposal that these ORFs encode a major transforming function (Schiller et al., 1986; DiMaio et al., 1986). A set of mRNAs, comprising six size classes, were identified in EEPV-transformed cells. At least two different promoters appear to control EEPV transcription in transformed cells.

Molecular cloning and nucleotide sequence of deer papillomavirus

The genome of deer papillomavirus (DPV) isolated from American white-tailed deer was cloned into pBR322, and the entire nucleotide sequence of 8,374 base pairs was determined. The overall genetic organization of the DPV genome was similar to that of other papillomaviruses. All significant open reading frames were located on one strand, and the locations of putative promoters and polyadenylation signals were similar to those identified in the closely related bovine papillomavirus type 1 (BPV-1) genome. The DPV genome was approximately colinear with BPV-1 except for a noncoding region separating the early and late regions. The regions of highest nucleotide sequence homology between DPV and BPV-1 were found in the E1 open reading frame coding for BPV-1 DNA replication function and in the L1 open reading frame, which encodes the major capsid protein of BPV-1.

Genome of an avian papillomavirus

A papillomavirus which we designate FPV was isolated from chaffinches (Fringilla coelebs). A physical map of the FPV genome was constructed, and selected regions of this genome were studied by nucleotide sequence analysis. The results make it possible to align the FPV genome with the genome of bovine papillomavirus type 1 and to show, moreover, that avian and mammalian papillomaviruses have a similar genome organization.