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.     

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.     

Rb-independent induction of apoptosis by bovine papillomavirus type 1 E7 in response to tumor necrosis factor alpha

Bovine papillomavirus type 1 (BPV-1) is a small DNA virus that causes fibropapillomas of the host. BPV-1 has served as the prototype for studies of the molecular biology of the papillomaviruses. BPV-1 efficiently induces anchorage-independent growth and focus formation in murine C127 cells. The transforming properties of BPV-1 primarily reside in two genes, E5 and E6. Each of these genes is sufficient to transform cells. Although no independent transformation activity has been detected for E7, it was shown to be required for full transformation of C127 by BPV-1. We investigated the biological activities of BPV-1 E7 in several assays. Our results indicate that expression of BPV-1 E7 sensitizes cells to tumor necrosis factor alpha (TNF)-induced apoptosis. The TNF-induced apoptosis in E7-expressing cells was accompanied by increased release of arachidonic acid, indicating that phospholipase A(2) was activated. Unlike the E7 proteins from the cancer-related human papillomaviruses, the BPV-1 E7 protein does not associate efficiently with the retinoblastoma protein (pRB) in vitro, nor does it significantly affect the pRB levels in cultured cells. Furthermore, BPV-1 E7 sensitizes Rb-null cells to TNF-induced apoptosis. These studies indicate that BPV-1 E7 can sensitize cells to apoptosis through mechanisms that are independent of pRB.     

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

The European elk papillomavirus (EEPV) genome was cloned in the BamHI cleavage site of the pBR322 vector. The cloned genome was used for construction of a physical map, employing restriction endonucleases BamHI, BglII, HindIII, PvuII, SacI, and XhoI. The sequence homology between the EEPV and bovine papillomavirus type 1 genomes was elucidated by performing hybridizations in different concentrations of formamide. Sequence homology could only be revealed under less stringent conditions, i.e., Tm - 43 degrees C. Nucleotide sequence information was also collected from the regions which lie adjacent to the three HindIII sites that are present in the EEPV genome. The results made it possible to align the EEPV and bovine papillomavirus type 1 genomes. Transformation by EEPV was demonstrated with the C127 mouse cell line, and fibrosarcomas were induced in young hamsters after subcutaneous injection. The transformed cells and the tumors contain multiple, nonintegrated copies of the EEPV genome. Virus particles could not be detected either in tumors or in transformed cells.     

Identification of a 68-kilodalton nuclear ATP-binding phosphoprotein encoded by bovine papillomavirus type 1.

E1 is the largest open reading frame (ORF) of bovine papillomavirus type 1 (BPV-1) and is highly conserved among all papillomaviruses, maintaining its size, amino acid composition, and location in the viral genome with respect to other early genes. Multiple viral replication functions have been mapped to the E1 ORF of BPV-1, and evidence suggested that more than one protein was encoded by this ORF. We previously identified a small protein (M) whose gene consists of two exons, one encoded by the 5' end of the E1 ORF. We show here that a 68-kilodalton (kDa) phosphoprotein made from the E1 ORF can be detected in BPV-1-transformed cells, and we present evidence that this protein is encoded by sequences colinear with the entire E1 ORF. The full-length E1 protein immunoprecipitated from virally transformed cells and identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis comigrates with a protein expressed from a recombinant DNA construct capable of producing only the complete E1 protein. In addition, two different antisera directed against polypeptides encoded from either the 3' or the 5' end of the E1 ORF both recognize the full-length E1 product. A mutation converting the first methionine codon in the ORF to an isoleucine codon abolishes BPV-1 plasmid replication and E1 protein production. Consistent with the notion that this methionine codon is the start site for E1, a mutant with a termination codon placed after the splice donor at nucleotide 1235 in E1 produces a truncated protein with the molecular mass predicted from the primary sequence as well as the previously identified M protein. When visualized by immunostaining, the E1 protein expressed in COS cells is localized to the cell nucleus. A high degree of similarity exists between the BPV-1 E1 protein and polyomavirus and simian virus 40 large-T antigens in regions of the T antigens that bind ATP. We show by ATP affinity labeling that the E1 protein produced in COS cells binds ATP and that this activity is abolished by a point mutation which converts the codon for proline 434 to serine. Furthermore, this mutation renders the viral genome defective for DNA replication, suggesting that the ATP-binding activity of E1 is necessary for its putative role in viral DNA replication.(ABSTRACT TRUNCATED AT 400 WORDS)     

Conserved polynucleotide sequences among the genomes of papillomaviruses.

The DNAs of different members of the Papillomavirus genus of papovaviruses were analyzed for nucleotide sequence homology. Under standard hybridization conditions (Tm - 28 degrees C), no homology was detectable among the genomes of human papillomavirus type 1 (HPV-1), bovine papillomavirus type 2 (BPV-2), or cottontail rabbit (Shope) papillomavirus (CRPV). However, under less stringent conditions (i.e., Tm - 43 degrees C), stable hybrids were formed between radiolabeled DNAs of CRPV, BPV-1, or BPV-2 and the HindIII-HpaI A, B, and C fragments of HPV-1. Under these same conditions, radiolabeled CRPV and HPV-1 DNAs formed stable hybrids with HincII B and C fragments of BPV-2 DNA. These results indicate that there are regions of homology with as much as 70% base match among all these papillomavirus genomes. Furthermore, unlabeled HPV-1 DNA competitively inhibited the specific hybridization of radiolabeled CRPV DNA to bpv-2 DNA fragments, indicating that the homologous DNA segments are common among these remotely related papillomavirus genomes. These conserved sequences are specific for the Papillomavirus genus of papovaviruses as evidenced by the lack of hybridization between HPV-1 DNA and either simian virus 40 or human papovavirus BK DNA under identical conditions. These results indicate a close evolutionary relationship among the papillomaviruses and further establish the papillomaviruses and polyoma viruses as distinct genera.     

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.     

The human papillomavirus type 6 and 16 E5 proteins are membrane-associated proteins which associate with the 16-kilodalton pore-forming protein.

The human papillomavirus (HPV) E5 proteins are predicted from DNA sequence analysis to be small hydrophobic molecules, and the HPV type 6 (HPV-6) and HPV-11 E5 proteins share several structural similarities with the bovine papillomavirus type 1 (BPV-1) E5 protein. Also similar to the BPV-1 E5 protein, the HPV-6 and HPV-16 E5 proteins exhibit transforming activity when assayed on NIH 3T3 and C127 cells. In this study, we expressed epitope-tagged E5 proteins from both the "low-risk" HPV-6 and the "high-risk" HPV-16 in order to permit their immunologic identification and biochemical characterization. While the HPV-6 and HPV-16 E5 proteins fail to form disulfide-linked dimers and oligomers, they did resemble the BPV-1 E5 protein in their intracellular localization to the Golgi apparatus, endoplasmic reticulum, and nuclear membranes. In addition, the HPV E5 proteins also bound to the 16-kDa pore-forming protein component of the vacuolar ATPase, a known characteristic of the BPV-1 E5 protein. These studies reveal a common intramembrane localization and potential cellular protein target for both the BPV and HPV E5 proteins.     

Stable maintenance of linear bovine papillomavirus 1 molecules in C127I cells.

This paper describes the characterization of cell lines that stably maintain linear copies of bovine papillomavirus 1 (BPV-1). Cell lines were generated by liposome-mediated transfection of BamH1-linearized virus into C127I cells. Two transfectants with morphologies differing from each other and from that of the parental cell line were characterized. Southern blots indicated that they contain ten to twelve copies of the BPV-1 genome per cell and that the predominant species in both cell lines are linear BPV-1 episomes. One to two copies per genome of a slow migrating species are also present. Both BPV-1 species found in these cells are sensitive to BAL31 digestion. Viral chromosomal ends were amplified by anchored PCR, cloned and sequenced. Our results indicate that no major rearrangements have occurred in the sequence flanking the BamH1 site where the virus used for transfection was linearized. No circular BPV-1 molecules were detected by PCR. The slow migrating species may serve as templates for replication for the linear forms by a yet unidentified mechanism.     

Bovine papillomavirus type 1 oncoprotein E5 stimulates the utilization of superoxide radicals in the mouse fibroblast cell line C127

The major transforming protein of bovine papillomavirus type 1 (BPV-1) is a small hydrophobic polypeptide, the E5 gene product, localized in the cellular membranes and modulating various pathways in the cell. Many studies have shown that reactive oxygen species (ROS) are essential in several biological processes, including cell transformation by oncogenes, but unregulated ROS are highly toxic to cells. We studied the effect of the bovine papillomavirus protein E5 and its mutants on the level of the superoxide radicals in the mouse fibroblast cell line C127. The superoxide level in C127 cells transfected with the E5-expressing plasmids were measured by nitroblue tetrazolium reduction. Relative concentrations of intracellular peroxide were determined by using 2,7-dichlorofluorescin diacetate. Our results showed that all transforming mutants of E5 reduced the level of superoxide in C127 cells, besides the activity of superoxide dismutase (SOD) and level of peroxides was not altered. In the presence of neopterin, an inhibitor of the superoxide-producing enzymes, the reduction of superoxide level correlated with the transforming ability of the E5-mutants. The inhibitor of the protein tyrosine kinase, tyrphostin 25 and inhibitors of oxygenases of the arachidonic acid metabolism, aspirin and nordihydroguaiaretic acid, blocked the effect of BPV-1 E5. We conclude that BPV-1 E5 and its transforming mutants are able to modulate the level of superoxide and stimulate the utilization of superoxide through protein tyrosine kinases and oxygenases of the arachidonic acid metabolism.     

Bovine papillomavirus type 1 3'' early region transformation and plasmid maintenance functions.

Human papillomavirus (HPV) 8 induces skin tumors which are at high risk for malignant conversion. The nucleotide sequence of HPV8 has been determined and compared to sequences of papillomaviruses with different oncogenic potential. The general organization of the HPV8 genome is similar to that of other types. Highly conserved, genus-specific sequences were found in open reading frames (ORFs) E1, E2, and L1. In ORFs E6, E7, and L2, HPV8 is more distantly related, but it was possible to differentiate subgenera in which HPV8 belonged to the HPV1-cottontail rabbit papillomavirus group. Sequences within ORF E4 and part of ORF L2 are rather type specific. HPV8 stands out by several unique features: the considerably reduced size of the noncoding region (397 base pairs), with a seemingly low potential for forming complex secondary structures; a cluster of putative promoter elements in the 3' half of ORF E1; an RNA polymerase III promoter-like sequence close to the C terminus of ORF E2; and of particular interest, the homology between the putative protein encoded by ORF E4 and the Epstein-Barr virus nuclear antigen 2 protein, which may reflect similar mechanisms in virus-mediated transformation.     

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.     

Bovine papillomavirus mutant temperature sensitive for transformation, replication and transactivation.

The genetic analysis of the papillomaviruses has been hampered by the lack of mutants conditionally defective for viral biological activities. We report here the construction and characterization of a temperature-sensitive papillomavirus mutant. The mutation is predicted to insert the sequence Pro-Arg-Ser-Arg into the N-terminal half of the bovine papillomavirus type 1 (BPV1) ORF E2 protein, the major viral regulatory protein. The cloned mutant viral DNA displays temperature-sensitive defects in the induction of focus formation in mouse C127 cells, in its establishment as an extrachromosomal plasmid and in transactivation of a BPV1 enhancer. Genetic experiments confirm that this pleiotropic phenotype is caused by the insertion mutation in ORF E2 and that the transformation and replication defects of the mutant at 37 degrees C are corrected in trans by wild-type E2 gene activity. Most cell lines stably transformed by the mutant at 32.5 degrees C display a reduced ability to overgrow a monolayer of normal cells following temperature shift to 37 degrees C and the mutant viral DNA after temperature shift is present in decreased copy number and/or in an integrated state. These results provide strong genetic evidence that continued ORF E2 activity is required for maintenance of BPV1-induced transformation and for normal viral DNA replication.     

Loss of bovine papillomavirus DNA replication control in growth-arrested transformed cells.

The bovine papillomavirus type 1 (BPV-1) genome replicates as a plasmid within the nuclei of BPV-1-transformed murine C127 cells at a constant multiple copy number, and spontaneous amplification of the viral DNA is rarely observed. We report here that a mutant BPV-1 plasmid within a contact-inhibited C127 cell line replicated as a stable multicopy plasmid in exponentially growing cells but amplified to a high level in confluent cell culture. In situ hybridization analysis revealed that most of the mutant viral DNA amplification occurred in a minor subpopulation of cells within the culture. These consisted of giant nondividing cells with greatly enlarged nuclei, a cell form which was specifically induced in stationary-phase cultures. These observations indicated that expression of a viral DNA replication factor was cell growth stage specific. Consistent with this hypothesis, considerable amplification of wild-type BPV-1 DNA associated with characteristic giant cell formation was observed in typical wild-type virus-transformed C127 cultures following a period of growth arrest achieved by serum deprivation. Further observations indicated that induction of the giant-cell phenotype was dependent on BPV-1 gene expression and implicated a viral E1 replication factor in this process. Moreover, heterogeneity in virus genome copy numbers within the giant-cell population suggested a complex regulation of induction of DNA synthesis in these cells. It appears that this process represents a mechanism employed by the virus to ensure maximal viral DNA synthesis within a growth-arrested cell. Fundamental questions concerning the integration of the virus-cell control circuitry in proliferating and resting cells are discussed.