Characterization of the complete RhPV 1 genomic sequence and an integration locus from a metastatic tumor

Molecular Mechanisms of MmuPV1 E6 and E7 and Implications for Human Disease

Human papillomaviruses (HPVs) cause a substantial amount of human disease from benign disease such as warts to malignant cancers including cervical carcinoma, head and neck cancer, and non-melanoma skin cancer. Our ability to model HPV-induced malignant disease has been impeded by species specific barriers and pre-clinical animal models have been challenging to develop. The recent discovery of a murine papillomavirus, MmuPV1, that infects laboratory mice and causes the same range of malignancies caused by HPVs provides the papillomavirus field the opportunity to test mechanistic hypotheses in a genetically manipulatable laboratory animal species in the context of natural infections. The E6 and E7 proteins encoded by high-risk HPVs, which are the HPV genotypes associated with human cancers, are multifunctional proteins that contribute to HPV-induced cancers in multiple ways. In this review, we describe the known activities of the MmuPV1-encoded E6 and E7 proteins and how those activities relate to the activities of HPV E6 and E7 oncoproteins encoded by mucosal and cutaneous high-risk HPV genotypes.

Mus musculus Papillomavirus 1: a New Frontier in Animal Models of Papillomavirus Pathogenesis

Animal models of viral pathogenesis are essential tools in human disease research. Human papillomaviruses (HPVs) are a significant public health issue due to their widespread sexual transmission and oncogenic potential. Infection-based models of papillomavirus pathogenesis have been complicated by their strict species and tissue specificity. In this Gem, we discuss the discovery of a murine papillomavirus, Mus musculus papillomavirus 1 (MmuPV1), and how its experimental use represents a major advancement in models of papillomavirus-induced pathogenesis/carcinogenesis, and their transmission.

Multiple regions of E6AP (UBE3A) contribute to interaction with papillomavirus E6 proteins and the activation of ubiquitin ligase activity

The HECT domain E3 ubiquitin ligase E6AP (UBE3A) is critical for the development of human papillomavirus (HPV) associated cancers, the neurodevelopment disorder Angelman Syndrome, and some cases of autism spectrum disorders. How E6AP recognizes its cellular targets and how its ubiquitin ligase activity is triggered remain poorly understood, and HPV E6 proteins are models for these processes. We examined diverse E6 proteins from human and non-human papillomaviruses and identified two different modes of interaction between E6 and E6AP. In Type I interactions, E6 can interact directly with the LXXLL peptide motif alone of E6AP (isolated from the rest of E6AP), and then recruit cellular substrates such as p53. In Type II interactions, E6 proteins require additional auxiliary regions of E6AP in either the amino terminus or in the carboxy-terminal HECT domain to interact with the LXXLL peptide motif of E6AP. A region of E6AP amino-terminal to the LXXLL peptide motif both augments association with E6 proteins and is required for E6 proteins to trigger ubiquitin ligase activity in the carboxy-terminal HECT ubiquitin ligase domain of E6AP. In Type I interactions, E6 can associate with E6AP and recruit p53, but a Type II interaction is required for the degradation of p53 or NHERF1. Interestingly, different E6 proteins varied in E6AP auxiliary regions that contributed to enhanced association, indicating evolutionary drift in the formation of Type II interactions. This classification of E6-E6AP interaction types and identification of a region in the E6AP amino terminus that is important for both E6 association and stimulation of ubiquitin ligase activity will inform future structural data of the E6-E6AP complex and future studies aiming to interfere with the activity of the E6-E6AP complex.

Complete Genome Sequences of Six Novel Macaca mulatta Papillomavirus Types Isolated from Genital Sites of Rhesus Monkeys in Hong Kong SAR, China

The complete genomes of six Macaca mulatta papillomavirus types isolated from genital sites of rhesus monkeys were characterized, and less than 72% identity with the complete L1 genes of known papillomaviruses was found. Macaca mulatta papillomavirus type 2 (MmPV2), MmPV3, and MmPV6 cluster into the genus Alphapapillomavirus, and MmPV4, MmPV5, and MmPV7 cluster into the genus Gammapapillomavirus.

Association of papillomavirus E6 proteins with either MAML1 or E6AP clusters E6 proteins by structure, function, and evolutionary relatedness

Papillomavirus E6 proteins bind to LXXLL peptide motifs displayed on targeted cellular proteins. Alpha genus HPV E6 proteins associate with the cellular ubiquitin ligase E6AP (UBE3A), by binding to an LXXLL peptide (ELTLQELLGEE) displayed by E6AP, thereby stimulating E6AP ubiquitin ligase activity. Beta, Gamma, and Delta genera E6 proteins bind a similar LXXLL peptide (WMSDLDDLLGS) on the cellular transcriptional co-activator MAML1 and thereby repress Notch signaling. We expressed 45 different animal and human E6 proteins from diverse papillomavirus genera to ascertain the overall preference of E6 proteins for E6AP or MAML1. E6 proteins from all HPV genera except Alpha preferentially interacted with MAML1 over E6AP. Among animal papillomaviruses, E6 proteins from certain ungulate (SsPV1 from pigs) and cetacean (porpoises and dolphins) hosts functionally resembled Alpha genus HPV by binding and targeting the degradation of E6AP. Beta genus HPV E6 proteins functionally clustered with Delta, Pi, Tau, Gamma, Chi, Mu, Lambda, Iota, Dyokappa, Rho, and Dyolambda E6 proteins to bind and repress MAML1. None of the tested E6 proteins physically and functionally interacted with both MAML1 and E6AP, indicating an evolutionary split. Further, interaction of an E6 protein was insufficient to activate degradation of E6AP, indicating that E6 proteins that target E6AP co-evolved to separately acquire both binding and triggering of ubiquitin ligase activation. E6 proteins with similar biological function clustered together in phylogenetic trees and shared structural features. This suggests that the divergence of E6 proteins from either MAML1 or E6AP binding preference is a major event in papillomavirus evolution.

Papillomaviruses are a large family of viruses with great medical and veterinary importance. This study explores the viral E6 oncoproteins from diverse papillomavirus genera to determine how E6 distinguishes in interaction between cellular proteins. E6 proteins have been previously found to interact with a ubiquitin ligase called E6AP and thereby target particular cellular proteins for degradation, or to interact with MAML family proteins to repress Notch signaling and thereby alter cellular differentiation. It has been unclear if diverse families of papillomavirus E6 proteins interact with only E6AP or MAML (or possibly both), how E6 distinguishes between these interactions, and if interaction of E6 with E6AP is coupled to ubiquitin ligase activation. We find here that none of the tested E6 proteins physically and functionally interacted with both E6AP and MAML1, indicating an evolutionary split that clustered E6 proteins by sequence similarity analysis. Currently, the categorization of papillomaviruses is complex, with thirty-eight genera so far described. This study establishes an early evolutionary split among most papillomavirus genera between those viruses that encode E6 proteins that physically and functionally associate with MAML compared to E6AP. This provides a structural and functional basis for categorizing most currently described papillomaviruses into two major functional groups.

ORONASAL SQUAMOUS CELL CARCINOMAS IN FRANÇOIS' LANGURS (TRACHYPITHECUS FRANCOISI)

Squamous cell carcinomas (SCCs) are common oronasal tumors in nonhuman primates. In this study, 11 cases of oronasal SCC in François' langurs ( Trachypithecus francoisi ) are described. Five initial cases were discovered on review of the North American François' langur studbook, with a potential familial pattern observed. The studbook was used to identify related individuals, and records were requested for review. Six additional cases were documented, and samples from all cases were submitted for microscopic review, as well as polymerase chain reaction (PCR), immunohistochemistry (IHC), and in situ hybridization (ISH), for generic papillomaviruses and PCR for herpesviruses because either virus may cause SCC in humans and other nonhuman primates. Affected langurs commonly presented with facial swelling or ocular discharge but frequently did not have clinical signs, and carcinomas were diagnosed during routine examinations. Carcinomas were located in the oral or nasal cavities affecting the oral mucosa, tongue, hard palate, or oropharynx. Histologically, SCCs comprised anastomosing cords and nests of neoplastic epithelial cells that differentiated synchronously and asynchronously from peripheral basal type cells to central squamous-type cells and were occasionally oriented around accumulations of necrotic cell debris. Nuclear pleomorphism, anisokaryosis, prominent nucleoli, occasional mitoses, and a scirrhous response were common features. All animals tested negative for both viruses, except two langurs that were positive for generic papillomavirus by PCR, but no papillomavirus was detected by either IHC or ISH. In most cases, affected animals died within 5 mo of diagnosis.

First New World Primate Papillomavirus Identification in the Atlantic Forest, Brazil: Alouatta guariba papillomavirus 1

We report here the complete genome sequence of the first papillomavirus detected in a New World primate, howler monkey, Alouatta guariba clamitans papillomavirus 1 (AgPV1), from the Atlantic Forest in São Paulo State, Brazil.

In vitro and Animal Models for Antiviral Therapy in Papillomavirus Infections

The need for antiviral therapies for papillomavirus infections is well recognized but the difficulties of reproducing the infectious cycle of papillomaviruses in vitro has hindered our understanding of virus-cell interactions and the regulation of viral gene expression during permissive growth. Recent advances in understanding the temporal expression and function of papillomavirus proteins has enabled consideration of a targeted approach to papillomavirus chemotherapy and in particular the inhibition of viral replication by targeting the E1 and E2 proteins. There are in vitro culture systems available for the screening of new chemotherapeutic agents, since significant advances have been made with culture systems which promote epithelial differentiation in vitro. However, to date, there are no published data which show that virions generated in vitro can infect keratinocytes and initiate another round of replication in vitro. In vivo animal models are therefore necessary to assess the efficacy of antivirals in preventing and treating viral infection, particularly for the low-risk genital viruses which are on the whole refractory to culture in vitro. Although papillomaviruses affect a wide variety of hosts in a species-specific manner, the animals most useful for modelling papillomavirus infections include the rabbit, ox, mouse, dog, horse, primate and sheep. The ideal animal model should be widely available, easy to house and handle, be large enough to allow for adequate tissue sampling, develop lesions on anatomical sites comparable with those in human diseases and these lesions should be readily accessible for monitoring and ideally should yield large amounts of infectious virus particles for use in both in vivo and in vitro studies. The relative merits of the various papillomavirus animal models available in relation to these criteria are discussed.

The Human Papillomavirus E6 PDZ Binding Motif: From Life Cycle to Malignancy

Cancer-causing HPV E6 oncoproteins are characterized by the presence of a PDZ binding motif (PBM) at their extreme carboxy terminus. It was long thought that this region of E6 had a sole function to confer interaction with a defined set of cellular substrates. However, more recent studies have shown that the E6 PBM has a complex pattern of regulation, whereby phosphorylation within the PBM can regulate interaction with two classes of cellular proteins: those containing PDZ domains and the members of the 14-3-3 family of proteins. In this review, we explore the roles that the PBM and its ligands play in the virus life cycle, and subsequently how these can inadvertently contribute towards the development of malignancy. We also explore how subtle alterations in cellular signal transduction pathways might result in aberrant E6 phosphorylation, which in turn might contribute towards disease progression.

Animal papillomaviruses

We provide an overview of the host range, taxonomic classification and genomic diversity of animal papillomaviruses. The complete genomes of 112 non-human papillomavirus types, recovered from 54 different host species, are currently available in GenBank. The recent characterizations of reptilian papillomaviruses extend the host range of the Papillomaviridae to include all amniotes. Although the genetically diverse papillomaviruses have a highly conserved genomic lay-out, deviations from this prototypic genome organization are observed in several animal papillomaviruses, and only the core ORFs E1, E2, L2 and L1 are present in all characterized papillomavirus genomes. The discovery of papilloma-polyoma hybrids BPCV1 and BPCV2, containing a papillomaviral late region but an early region encoding typical polyomaviral nonstructural proteins, and the detection of recombination breakpoints between the early and late coding regions of cetacean papillomaviruses, could indicate that early and late gene cassettes of papillomaviruses are relatively independent entities that can be interchanged by recombination.

Classification of papillomaviruses (PVs) based on 189 PV types and proposal of taxonomic amendments

We present an expansion of the classification of the family Papillomaviridae, which now contains 29 genera formed by 189 papillomavirus (PV) types isolated from humans (120 types), non-human mammals, birds and reptiles (64, 3 and 2 types, respectively). To accommodate the number of PV genera exceeding the Greek alphabet, the prefix "dyo" is used, continuing after the Omega-PVs with Dyodelta-PVs. The current set of human PVs is contained within five genera, whereas mammalian, avian and reptile PVs are contained within 20, 3 and 1 genera, respectively. We propose standardizations to the names of a number of animal PVs. As prerequisite for a coherent nomenclature of animal PVs, we propose founding a reference center for animal PVs. We discuss that based on emerging species concepts derived from genome sequences, PV types could be promoted to the taxonomic level of species, but we do not recommend implementing this change at the current time.

Genomic diversity and interspecies host infection of alpha12 Macaca fascicularis papillomaviruses (MfPVs)

Alpha human papillomaviruses (HPVs) are among the most common sexually transmitted agents of which a subset causes cervical neoplasia and cancer in humans. Alpha-PVs have also been identified in non-human primates although few studies have systematically characterized such types. We cloned and characterized 10 distinct types of PVs from exfoliated cervicovaginal cells from different populations of female cynomolgus macaques (Macaca fascicularis) originating from China and Indonesia. These include 5 novel genotypes and 5 previously identified genotypes found in rhesus (Macaca mulatta) (RhPV-1, RhPV-a, RhPV-b and RhPV-d) and cynomolgus macaques (MfPV-a). Type-specific primers were designed to amplify the complete PV genomes using an overlapping PCR method. Four MfPVs were associated with cervical intraepithelial neoplasia (CIN). The most prevalent virus type was MfPV-3 (formerly RhPV-d), which was identified in 60% of animals with CIN. In addition, the complete genomes of variants of MfPV-3 and RhPV-1 were characterized. These variants are 97.1% and 97.7% similar across the L1 nucleotide sequences with the prototype genomes, respectively. Sequence comparisons and phylogenetic analyses indicate that these novel MfPVs cluster together within the alpha12 PV species closely related to the alpha9 (e.g., HPV16) and alpha11 species (e.g., HPV34), and all share a most recent common ancestor. Our data expand the molecular diversity of non-human primate PVs and suggest a recent expansion of alpha-PV species groups. Moreover, identification of an overlapping set of MfPVs in rhesus and cynomolgus macaques indicates that non-human primate alpha-PVs might not be strictly species-specific and may represent past interspecies infection.

Human and primate tumour viruses use PDZ binding as an evolutionarily conserved mechanism of targeting cell polarity regulators

A unique feature of the cancer-causing mucosotropic human papillomaviruses (HPVs) is the ability of their E6 proteins to interact with a number of PDZ domain-containing cellular substrates, including the cell polarity regulators hDlg and hScrib. These interactions are essential for the ability of these viruses to induce malignant progression. Rhesus papillomaviruses (RhPV) are similar to their human counterparts in that they also cause anogenital malignancy in their host, the Rhesus Macaque. However, unlike HPV E6, the RhPV E6 has no PDZ-binding motif. We now show that such a motif is present on the RhPV E7 oncoprotein. This motif specifically confers PDZ-binding activity and directs the interaction of RhPV E7 with the cell polarity regulator Par3, which it targets for proteasome-mediated degradation. These results demonstrate an amazing evolutionary conservation of function between the RhPV and the HPV oncoproteins, where both target proteins of the same cell polarity control network, although through different components and pathways.

Papillomavirus infections--a major cause of human cancers

The papillomavirus family represents a remarkably heterogeneous group of viruses. At present, 77 distinct genotypes have been identified in humans and partial sequences have been obtained from more than 30 putative novel genotypes. Geographic differences in base composition of individual genotypes are generally small and suggest a low mutation rate and thus an ancient origin of today's prototypes. The relatively small size of the genome permitted an analysis of individual gene functions and of interactions of viral proteins with host cell components. Proliferating cells contain the viral genome in a latent form, large scale viral DNA replication, as well as translation and functional activity of late viral proteins, and viral particle assembly are restricted to differentiating layers of skin and mucosa. In humans papillomavirus infections cause a variety of benign proliferations: warts, epithelial cysts, intraepithelial neoplasias, anogenital, oro-laryngeal and -pharyngeal papillomas, keratoacanthomas and other types of hyperkeratoses. Their involvement in the etiology of some major human cancers is of particular interest: specific types (HPV 16, 18 and several others) have been identified as causative agents of at least 90% of cancers of the cervix and are also linked to more than 50% of other anogenital cancers. These HPV types are considered as 'high risk' infections. Their E6/E7 oncoproteins stimulate cell proliferation by activating cyclins E and A, and interfere with the functions of the cellular proteins RB and p53. The latter interaction appears to be responsible for their mutagenic and aneuploidizing activity as an underlying principle for the progression of these HPV-containing lesions and the role of high risk HPV types as solitary carcinogens. In non-transformed human keratinocytes transcription and function of viral oncoproteins is controlled by intercellular and intracellular signalling cascades, their interruption emerges as a precondition for immortalization and malignant growth. Recently, novel and known HPV types have also been identified in a high percentage of non-melanoma skin cancers (basal and squamous cell carcinomas). Similar to observations in patients with a rare hereditary condition, epidermodysplasia verruciformis, characterized by an extensive verrucosis and development of skin cancer, basal and squamous cell carcinomas develop preferentially in light-exposed sites. This could suggest an interaction between a physical carcinogen (UV-part of the sunlight) and a 'low risk' (non-mutagenic) papillomavirus infection. Reports on the presence of HPV infections in cancers of the oral cavity, the larynx, and the esophagus further emphasize the importance of this virus group as proven and suspected human carcinogens.

Human papillomavirus type 13 and pygmy chimpanzee papillomavirus type 1: comparison of the genome organizations

Human papillomavirus type 13(HPV-13) is associated with oral focal epithelial hyperplasia (FEH) in humans. A recent epidemic of a FEH-like disease in a pygmy chimpanzee (Pan paniscus) colony allowed us to clone a novel papillomavirus genome. To assess the homology between HPV-13 and the pygmy chimpanzee papillomavirus type 1 (PCPV-1), the complete nucleotide sequences of both FEH-related viruses were determined. In both viruses, all eight major open reading frames were located on one strand and the genomic organization was similar to that of other mucosal papillomaviruses. The genomes of PCPV-1 and HPV-13 showed extensive overall sequence homology (85%). They could be classified, using phylogenetic analysis, together with HPV types 6, 11, 43, and 44 in a group associated with benign orogenital lesions. These data indicate that two phylogenetically related papillomaviruses can elicit similar pathology in different primate host species, reflecting viral genomic similarities.

During negative regulation of the human papillomavirus-16 E6 promoter, the viral E2 protein can displace Sp1 from a proximal promoter element

The principal early promoter of human papillomaviruses (HPVs), designated P97 in the case of HPV-16, contains four characteristically aligned cis-responsive elements, namely one binding site for Sp1, two for the viral E2 proteins, and the TATA box. The Sp1 binding site is needed to mediate activation of P97 by the remote epithelial-specific enhancer, and the two E2 binding sites contribute to a negative feedback-loop of viral gene expression. The Sp1 consensus motif and the TATA-box distal E2 binding site are spaced in all genital papillomaviruses by a single nucleotide. We show here that at physiological concentrations, the binding of E2 proteins and Sp1 are mutually exclusive events, since a bandshift analysis with nuclear extracts from ID13, a mouse cell line transformed by BPV-1, showed only the E2 or the Sp1 bandshift, but no complex indicative of the concomitant binding of both factors. Increasing concentrations of in vitro translated E2 protein compete efficiently with the Sp1 factor for binding to an oligonucleotide containing both binding sites. Interference between Sp1 and E2 protein binding is apparently relevant for P97 repression in vivo, since a mutational analysis revealed that both E2 binding sites are necessary for negative transcriptional regulation: Alone, neither the distal site, where E2 protein can induce Sp1 displacement, nor the proximal site, where E2 protein interferes with formation and function of the pre-initiation complex, have a significant effect, but two functional E2 binding sites lead to repression of P97.

Rhesus papillomavirus type 1 cooperates with activated ras in transforming primary epithelial rat cells independent of dexamethasone

Rhesus Papillomavirus type 1 (RhPV-1) was recently cloned from a rhesus monkey lymph node metastasis of a penile squamous cell carcinoma. In this paper, we demonstrate that RhPV-1 cooperates with the activated ras oncogene to transform primary cells at a level comparable to human papillomavirus type 16. The viral DNAs were cloned such that their expression was under the control of their natural promoter elements. Unlike human papillomavirus type 16, RhPV-1 DNA cooperated with ras independently of the hormone dexamethasone. However, dexamethasone did have a positive influence on the ability of some RhPV-1 cotransformed cells to grow in soft-agar assays. The transformed cells are highly tumorigenic in vivo in nude mice.