Papillomavirus E1 proteins: form, function, and features

Case report: Mixed infection of bovine papillomaviruses associated with squamous papilloma of the upper alimentary tract in a dairy cow

Bovine papillomavirus (BPV) infection can induce neoplastic lesions in both cutaneous and mucosal epithelia in cattle. This study describes the BPV types associated with proliferative lesions with diverse histopathological features present in the upper alimentary tract of a dairy cow suffering from chronic diarrhea from Midwestern Brazil. At autopsy, warts and plaques composed of multiple spherical nodules were observed in the esophageal mucosa, the areas surrounding and constricting the opening of the cardia, and the rumen pillars. One esophageal papillomatous proliferative lesion and a smooth-surfaced proliferative lesion located at the rumen entrance were evaluated by histopathological and molecular analyses. PCR amplification of partial fragments of the BPV L1 and E1 genes was performed followed by sequencing of the obtained amplicons. Upon histopathological evaluation, the esophageal lesion was classified as a squamous papilloma, whereas the other ruminal proliferative lesion consisted of a fibropapilloma. Direct sequencing of PCR products obtained from ruminal fibropapilloma DNA revealed the presence of BPV2. Sequencing of inserts from selected clones containing partial fragments of the BPV L1 and E1 genes revealed a mixed infection of BPV types 2 and 4 in the esophageal squamous papilloma. The findings reported in our investigation reinforce the association of BPV with benign lesions of the bovine alimentary tract in both single and mixed infections, as previously demonstrated to occur in a buffalo. In addition, this report represents the documentation of the occurrence of massive alimentary papillomatosis associated with BPV types 2 and 4 in cattle raised on lands without infestation by bracken fern in Midwestern Brazil.

Roles of Nucleoporin RanBP2/Nup358 in Acute Necrotizing Encephalopathy Type 1 (ANE1) and Viral Infection

Ran Binding Protein 2 (RanBP2 or Nucleoporin358) is one of the main components of the cytoplasmic filaments of the nuclear pore complex. Mutations in the RANBP2 gene are associated with acute necrotizing encephalopathy type 1 (ANE1), a rare condition where patients experience a sharp rise in cytokine production in response to viral infection and undergo hyperinflammation, seizures, coma, and a high rate of mortality. Despite this, it remains unclear howRanBP2 and its ANE1-associated mutations contribute to pathology. Mounting evidence has shown that RanBP2 interacts with distinct viruses to regulate viral infection. In addition, RanBP2 may regulate innate immune response pathways. This review summarizes recent advances in our understanding of how mutations in RANBP2 contribute to ANE1 and discusses how RanBP2 interacts with distinct viruses and affects viral infection. Recent findings indicate that RanBP2 might be an important therapeutic target, not only in the suppression of ANE1-driven cytokine storms, but also to combat hyperinflammation in response to viral infections.

Human Papillomaviruses as Infectious Agents in Gynecological Cancers―Oncogenic Properties of Viral Proteins

Human papillomaviruses (HPVs), which belong to the Papillomaviridae family, constitute a group of small nonenveloped double-stranded DNA viruses. HPV has a small genome that only encodes a few proteins, and it is also responsible for 5% of all human cancers, including cervical, vaginal, vulvar, penile, anal, and oropharyngeal cancers. HPV types may be classified as high- and low-risk genotypes (HR-HPVs and LR-HPVs, respectively) according to their oncogenic potential. HR-HPV 16 and 18 are the most common types worldwide and are the primary types that are responsible for most HPV-related cancers. The activity of the viral E6 and E7 oncoproteins, which interfere with critical cell cycle points such as suppressive tumor protein p53 (p53) and retinoblastoma protein (pRB), is the major contributor to HPV-induced neoplastic initiation and progression of carcinogenesis. In addition, the E5 protein might also play a significant role in tumorigenesis. The role of HPV in the pathogenesis of gynecological cancers is still not fully understood, which indicates a wide spectrum of potential research areas. This review focuses on HPV biology, the distribution of HPVs in gynecological cancers, the properties of viral oncoproteins, and the molecular mechanisms of carcinogenesis.

HPV-mediated Cervical Cancer: A Systematic review on Immunological Basis, Molecular Biology and Immune evasion mechanisms

BACKGROUND

Human papillomavirus (HPV), one of the most frequently transmitted viruses globally, causing several malignancies including cervical cancer.

AIM

Owing to their unique pathogenicity HPV viruses can persist in the host organism for a longer duration than other virus types, to complete their lifecycle. During its association with the host, HPV causes various pathological conditions affecting the immune system by evading the host immune- mechanisms leading to the progression of various diseases, including cancer.

METHOD

To date, ~ 150 serotypes were identified, and certain high-risk HPV types are known to be associated with genital warts and cervical cancer. As of now, two prophylactic vaccines are in use for the treatment of HPV infection, however, no effective antiviral drug is available for HPV-associated disease/infections. Numerous clinical and laboratory studies are being investigated to formulate an effective and specific vaccine again HPV infections and associated diseases.

RESULT

As the immunological basis of HPV infection and associated disease progress persist indistinctly, deeper insights on immune evasion mechanism and molecular biology of disease would aid in developing an effective vaccine.

CONCLUSION

Thus this review focuses, aiming a systematic review on the immunological aspects of HPV-associated cervical cancer by uncovering immune evasion strategies adapted by HPV.

Maternal HPV Infection: Effects on Pregnancy Outcome

The human papilloma virus (HPV) infection, caused by a ubiquitous virus typically transmitted through the direct contact of infected organs, either through the skin or mucosa, is the most common sexually transmitted infection, placing young women at a high risk of contracting it. Although the vast majority of cases spontaneously clear within 1-2 years, persistent HPV infection remains a serious concern, as it has repeatedly been linked to the development of multiple malignancies, including cervical, anogenital, and oropharyngeal cancers. Additionally, more recent data suggest a harmful effect of HPV infection on pregnancy. As the maternal hormonal environment and immune system undergo significant changes during pregnancy, the persistence of HPV is arguably favored. Various studies have reported an increased risk of adverse pregnancy outcomes among HPV-positive women, with the clinical impact encompassing a range of conditions, including preterm birth, miscarriage, pregnancy-induced hypertensive disorders (PIHD), intrauterine growth restriction (IUGR), low birth weight, the premature rupture of membranes (PROM), and fetal death. Therefore, understanding the mechanisms employed by HPV that negatively impact pregnancy and assessing potential approaches to counteract them would be of interest in the quest to optimize pregnancy outcomes and improve child survival and health.

Whole Genomic Analysis and Comparison of Two Canine Papillomavirus Type 9 Strains in Malignant and Benign Skin Lesions

Papillomaviruses (PVs) usually cause benign proliferative lesions in the stratified epithelium of various animal species. However, some high-risk types of PVs have been proven to lead to malignant transformations. In dogs, several canine papillomaviruses (CPVs) have been identified in malignant lesions and are suggested as one of the risk factors for the development of squamous cell carcinomas (SCCs). In the present study, the full genomes of two CPV9 strains from recurrent SCCs of Dog 1 and skin viral papilloma (viral plaque) of Dog 2 were sequenced. Alignment of the two CPV9 sequences with the genome of the reference CPV9 strain (accession no. JF800656.1) derived from a solitary pigmented plaque was performed. Compared with the reference strain, a 27 bp in-frame insertion in the E1 gene was identified in both CPV9 strains in this study. In comparison with the CPV9 strains derived from benign lesions, the CPV9 from the SCCs of Dog 1 exhibited a 328 bp deletion at the 3′ end of the E2 and spacer sequence, which encoded a truncated deduced E2 protein and a chimeric E8^E2 protein. However, there was no difference in the mRNA expression levels of viral oncoproteins of E6 and E7 between the two CPV9 cases, suggesting that the oncogenesis of CPV9 for malignant transformation might be different from that of human papillomaviruses. The roles of E2 and E8^E2 deleted CPV9 in the oncogenesis of benign and malignant lesions should be further investigated.

Structure, Genome, Infection Cycle and Clinical Manifestations Associated with Human Papillomavirus

A small, non-enveloped, obligatory parasite, Human papillomavirus (HPV) is known to be the cause of a range of malignancies. These entail benign infections like genital warts as well as malignant, life-threatening conditions such as cervical cancer. Since a very high mortality rate is associated with HPV caused cancers (cervical cancer is a 2nd leading cause of death caused due to cancer among women globally), there is an escalating need to understand and search for ways to combat such medical conditions. Under the same light, the given article provides an insight into the world of this versatile pathogen. Distinct aspects related to HPV have been discussed here. Emphasis has been laid upon the composition, function and assembly of capsid proteins (structural studies) and various genetic elements and their gene products (genomic studies). The essence of the mechanism behind the development of persistent infection and modes responsible for the transmission of the infectious particles has been briefly covered. Finally, the review outlines various infections and diseases caused by HPV with a major focus on their clinical and histological manifestations.

Emerging Functions of Human IFIT Proteins in Cancer

Interferon-induced protein with tetratricopeptide repeats (IFIT) genes are prominent interferon-stimulated genes (ISGs). The human IFIT gene family consists of four genes named IFIT1, IFIT2, IFIT3, and IFIT5. The expression of IFIT genes is very low in most cell types, whereas their expression is greatly enhanced by interferon treatment, viral infection, and pathogen-associated molecular patterns (PAMPs). The proteins encoded by IFIT genes have multiple tetratricopeptide repeat (TPR) motifs. IFIT proteins do not have any known enzymatic roles. However, they execute a variety of cellular functions by mediating protein-protein interactions and forming multiprotein complexes with cellular and viral proteins through their multiple TPR motifs. The versatile tertiary structure of TPR motifs in IFIT proteins enables them to be involved in distinct biological functions, including host innate immunity, antiviral immune response, virus-induced translation initiation, replication, double-stranded RNA signaling, and PAMP recognition. The current understanding of the IFIT proteins and their role in cellular signaling mechanisms is limited to the antiviral immune response and innate immunity. However, recent studies on IFIT protein functions and their involvement in various molecular signaling mechanisms have implicated them in cancer progression and metastasis. In this article, we focused on critical molecular, biological and oncogenic functions of human IFIT proteins by reviewing their prognostic significance in health and cancer. Research suggests that IFIT proteins could be novel therapeutic targets for cancer therapy.

Current strategies against persistent human papillomavirus infection (Review)

Human papillomavirus (HPV) is the most common sexually transmitted infection, exhibiting a tropism for the epidermis and mucosae. The link between persistent HPV infection and malignancies involving the anogenital tract as well as the head and neck has been well‑established, and it is estimated that HPV‑related cancers involving various anatomical sites account for 4.5% of all human cancers. Current prophylactic vaccines against HPV have enabled the prevention of associated malignancies. However, the sizeable population base of current infection in whom prophylactic vaccines are not applicable, certain high‑risk HPV types not included in vaccines, and the vast susceptible population in developing countries who do not have access to the costly prophylactic vaccines, put forward an imperative need for effective therapies targeting persistent infection. In this article, the life cycle of HPV, the mechanisms facilitating HPV evasion of recognition and clearance by the host immune system, and the promising therapeutic strategies currently under investigation, particularly antiviral drugs and therapeutic vaccines, are reviewed.

Fecal Viral Diversity of Captive and Wild Tasmanian Devils Characterized Using Virion-Enriched Metagenomics and Metatranscriptomics

The Tasmanian devil is an iconic Australian marsupial that has suffered an 80% population decline due to a contagious cancer, devil facial tumor disease, along with other threats. Until now, viral discovery in this species has been confined to one gammaherpesvirus (dasyurid herpesvirus 2 [DaHV-2]), for which captivity was identified as a significant risk factor. Our discovery of 24 novel marsupial-associated RNA and DNA viruses, and that viral diversity is lower in captive than in wild devils, has greatly expanded our knowledge of gut-associated viruses in devils and provides important baseline information that will contribute to the conservation and captive management of this endangered species. Our results also revealed that a combination of virion-enriched metagenomics and metatranscriptomics may be a more comprehensive approach for virome characterization than either method alone. Our results thus provide a springboard for continuous improvements in the way we study complex viral communities.

The Tasmanian devil is an endangered carnivorous marsupial threatened by devil facial tumor disease (DFTD). While research on DFTD has been extensive, little is known about viruses in devils and whether any are of potential conservation relevance for this endangered species. Using both metagenomics based on virion enrichment and sequence-independent amplification (virion-enriched metagenomics) and metatranscriptomics based on bulk RNA sequencing, we characterized and compared the fecal viromes of captive and wild devils. A total of 54 fecal samples collected from two captive and four wild populations were processed for virome characterization using both approaches. In total, 24 novel marsupial-related viruses, comprising a sapelovirus, astroviruses, rotaviruses, picobirnaviruses, parvoviruses, papillomaviruses, polyomaviruses, and a gammaherpesvirus, were identified, as well as known mammalian pathogens such as rabbit hemorrhagic disease virus 2. Captive devils showed significantly lower viral diversity than wild devils. Comparison of the two virus discovery approaches revealed substantial differences in the number and types of viruses detected, with metatranscriptomics better suited for RNA viruses and virion-enriched metagenomics largely identifying more DNA viruses. Thus, the viral communities revealed by virion-enriched metagenomics and metatranscriptomics were not interchangeable and neither approach was able to detect all viruses present. An integrated approach using both virion-enriched metagenomics and metatranscriptomics constitutes a powerful tool for obtaining a complete overview of both the taxonomic and functional profiles of viral communities within a sample.

IMPORTANCE The Tasmanian devil is an iconic Australian marsupial that has suffered an 80% population decline due to a contagious cancer, devil facial tumor disease, along with other threats. Until now, viral discovery in this species has been confined to one gammaherpesvirus (dasyurid herpesvirus 2 [DaHV-2]), for which captivity was identified as a significant risk factor. Our discovery of 24 novel marsupial-associated RNA and DNA viruses, and that viral diversity is lower in captive than in wild devils, has greatly expanded our knowledge of gut-associated viruses in devils and provides important baseline information that will contribute to the conservation and captive management of this endangered species. Our results also revealed that a combination of virion-enriched metagenomics and metatranscriptomics may be a more comprehensive approach for virome characterization than either method alone. Our results thus provide a springboard for continuous improvements in the way we study complex viral communities.

Vaccination with human papillomavirus-18 E1 protein plus α-galactosyl-ceramide induces CD8+ cytotoxic response and impairs the growth of E1-expressing tumors

CD8+ T cell-mediated immune response plays a major role in the clearance of virus-infected cells, including human papillomavirus (HPV). The effective treatment of women with normal cytology but persistent high risk-HPV infection or with low-grade intraepithelial lesions could take advantage of novel strategies based on vaccination with viral immunological targets with a wide spectrum of cross-protection. The helicase E1, expressed early during viral replication in HPV infection, is among the most conserved papillomavirus proteins, which makes it a good vaccine candidate. In the present study, we examined E1-specific CD8+ T cell and NK immune responses in a mouse model with α-galactosylceramide (α-GalCer) as an adjuvant. We found that mice immunized with E1 combined with α-GalCer elicited an E1-specific CD8+ T and NK cell cytotoxic responses, which correlated with growth inhibition of grafted melanoma B16-F0 cells expressing E1, both in prophylactic and therapeutic protocols.

The HPV16 E1 Carboxyl Domain Provides a Helper Function for Adeno-Associated Virus Replication

BACKGROUND/AIMS

Recombinant adeno-associated virus (rAAV) is now in the clinic, yet production of rAAV remains problematic. We previously determined that human papillomavirus type 16 (HPV16) E1 protein boosts rAAV yields and E1 enhances AAV Rep78's replication-related biochemistries. Here, we deletion-mapped the helper domain within E1 to help glean its mechanism of action.

METHODS

Rep78-E1 interaction was analyzed by Gal4-based yeast two-hybrid (Y2H)-cDNA assay. rAAV DNA replication was studied by AAV/helper plasmid transfection into HEK293 cells and Southern blot. Gene expression analysis was made of AAV and E1 plasmid transfection, cDNA generation, and then quantitative polymerase chain reaction. NCBI protein BLAST was used for the homology analysis.

RESULTS

Gal4-Y2H- cDNA assay found in vivo Rep78-E1-binding activity across E1, but the carboxyl-third (amino acids [aa] 421-649) of E1 contained the predominant DNA replication helper domain. The amino-half of E1 (aa 1-337) inhibited transcription of rep (p5 promoter) and cap (p40, trending lower) from non-replicating helper plasmid by quantitative (q)RT-PCR.

CONCLUSIONS

The aa 421-649 helper domain of HPV16 E1 includes the ATP-binding/helicase region of E1 which boosts rAAV production and has homology with the analogous region of parvovirus NS-1/Rep78 by NCBI protein BLAST, suggesting these biochemistries are responsible for the mechanism of action in E1 helper function.

HPV: Molecular pathways and targets

Infection of high-risk human papillomaviruses (HPVs) is a prerequisite for the development of cervical carcinoma. HPV infections are also implicated in the development of other types of carcinomas. Chronic or persistent infection of HPV is essential but HPV alone is inadequate, additional endogenous or exogenous cues are needed along with HPV to induce cervical carcinogenesis. The strategies that high-risk HPVs have developed in differentiating epithelial cells to reach a DNA-synthesis competent state leading to tumorigenic transformation are basically due to overexpression of the E6 and E7 oncoproteins and the activation of diverse cellular regulatory or signaling pathways that are targeted by them. Moreover, the Wnt/β-catenin/Notch and phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathways are deregulated in various cancers, and have also been implicated in HPV-induced cancers. These are basically related to the "cancer hallmarks," and include sustaining proliferative signals, the evasion of growth suppression and immune destruction, replicative immortality, inflammation, invasion, metastasis and angiogenesis, as well as genome instability, resisting cell death, and deregulation of cellular energetics. These information could eventually aid in identifying or developing new diagnostic, prognostic biomarkers, and may contribute to design more effective targeted therapeutics and treatment strategies. Although surgery, chemotherapy and radiotherapy can cure more than 90% of women with early stage cervical cancer, the recurrent and metastatic disease remains a major cause of cancer mortality. Numerous efforts have been made to design new drugs and develop gene therapies to treat cervical cancer. In recent years, research on treatment strategies has proposed several options, including the role of HPV E5, E6, and E7 oncogenes, which are retained and overexpressed in most of the cervical cancers and whose respective oncoproteins are critical to the induction and maintenance of the malignant phenotype. Other efforts have been focused on antitumor immunotherapy strategies. It is known that during the development of cervical cancer, a cascade of abnormal events is induced, including disruption of cell cycle control, perturbation of antitumor immune response, alteration of gene expression, deregulation of microRNA and cancer stem cell and stemness related markers expression could serve as novel molecular targets for reliable diagnosis and treatment of HPV-positive cancers. However, the search for new proposals for disease control and prevention has brought new findings and approaches in the context of molecular biology indicating innovations and perspectives in the early detection and prevention of the disease. Thus, in this article, we discuss molecular signaling pathways activated by HPV and potential targets or biomarkers for early detection or prevention and the treatment of HPV-associated cancers.

Genomic characterization of the first oral avian papillomavirus in a colony of breeding canaries (Serinus canaria)

Papillomaviruses are non-enveloped, DNA viruses that infect skin and mucosa of a wide variety of vertebrates, causing neoplasias or simply persisting asymptomatically. Avian papillomaviruses, with six fully sequenced genomes, are the second most studied group after mammalian papillomaviruses. In this study, we describe the first oral avian papillomavirus, detected in the tongue of a dead Yorkshire canary (Serinus canaria) and in oral swabs of the same bird and other two live canaries from an aviary in Madrid, Spain. Its genome is 8,071 bp and presents the canonical papillomavirus architecture with six early (E6, E7, E1, E9, E2, E4) and two late open reading frames (L1 and L2) and a long control region between L1 and E6. This new avian papillomavirus L1 gene shares a 64% pairwise identity with FcPV1 L1, so it has been classified as a new species (ScPV1) within the Ethapapillomavirus genus. Although the canary died after showing breathing problems, there is no evidence that the papillomavirus caused those symptoms so it could be part of the oral microbiota of the birds. Hence, future investigations are needed to evaluate the clinical relevance of the virus.

Human papillomaviruses in epigenetic regulations

Human Papillomaviruses (HPVs) are double-stranded DNA viruses, that infect epithelial cells and are etiologically involved in the development of human cancer. Today, over 200 types of human papillomaviruses are known. They are divided into low-risk and high-risk HPVs depending on their potential to induce carcinogenesis, driven by two major viral oncoproteins, E6 and E7. By interacting with cellular partners, these proteins are involved in interdependent viral and cell cycles in stratified differentiating epithelium, and concomitantly induce epigenetic changes in infected cells and those undergoing malignant transformation. E6 and E7 oncoproteins interact with and/or modulate expression of many proteins involved in epigenetic regulation, including DNA methyltransferases, histone-modifying enzymes and subunits of chromatin remodeling complexes, thereby influencing host cell transcription program. Furthermore, HPV oncoproteins modulate expression of cellular micro RNAs. Most of these epigenetic actions in a complex dynamic interplay participate in the maintenance of persistent infection, cell transformation, and development of invasive cancer by a considerable deregulation of tumor suppressor and oncogenes. In this study, we have undertaken to discuss a number of studies concerning epigenetic regulations in HPV-dependent cells and to focus on those that have biological relevance to cancer progression.

HPV disease transmission protection and control

Human papillomaviruses (HPVs) represent a large collection of viral types associated with significant clinical disease of cutaneous and mucosal epithelium. HPV-associated cancers are found in anogenital and oral mucosa, and at various cutaneous sites. Papillomaviruses are highly species and tissue restricted, and these viruses display both mucosotropic, cutaneotropic or dual tropism for epithelial tissues. A subset of HPV types, predominantly mucosal, are also oncogenic and cancers with these HPV types account for more than 200,000 deaths world-wide. Host control of HPV infections requires both innate and adaptive immunity, but the viruses have developed strategies to escape immune detection. Viral proteins can disrupt both innate pathogen-sensing pathways and T-cell based recognition and subsequent destruction of infected tissues. Current treatments to manage HPV infections include mostly ablative strategies in which recurrences are common and only active disease is treated. Although much is known about the papillomavirus life cycle, viral protein functions, and immune responsiveness, we still lack knowledge in a number of key areas of PV biology including tissue tropism, site-specific cancer progression, codon usage profiles, and what are the best strategies to mount an effective immune response to the carcinogenic stages of PV disease. In this review, disease transmission, protection and control are discussed together with questions related to areas in PV biology that will continue to provide productive opportunities of discovery and to further our understanding of this diverse set of human viral pathogens.

Human papillomavirus in oropharyngeal cancer: The changing face of a disease

The last decade has brought about an unexpected rise in oropharyngeal squamous cell carcinoma (OPSCC) primarily in white males from the ages of 40-55years, with limited exposure to alcohol and tobacco. This subset of squamous cell carcinoma (SCC) has been found to be associated with human papillomavirus infection (HPV). Other Head and Neck Squamous Cell carcinoma (HNSCC) subtypes include oral cavity, hypopharyngeal, nasopharyngeal, and laryngeal SCC which tend to be HPV negative. HPV associated oropharyngeal cancer has proven to differ from alcohol and tobacco associated oropharyngeal carcinoma in regards to the molecular pathophysiology, presentation, epidemiology, prognosis, and improved response to chemoradiation therapy. Given the improved survival of patients with HPV associated SCC, efforts to de-intensify treatment to decrease treatment related morbidity are at the forefront of clinical research. This review will focus on the important differences between HPV and tobacco related oropharyngeal cancer. We will review the molecular pathogenesis of HPV related oropharyngeal cancer with an emphasis on new paradigms for screening and treating this disease.

Phosphorylation of bovine papillomavirus E1 by the protein kinase CK2 near the nuclear localization signal does not influence subcellular distribution of the protein in dividing cells

The bovine papillomavirus E1 helicase is essential for viral replication. In dividing cells, DNA replication maintains, but does not increase, the viral genome copy number. Replication is limited by low E1 expression and an E1 nucleocytoplasmic shuttling mechanism. Shuttling is controlled in part by phosphorylation of E1 by cellular kinases. Here we investigate conserved sites for phosphorylation by kinase CK2 within the E1 nuclear localization signal. When these CK2 sites are mutated to either alanine or aspartic acid, no change in replication phenotype is observed, and there is no effect on the subcellular distribution of E1, which remains primarily nuclear. This demonstrates that phosphorylation of E1 by CK2 at these sites is not a factor in regulating viral DNA replication in dividing cells.

Structural basis for DNA strand separation by a hexameric replicative helicase

Hexameric helicases are processive DNA unwinding machines but how they engage with a replication fork during unwinding is unknown. Using electron microscopy and single particle analysis we determined structures of the intact hexameric helicase E1 from papillomavirus and two complexes of E1 bound to a DNA replication fork end-labelled with protein tags. By labelling a DNA replication fork with streptavidin (dsDNA end) and Fab (5′ ssDNA) we located the positions of these labels on the helicase surface, showing that at least 10 bp of dsDNA enter the E1 helicase via a side tunnel. In the currently accepted ‘steric exclusion’ model for dsDNA unwinding, the active 3′ ssDNA strand is pulled through a central tunnel of the helicase motor domain as the dsDNA strands are wedged apart outside the protein assembly. Our structural observations together with nuclease footprinting assays indicate otherwise: strand separation is taking place inside E1 in a chamber above the helicase domain and the 5′ passive ssDNA strands exits the assembly through a separate tunnel opposite to the dsDNA entry point. Our data therefore suggest an alternative to the current general model for DNA unwinding by hexameric helicases.

The epigenetic regulation of autonomous replicons

The discovery of autonomous replicating sequences (ARSs) in Saccharomyces cerevisiae in 1979 was considered a milestone in unraveling the regulation of replication in eukaryotic cells. However, shortly afterwards it became obvious that in Saccharomyces pombe and all other higher organisms ARSs were not sufficient to initiate independent replication. Understanding the mechanisms of replication is a major challenge in modern cell biology and is also a prerequisite to developing application-oriented autonomous replicons for gene therapeutic treatments. This review will focus on the development of non-viral episomal vectors, their use in gene therapeutic applications and our current knowledge about their epigenetic regulation.

Papillomaviruses: Viral evolution, cancer and evolutionary medicine

Papillomaviruses (PVs) are a numerous family of small dsDNA viruses infecting virtually all mammals. PVs cause infections without triggering a strong immune response, and natural infection provides only limited protection against reinfection. Most PVs are part and parcel of the skin microbiota. In some cases, infections by certain PVs take diverse clinical presentations from highly productive self-limited warts to invasive cancers. We propose PVs as an excellent model system to study the evolutionary interactions between the immune system and pathogens causing chronic infections: genotypically, PVs are very diverse, with hundreds of different genotypes infecting skin and mucosa; phenotypically, they display extremely broad gradients and trade-offs between key phenotypic traits, namely productivity, immunogenicity, prevalence, oncogenicity and clinical presentation. Public health interventions have been launched to decrease the burden of PV-associated cancers, including massive vaccination against the most oncogenic human PVs, as well as systematic screening for PV chronic anogenital infections. Anti-PVs vaccines elicit protection against infection, induce cross-protection against closely related viruses and result in herd immunity. However, our knowledge on the ecological and intrapatient dynamics of PV infections remains fragmentary. We still need to understand how the novel anthropogenic selection pressures posed by vaccination and screening will affect viral circulation and epidemiology. We present here an overview of PV evolution and the connection between PV genotypes and the phenotypic, clinical manifestations of the diseases they cause. This differential link between viral evolution and the gradient cancer-warts-asymptomatic infections makes PVs a privileged playground for evolutionary medicine research.

Disruption of Bcl-2 and Bcl-xL by viral proteins as a possible cause of cancer

The Bcl proteins play a critical role in apoptosis, as mutations in family members interfere with normal programmed cell death. Such events can cause cell transformation, potentially leading to cancer. Recent discoveries indicate that some viral proteins interfere with Bcl proteins either directly or indirectly; however, these data have not been systematically described. Some viruses encode proteins that reprogramme host cellular signalling pathways controlling cell differentiation, proliferation, genomic integrity, cell death, and immune system recognition. This review analyses and summarises the existing data and discusses how viral proteins interfere with normal pro- and anti-apoptotic functions of Bcl-2 and Bcl-xL. Particularly, this article focuses on how viral proteins, such as Herpesviruses, HTLV-1, HPV and HCV, block apoptosis and how accumulation of such interference predisposes cancer development. Finally, we discuss possible ways to prevent and treat cancers using a combination of traditional therapies and antiviral preparations that are effective against these viruses.

IGF axis and other factors in HPV-related and HPV-unrelated carcinogenesis (review)

The insulin-like growth factor (IGF) axis promotes the growth of cells, tissues and organs. IGF-1 is mainly produced in the liver but is also secreted from local tissues. In the circulation, IGF-1 is bound to insulin-like binding proteins (IGFBPs), and when released it activates the insulin-like growth factor receptor (IGF-1R). The signal is further transmitted by intracellular signaling pathways leading to gene expression that regulates, among others, cell proliferation and survival. This review presents the IGF axis in the context of cell transformation and cancer development. Aspects involving IGF-1 deficiency and protection from cancer are also briefly described. Furthermore, human papillomaviruses (HPVs) interplaying with IGF axis components in cervical cancer development are described. These small dsDNA viruses are divided into low-risk and high-risk HPVs with regard to the potency of their oncogenic actions; they mainly infect epithelial or mucosal cells. Special attention is drawn to expression of two major HPV oncogenes (E6 and E7) initiating and maintaining cervical carcinogenesis, which is a multistep and multifactorial process; therefore, involvement of additional factors such as mitochondrial DNA changes, sex hormones, retinoic and folic acids are also discussed. Finally, IGF axis components and HPV oncogenes as targets in anticancer treatment are presented which include IGF-1R downregulation, RNA interference and anti-HPV therapeutic vaccines. The review concludes that despite an enormous advancement in research on IGF and HPV-related cancers, more molecular studies and clinical trials are needed before commercialized therapies are widely available for oncology patients.

E1-mediated recruitment of a UAF1-USP deubiquitinase complex facilitates human papillomavirus DNA replication

The human papillomavirus (HPV) E1 helicase promotes viral DNA replication through its DNA unwinding activity and association with host factors. The E1 proteins from anogenital HPV types interact with the cellular WD repeat-containing factor UAF1 (formerly known as p80). Specific amino acid substitutions in E1 that impair this interaction inhibit maintenance of the viral episome in immortalized keratinocytes and reduce viral DNA replication by up to 70% in transient assays. In this study, we determined by affinity purification of UAF1 that it interacts with three deubiquitinating enzymes in C33A cervical carcinoma cells: USP1, a nuclear protein, and the two cytoplasmic enzymes USP12 and USP46. Coimmunoprecipitation experiments indicated that E1 assembles into a ternary complex with UAF1 and any one of these three USPs. Moreover, expression of E1 leads to a redistribution of USP12 and USP46 from the cytoplasm to the nucleus. Chromatin immunoprecipitation studies further revealed that E1 recruits these threes USPs to the viral origin in association with UAF1. The function of USP1, USP12, and USP46 in viral DNA replication was investigated by overproduction of catalytically inactive versions of these enzymes in transient assays. All three dominant negative USPs reduced HPV31 DNA replication by up to 60%, an effect that was specific, as it was not observed in assays performed with a truncated E1 lacking the UAF1-binding domain or with bovine papillomavirus 1 E1, which does not bind UAF1. These results highlight the importance of the USP1, USP12, and USP46 deubiquitinating enzymes in anogenital HPV DNA replication.

IMPORTANCE

Human papillomaviruses are small DNA tumor viruses that induce benign and malignant lesions of the skin and mucosa. HPV types that infect the anogenital tract are the etiological agents of cervical cancer, the majority of anal cancers, and a growing proportion of head-and-neck cancers. Replication of the HPV genome requires the viral protein E1, a DNA helicase that also interacts with host factors to promote viral DNA synthesis. We previously reported that the E1 helicase from anogenital HPV types associates with the WD40 repeat-containing protein UAF1. Here, we show that UAF1 bridges the interaction of E1 with three deubiquitinating enzymes, USP1, USP12, and USP46. We further show that these deubiquitinases are recruited by E1/UAF1 to the viral origin of DNA replication and that overexpression of catalytically inactive versions of these enzymes reduces viral DNA replication. These results highlight the need for an E1-associated deubiquitinase activity in anogenital HPV genome replication.

An optimized yeast cell-free lysate system for in vitro translation of human virus mRNA

Yeast (Saccharomyces cerevisiae) as a model organism has long been established to study various aspects of eukaryotic cellular and molecular biology. Cell-free lysates prepared from different yeast strains have been used as a powerful tool to study eukaryotic protein expression in vitro. Recently, we established a yeast cell-free lysate system for in vitro translation long and short L1 capsid gene mRNAs of human papillomavirus type 58. We were able to significantly improve the translation efficiencies of the viral mRNAs in the established system by optimizing the concentrations of potassium and magnesium and controlling the physiological status of the yeast cells used for lysate preparation. We proved that a single specific amino acid can be rate limiting for translation of a target mRNA. Here, we describe the materials, method, and technique used for the development of an efficient yeast cell-free translation system.

Four novel papillomavirus sequences support a broad diversity among equine papillomaviruses

Papillomaviruses appear to be species-specific pathogens, and it was suggested that each animal species might harbour its own set of papillomaviruses. However, all approaches addressing the underlying evolutionary phenomena still suffer from very limited data about animal papillomaviruses. In case of the horse for example, only three equine papillomaviruses (EcPVs) have been identified. To further address the situation in this host, suspected papillomavirus-associated lesions were tested for EcPV DNA. Four novel EcPV types were detected and their genomes entirely cloned and sequenced. They display the characteristic organization, with early (E) and late (L) regions harbouring the seven classical open reading frames divided by non-coding regions. They were named EcPVs 4, 5, 6 and 7, according to their dissimilarity to other papillomaviruses. Most L1 nucleotide identities were shared with EcPV2 in case of EcPV4 (62 %) and EcPV5 (60 %) or with EcPV3 in case of EcPV6 (70 %) and EcPV7 (71 %). Thus, EcPVs 4 and 5 may establish novel species within the genus Dyoiota, while EcPVs 6 and 7 might fit into the genus Dyorho and belong to the same species as EcPV3. They were found in genital plaques (EcPV4), aural plaques (EcPV5, EcPV6) or penile masses (EcPV7). Interestingly, PCR analysis revealed the DNA of EcPV2 and EcPV4 as well as of EcPV3 and EcPV6 together in the same tissue samples, respectively. In conclusion, the DNA of four novel EcPV types was identified and cloned. They cluster with the known types and support broad genetic EcPV diversity in at least two of the known clades. Furthermore, PCR assays also provide evidence for EcPV co-infections in horses.

CK2 phosphorylation inactivates DNA binding by the papillomavirus E1 and E2 proteins

Papillomaviruses have complex life cycles that are understood only superficially. Although it is well established that the viral E1 and E2 proteins play key roles in controlling viral transcription and DNA replication, how these factors are regulated is not well understood. Here, we demonstrate that phosphorylation by the protein kinase CK2 controls the biochemical activities of the bovine papillomavirus E1 and E2 proteins by modifying their DNA binding activity. Phosphorylation at multiple sites in the N-terminal domain in E1 results in the loss of sequence-specific DNA binding activity, a feature that is also conserved in human papillomavirus (HPV) E1 proteins. The bovine papillomavirus (BPV) E2 protein, when phosphorylated by CK2 on two specific sites in the hinge, also loses its site-specific DNA binding activity. Mutation of these sites in E2 results in greatly increased levels of latent viral DNA replication, indicating that CK2 phosphorylation of E2 is a negative regulator of viral DNA replication during latent viral replication. In contrast, mutation of the N-terminal phosphorylation sites in E1 has no effect on latent viral DNA replication. We propose that the phosphorylation of the N terminus of E1 plays a role only in vegetative viral DNA replication, and consistent with such a role, caspase 3 cleavage of E1, which has been shown to be necessary for vegetative viral DNA replication, restores the DNA binding activity to phosphorylated E1.

Gene- and protein-delivered zinc finger-staphylococcal nuclease hybrid for inhibition of DNA replication of human papillomavirus

Previously, we reported that artificial zinc-finger proteins (AZPs) inhibited virus DNA replication in planta and in mammalian cells by blocking binding of a viral replication protein to its replication origin. However, the replication mechanisms of viruses of interest need to be disentangled for the application. To develop more widely applicable methods for antiviral therapy, we explored the feasibility of inhibition of HPV-18 replication as a model system by cleaving its viral genome. To this end, we fused the staphylococcal nuclease cleaving DNA as a monomer to an AZP that binds to the viral genome. The resulting hybrid nuclease (designated AZP–SNase) cleaved its target DNA plasmid efficiently and sequence-specifically in vitro. Then, we confirmed that transfection with a plasmid expressing AZP–SNase inhibited HPV-18 DNA replication in transient replication assays using mammalian cells. Linker-mediated PCR analysis revealed that the AZP–SNase cleaved an HPV-18 ori plasmid around its binding site. Finally, we demonstrated that the protein-delivered AZP–SNase inhibited HPV-18 DNA replication as well and did not show any significant cytotoxicity. Thus, both gene- and protein-delivered hybrid nucleases efficiently inhibited HPV-18 DNA replication, leading to development of a more universal antiviral therapy for human DNA viruses.

The biology of papillomavirus latency

The presence of viral DNA in the absence of disease has suggested that papillomaviruses, like many other viruses, can exist as latent infections in the skin or other epithelial sites. In animal models, where detailed investigation has been carried out, papillomavirus DNA can be found at sites of previous infection following immune regression, with the site of latent infection being the epithelial basal layer. Such studies suggest that immune surveillance can restrict viral gene expression in the basal and parabasal layers without efficiently suppressing viral genome replication, most probably through the action of memory T-cells in the skin or dermis. Although gradual papillomavirus genome loss appears to occur over time at latent sites, immunosuppression can arrest this, and can lead to an elevation in viral genome copy number in experimental systems. In addition to immune-mediated latency, it appears that a similar situation can be achieved following infection at low virus titres and/or infection at epithelial sites where the virus life cycle is not properly supported. Such silent of asymptomatic infections do not necessarily involve the host immune system and may be controlled by different mechanisms. It appears that virus reactivation can be triggered by mechanical irritation, wounding or by UV irradiation which changes the local environment. Although the duration of papillomavirus latency in humans is not yet known, it is likely that some of the basic principles will resemble those elucidated in these model systems, and that persistence in the absence of disease may be the default outcome for at least some period of time following regression.

Engagement of the ATR-dependent DNA damage response at the human papillomavirus 18 replication centers during the initial amplification

We have previously demonstrated that the human papillomavirus (HPV) genome replicates effectively in U2OS cells after transfection using electroporation. The transient extrachromosomal replication, stable maintenance, and late amplification of the viral genome could be studied for high- and low-risk mucosal and cutaneous papillomaviruses. Recent findings indicate that the cellular DNA damage response (DDR) is activated during the HPV life cycle and that the viral replication protein E1 might play a role in this process. We used a U2OS cell-based system to study E1-dependent DDR activation and the involvement of these pathways in viral transient replication. We demonstrated that the E1 protein could cause double-strand DNA breaks in the host genome by directly interacting with DNA. This activity leads to the induction of an ATM-dependent signaling cascade and cell cycle arrest in the S and G(2) phases. However, the transient replication of HPV genomes in U2OS cells induces the ATR-dependent pathway, as shown by the accumulation of γH2AX, ATR-interacting protein (ATRIP), and topoisomerase IIβ-binding protein 1 (TopBP1) in viral replication centers. Viral oncogenes do not play a role in this activation, which is induced only through DNA replication or by replication proteins E1 and E2. The ATR pathway in viral replication centers is likely activated through DNA replication stress and might play an important role in engaging cellular DNA repair/recombination machinery for effective replication of the viral genome upon active amplification.

Intratypic changes of the E1 gene and the long control region affect ori function of human papillomavirus type 18 variants

A persistent infection with high-risk human papillomavirus (HPV) constitutes the main aetiological factor for cervical cancer development. HPV16 and 18 are the most prevalent types found in cervical cancer worldwide. It has been proposed that HPV intratype variations may result in differences in biological behaviour. Three different HPV18 variants belonging to the Asian Amerindian (AsAi), European (E) and African (Af) branches have been associated with specific histological types of cervical cancer with different relative prognoses, suggesting that HPV18 genomic variations might participate in disease evolution. The E1 viral protein plays a critical role in controlling viral replication and load, requiring interaction with the E2 protein to bind to the long control region (LCR). In this work, we analysed if intratype variations in the LCR and E1 and E2 genes of HPV18 impact ori replication. While the changes found in E2 genes of the tested variants were irrelevant in replication, we found that variations in E1 and LCR in fact affect ori function. It was demonstrated that nucleotide differences in the LCR variants impact ori function. Nevertheless, HPV18 E1 Af gene was mainly involved in the highest ori replication, compared with the E and AsAi E1 variants. Immunofluorescence analysis showed increased levels of Af E1 in the nucleus, correlating with the enhanced ori function. Site-directed mutagenesis revealed that at least two positions in the N-terminal domain of E1 could impact its nuclear accumulation.

Characterization and whole genome analysis of human papillomavirus type 16 e1-1374^63nt variants

BACKGROUND

The variation of the most common Human papillomavirus (HPV) type found in cervical cancer, the HPV16, has been extensively investigated in almost all viral genes. The E1 gene variation, however, has been rarely studied. The main objective of the present investigation was to analyze the variability of the E6 and E1 genes, focusing on the recently identified E1-1374^63nt variant.

METHODOLOGY/PRINCIPAL FINDINGS

Variation within the E6 of 786 HPV16 positive cervical samples was analyzed using high-resolution melting, while the E1-1374^63nt duplication was assayed by PCR. Both techniques were supplemented with sequencing. The E1-1374^63nt duplication was linked with the E-G350 and the E-C109/G350 variants. In comparison to the referent HPV16, the E1-1374^63nt E-G350 variant was significantly associated with lower grade cervical lesions (p = 0.029), while the E1-1374^63nt E-C109/G350 variant was equally distributed between high and low grade lesions. The E1-1374^63nt variants were phylogenetically closest to E-G350 variant lineage (A2 sub-lineage based on full genome classification). The major differences between E1-1374^63nt variants were within the LCR and the E6 region. On the other hand, changes within the E1 region were the major differences from the A2 sub-lineage, which has been historically but inconclusively associated with high grade cervical disease. Thus, the shared variations cannot explain the particular association of the E1-1374^63nt variant with lower grade cervical lesions.

CONCLUSIONS/SIGNIFICANCE

The E1 region has been thus far considered to be well conserved among all HPVs and therefore uninteresting for variability studies. However, this study shows that the variations within the E1 region could possibly affect cervical disease, since the E1-1374^63nt E-G350 variant is significantly associated with lower grade cervical lesions, in comparison to the A1 and A2 sub-lineage variants. Furthermore, it appears that the silent variation 109T>C of the E-C109/G350 variant might have a significant role in the viral life cycle and warrants further study.

Inhibition of human papillomavirus DNA replication by an E1-derived p80/UAF1-binding peptide

The papillomavirus E1 helicase is recruited by E2 to the viral origin, where it assembles into a double hexamer that orchestrates replication of the viral genome. We previously identified the cellular WD40 repeat-containing protein p80/UAF1 as a novel interaction partner of E1 from anogenital human papillomavirus (HPV) types. p80 was found to interact with the first 40 residues of HPV type 31 (HPV31) E1, and amino acid substitutions within this domain abrogated the maintenance of the viral episome in keratinocytes. In this study, we report that these p80-binding substitutions reduce by 70% the ability of E1 to support transient viral DNA replication without affecting its interaction with E2 and assembly at the origin in vivo. Microscopy studies revealed that p80 is relocalized from the cytoplasm to discrete subnuclear foci by E1 and E2. Chromatin immunoprecipitation assays further revealed that p80 is recruited to the viral origin in an E1- and E2-dependent manner. Interestingly, overexpression of a 40-amino-acid-long p80-binding peptide, derived from HPV31 E1, was found to inhibit viral DNA replication by preventing the recruitment of endogenous p80 to the origin. Mutant peptides defective for p80 interaction were not inhibitory, demonstrating the specificity of this effect. Characterization of this E1 peptide by nuclear magnetic resonance (NMR) showed that it is intrinsically disordered in solution, while mapping studies indicated that the WD repeats of p80 are required for E1 interaction. These results provide additional evidence for the requirement for p80 in anogenital HPV DNA replication and highlight the potential of E1-p80 interaction as a novel antiviral target.

Regulation of the nucleocytoplasmic trafficking of viral and cellular proteins by ubiquitin and small ubiquitin-related modifiers

Nucleocytoplasmic trafficking of many cellular proteins is regulated by nuclear import/export signals as well as post-translational modifications such as covalent conjugation of ubiquitin and small ubiquitin-related modifiers (SUMOs). Ubiquitination and SUMOylation are rapid and reversible ways to modulate the intracellular localisation and function of substrate proteins. These pathways have been co-opted by some viruses, which depend on the host cell machinery to transport their proteins in and out of the nucleus. In this review, we will summarise our current knowledge on the ubiquitin/SUMO-regulated nuclear/subnuclear trafficking of cellular proteins and describe examples of viral exploitation of these pathways.

Novel snake papillomavirus does not cluster with other non-mammalian papillomaviruses

Papillomaviruses (PVs) are associated with the development of neoplasias and have been found in several different species, most of them in humans and other mammals. We identified, cloned and sequenced PV DNA from pigmented papilloma-like lesions of a diamond python (Morelia spilota spilota). This represents the first complete PV genome discovered in a Squamata host (MsPV1). It consists of 7048 nt and contains the characteristic open reading (ORF) frames E6, E7, E1, E2, L1 and L2. The L1 ORF sequence showed the highest percentage of sequence identities to human PV5 (57.9%) and Caribbean manatee (Trichechus manatus) PV1 (55.4%), thus, establishing a new clade. According to phylogenetic analysis, the MsPV1 genome clusters with PVs of mammalian rather than sauropsid hosts.

Serum antibodies to the HPV16 proteome as biomarkers for head and neck cancer

BACKGROUND

Human papillomavirus (HPV) type 16 is associated with oropharyngeal carcinomas (OPC). Antibodies (Abs) to HPV16 E6 and E7 oncoproteins have been detected in patient sera; however, Abs to other early HPV-derived proteins have not been well explored.

METHODS

Antibodies to the HPV16 proteome were quantified using a novel multiplexed bead assay, using C-terminal GST-fusion proteins captured onto Luminex beads. Sera were obtained from untreated patients with OPC (N=40), partners of patients with HPV16+ OPC (N=11), and healthy controls (N=50).

RESULTS

Oropharyngeal carcinomas patients with known virus-like capsid particle+ Abs had elevated serum Abs to HPV16 E1, E2, E4, E6, and E7, and L1 antibody levels, but not E5. The ratios of specific median fluorescence intensity to p21-GST compared with controls were E1: 50.7 vs 2.1; E4: 14.6 vs 1.3; E6: 11.3 vs 2.4; E7: 43.1 vs 2.6; and L1: 10.3 vs 2.6 (each P≤0.01). In a validation cohort, HPV16 E1, E2, and E7 antibody levels were significantly elevated compared with healthy control samples (P≤0.02) and partners of OPC patients (P≤0.01).

CONCLUSION

Patients with HPV16+ OPC have detectable Abs to E1, E2, and E7 proteins, which are potential biomarkers for HPV-associated OPC.

Nuclear accumulation of the papillomavirus E1 helicase blocks S-phase progression and triggers an ATM-dependent DNA damage response

Replication of the papillomavirus genome is initiated by the assembly of a complex between the viral E1 and E2 proteins at the origin. The E1 helicase is comprised of a C-terminal ATPase/helicase domain, a central domain that binds to the origin, and an N-terminal regulatory region that contains nuclear import and export signals mediating its nucleocytoplasmic shuttling. We previously reported that nuclear accumulation of E1 has a deleterious effect on cellular proliferation which can be prevented by its nuclear export. Here we have shown that nuclear accumulation of E1 from different papillomavirus types blocks cell cycle progression in early S phase and triggers the activation of a DNA damage response (DDR) and of the ATM pathway in a manner that requires both the origin-binding and ATPase activities of E1. Complex formation with E2 reduces the ability of E1 to induce a DDR but does not prevent cell cycle arrest. Transient viral DNA replication still occurs in S-phase-arrested cells but surprisingly is neither affected by nor dependent on induction of a DDR and of the ATM kinase. Finally, we provide evidence that a DDR is also induced in human papillomavirus type 31 (HPV31)-immortalized keratinocytes expressing a mutant E1 protein defective for nuclear export. We propose that nuclear export of E1 prevents cell cycle arrest and the induction of a DDR during the episomal maintenance phase of the viral life cycle and that complex formation with E2 further safeguards undifferentiated cells from undergoing a DDR when E1 is in the nucleus.

HPV episome levels are potently decreased by pyrrole-imidazole polyamides

Human papillomavirus (HPV) causes cervical cancer and other hyperproliferative diseases. There currently are no approved antiviral drugs for HPV that directly decrease viral DNA load and that have low toxicity. We report the potent anti-HPV activity of two N-methylpyrrole-imidazole polyamides of the hairpin type, polyamide 1 (PA1) and polyamide 25 (PA25). Both polyamides have potent anti-HPV activity against three different genotypes when tested on cells maintaining HPV episomes. The compounds were tested against HPV16 (in W12 cells), HPV18 (in Ker4-18 cells), and HPV31 (in HPV31 maintaining cells). From a library of polyamides designed to recognize AT-rich DNA sequences such as those in or near E1 or E2 binding sites of the HPV16 origin of replication (ori), four polyamides were identified that possessed apparent IC(50)s≤150nM with no evidence of cytotoxicity. We report two highly-active compounds here. Treatment of epithelia engineered in organotypic cultures with these compounds also causes a dose-dependent loss of HPV episomal DNA that correlates with accumulation of compounds in the nucleus. Bromodeoxyuridine (BrdU) incorporation demonstrates that DNA synthesis in organotypic cultures is suppressed upon compound treatment, correlating with a loss of HPV16 and HPV18 episomes. PA1 and PA25 are currently in preclinical development as antiviral compounds for treatment of HPV-related disease, including cervical dysplasia. PA1, PA25, and related polyamides offer promise as antiviral agents and as tools to regulate HPV episomal levels in cells for the study of HPV biology. We also report that anti-HPV16 activity for Distamycin A, a natural product related to our polyamides, is accompanied by significant cellular toxicity.

Nuclear export of human papillomavirus type 31 E1 is regulated by Cdk2 phosphorylation and required for viral genome maintenance

The initiator protein E1 from human papillomavirus (HPV) is a helicase essential for replication of the viral genome. E1 contains three functional domains: a C-terminal enzymatic domain that has ATPase/helicase activity, a central DNA-binding domain that recognizes specific sequences in the origin of replication, and a N-terminal region necessary for viral DNA replication in vivo but dispensable in vitro. This N-terminal portion of E1 contains a conserved nuclear export signal (NES) whose function in the viral life cycle remains unclear. In this study, we provide evidence that nuclear export of HPV31 E1 is inhibited by cyclin E/A-Cdk2 phosphorylation of two serines residues, S92 and S106, located near and within the E1 NES, respectively. Using E1 mutant proteins that are confined to the nucleus, we determined that nuclear export of E1 is not essential for transient viral DNA replication but is important for the long-term maintenance of the HPV episome in undifferentiated keratinocytes. The findings that E1 nuclear export is not required for viral DNA replication but needed for genome maintenance over multiple cell divisions raised the possibility that continuous nuclear accumulation of E1 is detrimental to cellular growth. In support of this possibility, we observed that nuclear accumulation of E1 dramatically reduces cellular proliferation by delaying cell cycle progression in S phase. On the basis of these results, we propose that nuclear export of E1 is required, at least in part, to limit accumulation of this viral helicase in the nucleus in order to prevent its detrimental effect on cellular proliferation.

HPV E1 up-regulates replication-related biochemistries of AAV Rep78

Human papillomavirus type 16 (HPV) E1 protein provides helper function for the adeno-associated virus type 2 (AAV) life cycle. E1 is the replication protein of HPV, analogous to AAV Rep78, but without the endonuclease/covalent attachment activity of Rep78. Previously we have shown that E1 and Rep78 interact in vitro. Here we investigated E1's effects on Rep78 interaction with AAV's inverted terminal repeat (ITR) DNA in vitro, using purified Rep78 and E1 proteins from bacteria. E1 enhanced Rep78-ITR binding, ATPase activity, Rep78-ITR-covalent linkage and Rep78-ITR-endonuclease activity (central to AAV replication). These enhancements occurred in a dose-dependent manner whenever assayed. However, overall Rep78-plus-E1 helicase activity was lower than Rep78's helicase activity. These data suggest that E1's broad-based helper function for the AAV life cycle (AAV DNA, mRNA, and protein levels are up-regulated by E1) is likely through its ability to enhance Rep78's critical replication-required biochemistries on ITR DNA.

Characterization of papillomavirus E1 helicase mutants defective for interaction with the SUMO-conjugating enzyme Ubc9

The E1 helicase from BPV and HPV16 interacts with Ubc9 to facilitate viral genome replication. We report that HPV11 E1 also interacts with Ubc9 in vitro and in the yeast two-hybrid system. Residues in E1 involved in oligomerization (353-435) were sufficient for binding to Ubc9 in vitro, but the origin-binding and ATPase domains were additionally required in yeast. Nuclear accumulation of BPV E1 was shown previously to depend on its interaction with Ubc9 and sumoylation on lysine 514. In contrast, HPV11 and HPV16 E1 mutants defective for Ubc9 binding remained nuclear even when the SUMO pathway was inhibited. Furthermore, we found that K514 in BPV E1 and the analogous K559 in HPV11 E1 are not essential for nuclear accumulation of E1. These results suggest that the interaction of E1 with Ubc9 is not essential for its nuclear accumulation but, rather, depends on its oligomerization and binding to DNA and ATP.

Recent advances in molecular gynaecological pathology

This review gives an overview of recent advances in our understanding of the molecular basis of gynaecological malignancy, including cervical, vulval, endometrial and ovarian tumours. These advances are beginning to influence clinical practice, perhaps most notably with the introduction of human papillomavirus vaccination for the prevention of anogenital neoplasia, but are likely to have broader clinical implications as further details emerge.

Human papillomavirus (HPV) type 18 induces extended growth in primary human cervical, tonsillar, or foreskin keratinocytes more effectively than other high-risk mucosal HPVs

Mucosal high-risk (HR) human papillomaviruses (HPVs) that cause cervical and other anogenital cancers also are found in approximately 25% of head and neck carcinomas (HNCs), especially those arising in the oropharynx and the tonsils. While many HR HPV types are common in anogenital cancer, over 90% of HPV-positive HNCs harbor HPV type 16 (HPV-16). Using a quantitative colony-forming assay, we compared the ability of full-length mucosal HPV genomes, i.e., the low-risk HPV-11 and HR HPV-16, -18, and -31, to persist in and alter the growth of primary human keratinocytes from the foreskin, cervix, and tonsils. The HR HPV types led to the formation of growing keratinocyte colonies in culture independent of the site of epithelial origin. However, HPV-18 induced colony growth in all keratinocytes >4-fold more effectively than HPV-16 or HPV-31 and >20-fold more efficiently than HPV-11 or controls. HPV-11-transfected or control colonies failed to expand beyond 32 to 36 population doublings postexplantation. In contrast, individual HR HPV-transfected clones exhibited no apparent slowdown of growth or "crisis," and many maintained HPV plasmid persistence beyond 60 population doublings. Keratinocyte clones harboring extrachromosomal HR HPV genomes had shorter population doubling times and formed dysplastic stratified epithelia in organotypic raft cultures, mirroring the pathological features of higher-grade intraepithelial lesions, yet did not exhibit chromosomal instability. We conclude that, in culture, the HR HPV type, rather than the site of epithelial origin of the cells, determines the efficacy of inducing continued growth of individual keratinocytes, with HPV-18 being the most aggressive mucosal HR HPV type tested.

Three novel canine papillomaviruses support taxonomic clade formation

More than 100 human papillomaviruses (HPVs) have been identified and had their whole genomes sequenced. Most of these HPVs can be classified into three distinct genera, the alpha-, beta- and gamma-papillomaviruses (PVs). Of note, only one or a small number of PVs have been identified for each individual animal species. However, four canine PVs (CPVs) (COPV, CPV2, CPV3 and CPV4) have been described and their entire genomic sequences have been published. Based on their sequence similarities, they belong to three distinct clades. In the present study, circular viral DNA was amplified from three dogs showing signs of pigmented plaques, endophytic papilloma or in situ squamous cell carcinoma. Analysis of the DNA sequences suggested that these are three novel viruses (CPV5, CPV6 and CPV7) whose genomes comprise all the conserved sequence elements of known PVs. The genomes of these seven CPVs were compared in order properly classify them. Interestingly, phylogenetic analyses, as well as pairwise sequence alignments of the putative amino acid sequences, revealed that CPV5 grouped well with CPV3 and CPV4, whereas CPV7 grouped with CPV2 but neither group fitted with other classified PVs. However, CPV6 grouped with COPV, a lambda-PV. Based on this evidence, allocation of CPVs into three distinct clades could therefore be supported. Thus, similar to HPVs, it might be that the known and currently unknown CPVs are related and form just a few clades or genera.

The EVER proteins as a natural barrier against papillomaviruses: a new insight into the pathogenesis of human papillomavirus infections

Infections by human papillomaviruses (HPVs) are the most frequently occurring sexually transmitted diseases. The crucial role of genital oncogenic HPV in cervical carcinoma development is now well established. In contrast, the role of cutaneous HPV in skin cancer development remains a matter of debate. Cutaneous beta-HPV strains show an amazing ubiquity. The fact that a few oncogenic genotypes cause cancers in patients suffering from epidermodysplasia verruciformis is in sharp contrast to the unapparent course of infection in the general population. Our recent investigations revealed that a natural barrier exists in humans, which protects them against infection with these papillomaviruses. A central role in the function of this HPV-specific barrier is played by a complex of the zinc-transporting proteins EVER1, EVER2, and ZnT-1, which maintain cellular zinc homeostasis. Apparently, the deregulation of the cellular zinc balance emerges as an important step in the life cycles not only of cutaneous but also of genital HPVs, although the latter viruses have developed a mechanism by which they can break the barrier and impose a zinc imbalance. Herein, we present a previously unpublished list of the cellular partners of EVER proteins, which points to future directions concerning investigations of the mechanisms of action of the EVER/ZnT-1 complex. We also present a general overview of the pathogenesis of HPV infections, taking into account the latest discoveries regarding the role of cellular zinc homeostasis in the HPV life cycle. We propose a potential model for the mechanism of function of the anti-HPV barrier.