The papillomavirus life cycle

Differential expression of papillomavirus L1 proteins encoded by authentic and codon modified L1 genes in methylcellulose-treated mouse keratinocytes

Papillomaviruses (PVs) are double-stranded DNA viruses that infect keratinocytes in differentiating epithelia and induce hyperproliferative lesions. Here, we used methylcellulose to induce cell differentiation of primary mouse keratinocytes (KCs) in in vitro culture and assessed the expression of authentic and codon-modified version of L1 capsid genes from two PV types (HPV6b and BPV1). Based on the quantitative RT-PCR analysis, methylcellulose treatment did not influence the transcriptional expression of both authentic and codon-modified L1 genes in KCs. Western blot showed that methylcellulose significantly increased the levels of the L1 proteins expressed from two authentic L1 genes. Conversely, methylcellulose dramatically decreased L1 protein expression in KCs transfected with two codon-modified L1 expression constructs. These data suggest that L1 protein expression is associated with KC differentiation induced by methylcellulose treatment and regulated at the post-transcriptional level.

Biology of papillomavirus replication in infected epithelium

Human papillomaviruses complete their life cycle in differentiating epithelial cells that would not normally be competent for either cellular or viral DNA replication. To overcome this, papillomaviruses encode two groups of proteins that work together in the upper epithelial layers to amplify viral genomes. The E6 and E7 proteins play a critical role in driving differentiating epithelial cells that have left the basal layer, back into the cell cycle, in order to produce a replication-competent environment that can be used by the virus for genome amplification. Papillomavirus replication is heavily dependent on cellular replication proteins, but in addition needs the viral E1 and E2 proteins, which act to unwind viral DNA around the origin of replication, and to recruit essential cellular proteins to the replication site. Recent work using mutant viral genomes has suggested that two other viral proteins, E4 and E5, contribute to efficient replication in the upper epithelial layers, although the mechanisms by which they do this have not yet been clearly established. Genome amplification in the upper epithelial layers differs from maintenance replication in the basal layer, where viral genome replication appears coupled to that of the cellular genome. The onset of genome amplification during differentiation is thought to be triggered at least in part by an increase in E1 and E2 levels, and possibly also by a change in the relative levels of the two proteins. The role of E6 and E7 in basal cell replication is, however, uncertain and there is even some question as to the exact requirement for E1. Although similarities in papillomavirus lifecycle organization and protein function suggest a common mechanism by which viral DNA replication is regulated, differences in the site of infection and transmission route appear to manifest themselves as differences in the timing and extent of genome amplification. Understanding the patterns of protein expression seen during natural infection will be important in fully understanding how these differences arise.

Persistence of Mastomys natalensis papillomavirus in multiple organs identifies novel targets for infection

The high incidence of multiple wart formation and skin cancer in organ-transplant recipients, as well as the question of an involvement of papillomaviruses in a variety of human cancers, require a model system for papillomavirus infections in immunocompetent animals. Such an in vivo model is represented by the multimammate rat Mastomys coucha, which is infected with Mastomys natalensis papillomavirus (MnPV). MnPV primarily induces benign skin tumours, such as papillomas and keratoacanthomas. Here, the incidence of MnPV infections in different skin areas and various organs is described. In situ hybridization showed that hair follicle cells were positive for viral DNA and that the amount of MnPV in normal skin may be considered a predictor for the development of skin tumours. MnPV infection is not restricted to the skin, but can also be detected in inner organs. As the blood and the lymphatic system were temporarily also found to be virus-positive, a haematogenic propagation of MnPV can be assumed. However, MnPV is apparently not transmitted through the germ line, as fetuses and newborns lack viral DNA, despite infection of their mothers. In conclusion, M. coucha is not only useful to study papillomavirus-induced skin carcinogenesis, but may also serve as a model to identify additional, still unknown target cells of papillomavirus infections and the potential pathological impact.

Phylogeny and evolution of papillomaviruses based on the E1 and E2 proteins

Papillomaviridae are a family of small double-stranded DNA viruses that infect stratified squamous epithelia in vertebrates. Members of this family are causative agents of malignant tumours, such as cervical cancer while others are associated with benign proliferative lesions. So far, Papillomaviruses (PVs) are classified according to the sequence identity in the capsid gene L1. However, evidence has accumulated indicating a discontinuity in the evolutionary history of the L1 and L2 genes of many PVs, giving rise to differences in the phylogenetic reconstructions of the early and of the late genes. Neither the oncogenes E5, E6 and E7 nor the upstream regulatory region are suitable for phylogenetic inference due to the poor conservation along the Papillomaviridae family. We have analysed here the evolutionary relationships of the PVs with respect to the E1 and E2 proteins, and the results provide both phylogeny and biologic behaviour of the viruses. The hierarchical taxonomic relationships can be structured as an alternative classification system in which mucosal high-risk viruses, mucosal low-risk viruses and viruses associated with cutaneous lesions are grouped separately and do not appear intermingled. Some important trends are also observed: first, evolution of the PVs has not been homogeneous, even in viruses that infect the same host, and second mucosal human PVs have evolved faster than their cutaneous counterparts. The evolutionary analysis based on the E1 and E2 proteins will allow us to better understand the generation of the diversity of the PVs and the development of malignancy associated with these viruses.

Intrabody strategies for the treatment of human papillomavirus-associated disease

Human papillomaviruses (HPVs) are associated with a variety of epithelial lesions, including benign genital warts and cervical intraepithelial neoplasia. Both cause significant morbidity in the general population, with cervical intraepithelial neoplasia progressing to cervical cancer in a subset of women who cannot resolve their infection. At present, there are no antiviral agents for the treatment of genital HPV infections, with many lesions requiring surgical intervention. Although other approaches are available for the treatment of genital warts, HPV infection cannot usually be cured and lesion recurrence is often a problem. A growing understanding of the molecular biology of HPV infection has identified several viral protein functions that may serve as drug targets. Among these are the HPV E1 and E2 proteins, which are necessary for viral genome replication and partitioning, and the E6 and E7 proteins, which are necessary for cell proliferation and apoptotic inhibition. With the exception of E1, these proteins lack enzymatic activity and achieve their effects by interacting with cellular proteins. Protein-protein interactions are in general quite difficult to inhibit using conventional small molecule drugs, but are amenable to inhibition using intracellular antibodies or intrabodies, which bind the viral proteins and sterically inhibit their association with cellular partners. The lack of homology between viral and cellular proteins, and the fact that HPV infections can be treated topically, makes them particularly well suited to the intrabody approach. This review covers the various strategies that are being considered for the treatment of HPV infections and the different intrabody formats that have been used to inhibit HPV function in model systems. The clinical utility of the approach is considered alongside the general difficulties of using protein molecules as intracellular therapeutics.

Susceptibility of drug-resistant clinical herpes simplex virus type 1 strains to essential oils of ginger, thyme, hyssop, and sandalwood

Acyclovir-resistant clinical isolates of herpes simplex virus type 1 (HSV-1) were analyzed in vitro for their susceptibilities to essential oils of ginger, thyme, hyssop, and sandalwood. All essential oils exhibited high levels of virucidal activity against acyclovir-sensitive strain KOS and acyclovir-resistant HSV-1 clinical isolates and reduced plaque formation significantly.

Diverse herpes simplex virus type 1 thymidine kinase mutants in individual human neurons and Ganglia

Mutations in the thymidine kinase gene (tk) of herpes simplex virus type 1 (HSV-1) explain most cases of virus resistance to acyclovir (ACV) treatment. Mucocutaneous lesions of patients with ACV resistance contain mixed populations of tk mutant and wild-type virus. However, it is unknown whether human ganglia also contain mixed populations since the replication of HSV tk mutants in animal neurons is impaired. Here we report the detection of mutated HSV tk sequences in human ganglia. Trigeminal and dorsal root ganglia were obtained at autopsy from an immunocompromised woman with chronic mucocutaneous infection with ACV-resistant HSV-1. The HSV-1 tk open reading frames from ganglia were amplified by PCR, cloned, and sequenced. tk mutations were detected in a seven-G homopolymer region in 11 of 12 ganglia tested, with clonal frequencies ranging from 4.2 to 76% HSV-1 tk mutants per ganglion. In 8 of 11 ganglia, the mutations were heterogeneous, varying from a deletion of one G to an insertion of one to three G residues, with the two-G insertion being the most common. Each ganglion had its own pattern of mutant populations. When individual neurons from one ganglion were analyzed by laser capture microdissection and PCR, 6 of 14 HSV-1-positive neurons were coinfected with HSV tk mutants and wild-type virus, 4 of 14 were infected with wild-type virus alone, and 4 of 14 were infected with tk mutant virus alone. These data suggest that diverse tk mutants arise independently under drug selection and establish latency in human sensory ganglia alone or together with wild-type virus.

The large and small isoforms of human papillomavirus type 16 E6 bind to and differentially affect procaspase 8 stability and activity

Human papillomavirus type 16 (HPV-16) has developed numerous ways to modulate host-initiated immune mechanisms. The HPV-16 E6 oncoprotein, for example, can modulate the cellular level, and consequently the activity, of procaspase 8, thus modifying the cellular response to cytokines of the tumor necrosis factor family. E6 from HPV-16, but not E6 from the low-risk types 6b and 11, alters the cellular level of procaspase 8 in a dose-dependent manner. Both the large and small (E6*) isoforms of E6, which originate by way of alternate splicing, can modulate procaspase 8 stability. Intriguingly, although both isoforms bind to procaspase 8, the large isoform accelerates the degradation of procaspase 8 while the small isoform stabilizes it. Binding leads to a change in the ability of procaspase 8 to bind either to itself or to FADD (Fas-associated death domain), with the large version of E6 able to inhibit this binding while the small isoform does not. Consistent with this model, knockdown of the large version of E6 by small interfering RNA leads to increases in the levels of procaspase 8 and its binding to both itself and FADD. Thus, these alternatively spliced isoforms can modulate both the level and the activity of procaspase 8 in opposite directions.

Human papillomavirus testing and molecular markers of cervical dysplasia and carcinoma

Cervical cancer is the second most common cancer in women worldwide. Human papillomavirus (HPV) is the etiologic agent for the vast majority of premalignant and malignant lesions, and high-risk HPV types can be detected in almost all cases of cervical dysplasia and carcinoma. HPV testing has been widely adopted for the triage of patients after a cervical cytology screening test (Papanicolaou smear or liquid-based cervical cytology such as ThinPrep or SurePath) interpretation of atypical squamous cells of undetermined significance (ASCUS), and HPV testing is increasingly used for screening in conjunction with cervical cytology. Although cervical cytology is a highly effective screening test for cancer, it has limited specificity for clinically significant lesions in cases with low-grade cytologic abnormalities. Up to a quarter of all patients may have a false-negative result on the basis of cervical cytology testing alone. This review focuses on HPV testing methods and molecular markers and their clinical relevance. HPV testing and surrogate molecular markers of HPV infection (p16INK4a) may help identify cases that are associated with underlying high-grade premalignant or malignant lesions and may also reduce aggressive treatment of patients with low-grade lesions.

Imiquimod et autres immunomodulateurs en gynécologie

Immunomodulators have been used for some time in various medical specialities, but have only recently been used in gynaecology. The first drug in this therapeutic class, Immiquimod (Aldara), has been shown to be effective in treating lesions induced by Human Papillomavirus (HPV) such as genital warts or cervical and vulvar dysplasia, by stimulating the immune system of an infected individual. Thanks to its ease of use and its few side effects, Imiquimod would appear to be, in the future, the treatment of choice for these types of viral infections, alone or in association with therapeutic vaccines or physical abative therapies as a prevention of relapses. This review aims at summarizing and clarifying the mechanism of action of the different immunomodulators, their indications and their effectiveness in gynecologic practice.

Epidermodysplasia Verruciformis and Cutaneous Human Papillomavirus DNA, but Not Genital Human Papillomavirus DNAs, Are Frequently Detected in Vulvar and Vaginal Melanoma

Vulvovaginal melanomas are rare and their etiology is unknown. Genital mucosal human papillomavirus (HPV) 16 has been identified in both cutaneous and mucosal melanoma, suggesting that it might play a role in the pathogenesis or progression of melanoma. In this study, we investigated the prevalence of HPV DNA by using a broad spectrum of degenerate and type-specific primers for genital-mucosal, epidermodysplasia verruciformis-associated (EV), and cutaneous HPV types in 6 vulvar and 3 vaginal melanomas. The patients were mostly postmenopausal women (8/9), had a mean age of 67 years (range, 44-85 years), and had mucosal lentiginous (7) or nodular (2) melanomas. In the adjacent skin/mucosa, mucosal melanosis was found in 5, lichen sclerosus or a lichenoid mucositis in 4, and blue nevi in 2 women. With nested polymerase chain reaction techniques followed by direct sequencing, HPV DNA was identified in 6 of 9 (67%) melanomas; these were either cutaneous (HPV 3) (4/9) or epidermodysplasia verruciformis-associated types (HPV 38, Z95969, AJ00151) (4/9). Epidermodysplasia verruciformis-associated HPV (type 15) was found solely in 1/10 (10%) normal vulvar controls. Genital-mucosal HPV types were not detected either by degenerate nested polymerase chain reaction or type-specific probes for HPV 16. We propose that the above findings are not coincidental but may represent a molecular record of HPV involvement in pathogenesis or progression of melanoma, which is consistent with the strong but poorly defined association of cutaneous HPV types with nonmelanoma skin cancers. The theory that HPV may act as a cofactor in melanoma development deserves further clinical and experimental investigations.

Nuclear import of bovine papillomavirus type 1 E1 protein is mediated by multiple alpha importins and is negatively regulated by phosphorylation near a nuclear localization signal

Papillomavirus DNA replication occurs in the nucleus of infected cells and requires the viral E1 protein, which enters the nuclei of host epithelial cells and carries out enzymatic functions required for the initiation of viral DNA replication. In this study, we investigated the pathway and regulation of the nuclear import of the E1 protein from bovine papillomavirus type 1 (BPV1). Using an in vitro binding assay, we determined that the E1 protein interacted with importins alpha3, alpha4, and alpha5 via its nuclear localization signal (NLS) sequence. In agreement with this result, purified E1 protein was effectively imported into the nucleus of digitonin-permeabilized HeLa cells after incubation with importin alpha3, alpha4, or alpha5 and other necessary import factors. We also observed that in vitro binding of E1 protein to all three alpha importins was significantly decreased by the introduction of pseudophosphorylation mutations in the NLS region. Consistent with the binding defect, pseudophosphorylated E1 protein failed to enter the nucleus of digitonin-permeabilized HeLa cells in vitro. Likewise, the pseudophosphorylation mutant showed aberrant intracellular localization in vivo and accumulated primarily on the nuclear envelope in transfected HeLa cells, while the corresponding alanine replacement mutant displayed the same cellular location pattern as wild-type E1 protein. Collectively, our data demonstrate that BPV1 E1 protein can be transported into the nucleus by more than one importin alpha and suggest that E1 phosphorylation by host cell kinases plays a regulatory role in modulating E1 nucleocytoplasmic localization. This phosphoregulation of nuclear E1 protein uptake may contribute to the coordination of viral replication with keratinocyte proliferation and differentiation.

Fulminant, acyclovir-resistant, herpes simplex virus type 2 hepatitis in an immunocompetent woman

We report an immunocompetent woman with multisystem organ failure following herpes simplex virus type 2 (HSV-2) hepatitis. After she initially responded to intravenous acyclovir, she was switched to oral valacyclovir. She developed respiratory failure and opportunistic infections and died. Autopsy confirmed disseminated HSV infection, and lung tissue grew acyclovir-resistant HSV-2.

Serum antibody response to Human papillomavirus (HPV) infections detected by a novel ELISA technique based on denatured recombinant HPV16 L1, L2, E4, E6 and E7 proteins

Background

Human papillomaviruses (HPVs) are the primary etiological agents of cervical cancer and are also involved in the development of other tumours (skin, head and neck). Serological survey of the HPV infections is important to better elucidate their natural history and to disclose antigen determinants useful for vaccine development. At present, the analysis of the HPV-specific antibodies has not diagnostic value for the viral infections, and new approaches are needed to correlate the antibody response to the disease outcome. The aim of this study is to develop a novel ELISA, based on five denatured recombinant HPV16 proteins, to be used for detection HPV-specific antibodies.

Methods

The HPV16 L1, L2, E4, E6 and E7 genes were cloned in a prokaryotic expression vector and expressed as histidine-tagged proteins. These proteins, in a denatured form, were used in ELISA as coating antigens. Human sera were collected from women with abnormal PAP smear enrolled during an ongoing multicenter HPV-PathogenISS study in Italy, assessing the HPV-related pathogenetic mechanisms of progression of cervical cancer precursor lesions. Negative human sera were collected from patients affected by other infectious agents. All the HPV-positive sera were also subjected to an avidity test to assess the binding strength in the antigen-antibody complexes.

Results

Most of the sera showed a positive reactivity to the denatured HPV16 proteins: 82% of the sera from HPV16 infected women and 89% of the sera from women infected by other HPV genotypes recognised at least one of the HPV16 proteins. The percentages of samples showing reactivity to L1, L2 and E7 were similar, but only a few serum samples reacted to E6 and E4. Most sera bound the antigens with medium and high avidity index, suggesting specific antigen-antibody reactions.

Conclusion

This novel ELISA, based on multiple denatured HPV16 antigens, is able to detect antibodies in women infected by HPV16 and it is not genotype-specific, as it detects antibodies also in women infected by other genital HPVs. The assay is easy to perform and has low cost, making it suitable for monitoring the natural history of HPV infections as well as for detecting pre-existing HPV antibodies in women who receive VLP-based HPV vaccination.

Papillomavirus and treatment

Human papillomaviruses (HPVs) are small DNA viruses responsible for a broad range of clinical presentations, characterized histologically by the proliferation of epithelial cells. HPVs are responsible for benign as well as malignant lesions, the most frequent of the latter being cervical carcinoma. A better knowledge of the immunobiology of these lesions allowed the development of prophylactic vaccines (for the most frequent genital types) that are presently under evaluation. The present paper describes different approaches for the treatment of HPV lesions, still mostly based on surgery, and underlines the importance of developing adjuvant therapies.

Progress in the development of a cervical cancer vaccine

Persistent infection by 'high risk' genotypes of human papilloma virus (HPV) is necessary but not sufficient for the development of over 98% of cervical cancers. Thus the development of vaccines that prevent HPV transmission represent an important opportunity to prevent cervical cancer. There are several prophylactic HPV vaccine formulations based upon L1 virus-like particles (VLPs) currently in phase III trials and recently released data are extremely promising. However, many practical issues surrounding implementation of these vaccines need to be addressed including, who and when to vaccinate, duration of protection, and integration with current screening programs. The vaccines currently being evaluated target the two most prevalent high risk HPV types which are responsible for approximately 70% of cervical cancers. To increase the breadth of protection, it is likely that L1 VLPs of other viral subtypes must be included, although vaccines targeting the conserved regions of the L2 minor capsid protein warrant further exploration in this regard. In addition the vaccines nearing licensing will not combat established HPV-related disease and a therapeutic vaccine, of which there are several candidates in early stages of development, would be desirable. This review discusses the background to and progress in vaccine development and the issues surrounding the introduction of HPV vaccines.

Carrageenan is a potent inhibitor of papillomavirus infection

Certain sexually transmitted human papillomavirus (HPV) types are causally associated with the development of cervical cancer. Our recent development of high-titer HPV pseudoviruses has made it possible to perform high-throughput in vitro screens to identify HPV infection inhibitors. Comparison of a variety of compounds revealed that carrageenan, a type of sulfated polysaccharide extracted from red algae, is an extremely potent infection inhibitor for a broad range of sexually transmitted HPVs. Although carrageenan can inhibit herpes simplex viruses and some strains of HIV in vitro, genital HPVs are about a thousand-fold more susceptible, with 50% inhibitory doses in the low ng/ml range. Carrageenan acts primarily by preventing the binding of HPV virions to cells. This finding is consistent with the fact that carrageenan resembles heparan sulfate, an HPV cell-attachment factor. However, carrageenan is three orders of magnitude more potent than heparin, a form of cell-free heparan sulfate that has been regarded as a highly effective model HPV inhibitor. Carrageenan can also block HPV infection through a second, postattachment heparan sulfate–independent effect. Carrageenan is in widespread commercial use as a thickener in a variety of cosmetic and food products, ranging from sexual lubricants to infant feeding formulas. Some of these products block HPV infectivity in vitro, even when diluted a million-fold. Clinical trials are needed to determine whether carrageenan-based products are effective as topical microbicides against genital HPVs.

Sexually transmitted human papillomavirus (HPV) infections are very common. Although most HPV infections don't cause noticeable symptoms, persistent infection with some genital HPV types can lead to cervical cancer or other anal/genital cancers. Another subset of HPV types can cause genital warts. Recent studies have suggested that condoms are not highly effective in preventing HPV infection. Although HPV vaccines will soon become available, they probably will not protect against all genital HPV types and will be too expensive for use in the developing world. Inexpensive HPV-inhibitory compounds (known as topical microbicides) might be useful for blocking the spread of HPV. Using a newly developed cell culture–based HPV inhibition test, we have discovered that an inexpensive gelling agent called carrageenan is an unexpectedly potent HPV infection inhibitor. Carrageenan is also under investigation as a topical microbicide targeting HIV and herpes viruses, but it is a thousand times more effective against HPV in cell culture tests. Interestingly, carrageenan is used as a thickener in some commercially available sexual lubricants and lubricated condoms. Several of these commercial lubricant products are potent HPV inhibitors in our cell culture–infection system. Clinical trials are needed to determine the effectiveness of carrageenan as a topical microbicide against HPV.

Presence of Human Papillomavirus DNA in Tonsillectomy Specimens

OBJECTIVES

The objectives of this prospective case-control study were to study the prevalence of human papillomavirus (HPV) in tonsillectomy specimens from pediatric patients without recurrent respiratory papillomatosis (RRP), and to study methods of HPV detection.

METHODS

Fifty pediatric patients without known RRP undergoing tonsillectomy for hypertrophy or recurrent tonsillitis were enrolled in the study. After tonsillectomy, a 20-mg section was subjected to DNA extraction, and DNA content and purity were confirmed with spectrophotometry. Polymerase chain reaction (PCR) was performed using consensus primer pools PGMY 09/11 targeted at the L1 region. Amplification products were detected and analyzed with standard agarose gel electrophoresis. Positive samples were then subjected to reverse line blot assay to determine virus genotype. Laryngeal papilloma specimens of 15 patients obtained during routine debulking procedures were also analyzed and served as positive controls.

RESULTS

Of 50 tonsil samples tested, two were positive for HPV DNA after PCR and gel electrophoresis. One of these samples was confirmed with typing and tested positive for HPV 11. All 15 papilloma specimens were positive for DNA of HPV types 6 and/or 11.

CONCLUSIONS

In the current study, the prevalence of HPV DNA in tonsillar tissue of patients without RRP is 2%, whereas the incidence of this disease is 2 to 4 cases per 100,000 (0.004%). These findings are significantly different (P = .005 within a 95% confidence interval) suggesting that host factors in addition to infection play a role in pathogenesis of RRP. The molecular methods described in this study are well suited for detection of HPV in tonsillar tissue.

Chapter 1: HPV in the etiology of human cancer

The causal role of human papillomavirus (HPV) in all cancers of the uterine cervix has been firmly established biologically and epidemiologically. Most cancers of the vagina and anus are likewise caused by HPV, as are a fraction of cancers of the vulva, penis, and oropharynx. HPV-16 and -18 account for about 70% of cancers of the cervix, vagina, and anus and for about 30-40% of cancers of the vulva, penis, and oropharynx. Other cancers causally linked to HPV are non-melanoma skin cancer and cancer of the conjunctiva. Although HPV is a necessary cause of cervical cancer, it is not a sufficient cause. Thus, other cofactors are necessary for progression from cervical HPV infection to cancer. Long-term use of hormonal contraceptives, high parity, tobacco smoking, and co-infection with HIV have been identified as established cofactors; co-infection with Chlamydia trachomatis (CT) and herpes simplex virus type-2 (HSV-2), immunosuppression, and certain dietary deficiencies are other probable cofactors. Genetic and immunological host factors and viral factors other than type, such as variants of type, viral load and viral integration, are likely to be important but have not been clearly identified.

Papillomavirus virus-like particles as vehicles for the delivery of epitopes or genes

Papillomaviruses (PVs) are simple double-strand DNA viruses whose virion shells are T = 7 icosahedrons and composed of major capsid protein L1 and minor capsid protein L2.L1 alone or together with L2 can self-assemble into virus-like particles (VLPs) when expressed in eukaryotic or prokaryotic expression systems. Although the VLPs lack the virus genome DNA, their morphological and immunological characteristics are very similar to those of nature papillomaviruses. PV VLP vaccination can induce high titers of neutralizing antibodies and can effectively protect animals or humans from PV infection. Moreover, PV VLPs have been good candidates for vehicles to deliver epitopes or genes to target cells. They are widely used in the fields of vaccine development, neutralizing antibody detection, basic virologic research on papillomaviruses, and human papillomavirus (HPV) screening. Besides the structural biology and immunological basis for PV VLPs used as vehicles to deliver epitopes or genes, this review details the latest findings on chimeric papillomavirus VLPs and papillomavirus pseudoviruses, which are two important forms of PV VLPs used to transfer epitopes or genes.

E7 proteins from high- and low-risk human papillomaviruses bind to TGF-β-regulated Smad proteins and inhibit their transcriptional activity

Human papillomaviruses (HPV) infect keratinocytes of skin and mucosa. Persistent infection can lead to the formation of benign tumors. In cases of high-risk HPV, such as HPV16 or 18, these may further progress to cancer. In order to support viral replication in suprabasal keratinocytes, the HPV E7 protein employs various strategies to keep keratinocytes in cycle and counteracts anti-proliferative signals from outside. HPV16 E7 can directly interfere with transforming growth factor-beta (TGF-beta) signalling by binding to Smad proteins mediating growth arrest. It has been speculated that this property of HPV16 E7 contributes to HPV-associated carcinogenesis. Here, we show that E7 proteins from different low- and high-risk HPV types bind to Smad 1 to 4. The E7 protein from HPV1, a low-risk HPV causing plantar warts, efficiently inhibited Smad 3-induced transcription. Our data strongly indicate that the Smad-binding capacity of E7 proteins from different HPVs may preserve keratinocyte proliferation required for the productive viral life cycle rather than promoting carcinogenesis.

A phosphorylation map of the bovine papillomavirus E1 helicase

BACKGROUND

Papillomaviruses undergo a complex life cycle requiring regulated DNA replication. The papillomavirus E1 helicase is essential for viral DNA replication and plays a key role in controlling viral genome copy number. The E1 helicase is regulated at least in part by protein phosphorylation, however no systematic approach to phosphate site mapping has been attempted. We have utilized mass spectrometry of purified bovine papillomavirus E1 protein to identify and characterize new sites of phosphorylation.

RESULTS

Mass spectrometry and in silico sequence analysis were used to identify phosphate sites on the BPV E1 protein and kinases that may recognize these sites. Five new and two previously known phosphorylation sites were identified. A phosphate site map was created and used to develop a general model for the role of phosphorylation in E1 function.

CONCLUSION

Mass spectrometric analysis identified seven phosphorylated amino acids on the BPV E1 protein. Taken with three previously identified sites, there are at least ten phosphoamino acids on BPV E1. A number of kinases were identified by sequence analysis that could potentially phosphorylate E1 at the identified positions. Several of these kinases have known roles in regulating cell cycle progression. A BPV E1 phosphate map and a discussion of the possible role of phosphorylation in E1 function are presented.

Human papillomavirus type 16 E5 protein as a therapeutic target

Cervical cancer is a progressive disease with an onset of one to two decades on average. During the productive replication stage, the Human papillomavirus (HPV) genome is maintained episomally in the infected cervical epithelium and early gene products, including E5, are expressed. Therefore, E5 has a potential to contribute to the HPV-associated carcinogenic process. In invasive malignancies, the HPV genomes are commonly integrated into the host genome, and E6 and E7 genes remain intact. However, the E5 is lost or, if present, under-expressed as compared with the E6 and E7 proteins. This suggests that E5 may play a critical role in the genesis of cervical cancer but less of a role in its persistence or progression. In the initiation of neoplasia and the premalignant stage, there are fewer malignant cells than in the invasive malignancies. Moreover, cells in the invasive malignant stage are found to have a very low level of MHC class I and II, which could hamper the presentation of the antigen and lead to a decreased immune response. Since the E5 protein is likely to play a role during the early tumorigenesis stage, a therapeutic vaccine to target and eliminate the E5-expressing cells may be a good strategy to prevent premalignant lesions from progressing toward invasive cervical cancers. This paper provides an overview of HPV-induced cervical carcinogenesis and strategies for designing prophylactic and therapeutic vaccines to prevent and cure the cervical cancer. In particular, focus will be on the rationale of targeting the E5 protein to develop therapeutic vaccines.

Regulation of human papillomavirus type 16 E7 activity through direct protein interaction with the E2 transcriptional activator

In order to ensure a productive life cycle, human papillomaviruses (HPVs) require fine regulation of their gene products. Uncontrolled activity of the viral oncoproteins E6 and E7 results in the immortalization of the infected epithelial cells and thus prevents the production of mature virions. Ectopically expressed E2 has been shown to suppress transcription of the HPV E6 and E7 region in cell lines where the viral DNA is integrated into the host genome, resulting in growth inhibition. However, it has been demonstrated that growth control of these cell lines can also occur independently of HPV E2 transcriptional activity in high-risk HPV types. In addition, E2 is unable to suppress transcription of the same region in cell lines derived from cervical tumors that harbor only episomal copies of the viral DNA. Here we show that HPV type 16 (HPV-16) E2 is capable of inhibiting HPV-16 E7 cooperation with an activated ras oncogene in the transformation of primary rodent cells. Furthermore, we demonstrate a direct interaction between the E2 and E7 proteins which requires the hinge region of E2 and the zinc-binding domain of E7. These viral proteins interact in vivo, and E2 has a marked effect upon both the stability of E7 and its cellular location, where it is responsible for recruiting E7 onto mitotic chromosomes at the later stages of mitosis. These results demonstrate a direct role for E2 in regulating the function of E7 and suggest an important role for E2 in directing E7 localization during mitosis.

Papillomaviruses: different genes have different histories

Papillomaviruses (PVs) infect stratified squamous epithelia in vertebrates. Some PVs are associated with different types of cancer and with certain benign lesions. It has been assumed that PVs coevolved with their hosts. However, recently it has been shown that different regions of the genome have different evolutionary histories. The PV genome has a modular nature and appeared after the addition of pre-existent blocks. This order of appearance in the PV genome is evident today in the different evolutionary rates of the different genes, with new genes--E5, E6 and E7--diverging faster than old genes--E1, E2, L2 and L1. Here, we propose an evolutionary framework aiming to integrate genome evolution, PV biology and epidemiology of PV infections.

Therapy for genital human papillomavirus-related disease

Genital human papillomavirus (HPV) infection is very common, and often sub-clinical and usually resolves without any treatment. Genital warts are caused by HPV 6/11 infection and are one of the commonest clinically recognised disease manifestations of genital HPV. Subjects with genital warts usually perceive them as cosmetically disfiguring, often leading to adverse psychological symptoms, and most subjects with genital warts will present requesting treatment. A wide variety of treatments are available including both provider- and patient-applied therapies. Various individual subject and disease factors mediate appropriate therapy choice. Some of the treatments that are used for genital warts can also be used for some cases of intraepithelial neoplasia caused by high-oncogenic risk HPVs occurring at vulval, anal or penile sites. Specific treatment considerations apply to genital warts in pregnancy and laryngeal papillomatosis and these are also discussed.

Immune control of human papillomavirus (HPV) associated anogenital disease and potential for vaccination

This review discusses: (1) immune mechanisms relevant to the natural control of a human papillomavirus (HPV) infection; (2) viral strategies to evade or subvert immune attack; (3) the significance of immune escape as a feature of the evolution of invasive cancer; (4) vaccine strategies for prevention and/or therapy. HPV infection and associated malignancy can induce humoral and cellular immunity to capsid and oncogene viral proteins, but it is not always clear whether such responses are a consequence of the disease rather than the resolving factor(s). Prophylactic strategies are utilising virus-like particles (VLP) composed of the L1 viral capsid protein to induce neutralising antibodies, while therapeutic approaches are aimed at generating specific T cells targeted at the viral E6 and/or E7 oncogenes. Thus far, HPV VLP vaccines have proved clinically efficacious in the early clinical trials to prevent infection. Different types of therapeutic vaccines including peptide, protein, DNA or viral vector encoded have proved safe and immunogenic in patients, although there is often no correlation with clinical outcome. Understanding the equilibrium between viral and immunological factors will be important in providing the appropriate tools to evoke effective prophylactic and therapeutic immunity. It seems likely that combined prophylactic and therapeutic vaccine approaches could offer the best prospect for any significant reduction in death from cervical cancer worldwide.