The promoter of a novel human papillomavirus (HPV77) associated with skin cancer displays UV responsiveness, which is mediated through a consensus p53 binding sequence

Ovine papillomaviruses: Diversity, pathogenicity, and evolution

The family Papillomaviridae includes a plethora of viral species infecting virtually all vertebrates excluding amphibians, with astonishing impact on human and animal health. Although more than 250 species have been described in humans, the total number of papillomaviruses (PVs) discovered in animals does not reach up to this number. In animals, PV infections are mostly asymptomatic or can cause variable clinical conditions ranging from self-limiting papillomas and other cutaneous and mucosal benign lesions to cancer. Most of animal PV types have been discovered in cattle, dogs, horses, and cats with other farm host species remaining overlooked. In particular, the number of PV types so far identified in sheep is limited. This paper comprehensively reviews ovine PVs features, including viral taxonomy and evolution; genome organization; viral tropism and pathogenesis; macroscopical features and histopathological patterns, as well as available diagnostics tools. Data are critically presented and discussed in terms of impact on veterinary and public health. The development of future dedicated research is also discussed.

Exposome and Skin. Part 2. The Influential Role of the Exposome, Beyond UVR, in Actinic Keratosis, Bowen's Disease and Squamous Cell Carcinoma: A Proposal

Actinic keratosis (AK) is the main risk factor for the development of cutaneous invasive squamous cell carcinoma (SCC). It represents the first sign of severe chronic ultraviolet radiation exposure, which has a clear significant effect. Nevertheless, the skin is exposed to many other exposome factors which should be thoroughly considered. Our aim was to assess the impact of exposome factors other than ultraviolet radiation (UVR) on the etiopathology of AK and Bowen's disease (BD) and progression of AK to SCC and to design tailored prevention strategies. We performed an exhaustive literature search in September 2021 through PubMed on the impact of exposome factors other than UVR on AK, BD and SCC. We conducted several parallel searches combining terms of the following topics: AK, BD, SCC and microbiome, hormones, nutrition, alcohol, tobacco, viral infections, chemical contaminants and air pollution. Notably, skin microbiome studies have shown how Staphylococcus aureus infections are associated with AK and AK-to-SCC progression by the production of chronic inflammation. Nutritional studies have demonstrated how a caloric restriction in fat intake, oral nicotinamide and moderate consumption of wine significantly reduce the number of premalignant keratoses and SCC. Regarding lifestyle factors, both alcohol and smoking are associated with the development of SCC in a dose-dependent manner. Relevant environmental factors are viral infections and chemical contaminants. Human papillomavirus infections induce deregulation of cellular proliferation and are associated with AK, BD and SCC. In addition to outdoor jobs, occupations such as industrial processing and farming also increase the risk of developing keratoses and SCC. The exposome of AK will undoubtedly help the understanding of its etiopathology and possible progression to SCC and will serve as a basis to design tailored prevention strategies.

Immunosuppression by UVB radiation exacerbates Leishmania mexicana skin lesions in mice

Cutaneous leishmaniasis is the most common form of leishmaniasis in humans. The disease is caused by several species, such as Leishmania mexicana, a protozoa parasite. Several major risk factors are associated with this disease, including poverty, poor housing, inadequate domestic hygiene, malnutrition, mobility, and occupational exposure. Solar radiation (UVB) has not been considered a risk factor because there is no scientific evidence demonstrating a correlation with increased susceptibility to cutaneous leishmaniasis. In this study, the shaved skin of the back of C57BL/6 mice was irradiated with 24.2 mJ/cm² of UVB. A delayed-type hypersensitivity (DTH) reaction was used to assess UV-induced immune suppression. Skin lesions were quantitated, and parasite burden and the presence of anti-Leishmania mexicana antibodies in serum and germinal centers in draining lymph nodes were determined. We found an increased in the lesion size and parasitic load in UVB-irradiated mice compared to the WT mice and B lymphocyte activation in draining lymph nodes and increased IgG1 production. Our results show an important role of UVB-induced suppression in cutaneous leishmaniasis through local production of IL-10 and systemic IgG1antibodies. This is the first study that demonstrates the effects of UVB radiation on cutaneous leishmaniasis by Leishmania mexicana.

Host cell p53 associates with the feline calicivirus major viral capsid protein VP1, the protease-polymerase NS6/7, and the double-stranded RNA playing a role in virus replication

p53 is implicated in several cellular pathways such as induction of cell-cycle arrest, differentiation, senescence, and apoptosis. p53 is activated by a broad range of stress signals, including viral infections. While some viruses activate p53, others induce its inactivation, and occasionally p53 is differentially modulated during the replicative cycle. During calicivirus infections, apoptosis is required for virus exit and spread into the host; yet, the role of p53 during infection is unknown. By confocal microscopy, we found that p53 associates with FCV VP1, the protease-polymerase NS6/7, and the dsRNA. This interaction was further confirmed by proximity ligation assays, suggesting that p53 participates in the FCV replication. Knocked-down of p53 expression in CrFK cells before infection, resulted in a strong reduction of the non-structural protein levels and a decrease of the viral progeny production. These results indicate that p53 is associated with the viral replication complex and is required for an efficient FCV replication.

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Host cell p53 protein levels and subcellular localization do not change during FCV infection.

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Host cell p53 associates with FCV major viral capsid protein VP1, protease-polymerase NS6/7, and the dsRNA in FCV infected cells.

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Host cell p53 is required for a FCV replication.

Papillomavirus Immune Evasion Strategies Target the Infected Cell and the Local Immune System

Persistent infection with human papillomavirus (HPV) initiates ~5% of all human cancers, and particularly cervical and oropharyngeal cancers. HPV vaccines prevent HPV infection, but do not eliminate existing HPV infections. Papillomaviruses induce hyperproliferation of epithelial cells. In this review we discuss how hyperproliferation renders epithelial cells less sensitive to immune attack, and impacts upon the efficiency of the local immune system. These observations have significance for the design of therapeutic HPV cancer immunotherapies.

Classical HLA alleles are associated with prevalent and persistent cervical high-risk HPV infection in African women

BACKGROUND

Persistent cervical high-risk human papillomavirus (hrHPV) infection is a necessary cause of cervical cancer. However, the host genetic factors underlying its risk are not well understood. We hypothesized that immunogenetic variation plays a role in hrHPV infection and persistence. Therefore, we conducted a study of classical HLA alleles and their association with hrHPV infection and persistence among women.

METHODS

We characterized HPV infection using SPF₁₀/LiPA₂₅in Nigerian women at baseline and at 6 months follow-up visits in 2014. hrHPV infection was prevalent if at least one carcinogenic HPV genotype was detected at the baseline visit and persistent if at least one carcinogenic HPV genotype was detected at the baseline and follow-up visits. Classical HLA alleles were imputed from genotypes in the MHC region using the HLA genotype imputation with attribute bagging (HIBAG) algorithm. HLA association tests were conducted under additive genetic models.

RESULTS

The mean (±SD) age of the 517 study participants was 38 (±8) years, 48% were HIV negative, 24% were hrHPV positive at baseline and 10% had persistent hrHPV infections. In multivariate regression models adjusted for age, HIV status and the first principal component, DQA1*01:02 and DQA1*02:01 were positively associated with prevalent but not persistent hrHPV infections, while DQA1*05:01 was negatively associated with prevalent hrHPV but positively associated with persistent cervical hrHPV infections. Four haplotypes (A*30:01-DQA1*05:01, B*07:02-C*07:02, B*07:02-DQA1*05:01 and C*07:02-DQA1*05:01) were significantly associated with prevalent cervical hrHPV infections and several haplotypes that included the DQA1*05:01 allelic variant were significantly associated with persistent cervical hrHPV infections. Six amino acid positions on DQα1 were associated with prevalent but not persistent cervical hrHPV infections.

CONCLUSIONS

In this first study to investigate the association between HLA alleles and persistent hrHPV in African women, we identified important risk alleles that merit further investigation. Our findings provide new insights into risk factors for hrHPV infection in African ancestry women.

Ovis aries Papillomavirus 3 in Ovine Cutaneous Squamous Cell Carcinoma

Squamous cell carcinoma (SCC) is a common malignancy affecting humans and other animals. Papillomaviruses (PVs) are frequently reported as causal agents of cutaneous benign and malignant epithelial lesions in different animal species, but only few studies have investigated their role in ovine SCC. In this study, we explore the possible involvement of the Ovine aries PVs (OaPV1, OaPV2, OaPV3) in cutaneous SCC using an integrated histological and molecular approach. Forty cutaneous SCCs from different anatomical locations of Sardinian sheep and 40 matched non-SCC samples were evaluated histologically and by polymerase chain reaction (PCR) to assess the presence of ovine PVs. In addition, DNA in situ hybridization (ISH) and reverse transcription-polymerase chain reaction (RT-PCR) were carried out to evaluate the cellular localization and viral transcriptional activity, respectively. OaPV3 DNA was detected in 26 of 40 (65%) SCCs and in 12 of 40 (30%) non-SCC samples using PCR. OaPV1 and OaPV2 were not detected. OaPV3 viral DNA was observed by ISH in malignant epithelial squamous cells of 18 of 40 (45%) SCCs. In addition, the viral transcriptional activity was identified in 24 of 40 (60%) SCCs by RT-PCR. Notably, a higher viral positivity was observed in SCCs compared with non-SCC samples. The considerable infection rate of OaPV3 in the most common skin tumor of the sheep suggests that PV could represent a key factor in the onset of ovine SCC.

Prevalence and viral load of oncogenic human papillomavirus (HPV) in pterygia in multi-ethnic patients in the Malay Peninsula

PURPOSE

The aim of the study was to determine the prevalence of human papillomavirus (HPV) in primary and recurrent pterygia samples collected from different ethnic groups in the equatorial Malay Peninsula.

METHODS

DNA was extracted from 45 specimens of freshly obtained primary and recurrent pterygia from patients and from 11 normal conjunctival swabs from volunteers with no ocular surface lesion as control. The presence of HPV DNA was detected by nested PCR. PCR-positive samples were subjected to DNA sequencing to determine the HPV genotypes. Real-time PCR with HPV16 and HPV18 type-specific TaqMan probes was employed to determine the viral DNA copy number.

RESULTS

Of 45 pterygia samples with acceptable DNA quality, 29 (64.4%) were positive for HPV DNA, whereas all the normal conjunctiva swabs were HPV negative. Type 18 was the most prevalent (41.4% of positive samples) genotype followed by type 16 (27.6%). There was one case each of the less common HPV58 and HPV59. Seven of the samples harboured mixed infections of both HPV16 and HPV18. All the four known recurrent pterygia samples were HPV-positive, whereas the sole early-stage pterygium sample in the study was HPV-negative. There was no significant association between HPV-positive status with gender or age. A high proportion of patients from the Indian ethnic group (five of six) were HPV-positive, whereas the Malay patients were found to have higher HPV positivity than the Chinese. The viral load of HPV18 samples ranged between 2 × 10(2) and 3 × 10(4) copies per μg, whereas the viral load of HPV16 specimen was 4 × 10(1) to 10(2) copies per μg.

CONCLUSION

This report describes for the first time the quantitative measurement of HPV viral DNA for pterygium samples. The high prevalence of oncogenic HPVs in our samples suggests a possible role for HPV in the pathogenesis of pterygia. Moreover, the relatively low HPV viral load is concordant with the premalignant nature of this ocular condition.

Identification of two novel functional p53 responsive elements in the herpes simplex virus-1 genome

Analysis of the herpes simplex virus-1 (HSV-1) genome reveals two candidate p53 responsive elements (p53RE), located in proximity to the replication origins oriL and oriS, referred to as p53RE-L and p53RE-S, respectively. The sequences of p53RE-L and p53RE-S conform to the p53 consensus site and are present in HSV-1 strains KOS, 17, and F. p53 binds to both elements in vitro and in virus-infected cells. Both p53RE-L and p53RE-S are capable of conferring p53-dependent transcriptional activation onto a heterologous reporter gene. Importantly, expression of the essential immediate early viral transactivator ICP4 and the essential DNA replication protein ICP8, that are adjacent to p53RE-S and p53RE-L, are repressed in a p53-dependent manner. Taken together, this study identifies two novel functional p53RE in the HSV-1 genome and suggests a complex mechanism of viral gene regulation by p53 which may determine progression of the lytic viral replication cycle or the establishment of latency.

The transmembrane channel-like protein family and human papillomaviruses: Insights into epidermodysplasia verruciformis and progression to squamous cell carcinoma

Epidermodysplasia verruciformis (EV) is a rare genodermatosis characterized by increased sensitivity to infection by the β-subtype of human papillomaviruses (β-HPVs), causing persistent, tinea versicolor-like dermal lesions. In a majority of affected individuals, these macular lesions progress to invasive cutaneous squamous cell carcinoma (CSCC) in sun-exposed areas. While mutations in transmembrane channel-like 6 (TMC6 / EVER1) and 8 (TMC8 / EVER2) have been causally linked to EV, their molecular functions are unclear. It is likely that their protective effects involve regulation of the β-HPV life cycle, host keratinocyte apoptosis vs. survival balance and/or T-cell interaction with infected host cells.

Pathways of tumor development and progression in drug-induced nonmelanoma skin cancer: a new hope or the next great confusion?

The factors that lead to the clinical manifestation of the nonmelanocytic skin tumors are different. Ultraviolet radiation, infections with human papillomaviruses, and inherited or iatrogenic-induced immunosuppression (in cases of autoimmune diseases and organ transplant recipients) are considered to be some of the most important generators and/or costimulating factors supporting the appearance of "de-novo" mutations and obstruct, in one or another way, the cell cycle arrest, the programmed cell death (apoptosis), and the immunosurveillance. Preconditions are thus created for the initial persistence and subsequent proliferation of the malignant cell branch in the genome, with the simultaneous increase of the risk of nonmelanocytic skin tumor manifestation.A number of medical drugs that possess a currently well-known selective, targeting, and immunomodulating effect, like the TNF-alpha inhibitors for example, most probably possess an additional blocking action on the death receptors within the framework of the extrinsic apoptotic pathway. In this way, they seem to be one of the major factors for the clinical manifestation not only of nonmelanocytic skin but also of a number of other type of tumors with a dependency on the genetic predisposition of each separate patient.This article focuses the attention on the basic exogenic and endogenic factors that affect the regulatory processes of the cellular cycle, apoptosis, immunosurveillance, and the human inflammasome in patients with nonmelanocytic skin tumors. These processes are interwoven in a complex network and are controlled by (1) the genome regulator p53, (2) its interaction with the proapoptotic acting proteins Bak and Bax, (3) as well as the interaction with the key regulatory protein of the inflammasome-ASC/TMS1.As a process, the malignant transformation is exceptionally dynamic, plastic, and adaptive. The exterior "interferences", on the part of the clinician, in the form of a planned therapy should be targeted at the simultaneous impact on the various pathogenetic chains with the objective of bringing the tumor cells to their total collapse. This can be made possible only after the careful and simultaneous-or parallel-examination of a much greater number of markers that serve to characterize the process of the malignant transformation-a fact, which is currently being disregarded by many researchers.

Longitudinal study of seroprevalence and serostability of 34 human papillomavirus types in European organ transplant recipients

Organ transplant recipients (OTR) are at increased risk of cutaneous squamous cell carcinoma, which may be related to reactivation of human papillomavirus (HPV) infections. Measurement of change in HPV antibodies after transplantation would help to explore this hypothesis. We measured antibodies to 34 HPV types on up to six occasions over 18 months in 441 OTRs from five European countries. At baseline (mean 24 days after transplantation), 80% of all OTRs were seropositive to at least one HPV type. The beta HPV genus had the highest seroprevalence (45%). For most HPV genera baseline seroprevalence peaked between 40 and 59 years old. Most OTRs retained their serostatus over time and antibody levels were stable. Seroprevalence in immunosuppressed OTRs is stable in the 18 months immediately after transplantation. Thus there is no short-term evidence that immunosuppression leads to new or reactivated skin infection with HPV sufficient to induce antibodies.

p53 and Sp1 cooperate to regulate the expression of Epstein-Barr viral Zta protein

Epstein-Barr virus (EBV) belongs to the gammaherpesvirus family. To produce infectious progeny, EBV reactivates from latency into the lytic cycle by expressing the determinative lytic transactivator, Zta. In the presence of histone deacetylase inhibitor (HDACi), p53 is a prerequisite for the initiation of the EBV lytic cycle by facilitating the expression of Zta. In this study, a serial mutational analysis of Zta promoter (Zp) indicated an important role for the ZID element in responding to HDACi induction and p53 binds to this ZID element together with Sp1, a universal transcription factor. Abolition of the DNA-binding ability of Sp1 reduces the inducibility of ZID by HDACi and also reduces the amount of p53 binding to ZID. Finally, it was shown that EBV in p53-positive-lymphoblastoid cell lines (LCLs) can enter into the lytic cycle spontaneously; however, knockdown of p53 in LCLs leads to retardation of EBV reactivation.

Association of human papilloma virus with pterygia and ocular-surface squamous neoplasia

There are more microorganisms that colonize the human body than resident cells; some are commensal whereas others are pathogenic. Pathogenic microorganisms are sensed by the innate or adaptive immune system, an immune response is initiated, and the infection is often cleared. Some microorganisms have developed strategies to evade immune defenses, ensuring their long-term survival with potentially devastating consequences for the host. Approximately 18% of all cancers can be attributed to infective agents; the most common being Helicobacter pylori, Human papilloma virus (HPV) and Hepatitis B and C virus in causing stomach, cervical and liver carcinoma, respectively. This review focuses on whether HPV infection is necessary for initiating pterygia, a common benign condition and ocular-surface squamous neoplasia (OSSN), a rare disease with metastatic potential. The search engine PubMed was used to identify articles from the literature related to HPV and pterygium or conjunctival neoplasia. From 34 investigations that studied HPV in pterygia and OSSN, a prevalence rate of 18.6% (136/731) and 33.8% (144/426), respectively, was recorded. The variation in HPV prevalence (0-100%) for both disease groups may have arisen from study-design faults and the techniques used to identify the virus. Overall, the data suggest that HPV is not necessary for initiating either condition but may be a co-factor in susceptible hosts. Currently, over 60 million people worldwide have been immunized with HPV vaccines, but any effect on pterygium and OSSN development may not be known for some time as these lesions can evolve over decades or occur in older individuals.

The human health effects of ozone depletion and interactions with climate change

Depletion of the stratospheric ozone layer has led to increased solar UV-B radiation (280-315 nm) at the surface of the Earth. This change is likely to have had an impact on human exposure to UV-B radiation with consequential detrimental and beneficial effects on health, although behavioural changes in society over the past 60 years or so with regard to sun exposure are of considerable importance. The present report concentrates on information published since our previous report in 2007. The adverse effects of UV radiation are primarily on the eye and the skin. While solar UV radiation is a recognised risk factor for some types of cataract and for pterygium, the evidence is less strong, although increasing, for ocular melanoma, and is equivocal at present for age-related macular degeneration. For the skin, the most common harmful outcome is skin cancer, including melanoma and the non-melanoma skin cancers, basal cell carcinoma and squamous cell carcinoma. The incidence of all three of these tumours has risen significantly over the past five decades, particularly in people with fair skin, and is projected to continue to increase, thus posing a significant world-wide health burden. Overexposure to the sun is the major identified environmental risk factor in skin cancer, in association with various genetic risk factors and immune effects. Suppression of some aspects of immunity follows exposure to UV radiation and the consequences of this modulation for the immune control of infectious diseases, for vaccination and for tumours, are additional concerns. In a common sun allergy (polymorphic light eruption), there is an imbalance in the immune response to UV radiation, resulting in a sun-evoked rash. The major health benefit of exposure to solar UV-B radiation is the production of vitamin D. Vitamin D plays a crucial role in bone metabolism and is also implicated in protection against a wide range of diseases. Although there is some evidence supporting protective effects for a range of internal cancers, this is not yet conclusive, but strongest for colorectal cancer, at present. A role for vitamin D in protection against several autoimmune diseases has been studied, with the most convincing results to date for multiple sclerosis. Vitamin D is starting to be assessed for its protective properties against several infectious and coronary diseases. Current methods for protecting the eye and the skin from the adverse effects of solar UV radiation are evaluated, including seeking shade, wearing protective clothing and sunglasses, and using sunscreens. Newer possibilities are considered such as creams that repair UV-induced DNA damage, and substances applied topically to the skin or eaten in the diet that protect against some of the detrimental effects of sun exposure. It is difficult to provide easily understandable public health messages regarding "safe" sun exposure, so that the positive effects of vitamin D production are balanced against the negative effects of excessive exposure. The international response to ozone depletion has included the development and deployment of replacement technologies and chemicals. To date, limited evidence suggests that substitutes for the ozone-depleting substances do not have significant effects on human health. In addition to stratospheric ozone depletion, climate change is predicted to affect human health, and potential interactions between these two parameters are considered. These include altering the risk of developing skin tumours, infectious diseases and various skin diseases, in addition to altering the efficiency by which pathogenic microorganisms are inactivated in the environment.

Pathogenesis of nonmelanoma skin cancers in organ transplant recipients

Nonmelanoma skin cancer (NMSC) is the most common human cancer, with an incidence of more than 1.2 million per year in the USA. The risk for the development of NMSCs increases by approximately 10-250 fold in chronically immune suppressed organ transplant recipients (OTRs). Solar UVB is the most common etiologic factor in the development of this neoplasm, both in immune competent and immune suppressed populations. This review provides a description of NMSC in OTRs. It also provides an account of the various immunologic and non-immune-dependent mechanisms involved in the pathogenesis and progression of NMSCs in OTRs. Finally, this review addresses possible strategies for the prevention of this cancer, particularly focusing on the aspects that may be incorporated to prevent negative effects of chemopreventive chemicals on graft survival.

Merkel cell polyomavirus small T antigen mRNA level is increased following in vivo UV-radiation

Merkel cell carcinoma (MCC) is a rare but aggressive skin cancer involving Merkel cells. Recently, a new human polyomavirus was implicated in MCC, being present in 80% of the samples analyzed. In virus-positive MCC, the Merkel cell polyomavirus (MCPyV) is clonally integrated into the patients DNA, and carries mutations in its large T antigen, leading to a truncated protein. In non-symptomatic tissue MCPyV can reside at very low levels. MCC is also associated with older age, immunosuppression and sun exposure. However, the link with solar exposure remains unknown, as the precise mechanism and steps involved between time of infection by MCPyV and the development of MCC. We thus investigated the potential impact of solar simulated radiation (SSR) on MCPyV transcriptional activity. We screened skin samples of 20 healthy patients enrolled in a photodermatological protocol based on in vivo-administered 2 and 4 J/cm(2) SSR. Two patients were infected with two new variants of MCPyV, present in their episomal form and RT-QPCR analyses on SSR-irradiated skin samples showed a specific and unique dose-dependent increase of MCPyV small t antigen transcript. A luciferase based in vitro assay confirmed that small t promoter is indeed UV-inducible. These findings demonstrate that solar radiation has an impact on MCPyV mRNA levels that may explain the association between MCC and solar exposure.

Shared and persistent asymptomatic cutaneous human papillomavirus infections in healthy skin

Cutaneous human papillomavirus (HPV) types are commonly found in normal skin, and some of them have been suspected to play a role in the development of non-melanoma skin cancer. This present study is divided into three sections, the aims of this study were to examine if certain HPV-types persist over time and if HPV-types are shared within families. From the first part of the study, swab samples from foreheads were collected for three longitudinal studies from one family with a newborn baby. Five specific HPV-types were isolated from the family with a newborn, with HPV-5 and FA67 being found at various time points and prevalence rates in all four members of the family. Part 2 consisted of a followed up study from two families with a 6 years interval. Six of the family members were found to have at least one of the HPV-types identified in the family 6 years earlier. Many of the HPV-types identified were shared within the families studied. Part 3 of this study involved weekly samples from four healthy females for 4 months. Among the four healthy individuals, 11%, 65%, and 56% of the weekly samples were HPV-DNA positive with one individual HPV-negative. All specimens were tested for HPV-DNA by PCR using the broad range HPV-type primer pair FAP59/64. The positive samples were HPV-type determined by cloning and sequencing. Specific cutaneous HPV-types persist over long periods of time in healthy skin in most individuals investigated and certain HPVs are shared between family members.

Molecular concepts of virus infections causing skin cancer in organ transplant recipients

Globally approximately 15% of all malignant tumors are caused by viruses and even a higher percentage is observed in organ transplant recipients (OTR). Here, nonmelanoma skin cancer (NMSC) is the most frequent malignancy, which correlates with cutaneous human papilloma virus (HPV) infection. In the present review, we reflect on some recent general concepts how tumor viruses can either act as direct or indirect carcinogens in the multistep process of carcinogenesis. Immunosuppressive drugs in OTR, which reduce the risk of organ rejection, could be critical in increasing the activation of persisting viral infections, thereby enhancing the probability to develop skin tumors. We discuss virus-induced transformation with special emphasis on the function of HPV as an indirect and HHV-8 as direct carcinogen in the development of NMSC and Kaposi sarcoma (KS), respectively. Moreover, we describe a rodent model system useful to examine future strategies in preventing skin tumor formation in immunosuppressed OTR.

Human papillomavirus type spectrum in normal skin of individuals with or without a history of frequent sun exposure

Cutaneous human papillomavirus (HPV) has been widely detected in healthy skin. Previous studies have found that UV radiation can activate several HPV types, and a possible role for cutaneous HPV in the development of non-melanoma skin cancer has been suggested. This study investigated the prevalence and type-spectrum of cutaneous HPV in relation to UV radiation by studying forehead skin swab samples from 50 healthy males frequently exposed to the sun and 50 healthy males who were not frequently exposed to the sun. A questionnaire including ethnic background of the participants, history of cancers and a self-assessment of sun-exposure was also conducted and analysed. PCR with the FAP primer pair was carried out to detect HPV DNA in samples. HPV prevalence was higher in individuals who spent more time outdoors and in individuals with a history of skin cancers (P=0.044 and P=0.04, respectively). Furthermore, individuals wearing sunglasses as a means of sun protection had a lower prevalence of HPV (P=0.018). Interestingly, HPV-76 was only detected in the group without frequent sun-exposure (P=0.001). These results suggest that increased UV radiation exposure may be a factor leading to a difference in prevalence of cutaneous HPV types.

Cutaneous Human Papillomaviruses as Recurrence Factor in Actinic Keratoses

Actinic keratoses (AK) are common, premalignant lesions cause mainly by UV DNA damage. Progression into squamous cell carcinoma may be influenced by other several factors such as chronic chemical exposure or viral infection. A carcinogenic role of Human Papillomaviruses (HPV) in early steps of skin tumour development was recently hypothesized; moreover the presence of HPV DNA seems to be higher in cancer precursor lesions. The aim of this work is to identify the presence of HPV DNA in biopsies from Actinic Keratoses (AK) and from normal skin samples collected from dermatological healthy subjects in Italy, in order to evaluate the severity and the clinical evolution of the HPV positive lesions. The DNA test revealed 37% HPV positivity in AK patients versus 0% in the control group; many different genotypes and variants were identified by direct sequencing of PCR product. The HPV positive AK were usually clinically indistinguishable from the HPV negative. All AK lesions were removed by laser treatment, but AK lesions recurred in all HPV positive patients after a period of 45–60 days whereas the same disappeared in the HPV negative ones. These data permit to hypothesize that the presence of HPV DNA could be an aggravating factor for AK lesion severity and recurrence.

p53 and the pathogenesis of skin cancer

The p53 tumor suppressor gene and gene product are among the most diverse and complex molecules involved in cellular functions. Genetic alterations within the p53 gene have been shown to have a direct correlation with cancer development and have been shown to occur in nearly 50% of all cancers. p53 mutations are particularly common in skin cancers and UV irradiation has been shown to be a primary cause of specific 'signature' mutations that can result in oncogenic transformation. There are certain 'hot-spots' in the p53 gene where mutations are commonly found that result in a mutated dipyrimidine site. This review discusses the role of p53 from normal function and its dysfunction in pre-cancerous lesions and non-melanoma skin cancers. Additionally, special situations are explored, such as Li-Fraumeni syndrome in which there is an inherited p53 mutation, and the consequences of immune suppression on p53 mutations and the resulting increase in non-melanoma skin cancer in these patients.

Cutaneous human papillomaviruses found in sun-exposed skin: Beta-papillomavirus species 2 predominates in squamous cell carcinoma

BACKGROUND

A spectrum of cutaneous human papillomaviruses (HPVs) is detectable in nonmelanoma skin cancers, as well as in healthy skin, but the significance that the presence of these types of HPV DNA has for the pathogenesis of skin cancer remains unclear.

METHODS

We studied 349 nonimmunosuppressed patients with skin lesions (82 with squamous cell carcinomas, 126 with basal cell carcinomas, 49 with actinic keratoses, and 92 with benign lesions). After superficial skin had been removed by tape, paired biopsy samples--from the lesion and from healthy skin from the same patient--were tested for HPV DNA. Risk factors for HPV DNA were analyzed in multivariate models.

RESULTS

Overall, 12% of healthy skin samples were positive for HPV DNA, compared with 26% of benign lesions, 22% of actinic keratoses, 18% of basal cell carcinomas, and 26% of squamous cell carcinomas. HPV DNA was associated with sites extensively exposed to the sun, both for the lesions (odds ratio [OR], 4.45 [95% confidence interval {CI}, 2.44-8.11]) and for the healthy skin samples (OR, 3.65 [95% CI 1.79-7.44]). HPV types of Beta-papillomavirus species 2 predominate in squamous cell carcinomas (OR, 4.40 [95% CI, 1.92-10.06]), whereas HPV types of Beta-papillomavirus species 1 are primarily found in benign lesions (OR, 3.47 [95% CI, 1.72-6.99]).

CONCLUSIONS

Cutaneous HPV types are primarily detected at sites extensively exposed to the sun. HPV types of Beta-papillomavirus species 2, but not of species 1, are associated with squamous cell carcinoma.

The oncogenic potential of human papillomaviruses: a review on the role of host genetics and environmental cofactors

Human papillomaviruses (HPVs), with over 100 genotypes, are a very complex group of human pathogenic viruses. In most cases, HPV infection results in benign epithelial proliferations (verrucae). However, oncogenic types of HPV may induce malignant transformation in the presence of cofactors. For example, over 99% of all cervical cancers and a majority of vulval, vaginal, anal and penile cancers are the result of oncogenic HPV types. Such HPV types have been increasingly linked to other epithelial cancers involving the skin, larynx and oesophagus. Although viral infection is necessary for neoplastic transformation, evidence suggests that host and environmental cofactors are also required. Research investigating HPV oncogenesis is complex and quite extensive. The inability to produce mature HPV virions in animal models has been a major limitation in fully elucidating the oncogenic potential and role of associated cofactors in promoting malignant transformation in HPV-infected cells. We have reviewed the literature and provide a brief account of the current understanding of HPV oncogenesis, emphasizing the role of genetic susceptibility, immune response, and environmental and infectious cofactors.

Human papillomavirus type 77 E7 protein is a weak deregulator of cell cycle

Human Papillomavirus type 77 is a skin type found in non-melanoma skin cancers of immuno-compromised individuals. Although, the HPV77 E6 oncoprotein has been well studied, nothing is known about E7. Studies on mucosal HPV types (e.g. HPV16) showed that E7 deregulates the cell cycle by binding to and promoting degradation of retinoblastoma protein (pRb). Here, we characterized the impact of HPV77 E7 on the cell cycle. We observed that HPV77 E7 associated with pRb with a lower affinity than HPV16 E7, promoting weakly its degradation. Although, HPV16 E7 led to cellular proliferation and accumulation of the cell cycle inhibitor p16(INK4a), both events were not clearly observed in HPV77 E7 cells. Together, these data indicate that HPV77 E7 does not efficiently deregulate the cell cycle, in contrast to several E7s of mucosal HPV types.

Beta-papillomaviruses in anogenital hairs plucked from healthy individuals

A total of 150 specimens of anogenital hairs plucked from the scrotal, pubic, and perianal region of 51 immunocompetent healthy male individuals were tested for the presence of beta-papillomaviruses (beta-HPV) using the nested M(a)/H(a) polymerase chain reaction. Beta-HPV were found in a total of 38 (25.3%) of 150 hair samples. According to the sampling sites, beta-HPV were detected in 18/51 (35.3%), 13/50 (26.0%), and 7/49 (14.3%) plucked hair samples obtained from the pubic, scrotal, and perianal region, respectively. The prevalence of beta-HPV in the plucked pubic hairs was significantly higher than in the perianal hairs (P = 0.013). In contrast, the difference in the prevalence of beta-HPV in the pubic and scrotal hairs as well as in scrotal and perianal hairs did not reach statistical significance (P = 0.302 and P = 0.227, respectively). The difference in the lifetime-cumulative sun exposure is the most likely explanation for the differences obtained on beta-HPV prevalence. Beta-HPV genotype HPV-38 was detected most frequently, followed by HPV-36, HPV-15, and HPV-14D. In addition to the beta-HPV recognized officially five partial DNA sequences suggesting putative new HPV genotypes were identified.

Skin lesions in adult liver transplant recipients: a study of 100 consecutive patients

BACKGROUND

The surgical advances made in the area of organ transplantation along with the use of more efficacious immunosuppression have meant an increase in patient survival. This longer-living transplant population has started to exhibit cutaneous problems, some of which lead to an increased mortality while others lead to a decline in the quality of life.

OBJECTIVES

The primary objective was to determine the different types of cutaneous lesions encountered in the adult liver transplant population. Secondary objectives were to determine the impact, if any, of the duration of transplant, the type of immunosuppression involved and the degree of sun exposure and skin phototype, on the skin cancers encountered in this transplanted population.

METHODS

Two dermatologists examined 100 consecutive liver transplant recipients (LTRs) attending the transplant outpatient department. Skin examination included the face and whole body and lesions found were categorized into the following groups: cutaneous malignancies, squamoproliferative lesions, cutaneous infections and others that did not fall into any of these categories.

RESULTS

The reasons for organ transplantation were numerous. The mean age at transplantation was 42.5 years. The average time since transplantation was 5.5 (range 0.75-16 years). Four patients developed skin cancers; among them there were a total of seven skin cancers (one squamous cell carcinoma, six basal cell carcinomas). Fungal infections accounted for 19% of all cutaneous infections seen, viral infections 2% and bacterial infections 5%. Triple-drug immunosuppressive therapy (ciclosporin A, azathioprine and prednisolone) was used in 35% of LTR patients, while dual therapy (tacrolimus and prednisolone) was used in 48% and monotherapy (tacrolimus) was used in 17% of LTRs.

CONCLUSIONS

Immunosuppressive therapy is believed to be one of the most important risk factors in the development of skin cancer in solid organ transplant recipients. The relatively low prevalence of skin cancer in our liver transplant population may in part be explained by the relatively high percentage of recipients on dual and monotherapy (48% and 17% respectively), and the shorter duration of therapy. Our study suggests that although LTRs are at higher risk of developing nonmelanoma skin cancer than the general population, the risk is comparable with other solid organ transplant recipients.

Diversity of cutaneous human papillomavirus types in individuals with and without skin lesion

BACKGROUND

Human papillomavirus (HPV) is ubiquitous on the skin of normal and immunosuppressed hosts.

OBJECTIVE

We describe the diversity of HPV types in skin specimens using PCR-sequencing directly and after cloning with FAP59/64 or HVP2/B5 primers.

STUDY DESIGN

Cross-sectional analysis of skin swabs.

RESULTS

Seventy-five (92.6%) of 81 subjects provided samples that could be analysed with PCR (34 healthy controls <50 years old, 13 healthy controls > or =50 years old, 12 with actinic keratosis (AK), 8 with squamous cell carcinoma (SCC) and 8 renal transplant recipients). HPV DNA was detected more frequently with FAP59/64 (68/75, 91%) than with HVP2/B5 (9/75, 12%) (p<0.001). Agreement of typing results using FAP59/64 primers with both sequencing strategies was fair (mean kappa 0.56+/-0.19, 95% CI: 0.46-0.65). HPV species 1 and 2 of the beta-papillomavirus genus were associated with the presence of AK (OR=24.8, 95% CI: 2.3-262.6). A greater number of HPV types per sample was found in individuals with AK or SCC (p=0.046) or AK alone (p=0.02), than in healthy participants.

CONCLUSION

HPV infection on the skin is best evaluated with a combination of primers and sequencing strategies. Novel putative types were frequently detected in SCC. Skin lesions have a greater number of HPV types than normal skin.

The mechanisms and consequences of ultraviolet-induced immunosuppression

Exposure to ultraviolet radiation (UVR) can result in immune suppression to antigens encountered within a few days of the irradiation. The process leading to the down-regulation in immune responses is complex. It is initiated by several photoreceptors located in the skin surface, namely DNA, trans-urocanic acid and membrane components. The absorption of UVR by these chromophores then leads to the release of a wide range of mediators that can affect antigen presenting cells locally or systemically. The final steps include the generation of antigen-specific T cells capable of regulating immunity. The consequences of the UV-induced changes in the skin immune system for the control of skin cancers, infectious diseases including vaccination, and autoimmune diseases are considered. Finally, the effects of active vitamin D, synthesised in the epidermis following UVR, are discussed in the context of the skin immune response.

The Effect of Ultraviolet Radiation on Human Viral Infections

Exposure to UV radiation is recognized to suppress cell-mediated immunity and therefore could adversely affect the course of a viral infection. Rodent models of viral infection confirm this possibility but the situation in human subjects is not so clear, apart from two exceptions. These are herpes simplex, in which sunlight exposure can cause reactivation, and certain papillomavirus types in which sunlight exposure can lead to the development of nonmelanoma skin cancer. In both cases, there are UV response elements in the viral genomes that alter the normal interactions between the viruses and the host following exposure, and UV-induced effects on the immune response occur in addition. These complex mechanisms are discussed, and the situation regarding UV radiation and viral exanthems plus other viruses, including the retroviruses, summarized. Finally viral vaccination is considered in the context of UV exposure and the importance of the host's genetic background emphasized. Further research is required to evaluate whether sunlight can significantly affect the resistance to common viral infections and vaccines.

E6* oncoprotein expression of human papillomavirus type-16 determines different ultraviolet sensitivity related to glutathione and glutathione peroxidase antioxidant defence

Clinical observations of non-melanoma skin cancer in immunocompromised patients, such as organ transplant recipients, suggest co-operative effects of human papillomavirus (HPV) and ultraviolet (UV) radiation. The aim of the present study is to evaluate UV sensitivity and DNA damage formation according to antioxidant status in HPV16-infected keratinocytes. We used SKv cell lines, infected with HPV16 and well characterized for their proliferative and tumorigenic capacities. We showed that SKv cell lines presented various E6* (a truncated form of E6) RNA levels. We demonstrated that the higher oncoprotein RNA expression level was associated with a higher resistance to solar-simulated radiation, more specifically to UVB radiation and to hydrogen peroxide. Moreover, this high resistance was associated with a low oxidative DNA damage formation after UV radiation and was related to high glutathione content and glutathione peroxidase activities. Therefore, the results of our study suggest that E6* levels could modulate the glutathione/glutathione peroxidase pathway providing a mechanism to protect HPV-infected keratinocytes against an environmental oxidative stress, such as UV radiation.

Human papillomaviruses and skin cancer

Cutaneous epidermodysplasia verruciformis (EV)-associated human papillomaviruses (HPVs) are found frequently in skin cancers especially in immunosuppressed people. They are also detectable in the normal skin and hair follicles of a proportion of individuals who have no immune defect. The available evidence to link HPVs causally with skin carcinogenesis is not conclusive, but includes epidemiological, molecular and immunological studies.

Iatrogenic skin cancer: induction by psoralen/ultraviolet A and immunosuppression of organ transplant recipients

Photochemotherapy (psoralen/UVA (PUVA)) is an efficient therapeutic tool for a wide range of skin diseases. Concern, however, exists regarding the long-term carcinogenic effects of this treatment modality and, as a consequence, is being used less frequently. PUVA remains an important treatment in our therapeutic armamentarium but must be used with caution in those patients with risk factors and cumulative dose exposure must be limited. PUVA-induced cancers show features in common with skin cancers induced by immunosuppressed organ transplant recipients. Tumours in the latter group of individuals are, however, much more aggressive and difficult to manage.

Human papillomavirus and extragenital in situ carcinoma

BACKGROUND

The relation between human papillomavirus (HPV) and extragenital Bowen's disease (BD) is controversial.

METHODS

This study used in situ hybridisation to evaluate the rate of HPV in extragenital cutaneous BD and investigated possible relations with immune status and exposure of skin to light.

RESULTS

HPV DNA was detected in 58% of 69 samples from 50 patients. The percentage of HPV detection was not significantly higher in exposed (55%) than unexposed areas (65%), and no difference in HPV rate was found between immunosuppressed and immunocompetent patients.

CONCLUSION

Thus, this study confirms the high rate of HPV detection in extragenital cutaneous BD and suggests that there is no apparent relation concerning exposed areas and immune status.

UV-B irradiation stimulates the promoter activity of the high-risk, cutaneous human papillomavirus 5 and 8 in primary keratinocytes

Human papillomaviruses (HPV) have been implicated in the development of non-melanoma skin cancer (NMSC). HPV types 5 and 8 are strongly associated with NMSC in patients with the inherited disease Epidermodysplasia verruciformis (Ev). In these patients tumours arise predominantly on sun-exposed skin and consistently harbour HPV DNAs. To determine whether UV-B irradiation modulates the noncoding region (NCR) promoter activity of the Ev-HPV types 5, 8, 9, 14, 23, 24, and 25 we performed transient transfection assays with NCR luciferase reporter gene constructs in primary human epithelial keratinocytes (PHEKs) and in p53-null RTS3b cells. Each of the HPVs showed different basal NCR activity in both cell types and reacted differently upon UVB treatment and p53 cotransfection in RTS3b cells. The NCR of HPV5 and 8 were the only ones to be activated by UV-B in PHEKs. The stimulation of the NCR activity of the high-risk cutaneous HPV types 5 and 8 by UV-B irradiation may point to a role of this interaction in the development of NMSC.

Human papillomavirus type 77 E6 protein selectively inhibits p53-dependent transcription of proapoptotic genes following UV-B irradiation

DNA damage, such as that elicited by UV-B, can induce either a cell cycle arrest or apoptosis that can be signalled by the p53 protein through the activation of a number of downstream cellular target genes. In contrast to oncogenic anogenital human papillomaviruses (HPVs), which mediate proteolytic degradation of p53, the E6 protein of cutaneous HPVs, such as HPV 77, do not promote p53 degradation. We have previously shown, however, that expression of HPV 77 E6 can effectively block UV-induced apoptosis in cells that have UV-activated p53. Here, we report that expression of the E6 protein from the cutaneous HPV 77 attenuates the UV-induced transactivation of p53-regulated proapoptotic genes Fas, PUMAbeta, Apaf-1, PIG3. This inhibition of p53-activation of proapoptotic genes by HPV77 E6 is exerted selectively, as the increased expression of p53 target genes involved in cell cycle arrest or regulatory functions regulation, such as p21 and Hdm2, is unaffected. Our data suggest that HPV 77 E6 may play an important role in specifically deregulating p53-dependent transactivation of proapoptotic genes upon UV-B irradiation.

High prevalence of cutaneous human papillomavirus DNA on the top of skin tumors but not in "Stripped" biopsies from the same tumors

Genomes of human papillomaviruses (HPV) are common in biopsies from non-melanoma skin cancers but are also found on healthy skin and it is possible that HPV positivity in tumor biopsies by PCR may merely reflect contamination of the lesion surface. To investigate this issue, 229 immunocompetent patients were tested for HPV DNA in swab samples collected on top of skin tumors and in biopsies of the same tumors, obtained after stripping with tape to remove superficial layers. HPV DNA was detected on top of 69% (159 of 229) of the lesions, and in 12% (28 of 229) of the stripped biopsies (p<0.001). The difference was seen for all four types of tumors studied. Seborrheic keratosis had 79% (34 of 43) HPV positivity on top of lesions versus 19% (eight of 43) in biopsies; actinic keratosis had 83% (38 of 46) HPV positivity on top versus 11% (five of 46) in biopsies; basal cell carcinoma had 63% (69 of 109) on top versus 8% (nine of 109) in biopsies and squamous cell carcinoma had 58% (18 of 31) on top versus 19% (six of 31) in biopsies. HPV DNA is common in superficial layers of lesions, but is not necessarily present throughout tumors.

Possible involvement of epidermodysplasia verruciformis human papillomaviruses in the immunopathogenesis of psoriasis: a proposed hypothesis

We have shown previously in psoriasis a very high prevalence of epidermodysplasia verruciforms-associated human papillomavirus 5 (EVHPV5) DNA and antibodies to human papillomavirus 5 (HPV5) virus-like particle (VLP) L1, and we suggested that this benign hyperproliferative disorder could be a reservoir for EVHPVs. Here we provide new data confirming the expression of EVHPVs in psoriasis and present our hypothesis on their possible involvement in the immunopathogenesis of the disorder. The new important finding was detection by radioimmunoprecipitation assay of a very high prevalence of antibodies to E6/E7 HPV5 oncoproteins, known to enhance keratinocyte proliferation. More recently, EV genes were identified, EVER1 and EVER2, whose mutations are responsible for epidermodysplasia verruciformis. Eidermodysplasia verruciforms-associated human papillomaviruses are harmless to the general population as a result of genetic restriction, which in psoriasis appears to be partly alleviated, and this may allow the viral gene expression. We hypothesize that induction of keratinocyte proliferation in psoriasis by various stimuli initiates the EVHPV life cycle with expression of early (E6/E7) and late (L1) viral proteins. The early proteins may, in turn, enhance the keratinocyte proliferation, and the late proteins could serve as target for specific-B- and T-cell-mediated responses. Immune responses against the viral antigens in the epidermis may result in the chemoattraction of leukocytes and Munro abscess formation, as well as in production of the psoriatic process. The novel immunomodulatory therapies could also inhibit immune responses against EVHPV proteins, leading to decreased cytokine production, keratinocyte proliferation and EVHPV expression. Thus the beneficial effect of these therapies is not discordant with the propose hypothesis of possible involvement of EVHPVs in the immunopathogenesis of psoriasis.

Sunlight exposure and (sero)prevalence of epidermodysplasia verruciformis-associated human papillomavirus

Ultraviolet radiation (UVR) is associated with an increased risk of squamous cell carcinoma (SCC), which is in part due to immunomodulation. In addition, human papilloma virus (HPV), especially the epidermodysplasia verruciformis (EV)-associated types, may be involved. In view of the capacity of UVR to impair host resistance to infections, we investigated the relationship between solar exposure and the prevalence of cutaneous HPV. In a case-control study on skin cancer (320 controls and 156 patients) a lifetime-retrospective questionnaire on sun exposure was administered. The presence of DNA of HPV types 5, 8, 15, 20, 24, and 38 in plucked eyebrow hair and type-specific seroreactivity were assessed and analyzed in relation to estimated exposure. Sunburn episodes in the past, especially at age 13-20 y, appeared to be associated with an enhanced risk of EV-HPV DNA positivity. In contrast, a higher lifetime sun exposure was associated with a lower risk of HPV infection. These results indicate that UVR at erythematogenic doses increases the risk of EV-HPV infection, possibly due to impaired host resistance to HPV and/or a direct effect of UVR on viral replication. The favorable association between lifetime sun exposure and HPV prevalence, however, underscores the enigmatic role of HPV in skin carcinogenesis.

Increased risk of skin cancer associated with the presence of epidermodysplasia verruciformis human papillomavirus types in normal skin

BACKGROUND

Human papillomaviruses (HPVs) are found in normal skin and in benign and malignant skin conditions. Epidermodysplasia verruciformis (EV) HPV types are those most plausibly linked to the development of squamous cell carcinomas of the skin.

OBJECTIVES

To assess the risk of nonmelanoma skin cancer (NMSC) associated with the presence of EV HPV in normal skin in immunocompetent (IC) individuals and renal transplant recipients (RTRs).

METHODS

Using a degenerate and nested polymerase chain reaction technique, HPV DNA was sought in 124 normal skin samples from sun-exposed and nonsun-exposed sites, from 39 IC individuals and 38 RTRs, both with and without NMSC. Data were analysed using the Mantel-Haenszel test and by logistic regression analysis.

RESULTS

HPV DNA was detected in 58/67 (87%) and 20/57 (35%) samples from renal transplant and IC patients, respectively. There was no difference in either the prevalence or spectrum of HPV types found in sun-exposed and nonsun-exposed normal skin. However, there was significant association between NMSC and the presence of EV HPV DNA. Multivariate analysis provided an odds ratio of 6.41 (95% confidence interval 1.79-22.9) for the association of EV HPV DNA in normal skin (irrespective of site) and NMSC status, even after stratifying for patient group and adjusting for the clustering effect of multiple sampling. Conversely, there was no association between skin cancer status and the presence of cutaneous or mucosal HPV types in either sun-exposed or nonsun-exposed skin.

CONCLUSIONS

HPV DNA is widespread in normal adult skin, particularly in transplant patients. In our study, the presence of EV but not cutaneous HPV DNA in normal skin was significantly associated with NMSC status and may prove to be of predictive value for skin cancer risk. These data provide reason to focus on EV HPV types as causal agents in skin cancer.

Viral warts in organ transplant recipients: new aspects in therapy

The long-term success of organ transplantation depends on the prevention of allograft rejection and improvement in quality of life for the patients. This has been achieved through better immunosuppressive regimens with lower dosages and a new generation of immunosuppressive drugs. However, these immunosuppressive agents not only impair the patient's reactivity to the graft, but also to infectious organisms, thereby making them more susceptible to opportunistic pathogens. Because of this, organ transplant recipients are predisposed to epithelial malignancies and infections. The majority of transplant recipients will develop warts induced by human papillomavirus (HPV). Some of these viral warts may present with atypical histological features and may progress into squamous cell carcinomas. The risk for cutaneous cancers after transplantation is much higher than in the immunocompetent population. Current therapies for HPV-associated skin tumours mainly depend on the destruction of affected skin areas. These treatment modalities are of limited efficacy and are usually painful for the patients. A promising novel therapeutic agent is imiquimod, an immune response modifier. Clinical efficacy of imiquimod has been observed for different skin lesions, including viral warts in both immunocompetent and immunosuppressed patients.

[Epidermodysplasia verruciformis--a model of virus induced oncogenesis in the skin]

<zakljucak> U osnovi HPV izazvane onkogeneze u kozi nalaze se visoko specificni mehanizmi HPV adaptacije. Koji su to, pokazace buduca istrazivanja.

Chapter 8: Human papillomavirus and skin cancer

A high prevalence of human papillomavirus (HPV) DNA, particularly in squamous cell skin carcinoma of immunosuppressed but also of immunocompetent patients, has renewed great interest in a possible etiologic role of HPV in nonmelanoma skin cancer. It is difficult, however, to interpret these findings against a background of low-level infections with multiple HPV types from supergroup B (HPV4-related and epidermodysplasia verruciformis [EV] HPV), probably acquired by everyone early in and throughout life. Thus far, no high-risk HPV types have been identified. Because of the low copy numbers of HPV DNA in skin cancers, probably not every tumor cell contains a viral genome, which is compatible with cutaneous HPV being possibly important for tumor initiation and progression, but not for maintenance of the malignant phenotype. The question with regard to high-risk types should, therefore, be readdressed in case-control studies on the basis of serology, which can reveal viral activities over years. The viruses lingering in all people are apparently activated by sunlight (UV) exposure, by immunosuppression, and by hyperproliferation of the epithelium (psoriasis) and/or in the specific genetic background of the host (EV). It is intriguing that most of these factors are established risk factors in skin carcinogenesis. The weak transforming activity of cutaneous HPV in vitro compared with the transforming activity of genital HPV may explain the need for activators and synergistic factors. The antiapoptotic activities of E6 proteins of cutaneous HPV could be relevant to oncogenesis in the interplay with UV exposure. Prospective studies should determine the kinetics of HPV activation relative to tumor development.