Human papillomaviruses and non-melanoma skin cancer: basic virology and clinical manifestations

Human papillomaviruses (HPV) infect cutaneous and mucosal epithelia and induce benign and malignant lesions. Non-melanoma skin cancer (NMSC), encompassing basal cell carcinoma and squamous cell carcinoma (SCC), is the most frequent cancer in the Caucasian population, and the incidence has increased dramatically worldwide. Ultraviolet (UV) radiation is a major risk factor for NMSC, and cutaneous HPV is also considered to play an active role during the pathogenesis of these cancers. The first evidence for the involvement of HPV in NMSC was reported in patients with Epidermodysplasia verruciformis (EV). HPV types detected in skin tumours of these patients are referred to as EV/cutaneous HPV types belonging to the beta- and gamma-papillomaviruses (PV). Epidemiological studies have shown a higher risk of several EV/cutaneous HPV types for NMSC. Furthermore, in vitro and animal models show transforming properties of some PV types. The anti-apoptotic activities, and the delay of DNA repair mechanism caused by some EV/cutaneous HPV E6 proteins in response to UV-induced mutations, may lead to the persistence of DNA-damaged keratinocytes. Thus, specific EV/cutaneous HPV types as co-factors in association with UV-radiation and the immune system seem to be involved in the early pathogenesis of cutaneous SCC.     

Human papillomaviruses in the pathogenesis of anogenital cancer.

Substantial experimental evidence accumulated over the past 8 years has indicated an etiological role for specific human papillomavirus (HPV) types in anogenital cancer and its premalignant precursors. Virus infection and viral gene expression emerge as necessary but obviously not sufficient factors for cancer induction. Additional modifications of host cell genes appear to be required for malignant progression of infected cells. The expression of viral oncoproteins in cells infected by "high-risk" types (e.g., HPV 16, HPV 18), in contrast to "low-risk" types (e.g., HPV 6, HPV 11), results in chromosomal instability and apparently in accumulation of mutational events. These "endogenous" modifications seem to be most important in the pathogenesis of premalignant lesions and tumor progression. Exogenous mutagens should act as additional cofactors.     

Human papillomaviruses

Until recently, the significance of HPV in the etiology of various benign, premalignant, and malignant lesions has been grossly underestimated. Because of new knowledge available through molecular biology techniques, we now know that the human morbidity due to papillomaviruses goes far beyond the common hand and plantar warts. Indeed, papillomaviruses represent a major sexually transmitted disease with probable oncogenic capabilities. They are, in fact, involved in some rare malignat-prone wart syndromes and perhaps in some other human cancers as well. With the current state of molecular biology, the biology of the viruses, their use as a role model for human oncogenesis and, perhaps, therapeutic strategies, are open to immediate study.     

Human papillomaviruses: a growing field

A combination of functional studies on human papillomavirus (HPV) oncoproteins and epidemiological studies on persistence of HPV infection firmly established a role for HPV in the etiology of cervical cancers. Understanding the viral life cycle of HPVs has been more difficult. In this issue of Genes & Development, Wang et al. (pp. 181 – 194) describe an efficient method to propagate infectious HPV in differentiating epithelium, providing clear evidence for temporal separation of viral and cellular replication.     

Human papillomaviruses in cervical screening

There is accepted evidence that a group of human papillomaviruses, designated ‘high-risk’ (HR-HPV) are found in almost all adequately studied cases of cervical cancer and are of key importance in its aetiology. The natural history of HR-HPV infection is known in general terms and the mechanism of oncogenic action and cancer development has been studied in some detail. It is also known that transient, sexually acquired cervical infection by HR-HPV is extremely common in young women, up to the age of 30 years. A persistent HR-HPV infection is necessary for the development and progression of high-grade pre-cancer. Persistent infection develops in a small percentage of women and continues beyond 30 years. These women are at risk of cervical cancer. Tests for cervical HR-HPV DNA appear to be very sensitive for high grade pre-cancer and also predict future risk of high grade pre-cancer. The tests have a very high negative predictive value for cervical cancer but do not have a high positive predictive value for high grade pre-cancer. Trials of effectiveness of HR-HPV testing in triage are in progress in the UK (TOMBOLA) and the USA (ALTS). Studies on primary screening are also in progress internationally. The cost-effectiveness and psychosocial consequences of using HR-HPV testing within screening programmes are still under investigation. Mathematical modelling is an important approach to investigating long-term consequences for cancer prevention as well as cost effectiveness. The limited data available supported by modelling exercises suggest the use of HR-HPV testing in triage will result in a small increase in effectiveness and be cost-neutral, or possibly reduce costs. HR-HPV testing could also be effective in primary screening when combined with cytological follow-up or in older women. HR-HPV testing may allow extension of screening intervals in older women, but withdrawing women over 50 years from cytological screening on the basis of a negative HR-HPV test would not seem likely to be cost effective. Public knowledge of HR-HPV is poor, and the implications of this for HR-HPV testing are unclear and of concern. More research is needed in these areas.New developments include the search for and evaluation of additional molecular markers and the use of quantitative approaches to improve the positive predictive value of molecular diagnostics, and the prospects of prophylactic vaccines and specific therapies for HR-HPV. The study of HR-HPV provides an interesting model for the development of evidence-based practice in the application of molecular pathology to disease prevention and diagnosis.     

Human papillomaviruses: are we ready to type?

The issue of determining which human papillomavirus (HPV) is present in a clinical specimen (typing specimens for HPVs) is receiving attention because HPVs cause condyloma acuminata and are associated with the continuum of disease which ranges from dysplasia to invasive genital cancer. Morphological inspection of precancerous lesions is not sufficient to determine which lesions will progress and which will not. A number of research tools based primarily on deoxyribonucleic acid hybridization have been developed. These permit identification and typing of HPV in genital tract scrapings or biopsies. Some HPV types (e.g., HPV-16 and HPV-18) have been identified in high-grade dysplasias and carcinomas more commonly than other types (e.g., HPV-6) and have been designated "high risk" types for cervical cancer. Thus, the question arises whether HPV typing would improve patient management by providing increased sensitivity for detection of patients at risk or by providing a prognostic indicator. In this review, the available typing methods are reviewed from the standpoint of their sensitivity, specificity, and ease of application to large-scale screening programs. Data implicating HPVs in the genesis of genital tract cancers are reviewed, as is the association of specific HPV types with specific outcomes. We conclude that there is currently no simple, inexpensive assay for HPV types, although such assays may be developed in the future. Analysis of the typing data indicates that, while HPV types can be designated high risk and low risk, these designations are not absolute and thus the low-risk group should not be ignored. In addition, interpretation of the data is complicated by finding high-risk types in individuals with no indication of disease. Insufficient data exist to indicate whether knowledge of the presence of a given HPV type is a better prognostic indicator than cytological or histological results. Thus, more research is needed before it can be determined whether typing information will augment the method currently in use for deciding treatment regimen and whether it warrants widespread use.     

Human papillomaviruses 53 and 66: clinical aspects and genetic analysis

Variants of HPV types may have different oncogenic potential. While HPV 16 and 18 variants have been extensively studied, little is known on the less frequent high-risk types such as HPV 53 and 66. Here, we analyzed the genetic variability of HPV 53 and 66 by sequencing the E6, E7, L1 genes and the Long Control Region (LCR) sequences of HPV 53 and HPV 66 from infected women. Fisher's exact-test was performed to correlate viral variants with cervical lesions. Higher-order interactions among identified mutations were analyzed by co-variation and cluster analyses. Antigenic-index alterations following L1 mutations were predicted by Jameson-Wolf algorithm.In HPV53, novel variants were identified in L1 (N = 9) and E6 (N = 1) genes. The novel L1 mutation P432L was statistically associated with L-SIL lesions (P = 0.04) and its development reduced the L1 predicted antigenicity (up to −2.3 for Glu433). HPV 53 E6 and L1 sequences clustered phylogenetically into two main clades.In HPV 66, novel polymorphisms were identified in L1 (N = 4) and E6 (N = 4) genes. The L1 protein mutations S405P and D458N were exclusively found in patients with L-SILs. Seven E7 variants and 10 LCR variants were for the first time analyzed.Novel HPV 53 and 66 variants were identified in this study. Some of these mutations were significantly associated with L-SIL lesions and affected the antigenic index of the L1 protein with possible interesting implications in vaccine design.     

Human alpha and beta papillomaviruses use different synonymous codon profiles

Human papillomaviruses use rare codons relative to their hosts. It has been theorized that this is a mechanism to allow the virus to escape immune surveillance. In the present study, we examined the codings of four major genes of 21 human alpha (mucosatropic) viruses and 16 human beta (cutaneous-tropic) viruses. We compared the codon usage of different genes from a given papillomavirus and also the same genes from different papillomaviruses. Our data showed that codon usage was not always uniform between two genes of a given papillomavirus or between the same genes of papillomaviruses from different genera. We speculate as to why this might be and conclude that codon usage in the papillomaviruses may not only play a role in facilitating escape from immune surveillance but may also underlie some of the unanswered questions in the papillomavirus field.     

Rethinking mechanisms of autoimmune pathogenesis

Why exactly some individuals develop autoimmune disorders remains unclear. The broadly accepted paradigm is that genetic susceptibility results in some break in immunological tolerance, may enhance the availability of autoantigens, and may enhance inflammatory responses. Some environmental insults that occur on this background of susceptibility may then contribute to autoimmunity. In this review we discuss some aspects related to inhibitory signaling and rare genetic variants, as well as additional factors that might contribute to autoimmunity including the possible role of clonal somatic mutations, the role of epigenetic events and the contribution of the intestinal microbiome. Genetic susceptibility alleles generally contribute to the loss of immunological tolerance, the increased availability of autoantigens, or an increase in inflammation. Apart from common genetic variants, rare loss-of-function genetic variants may also contribute to the pathogenesis of autoimmunity. Studies of an inhibitory signaling pathway in B cells helped identify a negative regulatory enzyme called sialic acid acetyl esterase. The study of rare genetic variants of this enzyme provides an illustrative example showing the importance of detailed functional analyses of variant alleles and the need to exclude functionally normal common or rare genetic variants from analysis. It has also become clear that pathways that are functionally impacted by either common or rare defective variants can also be more significantly compromised by gene expression changes that may result from epigenetic alterations. Another important and evolving area that has been discussed relates to the role of the intestinal microbiome in influencing helper T cell polarization and the development of autoimmunity.     

Human papillomaviruses and cervical cancer: analysis of histopathologic features associated with different viral types

The histopathologic features of 41 cervical carcinomas were correlated with the presence of human papillomavirus (HPV). Southern blots of DNA extracted from the tumors were hybridized with 32P-labeled type specific probes for HPV 6, 11, 16, 18, and 31. HPV was found in 26/41 (63%) of the tumors. The HPV types were: HPV 16 in 17 tumors (41%), HPV 18 in six tumors (15%) and HPV 31 in two tumors (5%). No tumor hybridized to either HPV 6 or HPV 11. HPV was identified in all histologic subtypes of cervical carcinoma; however, different HPV types were associated with specific histologic features. HPV 18 was identified in four of eight adenocarcinomas, while HPV 16 was found in only one. HPV 16 was most strongly associated with the keratinizing tumors. It was found in 10/13 (77%) of the large cell keratinizing (LCK) and in only 4/16 (25%) of the large cell nonkeratinizing cervical carcinomas (LCNK). A mucoepidermoid with extensive keratinization and pearl formation also contained HPV 16. One of three additional adenosquamous carcinomas had HPV 31, as did one LCNK tumor. In one LCK tumor, a HPV was identified that hybridized to both HPV 16 and 18. The LCNK group contained the highest percentage of tumors in which no papillomavirus DNA was identified (9/16 lacked HPV DNA). No papillomavirus was detected in six tumors from other sites or in five cervical specimens with no histologic evidence of HPV infection. These data indicate that HPV is involved in all major histologic types of cervical carcinoma, and suggest that the different HPV types transform slightly different cell populations, or that transformation by HPV 18 tends to induce adeno-differentiation while HPV 16 leads to squamous maturation.     

Human spermatogenesis: basic research and clinical issues]

Histological evaluation of human spermatogenesis suffers from the hazy border line between normal and pathological germ cell development. This border line needs better definition for histological fertility diagnosis and the early detection of germ cell tumors. Testicular biopsies from more than 2,900 patients with fertility disturbances and more than 1,900 patients with testicular tumors were investigated by means of semithin sectioning, different immunocytochemical methods and transmission electron microscopy. Cellular systems of the human testes possess a degree of autonomy from the body. Their morphological and functional heterogeneity reveals characteristics of cells that are not terminally differentiated. In the testis of an adult, fertile man not only the proliferation of spermatogonia, maturation divisions of spermatocytes and differentiation of spermatids take place, but also abortive germ cells, as well as apoptotic and degenerative cells appear. Disturbances of spermatogenesis are defined by the evaluation of quantity and quality of germ cell alterations. Compensatory and non compensatory defects of spermatogenesis may be distinguished. Deficiency of spermatogonial cell types, multilayered spermatogonia, megalospermatocytes, malformed spermatids and single tumor cells in the face of sufficient development of mature spermatids are considered compensatory defects of spermatogenesis. Dominating malformed germ cells or tumor cells accompanied by an arrest or lack of spermatogenesis, however, represent non-compensatory defects of spermatogenesis. In addition, normal organization and function of the microvasculature, Leydig cells and compartmentalizing cells in the intertubular space are prerequisites for spermatogenesis. The neuroendocrine function of Leydig cells may be responsible for regulating the blood flow rate and the permeability to hormones and nutritive substances. Finally, for patients a successful definition of the border line between normal and pathological events of germ cell development may be essential for early detection of germ cell tumors. Therefore, anatomical sciences not only contribute to basic research, advanced diagnostics and therapeutic concepts related to diseases of the male gonad, but also to the improvement of assisted reproduction.     

Epigenetic mechanisms in Alzheimer's disease: Implications for pathogenesis and therapy

The vast majority of Alzheimer's disease (AD) are late-onset forms (LOAD) likely due to the interplay of environmental influences and individual genetic susceptibility. Epigenetic mechanisms, including DNA methylation, histone modifications and non-coding RNAs, constitute dynamic intracellular processes for translating environmental stimuli into modifications in gene expression. Over the past decade it has become increasingly clear that epigenetic mechanisms play a pivotal role in aging the pathogenesis of AD. Here, we provide a review of the major mechanisms for epigenetic modification and how they are reportedly altered in aging and AD. Moreover, we also consider how aberrant epigenetic modifications may lead to AD pathogenesis, and we review the therapeutic potential of epigenetic treatments for AD.     

The role of human papillomaviruses in the pathogenesis and histologic classification of precancerous lesions of the cervix

It is clear that the relation between HPV infection and cervical neoplasia is more complex than initially realized. Preliminary molecular virologic data suggest preferential distributions of low- and high-risk HPV types in CIN that tend to correlate with the morphologic appearance. Thus, mild and moderate dysplasias (CIN I and II) contain a diverse distribution of HPV types, including a minority that have a high risk of malignant potential. HPV, therefore, appears to play a major role as a promoter. Neoplastic transformation is probably determined by specific HPV types but, in addition, requires initiation by some other carcinogenic stimulus, e.g., HSV II, cigarette smoking. Despite numerous studies, performed during the past 30 years, the long-term behavior of dysplasia remains uncertain. The natural history of HPV-associated lesions is unknown. Until this information is available, it is recommended that the conventional dysplasia--CIS or CIN nomenclature be used. The presence of associated viral changes can be considered and added to the diagnosis, e.g., "moderate dysplasia (CIN II) with evidence of papillomavirus infection." Treatment should be the same for all intraepithelial lesions, regardless of the presence of morphologic evidence of HPV. In the future, it may be necessary to modify the classification of precancerous lesions of the cervix if it is shown that a specific HPV type induces a characteristic morphologic alteration or that the HPV type, in and of itself, has greater prognostic significance. Until then, confusion will be minimized and management optimized if the conventional dysplasia--CIS or CIN nomenclature is employed.     

Norovirus pathogenesis: mechanisms of persistence and immune evasion in human populations

Summary: Noroviruses are important human pathogens known to cause epidemic outbreaks of severe gastroenteritis in communities, military barracks, cruise ships, hospitals, and assisted living communities, resulting in over 267 000 000 annual infections worldwide. Diversity within the norovirus genus allows this virus to persist in human populations, although a single genocluster, the GII.4 noroviruses, currently accounts for ∼80% of all infections. Noroviruses bind to the polymorphic histoblood group antigens (HBGAs), which act as the putative cellular receptor, and strains from different genoclusters bind various HBGAs. Human challenge studies using viruses from different genoclusters have demonstrated that norovirus immunity is complicated and probably confounded by pre-existing exposure histories and variable immune responses. Evidence for both short-term and long-term immunity has been demonstrated, but the molecular mechanisms mediating differential immune responses in the face of infection remain unclear. Studies with virus-like particles from the GII.4 genocluster demonstrated that variation in and around the receptor-binding domain results in differential HBGA binding and altered antigenicity. These observations suggest that the norovirus capsid evolves to evade the memory immune response while retaining its ability to bind any of several HBGAs. In this review, we discuss how evolution within the capsid drives receptor switching and allows escape from herd immunity.