The human papillomavirus E6 oncogene dysregulates the cell cycle and contributes to cervical carcinogenesis through two independent activities

HPV and Cervical Cancer: Molecular and Immunological Aspects, Epidemiology and Effect of Vaccination in Latin American Women

Cervical cancer is primarily caused by Human Papillomavirus (HPV) infection and remains a significant public health concern, particularly in Latin American regions. This comprehensive narrative review addresses the relationship between Human Papillomavirus (HPV) and cervical cancer, focusing on Latin American women. It explores molecular and immunological aspects of HPV infection, its role in cervical cancer development, and the epidemiology in this region, highlighting the prevalence and diversity of HPV genotypes. The impact of vaccination initiatives on cervical cancer rates in Latin America is critically evaluated. The advent of HPV vaccines has presented a significant tool in combating the burden of this malignancy, with notable successes observed in various countries, the latter due to their impact on immune responses. The review synthesizes current knowledge, emphasizes the importance of continued research and strategies for cervical cancer prevention, and underscores the need for ongoing efforts in this field.

Differential microRNA Expression Analysis in Patients with HPV-Infected Ovarian Neoplasms

This study aimed to identify microRNAs (miRNAs) whose expression levels are altered by high-risk human papillomavirus (HR-HPV) infection in women with epithelial ovarian neoplasms. MiRNA expression was quantified by real-time polymerase chain reaction, while HR-HPV DNA was quantified using digital-droplet PCR. Analysis of 11 miRNAs demonstrated significantly lower hsa-miR-25-5p expression in HPV-infected compared to uninfected ovarian tissues (p = 0.0405), while differences in miRNA expression in corresponding serum were statistically insignificant. The expression of hsa-miR-218-5p in ovarian tumors was significantly higher in high-grade serous ovarian carcinoma (HGSOC) cases than in other neoplasms (p = 0.0166). In addition, hsa-miR-218-5p was significantly upregulated, whereas hsa-miR-191-5p was significantly downregulated in tissues with stage III/IV FIGO (p = 0.0009 and p = 0.0305, respectively). Using unsupervised clustering, we identified three unique patient groups with significantly varied frequencies of HPV16/18-positive samples and varied miRNA expression profiles. In multivariate analysis, high expression of hsa-miR-16-5p was an independent prognostic factor for poor overall survival (p = 0.0068). This preliminary analysis showed the changes in miRNA expression in ovarian neoplasms during HPV infection and those collected from HGSOCs or patients with advanced disease. This prospective study can provide new insights into the pathogenesis of ovarian neoplasms and host-virus interactions.

Age at menopause is inversely related to the prevalence of common gynecologic cancers: a study based on NHANES

Background

The fluctuation or even loss of estrogen level caused by menopause in women, and most gynecological cancers often occur before and after menopause, so the age of menopause may be related to the occurrence of gynecological cancer.

Aim

To investigate whether the age at menopause is independently associated with the incidence of gynecological cancers and to analyze the possible influencing factors.

Methods

We selected the NHANES public database to conduct the study, and by excluding relevant influencing factors, we finally included 5706 NHANES participants who had full data on age at menopause and the occurrence of gynecologic cancers to analyze the relationship between the amount of age at menopause and gynecologic cancers based on univariate or multifactorial logistic regression analysis. Further, the relationship between age at menopause and the prevalence of different gynecologic cancers was investigated, and changes in the prevalence of different gynecologic cancers by age at menopause subgroups were observed. Finally, other relevant factors affecting the prevalence of gynecologic cancers were further investigated by subgroup analysis as well as subcluster analysis.

Results

Univariate logistic regression analysis between age at menopause and gynecologic tumor prevalence revealed a negative association between age at menopause and the prevalence of common gynecologic cancers ovarian and cervical cancer, and after adjusting for the effects of covariates, a higher risk of gynecologic tumors was found with statistically significant differences at earlier age at menopause. The regression results showed a negative association between age at menopause and gynecologic cancer prevalence in cervical and ovarian cancer patients (P<0.01,P<0.01). Cervical cancer (OR: 0.91, 95% CI: 0.87,0.94) and ovarian cancer (OR: 0.90, 95% CI: 0.86, 0.95) were more prevalent among those with younger age at menopause.

Conclusion

Age at menopause is negatively associated with the prevalence of cervical and ovarian cancers, and the earlier the age at menopause, the greater the risk of developing gynecological cancers.

Marine Sulfated Polysaccharide PMGS Synergizes with Paclitaxel in Inhibiting Cervical Cancer In Vitro

The incidence and mortality of cervical cancer in female malignancies are second only to breast cancer, which brings a heavy health and economic toll worldwide. Paclitaxel (PTX)-based regimens are the first-class choice; however, severe side effects, poor therapeutic effects, and difficulty in effectively preventing tumor recurrence or metastasis are unavoidable. Therefore, it is necessary to explore effective therapeutic interventions for cervical cancer. Our previous studies have shown that PMGS, a marine sulfated polysaccharide, exhibits promising anti-human papillomavirus (anti-HPV) effects through multiple molecular mechanisms. In this article, a continuous study identified that PMGS, as a novel sensitizer, combined with PTX exerted synergistic anti-tumor effects on cervical cancer associated with HPV in vitro. Both PMGS and PTX inhibited the proliferation of cervical cancer cells, and the combination of PMGS with PTX displayed significant synergistic effects on Hela cells. Mechanistically, PMGS synergizes with PTX by enhancing cytotoxicity, inducing cell apoptosis and inhibiting cell migration in Hela cells. Collectively, the combination of PTX and PMGS potentially provides a novel therapeutic strategy for cervical cancer.

Investigation of the Antineoplastic Effects of 2-(4-Chlorophenyl)-13α-Estrone Sulfamate against the HPV16-Positive Human Invasive Cervical Carcinoma Cell Line SiHa

Cervical carcinoma is one of the most frequent malignant gynecological cancers in women of reproductive age. Because of the poor tolerability of currently available chemotherapeutic agents, efforts have been focused on developing innovative molecules, including steroids, that exert antineoplastic effects with a better safety profile. In addition to their endocrine properties, certain estrogens exhibit additional biological activities, such as antiangiogenic and anticancer effects. Based on previous studies, the antineoplastic properties of 13α-estrone sulfamate derivatives (13AES1-3) were investigated, and the mechanism of action for the most promising compound 13AES3 was explored. Based on their effects on the viability of different human adherent gynecological cancer cells, the SiHa cervical cell line was used for mechanistic experiments. The most active analog 13AES3 was shown to exert considerable proapoptotic effects, as evidenced by a colorimetric caspase-3 assay and fluorescent double staining. It also elicited antimigratory and anti-invasive effects in a concentration-dependent manner, as evidenced by wound healing and Boyden chamber assays, respectively. Regarding their mechanism of action, 13AES derivatives were shown to inhibit tubulin polymerization, and computer simulations provided a possible explanation for the importance of the presence of the chlorophenyl ring on the estrane skeleton. 13AES3 is considered to be the first 13α-estrone derivative with a significant antineoplastic potency against SiHa cancer cells. Therefore, it might serve as a valuable lead molecule for the design of anticancer agents targeting cervical carcinomas.

Molecular dissection of the E6 PBM identifies essential residues regulating Chk1 phosphorylation and subsequent 14-3-3 recognition

Previous studies have shown that the high-risk HPV E6 oncoprotein PDZ binding motifs (PBMs) can interact with PDZ proteins or members of the 14-3-3 family, depending upon the E6 phosphorylation status. However, different HPV E6 oncoproteins are subjected to phosphorylation by different cellular kinases. We have therefore been interested in determining whether we can dissect E6's PDZ and 14-3-3 interactions at the molecular level. Using HPV-18 E6, we have found that its Chk1 phosphorylation requires residues both upstream and downstream of the phospho-acceptor site, in addition to the Chk1 consensus recognition motif. Furthermore, we demonstrate that different high-risk HPV E6 types are differentially phosphorylated by Chk1 kinases, potentially due to the differences in their carboxy-terminal residues, as they are critical for kinase recognition. Moreover, differences in the E6 phosphorylation levels of different HR HPV types directly link to their ability to interact with different 14-3-3 isoforms, based on their phospho-status. Interestingly, 14-3-3 recognition appears to be less dependent upon the precise sequence constraints of the E6 carboxy terminal region, whilst minor amino acid variations have a major impact upon PDZ recognition. These results demonstrate that changes in E6 phospho-status during the life cycle or during malignant progression will modulate E6 interactions and, potentially, inversely regulate the levels of PDZ and 14-3-3 proteins.

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

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

Proteases and HPV-Induced Carcinogenesis

Simple Summary

Human papillomavirus (HPV) infection is a sexually transmitted disease with high prevalence worldwide. Although most HPV infections do not lead to cancer, some HPV types are correlated with the majority of cervical cancers, and with some anogenital and oropharyngeal cancers. Moreover, enzymes known as proteases play an essential role in the pathogenic process in HPV-induced carcinogenesis. This review highlights the role of proteases and recent epidemiological data regarding HPV-dependent carcinogenesis.

Abstract

Persistent infection with Human papillomavirus (HPV) is the main etiologic factor for pre-malignant and malignant cervical lesions. Moreover, HPV is also associated with oropharynx and other anogenital carcinomas. Cancer-causing HPV viruses classified as group 1 carcinogens include 12 HPV types, with HPV 16 and 18 being the most prevalent. High-risk HPVs express two oncoproteins, E6 and E7, the products of which are responsible for the inhibition of p53 and pRB proteins, respectively, in human keratinocytes and cellular immortalization. p53 and pRB are pleiotropic proteins that regulate the activity of several signaling pathways and gene expression. Among the important factors that are augmented in HPV-mediated carcinogenesis, proteases not only control processes involved in cellular carcinogenesis but also control the microenvironment. For instance, genetic polymorphisms of matrix metalloproteinase 1 (MMP-1) are associated with carcinoma invasiveness. Similarly, the serine protease inhibitors hepatocyte growth factor activator inhibitor-1 (HAI-1) and -2 (HAI-2) have been identified as prognostic markers for HPV-dependent cervical carcinomas. This review highlights the most crucial mechanisms involved in HPV-dependent carcinogenesis, and includes a section on the proteolytic cascades that are important for the progression of this disease and their impact on patient health, treatment, and survival.

Small DNA tumor viruses and human cancer: Preclinical models of virus infection and disease

Human tumor viruses cause various human cancers that account for at least 15% of the global cancer burden. Among the currently identified human tumor viruses, two are small DNA tumor viruses: human papillomaviruses (HPVs) and Merkel cell polyomavirus (MCPyV). The study of small DNA tumor viruses (adenoviruses, polyomaviruses, and papillomaviruses) has facilitated several significant biological discoveries and established some of the first animal models of virus-associated cancers. The development and use of preclinical in vivo models to study HPVs and MCPyV and their role in human cancer is the focus of this review. Important considerations in the design of animal models of small DNA tumor virus infection and disease, including host range, cell tropism, choice of virus isolates, and the ability to recapitulate human disease, are presented. The types of infection-based and transgenic model strategies that are used to study HPVs and MCPyV, including their strengths and limitations, are also discussed. An overview of the current models that exist to study HPV and MCPyV infection and neoplastic disease are highlighted. These comparative models provide valuable platforms to study various aspects of virus-associated human disease and will continue to expand knowledge of human tumor viruses and their relationship with their hosts.

Molecular insights into the interaction of HPV-16 E6 variants against MAGI-1 PDZ1 domain

Oncogenic protein E6 from Human Papilloma Virus 16 (HPV-16) mediates the degradation of Membrane-associated guanylate kinase with inverted domain structure-1 (MAGI-1), throughout the interaction of its protein binding motif (PBM) with the Discs-large homologous regions 1 (PDZ1) domain of MAG1-1. Generic variation in the E6 gene that translates to changes in the protein’s amino acidic sequence modifies the interaction of E6 with the cellular protein MAGI-1. MAGI-1 is a scaffolding protein found at tight junctions of epithelial cells, where it interacts with a variety of proteins regulating signaling pathways. MAGI-1 is a multidomain protein containing two WW (rsp-domain-9), one guanylate kinase-like, and six PDZ domains. PDZ domains played an important role in the function of MAGI-1 and served as targets for several viral proteins including the HPV-16 E6. The aim of this work was to evaluate, with an in silico approach, employing molecular dynamics simulation and protein–protein docking, the interaction of the intragenic variants E-G350 (L83V), E-C188/G350 (E29Q/L83V), E-A176/G350 (D25N/L83V), E6-AAa (Q14H/H78Y/83V) y E6-AAc (Q14H/I27RH78Y/L83V) and E6-reference of HPV-16 with MAGI-1. We found that variants E-G350, E-C188/G350, E-A176/G350, AAa and AAc increase their affinity to our two models of MAGI-1 compared to E6-reference.

Estrogen Inhibits Epithelial Progesterone Receptor-Dependent Progestin Therapy Efficacy in a Mouse Model of Cervical Cancer

Although the uterine cervix responds to the female sex hormone change, the role of progesterone in cervical cancer is poorly understood. It has been shown that medroxyprogesterone acetate (MPA) regresses cervical cancer in the transgenic mouse model expressing human papillomavirus type 16 E6 and E7 oncogenes. As MPA interacts most strongly with progesterone receptor (PR), we reasoned that PR would contribute to MPA-induced regression of cervical cancer. We also hypothesized that estrogen influences the therapeutic activity of MPA because it promotes cervical cancer growth in the same mouse model. The present study showed that the deletion of Pgr in the cervical cancer cells ablated the MPA's therapeutic effect in the human papillomavirus transgenic mouse model. Additionally, estrogen attenuated cancer regression by MPA in the same model system. These observations indicate that MPA can effectively regress cervical cancer only when cancer cells express PR and estrogen levels are low. These results suggest that, if translatable, MPA should be administered when estrogen levels are low in patients with PR-positive cervical cancer.

The biology of papillomavirus PDZ associations: what do they offer papillomaviruses?

The high-risk α-type papillomaviruses have a C-terminal PDZ-binding motif (PBM) on one of the two major oncoproteins E6 or E7; the vast majority on E6. The PBM is essential for the high-risk HPV life cycle, for episomal maintenance of the virus genome, and for maintaining the mitotic stability of the infected cell. The question is why only these viruses have PBMs - are there specific constraints imposed by the mucosal epithelium in which these viruses replicate? However the low-risk α-HPVs, such as HPV-6 and HPV-11 replicate extremely efficiently without a PBM, while viruses of the alpha8 group, such as HPV-40, replicate well with a very primitive PBM. So what does PDZ-binding capacity contribute to the fitness of the virus?

Vitamin A deficiency in K14E7HPV expressing transgenic mice facilitates the formation of malignant cervical lesions

Infection with high-risk human papillomavirus (HR-HPV) is the main cause of cervical cancer (CC), but viral infection alone does not guarantee the development of this malignancy. Indeed, deficiencies of dietary micronutrients could favor cervical cancer development in individuals that harbor HR-HPV infections. The status of retinoid levels, natural and synthetic derivatives of vitamin A, is important in maintaining cellular differentiation of the cervical epithelium. Moreover, many studies show a link between deficient intake of retinoids or alteration of the retinoid receptors and CC development. In spite of this, the effect of vitamin A deficiency (VAD) in presence of HR-HPV oncoproteins on cervical carcinogenesis in vivo has not been reported. Transgenic mice expressing E6 or E7 oncoproteins (K14E6 or K14E7 mice, respectively) were used to evaluate the possible role of VAD in the development of malignant cervical lesions. The survival of the mice in VAD condition was studied, and histopathological analysis and immunohistochemical detection of molecular cancer markers such as the tumor suppressor retinoic acid receptor beta (RARβ), proliferating cell nuclear antigen (PCNA), cleaved caspase 3, and the tumor suppressor protein p16^INK4A (inhibitor of CDK4) were performed. Our results show that K14E6/VAD mice showed moderate cervical dysplasia; notably, K14E7/VAD mice developed severe cervical dysplasia and cervical in situ carcinoma at an early age. VAD synergizes with HPV16E7 oncoprotein expression favoring cervical carcinogenesis in vivo.

Functional roles of female sex hormones and their nuclear receptors in cervical cancer

There has been little progress for several decades in modalities to treat cervical cancer. While the cervix is a hormone-sensitive tissue, physiologic roles of estrogen receptor α (ERα), progesterone receptor (PR), and their ligands in this tissue are poorly understood. It has hampered critical assessments of data in early epidemiologic and clinical studies for cervical cancer. Experimental evidence obtained from studies using mouse models has provided new insights into the molecular mechanism of ERα and PR in cervical cancer. In a mouse model expressing human papillomavirus (HPV) oncogenes, exogenous estrogen promotes cervical cancer through stromal ERα. In the same mouse model, genetic ablation of PR promotes cervical carcinogenesis without exogenous estrogen. Medroxyprogesterone acetate, a PR-activating drug, regresses cervical cancer in the mouse model. These results support that ERα and PR play opposite roles in cervical cancer. They further support that ERα inhibition and PR activation may be translated into valuable treatment for a subset of cervical cancers.

Human papillomavirus E6 and E7: What remains?

Decades of research on the human papillomavirus oncogenes, E6 and E7, have given us huge amounts of data on their expression, functions and structures. We know much about the very many cellular proteins and pathways that they influence in one way or another. However, much of this information is quite discrete, referring to one activity examined under one condition. It is now time to join the dots to try to understand a larger picture: how, where and when do all these interactions occur... and why? Examining these questions will also show how many of the yet obscure cellular processes work together for cellular and tissue homeostasis in health and disease.

Development of DNA Vaccine Targeting E6 and E7 Proteins of Human Papillomavirus 16 (HPV16) and HPV18 for Immunotherapy in Combination with Recombinant Vaccinia Boost and PD-1 Antibody

Immunotherapy for cervical cancer should target high-risk human papillomavirus types 16 and 18, which cause 50% and 20% of cervical cancers, respectively. Here, we describe the construction and characterization of the pBI-11 DNA vaccine via the addition of codon-optimized human papillomavirus 18 (HPV18) E7 and HPV16 and 18 E6 genes to the HPV16 E7-targeted DNA vaccine pNGVL4a-SigE7(detox)HSP70 (DNA vaccine pBI-1). Codon optimization of the HPV16/18 E6/E7 genes in pBI-11 improved fusion protein expression compared to that in DNA vaccine pBI-10.1 that utilized the native viral sequences fused 3' to a signal sequence and 5' to the HSP70 gene of Mycobacterium tuberculosis Intramuscular vaccination of mice with pBI-11 DNA better induced HPV antigen-specific CD8+ T cell immune responses than pBI-10.1 DNA. Furthermore, intramuscular vaccination with pBI-11 DNA generated stronger therapeutic responses for C57BL/6 mice bearing HPV16 E6/E7-expressing TC-1 tumors. The HPV16/18 antigen-specific T cell-mediated immune responses generated by pBI-11 DNA vaccination were further enhanced by boosting with tissue-antigen HPV vaccine (TA-HPV). Combination of the pBI-11 DNA and TA-HPV boost vaccination with PD-1 antibody blockade significantly improved the control of TC-1 tumors and extended the survival of the mice. Finally, repeat vaccination with clinical-grade pBI-11 with or without clinical-grade TA-HPV was well tolerated in vaccinated mice. These preclinical studies suggest that the pBI-11 DNA vaccine may be used with TA-HPV in a heterologous prime-boost strategy to enhance HPV 16/18 E6/E7-specific CD8+ T cell responses, either alone or in combination with immune checkpoint blockade, to control HPV16/18-associated tumors. Our data serve as an important foundation for future clinical translation.IMPORTANCE Persistent expression of high-risk human papillomavirus (HPV) E6 and E7 is an obligate driver for several human malignancies, including cervical cancer, wherein HPV16 and HPV18 are the most common types. PD-1 antibody immunotherapy helps a subset of cervical cancer patients, and its efficacy might be improved by combination with active vaccination against E6 and/or E7. For patients with HPV16+ cervical intraepithelial neoplasia grade 2/3 (CIN2/3), the precursor of cervical cancer, intramuscular vaccination with a DNA vaccine targeting HPV16 E7 and then a recombinant vaccinia virus expressing HPV16/18 E6-E7 fusion proteins (TA-HPV) was safe, and half of the patients cleared their lesions in a small study (NCT00788164). Here, we sought to improve upon this therapeutic approach by developing a new DNA vaccine that targets E6 and E7 of HPV16 and HPV18 for administration prior to a TA-HPV booster vaccination and for application against cervical cancer in combination with a PD-1-blocking antibody.

WAPL induces cervical intraepithelial neoplasia modulated with estrogen signaling without HPV E6/E7

Since cervical cancer still afflicts women around the world, it is necessary to understand the underlying mechanism of cervical cancer development. Infection with HPV is essential for the development of cervical intraepithelial neoplasia (CIN). In addition, estrogen receptor signaling is implicated in the development of cervical cancer. Previously, we have isolated human wings apart-like (WAPL), which is expected to cause chromosomal instability in the process of HPV-infected precancerous lesions to cervical cancer. However, the role of WAPL in the development of CIN is still unknown. In this study, in order to elucidate the role of WAPL in the early lesion, we established WAPL overexpressing mice (WAPL Tg mice) and HPV E6/E7 knock-in (KI) mice. WAPL Tg mice developed CIN lesion without HPV E6/E7. Interestingly, in WAPL Tg mice estrogen receptor 1 (ESR1) showed reduction as compared with the wild type, but cell growth factors MYC and Cyclin D1 controlled by ESR1 expressed at high levels. These results suggested that WAPL facilitates sensitivity of ESR1 mediated by some kind of molecule, and as a result, affects the expression of MYC and Cyclin D1 in cervical cancer cells. To detect such molecules, we performed microarray analysis of the uterine cervix in WAPL Tg mice, and focused MACROD1, a co-activator of ESR1. MACROD1 expression was increased in WAPL Tg mice compared with the wild type. In addition, knockdown of WAPL induced the downregulation of MACROD1, MYC, and Cyclin D1 but not ESR1 expression. Furthermore, ESR1 sensitivity assay showed lower activity in WAPL or MACROD1 downregulated cells than control cells. These data suggested that WAPL increases ESR1 sensitivity by activating MACROD1, and induces the expression of MYC and Cyclin D1. Therefore, we concluded that WAPL not only induces chromosomal instability in cervical cancer tumorigenesis, but also plays a key role in activating estrogen receptor signaling in early tumorigenesis.

A novel cancer preventative botanical mixture, TriCurin, inhibits viral transcripts and the growth of W12 cervical cells harbouring extrachromosomal or integrated HPV16 DNA

BACKGROUND

The phytochemical mixture TriCurin (curcumin, epigallocatechin gallate (EGCG) and resveratrol) eliminates human papillomavirus (HPV) (+) cancer cells in vitro and in vivo. In this study, we further evaluate TriCurin.

METHODS

The activity of TriCurin and its individual compounds was assayed on W12 cells, derived from a cervical precancer containing episomal and integrated HPV16 DNA, using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays, microscopy and reverse transcription-polymerase chain reaction (RT-PCR), and on HeLa cells by gene expression analysis. The stability and toxicity of TriCurin microemulsion were tested in an organotypic cervical tissue model.

RESULTS

TriCurin and its individual compounds inhibit the growth of W12 cells, episomal, type 1 and 2 integrants; the relative order of activity is TriCurin, EGCG, curcumin, or resveratrol. RT-PCR shows that TriCurin activates p53 and suppresses HPV16 mRNAs E1, E2, E4, E6 and E7 at 24 h in W12 cells. Gene expression analysis shows that TriCurin activates pro-apoptotic genes and represses anti-apoptotic genes in HeLa cells. TriCurin in a microemulsion is stable and non-toxic to cervical tissue. The combination of TriCurin and tanshinone IIA exhibits additional synergy against HeLa cells.

CONCLUSIONS

TriCurin, and the combination of TriCurin with tanshinone IIA, are effective against HPV (+) cells. The phytochemical mixture, in the microemulsion-based cream, is a promising therapeutic for the prevention and treatment of cervical cancer.

Hormone replacement therapy and cervical cancer: a systematic review of the literature

Gynecological tumor treatment, including cervical cancer (CC) treatment, often leads to iatrogenic premature menopause. This highlights the critical importance of investigating indications for hormone replacement therapy (HRT), as most patients, thanks to the improvement in diagnosis and treatment, have to deal with the sequelae of their cancer treatments for many years. This systematic review aims to provide an overview of the current knowledge regarding the risks of HRT and CC. In particular, we aim to investigate whether the use of HRT can increase CC incidence, and evaluate its risk in CC survivors. A systematic review, in agreement with PRISMA guidelines, of the English literature present in PubMed and SCOPUS has been performed. A total of 2805 articles have been screened, of which 10 were considered eligible. Several studies reported a significantly reduced risk of developing cervical squamous cell carcinoma in postmenopausal women treated with HRT, while a weak increase in the incidence of adenocarcinoma has been shown. No evidence reports a harmful effect of HRT on CC oncological outcome, while several benefits, in terms of reduced metabolic risk and increased quality of life, have been described, thus concluding that HRT should be offered to young CC survivors for the management of early menopause.

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

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

Medroxyprogesterone Acetate Prevention of Cervical Cancer through Progesterone Receptor in a Human Papillomavirus Transgenic Mouse Model

Cervical dysplastic lesions called cervical intraepithelial neoplasias (CINs) need be treated to prevent cervical cancer. Currently available surgical procedures are effective, but the development of noninvasive treatment is warranted. In human papillomavirus transgenic mice engineered to express human papillomavirus type 16 E6 and E7, short-term treatment with 17β-estradiol induces CINs that progress to cervical cancer if the treatment is continued. In the present study, this mouse model was used to determine whether medroxyprogesterone acetate (MPA), a progestin drug, is chemopreventive. Human papillomavirus transgenic mice bearing CIN lesions were treated with MPA plus 17β-estradiol. Unlike control mice treated with 17β-estradiol alone, cervical cancer was absent in the MPA-treated mice. This observation suggests that MPA prevented CIN from progressing to invasive cancer. MPA was associated with inhibited cell proliferation and the promotion of apoptosis in CIN lesions. Confirming the role of the progesterone receptor, the preventive effect of MPA was absent in human papillomavirus transgenic mice in which the expression of progesterone receptor was genetically ablated. These results suggest that MPA is efficient in treating progesterone receptor–positive CIN lesions. These findings provide the basis for a biomarker-driven clinical trial of the secondary prevention of cervical cancer.

Paving the way for more precise diagnosis of EcPV2-associated equine penile lesions

Background

There is growing evidence that equine papillomavirus type 2 (EcPV2) infection is causally associated with the development of equine genital squamous cell carcinomas (SCCs). Early stages of disease present clinically as plaques or wart-like lesions which can gradually progress to tumoural lesions. Histologically these lesions are inconsistently described as benign hyperplasia, papilloma, penile intraepithelial neoplasia (PIN), carcinoma in situ (CIS) or SCC. Guidelines for histological classification of early SCC precursor lesions are not precisely defined, leading to potential misdiagnosis. The aim of this study was to identify histologic criteria and diagnostic markers allowing for a more accurate diagnosis of EcPV2-associated equine penile lesions.

Results

A total of 61 archived equine penile lesions were histologically re-assessed and classified as benign hyperplasia, papilloma, CIS or SCC. From these, 19 representative lesions and adjacent normal skin were comparatively analysed for the presence of EcPV2 DNA and transcripts using PCR and RNA in situ hybridisation (RISH). All lesional samples were positive by EcPV2 PCR and RISH, while adjacent normal skin was negative. RISH analysis yielded signal distribution patterns that allowed distinction of early (hyperplasia, papilloma) from late stage lesions (CIS, SCC). Subsequently, the 19 lesions were further assessed for expression of p53, Ki67, MCM7 and MMP1 by immunohistochemistry (IHC). All four proteins were expressed in both normal and lesional tissue. However, p53 expression was up-regulated in basal keratinocyte layers of papillomas, CIS and SCCs, as well as in upper keratinocyte layers of CIS and SCCs. MCM7 expression was only up-regulated in upper proliferating keratinocyte layers of papillomas, CIS and SCCs.

Conclusion

This study proposes combining a refined histological protocol for analysis of equine penile lesions with PCR- and/or RISH based EcPV2-screening and p53/MCM7 IHC to more accurately determine the type of lesion. This may help to guide the choice of optimum treatment strategy, especially at early stages of disease.

At the center of cervical carcinogenesis: synergism between high-risk HPV and the hyperactivated YAP1

Human papillomavirus (HPV) is recognized as a necessary, but insufficient cause of cervical cancer. Recent in vitro and in vivo evidence from our laboratory demonstrate that hyperactivation of yes-associated protein 1 (YAP1) is sufficient to induce cervical carcinogenesis. We found that synergism between hyperactivated YAP1 and high-risk HPV is a key driver of cervical cancer initiation and progression.

Association of estradiol and HPV/HPV16 infection with the occurrence of cervical squamous cell carcinoma

The associations between human papillomavirus (HPV) infection or hormonal exposure and cervical cancer risk are well established. However, to the best of our knowledge, the association between high endogenous estradiol levels in conjunction with HPV/HPV16 infection and the risk of cervical squamous cell carcinoma remains unknown. To investigate this, the current study conducted a matched case-control study in Shanxi Province, China, in which clinical samples were obtained from 74 females with newly diagnosed uterine cervix squamous cell carcinoma and 74 matched healthy females who were selected from 582 healthy females according to age, place of residence, marital status and menopausal status. From all participants, DNA was extracted from cells obtained from a cervical smear and serum was separated from venous blood withdrawn during days 5-8 of the menstrual cycle. HPV/HPV16 DNA and estradiol expression levels in the serum were measured by general polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Significant differences were identified in the positive HPV and HPV16 DNA expression rates between patients and controls, with odds ratios (95% confidence interval) of 3.74 (1.84-7.59) and 4.04 (1.97-8.28), respectively. Expression levels of estradiol in patients were significantly higher compared with the controls (P<0.001), however, this was only identified when the HPV16 E2 or E6 oncogene status was negative. Considering 40 ng/ml as the cut-off estradiol level, 78.38% of patients exhibited high estradiol levels, which was significantly higher than the percentage of controls (P<0.001). An additive interaction pattern was revealed between estradiol expression levels and HPV/HPV16 infection. The results suggest that among the various types of HPV, HPV16 may be most likely to cause uterine cervix squamous cell carcinoma and an abnormally high level of endogenous estradiol may further increase this risk. Therefore, estradiol therapy may represent a new treatment strategy for cases of cervical cancer associated with HPV infection.

Activating Mutations in Pik3ca Contribute to Anal Carcinogenesis in the Presence or Absence of HPV-16 Oncogenes

PURPOSE

Over 95% of human anal cancers are etiologically associated with high-risk HPVs, with HPV type 16 (HPV16) the genotype most commonly found. Activating mutations in the catalytic subunit of Phosphatidylinositol (3,4,5)-trisphosphate kinase (PI3K), encoded by the Pik3ca gene, are detected in approximately 20% of human anal cancers.Experimental Design: We asked if common activating mutations in Pik3ca contribute to anal carcinogenesis using an established mouse model for anal carcinogenesis in which mice are topically treated with the chemical carcinogen 7,12-Dimethylbenz(a)anthracene (DMBA). Mice expressing in their anal epithelium one of two activating mutations in Pik3ca genes, Pik3ca^H1047R or Pik3ca^E545K , were monitored for anal carcinogenesis in the presence or absence of transgenes expressing the HPV16 E6 and E7 oncogenes.

RESULTS

Both mutant forms of Pik3ca increased susceptibility to anal carcinogenesis in the absence of HPV16 oncogenes, and cooperated with HPV16 oncogenes to induce the highest level and earliest onset of anal cancers. The combination of HPV16 oncogenes and Pik3ca mutations led to anal cancers even in the absence of treatment with DMBA. We further observed that the investigational mTOR1/2 dual inhibitor, TAK-228, significantly reduced the size of anal cancer-derived tumor spheroids in vitro and reduced the growth rates of anal cancer-derived tumor grafts in vivo.

CONCLUSIONS

These data demonstrate that activating mutations in Pik3ca drive anal carcinogenesis together with HPV16 oncogenes, and that the PI3K/mTOR pathway is a relevant target for therapeutic intervention.

A therapeutic vaccine targeting HPV E6/E7 with intrinsic Toll-like receptor 2 agonist activity induces antitumor immunity

The E6 and E7 oncoproteins of human papillomavirus (HPV) are ideal targets for developing immunotherapeutic approaches to treat HPV-associated tumors. Our previous studies showed that a recombinant lipidated HPV16 E7 mutant (rlipo-E7m) with inactivation of the E7 oncogenic functions can activate antigen presenting cells through Toll-like receptor 2 (TLR2) and induce antitumor immunity. Given that some HPV-associated tumors overexpress E6 but not E7, it is necessary to include therapeutic agents containing HPV E6 in therapeutic vaccine development to broaden the utility of the vaccine. In this study, we further incorporated a mutant HPV16 E6 (E6m) into rlipo-E7m to generate rlipo-E6mE7m, which could elicit both E6- and E7-specific immune responses after immunization. The rlipo-E6mE7m immunization induced higher levels of T cell proliferation and cytotoxic T lymphocyte response than the nonlipidated recombinant E6mE7m (rE6mE7m) immunization. Accordingly, a single-dose administration of rlipo-E6mE7m at day 7 after tumor inoculation in mice showed complete inhibition of tumor growth, whereas administration of rE6mE7m did not. These results demonstrated that rlipo-E6mE7m could be used in tumors with E6 and/or E7 expression via the induction of E6- and E7-specific immunity.

Etiological role of human papillomavirus infection in the development of penile cancer

OBJECTIVE

To examine the association between human papillomavirus (HPV) infection and penile cancer among Japanese patients.

METHODS

Thirty-four patients with penile cancer were enrolled in this study. DNA was extracted from paraffin-embedded tumor tissue samples, and HPV-DNA tests and genotyping were performed. For all of the samples, in situ hybridization (ISH) was performed to locate HPV-DNA in tumor tissue. Furthermore, expression levels of p16-INK4a, mini-chromosome maintenance protein 7(mcm-7), HPV-L1, and Ki-67 were analyzed using immunohistochemical methods.

RESULTS

HPV and high-risk (HR)-HPV were detected in 14 (41.1%; 95% confidence interval (CI) 24.6-57.7%) and 12 (35.2%; 95% CI 19.2-51.4%) cases, respectively. HPV16 was the most frequently detected HPV type. Among the HR-HPV-positive cases, a punctate HR-HPV-DNA signal pattern was detected by ISH in tumor cell nuclei. P16-INK4a was expressed in 66.7% (95% CI 42.8-90.1%) of HR-HPV-positive cases and was significantly more frequent and stronger in HR-HPV-positive cases than in HPV-negative cases. There was no significant difference in the occurrence or distribution of mcm-7 or Ki-67 expression between HPV-positive and HPV-negative cases. HPV-L1 expression was not observed in any of the cases examined.

CONCLUSIONS

HPV infection may have had an etiological role in 41% of the examined cases of penile cancer in Japan.

Terc is dispensable for most of the short-term HPV16 oncogene-mediated phenotypes in mice

High-risk human papillomaviruses (HPVs) have been shown in vitro to impinge on telomere homeostasis in a number of ways. However, the in vivo interaction of viruses with the telomere homeostasis apparatus has not been previously explored. Since E6 and E7 are the main viral oncogenes and key for viral replication, we have explored here the short-term phenotypes of the genes in the context of defective telomere homeostasis. We examined the short-term phenotypes of E6 and E7 in a context where the Terc component of the telomerase holoenzyme was knocked out. We determined that Terc was dispensable for most oncogene-mediated phenotypes. Surprisingly, E7-mediated reduction of label retaining cells was found to be in part dependent on the presence of Terc. Under the conditions examined here, there appears to be no compelling evidence Terc is required for most short-term viral oncogene mediated phenotypes. Further studies will elucidate its role in longer-term phenotypes.

Upsetting the Balance: When Viruses Manipulate Cell Polarity Control

The central importance of cell polarity control is emphasized by the frequency with which it is targeted by many diverse viruses. It is clear that in targeting key polarity control proteins, viruses affect not only host cell polarity, but also influence many cellular processes, including transcription, replication, and innate and acquired immunity. Examination of the interactions of different virus proteins with the cell and its polarity controls during the virus life cycles, and in virally‐induced cell transformation shows ever more clearly how intimately all cellular processes are linked to the control of cell polarity.

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Multiple viruses target cell polarity.

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Viral targeting of polarity frequently occurs through PDZ recognition.

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Biological effects include immune-avoidance, cell proliferation and apoptosis inhibition.

Systematic assessment of cervical cancer initiation and progression uncovers genetic panels for deep learning-based early diagnosis and proposes novel diagnostic and prognostic biomarkers

Although many outstanding achievements in the management of cervical cancer (CxCa) have obtained, it still imposes a major burden which has prompted scientists to discover and validate new CxCa biomarkers to improve the diagnostic and prognostic assessment of CxCa. In this study, eight different gene expression data sets containing 202 cancer, 115 cervical intraepithelial neoplasia (CIN), and 105 normal samples were utilized for an integrative systems biology assessment in a multi-stage carcinogenesis manner. Deep learning-based diagnostic models were established based on the genetic panels of intrinsic genes of cervical carcinogenesis as well as on the unbiased variable selection approach. Survival analysis was also conducted to explore the potential biomarker candidates for prognostic assessment. Our results showed that cell cycle, RNA transport, mRNA surveillance, and one carbon pool by folate were the key regulatory mechanisms involved in the initiation, progression, and metastasis of CxCa. Various genetic panels combined with machine learning algorithms successfully differentiated CxCa from CIN and normalcy in cross-study normalized data sets. In particular, the 168-gene deep learning model for the differentiation of cancer from normalcy achieved an externally validated accuracy of 97.96% (99.01% sensitivity and 95.65% specificity). Survival analysis revealed that ZNF281 and EPHB6 were the two most promising prognostic genetic markers for CxCa among others. Our findings open new opportunities to enhance current understanding of the characteristics of CxCa pathobiology. In addition, the combination of transcriptomics-based signatures and deep learning classification may become an important approach to improve CxCa diagnosis and management in clinical practice.

Transgenic Mouse Models of Tumor Virus Action

Genetically engineered mice (GEMs) have provided valuable insights into the carcinogenic properties of various human tumor viruses, which, in aggregate, are etiologically associated with over 15% of all human cancers. This review provides an overview of seminal discoveries made through the use of GEM models for human DNA tumor viruses. Emphasis is placed on the discoveries made in the study of human papillomaviruses, Merkel cell carcinoma-associated polyomavirus, Epstein-Barr virus, and Kaposi's sarcoma-associated herpesvirus, because GEMs have contributed extensively to our understanding of how these DNA tumor viruses directly contribute to human cancers.

Mitotic control of human papillomavirus genome-containing cells is regulated by the function of the PDZ-binding motif of the E6 oncoprotein

The function of a conserved PDS95/DLG1/ZO1 (PDZ) binding motif (E6 PBM) at the C-termini of E6 oncoproteins of high-risk human papillomavirus (HPV) types contributes to the development of HPV-associated malignancies. Here, using a primary human keratinocyte-based model of the high-risk HPV18 life cycle, we identify a novel link between the E6 PBM and mitotic stability. In cultures containing a mutant genome in which the E6 PBM was deleted there was an increase in the frequency of abnormal mitoses, including multinucleation, compared to cells harboring the wild type HPV18 genome. The loss of the E6 PBM was associated with a significant increase in the frequency of mitotic spindle defects associated with anaphase and telophase. Furthermore, cells carrying this mutant genome had increased chromosome segregation defects and they also exhibited greater levels of genomic instability, as shown by an elevated level of centromere-positive micronuclei. In wild type HPV18 genome-containing organotypic cultures, the majority of mitotic cells reside in the suprabasal layers, in keeping with the hyperplastic morphology of the structures. However, in mutant genome-containing structures a greater proportion of mitotic cells were retained in the basal layer, which were often of undefined polarity, thus correlating with their reduced thickness. We conclude that the ability of E6 to target cellular PDZ proteins plays a critical role in maintaining mitotic stability of HPV infected cells, ensuring stable episome persistence and vegetative amplification.

The Hippo/YAP pathway interacts with EGFR signaling and HPV oncoproteins to regulate cervical cancer progression

The Hippo signaling pathway controls organ size and tumorigenesis through a kinase cascade that inactivates Yes-associated protein (YAP). Here, we show that YAP plays a central role in controlling the progression of cervical cancer. Our results suggest that YAP expression is associated with a poor prognosis for cervical cancer. TGF-α and amphiregulin (AREG), via EGFR, inhibit the Hippo signaling pathway and activate YAP to induce cervical cancer cell proliferation and migration. Activated YAP allows for up-regulation of TGF-α, AREG, and EGFR, forming a positive signaling loop to drive cervical cancer cell proliferation. HPV E6 protein, a major etiological molecule of cervical cancer, maintains high YAP protein levels in cervical cancer cells by preventing proteasome-dependent YAP degradation to drive cervical cancer cell proliferation. Results from human cervical cancer genomic databases and an accepted transgenic mouse model strongly support the clinical relevance of the discovered feed-forward signaling loop. Our study indicates that combined targeting of the Hippo and the ERBB signaling pathways represents a novel therapeutic strategy for prevention and treatment of cervical cancer.

miR-2861 acts as a tumor suppressor via targeting EGFR/AKT2/CCND1 pathway in cervical cancer induced by human papillomavirus virus 16 E6

Persistent infection with oncogenic human papillomavirus viruses (HPVs) is a casual factor for cervical cancer and its precursors, and the abnormal constitutive expression of viral oncoprotein E6 is a key event during the malignant transformation. Here, we performed miRNA microarray to identify changes of miRNAs following ectopic HPV16 E6 overexpression in HEK293T cells and found miR-2861 was greatly decreased in both HEK293T and HaCaT cells expressing HPV16 E6 compared to vector control. Further, we demonstrated a biological link among HPV16 E6, miR-2861, EGFR, AKT2, and CCND1 in cervical cancer cells. We showed that miR-2861 was downregulated in cervical cancer tissues and negatively correlated with advanced tumor stage and lymph node metastasis. Overexpression of miR-2861 suppressed cervical cancer cell proliferation and invasion and enhanced apoptosis. Subsequent investigation revealed that EGFR, AKT2, and CCND1 were all the direct targets of miR-2861. Importantly, silencing EGFR, AKT2, and/or CCND1 recapitulated the cellular effects seen upon miR-2861 overexpression. Restoration of EGFR, AKT2, and/or CCND1 counteracted the effects of miR-2861 expression. Thus, we identified a new pathway employing miR-2861, EGFR, AKT2, and CCND1 that may mediate HPV16 E6 induced initiation and progression of cervical cancer.

The high-risk HPV E6 target scribble (hScrib) is required for HPV E6 expression in cervical tumour-derived cell lines

The ability of high-risk HPV E6 oncoproteins to target cellular proteins which harbor PDZ domains is believed to play an important role in the virus life cycle and to influence the ability of these viruses to bring about malignant transformation. Whilst many of these PDZ proteins are potential tumour suppressors, involved in the control of cell polarity and cell-contact, recent studies suggest that mislocalisation or overexpression might result in the emergence of oncogenic functions. This has been shown most clearly for two E6 targets, hDlg and hScrib. In this study we show that hScrib plays such a role in HeLa cells, where its expression is required for maintaining high levels of HPV-18 E6 protein. Loss of hScrib has no effect on E6 stability but results in lower levels of E6 transcription and a reduced rate of E6 translation. We further show that, in the context of cervical tumour-derived cell lines, both hScrib and E6 cooperate in the activation of the S6 kinase signaling pathway, and thereby contribute towards maintaining high rates of protein translation. These results indicate that the residual hScrib that is present within HPV transformed cells is pro-oncogenic, and highlights the dual functions of E6 cell polarity targets.

Viral Interactions with PDZ Domain-Containing Proteins-An Oncogenic Trait?

Many of the human viruses with oncogenic capabilities, either in their natural host or in experimental systems (hepatitis B and C, human T cell leukaemia virus type 1, Kaposi sarcoma herpesvirus, human immunodeficiency virus, high-risk human papillomaviruses and adenovirus type 9), encode in their limited genome the ability to target cellular proteins containing PSD95/ DLG/ZO-1 (PDZ) interaction modules. In many cases (but not always), the viruses have evolved to bind the PDZ domains using the same short linear peptide motifs found in host protein-PDZ interactions, and in some cases regulate the interactions in a similar fashion by phosphorylation. What is striking is that the diverse viruses target a common subset of PDZ proteins that are intimately involved in controlling cell polarity and the structure and function of intercellular junctions, including tight junctions. Cell polarity is fundamental to the control of cell proliferation and cell survival and disruption of polarity and the signal transduction pathways involved is a key event in tumourigenesis. This review focuses on the oncogenic viruses and the role of targeting PDZ proteins in the virus life cycle and the contribution of virus-PDZ protein interactions to virus-mediated oncogenesis. We highlight how many of the viral associations with PDZ proteins lead to deregulation of PI3K/AKT signalling, benefitting virus replication but as a consequence also contributing to oncogenesis.

Homologous Recombination Repair Factors Rad51 and BRCA1 Are Necessary for Productive Replication of Human Papillomavirus 31

High-risk human papillomavirus 31 (HPV31)-positive cells exhibit constitutive activation of the ATM-dependent DNA damage response (DDR), which is necessary for productive viral replication. In response to DNA double-strand breaks (DSBs), ATM activation leads to DNA repair through homologous recombination (HR), which requires the principal recombinase protein Rad51, as well as BRCA1. Previous studies from our lab demonstrated that Rad51 and BRCA1 are expressed at high levels in HPV31-positive cells and localize to sites of viral replication. These results suggest that HPV may utilize ATM activity to increase HR activity as a means to facilitate viral replication. In this study, we demonstrate that high-risk HPV E7 expression alone is sufficient for the increase in Rad51 and BRCA1 protein levels. We have found that this increase occurs, at least in part, at the level of transcription. Studies analyzing protein stability indicate that HPV may also protect Rad51 and BRCA1 from turnover, contributing to the overall increase in cellular levels. We also demonstrate that Rad51 is bound to HPV31 genomes, with binding increasing per viral genome upon productive replication. We have found that depletion of Rad51 and BRCA1, as well as inhibition of Rad51's recombinase activity, abrogates productive viral replication upon differentiation. Overall, these results indicate that Rad51 and BRCA1 are required for the process of HPV31 genome amplification and suggest that productive replication occurs in a manner dependent upon recombination.

IMPORTANCE

Productive replication of HPV31 requires activation of an ATM-dependent DNA damage response, though how ATM activity contributes to replication is unclear. Rad51 and BRCA1 play essential roles in repair of double-strand breaks, as well as the restart of stalled replication forks through homologous recombination (HR). Given that ATM activity is required to initiate HR repair, coupled with the requirement of Rad51 and BRCA1 for productive viral replication, our findings suggest that HPV may utilize ATM activity to ensure localization of recombination factors to productively replicating viral genomes. The finding that E7 increases the levels of Rad51 and BRCA1 suggests that E7 contributes to productive replication by providing DNA repair factors required for viral DNA synthesis. Our studies not only imply a role for recombination in the regulation of productive HPV replication but provide further insight into how HPV manipulates the DDR to facilitate the productive phase of the viral life cycle.

Novel Functions of the Human Papillomavirus E6 Oncoproteins

Human papillomaviruses (HPVs) infect the epidermis as well as mucous membranes of humans. They are the causative agents of anogenital tract and some oropharyngeal cancers. Infections begin in the basal epithelia, where the viral genome replicates slowly along with its host cell. As infected cells begin to differentiate and progress toward the periphery, the virus drives proliferation in cells that would otherwise be quiescent. To uncouple differentiation from continued cellular propagation, HPVs express two oncoproteins, HPV E6 and E7. This review focuses on high-risk α-HPV E6, which in addition to supporting viral replication has transforming properties. HPV E6 promotes p53 degradation and activates telomerase, but the multifaceted oncoprotein has numerous other functions that are highlighted here.

The human papillomavirus 16 European-T350G E6 variant can immortalize but not transform keratinocytes in the absence of E7

Human papillomavirus type 16 is commonly implicated in HPV-related cancers. However, only a small number of infected individuals progress to this stage. Epidemiological evidence demonstrated that oncogenic risk is population-specific and variations within the viral oncogene, E6, have been suggested to play a role in these findings. Of focus in this study is the European-T350G variant, which is characterized by an L>V amino acid substitution at residue 83 of the prototype E6 protein. To elucidate the functional effects of this polymorphism, we followed keratinocytes transduced with E-T350G E6 for over 60 passages and compared them to keratinocytes transduced, in parallel, with prototype or Asian-American (Q14H/L83V/H78Y) E6. We found that although E-T350G E6 immortalized transduced keratinocytes in the absence of E7, these cells were not fully transformed. We also found that E-T350G down-regulated E-cadherin compared to the other variants, providing a possible link between its population-based oncogenicity and host genetic variations.

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

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

Cancer-causing human papillomavirus E6 proteins display major differences in the phospho-regulation of their PDZ interactions

Previous studies have shown that the cancer-causing high-risk human papillomavirus (HPV) E6 oncoproteins have PDZ binding potential, an activity which is important for their ability to support the viral life cycle and to cooperate in the induction of malignancy. However, PDZ interactions are not constitutive, and they can be negatively regulated by phosphorylation within the E6 PDZ binding motif (PBM). In this study, we have investigated the differential regulation of the HPV E6 PBMs from diverse high-risk HPV types. We show that, depending on the HPV type, PDZ binding activity can be regulated by phosphorylation with protein kinase A (PKA) or AKT, which, in turn, inhibits PDZ recognition. Such regulation is highly conserved between E6 proteins derived from HPV-16, HPV-18, and HPV-58 while being somewhat weaker or absent from other types such as HPV-31, HPV-33, and HPV-51. In the case of HPV31, PKA phosphorylation occurs within the core of the E6 protein and has no effect on PDZ interactions, and this demonstrates a surprising degree of heterogeneity among the different high-risk HPV E6 oncoproteins in how they are regulated by different cellular signaling pathways.

IMPORTANCE

This study demonstrated that the cancer-causing HPV E6 oncoproteins are all subject to posttranslational modification of their extreme C-terminal PDZ binding motifs through phosphorylation. However, the identities of the kinase are not the same for all HPV types. This demonstrates a very important divergence between these HPVs, and it suggests that changes in cell signaling pathways have different consequences for different high-risk virus infections and their associated malignancies.

Human papillomavirus infection and pathogenesis in urothelial cells: a mini-review

Several recent studies described that high-risk human papillomavirus (HPV) infection could have a potential role in the development of malignancies other than cervical cancer, such as laryngeal carcinoma, penile carcinoma, and anal carcinoma. However, the etiological role of HPV infection in the pathogenesis of urinary tract has not been clarified. Many epidemiological studies demonstrated that HPV infections frequently occur in the external genitalia through sexual contact; however, it was reported that HPV infection could also occur in the urinary tract, including the urethra and urinary bladder. Some morphological changes of cells associated with HPV infection and mild atypical cells, suspected to be intraneoplasia, were seen in HPV-positive samples obtained from the urinary tract. Some clinical studies and meta-analysis have indicated that HPV infection is likely to have a certain etiological correlation with the development of bladder carcinoma, although its prevalence may vary according to HPV type, study population, region, histological type, detection methods, and other variables. According to the results of previous studies, the prevalence of HPV greatly widely varies in cases of bladder carcinoma. Further research by case-control or large-scales studies is thus required to reach a more definite conclusion.

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

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

High incidence of female reproductive tract cancers in FA-deficient HPV16-transgenic mice correlates with E7's induction of DNA damage response, an activity mediated by E7's inactivation of pocket proteins

Fanconi anemia (FA) is a rare genetic disorder caused by defects in a DNA damage repair system, the FA pathway. FA patients frequently develop squamous cell carcinoma (SCC) at sites that are associated with human papillomavirus (HPV)-driven cancer including the female reproductive tract. To assess experimentally whether FA deficiency increases susceptibility to HPV-associated cervical/vaginal cancer, we monitored cancer incidence in the female lower reproductive tract of FA-deficient mice expressing HPV16 oncogenes, E6 and/or E7. FA deficiency specifically increased the incidence of cancers in mice expressing E7; but this effect was not observed in mice just expressing E6. We also observed that E7, but not E6, induced DNA damage as scored by induction of γ-H2AX and 53BP1 (p53 binding protein 1) nuclear foci, and this induction was heightened in FA-deficient tissue. Finally, we discovered that this induction of DNA damage responses was recapitulated in mice deficient in expression of 'pocket' proteins, pRb, p107 and p130, which are established targets of E7. Our findings support the hypothesis that E7 induces cancer by causing DNA damage at least in part through the inactivation of pocket proteins. This hypothesis explains why a deficiency in DNA damage repair would increase susceptibility to E7-driven cancer.