Human papillomavirus E6 and E7 oncoproteins as risk factors for tumorigenesis

Hypermethylation of the tumor-suppressor cell adhesion molecule 1 in human papillomavirus-transformed cervical carcinoma cells

Epigenetic modification at CpG islands located on the promoter regions of tumor-suppressor genes has been associated with tumor development in many human cancers. Our study showed that the cell adhesion molecule 1 (CADM1) is downregulated in human papillomavirus (HPV)-infected cervical cancer cell lines via its hypermethylation and demethylation using 5-aza-2′-deoxycyticine (5-aza-dC) restored the expression of CADM1 protein. Overexpression of CADM1 inhibited cell proliferation. p53 was involved in the regulation of CADM1. Our results demonstrate that epigenetic alteration of CADM1 was more frequent in HPV-positive cervical cancers and that restoration of CADM1 expression may be a potential strategy for cervical cancer therapy.

The high-risk HPV16 E7 oncoprotein mediates interaction between the transcriptional coactivator CBP and the retinoblastoma protein pRb

The oncoprotein E7 from human papillomavirus (HPV) strains that confer high cancer risk mediates cell transformation by deregulating host cellular processes and activating viral gene expression through recruitment of cellular proteins such as the retinoblastoma protein (pRb) and the cyclic-AMP response element binding binding protein (CBP) and its paralog p300. Here we show that the intrinsically disordered N-terminal region of E7 from high-risk HPV16 binds the TAZ2 domain of CBP with greater affinity than E7 from low-risk HPV6b. HPV E7 and the tumor suppressor p53 compete for binding to TAZ2. The TAZ2 binding site in E7 overlaps the LxCxE motif that is crucial for interaction with pRb. While TAZ2 and pRb compete for binding to a monomeric E7 polypeptide, the full-length E7 dimer mediates an interaction between TAZ2 and pRb by promoting formation of a ternary complex. Cell-based assays show that expression of full-length HPV16 E7 promotes increased pRb acetylation and that this response depends both on the presence of CBP/p300 and on the ability of E7 to form a dimer. These observations suggest a model for the oncogenic effect of high-risk HPV16 E7. The disordered region of one E7 molecule in the homodimer interacts with the pocket domain of pRb, while the same region of the other E7 molecule binds the TAZ2 domain of CBP/p300. Through its ability to dimerize, E7 recruits CBP/p300 and pRb into a ternary complex, bringing the histone acetyltransferase domain of CBP/p300 into proximity to pRb and promoting acetylation, leading to disruption of cell cycle control.

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.

Viral load, gene expression and mapping of viral integration sites in HPV16-associated HNSCC cell lines

HPV-related HNSCC generally have a better prognosis than HPV-negative HNSCC. However, a subgroup of HPV-positive tumors with poor prognosis has been recognized, particularly related to smoking, EGFR overexpression and chromosomal instability. Viral integration into the host genome might contribute to carcinogenesis, as is shown for cervical carcinomas. Therefore, all HPV16-positive HNSCC cell lines currently available have been carefully analyzed for viral and host genome parameters. The viral integration status, viral load, viral gene expression and the presence of aneusomies was evaluated in the cell lines UD-SCC-2, UM-SCC-047, UM-SCC-104, UPCI:SCC090, UPCI:SCC152, UPCI:SCC154 and 93VU147T. HPV integration was examined using FISH, APOT-PCR and DIPS-PCR. Viral load and the expression of the viral genes E2, E6 and E7 were determined via quantitative PCR. All cell lines showed integration-specific staining patterns and signals indicating transcriptional activity using FISH. APOT- and DIPS-PCR identified integration-derived fusion products in six cell lines and only episomal products for UM-SCC-104. Despite the observed differences in viral load and the number of viral integration sites, this did not relate to the identified viral oncogene expression. Furthermore, cell lines exhibited EGFR expression and aneusomy (except UPCI:SCC154). In conclusion, all HPV16-positive HNSCC cell lines showed integrated and/or episomal viral DNA that is transcriptionally active, although viral oncogene expression was independent of viral copy number and the number of viral integration sites. Because these cell lines also contain EGFR expression and aneusomy, which are parameters of poor prognosis, they should be considered suitable model systems for the development of new antiviral therapies.

Overexpression of RhoA promotes the proliferation and migration of cervical cancer cells

The pro-oncogenic role of RhoA has been well identified in other cancers, but rarely in cervical cancer (CC), one of the main causes of cancer-related death in women. In the present study, we identified the overexpression of RhoA and its downstream effectors, ROCK-1 and ROCK-II, in CC specimens using western blotting. Then, we determined the effect of RhoA on the proliferation and migration of Hela cells, one of CC cell lines, by upregulating or downregulating the RhoA expression in Hela cells. We found that there was an overexpression of RhoA, ROCK-I/II in CC, which was associated with the progression of CC. And we confirmed that RhoA promoted the proliferation and migration of CC cells. In conclusion, we found a positive correlation among RhoA with the progression of CC by in vivo and in vitro evidences. A high RhoA expression in CC may predict a high metastatic potential of CC.

"Equivocal" high-risk HPV DNA tests performed on ThinPrep specimens after ASC-US diagnoses are associated with an increased incidence of CIN3: a cytologic/histologic review of 315 cases

OBJECTIVE

The Hybrid Capture II high-risk HPV test (HC II hrHPVT) improves early detection of cervical neoplasia in Pap tests. However, weakly positive HC II results may be reported as indeterminate or "equivocal," for which there is little clinical guidance. This study is designed to evaluate the clinical outcome of equivocal HC II hrHPVTs and concurrent atypical squamous cells of undetermined significance (ASC-US) on ThinPrep Pap specimens through correlation with 2-year follow-up cervical biopsies.

MATERIALS AND METHODS

Over a 5-year period, ThinPrep Pap tests diagnosed as ASC-US were grouped according to their hrHPVT results (i.e., positive, negative, or equivocal) and correlated with histologic follow-up. All equivocal and representative positive and negative hrHPVTs were included. Biopsies showing high-grade dysplasia were reviewed by two pathologists.

RESULTS

Of 9,012 ASCUS Pap tests, 945 had corresponding hrHPVTs and follow-up cervical biopsies. High-grade squamous intraepithelial lesion (HSIL-cervical intraepithelial neoplasia grades 2/3, CIN2/3) was identified in 20.3% (14/69) of biopsies after equivocal hrHPVTs (CIN2-5.8%, CIN3-14.5% (p=.0261); 16.7% (25/150) after positive hrHPVT (CIN2-12%, CIN3-4.7%); and 5.4% (5/93) of biopsies after negative hrHPVT (CIN2-4.3%, CIN3-1.1%).

CONCLUSION

ASC-US in association with equivocal and positive HC II results respectively shows similar incidences of CIN2/3 on 2-year follow-up cervical biopsy. Additionally, a significant proportion of CIN3 biopsies are in the equivocal HC II cohort. As clinical decision making would be impacted by this finding, laboratories should consider evaluating the clinical performance of their HC II assay via correlation with subsequent cervical biopsies.

HPVdb: a data mining system for knowledge discovery in human papillomavirus with applications in T cell immunology and vaccinology

High-risk human papillomaviruses (HPVs) are the causes of many cancers, including cervical, anal, vulvar, vaginal, penile and oropharyngeal. To facilitate diagnosis, prognosis and characterization of these cancers, it is necessary to make full use of the immunological data on HPV available through publications, technical reports and databases. These data vary in granularity, quality and complexity. The extraction of knowledge from the vast amount of immunological data using data mining techniques remains a challenging task. To support integration of data and knowledge in virology and vaccinology, we developed a framework called KB-builder to streamline the development and deployment of web-accessible immunological knowledge systems. The framework consists of seven major functional modules, each facilitating a specific aspect of the knowledgebase construction process. Using KB-builder, we constructed the Human Papillomavirus T cell Antigen Database (HPVdb). It contains 2781 curated antigen entries of antigenic proteins derived from 18 genotypes of high-risk HPV and 18 genotypes of low-risk HPV. The HPVdb also catalogs 191 verified T cell epitopes and 45 verified human leukocyte antigen (HLA) ligands. Primary amino acid sequences of HPV antigens were collected and annotated from the UniProtKB. T cell epitopes and HLA ligands were collected from data mining of scientific literature and databases. The data were subject to extensive quality control (redundancy elimination, error detection and vocabulary consolidation). A set of computational tools for an in-depth analysis, such as sequence comparison using BLAST search, multiple alignments of antigens, classification of HPV types based on cancer risk, T cell epitope/HLA ligand visualization, T cell epitope/HLA ligand conservation analysis and sequence variability analysis, has been integrated within the HPVdb. Predicted Class I and Class II HLA binding peptides for 15 common HLA alleles are included in this database as putative targets. HPVdb is a knowledge-based system that integrates curated data and information with tailored analysis tools to facilitate data mining for HPV vaccinology and immunology. To our best knowledge, HPVdb is a unique data source providing a comprehensive list of HPV antigens and peptides. Database URL: http://cvc.dfci.harvard.edu/hpv/.

Comprehensive analysis of HPV16 integration in OSCC reveals no significant impact of physical status on viral oncogene and virally disrupted human gene expression

Infection with high-risk human papillomavirus (HPV) type 16 is an independent risk factor for the development of oropharyngeal squamous cell carcinomas (OSCC). However, it is unclear whether viral integration is an essential hallmark in the carcinogenic process of OSCC and whether HPV integration correlates with the level of viral gene transcription and influences the expression of disrupted host genes. We analyzed 75 patients with OSCC. HPV16-positivity was proven by p16(INK4A) immunohistochemistry, PCR and FISH. Viral integration was examined using DIPS- as well as APOT-PCR. Viral E2, E6 and E7 gene expression levels were quantified by quantitative reverse transcriptase (RT-q)PCR. Expression levels of 7 human genes disrupted by the virus were extracted from mRNA expression profiling data of 32 OSCCs. Viral copy numbers were assessed by qPCR in 73 tumors. We identified 37 HPV16-human fusion products indicating viral integration in 29 (39%) OSCC. In the remaining tumors (61%) only episome-derived PCR products were detected. When comparing OSCC with or without an integration-derived fusion product, we did not find significant differences in the mean RNA expression of viral genes E2, E6 and E7 or the viral copy numbers per cell, nor did the RNA expression of the HPV-disrupted genes differ from either group of OSCC. In conclusion, our data do not support the hypothesis that integration affects the levels of viral and/or HPV-disrupted human gene transcripts. Thus constitutive, rather than a high level, of expression of oncogene transcripts appears to be required in HPV-related OSCC.

Novel action modality of the diterpenoid anisomelic acid causes depletion of E6 and E7 viral oncoproteins in HPV-transformed cervical carcinoma cells

Cervical cancer, the second most common malignancy among women, is mainly caused by human papilloma virus (HPV) infection. In HPV-positive cervical cancer cells, the activity of p53 and the induction of p21 are inhibited by the HPV oncoproteins E6 and E7. Therefore, blocking the activity of E6 and E7 would serve as an important therapeutic target in these cancer cells. In this study, anisomelic acid (AA), a natural compound belonging to the same diterpenoid family of bioactive compounds as taxol, was found to deplete the E6 and E7 proteins in HPV-positive cervical cancer cells. Consequently, p53 and the p53-responsive gene, p21, were dramatically induced, leading to G2/M-phase cell cycle arrest. AA-mediated cell cycle arrest and p21 expression were canceled when p53 was down-regulated by p53-shRNA. AA also induced p53-independent intrinsic apoptosis by depletion of the cellular inhibitor of apoptosis protein 2 (cIAP2) whose proteosomal degradation is inhibited by E6. The in ovo chick embryo chorioallantoic membrane (CAM) assay showed that anisomelic acid inhibited the tumor growth of the cervical cancer SiHa cells. AA is revealed to hold a novel action modality based on specific targeting of the HPV oncoproteins, which restores p53-mediated growth arrest and induces apoptosis by terminating E6-mediated cIAP2 stabilization.

Risk of progression of early cervical lesions is associated with integration and persistence of HPV-16 and expression of E6, Ki-67, and telomerase

BACKGROUND

Low-grade squamous intraepithelial lesions (LSIL) are the earliest lesions of the uterine cervix, the persistence and integration of high-risk human papillomavirus (HR-HPV) as type 16, which promotes the development of more aggressive lesions.

AIM

To select more aggressive lesions with tendency to progress to invasive cervical cancer.

MATERIALS AND METHODS

A total of 75 cytological specimens in liquid base (Liqui-PREP) were analyzed: 25 specimens were with no signs of SIL (NSIL) and without HPV; 25 NSIL with HPV-16, and 25 with both LSIL and HPV-16. The expression of Ki-67, telomerase, and viral E6 was evaluated by immunocytochemistry; and the detection of viral DNA was done by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLPs) for genotyping or sequencing of HPV-16. The physical state of HPV-16 was evaluated by in situ hybridization with amplification with tyramide.

RESULTS

Of the total group, 58.6% had LSIL associated with persistence and of these 59.3% was associated with integrated state of HPV as intense expression of E6, Ki-67 (P = 0.013, P = 0.055) has except for the expression of telomerase present a non-significant association (P<0.341).

CONCLUSIONS

Overexpression of E6 and Ki-67 is associated with the integration of HPV-16, favoring viral persistence, and increasing the risk of progression in women with NSIL and LSIL.

The four steps in the prevention of human papillomavirus-associated neoplasia: considerations for preventive measures, screening, disease impact, and potential overtreatments in HPV-related pathology

There is no cure currently available for HPV infections, although ablative and excisional treatments of some dysplasias often result in a clinical and virological cure. Effective control measures of HPV-associated cancers rely on the prevention at four different levels. Apart from sexual abstinence, primary prevention is realized through vaccines targeting the most frequent HPV types: negative attitudes towards HPV vaccination and high costs are the main obstacles. The aim of secondary prevention is to detect precancerous changes before they develop into invasive cancer, while tertiary prevention involves actual treatment of high-grade lesions: in many countries routine screening with cytology is being challenged with HPV DNA testing. Quaternary prevention comprehends those actions adopted to mitigate or avoid unnecessary or excessive medical interventions, and may well be addressed in avoiding treatments for low-grade intraepithelial neoplasia. Though some gynecologists commonly recommend treatment for low-grade disease and women tend to prefer active management if not properly informed, harms arising from unnecessary treatments, increased costs, work overload for second-level health services, and induced psychosocial distress are causing on-going problems. Prevention efforts of genital HPV-associated cancers should concentrate in: (1) enhancing primary prevention through vaccination of all eligible subjects, (2) achieving high levels of adherence to routine screening programs, (3) treating precancerous lesions, and (4) monitoring current guidelines recommendations to avoid overtreatments. Novel research projects should be designed to study the delicate mechanisms of immune response to HPV.

Human papillomavirus screening in north Indian women

OBJECTIVES

Human papillomavirus (HPV) is the major etiological agent of cervical cancer, a leading cause of morbidity and mortality in women worldwide. Screening strategies for reducing the burden of HPV-mediated carcinogenesis are emerging as an effective means for cervical cancer control and prevention in developing countries. Our study, therefore, aimed to identify HPV infection status in North Indian women during random population screening.

METHODOLOGY

Cervical/vaginal exfoliated cells and/or Pap smear specimens were collected from 890 women of North Indian ethnicity residing in Lucknow and adjoining areas, during random population screening from June 2009-March 2012. HPV viral loads in clinical specimens were determined by the Hybrid Capture (hc)-2 HPV DNA assay, and subsequently, positive/negative/borderline HPV status was calculated.

RESULTS

The HPV incidence in the present study was 11.7%. 751 out of a total of 890 women (84.4%) participating in our HPV screening program were HPV negative (HPV -), 104 (11.7%) tested positive (HPV +) while 35 (3.9%) showed borderline (HPV *) infection status. Furthermore, in the HPV + subjects (N=104), 18 (17.3%) showed strong positivity. We observed that HPV positivity tends to increase with age in North Indian women; the higher the viral load with increasing age, higher is the susceptibility to HPV-mediated cervical cancer.

CONCLUSIONS

HPV viral load/genotyping may help in identifying women at risk of developing cervical cancer. However, cost- effective HPV screening protocols with a wider population coverage are warranted so as to reduce the burden of cervical cancer in women worldwide in the vaccine-era.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

Diverse roles for the paxillin family of proteins in cancer

The paxillin family of intracellular scaffold proteins includes paxillin, Hic-5, and leupaxin, and all have been identified as key regulators of the cellular migration machinery in both 2- and 3-dimensional microenvironments. Herein, we provide insight into the roles of these proteins during tumorigenesis and metastasis, highlighting their functions in cancer initiation as well as tumor cell dissemination and survival. Furthermore, we speculate on the potential of paxillin family proteins as both future prognostic and therapeutic targets.

Targeted radiosensitization by the Chk1 inhibitor SAR-020106

PURPOSE

To explore the activity of a potent Chk1 inhibitor (SAR-020106) in combination with radiation.

METHODS AND MATERIALS

Colony and mechanistic in vitro assays and a xenograft in vivo model.

RESULTS

SAR-020106 suppressed-radiation-induced G2/M arrest and reduced clonogenic survival only in p53-deficient tumor cells. SAR-020106 promoted mitotic entry following irradiation in all cell lines, but p53-deficient cells were likely to undergo apoptosis or become aneuploid, while p53 wild-type cells underwent a postmitotic G1 arrest followed by subsequent normal cell cycle re-entry. Following combined treatment with SAR-020106 and radiation, homologous-recombination-mediated DNA damage repair was inhibited in all cell lines. A significant increase in the number of pan-γH2AX-staining apoptotic cells was observed only in p53-deficient cell lines. Efficacy was confirmed in vivo in a clinically relevant human head-and-neck cell carcinoma xenograft model.

CONCLUSION

The Chk1 inhibitor SAR-020106 is a potent radiosensitizer in tumor cell lines defective in p53 signaling.

Comparative analysis of virus-host interactomes with a mammalian high-throughput protein complementation assay based on Gaussia princeps luciferase

Comparative interactomics is a strategy for inferring potential interactions among orthologous proteins or "interologs". Herein we focus, in contrast to standard homology-based inference, on the divergence of protein interaction profiles among closely related organisms, showing that the approach can correlate specific traits to phenotypic differences. As a model, this new comparative interactomic approach was applied at a large scale to human papillomaviruses (HPVs) proteins. The oncogenic potential of HPVs is mainly determined by the E6 and E7 early proteins. We have mapped and overlapped the virus-host protein interaction networks of E6 and E7 proteins from 11 distinct HPV genotypes, selected for their different tropisms and pathologies. We generated robust and comprehensive datasets by combining two orthogonal protein interaction assays: yeast two-hybrid (Y2H), and our recently described "high-throughput Gaussia princeps protein complementation assay" (HT-GPCA). HT-GPCA detects protein interaction by measuring the interaction-mediated reconstitution of activity of a split G. princeps luciferase. Hierarchical clustering of interaction profiles recapitulated HPV phylogeny and was used to correlate specific virus-host interaction profiles with pathological traits, reflecting the distinct carcinogenic potentials of different HPVs. This comparative interactomics constitutes a reliable and powerful strategy to decipher molecular relationships in virtually any combination of microorganism-host interactions.

Hedgehog pathway regulators influence cervical cancer cell proliferation, survival and migration

Human papillomavirus (HPV) infection is considered to be a primary hit that causes cervical cancer. However, infection with this agent, although needed, is not sufficient for a cancer to develop. Additional cellular changes are required to complement the action of HPV, but the precise nature of these changes is not clear. Here, we studied the function of the Hedgehog (Hh) signaling pathway in cervical cancer. The Hh pathway can have a role in a number of cancers, including those of liver, lung and digestive tract. We found that components of the Hh pathway are expressed in several cervical cancer cell lines, indicating that there could exists an autocrine Hh signaling loop in these cells. Inhibition of Hh signaling reduces proliferation and survival of the cervical cancer cells and induces their apoptosis as seen by the up-regulation of the pro-apoptotic protein cleaved caspase 3. Our results indicate that Hh signaling is not induced directly by HPV-encoded proteins but rather that Hh-activating mutations are selected in cells initially immortalized by HPV. Sonic Hedgehog (Shh) ligand induces proliferation and promotes migration of the cervical cancer cells studied. Together, these results indicate pro-survival and protective roles of an activated Hh signaling pathway in cervical cancer-derived cells, and suggest that inhibition of this pathway may be a therapeutic option in fighting cervical cancer.

Laboratory and clinical aspects of human papillomavirus testing

Human papillomavirus (HPV) infection is associated with a wide spectrum of disease that ranges from self-limited skin warts to life-threatening cancers. Since HPV plays a necessary etiological role in cervical cancer, it is logical to use HPV as a marker for early detection of cervical cancer and precancer. Recent advances in technology enable the development of high-throughput HPV assays of different formats, including DNA-based, mRNA-based, high-risk group-specific and type-specific methods. The ultimate goal of these assays is to improve the accuracy and cost-effectiveness of cervical screening programs. HPV testing has several potential advantages compared to cytology-based screening. However, since the cancer to transient infection ratio is always low in the general population, HPV test results are bound to have a low positive predictive value that may subject women to unnecessary follow-up investigations. The wide-spread administration of prophylactic HPV vaccine will substantially decrease the incidence of cancer and precancer. This poses a number of challenges to cytology-based screening, and the role of HPV testing is expected to increase. Finally, apart from technical and cost-effectiveness considerations, one should also keep in mind the psycho-social impact of using sexually-transmitted agents as a marker for cancer screening.

The HPV E6 oncoprotein targets histone methyltransferases for modulating specific gene transcription

Expression of viral proteins causes important epigenetic changes leading to abnormal cell growth. Whether viral proteins directly target histone methyltransferases (HMTs), a key family enzyme for epigenetic regulation, and modulate their enzymatic activities remains elusive. Here we show that the E6 proteins of both low-risk and high-risk human papillomavirus (HPV) interact with three coactivator HMTs, CARM1, PRMT1 and SET7, and downregulate their enzymatic activities in vitro and in HPV-transformed HeLa cells. Furthermore, these three HMTs are required for E6 to attenuate p53 transactivation function. Mechanistically, E6 hampers CARM1- and PRMT1-catalyzed histone methylation at p53-responsive promoters, and suppresses the binding of p53 to chromatinized DNA independently of E6-mediated p53 degradation. p53 pre-methylated at lysine-372 (p53K372 mono-methylation) by SET7 protects p53 from E6-induced degradation. Consistently, E6 downregulates p53K372 mono-methylation and thus reduces p53 protein stability. As a result of the E6-mediated inhibition of HMT activity, expression of p53 downstream genes is suppressed. Together, our results not only reveal a clever approach for the virus to interfere with p53 function, but also demonstrate the modulation of HMT activity as a novel mechanism of epigenetic regulation by a viral oncoprotein.

Identification and characterization of small molecule antagonists of pRb inactivation by viral oncoproteins

The retinoblastoma protein pRb is essential for regulating many cellular activities through its binding and inhibition of E2F transcription activators, and pRb inactivation leads to many cancers. pRb activity can be perturbed by viral oncoproteins including human papillomavirus (HPV) that share an LxCxE motif. Because there are no treatments for existing HPV infection leading to nearly all cervical cancers and other cancers to a lesser extent, we screened for compounds that inhibit the ability of HPV-E7 to disrupt pRb/E2F complexes. This lead to the identification of thiadiazolidinedione compounds that bind to pRb with mid-high nanomolar dissociation constants, are competitive with the binding of viral oncoproteins containing an LxCxE motif, and are selectively cytotoxic in HPV-positive cells alone and in mice. These inhibitors provide a promising scaffold for the development of therapies to treat HPV-mediated pathologies.

Next-generation treatment strategies for human papillomavirus-related head and neck squamous cell carcinoma: where do we go?

Oncogenic human papillomavirus (HPV) is currently recognised as a major risk factor for the development of head and neck squamous cell carcinomas (HNSCC). HPV is mostly detected in tumours arising from the oropharynx and more specifically from the tonsil. HPV-related tumours display clinical and molecular characteristics that are distinct from HPV-unrelated tumours, which are generally induced by alcohol and tobacco abuse. Detection of biologically active HPV in HNSCC has prognostic relevance, which warrants the separate classification of HPV-induced tumours and is a prerequisite for further optimisation of treatment protocols for this distinct group. Current guidelines for the treatment of oropharyngeal squamous cell carcinoma (OPSCC) have not incorporated specific treatment modalities for HPV-related tumours. The development of such treatment options is still in a preclinical phase or in early clinical trials. Recent data on treatment response of OPSCC have been obtained by retrospectively analysing HPV-status and indicate that patients with HPV-related tumours show a favourable prognosis, independent of the type of treatment. These patients may benefit from de-intensified treatment, which should be assessed in prospective clinical trials. The development and future use of new antiviral and immunomodulatory therapeutics may be instrumental in this approach to improve survival rates and decrease disease-and-treatment-related morbidity. In this review we will focus on present therapeutic HPV-targeting strategies and discuss future directions for de-intensified treatment of HPV-positive HNSCC.

Human papillomavirus type 16 E5 protein induces expression of beta interferon through interferon regulatory factor 1 in human keratinocytes

Crucial steps in high-risk human papillomavirus (HR-HPV)-related carcinogenesis are the integration of HR-HPV into the host genome and loss of viral episomes. The mechanisms that promote cervical neoplastic progression are, however, not clearly understood. During HR-HPV infection, the HPV E5 protein is expressed in precancerous stages but not after viral integration. Given that it has been reported that loss of HPV16 episomes and cervical tumor progression are associated with increased expression of antiviral genes that are inducible by type I interferon (IFN), we asked whether E5, expressed in early phases of cervical carcinogenesis, affects IFN-β signaling. We show that the HPV type 16 (HPV16) E5 protein expression per se stimulates IFN-β expression. This stimulation is specifically mediated by the induction of interferon regulatory factor 1 (IRF-1) which, in turn, induces transcriptional activation of IRF-1-targeted interferon-stimulated genes (ISGs) as double-stranded RNA-dependent protein kinase R (PKR) and caspase 8. Our data show a new and unexpected role for HR-HPV E5 protein and indicate that HPV16 E5 may contribute to the mechanisms responsible for cervical carcinogenesis in part via stimulation of IFN-β and an IFN signature, with IRF-1 playing a pivotal role. HPV16 E5 and IRF-1 may thus serve as potential therapeutic targets in HPV-associated premalignant lesions.

Aberrant upregulation of MUC4 mucin expression in cutaneous condyloma acuminatum and squamous cell carcinoma suggests a potential role in the diagnosis and therapy of skin diseases

AIM

Mucins comprise a family of high-molecular-weight glycoproteins. MUC4, a large transmembrane mucin, has recently emerged as a novel marker for diagnosis, prognosis and therapy in several malignancies. However, its role in skin pathologies remains unknown. The aim of this study was to analyse the expression of MUC4 in cutaneous pathologies by immunohistochemistry for potential diagnostic, prognostic and therapeutic applications.

METHODS

A total of 330 tissue spots representing the normal skin, and benign and malignant cutaneous diseases, were analysed after staining with the monoclonal antibody to human MUC4 (clone 8G7).

RESULTS

While the normal epidermis showed a negative to weak-positive expression of MUC4, its expression was significantly upregulated in squamous cell carcinomas (SCCs) where the intensity of staining correlated negatively with tumour grade and positively with age. A moderately strong MUC4 expression was also noted in 2/20 cancer adjacent normal skin and 2/21 chronically inflamed skin tissues, while 10/19 cases of vulval condyloma acuminate, 3/12 of vulval hyperplasia and 2 cases of verruca vulgaris also showed strong MUC4 positivity. Malignant melanoma, basal cell carcinoma and cutaneous cysts were negative.

CONCLUSION

The results indicate that MUC4 expression is aberrantly upregulated in cutaneous SCCs, vulval condylomas and verruca vulgaris. Further, it appears that MUC4 expression in the skin may be modulated by chronic inflammation and the presence of an adjacent cutaneous malignancy in certain cases. These observations suggest a novel role for MUC4 mucin in the pathogenesis of cutaneous SCC and a possible application as a diagnostic and/or prognostic marker in cutaneous pathologies.

The structural and dynamic response of MAGI-1 PDZ1 with noncanonical domain boundaries to the binding of human papillomavirus E6

PDZ domains are protein interaction domains that are found in cytoplasmic proteins involved in signaling pathways and subcellular transport. Their roles in the control of cell growth, cell polarity, and cell adhesion in response to cell contact render this family of proteins targets during the development of cancer. Targeting of these network hubs by the oncoprotein E6 of "high-risk" human papillomaviruses (HPVs) serves to effect the efficient disruption of cellular processes. Using NMR, we have solved the three-dimensional solution structure of an extended construct of the second PDZ domain of MAGI-1 (MAGI-1 PDZ1) alone and bound to a peptide derived from the C-terminus of HPV16 E6, and we have characterized the changes in backbone dynamics and hydrogen bonding that occur upon binding. The binding event induces quenching of high-frequency motions in the C-terminal tail of the PDZ domain, which contacts the peptide upstream of the canonical X-[T/S]-X-[L/V] binding motif. Mutations designed in the C-terminal flanking region of the PDZ domain resulted in a significant decrease in binding affinity for E6 peptides. This detailed analysis supports the notion of a global response of the PDZ domain to the binding event, with effects propagated to distal sites, and reveals unexpected roles for the sequences flanking the canonical PDZ domain boundaries.

The human papillomavirus-16 (HPV-16) oncoprotein E7 conjugates with and mediates the role of the transforming growth factor-beta inducible early gene 1 (TIEG1) in apoptosis

The human papillomavirus (HPV) oncoprotein E7 is a major transforming protein. The E7 protein does not possess intrinsic enzymatic activity, but rather functions through direct and indirect interactions with cellular proteins, several of which are well known cellular tumor suppressors. Using the yeast two-hybrid system, we found that transforming growth factor-beta inducible early gene 1 (TIEG1), a member of the Krüppel-like family (KLF) that has been implicated as a putative tumor suppressor, interacts and forms a specific complex with HPV-16 E7. TIEG1 has been shown to mimic the effects of TGF-beta in various carcinoma cells and plays a critical role in the apoptotic cascade. Our results indicate that E7 binds to the C-terminus of TIEG1 and induces its degradation via the ubiquitin pathway. E7 not only increased the ubiquitination of TIEG1 but also influenced the ability of TIEG1 to affect apoptosis. Our results suggest that suppression of TIEG1-mediated signaling by E7 may contribute to HPV-associated carcinogenesis.

Computational approaches for protein function prediction: a combined strategy from multiple sequence alignment to molecular docking-based virtual screening

The functional characterization of proteins represents a daily challenge for biochemical, medical and computational sciences. Although finally proved on the bench, the function of a protein can be successfully predicted by computational approaches that drive the further experimental assays. Current methods for comparative modeling allow the construction of accurate 3D models for proteins of unknown structure, provided that a crystal structure of a homologous protein is available. Binding regions can be proposed by using binding site predictors, data inferred from homologous crystal structures, and data provided from a careful interpretation of the multiple sequence alignment of the investigated protein and its homologs. Once the location of a binding site has been proposed, chemical ligands that have a high likelihood of binding can be identified by using ligand docking and structure-based virtual screening of chemical libraries. Most docking algorithms allow building a list sorted by energy of the lowest energy docking configuration for each ligand of the library. In this review the state-of-the-art of computational approaches in 3D protein comparative modeling and in the study of protein-ligand interactions is provided. Furthermore a possible combined/concerted multistep strategy for protein function prediction, based on multiple sequence alignment, comparative modeling, binding region prediction, and structure-based virtual screening of chemical libraries, is described by using suitable examples. As practical examples, Abl-kinase molecular modeling studies, HPV-E6 protein multiple sequence alignment analysis, and some other model docking-based characterization reports are briefly described to highlight the importance of computational approaches in protein function prediction.

High-risk human papilloma virus infection, tumor pathophenotypes, and BRCA1/2 and TP53 status in juvenile breast cancer

Juvenile breast cancer is rare and poorly known. We studied a series of five breast cancer patients diagnosed within 25 years of age that included two adolescents, 12- and 15-years-old, and 3 young women, 21-, 21-, and 25-years-old, respectively. All cases were scanned for germline mutations along the entire BRCA1/2 coding sequences and TP53 exons 4-10, using protein truncation test, denaturing high performance liquid chromatography and direct sequencing. Paraffin-embedded primary tumors (available for 4/5 cases), and a distant metastasis (from the 15-years-old) were characterized for histological and molecular tumor subtype, human papilloma virus (HPV) types 16/18 E6 sequences and tumor-associated mutations in TP53 exons 5-8. A BRCA2 germline mutation (p.Ile2490Thr), previously reported in breast cancer and, as compound heterozygote, in Fanconi anemia, was identified in the 21-year-old patient diagnosed after pregnancy, negative for cancer family history. The tumor was not available for study. Only germline polymorphisms in BRCA1/2 and/or TP53 were detected in the other cases. The tumors of the 15- and 12-years-old were, respectively, classified as glycogen-rich carcinoma with triple negative subtype and as secretory carcinoma with basal subtype. The tumors of the 25-year-old and of the other 21-year-old were, respectively, diagnosed as infiltrating ductal carcinoma with luminal A subtype and as lobular carcinoma with luminal B subtype. No somatic TP53 mutations were found, but tumor-associated HPV 16 E6 sequences were retrieved from the 12- and 25-year-old, while both HPV 16 and HPV 18 E6 sequences were found in the tumor of the 15-year-old and in its associated metastasis. Blood from the 15- and 25-year-old, diagnosed with high-stage disease, resulted positive for HPV 16 E6. All the HPV-positive cases were homozygous for arginine at TP53 codon 72, a genotype associated with HPV-related cancer risk, and the tumors showed p16(INK4A) immunostaining, a marker of HPV-associated cancers. Notably menarche at 11 years was reported for the two adolescents, while the 25-year-old was diagnosed after pregnancy and breast-feeding. Our data suggest that high-risk HPV infection is involved in a subset of histopathologically heterogeneous juvenile breast carcinomas associated with menarche or pregnancy and breast-feeding. Furthermore we implicate BRCA2 in a juvenile breast carcinoma diagnosed at 21 years of age, 4 years after an early full-term pregnancy, in absence of cancer family history.