Human papillomavirus type 16 E6 and E7 oncogenes abrogate radiation-induced DNA damage responses in vivo through p53-dependent and p53-independent pathways

Human Papillomavirus-Induced Chromosomal Instability and Aneuploidy in Squamous Cell Cancers

Chromosomal instability (CIN) and aneuploidy are hallmarks of cancer. CIN is defined as a continuous rate of chromosome missegregation events over the course of multiple cell divisions. CIN causes aneuploidy, a state of abnormal chromosome content differing from a multiple of the haploid. Human papillomavirus (HPV) is a well-known cause of squamous cancers of the oropharynx, cervix, and anus. The HPV E6 and E7 oncogenes have well-known roles in carcinogenesis, but additional genomic events, such as CIN and aneuploidy, are often required for tumor formation. HPV+ squamous cancers have an increased frequency of specific types of CIN, including polar chromosomes. CIN leads to chromosome gains and losses (aneuploidies) specific to HPV+ cancers, which are distinct from HPV- cancers. HPV-specific CIN and aneuploidy may have implications for prognosis and therapeutic response and may provide insight into novel therapeutic vulnerabilities. Here, we review HPV-specific types of CIN and patterns of aneuploidy in squamous cancers, as well as how this impacts patient prognosis and treatment.

Histology Specific Molecular Biomarkers: Ushering in a New Era of Precision Radiation Oncology

Histopathology and clinical staging have historically formed the backbone for allocation of treatment decisions in oncology. Although this has provided an extremely practical and fruitful approach for decades, it has long been evident that these data alone do not adequately capture the heterogeneity and breadth of disease trajectories experienced by patients. As efficient and affordable DNA and RNA sequencing have become available, the ability to provide precision therapy has become within grasp. This has been realized with systemic oncologic therapy, as targeted therapies have demonstrated immense promise for subsets of patients with oncogene-driver mutations. Further, several studies have evaluated predictive biomarkers for response to systemic therapy within a variety of malignancies. Within radiation oncology, the use of genomics/transcriptomics to guide the use, dose, and fractionation of radiation therapy is rapidly evolving but still in its infancy. The genomic adjusted radiation dose/radiation sensitivity index is one such early and exciting effort to provide genomically guided radiation dosing with a pan-cancer approach. In addition to this broad method, a histology specific approach to precision radiation therapy is also underway. Herein we review select literature surrounding the use of histology specific, molecular biomarkers to allow for precision radiotherapy with the greatest emphasis on commercially available and prospectively validated biomarkers.

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.

Persistent Human Papillomavirus Infection

Simple Summary

The success of HPV as an infectious agent lies not within its ability to cause disease, but rather in the adeptness of the virus to establish long-term persistent infection. The ability of HPV to replicate and maintain its genome in a stratified epithelium is contingent on the manipulation of many host pathways. HPVs must abrogate host anti-viral defense programs, perturb the balance of cellular proliferation and differentiation, and hijack DNA damage signaling and repair pathways to replicate viral DNA in a stratified epithelium. Together, these characteristics contribute to the ability of HPV to achieve long-term and persistent infection and to its evolutionary success as an infectious agent.

Abstract

Persistent infection with oncogenic human papillomavirus (HPV) types is responsible for ~5% of human cancers. The HPV infectious cycle can sustain long-term infection in stratified epithelia because viral DNA is maintained as low copy number extrachromosomal plasmids in the dividing basal cells of a lesion, while progeny viral genomes are amplified to large numbers in differentiated superficial cells. The viral E1 and E2 proteins initiate viral DNA replication and maintain and partition viral genomes, in concert with the cellular replication machinery. Additionally, the E5, E6, and E7 proteins are required to evade host immune responses and to produce a cellular environment that supports viral DNA replication. An unfortunate consequence of the manipulation of cellular proliferation and differentiation is that cells become at high risk for carcinogenesis.

Malignant Transformation of Fanconi Anemia Complementation Group D2-deficient (Fancd2 -/-) Hematopoietic Progenitor Cells by a Single HPV16 Oncogene

AIM

To demonstrate that Fanconi anemia complementation group D2-deficient (Fancd2^-/-) hematopoietic progenitor cell lines can be transformed by transfection with a plasmid containing either the E6 or E7 oncogene of human papillomavirus (HPV) to generate malignant plasmacytoma-inducing cell lines.

MATERIALS AND METHODS

In order to determine whether a single HPV type 16 (HPV16) oncogene induced malignant transformation, Fancd2^-/- and Fancd2^+/+ interleukin 3 (IL3)-dependent hematopoietic progenitor cell lines were transfected with plasmids containing E6 or E7 oncogene, or control empty plasmid.

RESULTS

Fancd2^-/- but not Fancd2^+/+ cells were transformed into malignant IL3-independent cells by both E6, and E7 oncogenes, but not by empty plasmid. Hematopoietic cell lines and tumors induced by Fancd2^-/- E6 and Fancd2^-/- E7 cell lines were positive for each respective HPV RNA and protein.

CONCLUSION

A single HPV16 oncogene is adequate to produce malignant transformation of Fancd2^-/- hematopoietic cells.

[Topical cyclosporine A and risk of ocular surface neoplasia]

INTRODUCTION

Cyclosporine A (CsA) has well-known cutaneous carcinogenic effects when administered systemically. In ophthalmology, it is increasingly used in the form of eye drops since its indication for moderate to severe eye dry eye. The goal of this review of the literature is to evaluate a possible link between topical ocular CsA use and the occurrence of ocular surface neoplasia.

MATERIALS AND METHODS

A literature review was performed. Publications evaluating the safety and efficacy of topical CsA as well as studies on the epidemiology and risk factors for conjunctival neoplasia and cases of conjunctival neoplasia were analyzed. Finally, post-market surveillance data from commercially available CsA eye drops were also evaluated.

RESULTS

Five cases of conjunctival neoplasia in patients treated with systemic and/or topical CsA have been described in the literature, three with systemic administration alone, another with combined systemic and local administration, and one case of local administration alone. In these cases, no direct link with the administration of ocular topical CsA could be determined. Among the numerous prospective studies evaluating the safety and efficacy of topical CsA as well as the case-control studies evaluating the risk factors for developing conjunctival neoplasia, no relationship between the occurrence of conjunctival neoplasia and the use of topical ocular CsA was observed.

CONCLUSION

Despite plausible pathophysiologic mechanisms, to date there is no evidence of an increased risk of ocular surface neoplasia with the use of topical ocular CsA. Further studies specifically addressing this question and with a longer duration are needed in order to precisely evaluate this theoretical risk.

Human papillomavirus and genome instability: from productive infection to cancer

Infection with high oncogenic risk human papillomavirus types is the etiological factor of cervical cancer and a major cause of other epithelial malignancies, including vulvar, vaginal, anal, penile and head and neck carcinomas. These agents affect epithelial homeostasis through the expression of specific proteins that deregulate important cellular signaling pathways to achieve efficient viral replication. Among the major targets of viral proteins are components of the DNA damage detection and repair machinery. The activation of many of these cellular factors is critical to process viral genome replication intermediates and, consequently, to sustain faithful viral progeny production. In addition to the important role of cellular DNA repair machinery in the infective human papillomavirus cycle, alterations in the expression and activity of many of its components are observed in human papillomavirus-related tumors. Several studies from different laboratories have reported the impact of the expression of human papillomavirus oncogenes, mainly E6 and E7, on proteins in almost all the main cellular DNA repair mechanisms. This has direct consequences on cellular transformation since it causes the accumulation of point mutations, insertions and deletions of short nucleotide stretches, as well as numerical and structural chromosomal alterations characteristic of tumor cells. On the other hand, it is clear that human papillomavirus-transformed cells depend on the preservation of a basal cellular DNA repair activity level to maintain tumor cell viability. In this review, we summarize the data concerning the effect of human papillomavirus infection on DNA repair mechanisms. In addition, we discuss the potential of exploiting human papillomavirus-transformed cell dependency on DNA repair pathways as effective antitumoral therapies.

Human papillomavirus E7 induces p63 expression to modulate DNA damage response

Cervical cancer is the third most common malignancy diagnosed in women worldwide. The major aetiological factor underlying the malignant transformation of cervical cells is the persistent infection with high-risk human papillomaviruses (HR-HPV), with more than 99% of cases expressing viral sequences. Here, we report a previously unknown mechanism driven by high-risk human papillomavirus E7 protein to modulate response to DNA damage in cervical cancer cells. Our data shows that HR-HPV E7 oncoprotein induces the transcription of the p53-family member p63, which modulates DNA damage response pathways, to facilitate repair of DNA damage. Based on our findings, we proposed a model, where HR-HPV could interfere with the sensitivity of transformed cells to radiation therapy by modulating DNA damage repair efficiency. Importantly, we have shown for the first time a critical role for p63 in response to DNA damage in cervical cancer cells.

DNA damage response is hijacked by human papillomaviruses to complete their life cycle

The DNA damage response (DDR) is activated when DNA is altered by intrinsic or extrinsic agents. This pathway is a complex signaling network and plays important roles in genome stability, tumor transformation, and cell cycle regulation. Human papillomaviruses (HPVs) are the main etiological agents of cervical cancer. Cervical cancer ranks as the fourth most common cancer among women and the second most frequent cause of cancer-related death worldwide. Over 200 types of HPVs have been identified and about one third of these infect the genital tract. The HPV life cycle is associated with epithelial differentiation. Recent studies have shown that HPVs deregulate the DDR to achieve a productive life cycle. In this review, I summarize current findings about how HPVs mediate the ataxia-telangiectasia mutated kinase (ATM) and the ATM-and RAD3-related kinase (ATR) DDRs, and focus on the roles that ATM and ATR signalings play in HPV viral replication. In addition, I demonstrate that the signal transducer and activator of transcription-5 (STAT)-5, an important immune regulator, can promote ATM and ATR activations through different mechanisms. These findings may provide novel opportunities for development of new therapeutic targets for HPV-related cancers.

Modulating the DNA Damage Response to Improve Treatment Response in Cervical Cancer

Cervical cancer is the fourth most common cause of cancer-related death in women worldwide and new therapeutic approaches are needed to improve clinical outcomes for this group of patients. Current treatment protocols for locally advanced and metastatic disease consist of ionising radiation and chemotherapy. Chemoradiation induces cytotoxic levels of DNA double-strand breaks, which activates programmed cell death via the DNA damage response (DDR). Cervical cancers are unique given an almost exclusive association with human papillomavirus (HPV) infection; a potent manipulator of the DDR, with the potential to alter tumour sensitivity to DNA-damaging agents and influence treatment response. This review highlights the wide range of therapeutic strategies in development that have the potential to modulate DDR and sensitise cervical tumours to DNA-damaging agents in the context of HPV oncogenesis.

Evolution of malignant plasmacytoma cell lines from K14E7 Fancd2-/- mouse long-term bone marrow cultures

We tested the effect of expression of the Human Papilloma Virus (HPV E7) oncogene on hematopoiesis in long-term bone marrow cultures (LTBMCs) derived from K14E7 (FVB) Fancd2-/- (129/Sv), K14E7 Fancd2+/+, Fancd2-/-, and control (FVB X 129/Sv) Fl mice. K14E7 Fancd2-/- and Fancd2-/- LTBMCs showed decreased duration of production of total nonadherent hematopoietic cells and progenitors forming day 7 and day 14 multilineage CFU-GEMM colonies in secondary cultures (7 wks and 8 wks respectively) compared to cultures from K14E7 Fancd2+/+ (17 wks) or control mice (18 wks) p < 0.0001. Marrow stromal cell lines derived from both K14E7 Fancd2-/- and Fancd2-/- cultures were radiosensitive, as were IL-3 dependent hematopoietic progenitor cell lines derived from K14E7 Fancd2-/- cultures. In contrast, Fancd2-/- mouse hematopoietic progenitor cell lines and fresh marrow were radioresistant. K14E7 Fancd2-/- mouse freshly explanted bone marrow expressed no detectable K14 or E7; however, LTBMCs produced K14 positive factor-independent (FI) clonal malignant plasmacytoma forming cell lines in which E7 was detected in the nucleus with p53 and Rb. Transfection of an E6/E7 plasmid into Fancd2-/-, but not control Fancd2+/+ IL-3 dependent hematopoietic progenitor cell lines, increased cloning efficiency, cell growth, and induced malignant cell lines. Therefore, the altered radiobiology of hematopoietic progenitor cells and malignant transformation in vitro by K14E7 expression in cells of the Fancd2-/- genotype suggests a potential role of HPV in hematopoietic malignancies in FA patients.

Immunocompromised and immunocompetent mouse models for head and neck squamous cell carcinoma

Mouse models can closely mimic human oral squamous epithelial carcinogenesis, greatly expand the in vivo research possibilities, and play a critical role in the development of diagnosis, monitoring, and treatment of head and neck squamous cell carcinoma. With the development of the recent research on the contribution of immunity/inflammation to cancer initiation and progression, mouse models have been divided into two categories, namely, immunocompromised and immunocompetent mouse models. And thus, this paper will review these two kinds of models applied in head and neck squamous cell carcinoma to provide a platform to understand the complicated histological, molecular, and genetic changes of oral squamous epithelial tumorigenesis.

Human papillomavirus type 16 E7 oncoprotein causes a delay in repair of DNA damage

BACKGROUND AND PURPOSE

Patients with human papillomavirus related (HPV+) head and neck cancers (HNCs) demonstrate improved clinical outcomes compared to traditional HPV negative (HPV-) HNC patients. We have recently shown that HPV+ HNC cells are more sensitive to radiation than HPV- HNC cells. However, roles of HPV oncogenes in regulating the response of DNA damage repair remain unknown.

MATERIAL AND METHODS

Using immortalized normal oral epithelial cell lines, HPV+ HNC derived cell lines, and HPV16 E7-transgenic mice we assessed the repair of DNA damage using γ-H2AX foci, single and split dose clonogenic survival assays, and immunoblot. The ability of E7 to modulate expression of proteins associated with DNA repair pathways was assessed by immunoblot.

RESULTS

HPV16 E7 increased retention of γ-H2AX nuclear foci and significantly decreased sublethal DNA damage repair. While phospho-ATM, phospho-ATR, Ku70, and Ku80 expressions were not altered by E7, Rad51 was induced by E7. Correspondingly, HPV+ HNC cell lines showed retention of Rad51 after γ-radiation.

CONCLUSIONS

Our findings provide further understanding as to how HPV16 E7 manipulates cellular DNA damage responses that may underlie its oncogenic potential and influence the altered sensitivity to radiation seen in HPV+ HNC as compared to HPV- HNC.

Validation of an HPV16-mediated carcinogenesis mouse model

BACKGROUND/AIM

Human papillomavirus Type 16 (HPV16) infection is a necessary but alone insufficient cause of invasive cervical cancer (ICC) and likely causes other genital cancers. Individual genetic variability influences the natural history of the neoplasm. Developing a variety of animal models to investigate HPV16-mediated carcinogenesis is important to Phase 1 trials for human cancer treatments.

MATERIALS AND METHODS

C57BL/6 mice expressing the HPV16-E7 transgene were treated with 100 nmoles of 7,12-dimethylbenz(a)anthracene (DMBA) on dorsal-thoracolumbar skin for ≤20 weeks.

RESULTS

Transgenic-HPV16E7 mice showed more tumors (14.11±1.49 vs. 7.2±0.73) that more quickly reached maximal size (17.53±0.53 vs. 28.75±0.67 weeks) than syngeneic controls.

CONCLUSION

DMBA topically-treated C57BL/6-HPV16E7 mice developed chronic inflammation as well as benign and malignant lesions, many of which ulcerated. Histology showed that the HPV16-E7 transgene more than doubled the effect of complete carcinogenesis against a C57BL/6 background alone, strongly influencing the number, size, and time-to-maximal tumor burden for DMBA-exposed transgenic-C57BL/6 mice.

Multiple biomarkers in molecular oncology. I. Molecular diagnostics applications in cervical cancer detection

The screening for cervical carcinoma and its malignant precursors (cervical neoplasia) currently employs morphology-based detection methods (Papanicolaou [Pap] smear) in addition to the detection of high-risk human papillomavirus. The combination of the Pap smear with human papillomavirus testing has achieved significant improvements in sensitivity for the detection of cervical disease. Diagnosis of cervical neoplasia is dependent upon histology assessment of cervical biopsy specimens. Attempts to improve the specificity of cervical disease screening have focused on the investigation of molecular biomarkers for adjunctive use in combination with the Pap smear. Active research into the genomic and proteomic alterations that occur during human papillomavirus-induced neoplastic transformation have begun to characterize some of the basic mechanisms inherent to the disease process of cervical cancer development. This research continues to demonstrate the complexity of multiple genomic and proteomic alterations that accumulate during the tumorigenesis process. Despite this diversity, basic patterns of uncontrolled signal transduction, cell cycle deregulation, activation of DNA replication and altered extracellular matrix interactions are beginning to emerge as common features inherent to cervical cancer development. Some of these gene or protein expression alterations have been investigated as potential biomarkers for screening and diagnostics applications. The contribution of multiple gene alterations in the development of cervical cancer suggests that the application of multiple biomarker panels has the potential to develop clinically useful molecular diagnostics. In this review, the application of biomarkers for the improvement of sensitivity and specificity of the detection of cervical neoplasia within cytology specimens will be discussed.

P16INK4A as a surrogate biomarker for human papillomavirus-associated oropharyngeal carcinoma: consideration of some aspects

Human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinomas (OPSCCs) frequently show different clinical and pathological features, which tend to be younger age, better performance status, less tobacco and alcohol consumption, more poorly differentiated histopathology, but usually with better treatment response and prognosis compared with HPV-negative OPSCCs. In tumor tissue, HPV infection is closely correlated with p16(INK4A) expression, which has been suggested to be a surrogate biomarker of HPV infection. However, there is diversity of sensitivity and specificity about p16(INK4A) in surrogate detection of HPV status. Herein, we summarize the current knowledge and note some aspects for consideration concerning p16(INK4A) as a surrogate biomarker for HPV-associated OPSCC.

Papilloma development and long-term ciclosporin use in chronic ocular allergy with associated keratoconus

PURPOSE

Conjunctival papillomata are squamous epithelial tumors with a strong association with human papilloma virus (HPV) types 6 and 11. They are benign conjunctival tumors that can be treated by surgical excision. We report a case where topical immunosuppressive therapy modified the local T-cell immunity in the conjunctiva resulting in papilloma development in a patient with keratoconus and a strong atopic history.

METHODS

A case report of a 44-year-old man with a history of severe ocular and generalized atopy is presented. We present the problems encountered in management of his severe ocular allergy and how these impeded the management of his keratoconus.

RESULTS

Conventional antiallergy topical medication was not producing symptom relief in this patient, and so topical immunosuppression was commenced using ciclosporin ointment 0.2%. This therapy modified the local T-cell immunity in the conjunctiva resulting in the development of papillomata which contributed to the intolerance of contact lens wear for visual rehabilitation of the keratoconus in the patient. These lesions were surgically removed but typically recurred and required further surgical excision. Adjunct cryotherapy was also performed at the time of the surgery to try to stem the recurrence of the papillomas.

CONCLUSIONS

To the best of our knowledge and following a review of the published literature using key databases that include Medline and PubMed, this is the first report confirming the development of conjunctival papillomas secondary to HPV type 6 in a ciclosporin-treated patient.

The papillomavirus E7 proteins

E7 is an accessory protein that is not encoded by all papillomaviruses. The E7 amino terminus contains two regions of similarity to conserved regions 1 and 2 of the adenovirus E1A protein, which are also conserved in the simian vacuolating virus 40 large tumor antigen. The E7 carboxyl terminus consists of a zinc-binding motif, which is related to similar motifs in E6 proteins. E7 proteins play a central role in the human papillomavirus life cycle, reprogramming the cellular environment to be conducive to viral replication. E7 proteins encoded by the cancer-associated alpha human papillomaviruses have potent transforming activities, which together with E6, are necessary but not sufficient to render their host squamous epithelial cell tumorigenic. This article strives to provide a comprehensive summary of the published research studies on human papillomavirus E7 proteins.

Papillomavirus E6 oncoproteins

Papillomaviruses induce benign and malignant epithelial tumors, and the viral E6 oncoprotein is essential for full transformation. E6 contributes to transformation by associating with cellular proteins, docking on specific acidic LXXLL peptide motifs found on these proteins. This review examines insights from recent studies of human and animal E6 proteins that determine the three-dimensional structure of E6 when bound to acidic LXXLL peptides. The structure of E6 is related to recent advances in the purification and identification of E6 associated protein complexes. These E6 protein-complexes, together with other proteins that bind to E6, alter a broad array of biological outcomes including modulation of cell survival, cellular transcription, host cell differentiation, growth factor dependence, DNA damage responses, and cell cycle progression.

Animal models to study the mutational landscape for oral cavity and oropharyngeal cancers

OBJECTIVES

Cancer is likely caused by alterations in gene structure or expression. Recently, next generation sequencing has documented mutations in 106 head and neck squamous cell cancer genomes, suggesting several new candidate genes. However, it remains difficult to determine which mutations directly contributed to cancer. Here, summarize the animal models which have already validated and may test cancer causing mutations identified by next generation sequencing approaches.

MATERIAL AND METHODS

We reviewed the existing literature on genetically engineered mouse models and next generation sequencing (NGS), as it relates to animal models of squamous cell cancers of the head and neck (HNSCC) in PubMed.

RESULTS

NSG has identified an average of 19 to 130 distinct mutations per HNSCC specimen. While many mutations likely had biological significance, it remains unclear which mutations were essential to, or "drive," carcinogenesis. In contrast, "passenger" mutations also exist that provide no selection advantage. The genes identified by NGS included p53, RAS, Human Papillomavirus oncogenes, as well as novel genes such as NOTCH1, DICER and SYNE1,2. Animal models of HNSCC have already validated some of these common gene mutations identified by NGS.

CONCLUSIONS

The advent of next generation sequencing will provide new leads to the genetic changes occurring in squamous cell cancers of the head and neck. Animal models will enable us to validate these new leads in order to better elucidate the biology of squamous cell cancers of the head and neck.

Pocket proteins suppress head and neck cancer

Head and neck squamous cell carcinomas (HNSCC) is a common cancer in humans long known to be caused by tobacco and alcohol use, but now an increasing percentage of HNSCC is recognized to be caused by the same human papillomaviruses (HPV) that cause cervical and other anogenital cancers. HPV-positive HNSCCs differ remarkably from HPV-negative HNSCCs in their clinical response and molecular properties. From studies in mice, we know that E7 is the dominant HPV oncoprotein in head and neck cancer. E7 is best known for its ability to inactivate pRb, the product of the retinoblastoma tumor susceptibility gene. However, loss of pRb function does not fully account for potency of E7 in causing head and neck cancer. In this study, we characterized the cancer susceptibility of mice deficient in the expression of pRb and either of two related "pocket" proteins, p107 and p130, that are also inactivated by E7. pRb/p107-deficient mice developed head and neck cancer as frequently as do HPV-16 E7 transgenic mice. The head and neck epithelia of the pRb/p107-deficient mice also displayed the same acute phenotypes and biomarker readouts as observed in the epithelia of E7 transgenic mice. Mice deficient for pRb and p130 in their head and neck epithelia showed intermediate acute and tumor phenotypes. We conclude that pRb and p107 act together to efficiently suppress head and neck cancer and are, therefore, highly relevant targets of HPV-16 E7 in its contribution to HPV-positive HNSCC.

The human papillomavirus type 16 E7 oncoprotein targets Myc-interacting zinc-finger protein-1

We demonstrate that HPV-16 E7 forms a complex with Miz-1. UV-induced expression of the CDK-inhibitor p21^Cip1 and subsequent cell cycle arrest depends upon endogenous Miz-1 in HPV-negative C33A cervical cancer cells containing mutated p53. Transient expression of E7 in C33A inhibits UV-induced expression of p21^Cip1 and overcomes Miz-1-induced G1-phase arrest. The C-terminal E7Δ79LEDLL83-mutant with reduced Miz-1-binding capacity was impaired in its capability to repress p21^Cip1 expression; whereas the pRB-binding-deficient E7C24G-mutant inhibited p21^Cip1 expression similar to wild-type E7. Using ChIP, we demonstrate that endogenous E7 is bound to the endogenous p21^Cip1 core-promoter in CaSki cells and RNAi-mediated knock down of Miz-1 abrogates E7-binding to the p21^Cip1 promoter. Co-expression of E7 with Miz-1 inhibited Miz-1-induced p21^Cip1 expression from the minimal-promoter via Miz-1 DNA-binding sites. Co-expression of E7Δ79LEDLL83 did not inhibit Miz-1-induced p21^Cip1 expression. E7C24G retained E7-wild-type capability to inhibit Miz-1-dependent transactivation. These findings suggest that HPV-16 E7 can repress Miz-1-induced p21^Cip1 gene expression.

Dominant role of HPV16 E7 in anal carcinogenesis

Ninety percent of anal cancer is associated with human papilloma viruses (HPVs). Using our previously established HPV transgenic mouse model for anal cancer, we tested the role of the individual oncogenes E6 and E7. K14E6 and K14E7 transgenic mice were treated with dimethylbenz[a]anthracene (DMBA) to the anal canal and compared to matched nontransgenic and doubly transgenic K14E6/E7 mice. K14E7 and K14E6/E7 transgenic mice developed anal tumors (papillomas, atypias and carcinomas combined) at significantly higher rates (88% and 100%, respectively) than either K14E6 or NTG mice (18% and 19%, respectively). Likewise, K14E7 and K14E6/E7 transgenic mice developed frank cancer (carcinomas) at significantly higher rates (85% and 85%, respectively) than either K14E6 or NTG mice (18% and 10%, respectively). These findings indicate that E7 is the more potent oncogene in anal cancer caused by HPVs.

Small molecule inhibitors of human papillomavirus protein - protein interactions

Human papillomaviruses (HPV) have now been identified as a necessary cause of benign and malignant lesions of the differentiating epithelium, particularly cervical cancer, the second most prevalent cancer in women worldwide. While two prophylactic HPV vaccines and screening programs are available, there is currently no antiviral drug for the treatment of HPV infections and associated diseases. The recent progress toward the identification and characterization of specific molecular targets for small molecule-based approaches provides prospect for the development of effective HPV antiviral compounds. Traditionally, antiviral therapies target viral enzymes. HPV encode for few proteins, however, and rely extensively on the infected cell for completion of their life cycle. This article will review the functions of the viral E1 helicase, which encodes the only enzymatic function of the virus, of the E2 regulatory protein, and of the viral E6 and E7 oncogenes in viral replication and pathogenesis. Particular emphasis will be placed on the recent progress made towards the development of novel small molecule inhibitors that specifically target and inhibit the functions of these viral proteins, as well as their interactions with other viral and/or cellular proteins.

The combined influence of oral contraceptives and human papillomavirus virus on cutaneous squamous cell carcinoma

The vast majority of cutaneous squamous cell carcinoma (CSCC) will occur in those with fair complexion, tendency to burn, and high ultraviolet radiation (UVR) exposure. Organ transplant recipients also are an important population at great risk for CSCC. An association has been reported between oral contraceptive (OC) use, human papillomavirus virus (HPV) and cervical cancer, and there could be a similar association for CSCC. The cutaneous HPV β-E6 protein, a close cousin of the transformative E6 protein underlying anogenital cancers, has been shown to inhibit apoptosis in response to UVR damage and stimulate morphologic transformation in rodent fibroblast cell lines. Furthermore, OC use has been shown to enhance HPV transcription and may contribute to CSCC risk through this pathway.

Radiosensitization of oropharyngeal squamous cell carcinoma cells by human papillomavirus 16 oncoprotein E6∗I

PURPOSE

Patients with oropharyngeal squamous cell carcinoma (OSCC) whose disease is associated with high-risk human papillomavirus (HPV) infection have a significantly better outcome than those with HPV-negative disease, but the reasons for the better outcome are not known. We postulated that they might relate to an ability of HPV proteins to confer a better response to radiotherapy, a commonly used treatment for OSCC.

METHODS AND MATERIALS

We stably expressed the specific splicing-derived isoforms, E6∗I and E6∗II, or the entire E6 open reading frame (E6total), which gives rise to both full length and E6∗I isoforms, in OSCC cell lines. Radiation resistance was measured in clonogenicity assays, p53 activity was measured using transfected reporter genes, and flow cytometry was used to analyze cell cycle and apoptosis.

RESULTS

E6∗I and E6total sensitized the OSCC cells to irradiation, E6∗I giving the greatest degree of radiosensitization (approximately eightfold lower surviving cell fraction at 10 Gy), whereas E6∗II had no effect. In contrast to radiosensitivity, E6∗I was a weaker inhibitor than E6total of tumor suppressor p53 transactivator activity in the same cells. Flow cytometric analyses showed that irradiated E6∗I expressing cells had a much higher G2M:G1 ratio than control cells, indicating that, after G2, cells were diverted from the cell cycle to programmed cell death.

CONCLUSION

This study supports a role for E6∗I in the enhanced responsiveness of HPV-positive oropharyngeal carcinomas to p53-independent radiation-induced death.

Deficiencies in the Fanconi anemia DNA damage response pathway increase sensitivity to HPV-associated head and neck cancer

Patients with the rare genetic disease, Fanconi anemia (FA), are highly susceptible to squamous cell carcinomas arising at multiple anatomic sites including the head and neck region. Human papillomaviruses (HPVs), particularly HPV16, are associated with ∼20% of head and neck squamous cell carcinomas (HNSCCs) in the general population. Some but not other investigators have reported that HNSCCs in FA patients are much more frequently positive for HPV. In addition, studies have demonstrated an interaction between the HPV16 E7 oncoprotein and the FA pathway, a DNA damage response pathway deficient in FA patients. On the basis of these studies, it was hypothesized that the FA pathway contributes to repair of DNA damage induced by HPV16 E7, providing one explanation for why FA patients are predisposed to HPV-associated HNSCCs. To determine the importance of the FA pathway in modulating the oncogenic abilities of E7, we crossed K14E7 transgenic (K14E7) and fancD2 knockout mice (FancD2(-/-)) to establish K14E7/FancD2(-/-) and K14E7/FancD2(+/+) mice and monitored their susceptibility to HNSCC when treated with a chemical carcinogen. K14E7/FancD2(-/-) mice had a significantly higher incidence of HNSCC compared with K14E7/FancD2(+/+) mice. This difference correlated with an increased proliferative index and the increase in expression of biomarkers that are used to assess levels of DNA damage. These animal studies support the hypotheses that FA patients have increased susceptibility to HPV-associated cancer and that the FA DNA damage response pathway normally attenuates the oncogenic potential of HPV16 E7.

Human papillomavirus 16 E6 increases the radiosensitivity of p53-mutated cervical cancer cells, associated with up-regulation of aurora A

PURPOSE

To examine the effect of the human papillomavirus (HPV) type 16-E6 (HPV 'early' gene) oncoprotein on in vitro radiosensitivity of HPV-negative/p53 mutant C33a cervical cancer cells.

METHODS AND MATERIALS

The human cervical cancer cell line C33a was stably transfected with either the HPV16 E6 cDNA cloned into the vector pcDNA3.0 (C33aE6) or the empty-vector control (C33aV). Radiosensitivity, DNA damage, and cell cycle measurements were made using standard clonogenic assays, immunofluorescent assessment of nuclear histone H2AX phosphorylated on serine-139 (gamma-H2AX) foci, and flow cytometry. Western immunoblotting and fluorescence confocal microscopy were used to analyse the changes in cellular proteins. Real-time polymerase chain reaction (PCR) was used to compare levels of aurora A mRNA.

RESULTS

Compared to C33aV cells, C33aE6 cells showed enhanced radiation cell killing. This was associated with a large amount of polyploidy which was followed by late cell death in C33aE6 cells. Aurora A was highly expressed in C33aE6 cells at pre- and post-irradiation times compared to C33aV cells. Silencing aurora A resulted in a reduced amount of residual gamma-H2AX foci in C33aE6 cells, and diminished the difference in radiosensitivity between the C33aE6 and C33aV cells.

CONCLUSION

Our in vitro results indicate that genetic instability could be augmented in the HPV-infected cancer cells by up-regulation of aurora A, especially against a background of dysfunctional p53. Further studies are needed to examine whether aurora A could be a viable therapeutic target in HPV-related tumours.

Human papillomavirus type 16 E6 and E7 oncoproteins act synergistically to cause head and neck cancer in mice

High-risk human papillomaviruses (HPVs) contribute to cervical and other anogenital cancers, and they are also linked etiologically to a subset of head and neck squamous cell carcinomas (HNSCC). We previously established a model for HPV-associated HNSCC in which we treated transgenic mice expressing the papillomaviral oncoproteins with the chemical carcinogen 4-nitroquinoline-1-oxide (4-NQO). We found that the HPV-16 E7 oncoprotein was highly potent in causing HNSCC, and its dominance masked any potential oncogenic contribution of E6, a second papillomaviral oncoprotein commonly expressed in human cancers. In the current study, we shortened the duration of treatment with 4-NQO to reduce the incidence of cancers and discovered a striking synergy between E6 and E7 in causing HNSCC. Comparing the oncogenic properties of wild-type versus mutant E6 genes in this model for HNSCC uncovered a role for some but not other cellular targets of E6 previously shown to contribute to cervical cancer.

E6-associated protein is required for human papillomavirus type 16 E6 to cause cervical cancer in mice

High-risk human papillomaviruses (HPV) cause certain anogenital and head and neck cancers. E6, one of three potent HPV oncogenes that contribute to the development of these malignancies, is a multifunctional protein with many biochemical activities. Among these activities are its ability to bind and inactivate the cellular tumor suppressor p53, induce expression of telomerase, and bind to various other proteins, including Bak, E6BP1, and E6TP1, and proteins that contain PDZ domains, such as hScrib and hDlg. Many of these activities are thought to contribute to the role of E6 in carcinogenesis. The interaction of E6 with many of these cellular proteins, including p53, leads to their destabilization. This property is mediated at least in part through the ability of E6 to recruit the ubiquitin ligase E6-associated protein (E6AP) into complexes with these cellular proteins, resulting in their ubiquitin-mediated degradation by the proteasome. In this study, we address the requirement for E6AP in mediating acute and oncogenic phenotypes of E6, including induction of epithelial hyperplasia, abrogation of DNA damage response, and induction of cervical cancer. Loss of E6AP had no discernible effect on the ability of E6 to induce hyperplasia or abrogate DNA damage responses, akin to what we had earlier observed in the mouse epidermis. Nevertheless, in cervical carcinogenesis studies, there was a complete loss of the oncogenic potential of E6 in mice nulligenic for E6AP. Thus, E6AP is absolutely required for E6 to cause cervical cancer.

The immortalizing and transforming ability of two common human papillomavirus 16 E6 variants with different prevalences in cervical cancer

Persistent infection with high-risk human papillomaviruses (HPVs), especially type 16 has been undeniably linked to cervical cancer. The Asian-American (AA) variant of HPV16 is more common in the Americas than the prototype in cervical cancer. The different prevalence is based on three amino acid changes within the E6 protein denoted Q14H/H78Y/L83V. To investigate the mechanism(s) behind this observation, both E6 proteins, in the presence of E7, were evaluated for their ability to extend the life span of and transform primary human foreskin keratinocytes (PHFKs). Long-term cell culture studies resulted in death at passage 9 of vector-transduced PHFKs (negative control), but survival of both E6 PHFKs to passage 65 (and beyond). Compared with E6/E7 PHFKs, AA/E7 PHFKs were significantly faster dividing, developed larger cells in monolayer cultures, showed double the epithelial thickness and expressed cytokeratin 10 when grown as organotypic raft cultures. Telomerase activation and p53 inactivation, two hallmarks of immortalization, were not significantly different between the two populations. Both were resistant to anoikis at later passages, but only AA/E7 PHFKs acquired the capacity for in vitro transformation. Proteomic analysis revealed markedly different protein patterns between E6/E7 and AA/E7, particularly with respect to key cellular metabolic enzymes. Our results provide new insights into the reasons underlying the greater prevalence of the AA variant in cervical cancer as evidenced by characteristics associated with higher oncogenic potential.

Human papillomavirus 16 E7 oncoprotein attenuates DNA damage checkpoint control by increasing the proteolytic turnover of claspin

The human papillomavirus (HPV) 16 E7 oncoprotein has been reported previously to stimulate DNA damage and to activate host cell DNA damage checkpoints. How HPV-16 E7 maintains proliferation despite activated DNA damage checkpoints is incompletely understood. Here, we provide evidence that cells expressing the HPV-16 E7 oncoprotein can enter mitosis in the presence of DNA damage. We show that this activity of HPV-16 E7 involves attenuation of DNA damage checkpoint control by accelerating the proteolytic turnover of claspin. Claspin mediates the activation of CHK1 by ATR in response to replication stress, and its degradation plays a critical role in DNA damage checkpoint recovery. Expression of a nondegradable mutant of claspin was shown to inhibit mitotic entry in HPV-16 E7-expressing cells. Multiple components of the SCF(beta-TrCP)-based claspin degradation machinery were found deregulated in the presence of HPV-16 E7, including cullin 1, beta-TrCP, Aurora A, and Polo-like kinase-1 (PLK1). In contrast, no difference in the expression level of the claspin deubiquitinating enzyme USP7 was detected. Levels of Aurora A and PLK1 as well as phosphorylated PLK1 at threonine 210, a prerequisite for DNA damage checkpoint recovery, remained detectable following replication stress in HPV-16 E7-expressing cells but not in control cells. In summary, our results suggest that the HPV-16 E7 oncoprotein alleviates DNA damage checkpoint responses and promotes mitotic entry by accelerating claspin degradation through a mechanism that involves deregulation of components of the SCF(beta-TrCP)-based claspin degradation machinery.

Persistence of high-grade cervical dysplasia and cervical cancer requires the continuous expression of the human papillomavirus type 16 E7 oncogene

Several mucosotropic human papillomaviruses (HPV), including HPV type 16 (HPV-16), are etiologic agents of a subset of anogenital cancers and head and neck squamous cell carcinomas. In mice, HPV-16 E7 is the most potent of the papillomaviral oncogenes in the development of cervical disease. Furthermore, interfering specifically with the expression of E7 in HPV-positive cell lines derived from human cervical cancers inhibits their ability to proliferate, indicating that the expression of E7 is important in maintaining the transformed phenotype in vitro. To assess the temporal role of E7 in maintaining HPV-associated tumors and precancerous lesions in vivo, we generated Bi-L E7 transgenic mice that harbor a tetracycline-inducible transgene that expresses both HPV-16 E7 and firefly luciferase. When we crossed Bi-L E7 mice to a K5-tTA transgene-inducing line of mice, which expresses a tetracycline-responsive transactivator selectively in the stratified squamous epithelia, the resulting Bi-L E7/K5-tTA bitransgenic mice expressed E7 and luciferase in the skin and cervical epithelium, and doxycycline repressed this expression. Bitransgenic mice displayed several overt and acute epithelial phenotypes previously shown to be associated with the expression of E7, and these phenotypes were reversed on treatment with doxycycline. Repressing the expression of E7 caused the regression of high-grade cervical dysplasia and established cervical tumors, indicating that they depend on the continuous expression of E7 for their persistence. These results suggest that E7 is a relevant target not only for anticancer therapy but also for the treatment of HPV-positive dysplastic cervical lesions.

The antitumorigenic response of neural precursors depends on subventricular proliferation and age

Glioblastomas, the most aggressive primary brain tumors, occur almost exclusively in adult patients. Neural precursor cells (NPCs) are antitumorigenic in mice, as they can migrate to glioblastomas and induce tumor cell death. Here, we show that the antitumor effect of NPCs is age-dependently controlled by cell proliferation in the subventricular zone (SVZ) and that NPCs accumulating at a glioblastoma are diverted from their normal migratory path to the olfactory bulb. Experimentally induced cortical glioblastomas resulted in decreased subventricular proliferation in adult (postnatal day 90) but not in young (postnatal day 30) mice. Adult mice supplied fewer NPCs to glioblastomas and had larger tumors than young mice. Apart from the difference in proliferation, there was neither a change in cell number and death rate in the SVZ nor a change in angiogenesis and immune cell density in the tumors. The ability to kill glioblastomas was similar in NPCs isolated from young and adult mice. The proliferative response of NPCs to glioblastomas depended on the expression of D-type cyclins. In young mice, NPCs express the cyclins D1 and D2, but the expression of cyclin D1 is lost during aging, and in adult NPCs only cyclin D2 remains. In young and adult cyclin D2-deficient mice we observed a reduced supply of NPCs to glioblastomas and the generation of larger tumors compared with wild-type mice. We conclude that cyclin D1 and D2 are nonredundant for the antitumor response of subventricular NPCs. Loss of a single D-type cyclin results in a smaller pool of proliferating NPCs, lower number of NPCs migrating to the tumor, and reduced antitumor activity. Disclosure of potential conflicts of interest is found at the end of this article.

The role of infectious agents in the etiology of ocular adnexal neoplasia

Given the fact that infectious agents contribute to around 18% of human cancers worldwide, it would seem prudent to explore their role in neoplasms of the ocular adnexa: primary malignancies of the conjunctiva, lacrimal glands, eyelids, and orbit. By elucidating the mechanisms by which infectious agents contribute to oncogenesis, the management, treatment, and prevention of these neoplasms may one day parallel what is already in place for cancers such as cervical cancer, hepatocellular carcinoma, gastric mucosa-associated lymphoid tissue lymphoma and gastric adenocarcinoma. Antibiotic treatment and vaccines against infectious agents may herald a future with a curtailed role for traditional therapies of surgery, radiation, and chemotherapy. Unlike other malignancies for which large epidemiological studies are available, analyzing ocular adnexal neoplasms is challenging as they are relatively rare. Additionally, putative infectious agents seemingly display an immense geographic variation that has led to much debate regarding the relative importance of one organism versus another. This review discusses the pathogenetic role of several microorganisms in different ocular adnexal malignancies, including human papilloma virus in conjunctival papilloma and squamous cell carcinoma, human immunodeficiency virus in conjunctival squamous carcinoma, Kaposi sarcoma-associated herpes virus or human herpes simplex virus-8 (KSHV/HHV-8) in conjunctival Kaposi sarcoma, Helicobacter pylori (H. pylori,), Chlamydia, and hepatitis C virus in ocular adnexal mucosa-associated lymphoid tissue lymphomas. Unlike cervical cancer where a single infectious agent, human papilloma virus, is found in greater than 99% of lesions, multiple organisms may play a role in the etiology of certain ocular adnexal neoplasms by acting through similar mechanisms of oncogenesis, including chronic antigenic stimulation and the action of infectious oncogenes. However, similar to other human malignancies, ultimately the role of infectious agents in ocular adnexal neoplasms is most likely as a cofactor to genetic and environmental risk factors.

Role of Rb-dependent and Rb-independent functions of papillomavirus E7 oncogene in head and neck cancer

Infection with high-risk human papillomaviruses (HPV) and in particular the expression of the viral proteins E6 and E7 have been associated with the etiology of a subset of head and neck squamous cell cancer (HNSCC). However, the individual consequences of E6 and E7 expression in an in vivo model have not been examined in these tissues. We have used transgenes that direct expression of the HPV16 E6 and E7 proteins to the head and neck tissues of mice to dissect the contribution of these proteins to head and neck carcinogenesis. We report here that E7 is the major transforming oncogene in HPV-associated HNSCC, whereas E6 is more likely to play a secondary role in contributing to later stages of carcinogenesis. Furthermore, a conditional deletion of Rb, a prominent target for E7, in the same tissues did not recapitulate all E7-mediated phenotypes. Although our results do not preclude an important role for the E7-pRb interaction, they highlight the importance of pRb-independent functions of E7 in head and neck carcinogenesis.

Critical roles for non-pRb targets of human papillomavirus type 16 E7 in cervical carcinogenesis

High-risk human papillomaviruses (HPV) encode two oncogenes, E6 and E7, expressed in nearly all cervical cancers. In vivo, HPV-16 E7 has been shown to induce multiple phenotypes in the context of transgenic mice, including cervical cancer. E7 is a multifunctional protein known best for its ability to inactivate the tumor suppressor pRb. To determine the importance of pRb inactivation by E7 in cervical cancer, we pursued studies with genetically engineered mice. E7 expression in estrogen-treated murine cervix induced dysplasia and invasive cancers as reported previously, but targeted Rb inactivation in cervical epithelium was not sufficient to induce any cervical dysplasia or neoplasia. Furthermore, E7 induced cervical cancer formation even when the E7-pRb interaction was disrupted by the use of a knock-in mouse carrying an E7-resistant mutant Rb allele. pRb inactivation was necessary but not sufficient for E7 to overcome differentiation-induced or DNA damage-induced cell cycle arrest, and expression patterns of the E2F-responsive genes Mcm7 and cyclin E indicate that other E2F regulators besides pRb are important targets of E7. Together, these data indicate that non-pRb targets of E7 play critical roles in cervical carcinogenesis.

The human papillomavirus type 16 E7 oncoprotein activates the Fanconi anemia (FA) pathway and causes accelerated chromosomal instability in FA cells

Fanconi anemia (FA) patients have an increased risk for squamous cell carcinomas (SCCs) at sites of predilection for infection with high-risk human papillomavirus (HPV) types, including the oral cavity and the anogenital tract. We show here that activation of the FA pathway is a frequent event in cervical SCCs. We found that FA pathway activation is triggered mainly by the HPV type 16 (HPV-16) E7 oncoprotein and is associated with an enhanced formation of large FANCD2 foci and recruitment of FANCD2 as well as FANCD1/BRCA2 to chromatin. Episomal expression of HPV-16 oncoproteins was sufficient to activate the FA pathway. Importantly, the expression of HPV-16 E7 in FA-deficient cells led to accelerated chromosomal instability. Taken together, our findings establish the FA pathway as an early host cell response to high-risk HPV infection and may help to explain the greatly enhanced susceptibility of FA patients to squamous cell carcinogenesis at anatomic sites that are frequently infected by high-risk HPVs.

Nitrative and oxidative DNA damage in cervical intraepithelial neoplasia associated with human papilloma virus infection

Recently, it was proposed that inflammation plays an integral role in the development of human papilloma virus (HPV)-induced cervical cancer. The present study sought to examine if 8-nitroguanine, a mutagenic nitrative DNA lesion formed during inflammation, contributes to cervical carcinogenesis. We obtained biopsy specimens from 30 patients with cervical intraepithelial neoplasia (CIN)1 (n = 9), CIN2 (n = 10), CIN3 (n = 6) and condyloma acuminatum (n = 5). We used immunohistochemistry to detect the formation of 8-nitroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), an oxidative DNA lesion, and compared it with the expression of the cyclin-dependent kinase inhibitor p16, which is considered to be a biomarker for cervical neoplasia. Double immunofluorescence labeling revealed that 8-nitroguanine and 8-oxodG were colocalized in cervical epithelial cells. Samples from CIN2-3 patients, most of whom were infected with high-risk HPV subtypes, exhibited significantly more intense staining for 8-nitroguanine than those with condyloma acuminatum. 8-Nitroguanine and 8-oxodG immunoreactivities correlated significantly with the CIN grade. We observed the expression of inducible nitric oxide synthase in epithelial and inflammatory cells from CIN lesions. Proliferating cell nuclear antigen was expressed specifically in dysplastic epithelial cells, but not in those of condyloma acuminatum. There were no statistically significant differences in p16 expression between CIN and condyloma acuminatum samples. These results suggest that high-risk HPV types promote inducible nitric oxide synthase-dependent DNA damage, which leads to dysplastic changes and carcinogenesis; in contrast, p16 appears to be merely a marker of HPV infection. Thus, 8-nitroguanine is a more suitable and promising biomarker for evaluating the risk of inflammation-mediated cervical carcinogenesis than p16.

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

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

High-Risk Human Papillomavirus Affects Prognosis in Patients With Surgically Treated Oropharyngeal Squamous Cell Carcinoma

Purpose

Human papillomavirus (HPV) DNA tumors actively integrating the E6 and E7 oncogenes have a distinct biologic behavior resulting in a more favorable prognosis. To which extent the viral integration by itself, and/or the associated wild-type (wt) TP53 status, and/or a functional p16 contribute to prognosis is unclear.

Patients and Methods

To clarify how the presence of high-risk (HR) -HPV, TP53, and p16INK4a status interact with clinical outcome, we considered a retrospective series of 90 consecutive oropharyngeal cancer patients treated primarily with surgery.

Results

Seventeen (19%) patients showed integrated HPV 16 DNA (HPV positive), wt TP53 in all but two patients, normal p16INK4a in 15 assessable patients, and p16 expression in all 17 patients. Thirty-five patients (39%), two of whom were HPV positive, harbored TP53 mutations. p16INK4a deletion and p16 null immunophenotype occurred in 28 and 58 patients, respectively, and was similarly distributed in both patients with mutated TP53 (48% and 82%, respectively) and in patients with wt TP53 (46% and 77%, respectively). Statistical analysis showed that HPV-positive status significantly affects all investigated end points: overall survival (P = .0018), incidence of tumor relapse (P = .0371), and second tumor (P = .0152), whereas TP53 and p16INK4a status and p16 expression were not prognostic by themselves.

Conclusion

Our molecular and clinical results are in agreement with previous findings but provide additional information into the biologic mechanisms involved in HR-HPV oropharyngeal cancer in comparison to HPV-negative tumors. According to the reduced risk of relapse and second tumors associated with HR-HPV positivity of oropharyngeal cancer, the therapeutic strategy and follow-up procedures should be reviewed.

HPV16 E6 confers p53-dependent and p53-independent phenotypes in the epidermis of mice deficient for E6AP

High-risk human papillomaviruses are the causative agents of cervical and other anogenital cancers. In these cancers, two viral oncogenes, E6 and E7, are expressed. E6 is best known for its ability to inactivate the tumor suppressor p53, which is thought to arise through ubiquitin-mediated degradation of p53 and involve a ternary complex between E6, p53 and the E3 ligase, E6AP. In mice transgenic for wild-type HPV16 E6, its expression leads to epithelial hyperplasia and an abrogation of normal cellular responses to DNA damage. Whereas only the latter phenotype is dependent upon E6's inactivation of p53, both are reduced in transgenic mice expressing an E6 mutant severely reduced in its binding to E6AP and other cellular proteins that bind E6 through a shared alpha-helix motif. Here, we investigated whether E6AP is required for the induction of the above phenotypes through the use of both E6AP-mutant and E6AP-null mice. E6, in the absence of E6AP retains an ability to induce epithelial hyperplasia, abrogate DNA damage responses and inhibit the induction of p53 protein following exposure to ionizing radiation. We conclude that E6 is able to induce both p53-dependent and p53-independent phenotypes through E6AP-independent pathways in the mouse.

Identification of biomarkers that distinguish human papillomavirus (HPV)-positive versus HPV-negative head and neck cancers in a mouse model

Head and neck squamous cell carcinoma (HNSCC) is a leading cause of cancer mortality worldwide. Recent reports have associated a subset of HNSCC with high-risk human papillomaviruses (HPVs), particularly HPV16, the same subset of HPVs responsible for the majority of cervical and anogenital cancers. In this study we describe a mouse model for HPV-associated HNSCC that employs mice transgenic for the HPV16 oncogenes E6 and E7. In these mice, E6 and E7 induce aberrant epithelial proliferation and, in the presence of a chemical carcinogen, they increase dramatically the animal's susceptibility to HNSCC. The cancers arising in the HPV16-transgenic mice mirror the molecular and histopathological characteristics of human HPV-positive HNSCC that distinguish the latter from human HPV-negative HNSCC, including overexpression of p16 protein and formation of more basaloid cancers. This validated model of HPV-associated HNSCC provides the means to define the contributions of individual HPV oncogenes to HNSCC and to understand the molecular basis for the differing clinical properties of HPV-positive and HPV-negative human HNSCC. From this study, we identify minichromosome maintenance protein 7 (MCM7) and p16 as potentially useful biomarkers for HPV-positive head and neck cancer.

Human papillomaviruses and cervical cancer

Carcinoma of the uterine cervix, a leading cause of cancer death in women worldwide, is initiated by infection with high-risk types of human papillomaviruses (HPVs). This review summarizes laboratory studies over the past 20 years that have elucidated the major features of the HPV life cycle, identified the functions of the viral proteins, and clarified the consequences of HPV infection for their host cells. This information has allowed the development of various strategies to prevent or treat infections, including prophylactic vaccination with virus-like particles, therapeutic vaccination against viral proteins expressed in cancer cells, and antiviral approaches to inhibit virus replication, spread, or pathogenesis. These strategies have the potential to cause a dramatic reduction in the incidence of cervical carcinoma and serve as the prototype for comprehensive efforts to combat virus-induced tumors.

Examination of the pRb-dependent and pRb-independent functions of E7 in vivo

High-risk human papillomaviruses encode two oncogenes, E6 and E7, expressed in nearly all cervical cancers. Although E7 protein is best known for its ability to inactivate the retinoblastoma tumor suppressor protein, pRb, many other activities for E7 have been proposed in in vitro studies. Herein, we describe studies that allowed us to define unambiguously the pRb-dependent and -independent activities of E7 for the first time in vivo. In these studies, we crossed mice transgenic for human papillomavirus 16 E7 to knock-in mice genetically engineered to express a mutant form of pRb (pRb(DeltaLXCXE)) that is selectively defective for binding E7. pRb inactivation was necessary for E7 to induce DNA synthesis and to overcome differentiation-dependent cell cycle withdrawal and DNA damage-induced cell cycle arrest. While most of E7's effects on epidermal differentiation were found to require pRb inactivation, a modest delay in terminal differentiation with resulting hyperplasia was observed in E7 mice on the Rb(DeltaLXCXE) mutant background. E7-induced p21 upregulation was also pRb dependent, and genetic Rb inactivation was sufficient to reproduce this effect. While E7-mediated p21 induction was partially p53 dependent, neither p53 nor p21 induction by E7 required p19(ARF). These data show that E7 upregulates the expression of p53 and p21 via pRb-dependent mechanisms distinct from the proposed p19-Mdm2 pathway. These results extend our appreciation of the importance of pRb as a relevant target for high-risk E7 oncoproteins.

Sensitization of cervical cancer cell lines to low-dose radiation by retinoic acid does not require functional p53

OBJECTIVE

Current therapy for cervical cancer includes radiation therapy. Retinoic acid (RA) can increase the sensitivity of cervical cancer cell lines to radiation. The mechanism of this sensitization may not involve the p53 protein because the human papillomavirus (HPV) E6 protein, which is present in the majority of cervical cancers, promotes p53 degradation. The objective of this study was to determine if p53 is involved in the mechanism of RA radiosensitization.

METHOD

The effects of radiation on cervical (SiHa, CC-1, and C33a) and vulvar (SW962) cancer cell lines under various experimental conditions were evaluated using clonogenic, Coulter Counter, electrophoretic mobility shift (EMSA) and a multi-probe RNase protection assay of p53-inducible genes.

RESULTS

RA (5 microM 9-cis-RA) radiosensitized the SiHa and CC-1 cell lines that contain HPV-degraded p53, but did not radiosensitize the SW962 cell line, which is HPV negative and contains wild-type p53, nor the C33a cell line, which contains mutant p53 (R273C). Expression of mutant p53 (R273H) in SiHa cells increased the growth rate, but did not prevent RA-induced differentiation or radiosensitization at clinically relevant doses. Inhibition of p53 transactivation with pifithirin alpha did not prevent RA radiosensitization of SiHa at 5 Gy. RA repressed c-fos mRNA expression in control and irradiated SiHa cultures, but did not repress bcl-x(L), p53, GADD45, p21, bax, bcl-2, or mcl-1 mRNA expression.

CONCLUSIONS

The mechanism of RA radiosensitization does not require functional p53 and may involve c-fos in cervical cancer cell lines.

Human papillomavirus status in advanced cervical cancer: predictive and prognostic significance for curative radiation treatment

Human papillomavirus (HPV) infection plays a major role in oncogenesis of squamous cell carcinoma of the cervix. This study was performed to investigate if HPV status and E2 gene integrity are prognostic parameters for clinical outcome and predictive for radiation response. Forty women with locally advanced cervical cancer treated with curative radiotherapy were analyzed for HPV infection and E2 gene integrity by multiplex polymerase chain reaction. Statistical analyses were performed for overall survival, disease-free survival (DFS), local progression-free survival, and treatment response (clinical complete remission). Twenty-eight (70%) of 40 carcinomas were HPV positive. The only significant factor for a better overall survival, DFS, and local progression-free survival was HPV positivity (P < 0.02, P= 0.02, and P < 0.05, log-rank, respectively). HPV-positive tumors had a significantly better clinical complete remission (67% vs 33%, P= 0.04, Fisher's exact test). An intact E2 gene region showed a trend for a better DFS (P= 0.1, log-rank). This study reveals HPV as an independent prognostic parameter for outcome and radiation response. Integration of the virus genome into host cell DNA might be a molecular target to determine the treatment response of HPV-positive cancers.

Human papillomavirus-associated head and neck cancer is a distinct epidemiologic, clinical, and molecular entity

There is currently sufficient evidence to conclude that human papillomavirus (HPV) plays a role in the pathogenesis of a distinct subset of head and neck squamous cell cancers (HNSCC), particularly tonsillar cancers. There is a strong and consistent association between high-risk HPV types, specifically HPV16, a known human carcinogen, and these distinctive oropharyngeal cancers with molecular characteristics indicative of viral oncogene function. Risk for HPV-HNSCC is increased by certain sexual behaviors after consideration of alcohol and tobacco exposure, consistent with an extensive literature that has established HPV infection as a sexually transmitted disease. Furthermore, exposure to HPV16 has been associated with increased risk for subsequent development of oropharyngeal cancer. Prophylactic and therapeutic vaccines targeted against the viral capsid components and oncoproteins will provide the ultimate evidence for a role for HPV in HNSCC, if demonstrated to be effective in the prevention or therapy of this disease. It is time for clinician scientists to translate knowledge of this newly recognized disease entity into potential applications for the prevention, detection, and treatment of HPV-HNSCC.

Human papillomavirus type 16 E7 protein increases acetylation of histone H3 in human foreskin keratinocytes

Histone acetylation plays an important role in chromatin remodeling and transcription control. Acetylation of histones is regulated by histone acetyltransferases and histone deacetylases (HDACs). Human papillomavirus type 16 (HPV16) E7 can inactivate retinoblastoma protein (pRB), which recruits histone deacetylases, and also physically interacts with histone acetyltransferases and histone deacetylases, suggesting E7 may affect histone acetylation. To test this, we have analyzed the state of acetylation of histone H3 in human foreskin keratinocytes. HPV16 E7 increased acetylation of histone H3 on lysine 9, which is related to transcription activation. The ability to bind both pRB and histone deacetylase was required for HPV16 E7 to increase histone acetylation. Chromatin immunoprecipitations showed HPV16 E7 increases histone acetylation on the E2F1 and cdc25A promoters. Consistent with this, RT-PCR analysis showed an increase in the expression of E2F-responsive genes involved in cell cycle control. HPV16 E7 affected neither the steady-state levels of histone acetyltransferases or deacetylases nor histone deacetylase activity. However, HPV16 E7 did increase the level of methylation of histone H3 on lysine 4, which normally requires displacement of histone deacetylase. In contrast, sodium butyrate, a known inhibitor of histone deacetylases, caused an increase in acetylated but not methylated histone H3. These data suggest HPV16 E7, by increasing histone acetylation, may create a transcriptionally active chromatin structure to promote expression of genes vital for cell cycle progression.