Modulation of apoptosis by human papillomavirus (HPV) oncoproteins

Down-regulation of human papillomavirus E6 oncogene and antiproliferative effect of Schisandra chinensis and Pueraria lobata natural extracts on Hela cell line

ETHNOPHARMACOLOGICAL RELEVANCE

Cervical cancer is one of the most common malignancies in women that continues to be a public health problem worldwide. Human papillomavirus (HPV) infection is closely related as the causative agent of almost all cases of cervical cancer. Currently, there is no effective treatment for the persistence of HPV. Although vaccines have shown promising results in recent years, they are still a costly strategy for developing countries and have no therapeutic effect on existing infections, which is why the need arises to search for new strategies that can be used in treatment, suppressing oncogenic HPV and disease progression. Extracts of Schisandra Chinensis and Pueraria lobata have been used in traditional medicine, and it has been shown in recent years that some of their bioactive compounds have pharmacological, antioxidant, antitumor, apoptotic, and proliferation effects in HPV-positive cells. However, its mechanism of action has yet to be fully explored.

AIM OF THE STUDY

The following study aimed to determine the chemical composition, antioxidant activity, and potential antiproliferative and viral oncogene effects of natural extracts of S. chinensis and P. lobata on HPV-18 positive cervical cancer cells.

MATERIALS AND METHODS

The HPV-18-positive HeLa cells were treated for 24 and 48 h with the ethanolic extracts of S chinensis and P. lobata. Subsequently, cell viability was evaluated using the resazurin method, the effect on the cell cycle of the extracts (1.0, 10, and 100 μg/mL) was measured by flow cytometry, the gene of expression of the E6/E7, P53, BCL-2, and E2F-1 were determined by RT-PCR and the protein expression of p53, Ki-67, x|and Bcl-2 by immunohistochemistry. Additionally, the chemical characterization of the two extracts was carried out using LC-MS, and the total phenolics content (TPC), Total flavonoid content (TFC), and DPPH radical scavenging capacity were determined. Data were analyzed using the Mann-Whitney and Kruskal Wallis U test with GraphPad Prism 6 software.

RESULTS

The natural extracts of Schisandra chinensis and Pueraria lobata induced down-regulation of E6 HPV oncogene (p<0.05) and a strong up-regulation of P53 (p<0.05), E2F-1 (p<0.05), and Bcl-2 (p<0.05) gene expression. Simultaneously, the natural extracts tend to increase the p53 protein levels and arrest the cell cycle of HeLa in the G1/S phase (p<0.05). Investigated extracts were characterized by the occurrence of bioactive lignans and isoflavones in S. chinensis and P. lobata, respectively.

CONCLUSION

The extracts of S. chinensis and P. lobata within their chemical characterization mainly present lignan and isoflavone-type compounds, which are probably responsible for inhibiting the expression of the HPV E6 oncogene and inducing an increase in the expression of p53, Bcl -2 and E2F-1 producing cell cycle detection in S phase in HeLa cells. Therefore, these extracts are good candidates to continue studying their antiviral and antiproliferative potential in cells transformed by HPV.

The effect of high-risk HPV E6/E7 mRNA on the efficacy of topical photodynamic therapy with 5-aminolevulinic acid for cervical high-grade squamous intraepithelial lesions

BACKGROUND

E6 and E7 high-risk human papillomavirus (HR-HPV) oncoproteins are closely associated with the initiation and progression of cervical cancer (CC) and pre-cancerous lesions. Cervical high-grade squamous intraepithelial lesions (HSIL), as pre-cancerous lesions, have a 5% chance of progressing to invasive cancer. Topical 5-aminolevulinic acid photodynamic therapy (ALA-PDT) is a novel non-invasive targeted therapy for intraepithelial lesions. Herein, we analyzed the effect of HR-HPV E6/E7 mRNA on ALA-PDT for cervical HSIL.

METHODS

A retrospective analysis of 148 HR-HPV-positive patients diagnosed with cervical HSIL and receiving ALA-PDT was carried out. ALA-PDT was performed with 20% ALA thermosensitive gel, and irradiation at wavelength of 635 nm and density of 80-100 J/cm² for 20-30 min. The therapeutic instruments of LED and semiconductor laser were applied for cervical lesions and lesions in endocervical canal, respectively. All patients were tested for HPV E6/E7 mRNA before and after PDT, and then followed up at 3, 6, and 12 months after treatment, and every six months thereafter.

RESULTS

At the 6-month follow up, the complete remission (CR) rate of patients' lesions was 86.5% (128/148), whereas the total HPV clearance rate was 72.3% (107/148). It was evident that positive E6/E7 mRNA before treatment had a significant effect on HPV clearance rate (66.3% VS 81.4%, P=0.045) and CR rate (80.9% VS 94.9%, P=0.015). The E6/E7 mRNA associated with HPV16/18 and HPV16/18 combined with other HR-HPV (HPV16/18 and other HR-HPV) affected HPV clearance (P=0.035) and lesions CR (P=0.039), respectively. Moreover, persistently positive E6/E7 mRNA after treatment was closely associated with poor efficacy (HPV clearance rate: P=0.000, CR rate: P=0.000). Throughout the follow up period, two cases recurred but none of the patients progressed.

CONCLUSIONS

This study has shown that ALA-PDT is an effective, safe, and alternative treatment for cervical HSIL, especially for the patients of childbearing age. However, its efficacy is relatively poor in patients with persistently positive E6/E7 mRNA before and after treatment, who are insensitive to ALA-PDT.

The ‘Why and How’ of Cervical Cancers and Genital HPV Infection

Knowing about the virology of human papillomavirus (HPV) including its structure, functions and mechanism of infection, helps in understanding the disease process and morphology of precancerous lesions for cervical cancer. Two types of HPV, low- and high-risk type, adopt different mechanisms of infection which cannot be differentiated on morphological basis. In addition to HPV infection, many other factors such as genetic predisposition, hormonal factors, host immune response, and multiple sexual partners can modify the course and progression of the disease. The viral genome comprises early and late proteins. These early and late genes are expressed in particular course of time after initial infection. Various products of early genes (E1–E7) coordinate for completion of viral life cycle in maturing squamous epithelium by utilizing replication factors and DNA polymerase enzyme of the host cell nucleus. The late genes are mainly concerned with packaging of the viral particles and their release through mature squamous cells. The episomal form of infection seen in the low-risk group of viruses results in productive infection whereas the integrated form seen in high-risk group of viruses is the basis of disruption of host cell growth cycle by inactivating two important tumor suppressor genes p53 and Rb gene by products of E6 and E7 genes. Cervical precancerous lesions and cancer are the resultant effect of the accumulation of mutations. This article discusses the virology of HPV, pathogenesis of HPV infection, and various other factors modifying the disease course.

PCNA in Cervical Intraepithelial Neoplasia and Cervical Cancer: An Interaction Network Analysis of Differentially Expressed Genes

The investigation of differentially expressed genes (DEGs) and their interactome could provide valuable insights for the development of markers to optimize cervical intraepithelial neoplasia (CIN) screening and treatment. This study investigated patients with cervical disease to identify gene markers whose dysregulated expression and protein interaction interface were linked with CIN and cervical cancer (CC). Literature search of microarray datasets containing cervical epithelial samples was conducted in Gene Expression Omnibus and Pubmed/Medline from inception until March 2021. Retrieved DEGs were used to construct two protein-protein interaction (PPI) networks. Module DEGs that overlapped between CIN and CC samples, were ranked based on 11 topological algorithms. The highest-ranked hub gene was retrieved and its correlation with prognosis, tissue expression and tumor purity in patients with CC, was evaluated. Screening of the literature yielded 9 microarray datasets (GSE7803, GSE27678, GSE63514, GSE6791, GSE9750, GSE29570, GSE39001, GSE63678, GSE67522). Two PPI networks from CIN and CC samples were constructed and consisted of 1704 and 3748 DEGs along 21393 and 79828 interactions, respectively. Two gene clusters were retrieved in the CIN network and three in the CC network. Multi-algorithmic topological analysis revealed PCNA as the highest ranked hub gene between the two networks, both in terms of expression and interactions. Further analysis revealed that while PCNA was overexpressed in CC tissues, it was correlated with favorable prognosis (log-rank P=0.022, HR=0.58) and tumor purity (P=9.86 × 10^-4, partial rho=0.197) in CC patients. This study identified that cervical PCNA exhibited multi-algorithmic topological significance among DEGs from CIN and CC samples. Overall, PCNA may serve as a potential gene marker of CIN progression. Experimental validation is necessary to examine its value in patients with cervical disease.

Nuclear factor erythroid 2-related factor 2 in human papillomavirus-related cancers

High-risk human papillomavirus (HR-HPV) infection is a necessary cause for the development of cervical cancer. Moreover, HR-HPV is also associated with cancers in the anus, vagina, vulva, penis and oropharynx. HR-HPVs target and modify the function of different cell biomolecules, such as glucose, amino acids, lipids and transcription factors (TF), such as p53, nuclear factor erythroid 2-related factor 2 (Nrf2), among others. The latter is a master TF that maintains redox homeostasis. Nrf2 also induces the transcription of genes associated with cell detoxification. Since both processes are critical for cell physiology, Nrf2 deregulation is associated with cancer development. Nrf2 is a crucial molecule in HPV-related cancer development but underexplored. Moreover, Nrf2 activation is also associated with resistance to chemotherapy and radiotherapy in these cancers. This review focusses on the importance of Nrf2 during HPV-related cancer development, resistance to therapy and potential therapies associated with Nrf2 as a molecular target.

Human Papillomavirus in Breast Carcinogenesis: A Passenger, a Cofactor, or a Causal Agent?

Simple Summary

Breast cancer (BC) is the most frequent tumor in women worldwide. A minority of BC patients have a family history of the disease, suggesting the importance of environmental and lifestyle factors. Human papillomavirus (HPV) infection has been detected in a subset of tumors, suggesting a potential role in BC. In this review, we summarized relevant information in respect to this topic and we propose a model of HPV-mediated breast carcinogenesis. Evidence suggests that breast tissue is accessible to HPV, which may be a causal agent of BC in a subset of cases.

Abstract

Breast cancer (BC) is the most commonly diagnosed malignancy in women worldwide as well as the leading cause of cancer-related death in this gender. Studies have identified that human papillomavirus (HPV) is a potential risk factor for BC development. While vaccines that protect against oncogenic HPVs infection have been commercially available, global disparities persist due to their high cost. Interestingly, numerous authors have detected an increased high risk (HR)-HPV infection in BC specimens when compared with non-tumor tissues. Therefore, it was suggested that HR-HPV infection could play a role in breast carcinogenesis in a subset of cases. Additional epidemiological and experimental evidence is still needed regarding the role of HR-HPV infection in the development and progression of BC.

Viral Manipulation of the Host Epigenome as a Driver of Virus-Induced Oncogenesis

Tumorigenesis due to viral infection accounts for a high fraction of the total global cancer burden (15–20%) of all human cancers. A comprehensive understanding of the mechanisms by which viral infection leads to tumor development is extremely important. One of the main mechanisms by which viruses induce host cell proliferation programs is through controlling the host’s epigenetic machinery. In this review, we dissect the epigenetic pathways through which oncogenic viruses can integrate their genome into host cell chromosomes and lead to tumor progression. In addition, we highlight the potential use of drugs based on histone modifiers in reducing the global impact of cancer development due to viral infection.

Prevalence of High Risk HPV in HIV-Infected Women From Belém, Pará, Amazon Region of Brazil: A Cross-Sectional Study

Human papillomavirus (HPV) is the most common sexually transmitted infection in the world. Several studies have shown a higher prevalence of HPV infection in HIV-infected women. The aim of this study was to determine the prevalence and the genotype diversity of HPV infection in HIV-infected women. From April 2010 to December 2012 cervical specimens were collected from 169 HIV-infected women who screening for cervical cancer at Reference Unit in Belém. The detection of HPV infection was performed by nested PCR and HPV type was performed using a commercial system. The prevalence of HPV infection was 63.3%. Of the 47 genotyped samples, 40.4% was found positive for high risk-HPV 16 and 12.8% for high risk-HPV 52. HPV infection was predominant in the group of women with no incidence of cytological abnormalities and more prevalent in women of reproductive age, unmarried, low education level, and who reported use condoms during sexual intercourse. It was observed an association between HPV infection and independent variables, such as condom use, multiple sexual partners, and history of sexually transmitted diseases. High-risk types of HPV infection were prevalent in our study. Infection with multiple high-risk HPV genotypes may potentiate the development of cervical cancer in HIV-infected women.

Cell death in head and neck cancer pathogenesis and treatment

Many cancer therapies aim to trigger apoptosis in cancer cells. Nevertheless, the presence of oncogenic alterations in these cells and distorted composition of tumour microenvironment largely limit the clinical efficacy of this type of therapy. Luckily, scientific consensus describes about 10 different cell death subroutines with different regulatory pathways and cancer cells are probably not able to avoid all of cell death types at once. Therefore, a focused and individualised therapy is needed to address the specific advantages and disadvantages of individual tumours. Although much is known about apoptosis, therapeutic opportunities of other cell death pathways are often neglected. Molecular heterogeneity of head and neck squamous cell carcinomas (HNSCC) causing unpredictability of the clinical response represents a grave challenge for oncologists and seems to be a critical component of treatment response. The large proportion of this clinical heterogeneity probably lies in alterations of cell death pathways. How exactly cells die is very important because the predominant type of cell death can have multiple impacts on the therapeutic response as cell death itself acts as a second messenger. In this review, we discuss the different types of programmed cell death (PCD), their connection with HNSCC pathogenesis and possible therapeutic windows that result from specific sensitivity to some form of PCD in some clinically relevant subgroups of HNSCC.

Biological and clinical aspects of HPV-related cancers

Cancer-related diseases represent the second overall cause of death worldwide. Human papilloma virus (HPV) is an infectious agent which is mainly sexually transmitted and may lead to HPV-associated cancers in both men and women. Almost all cervical cancers are HPV-associated, however, an increasing number of head and neck cancers (HNCs), especially oropharyngeal cancer, can be linked to HPV infection. Moreover, anogenital cancers, including vaginal, vulvar, penial, and anal cancers, represent a subset of HPV-related cancers. Whereas testing and prevention of cervical cancer have significantly improved over past decades, anogenital cancers remain more difficult to confirm. Current clinical trials including patients with HPV-related cancers focus on finding proper testing for all HPV-associated cancers as well as improve the currently applied treatments. The HPV viral oncoproteins, E6 and E7, lead to degradation of, respectively, p53 and pRb resulting in entering the S phase without G1 arrest. These high-risk HPV viral oncogenes alter numerous cellular processes, including DNA repair, angiogenesis, and/or apoptosis, which eventually result in carcinogenesis. Additionally, a comprehensive analysis of gene expression and alteration among a panel of DNA double strand breaks (DSB) repair genes in HPV-negative and HPV-positive HNC cancers reveals differences pointing to HPV-dependent modifications of DNA repair processes in these cancers. In this review, we discuss the current knowledge regarding HPV-related cancers, current screening, and treatment options as well as DNA damage response-related biological aspects of the HPV infection and clinical trials.

The oncogenic pathways of papillomaviruses

Papillomaviruses are oncogenic DNA viruses and induce hyperplastic benign lesions of both cutaneous and mucosal tissues in their various hosts, including many domestic and wild animals as well as humans. There are some Papillomavirus genotypes that can infect hosts different from their own, such as BPV 1 and BPV 2 originated from cattle, which can also infect horses and are responsible for fibroblastic tumours in horses. This review article summarizes the origin and evolution of papillomaviruses as an etiological agent in the historical process. The main focus in this review is the evaluation of the interactions between high-risk papillomavirus oncoproteins and programmed cell-death pathways. It further exemplifies the role of these interactions in the malignant cell transformation process. In parallel with this, the use and importance of the bovine model system to enlighten the papillomavirus-associated cancers is discussed with an in-depth examination. Furthermore, it focuses on the epidemiological situation of BPV infections in Turkey in the cattle herds.

Cellular Functions of HPV16 E5 Oncoprotein during Oncogenic Transformation

The human papillomavirus (HPV) is recognized as the main etiologic agent associated with cervical cancer. HPVs are epitheliotropic, and the ones that infect the mucous membranes are classified into low-risk (LR) and high-risk (HR) types. LR-HPVs produce benign lesions, whereas HR-HPVs produce lesions that may progress to cancer. HR-HPV types 16 and 18 are the most frequently found in cervical cancer worldwide. E6 and E7 are the major HPV oncogenic proteins, and they have been profusely studied. Moreover, it has been shown that the HPV16 E5 (16E5) oncoprotein generates transformation, although the molecular mechanisms through which it carries out its activity have not been well defined. In contrast to E6 and E7, the E5 open reading frame is lost during the integration of the episomal HPV DNA into the cellular genome. This suggests that E5 acts at the early stages of the transformation process. In this review, we focused on the biochemical characteristics and functions of the HPV E5 oncoprotein, mainly on its association with growth factor receptors and other cellular proteins. Knowledge of the HPV E5 biology is important to understand the role of this oncoprotein in maintaining the viral cycle through the modulation of proliferation, differentiation, and apoptosis, as well as the alteration of other processes, such as survival, adhesion, migration, and invasion during early carcinogenesis. Finally, we summarized recent research that uses the E5 oncoprotein as a therapeutic target, promising a novel approach to the treatment of cervical cancer in its early stages.

Role of Epstein-Barr Virus and Human Papillomavirus Coinfection in Cervical Cancer: Epidemiology, Mechanisms and Perspectives

High-risk human papillomavirus (HR-HPV) is etiologically associated with the development and progression of cervical cancer, although other factors are involved. Epstein-Barr virus (EBV) detection in premalignant and malignant tissues from uterine cervix has been widely reported; however, its contribution to cervical cancer development is still unclear. Here, a comprehensive analysis regarding EBV presence and its potential role in cervical cancer, the frequency of EBV/HR-HPV coinfection in uterine cervix and EBV infection in tissue-infiltrating lymphocytes were revised. Overall, reports suggest a potential link of EBV to the development of cervical carcinomas in two possible pathways: (1) Infecting epithelial cells, thus synergizing with HR-HPV (direct pathway), and/or (2) infecting tissue-infiltrating lymphocytes that could generate local immunosuppression (indirect pathway). In situ hybridization (ISH) and/or immunohistochemical methods are mandatory for discriminating the cell type infected by EBV. However, further studies are needed for a better understanding of the EBV/HR-HPV coinfection role in cervical carcinogenesis.

Human Papillomavirus E6 and E7: The Cervical Cancer Hallmarks and Targets for Therapy

Human papillomavirus (HPV)-induced cervical cancer is a major health issue among women from the poorly/under-developed sectors of the world. It accounts for a high-mortality rate because of its late diagnosis and poor prognosis. Initial establishment and subsequent progression of this form of cancer are completely dependent on two major oncogenes E6 and E7, which are expressed constitutively leading to tumorigenesis. Thus, manipulation of these genes represents the most successful form of cervical cancer therapy. In the present article, information on structural, functional, and clinical dimensions of E6 and E7 activity has been reviewed. The genome organization and protein structure of E6 and E7 have been discussed followed by their mechanism to establish the six major cancer hallmarks in cervical tissues for tumor propagation. The later section of this review article deals with the different modes of therapeutics, which functions by deregulating E6 and E7 activity. Since E6 and E7 are the biomarkers of a cervical cancer cell and are the ones driving the cancer progression, therapeutic approaches targeting E6 and E7 have been proved to be highly efficient in terms of focused removal of abnormally propagating malignant cells. Therapeutics including different forms of vaccines to advanced genome editing techniques, which suppress E6 and E7 activity, have been found to successfully bring down the population of cervical cancer cells infected with HPV. T-cell mediated immunotherapy is another upcoming successful form of treatment to eradicate HPV-infected tumorigenic cells. Additionally, therapeutics using natural compounds from plants or other natural repositories, i.e., phytotherapeutic approaches have also been reviewed here, which prove their anticancer potential through E6 and E7 inhibitory effects. Thus, E6 and E7 repression through any of these methods is a significant approach toward cervical cancer therapy, described in details in this review along with an insight into the signaling pathways and molecular mechanistic of E6 and E7 action.

Current strategies against persistent human papillomavirus infection (Review)

Human papillomavirus (HPV) is the most common sexually transmitted infection, exhibiting a tropism for the epidermis and mucosae. The link between persistent HPV infection and malignancies involving the anogenital tract as well as the head and neck has been well‑established, and it is estimated that HPV‑related cancers involving various anatomical sites account for 4.5% of all human cancers. Current prophylactic vaccines against HPV have enabled the prevention of associated malignancies. However, the sizeable population base of current infection in whom prophylactic vaccines are not applicable, certain high‑risk HPV types not included in vaccines, and the vast susceptible population in developing countries who do not have access to the costly prophylactic vaccines, put forward an imperative need for effective therapies targeting persistent infection. In this article, the life cycle of HPV, the mechanisms facilitating HPV evasion of recognition and clearance by the host immune system, and the promising therapeutic strategies currently under investigation, particularly antiviral drugs and therapeutic vaccines, are reviewed.

One-step detection of human papilloma viral infection using quantum dot-nucleotide interaction specificity

Due to the close relationship between carcinogenesis and human papillomavirus (HPV), and since they are transmitted via huge number of asymptomatic carriers, the detection of HPV is really needed to reduce the risk of developing cancer. According to the best of our knowledge, our study provides the very first method for one-step detection of viral infection and if it has initiated the subsequent cancer proliferation. The proposed novel nanosystem consists of magnetic glass particles (MGPs), which were attached with DNA probe on their surface to hybridize with target DNAs. The MGP-probe-DNA hybrid was finally conjugated with CdTe/ZnSe core/shell quantum dots (QDs). The proposed detection system is based on a novel mechanism in which the MGPs separate out the target DNAs from different biological samples using external magnetic field for better and clear detection and the QDs give different fluorescent maxima for different target DNAs due to their ability to interact differently with different nucleotides. Firstly, the method was optimized using HPV genes cloned into synthetic plasmids. Then it was applied directly on the samples from normal and cancerous cells. After that, the real hospital samples of head and neck squamous cell carcinoma (HNSCC) with or without the infection of HPV were also analyzed. Our novel nano-system is proved successful in detecting and distinguishing between the patients suffering by HPV infection with or without subsequent cancer having detection limit estimated as 1.0 x 10⁹ (GEq/mL). The proposed methodology is faster and cost-effective, which can be applied at the clinical level to help the doctors to decide the strategy of medication that may save the life of the patients with an early treatment.

Novel Approaches for Vaccination Against HPV-Induced Cancers

To date, more than 5 % of all cancers are as a result of human papillomavirus (HPV) infection, and this incidence is increasing. Early recognition of disease is associated with good survival, but late presentation results in devastating consequences. Prevention is better than cure, and there are now successful prophylactic vaccination programmes in place. We discuss these and the prospect of therapeutic vaccinations in the near future to address a growing need for improved therapeutic options.

Cervical cancer cell lines are sensitive to sub-erythemal UV exposure

High risk human papillomavirus (HPV) infections are the causative agent in virtually every cervical cancer as well as a host of other anogenital and oropharyngeal malignancies. These viruses must activate DNA repair pathways to facilitate their replication, while avoiding the cell cycle arrest and apoptosis that can accompany DNA damage. HPV oncoproteins facilitate each of these goals, but also reduce genome stability. Our data dissect the cytotoxic and cytoprotective characteristics of HPV oncogenes in cervical cancer cells. These data show that while the transformation of keratinocytes by HPV oncogene leaves these cells more sensitive to UV, the oncogenes also protect against UV-induced apoptosis. Cisplatin and UV resistant cervical cancer cell lines were generated and probed for their sensitivity to genotoxic agents. Cervical cancer cells can acquire resistance to one DNA crosslinking agent (UV or cisplatin) without gaining broad tolerance of crosslinked DNA. Further, cisplatin resistance may or may not result in sensitivity to PARP1 inhibition.

C33-A cells transfected with E6*I or E6*II the short forms of HPV-16 E6, displayed opposite effects on cisplatin-induced apoptosis

The HPV-16 E6/E7 bicistronic immature transcript produces 4 mature RNAs: the unspliced HPV-16 E6/E7^pre-mRNA product and 3 alternatively spliced mRNAs. The 3 spliced mRNAs encode short forms of the E6 oncoprotein, namely E6*I, E6*II and E6^E7. In this study we showed that transfection of C-33A cells with monocistronic constructs of these cDNAs fused to GFP, produced different effects on apoptosis, after the treatment with cisplatin. Transfection of C-33A cells with the full-length E6-GFP oncoprotein resulted in a 50% decrease in cell death, while the transfection with the E6*I-GFP construct showed only a 25% of diminution of cell death, compared to the control cells. Transfection with the E6^E7-GFP or E7-GFP construct had no effect on the number of the apoptotic cells, compared with control cells. Conversely, transfection with the E6*II construct resulted in higher cell death than the control cells. Taken together, these results suggested that E6*I or E6*II, the short forms of HPV-16 E6, displayed opposite effects on cisplatin-induced apoptosis, when transfected in C-33A cells.

How Human Papillomavirus Replication and Immune Evasion Strategies Take Advantage of the Host DNA Damage Repair Machinery

The DNA damage response (DDR) is a complex signalling network activated when DNA is altered by intrinsic or extrinsic agents. DDR plays important roles in genome stability and cell cycle regulation, as well as in tumour transformation. Viruses have evolved successful life cycle strategies in order to ensure a chronic persistence in the host, virtually avoiding systemic sequelae and death. This process promotes the periodic shedding of large amounts of infectious particles to maintain a virus reservoir in individual hosts, while allowing virus spreading within the community. To achieve such a successful lifestyle, the human papilloma virus (HPV) needs to escape the host defence systems. The key to understanding how this is achieved is in the virus replication process that provides by itself an evasion mechanism by inhibiting and delaying the host immune response against the viral infection. Numerous studies have demonstrated that HPV exploits both the ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia and rad3-related (ATR) DDR pathways to replicate its genome and maintain a persistent infection by downregulating the innate and cell-mediated immunity. This review outlines how HPV interacts with the ATM- and ATR-dependent DDR machinery during the viral life cycle to create an environment favourable to viral replication, and how the interaction with the signal transducers and activators of transcription (STAT) protein family and the deregulation of the Janus kinase (JAK)-STAT pathways may impact the expression of interferon-inducible genes and the innate immune responses.

Virus Infection and Death Receptor-Mediated Apoptosis

Virus infection can trigger extrinsic apoptosis. Cell-surface death receptors of the tumor necrosis factor family mediate this process. They either assist persistent viral infection or elicit the elimination of infected cells by the host. Death receptor-mediated apoptosis plays an important role in viral pathogenesis and the host antiviral response. Many viruses have acquired the capability to subvert death receptor-mediated apoptosis and evade the host immune response, mainly by virally encoded gene products that suppress death receptor-mediated apoptosis. In this review, we summarize the current information on virus infection and death receptor-mediated apoptosis, particularly focusing on the viral proteins that modulate death receptor-mediated apoptosis.

UV-B-induced cutaneous inflammation and prospects for antioxidant treatment in Kindler syndrome

Kindler syndrome (KS), a rare, autosomal recessive disorder comprises mechanical skin fragility and photosensitivity, which manifest early in life. The progression of the disorder is irreversible and results in tissue damage in form of cutaneous and mucosal atrophy and scarring and epithelial cancers. Here, we unravel molecular mechanisms of increased UV-B sensitivity of keratinocytes derived from KS patients. We show that the pro-inflammatory cytokines, IL-1ß, IL-6 and TNF-α, are upregulated in KS skin and in UV-B irradiated KS keratinocytes. These cytokines are dependent on p38 activation, which is increased in the absence of kindlin-1 and induced by higher ROS levels. Other dysregulated cytokines and growth factors were identified in this study and might be involved in paracrine interactions contributing to KS pathology. We show a direct relationship between kindlin-1 abundance and UV-B induced apoptosis in keratinocytes, whereas kindlin-2 overexpression has no compensatory effect. Importantly, low levels of kindlin-1 are sufficient to relieve or rescue this feature. Reduction of pro-inflammatory cytokines and of UV-B induced apoptosis is a valid therapeutic goal to influence long term complications of KS. Here, we demonstrate that antioxidants and the plant flavonoid luteolin represent feasible topical therapeutic approaches decreasing UV-B induced apoptosis in two-dimensional and organotypic KS cultures. We provide evidence for potential new therapeutic approaches to mitigate the progressive course of KS, for which no cure is available to date. Furthermore, we established organotypic KS models, a valuable in vitro tool for research with a morphology similar to the skin of patients in situ.

A Small Molecule Inhibitor Selectively Induces Apoptosis in Cells Transformed by High Risk Human Papilloma Viruses

A phenotypic high-throughput cell culture screen was performed to identify compounds that prevented proliferation of the human Papilloma virus type 16 (HPV-16) transformed cell line Ca Ski. A series of quinoxaline compounds exemplified by Compound 1 was identified. Testing against a panel of cell lines demonstrated that Compound 1 selectively inhibited replication of all HPV-16, HPV-18, and HPV-31 transformed cell lines tested with 50% Inhibitory Concentration (IC₅₀) values of 2 to 8 μM relative to IC₅₀ values of 28 to 73 μM in HPV-negative cell lines. Treatment with Compound 1 resulted in a cascade of multiple apoptotic events, including selective activation of effector caspases 3 and 7, fragmentation of cellular DNA, and PARP (poly(ADP-ribose) polymerase) cleavage in HPV-positive cells relative to HPV-negative cells. Unregulated proliferation of HPV transformed cells is dependent on the viral oncogenes, E6 and E7. Treatment with Compound 1 resulted in a decrease in HPV E7 protein in Ca Ski cells. However, the timing of this reduction relative to other effects of compound treatment suggests that this was a consequence, rather than a cause, of the apoptotic cascade. Likewise, compound treatment resulted in no obvious effects on the E6- and E7- mediated down regulation of p53 and Rb, or their downstream effectors, p21 or PCNA. Further investigation of apoptotic signals induced by Compound 1 revealed cleavage of Caspase-8 in HPV-positive cells as early as 2 hours post-treatment, suggesting the compound initiates apoptosis through the extrinsic, death receptor-mediated, pathway of cell death. These studies provide proof of concept that cells transformed by oncogenic Papillomaviruses can be selectively induced to undergo apoptosis by compound treatment.

Human Papilloma Virus' Life Cycle and Carcinogenesis

RATIONALE

Considering that the loss of cell cycle and apoptosis control constitutes a central event in human papilloma virus' (HPV)-mediated carcinogenesis, the reason of this study is to insight to the HPV life cycle.

OBJECTIVE

The purpose of the study is to analyze the HPV molecular biology and cervical cancer association.

METHODS AND RESULTS

Brief review of current literature on the HPV life cycle and cervical carcinogenesis.

DISCUSSION

Among the HPV associated cancers, cervical cancer still ranks number two in the global cancer incidence of women. A central component of the association between HPV and cervical carcinogenesis is the ability of HPV to persist in the lower genital tract for long periods of time without being cleared because of its evasion mechanisms.

Epigenetic Pathways of Oncogenic Viruses: Therapeutic Promises

Cancerous transformation comprises different events that are both genetic and epigenetic. The ultimate goal for such events is to maintain cell survival and proliferation. This transformation occurs as a consequence of different features such as environmental and genetic factors, as well as some types of infection. Many viral infections are considered to be causative agents of a number of different malignancies. To convert normal cells into cancerous cells, oncogenic viruses must function at the epigenetic level to communicate with their host cells. Oncogenic viruses encode certain epigenetic factors that lead to the immortality and proliferation of infected cells. The epigenetic effectors produced by oncogenic viruses constitute appealing targets to prevent and treat malignant diseases caused by these viruses. In this review, we highlight the importance of epigenetic reprogramming for virus-induced oncogenesis, with special emphasis on viral epigenetic oncoproteins as therapeutic targets. The discovery of molecular components that target epigenetic pathways, especially viral factors, is also discussed.

Current trends in the etiology and diagnosis of HPV-related head and neck cancers

Human papilloma virus (HPV) infection is a major risk factor for a distinct subset of head and neck squamous cell carcinoma (HNSCC). The current review summarizes the epidemiology of HNSCC and the disease burden, the infectious cycle of HPV, the roles of viral oncoproteins, E6 and E7, and the downstream cellular events that lead to malignant transformation. Current techniques for the clinical diagnosis of HPV-associated HNSCC will also be discussed, that is, the detection of HPV DNA, RNA, and the HPV surrogate marker, p16 in tumor tissues, as well as HPV-specific antibodies in serum. Such methods do not allow for the early detection of HPV-associated HNSCC and most cases are at an advanced stage upon diagnosis. Novel noninvasive approaches using oral fluid, a clinically relevant biological fluid, allow for the detection of HPV and cellular alterations in infected cells, which may aid in the early detection and HPV-typing of HNSCC tumors. Noninvasive diagnostic methods will enable early detection and intervention, leading to a significant reduction in mortality and morbidity associated with HNSCC.

[Expression of gamma interferon during HPV and Chlamydia trachomatis infection in cervical samples]

INTRODUCTION

The aim of this study was to mesure the expression of gamma interferon in HPV and Chlamydia trachomatis infection in squamous intraepithelial lesions.

METHOD

Samples from 100 patients diagnosed by colposcopy with or without squamous intraepithelial lesions were used in the present study. Each patient was found to be infected by HPV and C.trachomatis. Relative gamma interferon mRNA expression was assessed using a real-time reverse transcriptase PCR assay (RT-PCR).

RESULTS

The relative units of expression of gamma interferon mRNA were 13, 1.8 and 0.3, for HPV and C.trachomatis co-infection, or HPV or C.trachomatis infection, respectively.

CONCLUSION

HPV and C.trachomatis could overstimulate the expression of gamma interferon.

Prognostic evaluation of DNA index in HIV-HPV co-infected women cervical samples attending in reference centers for HIV-AIDS in Recife

INTRODUCTION

Persistence of cervical infection caused by human papillomavirus (HPV) types with high oncogenic risk may lead to cervical intraepithelial neoplasia (CIN). The aim of the present study was to evaluate whether, in HIV-positive women, the presence of aneuploidy in cervical cell samples is associated with presence and evolution of CIN.

METHODS

The present study had two stages. In the first stage, comprising a cross-sectional study, the association between the presence of aneuploidy seen via flow cytometry and sociodemographic characteristics, habits and characteristics relating to HPV and HIV infection was analyzed. In the second stage, comprising a cohort study, it was investigated whether aneuploidy was predictive of CIN evolution.

RESULTS

No association was observed between the presence of aneuploidy and HPV infection, or between its presence and alterations seen in oncotic cytological analysis. On the other hand, aneuploidy was associated with the presence of CIN (p = 0.030) in histological analysis and with nonuse of antiretroviral therapy (p = 0.001). Most of the HIV-positive women (234/272) presented normal CD4+ T lymphocyte counts (greater than 350 cells/mm3) and showed a greater aneuploidy regression rate (77.5%) than a progression rate (23.9%) over a follow-up of up to two years.

CONCLUSION

Although there was an association between the presence of cervical tissue lesions and the DNA index, the latter was not predictive of progression of the cervical lesion. This suggests that progression of the cervical lesion to cancer in HIV-positive women may also be changed through improvement of the immunological state enabled by using antiretroviral therapy.

Endogenous two-photon fluorescence imaging elucidates metabolic changes related to enhanced glycolysis and glutamine consumption in precancerous epithelial tissues

Alterations in the balance between different metabolic pathways used to meet cellular bioenergetic and biosynthetic demands are considered hallmarks of cancer. Optical imaging relying on endogenous fluorescence has been used as a noninvasive approach to assess tissue metabolic changes during cancer development. However, quantitative correlations of optical assessments with variations in the concentration of relevant metabolites or in the specific metabolic pathways that are involved have been lacking. In this study, we use high-resolution, depth-resolved imaging, relying entirely on endogenous two-photon excited fluorescence in combination with invasive biochemical assays and mass spectrometry to demonstrate the sensitivity and quantitative nature of optical redox ratio tissue assessments. We identify significant differences in the optical redox ratio of live, engineered normal and precancerous squamous epithelial tissues. We establish that while decreases in the optical redox ratio are associated with enhanced levels of glycolysis relative to oxidative phosphorylation, increases in glutamine consumption to support energy production are associated with increased optical redox ratio values. Such mechanistic insights in the origins of optical metabolic assessments are critical for exploiting fully the potential of such noninvasive approaches to monitor and understand important metabolic changes that occur in live tissues at the onset of cancer or in response to treatment.

Manipulation of cellular DNA damage repair machinery facilitates propagation of human papillomaviruses

In general, the interplay among viruses and DNA damage repair (DDR) pathways can be divided based on whether the interaction promotes or inhibits the viral lifecycle. The propagation of human papillomaviruses is both promoted and inhibited by DDR proteins. As a result, HPV proteins both activate repair pathways, such as the ATM and ATR pathways, and inhibit other pathways, most notably the p53 signaling pathway. Indeed, the role of HPV proteins, with regard to the DDR pathways, can be divided into two broad categories. The first set of viral proteins, HPV E1 and E2 activate a DNA damage response and recruit repair proteins to viral replication centers, where these proteins are likely usurped to replicate the viral genome. Because the activation of the DDR response typically elicits a cell cycle arrest that would impeded the viral lifecycle, the second set of HPV proteins, HPV E6 and E7, prevents the DDR response from pausing cell cycle progression or inducing apoptosis. This review provides a detailed account of the interactions among HPV proteins and DDR proteins that facilitate HPV propagation.

Molecular targets of HPV oncoproteins: potential biomarkers for cervical carcinogenesis

Cervical cancer is the second most common cancer among women worldwide and is responsible for 275,000 deaths each year. Persistent infection with high-risk human papillomavirus (HR-HPV) is an essential factor for the development of cervical cancer. Although the process is not fully understood, molecular mechanisms caused by HPV infection are necessary for its development and reveal a large number of potential biomarkers for diagnosis and prognosis. These molecules are host genes and/or proteins, and cellular microRNAs involved in cell cycle regulation that result from disturbed expression of HR-HPV E5, E6 and E7 oncoproteins. One of the current challenges in medicine is to discover potent biomarkers that can correctly diagnose cervical premalignant lesions and standardize clinical management. Currently, studies are showing that some of these molecules are potential biomarkers of cervical carcinogenesis, and it is possible to carry out a more accurate diagnosis and provide more appropriate follow-up treatment for women with cervical dysplasia. In this paper, we review recent research studies on cell cycle molecules deregulated by HPV infections, as well as their potential use for cervical cancer screening.

The role of inflammation in cervical cancer

Knowledge regarding cervical cancer and human papillomavirus is expanding rapidly. Inflammation subsequent to viral infection is a driving force that accelerates cancer development. The infiltrated immune cells and their secretory cytokines along with chemokines and growth factors greatly contribute the malignant traits of cervical cancer. A better understanding of the mechanisms related to inflammation and cancer progression in terms of pathogen survival, cancer development, progression, and metastasis will lead to innovative approach for treating cancer.

Human papillomavirus oncoproteins and apoptosis (Review)

The aim of this study was to review the literature and identify the association between human papillomavirus (HPV) oncoproteins and apoptosis. HPV-associated apoptosis may be primarily blocked by a number of oncoproteins, including E5, E6 and E7. E5 protein protects cells from tumor necrosis factor-associated apoptosis; the oncoprotein E6 predominantly inhibits apoptosis through the p53 pathway; and oncoprotein E7 is involved in apoptosis activation and inhibition. In addition, HPV oncoproteins are involved in activating or repressing the transcription of E6/E7. In conclusion, HPV oncoproteins, including E5, E6 and E7 protein, may interfere with apoptosis via certain regulatory principles.

The modulation of apoptosis by oncogenic viruses

Transforming viruses can change a normal cell into a cancer cell during their normal life cycle. Persistent infections with these viruses have been recognized to cause some types of cancer. These viruses have been implicated in the modulation of various biological processes, such as proliferation, differentiation and apoptosis. The study of infections caused by oncogenic viruses had helped in our understanding of several mechanisms that regulate cell growth, as well as the molecular alterations leading to cancer. Therefore, transforming viruses provide models of study that have enabled the advances in cancer research. Viruses with transforming abilities, include different members of the Human Papillomavirus (HPV) family, Hepatitis C virus (HCV), Human T-cell Leukemia virus (HTLV-1), Epstein Barr virus (EBV) and Kaposi’s Sarcoma Herpesvirus (KSHV).

Apoptosis, or programmed cell death, is a tightly regulated process that plays an important role in development and homeostasis. Additionally, it functions as an antiviral defense mechanism. The deregulation of apoptosis has been implicated in the etiology of diverse diseases, including cancer. Oncogenic viruses employ different mechanisms to inhibit the apoptotic process, allowing the propagation of infected and damaged cells. During this process, some viral proteins are able to evade the immune system, while others can directly interact with the caspases involved in apoptotic signaling. In some instances, viral proteins can also promote apoptosis, which may be necessary for an accurate regulation of the initial stages of infection.

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.

The invisible enemy - how human papillomaviruses avoid recognition and clearance by the host immune system

Human papillomavirus (HPV) needs to persist in squamous epithelia for a certain amount of time to complete its reproductive cycle. Therefore, the virus has evolved multiple immune evasion strategies. The interplay of these immune evasion mechanisms with the host immune system decides whether a HPV infection is cleared or becomes persistent. Clearance of HPV-induced lesions is mediated by a cellular immune response, consisting of both cytotoxic T lymphocyte and T helper cell responses. Persistent HPV infection, on the other hand, is the single most important risk factor for the development of HPV-associated premalignant lesions and HPV-driven cancers. This article reviews the immune evasion mechanisms employed by high-risk HPVs to escape host immune recognition and attack.

Human papillomavirus early proteins and apoptosis

INTRODUCTION

The human papillomavirus (HPV) associated apoptosis can be primarily attributed to some early proteins, such as E2, E5, E6, E7, and so on. Though these proteins have a low molecular size, they are capable to interact with a series of host cellular regulation proteins to induce or inhibit apoptosis. The oncoproteins E6 can inhibit the apoptosis mainly through p53 pathway. The E5 protein can protect cells from tumor necrosis factor-related apoptosis. The protein E2 protein have regulatory functions in viral transcription and induction of apoptosis. The oncoprotein E7 plays the role in both apoptosis activation and inhibition. In addition, the HPV full-length E2 proteins involve in activating or repressing the transcription of E6/E7, so as to regulating the apoptosis caused by E6 and E7.

MATERIALS AND METHODS

We search major databases (such as Elsevier) with the following selection criteria: HPV, early protein, apoptosis.

CONCLUSIONS

In this review, we summary the literature related with E2, E5, E6, and E7 proteins, and describe the regulatory principles and specific mechanism by which HPV early proteins can interfere with apoptosis and trigger gynaecopathias for women.

[HPV-associated squamous cell carcinogenesis]

About 7-8% of all human cancers are thought to be related to infections with high-risk (HR) human papilloma virus (HPV). Besides cervical cancer, especially squamous cell carcinomas of the anogenital and oropharyngeal regions are associated with HR-HPV. Transmission of HPV is due to sexual activity. Harald zur Hausen was awarded in 2008 with the Nobel price in medicine for the establishment of a causal link between certain HPV infections and cervical cancer. Meanwhile potent prophylactic vaccines are available to prevent infections with HPV-16 and HPV-18, the two most frequently observed HR HPV types worldwide. On molecular grounds a persistent HPV infection is the central risk factor for the development of HPV-associated neoplasias. Continued expression of the viral E6 and E7 oncogenes disrupts cell cycle control mechanisms in infected cells, thereby gaining limitless proliferative capacity and resistance against apoptotic signals. However acquisition of mutations and genomic instability might cause malignant transformation in these cells.

Spinocellular carcinoma from warts in a HPV infection natural history lasting 49 years. Virus strategy or host choice? Implications for researches and therapeutic vaccines

There is a very strong evidence that progression (also to cancer) in variable percentages of cases infected by HPV, HBV, HCV, and HIV depends on host immune response. A large number of observations demonstrate that virus set up a postulated "active strategy" to modify host reactions or to avoid it. But in all those infections it also seems that antigen load (viral RNA or DNA), chronic activation of immune response and time elapsing from the primary infection play a pivotal role in determining clearing or persisting outcomes. My wife's HPV and cancer natural history, lasting 49 years, started at the age of 10 years with facial warts and progressed to CIN 2/3, cervical in situ carcinoma, perineal warts, perianal carcinoma, inguinal lymph nodes, and invasion of bones and muscular structures, until death is paradigmatic: a progressive immune failure was detected in her scaling up all those clinical features, ending in a massive apoptosis of her lymphocytes collected by leukapheresis and cultured with HPV antigens E6/E7, with the aim of obtaining antigen presenting cells and CD8+ specific T lymphocytes. From this experience, a concept of "host choice to reach a tolerance (mainly by a Tregs mediated anergy) or symbiotic-like state" arises, underlining all the affected host's immune-responses to virus persistence (and to consequent tumors). It might be then postulated as the hallmark of a long-term host/parasites co-evolution, and considered a "normal" reaction when the host faces overwhelming numbers of non-self cancer cells (high antigen loads) preceded by persistent virus infections (chronic activation). This happens in patients who do not clear HPV or other viruses soon enough after infection. These observations may lead to a better understanding of many phenomena that are actually difficult to explain or still are open questions. The auto-limiting host's immune-responses are likely to be aimed to avoid risks arising mainly in the protection of "self" (autoimmunity), to prolong its own survival (balance with the virus), to avoid the risk of producing uncontrolled cells (dangerous outcomes). Finally, the postulated negative implications for therapeutic vaccines in cervical cancer, as they really seem to not work till now might be ascribed just to the cited host immune-specific state itself, through an activation induced cell death, elicited by recall antigens (E6/E7 in the case of my wife). Also this latter hypothesis, as well as the previous ones may be of some value to better account for clinical behaviors and researches.

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.

Human papillomavirus oncoproteins: pathways to transformation

An association between human papillomavirus (HPV) infection and the development of cervical cancer was initially reported over 30 years ago, and today there is overwhelming evidence that certain subtypes of HPV are the causative agents of these malignancies. The p53 and retinoblastoma proteins are well-characterized targets of the HPV E6 and E7 oncoproteins, but recent studies have shown that the alteration of additional pathways are equally important for transformation. These additional factors are crucial regulators of cell cycle progression, telomere maintenance, apoptosis and chromosomal stability. Understanding how HPV oncoproteins modify these activities provides novel insights into the basic mechanisms of oncogenesis.

Cysteine protease activation and apoptosis in Murine norovirus infection

Background

Noroviruses are the leading cause of viral gastroenteritis. Because a suitable in vitro culture system for the human virus has yet to be developed, many basic details of the infection process are unknown. Murine norovirus (MNV) serves as a model system for the study of norovirus infection. Recently it was shown that infection of RAW 264.7 cells involved a novel apoptotic pathway involving survivin.

Results

Using a different set of approaches, the up-regulation of caspases, DNA condensation/fragmentation, and membrane blebbing, all of which are markers of apoptosis, were confirmed. Live cell imaging and activity-based protein profiling showed that activation of caspase-like proteases occurred within two hours of infection, followed by morphological changes to the cells. MNV infection in the presence of caspase inhibitors proceeded via a distinct pathway of rapid cellular necrosis and reduced viral production. Affinity purification of activity-based protein profiling targets and identification by peptide mass fingerprinting showed that the cysteine protease cathepsin B was activated early in infection, establishing this protein as an upstream activator of the intrinsic apoptotic pathway.

Conclusion

This work adds cathepsin B to the noncanonical programmed cell death induced by MNV, and provides data suggesting that the virus may induce apoptosis to expand the window of time for viral replication. This work also highlights the significant power of activity-based protein profiling in the study of viral pathogenesis.