Characterization of transcription factor binding to human papillomavirus type 16 DNA during cellular differentiation

Oncogenic human papillomavirus DNA in female sex workers of Bihar, India

Objective

Human papillomavirus (HPV) is a sexually transmitted virus which play a vital role to developing Cervical cancer. It is presumed and accepted that sexually exposed women will have occurred HPV infection at least once in their whole life. Hence, determined the actual cause of transmission of HPV infection in sexually active women with single sex partner that is married women and sexually active women with multiple sex partners that is female sex works (FSWs).

Methods

A total 197 urine sample of FSWs and MW has been utilized through RT-PCR technique for HR-HPV detection. DNA extracted from urine samples and estimation and purification of DNA, used RT-PCR technique for HPV-16 and HPV-18 detection.

Results

The overall prevalence of HR-HPV was detected to be 16.75% (33/197) and 83.25% (164 out 197) negative results reported in both studied subjects. The results analysis of HPV-16 and HPV-18 reveals in which prevalence of HPV-16 was 14.21% (28/197) and HPV-18 was detected 2.53% (5/197) in studied subjects in both study groups. The prevalence of HPV-16 and HPV-18 among MW was high (18.75%) and HPV-16 and HPV-18 was low (14.85%) in FSWs. It did not differ significantly of HR-HPV prevalence in MW who has single sex partner and FSWs who has multiple sex partners.

Conclusion

The study indicates that oncogenic HPV prevalence did not different significantly in multiple sex partners, that is, FSWs and single sex partner, that is, MW. The probability of genital hygiene rather than multiple sexual partners stands more apt as a cause of HPV infection. This study advises to develop more awareness program about genital hygiene in women to reduce the HPV infection and can be prevented from cervical cancer. Hence, genital hygiene may be reducing the burden of HPV infection in women.

Short- and long-range cis interactions between integrated HPV genomes and cellular chromatin dysregulate host gene expression in early cervical carcinogenesis

Development of cervical cancer is directly associated with integration of human papillomavirus (HPV) genomes into host chromosomes and subsequent modulation of HPV oncogene expression, which correlates with multi-layered epigenetic changes at the integrated HPV genomes. However, the process of integration itself and dysregulation of host gene expression at sites of integration in our model of HPV16 integrant clone natural selection has remained enigmatic. We now show, using a state-of-the-art 'HPV integrated site capture' (HISC) technique, that integration likely occurs through microhomology-mediated repair (MHMR) mechanisms via either a direct process, resulting in host sequence deletion (in our case, partially homozygously) or via a 'looping' mechanism by which flanking host regions become amplified. Furthermore, using our 'HPV16-specific Region Capture Hi-C' technique, we have determined that chromatin interactions between the integrated virus genome and host chromosomes, both at short- (<500 kbp) and long-range (>500 kbp), appear to drive local host gene dysregulation through the disruption of host:host interactions within (but not exceeding) host structures known as topologically associating domains (TADs). This mechanism of HPV-induced host gene expression modulation indicates that integration of virus genomes near to or within a 'cancer-causing gene' is not essential to influence their expression and that these modifications to genome interactions could have a major role in selection of HPV integrants at the early stage of cervical neoplastic progression.

Proteomics Analysis of Andrographolide-Induced Apoptosis via the Regulation of Tumor Suppressor p53 Proteolysis in Cervical Cancer-Derived Human Papillomavirus 16-Positive Cell Lines

Regardless of the prophylactic vaccine accessibility, persistent infections of high-risk human papillomaviruses (hr-HPVs), recognized as an etiology of cervical cancers, continues to represent a major health problem for the world population. An overexpression of viral early protein 6 (E6) is linked to carcinogenesis. E6 induces anti-apoptosis by degrading tumor suppressor proteins p53 (p53) via E6-E6-associated protein (E6AP)-mediated polyubiquitination. Thus, the restoration of apoptosis by interfering with the E6 function has been proposed as a selective medicinal strategy. This study aimed to determine the activities of andrographolide (Androg) on the disturbance of E6-mediated p53 degradation in cervical cancer cell lines using a proteomic approach. These results demonstrated that Androg could restore the intracellular p53 level, leading to apoptosis-induced cell death in HPV16-positive cervical cancer cell lines, SiHa and CaSki. Mechanistically, the anti-tumor activity of Androg essentially relied on the reduction in host cell proteins, which are associated with ubiquitin-mediated proteolysis pathways, particularly HERC4 and SMURF2. They are gradually suppressed in Androg-treated HPV16-positive cervical cancer cells. Collectively, the restoration of p53 in HPV16-positive cervical cancer cells might be achieved by disruption of E3 ubiquitin ligase activity by Androg, which could be an alternative treatment for HPV-associated epithelial lesions.

Human Papillomavirus Infection in Head and Neck Squamous Cell Carcinomas: Transcriptional Triggers and Changed Disease Patterns

Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous group of cancers. Collectively, HNSCC ranks sixth in incidence rate worldwide. Apart from classical risk factors like tobacco and alcohol, infection of human papillomavirus (HPV) is emerging as a discrete risk factor for HNSCC. HPV-positive HNSCC represent a distinct group of diseases that differ in their clinical presentation. These lesions are well-differentiated, occur at an early age, and have better prognosis. Epidemiological studies have demonstrated a specific increase in the proportions of the HPV-positive HNSCC. HPV-positive and HPV-negative HNSCC lesions display different disease progression and clinical response. For tumorigenic-transformation, HPV essentially requires a permissive cellular environment and host cell factors for induction of viral transcription. As the spectrum of host factors is independent of HPV infection at the time of viral entry, presumably entry of HPV only selects host cells that are permissive to establishment of HPV infection. Growing evidence suggest that HPV plays a more active role in a subset of HNSCC, where they are transcriptionally-active. A variety of factors provide a favorable environment for HPV to become transcriptionally-active. The most notable are the set of transcription factors that have direct binding sites on the viral genome. As HPV does not have its own transcription machinery, it is fully dependent on host transcription factors to complete the life cycle. Here, we review and evaluate the current evidence on level of a subset of host transcription factors that influence viral genome, directly or indirectly, in HNSCC. Since many of these transcription factors can independently promote carcinogenesis, the composition of HPV permissive transcription factors in a tumor can serve as a surrogate marker of a separate molecularly-distinct class of HNSCC lesions including those cases, where HPV could not get a chance to infect but may manifest better prognosis.

The Dynamic Interface of Viruses with STATs

Viruses commonly antagonize the antiviral type I interferon response by targeting signal transducer and activator of transcription 1 (STAT1) and STAT2, key mediators of interferon signaling. Other STAT family members mediate signaling by diverse cytokines important to infection, but their relationship with viruses is more complex. Importantly, virus-STAT interaction can be antagonistic or stimulatory depending on diverse viral and cellular factors. While STAT antagonism can suppress immune pathways, many viruses promote activation of specific STATs to support viral gene expression and/or produce cellular conditions conducive to infection. It is also becoming increasingly clear that viruses can hijack noncanonical STAT functions to benefit infection. For a number of viruses, STAT function is dynamically modulated through infection as requirements for replication change. Given the critical role of STATs in infection by diverse viruses, the virus-STAT interface is an attractive target for the development of antivirals and live-attenuated viral vaccines. Here, we review current understanding of the complex and dynamic virus-STAT interface and discuss how this relationship might be harnessed for medical applications.

Human Papillomavirus Infection in Head and Neck Squamous Cell Carcinomas: Transcriptional Triggers and Changed Disease Patterns

Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous group of cancers. Collectively, HNSCC ranks sixth in incidence rate worldwide. Apart from classical risk factors like tobacco and alcohol, infection of human papillomavirus (HPV) is emerging as a discrete risk factor for HNSCC. HPV-positive HNSCC represent a distinct group of diseases that differ in their clinical presentation. These lesions are well-differentiated, occur at an early age, and have better prognosis. Epidemiological studies have demonstrated a specific increase in the proportions of the HPV-positive HNSCC. HPV-positive and HPV-negative HNSCC lesions display different disease progression and clinical response. For tumorigenic-transformation, HPV essentially requires a permissive cellular environment and host cell factors for induction of viral transcription. As the spectrum of host factors is independent of HPV infection at the time of viral entry, presumably entry of HPV only selects host cells that are permissive to establishment of HPV infection. Growing evidence suggest that HPV plays a more active role in a subset of HNSCC, where they are transcriptionally-active. A variety of factors provide a favorable environment for HPV to become transcriptionally-active. The most notable are the set of transcription factors that have direct binding sites on the viral genome. As HPV does not have its own transcription machinery, it is fully dependent on host transcription factors to complete the life cycle. Here, we review and evaluate the current evidence on level of a subset of host transcription factors that influence viral genome, directly or indirectly, in HNSCC. Since many of these transcription factors can independently promote carcinogenesis, the composition of HPV permissive transcription factors in a tumor can serve as a surrogate marker of a separate molecularly-distinct class of HNSCC lesions including those cases, where HPV could not get a chance to infect but may manifest better prognosis.

Analysis of Human Papillomavirus (HPV) 16 Variants Associated with Cervical Infection in Italian Women

This study aims to evaluate HPV16 variants distribution in a population of Italian women living in two different regions (Lombardy and Sardinia) by sequence analyses of HPV16-positive cervical samples, in order to reconstruct the phylogenetic relationship among variants to identify the currently circulating lineages. Analyses were conducted starting from DNA isolated from 67 HPV16-positive cervical samples collected from two different Italian centres (31 from Lombardy and 36 from Sardinia) of women with normal and abnormal cervical cytology. The entire long control region (LCR) and 300 nt of the E6 gene was sequenced to identify intra-type variants. Sequence comparison and phylogenetic analysis were made using a distance-based neighbour joining method (NJ) and Kimura two-parameter model. Data obtained reported that Italian sequences mainly belonged to the European lineage, in particular sublineage A2. Only five sequences clustered in non-European branches: two in North American lineage (sublineage D1), two in African-1 (sublineage B1) and one in African-2. A new 27 nucleotide duplication in the central segment of the LCR region was found in a sequence obtained from a sample isolated in Sardinia. A predominance of European variants was detected, with some degree of variability among the studied HPV16 strains. This study contributes to the implementation of data regarding the molecular epidemiology of HPV16 variants.

Unraveling the Regulatory G-Quadruplex Puzzle: Lessons From Genome and Transcriptome-Wide Studies

G-quadruplexes (G4s) are among the best-characterized DNA secondary structures and are enriched in regulatory regions, especially promoters, of several prokaryote and eukaryote genomes, indicating a possible role in cis regulation of genes. Many studies have focused on evaluating the impact of specific G4-forming sequences in the promoter regions of genes. However, the lack of correlation between the presence of G4s and the functional impact on cis gene regulation, evidenced by the variable expression fold change in the presence of G4 stabilizers, shows that not all G4s affect transcription in the same manner. This indicates that the regulatory effect of the G4 is significantly influenced by its position, the surrounding DNA topology, and other environmental factors within the cell. In this review, we compare individual gene studies with high-throughput differential expression studies to highlight the importance of formulating a combined approach that can be applied in humans, bacteria, and viruses to better understand the effect of G4-mediated gene regulation.

HPV type 16 E6 and NFX1-123 augment JNK signaling to mediate keratinocyte differentiation and L1 expression

The HPV life cycle is differentiation-dependent, with cellular differentiation driving initiation of the late, productive stage of the viral life cycle. Here, we identify a role for the protein NFX1-123 in regulating keratinocyte differentiation and events of the late HPV life cycle. NFX1-123 itself increased with differentiation of epithelial cells. Greater NFX1-123 augmented differentiation marker expression and JNK phosphorylation in differentiating 16E6-expressing human foreskin keratinocytes (16E6 HFKs). This was associated with altered expression of MKK4 and MKK7, upstream kinase regulators of JNK phosphorylation. Modulating levels of NFX1-123 in HPV16-positive W12E cells recapitulated the effects on differentiation markers, JNK phosphorylation, and MKK4/7 seen in 16E6 HFKs. Crucially, levels of NFX1-123 also correlated with expression of L1, the capsid protein of HPV. Altogether, these studies define a role for NFX1-123 in mediating epithelial differentiation through the JNK signaling pathway, potentially linking expression of cellular genes and HPV genes during differentiation.

Regulation of HPV transcription

Human papillomavirus infection is associated with the development of malignant and benign neoplasms. Approximately 40 viral types can infect the anogenital mucosa and are categorized into high- and low-risk oncogenic human papillomavirus, depending on their association with the development of cervical carcinoma. High-risk human papillomavirus 16 and 18 are detected in 55% and 15% of all invasive cervical squamous cell carcinomas worldwide, respectively. Low-risk human papillomavirus 6 and 11 are responsible for 90% of genital warts and are also associated with the development of recurrent respiratory papillomatosis. Human papillomavirus preferentially infects mitotic active cells of the basal layer from both mucosal and cutaneous epithelium through microabrasions. The viral life cycle synchronizes with the epithelial differentiation program, which may be due, in part, to the binding of differentially expressed cellular transcription factors to the long control region throughout the various epithelial layers. This review aimed to summarize the current knowledge regarding the mechanisms by which viral gene expression is regulated and the influence of human papillomavirus heterogeneity upon this phenomenon. A better understanding of the regulatory mechanisms may elucidate the particularities of human papillomavirus-associated pathogenesis and may provide new tools for antiviral therapy.

STAT3 activation by E6 is essential for the differentiation-dependent HPV18 life cycle

Human papillomaviruses (HPV) activate a number of host factors to control their differentiation-dependent life cycles. The transcription factor signal transducer and activator of transcription (STAT)-3 is important for cell cycle progression and cell survival in response to cytokines and growth factors. STAT3 requires phosphorylation on Ser727, in addition to phosphorylation on Tyr705 to be transcriptionally active. In this study, we show that STAT3 is essential for the HPV life cycle in undifferentiated and differentiated keratinocytes. Primary human keratinocytes containing high-risk HPV18 genomes display enhanced STAT3 phosphorylation compared to normal keratinocytes. Expression of the E6 oncoprotein is sufficient to induce the dual phosphorylation of STAT3 at Ser727 and Tyr705 by a mechanism requiring Janus kinases and members of the MAPK family. E6-mediated activation of STAT3 induces the transcription of STAT3 responsive genes including cyclin D1 and Bcl-xL. Silencing of STAT3 protein expression by siRNA or inhibition of STAT3 activation by small molecule inhibitors, or by expression of dominant negative STAT3 phosphorylation site mutants, results in blockade of cell cycle progression. Loss of active STAT3 impairs HPV gene expression and prevents episome maintenance in undifferentiated keratinocytes and upon differentiation, lack of active STAT3 abolishes virus genome amplification and late gene expression. Organotypic raft cultures of HPV18 containing keratinocytes expressing a phosphorylation site STAT3 mutant display a profound reduction in suprabasal hyperplasia, which correlates with a loss of cyclin B1 expression and increased differentiation. Finally, increased STAT3 expression and phosphorylation is observed in HPV positive cervical disease biopsies compared to control samples, highlighting a role for STAT3 activation in cervical carcinogenesis. In summary, our data provides evidence of a critical role for STAT3 in the HPV18 life cycle.

Mechanisms by which HPV Induces a Replication Competent Environment in Differentiating Keratinocytes

Human papillomaviruses (HPV) are the causative agents of cervical cancer and are also associated with other genital malignancies, as well as an increasing number of head and neck cancers. HPVs have evolved their life cycle to contend with the different cell states found in the stratified epithelium. Initial infection and viral genome maintenance occurs in the proliferating basal cells of the stratified epithelium, where cellular replication machinery is abundant. However, the productive phase of the viral life cycle, including productive replication, late gene expression and virion production, occurs upon epithelial differentiation, in cells that normally exit the cell cycle. This review outlines how HPV interfaces with specific cellular signaling pathways and factors to provide a replication-competent environment in differentiating cells.

Keratinocyte Differentiation-Dependent Human Papillomavirus Gene Regulation

Human papillomaviruses (HPVs) cause diseases ranging from benign warts to invasive cancers. HPVs infect epithelial cells and their replication cycle is tightly linked with the differentiation process of the infected keratinocyte. The normal replication cycle involves an early and a late phase. The early phase encompasses viral entry and initial genome replication, stimulation of cell division and inhibition of apoptosis in the infected cell. Late events in the HPV life cycle include viral genome amplification, virion formation, and release into the environment from the surface of the epithelium. The main proteins required at the late stage of infection for viral genome amplification include E1, E2, E4 and E5. The late proteins L1 and L2 are structural proteins that form the viral capsid. Regulation of these late events involves both cellular and viral proteins. The late viral mRNAs are expressed from a specific late promoter but final late mRNA levels in the infected cell are controlled by splicing, polyadenylation, nuclear export and RNA stability. Viral late protein expression is also controlled at the level of translation. This review will discuss current knowledge of how HPV late gene expression is regulated.

SOX2 as a New Regulator of HPV16 Transcription

Persistent infections with high-risk human papillomavirus (HPV) constitute the main risk factor for cervical cancer development. HPV16 is the most frequent type associated to squamous cell carcinomas (SCC), followed by HPV18. The long control region (LCR) in the HPV genome contains the replication origin and sequences recognized by cellular transcription factors (TFs) controlling viral transcription. Altered expression of E6 and E7 viral oncogenes, modulated by the LCR, causes modifications in cellular pathways such as proliferation, leading to malignant transformation. The aim of this study was to identify specific TFs that could contribute to the modulation of high-risk HPV transcriptional activity, related to the cellular histological origin. We identified sex determining region Y (SRY)-box 2 (SOX2) response elements present in HPV16-LCR. SOX2 binding to the LCR was demonstrated by in vivo and in vitro assays. The overexpression of this TF repressed HPV16-LCR transcriptional activity, as shown through reporter plasmid assays and by the down-regulation of endogenous HPV oncogenes. Site-directed mutagenesis revealed that three putative SOX2 binding sites are involved in the repression of the LCR activity. We propose that SOX2 acts as a transcriptional repressor of HPV16-LCR, decreasing the expression of E6 and E7 oncogenes in a SCC context.

Regulation of the human papillomavirus type 16 late promoter by transcriptional elongation

Transcripts from the late promoter of human papillomavirus type 16 (HPV16) are upregulated upon host cell differentiation. Differentiation-dependent transcript regulation is thought to sequester viral antigens in the uppermost epithelial layers, facilitating immune evasion. The mechanisms regulating late promoter upregulation during differentiation are poorly characterized. We show that the late promoter is upregulated at the transcriptional level and that the viral enhancer stimulates promoter activity. Using kinase inhibition and chromatin immunoprecipitation analysis, we show evidence for differentiation-dependent enhancement of transcript elongation. Three factors that promote transcript elongation, cyclin dependent kinase 9 (CDK9), CDK8 (a subunit of the Mediator complex), and bromodomain containing protein 4 (Brd4) are recruited to viral genomes upon differentiation, and each plays a role in promoter activity. These results shed light on the transcriptional processes utilized by HPV16 for proper regulation of gene expression during the viral life cycle.

HPV16 oncogene expression levels during early cervical carcinogenesis are determined by the balance of epigenetic chromatin modifications at the integrated virus genome

In cervical squamous cell carcinomas, high-risk human papillomavirus (HRHPV) DNA is usually integrated into host chromosomes. Multiple integration events are thought to be present within the cells of a polyclonal premalignant lesion and the features that underpin clonal selection of one particular integrant remain poorly understood. We previously used the W12 model system to generate a panel of cervical keratinocyte clones, derived from cells of a low-grade premalignant lesion naturally infected with the major HRHPV type, HPV16. The cells were isolated regardless of their selective advantage and differed only by the site of HPV16 integration into the host genome. We used this resource to test the hypothesis that levels of HPV16 E6/E7 oncogene expression in premalignant cells are regulated epigenetically. We performed a comprehensive analysis of the epigenetic landscape of the integrated HPV16 DNA in selected clones, in which levels of virus oncogene expression per DNA template varied ~6.6-fold. Across the cells examined, higher levels of virus expression per template were associated with more open chromatin at the HPV16 long control region, together with greater loading of chromatin remodelling enzymes and lower nucleosome occupancy. There were higher levels of histone post-translational modification hallmarks of transcriptionally active chromatin and lower levels of repressive hallmarks. There was greater abundance of the active/elongating form of the RNA polymerase-II enzyme (RNAPII-Ser2P), together with CDK9, the component of positive transcription elongation factor b complex responsible for Ser2 phosphorylation. The changes observed were functionally significant, as cells with higher HPV16 expression per template showed greater sensitivity to depletion and/or inhibition of histone acetyltransferases and CDK9 and less sensitivity to histone deacetylase inhibition. We conclude that virus gene expression per template following HPV16 integration is determined through multiple layers of epigenetic regulation, which are likely to contribute to selection of individual cells during cervical carcinogenesis.

Pathogenesis of human papillomavirus-associated mucosal disease

Human papillomaviruses (HPVs) are a necessary cause of carcinoma of the cervix and other mucosal epithelia. Key events in high-risk HPV (HRHPV)-associated neoplastic progression include persistent infection, deregulated expression of virus early genes in basal epithelial cells and genomic instability causing secondary host genomic imbalances. There are multiple mechanisms by which deregulated virus early gene expression may be achieved. Integration of virus DNA into host chromosomes is observed in the majority of cervical squamous cell carcinomas (SCCs), although in ∼15% of cases the virus remains extrachromosomal (episomal). Interestingly, not all integration events provide a growth advantage to basal cervical epithelial cells or lead to increased levels of the virus oncogenes E6 and E7, when compared with episome-containing basal cells. The factors that provide a competitive advantage to some integrants, but not others, are complex and include virus and host contributions. Gene expression from integrated and episomal HRHPV is regulated through host epigenetic mechanisms affecting the virus long control region (LCR), which appear to be of functional importance. New approaches to treating HRHPV-associated mucosal neoplasia include knockout of integrated HRHPV DNA, depletion of virus transcripts and inhibition of virus early gene transcription through targeting or use of epigenetic modifiers. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Human papillomavirus gene expression is controlled by host cell splicing factors

HPVs (human papillomaviruses) infect stratified epithelia and cause a variety of lesions ranging from benign warts to invasive tumours. The virus life cycle is tightly linked to differentiation of the keratinocyte it infects: papillomaviruses modulate host gene expression to ensure efficient virus replication. For example, the viral transcription factor E2 can directly up-regulate, in an epithelial differentiation-dependent manner, cellular SRSFs [SR (serine/arginine-rich) splicing factors] that control constitutive and alternative splicing. Changes in alternative splicing and the mechanisms controlling this for viral mRNAs have been the subject of intense exploration. However, to date experiments have only been carried out in model systems because the genetic systems suitable for studying alternative splicing of viral RNAs in the context of the virus life cycle are relatively recent and technically challenging. Now using these life cycle-supporting systems, our laboratory has identified SR proteins as important players in differentiation-dependent regulation of HPV gene expression. Better understanding of the role of cellular factors in regulating the virus life cycle is needed as it may help development of novel diagnostic approaches and antiviral therapies in the future.

Identification of novel cellular transcription factors that regulate early promoters of human papillomavirus types 18 and 16

BACKGROUND

The long control region (LCR) of human papillomavirus (HPV) regulates early gene transcription by interaction with several viral and cellular transcription factors (TFs).

METHODS

To identify novel TFs that could influence early expression of HPV type 18 (HPV-18) and HPV type 16 (HPV-16), a high-throughput transfection array was used.

RESULTS

Among the 704 TFs tested, 28 activated and 36 inhibited the LCR of HPV-18 by more than 2-fold. For validation, C33 cells were cotransfected with increasing amounts of selected TF expression plasmids in addition to LCR-luciferase vectors of different molecular variants of HPV-18 and HPV-16. Among the TFs identified, only GATA3, FOXA1, and MYC have putative binding sites within the LCR sequence, as indicated using the TRANSFAC database. Furthermore, we demonstrated FOXA1 and MYC in vivo binding to the LCR of both HPV types using chromatin immunoprecipitation assay.

CONCLUSIONS

We identified new TFs implicated in the regulation of the LCR of HPV-18 and HPV-16. Many of these factors are mutated in cancer or are putative cancer biomarkers and could potentially be involved in the regulation of HPV early gene expression.

Human papillomavirus: gene expression, regulation and prospects for novel diagnostic methods and antiviral therapies

Human papillomaviruses (HPVs) cause diseases ranging from benign warts to invasive tumors. A subset of these viruses termed 'high risk' infect the cervix where persistent infection can lead to cervical cancer. Although many HPV genomes have been sequenced, knowledge of virus gene expression and its regulation is still incomplete. This is due in part to the lack, until recently, of suitable systems for virus propagation in the laboratory. HPV gene expression is polycistronic initiating from multiple promoters. Gene regulation occurs at transcriptional, but particularly post-transcriptional levels, including RNA processing, nuclear export, mRNA stability and translation. A close association between the virus replication cycle and epithelial differentiation adds a further layer of complexity. Understanding HPV mRNA expression and its regulation in the different diseases associated with infection may lead to development of novel diagnostic approaches and will reveal key viral and cellular targets for development of novel antiviral therapies.

Stage-associated dynamic activity profile of transcription factors in nasopharyngeal carcinoma progression based on protein/DNA array analysis

Transcription factors (TFs) are crucial modulators of gene regulation during the development and progression of tumors. We previously reported the activation of TFs in nasopharyngeal carcinoma (NPC) cell lines. In this study, we explored the activity profiles of TFs in Protein/DNA array data of a 12-tissue independent set and a 13-tissue pooled set of NPC that included different clinical stages. TFs associated with tumor progression were revealed using a generalized linear model-based regression analysis. Immunohistochemical analysis of clinical NPC samples was used to validate the results of array analysis. We identified 26 TFs that showed increased activities. Of these 26 TFs, 16 were correlated with clinical stages. Activity changes of AP2 and ATF/CREB were confirmed by electrophoretic mobility shift assay (EMSA), and increased expression of AP2α, β, γ, ATF2, and ATF1 in nuclei of tumor cells was associated with clinical stages. In addition, the expressions of AP2α, ATF2, and ATF1 were correlated with those of their target genes (epithelia growth factor receptor (EGFR) and matrix metalloproteinase 2 (MMP-2), respectively). This study provides data and valuable clues that can be used to further investigate the laws of gene transcription regulation in NPC and to identify suitable targets for the development of TF-targeted antitumor agents.

Activities of E7 promoters in the human papillomavirus type 16 genome during cell differentiation

Worldwide, one of the most common cancer forms diagnosed in women is cervical cancer induced by infections with high-risk human papillomaviruses (HPVs) with HPV type 16 (HPV-16) being the most frequently identified. The oncogenicity is caused mainly by expression of the oncogenes E6 and E7 leading to deregulation of the cell cycle control. HPV-16 preferably infects the proliferating cells that will differentiate when they move upwards in the epithelium. The viral gene-expression is tightly coupled to the cellular differentiation program with early gene-expression being initiated in non- or low-differentiated cells and late gene-expression in more differentiated cells. We induced epithelial cells to differentiate by growth in medium with a high calcium concentration and measured the activity of different promoters thought to initiate E6 and/or E7 transcripts. The overall activity of the main promoter, P97, situated in the long control region as well as the two promoters, P441 and P542, in the E6 ORF upstream of the E7 ORF, were decreased during differentiation. However, P441 and P542 were not down-regulated as much as P97. Therefore, we suggest that P441 and P542 regulate gene-expression in differentiated cells.

Papillomavirus interaction with cellular chromatin

High-risk human papillomavirus (HPV) infection is the primary risk factor for cervical cancer. HPVs establish persistent infection by maintaining their genomes as extrachromosomal elements (episomes) that replicate along with host DNA in infected cells. The productive life cycle of HPV is intimately tied to the differentiation program of host squamous epithelium. This review examines the involvement of host chromatin in multiple aspects of the papillomavirus life cycle and the malignant progression of infected host cells. Papillomavirus utilizes host mitotic chromosomes as vehicles for transmitting its genetic materials across the cell cycle. By hitchhiking on host mitotic chromosomes, the virus ensures accurate segregation of the replicated viral episomes to the daughter cells during host cell division. This strategy allows persistent maintenance of the viral episome in the infected cells. In the meantime, the virus subverts the host chromatin-remodeling factors to promote viral transcription and efficient propagation of viral genomes. By associating with the host chromatin, papillomavirus redirects the normal cellular control of chromatin to create a cellular environment conducive to both its own survival and malignant progression of host cells. Comprehensive understanding of HPV-host chromatin interaction will offer new insights into the HPV life cycle as well as chromatin regulation. This virus-host interaction will also provide a paradigm for investigating other episomal DNA tumor viruses that share a similar mechanism for interacting with host chromatin.

Transcriptional regulation of the papillomavirus oncogenes by cellular and viral transcription factors in cervical carcinoma

Human papillomaviruses (HPV) are small DNA viruses that contain a compact and non-redundant genome. HPV, with the help of only few genes, can achieve a complete vegetative cycle specifically in the epidermal and mucosal keratinocytes. Modification of the host cell transcriptional regulation is one of the major ways to regulate the viral production and maturation. The vegetative cycle of papillomaviruses is linked to terminal differentiation of the epithelium and is dependent on the host cell regulatory networks for transcriptional control. The mucosal high risk HPV16 and HPV18 types have been the main models to explore this transcriptional regulation mainly because they are prevalent in cervical cancer as the best studied virally induced cancers in human. In addition, the availability of cell lines, grown from cervical cancers containing integrated HPV16 or 18, represent versatile in vitro models for transcription studies. We will describe here some aspects of the transcriptional regulation that contribute to cell specificity, the basis of which is not yet fully understood despite efforts of numerous groups during the past two decades. Another specificity of small DNA viruses is the multifunctional characteristics of their regulatory proteins due to extreme genomic constraint. We will describe the role played by the viral E2 proteins in the transcriptional repression of the high risk HPV oncogenes and its implication in cervical cancer.

Oncogenic human papilloma virus and cervical pre-cancerous lesions in brothel-based sex workers in India

A community-based cross-sectional study was conducted in brothel-based sex workers of West Bengal, Eastern India, to determine their oncogenic human papillomavirus (HPV) status and the presence of pre-cancerous lesions. A total of 229 sex workers from three districts of West Bengal participated in the study. All the study participants were interviewed with the aid of a pre-tested questionnaire to determine their sociodemographics, risk behaviour and risk perceptions after obtaining informed verbal consent. The interview was followed by collection of cervical cells from all participants using a disposable vaginal speculum and cervical cytobrush. Oncogenic HPV DNA was detected by real-time polymerase chain reaction (PCR). A simultaneous Papanicolaou test ('Pap smear') was performed to detect cervical cytological abnormalities. Overall, the prevalence of oncogenic HPV was found to be 25% (58/229) among the studied population. A subset (n=112) of the sample was tested separately to determine the existence and magnitude of HPV genotypes 16 and 18. The results showed that genotype 16 was prevalent in 10% (11/112), genotype 18 in 7% (8/112) and both genotype 16 and 18 in 7% (8/112). The HPV prevalence rate showed a decreasing trend with age, being 71.4% in the 10-19 years age group, 32.3% in the 20-29 years age group, 18.3% in the 30-39 years age group and 2.5% in the >or=40 years age group (statistically significant differences, P<or=0.00001). Considering the duration of sex work, oncogenic HPV prevalence was found to be 55% (n=21) and 19% (n=35) in sex workers with a sex working duration of <or=1 year and >1 year, respectively. This difference was found to be statistically significant both by univariate and multivariate analysis. In this study, it was observed that sex workers with an average number of daily clients of six or more had an HPV prevalence of 67% (n=6), those with four to five clients had a prevalence of 45% (n=9), those with two to three clients had a prevalence of 30% (n=34) and those with one or less clients had a prevalence of 10% (n=9) (statistically significant differences, P=0.00003). Multivariate analysis showed a statistical association only with a duration of sex work of <or=1 year [odds ratio (OR)=3.3; 95% confidence interval (CI) 1.4-7.6] and daily income of Rupees (Rp) >or=101 (OR=2.5; 95% CI 1.3-5). Regarding pre-cancerous lesions, 2 of 229 sex workers showed the presence of a low-grade squamous intraepithelial lesion along with high-risk HPV. Thus, 1% of the studied population suffer from a pre-cancerous lesion caused by high-risk HPV. This study concludes that young sex workers are particularly vulnerable to high-risk HPV, similar to human immunodeficiency virus (HIV). The observation of older sex workers relatively free from HPV supports the view of acquired immunity against HPV, which needs to be studied in-depth further. There is a need for a suitable community-based intervention programme targeted towards sex workers, with special reference to younger sex workers, for control and prevention of HPV and cervical cancer. Vaccination against HPV for newly entrant sex workers may be an important component for a successful intervention programme.

Regulation of human papillomavirus type 31 gene expression during the differentiation-dependent life cycle through histone modifications and transcription factor binding

The life cycle of high-risk human papillomaviruses is linked to epithelial differentiation with virion production restricted to highly differentiated suprabasal cells. Two major viral promoters direct high-risk HPV gene expression and their activities are dependent upon differentiation. The early promoter controls initiation of transcripts at sites upstream of the E6 open reading frame and is active in both undifferentiated as well as differentiated cells. The late viral promoter directs transcription from a series of heterogeneous start sites in E7 and is activated upon differentiation. In this study, the state of histones as well as the spectrum of transcription factors bound to the two major HPV 31 viral promoters in undifferentiated and differentiated cells were examined using chromatin immunoprecipitation assays. Our studies indicate that, in undifferentiated cells, the chromatin surrounding both promoter regions is in an open, transcriptionally active state as indicated by the presence of dimethylated forms of histone H3 K4 as well as acetylated H3 and acetylated H4. Upon differentiation, there was an increase of four to six fold in the levels of dimethylated H3K4 and acetylated H3 respectively around both promoter regions as well as an increase of approximately nine fold in acetylated H4 at the early promoter. This suggests that nucleosomes of both promoter regions are further activated through histone modifications during differentiation. Chromatin immunoprecipitation assays were also used to examine the binding of transcription factors to the keratinocyte enhancer (KE)/early promoter region in the upstream regulatory region (URR) and late promoter sequences throughout differentiation. Our results suggest that a dynamic change in transcription factor binding occurs in both regions upon differentiation; most notably a significant increase in C/EBP-beta binding to the KE/early promoter region as well as C/EBP-alpha binding to the late promoter region upon differentiation. These increases in binding cannot be solely explained by changes in the total cellular levels of these factors following differentiation, but instead reflect increased binding specific to HPV genomes. Finally, transient expression analyses confirmed that the KE/early promoter region of the URR contributes significantly to the activation of late gene expression and this is consistent with regulation through the combinatorial binding of multiple transcription factors.

Human papillomaviruses activate caspases upon epithelial differentiation to induce viral genome amplification

The life cycle of human papillomaviruses (HPVs) is linked to epithelial differentiation, with late viral events restricted to the uppermost stratified layers. Our studies indicated that HPV activates capases-3, -7, and -9 upon differentiation, whereas minimal activation was observed in differentiating normal keratinocytes. Activation occurred in the absence of significant levels of apoptosis, suggesting a potential role for caspases in the viral life cycle. In support of this, the addition of caspase inhibitors significantly impaired differentiation-dependent viral genome amplification. A conserved caspase cleavage motif was identified in the replication protein E1 ((46)DxxD(49)) that was targeted in vitro by both recombinant caspase-3 and caspase-7. Mutation of this site inhibited amplification of viral genomes, indicating that caspase cleavage is necessary for the productive viral life cycle. Our study demonstrates that HPV activates caspases upon differentiation to facilitate productive viral replication and represents a way by which HPV controls viral gene function in differentiating cells.