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

Proceedings of the 2024 Division of Translational Toxicology Satellite Symposium

The 2024 annual Division of Translational Toxicology (DTT) Satellite Symposium, entitled "Pathology Potpourri," was held in Baltimore, Maryland, at the Society of Toxicologic Pathology's 42nd annual meeting. The goal of this symposium was to present and discuss challenging diagnostic pathology and/or nomenclature issues. This article presents summaries of the speakers' talks along with select images that were used by the audience for voting and discussion. Various lesions and topics covered during the symposium included induced nonneoplastic lesions in the mouse kidney, induced and spontaneous neoplastic lesions in the mouse lung, infectious and proliferative lesions in nonhuman primates, an interesting inflammatory lesion in a transgenic mouse strain, and a lesson on artifact recognition.

Apoptotic Caspases Suppress Expression of Endogenous Retroviruses in HPV31+ Cells That Are Associated with Activation of an Innate Immune Response

Avoidance of an immune response is critical to completion of the human papillomavirus (HPV) life cycle, which occurs in the stratified epithelium and is linked to epithelial differentiation. We previously demonstrated that high-risk HPVs use apoptotic caspases to suppress an antiviral innate immune response during the productive phase of the life cycle. We found that caspase-8 and caspase-3 suppress a type I IFN-β and type III IFN-λ response by disabling the MDA5/MAVS double-stranded RNA (dsRNA) sensing pathway, indicating that immunogenic RNAs increase upon differentiation in HPV+ cells. In this study, we demonstrate that caspase inhibition results in aberrant transcription of a subset of endogenous retroviruses (ERVs) that have been shown to activate an IFN response through dsRNA-sensing pathways. We show that the increase in ERV transcription is accompanied by an enrichment in dsRNA formation. Additionally, we demonstrate that the robust increase in ERV expression requires activation of the JAK/STAT-signaling pathway, indicating that this subset of ERVs is IFN-inducible. Overall, these results suggest a model by which caspase activity blocks the reactivation of ERVs through the JAK/STAT pathway, protecting HPV+ cells from an increase in immunogenic dsRNAs that otherwise would trigger an IFN response that inhibits productive viral replication.

Fibroblast stromal support model for predicting human papillomavirus-associated cancer drug responses

Currently, there are no specific antiviral therapeutic approaches targeting Human papillomaviruses (HPVs), which cause around 5% of all human cancers. Specific antiviral reagents are particularly needed for HPV-related oropharyngeal cancers (HPV+OPCs) whose incidence is increasing and for which there are no early diagnostic tools available. We and others have demonstrated that the estrogen receptor alpha (ERα) is overexpressed in HPV+OPCs, compared to HPV-negative cancers in this region, and that these elevated levels are associated with an improved disease outcome. Utilizing this HPV+-specific overexpression profile, we previously demonstrated that estrogen attenuates the growth and cell viability of HPV+ keratinocytes and HPV+ cancer cells in vitro. Expansion of this work in vivo failed to replicate this sensitization. The role of stromal support from the tumor microenvironment (TME) has previously been tied to both the HPV lifecycle and in vivo therapeutic responses. Our investigations revealed that in vitro co-culture with fibroblasts attenuated HPV+-specific estrogen growth responses. Continuing to monopolize on the HPV+-specific overexpression of ERα, our co-culture models then assessed the suitability of the selective estrogen receptor modulators (SERMs), raloxifene and tamoxifen, and showed growth attenuation in a variety of our models to one or both of these drugs in vitro. Utilization of these SERMs in vivo closely resembled the sensitization predicted by our co-culture models. Therefore, the in vitro fibroblast co-culture model better predicts in vivo responses. We propose that utilization of our co-culture in vitro model can accelerate cancer therapeutic drug discovery.

IMPORTANCE

Human papillomavirus-related cancers (HPV+ cancers) remain a significant public health concern, and specific clinical approaches are desperately needed. In translating drug response data from in vitro to in vivo, the fibroblasts of the adjacent stromal support network play a key role. Our study presents the utilization of a fibroblast 2D co-culture system to better predict translational drug assessments for HPV+ cancers. We also suggest that this co-culture system should be considered for other translational approaches. Predicting even a portion of treatment paradigms that may fail in vivo with a co-culture model will yield significant time, effort, resource, and cost efficiencies.

Abortive Infection of Animal Cells: What Goes Wrong

Even if a virus successfully binds to a cell, defects in any of the downstream steps of the viral life cycle can preclude the production of infectious virus particles. Such abortive infections are likely common in nature and can provide fundamental insights into the cell and host tropism of viral pathogens. Research over the past 60 years has revealed an incredible diversity of abortive infections by DNA and RNA viruses in various animal cell types. Here we discuss the general causes of abortive infections and provide specific examples from the literature to illustrate the range of abortive infections that have been reported. We also discuss how abortive infections can have critical roles in shaping host immune responses and in the development of virus-induced cancers. Finally, we describe how abortive infections can be applied to basic and clinical research, underscoring the importance of understanding these fascinating aspects of virus biology.

HPV induced R-loop formation represses innate immune gene expression while activating DNA damage repair pathways

R-loops are trimeric nucleic acid structures that form when an RNA molecule hybridizes with its complementary DNA strand, displacing the opposite strand. These structures regulate transcription as well as replication, but aberrant R-loops can form, leading to DNA breaks and genomic instability if unresolved. R-loop levels are elevated in many cancers as well as cells that maintain high-risk human papillomaviruses. We investigated how the distribution as well as function of R-loops changed between normal keratinocytes and HPV positive cells derived from a precancerous lesion of the cervix (CIN I). The levels of R-loops associated with cellular genes were found to be up to 10-fold higher in HPV positive cells than in normal keratinocytes while increases at ALU1 elements increased by up to 500-fold. The presence of enhanced R-loops resulted in altered levels of gene transcription, with equal numbers increased as decreased. While no uniform global effects on transcription due to the enhanced levels of R-loops were detected, genes in several pathways were coordinately increased or decreased in expression only in the HPV positive cells. This included the downregulation of genes in the innate immune pathway, such as DDX58, IL-6, STAT1, IFN-β, and NLRP3. All differentially expressed innate immune genes dependent on R-loops were also associated with H3K36me3 modified histones. Genes that were upregulated by the presence of R-loops in HPV positive cells included those in the DNA damage repair such as ATM, ATRX, and members of the Fanconi Anemia pathway. These genes exhibited a linkage between R-loops and H3K36me3 as well as γH2AX histone marks only in HPV positive cells. These studies identify a potential link in HPV positive cells between DNA damage repair as well as innate immune regulatory pathways with R-loops and γH2AX/H3K36me3 histone marks that may contribute to regulating important functions for HPV pathogenesis.

HPV Infections-Classification, Pathogenesis, and Potential New Therapies

To date, more than 400 types of human papillomavirus (HPV) have been identified. Despite the creation of effective prophylactic vaccines against the most common genital HPVs, the viruses remain among the most prevalent pathogens found in humans. According to WHO data, they are the cause of 5% of all cancers. Even more frequent are persistent and recurrent benign lesions such as genital and common warts. HPVs are resistant to many disinfectants and relatively unsusceptible to external conditions. There is still no drug available to inhibit viral replication, and treatment is based on removing lesions or stimulating the host immune system. This paper presents the systematics of HPV and the differences in HPV structure between different genetic types, lineages, and sublineages, based on the literature and GenBank data. We also present the pathogenesis of diseases caused by HPV, with a special focus on the role played by E6, E7, and other viral proteins in the development of benign and cancerous lesions. We discuss further prospects for the treatment of HPV infections, including, among others, substances that block the entry of HPV into cells, inhibitors of viral early proteins, and some substances of plant origin that inhibit viral replication, as well as new possibilities for therapeutic vaccines.

Molecular aspects of cervical cancer: a pathogenesis update

Cervical cancer (CC) is a significant health problem, especially in low-income countries. Functional studies on the human papillomavirus have generated essential advances in the knowledge of CC. However, many unanswered questions remain. This mini-review discusses the latest results on CC pathogenesis, HPV oncogenesis, and molecular changes identified through next-generation technologies. Interestingly, the percentage of samples with HPV genome integrations correlates with the degree of the cervical lesions, suggesting a role in the development of CC. Also, new functions have been described for the viral oncoproteins E5, E6, and E7, resulting in the acquisition and maintenance of cancer hallmarks, including proliferation, immune response evasion, apoptosis, and genomic instability. Remarkably, E5 oncoprotein affects signaling pathways involved in the expression of interferon-induced genes and EGFR-induced proliferation, while E6 and E7 oncoproteins regulate the DNA damage repair and cell cycle continuity pathways. Furthermore, next-generation technologies provide vast amounts of information, increasing our knowledge of changes in the genome, transcriptome, proteome, metabolome, and epigenome in CC. These studies have identified novel molecular traits associated with disease susceptibility, degree of progression, treatment response, and survival as potential biomarkers and therapeutic targets.

Human Papillomavirus Infections and the Role Played by Cervical and Cervico-Vaginal Microbiota-Evidence from Next-Generation Sequencing Studies

This comprehensive review encompasses studies examining changes in the cervical and cervico-vaginal microbiota (CM and CVM) in relation to human papillomavirus (HPV) using next-generation sequencing (NGS) technology. HPV infection remains a prominent global health concern, with a spectrum of manifestations, from benign lesions to life-threatening cervical cancers. The CM and CVM, a unique collection of microorganisms inhabiting the cervix/vagina, has emerged as a critical player in cervical health. Recent research has indicated that disruptions in the CM and CVM, characterized by a decrease in Lactobacillus and the overgrowth of other bacteria, might increase the risk of HPV persistence and the progression of cervical abnormalities. This alteration in the CM or CVM has been linked to a higher likelihood of HPV infection and cervical dysplasia. NGS technology has revolutionized the study of the cervical microbiome, providing insights into microbial diversity, dynamics, and taxonomic classifications. Bacterial 16S rRNA gene sequencing, has proven invaluable in characterizing the cervical microbiome, shedding light on its role in HPV infections and paving the way for more tailored strategies to combat cervical diseases. NGS-based studies offer personalized insights into an individual's cervical microbiome. This knowledge holds promise for the development of novel diagnostic tools, targeted therapies, and preventive interventions for cervix-related conditions, including cervical cancer.

Impact of HPV strains on molecular mechanisms of cervix cancer

PURPOSE

Cervical cancer accounts for a high number of deaths worldwide. Risk factors are extensive for cervix cancer but Human papillomavirus (HPV) plays a prime role in its development. Different strains of HPV are prevalent globally, which show different grades of mortality and morbidity among women. This study is planned to evaluate the molecular mechanism of different strains of HPV infection and progression leading to cervix cancer.

METHODS

This review includes different research articles on cervix cancer progression reported from India and all over the world.

RESULTS

HPV 16 and 18 are prevalent strains using heparan sulfate-independent and dependent pathways for viral replication inside the cell. It also uses transcription mechanisms through NF-kappa B, FOXA-1, and AP-1 genes while strains like HPV-35, 45, and 52 are also predominant in India, which showed a very slow mechanism of progression due to which mortality rate is low after their infection with these strains.

CONCLUSION

HPV uses E6 and E7 proteins which activate NF-kappa B and AP-1 pathway which suppresses the tumor suppressor gene and activates cytokine production, causing inflammation and leading to a decrease in apoptosis due to Caspase-3 activation. In contrast, the E7 protein involves HOXA genes and decreases apoptotic factors due to which mortality and incidence rates are low in viruses that use E7 motifs. Some HPV strains employ the cap-dependent pathway, which is also associated with lower mortality and infection rates.

Interplay between the DNA damage response and the life cycle of DNA tumor viruses

Approximately 20 % of human cancers are associated with virus infection. DNA tumor viruses can induce tumor formation in host cells by disrupting the cell's DNA replication and repair mechanisms. Specifically, these viruses interfere with the host cell's DNA damage response (DDR), which is a complex network of signaling pathways that is essential for maintaining the integrity of the genome. DNA tumor viruses can disrupt these pathways by expressing oncoproteins that mimic or inhibit various DDR components, thereby promoting genomic instability and tumorigenesis. Recent studies have highlighted the molecular mechanisms by which DNA tumor viruses interact with DDR components, as well as the ways in which these interactions contribute to viral replication and tumorigenesis. Understanding the interplay between DNA tumor viruses and the DDR pathway is critical for developing effective strategies to prevent and treat virally associated cancers. In this review, we discuss the current state of knowledge regarding the mechanisms by which human papillomavirus (HPV), merkel cell polyomavirus (MCPyV), Kaposi's sarcoma-associated herpesvirus (KSHV), and Epstein-Barr virus (EBV) interfere with DDR pathways to facilitate their respective life cycles, and the consequences of such interference on genomic stability and cancer development.

Recent advancement of nanomedicine-based targeted delivery for cervical cancer treatment

Cervical cancer is a huge worldwide health burden, impacting women in impoverished nations in particular. Traditional therapeutic approaches, such as surgery, radiation therapy, and chemotherapy, frequently result in systemic toxicity and ineffectiveness. Nanomedicine has emerged as a viable strategy for targeted delivery of therapeutic drugs to cancer cells while decreasing off-target effects and increasing treatment success in recent years. Nanomedicine for cervical cancer introduces several novel aspects that distinguish it from previous treatment options such as tailored delivery system, precision targeting, combination therapies, real-time monitoring and diverse nanocarriers to overcome the limitations of one another. This abstract presents recent advances in nanomedicine-based tailored delivery systems for the treatment of cervical cancer. Liposomes, polymeric nanoparticles, dendrimers, and carbon nanotubes have all been intensively studied for their ability to transport chemotherapeutic medicines, nucleic acids, and imaging agents to cervical cancer cells. Because of the way these nanocarriers are designed, they may cross biological barriers and preferentially aggregate at the tumor site, boosting medicine concentration and lowering negative effects on healthy tissues. Surface modification of nanocarriers with targeting ligands like antibodies, peptides, or aptamers improves specificity for cancer cells by identifying overexpressed receptors or antigens on the tumor surface. Furthermore, nanomedicine-based techniques have made it possible to co-deliver numerous therapeutic drugs, allowing for synergistic effects and overcoming drug resistance. In preclinical and clinical investigations, combination treatments comprising chemotherapeutic medicines, gene therapy, immunotherapy, and photodynamic therapy have showed encouraging results, opening up new avenues for individualized and multimodal treatment regimens. Furthermore, the inclusion of contrast agents and imaging probes into nanocarrier systems has enabled real-time monitoring and imaging of treatment response. This enables the assessment of therapy efficacy, the early diagnosis of recurrence, and the optimization of treatment regimens.

p53-dependent R-loop formation and HPV pathogenesis

R-loops are trimeric RNA: DNA hybrids that are important physiological regulators of transcription; however, their aberrant formation or turnover leads to genomic instability and DNA breaks. High-risk human papillomaviruses (HPV) are the causative agents of genital as well as oropharyngeal cancers and exhibit enhanced amounts of DNA breaks. The levels of R-loops were found to be increased up to 50-fold in cells that maintain high-risk HPV genomes and were readily detected in squamous cell cervical carcinomas in vivo but not in normal cells. The high levels of R-loops in HPV-positive cells were present on both viral and cellular sites together with RNase H1, an enzyme that controls their resolution. Depletion of RNase H1 in HPV-positive cells further increased R-loop levels, resulting in impaired viral transcription and replication along with reduced expression of the DNA repair genes such as FANCD2 and ATR, both of which are necessary for viral functions. Overexpression of RNase H1 decreased total R-loop levels, resulting in a reduction of DNA breaks by over 50%. Furthermore, increased RNase H1 expression blocked viral transcription and replication while enhancing the expression of factors in the innate immune regulatory pathway. This suggests that maintaining elevated R-loop levels is important for the HPV life cycle. The E6 viral oncoprotein was found to be responsible for inducing high levels of R-loops by inhibiting p53's transcriptional activity. Our studies indicate that high R-loop levels are critical for HPV pathogenesis and that this depends on suppressing the p53 pathway.

Identification of HPV oncogene and host cell differentiation associated cellular heterogeneity in cervical cancer via single-cell transcriptomic analysis

Human Papillomaviruses (HPVs) are associated with around 5-10% of human cancer, notably nearly 99% of cervical cancer. The mechanisms HPV interacts with stratified epithelium (differentiated layers) during the viral life cycle, and oncogenesis remain unclear. In this study, we used single-cell transcriptome analysis to study viral gene and host cell differentiation-associated heterogeneity of HPV-positive cervical cancer tissue. We examined the HPV16 genes - E1, E6, and E7, and found they expressed differently across nine epithelial clusters. We found that three epithelial clusters had the highest proportion of HPV-positive cells (33.6%, 37.5%, and 32.4%, respectively), while two exhibited the lowest proportions (7.21% and 5.63%, respectively). Notably, the cluster with the most HPV-positive cells deviated significantly from normal epithelial layer markers, exhibiting functional heterogeneity and altered epithelial structuring, indicating that significant molecular heterogeneity existed in cancer tissues and that these cells exhibited unique/different gene signatures compared with normal epithelial cells. These HPV-positive cells, compared to HPV-negative, showed different gene expressions related to the extracellular matrix, cell adhesion, proliferation, and apoptosis. Further, the viral oncogenes E6 and E7 appeared to modify epithelial function via distinct pathways, thus contributing to cervical cancer progression. We investigated the HPV and host transcripts from a novel viewpoint focusing on layer heterogeneity. Our results indicated varied HPV expression across epithelial clusters and epithelial heterogeneity associated with viral oncogenes, contributing biological insights to this critical field of study.

Identification of HPV oncogene and host cell differentiation associated cellular heterogeneity in cervical cancer via single-cell transcriptomic analysis

Human Papillomaviruses (HPVs) are associated with around 5%-10% of human cancer, notably nearly 99% of cervical cancer. The mechanisms HPV interacts with stratified epithelium (differentiated layers) during the viral life cycle, and oncogenesis remain unclear. In this study, we used single-cell transcriptome analysis to study viral gene and host cell differentiation-associated heterogeneity of HPV-positive cervical cancer tissue. We examined the HPV16 genes-E1, E6, and E7, and found they expressed differently across nine epithelial clusters. We found that three epithelial clusters had the highest proportion of HPV-positive cells (33.6%, 37.5%, and 32.4%, respectively), while two exhibited the lowest proportions (7.21% and 5.63%, respectively). Notably, the cluster with the most HPV-positive cells deviated significantly from normal epithelial layer markers, exhibiting functional heterogeneity and altered epithelial structuring, indicating that significant molecular heterogeneity existed in cancer tissues and that these cells exhibited unique/different gene signatures compared with normal epithelial cells. These HPV-positive cells, compared to HPV-negative, showed different gene expressions related to the extracellular matrix, cell adhesion, proliferation, and apoptosis. Further, the viral oncogenes E6 and E7 appeared to modify epithelial function via distinct pathways, thus contributing to cervical cancer progression. We investigated the HPV and host transcripts from a novel viewpoint focusing on layer heterogeneity. Our results indicated varied HPV expression across epithelial clusters and epithelial heterogeneity associated with viral oncogenes, contributing biological insights to this critical field of study.

Molecular markers predicting the progression and prognosis of human papillomavirus-induced cervical lesions to cervical cancer

INTRODUCTION

Persistent Human Papillomavirus (HPV) infection is linked to 99% of cervical cancer (CC) cases. HPV types 16 and 18 alone result in 75% of CC cases and thus are considered to be high-risk types (HR-HPV). CC is the third most common cancer among women globally. Approximately, 7000 patients die from it yearly. It is worthy to note that not every patient with HPV precancerous lesions will progress to CC.

OBJECTIVES

The objectives of this review is to explore the utilization of molecular and viral biomarkers as a tool for early detection and prediction of HPV-induced cervical lesions that might progress to CC.

METHODS

The data bases PubMed, Google Scholar, EBSCO were searched using keywords CC screening, HPV, and recent molecular biomarkers. The search time frame was within the last 7 years. Studies on HPV-induced cancers other than CC were excluded; a total of 200 eligible articles were retrieved.

RESULTS

In this review we explored the current literature about HPV virology, virulence genes and early diagnostic/prognostic molecular biomarkers in CC. The oncogenic property of HPV is attributed to viral expression of various early proteins (E5, E6, E7). The interaction between viral oncoproteins and the cellular genetic apparatus alters the expression of many genes at different phases of the disease. There was an association between cervical lesions induced by HR-HPV and the overexpression of markers of oxidative DNA damage and other proteins. The markers p16INK4a, programmed cell death-1 (PD-1)/programmed cell death ligand 1, mismatch repair enzymes (MMR), miRNA-377, claudin family (CLDN) are dysregulated and are associated with high risk lesions. Furthermore, advanced older cervical lesions were associated with high methylation levels and higher risk to progress to CC.

CONCLUSION

Adding different the above markers to the CC screening program scheme might offer a triage for prioritizing patient management.

The SETD2 Methyltransferase Supports Productive HPV31 Replication through the LEDGF/CtIP/Rad51 Pathway

The human papillomavirus (HPV) life cycle takes place in the stratified epithelium, with the productive phase being activated by epithelial differentiation. The HPV genome is histone-associated, and the life cycle is epigenetically regulated, in part, by histone tail modifications that facilitate the recruitment of DNA repair factors that are required for viral replication. We previously showed that the SETD2 methyltransferase facilitates the productive replication of HPV31 through the trimethylation of H3K36 on viral chromatin. SETD2 regulates numerous cellular processes, including DNA repair via homologous recombination (HR) and alternative splicing, through the recruitment of various effectors to histone H3 lysine 36 trimethylation (H3K36me3). We previously demonstrated that the HR factor Rad51 is recruited to HPV31 genomes and is required for productive replication; however, the mechanism of Rad51 recruitment has not been defined. SET domain containing 2 (SETD2) promotes the HR repair of double-strand breaks (DSBs) in actively transcribed genes through the recruitment of carboxy-terminal binding protein (CtBP)-interacting protein (CtIP) to lens epithelium-derived growth factor (LEDGF)-bound H3K36me3, which promotes DNA end resection and thereby allows for the recruitment of Rad51 to damaged sites. In this study, we found that reducing H3K36me3 through the depletion of SETD2 or the overexpression of an H3.3K36M mutant leads to an increase in γH2AX, which is a marker of damage, on viral DNA upon epithelial differentiation. This is coincident with decreased Rad51 binding. Additionally, LEDGF and CtIP are bound to HPV DNA in a SETD2-dependent and H3K36me3-dependent manner, and they are required for productive replication. Furthermore, CtIP depletion increases DNA damage on viral DNA and blocks Rad51 recruitment upon differentiation. Overall, these studies indicate that H3K36me3 enrichment on transcriptionally active viral genes promotes the rapid repair of viral DNA upon differentiation through the LEDGF-CtIP-Rad51 axis. IMPORTANCE The productive phase of the HPV life cycle is restricted to the differentiating cells of the stratified epithelium. The HPV genome is histone-associated and subject to epigenetic regulation, though the manner in which epigenetic modifications contribute to productive replication is largely undefined. In this study, we demonstrate that SETD2-mediated H3K36me3 on HPV31 chromatin promotes productive replication through the repair of damaged DNA. We show that SETD2 facilitates the recruitment of the homologous recombination repair factors CtIP and Rad51 to viral DNA through LEDGF binding to H3K36me3. CtIP is recruited to damaged viral DNA upon differentiation, and, in turn, recruits Rad51. This likely occurs through the end resection of double-strand breaks. SETD2 trimethylates H3K36me3 during transcription, and active transcription is necessary for Rad51 recruitment to viral DNA. We propose that the enrichment of SETD2-mediated H3K36me3 on transcriptionally active viral genes upon differentiation facilitates the repair of damaged viral DNA during the productive phase of the viral life cycle.

The interactions between PML nuclear bodies and small and medium size DNA viruses

Promyelocytic leukemia nuclear bodies (PM NBs), often referred to as membraneless organelles, are dynamic macromolecular protein complexes composed of a PML protein core and other transient or permanent components. PML NBs have been shown to play a role in a wide variety of cellular processes. This review describes in detail the diverse and complex interactions between small and medium size DNA viruses and PML NBs that have been described to date. The PML NB components that interact with small and medium size DNA viruses include PML protein isoforms, ATRX/Daxx, Sp100, Sp110, HP1, and p53, among others. Interaction between viruses and components of these NBs can result in different outcomes, such as influencing viral genome expression and/or replication or impacting IFN-mediated or apoptotic cell responses to viral infection. We discuss how PML NB components abrogate the ability of adenoviruses or Hepatitis B virus to transcribe and/or replicate their genomes and how papillomaviruses use PML NBs and their components to promote their propagation. Interactions between polyomaviruses and PML NBs that are poorly understood but nevertheless suggest that the NBs can serve as scaffolds for viral replication or assembly are also presented. Furthermore, complex interactions between the HBx protein of hepadnaviruses and several PML NBs-associated proteins are also described. Finally, current but scarce information regarding the interactions of VP3/apoptin of the avian anellovirus with PML NBs is provided. Despite the considerable number of studies that have investigated the functions of the PML NBs in the context of viral infection, gaps in our understanding of the fine interactions between viruses and the very dynamic PML NBs remain. The complexity of the bodies is undoubtedly a great challenge that needs to be further addressed.

Human papillomavirus in the setting of immunodeficiency: Pathogenesis and the emergence of next-generation therapies to reduce the high associated cancer risk

Human papillomavirus (HPV), a common sexually transmitted virus infecting mucosal or cutaneous stratified epithelia, is implicated in the rising of associated cancers worldwide. While HPV infection can be cleared by an adequate immune response, immunocompromised individuals can develop persistent, treatment-refractory, and progressive disease. Primary immunodeficiencies (PIDs) associated with HPV-related disease include inborn errors of GATA, EVER1/2, and CXCR4 mutations, resulting in defective cellular function. People living with secondary immunodeficiency (e.g. solid-organ transplants recipients of immunosuppression) and acquired immunodeficiency (e.g. concurrent human immunodeficiency virus (HIV) infection) are also at significant risk of HPV-related disease. Immunocompromised people are highly susceptible to the development of cutaneous and mucosal warts, and cervical, anogenital and oropharyngeal carcinomas. The specific mechanisms underlying high-risk HPV-driven cancer development in immunocompromised hosts are not well understood. Current treatments for HPV-related cancers include surgery with adjuvant chemotherapy and/or radiotherapy, with clinical trials underway to investigate the use of anti-PD-1 therapy. In the setting of HIV co-infection, persistent high-grade anal intraepithelial neoplasia can occur despite suppressive antiretroviral therapy, resulting in an ongoing risk for transformation to overt malignancy. Although therapeutic vaccines against HPV are under development, the efficacy of these in the setting of PID, secondary- or acquired- immunodeficiencies remains unclear. RNA-based therapeutic targeting of the HPV genome or mRNA transcript has become a promising next-generation therapeutic avenue. In this review, we summarise the current understanding of HPV pathogenesis, immune evasion, and malignant transformation, with a focus on key PIDs, secondary immunodeficiencies, and HIV infection. Current management and vaccine regimes are outlined in relation to HPV-driven cancer, and specifically, the need for more effective therapeutic strategies for immunocompromised hosts. The recent advances in RNA-based gene targeting including CRISPR and short interfering RNA (siRNA), and the potential application to HPV infection are of great interest. An increased understanding of both the dysregulated immune responses in immunocompromised hosts and of viral persistence is essential for the design of next-generation therapies to eliminate HPV persistence and cancer development in the most at-risk populations.

Deregulation of host gene expression by HPV16 E8^E2 knock-out genomes is due to increased productive replication

Productive replication of human papillomaviruses (HPV) only takes place in differentiating keratinocytes. The HPV16 E8^E2 protein acts as a repressor of viral gene expression and genome replication and HPV16 E8^E2 knock-out (E8-) genomes display enhanced viral late protein expression in differentiated cells. Global transcriptome analysis of differentiated HPV16 wild-type and E8-cell lines revealed a small number of differentially expressed genes which are not related to cell cycle, DNA metabolism or keratinocyte differentiation. The analysis of selected genes suggested that deregulation requires cell differentiation and positively correlated with the expression of viral late, not early transcripts. Consistent with this, the additional knock-out of the viral E4 and E5 genes, which are known to enhance productive replication, attenuated the deregulation of these host cell genes. In summary, these data reveal that productive HPV16 replication modulates host cell transcription.

Downregulation of Sonic hedgehog signaling induces G2-arrest in genital warts

BACKGROUND

Human papillomavirus (HPV) infected keratinocyte dysfunction results in the formation of genital warts, and the specific role of Sonic hedgehog (SHh) signaling in genital warts remains elusive. Thus, this study aimed to identify the correlation between wart formation and SHh signaling.

MATERIALS AND METHODS

In this study, nine male patients with genital warts were recruited, and the expression of SHh and its downstream signal molecules Patched-1 and GLI family zinc finger 1 (Ptch1 and Gli1) was detected. Moreover, G2-phase cells in the collected genital warts samples were assessed with normal foreskin samples as a comparison. HPV6/11 were detected via in situ hybridization (ISH), and SHh expression of the corresponding paraffin sections was determined via immunohistochemical staining (IHC). In addition, an in vitro down-regulated SHh model was constructed by siRNA transfection of the HaCaT cell line, and the cell cycle was detected at 36 h by flow cytometry with propidium iodide staining.

RESULTS

SHh, Ptch1, and Gli1 in warts were significantly downregulated in the condyloma acuminatum (CA) group compared to the normal foreskin group. G2-phase cells in the middle section of the spinous layer of CA wart tissues were significantly increased. Moreover, the expression of HPV-DNA was amplified and negatively correlated with SHh activity in CA wart tissues. Lastly, the downregulation of SHh-induced G2 arrest in vitro.

CONCLUSIONS

The downregulation of the SHh signaling promotes HPV replication and the formation of warts by inducing G2/M arrest in the keratinocytes of CA.

Human Papilloma Virus-Infected Cells

Human papillomavirus (HPV) is associated with infection of different tissues, such as the cervix, anus, vagina, penis, vulva, oropharynx, throat, tonsils, back of the tongue, skin, the lungs, among other tissues. HPV infection may or may not be associated with the development of cancer, where HPVs not related to cancer are defined as low-risk HPVs and are associated with papillomatosis disease. In contrast, high-risk HPVs (HR-HPVs) are associated with developing cancers in areas that HR-HPV infects, such as the cervix. In general, infection of HPV target cells is regulated by specific molecules and receptors that induce various conformational changes of HPV capsid proteins, allowing activation of HPV endocytosis mechanisms and the arrival of the HPV genome to the human cell nucleus. After the transcription of the HPV genome, the HPV genome duplicates exponentially to lodge in a new HPV capsid, inducing the process of exocytosis of HPV virions and thus releasing a new HPV viral particle with a high potential of infection. This infection process allows the HPV viral life cycle to conclude and enables the growth of HPV virions. Understanding the entire infection process has been a topic that researchers have studied and developed for decades; however, there are many things to still understand about HPV infection. A thorough understanding of these HPV infection processes will allow new potential treatments for HPV-associated cancer and papillomatosis. This chapter focuses on HPV infection, the process that will enable HPV to complete its HPV life cycle, emphasizing the critical role of different molecules in allowing this infection and its completion during the HPV viral life cycle.

Regulation of the Innate Immune Response during the Human Papillomavirus Life Cycle

High-risk human papillomaviruses (HR HPVs) are associated with multiple human cancers and comprise 5% of the human cancer burden. Although most infections are transient, persistent infections are a major risk factor for cancer development. The life cycle of HPV is intimately linked to epithelial differentiation. HPVs establish infection at a low copy number in the proliferating basal keratinocytes of the stratified epithelium. In contrast, the productive phase of the viral life cycle is activated upon epithelial differentiation, resulting in viral genome amplification, high levels of late gene expression, and the assembly of virions that are shed from the epithelial surface. Avoiding activation of an innate immune response during the course of infection plays a key role in promoting viral persistence as well as completion of the viral life cycle in differentiating epithelial cells. This review highlights the recent advances in our understanding of how HPVs manipulate the host cell environment, often in a type-specific manner, to suppress activation of an innate immune response to establish conditions supportive of viral replication.

Apoptotic caspases suppress an MDA5-driven IFN response during productive replication of human papillomavirus type 31

Human papillomaviruses (HPVs) infect the basal proliferating cells of the stratified epithelium, but the productive phase of the life cycle (consisting of viral genome amplification, late gene expression, and virion assembly) is restricted to the highly differentiated suprabasal cells. While much is known regarding the mechanisms that HPVs use to block activation of an innate immune response in undifferentiated cells, little is known concerning how HPV prevents an interferon (IFN) response upon differentiation. Here, we demonstrate that high-risk HPVs hijack a natural function of apoptotic caspases to suppress an IFN response in differentiating epithelial cells. We show that caspase inhibition results in the secretion of type I and type III IFNs that can act in a paracrine manner to induce expression of interferon-stimulated genes (ISGs) and block productive replication of HPV31. Importantly, we demonstrate that the expression of IFNs is triggered by the melanoma differentiation-associated gene 5 (MDA5)-mitochondrial antiviral-signaling protein (MAVS)-TBK1 (TANK-binding kinase 1) pathway, signifying a response to double-stranded RNA (dsRNA). Additionally, we identify a role for MDA5 and MAVS in restricting productive viral replication during the normal HPV life cycle. This study identifies a mechanism by which HPV reprograms the cellular environment of differentiating cells through caspase activation, co-opting a nondeath function of proteins normally involved in apoptosis to block antiviral signaling and promote viral replication.

HPV16 and HPV18 Genome Structure, Expression, and Post-Transcriptional Regulation

Human papillomaviruses (HPV) are a group of small non-enveloped DNA viruses whose infection causes benign tumors or cancers. HPV16 and HPV18, the two most common high-risk HPVs, are responsible for ~70% of all HPV-related cervical cancers and head and neck cancers. The expression of the HPV genome is highly dependent on cell differentiation and is strictly regulated at the transcriptional and post-transcriptional levels. Both HPV early and late transcripts differentially expressed in the infected cells are intron-containing bicistronic or polycistronic RNAs bearing more than one open reading frame (ORF), because of usage of alternative viral promoters and two alternative viral RNA polyadenylation signals. Papillomaviruses proficiently engage alternative RNA splicing to express individual ORFs from the bicistronic or polycistronic RNA transcripts. In this review, we discuss the genome structures and the updated transcription maps of HPV16 and HPV18, and the latest research advances in understanding RNA cis-elements, intron branch point sequences, and RNA-binding proteins in the regulation of viral RNA processing. Moreover, we briefly discuss the epigenetic modifications, including DNA methylation and possible APOBEC-mediated genome editing in HPV infections and carcinogenesis.

Consideration of underlying immunodeficiency in refractory or recalcitrant warts: A review of the literature

Although the exact mechanisms have yet to be elucidated, it is clear that cellular immunity plays a role in clearance of human papillomavirus (HPV) infections as it relates to the development of warts. Patients with extensive, recalcitrant, or treatment‐refractory warts may have an underlying immune system impairment at the root of HPV susceptibility. Early recognition of genetic disorders associated with immunologic defects that allow for recalcitrant HPV infection may expedite appropriate treatment for patients. Early recognition is often pivotal in preventing subsequent morbidity and/or mortality that may arise from inborn errors of immunity, such as WHIM (Warts, Hypogammaglobulinemia, Infections, Myelokathexis) syndrome. Among these, cervical cancer is one of the most common malignancies associated with HPV, can be fatal if not treated early, and is seen more frequently in patients with underlying immune deficiencies. A review of diseases with susceptibility to HPV provides clues to understanding the pathophysiology of warts. We also present diagnostic guidance to facilitate the recognition of inborn errors of immunity in patients with extensive and/or recalcitrant HPV infections.

Phthalocyanine and Its Formulations: A Promising Photosensitizer for Cervical Cancer Phototherapy

Cervical cancer is one of the most common causes of cancer-related deaths in women worldwide. Despite advances in current therapies, women with advanced or recurrent disease present poor prognosis. Photodynamic therapy (PDT) has emerged as an effective therapeutic alternative to treat oncological diseases such as cervical cancer. Phthalocyanines (Pcs) are considered good photosensitizers (PS) for PDT, although most of them present high levels of aggregation and are lipophilic. Despite many investigations and encouraging results, Pcs have not been approved as PS for PDT of invasive cervical cancer yet. This review presents an overview on the pathophysiology of cervical cancer and summarizes the most recent developments on the physicochemical properties of Pcs and biological results obtained both in vitro in tumor-bearing mice and in clinical tests reported in the last five years. Current evidence indicates that Pcs have potential as pharmaceutical agents for anti-cervical cancer therapy. The authors firmly believe that Pc-based formulations could emerge as a privileged scaffold for the establishment of lead compounds for PDT against different types of cervical cancer.

Integrative meta-analysis of gene expression profiles identifies FEN1 and ENDOU as potential diagnostic biomarkers for cervical squamous cell carcinoma

Cervical carcinoma is a global public health burden. Given that it is usually asymptomatic at potentially curative stages, the development of clinically accurate tests is critical for early detection and individual risk stratification. The present study performed an integrative meta-analysis of the transcriptomes from 10 cervical carcinoma cohorts, with the aim of identifying biomarkers that are associated with malignant transformation of cervical epithelium, and establish their clinical applicability. From among the top ranked differentially expressed genes, flap structure-specific endonuclease 1 (FEN1) and poly (U)-specific endoribonuclease (ENDOU) were selected for further validation, and their clinical applicability was assessed using immunohistochemically stained microarrays comprising 110 tissue cores, using p16 and Ki67 staining as the comparator tests. The results demonstrated that FEN1 expression was significantly upregulated in 65% of tumor specimens (P=0.0001), with no detectable expression in the non-tumor tissues. Furthermore, its expression was significantly associated with Ki67 staining in tumor samples (P<0.0001), but no association was observed with p16 expression or the presence of human papilloma virus types 16/18, patient age, tumor grade or stage. FEN1 staining demonstrated lower sensitivity than p16 (69.3 vs. 96.8%) and Ki67 (69.3 vs. 76.3%); however, the specificity was identical to p16 and higher than that of Ki67 (100 vs. 71.4%).ENDOU staining was consistent with the microarray results, demonstrating 1% positivity in tumors and 40% positivity in non-tumor tissues. Gene set enrichment analysis of cervical tumors overexpressing FEN1 revealed its association with enhanced growth factor signaling, immune response inhibition and extracellular matrix remodeling, whereas tumors with low ENDOU expression exhibited inhibition of epithelial development and differentiation processes. Taken together, the results of the present study demonstrate the feasibility of the integrative meta-analysis approach to identify relevant biomarkers associated with cervical carcinogenesis. Thus, FEN1 and ENDOU may be useful diagnostic biomarkers for squamous cervical carcinoma. However, further studies are required to determine their diagnostic performance in larger patient cohorts and validate the results presented here.

Spatial and Functional Organization of Human Papillomavirus Replication Foci in the Productive Stage of Infection

The life cycle of human papillomavirus (HPV) depends on keratinocyte differentiation as the virus modulates and takes advantage of cellular pathways to replicate its genome and assemble viral particles in differentiated cells. Viral genomes are amplified in nuclear replication foci in differentiated keratinocytes, and DNA repair factors from the DNA damage response signaling pathway are recruited to replicate viral DNA. The HPV genome is associated with cellular histones at all stages of the infectious cycle, and here, we show that the histone variant macroH2A1 is bound to the HPV genome and enriched in viral replication foci in differentiated cells. macroH2A1 isoforms play important roles in cellular transcriptional repression, double-strand break repair, and replication stress. The viral E8^E2 protein also binds to the HPV genome and inhibits viral replication and gene expression by recruiting NCoR/SMRT complexes. We show here that E8^E2 and SMRT also localize within replication foci, though independently from macroH2A1. Conversely, transcription complexes containing RNA polymerase II and Brd4 are located on the surface of the foci. Foci generated with an HPV16 E8^E2 mutant genome are not enriched for SMRT or macroH2A1 but contain transcriptional complexes throughout the foci. We propose that both the cellular macroH2A1 protein and viral E8^E2 protein help to spatially separate replication and transcription activities within viral replication foci. IMPORTANCE Human papillomaviruses are small DNA viruses that cause chronic infection of cutaneous and mucosal epithelium. In some cases, persistent infection with HPV can result in cancer, and 5% of human cancers are the result of HPV infection. In differentiated cells, HPV amplifies viral DNA in nuclear replication factories and transcribes late mRNAs to produce capsid proteins. However, very little is known about the spatial organization of these activities in the nucleus. Here, we show that repressive viral and cellular factors localize within the foci to suppress viral transcription, while active transcription takes place on the surface. The cellular histone variant macroH2A1 is important for this spatial organization.

Dangerous Liaisons: Long-Term Replication with an Extrachromosomal HPV Genome

Papillomaviruses cause persistent, and usually self-limiting, infections in the mucosal and cutaneous surfaces of the host epithelium. However, in some cases, infection with an oncogenic HPV can lead to cancer. The viral genome is a small, double-stranded circular DNA molecule that is assembled into nucleosomes at all stages of infection. The viral minichromosome replicates at a low copy number in the nucleus of persistently infected cells using the cellular replication machinery. When the infected cells differentiate, the virus hijacks the host DNA damage and repair pathways to replicate viral DNA to a high copy number to generate progeny virions. This strategy is highly effective and requires a close association between viral and host chromatin, as well as cellular processes associated with DNA replication, repair, and transcription. However, this association can lead to accidental integration of the viral genome into host DNA, and under certain circumstances integration can promote oncogenesis. Here we describe the fate of viral DNA at each stage of the viral life cycle and how this might facilitate accidental integration and subsequent carcinogenesis.

Episome partitioning and symmetric cell divisions: Quantifying the role of random events in the persistence of HPV infections

Human Papillomaviruses (HPV) are one of the most prevalent sexually transmitted infections (STI) and the most oncogenic viruses known to humans. The vast majority of HPV infections clear in less than 3 years, but the underlying mechanisms, especially the involvement of the immune response, are still poorly known. Building on earlier work stressing the importance of randomness in the type of cell divisions in the clearance of HPV infection, we develop a stochastic mathematical model of HPV dynamics that combines the previous aspect with an explicit description of the intracellular level. We show that the random partitioning of virus episomes upon stem cell division and the occurrence of symmetric divisions dramatically affect viral persistence. These results call for more detailed within-host studies to better understand the relative importance of stochasticity and immunity in HPV infection clearance.

Every year, infections by Human Papillomaviruses (HPV) are responsible for a large share of infectious cancers. The prevalence of HPVs is very high, which makes it a major public health issue. Fortunately, most HPV infections (80 to 90%) are cleared naturally within three years. Among the few that persist into chronic infections, the majority also naturally regress. Hence for a given HPV infection, the risk of progression towards cancerous status is low. The immune response is often invoked to explain HPV clearance in non-persisting infections, but many uncertainties remain. Besides immunity, randomness was also suggested to play an important role. Here, we examine how random events occurring during the life cycle of the virus could alter the persistence of the virus inside the host. We develop a mechanistic model that explicitly follows the dynamic of viral copies inside host cells, as well as the dynamics of the epithelium. In our model, infection extinction occurs when all viral copies end up in differentiated cells and migrate towards the surface. This can happen upon cell division during the random allocation of the episomes (i.e. independent circular DNA copies of the viral genome) or when a stem cell divides symmetrically to generate two differentiated cells. We find that the combination of these random events drastically affects infection persistence. More generally, the importance of random fluctuations could match that of immunity and calls for further studies at the within-host and the epidemiological level.

Multiple Roles of Brd4 in the Infectious Cycle of Human Papillomaviruses

Human Papillomaviruses (HPV) reproduce in stratified epithelia by establishing a reservoir of low- level infection in the dividing basal cells and restricting the production of viral particles to terminally differentiated cells. These small DNA viruses hijack pivotal cellular processes and pathways to support the persistent infectious cycle. One cellular factor that is key to multiple stages of viral replication and transcription is the BET (bromodomain and extra-terminal domain) protein, Brd4 (Bromodomain containing protein 4). Here we provide an overview of the multiple interactions of Brd4 that occur throughout the HPV infectious cycle.

Proteasomal degradation of p130 facilitate cell cycle deregulation and impairment of cellular differentiation in high-risk Human Papillomavirus 16 and 18 E7 transfected cells

The High-Risk Human Papillomaviruses (HR-HPVs) 16 and 18 are known to cause cervical cancer, which is primarily attributed to E6 and E7 oncoproteins. In addition, recent studies have focused on the vital role of the p130 pocket protein as an oncosuppressor to limit the expression of E2F transcription factors required for cell cycle progression. In view of this, the current study was conducted to investigate the mechanism by which transfection with HPV16/18 E7 leads to the deregulation of the host cell cycle, altering the localisation of p130, and expression of differentiation genes in Human Keratinocytes (HaCaT) cells. Co-immunoprecipitation, Western blot analysis, immunofluorescence microscopy, flow cytometry, quantitative-Polymerase Chain Reaction (qPCR), and the inhibition of p130 by MG132 inhibitor were employed to investigate the loss of p130 and its disruption in HPV 16/18 E7-transfected HaCaT cells. The HPV16- and HPV18-transformed cells, known as CaSki and HeLa, respectively, were also used to complement the ectopic expressions of E7 in HaCaT cells. Normal keratinocytes displayed higher level of p130 expression than HPV-transformed cells. In addition, the immunofluorescence analysis revealed that both HPV 16/18 E7-transfected HaCaT and HPV-transformed cells exhibited higher level of cytoplasmic p130 compared to nuclear p130. A significant increase in the number of S/G2 phase cells in HPV-transformed cells was also recorded since E7 has been shown to stimulate proliferation through the deactivation of Retinoblastoma Protein (pRB)-dependent G1/S checkpoint. Furthermore, the findings recorded the down-regulation of keratinocyte differentiation markers, namely p130, keratin10, and involucrin. The proteasomal degradation of the exported p130 confirmed the cellular localisation pattern of p130, which was commonly observed in cancerous cells. The findings provide strong evidence that the localisation of nuclear p130 nuclear was disrupted by HPV16/18 E7 led to the deregulation of the cell cycle and the impairment of cellular differentiation ultimately lead to cellular transformation.

Identification of High-Risk Human Papillomavirus DNA, p16, and E6/E7 Oncoproteins in Laryngeal and Hypopharyngeal Squamous Cell Carcinomas

Human papillomavirus (HPV) was proven to play a significant role in cancer development in the oropharynx. However, its role in the development of laryngeal (LSCC) and hypopharyngeal squamous cell carcinoma (HPSCC) remains to be clarified. High-risk HPV (HR-HPV) viral proteins E6 and E7 are considered to be pertinent to HPV-related carcinogenesis. Hence, our aim was to estimate LSCC and HPSCC for HR-HPV DNA, p16, and E6/E7 oncoprotein status by using molecular virology and immunohistochemistry methods. The prevalence of HPV16 infection was 22/41 (53.7%) and 20/31 (64.5%) for LSCC and HPSCC, accordingly. The majority of HPV16+ tumor samples were stage III or IV. In most samples, the presence of either HPV16 E6 or HPV16 E7 viral protein in dysplastic or tumor cells was confirmed using immunohistochemistry. Our results suggest a high prevalence of HPV16 as a primary HR-HPV type in LSCC and HPSCC. The lack of HPV E6/E7 oncoproteins in some tumor samples may suggest either the absence of viral integration or the presence of other mechanisms of tumorigenesis. The utilization of p16 IHC as a surrogate marker of HR-HPV infection is impractical in LSCC and HPSCC.

Metabolic Reprogramming in Cancer: Role of HPV 16 Variants

Metabolic reprogramming is considered one of the hallmarks in cancer and is characterized by increased glycolysis and lactate production, even in the presence of oxygen, which leads the cancer cells to a process called “aerobic glycolysis” or “Warburg effect”. The E6 and E7 oncoproteins of human papillomavirus 16 (HPV 16) favor the Warburg effect through their interaction with a molecule that regulates cellular metabolism, such as p53, retinoblastoma protein (pRb), c-Myc, and hypoxia inducible factor 1α (HIF-1α). Besides, the impact of the E6 and E7 variants of HPV 16 on metabolic reprogramming through proteins such as HIF-1α may be related to their oncogenicity by favoring cellular metabolism modifications to satisfy the energy demands necessary for viral persistence and cancer development. This review will discuss the role of HPV 16 E6 and E7 variants in metabolic reprogramming and their contribution to developing and preserving the malignant phenotype of cancers associated with HPV 16 infection.

Epidemiology and Burden of Human Papillomavirus and Related Diseases, Molecular Pathogenesis, and Vaccine Evaluation

Diagnosed in more than 90% of cervical cancers, the fourth deadliest cancer in women, human papillomavirus (HPV) is currently the most common pathogen responsible for female cancers. Moreover, HPV infection is associated with many other diseases, including cutaneous and anogenital warts, and genital and upper aerodigestive tract cancers. The incidence and prevalence of these pathologies vary considerably depending on factors including HPV genotype, regional conditions, the study population, and the anatomical site sampled. Recently, features of the cervicovaginal microbiota are found to be associated with the incidence of HPV-related diseases, presenting a novel approach to identify high-risk women through both blood and cervical samples. Overall, the HPV repartition data show that HPV infection and related diseases are more prevalent in developing countries. Moreover, the available (2-, 4-, and 9-valent) vaccines based on virus-like particles, despite their proven effectiveness and safety, present some limitations in terms of system development cost, transport cold chain, and oncogenic HPV variants. In addition, vaccination programs face some challenges, leading to a considerable burden of HPV infection and related diseases. Therefore, even though the new (9-valent) vaccine seems promising, next-generation vaccines as well as awareness programs associated with HPV vaccination and budget reinforcements for immunization are needed.

Notch Signaling and Human Papillomavirus-Associated Oral Tumorigenesis

The NOTCH pathway is critical for the development of many cell types including the squamous epithelium lining of cutaneous and mucosal surfaces. In genetically engineered mouse models, Notch1 acts as one of the first steps to commit basal keratinocytes to terminally differentiate. Similarly, in human head and neck squamous cell cancers (HNSCCs), NOTCH1 is often lost consistent with its essential tumor-suppressive role for initiating keratinocyte differentiation. However, constitutive NOTCH1 activity in the epithelium results in expansion of the spinous keratinocyte layers and impaired terminal differentiation is consistent with the role of NOTCH1 as an oncogene in other cancers, especially in T-cell acute lymphoblastic leukemia. We have previously observed that NOTCH1 plays a dual role as both a tumor suppressor and oncogene, depending on the mutational context of the tumor. Namely, gain or loss or NOTCH1 activity promotes the development of human papillomavirus (HPV)-associated cancers. The additional HPV oncogenes likely disrupt the tumor-suppressive activities of NOTCH and enable the oncogenic pathways activated by NOTCH to promote tumor growth. In this review, we detail the role of NOTCH pathway in head and neck cancers with a focus on HPV-associated cancers.

Does involucrin have a role in verruca vulgaris? A clinical and immunohistochemical study

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Biological roles of the B cell receptor-associated protein 31: Functional Implication in Cancer

BAP31 is a ubiquitously expressed integral membrane protein of the endoplasmic reticulum. BAP31 is involved in various biological and molecular processes, including protein transport, viral processing, apoptosis signaling, MHC 1 antigen processing and presentation, mitochondria and ER calcium regulation, and proteasomal protein degradation. We employed a BAP31 interaction search using STRING and inBioMap™ protein-protein interaction networks, and the Metabolic Atlas, which revealed molecular and metabolic interactors involved in various pathways essential for cell growth, cell survival, and disease development. BAP31, as a chaperone and resident protein of the ER, was reported in the development of some central nervous system disorders and metabolic diseases about AD, ALS, and Liver disease. In addition, BAP31 is overexpressed in many cancers. Furthermore, research around BAP31 involvement in cancer has taken up a shape, focusing on its roles in cancer cell survival, disease prognosis, and targeted treatment. Here, we address published data on the Biological roles of BAP31 in both health and disease. We present an analytical description of BAP31 expression and functional implication in some human cancers and the impact of its expression and regulation while it models as a potential target in cancer therapy. Besides, a profound understanding of BAP31 is insightful of the gap between cancer development and neurodegeneration, thus generating novel ideas surrounding the link between the two different cell phenomena.

Vesicular trafficking permits evasion of cGAS/STING surveillance during initial human papillomavirus infection

Oncogenic human papillomaviruses (HPVs) replicate in differentiating epithelium, causing 5% of cancers worldwide. Like most other DNA viruses, HPV infection initiates after trafficking viral genome (vDNA) to host cell nuclei. Cells possess innate surveillance pathways to detect microbial components or physiological stresses often associated with microbial infections. One of these pathways, cGAS/STING, induces IRF3-dependent antiviral interferon (IFN) responses upon detection of cytosolic DNA. Virion-associated vDNA can activate cGAS/STING during initial viral entry and uncoating/trafficking, and thus cGAS/STING is an obstacle to many DNA viruses. HPV has a unique vesicular trafficking pathway compared to many other DNA viruses. As the capsid uncoats within acidic endosomal compartments, minor capsid protein L2 protrudes across vesicular membranes to facilitate transport of vDNA to the Golgi. L2/vDNA resides within the Golgi lumen until G2/M, whereupon vesicular L2/vDNA traffics along spindle microtubules, tethering to chromosomes to access daughter cell nuclei. L2/vDNA-containing vesicles likely remain intact until G1, following nuclear envelope reformation. We hypothesize that this unique vesicular trafficking protects HPV from cGAS/STING surveillance. Here, we investigate cGAS/STING responses to HPV infection. DNA transfection resulted in acute cGAS/STING activation and downstream IFN responses. In contrast, HPV infection elicited minimal cGAS/STING and IFN responses. To determine the role of vesicular trafficking in cGAS/STING evasion, we forced premature viral penetration of vesicular membranes with membrane-perturbing cationic lipids. Such treatment renders a non-infectious trafficking-defective mutant HPV infectious, yet susceptible to cGAS/STING detection. Overall, HPV evades cGAS/STING by its unique subcellular trafficking, a property that may contribute to establishment of infection.

Modeling the epithelial-mesenchymal transition process in a 3D organotypic cervical neoplasia

Here, we proposed an innovative organotypic cervical tumor model able to investigate the bi-directional crosstalk between epithelium and stroma as well as the key disease features of the epithelial-mesenchymal transition (EMT) process in vitro. By using a modular tissue assembling approach, we developed 3D cervical stromal models composed of primary human cervical fibroblasts (HCFs) or cervical cancer-associated fibroblasts (CCAFs) embedded in their own ECM to produce 3D normal cervical-instructed stroma (NCIS) or 3D cervical cancer-instructed stroma (CCIS), respectively. Then, we demonstrate the role of the tumor microenvironment (TME) in potentiating the intrinsic invasive attitude of cervical cancer derived SiHa cells and increasing their early viral gene expression by comparing the SiHa behavior when cultured on NCIS or CCIS (SiHa-NCIS or SiHa-CCIS). We proved the crucial role of the CCAFs and stromal microenvironment in the mesenchymalization of the cancer epithelial cells by analyzing several EMT markers. We further assessed the expression of the epithelial adhesion molecules, matricellular enzymes, non-collagenous proteins as well as ECM remodeling in terms of collagen fibers texture and assembly. This cervical tumor model, closely recapitulating key cervical carcinogenesis features, may provide efficient and relevant support to current approaches characterizing cancer progression and develop new anticancer therapy targeting stroma rather than cancer cells.

Anti-Retroviral Protease Inhibitors Regulate Human Papillomavirus 16 Infection of Primary Oral and Cervical Epithelium

Simple Summary

In 2016, globally, 36.7 million people were living with Human Immunodeficiency Virus (HIV), of which 53% had access to anti-retroviral therapy (ART) (UNAIDS 2017 Global HIV Statistics). The risk of Human Papillomavirus (HPV) associated oropharyngeal, cervical and anal cancers are higher among patients infected with HIV in the era of ART. Generally, HPV infections are self-limiting, however, persistent HPV infection is a major risk to carcinogenic progression. Long intervals between initial infection and cancer development imply cofactors are involved. Co-factors that increase infectivity, viral load, and persistence increase risk of cancer. We propose that the ART Protease Inhibitors (PI) class of drugs are novel co-factors that regulate HPV infection in HIV-infected patients. We developed a model system of organotypic epithelium to study impact of PI treatment on HPV16 infection. Our model could be used to study mechanisms of HPV infection in context of ART, and for developing drugs that minimize HPV infections.

Abstract

Epidemiology studies suggest that Human Immunodeficiency Virus (HIV)-infected patients on highly active anti-retroviral therapy (HAART) may be at increased risk of acquiring opportunistic Human Papillomavirus (HPV) infections and developing oral and cervical cancers. Effective HAART usage has improved survival but increased the risk for HPV-associated cancers. In this manuscript, we report that Protease Inhibitors (PI) treatment of three-dimensional tissues derived from primary human gingiva and cervical epithelial cells compromised cell-cell junctions within stratified epithelium and enhanced paracellular permeability of HPV16 to the basal layer for infection, culminating in de novo biosynthesis of progeny HPV16 as determined using 5-Bromo-2′-deoxyuridine (BrdU) labeling of newly synthesized genomes. We propose that HAART/PI represent a novel class of co-factors that modulate HPV infection of the target epithelium. Our in vitro tissue culture model is an important tool to study the mechanistic role of anti-retroviral drugs in promoting HPV infections in HAART-naïve primary epithelium. Changes in subsequent viral load could promote new infections, create HPV reservoirs that increase virus persistence, and increase the risk of oral and cervical cancer development in HIV-positive patients undergoing long-term HAART treatment.

Regulation of autophagy by high- and low-risk human papillomaviruses

While high-risk human papillomavirus (HR-HPV) infection is related to the development of cervical, vulvar, anal, penile and oropharyngeal cancer, low-risk human papillomavirus (LR-HPV) infection is implicated in about 90% of genital warts, which rarely progress to cancer. The carcinogenic role of HR-HPV is due to the overexpression of HPV E5, E6 and E7 oncoproteins which target and modify cellular proteins implicated in cell proliferation, apoptosis and immortalization. LR-HPV proteins also target and modify some of these processes; however, their oncogenic potential is lower than that of HR-HPV. HR-HPVs have substantial differences with LR-HPVs such as viral integration into the cell genome, induction of p53 and retinoblastoma protein degradation, alternative splicing in HR-HPV E6-E7 open reading frames, among others. In addition, LR-HPV can activate the autophagy process in infected cells while HR-HPV infection deactivates it. However, in cancer HR-HPV might reactivate autophagy in advance stages. Autophagy is a catabolic process that maintains cell homoeostasis by lysosomal degradation and recycling of damaged macromolecules and organelles; nevertheless, depending upon cellular context autophagy may also induce cell death. Therefore, autophagy can contribute either as a promotor or as a suppressor of tumours. In this review, we focus on the role of HR-HPV and LR-HPV in autophagy during viral infection and cancer development. Additionally, we review key regulatory molecules such as microRNAs in HPV present during autophagy, and we emphasize the potential use of cancer treatments associated with autophagy in HPV-related cancers.

Human papillomavirus genotyping as a tool for cervical cancer prevention: from commercially available human papillomavirus DNA test to next-generation sequencing

The biological importance of human papillomavirus (HPV) in the field of medicine – related to cervical carcinogenesis – has been extensively reported in the last decades. For the first time, a direct correlation between cause and effect to explain a cancer development was completely achieved in medical research. Consequently, the Nobel Prize was awarded to HZ Hausen in 2008 for his efforts to understand the effects of persistent infection of oncogenic types of HPV and malignancy transformation. The aim of the present review was to summarize the principal elements of HPV characteristics and their importance in oncology.

It is established that HPV is the main etiologic agent for the development of cervical cancer. With the evolution of diagnosis and molecular biology, many tools have become essential for an early diagnosis and thereby, considerably reducing mortality. Molecular biology continues to advance and provide new perspectives with the use of reverse-transcription PCR in automation and genotyping through next-generation sequencing. This article aims to provide an overview of what is currently used in HPV diagnostic and research and future perspectives with the help of technologies such as next-generation sequencing for screening and vaccination.

Epigenetic Regulation of the Human Papillomavirus Life Cycle

Persistent infection with certain types of human papillomaviruses (HPVs), termed high risk, presents a public health burden due to their association with multiple human cancers, including cervical cancer and an increasing number of head and neck cancers. Despite the development of prophylactic vaccines, the incidence of HPV-associated cancers remains high. In addition, no vaccine has yet been licensed for therapeutic use against pre-existing HPV infections and HPV-associated diseases. Although persistent HPV infection is the major risk factor for cancer development, additional genetic and epigenetic alterations are required for progression to the malignant phenotype. Unlike genetic mutations, the reversibility of epigenetic modifications makes epigenetic regulators ideal therapeutic targets for cancer therapy. This review article will highlight the recent advances in the understanding of epigenetic modifications associated with HPV infections, with a particular focus on the role of these epigenetic changes during different stages of the HPV life cycle that are closely associated with activation of DNA damage response pathways.

In Vitro Organotypic Systems to Model Tumor Microenvironment in Human Papillomavirus (HPV)-Related Cancers

Despite the well-known role of chronic human papillomavirus (HPV) infections in causing tumors (i.e., all cervical cancers and other human malignancies from the mucosal squamous epithelia, including anogenital and oropharyngeal cavity), its persistence is not sufficient for cancer development. Other co-factors contribute to the carcinogenesis process. Recently, the critical role of the underlying stroma during the HPV life cycle and HPV-induced disease have been investigated. The tumor stroma is a key component of the tumor microenvironment (TME), which is a specialized entity. The TME is dynamic, interactive, and constantly changing-able to trigger, support, and drive tumor initiation, progression, and metastasis. In previous years, in vitro organotypic raft cultures and in vivo genetically engineered mouse models have provided researchers with important information on the interactions between HPVs and the epithelium. Further development for an in-depth understanding of the interaction between HPV-infected tissue and the surrounding microenvironment is strongly required. In this review, we critically describe the HPV-related cancers modeled in vitro from the simplified 'raft culture' to complex three-dimensional (3D) organotypic models, focusing on HPV-associated cervical cancer disease platforms. In addition, we review the latest knowledge in the field of in vitro culture systems of HPV-associated malignancies of other mucosal squamous epithelia (anogenital and oropharynx), as well as rare cutaneous non-melanoma associated cancer.

Suppression of a Subset of Interferon-Induced Genes by Human Papillomavirus Type 16 E7 via a Cyclin Dependent Kinase 8-Dependent Mechanism

Persistent infection by human papillomaviruses (HPVs), small, double-stranded DNA viruses that infect keratinocytes of the squamous epithelia, can lead to the development of cervical and other cancers. The viral oncoprotein E7 contributes to viral persistence in part by regulating host gene expression through binding host transcriptional regulators, although mechanisms responsible for E7-mediated transcriptional regulation are incompletely understood. Type I IFN signaling promotes the expression of anti-viral genes, called interferon-stimulated genes (ISGs), through the phosphorylation and activation of STAT1. In this study, we have observed that the CR3 domain of E7 contributes to the episomal maintenance of viral genomes. Transcriptome analysis revealed that E7 transcriptionally suppresses a subset of ISGs but not through regulation of STAT1 activation. Instead, we discovered that E7 associates with Mediator kinase CDK8 and this is correlated with the recruitment of CDK8 to ISG promoters and reduced ISG expression. E7 fails to suppress ISGs in the absence of CDK8, indicating that CDK8 function contributes to the suppression of ISGs by E7. Altogether, E7/CDK8 association may be a novel mechanism by which E7 inhibits innate immune signaling.

Human Papillomavirus Infection and Cervical Cancer: Epidemiology, Screening, and Vaccination-Review of Current Perspectives

Viral infections contribute as a cause of 15–20% of all human cancers. Infection by oncogenic viruses can promote different stages of carcinogenesis. Among many types of HPV, around 15 are linked to cancer. In spite of effective screening methods, cervical cancer continues to be a major public health problem. There are wide differences in cervical cancer incidence and mortality by geographic region. In addition, the age-specific HPV prevalence varies widely across different populations and showed two peaks of HPV positivity in younger and older women. There have been many studies worldwide on the epidemiology of HPV infection and oncogenic properties due to different HPV genotypes. However, there are still many countries where the population-based prevalence has not yet been identified. Moreover, cervical cancer screening strategies are different between countries. Organized cervical screening programs are potentially more effective than opportunistic screening programs. Nevertheless, screening programs have consistently been associated with a reduction in cervical cancer incidence and mortality. Developed countries have achieved such reduced incidence and mortality from cervical cancer over the past 40 years. This is largely due to the implementation of organized cytological screening and vaccination programs. HPV vaccines are very effective at preventing infection and diseases related to the vaccine-specific genotypes in women with no evidence of past or current HPV infection. In spite of the successful implementation of the HPV vaccination program in many countries all over the world, problems related to HPV prevention and treatment of the related diseases will continue to persist in developing and underdeveloped countries.

Organization of the Skin Immune System and Compartmentalized Immune Responses in Infectious Diseases

The skin is an organ harboring several types of immune cells that participate in innate and adaptive immune responses. The immune system of the skin comprises both skin cells and professional immune cells that together constitute what is designated skin-associated lymphoid tissue (SALT). In this review, I extensively discuss the organization of SALT and the mechanisms involved in its responses to infectious diseases of the skin and mucosa. The nature of these SALT responses, and the cellular mediators involved, often determines the clinical course of such infections. I list and describe the components of innate immunity, such as the roles of the keratinocyte barrier and of inflammatory and natural killer cells. I also examine the mechanisms involved in adaptive immune responses, with emphasis on new cytokine profiles, and the role of cell death phenomena in host-pathogen interactions and control of the immune responses to infectious agents. Finally, I highlight the importance of studying SALT in order to better understand host-pathogen relationships involving the skin and detail future directions in the immunological investigation of this organ, especially in light of recent findings regarding the skin immune system.

Tissue-Specific Gene Expression during Productive Human Papillomavirus 16 Infection of Cervical, Foreskin, and Tonsil Epithelium

Epidemiological data confirm a much higher incidence of high-risk human papillomavirus 16 (HPV16)-mediated carcinogenesis of the cervical epithelium than for other target sites. In order to elucidate tissue-specific responses to virus infection, we compared gene expression changes induced by productive HPV16 infection of cervical, foreskin, and tonsil organotypic rafts. These rafts closely mimic persistent HPV16 infection, long before carcinogenesis sets in. The total number of gene expression changes varied considerably across the tissue types, with only 32 genes being regulated in common. Among them, we confirmed the Kelch-like family protein KLHL35 and the laminin-5 complex to be upregulated and downregulated, respectively, in all the three tissues. HPV16 infection induces upregulation of genes involved in cell cycle control, cell division, mitosis, DNA replication, and DNA damage repair in all the three tissues, indicative of a hyperproliferative environment. In the cervical and tonsil epithelium, we observe significant downregulation of genes involved in epidermis development, keratinocyte differentiation, and extracellular matrix organization. On the other hand, in HPV16-positive foreskin (HPV16 foreskin) tissue, several genes involved in interferon-mediated innate immunity, cytokine signaling, and cellular defenses were downregulated. Furthermore, pathway analysis and experimental validations identified important cellular pathways like STAT1 and transforming growth factor β (TGF-β) to be differentially regulated among the three tissue types. The differential modulation of important cellular pathways like TGF-β1 and STAT1 can explain the sensitivity of tissues to HPV cancer progression.IMPORTANCE Although the high-risk human papillomavirus 16 infects anogenital and oropharyngeal sites, the cervical epithelium has a unique vulnerability to progression of cancer. Host responses during persistent infection and preneoplastic stages can shape the outcome of cancer progression in a tissue-dependent manner. Our study for the first time reports differential regulation of critical cellular functions and signaling pathways during productive HPV16 infection of cervical, foreskin, and tonsil tissues. While the virus induces hyperproliferation in infected cells, it downregulates epithelial differentiation, epidermal development, and innate immune responses, according to the tissue type. Modulation of these biological functions can determine virus fitness and pathogenesis and illuminate key cellular mechanisms that the virus employs to establish persistence and finally initiate disease progression.