The E6 protein of human papillomavirus type 16 binds to and inhibits co-activation by CBP and p300

Advances in understanding the mechanisms of the human papillomavirus oncoproteins

High-risk human papillomaviruses (HPVs) are responsible for almost all cervical cancer cases and a growing number of oropharyngeal and anogenital cancers. The primary HPV oncoproteins, E6 and E7, act together to manipulate multiple cellular pathways that can ultimately result in malignant transformation. This includes the deregulation of several signalling pathways that regulate cell proliferation, cell cycle progression and cell survival. Although multiple functions of HPV E6 and E7 in driving oncogenesis are well known, recent studies have uncovered novel oncogenic functions of the HPV oncoproteins, including the manipulation of emerging mechanisms of cancer development, such as epigenetic modifications, cellular plasticity and genomic instability. This review explores current advances in understanding how the HPV oncoproteins interact with these cellular processes, highlighting potential therapeutic targets in HPV-associated cancers.

Rational Design of Stapled Covalent Peptide Modifiers of Oncoprotein E6 from Human Papillomavirus

Human Papillomavirus (HPV) is linked to multiple cancers, most significantly cervical cancer, for which HPV infection is associated with nearly all cases. Essential to the oncogenesis of HPV is the function of the viral protein E6 and its role in degrading the cell cycle regulator p53. Degradation of p53, and the resultant loss of cell cycle control, is mediated by E6 recruitment of the E3 ubiquitin ligase E6AP and subsequent ubiquitination of p53. Here, we report the design of a stapled peptide that mimics the LxxLL α-helical domain of E6AP to bind and covalently label a cysteine residue specific to HPV-16 E6. Several acrylamide- and haloacetamide-based warheads were evaluated for reactivity and specificity, and a panel of hydrocarbon-stapled peptides was evaluated for enhanced binding affinity and increased proteolytic stability. Structure-based modeling was used to rationalize the observed trends in the reactivity of the warheads and the impact of the hydrocarbon staple position on the binding affinity of the stapled peptides. The development of a proteolytically stable and reactive peptide represents a new class of peptide-based inhibitors of protein-protein interactions with a potential therapeutic value toward HPV-derived cancers.

NF-κB Activation Is Essential for Cervical Cell Proliferation and Malignant Transformation

NF-κB, a multifunctional transcription factor, is linked to cancer initiation and progression. As a key immune mediator, it may play a crucial role in HPV-induced cervical carcinogenesis. However, consensus is lacking on the activation timing of NF-κB during the transition from cervical intraepithelial neoplasia (CIN) to cervical squamous cell carcinoma (CSCC). In this study, immunohistochemical analysis was performed to examine RELA, one of the important members of the NF-κB family, and phospho-RELA expression in different cervical lesions. Then, we analyzed NF-κB regulation of differentially expressed genes (DEGs) in cervical lesions vs. normal tissues. Gene enrichment identified oncogenic DEGs, followed by expression and survival analyses. The impact of NF-κB activation on cervical cell proliferation, migration, and oncogenic regulation, as well as the effects of inhibiting NF-κB, were examined. Our study showed that NF-κB activation starts in cervical simple hyperplasia and intensifies as CIN evolves to CSCC. NF-κB-regulated DEGs show stage-specific functions: immune regulation in CIN and cancer promotion in CSCC. Short-term NF-κB activation boosts cervical cell proliferation and migration, which is reversible by an NF-κB inhibitor. Long-term NF-κB activation promotes the expression of cancer-promoting genes in normal cells and also maintains them in cancer tissues, which is linked to poorer prognosis. Inhibiting NF-κB downregulates these genes in cancer cells and suppresses the oncogenic abilities of cervical cancer cells. Collectively, NF-κB activation initiates during the simple hyperplasia stage of cervical cells, stimulating proliferation, migration, and oncogene expression. Throughout the transition from CIN to CSCC, NF-κB activation progressively intensifies, and its long-term activation promotes carcinogenesis. Thus, NF-κB is crucial in mediating cervical oncogenic transformation.

Molecular Insights into HR-HPV and HCMV Co-Presence in Cervical Cancer Development

BACKGROUND

Cervical cancer remains a significant health concern worldwide and the primary cause of cancerous cervical lesions is the infection with high-risk human papillomavirus (HR-HPV). However, emerging evidence suggests that HR-HPV infection alone is insufficient for cancer development, and other co-factors may contribute to cervical carcinogenesis. Human cytomegalovirus (HCMV), a common herpesvirus frequently detected in cervical cancer samples, has demonstrated oncogenic potential.

OBJECTIVES

This review aims to explore the molecular interactions between HR-HPV and HCMV in promoting cervical cancer progression.

METHODS

A comprehensive search was conducted in PubMed and Google Scholar, focusing on articles examining the role of HCMV in cervical tissues and/or cells, selected based on relevance and significance.

RESULTS

The reviewed literature indicates that HCMV and HR-HPV share several oncogenic mechanisms that could drive cervical cell transformation.

CONCLUSIONS

Both viruses may synergistically promote cervical epithelial transformation and tumor progression in multiple ways. HR-HPV may facilitate HCMV entry by increasing host cell receptors essential for viral attachment. Additionally, HR-HPV and HCMV may cooperatively disrupt cellular processes, enhancing carcinogenesis. Both viruses may also modulate the local immune environment, enabling immune evasion and lesion persistence. However, further in vitro and in vivo studies are required to validate these hypotheses.

De-regulation of aurora kinases by oncogenic HPV; implications in cancer development and treatment

Human papillomaviruses (HPVs) cause diseases ranging from benign warts to invasive cancers. HPVs are the cause of almost all cervical cancers and a sub-set of other epithelial malignancies including head and neck cancers, specifically within the oropharynx. The oncogenic properties of HPV are largely mediated through the viral oncoproteins E6 and E7, which disrupt many cellular pathways to drive uncontrolled cell proliferation. One family of proteins targeted by HPV is the Aurora kinase family. Aurora kinases are serine/threonine kinases including Aurora kinase A (AURKA), B (AURKB), and C (AURKC) which are often dysregulated in many cancer types, including HPV driven cancers. All three family members play essential roles in mitotic regulation and accurate cell division. The deregulation of Aurora kinases by HPV infection highlights their potential as therapeutic targets in HPV-associated malignancies. Targeting Aurora kinase activity, in combination with current HPV therapies, may provide new avenues for treating HPV-induced cancers and reducing the burden of HPV-related diseases. Combinatorial inhibition targets distinct but overlapping functions of these kinases, thereby reducing the potential for cancer cells to develop resistance. This broad impact emphasizes the capability for Aurora kinase inhibitors not only as anti-mitotic agents but also as modulators of multiple oncogenic pathways. This review explores the combinatorial effects of Aurora kinase inhibition, offering insights into novel therapeutic strategies for the treatment of HPV-driven cancers.

Roles of human papillomavirus in cancers: oncogenic mechanisms and clinical use

Human papillomaviruses, particularly high-risk human papillomaviruses, have been universally considered to be associated with the oncogenesis and progression of various cancers. The genome of human papillomaviruses is circular, double-stranded DNA that encodes early and late proteins. Each of the proteins is of crucial significance in infecting the epithelium of host cells persistently and supporting viral genome integrating into host cells. Notably, E6 and E7 proteins, classified as oncoproteins, trigger the incidence of cancers by fostering cell proliferation, hindering apoptosis, evading immune surveillance, promoting cell invasion, and disrupting the balance of cellular metabolism. Therefore, targeting human papillomaviruses and decoding molecular mechanisms by which human papillomaviruses drive carcinogenesis are of great necessity to better treat human papillomaviruses-related cancers. Human papillomaviruses have been applied clinically to different facets of human papillomavirus-related cancers, including prevention, screening, diagnosis, treatment, and prognosis. Several types of prophylactic vaccines have been publicly utilized worldwide and have greatly decreased the occurrence of human papillomavirus-related cancers, which have benefited numerous people. Although various therapeutic vaccines have been developed and tested clinically, none of them have been officially approved to date. Enhancing the efficacy of vaccines and searching for innovative technologies targeting human papillomaviruses remain critical challenges that warrant continuous research and attention in the future.

Repression of CADM1 transcription by HPV type 18 is mediated by three-dimensional rearrangement of promoter-enhancer interactions

Upon infection, human papillomavirus (HPV) manipulates host cell gene expression to create an environment that is supportive of a productive and persistent infection. The virus-induced changes to the host cell's transcriptome are thought to contribute to carcinogenesis. Here, we show by RNA-sequencing that oncogenic HPV18 episome replication in primary human foreskin keratinocytes (HFKs) drives host transcriptional changes that are consistent between multiple HFK donors. We have previously shown that HPV18 recruits the host protein CTCF to viral episomes to control the differentiation-dependent viral transcriptional programme. Since CTCF is an important regulator of host cell transcription via coordination of epigenetic boundaries and long-range chromosomal interactions, we hypothesised that HPV18 may also manipulate CTCF to contribute to host transcription reprogramming. Analysis of CTCF binding in the host cell genome by ChIP-Seq revealed that while the total number of CTCF binding sites is not altered by the virus, there are a sub-set of CTCF binding sites that are either enriched or depleted of CTCF. Many of these altered sites are clustered within regulatory elements of differentially expressed genes, including the tumour suppressor gene cell adhesion molecule 1 (CADM1), which supresses epithelial cell growth and invasion. We show that HPV18 establishment results in reduced CTCF binding at the CADM1 promoter and upstream enhancer. Loss of CTCF binding is coincident with epigenetic repression of CADM1, in the absence of CpG hypermethylation, while adjacent genes including the transcriptional regulator ZBTB16 are activated. These data indicate that the CADM1 locus is subject to topological rearrangement following HPV18 establishment. We tested this hypothesis using 4C-Seq (circular chromosome confirmation capture-sequencing) and show that HPV18 establishment causes a loss of long-range chromosomal interactions between the CADM1 transcriptional start site and the upstream transcriptional enhancer. These data show that HPV18 manipulates host cell promoter-enhancer interactions to drive transcriptional reprogramming that may contribute to HPV-induced disease progression.

Too many cooks in the kitchen: HPV driven carcinogenesis - The result of collaboration or competition?

Infection by Human Papillomaviruses accounts for the most widespread sexually transmitted infection worldwide. Clinical presentation of these infections can range from subclinical and asymptomatic to anogenital cancers, with the latter associated with persistent infection over a significant period of time. Of the over 200 isotypes of the human virus identified, a subset of these has been characterized as high-risk due to their ability to induce oncogenesis. At the core of Papillomavirus pathogenesis sits three virally encoded oncoproteins: E5, E6, and E7. In this review we will discuss the respective roles of these proteins and how they contribute to carcinogenesis, evaluating key distinguishing features that separate them from their low-risk counterparts. Furthermore, we will consider the complex relationship between this trio and how their interwoven functional networks underpin the development of cancer.

Viral Oncogenesis: Synergistic Role of Genome Integration and Persistence

Persistence is a strategy used by many viruses to evade eradication by the immune system, ensuring their permanence and transmission within the host and optimizing viral fitness. During persistence, viruses can trigger various phenomena, including target organ damage, mainly due to an inflammatory state induced by infection, as well as cell proliferation and/or immortalization. In addition to immune evasion and chronic inflammation, factors contributing to viral persistence include low-level viral replication, the accumulation of viral mutants, and, most importantly, maintenance of the viral genome and reliance on viral oncoprotein production. This review focuses on the process of genome integration, which may occur at different stages of infection (e.g., HBV), during the chronic phase of infection (e.g., HPV, EBV), or as an essential part of the viral life cycle, as seen in retroviruses (HIV, HTLV-1). It also explores the close relationship between integration, persistence, and oncogenesis. Several models have been proposed to describe the genome integration process, including non-homologous recombination, looping, and microhomology models. Integration can occur either randomly or at specific genomic sites, often leading to genome destabilization. In some cases, integration results in the loss of genomic regions or impairs the regulation of oncogene and/or oncosuppressor expression, contributing to tumor development.

Modulation of epithelial homeostasis by HPV using Notch and Wnt

Highly conserved signalling pathways such as Notch and Wnt are essential in the regulation of differentiation and proliferation processes during adult tissue homeostasis. Human papillomaviruses (HPVs) have evolved with humans to manipulate these signalling pathways to establish a basal reservoir of infected cells by limiting HPV-infected keratinocyte differentiation whilst ensuring that differentiating cells are in a replication-competent state. Here, we focus on the canonical Notch and Wnt signalling pathways and their crosstalk to ensure cell-fate lineage determination during epithelial homeostasis. We then examine how HPVs use their E6 and E7 proteins to inhibit differentiation and maintain stem-like characteristics using Notch and Wnt in HPV-infected cells. Determining the functions of E6 and E7 in the maintenance of the infected cell reservoir, and the molecular crosstalk between Notch and Wnt is vital for our understanding of HPV persistence, and may represent an important factor in the development of therapeutic agents for HPV-associated disease.

Determining the effect of long non-coding RNA maternally expressed gene 3 (lncRNA MEG3) on the transcriptome profile in cervical cancer cell lines

This study investigates the role of the long non-coding RNA Maternally Expressed Gene3 (lncRNA MEG3) gene in cervical cancer, as evidenced by its downregulation in cancerous cell lines. The study demonstrates the effects of the overexpression of lncRNA MEG3 in cervical cancer cell lines, particularly in C33A and CaSki. Through comprehensive analyses, including Next-Generation Sequencing (NGS), alterations in global mRNA expression were analyzed. In C33A cells, 67 genes were upregulated, while 303 genes were downregulated. Similarly, in CaSki cells, 221 genes showed upregulation and 248 genes displayed downregulation. Gene ontology and KEGG pathway analyses were conducted to gain insight into potential mechanisms. Furthermore, the study delves into gene regulatory networks, uncovering intricate interactions among genes. The RNA sequencing data were confirmed for eight genes: PAX3, EGR2, ROR1, NRP1, OAS2, STRA6, CA9, and EDN2 by Real-time PCR. The findings illuminate the complex landscape of gene expression alterations and pathways impacted by the overexpression of lncRNA MEG3. The impact of MEG3 on the overall cervical cancer cells' mRNA profile is reported for the first time. New biomarkers for the prognosis of cervical cancer are also reported in this study. Moreover, identifying specific genes within the regulatory networks provides valuable insights into potential therapeutic targets for managing cervical cancer.

Epigenetic alteration in cervical cancer induced by human papillomavirus

The critical role of a subset of Human Papillomavirus in cervical cancer has been widely acknowledged and studied. Despite progress in our understanding of the viral molecular mechanisms of pathogenesis, knowledge of how infection with HPV oncogenic variants progresses from latent infection to incurable cancer has not been completely elucidated. In this paper we reviewed the relationship between HPV infection and epigenetic mechanisms such as histone acetylation and deacetylation, DNA methylation and non-coding RNAs associated with this infection and the carcinogenic process.

HPV-driven heterogeneity in cervical cancer: study on the role of epithelial cells and myofibroblasts in the tumor progression based on single-cell RNA sequencing analysis

Background

Cervical cancer (CC) is a neoplasia with a high heterogeneity. We aimed to explore the characteristics of tumor microenvironment (TME) for CC treatment.

Methods

HPV positive (+) and negative (-) samples from cervical cancer (CC) patients were sourced from the Gene Expression Omnibus (GEO) database. The single-cell RNA sequencing (scRNA-seq) data were processed and annotated for cell types utilizing the Seurat package. Following this, the expression levels and biological roles of the marker genes were analyzed applying real-time PCR (RT-PCR) and transwell assays. Furthermore, the enrichment of genes with significantly differential expressions and copy number variations was assessed by the ClusterProlifer and inferCNV software packages.

Results

Seven main cell clusters were classified based on a total of 12,431 cells. The HPV- CC samples exhibited a higher immune cell infiltration level, while epithelial cells and myofibroblasts had higher proportion in the HPV+ CC samples with extensive heterogeneity. Immune pathways including antigen treatment and presentation, immunoglobulin production and T cell mediated immunity were significantly activated in the HPV- CC group with lower cell cycle and proliferation activity. However, the anti-tumor immunity of these cells was inhibited in HPV+ CC group with higher cell proliferation activity. Moreover, the amplification and loss of CNVs also supported that these cells in HPV- CC samples were prone to anti-tumor activation. Further cell validation results showed that except GZMA, the levels of APOC1, CEACAM6, FOXP3, SFRP4 and TFF3 were all higher in CC cells Hela, and that silencing TFF3 could inhibit the migration and invasion of CC cells in-vitro.

Conclusion

This study highlighted the critical role of HPV infection in CC progression, providing a novel molecular basis for optimizing the current preventive screening and personalized treatment for the cancer.

A human papillomavirus 16 E2-TopBP1 dependent SIRT1-p300 acetylation switch regulates mitotic viral and human protein levels and activates the DNA damage response

An interaction between human papillomavirus 16 (HPV16) E2 and the cellular proteins TopBP1 and BRD4 is required for E2 plasmid segregation function. The E2-TopBP1 interaction promotes increased mitotic E2 protein levels in U2OS and N/Tert-1 cells, as well as in human foreskin keratinocytes immortalized by HPV16 (HFK + HPV16). SIRT1 deacetylation reduces E2 protein stability and here we demonstrate that increased E2 acetylation occurs during mitosis in a TopBP1 interacting-dependent manner, promoting E2 mitotic stabilization. p300 mediates E2 acetylation and acetylation is increased due to E2 switching off SIRT1 function during mitosis in a TopBP1 interacting-dependent manner, confirmed by increased p53 stability and acetylation on lysine 382, a known target for SIRT1 deacetylation. SIRT1 can complex with E2 in growing cells but is unable to do so during mitosis due to the E2-TopBP1 interaction; SIRT1 is also unable to complex with p53 in mitotic E2 wild-type cells but can complex with p53 outside of mitosis. E2 lysines 111 and 112 are highly conserved residues across all E2 proteins and we demonstrate that K111 hyper-acetylation occurs during mitosis, promoting E2 interaction with Topoisomerase 1 (Top1). We demonstrate that K112 ubiquitination promotes E2 proteasomal degradation during mitosis. E2-TopBP1 interaction promotes mitotic acetylation of CHK2, promoting phosphorylation and activation of the DNA damage response (DDR). The results present a new model in which the E2-TopBP1 complex inactivates SIRT1 during mitosis, and activates the DDR. This is a novel mechanism of HPV16 activation of the DDR, a requirement for the viral life cycle.

IMPORTANCE

Human papillomaviruses (HPVs) are causative agents in around 5% of all human cancers. While there are prophylactic vaccines that will significantly alleviate HPV disease burden on future generations, there are currently no anti-viral strategies available for the treatment of HPV cancers. To generate such reagents, we must understand more about the HPV life cycle, and in particular about viral-host interactions. Here, we describe a novel mitotic complex generated by the HPV16 E2 protein interacting with the host protein TopBP1 that controls the function of the deacetylase SIRT1. The E2-TopBP1 interaction disrupts SIRT1 function during mitosis in order to enhance acetylation and stability of viral and host proteins. We also demonstrate that the E2-TopBP1 interaction activates the DDR. This novel complex is essential for the HPV16 life cycle and represents a novel anti-viral therapeutic target.

Biochemical and toxicity evaluation of Retama sphaerocarpa extracts and in-silico investigation of phenolic compounds as potential inhibitors against HPV16 E6 oncoprotein

Cervical cancer is a type of cancer which affects the cervix cells. The conventional treatments for cervical cancer including surgery, chemotherapy, and radiotherapy are only effective in premature stages and less effective in late stages of this tumor. Therefore, the therapeutic strategies based on biologically active substances from plants are needed to develop for the treatment of cervical cancer. The aim of the present study was to assess in vivo toxicity, hematological and biochemical blood parameters in Wistar rats fed Retama sphaerocarpa aqueous leaf extract (RS-AE), as well as to perform in silico molecular docking studies and dynamic simulation of phenolic compounds against HPV16 oncoprotein E6 in order to identify potential inhibitors. RS-AE was found not to induce acute or sub-acute oral toxicity or significant alterations in hematological and biochemical blood parameters in Wistar rats. A total of 11 phenolic compounds were identified in RS-AE, including dihydrodaidzein glucuronide, chrysoperiol pentoside, genistin and vitexin, which turned out to have the highest binding affinity to HPV16 oncoprotein E6. Based on these results, these RS-AE phenolic compounds could be used as natural drugs against the HPV16 E6 oncoprotein.

The Hallmarks of Cervical Cancer: Molecular Mechanisms Induced by Human Papillomavirus

Human papillomaviruses (HPVs) and, specifically, high-risk HPVs (HR-HPVs) are identified as necessary factors in the development of cancer of the lower genital tract, with CaCU standing out as the most prevalent tumor. This review summarizes ten mechanisms activated by HR-HPVs during cervical carcinogenesis, which are broadly associated with at least seven of the fourteen distinctive physiological capacities of cancer in the newly established model by Hanahan in 2022. These mechanisms involve infection by human papillomavirus, cellular tropism, genetic predisposition to uterine cervical cancer (CaCU), viral load, viral physical state, regulation of epigenetic mechanisms, loss of function of the E2 protein, deregulated expression of E6/E7 oncogenes, regulation of host cell protein function, and acquisition of the mesenchymal phenotype.

A human papillomavirus 16 E2-TopBP1 dependent SIRT1-p300 acetylation switch regulates mitotic viral and human protein levels

An interaction between human papillomavirus 16 (HPV16) E2 and the cellular proteins TopBP1 and BRD4 is required for E2 plasmid segregation function. The E2-TopBP1 interaction promotes increased mitotic E2 protein levels in U2OS and N/Tert-1 cells, as well as in human foreskin keratinocytes immortalized by HPV16 (HFK+HPV16). SIRT1 deacetylation reduces E2 protein stability and here we demonstrate that increased E2 acetylation occurs during mitosis in a TopBP1 interacting dependent manner, promoting E2 mitotic stabilization. p300 mediates E2 acetylation and acetylation is increased due to E2 switching off SIRT1 function during mitosis in a TopBP1 interacting dependent manner, confirmed by increased p53 stability and acetylation on lysine 382, a known target for SIRT1 deacetylation. SIRT1 can complex with E2 in growing cells but is unable to do so during mitosis due to the E2-TopBP1 interaction; SIRT1 is also unable to complex with p53 in mitotic E2 wild type cells but can complex with p53 outside of mitosis. E2 lysines 111 and 112 are highly conserved residues across all E2 proteins and we demonstrate that K111 hyper-acetylation occurs during mitosis, promoting E2 interaction with Topoisomerase 1 (Top1). We also demonstrate that K112 ubiquitination promotes E2 proteasomal degradation during mitosis. The results present a model in which the E2-TopBP1 complex inactivates SIRT1 during mitosis and E2 acetylation on K111 by p300 increases, promoting interaction with Top1 that protects K112 from ubiquitination and therefore E2 proteasomal degradation.

Importance

Human papillomaviruses are causative agents in around 5% of all human cancers. While there are prophylactic vaccines that will significantly alleviate HPV disease burden on future generations, there are currently no anti-viral strategies available for the treatment of HPV cancers. To generate such reagents, we must understand more about the HPV life cycle, and in particular about viral-host interactions. Here we describe a novel mitotic complex generated by the HPV16 E2 protein interacting with the host protein TopBP1 that controls the function of the deacetylase SIRT1. The E2-TopBP1 interaction disrupts SIRT1 function during mitosis in order to enhance acetylation and stability of viral and host proteins. This novel complex is essential for the HPV16 life cycle and represents a novel anti-viral therapeutic target.

Epidemiology, Molecular Pathogenesis, Immuno-Pathogenesis, Immune Escape Mechanisms and Vaccine Evaluation for HPV-Associated Carcinogenesis

Human papillomavirus (HPV) is implicated in over 90% of cervical cancer cases, with factors like regional variability, HPV genotype, the population studied, HPV vaccination status, and anatomical sample collection location influencing the prevalence and pathology of HPV-induced cancer. HPV-16 and -18 are mainly responsible for the progression of several cancers, including cervix, anus, vagina, penis, vulva, and oropharynx. The oncogenic ability of HPV is not only sufficient for the progression of malignancy, but also for other tumor-generating steps required for the production of invasive cancer, such as coinfection with other viruses, lifestyle factors such as high parity, smoking, tobacco chewing, use of contraceptives for a long time, and immune responses such as stimulation of chronic stromal inflammation and immune deviation in the tumor microenvironment. Viral evasion from immunosurveillance also supports viral persistence, and virus-like particle-based prophylactic vaccines have been licensed, which are effective against high-risk HPV types. In addition, vaccination awareness programs and preventive strategies could help reduce the rate and incidence of HPV infection. In this review, we emphasize HPV infection and its role in cancer progression, molecular and immunopathogenesis, host immune response, immune evasion by HPV, vaccination, and preventive schemes battling HPV infection and HPV-related cancers.

Comparative Analysis of Alpha and Beta HPV E6 Oncoproteins: Insights into Functional Distinctions and Divergent Mechanisms of Pathogenesis

Human papillomaviruses (HPVs) represent a diverse group of DNA viruses that infect epithelial cells of mucosal and cutaneous tissues, leading to a wide spectrum of clinical outcomes. Among various HPVs, alpha (α) and beta (β) types have garnered significant attention due to their associations with human health. α-HPVs are primarily linked to infections of the mucosa, with high-risk subtypes, such as HPV16 and HPV18, being the major etiological agents of cervical and oropharyngeal cancers. In contrast, β-HPVs are predominantly associated with cutaneous infections and are commonly found on healthy skin. However, certain β-types, notably HPV5 and HPV8, have been implicated in the development of non-melanoma skin cancers in immunocompromised individuals, highlighting their potential role in pathogenicity. In this review, we comprehensively analyze the similarities and differences between α- and β-HPV E6 oncoproteins, one of the major drivers of viral replication and cellular transformation, and how these impact viral fitness and the capacity to induce malignancy. In particular, we compare the mechanisms these oncoproteins use to modulate common cellular processes-apoptosis, DNA damage repair, cell differentiation, and the immune response-further shedding light on their shared and distinct features, which enable them to replicate at divergent locations of the human body and cause different types of cancer.

The HPV8 E6 protein targets the Hippo and Wnt signaling pathways as part of its arsenal to restrain keratinocyte differentiation

IMPORTANCE

Human papillomaviruses (HPVs) infect basal epithelial cells and cause a dramatic expansion of basal-like, proliferative cells. This reflects the ability of papillomaviruses to delay keratinocyte differentiation, thereby maintaining aspects of the basal cell identity of persistently infected cells. This may enable papillomaviruses to establish and maintain long-term infections in squamous epithelial tissues. Previous work has revealed that the ability of β-HPV8 E6 protein to inhibit Notch and transforming growth factor β signaling importantly contributes to this activity. Here, we present evidence that HPV8 E6 also subverts Hippo and Wnt signaling and that these activities also aid in restraining keratinocyte differentiation.

Oncogenic Viruses and the Epigenome: How Viruses Hijack Epigenetic Mechanisms to Drive Cancer

Globally, viral infections substantially contribute to cancer development. Oncogenic viruses are taxonomically heterogeneous and drive cancers using diverse strategies, including epigenomic dysregulation. Here, we discuss how oncogenic viruses disrupt epigenetic homeostasis to drive cancer and focus on how virally mediated dysregulation of host and viral epigenomes impacts the hallmarks of cancer. To illustrate the relationship between epigenetics and viral life cycles, we describe how epigenetic changes facilitate the human papillomavirus (HPV) life cycle and how changes to this process can spur malignancy. We also highlight the clinical impact of virally mediated epigenetic changes on cancer diagnosis, prognosis, and treatment.

Insights into Regulators of p53 Acetylation

The tumor suppressor p53 is a transcription factor that regulates the expression of dozens of target genes and diverse physiological processes. To precisely regulate the p53 network, p53 undergoes various post-translational modifications and alters the selectivity of target genes. Acetylation plays an essential role in cell fate determination through the activation of p53. Although the acetylation of p53 has been examined, the underlying regulatory mechanisms remain unclear and, thus, have attracted the interest of researchers. We herein discuss the role of acetylation in the p53 pathway, with a focus on p53 acetyltransferases and deacetylases. We also review recent findings on the regulators of these enzymes to understand the mode of p53 acetylation from a broader perspective.

The association of cervicovaginal Langerhans cells with clearance of human papillomavirus

Human papillomavirus (HPV) clearance is important in eliminating cervical cancer which contributes to high morbidity and mortality in women. Nevertheless, it remains largely unknown about key players in clearing pre-existing HPV infections. HPV antigens can be detected by the most important cervical antigen-presenting cells (Langerhans cells, LCs), of which the activities can be affected by cervicovaginal microbiota. In this review, we first introduce persistent HPV infections and then describe HPV-suppressed LCs activities, including but not limited to antigen uptake and presentation. Given specific transcriptional profiling of LCs in cervical epithelium, we also discuss the impact of cervicovaginal microbiota on LCs activation as well as the promise of exploring key microbial players in activating LCs and HPV-specific cellular immunity.

How to Inhibit Nuclear Factor-Kappa B Signaling: Lessons from Poxviruses

The Nuclear Factor-kappa B (NF-κB) family of transcription factors regulates key host inflammatory and antiviral gene expression programs, and thus, is often activated during viral infection through the action of pattern-recognition receptors and cytokine–receptor interactions. In turn, many viral pathogens encode strategies to manipulate and/or inhibit NF-κB signaling. This is particularly exemplified by vaccinia virus (VV), the prototypic poxvirus, which encodes at least 18 different inhibitors of NF-κB signaling. While many of these poxviral NF-κB inhibitors are not required for VV replication in cell culture, they virtually all modulate VV virulence in animal models, underscoring the important influence of poxvirus–NF-κB pathway interactions on viral pathogenesis. Here, we review the diversity of mechanisms through which VV-encoded antagonists inhibit initial NF-κB pathway activation and NF-κB signaling intermediates, as well as the activation and function of NF-κB transcription factor complexes.

In-Silico Molecular Modeling Studies to Identify Novel Potential Inhibitors of HPV E6 Protein

The etiological agent of some anogenital tract cancers is infection with the high-risk human papillomavirus (HPV). Currently, prophylactic vaccines against HPV have been validated, but the presence of drug treatment directed against the infection and its oncogenic effects remain essential. Among the best drug targets, viral oncoprotein E6 has been identified as a key factor in cell immortalization and tumor progression in HPV-positive cells. E6, through interaction with the cellular ubiquitin ligase E6AP, can promote the degradation of p53, a tumor suppressor protein. Therefore, suppression of the creation of the E6-E6AP complex is one of the essential strategies to inhibit the survival and proliferation of infected cells. In the present study, we proposed an in-silico approach for the discovery of small molecules with inhibitory activity on the E6-E6AP interaction. The first three compounds (F0679-0355, F33774-0275, and F3345-0326) were selected on the basis of virtual screening and prediction of the molecules' ADMET properties and docking with E6 protein, these molecules were selected for further study by investigating their stability in the E6 complex and their inhibitory effect on the E6-E6AP interaction by molecular dynamics (MD) simulation. The identified molecules thus represent a good starting point for the development of anti-HPV drugs.

AIB1 is a novel target of the high-risk HPV E6 protein and a biomarker of cervical cancer progression

The high-risk human papillomaviruses (HPV-16, -18) are critical etiologic agents in human malignancy, most importantly in cervical cancer. These oncogenic viruses encode the E6 and E7 proteins that are uniformly retained and expressed in cervical cancers and required for maintenance of the tumorigenic phenotype. The E6 and E7 proteins were first identified as targeting the p53 and pRB tumor suppressor pathways, respectively, in host cells, thereby leading to disruption of cell cycle controls. In addition to p53 degradation, a number of other functions and critical targets for E6 have been described, including telomerase, Myc, PDZ-containing proteins, Akt, Wnt, mTORC1, as well as others. In this study, we identified Amplified in Breast Cancer 1 (AIB1) as a new E6 target. We first found that E6 and hTERT altered similar profiling of gene expression in human foreskin keratinocytes (HFK), independent of telomerase activity. Importantly, AIB1 was a common transcriptional target of both E6 and hTERT. We then verified that high-risk E6 but not low-risk E6 expression led to increases in AIB1 transcript levels by real-time RT-PCR, suggesting that AIB1 upregulation may play an important role in cancer development. Western blots demonstrated that AIB1 expression increased in HPV-16 E6 and E7 expressing (E6E7) immortalized foreskin and cervical keratinocytes, and in three of four common cervical cancer cell lines as well. Then, we evaluated the expression of AIB1 in human cervical lesions and invasive carcinoma using immunohistochemical staining. Strikingly, AIB1 showed positivity in the nucleus of cells in the immediate suprabasal epithelium, while nuclei of the basal epithelium were negative, as evident in the Cervical Intraepithelial Neoplasia 1 (CIN1) samples. As the pathological grading of cervical lesions increased from CIN1, CIN2, CIN3 carcinoma in situ and invasive carcinoma, AIB1 staining increased progressively, suggesting that AIB1 may serve as a novel histological biomarker for cervical cancer development. For cases of invasive cervical carcinoma, AIB1 staining was specific to cancerous lesions. Increased expression of AIB1 was also observed in transgenic mouse cervical neoplasia and cancer models induced by E6E7 and estrogen. Knockdown of AIB1 expression in E6E7 immortalized human cervical cells significantly abolished cell proliferation. Taken together, these data support AIB1 as a novel target of HPV E6 and a biomarker of cervical cancer progression.

Oncogenic KPNA2 Serves as a Biomarker and Immune Infiltration in Patients With HPV Positive Tongue Squamous Cell Carcinoma

Human tongue squamous cell carcinoma (TSCC), the most prevalent type of oral cancer, is associated with human papillomavirus (HPV) infection. Our previous work showed Karyopherin α2 (KPNA2), as an oncogene of TSCC, by relegating the p53/autophagy signaling pathway. Nevertheless, the significance of KPNA2 in TSCC pathogenesis has not been established. KPNA2 levels were evaluated via the TCGA database, and its effects on survival outcomes were assessed by LASSO, Kaplan‐Meier, and COX regression analyses. CIBERSORT and ESTIMATE investigated the relationships between KPNA2 and immune infiltration. At the same time, KPNA2 and HPV infection was analyzed by immunohistochemistry. In addition, the association between downstream molecular regulation pathways and KPNA2 levels was determined by GO, GSEA, and WGCNA. In TSCC, KPNA2 levels were associated with clinical prognosis and tumor grade. Moreover, KPNA2 may be involved in cancer cell differentiation and facilitates tumor-related genes and signaling pathways, such as Cell Cycle, Mitotic G1 phase, G1/S transition, DNA Repair, and Transcriptional Regulation TP53 signaling pathways. Nevertheless, regulatory B cells, follicular helper B cells, and immune and stromal scores between low- and high-KPNA2 expression groups were insignificant. These results imply that KPNA2 is highly involved in tumor grade and prognosis of TSCC. KPNA2 levels correct with HPV 16 markedly regulated cell differentiation, several oncogenes, and cancer‐related pathways.

High-Risk Human Papillomavirus Oncogenic E6/E7 mRNAs Splicing Regulation

High-risk human papillomavirus infection may develop into a persistent infection that is highly related to the progression of various cancers, including cervical cancer and head and neck squamous cell carcinomas. The most common high-risk subtypes are HPV16 and HPV18. The oncogenic viral proteins expressed by high-risk HPVs E6/E7 are tightly involved in cell proliferation, differentiation, and cancerous transformation since E6/E7 mRNAs are derived from the same pre-mRNA. Hence, the alternative splicing in the E6/E7-coding region affects the balance of the E6/E7 expression level. Interrupting the balance of E6 and E7 levels results in cell apoptosis. Therefore, it is crucial to understand the regulation of E6/E7 splice site selection and the interaction of splicing enhancers and silencers with cellular splicing factors. In this review, we concluded the relationship of different E6/E7 transcripts with cancer progression, the known splicing sites, and the identified cis-regulatory elements within high-risk HPV E6/E7-coding region. Finally, we also reviewed the role of various splicing factors in the regulation of high-risk HPV oncogenic E6/E7 mRNA splicing.

p63 Directs Subtype-Specific Gene Expression in HPV+ Head and Neck Squamous Cell Carcinoma

The complex heterogeneity of head and neck squamous cell carcinoma (HNSCC) reflects a diverse underlying etiology. This heterogeneity is also apparent within Human Papillomavirus-positive (HPV+) HNSCC subtypes, which have distinct gene expression profiles and patient outcomes. One aggressive HPV+ HNSCC subtype is characterized by elevated expression of genes involved in keratinization, a process regulated by the oncogenic transcription factor ΔNp63. Furthermore, the human TP63 gene locus is a frequent HPV integration site and HPV oncoproteins drive ΔNp63 expression, suggesting an unexplored functional link between ΔNp63 and HPV+ HNSCC. Here we show that HPV+ HNSCCs can be molecularly stratified according to ΔNp63 expression levels and derive a ΔNp63-associated gene signature profile for such tumors. We leveraged RNA-seq data from p63 knockdown cells and ChIP-seq data for p63 and histone marks from two ΔNp63^high HPV+ HNSCC cell lines to identify an epigenetically refined ΔNp63 cistrome. Our integrated analyses reveal crucial ΔNp63-bound super-enhancers likely to mediate HPV+ HNSCC subtype-specific gene expression that is anchored, in part, by the PI3K-mTOR pathway. These findings implicate ΔNp63 as a key regulator of essential oncogenic pathways in a subtype of HPV+ HNSCC that can be exploited as a biomarker for patient stratification and treatment choices.

High-Risk Mucosal Human Papillomavirus 16 (HPV16) E6 Protein and Cutaneous HPV5 and HPV8 E6 Proteins Employ Distinct Strategies To Interfere with Interferon Regulatory Factor 3-Mediated Beta Interferon Expression

Persistent infection with some mucosal α-genus human papillomaviruses (HPVs; the most prevalent one being HPV16) can induce cervical carcinoma, anogenital cancers, and a subset of head and neck squamous cell carcinoma (HNSCC). Cutaneous β-genus HPVs (such as HPV5 and HPV8) associate with skin lesions that can progress into squamous cell carcinoma with sun exposure in Epidermodysplasia verruciformis patients and immunosuppressed patients. Here, we analyzed mechanisms used by E6 proteins from the α- and β-genus to inhibit the interferon-β (IFNB1) response. HPV16 E6 mediates this effect by a strong direct interaction with interferon regulatory factor 3 (IRF3). The binding site of E6 was localized within a flexible linker between the DNA-binding domain and the IRF-activation domain of IRF3 containing an LxxLL motif. The crystallographic structure of the complex between HPV16 E6 and the LxxLL motif of IRF3 was solved and compared with the structure of HPV16 E6 interacting with the LxxLL motif of the ubiquitin ligase E6AP. In contrast, cutaneous HPV5 and HPV8 E6 proteins bind to the IRF3-binding domain (IBiD) of the CREB-binding protein (CBP), a key transcriptional coactivator in IRF3-mediated IFN-β expression. IMPORTANCE Persistent HPV infections can be associated with the development of several cancers. The ability to persist depends on the ability of the virus to escape the host immune system. The type I interferon (IFN) system is the first-line antiviral defense strategy. HPVs carry early proteins that can block the activation of IFN-I. Among mucosal α-genus HPV types, the HPV16 E6 protein has a remarkable property to strongly interact with the transcription factor IRF3. Instead, cutaneous HPV5 and HPV8 E6 proteins bind to the IRF3 cofactor CBP. These results highlight the versatility of E6 proteins to interact with different cellular targets. The interaction between the HPV16 E6 protein and IRF3 might contribute to the higher prevalence of HPV16 than that of other high-risk mucosal HPV types in HPV-associated cancers.

Role of Histone Post-Translational Modifications in Inflammatory Diseases

Inflammation is a defensive reaction for external stimuli to the human body and generally accompanied by immune responses, which is associated with multiple diseases such as atherosclerosis, type 2 diabetes, Alzheimer’s disease, psoriasis, asthma, chronic lung diseases, inflammatory bowel disease, and multiple virus-associated diseases. Epigenetic mechanisms have been demonstrated to play a key role in the regulation of inflammation. Common epigenetic regulations are DNA methylation, histone modifications, and non-coding RNA expression; among these, histone modifications embrace various post-modifications including acetylation, methylation, phosphorylation, ubiquitination, and ADP ribosylation. This review focuses on the significant role of histone modifications in the progression of inflammatory diseases, providing the potential target for clinical therapy of inflammation-associated diseases.

High Risk-Human Papillomavirus in HNSCC: Present and Future Challenges for Epigenetic Therapies

Head and Neck Squamous Cell Carcinoma (HNSCC) is a highly heterogeneous group of tumors characterized by an incidence of 650,000 new cases and 350,000 deaths per year worldwide and a male to female ratio of 3:1. The main risk factors are alcohol and tobacco consumption and Human Papillomavirus (HPV) infections. HNSCC cases are divided into two subgroups, the HPV-negative (HPV−) and the HPV-positive (HPV+) which have different clinicopathological and molecular profiles. However, patients are still treated with the same therapeutic regimens. It is thus of utmost importance to characterize the molecular mechanisms underlying these differences to find new biomarkers and novel therapeutic targets towards personalized therapies. Epigenetic alterations are a hallmark of cancer and can be exploited as both promising biomarkers and potential new targets. E6 and E7 HPV oncoviral proteins besides targeting p53 and pRb, impair the expression and the activity of several epigenetic regulators. While alterations in DNA methylation patterns have been well described in HPV+ and HPV− HNSCC, accurate histone post-translational modifications (hPTMs) characterization is still missing. Herein, we aim to provide an updated overview on the impact of HPV on the hPTMs landscape in HNSCC. Moreover, we will also discuss the sex and gender bias in HNSCC and how the epigenetic machinery could be involved in this process, and the importance of taking into account sex and/or gender also in this field.

Harnessing the role of epigenetic histone modification in targeting head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most prevalent form of cancer worldwide. Despite advancements made in treatment strategies, the fatality rate of HNSCC is very high. An accumulating body of evidence suggests that epigenetic modification of histones plays an influential role in the development and progression of the disease. In this review we discuss the role of epigenetic modifications in HNSCC and the inter-relationships of human papillomavirus oncoproteins and histone-modifying agents. Further, we explore the possibility of identifying these modifications as biomarkers for their use as drugs in treatment strategies.

Repositioning Fenofibrate to Reactivate p53 and Reprogram the Tumor-Immune Microenvironment in HPV+ Head and Neck Squamous Cell Carcinoma

Simple Summary

A critical need for optimal management of human papillomavirus-associated head and neck squamous cell carcinoma (HPV+ HNSCC) patients is the development of therapeutic strategies to exploit the inherent vulnerabilities of this unique disease. We identified fenofibrate, an FDA-approved drug, as a potent anti-cancer agent for HPV+ HNSCC. Fenofibrate induced the accumulation of the p53 tumor suppressor and re-programmed the tumor microenvironment to drive immune cell infiltration. We provide compelling evidence to reposition fenofibrate as a single agent or in combination with standard therapies for the HPV+ HNSCC setting.

Abstract

Human papillomavirus-associated head and neck squamous cell carcinoma (HPV+ HNSCC) is recognized as a distinct disease with unique etiology and clinical features. Current standard of care therapeutic modalities are identical for HPV+ and HPV− HNSCC and thus, there remains an opportunity to develop innovative pharmacologic approaches to exploit the inherent vulnerabilities of HPV+ HNSCC. In this study, using an inducible HPVE6E7 knockdown system, we found that HPV+ HNSCC cells are addicted to HPVE6E7, such that loss of these viral oncogenes impaired tumorigenicity in vitro and in vivo. A number of druggable pathways, including PPAR and Wnt, were modulated in response to HPVE6E7 loss. Fenofibrate showed significant anti-proliferative effects in a panel of HPV+ cancer cell lines. Additionally, fenofibrate impaired tumor growth as monotherapy and potentiated the activity of cisplatin in a pre-clinical HPV+ animal model. Systemic fenofibrate treatment induced p53 protein accumulation, and surprisingly, re-programmed the tumor-immune microenvironment to drive immune cell infiltration. Since fenofibrate is FDA-approved with a favorable long-term safety record, repositioning of this drug, as a single agent or in combination with cisplatin or checkpoint blockade, for the HPV+ HNSCC setting should be prioritized.

Molecular mimicry of NF-κB by vaccinia virus protein enables selective inhibition of antiviral responses

Infection of mammalian cells with viruses activates NF-κB to induce the expression of cytokines and chemokines and initiate an antiviral response. Here, we show that a vaccinia virus protein mimics the transactivation domain of the p65 subunit of NF-κB to inhibit selectively the expression of NF-κB-regulated genes. Using co-immunoprecipitation assays, we found that the vaccinia virus protein F14 associates with NF-κB co-activator CREB-binding protein (CBP) and disrupts the interaction between p65 and CBP. This abrogates CBP-mediated acetylation of p65, after which it reduces promoter recruitment of the transcriptional regulator BRD4 and diminishes stimulation of NF-κB-regulated genes CXCL10 and CCL2. Recruitment of BRD4 to the promoters of NFKBIA and CXCL8 remains unaffected by either F14 or JQ1 (a competitive inhibitor of BRD4 bromodomains), indicating that BRD4 recruitment is acetylation-independent. Unlike other viral proteins that are general antagonists of NF-κB, F14 is a selective inhibitor of NF-κB-dependent gene expression. An in vivo model of infection demonstrated that F14 promotes virulence. Molecular mimicry of NF-κB may be conserved because other orthopoxviruses, including variola, monkeypox and cowpox viruses, encode orthologues of F14.

Virus against virus: strategies for using adenovirus vectors in the treatment of HPV-induced cervical cancer

Although most human papillomavirus (HPV) infections are harmless, persistent infection with high-risk types of HPV is known to be the leading cause of cervical cancer. Following the infection of the epithelium and integration into the host genome, the oncogenic proteins E6 and E7 disrupt cell cycle control by inducing p53 and retinoblastoma (Rb) degradation. Despite the FDA approval of prophylactic vaccines, there are still issues with cervical cancer treatment; thus, many therapeutic approaches have been developed to date. Due to strong immunogenicity, a high capacity for packaging foreign DNA, safety, and the ability to infect a myriad of cells, adenoviruses have drawn attention of researchers. Adenovirus vectors have been used for different purposes, including as oncolytic agents to kill cancer cells, carrier for RNA interference to block oncoproteins expression, vaccines for eliciting immune responses, especially in cytotoxic T lymphocytes (CTLs), and gene therapy vehicles for restoring p53 and Rb function.

High-Risk Human Papillomavirus and Epstein-Barr Virus Coinfection: A Potential Role in Head and Neck Carcinogenesis

Simple Summary

A subset of carcinomas that arise in the head and neck region show a viral etiology. In fact, a subgroup of oropharyngeal cancers are caused by some types of human papillomavirus (HPV), so-called high-risk (HR)-HPVs, whereas undifferentiated nasopharyngeal carcinomas are etiologically related to Epstein–Barr virus (EBV). However, studies have reported the presence of both HR-HPV and EBV in some types of head and neck cancers. In this review, we discuss the potential contribution and role of HR-HPV/EBV coinfection in head and neck carcinogenesis, as well as the mechanisms that are potentially involved. In addition, HR-HPV/EBV interaction models are proposed.

Abstract

High-risk human papillomaviruses (HR-HPVs) and Epstein–Barr virus (EBV) are recognized oncogenic viruses involved in the development of a subset of head and neck cancers (HNCs). HR-HPVs are etiologically associated with a subset of oropharyngeal carcinomas (OPCs), whereas EBV is a recognized etiological agent of undifferentiated nasopharyngeal carcinomas (NPCs). In this review, we address epidemiological and mechanistic evidence regarding a potential cooperation between HR-HPV and EBV for HNC development. Considering that: (1) both HR-HPV and EBV infections require cofactors for carcinogenesis; and (2) both oropharyngeal and oral epithelium can be directly exposed to carcinogens, such as alcohol or tobacco smoke, we hypothesize possible interaction mechanisms. The epidemiological and experimental evidence suggests that HR-HPV/EBV cooperation for developing a subset of HNCs is plausible and warrants further investigation.

Epigenetic approaches for cervical neoplasia screening (Review)

Human papillomavirus (HPV) infection is the leading cause of cervical cancer. The Papanicolaou cytology test is the usually employed type of screening for this infection; however, its sensibility is limited. Only a small percentage of women infected with high-risk HPV develop cervical cancer with an array of genetic and epigenetic modifications. Thus, it is necessary to develop rapid, reproducible and minimally invasive technologies for screening. DNA methylation has gained attention as an alternative method for molecular diagnosis and prognosis in HPV infection. The aim of the present review was to highlight the potential of DNA methylation in cervical neoplasia screening for clinical applications. It was observed that the methylation human and viral genes was correlated with high-grade lesions and cancer. Methylation biomarkers have shown a good capacity to discriminate between high-grade lesions with a transformative potential and cervical cancer, being able to detect these modifications at an early stage. With further research, the epigenetic profiles and subtypes of the tumors could be elaborated, which would aid in therapy selection by opening avenues in personalized precision medicine. Response to therapy could also be evaluated through such methods and the accessibility of liquid biopsies would allow a constant monitoring of the patient's status without invasive sampling techniques.

The Not-So-Good, the Bad and the Ugly: HPV E5, E6 and E7 Oncoproteins in the Orchestration of Carcinogenesis

Infection with HPV starts with the access of the viral particles to basal cells in the epidermis, potentially via microtraumas to the skin. The basal cells are able to keep away these pathogens in normal circumstances through a robust immune response from the host, as HPV infections are, in general, cleared within 2 to 3 weeks. However, the rare instances of persistent infection and/or in cases where the host immune system is compromised are major risk factors for the development of lesions potentially leading to malignancy. Evolutionarily, obligatory pathogens such as HPVs would not be expected to risk exposing the host to lethal cancer, as this would entail challenging their own life cycle, but infection with these viruses is highly correlated with cancer and malignancy-as in cancer of the cervix, which is almost always associated with these viruses. Despite this key associative cause and the availability of very effective vaccines against these viruses, therapeutic interventions against HPV-induced cancers are still a challenge, indicating the need for focused translational research. In this review, we will consider the key roles that the viral proteins play in driving the host cells to carcinogenesis, mainly focusing on events orchestrated by early proteins E5, E6 and E7-the not-so-good, the bad and the ugly-and discuss and summarize the major events that lead to these viruses mechanistically corrupting cellular homeostasis, giving rise to cancer and malignancy.

Almost famous: Human adenoviruses (and what they have taught us about cancer)

Papillomaviruses, polyomaviruses and adenoviruses are collectively categorized as the small DNA tumour viruses. Notably, human adenoviruses were the first human viruses demonstrated to be able to cause cancer, albeit in non-human animal models. Despite their long history, no human adenovirus is a known causative agent of human cancers, unlike a subset of their more famous cousins, including human papillomaviruses and human Merkel cell polyomavirus. Nevertheless, seminal research using human adenoviruses has been highly informative in understanding the basics of cell cycle control, gene expression, apoptosis and cell differentiation. This review highlights the contributions of human adenovirus research in advancing our knowledge of the molecular basis of cancer.

Biology of HPV Mediated Carcinogenesis and Tumor Progression

Human papillomavirus (HPV) is a ubiquitous DNA virus that infects squamous epithelia. Though HPV only encodes 8 genes, it is capable of causing cellular transformation and ultimately cancer in host cells. In this article we review the classification of HPV viruses, their genetic structure and life cycle, viral gene biology, and provide an overview of the role of HPV in cancer. We explain how the viral life cycle can lead to integration of viral DNA into the host genome leading to increased cell cycle progression, decreased apoptosis, altered DNA repair, and chromosomal instability. We describe the multifaceted roles of the canonical oncogenes E6 and E7 in promoting tumorigenesis and the important role of other viral genes in regulating cancer development. We also review how the virus actively suppresses innate and adaptive immunity to evade immune detection and promote a pro-tumorigenic microenvironment. The biology presented here will serve as a foundation to the other chapters in this edition and we hope it will incite enthusiasm for continued research on this fascinating virus that causes significant morbidity and mortality worldwide.

Role of Virus-Induced Host Cell Epigenetic Changes in Cancer

The tumor viruses human T-lymphotropic virus 1 (HTLV-1), hepatitis C virus (HCV), Merkel cell polyomavirus (MCPyV), high-risk human papillomaviruses (HR-HPVs), Epstein-Barr virus (EBV), Kaposi’s sarcoma-associated herpes virus (KSHV) and hepatitis B virus (HBV) account for approximately 15% of all human cancers. Although the oncoproteins of these tumor viruses display no sequence similarity to one another, they use the same mechanisms to convey cancer hallmarks on the infected cell. Perturbed gene expression is one of the underlying mechanisms to induce cancer hallmarks. Epigenetic processes, including DNA methylation, histone modification and chromatin remodeling, microRNA, long noncoding RNA, and circular RNA affect gene expression without introducing changes in the DNA sequence. Increasing evidence demonstrates that oncoviruses cause epigenetic modifications, which play a pivotal role in carcinogenesis. In this review, recent advances in the role of host cell epigenetic changes in virus-induced cancers are summarized.

Computational Analysis of Domains Vulnerable to HPV-16 E6 Oncoprotein and Corresponding Hot Spot Residues

BACKGROUND

Human Papilloma Virus (HPV) is the primary cause of cancers in cervix, head and neck regions. Oncoprotein E6 of HPV-16, after infecting human body, alters host protein- protein interaction networks. E6 interacts with several proteins, causing the infection to progress into cervical cancer. The molecular basis for these interactions is the presence of short linear peptide motifs on E6 identical to those on human proteins.

METHODS

Motifs of LXXLL and E/DLLL/V-G after identification on E6, were analyzed for their dynamic fluctuations by use of elastic network models. Correlation analysis of amino acid residues of E6 was also performed in specific regions of motifs.

RESULTS

Arginine, Leucine, Glutamine, Threonine and Glutamic acid have been identified as hot spot residues of E6 which can subsequently provide a platform for drug designing and understanding of pathogenesis of cervical cancer. These amino acids play a significant role in stabilizing interactions with host proteins, ultimately causing infections and cancers.

CONCLUSION

Our study validates the role of linear binding motifs of E6 of HPV in interacting with these proteins as an important event in the propagation of HPV in human cells and its transformation into cervical cancer. The study further predicts the domains of protein kinase and armadillo as part of the regions involved in the interaction of E6AP, Paxillin and TNF R1, with viral E6.

Human papillomavirus E6 and E7: What remains?

Decades of research on the human papillomavirus oncogenes, E6 and E7, have given us huge amounts of data on their expression, functions and structures. We know much about the very many cellular proteins and pathways that they influence in one way or another. However, much of this information is quite discrete, referring to one activity examined under one condition. It is now time to join the dots to try to understand a larger picture: how, where and when do all these interactions occur... and why? Examining these questions will also show how many of the yet obscure cellular processes work together for cellular and tissue homeostasis in health and disease.

PPI Modulators of E6 as Potential Targeted Therapeutics for Cervical Cancer: Progress and Challenges in Targeting E6

Advanced cervical cancer is primarily managed using cytotoxic therapies, despite evidence of limited efficacy and known toxicity. There is a current lack of alternative therapeutics to treat the disease more effectively. As such, there have been more research endeavors to develop targeted therapies directed at oncogenic host cellular targets over the past 4 decades, but thus far, only marginal gains in survival have been realized. The E6 oncoprotein, a protein of human papillomavirus origin that functionally inactivates various cellular antitumor proteins through protein–protein interactions (PPIs), represents an alternative target and intriguing opportunity to identify novel and potentially effective therapies to treat cervical cancer. Published research has reported a number of peptide and small-molecule modulators targeting the PPIs of E6 in various cell-based models. However, the reported compounds have rarely been well characterized in animal or human subjects. This indicates that while notable progress has been made in targeting E6, more extensive research is needed to accelerate the optimization of leads. In this review, we summarize the current knowledge and understanding of specific E6 PPI inhibition, the progress and challenges being faced, and potential approaches that can be utilized to identify novel and potent PPI inhibitors for cervical cancer treatment.

The human papillomavirus oncoproteins: a review of the host pathways targeted on the road to transformation

Persistent infection with high-risk human papillomaviruses (HR-HPVs) is the causal factor in over 99 % of cervical cancer cases, and a significant proportion of oropharyngeal and anogenital cancers. The key drivers of HPV-mediated transformation are the oncoproteins E5, E6 and E7. Together, they act to prolong cell-cycle progression, delay differentiation and inhibit apoptosis in the host keratinocyte cell in order to generate an environment permissive for viral replication. The oncoproteins also have key roles in mediating evasion of the host immune response, enabling infection to persist. Moreover, prolonged infection within the cellular environment established by the HR-HPV oncoproteins can lead to the acquisition of host genetic mutations, eventually culminating in transformation to malignancy. In this review, we outline the many ways in which the HR-HPV oncoproteins manipulate the host cellular environment, focusing on how these activities can contribute to carcinogenesis.

Molecular pathways in the development of HPV-induced cervical cancer

Recently, human papillomavirus (HPV) has gained considerable attention in cervical cancer research studies. It is one of the most important sexually transmitted diseases that can affect 160 to 289 out of 10000 persons every year. Due to the infectious nature of this virus, HPV can be considered a serious threat. The knowledge of viral structure, especially for viral oncoproteins like E6, E7, and their role in causing cancer is very important. This virus has different paths (PI3K/Akt, Wnt/β-catenin, ERK/MAPK, and JAK/STAT) that are involved in the transmission of signaling paths through active molecules like MEK (pMEK), ERK (pERK), and Akt (pAkt). It's eventually through these paths that cancer is developed. Precise knowledge of these paths and their signals give us the prognosis to adopt appropriate goals for prevention and control of these series of cancer.

Histone Deacetylase Inhibitors as Therapeutic Interventions on Cervical Cancer Induced by Human Papillomavirus

The role of epigenetic modifications on the carcinogenesis process has received a lot of attention in the last years. Among those, histone acetylation is a process regulated by histone deacetylases (HDAC) and histone acetyltransferases (HAT), and it plays an important role in epigenetic regulation, allowing the control of the gene expression. HDAC inhibitors (HDACi) induce cancer cell cycle arrest, differentiation, and cell death and reduce angiogenesis and other cellular events. Human papillomaviruses (HPVs) are small, non-enveloped double-stranded DNA viruses. They are major human carcinogens, being intricately linked to the development of cancer in 4.5% of the patients diagnosed with cancer worldwide. Long-term infection of high-risk (HR) HPV types, mainly HPV16 and HPV18, is one of the major risk factors responsible for promoting cervical cancer development. In vitro and in vivo assays have demonstrated that HDACi could be a promising therapy to HPV-related cervical cancer. Regardless of some controversial studies, the therapy with HDACi could target several cellular targets which HR-HPV oncoproteins could be able to deregulate. This review article describes the role of HDACi as a possible intervention in cervical cancer treatment induced by HPV, highlighting the main advances reached in the last years and providing insights for further investigations regarding those agents against cervical cancer.

Tumor microenvironment: an evil nexus promoting aggressive head and neck squamous cell carcinoma and avenue for targeted therapy

Head and neck squamous cell carcinoma (HNSCC) is a very aggressive disease with a poor prognosis for advanced-stage tumors. Recent clinical, genomic, and cellular studies have revealed the highly heterogeneous and immunosuppressive nature of HNSCC. Despite significant advances in multimodal therapeutic interventions, failure to cure and recurrence are common and account for most deaths. It is becoming increasingly apparent that tumor microenvironment (TME) plays a critical role in HNSCC tumorigenesis, promotes the evolution of aggressive tumors and resistance to therapy, and thereby adversely affects the prognosis. A complete understanding of the TME factors, together with the highly complex tumor-stromal interactions, can lead to new therapeutic interventions in HNSCC. Interestingly, different molecular and immune landscapes between HPV^+ve and HPV^-ve (human papillomavirus) HNSCC tumors offer new opportunities for developing individualized, targeted chemoimmunotherapy (CIT) regimen. This review highlights the current understanding of the complexity between HPV^+ve and HPV^-ve HNSCC TME and various tumor-stromal cross-talk modulating processes, including epithelial-mesenchymal transition (EMT), anoikis resistance, angiogenesis, immune surveillance, metastatic niche, therapeutic resistance, and development of an aggressive tumor phenotype. Furthermore, we summarize the recent developments and the rationale behind CIT strategies and their clinical applications in HPV^+ve and HPV^-ve HNSCC.