Human Papillomavirus 16 E6 and E7 Synergistically Repress Innate Immune Gene Transcription

High-risk HPV oncoproteins E6 and E7 and their interplay with the innate immune response: Uncovering mechanisms of immune evasion and therapeutic prospects

Human papillomaviruses (HPVs) are double-stranded DNA (dsDNA) tumor viruses causally associated with 5% of human cancers, comprising both anogenital and upper aerodigestive tract carcinomas. Despite the availability of prophylactic vaccines, HPVs continue to pose a significant global health challenge, primarily due to inadequate vaccine access and coverage. These viruses can establish persistent infections by evading both the intrinsic defenses of infected tissues and the extrinsic defenses provided by professional innate immune cells. Crucial for their evasion strategies is their unique intraepithelial life cycle, which effectively shields them from host detection. Thus, strategies aimed at reactivating the innate immune response within infected or transformed epithelial cells, particularly through the production of type I interferons (IFNs) and lymphocyte-recruiting chemokines, are considered viable solutions to counteract the adverse effects of persistent infections by these oncogenic viruses. This review focuses on the complex interplay between the high-risk HPV oncoproteins E6 and E7 and the innate immune response in epithelial cells and HPV-associated cancers. In particular, it details the molecular mechanisms by which E6 and E7 modulate the innate immune response, highlighting significant progress in our comprehension of these processes. It also examines forward-looking strategies that exploit the innate immune system to ameliorate existing anticancer therapies, thereby providing crucial insights into future therapeutic developments.

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.

Genetic and epigenetic alterations in DNA repair genes and treatment outcome of chemoradiotherapy in cervical cancer

Cervical cancer (CaCx) is the deadliest malignancy among women which is caused by human papillomavirus (HPV) and anthro-demographical/clinicopathological factors. HPV oncoproteins E6 and E7 target p53 and RB (retinoblastoma) protein degradation, Ataxia telangiectasia mutated (ATM), ATM-RAD3-related (ATR) inactivation and subsequent impairment of non-homologous end joining (NHEJ), homologous recombination, and base excision repair pathways. There is also an accumulation of genetic and epigenetic alterations in Tumor Growth Suppressors (TGS), oncogenes, and DNA repair genes leading to increased genome instability and CaCx development. These alterations might be responsible for differential clinical response to Cisplatin-based chemoradiotherapy (CRT) in patients. This review explores HPV-mediated DNA damage as a risk factor in CaCx development, the mechanistic role of genetic and epigenetic alterations in DNA repair genes and their association with CRT and outcome, It also explores new possibilities for the development of genetic and epigenetic-based biomarkers for diagnostic, prognostic, and molecular therapeutic interventions.

HPV E6/E7: insights into their regulatory role and mechanism in signaling pathways in HPV-associated tumor

Human papillomavirus (HPV) is a class of envelope-free double-stranded DNA virus. HPV infection has been strongly associated with the development of many malignancies, such as cervical, anal and oral cancers. The viral oncoproteins E6 and E7 perform central roles on HPV-induced carcinogenic processes. During tumor development, it usually goes along with the activation of abnormal signaling pathways. E6 and E7 induces changes in cell cycle, proliferation, invasion, metastasis and other biological behaviors by affecting downstream tumor-related signaling pathways, thus promoting malignant transformation of cells and ultimately leading to tumorigenesis and progression. Here, we summarized that E6 and E7 proteins promote HPV-associated tumorigenesis and development by regulating the activation of various tumor-related signaling pathways, for example, the Wnt/β-catenin, PI3K/Akt, and NF-kB signaling pathway. We also discussed the importance of HPV-encoded E6 and E7 and their regulated tumor-related signaling pathways for the diagnosis and effective treatment of HPV-associated tumors.

A bibliometric analysis of global research trends of inflammation in cervical cancer: A review

Cervical cancer is a common malignant tumor and a leading cause of death in women worldwide. It plays a crucial role in tumorigenesis and progression of cervical cancer. A total of 1606 references on inflammation in cervical cancer were retrieved from the Web of Science Core Collection and visual analysis was performed using VOSviewer. Inflammation in cervical cancer has attracted the attention of researchers. Even though China is the country that publishes the most papers, with the most of the top-ranking institutions, there is no extensive collaboration and exchange of papers by Chinese scholars. PLOS One is a popular journal on inflammation in cervical cancer. Instead, authors from other countries perform better, for example, the Sjoerd H. Van Der Burg is the most widely cited author and "M2 macrophages induced by prostaglandin E2 and IL-6 from cervical carcinoma are switched to activated M1 macrophages by CD4 + Th1 cells" (Moniek Heusinkveld, Leiden University Medical Center) is the most cited article of inflammation in cervical cancer. Keywords associated with "apoptosis," "HPV," "NF-κB," and "oxidative stress have been used in many studies, and keywords associated with "apoptosis," "human papillomavirus (HPV)," "NF-κB," and "oxidative stress" are involved in many studies, and there may be more research ideas in the future. From the perspective of precision medicine, more substantive research articles can promote scientific value, strengthen communication and cooperation, produce more extensive research results, and greatly promote the clinical diagnosis and treatment of cervical cancer. All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

The effects of HPV oncoproteins on host communication networks: Therapeutic connotations

Human papillomavirus (HPV) infections are a leading cause of viral-induced malignancies worldwide, with a prominent association with cervical and head and neck cancers. The pivotal role of HPV oncoproteins, E5, E6, and E7, in manipulating cellular events, which contribute to viral pathogenesis in various ways, has been extensively documented. This article reviews the influence of HPV oncoproteins on cellular signaling pathways within the host cell, shedding light on the underlying molecular mechanisms. A comprehensive understanding of these molecular alterations is essential for the development of targeted therapies and strategies to combat HPV-induced premalignancies and prevent their progress to cancer. Furthermore, this review underscores the intricate interplay between HPV oncoproteins and some of the most important cellular signaling pathways: Notch, Wnt/β-catenin, MAPK, JAK/STAT, and PI3K AKT/mTOR. The treatment efficacies of the currently available inhibitors on these pathways in an HPV-positive context are also discussed. This review also highlights the importance of continued research to advance our knowledge and enhance therapeutic interventions for HPV-associated diseases.

Human Papillomavirus 16 replication converts SAMHD1 into a homologous recombination factor and promotes its recruitment to replicating viral DNA

We have demonstrated that SAMHD1 (sterile alpha motif and histidine-aspartic domain HD-containing protein 1) is a restriction factor for the HPV16 life cycle. Here we demonstrate that in HPV negative cervical cancer C33a cells and human foreskin keratinocytes immortalized by HPV16 (HFK+HPV16), SAMHD1 is recruited to E1-E2 replicating DNA. Homologous recombination (HR) factors are required for HPV16 replication and viral replication promotes phosphorylation of SAMHD1, which converts it from a dNTPase to an HR factor independent from E6/E7 expression. A SAMHD1 phosphor-mimic (SAMHD1 T592D) reduces E1-E2 mediated DNA replication in C33a cells and has enhanced recruitment to the replicating DNA. In HFK+HPV16 cells SAMHD1 T592D is recruited to the viral DNA and attenuates cellular growth, but does not attenuate growth in isogenic HFK cells immortalized by E6/E7 alone. SAMHD1 T592D also attenuates the development of viral replication foci following keratinocyte differentiation. The results indicated that enhanced SAMHD1 phosphorylation could be therapeutically beneficial in cells with HPV16 replicating genomes. Protein phosphatase 2A (PP2A) can dephosphorylate SAMHD1 and PP2A function can be inhibited by endothall. We demonstrate that endothall reduces E1-E2 replication and promotes SAMHD1 recruitment to E1-E2 replicating DNA, mimicking the SAMHD1 T592D phenotypes. Finally, we demonstrate that in head and neck cancer cell lines with HPV16 episomal genomes endothall attenuates their growth and promotes recruitment of SAMHD1 to the viral genome. The results suggest that targeting cellular phosphatases has therapeutic potential for the treatment of HPV infections and cancers.

Importance

Human papillomaviruses are causative agents in around 5% of all human cancers. The development of anti-viral therapeutics depends upon an increased understanding of the viral life cycle. Here we demonstrate that HPV16 replication converts SAMHD1 into an HR factor via phosphorylation. This phosphorylation promotes recruitment of SAMHD1 to viral DNA to assist with replication. A SAMHD1 mutant that mimics phosphorylation is hyper-recruited to viral DNA and attenuates viral replication. Expression of this mutant in HPV16 immortalized cells attenuates the growth of these cells, but not cells immortalized by the viral oncogenes E6/E7 alone. Finally, we demonstrate that the phosphatase inhibitor endothall promotes hyper-recruitment of endogenous SAMHD1 to HPV16 replicating DNA and can attenuate the growth of both HPV16 immortalized human foreskin keratinocytes and HPV16 positive head and neck cancer cell lines. We propose that phosphatase inhibitors represent a novel tool for combating HPV infections and disease.

MmuPV1 E6 induces cell proliferation and other hallmarks of cancer

The E6 protein encoded by the murine papillomavirus (MmuPV1) is essential for MmuPV1-induced skin disease. Our previous work has identified a number of cellular interacting partners of MmuPV1 E6 and E7 through affinity purification/mass spectrometry analysis. These studies revealed that MmuPV1 E6 potently inhibits keratinocyte differentiation through multiple molecular mechanisms including inhibition of NOTCH and TGF-β signaling. Here, we report that MmuPV1 E6 has additional important oncogenic activities when expressed in its natural host cells, mouse keratinocytes, including increasing proliferation, overcoming density-mediated growth arrest, and proliferation under conditions of limited supply of growth factors. Unbiased proteomic/transcriptomic analyses of mouse keratinocytes expressing MmuPV1 E6 substantiated its effect on these cellular processes and divulged that some of these effects may be mediated in part through it upregulating E2F activity. Our analyses also revealed that MmuPV1 E6 may alter other cancer hallmarks including evasion of growth suppressors, inhibition of immune response, resistance to cell death, and alterations in DNA damage response. Collectively, our results suggest that MmuPV1 E6 is a major driver of multiple hallmarks of cancer in MmuPV1's natural host cells, mouse keratinocytes.IMPORTANCEThe Mus musculus papillomavirus 1 (MmuPV1) E6 and E7 proteins are required for MmuPV1-induced disease. Our understanding of the activities of MmuPV1 E6 has been based on affinity purification/mass spectrometry studies where cellular interacting partners of MmuPV1 E6 were identified, and these studies revealed that MmuPV1 E6 can inhibit keratinocyte differentiation through multiple mechanisms. We report that MmuPV1 E6 encodes additional activities including the induction of proliferation, resistance to density-mediated growth arrest, and decreased dependence on exogenous growth factors. Proteomic and transcriptomic analyses provided evidence that MmuPV1 E6 increases the expression and steady state levels of a number of cellular proteins that promote cellular proliferation and other hallmarks of cancer. These results indicate that MmuPV1 E6 is a major driver of MmuPV1-induced pathogenesis.

Immune microenvironment of cervical cancer and the role of IL-2 in tumor promotion

The tumor microenvironment (TME) is a heterogeneous mixture of resident and tumor cells that maintain close communication through their secretion products. The composition of the TME is dynamic and complex among the different types of cancer, where the immune cells play a relevant role in the elimination of tumor cells, however, under certain circumstances they contribute to tumor development. In cervical cancer (CC) the human papilloma virus (HPV) shapes the microenvironment in order to mediate persistent infections that favors transformation and tumor development. Interleukin-2 (IL-2) is an important TME cytokine that induces CD8+ effector T cells and NKs to eliminate tumor cells, however, IL-2 can also suppress the immune response through Treg cells. Recent studies have shown that CC cells express the IL-2 receptor (IL-2R), that are induced to proliferate at low concentrations of exogenous IL-2 through alterations in the JAK/STAT pathway. This review provides an overview of the main immune cells that make up the TME in CC, as well as the participation of IL-2 in the tumor promotion. Finally, it is proposed that the low density of IL-2 produced by immunocompetent cells is used by tumor cells through its IL-2R as a mechanism to proliferate simultaneously depleting this molecule in order to evade immune response.

Human papillomavirus associated cervical lesion: pathogenesis and therapeutic interventions

Human papillomavirus (HPV) is the most prevalent sexually transmitted virus globally. Persistent high-risk HPV infection can result in cervical precancerous lesions and cervical cancer, with 70% of cervical cancer cases associated with high-risk types HPV16 and 18. HPV infection imposes a significant financial and psychological burden. Therefore, studying methods to eradicate HPV infection and halt the progression of precancerous lesions remains crucial. This review comprehensively explores the mechanisms underlying HPV-related cervical lesions, including the viral life cycle, immune factors, epithelial cell malignant transformation, and host and environmental contributing factors. Additionally, we provide a comprehensive overview of treatment methods for HPV-related cervical precancerous lesions and cervical cancer. Our focus is on immunotherapy, encompassing HPV therapeutic vaccines, immune checkpoint inhibitors, and advanced adoptive T cell therapy. Furthermore, we summarize the commonly employed drugs and other nonsurgical treatments currently utilized in clinical practice for managing HPV infection and associated cervical lesions. Gene editing technology is currently undergoing clinical research and, although not yet employed officially in clinical treatment of cervical lesions, numerous preclinical studies have substantiated its efficacy. Therefore, it holds promise as a precise treatment strategy for HPV-related cervical lesions.

Therapeutic strategy for oncovirus-mediated oral cancer: A comprehensive review

Oral cancer is a neoplastic disorder of the oral cavities, including the lips, tongue, buccal mucosa, and lower and upper gums. Oral cancer assessment entails a multistep process that requires deep knowledge of the molecular networks involved in its progression and development. Preventive measures including public awareness of risk factors and improving public behaviors are necessary, and screening techniques should be encouraged to enable early detection of malignant lesions. Herpes simplex virus (HSV), human papillomavirus (HPV), Epstein-Barr virus (EBV), and Kaposi sarcoma-associated herpesvirus (KSHV) are associated with other premalignant and carcinogenic conditions leading to oral cancer. Oncogenic viruses induce chromosomal rearrangements; activate signal transduction pathways via growth factor receptors, cytoplasmic protein kinases, and DNA binding transcription factors; modulate cell cycle proteins, and inhibit apoptotic pathways. In this review, we present an up-to-date overview on the use of nanomaterials for regulating viral proteins and oral cancer as well as the role of phytocompounds on oral cancer. The targets linking oncoviral proteins and oral carcinogenesis were also discussed.

Human Papillomavirus Genome Copy Number Is Maintained by S-Phase Amplification, Genome Loss to the Cytosol during Mitosis, and Degradation in G1 Phase

The current model of human papillomavirus (HPV) replication is comprised of three modes of replication. Following infectious delivery, the viral genome is amplified during the establishment phase to reach up to some hundred copies per cell. The HPV genome copy number remains constant during the maintenance stage. The differentiation of infected cells induces HPV genome amplification. Using highly sensitive in situ hybridization (DNAscope) and freshly HPV16-infected as well as established HPV16-positive cell lines, we observed that the viral genome is amplified in each S phase of undifferentiated keratinocytes cultured as monolayers. The nuclear viral genome copy number is reset to pre-S-phase levels during mitosis. The majority of the viral genome fails to tether to host chromosomes and is lost to the cytosol. Cytosolic viral genomes gradually decrease during cell cycle progression. The loss of cytosolic genomes is blocked in the presence of NH₄Cl or other drugs that interfere with lysosomal acidification, suggesting the involvement of autophagy in viral genome degradation. These observations were also made with HPV31 cell lines obtained from patient samples. Cytosolic viral genomes were not detected in UMSCC47 cells carrying integrated HPV16 DNA. Analyses of organotypic raft cultures derived from keratinocytes harboring episomal HPV16 revealed the presence of cytosolic viral genomes as well. We conclude that HPV maintains viral genome copy numbers by balancing viral genome amplification during S phase with the loss of viral genomes to the cytosol during mitosis. It seems plausible that restrictions to viral genome tethering to mitotic chromosomes reset genome copy numbers in each cell cycle. IMPORTANCE HPV genome maintenance is currently thought to be achieved by regulating the expression and activity of the viral replication factors E1 and E2. In addition, the E8^E2 repressor has been shown to be important for restricting genome copy numbers by competing with E1 and E2 for binding to the viral origin of replication and by recruiting repressor complexes. Here, we demonstrate that the HPV genome is amplified in each S phase. The nuclear genome copy number is reset during mitosis by a failure of the majority of the genomes to tether to mitotic chromosomes. Rather, HPV genomes accumulate in the cytoplasm of freshly divided cells. Cytosolic viral DNA is degraded in G₁ in a lysosome-dependent manner, contributing to the genome copy reset. Our data imply that the mode of replication during establishment and maintenance is the same and further suggest that restrictions to genome tethering significantly contribute to viral genome maintenance.

Exploring the Bioactive Mycocompounds (Fungal Compounds) of Selected Medicinal Mushrooms and Their Potentials against HPV Infection and Associated Cancer in Humans

Medicinal mushrooms have been used as a medicinal tool for many centuries and, nowadays, are used in the prevention and therapy of various diseases, including as an adjunct to cancer treatment. It is estimated that 14-16% of global cancer cases are caused by infectious events; one well-known infectious agent that leads to cancer is the human papillomavirus (HPV). HPV is responsible for more than 99.7% of cervical cancer cases and also may play a role in vaginal, vulvar, penile, anal, rectal, and oropharyngeal carcinogenesis. Coriolus versicolor, a basidiomycetes class mushroom, consists of glycoproteins called polysaccharide-K (PSK) and polysaccharopeptide (PSP), which are mainly responsible for its effectiveness in the fight against a variety of cancers. Its beneficial effect lies in its ability to arrest different phases of the cell cycle, immunomodulation or induction of apoptosis. Coriolus versicolor extractcan reduces BCL-2 expression or increases the expression of p53 tumour suppressor genes in breast tumour cell lines. Inhibition of proliferation was also demonstrated with HeLa cells, while cervical cytology abnormalities improved in patients who locally applied Coriolus versicolor-based vaginal gel. Coriolus versicolor extract itself, and also its combination with another medicinal mushroom, Ganoderma lucidum, leads to improved HPV clearance in HPV cervical or oral-positive patients. Medicinal mushrooms can also increase the effectiveness of vaccination. This review considers the use of medicinal mushrooms as a suitable adjunct to the treatment of many cancers or precanceroses, including those caused by the HPV virus.

Human papillomavirus 16 E2 blocks cellular senescence in response to activation of the DNA damage response

Following infection by HPV16, the viral proteins E1 and E2 induce viral genome replication in association with host factors. Here we demonstrate that E2 also plays a role in promoting short-term cellular proliferation in the presence of an active DDR. Cisplatin treatment of E2 expressing cells results in short-term proliferation likely due to a block of cellular senescence and apoptosis. However, long-term growth of E2 expressing cells following cisplatin treatment is attenuated due to an accumulation of DNA damage. We discuss a possible role for this E2 function during the viral life cycle. It is also notable that E2 expressing HPV16 positive cancers have a better clinical outcome than non-E2 expressing tumors. While there are a variety of reasons for the better outcome of patients with E2 expressing tumors, this report suggests that E2 regulation of the DNA damage response may be a contributory factor.

HPV E6 regulates therapy responses in oropharyngeal cancer by repressing the PGC-1α/ERRα axis

Therapy with radiation plus cisplatin kills HPV+ oropharyngeal squamous cell carcinomas (OPSCCs) by increasing reactive oxygen species beyond cellular antioxidant capacity. To explore why these standard treatments fail for some patients, we evaluated whether the variation in HPV oncoprotein levels among HPV+ OPSCCs affects mitochondrial metabolism, a source of antioxidant capacity. In cell line and patient-derived xenograft models, levels of HPV full-length E6 (fl-E6) inversely correlated with oxidative phosphorylation, antioxidant capacity, and therapy resistance, and fl-E6 was the only HPV oncoprotein to display such correlations. Ectopically expressing fl-E6 in models with low baseline levels reduced mitochondrial mass, depleted antioxidant capacity, and sensitized to therapy. In this setting, fl-E6 repressed the peroxisome proliferator-activated receptor gamma co-activator 1α/estrogen-related receptor α (PGC-1α/ERRα) pathway for mitochondrial biogenesis by reducing p53-dependent PGC-1α transcription. Concordant observations were made in 3 clinical cohorts, where expression of mitochondrial components was higher in tumors of patients with reduced survival. These tumors contained the lowest fl-E6 levels, the highest p53 target gene expression, and an activated PGC-1α/ERRα pathway. Our findings demonstrate that E6 can potentiate treatment responses by depleting mitochondrial antioxidant capacity and provide evidence for low E6 negatively affecting patient survival. E6's interaction with the PGC-1α/ERRα axis has implications for predicting and targeting treatment resistance in OPSCC.

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.

A Critical Role for p53 during the HPV16 Life Cycle

Human papillomaviruses (HPV) are causative agents in ano-genital and oral cancers; HPV16 is the most prevalent type detected in human cancers. The HPV16 E6 protein targets p53 for proteasomal degradation to facilitate proliferation of the HPV16 infected cell. However, in HPV16 immortalized cells E6 is predominantly spliced (E6*) and unable to degrade p53. Here, we demonstrate that human foreskin keratinocytes immortalized by HPV16 (HFK+HPV16), and HPV16 positive oropharyngeal cancers, retain significant expression of p53. In addition, p53 levels increase in HPV16+ head and neck cancer cell lines following treatment with cisplatin. Introduction of full-length E6 into HFK+HPV16 resulted in attenuation of cellular growth (in hTERT immortalized HFK, E6 expression promoted enhanced proliferation). An understudied interaction is that between E2 and p53 and we investigated whether this was important for the viral life cycle. We generated mutant genomes with E2 unable to interact with p53 resulting in profound phenotypes in primary HFK. The mutant induced hyper-proliferation, but an ultimate arrest of cell growth; β-galactosidase staining demonstrated increased senescence, and COMET assays showed increased DNA damage compared with HFK+HPV16 wild-type cells. There was failure of the viral life cycle in organotypic rafts with the mutant HFK resulting in premature differentiation and reduced proliferation. The results demonstrate that p53 expression is critical during the HPV16 life cycle, and that this may be due to a functional interaction between E2 and p53. Disruption of this interaction has antiviral potential. IMPORTANCE Human papillomaviruses are causative agents in around 5% of all cancers. There are currently no antivirals available to combat these infections and cancers, therefore it remains a priority to enhance our understanding of the HPV life cycle. Here, we demonstrate that an interaction between the viral replication/transcription/segregation factor E2 and the tumor suppressor p53 is critical for the HPV16 life cycle. HPV16 immortalized cells retain significant expression of p53, and the critical role for the E2-p53 interaction demonstrates why this is the case. If the E2-p53 interaction is disrupted then HPV16 immortalized cells fail to proliferate, have enhanced DNA damage and senescence, and there is premature differentiation during the viral life cycle. Results suggest that targeting the E2-p53 interaction would have therapeutic benefits, potentially attenuating the spread of HPV16.

Human Beta Papillomavirus Type 8 E1 and E2 Proteins Suppress the Activation of the RIG-I-like Receptor MDA5

Persistent infections of the skin with the human papillomavirus of genus beta (β-HPV) in immunocompetent individuals are asymptomatic, but in immunosuppressed patients, β-HPV infections exhibit much higher viral loads on the skin and are associated with an increased risk of skin cancer. Unlike with HPV16, a high-risk α-HPV, the impact of β-HPV early genes on the innate immune sensing of viral nucleic acids has not been studied. Here, we used primary skin keratinocytes and U2OS cells expressing HPV8 or distinct HPV8 early genes and well-defined ligands of the nucleic-acid-sensing receptors RIG-I, MDA5, TLR3, and STING to analyze a potential functional interaction. We found that primary skin keratinocytes and U2OS cells expressed RIG-I, MDA5, TLR3, and STING, but not TLR7, TLR8, or TLR9. While HPV16-E6 downregulated the expression of RIG-I, MDA5, TLR3, and STING and, in conjunction with HPV16-E7, effectively suppressed type I IFN in response to MDA5 activation, the presence of HPV8 early genes showed little effect on the expression of these immune receptors, except for HPV8-E2, which was associated with an elevated expression of TLR3. Nevertheless, whole HPV8 genome expression, as well as the selective expression of HPV8-E1 or HPV8-E2, was found to suppress MDA5-induced type I IFN and the proinflammatory cytokine IL-6. Furthermore, RNA isolated from HPV8-E2 expressing primary human keratinocytes, but not control cells, stimulated a type I IFN response in peripheral blood mononuclear cells, indicating that the expression of HPV8-E2 in keratinocytes leads to the formation of stimulatory RNA ligands that require the active suppression of immune recognition. These results identify HPV8-E1 and HPV8-E2 as viral proteins that are responsible for the immune escape of β-HPV from the innate recognition of viral nucleic acids, a mechanism that may be necessary for establishing persistent β-HPV infections.

LOXL2 small molecule inhibitor restrains malignant transformation of cervical cancer cells by repressing LOXL2-induced epithelial-mesenchymal transition (EMT)

Lysyl oxidase-like 2 (LOXL2) is a member of the lysine oxidase (LOX) family. Although its overexpression is known to play pivotal roles in carcinogenesis, its involvement in cervical cancer remains undefined. Here, we comprehensively explored the expression level and functional mechanism of LOXL2 in cervical cancer using bioinformatics and experimental methods. Bioinformatics analysis revealed that LOXL2 was significantly upregulated in cervical cancer compared to normal tissues. Enrichment analysis showed that most positively or negatively correlated genes of LOXL2 were correlated with extracellular matrix (ECM) formation and epithelial-mesenchymal transition (EMT). Further experiments confirmed that overexpression of LOXL2 greatly enhanced the malignant transformation abilities (e.g., proliferation, invasion, and migration) of cervical cancer cells via mediation of EMT. Furthermore, the small molecule inhibitor of LOXL2 ((2-Chloropyridin-4-yl) methanamine hydrochloride) significantly decreased the invasive ability of cervical cancer by reversing the process of LOXL2-induced EMT. In summary, LOXL2 may be a promising diagnostic and therapeutic biomarker for cervical cancer, and its small molecule inhibitor may be an effective anti-tumor drug.

CK2 Phosphorylation of Human Papillomavirus 16 E2 on Serine 23 Promotes Interaction with TopBP1 and Is Critical for E2 Interaction with Mitotic Chromatin and the Viral Life Cycle

During the human papillomavirus 16 (HPV16) life cycle, the E2 protein interacts with host factors to regulate viral transcription, replication, and genome segregation/retention. Our understanding of host partner proteins and their roles in E2 functions remains incomplete. Here we demonstrate that CK2 phosphorylation of E2 on serine 23 promotes interaction with TopBP1 in vitro and in vivo and that E2 is phosphorylated on this residue during the HPV16 life cycle. We investigated the consequences of mutating serine 23 on E2 functions. E2-S23A (E2 with serine 23 mutated to alanine) activates and represses transcription identically to E2-WT (wild-type E2), and E2-S23A is as efficient as E2-WT in transient replication assays. However, E2-S23A has compromised interaction with mitotic chromatin compared with E2-WT. In E2-WT cells, both E2 and TopBP1 levels increase during mitosis compared with vector control cells. In E2-S23A cells, neither E2 nor TopBP1 levels increase during mitosis. Introduction of the S23A mutation into the HPV16 genome resulted in delayed immortalization of human foreskin keratinocytes (HFK) and higher episomal viral genome copy number in resulting established HFK. Remarkably, S23A cells had a disrupted viral life cycle in organotypic raft cultures, with a loss of E2 expression and a failure of viral replication. Overall, our results demonstrate that CK2 phosphorylation of E2 on serine 23 promotes interaction with TopBP1 and that this interaction is critical for the viral life cycle.

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.

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.

Using a Human Papillomavirus Model to Study DNA Replication and Repair of Wild Type and Damaged DNA Templates in Mammalian Cells

Human papillomaviruses have 8kbp DNA episomal genomes that replicate autonomously from host DNA. During initial infection, the virus increases its copy number to 20-50 copies per cell, causing torsional stress on the replicating DNA. This activates the DNA damage response (DDR) and HPV replicates its genome, at least in part, using homologous recombination. An active DDR is on throughout the HPV life cycle. Two viral proteins are required for replication of the viral genome; E2 binds to 12bp palindromic sequences around the A/T rich origin of replication and recruits the viral helicase E1 via a protein-protein interaction. E1 forms a di-hexameric complex that replicates the viral genome in association with host factors. Transient replication assays following transfection with E1-E2 expression plasmids, along with an origin containing plasmid, allow monitoring of E1-E2 replication activity. Incorporating a bacterial lacZ gene into the origin plasmid allows for the determination of replication fidelity. Here we describe how we exploited this system to investigate replication and repair in mammalian cells, including using damaged DNA templates. We propose that this system has the potential to enhance the understanding of cellular components involved in DNA replication and repair.

Werner Syndrome Protein (WRN) Regulates Cell Proliferation and the Human Papillomavirus 16 Life Cycle during Epithelial Differentiation

Human papillomaviruses recruit a host of DNA damage response factors to their viral genome to facilitate homologous recombination replication in association with the viral replication factors E1 and E2. We previously demonstrated that SIRT1 deacetylation of WRN promotes recruitment of WRN to E1-E2 replicating DNA and that WRN regulates both the levels and fidelity of E1-E2 replication. The deacetylation of WRN by SIRT1 results in an active protein able to complex with replicating DNA, but a protein that is less stable. Here, we demonstrate an inverse correlation between SIRT1 and WRN in CIN cervical lesions compared to normal control tissue, supporting our model of SIRT1 deacetylation destabilizing WRN protein. We CRISPR/Cas9 edited N/Tert-1 and N/Tert-1+HPV16 cells to knock out WRN protein expression and subjected the cells to organotypic raft cultures. In N/Tert-1 cells without WRN expression, there was enhanced basal cell proliferation, DNA damage, and thickening of the differentiated epithelium. In N/Tert-1+HPV16 cells, there was enhanced basal cell proliferation, increased DNA damage throughout the epithelium, and increased viral DNA replication. Overall, the results demonstrate that the expression of WRN is required to control the proliferation of N/Tert-1 cells and controls the HPV16 life cycle in these cells. This complements our previous data demonstrating that WRN controls the levels and fidelity of HPV16 E1-E2 DNA replication. The results describe a new role for WRN, a tumor suppressor, in controlling keratinocyte differentiation and the HPV16 life cycle.IMPORTANCE HPV16 is the major human viral carcinogen, responsible for around 3 to 4% of all cancers worldwide. Our understanding of how the viral replication machinery interacts with host factors to control/activate the DNA damage response to promote the viral life cycle remains incomplete. Recently, we demonstrated a SIRT1-WRN axis that controls HPV16 replication, and here we demonstrate that this axis persists in clinical cervical lesions induced by HPV16. Here, we describe the effects of WRN depletion on cellular differentiation with or without HPV16; WRN depletion results in enhanced proliferation and DNA damage irrespective of HPV16 status. Also, WRN is a restriction factor for the viral life cycle since replication is disrupted in the absence of WRN. Future studies will focus on enhancing our understanding of how WRN regulates viral replication. Our goal is to ultimately identify cellular factors essential for HPV16 replication that can be targeted for therapeutic gain.

Manipulation of JAK/STAT Signalling by High-Risk HPVs: Potential Therapeutic Targets for HPV-Associated Malignancies

Human papillomaviruses (HPVs) are small, DNA viruses that cause around 5% of all cancers in humans, including almost all cervical cancer cases and a significant proportion of anogenital and oral cancers. The HPV oncoproteins E5, E6 and E7 manipulate cellular signalling pathways to evade the immune response and promote virus persistence. The Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway has emerged as a key mediator in a wide range of important biological signalling pathways, including cell proliferation, cell survival and the immune response. While STAT1 and STAT2 primarily drive immune signalling initiated by interferons, STAT3 and STAT5 have widely been linked to the survival and proliferative potential of a number of cancers. As such, the inhibition of STAT3 and STAT5 may offer a therapeutic benefit in HPV-associated cancers. In this review, we will discuss how HPV manipulates JAK/STAT signalling to evade the immune system and promote cell proliferation, enabling viral persistence and driving cancer development. We also discuss approaches to inhibit the JAK/STAT pathway and how these could potentially be used in the treatment of HPV-associated disease.

Activating the DNA Damage Response and Suppressing Innate Immunity: Human Papillomaviruses Walk the Line

Activation of the DNA damage response (DDR) by external agents can result in DNA fragments entering the cytoplasm and activating innate immune signaling pathways, including the stimulator of interferon genes (STING) pathway. The consequences of this activation can result in alterations in the cell cycle including the induction of cellular senescence, as well as boost the adaptive immune response following interferon production. Human papillomaviruses (HPV) are the causative agents in a host of human cancers including cervical and oropharyngeal; HPV are responsible for around 5% of all cancers. During infection, HPV replication activates the DDR in order to promote the viral life cycle. A striking feature of HPV-infected cells is their ability to continue to proliferate in the presence of an active DDR. Simultaneously, HPV suppress the innate immune response using a number of different mechanisms. The activation of the DDR and suppression of the innate immune response are essential for the progression of the viral life cycle. Here, we describe the mechanisms HPV use to turn on the DDR, while simultaneously suppressing the innate immune response. Pushing HPV from this fine line and tipping the balance towards activation of the innate immune response would be therapeutically beneficial.

Subversion of Host Innate Immunity by Human Papillomavirus Oncoproteins

The growth of human papillomavirus (HPV)-transformed cells depends on the ability of the viral oncoproteins E6 and E7, especially those from high-risk HPV16/18, to manipulate the signaling pathways involved in cell proliferation, cell death, and innate immunity. Emerging evidence indicates that E6/E7 inhibition reactivates the host innate immune response, reversing what until then was an unresponsive cellular state suitable for viral persistence and tumorigenesis. Given that the disruption of distinct mechanisms of immune evasion is an attractive strategy for cancer therapy, the race is on to gain a better understanding of E6/E7-induced immune escape and cancer progression. Here, we review recent literature on the interplay between E6/E7 and the innate immune signaling pathways cGAS/STING/TBK1, RIG-I/MAVS/TBK1, and Toll-like receptors (TLRs). The overall emerging picture is that E6 and E7 have evolved broad-spectrum mechanisms allowing for the simultaneous depletion of multiple rather than single innate immunity effectors. The cGAS/STING/TBK1 pathway appears to be the most heavily impacted, whereas the RIG-I/MAVS/TBK1, still partially functional in HPV-transformed cells, can be activated by the powerful RIG-I agonist M8, triggering the massive production of type I and III interferons (IFNs), which potentiates chemotherapy-mediated cell killing. Overall, the identification of novel therapeutic targets to restore the innate immune response in HPV-transformed cells could transform the way HPV-associated cancers are treated.

Estrogen Attenuates the Growth of Human Papillomavirus-Positive Epithelial Cells

Human papillomaviruses cause around 5% of all human cancers, yet there are no specific antiviral therapeutic approaches available for combatting these cancers. These cancers are currently treated with standard chemoradiation therapy (CRT). Specific antiviral reagents are desperately required, particularly for HPV+HNSCC whose incidence is increasing and for which there are no diagnostic tools available for combatting this disease. Using data from The Cancer Genome Atlas (TCGA), we and others determined that the estrogen receptor alpha (ERα) is overexpressed in HPV+HNSCC and that elevated levels are associated with an improved disease outcome. This has led to the proposal that estrogen treatment could be a novel therapeutic approach for combatting HPV+cancers. Here, we demonstrate that estrogen attenuates the growth of HPV+epithelial cells using multiple mechanisms, supporting the idea that estrogen has potential as a therapeutic agent for the treatment of HPV+HNSCC.

Human papillomaviruses (HPVs) are small, double-stranded DNA viruses that are significant risk factors in the development of cancer, and HPV accounts for approximately 5% of all worldwide cancers. Recent studies using data from The Cancer Genome Atlas (TCGA) have demonstrated that elevated levels of estrogen receptor alpha (ERα) are associated with improved survival in oropharyngeal cancers, and these elevated receptor levels were linked with human papillomavirus-positive cancers (HPV+cancers). There has been a dramatic increase in HPV-related head and neck squamous cell carcinomas (HPV+HNSCCs) over the last 2 decades, and therapeutic options for this ongoing health crisis are a priority; currently, there are no antiviral therapeutics available for combatting HPV+cancers. During our TGCA studies on head and neck cancer, we had also discovered the overexpression of ERα in HPV+cancers. Here, we demonstrate that 17β-estradiol (estrogen) attenuates the growth/cell viability of HPV+cancers in vitro, but not HPV-negative cancer cells. In addition, N/Tert-1 cells (foreskin keratinocytes immortalized with human telomerase reverse transcriptase [hTERT]) containing human papillomavirus 16 (HPV16) have elevated levels of ERα and growth sensitivity after estrogen treatment compared with parental N/Tert-1 cells. Finally, we demonstrate that there are potentially two mechanisms contributing to the attenuation of HPV+ cell growth following estrogen treatment. First, estrogen represses the viral transcriptional long control region (LCR) downregulating early gene expression, including E6/E7. Second, expression of E6 and E7 by themselves sensitizes cells to estrogen. Overall, our results support the recent proposal that estrogen could be exploited therapeutically for the treatment of HPV-positive oral cancers.

IMPORTANCE Human papillomaviruses cause around 5% of all human cancers, yet there are no specific antiviral therapeutic approaches available for combatting these cancers. These cancers are currently treated with standard chemoradiation therapy (CRT). Specific antiviral reagents are desperately required, particularly for HPV+HNSCC whose incidence is increasing and for which there are no diagnostic tools available for combatting this disease. Using data from The Cancer Genome Atlas (TCGA), we and others determined that the estrogen receptor alpha (ERα) is overexpressed in HPV+HNSCC and that elevated levels are associated with an improved disease outcome. This has led to the proposal that estrogen treatment could be a novel therapeutic approach for combatting HPV+cancers. Here, we demonstrate that estrogen attenuates the growth of HPV+epithelial cells using multiple mechanisms, supporting the idea that estrogen has potential as a therapeutic agent for the treatment of HPV+HNSCC.