The HPV-16 E5 protein inhibits TRAIL- and FasL-mediated apoptosis in human keratinocyte raft cultures

Epidermal growth factor receptor-dependent stimulation of differentiation by human papillomavirus type 16 E5

Human papillomaviruses (HPVs) infect keratinocytes of stratified squamous epithelia, and persistent infection with high-risk HPV types, such as HPV16, may lead to the development of malignancies. HPV evades host immunity in part by linking its gene expression to the host differentiation program, and therefore relies on differentiation to complete its life cycle. Based on previous reports indicating that the HPV16 protein E5 is important in the late stages of the differentiation-dependent life cycle, we found that organotypic cultures harboring HPV16 genomes lacking E5 showed reduced markers of terminal differentiation compared to wild type HPV16-containing cultures. We found that epidermal growth factor receptor (EGFR) levels and activation were increased in an E5-depdendent manner in these tissues, and that EGFR promoted terminal differentiation and expression of the HPV16 L1 gene. These findings suggest a function for E5 in preserving the ability of HPV16 containing keratinocytes to differentiate, thus facilitating the production of new virus progeny.

Deciphering the role of HPV-mediated metabolic regulation in shaping the tumor microenvironment and its implications for immunotherapy in HNSCC

Head and neck squamous cell carcinoma (HNSCC), as a complex and variable malignancy, poses a significant threat to human health. Since the intricate association between HPV and HNSCC emerged, its role within the TME has garnered extensive attention. HPV+HNSCC exhibits distinct immunological characteristics within the TME, intricately intertwined with mechanisms of immune evasion. HPV employs multifaceted pathways to intervene in metabolic regulation within the TME, exerting influence over immune cell functionality and neoplastic cell genesis. Furthermore, the heightened immune reactivity exhibited by HPV+HNSCC within the TME augments responses to immune interventions such as immune checkpoint inhibitors. Therefore, amidst the current limitations of therapeutic approaches, immunotherapy stands as a promising strategy to overcome the conventional confines of treating HNSCC. This article comprehensively outlines the impact of HPV on the inception and progression of HNSCC while discussing the amalgamation of metabolic regulation within the TME and immunotherapeutic strategies. By intervening in the reciprocal interactions between HPV and HNSCC within the TME, the potential to modulate the efficacy of immune-based treatments becomes evident. Concurrently, a synthesis of pertinent biomarker development is summarized. Such endeavors hold paramount significance for personalized therapeutic approaches and the more effective management of HNSCC patients.

Advances in molecular mechanism of HPV16 E5 oncoprotein carcinogenesis

For a considerable duration, cervical cancer has posed a significant risk to the well-being and survival of women. The emergence and progression of cervical cancer have garnered extensive attention, with prolonged chronic infection of HPV serving as a crucial etiological factor. Consequently, investigating the molecular mechanism underlying HPV-induced cervical cancer has become a prominent research area. The HPV molecule is composed of a long control region (LCR), an early coding region and a late coding region.The early coding region encompasses E1, E2, E4, E5, E6, E7, while the late coding region comprises L1 and L2 ORF.The investigation into the molecular structure and function of HPV has garnered significant attention, with the aim of elucidating the carcinogenic mechanism of HPV and identifying potential targets for the treatment of cervical cancer. Research has demonstrated that the HPV gene and its encoded protein play a crucial role in the invasion and malignant transformation of host cells. Consequently, understanding the function of HPV oncoprotein is of paramount importance in comprehending the pathogenesis of cervical cancer. E6 and E7, the primary HPV oncogenic proteins, have been the subject of extensive study. Moreover, a number of contemporary investigations have demonstrated the significant involvement of HPV16 E5 oncoprotein in the malignant conversion of healthy cells through its regulation of cell proliferation, differentiation, and apoptosis via diverse pathways, albeit the precise molecular mechanism remains unclear. This manuscript aims to provide a comprehensive account of the molecular structure and life cycle of HPV.The HPV E5 oncoprotein mechanism modulates cellular processes such as proliferation, differentiation, apoptosis, and energy metabolism through its interaction with cell growth factor receptors and other cellular proteins. This mechanism is crucial for the survival, adhesion, migration, and invasion of tumor cells in the early stages of carcinogenesis. Recent studies have identified the HPV E5 oncoprotein as a promising therapeutic target for early-stage cervical cancer, thus offering a novel approach for treatment.

A Drosophila model of HPV16-induced cancer reveals conserved disease mechanism

High-risk human papillomaviruses (HR-HPVs) cause almost all cervical cancers and a significant number of vaginal, vulvar, penile, anal, and oropharyngeal cancers. HPV16 and 18 are the most prevalent types among HR-HPVs and together cause more than 70% of all cervical cancers. Low vaccination rate and lack of molecularly-targeted therapeutics for primary therapy have led to a slow reduction in cervical cancer incidence and high mortality rate. Hence, creating new models of HPV-induced cancer that can facilitate understanding of the disease mechanism and identification of key cellular targets of HPV oncogenes are important for development of new interventions. Here in this study, we used the tissue-specific expression technique, Gal4-UAS, to establish the first Drosophila model of HPV16-induced cancer. Using this technique, we expressed HPV16 oncogenes E5, E6, E7 and the human E3 ligase (hUBE3A) specifically in the epithelia of Drosophila eye, which allows simple phenotype scoring without affecting the viability of the organism. We found that, as in human cells, hUBE3A is essential for cellular abnormalities caused by HPV16 oncogenes in flies. Several proteins targeted for degradation by HPV16 oncoproteins in human cells were also reduced in the Drosophila epithelial cells. Cell polarity and adhesion were compromised, resulting in impaired epithelial integrity. Cells did not differentiate to the specific cell types of ommatidia, but instead were transformed into neuron-like cells. These cells extended axon-like structures to connect to each other and exhibited malignant behavior, migrating away to distant sites. Our findings suggest that given the high conservation of genes and signaling pathways between humans and flies, the Drosophila model of HPV16- induced cancer could serve as an excellent model for understanding the disease mechanism and discovery of novel molecularly-targeted therapeutics.

Implications and Emerging Therapeutic Avenues of Inflammatory Response in HPV+ Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinomas (HNSCC) are a heterogeneous group of malignancies which have shown exponential incidence in the last two decades especially due to human papillomavirus (HPV) infection. The HPV family comprises more than 100 types of viruses with HPV16 and HPV18 being the most prevalent strains in HNSCC. Literature data reveal that the mutation profile as well as the response to chemotherapy and radiotherapy are distinct among HPV+ versus HPV-negative tumors. Furthermore, the presence of the virus induces activation of an immune response, in particular the recruitment of specific antiviral T lymphocytes to tumor sites. These T cells when activated produce soluble factors including cytokines and chemokines capable of modifying the local immune tumor microenvironment and impact on tumor response to the treatment. In this comprehensive review we investigated current knowledge on how the presence of an HPV can modify the inflammatory response systemically and within the tumor microenvironment's immunological responses, thereby impacting on disease prognosis and survival. We highlighted the research gaps and emerging approaches necessary to discover novel immunotherapeutic targets for HPV-associated HNSCC.

Do or Die: HPV E5, E6 and E7 in Cell Death Evasion

Human papillomaviruses (HPVs) infect the dividing cells of human epithelia and hijack the cellular replication machinery to ensure their own propagation. In the effort to adapt the cell to suit their own reproductive needs, the virus changes a number of processes, amongst which is the ability of the cell to undergo programmed cell death. Viral infections, forced cell divisions and mutations, which accumulate as a result of uncontrolled proliferation, all trigger one of several cell death pathways. Here, we examine the mechanisms employed by HPVs to ensure the survival of infected cells manipulated into cell cycle progression and proliferation.

Cervical cancer therapies: current challenges and future perspectives

Cervical cancer is the fourth most common female cancer worldwide and results in over 300 000 deaths globally. The causative agent of cervical cancer is persistent infection with high-risk subtypes of the human papillomavirus and the E5, E6 and E7 viral oncoproteins cooperate with host factors to induce and maintain the malignant phenotype. Cervical cancer is a largely preventable disease and early-stage detection is associated with significantly improved survival rates. Indeed, in high-income countries with established vaccination and screening programs it is a rare disease. However, the disease is a killer for women in low- and middle-income countries who, due to limited resources, often present with advanced and untreatable disease. Treatment options include surgical interventions, chemotherapy and/or radiotherapy either alone or in combination. This review describes the initiation and progression of cervical cancer and discusses in depth the advantages and challenges faced by current cervical cancer therapies, followed by a discussion of promising and efficacious new therapies to treat cervical cancer including immunotherapies, targeted therapies, combination therapies, and genetic treatment approaches.

Unravelling the Immunomodulatory Effects of Viral Ion Channels, towards the Treatment of Disease

The current COVID-19 pandemic has highlighted the need for the research community to develop a better understanding of viruses, in particular their modes of infection and replicative lifecycles, to aid in the development of novel vaccines and much needed anti-viral therapeutics. Several viruses express proteins capable of forming pores in host cellular membranes, termed "Viroporins". They are a family of small hydrophobic proteins, with at least one amphipathic domain, which characteristically form oligomeric structures with central hydrophilic domains. Consequently, they can facilitate the transport of ions through the hydrophilic core. Viroporins localise to host membranes such as the endoplasmic reticulum and regulate ion homeostasis creating a favourable environment for viral infection. Viroporins also contribute to viral immune evasion via several mechanisms. Given that viroporins are often essential for virion assembly and egress, and as their structural features tend to be evolutionarily conserved, they are attractive targets for anti-viral therapeutics. This review discusses the current knowledge of several viroporins, namely Influenza A virus (IAV) M2, Human Immunodeficiency Virus (HIV)-1 Viral protein U (Vpu), Hepatitis C Virus (HCV) p7, Human Papillomavirus (HPV)-16 E5, Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) Open Reading Frame (ORF)3a and Polyomavirus agnoprotein. We highlight the intricate but broad immunomodulatory effects of these viroporins and discuss the current antiviral therapies that target them; continually highlighting the need for future investigations to focus on novel therapeutics in the treatment of existing and future emergent viruses.

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.

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.

Cellular Functions of HPV16 E5 Oncoprotein during Oncogenic Transformation

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

HTNV Sensitizes Host Toward TRAIL-Mediated Apoptosis-A Pivotal Anti-hantaviral Role of TRAIL

Hantaviruses can cause hemorrhagic fever with renal syndrome (HFRS) in Eurasia and have led to public health threat in China. The pathogenesis of HFRS is complex and involves capillary leakage due to the infection of vascular endothelial cells. Accumulating evidence has demonstrated that hantavirus can induce apoptosis in many cells, but the mechanism remains unclear. Our studies showed that Hantaan virus (HTNV) infection could induce TNF-related apoptosis-inducing ligand (TRAIL) expression in primary human umbilical vein endothelial cells (HUVECs) and sensitize host cells toward TRAIL-mediated apoptosis. Furthermore, TRAIL interference could inhibit apoptosis and enhance the production of HTNV as well as reduce IFN-β production, while exogenous TRAIL treatment showed reverse outcome: enhanced apoptosis and IFN-β production as well as a lower level of viral replication. We also observed that nucleocapsid protein (NP) and glycoprotein (GP) of HTNV could promote the transcriptions of TRAIL and its receptors. Thus, TRAIL was upregulated by HTNV infection and then exhibited significant antiviral activities in vitro, and it was further confirmed in the HTNV-infected suckling mice model that TRAIL treatment significantly reduced viral load, alleviated virus-induced tissue lesions, increased apoptotic cells, and decreased the mortality. In conclusion, these results demonstrate that TRAIL-dependent apoptosis and IFN-β production could suppress HTNV replication and TRAIL treatment might be a novel therapeutic target for HTNV infection.

Current strategies against persistent human papillomavirus infection (Review)

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

Human Papillomavirus 11 Early Protein E6 Activates Autophagy by Repressing AKT/mTOR and Erk/mTOR

Low-risk human papillomaviruses (LR-HPVs) are the causative agents of genital warts, which are a widespread sexually transmitted disease. How LR-HPVs affect autophagy and the specific proteins involved are unknown. In the current study, we investigated the impact of LR-HPV11 early protein 6 (E6) on the activity of the autophagy pathway. We transfected an HPV11 E6 (11E6) plasmid into HaCaT cells, H8 cells, and NHEK cells and established a stable cell line expressing the HPV11 E6 protein. The differences in autophagy activity and upstream regulatory pathways compared with those in the parent cell lines were investigated using a Western blot analysis of the total and phosphorylated protein levels and confocal microscopy of immunostained cells and cells transfected with an mCherry-green fluorescent protein-LC3 expression plasmid. We used short hairpin RNA (shRNA) to knock down 11E6 and showed that these effects require continued 11E6 expression. Compared with its expression in the control cells, the expression of HPV11 E6 in the cells activated the autophagy pathway. The increased autophagy activity was the result of the decreased phosphorylation levels of the canonical autophagy repressor mammalian target of rapamycin (mTOR) at its Ser2448 position (the mTOR complex 1 [mTORC1] phosphorylation site) and decreased AKT and Erk phosphorylation. Therefore, these results indicate that HPV11 E6 activates autophagy through the AKT/mTOR and Erk/mTOR pathways. Our findings provide novel insight into the relationship between LR-HPV infections and autophagy and could help elucidate the pathogenic mechanisms of LR-HPV.IMPORTANCE We transfected an HPV11 E6 plasmid into HaCaT cells, H8 cells, and NHEK cells and established a stable cell line expressing the HPV11 E6 protein. Then, we confirmed that HPV11 E6 induces autophagy by suppressing the AKT/mTOR and Erk/mTOR pathways. In contrast to the high-risk HPV E6 genes, HPV11 E6 did not affect the expression of p53. To the best of our knowledge, this study represents the first direct in-depth investigation of the relationship between the LR-HPV E6 gene and autophagy, which may help to reveal the pathogenesis of LR-HPV infection.

Mucosal and Cutaneous Human Papillomavirus Infections and Cancer Biology

Papillomaviridae is a family of small non-enveloped icosahedral viruses with double-stranded circular DNA. More than 200 different human papillomaviruses (HPVs) have been listed so far. Based on epidemiological data, a subgroup of alphapapillomaviruses (alpha HPVs) was referred to as high-risk (HR) HPV types. HR HPVs are the etiological agents of anogenital cancer and a subset of head and neck cancers. The cutaneous HPV types, mainly from beta and gamma genera, are widely present on the surface of the skin in the general population. However, there is growing evidence of an etiological role of betapapillomaviruses (beta HPVs) in non-melanoma skin cancer (NMSC), together with ultraviolet (UV) radiation. Studies performed on mucosal HR HPV types, such as 16 and 18, showed that both oncoproteins E6 and E7 play a key role in cervical cancer by altering pathways involved in the host immune response to establish a persistent infection and by promoting cellular transformation. Continuous expression of E6 and E7 of mucosal HR HPV types is essential to initiate and to maintain the cellular transformation process, whereas expression of E6 and E7 of cutaneous HPV types is not required for the maintenance of the skin cancer phenotype. Beta HPV types appear to play a role in the initiation of skin carcinogenesis, by exacerbating the accumulation of UV radiation-induced DNA breaks and somatic mutations (the hit-and-run mechanism), and they would therefore act as facilitators rather than direct actors in NMSC. In this review, the natural history of HPV infection and the transforming properties of various HPV genera will be described, with a particular focus on describing the state of knowledge about the role of cutaneous HPV types in NMSC.

HPV-Mediated Resistance to TNF and TRAIL Is Characterized by Global Alterations in Apoptosis Regulatory Factors, Dysregulation of Death Receptors, and Induction of ROS/RNS

Persistent infection with high-risk human papilloma virus (HR-HPV) is the main risk factor for the development of invasive cervical cancer although is not sufficient to cause cervical cancer. Several host and environmental factors play a key role in cancer initiation/progression, including cytokines and other immune-response mediators. Here, we characterized the response to the individual and combined action of the pro-inflammatory cytokines tumor necrosis factor (TNF) and TNF-related apoptosis-inducing ligand (TRAIL) on HPV-transformed cells and human keratinocytes ectopically expressing E6 and E7 early proteins from different HPV types. We showed that keratinocytes expressing HPV early proteins exhibited global alterations in the expression of proteins involved in apoptosis regulation/execution, including TNF and TRAIL receptors. Besides, we provided evidence that TNF receptor 1 (TNFR1) was down-regulated and may be retained in the cytoplasm of keratinocytes expressing HPV16 oncoproteins. Finally, fluorescence analysis demonstrated that cytokine treatment induced the production and release of reactive oxygen and nitrogen species (ROS/RNS) in cells expressing HPV oncogenes. Alterations in ROS/RNS production and apoptosis regulatory factors expression in response to inflammatory mediators may favor the accumulation of genetic alterations in HPV-infected cells. Altogether, our results suggested that these events may contribute to lesion progression and cancer onset.

Beyond Channel Activity: Protein-Protein Interactions Involving Viroporins

Viroporins are short polypeptides encoded by viruses. These small membrane proteins assemble into oligomers that can permeabilize cellular lipid bilayers, disrupting the physiology of the host to the advantage of the virus. Consequently, efforts during the last few decades have been focused towards the discovery of viroporin channel inhibitors, but in general these have not been successful to produce licensed drugs. Viroporins are also involved in viral pathogenesis by engaging in critical interactions with viral proteins, or disrupting normal host cellular pathways through coordinated interactions with host proteins. These protein-protein interactions (PPIs) may become alternative attractive drug targets for the development of antivirals. In this sense, while thus far most antiviral molecules have targeted viral proteins, focus is moving towards targeting host proteins that are essential for virus replication. In principle, this largely would overcome the problem of resistance, with the possibility of using repositioned existing drugs. The precise role of these PPIs, their strain- and host- specificities, and the structural determination of the complexes involved, are areas that will keep the fields of virology and structural biology occupied for years to come. In the present review, we provide an update of the efforts in the characterization of the main PPIs for most viroporins, as well as the role of viroporins in these PPIs interactions.

HPV16 E5 is produced from an HPV16 early mRNA spliced from SD226 to SA3358

The HPV16 E5 open reading frame (ORF) is present on the majority of all alternatively spliced HPV16 mRNAs, but it is currently unknown how well it is translated into E5 protein. To identify HPV16 mRNAs that are efficiently translated into E5, we have generated cDNA plasmids expressing individual, alternatively spliced HPV16 mRNAs with the potential to produce E5. By replacing the E5 ORF with sLuc, we could quantitate sLuc and determine how well each cDNA was translated. Our results showed that the upstream E1 and E7 AUGs inhibited translation of the E5 ORF and revealed that only one HPV16 mRNA produced high levels of E5. This was an HPV16 early mRNA spliced from SD226 to SA3358. These results were confirmed in the context of the entire HPV16 genome. Taken together, our results indicate that E5 is expressed early in the HPV16 replication cycle since it is translated efficiently only by one early mRNA.

Potential Role of E4 Protein in Human Papillomavirus Screening: a Review

In 2006, cervical cancer was reported as the second most common cancer in women of Malaysia. This type of cancer has been shown to correlate with persistent high risk human papillomavirus (HPV) infection. Although HPV is well known to induce cervical cancer, knowledge of pathways that link the latent stage of the viral replication cycle to precancerous and cancerous stages remains incomplete. However, it is interesting to note that the virus can be isolated from tissues ranging from normal to low-grade squamous intraepithelial lesions as well as high-grade intraepithelial lesions (HSILs), thus prompting scientists to develop HPV detection methods for screening. Detection of HPV using viral proteins such as L1 and E1 is proposed to be very useful in assisting the management of high risk infection and cervical cancer. These tests however can lead to false positive results, largely due to the exisstence of asymptomatic or transient HPV infections within any given individual. Somes observation indicate that use of HPV proteins such as E6 and E7 might lead to false positive results. However, one particular HPV protein, E4 shows potential as an accurate marker of the tissue state following HPV infection. E4 expression has been shown to correlate with the levels of HPV DNA incorporation by the host. Thus, it is possible that E4 could serve as a useful marker to define stages of viral carcinogenesis.

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

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

Human papillomavirus molecular biology and disease association

Human papillomaviruses (HPVs) have evolved over millions of years to propagate themselves in a range of different animal species including humans. Viruses that have co‐evolved slowly in this way typically cause chronic inapparent infections, with virion production in the absence of apparent disease. This is the case for many Beta and Gamma HPV types. The Alpha papillomavirus types have however evolved immunoevasion strategies that allow them to cause persistent visible papillomas. These viruses activate the cell cycle as the infected epithelial cell differentiates in order to create a replication competent environment that allows viral genome amplification and packaging into infectious particles. This is mediated by the viral E6, E7, and E5 proteins. High‐risk E6 and E7 proteins differ from their low‐risk counterparts however in being able to drive cell cycle entry in the upper epithelial layers and also to stimulate cell proliferation in the basal and parabasal layers. Deregulated expression of these cell cycle regulators underlies neoplasia and the eventual progression to cancer in individuals who cannot resolve high‐risk HPV infection. Most work to date has focused on the study of high‐risk HPV types such as HPV 16 and 18, which has led to an understanding of the molecular pathways subverted by these viruses. Such approaches will lead to the development of better strategies for disease treatment, including targeted antivirals and immunotherapeutics. Priorities are now focused toward understanding HPV neoplasias at sites other than the cervix (e.g. tonsils, other transformation zones) and toward understanding the mechanisms by which low‐risk HPV types can sometimes give rise to papillomatosis and under certain situations even cancers. Copyright © 2015 John Wiley & Sons, Ltd.

Protein-Protein Interactions of Viroporins in Coronaviruses and Paramyxoviruses: New Targets for Antivirals?

Viroporins are members of a rapidly growing family of channel-forming small polypeptides found in viruses. The present review will be focused on recent structural and protein-protein interaction information involving two viroporins found in enveloped viruses that target the respiratory tract; (i) the envelope protein in coronaviruses and (ii) the small hydrophobic protein in paramyxoviruses. Deletion of these two viroporins leads to viral attenuation in vivo, whereas data from cell culture shows involvement in the regulation of stress and inflammation. The channel activity and structure of some representative members of these viroporins have been recently characterized in some detail. In addition, searches for protein-protein interactions using yeast-two hybrid techniques have shed light on possible functional roles for their exposed cytoplasmic domains. A deeper analysis of these interactions should not only provide a more complete overview of the multiple functions of these viroporins, but also suggest novel strategies that target protein-protein interactions as much needed antivirals. These should complement current efforts to block viroporin channel activity.

Human papillomavirus E5 oncoprotein: function and potential target for antiviral therapeutics

ABSTRACT 

Mucosal human papillomaviruses express a small, hydrophobic, protein called E5, which plays an important role in the HPV life cycle by delaying normal epithelial cell differentiation while maintaining cell cycle progression. In addition, E5 exhibits transforming abilities in a number of cell culture systems and transgenic mouse models. Lacking any described enzymatic activity, E5 is thought to function by binding to host proteins and modulating their activities. In particular, members of the growth factor receptor family are known targets for subversion. This review article summarizes our latest understanding of this enigmatic oncoprotein, including its role in the HPV life cycle, interactions with host proteins and contribution toward tumorigenesis.

Nip the HPV encoded evil in the cancer bud: HPV reshapes TRAILs and signaling landscapes

HPV encoded proteins can elicit ectopic protein–protein interactions that re-wire signaling pathways, in a mode that promotes malignancy. Moreover, accumulating data related to HPV is now providing compelling substantiation of a central role played by HPV in escaping immunosurveillance and impairment of apoptotic response. What emerges is an intricate network of Wnt, TGF, Notch signaling cascades that forms higher-order ligand–receptor complexes routing downstream signaling in HPV infected cells. These HPV infected cells are regulated both extracellularly by ligand receptor axis and intracellularly by HPV encoded proteins and impair TRAIL mediated apoptosis. We divide this review into different sections addressing how linear signaling pathways integrate to facilitate carcinogenesis and compounds that directly or indirectly reverse these aberrant interactions offer new possibilities for therapy in cancer. Although HPV encoded proteins mediated misrepresentation of pathways is difficult to target, improved drug-discovery platforms and new technologies have facilitated the discovery of agents that can target dysregulated pathways in HPV infected cervical cancer cells, thus setting the stage for preclinical models and clinical trials.

The E5 proteins

The E5 proteins are short transmembrane proteins encoded by many animal and human papillomaviruses. These proteins display transforming activity in cultured cells and animals, and they presumably also play a role in the productive virus life cycle. The E5 proteins are thought to act by modulating the activity of cellular proteins. Here, we describe the biological activities of the best-studied E5 proteins and discuss the evidence implicating specific protein targets and pathways in mediating these activities. The primary target of the 44-amino acid BPV1 E5 protein is the PDGF β receptor, whereas the EGF receptor appears to be an important target of the 83-amino acid HPV16 E5 protein. Both E5 proteins also bind to the vacuolar ATPase and affect MHC class I expression and cell-cell communication. Continued studies of the E5 proteins will elucidate important aspects of transmembrane protein-protein interactions, cellular signal transduction, cell biology, virus replication, and tumorigenesis.

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

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

Human papillomavirus early proteins and apoptosis

INTRODUCTION

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

MATERIALS AND METHODS

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

CONCLUSIONS

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

The biology and life-cycle of human papillomaviruses

Human papillomaviruses (HPVs) comprise a diverse group, and have different epithelial tropisms and life-cycle strategies. Many HPVs are classified as low-risk, as they are only very rarely associated with neoplasia or cancer in the general population. These HPVs typically cause inapparent/inconspicuous infections, or benign papillomas, which can persist for months or years, but which are eventually resolved by the host's immune system. Low-risk HPVs are difficult to manage in immunosuppressed people and in individuals with genetic predispositions, and can give rise to papillomatosis, and in rare instances, to cancer. The high-risk HPV types are, by contrast, a cause of several important human cancers, including almost all cases of cervical cancer, a large proportion of other anogenital cancers and a growing number of head and neck tumours. The high-risk HPV types constitute a subset of the genus Alphapapillomavirus that are prevalent in the general population, and in most individuals cause only inconspicuous oral and genital lesions. Cancer progression is associated with persistent high-risk HPV infection and with deregulated viral gene expression, which leads to excessive cell proliferation, deficient DNA repair, and the accumulation of genetic damage in the infected cell. Although their life-cycle organisation is broadly similar to that of the low-risk HPV types, the two groups differ significantly in their capacity to drive cell cycle entry and cell proliferation in the basal/parabasal cell layers. This is thought to be linked, at least in part, to different abilities of the high- and low-risk E6 proteins to modulate the activity of p53 and PDZ-domain proteins, and the differential ability of the E7 proteins to target the several different members of the retinoblastoma protein family. This article forms part of a special supplement entitled "Comprehensive Control of HPV Infections and Related Diseases" Vaccine Volume 30, Supplement 5, 2012.

Human papillomavirus 16/18 E5 promotes cervical cancer cell proliferation, migration and invasion in vitro and accelerates tumor growth in vivo

High-risk human papillomaviruses (HR-HPVs) are consistently associated with human cervical cancer Additionally, the early oncoproteins of HPVs E5, E6 and E7 are known to contribute to tumor progression. The role of E5 is still nebulous. In this study, we aimed to explore the mechanism of E5 action during the human cervical carcinogenesis process. We created four cell models overexpressing HPV16 or HPV18 E5 (HPV16/18 E5) and investigated their ability to proliferate, along with their metastatic characteristics such as migration and invasion. The expression of HPV16/18 E5 protein in various cell lines was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). In addition, we compared the levels of phosphorylated paxillin as well as E-cadherin in cell models and controls by western blot analysis. Finally, we assessed the tumor growth rate of human cervical cancer cells overexpressing HPV16/18 E5 in vivo. We discovered that the expression of HPV16/18 E5 consistently increased the malignant potential of various human cervical cancer cells compared with the primary counterparts. We demonstrated the involvement of HPV16/18 E5 in proliferation, migration, invasion and regulation of the actin cytoskeleton in human cervical cancer cells. In particular we discovered that HPV16/18 E5 overexpression in human cervical cancer cells correlated with higher levels of paxillin proteins phosphorylated on tyrosine residues and with the downregulation of E-cadherin. Importantly, injection of HPV16/18 E5-overexpressing human cervical cancer cells into mice increased both HPV-and non-HPV-derived tumor growth. Collectively, our data indicate that HPV16/18 E5 influences progression of the human cervical cancer malignant phenotype. This study provides new insights into HPV16/18 E5 as a possible agent that may have an impact on the therapeutic strategies targeting human cervical cancer.

Quantitative measurement of human papillomavirus type 16 e5 oncoprotein levels in epithelial cell lines by mass spectrometry

The high-risk human papillomavirus type 16 (HPV-16) E5 protein (16E5) induces tumors in a transgenic mouse model and may contribute to early stages of cervical carcinogenesis. Although high-risk E5 expression is generally thought to be lost during the progression to cervical carcinoma following integration of HPV DNA into the host genome, episomal viral DNA has been documented in a subset of HPV-16-positive malignant lesions. Numerous studies have shown that transcripts that could potentially encode 16E5 are present in cervical biopsy specimens and cervical cancer cell lines, but the presence of E5 protein has been demonstrated in only two reports that have not been corroborated. In the present study, we show that trypsin cleavage of 16E5 generates a unique four-amino-acid C-terminal peptide (FLIT) that serves as a marker for E5 expression in transfected cells and epithelial cell lines containing integrated and episomal HPV-16 DNA. Following trypsin cleavage, reversed-phase chromatography and mass spectrometry (MS) were used to detect FLIT. Immunoprecipitation assays using a newly generated anti-16E5 antibody confirmed that 16E5 was solely responsible for the FLIT signal, and deuterated FLIT peptide provided an internal standard that enabled us to quantify the number of 16E5 molecules per cell. We show that 16E5 is expressed in the Caski but not in the SiHa cervical cancer cell line, suggesting that 16E5 may contribute to the malignant phenotype of some cervical cancers, even in cells exclusively containing an integrated HPV genome.

Papillomavirus E5: the smallest oncoprotein with many functions

Papillomaviruses (PVs) are established agents of human and animal cancers. They infect cutaneous and mucous epithelia. High Risk (HR) Human PVs (HPVs) are consistently associated with cancer of the uterine cervix, but are also involved in the etiopathogenesis of other cancer types. The early oncoproteins of PVs: E5, E6 and E7 are known to contribute to tumour progression. While the oncogenic activities of E6 and E7 are well characterised, the role of E5 is still rather nebulous. The widespread causal association of PVs with cancer makes their study worthwhile not only in humans but also in animal model systems. The Bovine PV (BPV) system has been the most useful animal model in understanding the oncogenic potential of PVs due to the pivotal role of its E5 oncoprotein in cell transformation. This review will highlight the differences between HPV-16 E5 (16E5) and E5 from other PVs, primarily from BPV. It will discuss the targeting of E5 as a possible therapeutic agent.

In vivo HPV 16 E5 mRNA: expression pattern in patients with squamous intra-epithelial lesions of the cervix

BACKGROUND

Human Papillomavirus (HPV) type 16 E5 is a small protein, which is reported to display transforming activity in vitro and in animal studies. The E5 transcriptional activity, however, has been rarely reported in vivo in literature.

OBJECTIVES

(a) To detect the E5 transcripts in vivo in a population of HPV 16 positive patients with abnormal cytology and (b) to correlate the level of expression to the degree of the cytological lesion.

STUDY DESIGN AND METHODS

250 cytological samples of HPV positive women were obtained and tested for the E6/E7 mRNA expression. Patients were selected if HPV 16 only mRNA positive and with a cytology consistent with low-grade/high-grade squamous intra-epithelial (LSIL/HSIL) lesions. Selected patients were tested for the E5 transcripts by reverse RT PCR, comparing the expression level in vivo with a transfected HPV 16 E5 HaCaT cell line.

RESULTS

27 HPV 16 E6/E7 mRNA positive LSIL/HSIL patients were selected. 13 out of 17 LSIL patients were tested positive for the E5 mRNA, showing an ample range of positivity. In the HSIL group 7 out of 10 patients were tested positive, displaying lower and more homogeneous levels of expression if compared with the transfected cells.

CONCLUSION

The HPV 16 E5 transcripts levels showed a broad distribution in vivo; the discrepancy was wider in LSIL patients, with HSIL patients displaying a more homogeneous profile. However, because of the limited number of patients, we could not draw a firm conclusion about the correlation between the E5 expression and the disease progression.

Local hyperthermia induces apoptosis of keratinocytes in both normal skin and condyloma acuminata via different pathways

Local hyperthermia has been successfully used in the treatment of viral warts. However, the mechanism of action of hyperthermia has largely remained unclear. In this study we evaluated the effect of local hyperthermia on the induction of apoptosis in human keratinocytes, and expression of apoptosis-related genes in both condyloma acuminata (CA) and normal skin. The study showed that higher hyperthermia increased the number of apoptotic keratinocytes in CA and normal skin. The temperature-dependent increased expression of Fas and Bax were observed in both CA and normal skin. In contrast, the expression of Bcl-2 in CA was decreased at both transcriptional and translational levels. Furthermore, the transcriptional expression of DR4 and DR5 were increased in a temperature-dependent manner in CA, but not in normal skin. These results suggest that different mechanisms of action might be involved in hyperthermia induced apoptosis in CA and normal skin.

A role for HPV16 E5 in cervical carcinogenesis

A subset of the mucosotropic human papillomaviruses (HPV), including HPV16, are etiologic agents for the vast majority of cervical cancers, other anogenital cancers, and a subset of head and neck squamous cell carcinomas. HPV16 encodes three oncogenes: E5, E6, and E7. Although E6 and E7 have been well-studied and clearly shown to be important contributors to these cancers, less is known about E5. In this study, we used E5 transgenic mice to investigate the role of E5 in cervical cancer. When treated for 6 months with estrogen, a cofactor for cervical carcinogenesis, E5 transgenic mice developed more severe neoplastic cervical disease than similarly treated nontransgenic mice, although no frank cancers were detected. In addition, E5 when combined with either E6 or E7 induced more severe neoplastic disease than seen in mice expressing only one viral oncogene. Prolonged treatment of E5 transgenic mice with exogenous estrogen uncovered an ability of E5 to cause frank cancer. These data indicate that E5 acts as an oncogene in the reproductive tracts of female mice.

Human papillomavirus type 16 E5 protein inhibits hydrogen-peroxide-induced apoptosis by stimulating ubiquitin-proteasome-mediated degradation of Bax in human cervical cancer cells

To investigate the mechanism by which the human papillomavirus (HPV) E5 protein contributes to the carcinogenesis of uterine cervical cancer, we studied the effect of HPV E5 on apoptosis of cervical cancer cells and its underlying mechanism. Expression of HPV16 E5 protein inhibited hydrogen peroxide-induced apoptosis in C-33A cervical cancer cells. E5 decreased the expression of Bax protein, and exogenous expression of Bax abolished the anti-apoptotic effect of E5. Knockdown of E5 by small interfering RNA sensitized CaSki cervical cancer cells to hydrogen peroxide-induced apoptosis with concurrent increase in Bax expression. Transient expression of E5 significantly increased the degradation rate of Bax protein by inducing the ubiquitination. The E5-induced decrease in Bax expression was inhibited by a cyclooxygenase-2 (COX-2) inhibitor, prostaglandin E2 (PGE(2)) receptor antagonists and cyclic adenosine monophosphate-dependent protein kinase (PKA) inhibitor. Treatment with PGE(2) decreased the expression of Bax and inhibited hydrogen peroxide-induced apoptosis of C-33A cells. We concluded that HPV16 E5 protein inhibits hydrogen peroxide-induced apoptosis of cervical cancer cells by stimulating the ubiquitin-proteasome-mediated degradation of Bax protein, and the pathway involves COX-2, PGE(2) and PKA. This finding suggests the possibility that HPV 16 E5 protein contributes to cervical carcinogenesis by inhibiting apoptosis of transformed cervical epithelial cells.

Effects of human papillomavirus type 16 E5 deletion mutants on epithelial morphology: functional characterization of each transmembrane domain

Human papillomavirus type 16 (HPV-16) is the cause of cervical cancer. The HPV genome encodes three transforming proteins, E5, E6 and E7. E6 and E7 are the main transforming proteins of HPV, while the role of E5 is still poorly understood. Using three dimensional organotypic raft cultures we show that HaCaT human keratinocytes expressing HPV-16 E5 form a very perturbed epithelium, with simultaneous hyperkeratinization of some cells and defective differentiation of other cells. The basal layer is disturbed and many cells invade the collagen matrix. Many cells among the differentiated layers show characteristics of basal cells: progression through the cell cycle, expression of cytokeratin 14, lack of cytokeratin 1 and production of matrix metalloproteases (MMP). Using deletion mutants which encompass the three hydrophobic domains of E5, we have assigned the ability to promote invasion of the matrix to the first hydrophobic domain, and the capacity to induce MMP9 to the C-terminal four amino acids. We also show that invasion and production of MMP9 can be dissociated, as mutants that are still capable of invasion do not produce MMP9 and vice versa.

Bap31 is a novel target of the human papillomavirus E5 protein

The E5 proteins of human papillomaviruses (HPVs) are small hydrophobic proteins that are expressed in the early and late stages of the viral life cycle; however, their role in HPV pathogenesis is not clearly understood. In this study, a split-ubiquitin yeast (Saccharomyces cerevisiae) two-hybrid system was used to identify B-cell-associated protein 31 (Bap31) as a binding partner of HPV E5 proteins. The association of these proteins was confirmed by coimmunoprecipitation of complexes of Bap31 with either HPV type 16 (HPV16) or HPV31 E5. In addition, Bap31 and E5 were found to colocalize in perinuclear patterns consistent with localization to the endoplasmic reticulum. Mutational analysis of E5 identified amino acids in the extreme C terminus as important for stabilizing the interaction with Bap31. Deletion of these C-terminal amino acids of E5 in the context of complete HPV31 genomes resulted in impaired proliferative capacity of HPV-positive keratinocytes following differentiation. When small interfering RNAs were used to reduce the levels of Bap31, the proliferative ability of HPV-positive keratinocytes upon differentiation was also reduced, implicating Bap31 as a regulator of this process. These studies identify a novel binding partner of the high-risk HPV E5 proteins and provide insight into how the E5 proteins may modulate the life cycle in differentiating cells.

Expression of the costimulatory molecule CD86, but not CD80, in keratinocytes of normal cervical epithelium and human papillomavirus-16 positive low squamous intraepithelial lesions

Keratinocytes have been traditionally considered as nonprofessional antigen presenting cells, since multipassaged cells from skin biopsies of healthy individuals do not constitutively express major histocompatibility complex (MHC) class II or costimulatory molecules, but can be induced to do so after exposure to interferon-gamma. In normal and human papillomavirus (HPV)-infected cervical epithelium, keratinocytes are affected by a variety of soluble mediators that could modulate the expression of molecules including costimulatory proteins; however, the presence of these molecules within the cervix has been poorly studied. Therefore, our aim was to further explore the presence of costimulatory molecules on normal cervical epithelium and HPV-16 positive low squamous intraepithelial lesions (LSIL). We found in situ CD86 (but not CD80) displayed on the surface of normal keratinocytes from the spinous layer of human cervical epithelium. The presence of the protein and its messenger RNA level (evaluated by in situ hybridization) was diminished in HPV-16 positive LSILs. Although downregulation of costimulatory molecules is frequently related to cytokines expression, we did not observe differences in the presence of interleukin-10, the main cytokine that inhibits CD86 expression. Expression of CD86 on keratinocytes from normal cervical epithelium could indicate the potentiality of these cells to activate cytotoxic T cells, while the shut-off of this molecule in HPV-16 positive lesions could be a mechanism for evading host immune surveillance, resulting in the persistent HPV infection and probable progression of cervical lesions.