A Conserved Amino Acid in the C Terminus of Human Papillomavirus E7 Mediates Binding to PTPN14 and Repression of Epithelial Differentiation

HPV18 E7 inhibits LATS1 kinase and activates YAP1 by degrading PTPN14

High-risk human papillomavirus (HPV) oncoproteins inactivate cellular tumor suppressors to reprogram host cell signaling pathways. HPV E7 proteins bind and degrade the tumor suppressor PTPN14, thereby promoting the nuclear localization of the YAP1 oncoprotein and inhibiting keratinocyte differentiation. YAP1 is a transcriptional coactivator that drives epithelial cell stemness and self-renewal. YAP1 activity is inhibited by the highly conserved Hippo pathway, which is frequently inactivated in human cancers. MST1/2 and LATS1/2 kinases form the core of the Hippo kinase cascade. Active LATS1 kinase is phosphorylated on threonine 1079 and inhibits YAP1 by phosphorylating it on amino acids including serine 127. Here, we tested the effect of high-risk (carcinogenic) HPV18 E7 on Hippo pathway activity. We found that either PTPN14 knockout or PTPN14 degradation by HPV18 E7 decreased the phosphorylation of LATS1 T1079 and YAP1 S127 in human keratinocytes and inhibited keratinocyte differentiation. Conversely, PTPN14-dependent differentiation required LATS kinases and certain PPxY motifs in PTPN14. Neither MST1/2 kinases nor the putative PTPN14 phosphatase active sites were required for PTPN14 to promote differentiation. Together, these data support that PTPN14 inactivation or degradation of PTPN14 by HPV18 E7 reduce LATS1 activity, promoting active YAP1 and inhibiting keratinocyte differentiation.IMPORTANCEThe Hippo kinase cascade inhibits YAP1, an oncoprotein and driver of cell stemness and self-renewal. There is mounting evidence that the Hippo pathway is targeted by tumor viruses including human papillomavirus. The high-risk HPV E7 oncoprotein promotes YAP1 nuclear localization and the carcinogenic activity of high-risk HPV E7 requires YAP1 activity. Blocking HPV E7-dependent YAP1 activation could inhibit HPV-mediated carcinogenesis, but the mechanism by which HPV E7 activates YAP1 has not been elucidated. Here we report that by degrading the tumor suppressor PTPN14, HPV18 E7 inhibits LATS1 kinase, reducing inhibitory phosphorylation on YAP1. These data support that an HPV oncoprotein can inhibit Hippo signaling to activate YAP1 and strengthen the link between PTPN14 and Hippo signaling in human epithelial cells.

HPV18 E7 inhibits LATS1 kinase and activates YAP1 by degrading PTPN14

High-risk human papillomavirus (HPV) oncoproteins inactivate cellular tumor suppressors to reprogram host cell signaling pathways. HPV E7 proteins bind and degrade the tumor suppressor PTPN14, thereby promoting the nuclear localization of the YAP1 oncoprotein and inhibiting keratinocyte differentiation. YAP1 is a transcriptional coactivator that drives epithelial cell stemness and self-renewal. YAP1 activity is inhibited by the highly conserved Hippo pathway, which is frequently inactivated in human cancers. MST1/2 and LATS1/2 kinases form the core of the Hippo kinase cascade. Active LATS1 kinase is phosphorylated on threonine 1079 and inhibits YAP1 by phosphorylating it on amino acids including serine 127. Here, we tested the effect of high-risk (carcinogenic) HPV18 E7 on Hippo pathway activity. We found that either PTPN14 knockout or PTPN14 degradation by HPV18 E7 decreased phosphorylation of LATS1 T1079 and YAP1 S127 in human keratinocytes and inhibited keratinocyte differentiation. Conversely, PTPN14-dependent differentiation required LATS kinases and certain PPxY motifs in PTPN14. Neither MST1/2 kinases nor the putative PTPN14 phosphatase active site were required for PTPN14 to promote differentiation. Taken together, these data support that PTPN14 inactivation or degradation of PTPN14 by HPV18 E7 reduce LATS1 activity, promoting active YAP1 and inhibiting keratinocyte differentiation.

Structural analysis of PTPN21 reveals a dominant-negative effect of the FERM domain on its phosphatase activity

PTPN21 belongs to the four-point-one, ezrin, radixin, moesin (FERM) domain-containing protein tyrosine phosphatases (PTP) and plays important roles in cytoskeleton-associated cellular processes like cell adhesion, motility, and cargo transport. Because of the presence of a WPE loop instead of a WPD loop in the phosphatase domain, it is often considered to lack phosphatase activity. However, many of PTPN21's biological functions require its catalytic activity. To reconcile these findings, we have determined the structures of individual PTPN21 FERM, PTP domains, and a complex between FERM-PTP. Combined with biochemical analysis, we have found that PTPN21 PTP is weakly active and is autoinhibited by association with its FERM domain. Disruption of FERM-PTP interaction results in enhanced ERK activation. The oncogenic HPV18 E7 protein binds to PTP at the same location as PTPN21 FERM, indicating that it may act by displacing the FERM domain from PTP. Our results provide mechanistic insight into PTPN21 and benefit functional studies of PTPN21-mediated processes.

HPV-associated oropharyngeal cancer: in search of surrogate biomarkers for early lesions

The incidence of oropharyngeal cancer (OPSCC) has escalated in the past few decades; this has largely been triggered by high-risk human papillomavirus (HPV). Early cancer screening is needed for timely clinical intervention and may reduce mortality and morbidity, but the lack of knowledge about premalignant lesions for OPSCC poses a significant challenge to early detection. Biomarkers that identify individuals at high risk for OPSCC may act as surrogate markers for precancer but these are limited as only a few studies decipher the multistep progression from HPV infection to OPSCC development. Here, we summarize the current literature describing the multistep progression from oral HPV infection, persistence, and tumor development in the oropharynx. We also examine key challenges that hinder the identification of premalignant lesions in the oropharynx and discuss potential biomarkers for oropharyngeal precancer. Finally, we evaluate novel strategies to improve investigations of the biological process that drives oral HPV persistence and OPSCC, highlighting new developments in the establishment of a genetic progression model for HPV + OPSCC and in vivo models that mimic HPV + OPSCC pathogenesis.

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.

Novel equid papillomavirus from domestic donkey

BACKGROUND

Papillomaviruses can be of great medical importance as they infect humans and animals such as Equus species, other livestock and pets. They are responsible for several papillomas and benign tumours in their host.

OBJECTIVES

To describe a novel equid papillomavirus detected in oral swab samples collected from donkeys (Equus asinus) found on the Northwest plateau of China.

STUDY DESIGN

Cross-sectional.

METHODS

Swab samples collected from the oral mucosa of 32 donkeys in the Gansu Province of China, were subjected to viral metagenomic analysis to detect the presence of Papillomavirus. After de novo assembly, a novel papillomavirus genome designated as Equus asinus papillomavirus 3 (EaPV3) was identified in the studied samples. Additional bioinformatic analysis of the assembled genome was done using the Geneious prime software (version 2022.0.2).

RESULTS

The complete circular genome of EaPV3 is 7430 bp in length with a GC content of 50.8%. The genome was predicted to contain five ORFs coding for three early proteins (E7, E1, and E2) and two late proteins (L1 and L2). Phylogenic analysis of the nucleotide sequences of the concatenated amino acid sequences of the E1E2L1L2 genes revealed that EaPV3 is most closely related to Equus asinus papillomavirus 1 (EaPV1). The genome analysis of EaPV3 revealed similar genome organisation with other equine papillomavirus and the presence of E7 papillomavirus oncoprotein.

MAIN LIMITATIONS

Since there were no warts in the oral cavity of the donkeys in this study, and no biopsy samples taken, we are unable to conclusively link the novel virus to any clinical condition in the donkeys.

CONCLUSIONS

The Comparative characterisation of EaPV3 and its closest relatives, as well as phylogenetic analysis demonstrated that it is a novel virus specie that clusters within the Dyochipapilloma PV genus.

MmuPV1 E6 induces cell proliferation and other hallmarks of cancer

IMPORTANCE

The 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.

A small molecule targeting the interaction between human papillomavirus E7 oncoprotein and cellular phosphatase PTPN14 exerts antitumoral activity in cervical cancer cells

Human papillomavirus (HPV)-induced cancers still represent a major health issue for worldwide population and lack specific therapeutic regimens. Despite substantial advancements in anti-HPV vaccination, the incidence of HPV-related cancers remains high, thus there is an urgent need for specific anti-HPV drugs. The HPV E7 oncoprotein is a major driver of carcinogenesis that acts by inducing the degradation of several host factors. A target is represented by the cellular phosphatase PTPN14 and its E7-mediated degradation was shown to be crucial in HPV oncogenesis. Here, by exploiting the crystal structure of E7 bound to PTPN14, we performed an in silico screening of small-molecule compounds targeting the C-terminal CR3 domain of E7 involved in the interaction with PTPN14. We discovered a compound able to inhibit the E7/PTPN14 interaction in vitro and to rescue PTPN14 levels in cells, leading to a reduction in viability, proliferation, migration, and cancer-stem cell potential of HPV-positive cervical cancer cells. Mechanistically, as a consequence of PTPN14 rescue, treatment of cancer cells with this compound altered the Yes-associated protein (YAP) nuclear-cytoplasmic shuttling and downstream signaling. Notably, this compound was active against cervical cancer cells transformed by different high-risk (HR)-HPV genotypes indicating a potential broad-spectrum activity. Overall, our study reports the first-in-class inhibitor of E7/PTPN14 interaction and provides the proof-of-principle that pharmacological inhibition of this interaction by small-molecule compounds could be a feasible therapeutic strategy for the development of novel antitumoral drugs specific for HPV-associated cancers.

Epstein-Barr virus LMP1 protein promotes proliferation and inhibits differentiation of epithelial cells via activation of YAP and TAZ

Latent Epstein-Barr virus (EBV) infection promotes undifferentiated nasopharyngeal carcinomas (NPCs) in humans, but the mechanism(s) for this effect has been difficult to study because EBV cannot transform normal epithelial cells in vitro and the EBV genome is often lost when NPC cells are grown in culture. Here we show that the latent EBV protein, LMP1 (Latent membrane protein 1), induces cellular proliferation and inhibits spontaneous differentiation of telomerase-immortalized normal oral keratinocytes (NOKs) in growth factor-deficient conditions by increasing the activity of the Hippo pathway effectors, YAP (Yes-associated protein) and TAZ (Transcriptional coactivator with PDZ-binding motif). We demonstrate that LMP1 enhances YAP and TAZ activity in NOKs both by decreasing Hippo pathway-mediated serine phosphorylation of YAP and TAZ and increasing Src kinase-mediated Y357 phosphorylation of YAP. Furthermore, knockdown of YAP and TAZ is sufficient to reduce proliferation and promote differentiation in EBV-infected NOKs. We find that YAP and TAZ are also required for LMP1-induced epithelial-to-mesenchymal transition. Importantly, we demonstrate that ibrutinib (an FDA-approved BTK inhibitor that blocks YAP and TAZ activity through an off-target effect) restores spontaneous differentiation and inhibits proliferation of EBV-infected NOKs at clinically relevant doses. These results suggest that LMP1-induced YAP and TAZ activity contributes to the development of NPC.

MmuPV1 E7's interaction with PTPN14 delays Epithelial differentiation and contributes to virus-induced skin disease

Human papillomaviruses (HPVs) contribute to approximately 5% of all human cancers. Species-specific barriers limit the ability to study HPV pathogenesis in animal models. Murine papillomavirus (MmuPV1) provides a powerful tool to study the roles of papillomavirus genes in pathogenesis arising from a natural infection. We previously identified Protein Tyrosine Phosphatase Non-Receptor Type 14 (PTPN14), a tumor suppressor targeted by HPV E7 proteins, as a putative cellular target of MmuPV1 E7. Here, we confirmed the MmuPV1 E7-PTPN14 interaction. Based on the published structure of the HPV18 E7/PTPN14 complex, we generated a MmuPV1 E7 mutant, E7K81S, that was defective for binding PTPN14. Wild-type (WT) and E7K81S mutant viral genomes replicated as extrachromosomal circular DNAs to comparable levels in mouse keratinocytes. E7K81S mutant virus (E7K81S MmuPV1) was generated and used to infect FoxN/Nude mice. E7K81S MmuPV1 caused neoplastic lesions at a frequency similar to that of WT MmuPV1, but the lesions arose later and were smaller than WT-induced lesions. The E7K81S MmuPV1-induced lesions also had a trend towards a less severe grade of neoplastic disease. In the lesions, E7K81S MmuPV1 supported the late (productive) stage of the viral life cycle and promoted E2F activity and cellular DNA synthesis in suprabasal epithelial cells to similar degrees as WT MmuPV1. There was a similar frequency of lateral spread of infections among mice infected with E7K81S or WT MmuPV1. Compared to WT MmuPV1-induced lesions, E7K81S MmuPV1-induced lesions had a significant expansion of cells expressing differentiation markers, Keratin 10 and Involucrin. We conclude that an intact PTPN14 binding site is necessary for MmuPV1 E7's ability to contribute to papillomavirus-induced pathogenesis and this correlates with MmuPV1 E7 causing a delay in epithelial differentiation, which is a hallmark of papillomavirus-induced neoplasia.

Systematic Analysis of IL-1 Cytokine Signaling Suppression by HPV16 Oncoproteins

The human papillomavirus (HPV) E6 and E7 oncogenes are expressed at all stages of HPV-mediated carcinogenesis and are essential drivers of cancers caused by high-risk HPV. Some of the activities of HPV E6 and E7, such as their interactions with host cellular tumor suppressors, have been characterized extensively. There is less information about how high-risk HPV E6 and E7 alter cellular responses to cytokines that are present in HPV-infected tissues and are an important component of the tumor microenvironment. We used several models of HPV oncoprotein activity to assess how HPV16 E6 and E7 alter the cellular response to the proinflammatory cytokine IL-1β. Models of early stage HPV infection and of established HPV-positive head and neck cancers exhibited similar dysregulation of IL-1 pathway genes and suppressed transcriptional responses to IL-1β treatment. Such overlap in cell responses supports that changes induced by HPV16 E6 and E7 early in infection could persist and contribute to a dysregulated immune environment throughout carcinogenesis. HPV16 E6 and E7 also drove the upregulation of several suppressors of IL-1 cytokine signaling, including SIGIRR, both in primary keratinocytes and in cancer cells. SIGIRR knockout was insufficient to increase IL-1β-dependent gene expression in the presence of HPV16 E6 and E7, suggesting that multiple suppressors of IL-1 signaling contribute to dampened IL-1 responses in HPV16-positive cells. IMPORTANCE Human papillomavirus (HPV) infection is responsible for nearly 5% of the worldwide cancer burden. HPV-positive tumors develop over years to decades in tissues that are subject to frequent stimulation by proinflammatory cytokines. However, the effects of HPV oncoproteins on the cellular response to cytokine stimulation are not well defined. We analyzed IL-1 cytokine signaling in several models of HPV biology and disease. We found that HPV16 E6 and E7 oncoproteins mediate a broad and potent suppression of cellular responses to IL-1β in models of both early and late stages of carcinogenesis. Our data provide a resource for future investigation of IL-1 signaling in HPV-positive cells and cancers.

Description of CRISPR-Cas9 development and its prospects in human papillomavirus-driven cancer treatment

Human papillomaviruses (HPVs) have been recognized as the etiologic agents of various cancers and are called HPV-driven cancers. Concerning HPV-mediated carcinogenic action, gene therapy can cure cancer at the molecular level by means of the correction of specific genes or sites. CRISPR-Cas9, as a novel genetic editing technique, can correct errors in the genome and change the gene expression and function in cells efficiently, quickly, and with relative ease. Herein, we overviewed studies of CRISPR-mediated gene remedies for HPV-driven cancers and summarized the potential applications of CRISPR-Cas9 in gene therapy for cancer.

HPV 16 E7 alters translesion synthesis signaling

A subset of human papillomaviruses (HPVs) are the cause of virtually every cervical cancer. These so-called "high-risk" HPVs encode two major oncogenes (HPV E6 and E7) that are necessary for transformation. Among "high-risk" HPVs, HPV16 causes most cervical cancers and is often used as a representative model for oncogenic HPVs. The HPV16 E7 oncogene facilitates the HPV16 lifecycle by binding and destabilizing RB, which ensures the virus has access to cellular replication machinery. RB destabilization increases E2F1-responsive gene expression and causes replication stress. While HPV16 E6 mitigates some of the deleterious effects associated with this replication stress by degrading p53, cells undergo separate adaptations to tolerate the stress. Here, we demonstrate that this includes the activation of the translesion synthesis (TLS) pathway, which prevents replication stress from causing replication fork collapse. We show that significantly elevated TLS gene expression is more common in cervical cancers than 15 out of the 16 the other cancer types that we analyzed. In addition to increased TLS protein abundance, HPV16 E7 expressing cells have a reduced ability to induct a critical TLS factor (POLη) in response to replication stress-inducing agents. Finally, we show that increased expression of at least one TLS gene is associated with improved survival for women with cervical cancer.

Molecular Mechanisms of MmuPV1 E6 and E7 and Implications for Human Disease

Human papillomaviruses (HPVs) cause a substantial amount of human disease from benign disease such as warts to malignant cancers including cervical carcinoma, head and neck cancer, and non-melanoma skin cancer. Our ability to model HPV-induced malignant disease has been impeded by species specific barriers and pre-clinical animal models have been challenging to develop. The recent discovery of a murine papillomavirus, MmuPV1, that infects laboratory mice and causes the same range of malignancies caused by HPVs provides the papillomavirus field the opportunity to test mechanistic hypotheses in a genetically manipulatable laboratory animal species in the context of natural infections. The E6 and E7 proteins encoded by high-risk HPVs, which are the HPV genotypes associated with human cancers, are multifunctional proteins that contribute to HPV-induced cancers in multiple ways. In this review, we describe the known activities of the MmuPV1-encoded E6 and E7 proteins and how those activities relate to the activities of HPV E6 and E7 oncoproteins encoded by mucosal and cutaneous high-risk HPV genotypes.

Two conserved amino acids differentiate the biology of high-risk and low-risk HPV E5 proteins

The high-risk alpha human papillomaviruses (HPVs) are responsible for 99% of cervical cancers. While the biological functions of the HPV E6 and E7 oncoproteins are well-characterized, the function of E5 has remained elusive. Here, we examined gene expression changes induced by E5 proteins from high-risk HPV-16 and low-risk HPV-6b in multiple pools of primary human keratinocytes. Surprisingly, microarray analysis revealed that over 700 genes were significantly regulated by HPV-6b E5, while only 25 genes were consistently and significantly regulated by HPV-16 E5 in three biological replicates. However, we observed that more than thousand genes were altered in individual sample compared with vector. The gene expression profile induced by 16E5 in primary genital keratinocytes was very different from what has been previously published using immortalized HaCaT cells. Genes altered by HPV-16 E5 were unaffected by HPV-6b E5. Our data demonstrate that E5 proteins from the high- and low-risk HPVs have different functions in the HPV-host cell. Interestingly, conversion of two amino acids in HPV-16 E5 to the low-risk HPV-6b sequence eliminated the induction of high-risk related cellular genes.

YAP1 activation by human papillomavirus E7 promotes basal cell identity in squamous epithelia

Persistent human papillomavirus (HPV) infection of stratified squamous epithelial cells causes nearly 5% of cancer cases worldwide. HPV-positive oropharyngeal cancers harbor few mutations in the Hippo signaling pathway compared to HPV-negative cancers at the same anatomical site, prompting the hypothesis that an HPV-encoded protein inactivates the Hippo pathway and activates the Hippo effector yes-associated protein (YAP1). The HPV E7 oncoprotein is required for HPV infection and for HPV-mediated oncogenic transformation. We investigated the effects of HPV oncoproteins on YAP1 and found that E7 activates YAP1, promoting YAP1 nuclear localization in basal epithelial cells. YAP1 activation by HPV E7 required that E7 binds and degrades the tumor suppressor protein tyrosine phosphatase non-receptor type 14 (PTPN14). E7 required YAP1 transcriptional activity to extend the lifespan of primary keratinocytes, indicating that YAP1 activation contributes to E7 carcinogenic activity. Maintaining infection in basal cells is critical for HPV persistence, and here we demonstrate that YAP1 activation causes HPV E7 expressing cells to be retained in the basal compartment of stratified epithelia. We propose that YAP1 activation resulting from PTPN14 inactivation is an essential, targetable activity of the HPV E7 oncoprotein relevant to HPV infection and carcinogenesis.

The ‘epithelial’ cells that cover our bodies are in a constant state of turnover. Every few weeks, the outermost layers die and are replaced by new cells from the layers below. For scientists, this raises a difficult question. Cells infected by human papillomaviruses, often known as HPV, can become cancerous over years or even decades. How do infected cells survive while the healthy cells around them mature and get replaced?

One clue could lie in PTPN14, a human protein which many papillomaviruses eliminate using their viral E7 protein; this mechanism could be essential for the virus to replicate and cause cancer. To find out the impact of losing PTPN14, Hatterschide et al. used human epithelial cells to make three-dimensional models of infected tissues. These experiments showed that, when papillomaviruses destroy PTPN14, a human protein called YAP1 turns on in the lowest, most long-lived layer of the tissue. Cells in which YAP1 is activated survive while those that carry the inactive version mature and die. This suggests that papillomaviruses turn on YAP1 to remain in tissues for long periods.

Papillomaviruses cause about five percent of all human cancers. Finding ways to stop them from activating YAP1 has the potential to prevent disease. Overall, the research by Hatterschide et al. also sheds light on other epithelial cancers which are not caused by viruses.

Human Papillomaviruses as Infectious Agents in Gynecological Cancers. Oncogenic Properties of Viral Proteins

Human papillomaviruses (HPVs), which belong to the Papillomaviridae family, constitute a group of small nonenveloped double-stranded DNA viruses. HPV has a small genome that only encodes a few proteins, and it is also responsible for 5% of all human cancers, including cervical, vaginal, vulvar, penile, anal, and oropharyngeal cancers. HPV types may be classified as high- and low-risk genotypes (HR-HPVs and LR-HPVs, respectively) according to their oncogenic potential. HR-HPV 16 and 18 are the most common types worldwide and are the primary types that are responsible for most HPV-related cancers. The activity of the viral E6 and E7 oncoproteins, which interfere with critical cell cycle points such as suppressive tumor protein p53 (p53) and retinoblastoma protein (pRB), is the major contributor to HPV-induced neoplastic initiation and progression of carcinogenesis. In addition, the E5 protein might also play a significant role in tumorigenesis. The role of HPV in the pathogenesis of gynecological cancers is still not fully understood, which indicates a wide spectrum of potential research areas. This review focuses on HPV biology, the distribution of HPVs in gynecological cancers, the properties of viral oncoproteins, and the molecular mechanisms of carcinogenesis.

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.

Transcription Factor Homeobox D9 Drives the Malignant Phenotype of HPV18-Positive Cervical Cancer Cells via Binding to the Viral Early Promoter

Simple Summary

Transcription factor homeobox D9 (HOXD9) was previously reported to bind to the P97 promoter of HPV16 to induce viral E6/E7 oncogenes. In this article, we investigated whether HOXD9 regulated the P105 promoter of HPV18 and examined the role of HOXD9 in intracellular signaling of cervical cancer (CC). HOXD9 was directly bound to the P105 promoter and regulated the expression of E6/E7 genes of HPV18. The HOXD9 knockdown suppressed the E6/E7 gene expression in HPV18-positive cervical cancer cells. It decreased the expression of E6, activated the p53 pathway, and induced apoptosis. In addition, downregulation of the E7 gene expression activated the Rb pathway, causing G1 arrest in the cell cycle and markedly suppressing cell proliferation. Our results indicate that HOXD9 has pivotal roles in the proliferation and immortalization of HPV18-positive cervical cancer cells through activating the P105 promoter.

Abstract

Persistent infections with two types of human papillomaviruses (HPV), HPV16 and HPV18, are the most common cause of cervical cancer (CC). Two viral early genes, E6 and E7, are associated with tumor development, and expressions of E6 and E7 are primarily regulated by a single viral promoter: P97 in HPV16 and P105 in HPV18. We previously demonstrated that the homeobox D9 (HOXD9) transcription factor is responsible for the malignancy of HPV16-positive CC cell lines via binding to the P97 promoter. Here, we investigated whether HOXD9 is also involved in the regulation of the P105 promoter using two HPV18-positive CC cell lines, SKG-I and HeLa. Following the HOXD9 knockdown, cell viability was significantly reduced, and E6 expression was suppressed and was accompanied by increased protein levels of P53, while mRNA levels of TP53 did not change. E7 expression was also downregulated and, while mRNA levels of RB1 and E2F were unchanged, mRNA levels of E2F-target genes, MCM2 and PCNA, were decreased, which indicates that the HOXD9 knockdown downregulates E7 expression, thus leading to an inactivation of E2F and the cell-cycle arrest. Chromatin immunoprecipitation and promoter reporter assays confirmed that HOXD9 is directly associated with the P105 promoter. Collectively, our results reveal that HOXD9 drives the HPV18 early promoter activity to promote proliferation and immortalization of the CC cells.

PTPN14 deficiency alleviates podocyte injury through suppressing inflammation and fibrosis by targeting TRIP6 in diabetic nephropathy

Diabetic nephropathy (DN) is a common complication of diabetes, and a leading cause of end-stage renal disease. However, the pathogenesis that contributes to DKD is still not fully understood. Protein tyrosine phosphatase non-receptor type 14 (PTPN14), a non receptor tyrosine phosphatase, has numerous cellular events, such as inflammation and cell death. But its potential on DKD has not been investigated yet. In this study, we found that PTPN14 expression was markedly up-regulated in kidney samples of DKD patients, which were confirmed in diabetic mice and were clearly localized in glomeruli. The diabetic mouse model was established using streptozotocin (STZ) in wild type (WT) or PTPN knockout (KO) mice. After, STZ challenge, STZ mice displayed improved kidney functions. The results also showed that STZ-induced histological changes and podocyte injury in renal tissues, which were effectively alleviated by PTPN14 deletion. Moreover, PTPN14 deficiency significantly mitigated inflammatory response and fibrosis in glomeruli of STZ-challenged mice through restraining the activation of nuclear factor-κB (NF-κB) and transforming growth factor (TGF)-β1 signaling pathways, respectively. The inhibitory effects of PTPN14 suppression on inflammation and fibrosis were confirmed in high glucose (HG)-incubated podocytes. We further found that thyroid receptor interactor protein 6 (TRIP6) expression was dramatically up-regulated in glomeruli of STZ-challenged mice, and was abolished by PTPN14 deletion, which was confirmed in HG-treated podocytes with PTPN14 knockdown. Intriguingly, our in vitro studies showed that PTPN14 directly interacted with TRIP6. Of note, over-expressing TRIP6 markedly abrogated the effects of PTPN14 silence to restrict inflammatory response and fibrosis in HG-incubated podocytes. Taken together, our findings demonstrated that targeting PTPN14 may provide feasible therapies for DKD treatment.

New insights in Hippo signalling alteration in human papillomavirus-related cancers

The persistent infection with high-risk human papillomavirus (HPV) is an etiologic factor for the development of different types of cancers, mainly attributed to the continuous expression of E6 and E7 HPV oncoproteins, which regulate several cell signalling pathways including the Hippo pathway. It has been demonstrated that E6 proteins promote the increase of the Hippo elements YAP, TAZ and TEAD, at protein level, as well as their transcriptional targets. Also, E6 and E7 oncoproteins promote nuclear YAP localization and a decrease in YAP negative regulators such as MST1, PTPN14 or SOCS6. Interestingly, Hippo signalling components modulate HPV activity, such as TEAD1 and the transcriptional co-factor VGLL1, induce the activation of HPV early and late promoters, while hyperactivation of YAP in specific cells facilitates virus infection by increasing putative HPV receptors and by evading innate immunity. Additionally, alterations in Hippo signalling elements have been found in HPV-related cancers and particularly, the involvement of HPV oncoproteins on the regulation of some of these Hippo components has been also proposed, although the precise mechanisms remain unclear. The present review addresses the recent findings describing the interplay between HPV and Hippo signalling in HPV-related cancers, a fact that highlights the importance of developing more in-depth studies in this field to establish key therapeutic targets.

PTPN14 aggravates inflammation through promoting proteasomal degradation of SOCS7 in acute liver failure

Acute liver failure (ALF) is a rare but life-threatening systemic disorder. The innate immune regulation has an important role in this process; however, the specific mechanisms are not completely clear. Using the LPS + D-GalN-induced ALF mouse model, we found that the survival rate of PTPN14-deficient mice was higher than that of the control group, while the release of inflammatory factors was significantly lower. We further showed that PTPN14 interacted with SOCS7, and promoted the degradation of SOCS7 through ubiquitination at K11 and K48, thereby reducing the protein level of SOCS7 and weakening the inhibitory effects on inflammatory factors. More importantly, SOCS7 blocked the NF-κB signaling pathway by preventing the activity of the IKK complex, and then reduced the expression of downstream inflammatory factors. In this study, we firstly reported the inhibitory effect of SOCS7 on the NF-κB pathway in the ALF mouse model and elucidated the mechanism of PTPN14–SOCS7–NF-κB axis in the regulation of inflammation. These results provide new insights into the clinical treatment of ALF.