Human Papillomavirus 16 E6 Oncoprotein Interferences with Insulin Signaling Pathway by Binding to Tuberin

Impact of HPV strains on molecular mechanisms of cervix cancer

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

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

JAK/STAT Signaling and Cervical Cancer: From the Cell Surface to the Nucleus

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway constitutes a rapid signaling module from the cell surface to the nucleus, and activates different cellular responses, such as proliferation, survival, migration, invasion, and inflammation. When the JAK/STAT pathway is altered, it contributes to cancer progression and metastasis. STAT proteins play a central role in developing cervical cancer, and inhibiting the JAK/STAT signaling may be necessary to induce tumor cell death. Several cancers show continuous activation of different STATs, including cervical cancer. The constitutive activation of STAT proteins is associated with a poor prognosis and overall survival. The human papillomavirus (HPV) oncoproteins E6 and E7 play an essential role in cervical cancer progression, and they activate the JAK/STAT pathway and other signals that induce proliferation, survival, and migration of cancer cells. Moreover, there is a crosstalk between the JAK/STAT signaling cascade with other signaling pathways, where a plethora of different proteins activate to induce gene transcription and cell responses that contribute to tumor growth. Therefore, inhibition of the JAK/STAT pathway shows promise as a new target in cancer treatment. In this review, we discuss the role of the JAK/STAT pathway components and the role of the HPV oncoproteins associated with cellular malignancy through the JAK/STAT proteins and other signaling pathways to induce tumor growth.

Targeting the PI3K Pathway in Gynecologic Malignancies

PURPOSE OF REVIEW

This review explores the PI3K pathway aberrations common in gynecologic malignancies, the relevant therapeutic targets that have been explored to date particularly given their success in endometrial cancers, and predictive biomarkers of response to therapy.

RECENT FINDINGS

Landmark trials have been noted involving this pathway, particularly in endometrial cancers. One phase II trial of the potent orally bioavailable mTOR inhibitor, everolimus, in combination with letrozole demonstrated an unprecedented clinical benefit rate (CBR) of 40% and high objective response rate (RR) of 32% in hormone agnostic endometrial cancers. This was followed by GOG 3007 that compared everolimus and letrozole to hormonal therapy yielding similar response rates but double progression-free survival rates. The phosphoinositide 3-kinase (PI3K) signaling pathway is implicated in tumorigenesis given its regulation over cell growth, cellular trafficking, and angiogenesis. In gynecologic malignancies, alterations in PI3K signaling are common. Therefore, developing modulators of the PI3K pathway and identifying molecular markers to predict response are of great interest for these cancer types.

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.

Ecdysoneless Protein Regulates Viral and Cellular mRNA Splicing to Promote Cervical Oncogenesis

High-risk human papillomaviruses (HPV), exemplified by HPV16/18, are causally linked to human cancers of the anogenital tract, skin, and upper aerodigestive tract. Previously, we identified Ecdysoneless (ECD) protein, the human homolog of the Drosophila ecdysoneless gene, as a novel HPV16 E6-interacting protein. Here, we show that ECD, through its C-terminal region, selectively binds to high-risk but not to low-risk HPV E6 proteins. We demonstrate that ECD is overexpressed in cervical and head and neck squamous cell carcinoma (HNSCC) cell lines as well as in tumor tissues. Using The Cancer Genome Atlas dataset, we show that ECD mRNA overexpression predicts shorter survival in patients with cervical and HNSCC. We demonstrate that ECD knockdown in cervical cancer cell lines led to impaired oncogenic behavior, and ECD co-overexpression with E7 immortalized primary human keratinocytes. RNA-sequencing analyses of SiHa cells upon ECD knockdown showed to aberrations in E6/E7 RNA splicing, as well as RNA splicing of several HPV oncogenesis-linked cellular genes, including splicing of components of mRNA splicing machinery itself. Taken together, our results support a novel role of ECD in viral and cellular mRNA splicing to support HPV-driven oncogenesis. IMPLICATIONS: This study links ECD overexpression to poor prognosis and shorter survival in HNSCC and cervical cancers and identifies a critical role of ECD in cervical oncogenesis through regulation of viral and cellular mRNA splicing.

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.

Redox-sensitive signalling pathways regulated by human papillomavirus in HPV-related cancers

High-risk human papillomavirus (HR-HPV) chronic infection is associated with the induction of different HPV-related cancers, such as cervical, anus, vaginal, vulva, penis and oropharynx. HPV-related cancers have been related to oxidative stress (OS), where OS has a significant role in cancer development and maintenance. Surgical resection is the treatment of choice for localised HPV-related cancers; however, these malignancies commonly progress to metastasis. In advanced stages, systemic therapies are the best option against HPV-related cancers. These therapies include cytokine therapy or a combination of tyrosine kinase inhibitors with immunotherapies. Nevertheless, these strategies are still insufficient. Cell redox-sensitive signalling pathways have been poorly studied, although they have been associated with the development and maintenance of HPV-related cancers. In this review, we analyse the known alterations of the following redox-sensitive molecules and signalling pathways by HR-HPV in HPV-related cancers: MAPKs, Akt/TSC2/mTORC1, Wnt/β-Cat, NFkB/IkB/NOX2, HIF/VHL/VEGF and mitochondrial signalling pathways as potential targets for redox therapy.

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.

Human Papillomavirus and Cellular Pathways: Hits and Targets

The Human Papillomavirus (HPV) is the causative agent of different kinds of tumors, including cervical cancers, non-melanoma skin cancers, anogenital cancers, and head and neck cancers. Despite the vaccination campaigns implemented over the last decades, we are far from eradicating HPV-driven malignancies. Moreover, the lack of targeted therapies to tackle HPV-related tumors exacerbates this problem. Biomarkers for early detection of the pathology and more tailored therapeutic approaches are needed, and a complete understanding of HPV-driven tumorigenesis is essential to reach this goal. In this review, we overview the molecular pathways implicated in HPV infection and carcinogenesis, emphasizing the potential targets for new therapeutic strategies as well as new biomarkers.

The high-risk HPV E6 proteins modify the activity of the eIF4E protein via the MEK/ERK and AKT/PKB pathways

Previous studies have proposed that the human papillomavirus (HPV) E6 oncoproteins modify the transcriptional activity of eIF4E through mechanisms dependent on p53 degradation. However, the effect of these oncoproteins on pathways regulating the activity of the eIF4E protein remains poorly understood. Hence, we investigated the mechanisms whereby E6 proteins regulate the activity of the eIF4E protein and its effect on target genes. Overexpression of E6 constructs (HPV-6, HPV-16, HPV-18, and HPV52) showed that E6 oncoproteins increased phosphorylation of the eIF4E protein (Serine-209). This result was mainly mediated by phosphorylation of the 4EBP1 protein via the PI3K/AKT pathway. Additionally, the pharmacological inhibition of eIF4E phosphorylation in cervical cancer cell lines substantially reduced the protein levels of CCND1 and ODC1, indicating that E6 of the high-risk genotypes may modify protein synthesis of the eIF4E target genes by increasing the activity of the AKT and ERK pathways.

Emerging translation strategies during virus-host interaction

Translation control is crucial during virus-host interaction. On one hand, viruses completely rely on the protein synthesis machinery of host cells to propagate and have evolved various mechanisms to redirect the host's ribosomes toward their viral mRNAs. On the other hand, the host rewires its translation program in an attempt to contain and suppress the virus early on during infection; the antiviral program includes specific control on protein synthesis to translate several antiviral mRNAs involved in quenching the infection. As the infection progresses, host translation is in turn inhibited in order to limit viral propagation. We have learnt of very diverse strategies that both parties utilize to gain or retain control over the protein synthesis machinery. Yet novel strategies continue to be discovered, attesting for the importance of mRNA translation in virus-host interaction. This review focuses on recently described translation strategies employed by both hosts and viruses. These discoveries provide additional pieces in the understanding of the complex virus-host translation landscape. This article is categorized under: Translation > Translation Mechanisms Translation > Translation Regulation.

Is viral E6 oncoprotein a viable target? A critical analysis in the context of cervical cancer

An understanding of the pathology of cervical cancer (CC) mediated by E6/E7 oncoproteins of high-risk human papillomavirus (HPV) was developed by late 80's. But if we look at the present scenario, not a single drug could be developed to inhibit these oncoproteins and in turn, be used specifically for the treatment of CC. The readers are advised not to presume the "viability of E6 protein" as mentioned in the title relates to just druggability of E6. The viability aspect will cover almost everything a researcher should know to develop E6 inhibitors until the preclinical stage. Herein, we have analysed the achievements and shortcomings of the scientific community in the last four decades in targeting HPV E6 against CC. Role of all HPV proteins has been briefly described for better perspective with a little detailed discussion of the role of E6. We have reviewed the articles from 1985 onward, reporting in vitro inhibition of E6. Recently, many computational studies have reported potent E6 inhibitors and these have also been reviewed. Subsequently, a critical analysis has been reported to cover the in vitro assay protocols and in vivo models to develop E6 inhibitors. A paragraph has been devoted to the role of public policy to fight CC employing vaccines and whether the vaccine against HPV has quenched the zeal to develop drugs against it. The review concludes with the challenges and the way forward.

Human papillomavirus type 16 E6 and E7 oncoproteins interact with the nuclear p53-binding protein 1 in an in vitro reconstructed 3D epithelium: new insights for the virus-induced DNA damage response

Background

Despite vaccination and screening measures, anogenital cancer, mainly promoted by HPV16 oncoproteins, still represents the fourth tumor and the second cause of death among women.

Cell replication fidelity is the result of the host DNA damage response (DDR). Unlike many DNA viruses that promote their life cycle through the DDR inactivation, HR-HPVs encourage cells proliferation despite the DDR turned on. Why and how it occurs has been only partially elucidated.

During HPV16 infection, E6 links and degrades p53 via the binding to the E6AP LXXLL sequence; unfortunately, E6 direct role in the DDR response has not clearly identified yet.

Similarly, E7 increases DDR by competing with E2F1-pRb interaction, thus leading to the inactivation of pRb, and promotion, E2F1 mediated, of DDR genes translation, by binding to the pRb-like proteins CBP/p300 and p107, that also harbour LXXLL sequence, and via the interaction and activation of several DDR proteins.

Methods

To gain information regarding E6 and E7 contribution in DDR activation, we produced an in vitro 3D HPV16-E6E7 infected epithelium, already consolidated study model for HPVs, and validated it by assessing H&E staining and BrdU, HPV16 DNA, E6E7 proteins and γH2A.X/53BP1 double-strand break (DSBs) sensors expression; then we made an immuno-colocalization of E6 and E7 with cyclin E2 and B1.

Since 53BP1, like E6 and E7, also binds p53 and pRb, we supposed their possible direct binding. To explore this hypothesis, we performed a double immunofluorescence of E6 and E7 with 53BP1, a sequence analysis of 53BP1 within its BRCT2 domain and then an in situ PLA within CaSki, E6E7HPV16 NHEKs and the 3D model.

Results

The in vitro epithelium resembled the histology and the events typical of in vivo infected tissues. E6E7HPV16 were both expressed in basal and differentiated strata and induced H2A.X phosphorylation and 53BP1 increment into nuclear foci.

After highlighting E6 and E7 co-expression with 53BP1 and a LKVLL sequence within the 53BP1 BRCT2 domain, we demonstrated the bindings via the PLA technique.

Conclusions

Our results reinforce E6 and E7 role in cellular function control providing potentially new insights into the activity of this tumor virus.

Battling for Ribosomes: Translational Control at the Forefront of the Antiviral Response

In the early stages of infection, gaining control of the cellular protein synthesis machinery including its ribosomes is the ultimate combat objective for a virus. To successfully replicate, viruses unequivocally need to usurp and redeploy this machinery for translation of their own mRNA. In response, the host triggers global shutdown of translation while paradoxically allowing swift synthesis of antiviral proteins as a strategy to limit collateral damage. This fundamental conflict at the level of translational control defines the outcome of infection. As part of this special issue on molecular mechanisms of early virus-host cell interactions, we review the current state of knowledge regarding translational control during viral infection with specific emphasis on protein kinase RNA-activated and mammalian target of rapamycin-mediated mechanisms. We also describe recent technological advances that will allow unprecedented insight into how viruses and host cells battle for ribosomes.

The human papillomavirus replication cycle, and its links to cancer progression: a comprehensive review

HPVs (human papillomaviruses) infect epithelial cells and their replication cycle is intimately linked to epithelial differentiation. There are over 200 different HPV genotypes identified to date and each displays a strict tissue specificity for infection. HPV infection can result in a range of benign lesions, for example verrucas on the feet, common warts on the hands, or genital warts. HPV infects dividing basal epithelial cells where its dsDNA episomal genome enters the nuclei. Upon basal cell division, an infected daughter cell begins the process of keratinocyte differentiation that triggers a tightly orchestrated pattern of viral gene expression to accomplish a productive infection. A subset of mucosal-infective HPVs, the so-called ‘high risk’ (HR) HPVs, cause cervical disease, categorized as low or high grade. Most individuals will experience transient HR-HPV infection during their lifetime but these infections will not progress to clinically significant cervical disease or cancer because the immune system eventually recognizes and clears the virus. Cancer progression is due to persistent infection with an HR-HPV. HR-HPV infection is the cause of >99.7% cervical cancers in women, and a subset of oropharyngeal cancers, predominantly in men. HPV16 (HR-HPV genotype 16) is the most prevalent worldwide and the major cause of HPV-associated cancers. At the molecular level, cancer progression is due to increased expression of the viral oncoproteins E6 and E7, which activate the cell cycle, inhibit apoptosis, and allow accumulation of DNA damage. This review aims to describe the productive life cycle of HPV and discuss the roles of the viral proteins in HPV replication. Routes to viral persistence and cancer progression are also discussed.

Virus/Host Cell Crosstalk in Hypoxic HPV-Positive Cancer Cells

Oncogenic types of human papillomaviruses (HPVs) are major human carcinogens. The expression of the viral E6/E7 oncogenes plays a key role for HPV-linked oncogenesis. It recently has been found that low oxygen concentrations (“hypoxia”), as present in sub-regions of HPV-positive cancers, strongly affect the interplay between the HPV oncogenes and their transformed host cell. As a result, a state of dormancy is induced in hypoxic HPV-positive cancer cells, which is characterized by a shutdown of viral oncogene expression and a proliferative arrest that can be reversed by reoxygenation. In this review, these findings are put into the context of the current concepts of both HPV-linked carcinogenesis and of the effects of hypoxia on tumor biology. Moreover, we discuss the consequences for the phenotype of HPV-positive cancer cells as well as for their clinical behavior and response towards established and prospective therapeutic strategies.

Marine Streptomyces sp. derived antimycin analogues suppress HeLa cells via depletion HPV E6/E7 mediated by ROS-dependent ubiquitin-proteasome system

Four new antimycin alkaloids (1–4) and six related known analogs (5–10) were isolated from the culture of a marine derived Streptomyces sp. THS-55, and their structures were elucidated by extensive spectroscopic analysis. All of the compounds exhibited potent cytotoxicity in vitro against HPV-transformed HeLa cell line. Among them, compounds 6–7 were derived as natural products for the first time, and compound 5 (NADA) showed the highest potency. NADA inhibited the proliferation, arrested cell cycle distribution, and triggered apoptosis in HeLa cancer cells. Our molecular mechanic studies revealed NADA degraded the levels of E6/E7 oncoproteins through ROS-mediated ubiquitin-dependent proteasome system activation. This is the first report that demonstrates antimycin alkaloids analogue induces the degradation of high-risk HPV E6/E7 oncoproteins and finally induces apoptosis in cervical cancer cells. The present work suggested that these analogues could serve as lead compounds for the development of HPV-infected cervical cancer therapeutic agents, as well as research tools for the study of E6/E7 functions.

Dysregulation of Autophagy Contributes to Anal Carcinogenesis

Introduction

Autophagy is an intracellular catabolic process that removes and recycles unnecessary/dysfunctional cellular components, contributing to cellular health and survival. Autophagy is a highly regulated cellular process that responds to several intracellular signals, many of which are deregulated by human papillomavirus (HPV) infection through the expression of HPV-encoded oncoproteins. This adaptive inhibitory response helps prevent viral clearance. A strong correlation remains between HPV infection and the development of squamous cell carcinoma (SCC) of the anus, particularly in HIV positive and other immunosuppressed patients. We hypothesize that autophagy is inhibited by HPV–encoded oncoproteins thereby promoting anal carcinogenesis (Fig 1).

Materials and Methods

HPV16 transgenic mice (K14E6/E7) and non-transgenic mice (FVB/N), both of which do not spontaneously develop anal tumors, were treated topically with the chemical carcinogen, 7,12-Dimethylbenz[a]anthracene (DMBA), to induce anal cancer. The anuses at different time points of treatment (5, 10, 15 and 20 weeks) were analyzed using immunofluorescence (IF) for two key autophagy marker proteins (LC3β and p62) in addition to histological grading. The anuses from the K14E6/E7 mice were also analyzed for visual evidence of autophagic activity by electron microscopy (EM). To see if there was a correlation to humans, archival anal specimens were assessed histologically for grade of dysplasia and then analyzed for LC3β and p62 protein content. To more directly examine the effect of autophagic inhibition on anal carcinogenesis, nontransgenic mice that do not develop anal cancer with DMBA treatment were treated with a known pharmacologic inhibitor of autophagy, chloroquine, and examined for tumor development and analyzed by IF for autophagic proteins.

Results

Histologically, we observed the progression of normal anoderm to invasive SCC with DMBA treatment in K14E6/E7 mice but not in nontransgenic, syngeneic FVB/N background control mice. With the development of low-grade dysplasia in the K14E6/E7 mice, there was an increase in both punctate LC3β and p62 expression while EM revealed increased autophagosomes without evidence of autophagolysosomes. These observations are consistent with autophagy being inhibited at a later stage in the autophagic process. In contrast, in high-grade dysplasia and SCC in the DMBA-treated K14E6/E7 mice, there were decreased levels of p62 with a continued increase in punctate LC3β expression by IF, while autophagolysosomes were seen on EM, consistent with the process of autophagy proceeded to completion. Similar findings, including histological grade dependent changes in LC3β and p62 expression, were noted with human samples upon analysis of IF. Finally, with pharmacologic inhibition of autophagy in DMBA-treated, nontrangenic FVB/N mice, there was a significant increase in anal cancer development similar to that observed in DMBA- treated K14E6/E7 mice.

Conclusion

Autophagic dysregulation is noted early on in HPV-associated anal carcinogenesis (low-grade dysplasia), with normalization of the autophagic process arising in late stages of HPV-associated anal carcinogenesis (high-grade dysplasia and invasive carcinoma).

LKB1 inhibits HPV-associated cancer progression by targeting cellular metabolism

Liver kinase B1 (LKB1) is mutationally inactivated in Peutz-Jeghers syndrome and in a variety of cancers including human papillomavirus (HPV)-caused cervical cancer. However, the significance of LKB1 mutations in cervical cancer initiation and progress has not been examined. Herein, we demonstrated that, in mouse embryonic fibroblasts, loss of LKB1 and transduction of HPV16 E6/E7 had an additive effect on constraining cell senescence while promoting cell proliferation and increasing glucose consumption, lactate production, and ATP generation. Knock-down of LKB1 increased and ectopic expression of LKB1 decreased glycolysis, anchorage-independent cell growth, and cell migration and invasion in HPV transformed cells. In the tumorigenesis and lung metastasis model in syngeneic mice, depletion of LKB1 markedly increased tumor metastatic colonies in lungs without affecting subcutaneous tumor growth. We showed that HPV16 E6/E7 enhanced the expression of hexokinase-ll (HK-II) in the glycolytic pathway through elevated c-MYC. Ectopic LKB1 reduced HK-II along with glycolysis. The inverse relationship between HK-II and LKB1 was also observed in normal and HPV-associated cervical lesions. We propose that LKB1 acts as a safeguard against HPV-stimulated aerobic glycolysis and tumor progression. These findings may eventually aid in the development of therapeutic strategy for HPV-associated malignancies by targeting cell metabolism.

A Drosophila Model of HPV E6-Induced Malignancy Reveals Essential Roles for Magi and the Insulin Receptor

Cervical cancer is one of the leading causes of cancer death in women worldwide. The causative agents of cervical cancers, high-risk human papillomaviruses (HPVs), cause cancer through the action of two oncoproteins, E6 and E7. The E6 oncoprotein cooperates with an E3 ubiquitin ligase (UBE3A) to target the p53 tumour suppressor and important polarity and junctional PDZ proteins for proteasomal degradation, activities that are believed to contribute towards malignancy. However, the causative link between degradation of PDZ proteins and E6-mediated malignancy is largely unknown. We have developed an in vivo model of HPV E6-mediated cellular transformation using the genetic model organism, Drosophila melanogaster. Co-expression of E6 and human UBE3A in wing and eye epithelia results in severe morphological abnormalities. Furthermore, E6, via its PDZ-binding motif and in cooperation with UBE3A, targets a suite of PDZ proteins that are conserved in human and Drosophila, including Magi, Dlg and Scribble. Similar to human epithelia, Drosophila Magi is a major degradation target. Magi overexpression rescues the cellular abnormalities caused by E6+UBE3A coexpression and this activity of Magi is PDZ domain-dependent. Drosophila p53 was not targeted by E6+UBE3A, and E6+UBE3A activity alone is not sufficient to induce tumorigenesis, which only occurs when E6+UBE3A are expressed in conjunction with activated/oncogenic forms of Ras or Notch. Finally, through a genetic screen we have identified the insulin receptor signaling pathway as being required for E6+UBE3A induced hyperplasia. Our results suggest a highly conserved mechanism of HPV E6 mediated cellular transformation, and establish a powerful genetic model to identify and understand the cellular mechanisms that underlie HPV E6-induced malignancy.

Human papillomaviruses (HPV) are the causative agents of cervical cancer, one of the leading causes of cancer death in women worldwide. The E6 oncoprotein encoded by HPV has been implicated in the progression of primary tumors to metastatic disease and we have developed a new model in the fruit fly (Drosophila melanogaster) to study the cellular effects of E6. The E6 protein recruits an E3 ubiquitin ligase (UBE3A) to induce the degradation of a number of cellular proteins, including members of the MAGUK family of scaffolding proteins that control the structure and polarity of epithelial cells: Dlg, Scribble and Magi. Expression of E6 and human UBE3A in the wing and eye of Drosophila disrupted these tissues. Similar to human cells we found that Drosophila Magi was a major E6 degradation target and that overexpression of Magi rescued the tissue disruption. However, Drosophila p53 was not degraded by E6/UBE3A, making our fly model potentially useful for studying the p53-independent activities of the E6+UBE3A complex. When we paired E6 expression with oncogenic proteins, including activated Ras, we observed that epithelia were transformed into mesechymal-like cells that left the epithelium and spread through the body. As a test of the potential of our system, we carried out a pilot genetic screen and identified the insulin receptor as a strong modulator of the E6-mediated disruption of Drosophila tissues. Therefore, we have developed a new system and approach to help us better understand the mechanisms that underlie how HPV infection leads to cell transformation and cancer.

Novel Somatic Copy Number Alteration Identified for Cervical Cancer in the Mexican American Population

Cervical cancer affects millions of Americans, but the rate for cervical cancer in the Mexican American is approximately twice that for non-Mexican Americans. The etiologies of cervical cancer are still not fully understood. A number of somatic mutations, including several copy number alterations (CNAs), have been identified in the pathogenesis of cervical carcinomas in non-Mexican Americans. Thus, the purpose of this study was to investigate CNAs in association with cervical cancer in the Mexican American population. We conducted a pilot study of genome-wide CNA analysis using 2.5 million markers in four diagnostic groups: reference (n = 125), low grade dysplasia (cervical intraepithelial neoplasia (CIN)-I, n = 4), high grade dysplasia (CIN-II and -III, n = 5) and invasive carcinoma (squamous cell carcinoma (SCC), n = 5) followed by data analyses using Partek. We observed a statistically-significant difference of CNA burden between case and reference groups of different sizes (>100 kb, 10-100 kb and 1-10 kb) of CNAs that included deletions and amplifications, e.g., a statistically-significant difference of >100 kb deletions was observed between the reference (6.6%) and pre-cancer and cancer (91.3%) groups. Recurrent aberrations of 98 CNA regions were also identified in cases only. However, none of the CNAs have an impact on cancer progression. A total of 32 CNA regions identified contained tumor suppressor genes and oncogenes. Moreover, the pathway analysis revealed endometrial cancer and estrogen signaling pathways associated with this cancer (p < 0.05) using Kyoto Encyclopedia of Genes and Genomes (KEGG). This is the first report of CNAs identified for cervical cancer in the U.S. Latino population using high density markers. We are aware of the small sample size in the study. Thus, additional studies with a larger sample are needed to confirm the current findings.

mTOR, metabolism, and the immune response in HPV-positive head and neck squamous cell cancer

Extensive preclinical studies have identified mammalian target of rapamycin (mTOR) activation as a frequent molecular signature underlying head and neck squamous cell carcinoma (HNSCC), including the distinct clinical subtype that is human papillomavirus (HPV) related, and have demonstrated the potential therapeutic utility of mTOR inhibitors in the treatment of these cancers. Numerous clinical studies have begun to evaluate this potential, however few have selected for and fewer have focused specifically on HPV-related disease. While HPV-positive (HPV+) HNSCC patients have a generally favorable prognosis, the overall number of patients who suffer failed treatment, recurrent disease, metastasis, and death is increasing due to the rapidly increasing incidence of HPV-related cancers. In this review, we discuss the rationale for proposing the adjuvant use of mTOR inhibition in the treatment of HPV+ HNSCC, highlighting the interplay of virally activated mTOR signaling, cellular metabolism, and the anti-tumor immune response.

Adapting the Stress Response: Viral Subversion of the mTOR Signaling Pathway

The mammalian target of rapamycin (mTOR) is a central regulator of gene expression, translation and various metabolic processes. Multiple extracellular (growth factors) and intracellular (energy status) molecular signals as well as a variety of stressors are integrated into the mTOR pathway. Viral infection is a significant stress that can activate, reduce or even suppress the mTOR signaling pathway. Consequently, viruses have evolved a plethora of different mechanisms to attack and co-opt the mTOR pathway in order to make the host cell a hospitable environment for replication. A more comprehensive knowledge of different viral interactions may provide fruitful targets for new antiviral drugs.

Focal Cortical Dysplasia in Childhood Epilepsy

Focal cortical dysplasia is a common cause of medication resistant epilepsy. A better understanding of its presentation, pathophysiology and consequences have helped us improved its treatment and outcome. This paper reviews the most recent classification, pathophysiology and imaging findings in clinical research as well as the knowledge gained from studying genetic and lesional animal models of focal cortical dysplasia. This review of this recently gained knowledge will most likely help develop new research models and new therapeutic targets for patients with epilepsy associated with focal cortical dysplasia.

Novel Functions of the Human Papillomavirus E6 Oncoproteins

Human papillomaviruses (HPVs) infect the epidermis as well as mucous membranes of humans. They are the causative agents of anogenital tract and some oropharyngeal cancers. Infections begin in the basal epithelia, where the viral genome replicates slowly along with its host cell. As infected cells begin to differentiate and progress toward the periphery, the virus drives proliferation in cells that would otherwise be quiescent. To uncouple differentiation from continued cellular propagation, HPVs express two oncoproteins, HPV E6 and E7. This review focuses on high-risk α-HPV E6, which in addition to supporting viral replication has transforming properties. HPV E6 promotes p53 degradation and activates telomerase, but the multifaceted oncoprotein has numerous other functions that are highlighted here.

Yolk sac tumor of the ovary in a young girl with tuberous sclerosis: A case report and review of the literature

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We reported the first tuberous sclerosis patient with an ovarian yolk sac tumor.

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Although angiomyolipoma is a common benign tumor in TS patients, abdominal malignancies must be considered.

Tuberous Sclerosis Complex Protein 2-Independent Activation of mTORC1 by Human Cytomegalovirus pUL38

The mammalian target of rapamycin complex 1 (mTORC1) controls cell growth and anabolic metabolism and is a critical host factor activated by human cytomegalovirus (HCMV) for successful infection. The multifunctional HCMV protein pUL38 previously has been reported to activate mTORC1 by binding to and antagonizing tuberous sclerosis complex protein 2 (TSC2) (J. N. Moorman et al., Cell Host Microbe 3:253-262, 2008, http://dx.doi.org/10.1016/j.chom.2008.03.002). pUL38 also plays a role in blocking endoplasmic reticulum stress-induced cell death during HCMV infection. In this study, we showed that a mutant pUL38 lacking the N-terminal 24 amino acids (pHA-UL3825-331) was fully functional in suppressing cell death during infection. Interestingly, pHA-UL3825-331 lost the ability to interact with TSC2 but retained the ability to activate mTORC1, although to a lesser extent than full-length pHA-UL38. Recombinant virus expressing pHA-UL3825-331 replicated with ∼10-fold less efficiency than the wild-type virus at a low multiplicity of infection (MOI), but it grew similarly well at a high MOI, suggesting an MOI-dependent importance of pUL38-TSC2 interaction in supporting virus propagation. Site-directed mutational analysis identified a TQ motif at amino acid residues 23 and 24 as critical for pUL38 interaction with TSC2. Importantly, when expressed in isolation, the TQ/AA substitution mutant pHA-UL38 TQ/AA was capable of activating mTORC1 just like pHA-UL3825-331. We also created TSC2-null U373-MG cell lines by CRISPR genome editing and showed that pUL38 was capable of further increasing mTORC1 activity in TSC2-null cells. Therefore, this study identified the residues important for pUL38-TSC2 interaction and demonstrated that pUL38 can activate mTORC1 in both TSC2-dependent and -independent manners.

IMPORTANCE

HCMV, like other viruses, depends exclusively on its host cell to propagate. Therefore, it has developed methods to protect against host stress responses and to usurp cellular processes to complete its life cycle. mTORC1 is believed to be important for virus replication, and HCMV maintains high mTORC1 activity despite the stressful cellular environment associated with infection. mTORC1 inhibitors suppressed HCMV replication in vitro and reduced the incidence of HCMV reactivation in transplant recipients. We demonstrated that mTORC1 was activated by HCMV protein pUL38 in both TSC2-dependent and TSC2-independent manners. The pUL38-independent mode of mTORC1 activation also has been reported. These novel findings suggest the evolution of sophisticated approaches whereby HCMV activates mTORC1, indicating its importance in the biology and pathogenesis of HCMV.

The role of the PI3K/Akt/mTOR signalling pathway in human cancers induced by infection with human papillomaviruses

Infection with Human papillomaviruses (HPVs) leads to the development of a wide-range of cancers, accounting for 5% of all human cancers. A prominent example is cervical cancer, one of the leading causes of cancer death in women worldwide. It has been well established that tumor development and progression induced by HPV infection is driven by the sustained expression of two oncogenes E6 and E7. The expression of E6 and E7 not only inhibits the tumor suppressors p53 and Rb, but also alters additional signalling pathways that may be equally important for transformation. Among these pathways, the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signalling cascade plays a very important role in HPV-induced carcinogenesis by acting through multiple cellular and molecular events. In this review, we summarize the frequent amplification of PI3K/Akt/mTOR signals in HPV-induced cancers and discuss how HPV oncogenes E6/E7/E5 activate the PI3K/Akt/mTOR signalling pathway to modulate tumor initiation and progression and affect patient outcome. Improvement of our understanding of the mechanism by which the PI3K/Akt/mTOR signalling pathway contributes to the immortalization and carcinogenesis of HPV-transduced cells will assist in devising novel strategies for preventing and treating HPV-induced cancers.

Computer-aided targeting of the PI3K/Akt/mTOR pathway: toxicity reduction and therapeutic opportunities

The PI3K/Akt/mTOR pathway plays an essential role in a wide range of biological functions, including metabolism, macromolecular synthesis, cell growth, proliferation and survival. Its versatility, however, makes it a conspicuous target of many pathogens; and the consequential deregulations of this pathway often lead to complications, such as tumorigenesis, type 2 diabetes and cardiovascular diseases. Molecular targeted therapy, aimed at modulating the deregulated pathway, holds great promise for controlling these diseases, though side effects may be inevitable, given the ubiquity of the pathway in cell functions. Here, we review a variety of factors found to modulate the PI3K/Akt/mTOR pathway, including gene mutations, certain metabolites, inflammatory factors, chemical toxicants, drugs found to rectify the pathway, as well as viruses that hijack the pathway for their own synthetic purposes. Furthermore, this evidence of PI3K/Akt/mTOR pathway alteration and related pathogenesis has inspired the exploration of computer-aided targeting of this pathway to optimize therapeutic strategies. Herein, we discuss several possible options, using computer-aided targeting, to reduce the toxicity of molecularly-targeted therapy, including mathematical modeling, to reveal system-level control mechanisms and to confer a low-dosage combination therapy, the potential of PP2A as a therapeutic target, the formulation of parameters to identify patients who would most benefit from specific targeted therapies and molecular dynamics simulations and docking studies to discover drugs that are isoform specific or mutation selective so as to avoid undesired broad inhibitions. We hope this review will stimulate novel ideas for pharmaceutical discovery and deepen our understanding of curability and toxicity by targeting the PI3K/Akt/mTOR pathway.

Pathogenetic mechanisms of focal cortical dysplasia

Focal cortical dysplasias (FCDs) constitute a prevalent cause of intractable epilepsy in children, and is one of the leading conditions requiring epilepsy surgery. Despite recent advances in the cellular and molecular biology of these conditions, the pathogenetic mechanisms of FCDs remain largely unknown. The purpose if this work is to review the molecular underpinnings of FCDs and to highlight potential therapeutic targets. A systematic review of the literature regarding the histologic, molecular, and electrophysiologic aspects of FCDs was conducted. Disruption of the mammalian target of rapamycin (mTOR) signaling comprises a common pathway underlying the structural and electrical disturbances of some FCDs. Other mechanisms such as viral infections, prematurity, head trauma, and brain tumors are also posited. mTOR inhibitors (i.e., rapamycin) have shown positive results on seizure management in animal models and in a small cohort of patients with FCD. Encouraging progress has been achieved on the molecular and electrophysiologic basis of constitutive cells in the dysplastic tissue. Despite the promising results of mTOR inhibitors, large-scale randomized trials are in need to evaluate their efficacy and side effects, along with additional mechanistic studies for the development of novel, molecular-based diagnostic and therapeutic approaches.

Mechanisms of epileptogenesis in pediatric epileptic syndromes: Rasmussen encephalitis, infantile spasms, and febrile infection-related epilepsy syndrome (FIRES)

The mechanisms of epileptogenesis in pediatric epileptic syndromes are diverse, and may involve disturbances of neurodevelopmental trajectories, synaptic homeostasis, and cortical connectivity, which may occur during brain development, early infancy, or childhood. Although genetic or structural/metabolic factors are frequently associated with age-specific epileptic syndromes, such as infantile spasms and West syndrome, other syndromes may be determined by the effect of immunopathogenic mechanisms or energy-dependent processes in response to environmental challenges, such as infections or fever in normally-developed children during early or late childhood. Immune-mediated mechanisms have been suggested in selected pediatric epileptic syndromes in which acute and rapidly progressive encephalopathies preceded by fever and/or infections, such as febrile infection-related epilepsy syndrome, or in chronic progressive encephalopathies, such as Rasmussen encephalitis. A definite involvement of adaptive and innate immune mechanisms driven by cytotoxic CD8(+) T lymphocytes and neuroglial responses has been demonstrated in Rasmussen encephalitis, although the triggering factor of these responses remains unknown. Although the beneficial response to steroids and adrenocorticotropic hormone of infantile spasms, or preceding fever or infection in FIRES, may support a potential role of neuroinflammation as pathogenic factor, no definite demonstration of such involvement has been achieved, and genetic or metabolic factors are suspected. A major challenge for the future is discovering pathogenic mechanisms and etiological factors that facilitate the introduction of novel targets for drug intervention aimed at interfering with the disease mechanisms, therefore providing putative disease-modifying treatments in these pediatric epileptic syndromes.

Emerging biological treatments for uterine cervical carcinoma

Cervical cancer is the third most common cancer worldwide, and the development of new diagnosis, prognostic, and treatment strategies is a major interest for public health. Cisplatin, in combination with external beam irradiation for locally advanced disease, or as monotherapy for recurrent/metastatic disease, has been the cornerstone of treatment for more than two decades. Other investigated cytotoxic therapies include paclitaxel, ifosfamide and topotecan, as single agents or in combination, revealing unsatisfactory results. In recent years, much effort has been made towards evaluating new drugs and developing innovative therapies to treat cervical cancer. Among the most investigated molecular targets are epidermal growth factor receptor and vascular endothelial growth factor (VEGF) signaling pathways, both playing a critical role in cervical cancer development. Studies with bevacizumab or VEGF receptor tyrosine kinase have given encouraging results in terms of clinical efficacy, without adding significant toxicity. A great number of other molecular agents targeting critical pathways in cervical malignant transformation are being evaluated in preclinical and clinical trials, reporting preliminary promising data.

In the current review, we discuss novel therapeutic strategies which are being investigated for the treatment of advanced cervical cancer.

DNA damage repair genes controlling human papillomavirus (HPV) episome levels under conditions of stability and extreme instability

DNA damage response (DDR) genes and pathways controlling the stability of HPV episomal DNA are reported here. We set out to understand the mechanism by which a DNA-binding, N-methylpyrrole-imidazole hairpin polyamide (PA25) acts to cause the dramatic loss of HPV DNA from cells. Southern blots revealed that PA25 alters HPV episomes within 5 hours of treatment. Gene expression arrays identified numerous DDR genes that were specifically altered in HPV16 episome-containing cells (W12E) by PA25, but not in HPV-negative (C33A) cells or in cells with integrated HPV16 (SiHa). A siRNA screen of 240 DDR genes was then conducted to identify enhancers and repressors of PA25 activity. Serendipitously, the screen also identified many novel genes, such as TDP1 and TDP2, regulating normal HPV episome stability. MRN and 9-1-1 complexes emerged as important for PA25-mediated episome destruction and were selected for follow-up studies. Mre11, along with other homologous recombination and dsDNA break repair genes, was among the highly significant PA25 repressors. The Mre11 inhibitor Mirin was found to sensitize HPV episomes to PA25 resulting in a ∼5-fold reduction of the PA25 IC50. A novel assay that couples end-labeling of DNA to Q-PCR showed that PA25 causes strand breaks within HPV DNA, and that Mirin greatly enhances this activity. The 9-1-1 complex member Rad9, a representative PA25 enhancer, was transiently phosphorylated in response to PA25 treatment suggesting that it has a role in detecting and signaling episome damage by PA25 to the cell. These results establish that DNA-targeted compounds enter cells and specifically target the HPV episome. This action leads to the activation of numerous DDR pathways and the massive elimination of episomal DNA from cells. Our findings demonstrate that viral episomes can be targeted for elimination from cells by minor groove binding agents, and implicate DDR pathways as important mediators of this process.

Focal malformations of cortical development: new vistas for molecular pathogenesis

Focal malformations of cortical development (FMCD) are highly associated with several neurological disorders including intractable epilepsy and neurocognitive disabilities. Over the past decade, several FMCD subtypes have been linked to hyperactivation of the mammalian target of rapamycin (mTOR) signaling cascade. In view of the roles that mTOR plays in cell proliferation, size, motility, and stem cell phenotype, many of the features of FMCD such as cytomegaly, disorganized lamination, and expression of stem cell markers can be explained by enhanced mTOR signaling. FMCD result from several distinct and fascinating molecular mechanisms including biallelic gene inactivation, somatic mutation, and potentially, viral infection. These mechanisms have been directly linked to mTOR activation. Perhaps most compelling, pharmacological inhibition of mTOR has been implemented successfully in clinical trials for select FMCD and provides a new vista for treatment.

Papillomavirus E6 oncoproteins

Papillomaviruses induce benign and malignant epithelial tumors, and the viral E6 oncoprotein is essential for full transformation. E6 contributes to transformation by associating with cellular proteins, docking on specific acidic LXXLL peptide motifs found on these proteins. This review examines insights from recent studies of human and animal E6 proteins that determine the three-dimensional structure of E6 when bound to acidic LXXLL peptides. The structure of E6 is related to recent advances in the purification and identification of E6 associated protein complexes. These E6 protein-complexes, together with other proteins that bind to E6, alter a broad array of biological outcomes including modulation of cell survival, cellular transcription, host cell differentiation, growth factor dependence, DNA damage responses, and cell cycle progression.

Phase II study of temsirolimus (CCI-779) in women with recurrent, unresectable, locally advanced or metastatic carcinoma of the cervix. A trial of the NCIC Clinical Trials Group (NCIC CTG IND 199)

OBJECTIVE

HPV infection has been associated with deregulation of the PI3K-Akt-mTOR pathway in invasive cervical carcinomas. This 2-stage phase II study assessed the activity of the mTOR inhibitor, temsirolimus, in patients with measurable metastatic and/or locally advanced, recurrent carcinoma of the cervix.

METHODS

Temsirolimus 25mg i.v. was administered weekly in 4 week cycles. One response among the first 18 patients was required to proceed to the second stage of accrual. Correlative molecular studies were performed on archival tumor tissue.

RESULTS

Thirty-eight patients were enrolled. Thirty-seven patients were evaluable for toxicity and 33 for response. One patient experienced a partial response (3.0%). Nineteen patients had stable disease (57.6%) [median duration 6.5 months (range 2.4-12.0mo)]. The 6-month progression free survival rate was 28% (95% CI: 14-43%). The median progression free survival was 3.52 months [95% CI (1.81-4.70)]. Adverse effects were mild-moderate in most cases and similar to other temsirolimus studies. No toxicity>grade 3 was observed. Assessment of PTEN and PIK3CA by IHC, copy number analyses and PTEN promoter methylation status did not reveal subsets associated with disease stability.

CONCLUSION

Single agent temsirolimus has modest activity in cervical carcinoma with about two-thirds of patients exhibiting stable disease. Molecular markers for treatment benefit remain to be identified.

HPV-18 E6 mutants reveal p53 modulation of viral DNA amplification in organotypic cultures

Human papillomaviruses (HPVs) amplify in differentiated strata of a squamous epithelium. The HPV E7 protein destabilizes the p130/retinoblastoma susceptibility protein family of tumor suppressors and reactivates S-phase reentry, thereby facilitating viral DNA amplification. The high-risk HPV E6 protein destabilizes the p53 tumor suppressor and many other host proteins. However, the critical E6 targets relevant to viral DNA amplification have not been identified, because functionally significant E6 mutants are not stably maintained in transfected cells. Using Cre-loxP recombination, which efficiently generates HPV genomic plasmids in transfected primary human keratinocytes, we have recapitulated a highly productive infection of HPV-18 in organotypic epithelial cultures. By using this system, we now report the characterization of four HPV-18 E6 mutations. An E6 null mutant accumulated high levels of p53 and amplified very poorly. p53 siRNA or ectopic WT E6 partially restored amplification, whereas three missense E6 mutations that did not effectively destabilize p53 complemented the null mutant poorly. Unexpectedly, in cis, two of the missense mutants amplified, albeit to a lower extent than the WT and only in cells with undetectable p53. These observations and others implicate p53 and additional host proteins in regulating viral DNA amplification and also suggest an inhibitory effect of E6 overexpression. We show that high levels of viral DNA amplification are critical for late protein expression and report several previously undescribed viral RNAs, including bicistronic transcripts predicted to encode E5 and L2 or an alternative form of E1^E4 and L1.

The HPV16 E6 oncoprotein causes prolonged receptor protein tyrosine kinase signaling and enhances internalization of phosphorylated receptor species

The high-risk human papillomavirus (HPV) E6 proteins are consistently expressed in HPV-associated lesions and cancers. HPV16 E6 sustains the activity of the mTORC1 and mTORC2 signaling cascades under conditions of growth factor deprivation. Here we report that HPV16 E6 activated mTORC1 by enhanced signaling through receptor protein tyrosine kinases, including epidermal growth factor receptor and insulin receptor and insulin-like growth factor receptors. This is evidenced by sustained signaling through these receptors for several hours after growth factor withdrawal. HPV16 E6 increased the internalization of activated receptor species, and the signaling adaptor protein GRB2 was shown to be critical for HPV16 E6 mediated enhanced EGFR internalization and mTORC1 activation. As a consequence of receptor protein kinase mediated mTORC1 activation, HPV16 E6 expression increased cellular migration of primary human epithelial cells. This study identifies a previously unappreciated mechanism by which HPV E6 proteins perturb host-signaling pathways presumably to sustain protein synthesis during the viral life cycle that may also contribute to cellular transforming activities of high-risk HPV E6 proteins.

High-risk human papillomavirus infections are associated with nearly all cases of cervical cancer. HPVs infect basal epithelial cells but virion production is restricted to the outer, terminally differentiated layers of the infected epithelia where supply of nutrients and growth factors may be limited. High-risk HPV E6 proteins have been shown to activate mTORC1 signaling and increase cap dependent translation. Here we show that HPV16 E6 activates the mTORC1 and MAP kinase signaling pathways through activating receptor protein tyrosine kinases (RPTKs) and increases EGFR internalization, even after growth factor withdrawal. The signaling adaptor protein GRB2 is a critical mediator of HPV16 E6 mediated EGFR internalization and mTORC1 activation. Lastly, we demonstrate that HPV16 E6 mediated activation of RPTK and mTORC1 signaling causes increased cellular migration even after growth factor withdrawal. These results suggest a previously unappreciated mechanism by which HPV E6 proteins may support the viral life cycle and that may contribute to the transforming activities of high-risk HPV E6 proteins. Hence, inhibition of RPTK signaling networks may be evaluated as a therapeutic strategy for HPV-associated lesions and cancers.

Detection of human papillomavirus in human focal cortical dysplasia type IIB

OBJECTIVE

Focal cortical dysplasia type IIB (FCDIIB) is a sporadic developmental malformation of the cerebral cortex highly associated with pediatric epilepsy. Balloon cells (BCs) in FCDIIB exhibit constitutive activation of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. Recently, the high-risk human papillomavirus type 16 oncoprotein E6 was identified as a potent activator of mTORC1 signaling. Here, we test the hypothesis that HPV16 E6 is present in human FCDIIB specimens.

METHODS

HPV16 E6 protein expression was assayed by immunohistochemistry in FCDIIB specimens (n = 50) and control brain specimens (n = 36). HPV16 E6 DNA was assayed by polymerase chain reaction (PCR) and in situ hybridization; HPV16 E6 mRNA was assayed by reverse transcriptase PCR. HPV16 E6 was transfected into fetal mouse brains by in utero electroporation to test the effects of E6 on cortical development.

RESULTS

HPV16 E6 protein was robustly expressed in all FCDIIB specimens in BCs, but not in regions without BCs or in control tissue specimens including normal brain, lymphoblasts, and fibroblasts, cortical tubers, and U87 glioma cells. E6 expression in FCDIIB colocalized with phosphoactivated S6 protein, a known mTORC1 substrate. HPV16 E6 DNA and mRNA were detected in representative specimens of FCDIIB but not control cortex, and were confirmed by sequencing. Transfection of E6 into fetal mouse brains caused a focal cortical malformation in association with enhanced mTORC1 signaling.

INTERPRETATION

Our results indicate a new association between HPV16 E6 and FCDIIB and demonstrate for the first time HPV16 E6 in the human brain. We propose a novel etiology for FCDIIB based on HPV16 E6 expression during fetal brain development.

PI3K pathway in gynecologic malignancies

Alterations in PI3K signaling are common in gynecologic malignancies. Alterations detected vary with gynecologic cancer type, histologic subtypes within these, and clinical phenotypes. The distinction into type I and type II endometrial and ovarian carcinomas is reflected in distribution of changes detected in several of the PI3K members. PIK3CA mutations and amplifications are common in endometrial, ovarian, and cervical cancers. PTEN mutations and deletions are frequent in endometrial cancers. Several immunohistochemical studies of protein expression have explored these and other potential surrogate markers for PI3K pathway activation. Biomarkers to measure level of PI3K activity in clinical samples are not established. Whether amplifications, mutations, and deletions of the PI3K pathway members, and in particular change in their expression levels, result in clinically relevant pathway activation needs to be further explored. Also, to what extent these alterations drive the tumor behavior and are critical targets for therapeutics to improve patient survival needs to be further tested to establish predictive biomarkers for response to PI3K inhibition.

Tinkering with translation: protein synthesis in virus-infected cells

Viruses are obligate intracellular parasites, and their replication requires host cell functions. Although the size, composition, complexity, and functions encoded by their genomes are remarkably diverse, all viruses rely absolutely on the protein synthesis machinery of their host cells. Lacking their own translational apparatus, they must recruit cellular ribosomes in order to translate viral mRNAs and produce the protein products required for their replication. In addition, there are other constraints on viral protein production. Crucially, host innate defenses and stress responses capable of inactivating the translation machinery must be effectively neutralized. Furthermore, the limited coding capacity of the viral genome needs to be used optimally. These demands have resulted in complex interactions between virus and host that exploit ostensibly virus-specific mechanisms and, at the same time, illuminate the functioning of the cellular protein synthesis apparatus.

Treatment of metastatic cervical cancer: future directions involving targeted agents

Cervical cancer is the third most common cause of female cancer mortality, and it remains a major health problem in populations with limited economic resources. Metastatic disease or recurrent lesions not amenable to radical local excision or regional radiation have a poor prognosis, and are treated with palliative platinum-based chemotherapy. There are few effective therapeutic options for patients who progressed after first-line chemotherapy. Future advances in the treatment of metastatic or recurrent disease may rely on more effective and better-tolerated therapies, and molecularly driven targeted agents could represent an attractive option. Inhibition of tumor angiogenesis and epidermal growth factor receptor directed therapies have focused the most recent clinical research efforts. A thorough molecular characterization of cervical cancer remains crucial for a rationale implementation of targeted agents and companion biomarkers. Alternative clinical trial designs may also be necessary to optimize the clinical development of new drugs for metastatic cervical cancer.

Modulation of autophagy-like processes by tumor viruses

Autophagy is an intracellular degradation pathway for long-lived proteins and organelles. This process is activated above basal levels upon cell intrinsic or environmental stress and dysregulation of autophagy has been linked to various human diseases, including those caused by viral infection. Many viruses have evolved strategies to directly interfere with autophagy, presumably to facilitate their replication or to escape immune detection. However, in some cases, modulation of autophagy appears to be a consequence of the virus disturbing the cell’s metabolic signaling networks. Here, we summarize recent advances in research at the interface of autophagy and viral infection, paying special attention to strategies that human tumor viruses have evolved.

Metformin impairs the growth of liver kinase B1-intact cervical cancer cells

OBJECTIVE

Metformin is one of the most widely used drugs for the treatment of type 2 diabetes. Recent investigations demonstrated that application of metformin reduces cancer risk. The present study aimed to determine the role of liver kinase B1 (LKB1) in the response of cervical cancer cells to metformin.

METHODS

LKB1 expression and the integrity of LKB1-AMPK signaling were determined with immunoblot in 6 cervical cancer cell lines. Cellular sensitivity to metformin was analyzed with MTT assay.

RESULTS

Metformin inhibited growth of cervical cancer cells, C33A, Me180, and CaSki, but was less effective against HeLa, HT-3, and MS751 cells. Analyzing the expression status and the integrity of LKB1-AMPK-mTOR signaling, we found that cervical cancer cells sensitive to metformin were LKB1 intact and exerted an integral AMPK-mTOR signaling response after the treatment. Ectopic expression of LKB1 with stable transduction system or inducible expression construct in endogenous LKB1 deficient cells improved the activation of AMPK, promoted the inhibition of mTOR, and prompted the sensitivity of cells to metformin. In contrast, knock-down of LKB1 compromised cellular response to metformin. Our further investigation demonstrated that metformin could induce both apoptosis and autophagy in cervical cancer cells when LKB1 is expressed.

CONCLUSIONS

Metformin is a potential drug for the treatment of cervical cancers, in particular to those with intact LKB1 expression. Administration of cell metabolism agonists may enhance LKB1 tumor suppression, inhibit cell growth, and reduce tumor cell viability via the activation of LKB1-AMPK signaling.

Activation of cap-dependent translation by mucosal human papillomavirus E6 proteins is dependent on the integrity of the LXXLL binding motif

The human papillomavirus (HPV) type 16 (HPV16) E6 protein can stimulate mechanistic target of rapamycin complex 1 (mTORC1) signaling and cap-dependent translation through activation of the PDK1 and mTORC2 kinases. Here we report that HPV18 E6 also enhances cap-dependent translation. The integrity of LXXLL and PDZ protein binding domains is important for activation of cap-dependent translation by high-risk mucosal HPV E6 proteins. Consistent with this model, low-risk mucosal HPV6b and HPV11 E6 proteins, which do not contain a PDZ protein binding motif, also activate cap-dependent translation and mTORC1, albeit at a lower efficiency than high-risk HPV E6 proteins. In contrast, cutaneous HPV5 and HPV8 E6 proteins, which lack LXXLL and PDZ motif protein binding, do not enhance cap-dependent translation. Mutagenic analyses of low-risk HPV E6 proteins revealed that association with the LXXLL motif containing ubiquitin ligase E6AP (UBE3A) correlates with activation of cap-dependent translation. Hence, activation of mTORC1 and cap-dependent translation may be important for the viral life cycle in specific epithelial tissue types and contribute to cellular transformation in cooperation with other biological activities of high-risk HPV E6-containing proteins.