Hypoxia-specific stabilization of HIF-1alpha by human papillomaviruses

Breaking down the evidence for bevacizumab in advanced cervical cancer: past, present and future

Despite the introduction of screening and, latterly, vaccination programs in the developed world, globally cervical cancer remains a significant health problem. For those diagnosed with advanced or recurrent disease even within resource rich communities, prognosis remains poor with an overall survival (OS) of just over 12 months. New therapeutic interventions are urgently required. Advances in our understanding of the mechanisms underlying tumor growth and the downstream effects of human papilloma virus (HPV) infection identified angiogenesis as a rational target for therapeutic intervention in cervical cancer. Anti-angiogenic agents showed promising activity in early phase clinical trials culminating in a randomized phase III study of the humanized monoclonal antibody to vascular endothelial growth factor (VEGF), bevacizumab, in combination with chemotherapy. This pivotal study, the Gynecologic Oncology Group protocol 240, met its primary endpoint demonstrating a significant improvement in OS. Bevacizumab became the first targeted agent to be granted regulatory approval by the United States Food and Drug Administration for use alongside chemotherapy in adults with persistent, recurrent or metastatic carcinoma of the cervix. This review outlines the rationale for targeting angiogenesis in cervical cancer focusing on the current indications for the use of bevacizumab in this disease and future directions.

Molecular transitions from papillomavirus infection to cervical precancer and cancer: Role of stromal estrogen receptor signaling

To study the multistep process of cervical cancer development, we analyzed 128 frozen cervical samples spanning normalcy, increasingly severe cervical intraepithelial neoplasia (CIN1- CIN3), and cervical cancer (CxCa) from multiple perspectives, revealing a cascade of progressive changes. Compared with normal tissue, expression of many DNA replication/repair and cell proliferation genes was increased in CIN1/CIN2 lesions and further sustained in CIN3, consistent with high-risk human papillomavirus (HPV)-induced tumor suppressor inactivation. The CIN3-to-CxCa transition showed metabolic shifts, including decreased expression of mitochondrial electron transport complex components and ribosomal protein genes. Significantly, despite clinical, epidemiological, and animal model results linking estrogen and estrogen receptor alpha (ERα) to CxCa, ERα expression declined >15-fold from normalcy to cancer, showing the strongest inverse correlation of any gene with the increasing expression of p16, a marker for HPV-linked cancers. This drop in ERα in CIN and tumor cells was confirmed at the protein level. However, ERα expression in stromal cells continued throughout CxCa development. Our further studies localized stromal ERα to FSP1+, CD34+, SMA- precursor fibrocytes adjacent to normal and precancerous CIN epithelium, and FSP1-, CD34-, SMA+ activated fibroblasts in CxCas. Moreover, rank correlations with ERα mRNA identified IL-8, CXCL12, CXCL14, their receptors, and other angiogenesis and immune cell infiltration and inflammatory factors as candidates for ERα-induced stroma-tumor signaling pathways. The results indicate that estrogen signaling in cervical cancer has dramatic differences from ERα+ breast cancers, and imply that estrogen signaling increasingly proceeds indirectly through ERα in tumor-associated stromal fibroblasts.

Exploring the therapeutic rationale for angiogenesis blockade in cervical cancer

PURPOSE

This review highlights the molecular and pathologic evidence that cervical cancer is driven by angiogenesis and presents a summary of the recent clinical research in antiangiogenesis therapy for advanced cervical cancer with a focus on the use of bevacizumab.

METHODS

The articles chosen for this review reveal the rationale for antiangiogenesis agents in cervical cancer from 3 perspectives: pathologic, molecular, and clinical data.

FINDINGS

Several translational investigations have revealed that proangiogenic signaling cascades are active in cervical carcinogenesis and can be used to improve patient outcomes in advanced disease. For example, in a recently published study of patients with recurrent and metastatic cervical cancer, bevacizumab was the first targeted agent to improve overall survival in a gynecologic cancer when successfully combined with 2 different chemotherapy regimens.

IMPLICATIONS

Because of recent advances in screening, aggressive management of cervical intraepithelial neoplasia, and human papillomavirus vaccination, cervical cancer is preventable and curable with radical surgery plus lymphadenectomy surgery or chemoradiation plus brachytherapy if detected early. Unfortunately, for patients with metastatic or recurrent disease, effective therapeutic options are limited for this aggressive life-threatening condition. However, molecularly targeted agents have provided a critical opportunity to improve patient outcomes beyond optimizing cytotoxic chemotherapy regimens so that they may benefit from other agents or emergent therapies in the future.

Angiogenesis and antiangiogenic agents in cervical cancer

Standard treatment of cervical cancer (CC) consists of surgery in the early stages and of chemoradiation in locally advanced disease. Metastatic CC has a poor prognosis and is usually treated with palliative platinum-based chemotherapy. Current chemotherapeutic regimens are associated with significant adverse effects and only limited activity, making identification of active and tolerable novel targeted agents a high priority. Angiogenesis is a complex process that plays a crucial role in the development of many types of cancer. The dominant role of angiogenesis in CC seems to be directly related to human papillomavirus-related inhibition of p53 and stabilization of hypoxia-inducible factor-1α. Both of these mechanisms are able to increase expression of vascular endothelial growth factor (VEGF). Activation of VEGF promotes endothelial cell proliferation and migration, favoring formation of new blood vessels and increasing permeability of existing blood vessels. Since bevacizumab, a recombinant humanized monoclonal antibody binding to all isoforms of VEGF, has been demonstrated to significantly improve survival in gynecologic cancer, some recent clinical research has explored the possibility of using novel therapies directed toward inhibition of angiogenesis in CC too. Here we review the main results from studies concerning the use of antiangiogenic drugs that are being investigated for the treatment of CC.

A role for vaccinia virus protein C16 in reprogramming cellular energy metabolism

Vaccinia virus (VACV) is a large DNA virus that replicates in the cytoplasm and encodes about 200 proteins of which approximately 50 % may be non-essential for viral replication. These proteins enable VACV to suppress transcription and translation of cellular genes, to inhibit the innate immune response, to exploit microtubule- and actin-based transport for virus entry and spread, and to subvert cellular metabolism for the benefit of the virus. VACV strain WR protein C16 induces stabilization of the hypoxia-inducible transcription factor (HIF)-1α by binding to the cellular oxygen sensor prolylhydroxylase domain-containing protein (PHD)2. Stabilization of HIF-1α is induced by several virus groups, but the purpose and consequences are unclear. Here, ¹H-NMR spectroscopy and liquid chromatography-mass spectrometry are used to investigate the metabolic alterations during VACV infection in HeLa and 2FTGH cells. The role of C16 in such alterations was examined by comparing infection to WT VACV (strain WR) and a derivative virus lacking gene C16L (vΔC16). Compared with uninfected cells, VACV infection caused increased nucleotide and glutamine metabolism. In addition, there were increased concentrations of glutamine derivatives in cells infected with WT VACV compared with vΔC16. This indicates that C16 contributes to enhanced glutamine metabolism and this may help preserve tricarboxylic acid cycle activity. These data show that VACV infection reprogrammes cellular energy metabolism towards increased synthesis of the metabolic precursors utilized during viral replication, and that C16 contributes to this anabolic reprogramming of the cell, probably via the stabilization of HIF-1α.

Lactate transporters and vascular factors in HPV-induced squamous cell carcinoma of the uterine cervix

Background

Tumour microenvironment is a fundamental aspect of tumour behaviour, modulating important events as cancer cell migration and invasion, as well as angiogenesis and metastisation. Among other microenvironment features, hypoxia and acidity play important roles in this modulation. As the metabolic reprogramming of cancer cells induces extracellular acidity, which in turn induces angiogenesis, and hypoxia induces both the metabolic reprogramming and angiogenesis, the present study aims to evaluate the immunohistochemical expression of a variety of metabolic and vascular markers as common targets of the hypoxic microenvironment in a series of cervical squamous cells carcinoma, as well as using an in vitro 3D culture model.

Methods

Immunohistochemical expression of MCT1, MCT4, CD147, GLUT1 and CAIX was assessed in a series of 28 chronic cervicitis, 34 LSIL, 29 HSIL, 38 cases of squamous cells carcinoma (SCC), as well as in in vitro 3D culture of keratinocytes expressing HPV genes. Furthermore, VEGF family members’ expression was assessed in the SCC cases. The expression profiles were associated with patients’ clinicopathological parameters.

Results

We found an increase of MCT4 expression along progression to malignancy in cervical samples. Also, MCT4 was associated with CD147 and CAIX expression. VEGF-A expression was more frequently found in cases without MCT1 expression. Both MCT4 and CD147 were more frequently expressed in younger patients at diagnosis while no associations were found between VEGF family and clinicopathological parameters. Finally, we show evidence for the upregulation of MCT4, as well as CD147 and CAIX, after HPV transfection.

Conclusions

The results herein presented point at MCT4 as a promising therapeutic target in squamous cells carcinoma of the uterine cervix. Importantly, we show a possible association between lactate transport and angiogenesis, which should be further explored.

Retinoblastoma binding protein 2 (RBP2) promotes HIF-1α-VEGF-induced angiogenesis of non-small cell lung cancer via the Akt pathway

Background

Pathological angiogenesis plays an essential role in tumor aggressiveness and leads to unfavorable prognosis. The aim of this study is to detect the potential role of Retinoblastoma binding protein 2 (RBP2) in the tumor angiogenesis of non-small cell lung cancer (NSCLC).

Methods

Immunohistochemical staining was used to detect the expression of RBP2, hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and CD34. Two pairs of siRNA sequences and pcDNA3-HA-RBP2 were used to down-regulate and up-regulate RBP2 expression in H1975 and SK-MES-1 cells. An endothelial cell tube formation assay, VEGF enzyme-linked immunosorbent assay, real-time PCR and western blotting were performed to detect the potential mechanisms mediated by RBP2 in tumor angiogenesis.

Results

Of the 102 stage I NSCLC specimens analyzed, high RBP2 protein expression is closely associated with tumor size (P = 0.030), high HIF-1α expression (P = 0.028), high VEGF expression (P = 0.048), increased tumor angiogenesis (P = 0.033) and poor prognosis (P = 0.037); high MVD was associated with high HIF-1α expression (P = 0.034), high VEGF expression (P = 0.001) and poor prognosis (P = 0.040). Multivariate analysis indicated that RBP2 had an independent influence on the survival of patients with stage I NSCLC (P = 0.044). By modulating the expression of RBP2, our findings suggested that RBP2 protein depletion decreased HUVECs tube formation by down-regulating VEGF in a conditioned medium. RBP2 stimulated the up-regulation of VEGF, which was dependent on HIF-1α, and activated the HIF-1α via phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Moreover, VEGF increased the activation of Akt regulated by RBP2.

Conclusions

The RBP2 protein may stimulate HIF-1α expression via the activation of the PI3K/Akt signaling pathway under normoxia and then stimulate VEGF expression. These findings indicate that RBP2 may play a critical role in tumor angiogenesis and serve as an attractive therapeutic target against tumor aggressiveness for early-stage NSCLC patients.

Human papillomavirus 16 E6 contributes HIF-1α induced Warburg effect by attenuating the VHL-HIF-1α interaction

Cervical cancer is still one of the leading causes of cancer deaths in women worldwide, especially in the developing countries. It is a major metabolic character of cancer cells to consume large quantities of glucose and derive more energy by glycolysis even in the presence of adequate oxygen, which is called Warburg effect that can be exaggerated by hypoxia. The high risk subtype HPV16 early oncoprotein E6 contributes host cell immortalization and transformation through interacting with a number of cellular factors. Hypoxia-inducible factor 1α (HIF-1α), a ubiquitously expressed transcriptional regulator involved in induction of numerous genes associated with angiogenesis and tumor growth, is highly increased by HPV E6. HIF-1α is a best-known target of the von Hippel-Lindau tumor suppressor (VHL) as an E3 ligase for degradation. In the present work, we found that HPV16 E6 promotes hypoxia induced Warburg effect through hindering the association of HIF-1α and VHL. This disassociation attenuates VHL-mediated HIF-1α ubiquitination and causes HIF-1α accumulation. These results suggest that oncoprotein E6 plays a major role in the regulation of Warburg effect and can be a valuable therapeutic target for HPV-related cancer.

Hypoxia-inducible factor 1 and its role in viral carcinogenesis

The advent of modern molecular biology has allowed for the discovery of several mechanisms by which oncoviruses promote carcinogenesis. Remarkably, nearly all human oncogenic viruses increase levels of the transcription factor hypoxia-inducible factor 1 (HIF-1). In this review, we highlight HIF-1׳s significance in viral oncogenesis, while providing an in-depth analysis of its activation mechanisms by the following oncoviruses: human papillomaviruses (HPVs), hepatitis B/C viruses (HBV/HCVs), Epstein-Barr virus (EBV), Kaposi׳s sarcoma-associated herpes virus (KSHV), and human T-cell lymphotropic virus (HTLV-1). We discuss virus-induced HIF-1׳s role in transcriptional upregulation of metabolic, angiogenic, and microenvironmental factors that are integral for oncogenesis. Admittedly, conclusive evidence is lacking as to whether activation of HIF-1 target genes is necessary for malignant transformation or merely a result thereof. In addition, a complete understanding of host-virus interactions, the effect of viral genomic variation, and the clinical (and potential therapeutic) relevance of HIF-1 in viral oncogenesis warrant further investigation.

The role of Hypoxia-inducible factor-1 α , glucose transporter-1, (GLUT-1) and carbon anhydrase IX in endometrial cancer patients

Hypoxia-inducible factor-1α (HIF-1α), glucose transporter-1 (GLUT-1), and carbon anhydrase IX (CAIX) are important molecules that allow adaptation to hypoxic environments. The aim of our study was to investigate the correlation between HIF-1α, GLUT-1, and CAIX protein level with the clinicopathological features of endometrial cancer patients. Materials and Methods. 92 endometrial cancer patients, aged 37–84, were enrolled to our study. In all patients clinical stage, histologic grade, myometrial invasion, lymph node, and distant metastases were determined. Moreover, the survival time was assessed. Immunohistochemical analyses were performed on archive formalin fixed paraffin embedded tissue sections. Results. High significant differences (P = 0.0115) were reported between HIF-1α expression and the histologic subtype of cancer. Higher HIF-1α expression was associated with the higher risk of recurrence (P = 0.0434). The results of GLUT-1 and CAIX expression did not reveal any significant differences between the proteins expression in the primary tumor and the clinicopathological features. Conclusion. The important role of HIF-1α in the group of patients with the high risk of recurrence and the negative histologic subtype of the tumor suggest that the expression of this factor might be useful in the panel of accessory pathomorphological tests and could be helpful in establishing more accurate prognosis in endometrial cancer patients.

microRNAs are biomarkers of oncogenic human papillomavirus infections

Cellular and viral microRNAs (miRNAs) are the transcriptional products of RNA polymerase II and are regulated by transcriptional factors for their differential expression. The altered expression of miRNAs in many cancer types has been explored as a marker for possible diagnosis and therapy. We report in this study that oncogenic human papillomaviruses (HPVs) induce aberrant expression of many cellular miRNAs and that HPV18 infection produces no detectable viral miRNA. Thirteen abundant host miRNAs were specifically regulated by HPV16 and HPV18 in organotypic raft cultures of foreskin and vaginal keratinocytes as determined by miRNA array in combination with small RNA sequencing. The increase of miR-16, miR-25, miR-92a, and miR-378 and the decrease of miR-22, miR-27a, miR-29a, and miR-100 could be attributed to viral oncoprotein E6, E7, or both, all of which are known to target many cellular transcription factors. The examination of 158 cervical specimens, including 38 normal, 52 cervical intraepithelial neoplasia (CIN), and 68 cervical cancer (CC) tissues, for the expression of these eight miRNAs showed a remarkable increase of miR-25, miR-92a, and miR-378 with lesion progression but no obvious change of miR-22, miR-29a, and miR-100 among the HPV-infected tissues. Further analyses indicate that an expression ratio ≥1.5 of miR-25/92a group over miR-22/29a group could serve as a cutoff value to distinguish normal cervix from CIN and from CIN to CC.

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.

Molecular characterization of CD133+ cancer stem-like cells in endometrial cancer

A small subset of cells with CD133 expression is thought to have increased chemoresistance and tumorigenicity, features of cancer stem cells (CSCs); the molecular mechanisms by which these properties arise remain unclear. We characterized CD133+ endometrial cancer cells based on microarray analyses of Ishikawa cells. Of the genes upregulated in CD133+ cells compared with CD133- cells, we noted several key factors involved in the aggressive behavior of cells, including ABCG2 and matrix metalloproteinase (MMP). Flow cytometric analyses identified a side-cell population (SP) with CSC features in Ishikawa cells, and they were found to be more enriched in CD133+ cells than CD133- cells. In particular, CD133+/SP cells exhibited higher proliferative and colony‑forming activity than CD133+/non-SP cells. Matrigel invasion assay revealed that CD133+ cells have enhanced invasive capacity with elevated MT1-MMP expression. siRNA‑based knockdown of MT1-MMP largely abolished the invasive capacity of CD133+ cells, but not CD133- cells due to low levels of constitutive MT1-MMP1 expression. These findings demonstrate that increased chemoresistance and tumorigenic potential of CD133+ cells are at least partly attributed to an enriched SP fraction as well as increased MMP-1 expression. These results will be of assistance in the establishment of molecular target therapy to CSCs in endometrial cancer.

A mechanism for induction of a hypoxic response by vaccinia virus

Viruses have evolved sophisticated strategies to exploit host cell function for their benefit. Here we show that under physiologically normal oxygen levels (normoxia) vaccinia virus (VACV) infection leads to a rapid stabilization of hypoxia-inducible factor (HIF)-1α, its translocation into the nucleus and the activation of HIF-responsive genes, such as vascular endothelial growth factor (VEGF), glucose transporter-1, and pyruvate dehydrogenase kinase-1. HIF-1α stabilization is mediated by VACV protein C16 that binds the human oxygen sensing enzyme prolyl-hydroxylase domain containing protein (PHD)2 and thereby inhibits PHD2-dependent hydroxylation of HIF-1α. The binding between C16 and PHD2 is direct and specific, and ectopic expression of C16 alone induces transcription of HIF-1α responsive genes. Conversely, a VACV strain lacking the gene for C16, C16L, is unable to induce HIF-1α stabilization. Interestingly, the N-terminal region of C16 is predicted to have a PHD2-like structural fold but lacks the catalytic active site residues of PHDs. The induction of a hypoxic response by VACV is reminiscent of the biochemical consequences of solid tumor formation, and illustrates a poxvirus strategy for manipulation of cellular gene expression and biochemistry.

Oxygen tension level and human viral infections

The role of oxygen tension level is a well-known phenomenon that has been studied in oncology and radiotherapy since about 60 years. Oxygen tension may inhibit or stimulate propagation of viruses in vitro as well as in vivo. In turn modulating oxygen metabolism may constitute a novel approach to treat viral infections as an adjuvant therapy. The major transcription factor which regulates oxygen tension level is hypoxia-inducible factor-1 alpha (HIF-1α). Down-regulating the expression of HIF-1α is a possible method in the treatment of chronic viral infection such as human immunodeficiency virus infection, chronic hepatitis B and C viral infections and Kaposi sarcoma in addition to classic chemotherapy. The aim of this review is to supply an updating concerning the influence of oxygen tension level in human viral infections and to evoke possible new therapeutic strategies regarding this environmental condition.

Regulation of the human papillomavirus type 16 late promoter by E7 and the cell cycle

Human papillomaviruses (HPVs) are the causative agents of cervical and other cancers. The oncoprotein E7 activates the cell cycle and makes possible replication of the viral genome in differentiating epithelia. The HPV16 late promoter is activated upon cellular differentiation and regulates late gene expression. We investigated the effect of E7 on the late promoter and found that E7 was able to activate the promoter. In contrast, the other known viral transcriptional regulator, E2, had no effect on the late promoter. Promoter activation by E7 occurred despite inhibition of promoter activity by factors involved in the cell cycle, such as cyclin dependent kinases and E2F transcription factors, and by the ability of E7 to disrupt several aspects of cellular differentiation. These results suggest a new role for E7 in the context of the viral life cycle and shed light on the complex regulation of viral gene expression in infected, differentiating epithelia.

Hypoxia-inducible factor-1 as a therapeutic target in cancer

Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that immortalizes tumors by inducing key genes in cancer biology, including angiogenesis, glycolysis, invasion, and metastasis. Overexpression of HIF-1α is thus associated with resistance to cancer chemotherapy and increased patient mortality in several cancer phenotypes. In the present review, we summarize the role of intratumoral hypoxia and bioactive lipids in enhancing HIF-1 activity, critically discussing the potential for HIF-1α inhibitors in cancer chemotherapy. Considering preclinical studies, HIF-1 inhibitors appear to have antitumor effects and thus represent a novel therapeutic strategy.

Effects of Acanthus ebracteatus Vahl on tumor angiogenesis and on tumor growth in nude mice implanted with cervical cancer

Purpose

The aim of this study was to examine the effects of the crude extract of Acanthus ebracteatus Vahl (AE) on tumor growth and angiogenesis by utilizing a tumor model in which nude mice were implanted with cervical cancer cells containing human papillomavirus 16 DNA (HPV-16 DNA).

Materials and methods

The growth-inhibitory effect of AE was investigated in four different cell types: CaSki (HPV-16 positive), HeLa (HPV-18 positive), hepatocellular carcinoma cells (HepG2), and human dermal fibroblast cells (HDFs). The cell viabilities and IC₅₀ values of AE were determined in cells incubated with AE for different lengths of time. To conduct studies in vivo, female BALB/c nude mice (aged 6–7 weeks, weighing 20–25 g) were used. A cervical cancer-derived cell line (CaSki) with integrated HPV-16 DNA was injected subcutaneously (1 × 10⁷ cells/200 μL) in the middle dorsum of each animal (HPV group). One week after injection, mice were fed orally with AE crude extract at either 300 or 3000 mg/kg body weight/day for 14 or 28 days (HPV-AE groups). Tumor microvasculature and capillary vascularity were determined using laser scanning confocal microscopy. Tumor tissue was collected from each mouse to evaluate tumor histology and vascular endothelial growth factor (VEGF) immunostaining.

Results

The time-response curves of AE and the dose-dependent effect of AE on growth inhibition were determined. After a 48-hour incubation period, the IC₅₀ of AE in CaSki was discovered to be significantly different from that of HDFs (P < 0.05). A microvascular network was observed around the tumor area in the HPV group on days 21 and 35. Tumor capillary vascularity in the HPV group was significantly increased compared with the control group (P < 0.001). High-dose treatment of AE extract (HPV-3000AE group) significantly attenuated the increase in VEGF expression and tumor angiogenesis in mice that received either the 14- or 28-day treatment period (P < 0.001).

Conclusion

Our novel findings demonstrated that AE crude extract could inhibit cervical cancer growth, VEGF expression, and angiogenesis in a CaSki-cell transplant model in mice.

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.

Oncogenic viruses and tumor glucose metabolism: like kids in a candy store

Oncogenic viruses represent a significant public health burden in light of the multitude of malignancies that result from chronic or spontaneous viral infection and transformation. Although many of the molecular signaling pathways that underlie virus-mediated cellular transformation are known, the impact of these viruses on metabolic signaling and phenotype within proliferating tumor cells is less well understood. Whether the interaction of oncogenic viruses with metabolic signaling pathways involves enhanced glucose uptake and glycolysis (both hallmark features of transformed cells) or dysregulation of molecular pathways that regulate oxidative stress, viruses are adept at facilitating tumor expansion. Through their effects on cell proliferation pathways, such as the PI3K and MAPK pathways, the cell cycle regulatory proteins p53 and ATM, and the cell stress response proteins HIF-1α and AMPK, viruses exert control over critical metabolic signaling cascades. Additionally, oncogenic viruses modulate the tumor metabolomic profile through direct and indirect interactions with glucose transporters, such as GLUT1, and specific glycolytic enzymes, including pyruvate kinase, glucose 6-phosphate dehydrogenase, and hexokinase. Through these pathways, oncogenic viruses alter the phenotypic characteristics and energy-use methods of transformed cells; therefore, it may be possible to develop novel antiglycolytic therapies to target these dysregulated pathways in virus-derived malignancies.

Angiogenesis: A Target in Solid Tumors, Also in Leukemia?

Targeting angiogenesis has become an established therapeutic approach to fighting solid tumor growth in cancer patients. Even though increased angiogenesis has long been recognized in various types of hematologic malignancies, the molecular basis underlying this angiogenic switch in leukemias remains poorly understood. The BM stroma is gaining increasing attention for its role in promoting leukemia growth and resistance against current treatments with tyrosine kinase inhibitors. This article provides a brief overview of the role of angiogenesis in leukemias, discusses recent insights into the role of placenta growth factor (PlGF), a VEGF family member, as a novel disease candidate in chronic myeloid leukemia (CML), and highlights the therapeutic potential of PlGF blockade for imatinib-resistant CML.

The roles of viruses in brain tumor initiation and oncomodulation

While some avian retroviruses have been shown to induce gliomas in animal models, human herpesviruses, specifically, the most extensively studied cytomegalovirus, and the much less studied roseolovirus HHV-6, and Herpes simplex viruses 1 and 2, currently attract more and more attention as possible contributing or initiating factors in the development of human brain tumors. The aim of this review is to summarize and highlight the most provoking findings indicating a potential causative link between brain tumors, specifically malignant gliomas, and viruses in the context of the concepts of viral oncomodulation and the tumor stem cell origin.

Assessment of hypoxia inducible factor levels in cancer cell lines upon hypoxic induction using a novel reporter construct

Hypoxia Inducible Factor (HIF) signaling pathway is important for tumor cells with limited oxygen supplies, as it is shown to be involved in the process of proliferation and angiogenesis. Given its pivotal role in cancer biology, robust assays for tracking changes in HIF expression are necessary for understanding its regulation in cancer as well as developing therapies that target HIF signaling. Here we report a novel HIF reporter construct containing tandem repeats of minimum HIF binding sites upstream of eYFP coding sequence. We show that the reporter construct has an excellent signal to background ratio and the reporter activity is HIF dependent and directly correlates with HIF protein levels. By utilizing this new construct, we assayed HIF activity levels in different cancer cell lines cultured in various degrees of hypoxia. This analysis reveals a surprising cancer cell line specific variation of HIF activity in the same level of hypoxia. We further show that in two cervical cancer cell lines, ME180 and HeLa, the different HIF activity levels observed correlate with the levels of hsp90, a cofactor that protects HIF against VHL-independent degradation. This novel HIF reporter construct serves as a tool to rapidly define HIF activity levels and therefore the therapeutic capacity of potential HIF repressors in individual cancers.

Hypoxia inducible factor-1 alpha expression is increased in infected positive HPV16 DNA oral squamous cell carcinoma and positively associated with HPV16 E7 oncoprotein

Background

There is increasing evidence for the role of High Risk (HR) Human PapillomaVirus (HPV) in the pathogenesis of Oral Squamous Cell Carcinoma (OSCC). The E6 and E7 oncogenes from HR HPVs are responsible for the deregulation of p53 and pRB proteins involved in cell cycle and apoptotic pathways. In cell lines experiments, the HPV E7 protein seems to be able to enhance Hypoxia Inducible Factor-1 alpha (HIF-1α) activity, normally involved in the response to hypoxia and able to enhance angiogenesis.

Results

We studied tumor specimens from 62 OSCC; a higher prevalence of tumors in TNM stage II and also in pT2 class between OSCC infected positive HPV16 DNA than non-infected ones was observed. HIF-1α positivity was detected throughout the analysed fields, not associated with areas of necrosis and also observed in cells immediately adjacent to blood vessels. A significant increase in mean values of the HIF-1α labeling indexes was observed for pT1-T2, as well for stage I-II, in the infected positive HPV16 DNA tumors than non-infected ones. HIF-1α and HPV16 E7 labeling indexes showed a significantly positive correlation which suggested a positive association between HPV16 E7 and HIF-1α expression.

Conclusions

In our specimens HIF-1α immunoreactivity hints for an O₂-independent regulatory mechanism in infected positive HPV16 DNA tumors, especially for pT1-T2 and stage I-II tumors, suggesting a very early involvement in the development of HPV-induced OSCC. HIF-1α and HPV16 E7 labeling indexes suggest also a positive association between the two proteins in infected positive HPV16 DNA OSCC.

Overexpression of human papillomavirus (HPV) type 16 oncoproteins promotes angiogenesis via enhancing HIF-1α and VEGF expression in non-small cell lung cancer cells

HPV-16 infection may play an important role in the development of non-small cell lung cancer (NSCLC) among never-smokers. Due to the critical role of angiogenesis in NSCLC development, we describe here the effect of HPV-16 oncoproteins on angiogenesis in NSCLC and the underlying mechanisms. We found that overexpression of HPV-16 E6 and E7 oncoproteins in NSCLC cells significantly promoted angiogenesis both in vitro and in vivo, and correspondingly, an enhanced expression of HIF-1α and VEGF, important pro-angiogenic factors in tumor angiogenesis. Meanwhile, overexpression of HPV-16 oncoproteins also led to HIF-1α-dependent increases in the secretion of several other pro-angiogenic factors, including IL-8. Our findings suggest that HPV-16 oncoproteins contribute to the development of NSCLC possibly by promoting HIF-1α/VEGF-mediated tumor angiogenesis.

The E7 open reading frame acts in cis and in trans to mediate differentiation-dependent activities in the human papillomavirus type 16 life cycle

Human papillomaviruses (HPVs) are the causative agents of several important genital and other mucosal cancers. The HPV16 E7 gene encodes a viral oncogene that is necessary for the continued growth of cancer cells, but its role in the normal, differentiation-dependent life cycle of the virus is not fully understood. The function of E7 in the viral life cycle was examined using a series of mutations of E7 created in the context of the complete HPV16 genome. The effect of these E7 mutations on key events of the viral life cycle, including immortalization, episomal maintenance, late promoter activation, and infectious virion synthesis, was examined. Our studies show that the pRb binding domain is indispensable for early viral activities, whereas the C-terminal zinc finger domain contributed primarily to very late events. Mutations of the casein kinase II phosphorylation site caused a complex phenotype involving both the function of E7 protein and a cis element necessary for the activation of the late promoter, identifying for the first time a promoter element important for late promoter function in the context of the viral genome. All mutant genomes tested showed reduced viral titers following growth in organotypic raft cultures. These studies clarify the role of E7 as a regulator of late events in the differentiation-dependent HPV life cycle.

Hypoxia-Inducible Factor 1α Polymorphisms and Early-Stage Cervical Cancer

Background:

Human papillomavirus can stabilize and induce hypoxia-inducible factor 1α (HIF-1α) protein, which is associated with diminished response to treatment and poor prognosis for cervical cancer. Hypoxia-inducible factor 1α polymorphisms (1772C>T and 1790G>A) in the N-terminal transactivation domain generate significantly increased transcriptional activity and have been linked to poor outcome in various malignancies.

Objective:

The aim of this study was to analyze the possible influence of HIF-1α genetic polymorphisms on cancer susceptibility, tumor aggressiveness, and survival of patients with early-stage cervical cancer.

Methods:

One hundred ninety-nine patients with early-stage cervical cancer who were treated with surgical resection were retrospectively investigated. Hypoxia-inducible factor 1α 1772C>T and 1790G>A genetic polymorphisms were compared with 205 healthy subjects and correlated with the clinical outcome of patients with early-stage cervical cancer.

Results:

The risk of cervical cancer was not affected by HIF-1α 1772C>T and 1790G>A polymorphisms. However, lymph node metastasis was significantly increased in patients who had the 1790 variant (adjusted odds ratio, 5.01; 95% confidence interval, 1.05-23.88;P= 0.043). In survival analysis, HIF-1α 1772C>T and 1790G>A polymorphisms were not related to disease-free survival and overall survival.

Conclusions:

Although HIF-1α genetic polymorphisms had little association with cervical cancer risk and prognosis, individual variance of HIF-1α gene may be associated with cervical cancer invasiveness.

Human papillomavirus E7 enhances hypoxia-inducible factor 1-mediated transcription by inhibiting binding of histone deacetylases

Infection by human papillomaviruses (HPV) leads to the formation of benign lesions, warts, and in some cases, cervical cancer. The formation of these lesions is dependent upon increased expression of proangiogenic factors. Angiogenesis is linked to tissue hypoxia through the activity of the oxygen-sensitive hypoxia-inducible factor 1α (HIF-1α). Our studies indicate that the HPV E7 protein enhances HIF-1 transcriptional activity whereas E6 functions to counteract the repressive effects of p53. Both high- and low-risk HPV E7 proteins were found to bind to HIF-1α through a domain located in the N-terminus. Importantly, the ability of E7 to enhance HIF-1 activity mapped to the C-terminus and correlated with the displacement of the histone deacetylases HDAC1, HDAC4, and HDAC7 from HIF-1α by E7. Our findings describe a novel role of the E7 oncoprotein in activating the function of a key transcription factor mediating hypoxic responses by blocking the binding of HDACs.

Persistence of human papillomavirus infection: keys to malignant progression

Human papillomaviruses (HPVs) are the etiologic agents of cervical and other epithelial cancers. Persistence of infections by high-risk HPV types is the single greatest risk factor for malignant progression. Although prophylactic vaccines have been developed that target high-risk HPV types, there is a continuing need to understand better the virus-host interactions that underlie persistent benign infection and progression to cancer. In this review we summarize the molecular events that facilitate the differentiation-dependent HPV life cycle, how the life cycle is organized to facilitate virus persistence, and how the activities of HPV regulatory proteins result in malignancy.

Beneficial effects of desferrioxamine on encapsulated human islets--in vitro and in vivo study

As many as 2000 IEQs (islet equivalent) of encapsulated human islets are required to normalize glucose levels in diabetic mice. To reduce this number, encapsulated islets were exposed to 100 μM desferrioxamine (DFO) prior to transplantation. Cell viability, glucose-induced insulin secretion, VEGF (Vascular endothelial growth factor), HIF-1α (Hypoxia inducible factor-1 alpha), caspase-3 and caspase-8 levels were assessed after exposure to DFO for 12, 24 or 72 h. Subsequently, 1000, 750 or 500 encapsulated IEQs were infused into peritoneal cavity of diabetic mice after 24 h exposure to DFO. Neither viability nor function in vitro was affected by DFO, and levels of caspase-3 and caspase-8 were unchanged. DFO significantly enhanced VEGF secretion by 1.6- and 2.5-fold at 24 and 72 h, respectively, with a concomitant increase in HIF-1α levels. Euglycemia was achieved in 100% mice receiving 1000 preconditioned IEQs, as compared to only 36% receiving unconditioned IEQs (p < 0.001). Similarly, with 750 IEQ, euglycemia was achieved in 50% mice receiving preconditioned islets as compared to 10% receiving unconditioned islets (p = 0.049). Mice receiving preconditioned islets had lower glucose levels than those receiving unconditioned islets. In summary, DFO treatment enhances HIF-1α and VEGF expression in encapsulated human islets and improves their ability to function when transplanted.

Toxoplasma gondii activates hypoxia-inducible factor (HIF) by stabilizing the HIF-1alpha subunit via type I activin-like receptor kinase receptor signaling

Toxoplasma gondii is an intracellular protozoan parasite that can cause devastating disease in fetuses and immune-compromised individuals. We previously reported that the alpha subunit of the host cell transcription factor, hypoxia-inducible factor-1 (HIF-1), is up-regulated by infection and necessary for Toxoplasma growth. Under basal conditions, HIF-1alpha is constitutively expressed but rapidly targeted for proteasomal degradation after two proline residues are hydroxylated by a family of prolyl hydroxylases (PHDs). The PHDs are alpha-ketoglutarate-dependent dioxygenases that have low K(m) values for oxygen, making them important cellular oxygen sensors. Thus, when oxygen levels decrease, HIF-1alpha is not hydroxylated, and HIF-1 is activated. How Toxoplasma activates HIF-1 under normoxic conditions remains unknown. Here, we report that Toxoplasma infection increases HIF-1alpha stability by preventing HIF-1alpha prolyl hydroxylation. Infection significantly decreases PHD2 abundance, which is the key prolyl hydroxylase for regulating HIF-1alpha. The effects of Toxoplasma on HIF-1alpha abundance and prolyl hydroxylase activity require activin-like receptor kinase signaling. Finally, parasite growth is severely diminished when signaling from this family of receptors is inhibited. Together, these data indicate that PHD2 is a key host cell factor for T. gondii growth and represent a novel mechanism by which a microbial pathogen subverts host cell signaling and transcription to establish its replicative niche.

Stromal issues in cervical cancer: a review of the role and function of basement membrane, stroma, immune response and angiogenesis in cervical cancer development

The carcinogenesis of cervical carcinoma implies an intricate interplay of neoplastic, human papillomavirus infected epithelial cells and stromal tissue, in which different factors have distinct but interacting influence. Persistent infection with an oncogenic human papillomavirus type may lead to epithelial dysplasia with progressive severity. To access the adjacent stromal tissue, tumour cells have to breach the basement membrane. The stroma partly controls tumour growth, invasion and angiogenesis. Last but not least there is considerable influence of the immune response. In this review we describe the importance of various stromal factors in carcinogenesis of cervical cancer.

Human papillomaviruses modulate expression of microRNA 203 upon epithelial differentiation to control levels of p63 proteins

Human papillomaviruses (HPV) link their life cycles to epithelial differentiation and induce productive replication of viral DNA in suprabasal cells. Viral-DNA amplification requires cells to remain active in the cell cycle upon differentiation. This is in contrast to normal cells, which lose proliferative capability upon differentiation. One factor that negatively regulates proliferative capability upon differentiation is microRNA 203 (miR-203), which is expressed primarily in suprabasal epithelial cells. Although HPVs do not encode their own microRNAs (miRNAs), they modulate expression of cellular miRNAs to regulate the activities of cellular proteins. We show that the HPV E7 protein downregulates miR-203 expression upon differentiation, which may occur through the mitogen-activated protein (MAP) kinase/protein kinase C (PKC) pathway. One target of miR-203 is the p63 family of transcription factors, and we demonstrate that HPV-positive cells maintain significantly higher levels of these factors upon differentiation than do normal keratinocytes. Several downstream targets of p63, CARM-1, p21, and Bax, were also increased in E7-expressing cells, and their levels were inversely correlated with amounts of miR-203. Introduction of expression vectors for miR-203 into keratinocytes that stably maintain HPV episomes resulted in short-term elevation of HPV genome copy numbers, but these were rapidly lost upon subsequent passage. When HPV-positive cells expressing high levels of miR-203 were induced to differentiate in methylcellulose, impaired genome amplification was observed. We conclude that high levels of miR-203 are inhibitory to HPV amplification and that HPV proteins act to suppress expression of this microRNA to allow productive replication in differentiating cells.

HIF-1 and NDRG2 contribute to hypoxia-induced radioresistance of cervical cancer Hela cells

Hypoxia inducible factor 1 (HIF-1), the key mediator of hypoxia signaling pathways, has been shown involved in hypoxia-induced radioresistance. However, the underlying mechanisms are unclear. The present study demonstrated that both hypoxia and hypoxia mimetic cobalt chloride could increase the radioresistance of human cervical cancer Hela cells. Meanwhile, ectopic expression of HIF-1 could enhance the resistance of Hela cells to radiation, whereas knocking-down of HIF-1 could increase the sensitivity of Hela cells to radiation in the presence of hypoxia. N-Myc downstream-regulated gene 2 (NDRG2), a new HIF-1 target gene identified in our lab, was found to be upregulated by hypoxia and radiation in a HIF-1-dependent manner. Overexpression of NDRG2 resulted in decreased sensitivity of Hela cells to radiation while silencing NDRG2 led to radiosensitization. Moreover, NDRG2 was proved to protect Hela cells from radiation-induced apoptosis and abolish radiation-induced upregulation of Bax. Taken together, these data suggest that both HIF-1 and NDRG2 contribute to hypoxia-induced tumor radioresistance and that NDRG2 acts downstream of HIF-1 to promote radioresistance through suppressing radiation-induced Bax expression. It would be meaningful to further explore the clinical application potential of HIF-1 and NDRG2 blockade as radiosensitizer for tumor therapy.

Defining the role of hypoxia-inducible factor 1 in cancer biology and therapeutics

Adaptation of cancer cells to their microenvironment is an important driving force in the clonal selection that leads to invasive and metastatic disease. O2 concentrations are markedly reduced in many human cancers compared with normal tissue, and a major mechanism mediating adaptive responses to reduced O2 availability (hypoxia) is the regulation of transcription by hypoxia-inducible factor 1 (HIF-1). This review summarizes the current state of knowledge regarding the molecular mechanisms by which HIF-1 contributes to cancer progression, focusing on (1) clinical data associating increased HIF-1 levels with patient mortality; (2) preclinical data linking HIF-1 activity with tumor growth; (3) molecular data linking specific HIF-1 target gene products to critical aspects of cancer biology and (4) pharmacological data showing anticancer effects of HIF-1 inhibitors in mouse models of human cancer.