Overexpression Of Hypoxia-inducible Factor Research Articles

The Skp1 Protein from Toxoplasma Is Modified by a Cytoplasmic Prolyl 4-Hydroxylase Associated with Oxygen Sensing in the Social Amoeba Dictyostelium

In diverse types of organisms, cellular hypoxic responses are mediated by prolyl 4-hydroxylases that use O(2) and α-ketoglutarate as substrates to hydroxylate conserved proline residues in target proteins. Whereas in metazoans these enzymes control the stability of the HIFα family of transcription factor subunits, the Dictyostelium enzyme (DdPhyA) contributes to O(2) regulation of development by a divergent mechanism involving hydroxylation and subsequent glycosylation of DdSkp1, an adaptor subunit in E3(SCF) ubiquitin ligases. Sequences related to DdPhyA, DdSkp1, and the glycosyltransferases that cap Skp1 hydroxyproline occur also in the genomes of Toxoplasma and other protists, suggesting that this O(2) sensing mechanism may be widespread. Here we show by disruption of the TgphyA locus that this enzyme is required for Skp1 glycosylation in Toxoplasma and that disrupted parasites grow slowly at physiological O(2) levels. Conservation of cellular function was tested by expression of TgPhyA in DdphyA-null cells. Simple gene replacement did not rescue Skp1 glycosylation, whereas overexpression not only corrected Skp1 modification but also restored the O(2) requirement to a level comparable to that of overexpressed DdPhyA. Bacterially expressed TgPhyA protein can prolyl hydroxylate both Toxoplasma and Dictyostelium Skp1s. Kinetic analyses showed that TgPhyA has similar properties to DdPhyA, including a superimposable dependence on the concentration of its co-substrate α-ketoglutarate. Remarkably, however, TgPhyA had a significantly higher apparent affinity for O(2). The findings suggest that Skp1 hydroxylation by PhyA is a conserved process among protists and that this biochemical pathway may indirectly sense O(2) by detecting the levels of O(2)-regulated metabolites such as α-ketoglutarate.

Gene expression analysis in chronic postradiation proctopathy

Radiotherapy is one of the important treatment modalities for tumors of pelvic organs. The fixed location of the rectum and its anatomic relationship with other pelvic organs makes it prone to radiation injury resulting in chronic radiation proctopathy in 5% to 20% of patients. Endothelial dysfunction has been associated with a number of pathophysiological processes. Endothelial cells synthesize and release various factors that regulate angiogenesis, inflammatory responses, hemostasis, as well as vascular tone and permeability. Rectum tissue samples from 20 patients with established chronic radiation proctopathy were analysed for the expression of genes related to oxidative stress, tissue hypoxia, angiogenesis, and inflammation [endoglin (ENG), activin receptor-like kinase 1 (ALK1), platelet endothelial cell adhesion molecule 1 (PECAM), vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF2), hypoxia-inducible factor 1 (HIF-1), and interleukin-1 beta (IL-1β)]. Overexpression of HIF-1, VEGF, FGF2, and IL-1β was detected in affected tissue. For the first time, a significant suppression of activin receptor-like kinase 1 and ENG could be revealed. The data provided here allow further insight into the pathogenesis of radiation-induced rectum injury. Radiation-induced damage is not confined to a single event but involves complex signaling between different pathways, enhancing and maintaining the processes that lead to mucosal damage. The results indicate that postradiation tissue hypoxia is critical for fibrosis, which involves changes in the expression of profibrotic and angiogenic factors in rectal tissue.

Transcriptional analysis of CXCR4, DNMT3A, DNMT3B and DNMT1 gene expression in primary advanced uterine cervical carcinoma

The development of cervical cancer requires genetic and epigenetic factors which result in the persistence of a malignant phenotype. Cervical cancer exhibits also some unique differences from other solid tumors. Normal cervical stratified epithelia have characteristics of hypoxic tissue with over-expression of HIF-1 (hypoxia-inducible factor-1) transcription factor, which targets the transcription of over 70 genes involved in many aspects of cancer biology. One of the genes, which could be induced by HIF-1 is chemokine (C-X-C motif) receptor 4 (CXCR4). CXCR4 could also be epigenetically regulated by methylation of CpG dinucleotides located in the promoter region. Here, we examined the CXCR4, DNMT3A, DNMT3B and DNMT1 transcript levels in cancer tissue (n=30) and non-cancer, normal uterine cervical tissue (n=30) from a Polish cohort. We also compared the methylation status of CXCR4 promoter region in cancer and normal tissue samples. Our result showed significantly higher levels of CXCR4, DNMT3A, DNMT3B and DNMT1 transcript (p=0.0058, 0.0163, 0.0003 and <0.0001, respectively) levels in cancer tissue as compared to normal samples. We did not observe DNA methylation in the CXCR4 promoter region in either control or cancer tissue samples. CXCR4 has a functional hypoxia response element (HRE) in the promoter region, located -1.3 kb from the transcription start site. Our work shows for the first time that HIF-1A could promote the induction of CXCR4 gene expression (Spearman's correlation coefficient = 0.515, p=0.003) in patients with primary advanced uterine cervical carcinoma.

Hypoxia-inducible transcription factor 2α promotes steatohepatitis through augmenting lipid accumulation, inflammation, and fibrosis

Oxygen dynamics in the liver is a central signaling mediator controlling hepatic homeostasis, and dysregulation of cellular oxygen is associated with liver injury. Moreover, the transcription factor relaying changes in cellular oxygen levels, hypoxia-inducible factor (HIF), is critical in liver metabolism, and sustained increase in HIF signaling can lead to spontaneous steatosis, inflammation, and liver tumorigenesis. However, the direct responses and genetic networks regulated by HIFs in the liver are unclear. To help define the HIF signal-transduction pathway, an animal model of HIF overexpression was generated and characterized. In this model, overexpression was achieved by Von Hippel-Lindau (Vhl) disruption in a liver-specific temporal fashion. Acute disruption of Vhl induced hepatic lipid accumulation in an HIF-2α-dependent manner. In addition, HIF-2α activation rapidly increased liver inflammation and fibrosis, demonstrating that steatosis and inflammation are primary responses of the liver to hypoxia. To identify downstream effectors, a global microarray expression analysis was performed using livers lacking Vhl for 24 hours and 2 weeks, revealing a time-dependent effect of HIF on gene expression. Increase in genes involved in fatty acid synthesis were followed by an increase in fatty acid uptake-associated genes, and an inhibition of fatty acid β-oxidation. A rapid increase in proinflammatory cytokines and fibrogenic gene expression was also observed. In vivo chromatin immunoprecipitation assays revealed novel direct targets of HIF signaling that may contribute to hypoxia-mediated steatosis and inflammation. These data suggest that HIF-2α is a critical mediator in the progression from clinically manageable steatosis to more severe steatohepatitis and liver cancer, and may be a potential therapeutic target.

Architecture and the extracellular matrix: the still unappreciated components of the adipose tissue

Fibrosis is usually characterized by the modification of both the amount and composition of a wide panel of extracellular matrix (ECM) proteins. In the liver, pancreas, kidney and lung the accumulation of fibrosis disrupts cellular processes and appears detrimental for organ function. This review highlights the available evidence supporting an important ECM remodelling in adipose tissue (AT) and, in particular, during the development of obesity. The modifications and occurrence of new adipose ECM components leads to an abnormal accumulation of fibrosis in this tissue. This phenomenon was well described in rodent models and evidence is beginning to emerge in humans; however, the origin and potential impact of these depots in AT biology are unclear. Two animal models with disruptions in ECM components (secreted proteins acidic in nature rich in cysteine null mice and ob/ob collagen VI null mice) suggest that fibrosis limits adipocyte hypertrophy and may cause the metabolic disorders associated with obesity. Over-expression of Hypoxia-inducible factor 1 leading to an increase in collagen expression suggests a role for hypoxia in fibrosis development. We conclude this review with possible hypotheses regarding the cellular and molecular contributors of fibrosis initiation.

Abstract 4506: CL67: A novel G-quadruplex stabilising agent inhibits the HIF-1 pathway

Abstract Hypoxic cancer cells are found in all solid tumours and are the most difficult cancer cells to kill. Hypoxia-inducible factor-1 (HIF-1) is a transcriptional activator that plays a critical role in mediating the growing tumours response to hypoxia. Downstream genes activated by HIF-1 lead to increased glycolysis, resistance to apoptosis and increased tumour angiogenesis. HIF-1 over-expression has been associated with increased patient mortality in several tumour types. HIF-1, a heterodimer, consists of a HIF-1α subunit whose rapid breakdown under aerobic conditions is mediated by the von Hippel Lindau protein (pVHL), and an oxygen-insensitive HIF-1ß (ARNT) subunit. HIF-1α protein is elevated many fold in cells under conditions of hypoxia (&amp;lt; 1- 5% O2), and has been found to be increased in many human tumours but is absent in most normal tissues. HIF-1α is, thus, an attractive molecular target for the development of novel cancer drugs with the potential to decrease cancer cell survival and inhibit angiogenesis. The promoter of HIF-1α contains a guanine-rich sequence capable of forming a G-quadruplex structure which modulates the activity of the HIF-1α promoter. We have identified a number of compounds which bind to G-quadruplex structures and preferentially inhibit the growth of renal cancer cells in vitro compared to other tumour cell lines (IC50 of 1.4 – 2.6 µM in the human renal cancer cell lines RCC4, RCC4VHL, 786-0 and A498 compared to IC50 of 8 – 63 µM in MCF-7 human breast, A549 human lung, MiaPaCa and Panc-1 human pancreatic, and PC-3 human prostate cancer cell lines). The lead compound (CL67) shows 2-fold increased sensitivity in RCC4 cells lacking the VHL gene compared to RCC4 cells transfected with the VHL gene (RCC4VHL) (IC50 of 1.3 µM and 2.6 µM respectively). Cell viability is also preferentially reduced in RCC4 cells compared with RCC4VHL cells, particularly under hypoxic conditions (1% O2; 2.1-fold decreased cell viability in RCC4 compared to RCC4VHL cells). CL67 inhibits HIF-1α protein under normoxia (20% O2) and hypoxia (1% O2) measured using Western blotting. However, HIF-1α protein is inhibited in both RCC4 and RCC4VHL cells suggesting that CL67 inhibits HIF-1α using a VHL-independent mechanism. HIF-1α protein is reduced in a dose-dependent manner within 2 hours of treatment of RCC4 cells with 5 × IC50. Maximal inhibition of HIF-1α protein (to 5% of pre-treatment levels) is achieved after 6 hours. HIF-1 transactivation, measured using transient transfection of cells with a plasmid expressing luciferase under the control of multiple copies of the hypoxia-response element (Professor G Melillo) is also reduced in a dose-dependent manner to 8% of pre-treatment activity after 4 hours. Xenograft studies are on-going. CL67 therefore represents a potent novel inhibitor of the HIF-1 pathway which shows preferential activity in renal cancer cell lines, likely by interfering with G-quadruplex structures within promoter sequences. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4506. doi:10.1158/1538-7445.AM2011-4506

Up-regulation of glyceraldehyde-3-phosphate dehydrogenase gene expression by HIF-1 activity depending on Sp1 in hypoxic breast cancer cells

Hypoxia up-regulates the expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in a cell type-specific manner. It is unknown whether this occurs in breast cancer. Here, we report that hypoxia up-regulates the GAPDH gene expression through breast cancer-specific molecular mechanisms in MCF-7 cells. Mutation analysis identified a novel hypoxia response element (HRE), in addition to the HRE found previously in prostate cancer LNCaP cells. Knockdown and overexpression of hypoxia-inducible factor (HIF)-1α indicated that HIF-1 contributed to the up-regulation of GAPDH gene expression by hypoxia. Although chromatin immunoprecipitation (ChIP) and plasmid immunoprecipitation analyses revealed the presence of HIF-1α on the novel HRE in both hypoxic cell lines, a mutation in either the novel HRE or its 3′-flanking GC-box resulted in a reduction of hypoxia-increased GAPDH promoter activity only in MCF-7 cells. ChIP analysis showed that Sp1 bound to the GC-box in MCF-7 cells, but not in LNCaP cells, in normoxia and hypoxia. Knockdown of Sp1 reduced hypoxia-increased promoter activity and expression level of GAPDH in MCF-7 cells. These results indicate that in MCF-7 cells, the activation of HIF-1 on the novel HRE contributes to the breast cancer-specific hypoxic induction of GAPDH gene expression and absolutely depends on the presence of Sp1 on the GC-box.

Cardiac-Specific Overexpression of HIF-1α Prevents Deterioration of Glycolytic Pathway and Cardiac Remodeling in Streptozotocin-Induced Diabetic Mice

Defective glycolysis and angiogenesis in the heart of diabetic patients and in experimental diabetic animal models have been reported. The aim of this study was to determine whether overexpression of hypoxia-inducible factor (HIF)-1alpha protects from myocardial injury in diabetic mice by increasing myocardial glycolysis and angiogenesis. Cardiac-specific HIF-1alpha-overexpressing transgenic and age-matched wild-type control mice were treated with streptozotocin to induce diabetes. Changes in glucose transporters, glycolytic enzymes, angiogenic factors and cardiac morphology were examined in the hearts by real-time RT-PCR, Western blotting, enzymatic assay, and histological assays. HIF-1alpha overexpression elevated hexokinase II (HK-II) protein level and total HK activity in nondiabetic heart and prevented the decreases in HK-II mRNA, protein, and total HK activity in diabetic heart. In addition, the reduction of glucose transporter I, but not glucose transporter 4, was restored in HIF transgenic mouse heart along with a recovery of myocardium ATP production. HIF-1alpha overexpression also normalized diabetes-reduced vascular endothelial growth factor concentration along with a sustained myocardial capillary density and an inhibition of cardiomyocyte hypertrophy and cardiac fibrosis. Therefore, elevation of HIF-1alpha provides a cardiac protection from diabetic-induced impairment in glucose metabolism and angiogenesis via up-regulation of HIF-1 target genes.

VHL Deletion Impairs Mammary Alveologenesis but Is Not Sufficient for Mammary Tumorigenesis

Overexpression of hypoxia inducible factor-1 (HIF-1)alpha, which is common in most solid tumors, correlates with poor prognosis and high metastatic risk in breast cancer patients. Because HIF-1alpha protein stability is tightly controlled by the tumor suppressor von Hippel-Lindau (VHL), deletion of VHL results in constitutive HIF-1alpha expression. To determine whether VHL plays a role in normal mammary gland development, and if HIF-1alpha overexpression is sufficient to initiate breast cancer, Vhl was conditionally deleted in the mammary epithelium using the Cre/loxP system. During first pregnancy, loss of Vhl resulted in decreased mammary epithelial cell proliferation and impaired alveolar differentiation; despite these phenotypes, lactation was sufficient to support pup growth. In contrast, in multiparous dams, Vhl(-/-) mammary glands exhibited a progressive loss of alveolar epithelium, culminating in lactation failure. Deletion of Vhl in the epithelium also impacted the mammary stroma, as there was increased microvessel density accompanied by hemorrhage and increased immune cell infiltration. However, deletion of Vhl was not sufficient to induce mammary tumorigenesis in dams bred continuously for up to 24 months of age. Moreover, co-deletion of Hif1a could not rescue the Vhl(-/-)-dependent phenotype as dams were unable to successfully lactate during the first lactation. These results suggest that additional VHL-regulated genes besides HIF1A function to maintain the proliferative and regenerative potential of the breast epithelium.

Abstract 437: A putative role of hypoxia in development of de novo chemoresistance

Abstract In this work we built a computational model that explores the concept of hypoxia induced de novo chemoresistance. We propose that the hypoxic regions of solid tumors not only protect tumor cells from chemotherapy (environmental resistance) but also are the birthplace of de novo multidrug phenotypically chemoresistant cells. These phenotypically resistant cells would be rare in an untreated tumor due to hypoxia and low external pH (pHe) induced quiescence in the environment where they grow. These cells, however, would be subject to a selective pressure for survival by disruption of apoptotic pathways and overexpression of hypoxia-inducible factors which are known to activate multidrug resistance genes, among other pro-survival mechanisms. Tumor cells under chronic hypoxic conditions are also subject to higher genetic instability than tumor cells in normoxia, due in part to the decrease in the expression of homologous recombination proteins, what could also increase the rate of evolution towards a multi-drug chemoresistant phenotype. In the presence of therapy, the sensitive cells (environmentally or phenotypically) are removed from the tumor, reducing hypoxia, normalizing pHe and allowing the phenotypically chemoresistant subpopulation of cells to grow and re-populate the tumor. This work extends our recent chemoresistance model by adding a representation of HIF-1alpha gene, whose response to hypoxia may change due to mutation from varying thresholds until constant activation or deactivation. The expression of this gene is linked to survival in low pHe, expression of multidrug resistance gene (MDR-1) and glycolysis. Our simulations show that HIF-1alpha expression is selected towards constitutive activation due to its increase in glycolysis and low pHe resistance, which in turn increase tumor survival and invasion. Multi-drug resistance is also increased in such cells as a consequence of the selection for these two phenotypes. This work proposes a mechanism for development of chemoresistance in absence of drug which is different from acquired resistance since the selection for this phenotype is not imposed by the drug itself but as side effect of the selection for survival in hypoxia and low pHe. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 437.

Constitutive HIF-1 activity in malignant melanoma

The hypoxia-inducible factor-1 (HIF-1), which consists of the constitutive HIF-1β and the oxygen-responsive HIF-1α subunit, is the master activator of the cellular transcriptional response to hypoxia coordinating gene expression during reduced oxygen tension. Overexpression of HIF-1 and increased transcriptional activity induced by hypoxia are linked to progression of many tumour types such as head and neck cancer, cervical carcinoma, leukaemia and renal cell carcinoma. In this study, we demonstrate that HIF activity is increased in malignant melanoma cells already under normoxic conditions in contrast to other tumour types. HIF-1α and -2α knockdown by siRNA transfection revealed that this effect is due to constitutive HIF-1α expression. Furthermore, the inhibition or activation of reactive oxygen species (ROS) decreased or activated, respectively, HIF-1 activity and HIF-1α protein expression. Interestingly, the inhibition of the NFkappaB pathway also reduced the accumulation of HIF-1α assuming a context between ROS and NFkappaB, and suggesting that ROS and NFkappaB activity contribute to HIF-1α accumulation. In summary, we identified an increased HIF-1α protein expression and activity in melanoma under normoxia mediated by ROS and the NFkappaB pathway.

Hypoxia-inducible factor-2 is a novel regulator of aberrant CXCL12 expression in multiple myeloma plasma cells

Multiple myeloma is an incurable malignancy of bone marrow plasma cells. Progression of multiple myeloma is accompanied by an increase in bone marrow angiogenesis. Studies from our laboratory suggest a role for the CXCL12 chemokine in this process, with circulating levels of CXCL12 correlating with bone marrow angiogenesis in patients with multiple myeloma. While the mechanisms responsible for aberrant plasma cell expression of CXCL12 remain to be determined, studies in other systems suggest a role for hypoxia and hypoxia-inducible transcription factors. The expression of hypoxia-inducible factor protein was examined in patients' bone marrow biopsy specimens using immunohistochemistry. The hypoxic regulation of CXCL12 was examined in multiple myeloma plasma cell lines using polymerase chain reaction and western blotting. The role of hypoxia-inducible factors-1 and -2 in the regulation of CXCL12 expression was examined using over-expression and short hairpin RNA knockdown constructs, electrophoretic mobility shift assays and chromatin immunoprecipitation. The contribution of CXCL12 to hypoxia-induced angiogenesis was examined in vivo using a subcutaneous murine model of neovascularization. Strong hypoxia-inducible factor-2 protein expression was detected in CD138(+) multiple myeloma plasma cells in patients' biopsy specimens. Prolonged exposure to hypoxia strongly up-regulated CXCL12 expression in multiple myeloma plasma cells and hypoxia-inducible factor-2 was found to play a key role in this response. Promoter analyses revealed increased hypoxia-inducible factor-2 binding to the CXCL12 promoter under hypoxic conditions. Over-expression of hypoxia-inducible factor in multiple myeloma plasma cells strongly induced in vivo angiogenesis, and administration of a CXCL12 antagonist decreased hypoxia-inducible factor-induced angiogenesis. Hypoxia-inducible factor-2 is a newly identified regulator of CXCL12 expression in multiple myeloma plasma cells and a major contributor to multiple myeloma plasma cell-induced angiogenesis. Targeting the hypoxic niche, and more specifically hypoxia-inducible factor-2, may represent a viable strategy to inhibit angiogenesis in multiple myeloma and progression of this disease.

Efficacy and Safety of Pazopanib in Patients With Metastatic Renal Cell Carcinoma

Inactivation of the von Hippel-Lindau gene in clear-cell renal cell carcinomas (RCC) leads to overexpression of hypoxia inducible factor, a transcription factor regulating vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) gene expression. Pazopanib, an angiogenesis inhibitor targeting VEGF receptor, PDGF receptor, and c-KIT, was evaluated in patients with RCC. This phase II study was designed as a randomized discontinuation study but was revised to an open-label study on the recommendation of the data monitoring committee (based on week 12 response rate [RR] of 38% in the first 60 patients). The primary end point was changed from progressive disease rate at 16 weeks postrandomization to RR. Pazopanib 800 mg was administered orally once daily. Pazopanib 800 mg was administered orally once daily. The study enrolled 225 patients with metastatic RCC; 155 patients (69%) were treatment naïve, and 70 patients (31%) had received one prior cytokine- or bevacizumab-containing regimen. Overall RR was 35%; median duration of response was 68 weeks. Median progression-free survival (PFS) was 52 weeks. Eastern Cooperative Oncology Group performance status of 0 and time from diagnosis to treatment of more than 1 year were correlated with prolonged PFS. Pazopanib was generally well tolerated. The most common adverse events were diarrhea, fatigue, and hair depigmentation. The most common laboratory abnormalities were elevated AST and ALT. Pazopanib demonstrated durable activity in patients with advanced RCC and was generally well tolerated in this population. These findings support the further development of pazopanib in advanced RCC.

Prognostic relevance of hypoxia inducible factor-1α expression in patients with melanoma

Overexpression of hypoxia inducible factor (HIF)-1alpha has been found in several human cancers and is thought to correlate with aggressive disease and poor response. A retrospective analysis was carried out on 89 patients with primary cutaneous melanoma. HIF-1alpha expression was assessed by immunohistochemistry in formalin-fixed, paraffin wax-embedded tumour sections. Overall survival (OS) and disease-free survival (DFS) were determined using univariate and multivariate analyses. Of the 89 patients, 78 (87.6%) expressed HIF-1alpha, and the remaining 11 patients (12.4%) did not. HIF-1alpha expression correlated with age (P = 0.002), but not with the main predictive factors in melanoma. Survival analysis disclosed no difference between the groups for OS and DFS. In multivariate analysis, only Breslow Index and ulceration were significantly associated with poor OS. Our results indicate that HIF-1alpha overexpression is present in most primary melanomas, but is not associated with clinicopathological variables, patient prognosis or survival.

Hypoxia downregulates farnesoid X receptor via a hypoxia‐inducible factor‐independent but p38 mitogen‐activated protein kinase‐dependent pathway

Farnesoid X receptor (FXR), a member of the nuclear receptor superfamily, has been shown to play pivotal roles in bile acid homeostasis by regulating the biosynthesis, conjugation, secretion and absorption of bile acids. Accumulating data suggest that FXR signaling is involved in the pathogenesis of liver and metabolic disorders. Here we show that FXR expression is significantly suppressed in HepG2 cells exposed to hypoxia. Concomitantly, the expression of the bile salt export pump, known as an FXR target gene product and responsible for the excretion of bile acids from the liver, is also decreased under hypoxia. Overexpression of hypoxia-inducible factor (HIF)-1alpha does not mimic the suppressive effect of hypoxia on FXR expression. Furthermore, simultaneous knockdown of HIF-1alpha, HIF-2alpha and HIF-3alpha fails to restore the FXR expression level under hypoxia, indicating that HIF is not involved in hypoxia-evoked FXR downregulation. Instead, we demonstrate that p38 mitogen-activated protein kinase is an indispensable factor for FXR downregulation under hypoxia. Thus, we propose a novel liver disorder model in which two signaling molecules, p38 mitogen-activated protein kinase and FXR, may contribute to the linkage of two pathogenic conditions, i.e. ischemia, a condition accompanying hypoxia, and cholestasis, a condition with intrahepatic accumulation of cytotoxic bile acids.

Reactive oxygen species and HIF-1 signalling in cancer

The heterodimeric transcription factor HIF-1 (hypoxia-inducible factor 1) represents the key mediator of hypoxia response. HIF-1 controls numerous genes of pivotal importance for cellular metabolism, angiogenesis, cell cycle regulation and inhibition of apoptosis. HIF-1 overexpression and enhanced transcriptional activity are linked to tumour initiation and progression. Malfunction of the HIF-1 signalling network has been associated with breast, ovarian and prostate cancers. Elevated reactive oxygen species (ROS), also observed in such tumours, have been implicated in HIF-1 signalling. Deciphering the role of ROS in cancer onset and their involvement in signalling networks should prove invaluable for the design of novel anticancer therapeutics.

Endothelin-1 mediates hypoxia-induced inhibition of voltage-gated K+ channel expression in pulmonary arterial myocytes

Prolonged exposure to decreased oxygen tension causes contraction and proliferation of pulmonary arterial smooth muscle cells (PASMCs) and pulmonary hypertension. Hypoxia-induced inhibition of voltage-gated K(+) (K(v)) channels may contribute to the development of pulmonary hypertension by increasing intracellular calcium concentration ([Ca(2+)](i)). The peptide endothelin-1 (ET-1) has been implicated in the development of pulmonary hypertension and acutely decreases K(v) channel activity. ET-1 also activates several transcription factors, although whether ET-1 alters K(V) channel expression is unclear. The hypoxic induction of ET-1 is regulated by the transcription factor hypoxia-inducible factor-1 (HIF-1), which we demonstrated to regulate hypoxia-induced decreases in K(V) channel activity. In this study, we tested the hypothesis that HIF-1-dependent increases in ET-1 lead to decreased K(v) channel expression and subsequent elevation in [Ca(2+)](i). Resting [Ca(2+)](i) and K(v) channel expression were measured in cells exposed to control (18% O(2), 5% CO(2)) and hypoxic (4% O(2), 5% CO(2)) conditions. Hypoxia caused a decrease in expression of K(v)1.5 and K(v)2.1 and a significant increase in resting [Ca(2+)](i). The increase in [Ca(2+)](i) was reduced by nifedipine, an inhibitor of voltage-dependent calcium channels, and removal of extracellular calcium. Treatment with BQ-123, an ET-1 receptor inhibitor, prevented the hypoxia-induced decrease in K(v) channel expression and blunted the hypoxia-induced increase in [Ca(2+)](i) in PASMCs, whereas ET-1 mimicked the effects of hypoxia. Both hypoxia and overexpression of HIF-1 under normoxic conditions increased ET-1 expression. These results suggest that the inhibition of K(v) channel expression and rise in [Ca(2+)](i) during chronic hypoxia may be the result of HIF-1-dependent induction of ET-1.

An In Vitro and In Vivo Evidence That Interleukin-8 Is a Pivotal Hypoxia-Regulated Pro-Angiopoietic Factor Secreted by Human Rhabdomyosarcomas (RMS) - Therapeutic Implications.

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of adolescence and childhood that frequently infiltrates bone marrow (BM). We have demonstrated that the stromal-derived factor (SDF)-1 (Blood 2002; 100:2597), hepatocyte growth factor (HGF) (Cancer Res . 2003; 63:7926) and leukemia inhibitory factor (LIF) (Cancer Res . 2007; 67:2131) play an important role in RMS metastasis. Since RMS tumors are very well vascularized we asked if these factors are secreted by RMS cells and if they stimulate angiogenesis. To address this issue, first we evaluated expression of SDF-1, HGF and LIF as well as several other proangiopoietic factors (IL-8, VEGF, FGF-2) in 9 human RMS cell lines. Expression of these factors was evaluated in both normal steady state conditions and in conditions that lead to overexpression of hypoxia inducible factor-1 (HIF-1a) due to hypoxia or exposure to CoCl2. We found by RQ-PCR and confirmed by ELISA assays that from all the factors evaluated, IL-8, which expression was very low in steady state conditions was very highly upregulated in all RMS cells lines during hypoxic conditions (∼30–135 times). This selective upregulation of IL-8 was somehow unique for RMS cells, and we did not observe similar phenomenon in several other solid tumor cell lines, where IL-8 was usually already very highly expressed in steady state conditions. To evaluate a biological significance of IL-8 in RMS angiogenesis, we collected conditioned media (CM) from RMS cells and found that they stimulate in IL-8 dependent manner in HUVEC i) phosphorylation of MAPKp42/44 and AKT, and ii) chemotactic responses. Pre-clearing of RMS-derived CM with antibodies against IL-8 significantly inhibited chemotaxis of HUVEC. Finally, by employing shRNA we inhibited expression of IL-8 in human RH-30 cells and noticed that such cells in vivo, if injected into skeletal muscles of immunodeficient mice, have the reduced ability to grow tumors and chemoattract co-transplanted human endothelial cells. We conclude that IL-8 is a pivotal pro-angiopoietic factor that is released by human RMS cells in hypoxic conditions, and that the targeting of IL-8 may prove to become a novel efficient strategy to inhibit RMS growth.

Targeting the Loss of the von Hippel-Lindau Tumor Suppressor Gene in Renal Cell Carcinoma Cells

Late-stage clear cell renal carcinoma poses a formidable clinical challenge due to the high mortality rate associated with this disease. Molecular and genetic studies have identified functional loss of the von Hippel-Lindau (VHL) gene as a frequent and crucial event in the development of the malignant phenotype of clear cell renal carcinomas. Loss of VHL function thus represents a pathognomonic molecular defect for therapeutic exploitation. The objective of this study was to evaluate the possibility of targeting VHL loss through pharmacologic means. Chromomycin A3 (ChA3) was identified through in silico analysis of existing publicly available drug profiles from the National Cancer Institute as an agent that seemed to selectively target VHL-deficient clear cell renal carcinoma cells. Genotype-selective toxicity was first determined through short-term viability assays and then confirmed with clonogenic studies. Coculture of fluorescently labeled VHL-deficient and VHL-positive cells showed discriminate killing of the VHL-deficient cells with ChA3. Mechanistically, overexpression of hypoxia-inducible factor (HIF)-2alpha in VHL-positive clear cell renal carcinoma cells phenocopied loss of VHL with respect to ChA3 toxicity, establishing ChA3 as a HIF-dependent cytotoxin. This study shows the feasibility of selectively targeting the loss of the VHL tumor suppressor gene in clear cell renal carcinoma for potential clinical benefit and may have greater ramifications in the development of new targeted therapies for the treatment of cancer and other genetic diseases.

Over-expression of hypoxia-inducible factor 1 alpha in ovarian clear cell carcinoma

Objective. Unlike other histological types of epithelial ovarian carcinoma, ovarian clear cell carcinoma is known to have very poor response to therapy even when discovered in its early stages. Since tumor hypoxia has been shown to be strongly associated with poor prognosis, deregulation of the representative factor of tissue hypoxia; hypoxia-inducible factor 1 alpha (HIF-1α) and related protein; Von Hippel-Lindau (VHL) may be associated with poor prognosis of ovarian clear cell carcinoma. Methods. Immunolocalization of both HIF-1α and VHL was performed on 56 cases of paraffin-embedded tissue sections of four different histological types of epithelial ovarian carcinoma and 5 cases of benign ovarian tumors as a control. Quantitative RT-PCR analysis of both HIF1A and VHL was performed on RNA isolated from 61 microdissected frozen tissues of four different histological types of epithelial ovarian carcinoma and 6 cases of normal ovarian epithelial cells. Expression levels of HIF-1α and VHL in different histological types and correlation between HIF-1α and VHL were determined by nonparametric analysis by Kruskal–Wallis and Spearman’s test. Results. HIF-1α expression levels were significantly higher in ovarian clear cell carcinoma than in other histological types ( P = 0.001). We found no correlation between mRNA and protein expression level in any type of carcinoma specimens. Among endometrioid, serous, and mucinous carcinoma, there were no differences in HIF-1α expression ( P = 0.643). There was a negative correlation between HIF-1α and VHL in serous ( r = − 0.661, P = 0.027) and in endometrioid carcinoma ( r = − 0.657 P = 0.039), but no correlation was found between HIF-1α and VHL expression levels in ovarian clear cell carcinoma ( P = 0.60). Conclusions. The results suggest that the role of hypoxia may change according to the histological type of ovarian carcinoma. High expression of HIF-1α and its independence from VHL in ovarian clear cell carcinoma may confer chemoresistance in this histological type.