Activation of hypoxia-inducible factor 1alpha: posttranscriptional regulation and conformational change by recruitment of the Arnt transcription factor

Regulation of the iron regulatory proteins by reactive nitrogen and oxygen species

Iron regulatory proteins 1 and 2 (IRP1 and IRP2) are RNA binding proteins that posttranscriptionally regulate the expression of mRNAs coding for proteins involved in the maintenance of iron and energy homeostasis. The RNA binding activities of the IRPs are regulated by changes in cellular iron. Thus, the IRPs are considered iron sensors and the principle regulators of cellular iron homeostasis. The mechanisms governing iron regulation of the IRPs are well described. Recently, however, much attention has focused on the regulation of IRPs by reactive nitrogen and oxygen species (RNS, ROS). Here we focus on summarizing the iron-regulated RNA binding activities of the IRPs, as well as the recent findings of IRP regulation by RNS and ROS. The recent observations that changes in oxygen tension regulate both IRP1 and IRP2 RNA binding activities will be addressed in light of ROS regulation of the IRPs.

Computational Structural Biology of S-nitrosylation of Cancer Targets

Nitric oxide (NO) plays an essential role in redox signaling in normal and pathological cellular conditions. In particular, it is well known to react in vivo with cysteines by the so-called S-nitrosylation reaction. S-nitrosylation is a selective and reversible post-translational modification that exerts a myriad of different effects, such as the modulation of protein conformation, activity, stability, and biological interaction networks. We have appreciated, over the last years, the role of S-nitrosylation in normal and disease conditions. In this context, structural and computational studies can help to dissect the complex and multifaceted role of this redox post-translational modification. In this review article, we summarized the current state-of-the-art on the mechanism of S-nitrosylation, along with the structural and computational studies that have helped to unveil its effects and biological roles. We also discussed the need to move new steps forward especially in the direction of employing computational structural biology to address the molecular and atomistic details of S-nitrosylation. Indeed, this redox modification has been so far an underappreciated redox post-translational modification by the computational biochemistry community. In our review, we primarily focus on S-nitrosylated proteins that are attractive cancer targets due to the emerging relevance of this redox modification in a cancer setting.

Integrated phosphorescence-based photonic biosensor (iPOB) for monitoring oxygen levels in 3D cell culture systems

Physiological processes, such as respiration, circulation, digestion, and many pathologies alter oxygen concentration in the blood and tissue. When designing culture systems to recapitulate the in vivo oxygen environment, it is important to integrate systems for monitoring and controlling oxygen concentration. Herein, we report the design and engineering of a system to remotely monitor and control oxygen concentration inside a device for 3D cell culture. We integrate a photonic oxygen biosensor into the 3D tissue scaffold and regulate oxygen concentration via the control of purging gas flow. The integrated phosphorescence-based oxygen biosensor employs the quenching of palladium-benzoporphyrin by molecular oxygen to transduce the local oxygen concentration in the 3D tissue scaffold. The system is validated by testing the effects of normoxic and hypoxic culture conditions on healthy and tumorigenic breast epithelial cells, MCF-10A cells and BT474 cells, respectively. Under hypoxic conditions, both cell types exhibited upregulation of downstream target genes for the hypoxia marker gene, hypoxia-inducible factor 1α (HIF1A). Lastly, by monitoring the real-time fluctuation of oxygen concentration, we illustrated the formation of hypoxic culture conditions due to limited diffusion of oxygen through 3D tissue scaffolds.

Need (more than) two to Tango: Multiple tools to adapt to changes in oxygen availability

Oxygen is a fundamental element for the life of a large number of living organisms allowing an efficient energetic utilization of substrates. Organisms relying on oxygen evolved complex structures for oxygen delivery and biochemical machineries dealing with its safe utilization and the ability to overcome the potentially harmful consequences of changes in oxygen availability. On fact, cells composing complex Eukaryotic organisms are set to live within an optimum narrow range of oxygen, quite specific for each cell type. Minute modifications of oxygen availability, either positive or negative, induce the expression of specific genes, the major actors of this responses being the transcription factors HIF and Nrf2 that control the attempt to cope with low oxygen (hypoxia) or to either high oxygen or to an oxygen "overflow," respectively. This review describes the interaction between these two transcription factors and their interaction with the transcription factor NF-κB acting as a pivotal determinant of final cell response. © 2018 BioFactors, 44(3):207-218, 2018.

Improved oxygenation dramatically alters metabolism and gene expression in cultured primary mouse hepatocytes

Primary hepatocyte culture is an important in vitro system for the study of liver functions. In vivo, hepatocytes have high oxidative metabolism. However, oxygen supply by means of diffusion in in vitro static cultures is much less than that by blood circulation in vivo. Therefore, we investigated whether hypoxia contributes to dedifferentiation and deregulated metabolism in cultured hepatocytes. To this end, murine hepatocytes were cultured under static or shaken (60 revolutions per minute) conditions in a collagen sandwich. The effect of hypoxia on hepatocyte cultures was examined by metabolites in media and cells, hypoxia-inducible factors (HIF)-1/2α western blotting, and real-time quantitative polymerase chain reaction for HIF target genes and key genes of glucose and lipid metabolism. Hepatocytes in shaken cultures showed lower glycolytic activity and triglyceride accumulation than static cultures, compatible with improved oxygen delivery and mitochondrial energy metabolism. Consistently, static cultures displayed significant HIF-2α expression, which was undetectable in freshly isolated hepatocytes and shaken cultures. Transcript levels of HIF target genes (glyceraldehyde 3-phosphate dehydrogenase [Gapdh], glucose transporter 1 [Glut1], pyruvate dehydrogenase kinase 1 [Pdk1], and lactate dehydrogenase A [Ldha]) and key genes of lipid metabolism, such as carnitine palmitoyltransferase 1 (Cpt1), apolipoprotein B (Apob), and acetyl-coenzyme A carboxylase 1 (Acc1), were significantly lower in shaken compared to static cultures. Moreover, expression of hepatocyte nuclear factor 4α (Hnf4α) and farnesoid X receptor (Fxr) were better preserved in shaken cultures as a result of improved oxygen delivery. We further revealed that HIF-2 signaling was involved in hypoxia-induced down-regulation of Fxr. Conclusion: Primary murine hepatocytes in static culture suffer from hypoxia. Improving oxygenation by simple shaking prevents major changes in expression of metabolic enzymes and aberrant triglyceride accumulation; in addition, it better maintains the differentiation state of the cells. The shaken culture is, therefore, an advisable strategy for the use of primary hepatocytes as an in vitro model. (Hepatology Communications 2018;2:299-312).

Repair of Critical-Sized Mandible Defects in Aged Rat Using Hypoxia Preconditioned BMSCs with Up-regulation of Hif-1α

The repair of bone defects in the geriatric population remains a challenge for modern medicine. Transplantation of bone marrow mesenchymal stem cells (BMSCs) combined with or without biomaterials has been a promising approach to bone restoration and regeneration. Typically, the transplanted BMSCs are cultured under normoxic conditions (21% O₂ and 10% serum medium) in vitro. However, the micro-environment of bone defect area is much more severe, in which lower physiological oxygen tension (<1%) and tissue ischemia were present. Therefore, how to improve the survival rate and osteogenesis of transplanted BMSCs at the low oxygenic and ischemic region in vivo is critical. Hypoxia inducible factor-1α (HIF-1α) plays an important role in the tolerance, angiogenesis and osteogenesis of BMSCs during bone regeneration after transplantation. Previous studies have demonstrated that Dimethyloxaloylglycine (DMOG) improves the angiogenic activity of BMSCs. Typically, angiogenesis and osteogenesis are coupled with each other. Therefore, we detected that hypoxia preconditioned BMSCs with the combined treatment of 1% O₂ and 0.5mM DMOG showing up-regulation of Hif-1α could enhance the survival rate of BMSCs under severe condition (serum-free medium and 1% O₂) in vitro and enhances the angiogenesis and osteogenesis potential of BMSCs under 1% O₂ microenvironment in vitro. The hypoxia preconditioned BMSCs were transplanted into critical-sized mandible defects in aged SD rats to test the effectiveness of hypoxic preconditioning approach. We found that hypoxia preconditioned BMSCs improved the repair of critical-sized mandible defects in vivo. These data showed that hypoxia preconditioned BMSCs with the up-regulation of Hif-1α have the potential of enhancing the bone healing process in geriatric individuals.

The Role of Hypoxia in Glioblastoma Invasion

Glioblastoma multiforme (GBM), a grade IV astrocytoma, is the most common and deadly type of primary malignant brain tumor, with a patient's median survival rate ranging from 15 to 17 months. The current treatment for GBM involves tumor resection surgery based on MRI image analysis, followed by radiotherapy and treatment with temozolomide. However, the gradual development of tumor resistance to temozolomide is frequent in GBM patients leading to subsequent tumor regrowth/relapse. For this reason, the development of more effective therapeutic approaches for GBM is of critical importance. Low tumor oxygenation, also known as hypoxia, constitutes a major concern for GBM patients, since it promotes cancer cell spreading (invasion) into the healthy brain tissue in order to evade this adverse microenvironment. Tumor invasion not only constitutes a major obstacle to surgery, radiotherapy, and chemotherapy, but it is also the main cause of death in GBM patients. Understanding how hypoxia triggers the GBM cells to become invasive is paramount to developing novel and more effective therapies against this devastating disease. In this review, we will present a comprehensive examination of the available literature focused on investigating how GBM hypoxia triggers an invasive cancer cell phenotype and the role of these invasive proteins in GBM progression.

Overexpression of hypoxia-inducible factor and metabolic pathways: possible targets of cancer

Cancer, the main cause of human deaths in the modern world is a group of diseases. Anticancer drug discovery is a challenge for scientists because of involvement of multiple survival pathways of cancer cells. An extensive study on the regulation of each step of these pathways may help find a potential cancer target. Up-regulated HIF-1 expression and altered metabolic pathways are two classical characteristics of cancer. Oxygen-dependent (through pVHL, PHDs, calcium-mediated) and independent (through growth factor signaling pathway, mdm2 pathway, HSP90) regulation of HIF-1α leads to angiogenesis, metastasis, and cell survival. The two subunits of HIF-1 regulates in the same fashion through different mechanisms. HIF-1α translation upregulates via mammalian target of rapamycin and mitogen-activated protein kinase signaling pathways, whereas HIF-1β through calmodulin kinase. Further, the stabilized interactions of these two subunits are important for proper functioning. Also, metabolic pathways crucial for the formation of building blocks (pentose phosphate pathway) and energy generation (glycolysis, TCA cycle and catabolism of glutamine) are altered in cancer cells to protect them from oxidative stress and to meet the reduced oxygen and nutrient supply. Up-regulated anaerobic metabolism occurs through enhanced expression of hexokinase, phosphofructokinase, triosephosphate isomerase, glucose 6-phosphate dehydrogenase and down-regulation of aerobic metabolism via pyruvate dehydrogenase kinase and lactate dehydrogenase which compensate energy requirements along with high glucose intake. Controlled expression of these two pathways through their common intermediate may serve as potent cancer target in future.

Immunohistochemical analysis of PDK1, PHD3 and HIF-1α expression defines the hypoxic status of neuroblastoma tumors

Neuroblastoma (NB) is the most common solid tumor during infancy and the first cause of death among the preschool age diseases. The availability of several NB genomic profiles improves the prognostic ability, but the outcome prediction for this pathology remains imperfect. We previously produced a novel prognostic gene signature based on the response of NB cells to hypoxia, a condition of tumor microenvironment strictly connected with cancer aggressiveness. Here we attempted to further define the expression of hypoxia-modulated specific genes, looking at their protein level in NB specimens, considering in particular the hypoxia inducible factor-1α (HIF-1α), the mitochondrial pyruvate dehydrogenase kinase 1 (PDK1), and the HIF-prolyl hydroxylase domain 3 (PHD3). The evaluation of expression was performed by Western blot and immunocytochemistry on NB cell lines and by immunohistochemistry on tumor specimens. Stimulation of both HIF-1α and PDK1 and inhibition of PHD3 expression were observed in NB cell lines cultured under prolonged hypoxic conditions as well as in most of the tumors with poor outcome. Our results indicate that the immunohistochemistry analysis of the protein expression of PDK1, PHD3, and HIF-1α defines the hypoxic status of NB tumors and can be used as a simple and relevant tool to stratify high-risk patients.

Hypoxia is a Key Driver of Alternative Splicing in Human Breast Cancer Cells

Adaptation to hypoxia, a hallmark feature of many tumors, is an important driver of cancer cell survival, proliferation and the development of resistance to chemotherapy. Hypoxia-induced stabilization of hypoxia-inducible factors (HIFs) leads to transcriptional activation of a network of hypoxia target genes involved in angiogenesis, cell growth, glycolysis, DNA damage repair and apoptosis. Although the transcriptional targets of hypoxia have been characterized, the alternative splicing of transcripts that occurs during hypoxia and the roles they play in oncogenesis are much less understood. To identify and quantify hypoxia-induced alternative splicing events in human cancer cells, we performed whole transcriptome RNA-Seq in breast cancer cells that are known to provide robust transcriptional response to hypoxia. We found 2005 and 1684 alternative splicing events including intron retention, exon skipping and alternative first exon usage that were regulated by acute and chronic hypoxia where intron retention was the most dominant type of hypoxia-induced alternative splicing. Many of these genes are involved in cellular metabolism, transcriptional regulation, actin cytoskeleton organisation, cancer cell proliferation, migration and invasion, suggesting they may modulate or be involved in additional features of tumorigenic development that extend beyond the known functions of canonical full-length transcripts.

The functional interplay between the HIF pathway and the ubiquitin system - more than a one-way road

The hypoxia inducible factor (HIF) pathway and the ubiquitin system represent major cellular processes that are involved in the regulation of a plethora of cellular signaling pathways and tissue functions. The ubiquitin system controls the ubiquitination of proteins, which is the covalent linkage of one or several ubiquitin molecules to specific targets. This ubiquitination is catalyzed by approximately 1000 different E3 ubiquitin ligases and can lead to different effects, depending on the type of internal ubiquitin chain linkage. The best-studied function is the targeting of proteins for proteasomal degradation. The activity of E3 ligases is antagonized by proteins called deubiquitinases (or deubiquitinating enzymes), which negatively regulate ubiquitin chains. This is performed in most cases by the catalytic removal of these chains from the targeted protein. The HIF pathway is regulated in an oxygen-dependent manner by oxygen-sensing hydroxylases. Covalent modification of HIFα subunits leads to the recruitment of an E3 ligase complex via the von Hippel-Lindau (VHL) protein and the subsequent polyubiquitination and proteasomal degradation of HIFα subunits, demonstrating the regulation of the HIF pathway by the ubiquitin system. This unidirectional effect of an E3 ligase on the HIF pathway is the best-studied example for the interplay between these two important cellular processes. However, additional regulatory mechanisms of the HIF pathway through the ubiquitin system are emerging and, more recently, also the reciprocal regulation of the ubiquitin system through components of the HIF pathway. Understanding these mechanisms and their relevance for the activity of each other is of major importance for the comprehensive elucidation of the oxygen-dependent regulation of cellular processes. This review describes the current knowledge of the functional bidirectional interplay between the HIF pathway and the ubiquitin system on the protein level.

Andrographolide inhibits hypoxia-induced HIF-1α-driven endothelin 1 secretion by activating Nrf2/HO-1 and promoting the expression of prolyl hydroxylases 2/3 in human endothelial cells

Andrographolide, the main bioactive component of the medicinal plant Andrographis paniculata, has been shown to possess potent anti-inflammatory activity. Endothelin 1 (ET-1), a potent vasoconstrictor peptide produced by vascular endothelial cells, displays proinflammatory property. Hypoxia-inducible factor 1α (HIF-1α), the regulatory member of the transcription factor heterodimer HIF-1α/β, is one of the most important molecules that responds to hypoxia. Changes in cellular HIF-1α protein level are the result of altered gene transcription and protein stability, with the latter being dependent on prolyl hydroxylases (PHDs). In this study, inhibition of pro-inflammatory ET-1 expression and changes of HIF-1α gene transcription and protein stability under hypoxia by andrographolide in EA.hy926 endothelial-like cells were investigated. Hypoxic conditions were created using the hypoxia-mimetic agent CoCl_2. We found that hypoxia stimulated the production of reactive oxygen species (ROS), the expression of HIF-1α mRNA and protein, and the expression and secretion of ET-1. These effects, however, were attenuated by co-exposure to andrographolide, bilirubin, and RuCO. Silencing Nrf2 and heme oxygenase 1 (HO-1) reversed the inhibitory effects of andrographolide on hypxoia-induced HIF-1α mRNA and protein expression. Moreover, andrographolide increased the expression of prolyl hydroxylases (PHD) 2/3, which hydroxylate HIF-1α and promotes HIF-1α proteasome degradation, with an increase in HIF-1α hydroxylation was noted under hypoxia. Inhibition of p38 MAPK abrogated the hypoxia-induced increases in HIF-1α mRNA and protein expression as well as ET-1 mRNA expression and secretion. Taken together, these results suggest that andrographolide suppresses hypoxia-induced pro-inflammatory ET-1 expression by activating Nrf2/HO-1, inhibiting p38 MAPK signaling, and promoting PHD2/3 expression. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 918-930, 2017.

Pyruvate dehydrogenase kinase 1 is essential for transplantable mouse bone marrow hematopoietic stem cell and progenitor function

Background

Accumulating evidence suggests that hypoxic areas in the bone marrow are crucial for maintenance of hematopoietic stem cells (HSCs) by supporting a quiescent state of cell cycle and regulating the transplantation capacity of long-term (LT)-HSCs. In addition, HSCs seem to express a metabolic profile of energy production away from mitochondrial oxidative phosphorylation in favor of glycolysis. At oxygen deprivation, hypoxia inducible factor 1α (HIF-1α) is known to induce glycolytic enzymes as well as suppressing mitochondrial energy production by inducing pyruvate dehydrogenase kinase 1 (Pdk1) in most cell types. It has not been established whether PDK1 is essential for HSC function and mediates hypoxia-adapting functions in HSCs. While the Pdk gene family contains four members (Pdk1-4), it was recently shown that Pdk2 and Pdk4 have an important role in regulating LT-HSCs.

Principle findings

Here we demonstrate that PDK1 activity is crucial for transplantable HSC function. Whereas Pdkl, Pdk2, and Pdk3 transcripts were expressed at higher levels in different subtypes of HSCs compared to differentiated cells, we could not detect any major differences in expression between LT-HSCs and more short-term HSCs and multipotent progenitors. When studying HIF-1α-mediated regulation of Pdk activity in vitro, Pdk1 was the most robust target regulated by hypoxia, whereas Pdk2, Pdk3, and Pdk4 were not affected. Contrary, genetic ablation in a cre-inducible Hif-1α knockout mouse did not support a link between HIF-1α and Pdk1. Silencing of Pdk1 by shRNA lentiviral gene transfer partially impaired progenitor colony formation in vitro and had a strong negative effect on both long-term and short-term engraftment in mice.

Conclusions

Our study demonstrates that PDK1 has broad effects in hematopoiesis and is a critical factor for engraftment of both HSCs and multipotent progenitors upon transplantation to recipient mice. While Pdk1 was a robust hypoxia-inducible gene mediated by HIF-1α in vitro, we could not find evidence of any in vivo links between Pdk1 and HIF-1α.

Genetic polymorphisms in key hypoxia-regulated downstream molecules and phenotypic correlation in prostate cancer

Background

In this study we sought if, in their quest to handle hypoxia, prostate tumors express target hypoxia-associated molecules and their correlation with putative functional genetic polymorphisms.

Methods

Representative areas of prostate carcinoma (n = 51) and of nodular prostate hyperplasia (n = 20) were analysed for hypoxia-inducible factor 1 alpha (HIF-1α), carbonic anhydrase IX (CAIX), lysyl oxidase (LOX) and vascular endothelial growth factor (VEGFR2) immunohistochemistry expression using a tissue microarray. DNA was isolated from peripheral blood and used to genotype functional polymorphisms at the corresponding genes (HIF1A +1772 C > T, rs11549465; CA9 + 201 A > G; rs2071676; LOX +473 G > A, rs1800449; KDR – 604 T > C, rs2071559).

Results

Immunohistochemistry analyses disclosed predominance of positive CAIX and VEGFR2 expression in epithelial cells of prostate carcinomas compared to nodular prostate hyperplasia (P = 0.043 and P = 0.035, respectively). In addition, the VEGFR2 expression score in prostate epithelial cells was higher in organ-confined and extra prostatic carcinoma compared to nodular prostate hyperplasia (P = 0.031 and P = 0.004, respectively). Notably, for LOX protein the immunoreactivity score was significantly higher in organ-confined carcinomas compared to nodular prostate hyperplasia (P = 0.015). The genotype-phenotype analyses showed higher LOX staining intensity for carriers of the homozygous LOX +473 G-allele (P = 0.011). Still, carriers of the KDR−604 T-allele were more prone to have higher VEGFR2 expression in prostate epithelial cells (P < 0.006).

Conclusions

Protein expression of hypoxia markers (VEGFR2, CAIX and LOX) on prostate epithelial cells was different between malignant and benign prostate disease. Two genetic polymorphisms (LOX +473 G > A and KDR−604 T > C) were correlated with protein level, accounting for a potential gene-environment effect in the activation of hypoxia-driven pathways in prostate carcinoma. Further research in larger series is warranted to validate present findings.

Electronic supplementary material

The online version of this article (doi:10.1186/s12894-017-0201-y) contains supplementary material, which is available to authorized users.

Hypoxia and HIF-1 activation in bacterial infections

For most of the living beings, oxygen is one of the essential elements required to sustain life. Deprivation of oxygen causes tissue hypoxia and this severely affects host cell and organ functions. Tissue hypoxia is a prominent microenvironmental condition occurring in infections and there is a body of evidence that hypoxia and inflammation are interconnected with each other. The primary key factor mediating the mammalian hypoxic response is hypoxia inducible factor (HIF)-1, which regulates oxygen homeostasis on cellular, tissue and organism level. Recent studies show that HIF-1 plays a central role in angiogenesis, cancer and cardiovascular disease but also in bacterial infections. Activation of HIF-1 depends on the nature of the pathogen and the characteristics of infections in certain hosts. Up to date, it is not completely clear whether the phenomenon of HIF-1 activation in infections has a protective or detrimental effect on the host. In this review, we give an overview of whether and how hypoxia and HIF-1 affect the course of infections.

Upregulation of P2Y2 nucleotide receptor in human hepatocellular carcinoma cells

Objective

To examine if hypoxia inducible factor-1α (HIF-1α) can induce the upregulation of the purinergic receptor P2Y2 (P2Y2) and thereby promote the viability of human hepatocellular carcinoma (HCC) cells under hypoxic conditions.

Methods

Archival HCC tumour specimens and corresponding non-cancerous tissues were examined immunohistochemically for P2Y2 protein. A series of in vitro experiments were undertaken using HCC cell lines to determine the effect of hypoxia on HIF-1α and P2Y2 levels, the effect of HIF-1α upregulation on P2Y2 levels, and the effect of P2Y2 upregulation on cell viability under hypoxic conditions.

Results

Human HCC specimens were positive for P2Y2. Hypoxia and upregulated HIF-1α both upregulated the P2Y2 levels in HCC cell lines. P2Y2 upregulation using plasmid transfection resulted in enhanced cell viability under hypoxia. Treatment of HepG2 cells with the selective P2Y2 antagonist MRS2312 downregulated P2Y2 and reduced cell viability in five HCC cell lines. P2Y2 knockdown reduced HepG2 cell viability under hypoxia.

Conclusions

These present results suggest that HCC cells upregulate P2Y2 levels during hypoxia, which in turn promotes their growth. P2Y2 could be a potential therapeutic target for treating HCC.

Glioblastoma, hypoxia and autophagy: a survival-prone 'ménage-à-trois'

Glioblastoma multiforme is the most common and the most aggressive primary brain tumor. It is characterized by a high degree of hypoxia and also by a remarkable resistance to therapy because of its adaptation capabilities that include autophagy. This degradation process allows the recycling of cellular components, leading to the formation of metabolic precursors and production of adenosine triphosphate. Hypoxia can induce autophagy through the activation of several autophagy-related proteins such as BNIP3, AMPK, REDD1, PML, and the unfolded protein response-related transcription factors ATF4 and CHOP. This review summarizes the most recent data about induction of autophagy under hypoxic condition and the role of autophagy in glioblastoma.

GLUT1 activity contributes to the impairment of PEDF secretion by the RPE

PURPOSE

In this study, we aimed to understand whether glucose transporter 1 (GLUT1) activity affects the secretion capacity of antiangiogenic factor pigment epithelium-derived factor (PEDF) by the RPE cells, thus explaining the reduction in PEDF levels observed in patients with diabetic retinopathy (DR).

METHODS

Analysis of GLUT1 expression, localization, and function was performed in vitro in RPE cells (D407) cultured with different glucose concentrations, corresponding to non-diabetic (5 mM of glucose) and diabetic (25 mM of glucose) conditions, further subjected to normoxia or hypoxia. The expression of PEDF was also evaluated in the secretome of the cells cultured in these conditions. Analysis of GLUT1 and PEDF expression was also performed in vivo in the RPE of Ins2(Akita) diabetic mice and age-matched wild-type (WT) controls.

RESULTS

We observed an increase in GLUT1 under hypoxia in a glucose-dependent manner, which we found to be directly associated with the translocation and stabilization of GLUT1 in the cell membrane. This stabilization led to an increase in glucose uptake by RPE cells. This increase was followed by a decrease in PEDF expression in RPE cells cultured in conditions that simulated DR. Compared with non-diabetic WT mice, the RPE of Ins2(Akita) mice showed increased GLUT1 overexpression with a concomitant decrease in PEDF expression.

CONCLUSIONS

Collectively, our data show that expression of GLUT1 is stimulated by hyperglycemia and low oxygen supply, and this overexpression was associated with increased activity of GLUT1 in the cell membrane that contributes to the impairment of the RPE secretory function of PEDF.

Redox Homeostasis and Cellular Antioxidant Systems: Crucial Players in Cancer Growth and Therapy

Reactive oxygen species (ROS) and their products are components of cell signaling pathways and play important roles in cellular physiology and pathophysiology. Under physiological conditions, cells control ROS levels by the use of scavenging systems such as superoxide dismutases, peroxiredoxins, and glutathione that balance ROS generation and elimination. Under oxidative stress conditions, excessive ROS can damage cellular proteins, lipids, and DNA, leading to cell damage that may contribute to carcinogenesis. Several studies have shown that cancer cells display an adaptive response to oxidative stress by increasing expression of antioxidant enzymes and molecules. As a double-edged sword, ROS influence signaling pathways determining beneficial or detrimental outcomes in cancer therapy. In this review, we address the role of redox homeostasis in cancer growth and therapy and examine the current literature regarding the redox regulatory systems that become upregulated in cancer and their role in promoting tumor progression and resistance to chemotherapy.

Hypoxia Decreases Invasin-Mediated Yersinia enterocolitica Internalization into Caco-2 Cells

Yersinia enterocolitica is a major cause of human yersiniosis, with enterocolitis being a typical manifestation. These bacteria can cross the intestinal mucosa, and invade eukaryotic cells by binding to host β₁ integrins, a process mediated by the bacterial effector protein invasin. This study examines the role of hypoxia on the internalization of Y. enterocolitica into intestinal epithelial cells, since the gastrointestinal tract has been shown to be physiologically deficient in oxygen levels (hypoxic), especially in cases of infection and inflammation. We show that hypoxic pre-incubation of Caco-2 cells resulted in significantly decreased bacterial internalization compared to cells grown under normoxia. This phenotype was absent after functionally blocking host β₁ integrins as well as upon infection with an invasin-deficient Y. enterocolitica strain. Furthermore, downstream phosphorylation of the focal adhesion kinase was also reduced under hypoxia after infection. In good correlation to these data, cells grown under hypoxia showed decreased protein levels of β₁ integrins at the apical cell surface whereas the total protein level of the hypoxia inducible factor (HIF-1) alpha was elevated. Furthermore, treatment of cells with the HIF-1 α stabilizer dimethyloxalylglycine (DMOG) also reduced invasion and decreased β₁ integrin protein levels compared to control cells, indicating a potential role for HIF-1α in this process. These results suggest that hypoxia decreases invasin-integrin-mediated internalization of Y. enterocolitica into intestinal epithelial cells by reducing cell surface localization of host β₁ integrins.

The Impact of Hypoxia and Mesenchymal Transition on Glioblastoma Pathogenesis and Cancer Stem Cells Regulation

Glioblastoma (GBM) is an aggressive primary brain tumor with potential for wide dissemination and resistance to standard treatments. Although GBM represents a single histopathologic diagnosis under current World Health Organization criteria, data from multiplatform molecular profiling efforts, including The Cancer Genome Atlas, indicate that multiple subgroups with distinct markers and biology exist. It remains unclear whether treatment resistance differs based on subgroup. Recent evidence suggests that hypoxia, or absence of normal tissue oxygenation, is important in generating tumor resistance through a signaling cascade driven by hypoxia-inducible factors and vascular endothelial growth factor. Hypoxia can result in isolation of tumor cells from therapeutic agents and activation of downstream tumor protective mechanisms. In addition, there are links between hypoxia and the phenomenon of mesenchymal transition in gliomas. Mesenchymal transformation in gliomas resembles at many levels the epithelial-mesenchymal transition that has been described in other solid tumors in which epithelial cells lose their epithelial characteristics and take on a more mesenchymal phenotype, but the mesenchymal transition in brain tumors is also distinct, perhaps related to the unique cell types and cellular organization in the brain and brain tumors. Cancer stem cells, which are specific cell populations involved in self-renewal, differentiation, and GBM pathophysiology, are also importantly regulated by hypoxia signaling pathways. In this review, we discuss the interplay of hypoxia and mesenchymal signaling in GBM including the key pathway regulators and downstream genes, the effect of these processes in regulation of the tumor microenvironment and cancer stem cells, and their role in treatment resistance.

Skeletal muscle as an endocrine organ: Role of [Na+]i/[K+]i-mediated excitation-transcription coupling

During the last two decades numerous research teams demonstrated that skeletal muscles function as an exercise-dependent endocrine organ secreting dozens of myokines. Variety of physiological and pathophysiological implications of skeletal muscle myokines secretion has been described; however, upstream signals and sensing mechanisms underlying this phenomenon remain poorly understood. It is well documented that in skeletal muscles intensive exercise triggers dissipation of transmembrane gradient of monovalent cations caused by permanent activation of voltage-gated Na+ and K+ channels. Recently, we demonstrated that sustained elevation of the [Na+]i/[K+]i ratio triggers expression of dozens ubiquitous genes including several canonical myokines, such as interleukin 6 and cyclooxygenase 2, in the presence of intra- and extracellular Ca2+ chelators. These data allowed us to suggest a novel [Na+]i/[K+]i-sensitive, Ca2+i-independent mechanism of excitation-transcription coupling which triggers myokine production. This pathway exists in parallel with canonical signaling mediated by Ca2+i, AMP-activated protein kinase and hypoxia-inducible factor 1α (HIF-1α). In our mini-review we briefly summarize data supporting this hypothesis as well as unresolved issues aiming to forthcoming studies.

Hydrogen sulfide promotes angiogenesis by downregulating miR-640 via the VEGFR2/mTOR pathway

We previously found hydrogen sulfide (H2S) to be a new proangiogenic factor. However, the mechanisms underlying the cardiovascular effect of this small gas molecule remain largely unknown. The aim of the present study was to identify the essential microRNAs (miRNAs) involved in the transduction of H2S signals in vascular endothelial cells (ECs). The expression of miR-640 and its signaling elements, vascular endothelial growth factor receptor 2 (VEGFR2), hypoxia inducible factor 1-α (HIF1A), and mammalian target of rapamycin (mTOR), was measured using quantitative PCR and Western blotting. Overexpression and inhibition of miR-640 were performed to clarify their roles in mediating the effect of H2S. In addition, knockdown of VEGFR2, HIF1A, and mTOR was performed using siRNAs, dominant negative mutants, or inhibitors to examine their roles in the transduction of the H2S signals. miR-640 levels decreased in vascular ECs that were treated with H2S, whereas overexpression of miR-640 blunted the proangiogenic effect of H2S. Knockdown of either VEGFR2 or mTOR blunted the downregulation of miR-640 and the proangiogenic effect induced by H2S. In addition, miR-640 bound to the 3'-UTR of HIF1A mRNA and then inhibited the expression of HIF1A. The inhibition could be recovered by treating cells with H2S. Thus we concluded that miR-640 plays a pivotal role in mediating the proangiogenic effect of H2S; H2S acts through downregulation of the expression of miR-640 and increasing the levels of HIF1A through the VEGFR2-mTOR pathway.

Therapeutic Implications for Overcoming Radiation Resistance in Cancer Therapy

Ionizing radiation (IR), such as X-rays and gamma (γ)-rays, mediates various forms of cancer cell death such as apoptosis, necrosis, autophagy, mitotic catastrophe, and senescence. Among them, apoptosis and mitotic catastrophe are the main mechanisms of IR action. DNA damage and genomic instability contribute to IR-induced cancer cell death. Although IR therapy may be curative in a number of cancer types, the resistance of cancer cells to radiation remains a major therapeutic problem. In this review, we describe the morphological and molecular aspects of various IR-induced types of cell death. We also discuss cytogenetic variations representative of IR-induced DNA damage and genomic instability. Most importantly, we focus on several pathways and their associated marker proteins responsible for cancer resistance and its therapeutic implications in terms of cancer cell death of various types and characteristics. Finally, we propose radiation-sensitization strategies, such as the modification of fractionation, inflammation, and hypoxia and the combined treatment, that can counteract the resistance of tumors to IR.

Ascorbic acid and ascorbate-2-phosphate decrease HIF activity and malignant properties of human melanoma cells

Background

Hypoxia inducible factor-1 alpha (HIF-1α) is thought to play a role in melanoma carcinogenesis. Posttranslational regulation of HIF-1α is dependent on Prolyl hydroxylase (PHD 1–3) and Factor Inhibiting HIF (FIH) hydroxylase enzymes, which require ascorbic acid as a co-factor for optimal function. Depleted intra-tumoral ascorbic acid may thus play a role in the loss of HIF-1α regulation in melanoma. These studies assess the ability of ascorbic acid to reduce HIF-1α protein and transcriptional activity in metastatic melanoma and reduce its invasive potential.

Methods

HIF-1α protein was evaluated by western blot, while transcriptional activity was measured by HIF-1 HRE-luciferase reporter gene activity. Melanoma cells were treated with ascorbic acid (AA) and ascorbate 2-phosphate (A2P) to assess their ability to reduce HIF-1α accumulation and activity. siRNA was used to deplete cellular PHD2 in order to evaluate this effect on AA’s ability to lower HIF-1α levels. A2P’s effect on invasive activity was measured by the Matrigel invasion assay. Data was analyzed by One-way ANOVA with Tukey’s multiple comparisons test, or Student-T test as appropriate, with p < .05 considered significant.

Results

Supplementation with both AA and A2P antagonized normoxic as well as cobalt chloride- and PHD inhibitor ethyl 3, 4-dihydroxybenzoate induced HIF-1α protein stabilization and transcriptional activity. Knockdown of the PHD2 isoform with siRNA did not impede the ability of AA to reduce normoxic HIF-1α protein. Additionally, reducing HIF-1α levels with A2P resulted in a significant reduction in the ability of the melanoma cells to invade through Matrigel.

Conclusion

These studies suggest a positive role for AA in regulating HIF-1α in melanoma by demonstrating that supplementation with either AA, or its oxidation-resistant analog A2P, effectively reduces HIF-1α protein and transcriptional activity in metastatic melanoma cells. Our data, while supporting the function of AA as a necessary cofactor for PHD and likely FIH activity, also suggests a potential non-PHD/FIH role for AA in HIF-1α regulation by its continued ability to reduce HIF-1α in the presence of PHD inhibition. The use of the oxidation-resistant AA analog, A2P, to reduce the ability of HIF-1α to promote malignant progression in melanoma cells and enhance their response to therapy warrants further investigation.

Measuring oxygen levels in Caco-2 cultures

PURPOSE

Measuring oxygen levels in three different systems of Caco-2 cell culture.

METHODS

Caco-2 cells were cultured in three different systems, using conventional polystyrene 24-well plates, special 24-well gas permeable plates, or on membrane inserts in conventional plates. Optical sensor spots were used to measure dissolved O₂ levels in these cultured cells over the course of 6 days under normoxia (143 mmHg) and for 6 hours under hypoxia (7 mmHg). Western blot analysis was used to determine the protein levels of hypoxia-inducible factor 1α (HIF-1α) in the different cultures.

RESULTS

All culture systems displayed lower O₂ levels over time than expected when cultured under normoxia conditions. On average, O₂ levels reached as low as 25 mmHg in 24-well plates but remained at 97 and 117 mmHg in gas permeable plates and membrane inserts, respectively. Under hypoxia, 1 mL cell cultures equilibrated to 7 mmHg O₂ within the first 60 minutes and dropped to 0.39 and 0.61 mmHg O₂ in 24-well and gas permeable plates, respectively, after the 6-hour incubation period. Cultures in membrane inserts did not equilibrate to 7 mmHg by the end of the 6-hour incubation period, where the lowest O₂ measurements reached 23.12 mmHg. Western blots of HIF-1α protein level in the whole cell lysates of the different Caco-2 cultures revealed distinct stabilization of HIF-1α after hypoxic incubation for 1, 2, and 4 hours in 24-well plates as well as gas permeable plates. For membrane inserts, notable HIF-1α was seen after 4 hours of hypoxic incubation.

CONCLUSION

Cellular oxygen depletion was achieved in different hypoxic Caco-2 culture systems. However, different oxygen levels comparing different culture systems indicate that O₂ level should be carefully considered in oxygen-dependent experiments.

HIF-1α pathway: role, regulation and intervention for cancer therapy

Hypoxia-inducible factor-1 (HIF-1) has been recognized as an important cancer drug target. Many recent studies have provided convincing evidences of strong correlation between elevated levels of HIF-1 and tumor metastasis, angiogenesis, poor patient prognosis as well as tumor resistance therapy. It was found that hypoxia (low O2 levels) is a common character in many types of solid tumors. As an adaptive response to hypoxic stress, hypoxic tumor cells activate several survival pathways to carry out their essential biological processes in different ways compared with normal cells. Recent advances in cancer biology at the cellular and molecular levels highlighted the HIF-1α pathway as a crucial survival pathway for which novel strategies of cancer therapy could be developed. However, targeting the HIF-1α pathway has been a challenging but promising progresses have been made in the past twenty years. This review summarizes the role and regulation of the HIF-1α in cancer, and recent therapeutic approaches targeting this important pathway.

Hypoxia-Inducible Factor 1 Is an Inductor of Transcription Factor Activating Protein 2 Epsilon Expression during Chondrogenic Differentiation

The transcription factor AP-2ε (activating enhancer-binding protein epsilon) is expressed in cartilage of humans and mice. However, knowledge about regulatory mechanisms influencing AP-2ε expression is limited. Using quantitative real time PCR, we detected a significant increase in AP-2ε mRNA expression comparing initial and late stages of chondrogenic differentiation processes in vitro and in vivo. Interestingly, in these samples the expression pattern of the prominent hypoxia marker gene angiopoietin-like 4 (Angptl4) strongly correlated with that of AP-2ε suggesting that hypoxia might represent an external regulator of AP-2ε expression in mammals. In order to show this, experiments directly targeting the activity of hypoxia-inducible factor-1 (HIF1), the complex mediating responses to oxygen deprivation, were performed. While the HIF1-activating compounds 2,2'-dipyridyl and desferrioxamine resulted in significantly enhanced mRNA concentration of AP-2ε, siRNA against HIF1α led to a significantly reduced expression rate of AP-2ε. Additionally, we detected a significant upregulation of the AP-2ε mRNA level after oxygen deprivation. In sum, these different experimental approaches revealed a novel role for the HIF1 complex in the regulation of the AP-2ε gene in cartilaginous cells and underlined the important role of hypoxia as an important external regulatory stimulus during chondrogenic differentiation modulating the expression of downstream transcription factors.

The action of HIF-3α variants on HIF-2α-HIF-1β heterodimer formation is directly probed in live cells

Hypoxia-inducible factors (HIFs), consisting of α and β subunits, activate various genes to adapt to low oxygen environments through their heterodimeric complex formation in the nucleus. While most of the studies have been extensively focused on the HIF-1α isoform, the effect of HIF-α isoforms on the complex formation between HIF-2α and HIF-1β in live cells has not been reported in detail. To probe these interactions in a physiological condition, we established a fluorescence resonance energy transfer (FRET) assay by introducing fluorescent reporter proteins onto the N-termini of HIF-2α and HIF-1β in live PC3 cells. After thorough validations of our FRET assay system, we showed that both HIF-1α and HIF-3α variants likely function as negative regulators on the heterodimer formation of HIF-2α with HIF-1β in cells. We also characterized the localization and stabilization of HIF-3α variants and measured the interaction between HIF-3α variants and other HIF isoforms in live cells. In contrast to the previous results showing HIF-3α-mediated blockage of HIF-1α translocation, the presence of HIF-3α did not affect the localization of HIF-2α, suggesting distinct roles of HIF-3α in regulation of two HIF-α isoforms.

Design, Synthesis and Biological Evaluation of Novel HIF1α Inhibitors

Elevated levels of hypoxia inducible factor-1 (HIF1) are linked to tumor metastasis, angiogenesis, poor patient prognosis and response to chemotherapy. HIF1α is a master regulator of the hypoxic response, including in cancer cells, through transcriptional activation of several target genes. Previously, we identified compound CJ-3k with high anti-HIF1α activity based on the structure of a well-known HIF1α inhibitor, YC-1. In this study, the CJ-3k scaffold was systematically modified to explore the structure-activity relationships. Fifty-three new CJ-3k analogs were synthesized and screened for their anti-HIF-1α activity in a luciferase-transfected human breast cancer cell line (MDA-MB-231). Some of these new analogs have a significantly greater activity than that of CJ-3k and hold potential for development as new therapeutic agents for the treatment of cancer.

Curcumin inhibits hypoxia-induced migration in K1 papillary thyroid cancer cells

Curcumin, traditionally used as food and medicinal purposes, has recently been reported to have protective efficacy against hypoxia. Hypoxia is one of the important reactive factors in tumor metastasis, which is a key problem in clinical thyroid cancer therapy. In present study, we investigate the anti-metastatic effect of curcumin on the K1 papillary thyroid cancer cells as well as its potential mechanisms. The results show that curcumin effectively inhibits hypoxia-induced reactive oxygen species (ROS) upregulation and significantly decreases the mRNA and protein expression levels of hypoxia-inducible factor-1α (HIF-1α) in K1 cells. Curcumin also decreases the DNA binding ability of HIF-1α to hypoxia response element (HRE). Furthermore, curcumin enhances E-cadherin expression, inhibits metalloproteinase-9 (MMP-9) enzyme activity, and weakens K1 cells migration under hypoxic conditions. In summary, these results indicate that curcumin possesses a potent anti-metastatic effect and might be an effective tumoristatic agent for the treatment of aggressive papillary thyroid cancers.

The Three A's in Asthma - Airway Smooth Muscle, Airway Remodeling & Angiogenesis

Asthma affects more than 300 million people worldwide and its prevalence is still rising. Acute asthma attacks are characterized by severe symptoms such as breathlessness, wheezing, tightness of the chest, and coughing, which may lead to hospitalization or death. Besides the acute symptoms, asthma is characterized by persistent airway inflammation and airway wall remodeling. The term airway wall remodeling summarizes the structural changes in the airway wall: epithelial cell shedding, goblet cell hyperplasia, hyperplasia and hypertrophy of the airway smooth muscle (ASM) bundles, basement membrane thickening and increased vascular density. Airway wall remodeling starts early in the pathogenesis of asthma and today it is suggested that remodeling is a prerequisite for other asthma pathologies. The beneficial effect of bronchial thermoplasty in reducing asthma symptoms, together with the increased potential of ASM cells of asthmatics to produce inflammatory and angiogenic factors, indicate that the ASM cell is a major effector cell in the pathology of asthma. In the present review we discuss the ASM cell and its role in airway wall remodeling and angiogenesis.

Hypoxia-Inducible Factor-1 in Physiological and Pathophysiological Angiogenesis: Applications and Therapies

The cardiovascular system ensures the delivery of oxygen and nutrients to all cells, tissues, and organs. Under extended exposure to reduced oxygen levels, cells are able to survive through the transcriptional activation of a series of genes that participate in angiogenesis, glucose metabolism, and cell proliferation. The oxygen-sensitive transcriptional activator HIF-1 (hypoxia-inducible factor-1) is a key transcriptional mediator of the response to hypoxic conditions. The HIF-1 pathway was found to be a master regulator of angiogenesis. Whether the process is physiological or pathological, HIF-1 seems to participate in vasculature formation by synergistic correlations with other proangiogenic factors such as VEGF (vascular endothelial growth factor), PlGF (placental growth factor), or angiopoietins. Considering the important contributions of HIF-1 in angiogenesis and vasculogenesis, it should be considered a promising target for treating ischaemic diseases or cancer. In this review, we discuss the roles of HIF-1 in both physiological/pathophysiological angiogenesis and potential strategies for clinical therapy.

Roles of hypoxia, stem cells and epithelial-mesenchymal transition in the spread and treatment resistance of head and neck cancer

Evidence from a wide range of studies indicates that hypoxia and the resulting cellular changes that are induced by HIF-1α lead to transcriptional up-regulation of a diversity of genes that play major roles in modifying the cellular behaviour of head and neck squamous cell carcinoma (HNSCC). Although the mechanisms of cell adaptation to hypoxia are still not entirely clear, many studies relate hypoxia to enhanced survival of malignant cells. Stronger staining of tissue sections for HIF-1α correlates with poor prognostic outcomes, and the hypoxic tumour microenvironment generates selective pressures that enhance the ability of cancer stem cells (CSCs) to evade therapeutically induced cell death. The ability of hypoxia to further increase the resistance of CSCs to conventional therapeutics, whether they act by induction of apoptosis, senescence or autophagy, appears to limit therapeutic effectiveness of current agents. The demonstration of hypoxic induction of phenotypic changes leading to a subpopulation of CSCs with high motility, greater invasive properties and yet greater therapeutic resistance, complicates the issue still further. It appears that therapeutic interventions that allow manipulation of HIF-1α levels and responses, whether induced by hypoxia or by other mechanisms, could provide more effective actions of chemo- and radiotherapies at lower therapeutic dosages and thus result in better control of tumours with less toxicity to patients.

The effect of triamcinolone acetonide on laser-induced choroidal neovascularization in mice using a hypoxia visualization bio-imaging probe

Hypoxic stress is a risk factor of ocular neovascularization. Hypoxia visualization may provide clues regarding the underlying cause of angiogenesis. Recently, we developed a hypoxia-specific probe, protein transduction domain-oxygen-dependent degradation domain-HaloTag-Rhodamine (POH-Rhodamine). In this study, we observed the localization of HIF-1α proteins by immunohistochemistry and the fluorescence of POH-Rhodamine on RPE-choroid flat mounts. Moreover, we compared the localization of POH-Rhodamine with pimonidazole which is a standard reagent for detecting hypoxia. Next, we investigated the effects of triamcinolone acetonide (TAAC) against visual function that was evaluated by recording electroretinogram (ERG) and choroidal neovascularization (CNV) development. Mice were given laser-induced CNV using a diode laser and treated with intravitreal injection of TAAC. Finally, we investigated POH-Rhodamine on CNV treated with TAAC. In this study, the fluorescence of POH-Rhodamine and HIF-1α were co-localized in laser-irradiated sites, and both the POH-Rhodamine and pimonidazole fluorescent areas were almost the same. Intravitreal injection of TAAC restored the reduced ERG b-wave but not the a-wave and decreased the mean CNV area. Furthermore, the area of the POH-Rhodamine-positive cells decreased. These findings indicate that POH-Rhodamine is useful for evaluating tissue hypoxia in a laser-induced CNV model, suggesting that TAAC suppressed CNV through tissue hypoxia improvement.

Hypoxia signalling manipulation for bone regeneration

Hypoxia-inducible factor (HIF) signalling is intricately involved in coupling angiogenesis and osteogenesis during bone development and repair. Activation of HIFs in response to a hypoxic bone micro-environment stimulates the transcription of multiple genes with effects on angiogenesis, precursor cell recruitment and differentiation. Substantial progress has been made in our understanding of the molecular mechanisms by which oxygen content regulates the levels and activity of HIFs. In particular, the discovery of the role of oxygen-dependent hydroxylase enzymes in modulating the activity of HIF-1α has sparked interest in potentially promising therapeutic strategies in multiple clinical fields and most recently bone healing. Several small molecules, termed hypoxia mimics, have been identified as activators of the HIF pathway and have demonstrated augmentation of both bone vascularity and bone regeneration in vivo. In this review we discuss key elements of the hypoxic signalling pathway and its role in bone regeneration. Current strategies for the manipulation of this pathway for enhancing bone repair are presented with an emphasis on recent pre-clinical in vivo investigations. These findings suggest promising approaches for the development of therapies to improve bone repair and tissue engineering strategies.

Simulation predicts IGFBP2-HIF1α interaction drives glioblastoma growth

Tremendous strides have been made in improving patients’ survival from cancer with one glaring exception: brain cancer. Glioblastoma is the most common, aggressive and highly malignant type of primary brain tumor. The average overall survival remains less than 1 year. Notably, cancer patients with obesity and diabetes have worse outcomes and accelerated progression of glioblastoma. The root cause of this accelerated progression has been hypothesized to involve the insulin signaling pathway. However, while the process of invasive glioblastoma progression has been extensively studied macroscopically, it has not yet been well characterized with regards to intracellular insulin signaling. In this study we connect for the first time microscale insulin signaling activity with macroscale glioblastoma growth through the use of computational modeling. Results of the model suggest a novel observation: feedback from IGFBP2 to HIF1α is integral to the sustained growth of glioblastoma. Our study suggests that downstream signaling from IGFI to HIF1α, which has been the target of many insulin signaling drugs in clinical trials, plays a smaller role in overall tumor growth. These predictions strongly suggest redirecting the focus of glioma drug candidates on controlling the feedback between IGFBP2 and HIF1α.

Current treatment for glioblastoma patients is limited to nonspecific methods: surgery followed by a combination of radio- and chemotherapy. With these methods, glioma patient survival is less than one year post-diagnosis. Targeting specific protein signaling pathways offers potentially more potent therapies. One promising potential target is the insulin signaling pathway, which is known to contribute to glioblastoma progression. However, drugs targeting this pathway have shown mixed results in clinical trials, and the detailed mechanisms of how the insulin signaling pathway promotes glioblastoma growth remain to be elucidated. Here, we developed a computational model of insulin signaling in glioblastoma in order to study this pathway’s role in tumor progression. Using the model, we systematically test contributions of different insulin signaling protein interactions on glioblastoma growth. Our model highlights a key driver for the growth of glioblastoma: IGFBP2-HIF1α feedback. This interaction provides a target that could open the door for new therapies in glioma and other solid tumors.

Hypoxia and Prostate Cancer Aggressiveness: A Tale With Many Endings

Angiogenesis, increased glycolysis, and cellular adaptation to hypoxic microenvironment are characteristic of solid tumors, including prostate cancer. These representative features are the cornerstone of cancer biology, which are well correlated with invasion, metastasis, and lethality, as well as likely with the success of prostate cancer treatment (eg, tumor hypoxia has been associated with resistance to chemotherapy and radiotherapy). It is well established that prostate cancer cells also metabolically depend on enhanced glucose transport and glycolysis for expansion, whereas growth is contingent with neovascularization to permit diffusion of oxygen and glucose. While hypoxia inducible factor 1 alpha (HIF-1α) remains the central player, the succeeding activated molecules and pathways track distinct branches, all positively correlated with the degree of intratumoral hypoxia. Among these, the vascular endothelial growth factor axis as well as the lysyl oxidase and carbonic anhydrase IX activities are notable in prostate cancer and merit further study. Here, we demonstrate their linkage with HIF-1α as a tentative explanatory mechanism of prostate cancer aggressiveness. Hypoxia drives a tale where HIF-1α-dependent effects lead to many influences in distinct key cancer biology features, rendering targeted therapies toward targets at the endings less efficient. The most appropriate approach will be to inhibit the upstream common driver (HIF-1α) activity. Additional translational and clinical research initiatives in prostate cancer are required to prove its usefulness.

Nuclear-cytoplasmatic shuttling of proteins in control of cellular oxygen sensing

In order to pass through the nuclear pore complex, proteins larger than ∼40 kDa require specific nuclear transport receptors. Defects in nuclear-cytoplasmatic transport affect fundamental processes such as development, inflammation and oxygen sensing. The transcriptional response to O2 deficiency is controlled by hypoxia-inducible factors (HIFs). These are heterodimeric transcription factors of each ∼100-120 kDa proteins, consisting of one out of three different O2-labile α subunits (primarily HIF-1α) and a more constitutive 1β subunit. In the presence of O2, the α subunits are hydroxylated by specific prolyl-4-hydroxylase domain proteins (PHD1, PHD2, and PHD3) and an asparaginyl hydroxylase (factor inhibiting HIF-1, FIH-1). The prolyl hydroxylation causes recognition by von Hippel-Lindau tumor suppressor protein (pVHL), ubiquitination, and proteasomal degradation. The activity of the oxygen sensing machinery depends on dynamic intracellular trafficking. Nuclear import of HIF-1α and HIF-1β is mainly mediated by importins α and β (α/β). HIF-1α can shuttle between nucleus and cytoplasm, while HIF-1β is permanently inside the nucleus. pVHL is localized to both compartments. Nuclear import of PHD1 relies on a nuclear localization signal (NLS) and uses the classical import pathway involving importin α/β receptors. PHD2 shows an atypical NLS, and its nuclear import does not occur via the classical pathway. PHD2-mediated hydroxylation of HIF-1α occurs predominantly in the cell nucleus. Nuclear export of PHD2 involves a nuclear export signal (NES) in the N-terminus and depends on the export receptor chromosome region maintenance 1 (CRM1). Nuclear import of PHD3 is mediated by importin α/β receptors and depends on a non-classical NLS. Specific modification of the nuclear translocation of the three PHD isoforms could provide a promising strategy for the development of new therapeutic substances to tackle major diseases.

Effect of HIF-1α on biological activation of human tongue squamous cell carcinoma SCC-15 cells in vitro

Hypoxia-inducible factor-1α (HIF-1α) is a key regulator for tumor cells and tissues to adapt to hypoxic condition. Suppressing the expression of HIF-1α is important to evaluate its effect on cancer cells. This study was carried out to analyze the effect of HIF-1α on the biological activation of human tongue squamous cell carcinoma (TSCC) SCC-15 cells. In this experiment, deferoxamine mesylate (DFO) was used to induce hypoxic condition. HIF-1α gene was suppressed by lentiviral vector. The effect of the level of HIF-1α expression was tested on the proliferation, cell cycle, cell apoptosis and cell invasion of SCC-15 cells. We demonstrated that SCC-15 cells showed a more aggressive phenotype after treated with DFO. Additionally, DFO was able to induce the expression of HIF-1α protein. Lentiviral vector can effectively inhibit HIF-1α expression on mRNA and protein level. Under normoxic or hypoxic conditions, downregulation of HIF-1α for SCC-15 cells induced cell apoptosis and inhibited growth and invasion. These results showed that suppressing the expression of HIF-1α inhibited the aggressive potential of SCC-15 cells under normoxic and hypoxic condition. Thus, finding an effective and safe pathway to inhibit the expression of HIF-1α can help us to improve the survival rate of human TSCC patients.

Hypoxia and free radicals: role in tumor progression and the use of engineering-based platforms to address these relationships

Hypoxia is a feature of all solid tumors, contributing to tumor progression and therapy resistance. Through stabilization of the hypoxia-inducible factor 1 alpha (HIF-1α), hypoxia activates the transcription of a number of genes that sustain tumor progression. Since the seminal discovery of HIF-1α as a hypoxia-responsive master regulator of numerous genes and transcription factors, several groups have reported a novel mechanism whereby hypoxia mediates stabilization of HIF-1α. This process occurs as a result of hypoxia-generated reactive oxygen species (ROS), which, in turn, stabilize the expression of HIF-1α. As a result, a number of genes regulating tumor growth are expressed, fueling ongoing tumor progression. In this review, we outline a role for hypoxia in generating ROS and additionally define the mechanisms contributing to ROS-induced stabilization of HIF-1α.We further explore how ROS-induced HIF-1α stabilization contributes to tumor growth, angiogenesis, metastasis, and therapy response. We discuss a future outlook, describing novel therapeutic approaches for attenuating ROS production while considering how these strategies should be carefully selected when combining with chemotherapeutic agents. As engineering-based approaches have been more frequently utilized to address biological questions, we discuss opportunities whereby engineering techniques may be employed to better understand the physical and biochemical factors controlling ROS expression. It is anticipated that an improved understanding of the mechanisms responsible for the hypoxia/ROS/HIF-1α axis in tumor progression will yield the development of better targeted therapies.

Advances in Anti-Cancer Drug Development Targeting Carbonic Anhydrase IX and XII

The microenvironment within a solid tumor is heterogeneous with regions being both acidic and hypoxic. As a result of this, cancer cells upregulate genes that allow survival in such environments. Some of these genes are pH regulatory factors, including carbonic anhydrase IX (CA IX) and in some cases XII (CA XII). CA IX helps to maintain normal cytoplasmic pH (pHi) while simultaneously contributing to the extracellular pH (pHe). CA XII is also thought to be responsible for stabilizing pHe at physiological conditions. Extracellular acidification of the tumor microenvironment promotes local invasion and metastasis while decreasing the effectiveness of adjuvant therapies, thus contributing to poor cancer clinical outcomes. In this review, we describe the properties of CA IX and CA XII that substantiate their potential use as anticancer targets. We also discuss the current status of CA isoform-selective inhibitor development and patents of CA IX/XII targeted inhibitors that show potential for treating aggressive tumors. Some of the recently published patents discussed include sulfonamide-based small molecule inhibitors including derivatives of boron cluster compounds; metal complexes of poly(carboxyl)amine-containing ligands; nitroi-midazole-, ureidosulfonamide-, and coumarin-based compounds; as well as G250 and A610 monoclonal antibodies for cancer treatment.

Poly (ADP-ribose) polymerase-1: an emerging target in right ventricle dysfunction associated with pulmonary hypertension

Recently, inhibition of poly (ADP-ribose) polymerase-1 (PARP1) was shown to be protective in experimental pulmonary hypertension (PH) and prevented right ventricular hypertrophy (RVH) associated with it. However, molecular mechanism behind cardioprotection by PARP1 inhibition in PH still needs detailed exploration. Therefore, effect of inhibition of PARP1 on the right ventricle (RV) dysfunction was studied in monocrotaline (MCT) induced PH model. Following a single dose administration of MCT (60 mg/kg, s.c.), male Sprague-Dawley rats were treated with PARP1 inhibitor 1,5-Isoquinolinediol (ISO, 3 mg/kg, i.p.) for 35 days for preventive study and from day 21-35 for curative study. RV pressure (RVP) and RVH were measured after 35 days. Histophathological studies, PARP1 activity, mRNA and protein expression were studied in isolated RV. Oxidative and nitosative stress, inflammation and Matrix metalloproteinases (MMPs)/Tissue inhibitor of metalloproteinase 2 (TIMP2) were also assessed. Mitochondrial dysfunction was studied by mitochondrial membrane permeability and estimation of Nicotinamide adenine dinucleotide (NAD) and Adenosine triphosphate (ATP). Apoptosis in RV was assessed by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), caspase 3 activity and cleaved PARP1 expression. PARP1 inhibition significantly reversed the increase in RVP and RVH in both preventive and curative treatment in the MCT-injected rats. ISO lowered oxidative and nitrosative stress and inflammation and restored the balance of MMPs/TIMP2 expression. PARP1 inhibition prevented mitochondrial dysfunction and the release of cell death factors from mitochondria. ISO also decreased apoptosis by decreasing number of TUNEL positive cells, caspase 3 activity and PARP1 cleavage in RV. Thus, PARP1 inhibition ameliorated PH induced RV hypertrophy and may emerge as a new therapeutic target for PH.

Hypoxia interferes with aryl hydrocarbon receptor pathway in hCMEC/D3 human cerebral microvascular endothelial cells

The expression of aryl hydrocarbon receptor (AhR) transcription factor was detected at transcript level in freshly isolated human brain microvessels and in the hCMEC/D3 human cerebral microvascular endothelial cell line. Recent studies have demonstrated that AhR pathway is able to crosstalk with other pathways such as hypoxia signaling pathway. Therefore, we used the hCMEC/D3 cell line to investigate the potential crosstalk between AhR and hypoxia signaling pathways. First, we performed two different hypoxia-like procedures in hCMEC/D3 cells; namely, exposition of cells to 150 μM deferoxamine or to glucose and oxygen deprivation for 6 h. These two procedures led to hypoxia-inducible factor (HIF)-1α and HIF-2α proteins accumulation together with a significant induction of the two well-known hypoxia-inducible genes VEGF and GLUT-1. Both HIF-1α and -2α functionally mediated hypoxia response in the hCMEC/D3 cells. Then, we observed that a 6 h exposure to 25 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin, a strong AhR ligand, up-regulated CYP1A1 and CYP1B1 expression, and that this effect was AhR dependent. Regarding AhR and hypoxia crosstalk, our experiments revealed that an asymmetric interference between these two pathways effectively occurred in hCMEC/D3 cells: hypoxia pathway interfered with AhR signaling but not the other way around. We studied the putative crosstalk of AhR and hypoxia pathways in hCMEC/D3 human cerebral microvascular endothelial cells. While hypoxia decreased the expression of the two AhR target genes CYP1A1 and CYP1B1, AhR activation results in no change in hypoxia target gene expression. This is the first sign of AhR and hypoxia pathway crosstalk in an in vitro model of the human cerebral endothelium.

Transcriptomic changes triggered by hypoxia: evidence for HIF-1α-independent, [Na+]i/[K+]i-mediated, excitation-transcription coupling

This study examines the relative impact of canonical hypoxia-inducible factor-1alpha- (HIF-1α and Na⁺_i/K⁺_i-mediated signaling on transcriptomic changes evoked by hypoxia and glucose deprivation. Incubation of RASMC in ischemic conditions resulted in ∼3-fold elevation of [Na⁺]_i and 2-fold reduction of [K⁺]_i. Using global gene expression profiling we found that Na⁺,K⁺-ATPase inhibition by ouabain or K⁺-free medium in rat aortic vascular smooth muscle cells (RASMC) led to the differential expression of dozens of genes whose altered expression was previously detected in cells subjected to hypoxia and ischemia/reperfusion. For further investigations, we selected Cyp1a1, Fos, Atf3, Klf10, Ptgs2, Nr4a1, Per2 and Hes1, i.e. genes possessing the highest increments of expression under sustained Na⁺,K⁺-ATPase inhibition and whose implication in the pathogenesis of hypoxia was proved in previous studies. In ouabain-treated RASMC, low-Na⁺, high-K⁺ medium abolished amplification of the [Na⁺]_i/[K⁺]_i ratio as well as the increased expression of all tested genes. In cells subjected to hypoxia and glucose deprivation, dissipation of the transmembrane gradient of Na⁺ and K⁺ completely eliminated increment of Fos, Atf3, Ptgs2 and Per2 mRNAs and sharply diminished augmentation expression of Klf10, Edn1, Nr4a1 and Hes1. In contrast to low-Na⁺, high-K⁺ medium, RASMC transfection with Hif-1a siRNA attenuated increments of Vegfa, Edn1, Klf10 and Nr4a1 mRNAs triggered by hypoxia but did not impact Fos, Atf3, Ptgs2 and Per2 expression. Thus, our investigation demonstrates, for the first time, that Na⁺_i/K⁺_i-mediated, Hif-1α- -independent excitation-transcription coupling contributes to transcriptomic changes evoked in RASMC by hypoxia and glucose deprivation.

Hypoxia-inducible factor-1alpha in hepatic fibrosis: A promising therapeutic target

Hypoxia-inducible factor-1alpha (HIF-1α) is a regulated subunit of the hypoxia-inducible factor 1 (HIF1), which functions as a key transcription factor in response to hypoxic stress by regulating genes involved in maintaining oxygen homeostasis. In recent years, a growing body of studies showed that HIF-1α was significantly increased in hepatic fibrotic tissues and activated hepatic stellate cells (HSCs). Furthermore, knockdown of HIF-1α expression inhibited the proliferation and activation of HSCs. In addition, HIF-1α-dependent genes and the extensive network of signaling cascades focus on HIF-1α have been reported to associate with the development of hepatic fibrosis, suggesting that HIF-1α might play a crucial role in hepatic fibrosis. However, the mechanisms by which HIF-1α regulates hepatic fibrosis are still undefined. In this review, we concentrate on multiple signaling pathways and genes related with HIF-1α which may be involved in the development of hepatic fibrosis, further discussing its potential as a novel therapeutic target for hepatic fibrosis.