Regulation of hypoxia-inducible factor 1 by prolyl and asparaginyl hydroxylases

The chromatin remodeler ISWI regulates the cellular response to hypoxia: role of FIH

The hypoxia-inducible factor (HIF) is a master regulator of the cellular response to hypoxia. Study of the role of imitation switch (ISWI) in the cellular response to hypoxia shows that ISWI depletion alters a subset of HIF target genes by regulating factor inhibiting HIF. ISWI depletion alters the cellular response to hypoxia by reducing autophagy and increasing apoptosis.

The hypoxia-inducible factor (HIF) is a master regulator of the cellular response to hypoxia. Its levels and activity are controlled by dioxygenases called prolyl-hydroxylases and factor inhibiting HIF (FIH). To activate genes, HIF has to access sequences in DNA that are integrated in chromatin. It is known that the chromatin-remodeling complex switch/sucrose nonfermentable (SWI/SNF) is essential for HIF activity. However, no additional information exists about the role of other chromatin-remodeling enzymes in hypoxia. Here we describe the role of imitation switch (ISWI) in the cellular response to hypoxia. We find that unlike SWI/SNF, ISWI depletion enhances HIF activity without altering its levels. Furthermore, ISWI knockdown only alters a subset of HIF target genes. Mechanistically, we find that ISWI is required for full expression of FIH mRNA and protein levels by changing RNA polymerase II loading to the FIH promoter. Of interest, exogenous FIH can rescue the ISWI-mediated upregulation of CA9 but not BNIP3, suggesting that FIH-independent mechanisms are also involved. Of importance, ISWI depletion alters the cellular response to hypoxia by reducing autophagy and increasing apoptosis. These results demonstrate a novel role for ISWI as a survival factor during the cellular response to hypoxia.

Interplay of hypoxia and A2B adenosine receptors in tissue protection

That adenosine signaling can elicit adaptive tissue responses during conditions of limited oxygen availability (hypoxia) is a long-suspected notion that recently gained general acceptance from genetic and pharmacologic studies of the adenosine signaling pathway. As hypoxia and inflammation share an interdependent relationship, these studies have demonstrated that adenosine signaling events can be targeted to dampen hypoxia-induced inflammation. Here, we build on the hypothesis that particularly the A(2B) adenosine receptor (ADORA(2B)) plays a central role in tissue adaptation to hypoxia. In fact, the ADORA(2B) requires higher adenosine concentrations than any of the other adenosine receptors. However, during conditions of hypoxia or ischemia, the hypoxia-elicited rise in extracellular adenosine is sufficient to activate the ADORA(2B). Moreover, several studies have demonstrated very robust induction of the ADORA(2B) elicited by transcriptional mechanisms involving hypoxia-dependent signaling pathways and the transcription factor "hypoxia-induced factor" 1. In the present chapter, genetic and pharmacologic evidence is presented to support our hypothesis of a tissue protective role of ADORA(2B) signaling during hypoxic conditions, including hypoxia-elicited vascular leakage, organ ischemia, or acute lung injury. All these disease models are characterized by hypoxia-elicited tissue inflammation. As such, the ADORA(2B) has emerged as a therapeutic target for dampening hypoxia-induced inflammation and tissue adaptation to limited oxygen availability.

Isolated erythrocytosis: study of 67 patients and identification of three novel germ-line mutations in the prolyl hydroxylase domain protein 2 (PHD2) gene

The oxygen sensing pathway modulates erythropoietin expression. In normal cells, intracellular oxygen tensions are directly sensed by prolyl hydroxylase domain (PHD)-containing proteins. PHD2 isozyme has a key role in tagging hypoxia-inducible factor (HIF)-α subunits for polyubiquitination and proteasomal degradation. Erythrocytosis-associated PHD2 mutations reduce hydroxylation of HIF-α. The investigation of 67 patients with isolated erythrocytosis, either sporadic or familial, allowed the identification of three novel mutations in the catalytic domain of the PHD2 protein. All new mutations are germ-line, heterozygous and missense, and code for a predicted full length mutant PHD2 protein. Identification of the disease-causing genes will be of critical importance for a better classification of familial and acquired erythrocytosis, offering additional insight into the erythropoietin regulating oxygen sensing pathway.

Effects of n-propyl gallate on neuronal survival after forebrain ischemia in rats

THE AIM OF THE STUDY

The present study was conducted to assess the effects of intraperitoneal administration of n-propyl gallate (PG) on hippocampal neuronal survival after forebrain ischemia.

METHODS

Forty male Sprague-Dawley rats were randomly assigned to one of 6 groups. Animals in the PG-I-10, PG-I-8 and PG-S groups received intraperitoneal injection of PG (100mg/kg) 72, 48, 24h and 30 min before severe (10 min) or moderate (8 min) ischemia or sham operation, respectively, while animals in the V-I-10, V-I-8 and V-S groups received the vehicle (10% DMSO) in the same manner. Forebrain ischemia was produced by bilateral carotid occlusion combined with hypotension (35 mmHg) under isoflurane anesthesia. Animals were killed 7 days after reperfusion. Histological assessments were performed using hematoxylin and eosin staining. In separate groups of animals that received PG or vehicle, m-RNA levels of hypoxia-inducible factor 1α (HIF-1α), erythropoietin (EPO) and vascular endothelial growth factor (VEGF) were measured using the reverse transcription-PCR protocol.

RESULTS

The number of normal neurons was significantly higher in the PG-I-8 group compared with that in the V-I-8 group, whereas it was similar between the PG-I-10 and V-I-10 groups. Animals that received PG had significantly higher levels of HIF-1α, EPO and VEGF expression compared with those that received vehicle.

CONCLUSION

The results indicated that intraperitoneal administration of PG may have neuroprotective effects in a model of moderate, but not severe, forebrain ischemia in rats.

Expanding the proteome: disordered and alternatively folded proteins

Proteins provide much of the scaffolding for life, as well as undertaking a variety of essential catalytic reactions. These characteristic functions have led us to presuppose that proteins are in general functional only when well structured and correctly folded. As we begin to explore the repertoire of possible protein sequences inherent in the human and other genomes, two stark facts that belie this supposition become clear: firstly, the number of apparent open reading frames in the human genome is significantly smaller than appears to be necessary to code for all of the diverse proteins in higher organisms, and secondly that a significant proportion of the protein sequences that would be coded by the genome would not be expected to form stable three-dimensional (3D) structures. Clearly the genome must include coding for a multitude of alternative forms of proteins, some of which may be partly or fully disordered or incompletely structured in their functional states. At the same time as this likelihood was recognized, experimental studies also began to uncover examples of important protein molecules and domains that were incompletely structured or completely disordered in solution, yet remained perfectly functional. In the ensuing years, we have seen an explosion of experimental and genome-annotation studies that have mapped the extent of the intrinsic disorder phenomenon and explored the possible biological rationales for its widespread occurrence. Answers to the question 'why would a particular domain need to be unstructured?' are as varied as the systems where such domains are found. This review provides a survey of recent new directions in this field, and includes an evaluation of the role not only of intrinsically disordered proteins but also of partially structured and highly dynamic members of the disorder-order continuum.

Fentanyl activates hypoxia-inducible factor 1 in neuronal SH-SY5Y cells and mice under non-hypoxic conditions in a μ-opioid receptor-dependent manner

Hypoxia-inducible factor 1 (HIF-1) is the main transcription factor responsible for hypoxia-induced gene expression. Perioperative drugs including anesthetics have been reported to affect HIF-1 activity. However, the effect of fentanyl on HIF-1 activity is not well documented. In this study, we investigated the effect of fentanyl and other opioids on HIF-1 activity in human SH-SY5Y neuroblastoma cells, hepatoma Hep3B cells, lung adenocarcinoma A549 cells and mice. Cells were exposed to fentanyl, and HIF-1 protein expression was examined by Western blot analysis using anti-HIF-1α and β antibodies. HIF-1-dependent gene expression was investigated by semi-quantitative real-time reverse transcriptase (RT)-PCR (qRT-PCR) and luciferase assay. Furthermore, fentanyl was administered intraperitoneally and HIF-1-dependent gene expression was investigated by qRT-PCR in the brains and kidneys of mice. A 10-μM concentration of fentanyl and other opioids, including 1 μM morphine and 4 μM remifentanil, induced HIF-1α protein expression and HIF-1 target gene expression in an opioid receptor-dependent manner in SH-SY5Y cells with activity peaking at 24h. Fentanyl did not augment HIF-1α expression during hypoxia-induced induction. HIF-1α stabilization assays and experiments with cycloheximide revealed that fentanyl increased translation from HIF-1α mRNA but did not stabilize the HIF-1α protein. Furthermore, fentanyl induced HIF-1 target gene expression in the brains of mice but not in their kidneys in a naloxone-sensitive manner. In this report, we describe for the first time that fentanyl, both in vitro and in vivo, induces HIF-1 activation under non-hypoxic conditions, leading to increases in expression of genes associated with adaptation to hypoxia.

Hypoxia-inducible factor in thyroid carcinoma

Intratumoural hypoxia (low oxygen tension) is associated with aggressive disease and poor prognosis. Hypoxia-inducible factor-1 is a transcription factor activated by hypoxia that regulates the expression of genes that promote tumour cell survival, progression, metastasis, and resistance to chemo/radiotherapy. In addition to hypoxia, HIF-1 can be activated by growth factor-signalling pathways such as the mitogen-activated protein kinases- (MAPK-) and phosphatidylinositol-3-OH kinases- (PI3K-) signalling cascades. Mutations in these pathways are common in thyroid carcinoma and lead to enhanced HIF-1 expression and activity. Here, we summarise current data that highlights the potential role of both hypoxia and MAPK/PI3K-induced HIF-1 signalling in thyroid carcinoma progression, metastatic characteristics, and the potential role of HIF-1 in thyroid carcinoma response to radiotherapy. Direct or indirect targeting of HIF-1 using an MAPK or PI3K inhibitor in combination with radiotherapy may be a new potential therapeutic target to improve the therapeutic response of thyroid carcinoma to radiotherapy and reduce metastatic burden.

Pro-apoptotic activity of inhibitory PAS domain protein (IPAS), a negative regulator of HIF-1, through binding to pro-survival Bcl-2 family proteins

Inhibitory PAS (Per/Arnt/Sim) domain protein (IPAS) is a dominant negative transcription factor that represses hypoxia-inducible factor 1 (HIF-1) activity. In this study, we show that IPAS also functions as a pro-apoptotic protein through binding to pro-survival Bcl-2 family members. In a previous paper, we reported that NF-κB-dependent IPAS induction by cobalt chloride repressed the hypoxic response in PC12 cells. We found that prolonged incubation under the same conditions caused apoptosis in PC12 cells. Repression of IPAS induction protected cells from apoptosis. Furthermore, knockdown of IPAS recovered cell viability. EGFP-IPAS protein was localized in both the nucleus and the cytoplasm, with a large fraction associated with mitochondria. Mitochondrial IPAS induced mitochondria depolarization and caspase-3 activation. Immunoprecipitation assays revealed that IPAS is associated with Bcl-x(L), Bcl-w and Mcl-1. The association of IPAS with Bcl-x(L) was also observed in living cells by the FLIM-based FRET analysis, indicating direct binding between the two proteins. IPAS contributed to dysfunction of Bcl-x(L) by inhibiting the interaction of Bcl-x(L) with Bax. These results demonstrate that IPAS functions as a dual function protein involved in transcription repression and apoptosis.

How can we overcome tumor hypoxia in radiation therapy?

Local recurrence and distant metastasis frequently occur after radiation therapy for cancer and can be fatal. Evidence obtained from radiochemical and radiobiological studies has revealed these problems to be caused, at least in part, by a tumor-specific microenvironment, hypoxia. Moreover, a transcription factor, hypoxia-inducible factor 1 (HIF-1), was identified as pivotal to hypoxia-mediated radioresistance. To overcome the problems, radiation oncologists have recently obtained powerful tools, such as "simultaneous integrated boost intensity-modulated radiation therapy (SIB-IMRT), which enables a booster dose of radiation to be delivered to small target fractions in a malignant tumor", "hypoxia-selective cytotoxins/drugs", and "HIF-1 inhibitors" etc. In order to fully exploit these innovative and interdisciplinary strategies in cancer therapy, it is critical to unveil the characteristics, intratumoral localization, and dynamics of hypoxia/HIF-1-active tumor cells during tumor growth and after radiation therapy. We have performed optical imaging experiments using tumor-bearing mice and revealed that the locations of HIF-1-active tumor cells changes dramatically as tumors grow. Moreover, HIF-1 activity changes markedly after radiation therapy. This review overviews 1) fundamental problems surrounding tumor hypoxia in current radiation therapy, 2) the function of HIF-1 in tumor radioresistance, 3) the dynamics of hypoxic tumor cells during tumor growth and after radiation therapy, and 4) how we should overcome the difficulties with radiation therapy using innovative interdisciplinary technologies.

Inhibition of prolyl hydroxylases increases erythropoietin production in ESRD

The reasons for inadequate production of erythropoietin (EPO) in patients with ESRD are poorly understood. A better understanding of EPO regulation, namely oxygen-dependent hydroxylation of the hypoxia-inducible transcription factor (HIF), may enable targeted pharmacological intervention. Here, we tested the ability of fibrotic kidneys and extrarenal tissues to produce EPO. In this phase 1 study, we used an orally active prolyl-hydroxylase inhibitor, FG-2216, to stabilize HIF independent of oxygen availability in 12 hemodialysis (HD) patients, six of whom were anephric, and in six healthy volunteers. FG-2216 increased plasma EPO levels 30.8-fold in HD patients with kidneys, 14.5-fold in anephric HD patients, and 12.7-fold in healthy volunteers. These data demonstrate that pharmacologic manipulation of the HIF system can stimulate endogenous EPO production. Furthermore, the data indicate that deranged oxygen sensing--not a loss of EPO production capacity--causes renal anemia.

Hydroxylase inhibition attenuates colonic epithelial secretory function and ameliorates experimental diarrhea

Hydroxylases are oxygen-sensing enzymes that regulate cellular responses to hypoxia. Transepithelial Cl(-) secretion, the driving force for fluid secretion, is dependent on O(2) availability for generation of cellular energy. Here, we investigated the role of hydroxylases in regulating epithelial secretion and the potential for targeting these enzymes in treatment of diarrheal disorders. Ion transport was measured as short-circuit current changes across voltage-clamped monolayers of T(84) cells and mouse colon. The antidiarrheal efficacy of dimethyloxallyl glycine (DMOG) was tested in a mouse model of allergic disease. Hydroxylase inhibition with DMOG attenuated Ca(2+)- and cAMP-dependent secretory responses in voltage-clamped T(84) cells to 20.2 ± 2.6 and 38.8 ± 6.7% (n=16; P≤0.001) of those in control cells, respectively. Antisecretory actions of DMOG were time and concentration dependent, being maximal after 18 h of DMOG (1 mM) treatment. DMOG specifically inhibited Na(+)/K(+)-ATPase pump activity without altering its expression or membrane localization. In mice, DMOG inhibited agonist-induced secretory responses ex vivo and prevented allergic diarrhea in vivo. In conclusion, hydroxylases are important regulators of epithelial Cl(-) and fluid secretion and present a promising target for development of new drugs to treat transport disorders.

Evidence for the slow reaction of hypoxia-inducible factor prolyl hydroxylase 2 with oxygen

The response of animals to hypoxia is mediated by the hypoxia-inducible transcription factor. Human hypoxia-inducible factor is regulated by four Fe(II)- and 2-oxoglutarate-dependent oxygenases: prolyl hydroxylase domain enzymes 1-3 catalyse hydroxylation of two prolyl-residues in hypoxia-inducible factor, triggering its degradation by the proteasome. Factor inhibiting hypoxia-inducible factor catalyses the hydroxylation of an asparagine-residue in hypoxia-inducible factor, inhibiting its transcriptional activity. Collectively, the hypoxia-inducible factor hydroxylases negatively regulate hypoxia-inducible factor in response to increasing oxygen concentration. Prolyl hydroxylase domain 2 is the most important oxygen sensor in human cells; however, the underlying kinetic basis of the oxygen-sensing function of prolyl hydroxylase domain 2 is unclear. We report analyses of the reaction of prolyl hydroxylase domain 2 with oxygen. Chemical quench/MS experiments demonstrate that reaction of a complex of prolyl hydroxylase domain 2, Fe(II), 2-oxoglutarate and the C-terminal oxygen-dependent degradation domain of hypoxia-inducible factor-α with oxygen to form hydroxylated C-terminal oxygen-dependent degradation domain and succinate is much slower (approximately 100-fold) than for other similarly studied 2-oxoglutarate oxygenases. Stopped flow/UV-visible spectroscopy experiments demonstrate that the reaction produces a relatively stable species absorbing at 320 nm; Mössbauer spectroscopic experiments indicate that this species is likely not a Fe(IV)=O intermediate, as observed for other 2-oxoglutarate oxygenases. Overall, the results obtained suggest that, at least compared to other studied 2-oxoglutarate oxygenases, prolyl hydroxylase domain 2 reacts relatively slowly with oxygen, a property that may be associated with its function as an oxygen sensor.

Structural basis for binding of cyclic 2-oxoglutarate analogues to factor-inhibiting hypoxia-inducible factor

Aromatic analogues of the 2-oxoglutarate co-substrate of the hypoxia-inducible factor hydroxylases are shown to bind at the active site iron: Pyridine-2,4-dicarboxylate binds as anticipated with a single molecule chelating the iron in a bidentate manner. The binding mode of a hydroxamic acid analogue, at least in the crystalline state, is unusual because two molecules of the inhibitor are observed at the active site and partial displacement of the iron binding aspartyl residue was observed.

Utilization of an in vivo reporter for high throughput identification of branched small molecule regulators of hypoxic adaptation

Small molecules inhibiting hypoxia inducible factor (HIF) prolyl hydroxylases (PHDs) are the focus of drug development efforts directed toward the treatment of ischemia and metabolic imbalance. A cell-based reporter produced by fusing HIF-1 alpha oxygen degradable domain (ODD) to luciferase was shown to work as a capture assay monitoring stability of the overexpressed luciferase-labeled HIF PHD substrate under conditions more physiological than in vitro test tubes. High throughput screening identified novel catechol and oxyquinoline pharmacophores with a "branching motif" immediately adjacent to a Fe-binding motif that fits selectively into the HIF PHD active site in in silico models. In accord with their structure-activity relationship in the primary screen, the best "hits" stabilize HIF1 alpha, upregulate known HIF target genes in a human neuronal line, and exert neuroprotective effects in established model of oxidative stress in cortical neurons.

Force field design and molecular dynamics simulations of factor-inhibiting HIF-1 and its complex with known inhibitors: implications for rational inhibitor design

Based on molecular dynamics simulations in aqueous solution, we investigate the dynamic properties of factor-inhibiting HIF-1 (FIH1) and its complexes with the substrate 2-oxoglutarate (2OG) and the two known inhibitors, N-oxalylglycine (NOG) and N-oxalyl-D-phenylalanine (NODP). The results obtained with the newly developed force field parameters for the coordination environment of the active-site ferrous ion show that FIH1 undergoes a significant conformational stabilization with a decrease in motional amplitude upon binding of the substrate or the inhibitors. Two loop structures around the active-site reveal a high flexibility in the resting form of FIH1 with the high B-factor values. These high-amplitude motions of the flexible loops are found to be weakened significantly in the presence of the substrate or a weak inhibitor (NOG), and damped out upon binding of a potent and selective inhibitor (NODP) in the active site. A characteristic feature that discriminates the coordination structures of the active-site ferrous ion in complex with 2OG and NOG in solution from those in the X-ray crystal structures lies in the presence of a structural water molecule from bulk solvent at the sixth coordination position, which leads to the formation of a stable octahedral coordination geometry. However, the approach of such a structural water molecule to the active-site ferrous ion is prohibited in the FIH1-NODP complex, which should be attributed to the formation of hydrophobic contacts between the phenyl ring of the inhibitor and the side chains of Tyr102, Leu186, and Trp296 at the entrance of the active site. This indicates that the D-enantiomeric side-chain phenyl group of NODP should play an essential role in potent and selective inhibition of FIH1.

The histone deacetylase Sirt6 regulates glucose homeostasis via Hif1alpha

SIRT6 is a member of a highly conserved family of NAD(+)-dependent deacetylases with various roles in metabolism, stress resistance, and life span. SIRT6-deficient mice develop normally but succumb to a lethal hypoglycemia early in life; however, the mechanism underlying this hypoglycemia remained unclear. Here, we demonstrate that SIRT6 functions as a histone H3K9 deacetylase to control the expression of multiple glycolytic genes. Specifically, SIRT6 appears to function as a corepressor of the transcription factor Hif1alpha, a critical regulator of nutrient stress responses. Consistent with this notion, SIRT6-deficient cells exhibit increased Hif1alpha activity and show increased glucose uptake with upregulation of glycolysis and diminished mitochondrial respiration. Our studies uncover a role for the chromatin factor SIRT6 as a master regulator of glucose homeostasis and may provide the basis for novel therapeutic approaches against metabolic diseases, such as diabetes and obesity.

Aiming straight for the heart: prolyl hydroxylases set the BAR

The cellular response to a reduced oxygen state (or hypoxia) includes de novo alterations in gene expression patterns, many of which are controlled by hypoxia-inducible factor (HIF) transcription factors. HIF signaling is predominantly regulated by the dioxygenase family of prolyl hydroxylases (PHDs), also known as EGL nine homologs (EGLNs). The PHD family in higher eukaryotes, like the HIF alpha family, is composed of multiple members that have some shared biochemical properties yet have unique biological roles. Although HIF members are the major substrates identified to date for the PHD members, a reasonable expectation is that other proteins whose activities are altered by hypoxia may also serve as PHD substrates. Indeed, the beta(2)-adrenergic receptor, a major adrenergic heterotrimeric guanine nucleotide-binding protein-coupled receptor in the heart, has been identified as a substrate for PHD3.

Construction of recombinant adenovirus vector containing a modified gene that codes for human hypoxia-inducible factor-1alpha without oxygen-dependent degradation domain

The expression of hypoxia-inducible factor-1alpha (HIF-1alpha) in heart allografts is an important mechanism in response to ischemia/reperfusion (I/R) injury which represents the single major non-immunologic factor implicated in pathogenesis of chronic graft dysfunction (CGD). Adenoviral mediated overexpression of HIF-1alpha is a useful way to investigate the molecular mechanisms of I/R injury and the cardiac function during heart transplantation. The oxygen-dependent degradation (ODD) domain of HIF-1alpha can lead to degradation of the HIF-1alpha protein in normoxia. This will be an obstacle to steady expression of HIF-1alpha in heart allograft after transduction. In this study, we obtained the coding sequence of HIF-1alpha without ODD domain (HIF-1alphaDeltaODD) through a PCR-based method, and then generated the HIF-1alphaDeltaODD-expressing adenovirus. In normoxia, adenoviral mediated expression of HIF-1alphaDeltaODD shows constitutive activity in human cardiomyocytes, and can up-regulate heme oxygenase (HO)-1 mRNA levels significantly compared with the group transduced with HIF-1alpha-expressing adenovirus. The constructed HIF-1alphaDeltaODD-expressing adenovirus can be used to transduce allografts in animal studies to investigate the mechanism of CGD and provide a useful model to study the regulation mechanisms of genes regulated by HIF-1alpha alone.

Magnesium deficiency causes loss of response to intermittent hypoxia in paraganglion cells

Magnesium deficiency is suggested to contribute to many age-related diseases. Hypoxia-inducible factor 1alpha (HIF-1alpha) is known to be a master regulator of hypoxic response. Here we show that hypomagnesemia suppresses reactive oxygen species (ROS)-induced HIF-1alpha activity in paraganglion cells of the adrenal medulla and carotid body. In PC12 cells cultured in the low magnesium medium and treated with cobalt chloride (CoCl(2)) or exposed to intermittent hypoxia, ROS-mediated HIF-1alpha activity was suppressed. This suppression was due to up-regulation of inhibitory PAS (Per/Arnt/Sim) domain protein (IPAS) that was caused by NF-kappaB activation, which resulted from ROS and calcium influx mainly through the T-type calcium channels. Induction of tyrosine hydroxylase, a target of HIF-1, by CoCl(2) injection was suppressed in the adrenal medulla of magnesium-deficient mice because of up-regulation of IPAS. Also in the carotid body of magnesium-deficient mice, CoCl(2) and chronic intermittent hypoxia failed to enhance the tyrosine hydroxylase expression. These results demonstrate that serum magnesium levels are a key determinant for ROS-induced hypoxic responses.

Role of the intracellular localization of HIF-prolyl hydroxylases

Hypoxia-inducible factor-1 (HIF-1) is a major transcription factor regulating the response of tumor cells to hypoxia and is comprised of HIF-1alpha and Arnt (HIF-1beta). In mammalian cells, HIF-1 protein levels are regulated by three HIF-prolyl hydroxylases, termed PHD1, PHD2 and PHD3. To assess whether intracellular localization of PHD1 and PHD2 affects the hypoxic response via HIF-1, we investigated the localization signal of PHDs. PHD1 possessed at least one nuclear localization signal (NLS), and PHD2 contained a region as essential for nuclear export in their N-terminal region. Treatment of cells with leptomycin B revealed that PHD2 was able to shuttle between the cytoplasm and the nucleus. Reporter assay indicated that differences in the intracellular distribution of PHD1 did not influence on HIF-1alpha activity. However, a PHD2 mutant lacking the region for nuclear export exhibited significantly reduced effect to HIF-1alpha activity compared to wild-type PHD2, suggesting that the regulation of the intracellular distribution of PHD2 is an effective pathway for the control of the hypoxic response.

The calcium channel blocker cilnidipine selectively suppresses hypoxia-inducible factor 1 activity in vascular cells

Calcium ion is one of the most important second messengers of cellular signal transduction including hypoxia-elicited signals. In this study, we investigated the effects of the L-type calcium channel blockers such as nifedipine, efonidipine cilnidipine, diltiazem, and verapamil, on the activity of hypoxia-inducible factor-1 (HIF-1), a key transcription factor in control of hypoxia-induced gene expression. Using the lung carcinoma cell line A549 cells, human aortic smooth muscle cells, and human umbilical vein endothelial cells, we demonstrated that cilnidipine exclusively suppressed HIF-1 activity and the expressions of downstream genes in a cell-type specific manner. We also demonstrated that cilnidipine blocked the synthesis of the HIF-1alpha protein not by affecting activity of the intracellular hypoxia-sensing element prolyl hydroxylases but inhibiting activity of Akt and mitogen-activated protein kinase and that the inhibition is not dependent on the effect on calcium homeostasis.

The zebrafish embryo as a dynamic model of anoxia tolerance

Developing organisms depend upon a delicate balance in the supply and demand of energy to adapt to variable oxygen availability, although the essential mechanisms determining such adaptation remain elusive. In this study, we examine reversible anoxic arrest and dynamic bioenergetic transitions during zebrafish development. Our data reveal that the duration of anoxic viability corresponds to the developmental stage and anaerobic metabolic rate. Diverse chemical inhibitors of mitochondrial oxidative phosphorylation induce a similar arrest in normoxic embryos, suggesting a pathway responsive to perturbations in aerobic energy production rather than molecular oxygen. Consistent with this concept, arrest is accompanied by rapid activation of the energy-sensing AMP-activated protein kinase pathway, demonstrating a potential link between the sensing of energy status and adaptation to oxygen availability. These observations permit mechanistic insight into energy homeostasis during development that now enable genetic and small molecule screens in this vertebrate model of anoxia tolerance.

Stabilization of HIF-1alpha is critical to improve wound healing in diabetic mice

Relative hypoxia is essential in wound healing since it normally plays a pivotal role in regulation of all the critical processes involved in tissue repair. Hypoxia-inducible factor (HIF) 1alpha is the critical transcription factor that regulates adaptive responses to hypoxia. HIF-1alpha stability and function is regulated by oxygen-dependent soluble hydroxylases targeting critical proline and asparaginyl residues. Here we show that hyperglycemia complexly affects both HIF-1alpha stability and activation, resulting in suppression of expression of HIF-1 target genes essential for wound healing both in vitro and in vivo. However, by blocking HIF-1alpha hydroxylation through chemical inhibition, it is possible to reverse this negative effect of hyperglycemia and to improve the wound healing process (i.e., granulation, vascularization, epidermal regeneration, and recruitment of endothelial precursors). Local adenovirus-mediated transfer of two stable HIF constructs demonstrated that stabilization of HIF-1alpha is necessary and sufficient for promoting wound healing in a diabetic environment. Our findings outline the necessity to develop specific hydroxylase inhibitors as therapeutic agents for chronic diabetes wounds. In conclusion, we demonstrate that impaired regulation of HIF-1alpha is essential for the development of diabetic wounds, and we provide evidence that stabilization of HIF-1alpha is critical to reverse the pathological process.

Inactivation of the CYLD deubiquitinase by HPV E6 mediates hypoxia-induced NF-kappaB activation

The biochemical mechanisms that underlie hypoxia-induced NF-kappaB activity have remained largely undefined. Here, we find that prolonged hypoxia-induced NF-kappaB activation is restricted to cancer cell lines infected with high-risk human papillomavirus (HPV) serotypes. The HPV-encoded E6 protein is necessary and sufficient for prolonged hypoxia-induced NF-kappaB activation in these systems. The molecular target of E6 in the NF-kappaB pathway is the CYLD lysine 63 (K63) deubiquitinase, a negative regulator of the NF-kappaB pathway. Specifically, hypoxia stimulates E6-mediated ubiquitination and proteasomal degradation of CYLD. Given the established role of NF-kappaB in human carcinogenesis, these findings provide a potential molecular/viral link between hypoxia and the adverse clinical outcomes observed in HPV-associated malignancies.

Short hairpin RNA interference therapy for ischemic heart disease

BACKGROUND

During hypoxia, upregulation of hypoxia inducible factor-1 alpha transcriptional factor can activate several downstream angiogenic genes. However, hypoxia inducible factor-1 alpha is naturally degraded by prolyl hydroxylase-2 (PHD2) protein. Here we hypothesize that short hairpin RNA (shRNA) interference therapy targeting PHD2 can be used for treatment of myocardial ischemia and this process can be followed noninvasively by molecular imaging.

METHODS AND RESULTS

PHD2 was cloned from mouse embryonic stem cells by comparing the homolog gene in human and rat. The best candidate shRNA sequence for inhibiting PHD2 was inserted into the pSuper vector driven by the H1 promoter followed by a separate hypoxia response element-incorporated promoter driving a firefly luciferase reporter gene. This construct was used to transfect mouse C2C12 myoblast cell line for in vitro confirmation. Compared with the control short hairpin scramble (shScramble) as control, inhibition of PHD2 increased levels of hypoxia inducible factor-1 alpha protein and several downstream angiogenic genes by >30% (P<0.01). Afterward, shRNA targeting PHD2 (shPHD2) plasmid was injected intramyocardially following ligation of left anterior descending artery in mice. Animals were randomized into shPHD2 experimental group (n=25) versus shScramble control group (n=20). Bioluminescence imaging detected plasmid-mediated transgene expression for 4 to 5 weeks. Echocardiography showed the shPHD2 group had improved fractional shortening compared with the shScramble group at Week 4 (33.7%+/-1.9% versus 28.4%+/-2.8%; P<0.05). Postmortem analysis showed increased presence of small capillaries and venules in the infarcted zones by CD31 staining. Finally, Western blot analysis of explanted hearts also confirmed that animals treated with shPHD2 had significantly higher levels of hypoxia inducible factor-1 alpha protein.

CONCLUSIONS

This is the first study to image the biological role of shRNA therapy for improving cardiac function. Inhibition of PHD2 by shRNA led to significant improvement in angiogenesis and contractility by in vitro and in vivo experiments. With further validation, the combination of shRNA therapy and molecular imaging can be used to track novel cardiovascular gene therapy applications in the future.

The role of 15-deoxy-delta(12,14)-prostaglandin J(2), an endogenous ligand of peroxisome proliferator-activated receptor gamma, in tumor angiogenesis

Peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear hormone receptor, is a ligand-activated transcription factor involved in adipogenesis, glucose homeostasis and lipid metabolism. 15-Deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), an endogenous ligand of PPARgamma, has multifaceted cellular functions. Angiogenesis plays an important role in the pathophysiology of ischemic and neoplastic disorders, especially cancer. 15d-PGJ(2) is involved in regulation of angiogenic mediators including vascular endothelial growth factor and hence participates in the blood vessel formation by means of angiogenesis. However, depending on the experimental conditions, this cyclopentenone prostaglandin can exert opposite effects on angiogenesis. 15d-PGJ(2) inhibits angiogenesis via suppression of pro-inflammatory enzymes and cytokines, while it also stimulates angiogenesis via induction of heme oxygenase-1, endothelial nitric-oxide synthase, and hypoxia inducible factor-1alpha. The aim of this review is to highlight such dual effects of 15d-PGJ(2) on angiogenesis and underlying molecular mechanisms.

Monoclonal antibody-based screening assay for factor inhibiting hypoxia-inducible factor inhibitors

The factor-inhibiting hypoxia-inducible factor (FIH) hydroxylates the asparagine 803 (Asn803) residue of the hypoxia-inducible factor 1alpha (HIF-1alpha), and the modification abrogates the transcriptional activity of HIF-1alpha. Because FIH is more active on HIF-1alpha than prolyl hydroxylase domain proteins under hypoxic conditions, its inhibitors have potential to be developed as anti-ischemic drugs targeting normal cells stressed by hypoxia. In this study, the authors developed the first monoclonal antibody, SHN-HIF1alpha, specifically to Asn803 hydroxylated HIF-1alpha and a sensitive assay system for FIH inhibitors using the monoclonal antibody (Mab). SHN-HIF1alpha showed 740 times higher affinity to the Asn803 hydroxylated HIF-1alpha peptide than the unmodified one. An enzyme-linked immunosorbent assay-based system using SHN-HIF1alpha displayed at least 30 times more sensitivity than previous methods for screening FIH inhibitors and was easily applicable to develop a high-throughput screening system. SHN-HIF1alpha also showed an Asn803 hydroxylation-dependent specificity to HIF-1alpha in cells. Taken together, the results suggest that it may be used to analyze the in vivo and in vitro activities of FIH inhibitors.

Macrophage migration inhibitory factor activates hypoxia-inducible factor in a p53-dependent manner

Background

Macrophage migration inhibitory factor (MIF) is not only a cytokine which has a critical role in several inflammatory conditions but also has endocrine and enzymatic functions. MIF is identified as an intracellular signaling molecule and is implicated in the process of tumor progression, and also strongly enhances neovascularization. Overexpression of MIF has been observed in tumors from various organs. MIF is one of the genes induced by hypoxia in an hypoxia-inducible factor 1 (HIF-1)-dependent manner.

Methods/Principal Findings

The effect of MIF on HIF-1 activity was investigated in human breast cancer MCF-7 and MDA-MB-231 cells, and osteosarcoma Saos-2 cells. We demonstrate that intracellular overexpression or extracellular administration of MIF enhances activation of HIF-1 under hypoxic conditions in MCF-7 cells. Mutagenesis analysis of MIF and knockdown of 53 demonstrates that the activation is not dependent on redox activity of MIF but on wild-type p53. We also indicate that the MIF receptor CD74 is involved in HIF-1 activation by MIF at least when MIF is administrated extracellularly.

Conclusion/Significance

MIF regulates HIF-1 activity in a p53-dependent manner. In addition to MIF's potent effects on the immune system, MIF is linked to fundamental processes conferring cell proliferation, cell survival, angiogenesis, and tumor invasiveness. This functional interdependence between MIF and HIF-1α protein stabilization and transactivation activity provide a molecular mechanism for promotion of tumorigenesis by MIF.

Regulation of gene expression by hypoxia: integration of the HIF-transduced hypoxic signal at the hypoxia-responsive element

Cells experiencing lowered O(2) levels (hypoxia) undergo a variety of biological responses in order to adapt to these unfavorable conditions. The master switch, orchestrating the cellular response to low O(2) levels, is the transcription factor, termed hypoxia-inducible factor (HIF). The alpha subunits of HIF are regulated by 2-oxoglutarate-dependent oxygenases that, in the presence of O(2), hydroxylate specific prolyl and asparaginyl residues of HIF-alpha, inducing its proteasome-dependent degradation and repression of transcriptional activity, respectively. Hypoxia inhibits oxygenases, stabilized HIF-alpha translocates to the nucleus, dimerizes with HIF-beta, recruits the coactivators p300/CBP, and induces expression of its transcriptional targets via binding to hypoxia-responsive elements (HREs). HREs are composite regulatory elements, comprising a conserved HIF-binding sequence and a highly variable flanking sequence that modulates the transcriptional response. In summary, the transcriptional response of a cell is the end product of two major functions. The first (trans-acting) is the level of activation of the HIF pathway that depends on regulation of stability and transcriptional activity of the HIF-alpha. The second (cis-acting) comprises the characteristics of endogenous HREs that are determined by the availability of transcription factors cooperating with HIF and/or individual HIF-alpha isoforms.

HIF-1-regulated glucose metabolism in the control of apoptosis signaling

Resistance of human cancers to current treatment approaches remains a major concern in oncology. Therefore, much effort has been focused on identifying molecular pathways that are responsible for primary or acquired resistance of cancers in order to overcome resistance. Hypoxia is one of the hallmarks of solid tumors and usually correlates with poor prognosis. Under hypoxic conditions, cancer cells undergo a variety of adoptive changes, including the activation of signaling pathways, which promote cancer cell survival and block cell death. Hypoxia inducible factor (HIF)-1 is the key transcription factor that mediates adaptation of cancer cells to the hypoxic environment. There is increasing evidence that HIF-1 promotes tumor growth, at least in part, by upregulating genes that are involved in cellular energy metabolism. Thus, HIF-1 and hypoxia-inducible genes represent attractive targets for the design of molecular targeted therapies, which may offer new therapeutic options for a wide range of malignancies.

LPS induces hypoxia-inducible factor 1 activation in macrophage-differentiated cells in a reactive oxygen species-dependent manner

A prominent feature of various inflamed and diseased tissue is the presence of low oxygen tension (hypoxia). Effector cells of the innate immune system must maintain their viability and physiologic functions in a hypoxic microenvironment. Monocytes circulating in the bloodstream differentiate into macrophages. During this process, cells acquire the ability to exert effects at hypoxic sites of inflammation. The transcription factor hypoxia-inducible factor 1 (HIF-1) mediates adaptive responses to reduced oxygen availability. In this study, we demonstrated that lipopolysaccharide (LPS) induces HIF-1 activation by enhancing both HIF-1alpha protein expression through a translation-dependent pathway and HIF-1alpha transcriptional activity in THP-1 human myeloid cells that have undergone macrophage differentiation but not in undifferentiated monocytic THP-1 cells. LPS-induced HIF-1 activation was blocked by treatment with antioxidant (N-acetylcysteine or thioredoxin-1), NADPH oxidase inhibitor (diphenyleneiodonium), indicating that reactive oxygen species generated in response to LPS are essential in this process. LPS-mediated activation of HIF-1 was independent of NF-kappaB activity. LPS-induced ROS generation and HIF-1 activation required the expression of Toll-like receptor 4 or myeloid differentiation factor (MyD) 88, thus providing a molecular basis for the selective activation of HIF-1 in differentiated THP-1 cells.

2-Oxoglutarate-dependent oxygenases control hepcidin gene expression

BACKGROUND/AIMS

Hepcidin is a liver-produced hormone that regulates systemic iron homeostasis. Hepcidin expression is stimulated upon iron overload or inflammation while iron deficiency, anemia and tissue hypoxia are negative regulators. We investigated the involvement of 2-oxoglutarate-dependent oxygenases, HIF-1 and other transcription factors in the hypoxic suppression of hepcidin.

METHODS

Northern blotting analysis and real time PCR were used to determine hepcidin mRNA levels in hepatoma cells and hepcidin promoter activity was measured using Huh7 cells transfected with suitable reporter constructs under various conditions.

RESULTS

Treatment of human cultured hepatoma cells with hypoxia or known inhibitors of 2-oxoglutarate-dependent oxygenases, such as the iron chelator desferrioxamine, cobalt or the 2-oxoglutarate analogue dimethyl-oxalylglycine significantly reduced hepcidin mRNA levels and down-regulated its gene promoter activity. This effect was not dependent on the HREs or other known putative response elements in the hepcidin promoter and was observed even under interleukin-6 treatment.

CONCLUSIONS

2-Oxoglutarate-dependent oxygenases are important to maintain high hepcidin mRNA expression in a HIF-1-independent manner. We suggest that modulation of oxygenase activity may be of therapeutic value in iron-related disorders.

Oxygen-regulated degradation of fission yeast SREBP by Ofd1, a prolyl hydroxylase family member

Sre1, the fission yeast sterol regulatory element binding protein, is an endoplasmic reticulum membrane-bound transcription factor that responds to changes in oxygen-dependent sterol synthesis as an indirect measure of oxygen availability. Under low oxygen, Sre1 is proteolytically cleaved and the released N-terminal transcription factor (Sre1N) activates gene expression essential for hypoxic growth. Here, we describe an oxygen-dependent mechanism for regulation of Sre1 that is independent of sterol-regulated proteolysis. Using yeast expressing only Sre1N, we show that Sre1N turnover is regulated by oxygen. Ofd1, an uncharacterized prolyl 4-hydroxylase-like 2-oxoglutarate-Fe(II) dioxygenase, accelerates Sre1N degradation in the presence of oxygen. However, unlike the prolyl 4-hydroxylases that regulate mammalian hypoxia-inducible factor, Ofd1 uses multiple domains to regulate Sre1N degradation by oxygen; the Ofd1 N-terminal dioxygenase domain is required for oxygen sensing and the Ofd1 C-terminal domain accelerates Sre1N degradation. Our data support a model whereby the Ofd1 N-terminal dioxygenase domain is an oxygen sensor that regulates the activity of the C-terminal degradation domain.

The FH mutation database: an online database of fumarate hydratase mutations involved in the MCUL (HLRCC) tumor syndrome and congenital fumarase deficiency

Background

Fumarate hydratase (HGNC approved gene symbol – FH), also known as fumarase, is an enzyme of the tricarboxylic acid (TCA) cycle, involved in fundamental cellular energy production. First described by Zinn et al in 1986, deficiency of FH results in early onset, severe encephalopathy. In 2002, the Multiple Leiomyoma Consortium identified heterozygous germline mutations of FH in patients with multiple cutaneous and uterine leiomyomas, (MCUL: OMIM 150800). In some families renal cell cancer also forms a component of the complex and as such has been described as hereditary leiomyomatosis and renal cell cancer (HLRCC: OMIM 605839). The identification of FH as a tumor suppressor was an unexpected finding and following the identification of subunits of succinate dehydrogenase in 2000 and 2001, was only the second description of the involvement of an enzyme of intermediary metabolism in tumorigenesis.

Description

The FH mutation database is a part of the TCA cycle gene mutation database (formerly the succinate dehydrogenase gene mutation database) and is based on the Leiden Open (source) Variation Database (LOVD) system. The variants included in the database were derived from the published literature and annotated to conform to current mutation nomenclature. The FH database applies HGVS nomenclature guidelines, and will assist researchers in applying these guidelines when directly submitting new sequence variants online. Since the first molecular characterization of an FH mutation by Bourgeron et al in 1994, a series of reports of both FH deficiency patients and patients with MCUL/HLRRC have described 107 variants, of which 93 are thought to be pathogenic. The most common type of mutation is missense (57%), followed by frameshifts & nonsense (27%), and diverse deletions, insertions and duplications. Here we introduce an online database detailing all reported FH sequence variants.

Conclusion

The FH mutation database strives to systematically unify all current genetic knowledge of FH variants. We believe that this knowledge will assist clinical geneticists and treating physicians when advising patients and their families, will provide a rapid and convenient resource for research scientists, and may eventually assist in gaining novel insights into FH and its related clinical syndromes.

Rapid degradation of hypoxia-inducible factor-1alpha by KRH102053, a new activator of prolyl hydroxylase 2

BACKGROUND AND PURPOSE

Hypoxia-inducible factor (HIF) is a transcription factor induced by hypoxia and degraded by ubiquitin-dependent proteasomes in normoxic conditions. Under hypoxic conditions, hydroxylation of HIF-1alpha subunit by prolyl hydroxylase (PHD) is suppressed, thus leading to increased levels of HIF. Although PHD2 plays a key role in regulating the levels of HIF, chemical activators of PHD2 are relatively unknown. The aim of this study was to identify small molecule activators of PHD2 that could be used, eventually, to suppress the level of HIF-1alpha.

EXPERIMENTAL APPROACH

By using the overproduced PHD2 as a target, a molecular library consisting of more than 600 small molecules with a benzopyran structure was screened with an HPLC assay method.

KEY RESULTS

We found a potent activator of PHD2, KRH102053 (2-amino-4-methylsulphanyl-butylic acid-4-methoxy-6-(4-methoxy-benzylamino)-2,2-dimethyl-chroman-3-yl ester). The effects of KRH102053 on controlling HIF were studied in human HOS osteosarcoma, rat PC12 phaeochromocytoma and human HepG2 hepatoma cells. Under our experimental conditions, KRH102053 decreased the protein level of HIF-1alpha and the mRNA levels of HIF-regulated downstream target genes, such as vascular endothelial growth factor, aldolase A, enolase 1 and monocarboxylate transporter 4. Consistent with these results, KRH102053 also inhibited the rates of HIF-related migration and invasion of HOS cells as well as the degree of tube formation in human umbilical vein endothelium cells.

CONCLUSIONS AND IMPLICATIONS

These results suggest that KRH102053 and its structural analogues have the potential for use as therapeutic agents against various diseases associated with HIF.

Abundance of aspargynyl-hydroxylase FIH is regulated by Siah-1 under normoxic conditions

The activity of hypoxia-inducible factors-1alpha (HIF-1alpha) is regulated by two types of hydroxylases, prolyl-hydroxylase (PHD) and aspargynyl-hydroxylase factor inhibiting HIF-1alpha (FIH). Hydroxylation of HIF-1alpha by PHD and FIH causes proteasomal degradation and transcriptional inhibition of HIF-1alpha, respectively. Siah ubiquitin ligases regulate the abundance of PHD via targeting for proteasomal degradation. The present study investigated the role of Siah-1 in the regulation of FIH abundance under normoxic conditions. Immunohistochemical analysis of the rat brains revealed that both Siah-1 and FIH were widely distributed in the central nervous system including the cerebral cortex, the hippocampus, the striatum, the olfactory bulb, the putamen, the thalamus, the celleberum, and the brain stem. In the hippocampus, both Siah-1 and FIH predominantly expressed in neurons. Siah-1 and FIH localized mostly in the cytoplasm. In mammalian cells, FIH expression levels were increased in the presence of a proteasomal inhibitor MG132, suggesting that FIH is degraded by the ubiquitin-proteasome system. Immunoprecipitation assay and ubiquitination assay revealed that Siah-1 interacted with, and ubiquitinated FIH. Under normoxic conditions, Siah-1 facilitated degradation of FIH. On the other hand, when endogenous Siah-1 expression was suppressed using siRNA, FIH expression levels were increased, as compared to control. These results suggest that Siah-1 might play a role as a regulator of FIH abundance under normoxic conditions.

Fundulus as the premier teleost model in environmental biology: opportunities for new insights using genomics

A strong foundation of basic and applied research documents that the estuarine fish Fundulus heteroclitus and related species are unique laboratory and field models for understanding how individuals and populations interact with their environment. In this paper we summarize an extensive body of work examining the adaptive responses of Fundulus species to environmental conditions, and describe how this research has contributed importantly to our understanding of physiology, gene regulation, toxicology, and ecological and evolutionary genetics of teleosts and other vertebrates. These explorations have reached a critical juncture at which advancement is hindered by the lack of genomic resources for these species. We suggest that a more complete genomics toolbox for F. heteroclitus and related species will permit researchers to exploit the power of this model organism to rapidly advance our understanding of fundamental biological and pathological mechanisms among vertebrates, as well as ecological strategies and evolutionary processes common to all living organisms.