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PubMed1997

Hypoxia-inducible factor 1alpha (HIF-1alpha) protein is rapidly degraded by the ubiquitin-proteasome system under normoxic conditions. Its stabilization by hypoxia depends on redox-induced changes.

The hypoxia-inducible factor 1 transcriptional activator complex (HIF-1) is involved in the activation of the erythropoietin and several other hypoxia-responsive genes. The HIF-1 complex is composed of two protein subunits: HIF-1beta/ARNT (aryl hydrocarbon receptor nuclear translocator), which is constitutively expressed, and HIF-1alpha, which is not present in normal cells but induced under hypoxic conditions. The HIF-1alpha subunit is continuously synthesized and degraded under normoxic conditions, while it accumulates rapidly following exposure to low oxygen tensions. The involvement of the ubiquitin-proteasome system in the proteolytic destruction of HIF-1 in normoxia was studied by the use of specific inhibitors of the proteasome system. Lactacystin and MG-132 were found to protect the degradation of the HIF-1 complex in cells transferred from hypoxia to normoxia. The same inhibitors were able to induce HIF-1 complex formation when added to normoxic cells. Final confirmation of the involvement of the ubiquitin-proteasome system in the regulated degradation of HIF-1alpha was obtained by the use of ts20TGR cells, which contain a temperature-sensitive mutant of E1, the ubiquitin-activating enzyme. Exposure of ts20 cells, under normoxic conditions, to the non-permissive temperature induced a rapid and progressive accumulation of HIF-1. The effect of proteasome inhibitors on the normoxic induction of HIF-1 binding activity was mimicked by the thiol reducing agent N-(2-mercaptopropionyl)-glycine and by the oxygen radical scavenger 2-acetamidoacrylic acid. Furthermore, N-(2-mercaptopropionyl)-glycine induced gene expression as measured by the stimulation of a HIF-1-luciferase expression vector and by the induction of erythropoietin mRNA in normoxic Hep 3B cells. These last findings strongly suggest that the hypoxia induced changes in HIF-1alpha stability and subsequent gene activation are mediated by redox-induced changes.

Cell Line↗
PubMed2001

Hypoxia-inducible factor-2alpha (HIF-2alpha) is involved in the apoptotic response to hypoglycemia but not to hypoxia.

Deprivation of oxygen (hypoxia) and/or glucose (hypoglycemia) represents a serious stress that affects cellular survival. The hypoxia-inducible transcription factor-1alpha (HIF-1alpha), which has been implicated in the cellular response to hypoxia (Semenza, G. L. (1999) Annu. Rev. Cell Dev. Biol. 15, 551-578), mediates apoptosis during hypoxia (Halterman, M. W., Miller, C. C., and Federoff, H. J. (1999) J. Neurosci. 19, 6818-6824 and Carmeliet, P., Dor, Y., Herbert, J. M., Fukumura, D., Brusselmans, K., Dewerchin, M., Neeman, M., Bono, F., Abramovitch, R., Maxwell, P., Koch, C. J., Ratcliffe, P., Moons, L., Jain, R. K., Collen, D., and Keshet, E. (1998) Nature 394, 485-490), but the function of its homologue HIF-2alpha remains unknown. Therefore, the role of HIF-2alpha in cellular survival was studied by targeted inactivation of the HIF-2alpha gene (HIF-2alpha(-/-)) in murine embryonic stem (ES) cells. In contrast to HIF-1alpha deficiency, loss of HIF-2alpha did not protect ES cells against apoptosis during hypoxia. Both HIF-1alpha(-/-) and HIF-2alpha(-/-) ES cells were, however, resistant to apoptosis in response to hypoglycemia. When co-cultured with wild type ES cells, HIF-2alpha(-/-) ES cells became rapidly and progressively enriched in hypoglycemia but not in hypoxia. Thus, HIF-1alpha and HIF-2alpha may have distinct roles in responses to environmental stress, and despite its name, HIF-2alpha may be more important in the survival response to environmental variables other than the level of oxygen.

Animals↗
PubMed2001

Characterization of a hypoxia-inducible factor (HIF-1alpha ) from rainbow trout. Accumulation of protein occurs at normal venous oxygen tension.

The mammalian hypoxia-inducible factor-1 (HIF-1) is a heterodimeric transcription factor that controls the induction of several genes involved in glycolysis, erythropoiesis, and angiogenesis when cells are exposed to hypoxic conditions. Until now, the expression and function of HIF-1alpha have not been studied in fish, which experience wide fluctuations of oxygen tensions in their natural environment. Using electrophoretic mobility shift assay, we have ascertained that a hypoxia-inducible factor is present in rainbow trout cells. We have also cloned the full-length cDNA (3605 base pairs) of the HIF-1alpha from rainbow trout with a predicted protein sequence of 766 amino acids that showed a 61% similarity to human and mouse HIF-1alpha. Polyclonal antibodies against the N-terminal part (amino acids 12-363) and the C-terminal part (amino acids 330-730) of rainbow trout HIF-1alpha protein recognized rainbow trout and chinook salmon HIF-1alpha protein in Western blot analysis. Also, the human and mouse HIF-1alpha proteins were recognized by the N-terminal rainbow trout anti-HIF-1alpha antibody but not by the C-terminal HIF-1alpha antibody. The accumulation of HIF-1alpha was studied by incubating rainbow trout and chinook salmon cells at different oxygen concentrations from 20 to 0.2% O(2) for 1 h. The greatest accumulation of HIF-1alpha protein occurred at 5% O(2) (38 torr), a typical oxygen tension of venous blood in normoxic animals. The protein stability experiments in the absence or presence of a proteasome inhibitor, MG-132, demonstrated that the inhibitor is able to stabilize the protein, which normally is degraded via the proteasome pathway both in normoxia and hypoxia. Notably, the hypoxia response element of oxygen-dependent degradation domain is identical in mammalian, Xenopus, and rainbow trout HIF-1alpha proteins, suggesting a high degree of evolutionary conservation in degradation of HIF-1alpha protein.

Amino Acid Sequence↗
PubMed2003

Nitric oxide impairs normoxic degradation of HIF-1alpha by inhibition of prolyl hydroxylases.

Hypoxia inducible factor-1 (HIF-1) is the master regulator of metabolic adaptation to hypoxia. It is appreciated that HIF-1alpha accumulation is achieved under normoxic conditions by e.g., nitric oxide. We determined molecular mechanisms of HIF-1alpha accumulation under the impact of S-nitrosoglutathione (GSNO). In human embryonic kidney cells GSNO provoked nuclear accumulation of HIF-1alpha. This appeared unrelated to gene transcription and protein translation, thus pointing to inhibition of HIF-1alpha degradation. Indeed, GSNO as well as the hypoxia mimic CoCl2 decreased ubiquitination of HIF-1alpha and GSNO-induced HIF-1alpha failed to coimmunoprecipitate with pVHL (von Hippel Lindau protein). Considering that HIF-1alpha-pVHL interactions require prolyl hydroxylation of HIF-1alpha, we went on to demonstrate inhibition of HIF-1alpha prolyl hydroxylases (PHDs) by GSNO. In vitro HIF-1alpha-pVHL interactions revealed that GSNO dose-dependently inhibits PHD activity but not the interaction of a synthetic peptide resembling the hydroxylated oxygen-dependent degradation domain of HIF-1alpha with pVHL. We conclude that GSNO-attenuated prolyl hydroxylase activity accounts for HIF-1alpha accumulation under conditions of NO formation during normoxia and that PHD activity is subject to regulation by NO.

Cell Hypoxia↗
PubMed2003

Nitric oxide and reactive oxygen species exert opposing effects on the stability of hypoxia-inducible factor-1alpha (HIF-1alpha) in explants of human pial arteries.

Hypoxia induces angiogenesis, partly through stabilization of hypoxia-inducible factor-1alpha (HIF-1alpha), leading to transcription of pro-angiogenic factors. Here we examined the regulation of HIF-1alpha by hypoxia and nitric oxide (NO) in explants of human cerebrovascular smooth muscle cells. Cells were treated with NO donors under normoxic or hypoxic (2% O2) conditions, followed by analysis of HIF-1alpha protein levels. Treatment with the NO donor sodium nitroprusside reduced levels of HIF-1alpha, whereas NO donors, NOC-18 and S-nitrosoglutathione, increased HIF-1alpha levels. SIN-1, which releases both NO and superoxide (O2*-), reduced HIF-1alpha levels, suggesting that inhibitory NO donors may elicit effects through peroxynitrite (ONOO*-). O2*- generation by xanthine/xanthine oxidase also reduced HIF-1alpha levels, confirming an inhibitory role for reactive oxygen species (ROS). Furthermore, superoxide dismutase increased HIF-1alpha levels, and the NO scavenger carboxy-PTIO reversed HIF-1alpha stabilization by NO donors. Effects on HIF-1alpha levels correlated with vascular endothelial growth factor transcription but did not affect HIF-1alpha transcription, as measured by RT-PCR and luciferase-reporter assays. The results indicate that HIF-1alpha is stabilized by agents that produce NO and reduce ROS but destabilized by agents that increase ROS, including O2*- and ONOO*-. Thus we propose that the effect of NO on HIF-1alpha signaling is critically dependent on the form of NO and the physiological environment of the responding cell.

Arteries↗
PubMed2005

Up-regulation of HIF in experimental acute renal failure: evidence for a protective transcriptional response to hypoxia.

BACKGROUND: Medullary hypoxia is believed to play an important role in the pathogenesis of acute renal failure (ARF). Hypoxia-inducible transcription factors (HIF) are recognized as master regulators of hypoxic adaptation, but little is known about their role in renal disease. METHODS: A multi-insult rat model of ARF combining the application of contrast medium with nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibition was used to study chronology and distribution of the oxygen regulated HIF isoforms HIF-1alpha and HIF-2alpha in comparison with the hypoxia-marker pimonidazole between 10 minutes and 48 hours after injury induction. Treatment with furosemide was used to study HIF expression under conditions of ameliorated tissue injury. RESULTS: Contrast medium in combination with NOS and COX inhibition resulted in widespread induction of HIF in the outer and inner medulla that was initiated within 10 minutes, reached the highest levels at 2 hours and diminished 8 hours to 24 hours thereafter. HIF isoforms were expressed in a cell type-specific fashion: HIF-1alpha in tubular and HIF-2alpha in interstitial and endothelial cells. The degree of HIF-1alpha accumulation varied between nephron segments, being much stronger in collecting ducts than in medullary thick ascending limb of the loop of Henle (mTAL). Comparison with pimonidazole staining and the effect of furosemide indicated that HIF induction in mTAL is maximal with moderate hypoxia and declines with increasing severity of hypoxia. CONCLUSION: A complex pattern of HIF activation appears to play an important role in tissue preservation as a response to regional renal hypoxia. The limited capacity of mTAL cells for HIF activation may explain their susceptibility to injury.

Acute Kidney Injury↗
PubMed2003

A common polymorphism in the oxygen-dependent degradation (ODD) domain of hypoxia inducible factor-1alpha (HIF-1alpha) does not impair Pro-564 hydroxylation.

BACKGROUND: The hypoxia-inducible factor (HIF) transcription complex, which is activated by low oxygen tension, controls a diverse range of cellular processes including angiogenesis and erythropoiesis. Under normoxic conditions, the alpha subunit of HIF is rapidly degraded in a manner dependent on hydroxylation of two conserved proline residues at positions 402 and 564 in HIF-1alpha in the oxygen-dependent degradation (ODD) domain. This allows subsequent recognition by the von Hippel-Lindau (VHL) tumor suppressor protein, which targets HIF for degradation by the ubiquitin-proteasome pathway. Under hypoxic conditions, prolyl hydroxylation of HIF is inhibited, allowing it to escape VHL-mediated degradation. The transcriptional regulation of the erythropoietin gene by HIF raises the possibility that HIF may play a role in disorders of erythropoiesis, such as idiopathic erythrocytosis (IE). RESULTS: Patients with IE were screened for changes in the HIF-1alpha coding sequence, and a change in the ODD domain that converts Pro-582 to Ser was identified in several patients. This same change, however, was also detected at a significant frequency, 0.073, in unaffected controls compared to 0.109 in the IE patient group. In vitro hydroxylation assays examining this amino acid change failed to reveal a discernible effect on HIF hydroxylation at Pro-564. CONCLUSION: The Pro582Ser change represents a common polymorphism of HIF-1alpha that does not impair HIF-1alpha prolyl hydroxylation. Although the Pro582Ser polymorphism is located in the ODD domain of HIF-1alpha it does not diminish the association of HIF-1alpha with VHL. Thus, it is unlikely that this polymorphism accounts for the erythrocytosis in the group of IE patients studied.

Binding Sites↗
PubMed2004

Redox state regulates HIF-1alpha and its DNA binding and phosphorylation in salmonid cells.

Rainbow trout (Oncorhynchus mykiss) hypoxia-inducible factor-1 (HIF-1) is a heterodimeric transcription factor structurally similar to mammalian HIF-1. It consists of HIF-1alpha and HIF-1beta subunits, of which the HIF-1alpha subunit confers the hypoxia sensitivity. HIF-1alpha is rapidly degraded by a proteasome under normal oxygen (21% O2) conditions, mainly as a result of prolyl hydroxylation needed for protein destabilization. Although prolyl hydroxylation at conserved proline residues is a major factor controlling HIF-1alpha stability, the redox state of the cells may, in addition, influence the function of HIF-1alpha like proteins by influencing their stability, DNA binding and phosphorylation. Sensitivity of the protein to oxidation/reduction may be due to cysteine residues at critical positions. The predicted amino acid sequence of rainbow trout HIF-1alpha contains several unique cysteine residues, notably in the DNA-binding area at position 28 and in the transactivation domain of the molecule in the vicinity of the conserved proline residue at position 564 of mammalian HIF-1alpha. In the present studies we have investigated if the redox state influences HIF-1alpha stability, DNA binding and phosphorylation in two established salmonid cell lines RTG-2 and CHSE-214. The results indicate that reducing conditions, achieved using N-propylgallate (nPG) or N-acetylcysteine (NAC), stabilize HIF-1alpha, facilitate its DNA binding, and increase its phosphorylation even under normal oxygen conditions. On the other hand, oxidizing conditions, achieved using L-buthionine sulfoximine (BSO) dampen the hypoxia response. Furthermore, the hypoxia-like effect of cobalt is increased in the presence of the reducing agent. On the basis of these results, we suggest that redox state influences the accessibility of the conserved prolyl residues to oxygen-dependent hydroxylation and the accessibility of the residues involved in the phosphorylation of HIF-1alpha.

Acetylcysteine↗
PubMed2003

The role of nitric oxide (NO) in stability regulation of hypoxia inducible factor-1alpha (HIF-1alpha).

Hypoxia inducible factor-1 (HIF-1) is a master regulator under conditions of decreased oxygen availability. As a hypoxia inducible transcription factor HIF-1 is a heterodimer composed of the helix-loop-helix-Per-Arnt-Sim (bHLH-PAS) proteins HIF-1alpha and the aryl hydrocarbon nuclear translocator (ARNT) also known as HIF-1beta. The HIF-1 transcriptional system senses decreased oxygen availability and transmits this signal into patho-physiological responses such as angiogenesis, erythropoiesis, vasomotor control, an altered energy metabolism, as well as cell survival decisions. Among recent advances are the discoveries that reactive nitrogen species (RNS), oxygen species (ROS), cytokines, and growth factors participate in stability regulation of HIF-1alpha and HIF-1 transactivation during normoxia. Here we summarize current knowledge and existing concepts that help to understand how NO affects protein accumulation of HIF-1alpha. Considering the fundamental role of radicals, especially NO, as signaling molecules makes HIF-1alpha an attractive target under conditions of NO formation that may be attributed to both, physiology and pathology. Although initial observations showed that NO inhibits hypoxia-induced HIF-1alpha stabilization and HIF-1 transcriptional activation, later studies indicated that exposure of various cells to chemically diverse NO donors or conditions of endogenous NO formation under normoxic conditions induced HIF-1alpha accumulation, HIF-1-DNA binding, and activation of downstream target gene expression. These contrasting situations evoked by NO provide insights into basic chemical reactions, biochemical signal transduction pathways with broad implications for medicine.

DNA-Binding Proteins↗
PubMed2006

Natural product-derived small molecule activators of hypoxia-inducible factor-1 (HIF-1).

Hypoxia-inducible factor-1 (HIF-1) is a key mediator of oxygen homeostasis that was first identified as a transcription factor that is induced and activated by decreased oxygen tension. Upon activation, HIF-1 upregulates the transcription of genes that promote adaptation and survival under hypoxic conditions. HIF-1 is a heterodimer composed of an oxygen-regulated subunit known as HIF-1alpha and a constitutively expressed HIF-1beta subunit. In general, the availability and activity of the HIF-1alpha subunit determines the activity of HIF-1. Subsequent studies have revealed that HIF-1 is also activated by environmental and physiological stimuli that range from iron chelators to hormones. Preclinical studies suggest that HIF-1 activation may be a valuable therapeutic approach to treat tissue ischemia and other ischemia/hypoxia-related disorders. The focus of this review is natural product-derived small molecule HIF-1 activators. Natural products, relatively low molecular weight organic compounds produced by plants, animals, and microbes, have been and continue to be a major source of new drugs and molecular probes. The majority of known natural product-derived HIF-1 activators were discovered through the pharmacological evaluation of specifically selected individual compounds. On the other hand, the combination of natural products chemistry with appropriate high-throughput screening bioassays may yield novel natural product-derived HIF-1 activators. Potent natural product-derived HIF-1 activators that exhibit a low level of toxicity and side effects hold promise as new treatment options for diseases such as myocardial and peripheral ischemia, and as chemopreventative agents that could be used to reduce the level of ischemia/reperfusion injury following heart attack and stroke.

Animals↗
PubMed2006

Natural product-based inhibitors of hypoxia-inducible factor-1 (HIF-1).

The transcription factor hypoxia-inducible factor-1 (HIF-1) regulates the expression of more than 70 genes involved in cellular adaptation and survival under hypoxic stress. Activation of HIF-1 is associated with numerous physiological and pathological processes that include tumorigenesis, vascular remodeling, inflammation, and hypoxia/ischemia-related tissue damage. Clinical studies suggested that HIF-1 activation correlates directly with advanced disease stages and treatment resistance among cancer patients. Preclinical studies support the inhibition of HIF-1 as a major molecular target for antitumor drug discovery. Considerable effort is underway, in government laboratories, industry and academia, to identify therapeutically useful small molecule HIF-1 inhibitors. Natural products (low molecular weight organic compounds produced by plants, microbes, and animals) continue to play a major role in modern antitumor drug discovery. Most of the compounds discovered to inhibit HIF-1 are natural products or synthetic compounds with structures that are based on natural product leads. Natural products have also served a vital role as molecular probes to elucidate the pathways that regulate HIF-1 activity. Natural products and natural product-derived compounds that inhibit HIF-1 are summarized in light of their biological source, chemical class, and effect on HIF-1 and HIF-mediated gene regulation. When known, the mechanism(s) of action of HIF-1 inhibitors are described. Many of the substances found to inhibit HIF-1 are non-druggable compounds that are too cytotoxic to serve as drug leads. The application of high-throughput screening methods, complementary molecular-targeted assays, and structurally diverse chemical libraries hold promise for the discovery of therapeutically useful HIF-1 inhibitors.

Animals↗
PubMed2006

[Overexpression of hypoxia inducible factor-1alpha (HIF-1alpha) promotes the differentiation of endothelial progenitor cell ex vivo].

To investigate the influence of HIF-1alpha overexpression on the differentiation of endothelial progenitor cells (EPCs) ex vivo, EPCs were isolated from human peripheral blood by density gradient centrifugation, overexpressed HIF-1alpha was transfected to EPCs by electroporation; HIF1alpha, HIF1beta, vascular endothelial growth factor (VEGF) mRNA level were measured with RT-PCR; HIF-1alpha protein was detected with immunohistochemistry in a time course. CD31(+) cells were measured with flow cytometry. Cell morphology was observed after transfection. The results showed that the transfection efficiency of HIF-1alpha to EPCs was about 20%. HIF-1alpha and its controlled target gene VEGF were markedly induced by HIF-1alpha vector (P < 0.05). HIF1beta had its same level as it before interference (P > 0.05). HIF-1alpha protein was induced by HIF-1alpha transfection after 12 hours but was undetectable at 24 hours. After 7 - 14 days cultured in 21% oxygen pressure, fluorescence-trace experiments revealed that CD31 + EPCs/EC could be generated more efficiently from overexpressed HIF-1alpha than that from pEGFP transfected group (P > 0.05). EPC morphology was observed by light microscopy. HIF-1alpha-transfected cells under normoxia sprouted more rapidly from the EPC colonies than the untransfected cells or cells transfected with an GFP vector, which essentially maintained the original colony formation. HIF-1alpha transfected cells took on an array-like arrangement rather than random dispersal, suggesting that they were in an advanced state of differentiation. It is concluded that the utility of overexpression of HIF-1alpha can induce target genes which have influence on cell differentiation. HIF-1alpha transfection was found to give a prospected way to do the insight research on ischemic treatment in vivo.

Cell Differentiation↗
PubMed2005

Overexpression of hypoxia-inducible factor HIF-1alpha predicts early relapse in breast cancer: retrospective study in a series of 745 patients.

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a transcription factor that is involved in tumour growth and metastasis by regulating genes involved in response to hypoxia. HIF-1alpha protein overexpression has been shown in a variety of human cancers, but only 2 studies have documented the prognostic relevance of HIF-1alpha expression in breast cancer. The aim of our study was to determine accurately the impact of HIF-1alpha expression on prognosis in a large series (n = 745) of unselected patients with invasive breast cancer in terms of overall survival, local recurrence and distant metastasis risk. HIF-1alpha expression was investigated using immunohistochemical assays on frozen sections, and correlated with patients' outcome (median follow-up = 13.5 years). Univariate (Kaplan-Meier) analysis showed that high levels of HIF-1alpha expression (cutoff = 10%) significantly correlated with poor overall survival (p = 0.019). HIF-1alpha expression correlated with high metastasis risk among the whole group of patients (p = 0.008). Multivariate analysis (Cox model) showed that the HIF-1alpha predictive value was independent of other current prognostic indicators. Moreover among node negative ones, HIF-1alpha expression was also significantly predictive of metastasis risk (p = 0.03) and of relapse (p = 0.035). All the data suggest that HIF-1alpha is associated with a worse prognosis in patients with invasive breast carcinoma. Furthermore HIF-1alpha immunodetection may be considered as a potential indicator for selecting patients who could benefit from specific therapies interfering with HIF-1alpha pathway.

Adult↗
PubMed2002

Identification and functional characterization of hypoxia-inducible factor 2alpha from the estuarine teleost, Fundulus heteroclitus: interaction of HIF-2alpha with two ARNT2 splice variants.

The hypoxia-inducible factors (HIFs) are dimeric transcription factors that mediate changes in gene expression during adaptation of animals to oxygen stress. Both alpha (HIFalpha) and beta (ARNT) subunits are members of the basic helix-loop-helix/Per-ARNT-Sim family of proteins. Mammals have at least three different HIF-alpha subunits, paralogous proteins expressed in tissue-specific fashion (HIF-1alpha, HIF-2alpha, and HIF-3alpha). However, the diversity and functional properties of teleost HIFs are poorly understood. In efforts to characterize mechanisms of hypoxia adaptation in estuarine fish, we have isolated cDNAs encoding HIF subunits from Fundulus heteroclitus (Atlantic killifish or mummichog), including a HIF-2alpha homolog and ARNT2alt, a splice variant of ARNT2 that contains an additional exon encoding 16 amino acids near the amino terminus. HIF-2alpha protein synthesized in vitro binds cognate DNA elements in concert with either Fundulus ARNT2 splice variant or murine ARNT1. HIF-2alpha, ARNT2, and ARNT2alt mRNAs are expressed in all organs examined. The HIF-2alpha cDNA encodes a protein of 96.4 kDa, sharing 53-54% identity with mammalian and avian orthologs. The oxygen-dependent degradation domain, however, exhibits substantial divergence from well-conserved mammalian sequences, suggesting the possibility of important functional differences, perhaps in the sensitivity to induction of activity by hypoxia. Hypoxia-tolerant fishes such as F. heteroclitus represent a unique opportunity for the study of functional and evolutionary aspects of adaptation to hypoxia at the molecular, cellular, and organismal levels. This study extends the understanding of hypoxia signaling in fish, the evolution and diversity of HIF function, and the evolution of the PAS family of proteins.

Alternative Splicing↗
PubMed2005

Inconsistent effects of acidosis on HIF-alpha protein and its target genes.

The transcription factor HIF-1alpha has been identified as a key regulator in the cellular and systemic response to hypoxia. Because hypoxia is frequently associated with acidosis, like in ischemia or tumour growth, we studied the impact of acidosis on the expression of the HIF-1alpha and HIF-2alpha proteins and that of the three HIF target genes carbonic anhydrase-9 (CA-9), glucose transporter-1 (Glut-1) and erythropoietin (EPO). Since the HIF-prolyl hydroxylases (PHD) modulate cellular HIF-alpha protein levels we also investigated changes in PHD mRNA expression under hypoxia and acidosis. HIF-1alpha immunoblots revealed, depending on the cell line investigated, a moderate induction of HIF-alpha protein levels by acidosis in normoxia (Hep3B cells) or hypoxia (HeLa cells). Concordantly, the activity of HIF-driven luciferase reporters was slightly enhanced at pH 7.0. In contrast, HIF target genes exhibited divergent responses to acidosis: basal and hypoxia-induced CA-9 mRNA levels were further increased, whereas hypoxic EPO mRNA induction was attenuated, and Glut-1 mRNA levels were not altered by acidosis. Except from a small increase of hypoxia-induced PHD3 mRNA levels in HeLa cells, there was also no significant effect of acidosis on PHD expression. In conclusion, albeit HIF protein levels slightly induced by acidosis and the inconsistent regulation of HIF target genes under acidosis suggest additional, yet unidentified pH-sensitive factors to be involved in the regulation of these genes.

Acidosis↗
PubMed2003

RNA interference for HIF-1alpha inhibits its downstream signalling and affects cellular proliferation.

Transcription factor HIF-1 is a key determinant of oxygen-dependent gene regulation. Suppression of HIF-1alpha is important for exploring HIF-1-dependent processes and for interfering with hypoxia-induced pathophysiological events. This study applied RNA-interference targeting HIF-1alpha to the human lung A549 cell line. Transfection of HIF-1alpha-siRNA reduced HIF-1alpha synthesis as measured on mRNA and protein level by realtime RT-PCR, Western blot, and immuncytochemistry. A time kinetic for hypoxic stabilization of HIF-1alpha protein and its inhibition by HIF-1alpha-siRNA is included. Hypoxic induction of HIF-1-controlled target genes as heme oxygenase I (HO-1), phosphoglycerate kinase (PGK), and vascular endothelial growth factor (VEGF) was markedly attenuated by HIF-1alpha-siRNA treatment. Correspondingly, gene activation via hypoxia-responsive-element, as shown by reporter gene assay, was inhibited by HIF-1alpha-siRNA. Moreover, this approach was found to suppress the shift from from S-phase to G1-phase observed in A549 cells in response to hypoxia, supporting a role of HIF-1alpha in oxygen-dependent cell cycle regulation.

Cell Division↗
PubMed2006

cDNA cloning, gene organization and variant specific expression of HIF-1 alpha in high altitude yak (Bos grunniens).

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric basic-helix-loop-helix-PER-ARNT-SIM (bHLH-PAS) transcription factor consisting of HIF-1alpha and HIF-1beta subunits. HIF-1alpha is the oxygen-regulated subunit of HIF-1, which regulates the transcription of genes involved in oxygen homeostasis in response to hypoxia. Yak (Bos grunniens), a mammal native to high altitude (HA) region ( approximately 3500-5500 m), has successfully adapted over many generations to the chronic hypoxia of HA. In the present work, cDNA encoding HIF-1alpha has been cloned from the blood of yak. Tissue specific expression of the mRNA was analyzed in blood, heart, lung, liver and kidney by RT-PCR with primers from three different regions of cDNA. The HIF-1alpha expression was liver and blood specific. The HIF-1alpha mRNA contains 823 bp long 3'UTR that is AU-rich and contains ten AUUUA pentamers and two overlapping copies of the nonamer UUAUUUAUUUAUU. Three potential microRNAs, hsa-miR-107/mmu-miR-107/rno-miR-107, hsa-miR-18b and hsa-miR-135a/mmu-miR-135a/rno-miR-135a, targeting 3'UTR of yak HIF-1alpha, were identified by using target prediction software. The CDS encodes for 823 residues of amino acids and showed 99%, 95%, 92%, 90% and 90% similarity to domestic cattle, human, plateau pika, mouse and rat HIF-1alpha, respectively. HIF-1alpha cDNA, cloned and sequenced in the present work has revealed the evolutionary conservation through multiple sequence alignment. Liver and blood specific stability of HIF-1alpha mRNA appears miR-107 regulated.

Altitude↗
PubMed2006

Evidence that hypoxia-inducible factor-1 (HIF-1) mediates transcriptional activation of interleukin-1beta (IL-1beta) in astrocyte cultures.

Hypoxia-inducible factor-1 (HIF-1) is a heterodimeric transcription factor composed of HIF-1alpha and HIF-1beta subunits and involved in the regulation of gene expression in adaptive response to hypoxia. This study reports that the inflammatory cytokine interleukin-1beta (IL-1beta) shares common features of other known HIF-1alpha-regulated genes. Both human and mouse IL-1beta genes carry multiple HIF-1-binding sites in their promoter regions and are up-regulated by hypoxia and CoCl2 in human and mouse astrocytes in parallel with up-regulation of HIF-1alpha mRNA and protein. Inhibition of HIF-1alpha degradation by proteasome inhibitor, MG-132, potentiated hypoxia-induced IL-1beta release from human astrocytes, and this response was blocked in the presence of CdCl2. Mouse astrocytes with Hif1alpha+/- genotype demonstrated attenuated up-regulation of both HIF-1alpha and IL-1beta by hypoxia and CoCl2. Mutation of HIF-1-binding sites in the IL-1beta promoter abolished hypoxia-induced transactivation of the reporter gene transfected into human astrocytes. Similarly, HIF-1 binding "decoy" oligonuleotide transfected into astrocytes inhibited both hypoxia-induced transactivation of the HIF-1 reporter gene and IL-1beta secretion from transfected astrocytes. Collectively, the evidence suggests that the transcriptional activation of IL-1beta in astrocytes exposed to hypoxia occurs via HIF-1.

Analysis of Variance↗