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PubMed2006

p300 and p53 levels determine activation of HIF-1 downstream targets in invasive breast cancer.

In previous studies, we noted that overexpression of hypoxia-inducible factor (HIF)-1alpha in breast cancer, especially the diffuse form, does not always lead to functional activation of its downstream genes. Transcriptional activity of HIF-1 may be repressed by p53 through competition for transcriptional coactivators such as p300. The aim of this study was therefore to explore the role of p53 and p300 in relation to overexpression of HIF-1alpha and activation of HIF-1 downstream genes in invasive breast cancer. p300 immunohistochemistry was performed in a group of 183 early-stage invasive breast cancers, and related to p53 accumulation, overexpression of HIF-1alpha, and several HIF-1 downstream genes. p300 was expressed in varying degrees in 84% of invasive breast cancers. p300 staining intensity correlated positively with HIF-1alpha expression (P = .04), p53 accumulation (P = .001), and overexpression of glucose transporter 1 (GLUT-1) (P < .001), a glucose transporter downstream target gene of HIF-1. GLUT-1 levels were significantly associated with p300 in HIF-1alpha positive patients (P = .02). p53 accumulation significantly positively correlated with carbonic anhydrase IX (CAIX)/GLUT-1 coexpression in HIF-1alpha-positive patients (P = .007). p53 accumulation/high p300 levels, the most favorable situation for HIF-1 downstream activation, were significantly associated with GLUT-1 overexpression (P = .01) and coexpression of CAIX/GLUT-1 (P = .03), compared with low p53/low p300 levels, the most unfavorable situation for HIF-1 downstream activation. p300 is a cofactor highly associated with p53 accumulation and HIF-1alpha levels in invasive breast cancer. Furthermore, low levels of p300 may explain absence of downstream effects in HIF-1alpha-overexpressing cancers, an effect that seems to be enhanced by wild-type levels of p53. This underlines the importance of p300 levels and p53 accumulation in the HIF-1-regulated response toward hypoxia.

Antigens, Neoplasm↗
PubMed2006

Histone deacetylase inhibitors repress the transactivation potential of hypoxia-inducible factors independently of direct acetylation of HIF-alpha.

Hypoxia-inducible factors (HIFs) are heterodimeric transcription factors regulating the oxygen supply, glucose metabolism, and angiogenesis. HIF function requires the recruitment of p300/CREB-binding protein, two coactivators with histone acetyltransferase activity, by the C-terminal transactivation domain of HIF-alpha (HIF-alphaCAD). Histone deacetylase inhibitors (HDAIs) induce differentiation or apoptosis and repress tumor growth and angiogenesis, hence being explored intensively as anti-cancer agents. Using combined pharmacological, biochemical, and genetic approaches, here we show that HDAIs repress the transactivation potential of HIF-alphaCAD. This repression is independent of the function of tumor suppressors von Hippel-Lindau or p53 or the degradation of HIF-alpha. We also demonstrate the sufficiency of low concentrations of HDAIs in repression of HIF target genes in tumor cells. We further show that HDAIs induce hyperacetylation of p300 and repress the HIF-1alpha.p300 complex in vivo. In vitro acetylation analysis reveals that the p300CH1 region, but not HIF-alphaCAD, is susceptible to acetylation. Taken together, our data demonstrate that a deacetylase activity is indispensable for the transactivation potential of HIF-alphaCAD and support a model that acetylation regulates HIF function by targeting HIF-alpha.p300 complex, not by direct acetylating HIF-alpha. The demonstration that HDAIs repress both HIF-1alpha and HIF-2alpha transactivation potential independently of von Hippel-Lindau tumor suppressor and p53 function indicates that HDAIs may have biological effects in a broad range of tissues in addition to tumors.

Basic Helix-Loop-Helix Proteins↗
PubMed2005

Differential prognostic impact of hypoxia induced and diffuse HIF-1alpha expression in invasive breast cancer.

BACKGROUND: Intratumorous hypoxia triggers a broad cellular response mediated by the transcription factor hypoxia inducible factor 1 (HIF-1). HIF-1alpha concentrations increase during breast carcinogenesis, and are associated with poor prognosis. An earlier study noted two HIF-1alpha overexpression patterns: diffuse scattered throughout the tissue and confined to perinecrotic cells. AIMS: To investigate the prognostic impact of these different HIF-1alpha overexpression patterns in relation to its downstream effectors carbonic anhydrase (CA) IX and glucose transporter 1 (GLUT-1). METHODS: HIF-1alpha, CA IX, and GLUT-1 expression was studied by immunohistochemistry, including double staining for CA IX and HIF-1alpha. Clinical data included disease free survival, lymph node status, and tumour size. RESULTS: HIF-1alpha overexpression (44% of cases) had a perinecrotic (13.5%) or diffuse staining pattern (30.5%). CA IX expression was detectable in 12.5% of breast cancers, whereas GLUT-1 expression was seen in 29%, with both showing perinecrotic membrane staining. Perinecrotic HIF-1alpha overexpression was highly associated with CA IX and GLUT-1 overexpression, and double staining for HIF-1alpha and CA IX showed strong expression in the same cells. Diffusely overexpressed HIF-1alpha was not associated with CA IX or GLUT-1 expression. Patients with diffuse HIF-1alpha staining had a significantly better prognosis than patients with perinecrotically overexpressed HIF-1alpha. CONCLUSIONS: Different regulation pathways of HIF-1alpha overexpression exist in breast cancer: (1) hypoxia induced, perinecrotic HIF-1alpha overexpression with strong expression of hypoxia associated genes (CA IX and GLUT-1), which is associated with a poor prognosis; and (2) diffuse HIF-1alpha overexpression lacking major hypoxia associated downstream effects, resulting in a more favourable prognosis.

Antigens, Neoplasm↗
PubMed2006

The transcriptional activator hypoxia inducible factor 2 (HIF-2/EPAS-1) regulates the oxygen-dependent expression of erythropoietin in cortical astrocytes.

In the ischemic or hypoxic brain, astrocytes appear to be one of the main sources of erythropoietin (EPO). In this study, we investigated the differential contribution of hypoxia inducible factor (HIF) isoforms to the regulation of hypoxic EPO expression in cultured astrocytes. In addition, using an in vitro model of oxygen-glucose deprivation (OGD), we studied the role of HIF-1alpha and HIF-2alpha in the generation of paracrine protective signals by astrocytes that modulate the survival of neurons exposed to OGD. Expression of HIF-1alpha or HIF-2alpha was abrogated by infecting astrocytes with lentiviral particles encoding small interference RNA specific for HIF-1alpha or HIF-2alpha (siHIF-1alpha or siHIF-2alpha). Astrocytes infected with siHIF-1alpha showed abrogated hypoxic induction of vascular endothelial growth factor (VEGF) and lactate dehydrogenase (LDH) but normal EPO induction. In contrast, reduction of HIF-2alpha expression by siHIF-2alpha led to a drastic decrease of EPO hypoxic expression, but it did not affect LDH or VEGF upregulation. To further test whether HIF-2 is sufficient to drive EPO upregulation, we expressed oxygen-insensitive mutant forms of HIF-1alpha (mtHIF-1alpha) (P402A/P577A) and HIF-2alpha (mtHIF-2alpha) (P405A/P530A). Expression of mtHIF-2alpha but not mtHIF-1alpha in normoxic astrocytes resulted in a significant upregulation of EPO mRNA and protein. Accordingly, HIF-2alpha but not HIF-1alpha was found to be associated with the EPO hypoxia-response element by a chromatin immunoprecipitation assay. Interestingly, conditioned medium from astrocytes challenged by sublethal OGD improved neuronal survival to OGD; however, this effect was abolished during the downregulation of astrocytic HIF-2alpha using siHIF-2alpha. These results indicate that HIF-2alpha mediates the transcriptional activation of EPO expression in astrocytes, and this pathway may promote astrocytic paracrine-dependent neuronal survival during ischemia.

Animals↗
PubMed2004

[Activation of HIF-1 by bFGF in breast cancer: role of PI-3K and MEK1/ERK pathways].

OBJECTIVE: To explore the mechanism of basic fibroblast growth factor (bFGF)-mediated hypoxia inducible factor (HIF-1) activation and the down-stream signaling pathways involved. METHODS: Human breast cancer cells of the line T47D were cultured and lysed to extract the total protein in the supernatant. The amounts of extracellular signal kinase 1/2 (ERK1/2), Akt, p38, and beta-tubulin were measured. T47D cells were inoculated into a 24-well plate, co-transfected with luciferase vector OB-HRE containing HIF-1 functional sequence (HRE) and pRL-SV40 (as inner marker), pretreated with SU5402, inhibitor of FGFR1, SB203580, inhibitors of PI-3K, PD98059, inhibitors of MEK1, or LY294002, inhibitors of p38, treated with basic fibroblast growth factor (bFGF), and then lysed. The amounts of ERK1/2, Akt, p38, and beta-tubulin were measured. Western blotting was used to detect the HIF-1alpha level in total protein. Dual luciferase assay was used to analyze the transactivity of HIF-1. The firefly/renilla luciferase ratio was measured to access the transcription activity of HIF-1. Western blotting was used to detect the expression of HIF-1alpha protein and phosphorylated Akt, ERK1/2 and p38 in whole cell extract. RESULTS: After the addition of bFGF Western blotting showed that the and phosphorylation of Akt, ERK1/2 and p38 in the T47D cells were increased time- and dose-dependent manner, and dual luciferase assay showed that the fluorescent intensity was increased, signifying the increase of expression of HIF-1alpha protein. Ten minutes after the addition of CHX the expression of HIF-1alpha protein began to be decreased and ceased 90 minutes after. SU5402 remarkably dose-dependently blocked the bFGF-induced phosphorylation of ERK1/2, Akt and p38. 15 micromol/L LY294002 completely blocked the bFGF-induced phosphorylation of Akt. 5 micromol/L PD98059 blocked 80% of the bFGF-induced phosphorylation of ERK1/2. 10 approximately 20 micromol/L SB203580 basically blocked the bFGF-induced phosphorylation of p38. SU5402 and LY294002 100% inhibited the bFGF-induced expression of HIF-1alpha protein. However, PD98059 and SB203580 did not significantly influence the expression of HIF-1alpha protein induced by bFGF. Luciferase assay showed that SU5402 and PD98059 inhibited the bFGF-induced transcription activity of HIF-1 by 94.8% and 81.7% respectively. LY294002 not only completely inhibited the bFGF-induced transcription activity of HIF-1 but also inhibited the basic transcription of HIF-1, and SB203580 did not significantly influence the transcription activity of HIF-1. CONCLUSION: bFGF activates HIF-1 via the PI-3K/Akt and MEK1/ERK pathways that co-operatively and differentially regulate this process with PI-3K/Akt pathway playing a more important role.

Breast Neoplasms↗
PubMed2002

Human hormone-refractory prostate cancers can harbor mutations in the O(2)-dependent degradation domain of hypoxia inducible factor-1alpha (HIF-1alpha).

PURPOSE: Androgen ablation, the preferred therapy for advanced prostate cancer, reduces blood flow and induces hypoxia in androgen-dependent tissues. Given the transient effectiveness of this therapy, we must consider whether a hypoxia-resistance mechanism might be involved in the development of therapeutic resistance by prostate cancer cells. The transcription factor protein, hypoxia-inducible factor 1alpha (HIF-1alpha), helps increase the expression of gene products that enable cells to survive conditions of hypoxic stress. Enhanced HIF-1alpha expression during hypoxia results from a drastic reduction of its degradation rate within a critical region of the protein referred to as the "oxygen-dependent degradation (ODD) domain". We sequenced HIF-1alpha cDNAs amplified from human prostate cancer cell lines and from hormone resistant prostate cancer specimens to determine whether prostate cancer cells might harbor mutations within the HIF-1alpha ODD domain. METHODS: HIF-1alpha cDNAs were RT-PCR amplified from three prostate cancer cell lines (LNCaP, PC-3, and DU145), from five different human hormone-resistant prostate cancers and one normal prostate, all microdissected, and were sequenced to determine whether the HIF-1alpha gene products were wildtype or mutant. One specimen containing a hormone-resistant prostate tumor that expressed a mutated HIF-1alpha cDNA was further microdissected into benign and tumorous regions and DNAs extracted from these regions were directly amplified by PCR and sequenced to determine whether the HIF-1alpha mutation was specific to the tumor. RESULTS: Although the HIF-1alpha cDNAs of all cell lines, the normal prostate, and three of the tumors were found to have a wildtype sequence, HIF-1alpha cDNAs amplified from two hormone-resistant tumors had nucleic acid substitutions that resulted in significant amino acid changes within the ODD domain of the HIF-1alpha protein. Analysis of the DNA extracted from a benign or tumorous region of one of these specimens showed that only the wildtype (nonmutated) form of the HIF-1alpha gene was amplified from the normal DNA whereas only the mutated form of the HIF-1alpha gene was amplified from the tumor. CONCLUSIONS: Some human hormone-refractory prostate cancers have mutations in a critical regulatory domain of the HIF-1alpha protein. We believe that these mutations might enable expression of this protein under inappropriate conditions and contribute to the development of therapeutic resistance by the cancer cells. This hypothesis is currently being tested.

Base Sequence↗
PubMed2004

Sumoylation increases HIF-1alpha stability and its transcriptional activity.

HIF-1 is closely involved in various biological processes, including angiogenesis, energy metabolism, and cell survival. HIF-1 consists of an oxygen-sensitive HIF-1alpha and oxygen-insensitive HIF-1beta. Oxygen-sensitive HIF-1alpha is subjected to post-translational modifications such as hydroxylation, ubiquitination, and acetylation, which are related to the regulation of its stability. In this present study, we found that the ectopic expression of SUMO-1 increased HIF-1alpha stability by the co-transfection study with HIF-1alpha and SUMO-1. Furthermore, the ectopic expression of SUMO-1 enhanced the transcriptional activity of HIF-1alpha. In the subsequent immunoprecipitation assay, SUMO-1 was co-immunoprecipitated with HIF-1alpha, implying that HIF-1alpha is covalently modified by SUMO-1. Thereafter, using a series of lysine mutants in the ODD domain, we found that HIF-1alpha was sumoylated at Lys(391) and Lys(477), suggesting that sumoylation at these two lysine residues enhances HIF-1alpha stability by possibly modulating other post-translational modifications. Altogether, we demonstrate that HIF-1alpha is upregulated through SUMO-1 modification at Lys(391)/Lys(477) residues, which may stabilize HIF-1alpha and enhance its transcriptional activity.

Amino Acid Sequence↗
PubMed2003

Dibenzoylmethane, a natural dietary compound, induces HIF-1 alpha and increases expression of VEGF.

Hypoxia-inducible factor 1 (HIF-1) is the major transcription factor activated during hypoxia. It is composed of HIF-1 alpha and HIF-1 beta subunits. While HIF-1 beta is constitutively expressed, HIF-1 alpha is targeted to proteasome degradation under normoxic conditions. Under hypoxia, HIF-1 alpha is stabilized and heterodimerizes with HIF-1 beta. Iron chelators have also been reported to stabilize HIF-1 alpha protein and activate HIF-1. In this study, we investigated the effects of dibenzoylmethane (DBM), a natural dietary compound and an iron chelator, on HIF-1 pathway. We found that DBM increases HIF-1 alpha protein levels in a dose- and time-dependent manner. This induction was accompanied with activation of HIF-1, measured by reporter gene assay and increased production of its downstream target, the vascular endothelial growth factor. Mechanistically, HIF-1 alpha was stabilized by DBM at a step prior to ubiquitination. The effect of DBM on HIF-1 and its low toxicity profile might be therapeutically beneficial in ischemic diseases.

Benzoates↗
PubMed2003

HIF-1 alpha protein as a target for S-nitrosation.

Hypoxia-inducible factor-1 alpha (HIF-1 alpha) is a master regulator to sense decreased oxygen partial pressure. HIF-1 alpha stability regulation initiates a complex biological response that allows cells to act appropriately to meet patho-physiological situations of decreased oxygen availability. Recently, nitric oxide emerged as a messenger with the ability to stabilize HIF-1 alpha and to transactivate HIF-1 under normoxia. Considering that reactive nitrogen species are recognized for post-translation protein modifications, among others S-nitrosation, we asked whether HIF-1 alpha is a target for S-nitrosation. In vitro NO+ donating NO donors such as GSNO and SNAP provoked massive S-nitrosation of purified HIF-1 alpha. All 15 free thiol groups found in human HIF-1 alpha are subjected to S-nitrosation. Thiol modification is not shared by spermine-NONOate, a NO radical donating compound. However, spermine-NONOate in the presence of O(2)(-), generated by xanthine/xanthine oxidase, regained S-nitrosation, most likely via formation of a N(2)O(3)-like species. In vitro, S-nitrosation of HIF-1 alpha was attenuated by the addition of GSH or ascorbate. In RCC4 and HEK293 cells GSNO or SNAP reproduced S-nitrosation of HIF-1 alpha, however with a significantly reduced potency that amounted to modification of three to four thiols, only. Importantly, endogenous formation of NO in RCC4 cells via inducible NO synthase elicited S-nitrosation of HIF-1 alpha that was sensitive to inhibition of inducible NO synthase activity with N-monomethyl-L-arginine. NO-stabilized HIF-1 alpha was susceptible to the addition of N-acetyl-cysteine that destabilized HIF-1 alpha in close correlation to the disappearance of S-nitrosated HIF-1 alpha. In conclusion, HIF-1 alpha is a target for S-nitrosation by exogenously and endogenously produced NO.

Acetylcysteine↗
PubMed2006

Bacterial lipopolysaccharide induces HIF-1 activation in human monocytes via p44/42 MAPK and NF-kappaB.

Inflammatory mediators activate the transcriptional complex HIF-1 (hypoxia-inducible factor-1), the key regulator of hypoxia-induced gene expression. Here we report that bacterial LPS (lipopolysaccharide) induces HIF-1alpha mRNA expression and HIF-1alpha protein accumulation in human monocytes as well as in non-differentiated and differentiated cells of the human monocytic cell line THP-1 under normoxic conditions. LPS and hypoxia synergistically activated HIF-1. Whereas LPS increased HIF-1alpha mRNA expression through activation of a NF-kappaB (nuclear factor kappaB) site in the promoter of the HIF-1alpha gene, hypoxia post-translationally stabilized HIF-1alpha protein. HIF-1alpha activation was followed by increased expression of the HIF-1 target gene encoding ADM (adrenomedullin). Knocking down HIF-1alpha by RNA interference significantly decreased ADM expression, which underlines the importance of HIF-1 for the LPS-induced ADM expression in normoxia. Simultaneously with HIF-1 activation, an increase in p44/42 MAPK (mitogen-activated protein kinase) phosphorylation was observed after incubation with LPS. In cells pretreated with the p44/42 MAPK inhibitor PD 98059 or with RNAi (interfering RNA) directed against p44/42 MAPK, LPS-induced HIF-1alpha accumulation and ADM expression were significantly decreased. From these results we conclude that LPS critically involves the p44/42 MAPK and NF-kappaB pathway in the activation of HIF-1, which is an important transcription factor for LPS-induced ADM expression.

Adrenomedullin↗
PubMed2002

Microtubule disruption utilizes an NFkappa B-dependent pathway to stabilize HIF-1alpha protein.

Hypoxia-inducible factor (HIF)-1alpha levels are elevated in normoxic cells undergoing physiological processes involving large scale microtubule reorganization, such as embryonic development, wound healing, and tumor cell metastasis. Although alterations in microtubules affect numerous cellular responses, no data have yet implicated microtubule dynamics in HIF-1alpha regulation. To investigate the effect of microtubule change upon HIF-1alpha regulation, we treated cells with the microtubule-depolymerizing agents (MDAs) colchicine, vinblastine or nocodazole. We demonstrate that these agents are able to induce transcriptionally active HIF-1. MDA-mediated induction of HIF-1alpha required microtubule depolymerization, since HIF-1alpha levels were unchanged in cells treated with either the microtubule-stabilizing agent paclitaxel, or an inactive form of colchicine, or in colchicine-resistant cells. HIF-1 induction was dependent upon cellular transcription, as transcription inhibitors abrogated HIF-1alpha protein up-regulation. The ability of transcriptional inhibitors to interfere with HIF-1alpha accumulation was specific to the MDA-initiated pathway, as they were ineffective in preventing hypoxia-mediated HIF-1 induction, which occurs by a distinct post-translational pathway. Moreover, we provide evidence implicating a requirement for NFkappaB transcription in the HIF-1 induction mediated by MDAs. The ability of MDAs to induce HIF-1alpha is dependent upon activation of NFkappaB, since inhibition of NFkappaB either pharmacologically or by transfection of an NFkappaB super-repressor plasmid abrogated this induction. Collectively, these data support a model in which NFkappaB is a focal point for the convergence of MDA-mediated signaling events leading to HIF-1 induction, thus revealing a novel aspect of HIF-1alpha regulation and function.

Animals↗
PubMed2007

Enhanced bone regeneration associated with decreased apoptosis in mice with partial HIF-1alpha deficiency.

UNLABELLED: HIF-1alpha activates genes under hypoxia and was hypothesized to regulate bone regeneration. Surprisingly, HIF-1alpha+/- fracture calluses are larger, stronger, and stiffer than HIF-1alpha+/+ calluses because of decreased apoptosis. These data identify apoptosis inhibition as a means to enhance bone regeneration. INTRODUCTION: Bone regeneration subsequent to fracture involves the synergistic activation of multiple signaling pathways. Localized hypoxia after fracture activates hypoxia-inducible factor 1alpha (HIF-1alpha), leading to increased expression of HIF-1 target genes. We therefore hypothesized that HIF-1alpha is a key regulator of bone regeneration. MATERIALS AND METHODS: Fixed femoral fractures were generated in mice with partial HIF-1alpha deficiency (HIF-1alpha+/-) and wildtype littermates (HIF-1alpha+/+). Fracture calluses and intact contralateral femurs from postfracture days (PFDs) 21 and 28 (N=5-10) were subjected to microCT evaluation and four-point bending to assess morphometric and mechanical properties. Molecular analyses were carried out on PFD 7, 10, and 14 samples (N=3) to determine differential gene expression at both mRNA and protein levels. Finally, TUNEL staining was performed on PFD 14 samples (N=2) to elucidate differential apoptosis. RESULTS: Surprisingly, fracture calluses from HIF-1alpha+/- mice exhibited greater mineralization and were larger, stronger, and stiffer. Microarray analyses focused on hypoxia-induced genes revealed differential expression (between genotypes) of several genes associated with the apoptotic pathway. Real-time PCR confirmed these results, showing higher expression of proapoptotic protein phosphatase 2a (PP2A) and lower expression of anti-apoptotic B-cell leukemia/lymphoma 2 (BCL2) in HIF-1alpha+/+ calluses. Subsequent TUNEL staining showed that HIF-1alpha+/+ calluses contained larger numbers of TUNEL+ chondrocytes and osteoblasts than HIF-1alpha+/- calluses. CONCLUSIONS: We conclude that partial HIF-1alpha deficiency results in decreased chondrocytic and osteoblastic apoptosis, thereby allowing the development of larger, stiffer calluses and enhancing bone regeneration. Furthermore, apoptosis inhibition may be a promising target for developing new treatments to accelerate bone regeneration.

Animals↗
PubMedDate not supplied

Hypoxia-inducible factor (HIF-1) and its relationship to apoptosis and proliferation in lung cancer.

Hypoxia-inducible factor 1 (HIF-1) plays an important role in the pleiotropic response observed under hypoxia. In this study we examined whether a relationship exists between HIF-1 proteins and proliferation and apoptosis in lung cancer. To this purpose, we used immunohistochemistry to analyze HIF-1 alpha and HIF-1 beta in formalin-fixed, paraffin-embedded, non-small cell lung carcinomas (n = 96) and compared the HIF expression with cyclin A protein expression, cell cycle phases, the apoptotic index and the expression of caspase 3, Fas and Fas ligand. Additionally, we examined whether HIF-1 determinations can improve the prognostic information concerning a patient's overall survival. A relationship between HIF-1 alpha or HIF-1 beta and proliferation could not be observed. However, a significant correlation between HIF-1 expression, apoptosis and the pro-apoptotic factors caspase-3, Fas, and Fas ligand could be detected. Patients with HIF-positive carcinomas had significantly longer median survival times than patients with HIF-negative carcinomas (HIF-1 alpha: 191 vs. 60 weeks; P = 0.05; HIF-1 beta: 111 vs. 41 weeks; P = 0.003). Multivariate analyses demonstrated that the presence of HIF-1 at a given stage or extent of lymph node involvement is an independent prognostic factor for the survival of patients with non-small cell lung carcinomas.

Apoptosis↗
PubMed2004

Treatment with siRNA and antisense oligonucleotides targeted to HIF-1alpha induced apoptosis in human tongue squamous cell carcinomas.

Overexpression of hypoxia inducible factor-1alpha (HIF-1alpha) in cancers has been correlated to a more aggressive tumor phenotype. We investigated the effect of HIF-1alpha knockout on the in vitro survival and death of human tongue squamous cell carcinomas (SCC-4 and SCC-9). Under normoxic condition, a basal level of HIF-1alpha protein was constitutively expressed in SCC-9 cells, albeit an undetectable level of HIF-1alpha messages. Exposure to hypoxia induced only a transient increase in mRNA transcript but a prolonged elevation of HIF-1alpha protein and its immediate downstream target gene product, VEGF. Under normoxic or hypoxic conditions, treatment of SCC-9 cells with AS-HIF-1alpha ODN suppressed both constitutive and hypoxia-induced HIF-1alpha expression at both mRNA and protein levels. Knockout of HIF-1alpha gene expression via either AS-HIF-1alpha ODN or siRNA (siRNAHIF-1alpha) treatment resulted in inhibition of cell proliferation and induced apoptosis in SCC-4 and SCC-9 cells. We also demonstrated that exposure of SCC-9 cells to hypoxia led to a time-dependent increase in the expression of bcl-2 and IAP-2, but not p53. The attenuated levels of bcl-2 and IAP-2, and the enhanced activity of caspase-3 after treatment with AS-HIF-1alpha ODN may contribute partly to the effects of HIF-1alpha blockade on SCC-9 cell death. Collectively, our data suggest that a constitutive or hypoxia-induced expression of HIF-1alpha in SCC-9 and SCC-4 cells is sufficient to confer target genes expression essential for tumor proliferation and survival. As a result, interfering with HIF-1alpha pathways by antisense or siRNA strategy may provide a therapeutic target for human tongue squamous cell carcinomas.

Apoptosis↗
PubMed2005

In vitro study of HIF-1 activation and VEGF release by bFGF in the T47D breast cancer cell line under normoxic conditions: involvement of PI-3K/Akt and MEK1/ERK pathways.

Hypoxia-inducible factor (HIF) is critical in the modulation of tumour angiogenesis in response to hypoxia. In the present study, the mechanisms underlying basic fibroblast growth factor (bFGF)-induced activation of HIF-1 and the subsequent release of vascular endothelial growth factor (VEGF) in a human breast cancer cell line (T47D) under normoxic conditions were explored. The data show that HIF-1alpha expression is induced by bFGF in a dose- and time-dependent fashion, while increased HIF-1alpha protein expression and transactivity of HIF-1 are due to the phosphorylation of Akt by bFGF, as indicated by application of the phosphatidylinositol 3-kinase (PI-3K) inhibitor LY294002. The data also show that the MEK1 (mitogen-activated protein kinase kinase-1)/ERK (extracellular signal-regulated kinase) pathway is only involved in bFGF-induced transactivity of HIF-1, but not HIF-1alpha expression, indicating roles for both the PI-3K/Akt and the MEK1/ERK pathways in bFGF activity. In addition, the translation inhibitor cycloheximide confirmed that bFGF-induced HIF-1alpha protein expression was due to de novo protein synthesis. In contrast, p38 was not required for the expression of HIF-1alpha or HIF-1 transactivity, although significant phosphorylation of p38 was observed after bFGF treatment. Treatment of the cells with bFGF increased the amount of VEGF release, and this could be suppressed by either PD98059 or LY294002, suggesting the presence of a HIF-1alpha-dependent pathway for bFGF-induced VEGF production. In conclusion, the PI-3K/Akt and MEK1/ERK pathways, in a potentially independent and co-operative fashion, can modulate HIF-1 activation by bFGF. Further studies will pinpoint whether HIF-1 is the transcriptional factor responsible for the increased VEGF production following bFGF treatment of breast tumour cells.

Breast Neoplasms↗
PubMed2006

The zinc chelator, N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine, increases the level of nonfunctional HIF-1alpha protein in normoxic cells.

The hypoxia-inducible factor-1alpha (HIF-1alpha) subunit is activated in response to lack of oxygen. HIF-1alpha-specific prolyl hydroxylase and factor inhibiting HIF-1alpha (FIH-1) catalyze hydroxylation of the proline and asparagine residues of HIF-1alpha, respectively. The hydroxyproline then interacts with ubiquitin E3 ligase, the von Hippel-Lindau protein, leading to degradation of HIF-1alpha by ubiquitin-dependent proteasomes, while the hydroxylation of the asparagine residue prevents recruitment of the coactivator, cAMP-response element-binding protein (CBP), thereby decreasing the transactivation ability of HIF-1alpha. We found that the Zn-specific chelator, N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), enhances the activity of HIF-1alpha-proline hydroxylase 2 but the level of HIF-1alpha protein does not fall because TPEN also inhibits ubiquitination. Since the Zn chelator does not prevent FIH-1 from hydroxylating the asparagine residue of HIF-1alpha, its presence leads to the accumulation of HIF-1alpha that is both prolyl and asparaginyl hydroxylated and is therefore nonfunctional. In hypoxic cells, TPEN also prevents HIF-1alpha from interacting with CBP, so reducing expression of HIF-1alpha target genes. As a result, Zn chelation causes the accumulation of nonfunctional HIF-1alpha protein in both normoxia and hypoxia.

Cell Hypoxia↗
PubMed2005

Mutation analysis of the HIF-1alpha oxygen-dependent degradation domain in invasive breast cancer.

Hypoxia inducible factor-1 (HIF-1) is an important transcription factor that stimulates tumor growth and metastases via several pathways. Activation of HIF-1 depends on the presence of its alpha-subunit. Hypoxia increases HIF-1alpha levels by inhibiting prolyl-hydroxylase--mediated hydroxylation and thereby preventing proteosome degradation. Various other mechanisms might also contribute to HIF-1alpha expression, such as mutation of the oxygen dependent degradation domain (ODD), which prevents binding of prolyl-hydroxylases. Therefore, the presence of ODD mutations was evaluated as a possible explanation for diffuse HIF-1alpha protein expression often seen in invasive breast cancer. From a group of 200 primary breast cancers, 24 strong diffusely HIF-1alpha-positive tumor samples were identified with HIF-1alpha immunohistochemistry. DNA from these tumors was extracted from microdissected paraffin material and, after nested polymerase chain reaction, sequence analysis was performed to detect hif-1alpha ODD mutations. Additionally, five perinecrotically HIF-1alpha-positive breast cancers were analyzed as controls. All 24 diffuse and perinecrotic HIF-1alpha-positive breast cancers showed wild-type DNA sequences in the ODD domain. No mutations seem to occur in the ODD of hif-1alpha in HIF-1alpha overexpressing invasive breast cancer, which rules ODD mutations out as a possible explanation for the diffuse HIF-1alpha expression pattern often seen in this cancer.

Base Sequence↗
PubMed2006

6-Mercaptopurine, an activator of Nur77, enhances transcriptional activity of HIF-1alpha resulting in new vessel formation.

Hypoxia-inducible factor-1alpha (HIF-1alpha) plays a central role in oxygen homeostasis. Previously, we reported that the orphan nuclear receptor Nur77 functions in stabilizing HIF-1alpha. Here, we demonstrate that 6-mercaptopurine (6-MP), an activator of the NR4A family members, enhances transcriptional activity of HIF-1. 6-MP enhanced the protein-level of HIF-1alpha as well as vascular endothelial growth factor (VEGF) in a dose- and time-dependent manner. The induction of HIF-1alpha was abolished by the transfection of either a dominant-negative Nur77 mutant or si-Nur77, indicating a critical role of Nur77 in the 6-MP action. The HIF-1alpha protein level remained up to 60 min in the presence of 6-MP when de novo protein synthesis was blocked by cycloheximide, suggesting that 6-MP induces stabilization of the HIF-1alpha protein. The fact that 6-MP decreased the association of HIF-1alpha with von Hippel-Lindau protein and the acetylation of HIF-1alpha, may explain how 6-MP induced stability of HIF-1alpha. Further, 6-MP induced the transactivation function of HIF-1alpha by recruiting co-activator cyclic-AMP-response-element-binding protein. Finally, 6-MP enhanced the expression of HIF-1alpha and VEGF, and the formation of capillary tubes in human umbilical vascular endothelial cells. Together, our results provide a new insight for 6-MP action in the stabilization of HIF-1alpha and imply a potential application of 6-MP in hypoxia-associated human vascular diseases.

Cell Line, Tumor↗