Tetramethylpyrazine suppresses HIF-1alpha, TNF-alpha, and activated caspase-3 expression in middle cerebral artery occlusion-induced brain ischemia in rats

AIM

To examine the detailed mechanisms underlying the inhibitory effect of tetramethylpyrazine (TMPZ) in inflammatory and apoptotic responses induced by middle cerebral artery occlusion (MCAO) in rats.

METHODS

MCAO-induced focal cerebral ischemia in rats was used in this study. The hypoxia-inducible factor-1alpha(HIF-1alpha), activation of caspase-3, and TNF-alpha mRNA transcription in ischemic regions were detected by immunoblotting and RT-PCR, respectively. Anti-oxidative activity was investigated using a thiobarbituric acid-reactive substance (TBARS) test in rat brain homogenate preparations.

RESULTS

We showed the statistical results of the infarct areas of solvent- and TMPZ (20 mg/kg)-treated groups at various distances from the frontal pole in MCAO-induced focal cerebral ischemia in rats. Treatment with TMPZ (20 mg/kg) markedly reduced the infarct area in all regions, especially in the third to fifth sections. MCAO-induced focal cerebral ischemia was associated with increases in HIF-1alpha and the activation of caspase-3, as well as TNF-alpha transcription in ischemic regions. These expressions were markedly inhibited by treatment with TMPZ (20 mg/kg). However, TMPZ (0.5-5 mmol/L) did not significantly inhibit TBARS reaction in rat brain homogenates.

CONCLUSION

The neuroprotective effect of TMPZ may be mediated at least by a portion of the inhibition of HIF-1alpha and TNF-alpha activations, followed by the inhibition of apoptosis formation (active caspase-3), resulting in a reduction in the infarct volume in ischemia-reperfusion brain injury. Thus, TMPZ treatment may represent an ideal approach to lowering the risk of or improving function in ischemia- reperfusion brain injury-related disorders.

The involvement of hypoxia-inducible factor-1alpha in the susceptibility to gamma-rays and chemotherapeutic drugs of oral squamous cell carcinoma cells

The transcription factor hypoxia-inducible factor-1alpha (HIF-1alpha) is the key regulator that controls the hypoxic response of mammalian cells. The overexpression of HIF-1alpha has been demonstrated in many human tumors. However, the role of HIF-1alpha in the therapeutic efficacy of chemotherapy and radiotherapy in cancer cells is poorly understood. In this study, we investigated the influence of HIF-1alpha expression on the susceptibility of oral squamous cell carcinoma (OSCC) cells to chemotherapeutic drugs (cis-diamminedichloroplatinum and 5-fluorouracil) and gamma-rays. Treatment with chemotherapeutic drugs and gamma-rays enhanced the expression and nuclear translocation of HIF-1alpha, and the susceptibility of OSCC cells to the drugs and gamma-rays was negatively correlated with the expression level of HIF-1alpha protein. The overexpression of HIF-1alpha induced OSCC cells to become more resistant to the anticancer agents, and down-regulation of HIF-1alpha expression by small interfering RNA enhanced the susceptibility of OSCC cells to them. In the HIF-1alpha-knockdown OSCC cells, the expression of P-glycoprotein, heme oxygenase-1, manganese-superoxide dismutase and ceruloplasmin were downregulated and the intracellular levels of chemotherapeutic drugs and reactive oxygen species were sustained at higher levels after the treatment with the anticancer agents. These results suggest that enhanced HIF-1alpha expression is related to the resistance of tumor cells to chemo- and radio-therapy and that HIF-1alpha is an effective therapeutic target for cancer treatment.

Nutlin3 blocks vascular endothelial growth factor induction by preventing the interaction between hypoxia inducible factor 1alpha and Hdm2

Hdm2 is elevated in numerous types of malignancies and is thought to impede the function of wild-type p53. Reactivation of p53 by disrupting the association with Hdm2 was the impetus for the development of Nutlin3. Although regulation of p53 has been the central focus of Hdm2 activity, it also binds other proteins through its p53-binding domain. Here, we show that hypoxia-inducible factor 1alpha (HIF1alpha) binds to Hdm2 in the domain designated to bind p53. HIF1alpha and p53 share a conserved motif that is required to bind Hdm2. Distinct complexes form between Hdm2-HIF1alpha and Hdm2-p53 as determined by immunoprecipitation of nuclear extracts and in vitro. The Hdm2 antagonist Nutlin3 prevents the association between Hdm2 and HIF1alpha. The vascular endothelial growth factor (VEGF) gene is a transcriptional target of HIF1alpha, and under normoxic or hypoxic conditions, Hdm2 increases HIF1alpha activity to induce VEGF production. Blocking the association of Hdm2 and HIF1alpha by Nutlin3, or ablating Hdm2 expression, diminished the level of VEGF under conditions of normoxia or hypoxia. Our findings establish a unique role for Nutlin3 in attenuating VEGF induction by preventing the association of Hdm2 with HIF1alpha.

Identification of a new natural camptothecin analogue in targeted screening for HIF-1alpha inhibitors

Screening to detect compounds that inhibit the HIF-1alpha transcriptional activation pathway identified an extract of Ophiorrhiza trichocarpon for investigation. A high throughput dereplication strategy was employed, involving chromatography with spectral data acquisition supported by bioactivity testing and literature referencing, which led to rapid identification of camptothecin (1) and three analogues (2 - 4) as the active compounds. 9,10-Methylenedioxy-(20S)-camptothecin (4) was found for the first time from a plant.

Prolyl Hydroxylase Domain 2 Protein Suppresses Hypoxia-Induced Endothelial Cell Proliferation

Prolyl hydroxylase domain 2 protein (PHD2) signals the degradation of hypoxia-inducible factor (HIF)-1α by hydroxylating specific prolyl residues located within oxygen-dependent degradation domains. As expected, endothelial cells (ECs) overexpressing PHD2 had reduced HIF-1α and vascular endothelial growth factor-A expression and failed to accelerate their proliferation in response to hypoxia. Surprisingly, although these cells displayed further reductions in HIF-1α and vascular endothelial growth factor-A expression when cultured under normoxia, there was no further reduction in EC proliferation. Thus, there seemed to be no consistent correlation between PHD2 hydroxylase–mediated suppression of HIF-1α expression and inhibition of EC growth. Indeed, overexpression of a mutant PHD2 lacking hydroxylase activity also greatly diminished EC response to hypoxia-induced increase in proliferation, in spite of the fact that hypoxia-induced HIF-1α accumulation was not affected by mutant PHD2. These data strongly suggest the existence of a hydroxylase-independent mechanism for PHD2-mediated inhibition of EC proliferation under hypoxia. In support of a physiological relevance of PHD2 overexpression, we found that endogenous PHD2 expression was significantly upregulated by hypoxia and that silencing of the Phd2 gene by RNA interference significantly enhanced hypoxia-induced EC proliferation. In conclusion, this study demonstrates that PHD2 may act as a negative feedback regulator to antagonize hypoxia-induced EC proliferation.

Vitexin, an HIF-1alpha inhibitor, has anti-metastatic potential in PC12 cells

Vitexin, a natural flavonoid compound identified as apigenin-8-C-b-D-glucopyranoside, has been reported to exhibit antioxidative and anti-inflammatory properties. In this study, we investigated its effect on hypoxia-inducible factor-1a (HIF-1a) in rat pheochromacytoma (PC12), human osteosarcoma (HOS) and human hepatoma (HepG2) cells. Vitexin inhibited HIF-1a in PC12 cells, but not in HOS or HepG2 cells. In addition, it diminished the mRNA levels of hypoxia-inducible genes such as vascular endothelial growth factor (VEGF), smad3, aldolase A, enolase 1, and collagen type III in the PC12 cells. We found that vitexin inhibited the migration of PC12 cells as well as their invasion rates, and it also inhibited tube formation by human umbilical vein endothelium cells (HUVECs). Interestingly, vitexin inhibited the hypoxia-induced activation of c-jun N-terminal kinase (JNK), but not of extracellular-signal regulated protein kinase (ERK), implying that it acts in part via the JNK pathway. Overall, these results suggest the potential use of vitexin as a treatment for diseases such as cancer.

Inhibition of hypoxia-induced angiogenesis by trichostatin A via suppression of HIF-1a activity in human osteosarcoma

The purpose of this study is to determine whether trichostatin A (TSA), a HDAC specific inhibitor, inhibited the induction and functional activity of hypoxia-inducible factor-1 a(HIF-1a) and hypoxia-induced angiogenesis in vitro in human osteosarcoma. The relationship between expression of HIF-1a proteion and angiogenesis in tumor specimens was also studied. Hypoxic regulation of VEGF was studied by RT-PCR, western blotting analysis and enzyme linked immunosorbent assay. The expression of HIF-la and VEGF in human osteosarcoma specimens was studied by immunohistochemical analysis. Under hypoxia, no regulation of HIF-1a mRNA expression was found. However, HIF-1a protein levels increased dramatically in response to hypoxia. Hypoxia increased VEGF mRNA level, but it was significantly inhibited by trichostatin A in a time- and dose-dependent manner (p < 0.05). Strongly positive immunostaining for HIF-1a and VEGF were detectable in the nuclear and cytoplasm of osteosarcoma cells. HIF-1a expressing cells were prominent in areas with high MVD. Significant correlation were found between HIF-1a expression and MVD (p = 0.005, r = 0.767), as well as between VEGF and MVD (p < 0.002, r = 0.701) by Spearman's rank coefficient analysis. These results indicated that HIF-1a is a key factor responsible for angiogenesis by the induction of VEGF. TSA downregulates hypoxia-response genes and hypoxia-induced angiogenesis by the suppression of HIF-1a activity.

Role of hypoxia-inducible factor-1alpha as a cancer therapy target

Hypoxia occurs in solid tumours due to a mismatch between tumour growth and angiogenesis. Hypoxia in solid tumours is associated with an aggressive phenotype and resistance to radiation therapy and chemotherapy leading to poor patient prognosis. Hypoxia-inducible factor-1 (HIF-1) is a transcription factor, which is activated in response to intratumoural hypoxia and as a result of genetic alterations that activate oncogenes and inactivate tumour suppressor genes. It plays a key role in the adaptation of tumour cells to hypoxia by activating the transcription of genes, which regulate several biological processes including angiogenesis, cell proliferation and survival, glucose metabolism, pH regulation and migration. This makes HIF-1 an attractive target for the development of anticancer agents. The success of these agents depends on reliable methods to identify those patients most likely to benefit from HIF-1-targeted therapy. Several novel small molecule inhibitors of HIF-1 have been identified and are moving towards clinical trials, but none of these are specific for HIF-1. Further work is ongoing to identify more selective HIF-1 inhibitors.

Microwave expedited synthesis of 5-aminocamptothecin analogs: Inhibitors of hypoxia inducible factor HIF-1α

A series of 5-aminosubstituted camptothecin analogs were prepared from the corresponding 5-hydroxycamptothecin using microwave irradiation. The analogs were assayed for ability to inhibit the action of hypoxia inducible factors (HIF-1alpha and HIF-2alpha). The 5-fluoroethyl analog showed potent inhibitory activity and is now the focus of ongoing pathway analysis and potential as an antiproliferative agent.

Role of HIF-1 in Iron Regulation: Potential Therapeutic Strategy for Neurodegenerative Disorders

A disruption in optimal iron levels within different brain regions has been demonstrated in several neurodegenerative disorders. Although iron is an essential element that is required for many processes in the human body, an excess can lead to the generation of free radicals that can damage cells. Iron levels are therefore stringently regulated within cells by a host of regulatory proteins that keep iron levels in check. The iron regulatory proteins (IRPs) have the ability to sense and control the level of intracellular iron by binding to iron responsive elements (IREs) of several genes encoding key proteins such as the transferrin receptor (TfR) and ferritin. Concurrently, the hypoxia-inducible factor (HIF) has also been shown in previous studies to regulate intracellular iron by binding to HIF-responsive elements (HREs) that are located within the genes of iron-related proteins such as TfR and heme oxygenase-1 (HO-1). This review will focus on the interactions between the IRP/IRE and HIF/HRE systems and how cells utilize these intricate networks to regulate intracellular iron levels. Additionally, since iron chelation has been suggested to be a therapeutic treatment for disorders such as Parkinson's and Alzheimer's disease, understanding the exact mechanisms by which iron acts to cause disease and how the brain would be impacted by iron chelation could potentially give us novel insights into new therapies directed towards preventing or slowing neuronal cell loss associated with these disorders.

Anthracyclines, small-molecule inhibitors of hypoxia-inducible factor-1 alpha activation

Hypoxia-inducible factor-1 (HIF-1) is a central mediator of cellular responses to low oxygen and has recently become an important therapeutic target for solid tumor therapy. To identify small molecule inhibitors of the HIF-1 transcriptional activation, we have established a high through-put assay system using a stable transformant of mammalian cells that express the luciferase reporter gene construct containing a HIF-1 binding site. Using this system, we screened 5000 cultured broths of microorganisms, and we found that cinerubin (1-hydroxy aclacinomycin B) showed a significant inhibition of the reporter activity induced by hypoxic conditions. In addition, we demonstrated that aclarubicin also inhibited the HIF-1 transcriptional activity under hypoxic conditions, but neither doxorubicin nor daunorubicin inhibited it. Consistent with these results, cinerubin and aclarubicin inhibited the hypoxic induction of the vascular endothelial growth factor (VEGF) protein in HepG2 cells, but neither doxorubicin nor daunorubicin affected it. Thus, our results suggested that some anthracyclines are also acting as angiogenesis inhibitors.

Regulation of lipopolysaccharide-induced increases in neutrophil glucose uptake

The pathogenesis of many lung diseases involves neutrophilic inflammation. Neutrophil functions, in turn, are critically dependent on glucose uptake and glycolysis to supply the necessary energy to meet these functions. In this study, we determined the effects of p38 mitogen-activated protein kinase and hypoxia-inducible factor (HIF)-1, as well as their potential interaction, on the expression of membrane glucose transporters and on glucose uptake in murine neutrophils. Neutrophils were harvested and purified from C57BL/6 mice and stimulated with lipopolysaccharide (LPS) in the presence or absence of specific p38 and HIF-1 inhibitors. Glucose uptake was measured as the rate of [3H]deoxyglucose (DG) uptake. We identified GLUT-1 in mouse neutrophils, but neither GLUT-3 nor GLUT-4 were detected using Western blot analysis, even after LPS stimulation. LPS stimulation did not increase GLUT-1 protein levels but did cause translocation of GLUT-1 from the cell interior to the cell surface, together with a dose-dependent increase in [3H]DG uptake, indicating that glucose uptake is regulated in these cells. LPS also activated both p38 and the HIF-1 pathway. Inhibitors of p38 and HIF-1 blocked GLUT-1 translocation and [3H]DG uptake. These data suggest that LPS-induced increases in neutrophil glucose uptake are mediated by GLUT-1 translocation to the cell surface in response to sequential activation of neutrophil p38 and HIF-1alpha in neutrophils. Given that neutrophil function and glucose metabolism are closely linked, control of the latter may represent a new target to ameliorate the deleterious effects of neutrophils on the lungs.

Inhibitory Activity of the Hypoxia-inducible Factor-1 Pathway by Tartrolone C

Hypoxia-inducible factor-1 (HIF-1) is a central mediator of cellular responses to low oxygen and has recently become an important therapeutic target for solid tumor therapy. To identify small molecule inhibitors of the HIF-1 transcriptional activation, we have established a high through-put assay system using a stable transformant of mammalian cells that express a luciferase reporter gene construct containing a HIF-1 binding site. Using this system, we screened 5000 cultured broths of microorganisms, and we found that fermentation broth produced by Streptomyces strain 1759-27 showed significant inhibition of the reporter activity induced by hypoxic conditions. The active substance NBRI759-27 was purified and determined to be tartrolone C by several methods including X-ray crystallography. In the reporter gene assay, tartrolone C inhibited the HIF-1 transcriptional activity under hypoxic conditions with an IC50 value of 0.17 microg/ml.

Apigenin inhibits tumor angiogenesis through decreasing HIF-1alpha and VEGF expression

Apigenin is a non-toxic dietary flavonoid with anti-tumor properties. We recently showed that apigenin-inhibited hypoxia-inducible factor-1 (HIF-1) and vascular endothelial growth factor (VEGF) expression in human ovarian cancer cells under normoxic condition. However, the effect of apigenin in angiogenesis remains to be elucidated. Angiogenesis is the formation of new blood vessels and is required for tumor growth and metastasis. In this study, we showed that apigenin-inhibited expression of HIF-1 and VEGF in different cancer cells under both normoxic and hypoxic conditions. We demonstrated that apigenin significantly inhibited tumor angiogenesis in vivo, by using both the chicken chorioallantoic membrane and Matrigel plug assays. The inhibition of tumor angiogenesis was associated with the decrease of HIF-1 and VEGF in tumor tissues. Taken together, our results show that apigenin suppresses tumor angiogenesis through HIF-1 and VEGF expression.

Immunophilin-ligands FK506 and CsA inhibit HIF1alpha expression by a VHL- and ubiquitin-independent mechanism

Hypoxia inducible factor-1alpha (HIF1alpha) plays a key role in the regulation of genes controlling oxygen supply, glucose metabolism and angiogenesis. Its expression in tumors appears to confer an adaptive advantage to their hypoxic microenvironment. We have evaluated the effect of the immunophilin ligands FK506 and cyclosporin A on HIF1alpha levels in different tumor cell lines. Our results indicate that both drugs are potent suppressors of HIF1alpha expression by accelerating the proteasomal degradation of the protein. Unexpectedly, the suppressive effect of these compounds was found to be independent of the presence of von Hippel Lindau factor and the degree of hydroxylation of the HIF1alpha protein. Moreover, HIF1alpha degradation induced by these compounds did not required ubiquitination, as it was also induced in E1 ligase-incompetent cells.

Development of novel therapeutic strategies that target HIF-1

Activity of hypoxia-inducible factor 1 (HIF-1) is increased in human cancers as a result of the physiological induction of HIF-1alpha in response to intratumoural hypoxia and as a result of genetic alterations that activate oncogenes and inactivate tumour suppressor genes. In many cancer types, increased HIF-1alpha expression is associated with increased risk of patient mortality. HIF-1 plays important roles in every major aspect of cancer biology through the transcriptional regulation of hundreds of genes. The efficacy of many novel anticancer agents that target signal transduction pathways may be due in part to their indirect inhibition of HIF-1. Several novel compounds with anticancer activity have been shown to inhibit HIF-1 and may be useful as components of individualised multidrug therapeutic regimens chosen based on molecular analyses of tumour biopsies.

Identification of novel small-molecule inhibitors of hypoxia-inducible factor-1 transactivation and DNA binding

Hypoxia-inducible factor-alpha (Hif-alpha) plays an important role in tumor growth by increasing resistance to apoptosis and the production of angiogenic factors, such as vascular endothelial growth factor (VEGF). Therefore, Hif-alpha is an attractive target for development of novel cancer therapeutics. We have generated Chinese hamster ovary cells, which stably express luciferase reporter construct under the control of a hypoxia response element to screen 15,000 compounds. We identified 40 compounds that inhibited hypoxic up-regulation of luciferase, and the top 30 compounds were further screened in a secondary assay using MDA-468 breast cancer cell line. Eight compounds were shown to inhibit VEGF expression in hypoxic cells at subtoxic concentrations. Three top putative Hif inhibitors, DJ12, DJ15, and DJ30, were chosen for further analysis. Transient transfection of cells with hypoxia-regulated luciferase reporter plasmids further validated that these compounds inhibit hypoxia up-regulated genes. All three compounds failed to inhibit Hif-1alpha protein levels but they did inhibit induction of downstream targets of Hif-alpha under hypoxia. Two of the three compounds were cell type specific, whereas compound DJ12 inhibited VEGF at subtoxic levels in breast cancer cell lines MDA-468 and ZR-75, melanoma cell line MDA-435, and pVHL mutant renal cancer cell lines RCC4 and 786-0. Compound DJ12 down-regulated mRNA of downstream targets of Hif-alpha, and significantly inhibited Hif-1alpha transactivation activity by blocking Hif-1alpha hypoxia response element-DNA binding. Our cell-based approach and deconvolution of the inhibitory effect of DJ12 has identified a novel compound that targets the hypoxia pathway by inhibiting Hif-alpha-inducible transcription.

Inhibition of angiogenesis and HIF-1alpha activity by antimycin A1

We identified antimycin A1 as an inhibitor of the hypoxia-response element (HRE) from screening using a reporter under the control of HRE under hypoxic conditions. Antimycin A1 was effective at 20 pg/ml in inhibiting the reporter activity. The expression of vascular endothelial growth factor (VEGF) mRNA during hypoxia was also inhibited by antimycin A1. Angiogenesis induced by implantation of mouse sarcoma-180 cells was significantly inhibited by non-toxic doses of antimycin A1. Hypoxia inducible factor (HIF)-1alpha protein levels were significantly decreased by antimycin A1, but its mRNA level was not affected. Antimycin A1 is known to be an inhibitor of mitochondrial electron transport system, and depletion of mitochondria abolished antimycin A1-effect, at least in part. Inhibitors of proteasome or protein synthesis did not affect the decrease in HIF-1alpha level induced by antimycin A1. These results indicate that antimycin A1 inhibited angiogenesis through decrease in VEGF production caused by inhibition of HIF-1alpha activation.

Inhibiting hypoxia-inducible factor 1 for cancer therapy

Hypoxia has long been recognized as a common feature of solid tumors and a negative prognostic factor for response to treatment and survival of cancer patients. The discovery of hypoxia-inducible factor 1 (HIF-1), a molecular determinant of the response of mammalian cells to hypoxia, has led to the identification of a "molecular target" of hypoxia suitable for the development of cancer therapeutics. Early controversy about whether or not HIF-1 is a good target for therapy has not discouraged academic groups and pharmaceutical companies from actively engaging in the discovery of small-molecule inhibitors of HIF. However, what is the best strategy to inhibit HIF and how HIF inhibitors should be developed for treatment of human cancers is still poorly defined. In this review, aspects related to the identification and early development of novel HIF inhibitors are discussed. Identification and validation of pharmacodynamic end points relevant to the HIF-1 pathway is essential for a rational development of HIF inhibitors. Integration of these biomarkers in early clinical trials may provide valuable information to determine the contribution of HIF inhibitors to response to therapy. Finally, HIF inhibitors should be incorporated in combination strategies to effectively target multiple cellular components of the tumor microenvironment and redundant signaling pathways frequently deregulated in human cancer.

Loss of VHL confers hypoxia-inducible factor (HIF)-dependent resistance to vesicular stomatitis virus: role of HIF in antiviral response

Hypoxia-inducible factor (HIF) is a central regulator of cellular responses to hypoxia, and under normal oxygen tension the catalytic alpha subunit of HIF is targeted for ubiquitin-mediated destruction via the VHL-containing E3 ubiquitin ligase complex. Principally known for its association with oncogenesis, HIF has been documented to have a role in the antibacterial response. Interferons, cytokines with antiviral functions, have been shown to upregulate the expression of HIF-1alpha, but the significance of HIF in the antiviral response has not been established. Here, using renal carcinoma cells devoid of VHL or reconstituted with functional wild-type VHL or VHL mutants with various abilities to negatively regulate HIF as an ideal model system of HIF activity, we show that elevated HIF activity confers dramatically enhanced resistance to vesicular stomatitis virus (VSV)-mediated cytotoxicity. Inhibition of HIF activity using a small-molecule inhibitor, chetomin, enhanced cellular sensitivity to VSV, while treatment with hypoxia mimetic CoCl2 promoted resistance. Similarly, targeting HIF-2alpha by RNA interference also enhanced susceptibility to VSV. Expression profiling studies show that upon VSV infection, the induction of genes with known antiviral activity, such as that encoding beta interferon (IFN-beta), is significantly enhanced by HIF. These results reveal a previously unrecognized role of HIF in the antiviral response by promoting the expression of the IFN-beta gene and other genes with antiviral activity upon viral infection.

HIF-1alpha contributes to tumour-selective killing by the sigma receptor antagonist rimcazole

We have previously reported tumour-selective killing by the sigma (sigma) receptor ligand rimcazole. We now report that rimcazole elevates hypoxia inducible factor-1alpha (HIF-1alpha) protein levels under normoxic conditions in colorectal (HCT-116) and mammary carcinoma (MDA MB 231) cells but fails to induce HIF-1alpha in normal fibroblasts or mammary epithelial cells. Combining the sigma-1 agonist (+)-pentazocine with rimcazole substantially reduces the accumulation of HIF-1alpha, confirming that the effect is mediated at least partly by antagonism of sigma-1 sites. HIF-1alpha knockdown by RNA interference attenuates rimcazole-induced cell death in both cell types. Thus, the induction of HIF-1alpha by rimcazole contributes to tumour cell killing. In a comparison of HCT-116p53+/+ and HCT-116p53-/- cells, HIF-1alpha levels are consistently higher after rimcazole treatment in HCT-116p53+/+ cells. Furthermore, although rimcazole kills HCT-116p53-/- cells, it has a more potent apoptosis-inducing effect in HCT-116p53+/+ cells. This suggests that the presence of functional p53 protein may enhance death induction by rimcazole in part through greater induction of HIF-1alpha. p53 is not required, however, for the rimcazole-induced engagement of HIF-1alpha in proapoptotic mode as HIF-1alpha knockdown attenuates rimcazole-induced death to comparable extents in p53 mutant and wild-type cell systems. Knowledge of HIF-1alpha involvement may assist the re-profiling of rimcazole and other sigma ligands as cancer therapeutics.

Role of ETS transcription factors in the hypoxia-inducible factor-2 target gene selection

Tumor hypoxia often directly correlates with aggressive phenotype, metastasis progression, and resistance to chemotherapy. Two transcription factors [hypoxia-inducible factor-1alpha (HIF-1alpha) and HIF-2alpha] are dramatically induced in hypoxic areas and regulate the expression of genes necessary for tumor adaptation to the conditions of low oxygen; however, the relative contribution of these factors is controversial. We used RNA interference-mediated inactivation of HIF-1alpha or HIF-2alpha followed by microarray analysis to identify genes specifically regulated by either HIF-1 or HIF-2 in hypoxia. We found that, in the MCF7 cell line, the vast majority of hypoxia-responsive genes (>80%) were dependent on the presence of HIF-1alpha. However, a small group of genes were preferentially regulated by HIF-2alpha. Promoter analysis for this group of genes revealed that all of them have putative binding sites for ETS family transcription factors, and 10 of 11 HIF-2alpha-dependent genes had at least one potential hypoxia-responsive element (HRE) in proximity to an ETS transcription factor binding site. Knockdown of ELK-1, the most often represented member of ETS family, significantly reduced hypoxic induction of the HIF-2alpha-dependent genes. Physical and functional interaction between ELK-1 and HIF-2alpha were supported by coimmunoprecipitation of these two proteins, luciferase reporter assay using CITED2 promoter, and binding of ELK-1 protein to the promoters of CITED2 and WISP2 genes in proximity to a HRE. These data suggest that the choice of the target genes by HIF-1 or HIF-2 depends on availability and cooperation of HIFs with other factors recognizing their cognate elements in the promoters.

YC-1 Induces S Cell Cycle Arrest and Apoptosis by Activating Checkpoint Kinases

Hypoxia-inducible factor-1alpha (HIF-1alpha) seems central to tumor growth and progression because it up-regulates genes essential for angiogenesis and the hypoxic adaptation of cancer cells, which is why HIF-1alpha inhibition is viewed as a cancer therapy strategy. Paradoxically, HIF-1alpha also leads to cell cycle arrest or the apoptosis of cancer cells. Thus, the possibility cannot be ruled out that HIF-1alpha inhibitors unlock cell cycle arrest under hypoxic conditions and prevent cell death, which would limit the anticancer effect of HIF-1alpha inhibitors. Previously, we reported on the development of YC-1 as an anticancer agent that inhibits HIF-1alpha. In the present study, we evaluated the effects of YC-1 on hypoxia-induced cell cycle arrest and cell death. It was found that YC-1 does not reverse the antiproliferative effect of hypoxia, but rather that it induces S-phase arrest and apoptosis at therapeutic concentrations that inhibit HIF-1alpha and tumor growth; however, YC-1 did not stimulate cyclic guanosine 3',5'-monophosphate production in this concentration range. It was also found that YC-1 activates the checkpoint kinase-mediated intra-S-phase checkpoint, independently of ataxia-telangiectasia mutated kinase or ataxia-telangiectasia mutated and Rad3-related kinase. These results imply that YC-1 does not promote the regrowth of hypoxic tumors because of its cell cycle arrest effect. Furthermore, YC-1 may induce the combined anticancer effects of HIF-1alpha inhibition and cell growth inhibition.

[Reversion the multidrug resistance of human breast carcinoma cells by RNA interference targeting HIF-1 alpha gene]

OBJECTIVE

To reverse the multidrug resistant (MDR) phenotype of human breast carcinoma cells by small hairpin RNA (shRNA) technique targeting hypoxia-inducible factor (HIF)-1alpha gene.

METHODS

Small hairpin RNA (shRNA) eukaryotic expression vector targeting HIF-1alpha gene, named pSilencer-HIF, was constructed and transfected into MCF-7/ADR human breast cancer cells by liposome technique. Tumor cell livability (TCL) and Rhodamine 123 efflux assay were used to monitor the biological changes of the transfected cells. The mRNA and protein expression of HIF-1alpha and mdr-1 were investigated by RT-PCR and Western blot.

RESULTS

The successful construction of pSilencer-HIF plasmid was confirmed by DNA sequencing. HIF-1alpha mRNA and protein levels were significantly decreased in MCF-7/ADR cells after the transfection and there was a direct correlation between HIF-1alpha and mdr-1 expression. By comparing the cells transfected with control vector and the MCF-7/ADR cells transfected with pSilencer-HIF, a reduced TCL from 76% to 43%, and an increased Rhodamine 123 fluorescence intensity from 22.0% to 86.6% were observed.

CONCLUSIONS

pSilencer-HIF-1alpha has been successfully constructed. The inhibition of HIF-1alpha expression through shRNA technique can significantly reverse the multidrug resistance phenotype of MCF-7/ADR cells.

Expression of Vascular Endothelial Growth Factor Receptor 1 in Bone Marrow-derived Mesenchymal Cells Is Dependent on Hypoxia-inducible Factor 1

Bone marrow-derived cells are recruited to sites of ischemia, where they promote tissue vascularization. This response is dependent upon the expression of vascular endothelial growth factor (VEGF) receptor 1 (VEGFR1), which mediates cell migration in response to VEGF or placental growth factor (PLGF). In this study, we found that exposure of cultured mouse bone marrow-derived mesenchymal stromal cells (MSC) to hypoxia or an adenovirus encoding a constitutively active form of hypoxia-inducible factor 1 (HIF-1) induced VEGFR1 mRNA and protein expression and promoted ex vivo migration in response to VEGF or PLGF. MSC in which HIF-1 activity was inhibited by a dominant negative or RNA interference approach expressed markedly reduced levels of VEGFR1 and failed to migrate or activate AKT in response to VEGF or PLGF. Thus, loss-of-function and gain-of-function approaches demonstrated that HIF-1 activity is necessary and sufficient for basal and hypoxia-induced VEGFR1 expression in bone marrow-derived MSC.