Stabilization of vascular endothelial growth factor mRNA by hypoxia-inducible factor 1.

Hypoxia regulates expression of vascular endothelial growth factor (VEGF) by increasing its transcription and by stabilizing its mRNA. Despite the pivotal role of hypoxia-inducible factor 1 (HIF-1) in transcriptional activation of hypoxia-responsive genes, it is not known whether HIF-1 mediates hypoxia-induced stabilization of VEGF mRNA. We constructed adenoviral vectors expressing either the wild-type HIF-1 alpha (Ad2/HIF-1 alpha/FL), a constitutively stable hybrid form of HIF-1 alpha (Ad2/HIF-1 alpha/VP16), or no transgene (Ad2/CMVEV). In rat glioma (C6) cells and human cardiac, vascular smooth muscle, and endothelial cells, infection with Ad2/HIF-1 alpha/VP16 or Ad2/HIF-1 alpha/FL increased VEGF expression at both the mRNA and protein levels. Under normoxic conditions, the half-life of VEGF mRNA was 42 min in C6 cells. Hypoxia and Ad2/HIF-1 alpha/VP16 increased the half-life of VEGF mRNA to 3.3 and 2.7 h, respectively, while Ad2/CMVEV had no effect. These studies are the first to demonstrate that overexpression of HIF-1 alpha increases VEGF mRNA stability. Our results also suggest that stabilization of VEGF mRNA by hypoxia is mediated, at least in part, by HIF-1.

Liu LX ，Lu H ，Luo Y ，Date T ，Belanger AJ ，Vincent KA ，Akita GY ，Goldberg M ，Cheng SH ，Gregory RJ ，Jiang C ... -  《BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS》

Relation of vascular endothelial growth factor production to expression and regulation of hypoxia-inducible factor-1 alpha and hypoxia-inducible factor-2 alpha in human bladder tumors and cell lines.

Hypoxia is an important regulator of vascular endothelial growth factor (VEGF) expression, and VEGF is associated with poor prognosis in bladder cancer. To investigate further the mechanisms of VEGF regulation, we examined VEGF expression by mRNA and protein analysis in four human bladder cancer cell lines, showing a progression from well to poorly differentiated phenotypes under varying conditions of confluence and hypoxia (0.1% O(2)) and with chemical mimics of hypoxia. Hypoxia significantly increased VEGF protein expression in all cell lines, although this effect was dependent on the degree of confluence. The superficial bladder cancer cell line RT4 lost hypoxia inducibility at confluence, whereas inducibility was maintained in the invasive cell lines 253J and EJ28. This pattern of VEGF expression in the invasive cell lines correlated with the expression of the transcription factor hypoxia inducible factor-1 alpha (HIF-1 alpha) and with hypoxia-inducible factor-2 alpha (HIF-2 alpha) and in RT4 correlated with a marked reduction in HIF-1 alpha inducibility at confluence. Using the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor LY 294002, we show that this VEGF hypoxia-inducible pathway regulated by HIF-1 alpha is distinct from a PI 3-kinase-dependent pathway, which regulates basal amounts of VEGF, but does not affect inducibility. Both HIF-1 alpha and HIF-2 alpha protein and mRNA were up-regulated in primary human bladder tumors (n = 12) compared with normal bladder specimens (n = 4), with significant intertumor variation. These results suggest that components of the hypoxia response pathway, including HIF-1 alpha and HIF-2 alpha, are important cofactors in the regulation of VEGF in bladder cancer and are therapeutic targets in this disease.

Jones A ，Fujiyama C ，Blanche C ，Moore JW ，Fuggle S ，Cranston D ，Bicknell R ，Harris AL ... -  《CLINICAL CANCER RESEARCH》

Up-regulation of vascular endothelial growth factor expression in a rat glioma is conferred by two distinct hypoxia-driven mechanisms.

Up-regulation of vascular endothelial growth factor (VEGF) expression is a major event leading to neovascularization in malignant gliomas. Hypoxia is believed to be the crucial environmental stimulus for this up-regulation. To critically assess this hypothesis, we asked whether the mechanisms defined previously for hypoxia-induced VEGF expression in vitro are similarly involved and sufficient for up-regulation of VEGF gene expression in vivo, using a lacZ reporter gene under the control of VEGF regulatory sequences in an experimental glioma model. Inclusion of the binding site for hypoxia-inducible factor 1 (HIF 1) in the 5' regulatory sequences used in the hybrid gene produced weak beta-galactosidase staining in a special tumor cell subtype, the so-called perinecrotic palisading (PNP) cells that flank necrotic regions within the tumor. Deletion of the HIF 1 binding site abolished reporter gene expression in the PNP cells, indicating that transcriptional activation of VEGF expression in gliomas is mediated by HIF 1. Inclusion of 3' untranslated sequences from the VEGF gene in the reporter constructs resulted in an increased beta-galactosidase staining in the PNP cells, suggesting that mRNA stabilization also contributes to VEGF up-regulation in glioblastoma cells growing as solid tumors. Combination of the 5' flanking region including the HIF 1 site along with 3' untranslated sequences produced increased levels of beta-galactosidase expression in PNP cells. EF 5 immunostaining for regions of low oxygen partial pressure covered the same PNP cells that were stained for beta-galactosidase. Collectively, the data provide experimental evidence that VEGF gene expression is activated in a distinct tumor cell subpopulation, the perinecrotic palisading cells of gliomas, by two distinct hypoxia-driven regulatory mechanisms.

Damert A ，Machein M ，Breier G ，Fujita MQ ，Hanahan D ，Risau W ，Plate KH ... -  《CANCER RESEARCH》

Identification of small molecule inhibitors of hypoxia-inducible factor 1 transcriptional activation pathway.

Hypoxia-inducible factor 1 (HIF-1) is a master regulator of the transcriptional response to oxygen deprivation. HIF-1 has been implicated in the regulation of genes involved in angiogenesis [e.g., vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase] and anaerobic metabolism (e.g., glycolytic enzymes). HIF-1 is essential for angiogenesis and is associated with tumor progression. In addition, overexpression of HIF-1 alpha has been demonstrated in many common human cancers. Therefore, HIF-1 is an attractive molecular target for development of novel cancer therapeutics. We have developed a cell-based high-throughput screen for the identification of small molecule inhibitors of the HIF-1 pathway. We have genetically engineered U251 human glioma cells to stably express a recombinant vector in which the luciferase reporter gene is under control of three copies of a canonical hypoxia-responsive element (U251-HRE). U251-HRE cells consistently expressed luciferase in a hypoxia- and HIF-1-dependent fashion. We now report the results of a pilot screen of the National Cancer Institute "Diversity Set," a collection of approximately 2000 compounds selected to represent the greater chemical diversity of the National Cancer Institute chemical repository. We found four compounds that specifically inhibited HIF-1-dependent induction of luciferase but not luciferase expression driven by a constitutive promoter. In addition, these compounds inhibited hypoxic induction of VEGF mRNA and protein expression in U251 cells. Interestingly, three compounds are closely related camptothecin analogues and topoisomerase (Topo)-I inhibitors. We show that concomitant with HIF-1 and VEGF inhibition, the activity of the Topo-I inhibitors tested is associated with induction of cyclooxygenase 2 mRNA expression. The luciferase-based high-throughput screen is a feasible tool for the identification of small molecule inhibitors of HIF-1 transcriptional activation. In addition, our results suggest that altered Topo-I function may be associated with repression of HIF-1-dependent induction of gene expression.

Rapisarda A ，Uranchimeg B ，Scudiero DA ，Selby M ，Sausville EA ，Shoemaker RH ，Melillo G ... -  《CANCER RESEARCH》

V-SRC induces expression of hypoxia-inducible factor 1 (HIF-1) and transcription of genes encoding vascular endothelial growth factor and enolase 1: involvement of HIF-1 in tumor progression.

Adaptation to hypoxia represents an important aspect of tumor progression. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that mediates essential homeostatic responses to cellular and systemic hypoxia by activating transcription of multiple genes including those encoding glycolytic enzymes and vascular endothelial growth factor (VEGF). In this report, we demonstrate that whereas C-SRC expression is not required for expression of HIF-1 or transcriptional activation of genes encoding VEGF and enolase 1 (ENO1), cells expressing the v-Src oncogene have increased expression of HIF-1, VEGF, and ENO1 under both hypoxic and nonhypoxic conditions. Expression of V-SRC was associated with increased transcription of reporter genes containing cis-acting hypoxia-response elements from the VEGF and ENO1 genes, and this transcriptional activation required an intact HIF-1 binding site. When three rat hepatoma subclones that differed with respect to the level of HIF-1 expression were injected into nude mice, tumor growth correlated with HIF-1 expression, suggesting that HIF-1 may be generally involved in tumor progression. These studies link an oncogene to the induction of HIF-1 expression, thus providing a mechanism for hypoxic adaptation by tumor cells.

Jiang BH ，Agani F ，Passaniti A ，Semenza GL ... -  《CANCER RESEARCH》