Article

Carmeliet, P. et al. Role of HIF-1 in hypoxia-mediated apoptosis, cell proliferation and tumour angiogenesis. Nature 394, 485-490

Center for Transgene Technology and Gene Therapy, Flanders Interuniversity Institute for Biotechnology, KU Leuven, Belgium.
Nature (Impact Factor: 42.35). 08/1998; 394(6692):485-90. DOI: 10.1038/28867
Source: PubMed

ABSTRACT As a result of deprivation of oxygen (hypoxia) and nutrients, the growth and viability of cells is reduced. Hypoxia-inducible factor (HIF)-1alpha helps to restore oxygen homeostasis by inducing glycolysis, erythropoiesis and angiogenesis. Here we show that hypoxia and hypoglycaemia reduce proliferation and increase apoptosis in wild-type (HIF-1alpha+/+) embryonic stem (ES) cells, but not in ES cells with inactivated HIF-1alpha genes (HIF-1alpha-/-); however, a deficiency of HIF-1alpha does not affect apoptosis induced by cytokines. We find that hypoxia/hypoglycaemia-regulated genes involved in controlling the cell cycle are either HIF-1alpha-dependent (those encoding the proteins p53, p21, Bcl-2) or HIF-1alpha-independent (p27, GADD153), suggesting that there are at least two different adaptive responses to being deprived of oxygen and nutrients. Loss of HIF-1alpha reduces hypoxia-induced expression of vascular endothelial growth factor, prevents formation of large vessels in ES-derived tumours, and impairs vascular function, resulting in hypoxic microenvironments within the tumour mass. However, growth of HIF-1alpha tumours was not retarded but was accelerated, owing to decreased hypoxia-induced apoptosis and increased stress-induced proliferation. As hypoxic stress contributes to many (patho)biological disorders, this new role for HIF-1alpha in hypoxic control of cell growth and death may be of general pathophysiological importance.

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    ABSTRACT: In der vorliegenden Arbeit wurde der Effekt von Hypoxie und Angiotensin II auf HIF-1alpha in zwei Zellsystemen der Lunge dargestellt. Zum einen wurden Untersuchungen im Alveolarepithel durchgeführt. Dabei wurde die Adenokarzinom-Zelllinie A549 mit Eigenschaften der Pneumozyten Typ II verwendet. Zum anderen erfolgten Untersuchungen in pulmonalarteriellen Fibroblasten. Hierfür wurden primär isolierte Zellen aus der Kaninchenlunge verwendet. Es zeigte sich, dass in beiden Zellsystemen HIF-1alpha in Abhängigkeit von der Hypoxiedauer induziert wird, dabei besteht ein transienter Verlauf mit Maximum nach vier Stunden Hypoxie. Vor dem Hintergrund, dass Angiotensin II (Ang II) in SMC HIF-1alpha bereits in Normoxie induziert [63], wurde der Einfluss des nicht hypoxischen Stimulus auf beide Zellsysteme untersucht. Die Studie ergab, dass weder in alveolären Epithelzellen, noch in pulmonalarteriellen Fibroblasten eine Induktion von HIF-1alpha auf Proteinebene nachgewiesen werden kann. Führt man eine Stimulation in hypoxischer Atmosphäre durch, dann ist eine signifikant gesteigerte HIF-1alpha Induktion zu verzeichnen. Die optimale Ang II Dosis unterscheidet sich in den Zellsystemen. Während in den alveolären Epithelzellen bereits unter Stimulation mit 10 nM Ang II eine signifikante Steigerung vorhanden ist, kann man in pulmonalarteriellen Fibroblasten dies erst nach Stimulation mit 100 nM beobachten. Parallel zur verstärkten Proteinexpression in alveolären Epithelzellen ergab die Analyse der HRE-Reportergen-Aktivität, repräsentativ für die Aktivierung bekannter HIF-abhängiger Zielgene, ebenfalls eine starke Induktion in hypoxischen alveolären Epithelzellen. Betrachtet man die HRE-Aktivität nach Ang II Stimulation, ist diese bereits in Normoxie gesteigert, wobei der Effekt unter hypoxischen Bedingungen noch ausgeprägter ist. Diese Ergebnisse führen zu der Hypothese, dass unter Hypoxie über Induktion von HIF-1alpha der Gefäßumbau im Sinne des Remodellings und Ausbildung einer Fibrose durch Aktivierung der HIF-abhängigen Zielgene mit Proliferation der Fibroblasten [39] und Apoptose der alveolären Epithelzellen [38] eingeleitet wird. Außerdem induziert der vasoaktive und pro-proliferative Mediator Ang II HIF-1alpha, so dass hier möglicherweise durch spezifische Inhibitoren Therapie Strategien im Sinne eines „Anti-Remodelling“ entwickelt werden könnten. The hypoxia inducible transcription factor HIF-1alpha is a master regulator in the adaptation to alveolar hypoxia. In our study we analyzed the effect of hypoxia and angiotensin II (Ang II) on HIF-1alpha in alveolar epithelial cells (AEC II) and pulmonary artery adventitial fibroblasts (FBPA). Our results showed after exposure to 4 hours of hypoxia a stronger increase of HIF-1alpha in both cell systems as after 24 hours O2 deprivation. As second step, we investigated the effects of Ang II. Dose-dependent increase of HIF-1alpha was noted. A strong induction of HIF-1alpha protein expression could be observed when AEC II were treated for 4 h with 10 nM Ang II. FBPA showed in contrast a strong increase of HIF-1alpha after incubation for 24 h with 100 nM Ang II. In addition hypoxia responsive element (HRE) as regulatory component was strongly activated in hypoxic-rendered AEC II. These reactions of AEC II and FBPA may play a central role in lung vascular remodelling under hypoxic conditions resulting in chronic lung disease such as pulmonary hypertension.
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    ABSTRACT: Hypoxia is a common microenvironment in solid tumors and is correlated with tumor progression by regulating cancer cell survival. Recent studies suggest that activation of double-stranded RNA-dependent protein kinase-like endoplasmic reticulum-related kinase (PERK) and phosphorylation of α subunit of eIF2 (eIF2α) confer cell adapta- tion to hypoxic stress. However, eIF2α is still phosphorylated at a lowered level in PERK knockout cells under hyp- oxic conditions. The mechanism for eIF2α kinase(s) (EIF2AK)-increased cell survival is not clear. In this report, we provide evidence that another EIF2AK, the amino acid starvation-dependent general control of amino acid biosyn- thesis kinase (GCN2), is also involved in hypoxia-induced eIF2α phosphorylation. We demonstrate that both GCN2 and PERK mediate the cell adaptation to hypoxic stress. High levels of eIF2α phosphorylation lead to G1 arrest and protect cells from hypoxia-induced apoptosis. Reduced phosphorylation of eIF2α by knocking out either PERK or GCN2 suppresses hypoxia-induced G1 arrest and promotes apoptosis in accompany with activation of p53 signal cascade. However, totally abolishing phosphorylation of eIF2α inhibits G1 arrest without promoting apoptosis. On the basis of our results, we propose that the levels of eIF2α phosphorylation serve as a "switch" in regulation of G1 arrest or apoptosis under hypoxic conditions.
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Jean-Marc Herbert