Hypoxia signalling in the control of erythropoietin gene expression in rat hepatocytes

Abstract

This study aimed to investigate the sequence of events involved in the stimulation of erythropoietin (EPO) gene expression by hypoxia in hepatocytes. To this end, primary cultures of rat hepatocytes were kept at either high (40% O2) or low (3% O2) oxygen tensions for 2.5 h. Hypoxia increased EPO mRNA about fifteen-fold, whilst the divalent cation cobalt (50-100 microM) or the iron chelator desferrioxamine (10-200 microM) did not increase EPO mRNA levels. Addition of hydrogen peroxide (100-500 microM) to the culture medium did also not change EPO mRNA levels at high or low oxygen tension. Addition of catalase (50-200 micrograms/ml) to the culture medium resulted in a lower level of hypoxia-induced EPO mRNA. Inhibition of protein synthesis by cycloheximide (100 microM) completely abolished the increase of EPO mRNA in response to hypoxia. Hypoxia but not cobalt increased the appearance of the hypoxia-inducible factor 1 (HIF-1), and this increase was blunted by cycloheximide. Taken together, these findings suggest that a classic heme protein and a related oxygen-dependent production of oxygen radicals is less likely to be involved in the regulation of the EPO gene by oxygen in hepatocytes. On the other hand, intact protein synthesis is an absolute requirement for the hypoxia-induced appearance of HIF-1 and for hypoxia-stimulated expression of the EPO gene in hepatocytes.

Hypoxia-inducible factor-1α correlates with MET and metastasis in node-negative breast cancer

“…The level of HIF-1a protein expression in the nucleus determines the functional activity of HIF-1. Expression of HIF-1a alters the transcription of a spectrum of target genes mainly involved in erythropoiesis, angiogenesis, and glucose metabolism [8][9][10]. However, metastasis promoted by tumor hypoxia is difficult to explain based solely on these modulations.…”

“…Under normoxic conditions, the HIF-1a protein is degraded within minutes, whereas under hypoxic conditions it is stabilized and upregulated. HIF-1a alters the transcription of a spectrum of target genes mainly involved in the modulation of erythropoiesis, angiogenesis, and glucose metabolism [8][9][10], which allow tumor cells to increase oxygen delivery or to activate alternate metabolic pathways that do not require oxygen. Overexpression of HIF-1a protein has been shown in several types of human cancers and metastases [11].…”

Hypoxia-Inducible Factor 1α Expression as an Intrinsic Marker of Hypoxia

“…All cells, whether normal or abnormal, sense a decrease in oxygen and respond by activating a number of physiologic responses such as erythropoiesis (4), glycolysis, and angiogenesis (5,6). This response is mediated by activation of the hypoxia-inducible factor (HIF) family of genes, which code for heterodimeric basic helix-loop-helix proteins composed of ␣ and ␤ subunits.…”

“…The stabilized HIF-1␣ dimerizes with HIF-1␤, and the heterodimers bind to DNA on the hypoxia response elements contained within the promotor regions of target genes. These target genes such as carbonic anhydrase 9 (CA9), Glut-1, vascular endothelial growth factor, and erythropoietin are involved in the adaptation of a tumor to its environment and thus in the development of a more malignant phenotype (4,5).…”

Relation of hypoxia inducible factor 1α and 2α in operable non-small cell lung cancer to angiogenic/molecular profile of tumours and survival

“…Hypoxia has been recognized as a key factor involved in the regulation of a cascade of physiological responses such as erythropoiesis (Gopfert et al, 1996), glycolysis (Ebert et al, 1996), glucose transport (Tagaki et al, 1998), angiogenesis and vasodilatation (Griffiths et al, 1997;Carmeliet et al, 1998;Faller, 1999). A large group of genes that includes erythropoietin (Goldberg et al, 1988), nitric oxide synthase (Palmer et al, 1998), tyrosine hydroxylase (Norris and Millhorn, 1995), VEGF (Forsythe et al, 1996;Ema et al, 1997), lactate dehydrogenase, haem oxygenase, transferin receptor and others are regulated by hypoxia (Blancher and Harris, 1998).…”