Activator-protein-1 binding potentiates the hypoxia-induciblefactor-1-mediated hypoxia-induced transcriptional activation of vascular-endothelial growth factor expression in C6 glioma cells.
The endothelial cell-specific mitogen vascular-endothelial growth factor (VEGF) plays a key role in both physiological and pathological angiogenesis. The up-regulation of VEGF expression in response to reduced oxygen tension occurs through transcriptional and post-transcriptional mechanisms. To investigate the molecular mechanisms of transcriptional activation by hypoxia (1% oxygen), fine mapping of a hypoxia-responsive region of the human VEGF promoter was carried out using luciferase reporter-gene constructs in C6 glioma cells. Here, we report that the binding site of hypoxia-inducible factor 1 (HIF1) is crucial for the hypoxic induction of VEGF gene expression. However, an enhancer subfragment containing the HIF1 binding site was not sufficient to confer full hypoxia responsiveness. Addition of upstream sequences restored the full sensitivity to hypoxia induction. This potentiating effect is due to activator protein 1 binding. The 'potentiating' sequences are unable to confer hypoxia responsiveness on their own. Our results strongly suggest that in C6 glioma cells a complex array of trans-acting factors facilitates full transcriptional induction of VEGF gene expression by hypoxia.
Damert
A
A
Max-Planck-Institut für physiologische und klinische Forschung, W.G. Kerckhoff-Institut, Abteilung Molekulare Zellbiologie, Parkstrasse 1, 61231 Bad Nauheim, Germany.
Ikeda
E
E
Risau
W
W
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015687:Cell Hypoxia; D004268:DNA-Binding Proteins / Q000378:metabolism*; D016228:Endothelial Growth Factors / Q000096:biosynthesis* / Q000235:genetics; D004742:Enhancer Elements, Genetic; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D005910:Glioma; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008156:Luciferases / Q000096:biosynthesis; D008222:Lymphokines / Q000096:biosynthesis* / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D004268:DNA-Binding Proteins; D016228:Endothelial Growth Factors; C497442:HIF1A protein, human; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008222:Lymphokines; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D011993:Recombinant Fusion Proteins; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D008156:Luciferases