Regulation of a rat VL30 element in human breast cancer cells in hypoxia and anoxia: role of HIF-1.
Novel approaches to cancer gene therapy currently exploit tumour hypoxia to achieve transcriptional targeting using oxygen-regulated enhancer elements called hypoxia response elements. The activity of such elements in hypoxic cells is directly dependent on upregulation of the hypoxia-inducible transcription factor-1 However tumours also contain areas of anoxia, which may be considered a more tumour-selective transcriptional stimulus than hypoxia for targeting gene therapy to tumours. Another element, from the rat virus-like retrotransposon, VL30 (termed the "secondary anoxia response element") has been reported to be more highly inducible in rat fibroblasts under anoxia than hypoxia. To investigate anoxia as a potential transcriptional target in human tumours, we have examined secondary anoxia response element inducibility in two human breast cancer cell lines, MCF-7 and T47D, under anoxia, hypoxia and normoxia. In both cell types, the trimerised secondary anoxia response element showed greater inducibility in anoxia than hypoxia (1% and 0.5% O(2)). The anoxic response of the secondary anoxia response element was shown to be dependent on hypoxia-inducible transcription factor-1 and the presence of a hypoxia-inducible transcription binding site consensus (5'-ACGTG-3'). Mutational analysis demonstrated that the base immediately 5' to this modulates the anoxic/hypoxic induction of the secondary anoxia response element, such that TACGTG>GACGTG>>CACGTG. A similar correlation was found for erythropoietin, phosphoglycerate kinase 1, and aldolase hypoxia response elements, which contain these respective 5' flanking bases.
Ameri
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Tumour Targeting Group, Division of Genomic Medicine, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK.
Burke
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B
Lewis
C E
CE
Harris
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AL
D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000628:therapy*; D016466:CHO Cells; D015687:Cell Hypoxia; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000032:analysis / Q000502:physiology*; D004921:Erythropoietin / Q000494:pharmacology; D005260:Female; D015316:Genetic Therapy; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins / Q000032:analysis / Q000502:physiology*; D010100:Oxygen / Q000494:pharmacology; D051381:Rats; D020218:Response Elements / Q000502:physiology*; D018626:Retroelements; D014157:Transcription Factors; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; C497444:Hif1a protein, rat; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D018626:Retroelements; D014157:Transcription Factors; D004921:Erythropoietin; D010100:Oxygen