title: Real-time imaging of hypoxia-inducible factor-1 activity in tumor xenografts.
abstract: Hypoxia-inducible factor-1 (HIF-1) is responsible for various gene expressions related to tumor malignancy, such as metastasis, invasion and angiogenesis. Therefore, monitoring HIF-1 activity in solid tumors is becoming increasingly important in clinical and basic studies. To establish a convenient system for visualizing HIF-1 activity in tumor xenografts, we employed a promoter consisting of five copies of hypoxia response elements (5HRE), whose activity depends on HIF-1, and used a derivative of green fluorescence protein (d2EGFP) as a reporter gene. A human melanoma cell line, Be11, which contains the 5HRE-d2EGFP gene, showed fluorescence in response to hypoxia. The fluorescent intensity correlated inversely with the surrounding oxygen tension, and was time-dependent for the hypoxic treatment. Reoxygenation resulted in a rapid decrease in fluorescence due to the signal sequence for protein degradation encoded in d2EGFP, which enabled monitoring of HIF-1 activity in real-time. Heterogeneous fluorescence was observed in the solid tumor of a non-sacrificed tumor-bearing mouse. Immunohistochemical analysis confirmed that d2EGFP-expressing regions overlapped with the ones stained with a hypoxia marker, pimonidazole. These results suggest that the 5HRE-d2EGFP gene is suitable for the real-time imaging of HIF-1-activating cells in vivo, due to the short half-life of the d2EGFP protein as well as the specificity of the 5HRE promoter for HIF-1 activity.
authors.affiliation: Department of Therapeutic Radiology and Oncology, Kyoto University Graduate School of Medicine, Kyoto, Japan.
authors.forename: Junye
authors.initials: J
authors.lastname: Liu
authors.forename: Runjiang
authors.initials: R
authors.lastname: Qu
authors.forename: Masakazu
authors.initials: M
authors.lastname: Ogura
authors.forename: Toru
authors.initials: T
authors.lastname: Shibata
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Harada
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D014408:Biomarkers, Tumor / Q000378:metabolism; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D003199:Computer Systems; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005434:Flow Cytometry / Q000379:methods*; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology*; D008856:Microscopy, Fluorescence / Q000379:methods*; D009687:Nuclear Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014183:Transplantation, Heterologous / Q000379:methods* / Q000473:pathology*
chemical_list: D014408:Biomarkers, Tumor; D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D014157:Transcription Factors