Fig. 5. Limited HIF-1 transcriptional activity in episodic hypoxia. Cells were transfected with a pGL3-Promoter Luciferase construct and its modified variant containing six hypoxia-response elements (6x HRE). Schematic of the used promoter constructs is shown in the left panel. Hypoxia typically induces an increase in 6x HRE-dependent transcription via HIF-1α stabilization and a subsequent increase in HIF-1 activity. Following exposure to the different types of hypoxia, HRE-dependent transcription of the luciferase gene was measured directly in cellular extracts from DCT (middle panel) and HT1080 (right panel) cells. Transfection efficiency was normalized to the co-transfected renilla luminescence values. Data are expressed relative to the reporter construct without the 6x HRE. Error bars indicate standard deviation (n=8). Significance to normoxia: #: p<0.05, ##: p<0.01, ###: p<0.001. Asterisks denote significance between hypoxic groups. ***: p<0.001.