Transactivation of hTERT promoter activity by hypoxia exposure and HIF-1 overexpression. (a) Schematic representations of the HIF-1 response elements and the pGL181-luc, pGL181mt1-luc, pGL181mt2-luc, and pGL181mt-luc reporters are shown. (b) JEG-3 cells were cotransfected with the pGL181-luc, pGL181mt1-luc, pGL181mt2-luc, and pGL181mt-luc (0.3 μg each) constructs and 1.0 μg (each) of the HIF-1 expression constructs (HIF-1α and ARNT) or the empty vector pcDNA3 under hypoxic conditions (1% O2); activity is reported as relative luminescence units (RLU). Error bars indicate standard deviations in triplicate assays.