Effects of gcHIF-1α and gcHIF-4α on HRE-Luc reporter activity in CHO cells. CHO-K1 C4.5 cells were cotransfected with pBK-CMV-gcHIF-1α, pBK-CMV-gcHIF-4α or pBK-CMV empty vector (with or without pBK-CMV-gcARNT2b) along with the p(HRE)4-Luc reporter and pSVβ-galactosidase plasmids. Transfected cells were exposed to normoxia (N, open bars) or hypoxia (H, shaded bars) for 16 h and then assayed for luciferase and β-galactosidase activities. The constituent plasmid(s) in each transfection experiment is/are indicated by a + sign underneath the respective bar charts. Luciferase was normalized against β-gal activity and data represent the mean ± SEM of 5 independent experiments. *, P < 0.05 between the gcHIF-α – and empty vector-transfected groups under normoxia; **, P < 0.05 between the gcHIF-α – and empty vector-transfected groups under hypoxia.