Fig. 4. HIF-1α induced by PHD2 silencing is functionally active. The indicated siRNAs (20 nM) were transfected into HeLa cells with 50 ng of a reporter vector (pRE-Δtk-LUC) containing three copies of the HRE from the erythropoietin gene. In all cases, 100 ng of a plasmid for β-galactosidase were co-transfected to normalize for transfection efficiency. After 48 h of transfection, luciferase activity was measured. As a control for HIF-1 activation, cells were incubated in the presence of Co²⁺ (200 µM) or in hypoxia (1–2% O₂) for 16 h. Results are representative of three independent experiments performed in triplicate.