Suppression and over-expression of HIF-1α: western analysis. A549 cells were transfected with HIF-1α siRNA vector or a HIF-1 expression plasmid. Cells were allowed to recover in regular culture medium for 20 h after transfection, then exposed to normoxia or hypoxia for 24 h, at which point cellular protein extracts were prepared (n = 5 in each group). Proteins were separated by SDS-PAGE and transferred to membrane for western blot analysis. siRNA: HIF-1α plasmid transfected, Mock: mock transfected, HIF: HIF-1α expression plasmid transfected.