Inhibition HIF-1α mRNA expression in A549 by siRNA. A549 were transfected with the siRNA-expressing EGFP-pSUPER vector or a HIF-1 expression plasmid. Cells were allowed to recover in regular culture medium for 20 h after transfection, then exposed to a normoxic or hypoxic environment for an additional 24 h. Experiments were performed five times with the similar results (n = 5 in each group). $, P < 0.05 compared to control and HIF-1α siRNA; #, P < 0.05 compared to normoxic or hypoxic HIF-1α siRNA; *, P < 0.05 compared to hypoxic mock-transfected and scrambled HIF-1α control siRNA transfection. siRNA: HIF-1α plasmid transfected, Mock: mock transfected, HIF: HIF-1α expression plasmid transfected.