Hypoxia mediates cellular iron deficiency by increasing TfR1 and IRP binding. MDA-MB-231 and MCF-7 cells were exposed to Fe (FAC, 50 μM) or DFO (500 μM). Co-treatments were administered 2 h prior to the initiation of hypoxic exposures (37°C, 6 h). Thirty μg total protein/sample were immunoblotted for TfR1 determination (A and B). IRP binding in MDA-MB-231 cells was assessed by EMSA (C). Means of two densitometric analyses were from the IRPs binding experiments (D). Bars represent % IRP binding in samples treated in the absence of ME in comparison to +2-ME controls (n = 2).