HIF-1α stabilization in MDA-MB-231 cells by various treatments. A: normoxia, hypoxia (1% O2, 6 h), anti-human TfR1 antibody (Ab, 10 μg/ml, 24 h), or 0.5 mM DFO (6 h). B: normoxia, hypoxia (1% O2, 6 h), and hypoxia with Fe pre-treatment (50 μM, 3 h). Samples were analyzed by Western blotting and co-stained for β-tubulin. One representative gel from three independent experiments is shown.