FIG. 6.

Effect of hypoxia, cobalt, and heregulin stimulation on HIF-1α stability. HIF-1α expression was induced by exposure of MCF-7 cells to 1% O₂ (Hypoxia), 100 μM CoCl₂ (Cobalt), or 100 ng of heregulin/ml for 6 h. Cycloheximide (CHX) was added to a final concentration of 100 μM, and the cells were harvested after being incubated for the indicated time in the presence of CHX and the inducer. Nuclear extracts were analyzed for the expression of HIF-1α (top) and HIF-1β (bottom) by immunoblot assay.