The regulated iron uptake from transferrin is HFE-expression–dependent. HtTA cells (•) and HtTA-HFE cells (○) were grown in the absence of doxycycline. Cells were divided and either left untreated or doxycycline (1 μg/mL) was added. At different times after onset of doxycycline-mediated HFE repression, iron uptake was examined in doxycycline-treated and untreated cells. Uptake was determined for 30 minutes at 37°C with 5 μg/mL⁵⁹Fe-diferric transferrin as substrate. The results are given as quotient of uptake rates of doxycyline treated vuntreated cells. All data are derived from triplicate samples.