Regulated expression of HFE in stably transfected HtTA-HFE cells. HtTA cells, stably transfected with the HFE-expressing plasmid pSGH-1, were grown for 4 days in the presence (+) or absence (−) of 1 μg/mL doxycycline. Protein lysates (corresponding to ≈1 × 10⁵ cells per lane) were prepared and subjected to SDS-PAGE followed by Western blotting with HFE antisera. Results are for 4 individual HtTA-HFE clones, all showing expression of a 43/48-kD HFE protein double band. No HFE expression is detected in HtTA controls.