Barbara Corsi

Overexpression of the hereditary hemochromatosis protein, HFE, in HeLa cells induces an iron-deficient phenotype

A transfectant HeLa cell clone expressing HFE under the control of a tetracycline‐repressible promoter was generated. HFE expression was fully repressed by the presence of doxycycline, while it was strongly induced by growth in the absence of doxycycline. HFE accumulation was accompanied by a large (∼10‐fold) decrease in H‐ and L‐ferritin levels, by a ∼3–4‐fold increase in transferrin receptor, and a ∼2‐fold increase in iron regulatory protein activity. These indices of cellular iron deficiency were reversed by iron supplementation complexes. The overexpressed HFE immunoprecipitated together with transferrin receptor, indicating a physical association which is the likely cause for the observed ∼30% decrease in 55Fe‐transferrin incorporation after 18 h incubation. In the HFE‐expressing cells the reduction in transferrin‐mediated iron incorporation was partially compensated by a ∼30% increase in non‐transferrin iron incorporation from 55Fe‐NTA, evident after prolonged, 18 h, incubations. The findings indicate that HFE binding to transferrin receptor reduces cellular iron availability and regulates the balance between transferrin‐mediated and non‐transferrin‐mediated cellular iron incorporation.

Role of iron and ferritin in TNFα-induced apoptosis in HeLa cells

We found that tumor necrosis factor α (TNFα)‐induced apoptosis in HeLa cells was accompanied by a ∼2‐fold increase in H‐ and L‐ferritin and a decrease in transferrin receptor, two indices of increased iron availability. Iron supplementation and overexpression of H‐ferritin or its mutant with an inactivated ferroxidase center reduced by about ∼50% the number of apoptotic cells after TNFα‐treatment, while overexpression of L‐ferritin was ineffective. The data indicate that H‐ferritin has an anti‐apoptotic activity unrelated to its ferroxidase activity and to its capacity to modify cellular iron metabolism.