Christopher R Chitambar1, Janine P Wereley. 1. Division of Neoplastic Diseases, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA. chitambr@mcw.edu
Abstract
UNLABELLED: Recent studies have revealed that the wild-type hemochromatosis protein (HFE) interacts with the transferrin receptor (TfR) and modulates TfR-mediated iron uptake by cells. Because of similarities in the transport of gallium and iron and the use of (67)Ga scanning in lymphoid malignancies, we examined the effect of HFE expression on (67)Ga uptake. METHODS: (67)Ga and (59)Fe uptakes were measured in HeLa cells transfected with a FLAG-tagged wild-type HFE (fHFE) gene under control of a tetracycline-repressible promoter. fHFE and TfR protein levels were measured by Western blotting; cellular transferrin (Tf) binding sites were measured by (125)I-Tf binding assay. RESULTS: Induction of fHFE expression produced an increase in TfR protein that was accompanied by a decrease, rather than an increase, in cellular (67)Ga and (59)Fe uptake. The difference in (67)Ga uptake between fHFE-expressing and fHFE-nonexpressing cells was markedly increased in the presence of Tf. Although fHFE expression produced an increase in cellular TfR protein, cell surface and intracellular Tf binding sites were actually decreased in these cells. CONCLUSION: Our studies suggest that expression of wild-type HFE in cells produces a decrease in (67)Ga uptake due to a reduction in available Tf binding sites for (67)Ga-Tf on the TfR. These results imply that (67)Ga uptake by cells with wild-type HFE may differ from cells with the HFE C282Y mutation.
UNLABELLED: Recent studies have revealed that the wild-type hemochromatosis protein (HFE) interacts with the transferrin receptor (TfR) and modulates TfR-mediated iron uptake by cells. Because of similarities in the transport of gallium and iron and the use of (67)Ga scanning in lymphoid malignancies, we examined the effect of HFE expression on (67)Ga uptake. METHODS: (67)Ga and (59)Fe uptakes were measured in HeLa cells transfected with a FLAG-tagged wild-type HFE (fHFE) gene under control of a tetracycline-repressible promoter. fHFE and TfR protein levels were measured by Western blotting; cellular transferrin (Tf) binding sites were measured by (125)I-Tf binding assay. RESULTS: Induction of fHFE expression produced an increase in TfR protein that was accompanied by a decrease, rather than an increase, in cellular (67)Ga and (59)Fe uptake. The difference in (67)Ga uptake between fHFE-expressing and fHFE-nonexpressing cells was markedly increased in the presence of Tf. Although fHFE expression produced an increase in cellular TfR protein, cell surface and intracellular Tf binding sites were actually decreased in these cells. CONCLUSION: Our studies suggest that expression of wild-type HFE in cells produces a decrease in (67)Ga uptake due to a reduction in available Tf binding sites for (67)Ga-Tf on the TfR. These results imply that (67)Ga uptake by cells with wild-type HFE may differ from cells with the HFEC282Y mutation.