Release of the soluble transferrin receptor is directly regulated by binding of its ligand ferritransferrin
Katrin Dassler1, Martin Zydek, Krzysztof Wandzik
1Institut für Klinische Chemie und Pathobiochemie, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin 12200, Germany.
Abstract:
The human transferrin receptor (TfR) is shed by an integral metalloprotease releasing a soluble form (sTfR) into serum. The sTfR reflects the iron demand of the body and is postulated as a regulator of iron homeostasis via binding to the hereditary hemochromatosis protein HFE. To study the role of transferrin in this process, we investigated TfR shedding in HL60 cells and TfR-deficient Chinese hamster ovary cells transfected with human TfR. Independent of TfR expression, sTfR release decreases with increasing ferritransferrin concentrations, whereas apo-transferrin exhibits no inhibitory effect. To investigate the underlying mechanism, we generated several TfR mutants with different binding affinities for transferrin. Shedding of TfR mutants in transfected cells correlates exactly with their binding affinity, implying that the effect of ferritransferrin on TfR shedding is mediated by a direct molecular interaction. Analysis of sTfR release from purified microsomal membranes revealed that the regulation is independent from intracellular trafficking or cellular signaling events. Our results clearly demonstrated that sTfR does not only reflect the iron demand of the cells but also the iron availability in the bloodstream, mirrored by iron saturation of transferrin, corroborating the important potential function of sTfR as a regulator of iron homeostasis.
Related Concept Videos
The Early Endosome: Endocytosis of Transferrin
Receptor-mediated Endocytosis
Receptor-mediated Endocytosis
Clathrin-Mediated Endocytosis of LDL
One well-characterized example of receptor-mediated endocytosis is the...
Receptor Downregulation in MVBs
The EGFR can initiate signaling pathways that lead to cell proliferation, migration, and differentiation. Overexpression of EGFR stimulates cells to proliferate. Excessive EGFR activation may...
Regulation of Nuclear Protein Sorting
Directing Proteins to the Rough Endoplasmic Reticulum


