The transferrin receptor: a key function in iron metabolism.

Iron is essential to cell proliferation. Its uptake by cells requires specific binding of the major serum iron-transport protein, transferrin, to cell surface transferrin receptors, followed by endocytosis of the receptor-ligand complexes and release of iron from endosomal vesicles to the cytoplasm. The structural and functional aspects of this pathway are reviewed. Intracellular iron either serves as a substrate for the biosynthesis of haem and iron-containing proteins or is stored in ferritin deposits. Recent studies are presented which establish that iron plays an important role in the maintenance of its own homeostasis by regulating coordinately the expression of both the transferrin receptor and ferritin. The elucidation of these regulatory mechanisms may become important to the understanding of certain disorders in iron-metabolism.