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Subcellular localization of the metal‐ion transporters Zip14 and DMT1 in human hepatoma (HepG2) cells
Author(s) -
Zhao Ningning,
Knutson Mitchell
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.105.3
Subject(s) - endosome , dmt1 , transferrin , transferrin receptor , microbiology and biotechnology , cytosol , transport protein , internalization , green fluorescent protein , endocytosis , fusion protein , transporter , intracellular , chemistry , subcellular localization , cell membrane , hepatocyte , transmembrane protein , biochemistry , cell , biology , receptor , cytoplasm , gene , enzyme , recombinant dna , in vitro
The liver is the main storage site for body iron. This organ normally takes up plasma transferrin‐bound iron (TBI), but can also acquire non‐transferrin‐bound iron (NTBI), which appears in plasma in iron overload. Uptake of TBI involves binding to the transferrin‐receptor at the cell surface, followed by internalization into recycling endosomes. Upon endosomal acidification, iron is released from transferrin and translocated into the cytosol by a transmembrane protein. We used confocal laser‐scanning microscopy to examine the subcellular distribution of the transmembrane metal‐ion transporters DMT1 (Divalent Metal Transporter 1) and Zip14 in HepG2 hepatoma cells. For the localization studies, cells were transfected to express green fluorescent protein (GFP) fusion proteins. We found that Zip14‐GFP was readily detectable at the hepatocyte plasma membrane whereas DMT1‐GFP was not. Both fusion proteins displayed abundant punctuate intracellular staining that partially colocalized with internalized Texas‐red labeled transferrin, a marker of recycling endosomes. Localization of Zip14‐GFP to the plasma membrane is consistent with its postulated role in the uptake of NTBI at the cell surface. Detection of Zip14‐GFP in recycling endosomes further implicates this protein in the assimilation of TBI. We conclude that Zip14 may therefore play a role in normal uptake of iron by the liver. Supported by NIH grant R01DK080706 (MK).