Dynamic Traffic through the Recycling Compartment Couples the Metal Transporter Nramp2 (DMT1) with the Transferrin Receptor
Open Access
- 11 July 2003
- journal article
- Published by Elsevier BV
- Vol. 278 (28), 25548-25557
- https://doi.org/10.1074/jbc.m212374200
Abstract
Nramp2 (natural resistance-associated macrophage protein 2, also called DMT1 and Slc11a2) is a proton-dependent cation transporter, which plays a central role in iron homeostasis. To study the subcellular distribution and dynamics of the transporter, we generated a construct encoding the long splice variant of Nramp2 (isoform II) tagged with the hemagglutinin epitope on a predicted extracellular loop. Cells stably transfected with this construct revealed the presence of Nramp2 in both the plasma membrane and in an endomembrane compartment. By labeling the exofacial epitope with a pH-sensitive fluorescent indicator, we were able to establish that this variant of Nramp2 resides in a vesicular compartment with an acidic lumen (pH 6.2) and that acidification was maintained by vacuolar-type ATPases. Dual labeling experiments identified this compartment as sorting and recycling endosomes. Kinetic studies by surface labeling with 125I-labeled antibodies established that the fraction of endomembrane Nramp2 was approximately equal to that on the cell surface. The two components are in dynamic equilibrium: surface transporters are internalized continuously via a clathrin and dynamin-dependent process, whereas endosomal Nramp2 is recycled to the plasmalemma by a phosphatidylinositol 3-kinase-dependent exocytic process. Depletion of cholesterol had no discernible effect on Nramp2 internalization, suggesting that rafts or caveolae are not essential. Because the pH at the cell surface and in endosomes differs by ≥1 unit, the rates of transport of Nramp2 at the surface and in endomembrane compartments will differ drastically. Their subcellular colocalization and parallel trafficking suggest that Nramp2 and transferrin receptors are functionally coupled to effect pH-dependent iron uptake across the endosomal membrane.Keywords
This publication has 39 references indexed in Scilit:
- Expression of the iron transporter DMT1 in kidney from normal and anemic mk miceKidney International, 2002
- Characterization of the iron transporter DMT1 (NRAMP2/DCT1) in red blood cells of normal and anemic mk/mkmiceBlood, 2001
- Human NRAMP2/DMT1, Which Mediates Iron Transport across Endosomal Membranes, Is Localized to Late Endosomes and Lysosomes in HEp-2 CellsJournal of Biological Chemistry, 2000
- A Novel Duodenal Iron-Regulated Transporter, IREG1, Implicated in the Basolateral Transfer of Iron to the CirculationMolecular Cell, 2000
- Disorders of Iron MetabolismNew England Journal of Medicine, 1999
- The G185R Mutation Disrupts Function of the Iron Transporter Nramp2Blood, 1998
- Microcytic anaemia mice have a mutation in Nramp2, a candidate iron transporter geneNature Genetics, 1997
- Cloning and characterization of a mammalian proton-coupled metal-ion transporterNature, 1997
- Cloning and characterization of a second human NRAMP gene on chromosome 12q13Mammalian Genome, 1995
- Identification and characterization of a second mouse Nramp geneGenomics, 1995