Nramp2 Expression Is Associated with pH-dependent Iron Uptake across the Apical Membrane of Human Intestinal Caco-2 Cells*
- Sarah Tandy‡§,
- Mark Williams‡¶,
- Aime Leggett‡,
- Marta Lopez-Jimenez‡,
- Markos Dedes‡,
- Bala Ramesh‖,
- Surjit Kaila Srai‖ and
- Paul Sharp‡¶**
- From the ‡School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, ¶Institute of Food Research, Norwich, NR4 7UA, and ‖Department of Biochemistry and Molecular Biology, Royal Free Hospital and University College Medical School, London NW3 2PF, United Kingdom
Abstract
The absorption of dietary non-heme iron by intestinal enterocytes is crucial to the maintenance of body iron homeostasis. This process must be tightly regulated since there are no distinct mechanisms for the excretion of excess iron from the body. An insight into the cellular mechanisms has recently been provided by expression cloning of a divalent cation transporter (DCT1) from rat duodenum and positional cloning of its human homologue, Nramp2. Here we demonstrate that Nramp2 is expressed in the apical membrane of the human intestinal epithelial cell line, Caco 2 TC7, and is associated with functional iron transport in these cells with a substrate preference for iron over other divalent cations. Iron transport occurs by a proton-dependent mechanism, exhibiting a concurrent intracellular acidification. Taken together, these data suggest that the expression of the Nramp2 transporter in human enterocytes may play an important role in intestinal iron absorption.
Footnotes
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ Supported by a Biotechnology and Biological Sciences Research Council Research Committee Studentship.
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↵** To whom correspondence should be addressed. Tel.: 44 1603 592244; Fax: 44 1603 592250; E-mail: p.a.sharp@uea.ac.uk.
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↵2 P. Sharp, E. Debnam, and S. Srai, unpublished information.
- Abbreviations:
- BCECF
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2′,7′-bis(2-carboxyethyl)-5-(6)-carboxyfluorescein
- pHa
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apical pH, pHb, basolateral pH
- pHi
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intracellular pH
- pHo
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extracellular pH
- Pipes
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piperazine-N,N′-bis-(2-ethanesulfonic acid)
- MES
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4-morpholineethanesulfonic acid
- HBSS
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Hepes-buffered salt solution
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- Received April 16, 1999.
- Revision received September 20, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
