Modulation of iron regulatory protein-1 by various metals

Interactions between iron and manganese in neurotoxicity

The essential and naturally occurring transition metal manganese (Mn) is present in the soil, water, air, and various foods. Manganese can accumulate in the brain if the Mn intake or exposure is excessive and this can result in neurotoxic effects. Manganese is important for the proper activation of different metabolic and antioxidant enzymes. There are numerous Mn importers and exporters. However, the exact transport mechanism for Mn is not fully understood. On the other hand, iron (Fe) is another well-known essential metal, which has redox activity in addition to chemical characteristics resembling those of Mn. Existing data show that interactions occur between Fe and Mn due to certain similarities regarding their mechanisms of the absorption and the transport. It has been disclosed that Mn-specific transporters, together with Fe transporters, regulate the Mn distribution in the brain and other peripheral tissues. In PC12 cells, a significant increase of transferrin receptor (TfR) mRNA expression was linked to Mn exposure and accompanied by elevated Fe uptake. In both humans and animals, there is a strong relationship between Fe and Mn metabolism. In the present review, special attention is paid to the interaction between Mn and Fe. In particular, Fe and Mn distribution, as well as the potential molecular mechanisms of Mn-induced neurotoxicity in cases of Fe deficiency, are discussed.

Novel upregulation of amyloid-β precursor protein (APP) by microRNA-346 via targeting of APP mRNA 5'-untranslated region: Implications in Alzheimer's disease

In addition to the devastating symptoms of dementia, Alzheimer's disease (AD) is characterized by accumulation of the processing products of the amyloid-β (Aβ) peptide precursor protein (APP). APP's non-pathogenic functions include regulating intracellular iron (Fe) homeostasis. MicroRNAs are small (~ 20 nucleotides) RNA species that instill specificity to the RNA-induced silencing complex (RISC). In most cases, RISC inhibits mRNA translation through the 3'-untranslated region (UTR) sequence. By contrast, we report a novel activity of miR-346: specifically, that it targets the APP mRNA 5'-UTR to upregulate APP translation and Aβ production. This upregulation is reduced but not eliminated by knockdown of argonaute 2. The target site for miR-346 overlaps with active sites for an iron-responsive element (IRE) and an interleukin-1 (IL-1) acute box element. IREs interact with iron response protein1 (IRP1), an iron-dependent translational repressor. In primary human brain cultures, miR-346 activity required chelation of Fe. In addition, miR-346 levels are altered in late-Braak stage AD. Thus, miR-346 plays a role in upregulation of APP in the CNS and participates in maintaining APP regulation of Fe, which is disrupted in late stages of AD. Further work will be necessary to integrate other metals, and IL-1 into the Fe-miR-346 activity network. We, thus, propose a "FeAR" (Fe, APP, RNA) nexus in the APP 5'-UTR that includes an overlapping miR-346-binding site and the APP IRE. When a "healthy FeAR" exists, activities of miR-346 and IRP/Fe interact to maintain APP homeostasis. Disruption of an element that targets the FeAR nexus would lead to pathogenic disruption of APP translation and protein production.

Interactions of iron with manganese, zinc, chromium, and selenium as related to prophylaxis and treatment of iron deficiency

Iron (Fe) deficiency is considered as the most common nutritional deficiency. Iron deficiency is usually associated with low Fe intake, blood loss, diseases, poor absorption, gastrointestinal parasites, or increased physiological demands as in pregnancy. Nutritional Fe deficiency is usually treated with Fe tablets, sometimes with Fe-containing multimineral tablets. Trace element interactions may have a significant impact on Fe status. Existing data demonstrate a tight interaction between manganese (Mn) and Fe, especially in Fe-deficient state. The influence of Mn on Fe homeostasis may be mediated through its influence on Fe absorption, circulating transporters like transferrin, and regulatory proteins. The existing data demonstrate that the influence of zinc (Zn) on Fe status may be related to their competition for metal transporters. Moreover, Zn may be involved in regulation of hepcidin production. At the same time, human data on the interplay between Fe and Zn especially in terms of Fe-deficiency and supplementation are contradictory, demonstrating both positive and negative influence of Zn on Fe status. Numerous data also demonstrate the possibility of competition between Fe and chromium (Cr) for transferrin binding. At the same time, human data on the interaction between these metals are contradictory. Therefore, while managing hypoferremia and Fe-deficiency anemia, it is recommended to assess the level of other trace elements in parallel with indices of Fe homeostasis. It is supposed that simultaneous correction of trace element status in Fe deficiency may help to decrease possible antagonistic or increase synergistic interactions.

A novel branched TAT(47-57) peptide for selective Ni(2+) introduction into the human fibrosarcoma cell nucleus

A TAT47-57 peptide was modified on the N-terminus by elongation with a 2,3-diaminopropionic acid residue and then by coupling of two histidine residues on its N-atoms. This branched peptide could bind to Ni under physiological conditions as a 1 : 1 complex. We demonstrated that the complex was quantitatively taken up by human fibrosarcoma cells, in contrast to Ni(2+) ions. Ni localization (especially at the nuclei) was confirmed by imaging using both scanning X-ray fluorescence microscopy and Newport Green fluorescence. A competitive assay with Newport Green showed that the latter displaced the peptide ligand from the Ni-complex. Ni(2+) delivered as a complex with the designed peptide induced substantially more DNA damage than when introduced as a free ion. The availability of such a construct opens up the way to investigate the importance of the nucleus as a target for the cytotoxicity, genotoxicity or carcinogenicity of Ni(2+).

Nickel and human health

This review focuses on the impact of nickel on human health. In particular, the dual nature of nickel as an essential as well as toxic element in nature is described, and the main forms of nickel that can come in contact with living systems from natural sources and anthropogenic activities are discussed. Concomitantly, the main routes of nickel uptake and transport in humans are covered, and the potential dangers that nickel exposure can represent for health are described. In particular, the insurgence of nickel-derived allergies, nickel-induced carcinogenesis as well as infectious diseases caused by human pathogens that rely on nickel-based enzymes to colonize the host are reviewed at different levels, from their macroscopic aspects on human health to the molecular mechanisms underlying these points. Finally, the importance of nickel as a beneficial element for human health, especially being essential for microorganisms that colonize the human guts, is examined.

Impairment of interrelated iron- and copper homeostatic mechanisms in brain contributes to the pathogenesis of neurodegenerative disorders

Iron and copper are important co-factors for a number of enzymes in the brain, including enzymes involved in neurotransmitter synthesis and myelin formation. Both shortage and an excess of iron or copper will affect the brain. The transport of iron and copper into the brain from the circulation is strictly regulated, and concordantly protective barriers, i.e., the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (BCB) have evolved to separate the brain environment from the circulation. The uptake mechanisms of the two metals interact. Both iron deficiency and overload lead to altered copper homeostasis in the brain. Similarly, changes in dietary copper affect the brain iron homeostasis. Moreover, the uptake routes of iron and copper overlap each other which affect the interplay between the concentrations of the two metals in the brain. The divalent metal transporter-1 (DMT1) is involved in the uptake of both iron and copper. Furthermore, copper is an essential co-factor in numerous proteins that are vital for iron homeostasis and affects the binding of iron-response proteins to iron-response elements in the mRNA of the transferrin receptor, DMT1, and ferroportin, all highly involved in iron transport. Iron and copper are mainly taken up at the BBB, but the BCB also plays a vital role in the homeostasis of the two metals, in terms of sequestering, uptake, and efflux of iron and copper from the brain. Inside the brain, iron and copper are taken up by neurons and glia cells that express various transporters.

Effects of mercury on Dictyostelium discoideum: proteomics reveals the molecular mechanisms of physiological adaptation and toxicity

Dictyostelium discoideum amoebae were exposed to Hg 2 microM corresponding to a sublethal concentration and Hg 10 microM with the first effects on mortality and replication rate. A total of 900 spots were visualized by 2-DE electrophoresis. Two-hundred fifty single proteins were identified by mass spectrometry. Low Hg concentration (2 microM) treatment induced up-regulation of 13 spots, mainly involved in oxidative stress response/detoxification, oxidoreductase activity, and metabolic processes. High Hg concentration (10 microM) treatment showed a different PES with 12 proteins downregulated and only two up-regulated, mainly involved in cellular metabolic processes, metal ion binding, and transferase activity. The analyses for the carbonylation show no changes after 2 microM Hg(2+) treatment and 13 differentially carbonylated proteins after 10 microM Hg(2+) involved in a broad range of cellular processes. Our findings provide insight into the mechanisms of physiological adaptation and toxicity to a low and an high mercury concentration, respectively, of Dictyostelium amoebae.

Detection of Changes in Alveolar Macrophage Iron Status Induced by Select PM2.5-Associated Components Using Iron-Response Protein Binding Activity

The extent of adverse health effects, including induction/exacerbation of infectious lung disease, arising from entrainment of equivalent amounts (or exposure to a fixed increment) of fine particulate matter (PM2.5) can vary from region to region or city to city in a region. To begin to explain how differing effects on host resistance might arise after exposure to PM2.5 from various sites, we hypothesized that select metals (e.g., V, Al, and Mn) in each PM2.5 caused changes in alveolar macrophage (AM) Fe status that, ultimately, would lead to altered antibacterial function. To test this, iron-response protein (IRP) binding activity in a rat AM cell line was assessed after exposure to Fe alone and in conjunction with V, Mn, and/or Al at ratios of V:Fe, Al:Fe, or Mn:Fe encountered in PM2.5 samples from New York City, Los Angeles, and Seattle. Results indicated that V and Al each significantly altered IRP activity, though effects were not consistently ratio-(i.e., dose-) dependent; Mn had little impact on activity. We conclude that the reductions in Fe status detected here via the IRP assay arose, in part, from effects on transferrin-mediated Fe3+ delivery to the AM. Ongoing studies using this assay are allowing us to better determine: (1) whether mass (and/or molar) relationships between Fe and V, Al, and/or Mn in any PM2.5 sample consistently govern the extent of change in AM Fe status; (2) how much any specified PM2.5 constituent (metal or nonmetal) contributes to the overall disruption of Fe status found induced by an intact parent sample; and (3) whether induced changes in binding activity are relatable to other changes expected to occur in the AM, that is, in IRP-dependent mRNA/levels of ferritin/transferrin receptor and Fe-dependent functions. These studies demonstrate that pollutant-induced effects on lung cell Fe status can be assessed in a reproducible manner using an assay that can be readily performed by investigators who might otherwise have no access to other very costly analytical equipment, such as graphite atomic absorption or x-ray fluorescence spectro(photo)meters.

Pharmacokinetic modeling of manganese. I. Dose dependencies of uptake and elimination

Homeostatic mechanisms controlling uptake, storage, and elimination of dietary manganese (Mn) afford protection against fluctuations in tissue manganese (Mn) levels. Homeostatic control of inhaled Mn is less well understood, but important in assessing likely risks of Mn inhalation. Two compartmental kinetic models were used to characterize the influence of Mn exposure level and route (oral, inhalation) on uptake, elimination, and transport of Mn. The models were fitted to or used to interpret data from five whole-body Mn elimination studies: one dietary Mn balance study, two biliary elimination studies, and one acute and one chronic. As dietary Mn concentrations increased from low sufficiency (1.5 ppm) to sufficiency (20 ppm), control of Mn uptake shifts from the intestine (principally) to more proportional control by both intestinal tissues and liver. Using a two-compartment distribution model, the increased elimination of 54Mn tracer doses in response to increases in dietary Mn (rats and mice) or inhaled Mn (rats) resulted from elevation in Mn elimination rate constants rather than changes in intercompartmental transfer rate constants between a central compartment and deep compartment. The pharmacokinetic (PK) analysis also indicated differential control of absorption in single gavage oral dose studies versus continuous high oral doses in the feed. The gavage study indicated increased elimination rate constants, and the chronic study showed reduced rate constants for absorption. These dose dependencies in uptake and elimination are necessary inputs for comprehensive PK models guiding human health risk assessments with Mn.

Effects of 12 metal ions on iron regulatory protein 1 (IRP-1) and hypoxia-inducible factor-1 alpha (HIF-1alpha) and HIF-regulated genes

Several metal ions that are carcinogenic affect cellular iron homeostasis by competing with iron transporters or iron-regulated enzymes. Some metal ions can mimic a hypoxia response in cells under normal oxygen tension, and induce expression of HIF-1alpha-regulated genes. This study investigated whether 12 metal ions altered iron homeostasis in human lung carcinoma A549 cells as measured by an activation of IRP-1 and ferritin level. We also studied hypoxia signaling by measuring HIF-1alpha protein levels, hypoxia response element (HRE)-driven luciferase reporter activity, and Cap43 protein level (an HIF-1alpha responsive gene). Our results show the following: (i) Ni(II), Co(II), V(V), Mn(II), and to a lesser extent As(III) and Cu(II) activated the binding of IRP-1 to IRE after 24 h, while the other metal ions had no effect; (ii) 10 of 12 metal ions induced HIF-1alpha protein but to strikingly different degrees. Two of these metal ions, Al(III) and Cd(II), did not induce HIF-1alpha protein; however, as indicated below, only Ni(II), Co (II), and to lesser extent Mn(II) and V(V) activated HIF-1alpha-dependent transcription. The combined effects of both [Ni(II) + As(III)] and [Ni(II) + Cr(VI)] on HIF-1alpha protein were synergistic; (iii) Addition of Fe(II) with Ni(II), Co(II), and Cr(VI) attenuated the induction of HIF-1alpha after 4 h treatment; (iv) Ni(II), Co(II), and Mn(II) significantly decrease ferritin level after 24 h exposure; (v) Ni(II), Co(II), V(V), and Mn(II) activated HRE reporter gene after 20 h treatment; (vi) Ni(II), Co(II), V(V), and Mn(II) increased the HIF-1-dependent Cap43 protein level after 24 h treatment. In conclusion, only Ni (II), Co (II), and to a lesser extent Mn(II) and V(V) significantly stabilized HIF-1alpha protein, activated IRP, decreased the levels of ferritin, induced the transcription of HIF-dependent reporter, and increased the expression of Cap43 protein levels (HIF-dependent gene). The mechanism for the significant stabilization and elevation of HIF-1alpha protein which drives these other parameters was previously shown by us and others to involve a loss of cellular Fe as well as inhibition of HIF-1alpha-dependent prolyl hydroxylases which target the binding of VHL ubiquitin ligase and degrade HIF-1alpha. Even though there were small effects of some of the other metals on IRP and HIF-1alpha, downstream effects of HIF-1alpha activation and therefore robust hypoxia signaling were only observed with Ni(II), Co(II), and to much lesser extents with Mn(II) and V(V) in human A549 lung cells. It is of interest that the metal ions that were most effective in activating hypoxia signaling were the ones that were poor inducers of metallothionein protein and also decreased Ferritin levels, since both of these proteins can bind metal ions and protect the cell against toxicity in human lung cells. It is important to study effects of these metals in human lung cells since this represents a major route of human environmental and occupational exposure to these metal ions.

Soluble nickel interferes with cellular iron homeostasis

Soluble nickel compounds are likely human carcinogens. The mechanism by which soluble nickel may contribute to carcinogenesis is unclear, though several hypotheses have been proposed. Here we verify the ability of nickel to enter the cell via the divalent metal ion transporter 1 (DMT1) and disturb cellular iron homeostasis. Nickel may interfere with iron at both an extracellular level, by preventing iron from being transported into the cell, and at an intracellular level, by competing for iron sites on enzymes like the prolyl hydroxylases that modify hypoxia inducible factor-1alpha (HIF-1alpha). Nickel was able to decrease the binding of the Von Hippel-Lindau (VHL) protein to HIF-1alpha, indicating a decrease in prolyl hydroxylase activity. The ability of nickel to affect various iron dependent processes may be an important step in nickel dependent carcinogenesis. In addition, understanding the mechanisms by which nickel activates the HIF-1alpha pathway may lead to new molecular targets in fighting cancer.

The molecular basis of copper and iron interactions

The intimate relationship between Fe and Cu in human nutrition has been recognised for many years. The best-characterised link is provided by caeruloplasmin, a multiCu-binding protein that acts as a serum ferrioxidase and is essential for the mobilisation of Fe from storage tissues. Decreased Cu status has been shown to reduce holo-caeruloplasmin production and impair ferrioxidase activity, leading, in a number of cases, to decreased tissue Fe release and the generation of anaemia that is responsive to dietary supplementation with Cu but not Fe. Dietary Fe absorption also requires the presence of a multiCu ferrioxidase. Hephaestin, a caeruloplasmin homologue, works in concert with the IREG1 transporter to permit Fe efflux from enterocytes for loading onto transferrin. The essential role of hephaestin in this process has been recognised from studies in the sex-linked anaemic (sla) mouse, in which Fe efflux is markedly impaired as a result of a mutation in the hephaestin gene that results in a truncated and non-functional version of the protein. There is emerging evidence that a number of other components of the intestinal Fe transport pathway are also Cu sensitive. Divalent metal transporter 1 (DMT1), the Fe transporter located at the apical membrane of enterocytes, is also a physiologically-relevant Cu transporter, suggesting that these two metals may compete with each other for uptake into the duodenal enterocytes. Furthermore, expression of both DMT1 and the basolateral Fe-efflux transporter IREG1 can be regulated by Cu, suggesting that the Fe-Cu relationship may be more complex than first thought.

Nickel decreases cellular iron level and converts cytosolic aconitase to iron-regulatory protein 1 in A549 cells

Nickel (Ni) compounds are well-established carcinogens and are known to initiate a hypoxic response in cells via the stabilization and transactivation of hypoxia-inducible factor-1 alpha (HIF-1alpha). This change may be the consequence of nickel's interference with the function of several Fe(II)-dependent enzymes. In this study, the effects of soluble nickel exposure on cellular iron homeostasis were investigated. Nickel treatment decreased both mitochondrial and cytosolic aconitase (c-aconitase) activity in A549 cells. Cytosolic aconitase was converted to iron-regulatory protein 1, a form critical for the regulation of cellular iron homeostasis. The increased activity of iron-regulatory protein 1 after nickel exposure stabilized and increased transferrin receptor (Tfr) mRNA and antagonized the iron-induced ferritin light chain protein synthesis. The decrease of aconitase activity after nickel treatment reflected neither direct interference with aconitase function nor obstruction of [4Fe-4S] cluster reconstitution by nickel. Exposure of A549 cells to soluble nickel decreased total cellular iron by about 40%, a decrease that likely caused the observed decrease in aconitase activity and the increase of iron-regulatory protein 1 activity. Iron treatment reversed the effect of nickel on cytosolic aconitase and iron-regulatory protein 1. To assess the mechanism for the observed effects, human embryonic kidney (HEK) cells over expressing divalent metal transporter-1 (DMT1) were compared to A549 cells expressing only endogenous transporters for inhibition of iron uptake by nickel. The inhibition data suggest that nickel can enter via DMT1 and compete with iron for entry into the cell. This disturbance of cellular iron homeostasis by nickel may have a great impact on the ability of the cell to regulate a variety of cell functions, as well as create a state of hypoxia in cells under normal oxygen tension. These effects may be very important in how nickel exerts phenotypic selection pressure to convert a normal initiated cell into a cancer cell.

Decreased transferrin receptor expression by neuromelanin cells in restless legs syndrome

BACKGROUND

Restless legs syndrome (RLS) is a sensory-movement disorder affecting 5 to 10% of the population. Its etiology is unknown, but MRI analyses and immunohistochemical studies on autopsy tissue suggest the substantia nigra (SN) of patients with RLS has subnormal amounts of iron.

METHODS

Neuromelanin cells from the SN of four RLS and four control brains were isolated by laser capture microdissection, and a profile of iron-management protein expression was obtained by immunoblot analysis. Binding assays for iron regulatory protein activity were performed on cell homogenates.

RESULTS

Ferritin, divalent metal transporter 1, ferroportin, and transferrin receptor (TfR) were decreased in RLS neuromelanin cells compared with control. Transferrin was increased in RLS neuromelanin cells. This protein profile in RLS neuromelanin cells is consistent with iron deficiency with the exception that TfR expression was decreased rather than increased. The concentration and activity of the iron regulatory proteins (IRP1 and IRP2) were analyzed to determine whether there was a functional deficit in the post-transcriptional regulatory mechanism for TfR expression. Total IRP activity, IRP1 activity, and IRP1 protein levels were decreased in RLS, but total IRP2 protein levels were not decreased in RLS.

CONCLUSION

Restless legs syndrome may result from a defect in iron regulatory protein 1 in neuromelanin cells that promotes destabilization of the transferrin receptor mRNA, leading to cellular iron deficiency.

Detection of intracellular iron by its regulatory effect

Intracellular iron regulates gene expression by inhibiting the interaction of iron regulatory proteins (IRPs) with RNA motifs called iron-responsive elements (IREs). To assay this interaction in living cells we have developed two fluorescent IRE-based reporters that rapidly, reversibly, and specifically respond to changes in cellular iron status as well as signaling that modifies IRP activity. The reporters were also sufficiently sensitive to distinguish apo- from holotransferrin in the medium, to detect the effect of modifiers of the transferrin pathway such as HFE, and to detect the donation or chelation of iron by siderophores bound to the lipocalin neutrophil gelatinase-associated lipocalin (Ngal). In addition, alternative configurations of the IRE motif either enhanced or repressed fluorescence, permitting a ratio analysis of the iron-dependent response. These characteristics make it possible to visualize iron-IRP-IRE interactions in vivo.

Human cytomegalovirus-induced host cell enlargement is iron dependent

A hallmark of human cytomegalovirus (HCMV) infection is the characteristic enlargement of the host cells (i.e., cytomegaly). Because iron (Fe) is required for cell growth and Fe chelators inhibit viral replication, we investigated the effects of HCMV infection on Fe homeostasis in MRC-5 fibroblasts. Using the metallosensitive fluorophore calcein and the Fe chelator salicylaldehyde isonicotinoyl hydrazone (SIH), the labile iron pool (LIP) in mock-infected cells was determined to be 1.04 +/- 0.05 microM. Twenty-four hours postinfection (hpi), the size of the LIP had nearly doubled. Because cytomegaly occurs between 24 and 96 hpi, access to this larger LIP could be expected to facilitate enlargement to approximately 375% of the initial cell size. The ability of Fe chelation by 100 microM SIH to limit enlargement to approximately 180% confirms that the LIP plays a major role in cytomegaly. The effect of SIH chelation on the mitochondrial membrane potential (DeltaPsi(M)) and morphology was studied using the mitochondrial voltage-sensitive dye JC-1. The mitochondria in mock-infected cells were heterogeneous with a broad distribution of DeltaPsi(M) and were threadlike. In contrast, the mitochondria of HCMV-infected cells had a more depolarized DeltaPsi(M) distributed over a narrow range and were grainlike in appearance. However, the HCMV-induced alteration in DeltaPsi(M) was not affected by SIH chelation. We conclude that the development of cytomegaly is inhibited by Fe chelation and may be facilitated by an HCMV-induced increase in the LIP.

Unexpected anthracycline-mediated alterations in iron-regulatory protein-RNA-binding activity: the iron and copper complexes of anthracyclines decrease RNA-binding activity

Anthracyclines are effective antineoplastic agents. However, the interaction of these drugs with iron (Fe) is an important cause of myocardial toxicity, limiting their therapeutic use (J Lab Clin Med 122:245-251, 1993). To overcome this limitation, it is crucial to understand how anthracyclines interact with the Fe metabolism of myocardial and neoplastic cells. Iron-regulatory proteins (IRPs) play vital roles in regulating cellular Fe metabolism via their mRNA-binding activity. We showed that doxorubicin (DOX) and its analogs interfere with tumor and myocardial cell Fe metabolism by affecting the RNA-binding activity of IRPs. Unexpectedly, experiments with the free radical scavengers, catalase, superoxide dismutase, ebselen, and Mn(III) tetrakis (4-benzoic acid) porphyrin complex, suggested that the effects of DOX on IRP-RNA-binding activity were not due to anthracycline-mediated free radical production. In contrast to previous studies, we showed that the DOX metabolite, doxorubicinol, had no effect on IRP-RNA-binding activity. Rather, the anthracycline-Fe and -copper (Cu) complexes decreased IRP-RNA-binding activity, indicating that formation of anthracycline-metal complexes may affect cellular Fe metabolism. In addition, anthracyclines prevented the response of IRPs to the depletion of intracellular Fe by chelators. This information may be useful in designing novel therapeutic strategies against tumor cells by combining chelators and anthracyclines. Interestingly, the effect of DOX on primary cultures of cardiomyocytes was similar to that observed using neoplastic cells, and particularly notable was the decrease in IRP2-RNA-binding activity. Our results add significant new information regarding the effects of anthracyclines on Fe metabolism that may lead to the design of more effective treatments.

Effects of copper on the expression of metal transporters in human intestinal Caco-2 cells

Copper is an essential dietary trace metal, however the mechanisms involved in intestinal copper uptake are unclear. Two putative copper transporters are expressed in Caco-2 cells, the divalent metal transporter (DMT1) and copper transporter (Ctr1). Our data demonstrate that copper could compete with iron for uptake via DMT1 and that DMT1 protein and mRNA expression were decreased following exposure (24 h) to high copper. Expression of Ctr1, which acts as a copper transporter in transfected cell lines, was unaffected by copper treatment. Interestingly, exposure to copper increased iron efflux from Caco-2 cells and up regulated IREG1 (iron-regulated mRNA) expression.