Ctr1 is an apical copper transporter in mammalian intestinal epithelial cells in vivo that is controlled at the level of protein stability

Copper physiology in ruminants: trafficking of systemic copper, adaptations to variation in nutritional supply and thiomolybdate challenge

Ruminants are recognised to suffer from Cu-responsive disorders. Present understanding of Cu transport and metabolism is limited and inconsistent across vets and veterinary professionals. There has been much progress from the studies of the 1980s and early 1990s in cellular Cu transport and liver metabolism which has not been translated into agricultural practice. Cu metabolism operates in regulated pathways of Cu trafficking rather than in pools of Cu lability. Cu in the cell is chaperoned to enzyme production, retention within metallothionein or excretion via the Golgi into the blood. The hepatocyte differs in that Cu-containing caeruloplasmin can be synthesised to provide systemic Cu supply and excess Cu is excreted via bile. The aim of the present review is to improve understanding and highlight the relevant progress in relation to ruminants through the translation of newer findings from medicine and non-ruminant animal models into ruminants.

Brain–Barrier Regulation, Metal (Cu, Fe) Dyshomeostasis, and Neurodegenerative Disorders in Man and Animals

The neurodegenerative diseases (Alzheimers, Parkinsons, amyotrophic lateral sclerosis, Huntingtons) and the prion disorders, have in common a dysregulation of metalloprotein chemistry involving redox metals (Cu, Fe, Mn). The consequent oxidative stress is associated with protein plaques and neuronal cell death. An equilibrium exists between the functional requirement of the brain for Cu and Fe and their destructive potential with the production of reactive oxygen species. The importance of the brain barrier is highlighted in regulating the import of these metals. Upregulation of key transporters occurs in fetal and neonatal life when brain metal requirement is high, and is downregulated in adult life when need is minimal. North Ronaldsay sheep are introduced as an animal model in which a neonatal mode of CTR1 upregulation persists into adulthood and leads to the premise that metal regulation may return to this default setting in ageing, with implications for the neurodegenerative diseases.

Silver Ions as a Tool for Understanding Different Aspects of Copper Metabolism

In humans, copper is an important micronutrient because it is a cofactor of ubiquitous and brain-specific cuproenzymes, as well as a secondary messenger. Failure of the mechanisms supporting copper balance leads to the development of neurodegenerative, oncological, and other severe disorders, whose treatment requires a detailed understanding of copper metabolism. In the body, bioavailable copper exists in two stable oxidation states, Cu(I) and Cu(II), both of which are highly toxic. The toxicity of copper ions is usually overcome by coordinating them with a wide range of ligands. These include the active cuproenzyme centers, copper-binding protein motifs to ensure the safe delivery of copper to its physiological location, and participants in the Cu(I) ↔ Cu(II) redox cycle, in which cellular copper is stored. The use of modern experimental approaches has allowed the overall picture of copper turnover in the cells and the organism to be clarified. However, many aspects of this process remain poorly understood. Some of them can be found out using abiogenic silver ions (Ag(I)), which are isoelectronic to Cu(I). This review covers the physicochemical principles of the ability of Ag(I) to substitute for copper ions in transport proteins and cuproenzyme active sites, the effectiveness of using Ag(I) to study copper routes in the cells and the body, and the limitations associated with Ag(I) remaining stable in only one oxidation state. The use of Ag(I) to restrict copper transport to tumors and the consequences of large-scale use of silver nanoparticles for human health are also discussed.

Copper Transport and Disease: What Can We Learn from Organoids?

Many metals have biological functions and play important roles in human health. Copper (Cu) is an essential metal that supports normal cellular physiology. Significant research efforts have focused on identifying the molecules and pathways involved in dietary Cu uptake in the digestive tract. The lack of an adequate in vitro model for assessing Cu transport processes in the gut has led to contradictory data and gaps in our understanding of the mechanisms involved in dietary Cu acquisition. The recent development of organoid technology has provided a tractable model system for assessing the detailed mechanistic processes involved in Cu utilization and transport in the context of nutrition. Enteroid (intestinal epithelial organoid)-based studies have identified new links between intestinal Cu metabolism and dietary fat processing. Evidence for a metabolic coupling between the dietary uptake of Cu and uptake of fat (which were previously thought to be independent) is a new and exciting finding that highlights the utility of these three-dimensional primary culture systems. This review has three goals: (a) to critically discuss the roles of key Cu transport enzymes in dietary Cu uptake; (b) to assess the use, utility, and limitations of organoid technology in research into nutritional Cu transport and Cu-based diseases; and (c) to highlight emerging connections between nutritional Cu homeostasis and fat metabolism.

Copper transporter 1 (CTR1) expression by mouse testicular germ cells, but not Sertoli cells, is essential for functional spermatogenesis

An imbalance in copper (Cu) tissue homeostasis has a degenerative effect on spermatogenesis and male fertility. The high-affinity Cu transporter 1 (CTR1; SLC31A1) is the major protein responsible for Cu acquisition in eukaryotes and is highly expressed in mouse testes. Studies on yeast and Drosophila have demonstrated the conserved essential function of Cu and CTR1 for meiosis and fertility, implying that CTR1 may play an essential function in mammalian spermatogenesis. In mice, spermatogenesis takes place within the seminiferous epithelium, where tight junctions between somatic Sertoli cells (SCs) create a specialized microenvironment for the development of meiotic germ cells (GCs) by tightly regulating the free transport of metabolites and ions to reach these cells. Here, it is demonstrated that within the seminiferous epithelium, CTR1 is expressed on the membrane of primary pachytene spermatocytes and SCs. To examine the physiological significance of CTR1 in spermatogenesis, mice with a GC-specific (Ctr1ΔGC) and SC-specific (Ctr1ΔSC) disruption of the Ctr1 gene were generated. The testis of Ctr1ΔGC mice exhibits a severe progressive loss of GCs starting at postnatal day (PND) 28 leading to testis hypoplasia by adulthood. No spermatogenic recovery was observed in Ctr1ΔGC testis beyond PND 41, despite the presence of FOXO-1 expressing undifferentiated spermatogonial cells. However, Ctr1ΔSC mice displayed functional spermatogenesis and were fertile, even though testicular Cu levels and Cu-dependent cellular activities were significantly reduced. These results reveal, for the first time, the importance of CTR1 expression by GCs for maintaining functional spermatogenesis.

Cytotoxic phenanthroline derivatives alter metallostasis and redox homeostasis in neuroblastoma cells

Copper homeostasis is generally investigated focusing on a single component of the metallostasis network. Here we address several of the factors controlling the metallostasis for neuroblastoma cells (SH-SY5Y) upon treatment with 2,9-dimethyl-1,10-phenanthroline-5,6-dione (phendione) and 2,9-dimethyl-1,10-phenanthroline (cuproindione). These compounds bind and transport copper inside cells, exert their cytotoxic activity through the induction of oxidative stress, causing apoptosis and alteration of the cellular redox and copper homeostasis network. The intracellular pathway ensured by copper transporters (Ctr1, ATP7A), chaperones (CCS, ATOX, COX 17, Sco1, Sco2), small molecules (GSH) and transcription factors (p53) is scrutinised.

Copper Metabolism of Newborns Is Adapted to Milk Ceruloplasmin as a Nutritive Source of Copper: Overview of the Current Data

Copper, which can potentially be a highly toxic agent, is an essential nutrient due to its role as a cofactor for cuproenzymes and its participation in signaling pathways. In mammals, the liver is a central organ that controls copper turnover throughout the body, including copper absorption, distribution, and excretion. In ontogenesis, there are two types of copper metabolism, embryonic and adult, which maintain the balance of copper in each of these periods of life, respectively. In the liver cells, these types of metabolism are characterized by the specific expression patterns and activity levels of the genes encoding ceruloplasmin, which is the main extracellular ferroxidase and copper transporter, and the proteins mediating ceruloplasmin metalation. In newborns, the molecular genetic mechanisms responsible for copper homeostasis and the ontogenetic switch from embryonic to adult copper metabolism are highly adapted to milk ceruloplasmin as a dietary source of copper. In the mammary gland cells, the level of ceruloplasmin gene expression and the alternative splicing of its pre-mRNA govern the amount of ceruloplasmin in the milk, and thus, the amount of copper absorbed by a newborn is controlled. In newborns, the absorption, distribution, and accumulation of copper are adapted to milk ceruloplasmin. If newborns are not breast-fed in the early stages of postnatal development, they do not have this natural control ensuring alimentary copper balance in the body. Although there is still much to be learned about the neonatal consequences of having an imbalance of copper in the mother/newborn system, the time to pay attention to this problem has arrived because the neonatal misbalance of copper may provoke the development of copper-related disorders.

Absorption Mechanisms of Iron, Copper, and Zinc: An Overview

Essential trace elements play pivotal roles in numerous structural and catalytic functions of proteins. Adequate intake of essential trace elements from the daily diet is indispensable to the maintenance of health, and their deficiency leads to a variety of conditions. However, excessive amounts of these trace elements may be highly toxic, and in some cases, may cause damage by the production of harmful reactive oxygen species. Homeostatic dysregulation of their metabolism increases the risk of developing diseases. Specific transport proteins that facilitate influx or efflux of trace elements play key roles in maintaining the homeostasis. Recent elucidation of their crucial functions significantly facilitated our understanding of the molecular mechanisms of iron (Fe), copper (Cu), and zinc (Zn) absorption in the small intestine. This paper summarizes their absorption mechanisms, with a focus on indispensable functions of the molecules involved in it, and briefly discusses the mechanisms of homeostatic control of each element at the cellular and systemic levels.

Intestinal DMT1 Is Essential for Optimal Assimilation of Dietary Copper in Male and Female Mice with Iron-Deficiency Anemia

Background

Divalent metal-ion transporter 1 (DMT1) may transport copper, but studies to date on this topic have been equivocal. Previously, an ex vivo experiment showed that intestinal copper transport was impaired in Dmt1-mutant Belgrade rats.

Objective

In this study, we tested the hypothesis that intestinal DMT1 transports copper in vivo.

Methods

Intestine-specific Dmt1 knockout (Dmt1int/int) mice and normal (control) littermates (Dmt1fl/fl) were used. In study 1, intestinal copper absorption was assessed in 7-wk-old mice of both sexes and genotypes by oral-intragastric gavage of 64Cu under normal and iron-deficiency anemia (IDA) conditions. In study 2, both sexes and genotypes of 8-wk-old mice were fed diets with adequate iron concentrations [72 parts per million (ppm)] plus adequate (9 ppm) or excessive (183 ppm) copper concentrations for 4 wk. Iron- and copper-related physiologic variables were subsequently assessed.

Results

Study 1 showed that intestinal copper transport was enhanced in normal (∼11% increase in males, 35% in females) and anemic (∼42% increase in males, 35% in females) Dmt1int/int mice. Study 2 showed that, with adequate copper intakes, serum ceruloplasmin (Cp) activity was decreased (by ∼29% in males and 20% in females) and spleens were enlarged (by 3-fold in both sexes) in Dmt1int/int mice. Higher dietary copper increased hepatic copper concentrations (by ∼3.3-fold in males and 1.5-fold in females), restored serum Cp activity, and mitigated the noted splenomegaly in Dmt1int/int mice.

Conclusions

Copper homeostasis was disrupted in Dmt1int/int mice, particularly during IDA, despite the noted increases in intestinal copper transport. This was exemplified by the fact that extra dietary copper was required to restore serum Cp activity (a biomarker of copper status) and reduce the severity of the noted splenomegaly (which could reflect changes in erythropoietic demand) in Dmt1int/int mice. Collectively, these observations show that intestinal DMT1 is essential for the assimilation of sufficient quantities of dietary copper to maintain systemic copper homeostasis during IDA.

Organ‑specific expression of the divalent ion channel proteins NCKX3, TRPV2, CTR1, ATP7A, IREG1 and HEPH in various canine organs

Transmembrane cation channels include those for calcium, copper and iron ion transport. Each channel has physiological significance, and all have been associated with disease. However, the comparative study of transcriptional‑translational levels in canine organs has not been previously reported. In the present study, organ‑specific expression of calcium channels, including sodium/potassium/calcium exchanger 3 (NCKX3) and transient receptor potential cation channel subfamily V member 2 (TRPV2), copper channels, including high affinity copper uptake protein 1 (CTR1) and copper‑transporting ATPase 1 (ATP7A), and iron channels, including iron‑regulated transporter 1 (IREG1) and hephaestin (HEPH) proteins and their mRNAs were examined in the canine duodenum, kidney, spleen and liver. NCKX3 protein expression was highest in the kidney, moderate in the duodenum, and lowest in the spleen and liver, whereas TRPV2 protein was highly expressed in the kidney, duodenum and liver, and was low in the spleen. The CTR1 protein expression level was highest in the liver, followed (in descending order) by the duodenum, kidney and spleen. The ATP7A protein expression level was highest in the duodenum and lowest in the spleen. The IREG1 protein expression level was highest in the liver, followed (in descending order) by the kidney, duodenum and spleen. The HEPH protein level was high in liver, moderate in the duodenum and kidney, and low in the spleen. The results of the immunohistochemistry analysis demonstrated ion channel protein localizations. These results suggested that cation channel proteins are differentially expressed among canine organs, and they may be involved in organ‑specific functions associated with the maintenance of physiological homeostasis.

Interaction of the New Monofunctional Anticancer Agent Phenanthriplatin With Transporters for Organic Cations

Cancer treatment with platinum compounds is an important achievement of modern chemotherapy. However, despite the beneficial effects, the clinical impact of these agents is hampered by the development of drug resistance as well as dose-limiting side effects. The efficacy but also side effects of platinum complexes can be mediated by uptake through plasma membrane transporters. In the kidneys, plasma membrane transporters are involved in their secretion into the urine. Renal secretion is accomplished by uptake from the blood into the proximal tubules cells, followed by excretion into the urine. The uptake process is mediated mainly by organic cation transporters (OCT), which are expressed in the basolateral domain of the plasma membrane facing the blood. The excretion of platinum into the urine is mediated by exchange with protons via multidrug and toxin extrusion proteins (MATE) expressed in the apical domain of plasma membrane. Recently, the monofunctional, cationic platinum agent phenanthriplatin, which is able to escape common cellular resistance mechanisms, has been synthesized and investigated. In the present study, the interaction of phenanthriplatin with transporters for organic cations has been evaluated. Phenanthriplatin is a high affinity substrate for OCT2, but has a lower apparent affinity for MATEs. The presence of these transporters increased cytotoxicity of phenanthriplatin. Therefore, phenanthriplatin may be especially effective in the treatment of cancers that express OCTs, such as colon cancer cells. However, the interaction of phenanthriplatin with OCTs suggests that its use as chemotherapeutic agent may be complicated by OCT-mediated toxicity. Unlike cisplatin, phenanthriplatin interacts with high specificity with hMATE1 and hMATE2K in addition to hOCT2. This interaction may facilitate its efflux from the cells and thereby decrease overall efficacy and/or toxicity.

CHCA-1 is a copper-regulated CTR1 homolog required for normal development, copper accumulation, and copper-sensing behavior in Caenorhabditis elegans

Copper plays key roles in catalytic and regulatory biochemical reactions essential for normal growth, development, and health. Dietary copper deficiencies or mutations in copper homeostasis genes can lead to abnormal musculoskeletal development, cognitive disorders, and poor growth. In yeast and mammals, copper is acquired through the activities of the CTR1 family of high-affinity copper transporters. However, the mechanisms of systemic responses to dietary or tissue-specific copper deficiency remain unclear. Here, taking advantage of the animal model Caenorhabditis elegans for studying whole-body copper homeostasis, we investigated the role of a C. elegans CTR1 homolog, CHCA-1, in copper acquisition and in worm growth, development, and behavior. Using sequence homology searches, we identified 10 potential orthologs to mammalian CTR1 Among these genes, we found that chca-1, which is transcriptionally up-regulated in the intestine and hypodermis of C. elegans during copper deficiency, is required for normal growth, reproduction, and maintenance of systemic copper balance under copper deprivation. The intestinal copper transporter CUA-1 normally traffics to endosomes to sequester excess copper, and we found here that loss of chca-1 caused CUA-1 to mislocalize to the basolateral membrane under copper overload conditions. Moreover, animals lacking chca-1 exhibited significantly reduced copper avoidance behavior in response to toxic copper conditions compared with WT worms. These results establish that CHCA-1-mediated copper acquisition in C. elegans is crucial for normal growth, development, and copper-sensing behavior.

Organ-specific regulation of ATP7A abundance is coordinated with systemic copper homeostasis

Copper (Cu) is an essential cofactor for various enzymatic activities including mitochondrial electron transport, iron mobilization, and peptide hormone maturation. Consequently, Cu dysregulation is associated with fatal neonatal disease, liver and cardiac dysfunction, and anemia. While the Cu transporter ATP7A plays a major role in both intestinal Cu mobilization to the periphery and prevention of Cu over-accumulation, it is unclear how regulation of ATP7A contributes to Cu homeostasis in response to systemic Cu fluctuation. Here we show, using Cu-deficient mouse models, that steady-state levels of ATP7A are lower in peripheral tissues (including the heart, spleen, and liver) under Cu deficiency and that subcutaneous administration of Cu to these animals restore normal ATP7A levels in these tissues. Strikingly, ATP7A in the intestine is regulated in the opposite manner - low systemic Cu increases ATP7A while subcutaneous Cu administration decreases ATP7A suggesting that intestine-specific non-autonomous regulation of ATP7A abundance may serve as a key homeostatic control for Cu export into the circulation. Our results support a systemic model for how a single transporter can be inversely regulated in a tissue-specific manner to maintain organismal Cu homeostasis.

The copper transporter (SLC31A1/CTR1) is expressed in bovine spermatozoa and oocytes: Copper in IVF medium improves sperm quality

Adequate dietary intake of copper (Cu) is required for normal reproductive performance in cattle. The objective of this study was to investigate the pregnancy rates from cattle with deficient, marginal and adequate Cu plasma concentration at the beginning of artificial insemination protocol. Moreover, we determined Cu concentrations present in bovine oviductal fluid (OF), and the effects of Cu on fertilizing ability of bovine spermatozoa. Also, the presence of Cu transporter, SLC31A1 (also known as CTR1), in spermatozoa and in vitro matured oocyte were investigated. We found no differences in pregnancy rates among animals with adequate, marginal, and deficient Cu concentrations measured in plasma at the beginning of fixed-time artificial insemination (FTAI) protocol. Copper concentrations in OF were 38.3 ± 2.17 μg/dL (mean ± SEM) regardless of cupremia levels. The addition of 40 μg/dL Cu to IVF medium enhanced total and progressive motility, sperm viability, functional sperm membrane integrity (HOST), sperm-zona binding, and pronuclear formation. On the other hand, the presence of Cu in IVF medium did not modify acrosome integrity and cleavage rates after IVF, but impaired blastocyst rates. Cu transporter SLC31A1 was detected in bovine spermatozoa in the apical segment of acrosome, and in the oocyte matured in vitro. In conclusion, the results obtained in the present study determined that cupremia levels at the beginning of FTAI protocol did not influence the pregnancy rates at 60 d after insemination. The presence of CTR1 in bovine mature oocyte and spermatozoa, as well as the beneficial effect of Cu on sperm quality would suggest an important role of this mineral during the fertilization process.

Numerical Simulations Reveal Randomness of Cu(II) Induced Aβ Peptide Dimerization under Conditions Present in Glutamatergic Synapses

The interactions between the Aβ1-40 molecules species and the copper ions (Cu(II)) were intensively investigated due to their potential role in the development of the Alzheimer Disease (AD). The rate and the mechanism of the Cu(II)-Aβ complexes formation determines the aggregation pathway of the Aβ species, starting from smaller but more cytotoxic oligomers and ending up in large Aβ plaques, being the main hallmark of the AD. In our study we exploit the existing knowledge on the Cu(II)-Aβ interactions and create the theoretical model of the initial phase of the copper- driven Aβ aggregation mechanism. The model is based on the direct solution of the Chemical Master Equations, which capture the inherent stochastics of the considered system. In our work we argue that due to a strong Cu(II) affinity to Aβ and temporal accessibility of the Cu(II) ions during normal synaptic activity the aggregation driven by Cu(II) dominates the pure Aβ aggregation. We also demonstrate the dependence of the formation of different Cu(II)-Aβ complexes on the concentrations of reagents and the synaptic activity. Our findings correspond to recent experimental results and give a sound hypothesis on the AD development mechanisms.

Neurotoxicity of Copper

Copper is an essential trace metal that is required for several important biological processes, however, an excess of copper can be toxic to cells. Therefore, systemic and cellular copper homeostasis is tightly regulated, but dysregulation of copper homeostasis may occur in disease states, resulting either in copper deficiency or copper overload and toxicity. This chapter will give an overview on the biological roles of copper and of the mechanisms involved in copper uptake, storage, and distribution. In addition, we will describe potential mechanisms of the cellular toxicity of copper and copper oxide nanoparticles. Finally, we will summarize the current knowledge on the connection of copper toxicity with neurodegenerative diseases.

Orchestration of dynamic copper navigation – new and missing pieces

A general principle in all cells in the body is that an essential metal – here copper – is taken up at the plasma membrane, directed through cellular compartments for use in specific enzymes and pathways, stored in specific scavenging molecules if in surplus, and finally expelled from the cells.

Acute Copper and Ascorbic Acid Supplementation Inhibits Non-heme Iron Absorption in Humans

The objective of the study is to determine the effect of copper (Cu) plus the reducing agent ascorbic acid (AA) on the absorption of non-heme iron (Fe). Experimental study with block design in which each subject was his own control. After signing an informed consent, 14 adult women using an effective method of contraception and negative pregnancy test received 0.5 mg Fe, as ferrous sulfate, alone or with Cu, as copper sulfate, plus ascorbic acid (AA/Cu 2/1 molar ratio) at 4/1; 6/1 and 8/1 Cu/Fe molar ratios as an aqueous solution on days 1, 2, 14, and 15 of the study. Fe absorption was assessed by erythrocyte incorporation of iron radioisotopes (55)Fe and (59)Fe. Geometric mean (range ± SD) absorption of Fe at 4/1 and 6/1 Cu/Fe molar ratios (and AA/Cu 2/1 molar ratio) and Fe alone was 57.4 % (35.7-92.1 %), 64.2 % (45.8-89.9 %), and 38.8 % (20.4-73.8 %), respectively (ANOVA for repeated measures p < 0.001; post hoc test Scheffé, p < 0.05). This is attributable to the enhancing effect of AA on non-heme Fe absorption; however, Fe absorption at Cu/Fe 8/1 molar ratio was 47.3 % (27.7-80.8) (p = NS compared with Fe alone). It was expected that Fe absorption would have been equal or greater than at 4/1 and 6/1 molar ratios. Copper in the presence of ascorbic acid inhibits non-heme Fe absorption at Cu/Fe 8/1 molar ratio.

Cathepsin Protease Controls Copper and Cisplatin Accumulation via Cleavage of the Ctr1 Metal-binding Ectodomain

Copper is an essential metal ion for embryonic development, iron acquisition, cardiac function, neuropeptide biogenesis, and other critical physiological processes. Ctr1 is a high affinity Cu(+) transporter on the plasma membrane and endosomes that exists as a full-length protein and a truncated form of Ctr1 lacking the methionine- and histidine-rich metal-binding ectodomain, and it exhibits reduced Cu(+) transport activity. Here, we identify the cathepsin L/B endolysosomal proteases functioning in a direct and rate-limiting step in the Ctr1 ectodomain cleavage. Cells and mice lacking cathepsin L accumulate full-length Ctr1 and hyper-accumulate copper. As Ctr1 also transports the chemotherapeutic drug cisplatin via direct binding to the ectodomain, we demonstrate that the combination of cisplatin with a cathepsin L/B inhibitor enhances cisplatin uptake and cell killing. These studies identify a new processing event and the key protease that cleaves the Ctr1 metal-binding ectodomain, which functions to regulate cellular Cu(+) and cisplatin acquisition.

Intestinal DMT1 is critical for iron absorption in the mouse but is not required for the absorption of copper or manganese

Divalent metal-ion transporter-1 (DMT1) is a widely expressed iron-preferring membrane-transport protein that serves a critical role in erythroid iron utilization. We have investigated its role in intestinal metal absorption by studying a mouse model lacking intestinal DMT1 (i.e., DMT1(int/int)). DMT1(int/int) mice exhibited a profound hypochromic-microcytic anemia, splenomegaly, and cardiomegaly. That the anemia was due to iron deficiency was demonstrated by the following observations in DMT1(int/int) mice: 1) blood iron and tissue nonheme-iron stores were depleted; 2) mRNA expression of liver hepcidin (Hamp1) was depressed; and 3) intraperitoneal iron injection corrected the anemia, and reversed the changes in blood iron, nonheme-iron stores, and hepcidin expression levels. We observed decreased total iron content in multiple tissues from DMT1(int/int) mice compared with DMT1(+/+) mice but no meaningful change in copper, manganese, or zinc. DMT1(int/int) mice absorbed (64)Cu and (54)Mn from an intragastric dose to the same extent as did DMT1(+/+) mice but the absorption of (59)Fe was virtually abolished in DMT1(int/int) mice. This study reveals a critical function for DMT1 in intestinal nonheme-iron absorption for normal growth and development. Further, this work demonstrates that intestinal DMT1 is not required for the intestinal transport of copper, manganese, or zinc.

The copper transporter 1 (CTR1) is required to maintain the stability of copper transporter 2 (CTR2)

Mammalian cells have two influx Cu transporters that form trimers in membranes. CTR1 is the high affinity transporter that resides largely in the plasma membrane, and CTR2 is the low affinity transporter that is primarily associated with vesicular structures inside the cell. The major differences between CTR1 and CTR2 are that CTR1 contains a HIS/MET-rich domain N-terminal of the METS that participate in the first two stacked rings that form the pore, and a longer C-terminal tail that includes a Cu binding HIS-CYS-HIS (HCH) motif right at the end. It has been reported that CTR1 and CTR2 are physically associated with each other in the cell. We used the CRISPR-Cas9 technology to knock out either CTR1 or CTR2 in fully malignant HEK293T and OVCAR8 human ovarian cancer cells to investigate the interaction of CTR1 and CTR2. We report here that the level of CTR2 protein is markedly decreased in CTR1 knockout clones while the CTR2 transcript level remains unchanged. CTR2 was found to be highly ubiquitinated in the CTR1 knock out cells, and inhibition of the proteasome prevented the degradation of CTR2 when CTR1 was not present while inhibition of autophagy had no effect. Re-expression of CTR1 rescued CTR2 from degradation in the CTR1 knockout cells. We conclude that CTR1 is essential to maintain the stability of CTR2 and that in the absence of CTR1 CTR2 is degraded by the proteasome. This reinforces the concept that the functions of CTR1 and CTR2 are inter-dependent within the Cu homeostasis system.

Adaptor Protein-1 Complex Affects the Endocytic Trafficking and Function of Peptidylglycine α-Amidating Monooxygenase, a Luminal Cuproenzyme

The adaptor protein-1 complex (AP-1), which transports cargo between the trans-Golgi network and endosomes, plays a role in the trafficking of Atp7a, a copper-transporting P-type ATPase, and peptidylglycine α-amidating monooxygenase (PAM), a copper-dependent membrane enzyme. Lack of any of the four AP-1 subunits impairs function, and patients with MEDNIK syndrome, a rare genetic disorder caused by lack of expression of the σ1A subunit, exhibit clinical and biochemical signs of impaired copper homeostasis. To explore the role of AP-1 in copper homeostasis in neuroendocrine cells, we used corticotrope tumor cells in which AP-1 function was diminished by reducing expression of its μ1A subunit. Copper levels were unchanged when AP-1 function was impaired, but cellular levels of Atp7a declined slightly. The ability of PAM to function was assessed by monitoring 18-kDa fragment-NH2 production from proopiomelanocortin. Reduced AP-1 function made 18-kDa fragment amidation more sensitive to inhibition by bathocuproine disulfonate, a cell-impermeant Cu(I) chelator. The endocytic trafficking of PAM was altered, and PAM-1 accumulated on the cell surface when AP-1 levels were reduced. Reduced AP-1 function increased the Atp7a presence in early/recycling endosomes but did not alter the ability of copper to stimulate its appearance on the plasma membrane. Co-immunoprecipitation of a small fraction of PAM and Atp7a supports the suggestion that copper can be transferred directly from Atp7a to PAM, a process that can occur only when both proteins are present in the same subcellular compartment. Altered luminal cuproenzyme function may contribute to deficits observed when the AP-1 function is compromised.

Elemental mapping of the entire intact Drosophila gastrointestinal tract

The main role of the animal gastrointestinal (GI) tract is the selective absorption of dietary nutrients from ingested food sources. One class of vital micronutrients are the essential biometals such as copper, zinc and iron, which participate in a plethora of biological process, acting as enzymatic or structural co-factors for numerous proteins and also as important cellular signalling molecules. To help elucidate the mechanisms by which biometals are absorbed from the diet, we mapped elemental distribution in entire, intact Drosophila larval GI tracts using synchrotron X-ray fluorescence microscopy. Our results revealed distinct regions of the GI tract enriched for specific metals. Copper was found to be concentrated in the copper cell region but also in the region directly anterior to the copper cells and unexpectedly, in the middle midgut/iron cell region as well. Iron was observed exclusively in the iron cell region, confirming previous work with iron-specific histological stains. Zinc was observed throughout the GI tract with an increased accumulation in the posterior midgut region, while manganese was seen to co-localize with calcium specifically in clusters in the distal Malpighian tubules. This work simultaneously reveals distribution of a number of biologically important elements in entire, intact GI tracts. These distributions revealed not only a previously undescribed Ca/Mn co-localization, but also the unexpected presence of additional Cu accumulations in the iron cell region.

Targeting drug transport mechanisms for improving platinum-based cancer chemotherapy

INTRODUCTION

Platinum (Pt)-based antitumor agents remain important chemotherapeutic agents for treating many human malignancies. Elevated expression of the human high-affinity copper transporter 1 (hCtr1), resulting in enhanced Pt drug transport into cells, has been shown to be associated with improved treatment efficacy. Thus, targeting hCtr1 upregulation is an attractive strategy for improving the treatment efficacy of Pt-based cancer chemotherapy.

AREA COVERED

Regulation of hCtr1 expression by cellular copper homeostasis is discussed. Association of elevated hCtr1 expression with intrinsic sensitivity of ovarian cancer to Pt drugs is presented. Mechanism of copper-lowering agents in enhancing hCtr1-mediated cis-diamminedichloroplatinum (II) (cisplatin, cDDP) transport is reviewed. Applications of copper chelation strategy in overcoming cDDP resistance through enhanced hCtr1 expression are evaluated.

EXPERT OPINION

While both transcriptional and post-translational mechanisms of hCtr1 regulation by cellular copper bioavailability have been proposed, detailed molecular insights into hCtr1 regulation by copper homeostasis remain needed. Recent clinical study using a copper-lowering agent in enhancing hCtr1-mediated drug transport has achieved incremental improvement in overcoming Pt drug resistance. Further improvements in identifying predictive measures in the subpopulation of patients that can benefit from the treatment are needed.

Duodenal cytochrome b (DCYTB) in iron metabolism: an update on function and regulation

Iron and ascorbate are vital cellular constituents in mammalian systems. The bulk-requirement for iron is during erythropoiesis leading to the generation of hemoglobin-containing erythrocytes. Additionally, both iron and ascorbate are required as co-factors in numerous metabolic reactions. Iron homeostasis is controlled at the level of uptake, rather than excretion. Accumulating evidence strongly suggests that in addition to the known ability of dietary ascorbate to enhance non-heme iron absorption in the gut, ascorbate regulates iron homeostasis. The involvement of ascorbate in dietary iron absorption extends beyond the direct chemical reduction of non-heme iron by dietary ascorbate. Among other activities, intra-enterocyte ascorbate appears to be involved in the provision of electrons to a family of trans-membrane redox enzymes, namely those of the cytochrome b₅₆₁ class. These hemoproteins oxidize a pool of ascorbate on one side of the membrane in order to reduce an electron acceptor (e.g., non-heme iron) on the opposite side of the membrane. One member of this family, duodenal cytochrome b (DCYTB), may play an important role in ascorbate-dependent reduction of non-heme iron in the gut prior to uptake by ferrous-iron transporters. This review discusses the emerging relationship between cellular iron homeostasis, the emergent “IRP1-HIF2α axis”, DCYTB and ascorbate in relation to iron metabolism.

Influence of ZIP14 (slc39A14) on intestinal zinc processing and barrier function

ZIP14 is a zinc transport protein with high expression in the small intestine and liver. Zip14 is upregulated during endotoxemia and leads to increased liver zinc content and transient hypozinemia. Since body zinc status and inflammation are associated with changes in intestinal permeability, we hypothesized that ZIP14 may influence intestinal permeability. Wild-type (WT) and Zip14 knockout (KO) mice were used to determine ZIP14-associated intestinal zinc metabolism and effects on permeability. Fractionation of plasma membranes revealed that ZIP14 is localized to the basolateral membrane of enterocytes. Studies utilizing (65)Zn administered by subcutaneous injection revealed greater zinc accumulation in the SI of Zip14 KO mice compared with WT mice. Isolation of endosomes confirmed the presence of ZIP14. Quantification of endosomal zinc concentration by FluoZin-3AM fluorescence demonstrated that zinc is trapped in endosomes of Zip14 KO mice. Intestinal permeability assessed both by plasma FITC-dextran following gavage and by serum endotoxin content was greater in Zip14 KO mice. Threonine phosphorylation of the tight junction protein occludin, which is necessary for tight junction assembly, was reduced in KO mice. Claudin 1 and 2, known to have an inverse relationship in regards to tight junction integrity, reflected impaired barrier function in KO jejunum. These data suggest involvement of ZIP14 in providing zinc for a regulatory role needed for maintenance of the intestinal barrier. In conclusion, ZIP14 is a basolaterally localized protein in enterocytes and is involved in endosomal trafficking of zinc and is necessary for proper maintenance of intestinal tight junctions.

Molecular mechanisms underlying copper homeostasis in Mammalian cells

Copper (Cu) is an essential metal for living organisms that utilize oxygen for respiration and is required as a cofactor of redox-regulating enzymes, such as superoxide dismutase, ceruloplasmin, lysyl oxidase, tyrosinase, and dopamine β-hydroxylase. However, the redox-active property of this metal may have toxic effects on cells due to the generation of harmful reactive oxygen species. Given these circumstances, it is said that cells have a dependable system for Cu homeostasis that efficiently distributes this essential metal to cuproenzymes, thereby preventing damage to proteins, nucleic acids, sugars, and lipids. In particular, influx, efflux, and intracellular distribution with maintenance of the oxidation state of Cu are strictly regulated. Several groups of Cu-regulating factors have been identified in mammalian cells, i.e., Cu transporters, Cu chaperones, Cu-binding proteins/peptides, and others. In this review, the features of the Cu-regulating factors are concisely examined in terms of molecular mechanisms underlying Cu homeostasis in cells.

The role of copper ions in pathophysiology and fluorescent sensors for the detection thereof

Copper ions are crucial to life, and some fundamental roles of copper in pathophysiology have been elucidated using fluorescent sensors.

Copper signaling axis as a target for prostate cancer therapeutics

Previously published reports indicate that serum copper levels are elevated in patients with prostate cancer and that increased copper uptake can be used as a means to image prostate tumors. It is unclear, however, to what extent copper is required for prostate cancer cell function as we observed only modest effects of chelation strategies on the growth of these cells in vitro. With the goal of exploiting prostate cancer cell proclivity for copper uptake, we developed a "conditional lethal" screen to identify compounds whose cytotoxic actions were manifested in a copper-dependent manner. Emerging from this screen was a series of dithiocarbamates, which, when complexed with copper, induced reactive oxygen species-dependent apoptosis of malignant, but not normal, prostate cells. One of the dithiocarbamates identified, disulfiram (DSF), is an FDA-approved drug that has previously yielded disappointing results in clinical trials in patients with recurrent prostate cancer. Similarly, in our studies, DSF alone had a minimal effect on the growth of prostate cancer tumors when propagated as xenografts. However, when DSF was coadministered with copper, a very dramatic inhibition of tumor growth in models of hormone-sensitive and of castrate-resistant disease was observed. Furthermore, we determined that prostate cancer cells express high levels of CTR1, the primary copper transporter, and additional chaperones that are required to maintain intracellular copper homeostasis. The expression levels of most of these proteins are increased further upon treatment of androgen receptor (AR)-positive prostate cancer cell lines with androgens. Not surprisingly, robust CTR1-dependent uptake of copper into prostate cancer cells was observed, an activity that was accentuated by activation of AR. Given these data linking AR to intracellular copper uptake, we believe that dithiocarbamate/copper complexes are likely to be effective for the treatment of patients with prostate cancer whose disease is resistant to classical androgen ablation therapies.

Copper: from neurotransmission to neuroproteostasis

Copper is critical for the Central Nervous System (CNS) development and function. In particular, different studies have shown the effect of copper at brain synapses, where it inhibits Long Term Potentation (LTP) and receptor pharmacology. Paradoxically, according to recent studies copper is required for a normal LTP response. Copper is released at the synaptic cleft, where it blocks glutamate receptors, which explain its blocking effects on excitatory neurotransmission. Our results indicate that copper also enhances neurotransmission through the accumulation of PSD95 protein, which increase the levels of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors located at the plasma membrane of the post-synaptic density. Thus, our findings represent a novel mechanism for the action of copper, which may have implications for the neurophysiology and neuropathology of the CNS. These data indicate that synaptic configuration is sensitive to transient changes in transition metal homeostasis. Our results suggest that copper increases GluA1 subunit levels of the AMPA receptor through the anchorage of AMPA receptors to the plasma membrane as a result of PSD-95 accumulation. Here, we will review the role of copper on neurotransmission of CNS neurons. In addition, we will discuss the potential mechanisms by which copper could modulate neuronal proteostasis (“neuroproteostasis”) in the CNS with focus in the Ubiquitin Proteasome System (UPS), which is particularly relevant to neurological disorders such as Alzheimer’s disease (AD) where copper and protein dyshomeostasis may contribute to neurodegeneration. An understanding of these mechanisms may ultimately lead to the development of novel therapeutic approaches to control metal and synaptic alterations observed in AD patients.

Effects of different sources of copper on Ctr1, ATP7A, ATP7B, MT and DMT1 protein and gene expression in Caco-2 cells

Copper sulfate (CuSO4), micron copper oxide (micron CuO) and nano copper oxide (nano CuO) at different concentrations were, respectively, added to culture media containing Caco-2 cells and their effects on Ctr1, ATP7A/7B, MT and DMT1 gene expression and protein expression were investigated and compared. The results showed that nano CuO promoted mRNA expression of Ctr1 in Caco-2 cells, and the difference was significant compared with micron CuO and CuSO4. Nano CuO was more effective in promoting the expression of Ctr1 protein than CuSO4 and micron CuO at the same concentration. Nano CuO at a concentration of 62.5 μM increased the mRNA expression levels of ATP7A and ATP7B, and the difference was significant compared with CuSO4. The addition of CuSO4 and nano CuO to the culture media promoted the expression of ATP7B proteins. CuSO4 at a concentration of 125 μM increased the mRNA expression level of MT in Caco-2 cells, and the difference was significant compared with nano CuO and micron CuO. Nano CuO at a concentration of 62.5 μM inhibited the mRNA expression of DMT1, and the difference was significant compared with CuSO4 and micron CuO. Thus, the effects of CuSO4, micron CuO and nano CuO on the expression of copper transport proteins and the genes encoding these proteins differed considerably. Nano CuO has a different uptake and transport mechanism in Caco-2 cells to those of CuSO4 and micron CuO.

What can flies tell us about copper homeostasis?

Copper (Cu) is an essential redox active metal that is potentially toxic in excess. Multicellular organisms acquire Cu from the diet and must regulate uptake, storage, distribution and export of Cu at both the cellular and organismal levels. Systemic Cu deficiency can be fatal, as seen in Menkes disease patients. Conversely Cu toxicity occurs in patients with Wilson disease. Cu dyshomeostasis has also been implicated in neurodegenerative disorders such as Alzheimer's disease. Over the last decade, the fly Drosophila melanogaster has become an important model organism for the elucidation of eukaryotic Cu regulatory mechanisms. Gene discovery approaches with Drosophila have identified novel genes with conserved protein functions relevant to Cu homeostasis in humans. This review focuses on our current understanding of Cu uptake, distribution and export in Drosophila and the implications for mammals.

How copper traverses cellular membranes through the mammalian copper transporter 1, Ctr1

The copper transporter 1, Ctr1, is part of a major pathway for cellular copper (Cu) uptake in the intestinal epithelium, in hepatic and cardiac tissue, and likely in many other mammalian cells and tissues. Here, we summarize what is currently known about how extracellular Cu travels across the plasma membrane to enter the cytoplasm for intracellular distribution and for use by proteins and enzymes, the physiological roles of Ctr1, and its regulation. As a critical Cu importer, Ctr1 occupies a strategic position to exert a strong modifying influence on diseases and pathophysiological states caused by imbalances in Cu homeostasis. A more thorough understanding of the mechanisms that regulate Ctr1 abundance, trafficking, and function will provide new insights and opportunities for disease therapies.

Characterization of a monoclonal antibody capable of reliably quantifying expression of human Copper Transporter 1 (hCTR1)

Human copper transporter 1 (hCTR1) is the high-affinity copper influx transporter in mammalian cells that also mediates the influx of cisplatin. Loss of hCTR1 expression has been implicated in the development of resistance to this cancer chemotherapeutic agent. It has turned out to be very difficult to develop antibodies to hCTR1 and polyclonal antibodies produced by different laboratories have yielded conflicting results. We have characterized a newly-available rabbit monoclonal antibody that reacts with an epitope on the N-terminal end of hCTR1 that now permits rigorous identification and quantification of hCTR1 using Western blot analysis. Postnuclear membrane (PNM) preparations made from cells engineered to express high levels of myc-tagged hCTR1, and cells in which the expression of hCTR1 was knocked down, were used to characterize the antibody. The identity of the bands detected was confirmed by immunoprecipitation, surface biotinylation and deglycosylation of myc-tagged hCTR1. Despite the specificity expected of a monoclonal antibody, the anti-hCTR1 detected a variety of bands in whole cell lysates (WCL), which made it difficult to quantify hCTR1. This problem was overcome by isolating post-nuclear membranes and using these for further analysis. Three bands were identified using this antibody in PNM preparations that migrated at 28, 33-35 and 62-64kDa. Multiple lines of evidence presented here suggest that the 33-35 and 62-64kDa bands are hCTR1 whereas the 28kDa band is a cross-reacting protein of unknown identify. The 33-35kDa band is consistent with the expected MW of the glycosylated hCTR1 monomer. This analysis now permits rigorous identification and quantification of hCTR1.

The role of Ctr1 and Ctr2 in mammalian copper homeostasis and platinum-based chemotherapy

Copper (Cu) is an essential metal for growth and development that has the potential to be toxic if levels accumulate beyond the ability of cells to homeostatically balance uptake with detoxification. One system for Cu acquisition is the integral membrane Cu(+) transporter, Ctr1, which has been quite well characterized in terms of its function and physiology. The mammalian Ctr2 protein has been a conundrum for the copper field, as it is structurally closely related to the high affinity Cu transporter Ctr1, sharing important motifs for Cu transport activity. However, in contrast to mammalian Ctr1, Ctr2 fails to suppress the Cu-dependent growth phenotype of yeast cells defective in Cu(+) import, nor does it appreciably stimulate Cu acquisition when over-expressed in mammalian cells, underscoring important functional dissimilarities between the two proteins. Several roles for the mammalian Ctr2 have been suggested both in vitro and in vivo. Here, we summarize and discuss current insights into the Ctr2 protein and its interaction with Ctr1, its functions in mammalian Cu homeostasis and platinum-based chemotherapy.

Theranostics of malignant melanoma with 64CuCl2

Human copper transporter 1 (CTR1) is overexpressed in a variety of cancers. This study aimed to evaluate the use of (64)CuCl2 as a theranostic agent for PET and radionuclide therapy of malignant melanoma.

METHODS

CTR1 expression levels were detected by Western blot analysis of a group of tumor cell lines. Two melanoma cell lines (B16F10 and A375M) that highly expressed CTR1 were then selected to study the uptake and efflux of (64)CuCl2. Mice bearing B16F10 or A375M tumors (n = 4 for each group) were subjected to 5 min of static whole-body PET scans at different time points after intravenous injection of (64)CuCl2. Dynamic scans were also obtained for B16F10 tumor-bearing mice. All mice were sacrificed at 72 h after injection of (64)CuCl2, and biodistribution studies were performed. Mice bearing B16F10 or A375M tumors were further subjected to (64)CuCl2 radionuclide therapy. Specifically, when the tumor size reached 0.5-0.8 cm in diameter, tumor-bearing mice were systemically administered (64)CuCl2 (74 MBq) or phosphate-buffered saline, and tumor sizes were monitored over the treatment period.

RESULTS

CTR1 was found to be overexpressed in the cancer cell lines tested at different levels, and high expression levels in melanoma cells and tissues were observed (melanotic B16F10 and amelanotic A375M). (64)CuCl2 displayed high and specific uptake in B16F10 and A375M cells. In vivo (64)CuCl2 PET imaging demonstrated that both B16F10 and A375M tumors were clearly visualized. Radionuclide treatment studies showed that the tumor growth in both the B16F10 and the A375M models under (64)CuCl2 treatment were much slower than that of the control group.

CONCLUSION

Both melanotic and amelanotic melanomas (B16F10 and A375M) tested were found to overexpress CTR1. The tumors can be successfully visualized by (64)CuCl2 PET and further treated by (64)CuCl2, highlighting the high potential of using (64)CuCl2 as a theranostic agent for the management of melanoma.

The families of zinc (SLC30 and SLC39) and copper (SLC31) transporters

The solute carriers families 30 (SLC30; ZnT), 39 (SLC39; ZIP), and 31 (SLC31; CTR) are involved in the essential maintenance of cellular zinc (Zn²⁺) and copper (Cu²⁺) homeostasis, respectively. ZnTs mediate Zn²⁺ extrusion from cells (SLC30A1) or transport Zn²⁺ into organelles and secretory vesicles/granules (SLC30A2-SLC30A8). SLC39 family members are predominantly localized to the cell membrane where they perform Zn²⁺ uptake and increase the availability of cytosolic Zn²⁺. SLC39A1 is ubiquitously expressed, whereas other ZIP transporters (e.g., SLC39A2 and SLC39A3) show a more tissue-restricted expression consistent with organ-specific functions of these proteins. The members A1 (CTR1) and A2 (CTR2) of the SLC31 family of solute carriers belong to a network of proteins that acts to regulate the intracellular Cu²⁺ concentration within a certain range. SLC31A1 is predominantly localized to the plasma membrane, whereas SLC31A2 is mainly found in intracellular membranes of the late endosome and lysosome. The specific function of SLC31A2 is not known. SLC31A1 is ubiquitously expressed and has been characterized as a high-affinity importer of reduced copper (Cu⁺). Cu²⁺ transport function of CTR proteins is associated with oligomerization; SLC31A1 trimerizes and thereby forms a channel-like structure enabling Cu²⁺ translocation across the cell membrane. The molecular characteristics and structural details (e.g., membrane topology, conserved Zn²⁺, and Cu²⁺ binding sites) and mechanisms of translational and posttranslational regulation of expression and/or activity have been described for SLC30 and SLC39 family members, and for SLC31A1. For SLC31A1, data on tissue-specific functions (e.g., in the intestine, heart, and liver) are also available. A link between SLC31A1, immune function, and disorders such as Alzheimer's disease or cancer makes the protein a candidate therapeutic target. In secretory tissues (e.g., the mammary gland and pancreas), Zn²⁺ transporters of SLC families 30 and 39 are involved in specific functions such as insulin synthesis and secretion, metallation of digestive proenzymes, and transfer of nutrients into milk. Defective or dysregulated Zn²⁺ metabolism in these organs is associated with disorders such as diabetes and cancer, and impaired Zn²⁺ secretion into milk.

Involvement of CTR1 and ATP7A in lead (Pb)-induced copper (Cu) accumulation in choroidal epithelial cells

The blood-cerebrospinal fluid barrier (BCB) plays a key role in maintaining copper (Cu) homeostasis in the brain. Cumulative evidences indicate that lead (Pb) exposure alters cerebral Cu homeostasis, which may underlie the development of neurodegenerative diseases. This study investigated the roles of Cu transporter 1 (CTR1) and ATP7A, two Cu transporters, in Pb-induced Cu accumulation in the choroidal epithelial cells. Pb exposure resulted in increased intracellular (64)Cu retention, accompanying with up-regulated CTR1 level. Knockdown of CTR1 using siRNA before Pb exposure diminished the Pb-induced increase of (64)Cu uptake. The expression level of ATP7A was down-regulated following the Pb exposure. ATP7A siRNA knockdown, or PCMB treatment, inhibited the (64)Cu efflux from the cells, while the following additional incubation with Pb failed to further increase the intracellular (64)Cu retention. Cu exposure, or intracellular Cu accumulation following the tetracycline (Tet)-induced overexpression of CTR1, did not result in significant change in ATP7A expression. Taken together, these data indicate that CTR1 and ATP7A play important roles in Cu transport in choroidal epithelial cells, and the Pb-induced intracellular Cu accumulation appears to be mediated, at least in part, via the alteration of CTR1 and ATP7A expression levels following Pb exposure.

Ctr2 regulates biogenesis of a cleaved form of mammalian Ctr1 metal transporter lacking the copper- and cisplatin-binding ecto-domain

Copper is an essential catalytic cofactor for enzymatic activities that drive a range of metabolic biochemistry including mitochondrial electron transport, iron mobilization, and peptide hormone maturation. Copper dysregulation is associated with fatal infantile disease, liver, and cardiac dysfunction, neuropathy, and anemia. Here we report that mammals regulate systemic copper acquisition and intracellular mobilization via cleavage of the copper-binding ecto-domain of the copper transporter 1 (Ctr1). Although full-length Ctr1 is critical to drive efficient copper import across the plasma membrane, cleavage of the ecto-domain is required for Ctr1 to mobilize endosomal copper stores. The biogenesis of the truncated form of Ctr1 requires the structurally related, previously enigmatic copper transporter 2 (Ctr2). Ctr2(-/-) mice are defective in accumulation of truncated Ctr1 and exhibit increased tissue copper levels, and X-ray fluorescence microscopy demonstrates that copper accumulates as intracellular foci. These studies identify a key regulatory mechanism for mammalian copper transport through Ctr2-dependent accumulation of a Ctr1 variant lacking the copper- and cisplatin-binding ecto-domain.

Regulation of the high-affinity copper transporter (hCtr1) expression by cisplatin and heavy metals

Platinum-based antitumor agents have been the mainstay in cancer chemotherapy for many human malignancies. Drug resistance is an important obstacle to achieving the maximal therapeutic efficacy of these drugs. Understanding how platinum drugs enter cells is of great importance in improving therapeutic efficacy. It has been demonstrated that human high-affinity copper transporter 1 (hCtr1) is involved in transporting cisplatin into cells to elicit cytotoxic effects, although other mechanisms may exist. In this communication, we demonstrate that cisplatin transcriptionally induces the expression of hCtr1 in time- and concentration-dependent manners. Cisplatin functions as a competitor for hCtr1-mediated copper transport, resulting in reduced cellular copper levels and leading to upregulated expression of Sp1, which is a positive regulator for hCtr1 expression. Thus, regulation of hCtr1 expression by cisplatin is an integral part of the copper homeostasis regulation system. We also demonstrate that Ag(I) and Zn(II), which are known to suppress hCtr1-mediated copper transport, can also induce hCtr1/Sp1 expression. In contrast, Cd(II), another inhibitor of copper transport, downregulates hCtr1 expression by suppressing Sp1 expression. Collectively, our results demonstrate diverse mechanisms of regulating copper metabolism by these heavy metals.

SLC31 (CTR) family of copper transporters in health and disease

Copper is a vital mineral for many organisms, yet it is highly toxic as demonstrated by serious health concerns associated with its deficiency or excess accumulation. The SLC31 (CTR) family of copper transporters is a major gateway of copper acquisition in eukaryotes, ranging from yeast to humans. Characterization of the function, modes of action, and regulation of CTR and other molecular factors that functionally cooperate with CTR for copper transport, compartmentalization, incorporation into cuproproteins, and detoxification has revealed that organisms have evolved fascinating mechanisms for tight control of copper metabolism. This research progress further indicates the significance of copper in health and disease and opens avenues for therapeutic control of copper bioavailability and its metabolic pathways.

Intestinal expression of metal transporters in Wilson's disease

In Wilson’s disease (WND), biallelic ATP7B gene mutation is responsible for pathological copper accumulation in the liver, brain and other organs. It has been proposed that copper transporter 1 (CTR1) and the divalent metal transporter 1 (DMT1) translocate copper across the human intestinal epithelium, while Cu-ATPases: ATP7A and ATP7B serve as copper efflux pumps. In this study, we investigated the expression of CTR1, DMT1 and ATP7A in the intestines of both WND patients and healthy controls to examine whether any adaptive mechanisms to systemic copper overload function in the enterocytes. Duodenal biopsy samples were taken from 108 patients with Wilson’s disease and from 90 controls. CTR1, DMT1, ATP7A and ATP7B expression was assessed by polymerase chain reaction and Western blot. Duodenal CTR1 mRNA and protein expression was decreased in WND patients in comparison to control subjects, while ATP7A mRNA and protein production was increased. The variable expression of copper transporters may serve as a defense mechanism against systemic copper overload resulting from functional impairment of ATP7B.

Regulatory effects of Cu, Zn, and Ca on Fe absorption: the intricate play between nutrient transporters

Iron is an essential nutrient for almost every living organism because it is required in a number of biological processes that serve to maintain life. In humans, recycling of senescent erythrocytes provides most of the daily requirement of iron. In addition, we need to absorb another 1–2 mg Fe from the diet each day to compensate for losses due to epithelial sloughing, perspiration, and bleeding. Iron absorption in the intestine is mainly regulated on the enterocyte level by effectors in the diet and systemic regulators accessing the enterocyte through the basal lamina. Recently, a complex meshwork of interactions between several trace metals and regulatory proteins was revealed. This review focuses on advances in our understanding of Cu, Zn, and Ca in the regulation of iron absorption. Ascorbate as an important player is also considered.

Copper: effects of deficiency and overload

Copper is an essential trace metal that is required for the catalysis of several important cellular enzymes. However, since an excess of copper can also harm cells due to its potential to catalyze the generation of toxic reactive oxygen species, transport of copper and the cellular copper content are tightly regulated. This chapter summarizes the current knowledge on the importance of copper for cellular processes and on the mechanisms involved in cellular copper uptake, storage and export. In addition, we will give an overview on disturbances of copper homeostasis that are characterized by copper overload or copper deficiency or have been connected with neurodegenerative disorders.

Membrane transporters as mediators of Cisplatin effects and side effects

Transporters are important mediators of specific cellular uptake and thus, not only for effects, but also for side effects, metabolism, and excretion of many drugs such as cisplatin. Cisplatin is a potent cytostatic drug, whose use is limited by its severe acute and chronic nephro-, oto-, and peripheral neurotoxicity. For this reason, other platinum derivatives, such as carboplatin and oxaliplatin, with less toxicity but still with antitumoral action have been developed. Several transporters, which are expressed on the cell membranes, have been associated with cisplatin transport across the plasma membrane and across the cell: the copper transporter 1 (Ctr1), the copper transporter 2 (Ctr2), the P-type copper-transporting ATPases ATP7A and ATP7B, the organic cation transporter 2 (OCT2), and the multidrug extrusion transporter 1 (MATE1). Some of these transporters are also able to accept other platinum derivatives as substrate. Since membrane transporters display a specific tissue distribution, they can be important molecules that mediate the entry of platinum derivatives in target and also nontarget cells possibly mediating specific effects and side effects of the chemotherapeutic drug. This paper summarizes the literature on toxicities of cisplatin compared to that of carboplatin and oxaliplatin and the interaction of these platinum derivatives with membrane transporters.