Throughout evolution, all organisms have harnessed the redox properties of copper (Cu) and iron (Fe) as a cofactor or structural determinant of proteins that perform critical functions in biology. At its most sobering stance to Earth’s biome, Cu biochemistry allows photosynthetic organisms to harness solar energy and convert it into the organic energy that sustains the existence of all nonphotosynthetic life forms. The conversion of organic energy, in the form of nutrients that include carbohydrates, amino acids and fatty acids, is subsequently released during cellular respiration, itself a Cu-dependent process, and stored as ATP that is used to drive a myriad of critical biological processes such as enzyme-catalyzed biosynthetic processes, transport of cargo around cells and across membranes, and protein degradation. The life-supporting properties of Cu incur a significant challenge to cells that must not only exquisitely balance intracellular Cu concentrations, but also chaperone this redox-active metal from its point of cellular entry to its ultimate destination so as to avert the potential for inappropriate biochemical interactions or generation of damaging reactive oxidative species (ROS). In this review we chart the travels of Cu from the extracellular milieu of fungal and mammalian cells, its path within the cytosol as inferred by the proteins and ligands that escort and deliver Cu to intracellular organelles and protein targets, and its journey throughout the body of mammals.

Significance Copper is essential for normal growth and development because it serves roles in catalysis, signaling, and structure. Cells acquire copper through the copper transporter 1 (Ctr1) protein, a copper transporter that localizes to the cell membrane and intracellular vesicles. Both copper and the anticancer drug cisplatin are imported by Ctr1 by virtue of an extracellular domain rich in metal-binding amino acids. In this report we demonstrate that a protein structurally related to Ctr1, called Ctr2, plays a role in the generation or stability of a truncated form of Ctr1 lacking a large portion of the extracellular domain. Retention of this domain in mice or cells lacking Ctr2 enhances copper and cisplatin uptake, thereby establishing Ctr2 as a regulator of Ctr1 function.

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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.

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 hypochromicmicrocytic 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 ϩ/ϩ 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 ϩ/ϩ 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. copper absorption; iron deficiency; iron-deficiency anemia; iron-refractive iron-deficiency anemia; manganese absorption; SLC11A2; zinc metabolism IRON DEFICIENCY is the most prevalent micronutrient deficiency worldwide (4, 50). Its deficiency leads to irondeficiency anemia, and to neurological and developmental disorders in children (3, 4). Since there exists no regulated mechanism for the excretion of iron, regulation of the whole body iron economy is achieved by tightly controlling absorption of the metal (21). Failure to regulate iron absorption in a manner appropriate to iron status is characteristic of several hereditary iron-overload disorders and iron-refractive iron-deficiency anemia (12,19,21).Divalent metal-ion transporter-1 (DMT1; reviewed in Ref. 52) is a widely expressed mammalian proton-coupled iron transporter (23,38). Mice in which the SLC11A2 gene coding for DMT1 was globally inactivated (i.e., SLC11A2 Ϫ/Ϫ ) exhibited a severe hypochromic-microcytic anemia and did not survive more than 7 days (22). A critical role for DMT1 in erythroid iron acquisition was confirmed by the following observations: 1) transfusion of red blood cells, but not parenteral iron injections, improved survival of SLC11A2 Ϫ/Ϫ mice; and 2) lethal dose-irradiated wild-type mice into which the investigators transplanted hematopoietic stem cells from SLC11A2 Ϫ/Ϫ mice exhibited defective erythropoiesis (22). The microcytic (mk) mouse and Belgrade (b) rat models, inbred strains that harbor a Gly185¡Arg mutation in DMT1 (17, 18), also exhibited an anemia phenotype. Parenteral iron injections partially improved the condition, and tissue or vesicle preparations from the m...

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.Copper is essential for key biological processes, including electron transfer, iron acquisition, dopamine hydrolysis, and superoxide disproportionation, and defects in copper metabolism are associated with cardiomyopathy, anemia, peripheral neuropathy, and neutropenia (1-6). Although many proteins involved in the acquisition and intracellular distribution of copper have been identified, little is known about the regulation of copper import. The transport of Cu ϩ from the extracellular environment is accomplished by the evolutionarily conserved homotrimeric integral membrane protein, copper transporter 1 (Ctr1) (7-13), which resides on the plasma membrane and in endosomal compartments (14 -18). High affinity Cu ϩ import via Ctr1 requires a methionine-and histidine-rich metal-binding extracellular domain (ectodomain) that is thought to concentrate extracellular Cu ϩ near the ion trans-membrane pore (19 -23). Additionally, Ctr1 binds the chemotherapeutic agent cisplatin via the methionine ligands in the ectodomain and imports cisplatin and other platinum-based chemotherapeutic agents via an endocytic mechanism (24 -28). Despite a critical role for the Ctr1 ectodomain in both Cu ϩ and cisplatin import, both a full-length form and a truncated form of Ctr1 (tCtr1) 4 are present in cultured cells and tissues (18,29,30). The latter lacks the ectodomain and drives ϳ50% of the Cu ϩ uptake as compared with full-length Ctr1 (31).Previously, an integral membrane protein similar to Ctr1, denoted Ctr2, was shown to both interact with and regulate the ratio of full-length Ctr1 to tCtr1 in mouse embryonic fibroblasts (MEFs) and in specific tissues in Ctr2 knock-out mice (32). In the absence of Ctr2, MEFs possess dramatically lower levels of tCtr1, while simultaneously expressing high levels of full-length Ctr1 and accumulating Cu ϩ and cisplatin. A large fraction of the Cu ϩ accumulated in Ctr2 Ϫ/Ϫ MEFs and mouse tissues is found in endosomal compartments (32). The mechanism by which Ct...

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. Here we attempt to provide a critical view on key concepts involved in copper transfer across membranes and through compartments in the human body. The focus of this review is on the influence of bioinorganic and thermodynamic rules on the flow in cellular copper networks. Transition of copper from one oxidation state to another will often lead to errant electrons that are highly reactive and prone to form radicals and reactive oxygen or nitrogen species (ROS and RNS). Strict control of potentially toxic oxidative species is an important part of understanding the edge of human copper metabolism. The present review critically covers translocation across simple and complex membranes as well as extracellular and intracellular copper routing. We discuss in depth four tissues with polarized cell barriers - the gut, liver, kidneys, and brain - to illustrate the similarities and differences in transcellular transfer. Copper chaperoning, buffering and binding dynamics to guide the metal to different sites are also covered, while individual molecular interaction kinetics are not detailed. Sorting and targeting mechanisms and principles crucial for correct localisation will also be touched upon.