Regulation Of Copper Homeostasis Research Articles

Abstract 3892: Discovery and analysis of COMMD1 in the DNA damage response network

Abstract Spatially distinct domains impart functionality to the proteins and are often under evolutionary pressure to maintain sequence and/or structure. The BRCA1 C-terminal (BRCT) domain has an established role in cancer susceptibility and in the DNA damage response (DDR), as mutations in cases of familial breast cancer often result in a truncated protein lacking the two BRCT domains which are required for interactions with proteins such as p53, ABRAXAS, BACH1, and CtIP. BRCT domains can occur as singletons or as tandem domains (tBRCT) that function as a single cohesive structural unit involved in binding phosphorylated peptides targeted by PI3K-like proteins such as ATM in response to DNA damage. Using the Yeast Two-Hybrid system (Y2H) as well as Tandem Affinity Purification coupled to mass spectrometry (TAP-MS), we have built a domain centric protein-protein interaction network for a subset of tBRCT domains from BRCA1, TP53BP1, LIG4, PAXIP1, ECT2, BARD1, and MDC1. Evaluation of this network has revealed a number of interesting interactions and highlighted the interconnectivity potential found in these domains. Analysis of this network has revealed several interesting proteins that are highly interconnected with tBRCT domains, such as COMMD1 (an important regulator of copper homeostasis, sodium transport, NF-κB, and HIF-1), which has not yet been characterized to participate in the DDR, but was found to interact with the tBRCT domains of BARD1, BRCA1, and LIG4. Furthermore, an earlier Y2H screen conducted by our laboratory found COMMD1 as an interaction partner of CHK2. Therefore, we sought to determine the role of COMMD1 in response DNA damaging agents. Convincingly, the levels of COMMD1 are inversely related to apoptotic induction caused by cisplatin and doxorubicin. Furthermore, CHK2 signaling appears to control the ability of COMMD1 to enhance cisplatin induced apoptosis as wild type but not CHK2-/- HCT116 cells exhibited a repression in cisplatin induced apoptosis when COMMD1 was over expressed. These results indicate the importance of COMMD1 for cellular susceptibility to traditional chemotherapeutics. Currently, we are exploring the mechanisms by which COMMD1 in coordination with tBRCT domain containing proteins and CHK2 sensitizes cells to DNA damaging agents. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3892. doi:10.1158/1538-7445.AM2011-3892

Global Analysis of Copper Responsiveness in Chlamydomonas

Aerobic organisms require copper due to its key roles in oxygen-requiring chemical reactions. Copper ions aid electron transfer to molecular oxygen during aerobic respiration, act as cofactors in superoxide dismutases, and are an essential component of plastocyanin, an electron carrier in oxygenic photosynthesis. Previous work by Eriksson et al. (2004) identified COPPER RESPONSE REGULATOR1 (CRR1) as a key regulator of copper homeostasis in Chlamydomonas. In copper-deficient conditions, CRR1 activates copper sparing pathways to conserve copper. For example, it downregulates the copper-containing plastocyanin protein and upregulates the iron-containing cytochrome c6 protein that can serve as its replacement. Castruita et al. (pages 1273–1292) used high-sensitivity global transcriptomic, proteomic, and lipidomic methods to identify Chlamydomonas genes regulated by copper, test whether mRNA abundance correlates with protein abundance, and examine the role of copper nutrition in the modification of thylakoid membrane lipids. By identifying differentially expressed transcripts in pairwise combinations of conditions (see figure) they defined a nutritional copper regulon and distinguished between primary responses to copper limitation versus secondary responses due to reduced growth rate as a result of limiting copper. Using digital gene expression tag profiling (’t Hoen et al., 2008) and RNA sequencing (Nagalakshmi et al., 2008), they reproducibly identified distinct sets of differentially regulated genes with expression levels as low as 1 mRNA per cell and showed that any variance was independent of the method used. Using an iterative alignment protocol, over 90% of expressed sequences were aligned uniquely to the Chlamydomonas genome. Real-time PCR conducted in parallel gave good correlations (0.88 and 0.97) with these results. Among differentially expressed CRR1 targets, redox proteins were overrepresented. For phototrophic cells, copperresponsive expression was seen in copper transport proteins and in several proteins involved in iron homeostasis, highlighting the role of copper in iron assimilation. RNA and protein abundance for fatty acid desaturases also increased in copper limiting conditions, and lipid analysis showed an increase in polyunsaturated fatty acids, especially in digalactosyldiacylglyceride, a major thylakoid lipid. The authors then used elevated liquid chromatography mass spectrometry (LC-MS E ; Silva et al., 2006) to identify and quantify over 1000 proteins. For 17 of 18 proteins corresponding to differentially expressed transcripts, the change in protein abundance paralleled the change in mRNA abundance. The authors discuss the technical and biological advantages of these methods, validate their methods and analysis pipeline with simulation studies, and present a comprehensive model for copper allocation under copper limiting conditions. This work not only advances our understanding of copper biology in Chlamydomonas but also provides a general strategy to analyze the global response to essential nutrients and strategies for survival under nutrientlimiting conditions.

Mechanism of tumor resistance to cisplatin mediated by the copper transporter ATP7BThis paper is one of a selection of papers published in a Special Issue entitled CSBMCB 53rd Annual Meeting — Membrane Proteins in Health and Disease, and has undergone the Journal’s usual peer review process.

The Wilson disease protein (ATP7B) is a copper-transporting ATPase that is responsible for regulating copper homeostasis in human tissues. ATP7B is associated with cancer resistance to cisplatin, one of the most widely used anticancer drugs. This minireview discusses the possible mechanisms of tumor resistance to cisplatin mediated by ATP7B. Cisplatin binds to the N-terminal cytosolic domain of ATP7B, which contains multiple copper-binding sites. Active platinum efflux catalyzed by ATP7B is unlikely to significantly contribute to cisplatin resistance in vivo. Transient platinum sequestration in the metal-binding domain followed by transfer to an acceptor protein or a low molecular weight compound is proposed as an alternative mechanism of cisplatin detoxification in the cell.

Altered microglial copper homeostasis in a mouse model of Alzheimer’s disease

Alzheimer's disease (AD) is characterized by progressive neurodegeneration associated with the aggregation and deposition of β-amyloid (Aβ(40) and Aβ(42) ) peptide in senile plaques. Recent studies suggest that copper may play an important role in AD pathology. Copper concentrations are elevated in amyloid plaques and copper binds with high affinity to the Aβ peptide and promotes Aβ oligomerization and neurotoxicity. Despite this connection between copper and AD, it is unknown whether the expression of proteins involved in regulating copper homeostasis is altered in this disorder. In this study, we demonstrate that the copper transporting P-type ATPase, ATP7A, is highly expressed in activated microglial cells that are specifically clustered around amyloid plaques in the TgCRND8 mouse model of AD. Using a cultured microglial cell line, ATP7A expression was found to be increased by the pro-inflammatory cytokine interferon-gamma, but not by TNF-α or IL-1β. Interferon-gamma also elicited marked changes in copper homeostasis, including copper-dependent trafficking of ATP7A from the Golgi to cytoplasmic vesicles, increased copper uptake and elevated expression of the CTR1 copper importer. These findings suggest that pro-inflammatory conditions associated with AD cause marked changes in microglial copper trafficking, which may underlie the changes in copper homeostasis in AD. It is concluded that copper sequestration by microglia may provide a neuroprotective mechanism in AD.

Regulation of the Copper Chaperone CCS by XIAP-Mediated Ubiquitination

In order to balance the cellular requirements for copper with its toxic properties, an elegant set of mechanisms has evolved to regulate and buffer intracellular copper. The X-linked inhibitor of apoptosis (XIAP) protein was recently identified as a copper-binding protein and regulator of copper homeostasis, although the mechanism by which XIAP binds copper in the cytosol is unclear. Here we describe the identification of the copper chaperone for superoxide dismutase (CCS) as a mediator of copper delivery to XIAP in cells. We also find that CCS is a target of the E3 ubiquitin ligase activity of XIAP, although interestingly, ubiquitination of CCS by XIAP was found to lead to enhancement of its chaperone activity toward its physiologic target, superoxide dismutase 1, rather than proteasomal degradation. Collectively, our results reveal novel links among apoptosis, copper metabolism, and redox regulation through the XIAP-CCS complex.

The role of miR398 in plant stress responses

MicroRNAs (miRNAs) are a new class of small RNAs, which act as post-transcriptional negative regulators of gene expression. Plant miRNAs are important in the regulation of plant growth, development and in response to various abiotic and biotic stresses. miR398 is the first reported miRNA to be down-regulated by oxidative stresses. miR398 plays an impor-tant role in stresses, such as regulating copper homeostasis, in response to abiotic stresses including heavy metals, sucrose, and ozone and biotic stresses via down-regulating the expression of Cu/Zn-superoxide dismutase (CSD). This review fo-cused on the crucial role of miR398 in regulation of different stresses and the transcriptional regulation of MIR398 gene.

Copper handling machinery of the brain

Copper plays an indispensable role in the physiology of the human central nervous system (CNS). As a cofactor of dopamine-β-hydroxylase, peptidyl-α-monooxygenase, superoxide dismutases, and many other enzymes, copper is a critical contributor to catecholamine biosynthesis, activation of neuropeptides and hormones, protection against reactive oxygen species, respiration and other processes essential for normal CNS function. Copper content in the CNS is tightly regulated, and changes in copper levels in the brain are associated with a wide spectrum of pathologies. However, the mechanistic understanding of copper transport in the CNS is still in its infancy. Little is known about copper distribution among various cell types or cell-specific regulation of copper homeostasis, despite the fact that the molecules mediating copper transport and distribution in the brain (CTR1, Atox1, CCS, ScoI/II, ATP7A and ATP7B) have been identified and their importance in CNS function increasingly understood. In this review, we summarize current knowledge about copper levels and uses in the CNS and describe the molecules involved in maintaining copper homeostasis in the brain.

The role of microRNAs in copper and cadmium homeostasis

Essential heavy metals (e.g., copper) and non-essential metals (e.g., cadmium) are both toxic to plants at high concentrations. Recently, microRNAs (miRNAs) have emerged as important modulators of plants adaptive response to heavy metal stress. Plant miRNAs negatively regulate target mRNAs by post-transcriptional cleavage. miR398 regulates copper homeostasis via down-regulating the expression of Cu,Zn-superoxide dismutase (CSD), a scavenger of superoxide radicals. miR393 and miR171 play an important role in cadmium stress mediation. This review focuses on the recent advance in the involvement of miRNAs in copper and cadmium stress regulatory networks in plants.

Copper in plants: acquisition, transport and interactions.

Copper is an essential metal for plants. It plays key roles in photosynthetic and respiratory electron transport chains, in ethylene sensing, cell wall metabolism, oxidative stress protection and biogenesis of molybdenum cofactor. Thus, a deficiency in the copper supply can alter essential functions in plant metabolism. However, copper has traditionally been used in agriculture as an antifungal agent, and it is also extensively released into the environment by human activities that often cause environmental pollution. Accordingly, excess copper is present in certain regions and environments, and exposure to such can be potentially toxic to plants, causing phytotoxicity by the formation of reactive oxygen radicals that damage cells, or by the interaction with proteins impairing key cellular processes, inactivating enzymes and disturbing protein structure. Plants have a complex network of metal trafficking pathways in order to appropriately regulate copper homeostasis in response to environmental copper level variations. Such strategies must prevent accumulation of the metal in the freely reactive form (metal detoxification pathways) and ensure proper delivery of this element to target metalloproteins. The mechanisms involved in the acquisition and the distribution of copper have not been clearly defined, although emerging data in last decade, mainly obtained on copper uptake, and both intra- and intercellular distribution, as well as on long-distance transport, are contributing to the understanding of copper homeostasis in plants and the response to copper stress. This review gives an overview of the current understanding of main features concerning copper function, acquisition and trafficking network as well as interactions between copper and other elements.

Effect of EGb761 supplementation on the content of copper in mouse brain in an animal model of Parkinson's disease

Objective EGb761 is a well-defined mixture of active compounds extracted from Ginkgo biloba leaves with neuroprotective effects in an animal model of Parkinson's disease induced by 1-methyl-4-phenylpyridinium (MPP +). Because copper has been implicated in Parkinson's disease, we investigated whether the protective effect of EGb761 in MPP + neurotoxicity is related to the regulation of copper in the brain. Methods C-57BL/6 mice were pretreated with EGb761 (10 mg/kg) daily for 17 d followed by administration of MPP + (0.72 mg/kg); the mice were sacrificed 24 h later. The copper content of the striatum, midbrain, hippocampus, frontal cortex, and cerebellum was analyzed by graphite furnace atomic absorption spectrophotometry. Copper content is expressed as μg of copper per gram of wet tissue. Results Copper content was reduced in the corpus striatum (45%; P < 0.05), and increased in the midbrain (65%; P < 0.05) and hippocampus (116%; P < 0.001) after MPP + administration. EGb761 pretreatment of the MPP + group prevented changes in the copper content of the striatum, midbrain, and hippocampus. No significant changes were found in the copper content of the cerebellum and frontal cortex in all treatment groups. Conclusion We showed that the protective effect of EGb761 against MPP + neurotoxicity may be due in part to the regulation of copper homeostasis in the brain.

Intestinal regulation of copper homeostasis: a developmental perspective

Stable-isotope studies in human infants and adults have shown that copper homeostasis occurs, but the contribution of the small intestine to this regulation is still not well understood. Copper first needs to be reduced to the cuprous form, most likely by Steap proteins on the apical membrane. Copper is subsequently absorbed by Ctr1 and then transferred in the enterocyte by the chaperone Atox1 to reach ATP7A for export from the cell. The role of ATP7B, shown to be present in the small intestine, is still poorly understood. In situations of high copper exposure, Ctr1 is endocytosed, metallothionein is induced, and ATP7A moves to a more basolateral localization. However, the ontogeny of regulation of copper homeostasis has received little attention. In rat pups, tissue copper and total-body 67Cu retention decrease throughout postnatal development, whereas liver 67Cu retention, serum copper, and ceruloplasmin activity increase. Total 67Cu absorption decreases and intestinal 67Cu retention increases with increased copper intake. During early infancy (day 10), copper supplementation increases intestinal copper and metallothionein gene expression, and Ctr1 protein levels increase, whereas Atp7A and Atp7B are unaffected. However, during late infancy (day 20), intestinal copper concentrations are unaffected by supplementation, but Ctr1, ATP7A, and Atp7B protein levels are higher than in controls. Thus, maturation of small intestine copper transport occurs through increased abundance and altered localization of Ctr1, Atp7A, and Atp7B. The mechanisms behind this maturation, including both transcriptional and posttranscriptional regulation, require further studies.

Transcription Factor Sp1 Plays an Important Role in the Regulation of Copper Homeostasis in Mammalian Cells

Copper is an essential metal nutrient, yet copper overload is toxic. Here, we report that human copper transporter (hCtr) 1 plays an important role in the maintenance of copper homeostasis by demonstrating that expression of hCtr1 mRNA was up-regulated under copper-depleted conditions and down-regulated under copper-replete conditions. Overexpression of full-length hCtr1 by transfection with a recombinant hCtr1 cDNA clone reduced endogenous hCtr1 mRNA levels, whereas overexpression of N terminus-deleted hCtr1 did not change endogenous hCtr1 mRNA levels, suggesting that increased functional hCtr1 transporter, which leads to increased intracellular copper content, down-regulates the endogenous hCtr1 mRNA. A luciferase assay using reporter constructs containing the hCtr1 promoter sequences revealed that three Sp1 binding sites are involved in the basal and copper concentration-dependent regulation of hCtr1 expression. Modulation of Sp1 levels affected the expression of hCtr1. We further demonstrated that the zinc-finger domain of Sp1 functions as a sensor of copper that regulates hCtr1 up and down in response to copper concentration variations. Our results demonstrate that mammalian copper homeostasis is maintained at the hCtr1 mRNA level, which is regulated by the Sp1 transcription factor.

Regulation of Copper Homeostasis by Micro-RNA in Arabidopsis

Major copper proteins in the cytoplasm of plant cells are plastocyanin, copper/zinc superoxide dismutase, and cytochrome c oxidase. Under copper limited conditions, expression of copper/zinc superoxide dismutase is down-regulated and the protein is replaced by iron superoxide dismutase in chloroplasts. We present evidence that a micro-RNA, miR398, mediates this regulation in Arabidopsis thaliana, by directing the degradation of copper/zinc superoxide dismutase mRNA when copper is limited. Sequence analysis indicated that the transcripts encoding cytosolic copper/zinc superoxide dismutase and COX5b-1, a subunit of the mitochondrial cytochrome c oxidase, are also targeted by miR398. This regulation via miR398 takes place in response to changes in a low range of copper levels (0.2-0.5 microM), indicating that miR398 is involved in a response to copper limitation. On the other hand, another major copper protein, plastocyanin, which is involved in photosynthetic electron flow and is essential in higher plants, was not regulated via miR398. We propose that miR398 is a key factor in copper homeostasis in plants and regulates the stability of mRNAs of major copper proteins under copper-limited conditions.

Characterization and Copper Binding Properties of Human COMMD1 (MURR1)

COMMD1 (copper metabolism gene MURR1 (mouse U2af1-rs1 region1) domain) belongs to a family of multifunctional proteins that inhibit nuclear factor NF-kappaB. COMMD1 was implicated as a regulator of copper metabolism by the discovery that a deletion of exon 2 of COMMD1 causes copper toxicosis in Bedlington terriers. Here, we report the detailed characterization and specific copper binding properties of purified recombinant human COMMD1 as well as that of the exon 2 product, COMMD(61-154). By using various techniques including native-PAGE, EPR, UV-visible electronic absorption, intrinsic fluorescence spectroscopies as well as DEPC modification of histidines, we demonstrate that COMMD1 specifically binds copper as Cu(II) in 1:1 stoichiometry and does not bind other divalent metals. Moreover, the exon 2 product, COMMD(61-154), alone was able to bind Cu(II) as well as the wild type protein, with a stoichiometry of 1 mol of Cu(II) per protein monomer. The protection of DEPC modification of COMMD1 by Cu(II) implied that Cu(II) binding involves His residues. Further investigation by DEPC modification of COMMD(61-154) and subsequent MALDI MS mapping and MS/MS sequencing identified the protection of His101 and His134 residues in the presence of Cu(II). Fluorescence studies of single point mutants of the full-length protein revealed the involvement of M110 in addition to H134 in direct Cu(II) binding. Taken together, the data provide insight into the function of COMMD1 and especially COMMD(61-154), a product of exon 2 that is deleted in terriers affected by copper toxicosis, as a regulator of copper homeostasis.

Hepatic copper-transporting ATPase ATP7B: function and inactivation at the molecular and cellular level

Copper-transporting ATPase ATP7B (Wilson disease protein) is a member of the P-type ATPase family with characteristic domain structure and distinct ATP-binding site. ATP7B plays a central role in the regulation of copper homeostasis in the liver by delivering copper to the secretory pathway and mediating export of excess copper into the bile. The dual function of ATP7B in hepatocytes is coupled with copper-dependent intracellular relocalization of the transporter. The final destination of ATP7B in hepatocytes during the copper-induced trafficking process is still under debate. We show the results of immunocytochemistry experiments in polarized HepG2 cells that support the model in which elevated copper induces trafficking of ATP7B to sub-apical vesicles, and transiently to the canalicular membrane. In Atp7b-/- mice, an animal model of Wilson disease, both copper delivery to the trans-Golgi network and copper export into the bile are disrupted despite large accumulation of copper in the cytosol. We review the biochemical and physiological changes associated with Atp7b inactivation in mouse liver and discuss the pleiotropic consequences of the common Wilson disease mutation, His1069Gln.

Copper-dependent interaction of glutaredoxin with the N termini of the copper-ATPases (ATP7A and ATP7B) defective in Menkes and Wilson diseases

The P-type ATPases affected in Menkes and Wilson diseases, ATP7A and ATP7B, respectively, are key copper transporters that regulate copper homeostasis. The N termini of these proteins are critical in regulating their function and activity, and contain six copper-binding motifs MxCxxC. In this study, we describe the identification of glutaredoxin (GRX1) as an interacting partner of both ATP7A and ATP7B, confirmed by yeast two-hybrid technology and by co-immunoprecipitation from mammalian cells. The interaction required the presence of copper and intact metal-binding motifs. In addition, the interaction was related to the number of metal-binding domains available. GRX1 catalyses the reduction of disulphide bridges and reverses the glutathionylation of proteins to regulate and/or protect protein activity. We propose that GRX1 is essential for ATPase function and catalyses either the reduction of intramolecular disulphide bonds or the deglutathionylation of the cysteine residues within the CxxC motifs to facilitate copper-binding for subsequent transport.

Solution structure of the N-domain of Wilson disease protein: Distinct nucleotide-binding environment and effects of disease mutations

Wilson disease protein (ATP7B) is a copper-transporting P(1B)-type ATPase that regulates copper homeostasis and biosynthesis of copper-containing enzymes in human tissues. Inactivation of ATP7B or related ATP7A leads to severe neurodegenerative disorders, whereas their overexpression contributes to cancer cell resistance to chemotherapeutics. Copper-transporting ATPases differ from other P-type ATPases in their topology and the sequence of their nucleotide-binding domain (N-domain). To gain insight into the structural basis of ATP7B function, we have solved the structure of the ATP7B N-domain in the presence of ATP by using heteronuclear multidimensional NMR spectroscopy. The N-domain consists of a six-stranded beta-sheet with two adjacent alpha-helical hairpins and, unexpectedly, shows higher similarity to the bacterial K(+)-transporting ATPase KdpB than to the mammalian Ca(2+)-ATPase or Na(+),K(+)-ATPase. The common core structure of P-type ATPases is retained in the 3D fold of the N-domain; however, the nucleotide coordination environment of ATP7B within this fold is different. The residues H1069, G1099, G1101, I1102, G1149, and N1150 conserved in the P(1B)-ATPase subfamily contribute to ATP binding. Analysis of the frequent disease mutation H1069Q demonstrates that this mutation does not significantly affect the structure of the N-domain but prevents tight binding of ATP. The structure of the N-domain accounts for the disruptive effects of >30 known Wilson disease mutations. The unique features of the N-domain provide a structural basis for the development of specific inhibitors and regulators of ATP7B.

Virulence Attributes and Hyphal Growth of C. neoformans Are Quantitative Traits and the MATα Allele Enhances Filamentation

Cryptococcus neoformans is a fungal human pathogen with a bipolar mating system. It undergoes a dimorphic transition from a unicellular yeast to hyphal filamentous growth during mating and monokaryotic fruiting. The traditional sexual cycle that leads to the production of infectious basidiospores involves cells of both α and a mating type. Monokaryotic fruiting is a modified form of sexual reproduction that involves cells of the same mating type, most commonly α, which is the predominant mating type in both the environment and clinical isolates. However, some a isolates can also undergo monokaryotic fruiting. To determine whether mating type and other genetic loci contribute to the differences in fruiting observed between α and a cells, we applied quantitative trait loci (QTL) mapping to an inbred population of F2 progeny. We discovered that variation in hyphal length produced during fruiting is a quantitative trait resulting from the combined effects of multiple genetic loci, including the mating type (MAT) locus. Importantly, the α allele of the MAT locus enhanced hyphal growth compared with the a allele. Other virulence traits, including melanization and growth at 39 °C, also are quantitative traits that share a common QTL with hyphal growth. The Mac1 transcription factor, encoded in this common QTL, regulates copper homeostasis. MAC1 allelic differences contribute to phenotypic variation, and mac1Δ mutants exhibit defects in filamentation, melanin production, and high temperature growth. Further characterization of these QTL regions will reveal additional quantitative trait genes controlling biological processes central to fungal development and pathogenicity.

A novel role for XIAP in copper homeostasis through regulation of MURR1.

XIAP is a potent suppressor of apoptosis that directly inhibits specific members of the caspase family of cysteine proteases. Here we demonstrate a novel role for XIAP in the control of intracellular copper levels. XIAP was found to interact with MURR1, a factor recently implicated in copper homeostasis. XIAP binds to MURR1 in a manner that is distinct from that utilized by XIAP to bind caspases, and consistent with this, MURR1 did not affect the antiapoptotic properties of XIAP. However, cells and tissues derived from Xiap-deficient mice were found to contain reduced copper levels, while suppression of MURR1 resulted in increased intracellular copper in cultured cells. Consistent with these opposing effects, XIAP was observed to negatively regulate MURR1 protein levels by the formation of K48 polyubiquitin chains on MURR1 that promote its degradation. These findings represent the first described phenotypic alteration in Xiap-deficient mice and demonstrate that XIAP can function through MURR1 to regulate copper homeostasis.

Genetic Defects in Copper Metabolism

Genetic defects in copper metabolism highlight the delicate balance mammalian systems have developed to maintain normal copper homeostasis. Menkes disease, the mottled mouse, the Atox-1-deficient mouse and the ctr1 knockout mouse reveal the importance of adequate copper intake during embryogenesis and early development, especially in the central nervous system. The toxicity associated with excess copper as manifest in Wilson disease, the toxic milk mouse, the LEC rat and copper toxicosis in the Bedlington terrier demonstrate the profound cellular susceptibility to copper overload, in particular, in the brain and liver. Ceruloplasmin (Cp) contains 95% of the copper found in human serum, and inherited loss of this protein results in diabetes, retinal degeneration and neurodegeneration. Despite normal copper metabolism, aceruloplasminemic patients and the Cp knockout mouse have disturbed iron homeostasis and mild hepatic copper retention. These genetic disorders of copper metabolism provide valuable insight into the mechanisms regulating copper homeostasis and models to further dissect the role of this essential metal in health and disease.