Structure and mechanism of the human copper transporting ATPases: Fitting the pieces into a moving puzzle

Human copper transporters ATP7B and ATP7A deliver copper to biosynthetic pathways and maintain copper homeostasis in the cell. These enzymes combine several challenges for structural biology because they are large low abundance membrane proteins with many highly mobile domains and long disordered loops. No method has yet succeeded in solving the structure of the complete fully functional protein. Still, X-ray crystallography, Cryo-EM and NMR helped to piece together a structure based model of the enzyme activity and regulation by copper. We review the structures of ATP7B and ATP7A with an emphasis on the mechanistic insights into the unique aspects of the transport function and regulation of the human copper ATPases that have emerged from more than twenty years of research.

AP-1γ2 is an adaptor protein 1 variant required for endosome-to-Golgi trafficking of the mannose-6-P receptor (CI-MPR) and ATP7B copper transporter

Selective retrograde transport from endosomes back to the trans-Golgi network (TGN) is important for maintaining protein homeostasis, recycling receptors, and returning molecules that were transported to the wrong compartments. Two important transmembrane proteins directed to this pathway are the Cation-Independent Mannose-6-phosphate receptor (CI-MPR) and the ATP7B copper transporter. Among CI-MPR functions is the delivery of acid hydrolases to lysosomes, while ATP7B facilitates the transport of cytosolic copper ions into organelles or the extracellular space. Precise subcellular localization of CI-MPR and ATP7B is essential for the proper functioning of these proteins. This study shows that both CI-MPR and ATP7B interact with a variant of the clathrin adaptor 1 (AP-1) complex that contains a specific isoform of the γ-adaptin subunit called γ2. Through synchronized anterograde trafficking and cell-surface uptake assays, we demonstrated that AP-1γ2 is dispensable for ATP7B and CI-MPR exit from the TGN while being critically required for ATP7B and CI-MPR retrieval from endosomes to the TGN. Moreover, AP-1γ2 depletion leads to the retention of endocytosed CI-MPR in endosomes enriched in retromer complex subunits. These data underscore the importance of AP-1γ2 as a key component in the sorting and trafficking machinery of CI-MPR and ATP7B, highlighting its essential role in the transport of proteins from endosomes.

Regulation of the apico-basolateral trafficking polarity of the homologous copper-ATPases ATP7A and ATP7B

The homologous P-type copper-ATPases (Cu-ATPases) ATP7A and ATP7B are the key regulators of copper homeostasis in mammalian cells. In polarized epithelia, upon copper treatment, ATP7A and ATP7B traffic from the trans-Golgi network (TGN) to basolateral and apical membranes, respectively. We characterized the sorting pathways of Cu-ATPases between TGN and the plasma membrane and identified the machinery involved. ATP7A and ATP7B reside on distinct domains of TGN in limiting copper conditions, and in high copper, ATP7A traffics to basolateral membrane, whereas ATP7B traverses common recycling, apical sorting and apical recycling endosomes en route to apical membrane. Mass spectrometry identified regulatory partners of ATP7A and ATP7B that include the adaptor protein-1 complex. Upon knocking out pan-AP-1, sorting of both Cu-ATPases is disrupted. ATP7A loses its trafficking polarity and localizes on both apical and basolateral surfaces in high copper. By contrast, ATP7B loses TGN retention but retained its trafficking polarity to the apical domain, which became copper independent. Using isoform-specific knockouts, we found that the AP-1A complex provides directionality and TGN retention for both Cu-ATPases, whereas the AP-1B complex governs copper-independent trafficking of ATP7B solely. Trafficking phenotypes of Wilson disease-causing ATP7B mutants that disrupts putative ATP7B-AP1 interaction further substantiates the role of AP-1 in apical sorting of ATP7B.

ATP7A-dependent copper sequestration contributes to termination of β-CATENIN signaling during early adipogenesis

OBJECTIVES

Adipocyte fate determination is tightly regulated by extrinsic signaling pathways and intrinsic metabolic and morphologic changes that maintain adipose tissue function. Copper (Cu) homeostasis is required for the normal metabolism of mature adipocytes, whereas the role of Cu in adipogenesis is unclear.

METHODS

To determine the role of Cu is adipocytes differentiation, we used 3T3-L1 adipocytes, immunocytochemistry, X-ray fluorescence, mass-spectrometry, pharmacological treatments, and manipulations of copper levels.

RESULTS

In differentiating 3T3-L1 cells, adipogenic stimuli trigger the upregulation and trafficking of the Cu transporter Atp7a, thus causing Cu redistribution from the cytosol to vesicles. Disrupting Cu homeostasis by the deletion of Atp7a results in Cu elevation and inhibition of adipogenesis. The upregulation of C/EBPβ, an initial step of adipogenesis, is not affected in Atp7a-/- cells, whereas the subsequent upregulation of PPARγ is inhibited. Comparison of changes in the Atp7a-/- and wild type cells proteomes during early adipogenesis revealed stabilization of β-catenin, a negative regulator of adipogenesis. Cu chelation, or overexpression of the Cu transporter ATP7B in Atp7a-/- cells, restored β-catenin down-regulation and intracellular targeting.

CONCLUSIONS

Cu buffering during early adipogenesis contributes to termination of β-catenin signaling. Abnormal upregulation of β-catenin was also observed in vivo in the livers of Atp7b-/- mice, which accumulate Cu, suggesting a tissue-independent crosstalk between Cu homeostasis and the Wnt/β-catenin pathway. These results point to a new regulatory role of Cu in adipocytes and contribute to better understanding of human disorders of Cu misbalance.

A new Caenorhabditis elegans model to study copper toxicity in Wilson disease

Wilson disease (WD) is caused by mutations in the ATP7B gene that encodes a copper (Cu) transporting ATPase whose trafficking from the Golgi to endo-lysosomal compartments drives sequestration of excess Cu and its further excretion from hepatocytes into the bile. Loss of ATP7B function leads to toxic Cu overload in the liver and subsequently in the brain, causing fatal hepatic and neurological abnormalities. The limitations of existing WD therapies call for the development of new therapeutic approaches, which require an amenable animal model system for screening and validation of drugs and molecular targets. To achieve this objective, we generated a mutant Caenorhabditis elegans strain with a substitution of a conserved histidine (H828Q) in the ATP7B ortholog cua-1 corresponding to the most common ATP7B variant (H1069Q) that causes WD. cua-1 mutant animals exhibited very poor resistance to Cu compared to the wild-type strain. This manifested in a strong delay in larval development, a shorter lifespan, impaired motility, oxidative stress pathway activation, and mitochondrial damage. In addition, morphological analysis revealed several neuronal abnormalities in cua-1 mutant animals exposed to Cu. Further investigation suggested that mutant CUA-1 is retained and degraded in the endoplasmic reticulum, similarly to human ATP7B-H1069Q. As a consequence, the mutant protein does not allow animals to counteract Cu toxicity. Notably, pharmacological correctors of ATP7B-H1069Q reduced Cu toxicity in cua-1 mutants indicating that similar pathogenic molecular pathways might be activated by the H/Q substitution and, therefore, targeted for rescue of ATP7B/CUA-1 function. Taken together, our findings suggest that the newly generated cua-1 mutant strain represents an excellent model for Cu toxicity studies in WD.

Copper-independent lysosomal localisation of the Wilson disease protein ATP7B

In hepatocytes, the Wilson disease protein ATP7B resides on the trans-Golgi network (TGN) and traffics to peripheral lysosomes to export excess intracellular copper through lysosomal exocytosis. We found that in basal copper or even upon copper chelation, a significant amount of ATP7B persists in the endolysosomal compartment of hepatocytes but not in non-hepatic cells. These ATP7B-harbouring lysosomes lie in close proximity of ~10 nm to the TGN. ATP7B constitutively distributes itself between the sub-domain of the TGN with a lower pH and the TGN-proximal lysosomal compartments. The presence of ATP7B on TGN-lysosome colocalising sites upon Golgi disruption suggested a possible exchange of ATP7B directly between the TGN and its proximal lysosomes. Manipulating lysosomal positioning significantly alters the localisation of ATP7B in the cell. Contrary to previous understanding, we found that upon copper chelation in a copper-replete hepatocyte, ATP7B is not retrieved back to TGN from peripheral lysosomes; rather, ATP7B recycles to these TGN-proximal lysosomes to initiate the next cycle of copper transport. We report a hitherto unknown copper-independent lysosomal localisation of ATP7B and the importance of TGN-proximal lysosomes but not TGN as the terminal acceptor organelle of ATP7B in its retrograde pathway.

The interplay between copper metabolism and microbes: in perspective of host copper-dependent ATPases ATP7A/B

Copper, a vital element in various physiological processes, is transported from the gastrointestinal tract to tissues and cells through diverse copper transporters. Among these transporters, ATP7A and ATP7B play significant roles in regulating systemic copper metabolism and exhibit precise regulation in their intracellular trafficking. These transporters undergo dynamic shuttling between the trans-Golgi network (TGN) and the plasma membrane via the endocytic recycling mechanism, which involves the retromer and other associated factors. Interestingly, the antimicrobial attribute of copper implies a potential connection between microbial infection and copper metabolism. Several microbes, including Salmonella enterica, Cryptococcus, Influenza A virus (IAV) and Zika virus (ZIKV) have been observed to impact the regulatory mechanisms of ATP7A/B, either directly or indirectly, as a means of survival. This review summarizes the key features and trafficking mechanisms of the copper transporters ATP7A/B, and examines the intricate interplay between microbes and copper metabolism. Ultimately, it highlights how microbes can perturb copper homeostasis through interactions with host factors, offering valuable insights into the mechanistic aspects of host-microbe interactions.

Bioactive copper(II) agents and their potential involvement in the treatment of copper deficiency-related orphan diseases

The deregulation of copper homoeostasis can promote various diseases such as Menkes disease or hypertrophic cardioencephalomyopathy. We have recently synthesized solid copper(II) complexes ([Cu(His)2Cl2] and [Cu(Ser)2]), stable in physiological media and with potential as therapeutic agents. This report describes: i) the biocompatibility of these complexes at concentrations up to 100 μM using a differentiated Caco-2 cells model; ii) their transport across the intestinal epithelium using a transepithelial resistance assay and monitoring the amount of copper complexes at the apical and basolateral sides of the cells. The results suggest that the flow occurs through paracellular routes. The intracellular copper retention was <2.7% with no significant differences in intracellular copper content between 6 h and 48 h, suggesting an early copper retention process. Furthermore, this is the first evidence that demonstrates [Cu(His)2Cl2] and [Cu(Ser)2] induce transcriptional downregulation of the four major copper transporters (CTR1, DMT1, ATP7A, ATP7B), and the upregulation of the metallothionein gene expression. A remarkable finding was the increase in cytochrome c oxidase activity observed after the treatment of differentiated Caco-2 cells with copper(II) complexes at concentrations of 50-100 μM. The understanding of the transport mechanisms of these copper(II) complexes across the intestinal epithelium and of their subsequent biological activities could contribute to the development of optimal pharmaceutical formulations for the therapy of copper deficiency-related diseases.

ATP7B-Deficient Hepatocytes Reveal the Importance of Protein Misfolding Induced at Low Copper Concentration

Copper is a transition metal essential for human life. Its homeostasis is regulated in the liver, which delivers copper to the whole body and excretes its excess outside the organism in the feces through the bile. These functions are regulated within hepatocytes, and the ATP7B copper transporter is central to making the switch between copper use and excretion. In Wilson disease, the gene coding for ATP7B is mutated, leading to copper overload, firstly, in the liver and the brain. To better understand the role of ATP7B in hepatocytes and to provide a smart tool for the development of novel therapies against Wilson disease, we used the CrispR/Cas9 tool to generate hepatocyte cell lines with the abolished expression of ATP7B. These cell lines revealed that ATP7B plays a major role at low copper concentrations starting in the micromolar range. Moreover, metal stress markers are induced at lower copper concentrations compared to parental cells, while redox stress remains not activated. As shown recently, the main drawback induced by copper exposure is protein unfolding that is drastically exacerbated in ATP7B-deficient cells. Our data enabled us to propose that the zinc finger domain of DNAJ-A1 would serve as a sensor of Cu stress. Therefore, these Wilson-like hepatocytes are of high interest to explore in more detail the role of ATP7B.

Lack of evidence for ribosomal frameshifting in ATP7B mRNA decoding

The research article describing the discovery of ribosomal frameshifting in the bacterial CopA gene also reported the occurrence of frameshifting in the expression of the human ortholog ATP7B based on assays using dual luciferase reporters. An examination of the publicly available ribosome profiling data and the phylogenetic analysis of the proposed frameshifting site cast doubt on the validity of this claim and prompted us to reexamine the evidence. We observed similar apparent frameshifting efficiencies as the original authors using the same type of vector that synthesizes both luciferases as a single polyprotein. However, we noticed anomalously low absolute luciferase activities from the N-terminal reporter that suggests interference of reporter activity or levels by the ATP7B test cassette. When we tested the same proposed ATP7B frameshifting cassette in a more recently developed reporter system in which the reporters are released without being included in a polyprotein, no frameshifting was detected above background levels.

Copper binding leads to increased dynamics in the regulatory N-terminal domain of full-length human copper transporter ATP7B

ATP7B is a human copper-transporting P_1B-type ATPase that is involved in copper homeostasis and resistance to platinum drugs in cancer cells. ATP7B consists of a copper-transporting core and a regulatory N-terminal tail that contains six metal-binding domains (MBD1-6) connected by linker regions. The MBDs can bind copper, which changes the dynamics of the regulatory domain and activates the protein, but the underlying mechanism remains unknown. To identify possible copper-specific structural dynamics involved in transport regulation, we constructed a model of ATP7B spanning the N-terminal tail and core catalytic domains and performed molecular dynamics (MD) simulations with (holo) and without (apo) copper ions bound to the MBDs. In the holo protein, MBD2, MBD3 and MBD5 showed enhanced mobilities, which resulted in a more extended N-terminal regulatory region. The observed separation of MBD2 and MBD3 from the core protein supports a mechanism where copper binding activates the ATP7B protein by reducing interactions among MBD1-3 and between MBD1-3 and the core protein. We also observed an increased interaction between MBD5 and the core protein that brought the copper-binding site of MBD5 closer to the high-affinity internal copper-binding site in the core protein. The simulation results assign specific, mechanistic roles to the metal-binding domains involved in ATP7B regulation that are testable in experimental settings.

Living organisms depend upon active transport against gradients across biological membranes for survival. Such transport can be accomplished by ATP-dependent membrane protein transporters for which the activity must be regulated to maintain optimal concentrations in the cellular compartments. The regulatory mechanisms often involve structural responses inherent to the protein structure, which because of their dynamic nature can be hard to assess experimentally. A prime example is regulation of cellular copper levels by a copper-binding tail in the human copper transporter ATP7B. Dysregulation can cause severe diseases, for example the copper metabolism disorder Wilson’s disease, which is caused by mutations in ATP7B regulation machinery. Due to the practical difficulties in working with membrane proteins, most studies of ATP7B have been conducted in the absence of the membrane-bound protein core. Here, we used computer simulations of full-length ATP7B to study how structural dynamics in the regulatory tail differ between copper-bound and copper-free states. Copper induced increased dynamics in the tail, resulting in an overall movement towards the ion-binding site in the protein core. The simulations identified several, hitherto not reported, interactions between the regulatory tail and the protein core that can be targeted experimentally to enhance our understanding of this medically relevant regulatory mechanism.

Sensitization of cancer cells towards Cisplatin and Carboplatin by protein kinase D inhibitors through modulation of ATP7A/B (copper transport ATPases)

Drug resistance of cancer cells is a significant impediment to effective chemotherapy. One primary reason for this is copper exporters - ATPase copper transporting alpha (ATP7A) and ATPase copper transporting beta (ATP7B). These molecular pumps belong to P-type ATPases and dispose off the Platinum (Pt) based anticancer drugs from cancer cells, causing resistance in them. For the disposal of Pt-drugs, copper exporters require phosphorylation mediated by protein kinase D (PKD) for their activation and trafficking. Even though various research works are underway to overcome resistance to anticancer drugs, the role of PKD is mainly ignored. In this study, we have found a significant upregulation of ATP7A and ATP7B in cervical cancer cells (HeLa) and Liver Hepatocellular Carcinoma cells (HepG2) in the presence of Cisplatin or Carboplatin; both at transcriptional as well as translational levels. Interestingly, the expression of ATP7A and ATP7B were significantly downregulated in the presence of a PKD inhibitor (CID2011756), resulting in the reduction of PKD mediated phosphorylation of ATP7A/7B. This causes enhancement of proteasome-mediated degradation of ATP7A/7B and thereby sensitizes the cells towards Cisplatin and Carboplatin. Similarly, the treatment of Cisplatin resistant HepG2 cells with PKD inhibitor causes enhanced sensitivity towards Cisplatin drug. However, the presence of proteasome inhibitor (MG132) reversed the effect of the PKD inhibitor on the expression level of ATP7A/7B, indicating the necessity of phosphorylation for its stability. Hence, we conclude that the combinatorial usage of Cisplatin with drugs targeting PKD can be developed as an effective chemotherapeutic approach to overcome drug resistance.

Analysis of Wilson disease mutations in copper binding domain of ATP7B gene

Wilson’s disease (WD) is an autosomal recessive disorder, resulting from variations in ATP7B gene. Clinical heterogeneity, including neuropsychiatric and hepatic manifestations over a large range of age groups make diagnosis difficult. Most of WD patients suffer severe disabilities and even die. So, overall goal of proposed study is the genetic and clinical characterization of Wilson’s disease cases from Pakistani population. Clinical data was collected, and patients were investigated for variations in selected ATP7B exons using PCR based Sanger sequencing. Pathogenic effect predictions for detected variants were carried out using PROVEAN, MutationTaster2, and HSF software’s. Clinical heterogeneity was observed in patients including reduced serum ceruloplasmin, signs of chronic liver damage and raised 24 h urinary copper excretion. Mean age of onset was 11.3 years. Kayser-Fleischer rings were present in 75% of cases. About 82.5% patients belonged to inbred families. Patients having neurological disorder were above 12 years of age. Total ten variants in analyzed region of ATP7B gene, including a reported variation (p. L227Yfs*35) were found in patients. The study also identified 4 putative novel synonymous variants (c.251A>C, c.15T>A, c.6T>C, c.238C>T) and 5 reported polymorphisms (c.83C>A, c.39_40insCGGCG, p.V456L, c.39_40insCGCCG and c.1544-53A>C). Reliable understanding of clinical presentations and genotype-phenotype correlation provide insight to function and structure of ATP7B and may assist in disease prognosis and family counseling. The study revealed clinical presentation of Pakistani WD cases and identification of sequence variants in screened region of ATP7B.

Quantitative Ubiquitinomics Revealed Abnormal Ubiquitinated ATP7A Involved in Down-Regulation of ACTH in Silent Corticotroph Adenomas

Ubiquitination is reported to be a critical biological event on ACTH secretion in corticotroph adenomas. However, the effect of ubiquitylation on ACTH secretion in silent corticotroph adenomas (SCAs) remains unclear. The aim of our study was to explore the mechanism of decreased secretion of ACTH in SCAs with ubiquitinomics. The differently expressed ubiquitinated proteins between SCAs and functioning corticotroph adenomas (FCAs) were identified by 4D label-free mass spectrometer, followed by bioinformatics analysis. The function of the candidate ubiquitinated protein ATP7A (K333) was validated in AtT20 cells. A total of 111 ubiquitinated sites corresponding to 94 ubiquitinated proteins were typically different between SCAs and FCAs. Among all the ubiquitinated sites, 102 showed decreased ubiquitination in SCAs, which mapped to 85 ubiquitinated proteins. Pathway enrichment analysis revealed that ubiquitinated proteins were mainly enriched in vesicle pathway and protein secretion pathway. ATP7A (K333) was one of the proteins enriched in vesicle pathway and protein secretion pathway with decreased ubiquitination level in SCAs. In vitro assay indicated that both ATP7A siRNA and omeprazole (ATP7A protein inhibitor) increased the secretion of ACTH in AtT20 cell supernatant compared to control groups (p<0.05). These results indicated that ATP7A might be related to the abnormal expression of ACTH in SCAs and potential for the treatment of SCAs.

Copper-histidine therapy in an infant with novel splice-site variant in the ATP7A gene of Menkes disease: the first experience in South East Asia and literature review

Menkes disease (MD) is an X linked recessive multi-systemic disorder of copper metabolism, resulting from an ATP7A gene mutation. We report a male infant aged 4 months who presented with kinky hair, hypopigmented skin, epilepsy and delayed development. Magnetic resonance imaging (MRI) of brain demonstrated multiple tortuosities of intracranial vessels and brain atrophy. Investigation had showed markedly decreased serum copper and ceruloplasmin. The novel c.2172+1G>T splice-site mutation in the ATP7A gene confirmed MD. He was treated with subcutaneous administration of locally prepared copper-histidine (Cu-His). Following the therapy, hair manifestation was restored and serum ceruloplasmin was normalised 1 month later. Despite the treatment, epilepsy, neurodevelopment and osteoporosis still progressed. He died from severe respiratory tract infection at the age of 9.5 months. These findings suggest that the benefit of Cu-His in our case is limited which might be related to severe presentations and degree of ATP7A mutation.

Copper dependent ERK1/2 phosphorylation is essential for the viability of neurons and not glia

Intracellular copper [Cu(I)] has been hypothesized to play role in the differentiation of the neurons. This necessitates understanding the role of Cu(I) not only in the neurons but also in the glia considering their anatomical proximity, contribution towards ion homeostasis, and neurodegeneration. In this study, we did a systematic investigation of the changes in the cellular copper homeostasis during neuronal and glial differentiation and the pathways triggered by them. Our study demonstrates increased mRNA for the plasma membrane copper transporter CTR1 leading to increased Cu(I) during the neuronal (PC-12) differentiation. ATP7A is retained in the trans-Golgi network (TGN) despite high Cu(I) demonstrating its utilization towards the neuronal differentiation. Intracellular copper triggers pathways essential for neurite generation and ERK1/2 activation during the neuronal differentiation. ERK1/2 activation also accompanies the differentiation of the foetal brain derived neuronal progenitor cells. The study demonstrates that ERK1/2 phosphorylation is essential for the viability of the neurons. In contrast, differentiated C-6 (glia) cells contain low intracellular copper and significant downregulation of the ERK1/2 phosphorylation demonstrating that ERK1/2 activation does not regulate the viability of the glia. But ATP7A shows vesicular localization despite low copper in the glia. In addition to the TGN, ATP7A localizes into RAB11 positive recycling endosomes in the glial neurites. Our study demonstrates the role of copper dependent ERK1/2 phosphorylation in the neuronal viability. Whereas glial differentiation largely involves sequestration of Cu(I) into the endosomes potentially (i) for ready release and (ii) rendering cytosolic copper unavailable for pathways like the ERK1/2 activation.

OUP accepted manuscript

The mutations in modifier genes may contribute to some inherited diseases including Wilson disease (WD). This study was designed to identify potential modifier genes that contribute to WD. A total of 10 WD patients with single or no heterozygous ATP7B mutations were recruited for whole-exome sequencing (WES). Five hundred and thirteen candidate genes, of which the genetic variants present in at least two patients, were identified. In order to clarify which proteins might be involved in copper transfer or metabolism processes, the isobaric tags for relative and absolute quantitation (iTRAQ) was performed to identify the differentially expressed proteins between normal and CuSO₄-treated cell lines. Thirteen genes/proteins were identified by both WES and iTRAQ, indicating that disease-causing variants of these genes may actually contribute to the aberrant copper ion accumulation. Additionally, the c.86C > T (p.S29L) mutation in the SLC31A2 gene (coding CTR2) has a relative higher frequency in our cohort of WD patients (6/191) than reported (0.0024 in gnomAD database) in our healthy donors (0/109), and CTR2^S29L leads to increased intracellular Cu concentration and Cu-induced apoptosis in cultured cell lines. In conclusion, the WES and iTRAQ approaches successfully identified several disease-causing variants in potential modifier genes that may be involved in the WD phenotype.

Hepatic Steatosis in the Mouse Model of Wilson Disease Coincides with a Muted Inflammatory Response

Wilson disease (WND) is caused by inactivation of the copper transporter ATP7B and copper accumulation in tissues. WND presentations vary from liver steatosis to inflammation, fibrosis, and liver failure. Diets influence the liver phenotype in WND, but findings are inconsistent. To better understand the impact of excess calories on liver phenotype in WND, the study compared C57BL/6J Atp7b-/- and C57BL/6J mice fed for 12 weeks with Western diet or normal chow. Serum and liver metabolites, body fat content, liver histology, hepatic proteome, and copper content were analyzed. Wild-type and Atp7b-/- livers showed striking similarities in their responses to Western diet, most notably down-regulation of cholesterol biosynthesis, altered nuclear receptor signaling, and changes in cytoskeleton. Western diet increased body fat content and induced liver steatosis in males and females regardless of genotype; however, the effects were less pronounced in Atp7b-/- mice compared with those in the wild type mice. Although hepatic copper remained elevated in Atp7b-/- mice, liver inflammation was reduced. The diet diminished signaling by Rho GTPases, integrin, IL8, and reversed changes in cell cycle machinery and cytoskeleton. Overall, high calories decreased inflammatory response in favor of steatosis without improving markers of cell viability. Similar changes of cellular pathways during steatosis development in wild-type and Atp7b-/- mice explain histologic overlap between WND and non-alcoholic fatty liver disease despite opposite copper changes in these disorders.

Elesclomol induces copper-dependent ferroptosis in colorectal cancer cells via degradation of ATP7A

Cancer cells reprogram their copper metabolism to adapt to adverse microenvironments, such as oxidative stress. The copper chelator elesclomol has been reported to have considerable anticancer efficacy, but the underlying mechanisms remain largely unknown. In this study, we found that elesclomol-mediated copper overload inhibits colorectal cancer (CRC) both in vitro and in vivo. Elesclomol alone promotes the degradation of the copper transporter copper-transporting ATPase 1 (ATP7A), which retards the proliferation of CRC cells. This property distinguishes it from several other copper chelators. Combinational treatment of elesclomol and copper leads to copper retention within mitochondria due to ATP7A loss, leading to reactive oxygen species accumulation, which in turn promotes the degradation of SLC7A11, thus further enhancing oxidative stress and consequent ferroptosis in CRC cells. This effect accounts for the robust antitumour activity of elesclomol against CRC, which can be reversed by the administration of antioxidants and ferroptosis inhibitors, as well as the overexpression of ATP7A. In summary, our findings indicate that elesclomol-induced copper chelation inhibits CRC by targeting ATP7A and regulating ferroptosis.

Cognitive impairment in stable Wilson disease across phenotype

In Wilson disease (WD), mutations in the gene encoding the ATP7B copper transport protein causes accumulation of copper especially in liver and brain. WD typically presents with hepatic and/or neuropsychiatric symptoms. Impaired cognition is a well-described feature in patients with neurological WD, while the reports on cognition in hepatic WD patients are fewer and less conclusive. We examined cognition in a cohort of WD patients with both phenotypes. In this cross-sectional pilot study, we investigated cognition in 28 stable Danish WD patients by the PortoSystemic Encephalopathy (PSE) and the Continuous Reaction Time (CRT) tests. Half of the patients were female, and their median age was 35.5 years (IQR 24.5). Their phenotype was hepatic in 14 (50%), neurologic in 10 (36%) and mixed in 4 (14%). The duration of treatment was > 2 year in all patients, and their condition was stable as judged by urinary copper excretion, liver enzymes, and clinical assessment. The hepatic patients did not show signs of liver failure. In total, 16 (57%) patients performed worse than normal in the PSE and/or the CRT tests. The two tests were correlated (rho = 0.60, p = 0.0007), but neither correlated with phenotype, MELD-, Child-Pugh score, 24 h-U-Cu, or treatment type. Measurable cognitive impairment was present in more than half of the stable WD patients independent of phenotype. Thus, our data questions the existence of a purely hepatic phenotype.

Membrane Transporters Involved in the Antimicrobial Activities of Pyrithione in Escherichia coli

Pyrithione (2-mercaptopyridine-N-oxide) is a metal binding modified pyridine, the antibacterial activity of which was described over 60 years ago. The formulation of zinc-pyrithione is commonly used in the topical treatment of certain dermatological conditions. However, the characterisation of the cellular uptake of pyrithione has not been elucidated, although an unsubstantiated assumption has persisted that pyrithione and/or its metal complexes undergo a passive diffusion through cell membranes. Here, we have profiled specific membrane transporters from an unbiased interrogation of 532 E. coli strains of knockouts of genes encoding membrane proteins from the Keio collection. Two membrane transporters, FepC and MetQ, seemed involved in the uptake of pyrithione and its cognate metal complexes with copper, iron, and zinc. Additionally, the phenotypes displayed by CopA and ZntA knockouts suggested that these two metal effluxers drive the extrusion from the bacterial cell of potentially toxic levels of copper, and perhaps zinc, which hyperaccumulate as a function of pyrithione. The involvement of these distinct membrane transporters contributes to the understanding of the mechanisms of action of pyrithione specifically and highlights, more generally, the important role that membrane transporters play in facilitating the uptake of drugs, including metal-drug compounds.

Computational Investigation of the pH Dependence of Stability of Melanosome Proteins: Implication for Melanosome formation and Disease

Intravesicular pH plays a crucial role in melanosome maturation and function. Melanosomal pH changes during maturation from very acidic in the early stages to neutral in late stages. Neutral pH is critical for providing optimal conditions for the rate-limiting, pH-sensitive melanin-synthesizing enzyme tyrosinase (TYR). This dramatic change in pH is thought to result from the activity of several proteins that control melanosomal pH. Here, we computationally investigated the pH-dependent stability of several melanosomal membrane proteins and compared them to the pH dependence of the stability of TYR. We confirmed that the pH optimum of TYR is neutral, and we also found that proteins that are negative regulators of melanosomal pH are predicted to function optimally at neutral pH. In contrast, positive pH regulators were predicted to have an acidic pH optimum. We propose a competitive mechanism among positive and negative regulators that results in pH equilibrium. Our findings are consistent with previous work that demonstrated a correlation between the pH optima of stability and activity, and they are consistent with the expected activity of positive and negative regulators of melanosomal pH. Furthermore, our data suggest that disease-causing variants impact the pH dependence of melanosomal proteins; this is particularly prominent for the OCA2 protein. In conclusion, melanosomal pH appears to affect the activity of multiple melanosomal proteins.

The P-type ATPase transporter ATP7A promotes angiogenesis by limiting autophagic degradation of VEGFR2

VEGFR2 (KDR/Flk1) signaling in endothelial cells (ECs) plays a central role in angiogenesis. The P-type ATPase transporter ATP7A regulates copper homeostasis, and its role in VEGFR2 signaling and angiogenesis is entirely unknown. Here, we describe the unexpected crosstalk between the Copper transporter ATP7A, autophagy, and VEGFR2 degradation. The functional significance of this Copper transporter was demonstrated by the finding that inducible EC-specific ATP7A deficient mice or ATP7A-dysfunctional ATP7Amut mice showed impaired post-ischemic neovascularization. In ECs, loss of ATP7A inhibited VEGF-induced VEGFR2 signaling and angiogenic responses, in part by promoting ligand-induced VEGFR2 protein degradation. Mechanistically, VEGF stimulated ATP7A translocation from the trans-Golgi network to the plasma membrane where it bound to VEGFR2, which prevented autophagy-mediated lysosomal VEGFR2 degradation by inhibiting autophagic cargo/adapter p62/SQSTM1 binding to ubiquitinated VEGFR2. Enhanced autophagy flux due to ATP7A dysfunction in vivo was confirmed by autophagy reporter CAG-ATP7Amut -RFP-EGFP-LC3 transgenic mice. In summary, our study uncovers a novel function of ATP7A to limit autophagy-mediated degradation of VEGFR2, thereby promoting VEGFR2 signaling and angiogenesis, which restores perfusion recovery and neovascularization. Thus, endothelial ATP7A is identified as a potential therapeutic target for treatment of ischemic cardiovascular diseases.

Copper Dependent Modulation of α-Synuclein Phosphorylation in Differentiated SHSY5Y Neuroblastoma Cells

Copper (Cu) dyshomeostasis plays a pivotal role in several neuropathologies, such as Parkinson's disease (PD). Metal accumulation in the central nervous system (CNS) could result in loss-of-function of proteins involved in Cu metabolism and redox cycling, generating reactive oxygen species (ROS). Moreover, neurodegenerative disorders imply the presence of an excess of misfolded proteins known to lead to neuronal damage. In PD, Cu accumulates in the brain, binds α-synuclein, and initiates its aggregation. We assessed the correlation between neuronal differentiation, Cu homeostasis regulation, and α-synuclein phosphorylation. At this purpose, we used differentiated SHSY5Y neuroblastoma cells to reproduce some of the characteristics of the dopaminergic neurons. Here, we reported that differentiated cells expressed a significantly higher amount of a copper transporter protein 1 (CTR1), increasing the copper uptake. Cells also showed a significantly more phosphorylated form of α-synuclein, further increased by copper treatment, without modifications in α-synuclein levels. This effect depended on the upregulation of the polo-like kinase 2 (PLK2), whereas the levels of the relative protein phosphatase 2A (PP2A) remained unvaried. No changes in the oxidative state of the cells were identified. The Cu dependent alteration of α-synuclein phosphorylation pattern might potentially offer new opportunities for clinical intervention.

Altered copper homeostasis underlies sensitivity of hepatocellular carcinoma to copper chelation

Hepatocellular carcinoma (HCC), the most common primary liver cancer, of which ∼800 000 new cases will be diagnosed worldwide this year, portends a five-year survival rate of merely 17% in patients with unresectable disease. This dismal prognosis is due, at least in part, from the late stage of diagnosis and the limited efficacy of systemic therapies. As a result, there is an urgent need to identify risk factors that contribute to HCC initiation and provide targetable vulnerabilities to improve patient survival. While myriad risk factors are known, elevated copper (Cu) levels in HCC patients and the incidence of hepatobiliary malignancies in Wilson disease patients, which exhibit hereditary liver Cu overload, suggests the possibility that metal accumulation promotes malignant transformation. Here we found that expression of the Cu transporter genes ATP7A, ATP7B, SLC31A1, and SLC31A2 was significantly altered in liver cancer samples and were associated with elevated Cu levels in liver cancer tissue and cells. Further analysis of genomic copy number data revealed that alterations in Cu transporter gene loci correlate with poorer survival in HCC patients. Genetic loss of the Cu importer SLC31A1 (CTR1) or pharmacologic suppression of Cu decreased the viability, clonogenic survival, and anchorage-independent growth of human HCC cell lines. Mechanistically, CTR1 knockdown or Cu chelation decreased glycolytic gene expression and downstream metabolite utilization and as a result forestalled tumor cell survival after exposure to hypoxia, which mimics oxygen deprivation elicited by transarterial embolization, a standard-of-care therapy used for patients with unresectable HCC. Taken together, these findings established an association between altered Cu homeostasis and HCC and suggest that limiting Cu bioavailability may provide a new treatment strategy for HCC by restricting the metabolic reprogramming necessary for cancer cell survival.

A novel deep intronic variant in ATP7B in five unrelated families affected by Wilson disease

BACKGROUND

Wilson disease is an autosomal recessive metabolic disorder resulting from accumulation of excess copper especially in the liver and brain. This disease is mainly characterized by hepatic disorders and less frequently by neuro-psychiatric disturbances. This recessive disease is due to mutation in ATP7B, which codes for an ATPase involved in copper-transport across the plasma membrane. Molecular diagnosis of WD is positive in approximately 98% of cases. Also, in few cases, WD patients present a single deleterious mutation (heterozygous) or no mutation after sanger and NGS standard sequencing analysis of ATP7B. Therefore, in these problematic WD cases, we hypothesized that deleterious mutations reside in intronic regions of ATP7B.

METHODS

Complete ATP7B gene was sequenced by Next Generation Sequencing including its promoter.

RESULTS

Five unrelated families with Wilson disease shared the same novel, deep intronic NG_008806.1 (ATP7B_v001):c.2866-1521G>A variant in ATP7B. Analysis of RNA transcripts from primary fibroblasts of one patient confirmed the deleterious impact of the intronic variant on splicing and its likely pathologic effect in this compound heterozygote.

CONCLUSION

This discovery of a novel intronic mutation in ATP7B has improved the molecular diagnosis of WD in the French patient cohort to greater than 98%. Thus, we recommend complete sequencing of ATP7B gene, including introns, as a molecular diagnostic approach in cases of clinically confirmed WD which lack pathogenic exon or promoter variants in one or both alleles.

Role of metal speciation in the exposure medium on the toxicity, bioavailability and bio-reactivity of copper, silver, cadmium and zinc in the rainbow trout gut cell line (RTgutGC)

The role of metal speciation on metal bioavailability, bio-reactivity and toxicity at the fish intestine is poorly understood. To investigate these processes, we used an in vitro model of the rainbow trout (Oncorhynchus mykiss) intestine, the RTgutGC cell line. Cells were exposed to two essential metals (copper and zinc) and two non-essential metals (cadmium and silver) in a medium of well-defined composition, which allowed the determination of metal speciation in solution. Concentrations resulting in a 50% cell viability reduction (EC₅₀) were measured using a viability assay based on two endpoints: metabolic activity and membrane integrity. Metal bioavailability and bio-reactivity was studied at non-toxic (300 nM all metals) and toxic (EC₁₀; Ag-0.6, Cu-0.9, Cd-3, and Zn-9 μM) concentrations. Bioavailability (i.e. intracellular metal accumulation) was determined by ICP-MS, while bio-reactivity (i.e. induction of a metal specific transcriptional response) was determined by measuring the mRNA levels of a known biomarker of metal exposure (i.e. metallothionein) and of copper and zinc transporters (i.e. ATP7A and ZnT1). Dominant metal species in the exposure medium were Zn²⁺, CuHPO₄, CdCl⁺, and AgCl₂^- respectively for Zn, Cu, Cd, and Ag. The EC_50s showed the metal toxicity hierarchy: Ag > Cu > Cd > Zn. In RTgutGC cells, essential metal homeostasis was tightly regulated while non-essential metals accumulated more readily. Non-essential metals were also more bio-reactive inducing higher MT and ZnT1 mRNA levels. Taken together these findings indicate that metal toxicity in RTgutGC cannot solely be explained by extracellular metal speciation but requires the evaluation of metal bioavailability and bio-reactivity.

Protein Adsorption on Solid Supported Membranes: Monitoring the Transport Activity of P-Type ATPases

P-type ATPases are a large family of membrane transporters that are found in all forms of life. These enzymes couple ATP hydrolysis to the transport of various ions or phospholipids across cellular membranes, thereby generating and maintaining crucial electrochemical potential gradients. P-type ATPases have been studied by a variety of methods that have provided a wealth of information about the structure, function, and regulation of this class of enzymes. Among the many techniques used to investigate P-type ATPases, the electrical method based on solid supported membranes (SSM) was employed to investigate the transport mechanism of various ion pumps. In particular, the SSM method allows the direct measurement of charge movements generated by the ATPase following adsorption of the membrane-bound enzyme on the SSM surface and chemical activation by a substrate concentration jump. This kind of measurement was useful to identify electrogenic partial reactions and localize ion translocation in the reaction cycle of the membrane transporter. In the present review, we discuss how the SSM method has contributed to investigate some key features of the transport mechanism of P-type ATPases, with a special focus on sarcoplasmic reticulum Ca²⁺-ATPase, mammalian Cu⁺-ATPases (ATP7A and ATP7B), and phospholipid flippase ATP8A2.

An EPR Study on the Interaction between the Cu(I) Metal Binding Domains of ATP7B and the Atox1 Metallochaperone

Copper’s essentiality and toxicity mean it requires a sophisticated regulation system for its acquisition, cellular distribution and excretion, which until now has remained elusive. Herein, we applied continuous wave (CW) and pulsed electron paramagnetic resonance (EPR) spectroscopy in solution to resolve the copper trafficking mechanism in humans, by considering the route travelled by Cu(I) from the metallochaperone Atox1 to the metal binding domains of ATP7B. Our study revealed that Cu(I) is most likely mediated by the binding of the Atox1 monomer to metal binding domain 1 (MBD1) and MBD4 of ATP7B in the final part of its extraction pathway, while the other MBDs mediate this interaction and participate in copper transfer between the various MBDs to the ATP7B membrane domain. This research also proposes that MBD1-3 and MBD4-6 act as two independent units.

Wilson disease

PURPOSE OF REVIEW

The aim of this article is to review recent developments in the areas of the disease features and treatment of Wilson disease, and survey disorders that share its pathophysiology or clinical symptoms.

RECENT FINDINGS

Knowledge of the clinical spectrum of Wilson disease has expanded with recognition of patients who present in atypical age groups - patients with very early onset (<5 years) and those in whom symptoms present in mid-to-late adulthood. A disease phenotype with dominant psychiatric features and increased risk of cardiac problems and various sleep disorders have been identified.In addition to a better understanding of the phenotype of Wilson disease itself, features of some related disorders ('Wilson disease-mimics') have been described leading to a better understanding of copper homeostasis in humans. These disorders include diseases of copper disposition, such as mental retardation, enteropathy, deafness, neuropathy, ichthyosis, keratoderma syndrome, Niemann-Pick type C, and certain congenital disorders of glycosylation, as well as analogous disorders of iron and manganese metabolism.Outcomes for existing treatments, including in certain patient subpopulations of interest, are better known. Novel treatment strategies being studied include testing of bis-choline tetrathiomolybdate in phase 2 clinical trial as well as various preclinical explorations of new copper chelators and ways to restore ATP7B function or repair the causative gene.

SUMMARY

Recent studies have expanded the phenotype of Wilson disease, identified rare inherited metal-related disorders that resemble Wilson disease, and studied long-term outcomes of existing treatments. These developments can be expected to have an immediate as well as a long-term impact on the clinical management of the disease, and point to promising avenues for future research.

Metallothioneins regulate ATP7A trafficking and control cell viability during copper deficiency and excess

Copper (Cu) is an essential, yet potentially toxic nutrient, as illustrated by inherited diseases of copper deficiency and excess. Elevated expression of the ATP7A Cu exporter is known to confer copper tolerance, however, the contribution of metal-binding metallothioneins is less clear. In this study, we investigated the relative contributions of ATP7A and the metallothioneins MT-I and MT-II to cell viability under conditions of Cu excess or deficiency. Although the loss of ATP7A increased sensitivity to low Cu concentrations, the absence of MTs did not significantly affect Cu tolerance. However, the absence of all three proteins caused a synthetic lethal phenotype due to extreme Cu sensitivity, indicating that MTs are critical for Cu tolerance only in the absence of ATP7A. A lack of MTs resulted in the trafficking of ATP7A from the trans-Golgi complex in a Cu-dependent manner, suggesting that MTs regulate the delivery of Cu to ATP7A. Under Cu deficiency conditions, the absence of MTs and / or ATP7A enhanced cell proliferation compared to wild type cells, suggesting that these proteins compete with essential Cu-dependent pathways when Cu is scarce. These studies reveal new roles for ATP7A and metallothioneins under both Cu deficiency and excess.

MTF1 binds to metal-responsive element e within the ATP7B promoter and is a strong candidate in regulating the ATP7B expression

Wilson's disease is an autosomal recessive disorder resulting from copper excess. Some patients with clinical Wilson's disease symptoms exhibit no or only heterozygous pathogenic variants in the coding region of the disease-causing ATP7B gene. Therefore, the ATP7B promoter region is of special interest. Metal-responsive elements (MREs) located in the ATP7B promoter are promising motifs in modulating the ATP7B expression. We studied protein interaction of MREe, MREc, and MREd by electrophoretic mobility shift assays and revealed specific interactions for all MREs. We further narrowed down the specific binding site. Proteins potentially binding to the three MREs were identified by MatInspector analyses. Metal regulatory transcription factor 1 (MTF1) could be validated to bind to MREe by electrophoretic mobility shift assays. ATP7B promoter-driven reporter gene expression was significantly increased because of this interaction. MTF1 is a strong candidate in regulating the ATP7B expression through MREe binding.

Oxamusplatin: a cytotoxic Pt(ii) complex of a nitrogen mustard with resistance to thiol based sequestration displays enhanced selectivity towards cancer

Pt(ii) drugs and nitrogen mustards show severe side effects, poor tumour selectivity and face growing resistance by cancer cells due to sequestration by thiol-containing molecules (viz. glutathione (GSH) and copper ATPases like ATP7A/7B). ATP7A and ATP7B-sequestered Pt(ii) complexes show dose inefficacy and resistance. The incorporation of bulky ligands and chelating leaving groups may prevent deactivation by thiols. In this work, we have synthesised four new Pt(ii) complexes (3-6) of two carrier ligands, bis(2-hydroxyethyl)pyridylmethylamine (L1) and bis(2-chloroethyl)pyridylmethylamine (L2) with oxalato and cyclobutanedicarboxylato leaving groups. Among these four new complexes, the Pt(ii) complex of L2 with the oxalato leaving group (5, termed "oxamusplatin") is cytotoxic. Oxamusplatin is more resistant than cisplatin or oxaliplatin towards hydrolysis, thiol binding and sequestration by ATP7B. It targets cellular DNA and is capable of disrupting the microtubule network in the cytoskeleton. Oxamusplatin demonstrates better selectivity than oxaliplatin towards cancerous cells. It is ca. 4-10 times more cytotoxic towards metastatic prostate carcinoma (DU-145, IC50 = 21 ± 1 μM) and ca. 10-24 times more cytotoxic towards breast adenocarcinoma (MCF-7, IC50 = 8.1 ± 0.8 μM) compared to the three noncancerous cells investigated.

CtpB is a plasma membrane copper (I) transporting P-type ATPase of Mycobacterium tuberculosis

BACKGROUND

The intracellular concentration of heavy-metal cations, such as copper, nickel, and zinc is pivotal for the mycobacterial response to the hostile environment inside macrophages. To date, copper transport mediated by P-type ATPases across the mycobacterial plasma membrane has not been sufficiently explored.

RESULTS

In this work, the ATPase activity of the putative Mycobacterium tuberculosis P1B-type ATPase CtpB was associated with copper (I) transport from mycobacterial cells. Although CtpB heterologously expressed in M. smegmatis induced tolerance to toxic concentrations of Cu2+ and a metal preference for Cu+, the disruption of ctpB in M. tuberculosis cells did not promote impaired cell growth or heavy-metal accumulation in whole mutant cells in cultures under high doses of copper. In addition, the Cu+ ATPase activity of CtpB embedded in the plasma membrane showed features of high affinity/slow turnover ATPases, with enzymatic parameters KM 0.19 ± 0.04 µM and Vmax 2.29 ± 0.10 nmol/mg min. In contrast, the ctpB gene transcription was activated in cells under culture conditions that mimicked the hostile intraphagosomal environment, such as hypoxia, nitrosative and oxidative stress, but not under high doses of copper.

CONCLUSIONS

The overall results suggest that M. tuberculosis CtpB is associated with Cu+ transport from mycobacterial cells possibly playing a role different from copper detoxification.

Metabolic dysregulation in the Atp7b-/- Wilson's disease mouse model

Inactivating mutations in the copper transporter Atp7b result in Wilson's disease. The Atp7b-/- mouse develops hallmarks of Wilson's disease. The activity of several nuclear receptors decreased in Atp7b-/- mice, and nuclear receptors are critical for maintaining metabolic homeostasis. Therefore, we anticipated that Atp7b-/- mice would exhibit altered progression of diet-induced obesity, fatty liver, and insulin resistance. Following 10 wk on a chow or Western-type diet (40% kcal fat), parameters of glucose and lipid homeostasis were measured. Hepatic metabolites were measured by liquid chromatography-mass spectrometry and correlated with transcriptomic data. Atp7b-/- mice fed a chow diet presented with blunted body-weight gain over time, had lower fat mass, and were more glucose tolerant than wild type (WT) littermate controls. On the Western diet, Atp7b-/- mice exhibited reduced body weight, adiposity, and hepatic steatosis compared with WT controls. Atp7b-/- mice fed either diet were more insulin sensitive than WT controls; however, fasted Atp7b-/- mice exhibited hypoglycemia after administration of insulin due to an impaired glucose counterregulatory response, as evidenced by reduced hepatic glucose production. Coupling gene expression with metabolomic analyses, we observed striking changes in hepatic metabolic profiles in Atp7b-/- mice, including increases in glycolytic intermediates and components of the tricarboxylic acid cycle. In addition, the active phosphorylated form of AMP kinase was significantly increased in Atp7b-/- mice relative to WT controls. Alterations in hepatic metabolic profiles and nuclear receptor signaling were associated with improved glucose tolerance and insulin sensitivity as well as with impaired fasting glucose production in Atp7b-/- mice.

CRISPR-mediated gene correction links the ATP7A M1311V mutations with amyotrophic lateral sclerosis pathogenesis in one individual

Amyotrophic lateral sclerosis (ALS) is a severe disease causing motor neuron death, but a complete cure has not been developed and related genes have not been defined in more than 80% of cases. Here we compared whole genome sequencing results from a male ALS patient and his healthy parents to identify relevant variants, and chose one variant in the X-linked ATP7A gene, M1311V, as a strong disease-linked candidate after profound examination. Although this variant is not rare in the Ashkenazi Jewish population according to results in the genome aggregation database (gnomAD), CRISPR-mediated gene correction of this mutation in patient-derived and re-differentiated motor neurons drastically rescued neuronal activities and functions. These results suggest that the ATP7A M1311V mutation has a potential responsibility for ALS in this patient and might be a potential therapeutic target, revealed here by a personalized medicine strategy.

The expression of copper transporters associated with the ototoxicity induced by platinum-based chemotherapeutic agents

BACKGROUND

Antitumor agents based on platinum have gained a well-established place in the treatment of several forms of cancer. Their efficiency is hampered by serious toxic effects against healthy tissues as well. Ototoxicity is a serious side effect leading to hearing impairment and represents an important issue affecting the patients' quality of life. The currently used platinum chemotherapeutics exert different toxicity towards cochlear cells. The aim of our study was to answer some questions regarding the differential uptake and cellular pharmacodynamics of Cisplatin (CDDP), Carboplatin (CBDCA) and Oxaliplatin (L-OHP) in the HEI-OC1 cochlear cell line.

METHODS

We studied the expression of copper transporters CTR1, ATP7A and ATP7B which are presumably involved in the uptake, cellular transport and efflux of platinum compounds by immunofluorescence microscopy and flow-cytometry. The cellular uptake of the compounds was evaluated through the determination of intracellular platinum concentration by atomic absorption spectroscopy. The effects of the treatment of HEI-OC1 cells with platinum compounds were also evaluated: cytotoxicity with the Cell Titer Blue viability test, formation of reactive oxygen species with 2',7' -dichlorofluorescein diacetate, genotoxicity with the comet assay and apoptosis with the cleaved PARP ELISA test.

RESULTS

CTR1, ATP7A and ATP7B were all expressed by HEI-OC1 cells. The treatment with the platinum compounds led to a modulation of their expression, manifested in a differential platinum uptake. Treatment with Cisplatin led to the highest intracellular concentration of platinum compared to Oxaliplatin and Carboplatin at the same dose. Treatment with CuSO4 reduced platinum uptake of all the compounds, significantly in the case of Cisplatin and Carboplatin. CDDP was the most cytotoxic against HEI-OC1 cells, with an IC50 = 65.79  μM, compared to 611.7 μM for L-OHP and 882.9 μM for CBDCA, at the same molar concentration. The production of ROS was the most intense after CDDP, followed by L-OHP and CBDCA. In the comet assay, at the 100 μM concentration, L-OHP and CBDCA induced DNA adducts while CDDP induced adducts as well as DNA strand breaks. CBDCA and L-OHP lead to a significant increase of cleaved PARP at 24h (p < 0.001), suggesting an important apoptotic process induced by these compounds at the used concentrations.

CONCLUSIONS

The results obtained in the current study suggest that the modulation of copper transporters locally may represent a new strategy against platinum drugs ototoxicity.

Copper ions are novel therapeutic agents for uterine leiomyosarcoma

BACKGROUND

Multidrug resistance is a major concern in uterine leiomyosarcoma treatment. Development of effective chemotherapies and management of drug resistance in patients is necessary. The copper efflux transporter adenosine triphosphatase copper transporting beta is a member of the P-type adenosine triphosphatase family and is also known as a strong platinum efflux transporter. Various reports have shown the association between adenosine triphosphatase copper transporting beta and platinum resistance; however, suitable inhibitors or methods for inhibiting platinum efflux via adenosine triphosphatase copper transporting beta are not developed.

OBJECTIVE

Our study focused on platinum resistance in uterine leiomyosarcoma. The role of adenosine triphosphatase copper transporting beta in uterine leiomyosarcoma resistance to platinum drugs was investigated both in vitro and in vivo.

STUDY DESIGN

Adenosine triphosphatase copper transporting beta expression was investigated by Western blotting and the efficacy of copper sulfate pretreatment and cisplatin administration in adenosine triphosphatase copper transporting beta-expressing cells was investigated both in vitro and in vivo.

RESULTS

Western blot analysis of SK-LMS-1 cells (uterine leiomyosarcoma cell line) revealed strong adenosine triphosphatase copper transporting beta expression. A permanent SK-LMS-ATPase copper transporting beta-suppressed cell line (SK-LMS-7B cells) was generated, and cisplatin exhibited a significant antitumor effect in SK-LMS-7B cells, both in vitro (SK-LMS-1 cells, half-maximal inhibitory concentration, 17.2 μM; SK-LMS-7B cells, half-maximal inhibitory concentration, 4.2 μM, P < .01) and in xenografts compared with that in SK-LMS-1 cells (5.8% vs 62.8%, P < .01). Copper sulfate was identified as a preferential inhibitor of platinum efflux via adenosine triphosphatase copper transporting beta. In SK-LMS-1 cells pretreated with 15 μM copper sulfate for 3 hours, the cisplatin half-maximal inhibitory concentration decreased significantly compared with that in untreated cells and resulted in significantly increased intracellular platinum accumulation (1.9 pg/cell vs 8.6 pg/cell, P < .01). The combination of copper sulfate pretreatment with cisplatin administration was also effective in vivo and caused cisplatin to exhibit significantly increased antitumor effects in mice with SK-LMS-1 xenografts (3.1% vs 62.7%, P < .01).

CONCLUSION

Our study demonstrates that adenosine triphosphatase copper transporting beta is overexpressed in uterine leiomyosarcoma cells and that copper sulfate, which acts as an inhibitor of platinum efflux via adenosine triphosphatase copper transporting beta, may be a therapeutic agent in the treatment of uterine leiomyosarcoma.

Copper modulates sex-specific fructose hepatoxicity in nonalcoholic fatty liver disease (NALFD) Wistar rat models

This study aimed to characterize the impact of dietary copper on the biochemical and hepatic metabolite changes associated with fructose toxicity in a Wistar rat model of fructose-induced liver disease. Twenty-four male and 24 female, 6-week-old, Wister rats were separated into four experimental dietary treatment groups (6 males and 6 females per group), as follows: (1) a control diet: containing no fructose with adequate copper (i.e., CuA/0% Fruct); (2) a diet regimen identical to the control and supplemented with 30% w/v fructose in the animals' drinking water (CuA/30% Fruct); (3) a diet identical to the control diet but deficient in copper content (CuD/0% Fruct) and (4) a diet identical to the control diet but deficient in copper content and supplemented with 30% w/v fructose in the drinking water (CuD/30% Fruct). The animals were fed the four diet regimens for 5 weeks, followed by euthanization and assessment of histology, elemental profiles and identification and quantitation of liver metabolites. Results from ¹H nuclear magnetic resonance metabolomics revealed mechanistic insights into copper modulation of fructose hepatotoxicity through identification of distinct metabolic phenotypes that were highly correlated with diet and sex. This study also identified previously unknown sex-specific responses to both fructose supplementation and restricted copper intake, while the presence of adequate dietary copper promoted most pronounced fructose-induced metabolite changes.

Adipocyte-specific disruption of ATPase copper transporting α in mice accelerates lipoatrophy

AIMS/HYPOTHESIS

ATPase copper transporting α (ATP7A), also known as Menkes disease protein, is a P-type ATPase that transports copper across cell membranes. The critical role of ATP7A-mediated copper homeostasis has been well recognised in various organs, such as the intestine, macrophages and the nervous system. However, the importance of adipocyte ATP7A-mediated copper homeostasis on fat metabolism is not well understood. Here, we sought to reveal the contribution of adipose ATP7A to whole-body fat metabolism in mice.

METHODS

We generated adipocyte-specific Atp7a-knockout (ASKO) mice using the Cre/loxP system, with Cre expression driven by the adiponectin promoter. ASKO mice and littermate control mice were aged on a chow diet or fed with a high-fat diet (HFD); body weight, fat mass, and glucose and insulin metabolism were analysed. Histological analysis, transmission electron microscopy and RNA-sequencing (RNA-Seq) analysis of white adipose tissue (WAT) were used to understand the physiological and molecular changes associated with loss of copper homeostasis in adipocytes.

RESULTS

Significantly increased copper concentrations were observed in adipose tissues of ASKO mice compared with control mice. Aged or HFD-fed ASKO mice manifested a lipoatrophic phenotype characterised by a progressive generalised loss of WAT. Dysfunction of adipose tissues in these ASKO mice was confirmed by decreased levels of both serum leptin and adiponectin and increased levels of triacylglycerol and insulin. Systemic metabolism was also impaired in these mice, as evidenced by a pronounced glucose intolerance, insulin resistance and hepatic steatosis. Moreover, we demonstrate a significant induction of lipolysis and DNA-damage signalling pathways in gonadal WAT from aged and HFD-fed ASKO mice. In vitro studies suggest that copper overload is responsible for increased lipolysis and DNA damage.

CONCLUSIONS/INTERPRETATION

Our results show a previously unappreciated role of adipocyte Atp7a in the regulation of ageing-related metabolic disease and identify new metallophysiologies in whole-body fat metabolism.

DATA AVAILABILITY

The datasets generated during the current study are available in the Genome Sequence Archive in BIG Data Center, Beijing Institute of Genomics (BIG), Chinese Academy of Sciences, under accession number CRA001769 (http://bigd.big.ac.cn/gsa).

Unraveling the Impact of Cysteine-to-Serine Mutations on the Structural and Functional Properties of Cu(I)-Binding Proteins

Appropriate maintenance of Cu(I) homeostasis is an essential requirement for proper cell function because its misregulation induces the onset of major human diseases and mortality. For this reason, several research efforts have been devoted to dissecting the inner working mechanism of Cu(I)-binding proteins and transporters. A commonly adopted strategy relies on mutations of cysteine residues, for which Cu(I) has an exquisite complementarity, to serines. Nevertheless, in spite of the similarity between these two amino acids, the structural and functional impact of serine mutations on Cu(I)-binding biomolecules remains unclear. Here, we applied various biochemical and biophysical methods, together with all-atom simulations, to investigate the effect of these mutations on the stability, structure, and aggregation propensity of Cu(I)-binding proteins, as well as their interaction with specific partner proteins. Among Cu(I)-binding biomolecules, we focused on the eukaryotic Atox1-ATP7B system, and the prokaryotic CueR metalloregulator. Our results reveal that proteins containing cysteine-to-serine mutations can still bind Cu(I) ions; however, this alters their stability and aggregation propensity. These results contribute to deciphering the critical biological principles underlying the regulatory mechanism of the in-cell Cu(I) concentration, and provide a basis for interpreting future studies that will take advantage of cysteine-to-serine mutations in Cu(I)-binding systems.

Life-time exposure to waterborne copper II: Patterns of tissue accumulation and gene expression of the metal-transport proteins ctr1 and atp7b in the killifish Poecilia vivipara

The involvement of transporting proteins on copper (Cu) bioaccumulation was evaluated in the killifish Poecilia vivipara chronically exposed to environmentally relevant concentrations of waterborne Cu. Fish (<24 h-old) were maintained under control condition or exposed to different waterborne Cu concentrations (5, 9 and 20 μg/L) for 28 and 345 days in saltwater. Following exposure periods, Cu accumulation and the expression of genes encoding for the high affinity Cu-transporter (ctr1) and the P-type Cu-ATPase (atp7b) were evaluated. Whole-body metal accumulation and gene expression were evaluated in fish exposed to 28 days. Similarly, in fish exposed to 345 days, liver, gills and gut were also evaluated. No fish survival was observed after exposure to 20 μg/L for 345 days. Whole-body Cu accumulation was significantly higher in fish exposed to 20 μg/L Cu for 28 days and in fish exposed to 9 μg/L for 345 days in comparison to control animals. Similarly, tissue Cu accumulation was significantly higher in fish exposed to 9 μg/L for 345 days in comparison to control animal. However, no significant accumulation was observed in fish muscle. Following exposure for 28 days, whole-body ctr1 expression was slightly induced in fish exposed to 9 μg/L. In turn, no significant change in ctr1 expression was observed following exposure to Cu for 345 days. Differently, whole-body atp7b expression was markedly up-regulated in the whole-body of fish exposed Cu for 28 days and in tissues of fish exposed to Cu for 345 days. These findings indicate the expression of atp7b is more responsive to Cu accumulation in P. vivipara than ctr1 expression and, therefore, more suitable to be used as a biomarker of exposure to this metal. Also, we argue that the expression of atp7b is sustained at elevated levels for as much time as fish are maintained in Cu contaminated water.

Antibiotic treatment affects the expression levels of copper transporters and the isotopic composition of copper in the colon of mice

Copper is a critical enzyme cofactor in the body but also a potent cellular toxin when intracellularly unbound. Thus, there is a delicate balance of intracellular copper, maintained by a series of complex interactions between the metal and specific copper transport and binding proteins. The gastrointestinal (GI) tract is the primary site of copper entry into the body and there has been considerable progress in understanding the intricacies of copper metabolism in this region. The GI tract is also host to diverse bacterial populations, and their role in copper metabolism is not well understood. In this study, we compared the isotopic fractionation of copper in the GI tract of mice with intestinal microbiota significantly depleted by antibiotic treatment to that in mice not receiving such treatment. We demonstrated variability in copper isotopic composition along the length of the gut. A significant difference, ∼1.0‰, in copper isotope abundances was measured in the proximal colon of antibiotic-treated mice. The changes in copper isotopic composition in the colon are accompanied by changes in copper transporters. Both CTR1, a copper importer, and ATP7A, a copper transporter across membranes, were significantly down-regulated in the colon of antibiotic-treated mice. This study demonstrated that isotope abundance measurements of metals can be used as an indicator of changes in metabolic processes in vivo. These measurements revealed a host-microbial interaction in the GI tract involved in the regulation of copper transport.

Liver pathology in Wilson's disease: From copper overload to cirrhosis

Wilson's disease (WD) is a genetic metabolic disease strictly associated with liver cirrhosis. In this review, the genetic bases of the disease are discussed, with emphasis on the role of ATP7B (the Wilson disease protein) dysfunction as a determinant factor of systemic copper overload. Regarding the different multiple mutations described in WD patients, the peculiarity of Sardinian population is highlighted, Sardinians carrying a rare deletion in the promoter (5' UTR) of the WD gene. The role of epigenetic changes in the clinical presentation and evolution of liver disease in WD patients is also discussed, nutrition probably representing a relevantly risk factor in WD patients. The role of transmission electron microscopy in the diagnosis of WD-related liver disease is underlined. Mitochondrial changes, increased peroxisomes fat droplets, lipolysosomes and intranuclear glycogen inclusions are reported as the most frequent ultrastructural changes in the liver of WD carriers. The role of histochemical stains for copper is analyzed, and the Timm's method is suggested as the most sensitive one for revealing hepatic copper overload in all stage of WD. The marked variability of the histological liver changes occurring in WD is underlined simple steatosis may represent the only pathological changes, frequently associated with glycogenated nuclei. Mallory-Denk bodies lipogranulomas alcoholic and non-alcoholic fatty liver disease ending with bridging fibrosis and cirrhosis. Finally, the reversal of fibrosis as a possible therapeutic objective in WD is discussed.

A High-Calorie Diet Aggravates Mitochondrial Dysfunction and Triggers Severe Liver Damage in Wilson Disease Rats

BACKGROUND & AIMS

In Wilson disease, ATP7B mutations impair copper excretion into bile. Hepatic copper accumulation may induce mild to moderate chronic liver damage or even acute liver failure. Etiologic factors for this heterogeneous phenotype remain enigmatic. Liver steatosis is a frequent finding in Wilson disease patients, suggesting that impaired copper homeostasis is linked with liver steatosis. Hepatic mitochondrial function is affected negatively both by copper overload and steatosis. Therefore, we addressed the question of whether a steatosis-promoting high-calorie diet aggravates liver damage in Wilson disease via amplified mitochondrial damage.

METHODS

Control Atp7b+/- and Wilson disease Atp7b-/- rats were fed either a high-calorie diet (HCD) or a normal diet. Copper chelation using the high-affinity peptide methanobactin was used in HCD-fed Atp7b-/- rats to test for therapeutic reversal of mitochondrial copper damage.

RESULTS

In comparison with a normal diet, HCD feeding of Atp7b-/- rats resulted in a markedly earlier onset of clinically apparent hepatic injury. Strongly increased mitochondrial copper accumulation was observed in HCD-fed Atp7b-/- rats, correlating with severe liver injury. Mitochondria presented with massive structural damage, increased H2O2 emergence, and dysfunctional adenosine triphosphate production. Hepatocellular injury presumably was augmented as a result of oxidative stress. Reduction of mitochondrial copper by methanobactin significantly reduced mitochondrial impairment and ameliorated liver damage.

CONCLUSIONS

A high-calorie diet severely aggravates hepatic mitochondrial and hepatocellular damage in Wilson disease rats, causing an earlier onset of the disease and enhanced disease progression.

In Atp7b-/- Mice Modeling Wilson's Disease Liver Repopulation With Bone Marrow-Derived Myofibroblasts or Inflammatory Cells and Not Hepatocytes Is Deleterious

In Wilson's disease, Atp7b mutations impair copper excretion with liver or brain damage. Healthy transplanted hepatocytes repopulate the liver, excrete copper, and reverse hepatic damage in animal models of Wilson's disease. In Fah^-/- mice with tyrosinemia and α-1 antitrypsin mutant mice, liver disease is resolved by expansions of healthy hepatocytes derived from transplanted healthy bone marrow stem cells. This potential of stem cells has not been defined for Wilson's disease. In diseased Atp7b^-/- mice, we reconstituted bone marrow with donor cells expressing green fluorescent protein reporter from healthy transgenic mice. Mature hepatocytes originating from donor bone marrow were identified by immunostaining for green fluorescence protein and bile canalicular marker, dipeptidylpeptidase-4. Mesenchymal and inflammatory cell markers were used for other cells from donor bone marrow cells. Gene expression, liver tests, and tissues were analyzed for outcomes in Atp7b^-/- mice. After bone marrow transplantation in Atp7b^-/- mice, donor-derived hepatocytes containing bile canaliculi appeared within weeks. Despite this maturity, donor-derived hepatocytes neither divided nor expanded. The liver of Atp7b^-/- mice was not repopulated by donor-derived hepatocytes: Atp7b mRNA remained undetectable; liver tests, copper content, and fibrosis actually worsened. Restriction of proliferation in hepatocytes accompanied oxidative DNA damage. By contrast, donor-derived mesenchymal and inflammatory cells extensively proliferated. These contributed to fibrogenesis through greater expression of inflammatory cytokines. In Wilson's disease, donor bone marrow-derived cells underwent different fates: hepatocytes failed to proliferate; inflammatory cells proliferated to worsen disease outcomes. This will help guide stem cell therapies for conditions with proinflammatory or profibrogenic microenvironments.

An MTF1 binding site disrupted by a homozygous variant in the promoter of ATP7B likely causes Wilson Disease

Approximately 2% of the human genome accounts for protein-coding genes, yet most known Mendelian disease-causing variants lie in exons or splice sites. Individuals who symptomatically present with monogenic disorders but do not possess function-altering variants in the protein-coding regions of causative genes may harbor variants in the surrounding gene regulatory domains. We present such a case: a male of Afghani descent was clinically diagnosed with Wilson Disease-a disorder of systemic copper buildup-but was found to have no function-altering coding variants in ATP7B (ENST00000242839.4), the typically causative gene. Our analysis revealed the homozygous variant chr13:g.52,586,149T>C (NC_000013.10, hg19) 676 bp into the ATP7B promoter, which disrupts a metal regulatory transcription factor 1 (MTF1) binding site and diminishes expression of ATP7B in response to copper intake, likely resulting in Wilson Disease. Our approach to identify the causative variant can be generalized to systematically discover function-altering non-coding variants underlying disease and motivates evaluation of gene regulatory variants.

MEDNIK syndrome with a frame shift causing mutation in AP1S1 gene and literature review of the clinical features

MEDNIK syndrome is an autosomal recessive rare disease as one of the most recently described copper metabolism disorder characterized by intellectual disability, ichthyosis, hearing loss, peripheral neuropathy, enteropathy and keratodermia. Here in, we reported a case presented with ichthyosis and intellectual disability with MEDNIK syndrome that confirmed by mutation analysis in a Turkish child. She was finally diagnosed with MEDNIK syndrome by clinical findings, which were confirmed by molecular genetic testing. Sequencing of AP1S1 gene showed a homozygous insertion c.364dupG (NM_001283.4), which is predicted to cause a frameshift of the reading frame (p.D122Gfs*18). To our knowledge, this is the first case of MEDNIK syndrome from Turkey. Diagnosis of MEDNIK syndrome is still challenging and we hope that this case will contribute to further understanding.

An important role for periplasmic storage in Pseudomonas aeruginosa copper homeostasis revealed by a combined experimental and computational modeling study

Biological systems require precise copper homeostasis enabling metallation of cuproproteins while preventing metal toxicity. In bacteria, sensing, transport, and storage molecules act in coordination to fulfill these roles. However, there is not yet a kinetic schema explaining the system integration. Here, we report a model emerging from experimental and computational approaches that describes the dynamics of copper distribution in Pseudomonas aeruginosa. Based on copper uptake experiments, a minimal kinetic model describes well the copper distribution in the wild-type bacteria but is unable to explain the behavior of the mutant strain lacking CopA1, a key Cu+ efflux ATPase. The model was expanded through an iterative hypothesis-driven approach, arriving to a mechanism that considers the induction of compartmental pools and the parallel function of CopA and Cus efflux systems. Model simulations support the presence of a periplasmic copper storage with a crucial role under dyshomeostasis conditions in P. aeruginosa. Importantly, the model predicts not only the interplay of periplasmic and cytoplasmic pools but also the existence of a threshold in the concentration of external copper beyond which cells lose their ability to control copper levels.

Metal accumulation and expression of genes encoding for metallothionein and copper transporters in a chronically exposed wild population of the fish Hyphessobrycon luetkenii

In the present study, metal (As, Cd, Cu, Fe, Mn, Pb and Zn) accumulation and expression of genes involved in metal metabolism (metallothioneins, ATP7A and CTR1) were evaluated in gills and muscle of the fish Hyphessobrycon luetkenii living in the João Dias creek, a site historically (~1870-1996) contaminated with a metal mixture associated with copper mining (Minas do Camaquã, southern Brazil). Fish were collected in a metal impacted site of the João Dias creek and kept in a cage at this site (PP fish) or translocated to a non-metal impacted reach of this creek (PC fish). Gill metal concentrations and metallothionein gene expression were lower in PC fish than in PP fish at any experimental time (24, 48 and 72 h). In muscle, no significant changes were observed. These findings indicate that metal accumulated in gills of wild fish chronically exposed to the metal mixture are more easily excreted than those accumulated in the muscle. In this case, expression of gene encoding for metallothionein is shown to play a key role in the regulation of metal accumulation in gills of H. luetkenii living in an area historically contaminated with a metal mixture associated with copper mining.