Structural and Functional Diversity Among the Members of CTR, the Membrane Copper Transporter Family

Molecular Regulatory Mechanism of Nano-Se Against Copper-Induced Spermatogenesis Disorder

Selenium nanoparticle (Nano-Se) is a new type of selenium supplement, which can improve the deficiency of traditional selenium supplements and maintain its physiological activity. Due to industrial pollution and irrational use in agriculture, Cu overexposure often occurs in animals and humans. In this study, Nano-Se alleviated CuSO4-induced testicular Cu accumulation, serum testosterone level decrease, testicular structural damage, and decrease in sperm quality. Meanwhile, Nano-Se reduced the ROS content in mice testis and enhanced the activities of T-AOC, GSH, SOD, and CAT compared with CuSO4 group. Furthermore, Nano-Se alleviated CuSO4-induced apoptosis by increasing the protein expression of Cleaved-Caspase-3, Cleaved-Caspase-9, Cleaved-Caspase-12, and Bax/Bcl-2 compared with CuSO4 group. At the same time, Nano-Se reversed CuSO4-induced increase of γ-H2AX protein expression in mice testis. In conclusion, this study confirmed that Nano-Se could alleviate oxidative stress, apoptosis, and DNA damage in the testis of mice with Cu excess, thereby protecting the spermatogenesis disorder induced by Cu.

Copper homeostasis and cuproptosis in tumor pathogenesis and therapeutic strategies

Copper is an indispensable micronutrient for the development and replication of all eukaryotes, and its redox properties are both harmful and beneficial to cells. An imbalance in copper homeostasis is thought to be involved in carcinogenesis. Importantly, cancer cell proliferation, angiogenesis, and metastasis cannot be separated from the effects of copper. Cuproposis is a copper-dependent form of cell death that differs from other existing modalities of regulatory cell death. The role of cuproptosis in the pathogenesis of the nervous and cardiovascular systems has been widely studied; however, its impact on malignant tumors is yet to be fully understood from a clinical perspective. Exploring signaling pathways related to cuproptosis will undoubtedly provide a new perspective for the development of anti-tumor drugs in the future. Here, we systematically review the systemic and cellular metabolic processes of copper and the regulatory mechanisms of cuproptosis in cancer. In addition, we discuss the possibility of targeting copper ion drugs to prolong the survival of cancer patients, with an emphasis on the most representative copper ionophores and chelators. We suggest that attention should be paid to the potential value of copper in the treatment of specific cancers.

AMPK phosphorylates and stabilises copper transporter 1 to synergise metformin and copper chelator for breast cancer therapy

BACKGROUND

Predominant roles of copper and its transporter, copper transporter 1 (CTR1), in tumorigenesis have been explored recently; however, the upstream regulation of CTR1 and combinational intervention of copper chelators in malignancies remain largely unclear.

METHODS

CRISPR/Cas9-based kinome screening was used to identify the CTR1 upstream kinases. Immunofluorescence assays were utilised to detect CTR1 localisation. In vitro kinase assays and mass spectrometry were performed to detect CTR1 phosphorylation. Ubiquitination assays were performed to validate CTR1 stability. Colony formation, EdU labelling, Annexin V-FITC/PI-based apoptosis assays were carried out to detect the drug effect on cell growth and apoptosis. Xenografted mouse models were employed to investigate drug effects in vivo.

RESULTS

We identify that CTR1 undergoes AMPK-mediated phosphorylation, which enhances CTR1 stabilisation and membrane translocation by affecting Nedd4l interaction, resulting in increased oncogenic roles in breast cancer. Importantly, activation of AMPK with its agonist metformin markedly enhances CTR1 levels, and leads to the combinational usage of AMPK agonists and copper chelators for breast cancer treatment.

CONCLUSIONS

Our findings not only reveal the crosstalk between energy response and copper uptake via AMPK-mediated CTR1 phosphorylation and stability but also highlight the strategy to combat breast cancer by a combination of AMPK agonists and copper chelators.

SIGNIFICANCE

The connection between energy response and copper homoeostasis is linked by AMPK phosphorylating and stabilising CTR1, which provides a promising strategy to combat breast cancer by combining AMPK agonists and copper chelators.

Properties of recombinant extracellular N-terminal domain of human high-affinity copper transporter 1 (hNdCTR1) and its interactions with Cu(II) and Ag(I) ions

High-affinity copper transporter 1 (CTR1) is a key link in the transfer of copper (Cu) from the extracellular environment to the cell. Violation in the control system of its expression, or mutations in this gene, cause a global copper imbalance. However, the mechanism of copper transfer via CTR1 remains unclear. It has been shown that transformed bacteria synthesizing the fused GB1-NdCTR become resistant to toxic silver ions. According to UV-Vis spectrophotometry and isothermal titration calorimetry, electrophoretically pure GB1-NdCTR specifically and reversibly binds copper and silver ions, and binding is associated with aggregation. Purified NdCTR1 forms SDS-resistant oligomers. The link between nontrivial properties of NdCTR1 and copper import mechanism from extracellular space, as well as potential chelating properties of NdCTR1, are discussed.

Exploration of the Potential Role of Serum Albumin in the Delivery of Cu(I) to Ctr1

Human serum albumin (HSA) is the major copper (Cu) carrier in blood. The majority of previous studies that have investigated Cu interactions with HSA have focused primarily on the Cu(II) oxidation state. Yet, cellular Cu uptake by the human copper transport protein (Ctr1), a plasma membrane-embedded protein responsible for Cu uptake into cells, requires Cu(I). Recent in vitro work has determined that reducing agents, such as the ascorbate present in blood, are sufficient to reduce the Cu(II)HSA complex to form Cu(I)HSA and that Cu(I) is bound to HSA with pM affinity. The biological accessibility of Cu(I)HSA suggests that HSA-bound Cu(I) may be an unappreciated form of Cu cargo and a key player in extracellular Cu trafficking. To better understand Cu trafficking by HSA, we sought to investigate the exchange of Cu(I) from HSA to a model peptide of the Cu-binding ectodomain of Ctr1. In this study, we used X-ray absorption near-edge spectroscopy to show that Cu(I) becomes more highly coordinated as increasing amounts of the Ctr_1-14 model peptide are added to a solution of Cu(I)HSA. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to further characterize the interaction of Cu(I)HSA with Ctr_1-14 by determining the ligands coordinating Cu(I) and their bond lengths. The EXAFS data support that some Cu(I) likely undergoes complete transfer from HSA to Ctr_1-14. This finding of HSA interacting with and releasing Cu(I) to an ectodomain model peptide of Ctr1 suggests a mechanism by which HSA delivers Cu(I) to cells under physiological conditions.

Molecular Mechanisms of Cellular Copper Homeostasis in Mammals

Copper (Cu) is a trace element necessary for the growth and development of all living organisms, and is the third most abundant trace metal in the body after iron and zinc. Copper is essential for maintaining the life processes in all living cells, because several copper-dependent enzymes play an important role in key physiological processes like cellular respiration, oxygen radical scavenging, the transport of iron and neurotransmitter synthesis. Maintaining copper homeostasis implies maintaining the constancy of copper levels in the cells and fluids throughout the body, in order to support the enzymes and other factors that underlie normal life processes. Therefore, living organisms have developed complex mechanisms for maintaining their physiological copper level, because an excess copper level can be toxic for the cells. In the cell, copper homeostasis is controlled by a network of copper-binding proteins and transporters. Furthermore, copper uptake is mediated by the membrane transporter CTR1 and CTR2 proteins. In the cytoplasm, it is bound to a unique group of metallochaperones (ATOX1, CCS COX17) and transported to different cell compartments, where it is linked to the recipient proteins. The Cu-transporting ATPases (ATP7A and ATP7B) are responsible for transferring copper into the Golgi apparatus, where the copper is added to the active sites of enzymes, and it is also directed onto the path of excess cellular copper removal to prevent the occurrence of toxicity.

The copper transporter CTR1 and cisplatin accumulation at the single-cell level by LA-ICP-TOFMS

More than a decade ago, studies on cellular cisplatin accumulation via active membrane transport established the role of the high affinity copper uptake protein 1 (CTR1) as a main uptake route besides passive diffusion. In this work, CTR1 expression, cisplatin accumulation and intracellular copper concentration was assessed for single cells revisiting the case of CTR1 in the context of acquired cisplatin resistance. The single-cell workflow designed for in vitro experiments enabled quantitative imaging at resolutions down to 1 µm by laser ablation-inductively coupled plasma-time-of-flight mass spectrometry (LA-ICP-TOFMS). Cisplatin-sensitive ovarian carcinoma cells A2780 as compared to the cisplatin-resistant subline A2780cis were investigated. Intracellular cisplatin and copper levels were absolutely quantified for thousands of individual cells, while for CTR1, relative differences of total CTR1 versus plasma membrane-bound CTR1 were determined. A markedly decreased intracellular cisplatin concentration accompanied by reduced copper concentrations was observed for single A2780cis cells, along with a distinctly reduced (total) CTR1 level as compared to the parental cell model. Interestingly, a significantly different proportion of plasma membrane-bound versus total CTR1 in untreated A2780 as compared to A2780cis cells was observed. This proportion changed in both models upon cisplatin exposure. Statistical analysis revealed a significant correlation between total and plasma membrane-bound CTR1 expression and cisplatin accumulation at the single-cell level in both A2780 and A2780cis cells. Thus, our study recapitulates the crosstalk of copper homeostasis and cisplatin uptake, and also indicates a complex interplay between subcellular CTR1 localization and cellular cisplatin accumulation as a driver for acquired resistance development.

Role of Trientine in Hypertrophic Cardiomyopathy: A Review of Mechanistic Aspects

Abnormality in myocardial copper homeostasis is believed to contribute to the development of cardiomyopathy. Trientine, a copper-chelating drug used in the management of patients with Wilson's disease, demonstrates beneficial effects in patients with hypertrophic cardiomyopathy. This review aims to present the updated development of the roles of trientine in hypertrophic cardiomyopathy. The drug has been demonstrated in animal studies to restore myocardial intracellular copper content. However, its mechanisms for improving the medical condition remain unclear. Thus, comprehending its mechanistic aspects in cardiomyopathy is crucial and could help to expedite future research.

Pseudo-Tetrahedral Copper(I) Symmetrical Formamidine Dithiocarbamate-Phosphine Complexes: Antibacterial, Antioxidant and Pharmacokinetics Studies

Three copper(I) dithiocarbamate–phosphine complexes of the general formula Cu(PPh3)2L were synthesized by metathesis reactions of the potassium salt of the dithiocarbamate ligand L and the precursor complex Cu(PPh3)2NO3 in an equimolar ratio. L represents N,N′-bis(2,6-dimethylphenyl)formamidine dithiocarbamate L1 in complex 1, N,N′-bis(2,6-disopropylphenyl) formamidine dithiocarbamate L2 in complex 2, and N,N′-dimesitylformamidine dithiocarbamate L3 in complex 3. The single-crystal X-ray structure revealed the coordination of the copper atom to two sulfur atoms of the dithiocarbamates, as well as two phosphorus atoms of the PPh3 units, which resulted in distorted tetrahedral geometries. The calculated τ4 (tau factor) values for 1, 2 and 3 were 0.82, 0.81 and 0.85, respectively, confirming the pseudo-tetrahedral geometry proposed. Complexes 1–3 showed remarkable luminescent properties in CH2Cl2 at room temperature. All three complexes showed moderate-to-low antibacterial potential against Gram-negative bacteria, while none of the complexes were active against Gram-positive bacteria. The DPPH assay studies showed that complex 2 had the lowest IC50 (4.99 × 10−3 mM),and had higher DPPH free radical scavenging ability than 1 and 3. The pharmacological estimations of 1–3 showed that all of the complexes showed minimal violation of Lipinski’s rule.

A Deeper Insight in Metal Binding to the hCtr1 N-terminus Fragment: Affinity, Speciation and Binding Mode of Binuclear Cu2+ and Mononuclear Ag+ Complex Species

Ctr1 regulates copper uptake and its intracellular distribution. The first 14 amino acid sequence of the Ctr1 ectodomain Ctr1_(1-14) encompasses the characteristic Amino Terminal Cu²⁺ and Ni²⁺ binding motif (ATCUN) as well as the bis-His binding motif (His5 and His6). We report a combined thermodynamic and spectroscopic (UV-vis, CD, EPR) study dealing with the formation of Cu²⁺ homobinuclear complexes with Ctr1_(1-14), the percentage of which is not negligible even in the presence of a small Cu²⁺ excess and clearly prevails at a M/L ratio of 1.9. Ascorbate fails to reduce Cu²⁺ when bound to the ATCUN motif, while it reduces Cu²⁺ when bound to the His5-His6 motif involved in the formation of binuclear species. The histidine diade characterizes the second binding site and is thought to be responsible for ascorbate oxidation. Binding constants and speciation of Ag⁺ complexes with Ctr1_(1-14), which are assumed to mimic Cu⁺ interaction with N-terminus of Ctr1_(1-14), were also determined. A preliminary immunoblot assay evidences that the anti-Ctr1 extracellular antibody recognizes Ctr1_(1-14) in a different way from the longer Ctr1_(1-25) that encompasses a second His and Met rich domain.

Copper(II) import and reduction are dependent on His-Met clusters in the extracellular amino terminus of human copper transporter-1

Copper(I) is an essential metal for all life forms. Though Cu(II) is the most abundant and stable state, its reduction to Cu(I) via an unclear mechanism is prerequisite for its bioutilization. In eukaryotes, the copper transporter-1 (CTR1) is the primary high-affinity copper importer, although its mechanism and role in Cu(II) reduction remain uncharacterized. Here we show that extracellular amino-terminus of human CTR1 contains two methionine-histidine clusters and neighboring aspartates that distinctly bind Cu(I) and Cu(II) preceding its import. We determined that hCTR1 localizes at the basolateral membrane of polarized MDCK-II cells and that its endocytosis to Common-Recycling-Endosomes is regulated by reduction of Cu(II) to Cu(I) and subsequent Cu(I) coordination by the methionine cluster. We demonstrate the transient binding of both Cu(II) and Cu(I) during the reduction process is facilitated by aspartates that also act as another crucial determinant of hCTR1 endocytosis. Mutating the first Methionine cluster (⁷Met-Gly-Met⁹) and Asp¹³ abrogated copper uptake and endocytosis upon copper treatment. This phenotype could be reverted by treating the cells with reduced and nonreoxidizable Cu(I). We show that histidine clusters, on other hand, bind Cu(II) and are crucial for hCTR1 functioning at limiting copper. Finally, we show that two N-terminal His-Met-Asp clusters exhibit functional complementarity, as the second cluster is sufficient to preserve copper-induced CTR1 endocytosis upon complete deletion of the first cluster. We propose a novel and detailed mechanism by which the two His-Met-Asp residues of hCTR1 amino-terminus not only bind copper, but also maintain its reduced state, crucial for intracellular uptake.

Production and Preparation of Isotopically Labeled Human Membrane Proteins in Pichia pastoris for Fast-MAS-NMR Analyses

Membrane proteins (MPs) comprise about one-third of the human proteome, playing critical roles in many physiological processes and associated disorders. Consistently, they represent one of the largest classes of targets for the pharmaceutical industry. Their study at the molecular level is however particularly challenging, resulting in a severe lack of structural and dynamic information that is hindering their detailed functional characterization and the identification of novel potent drug candidates.Magic Angle Spinning (MAS) NMR is a reliable and efficient method for the determination of protein structures and dynamics and for the identification of ligand binding sites and equilibria. MAS-NMR is particularly well suited for MPs since they can be directly analysed in a native-like lipid bilayer environment but used to require aggravating large amounts of isotope enriched material. The frequent toxicity of human MP overexpression in bacterial cultures poses an additional hurdle, resulting in the need for alternative (and often more costly) expression systems. The recent development of very fast (up to 150 kHz) MAS probes has revolutionized the field of biomolecular solid-state NMR enabling higher spectral resolution with significant reduction of the required sample, rendering eukaryotic expression systems cost-effective.Here is presented a set of accessible procedures validated for the production and preparation of eukaryotic MPs for Fast-MAS ¹H-detected NMR analysis. The methodology is illustrated with the human copper uptake protein hCTR1 recombinantly produced and ¹³C-¹⁵N uniformly labeled with the versatile and affordable Pichia pastoris system. Subsequent purification procedures allow the recovery of mg amounts that are then reconstituted into liposome formulations compatible with solid-state NMR handling and analysis.

A novel leishmanial copper P-type ATPase plays a vital role in parasite infection and intracellular survival

Copper (Cu) is essential for all life forms; however, in excess, it becomes toxic. Toxic properties of Cu are known to be utilized by host species against various pathogenic invasions. Leishmania, in both free-living and intracellular forms, exhibits appreciable tolerance toward Cu stress. While determining the mechanism of Cu-stress evasion employed by Leishmania, we identified and characterized a hitherto unknown Cu-ATPase in Leishmania major and established its role in parasite survival in host macrophages. This novel L. major Cu-ATPase, LmATP7, exhibits homology with its orthologs at multiple motifs. In promastigotes, LmATP7 primarily localized at the plasma membrane. We also show that LmATP7 exhibits Cu-dependent expression patterns and complements Cu transport in a Cu-ATPase-deficient yeast strain. Promastigotes overexpressing LmATP7 exhibited higher survival upon Cu stress, indicating efficacious Cu export compared with Wt and heterozygous LmATP7 knockout parasites. We further explored macrophage–Leishmania interactions with respect to Cu stress. We found that Leishmania infection triggers upregulation of major mammalian Cu exporter, ATP7A, in macrophages, and trafficking of ATP7A from the trans-Golgi network to endolysosomes in macrophages harboring amastigotes. Simultaneously, in Leishmania, we observed a multifold increase in LmATP7 transcripts as the promastigote becomes established in macrophages and morphs to the amastigote form. Finally, overexpressing LmATP7 in parasites increases amastigote survivability within macrophages, whereas knocking it down reduces survivability drastically. Mice injected in their footpads with an LmATP7-overexpressing strain showed significantly larger lesions and higher amastigote loads as compared with controls and knockouts. These data establish the role of LmATP7 in parasite infectivity and intramacrophagic survivability.

Intermediate Cu(II)-Thiolate Species in the Reduction of Cu(II)GHK by Glutathione: A Handy Chelate for Biological Cu(II) Reduction

Gly-His-Lys (GHK) is a tripeptide present in the human bloodstream that exhibits a number of biological functions. Its activity is attributed to the copper-complexed form, Cu(II)GHK. Little is known, however, about the molecular aspects of the mechanism of its action. Here, we examined the reaction of Cu(II)GHK with reduced glutathione (GSH), which is the strongest reductant naturally occurring in human plasma. Spectroscopic techniques (UV–vis, CD, EPR, and NMR) and cyclic voltammetry helped unravel the reaction mechanism. The impact of temperature, GSH concentration, oxygen access, and the presence of ternary ligands on the reaction were explored. The transient GSH-Cu(II)GHK complex was found to be an important reaction intermediate. The kinetic and redox properties of this complex, including tuning of the reduction rate by ternary ligands, suggest that it may provide a missing link in copper trafficking as a precursor of Cu(I) ions, for example, for their acquisition by the CTR1 cellular copper transporter.

Gly-His-Lys (GHK) is a human bioactive tripeptide thought to be activated by Cu(II) binding, but little is known about the molecular aspects of its action. UV−vis, circular dichroism (CD), EPR, and NMR spectroscopies, and cyclic voltammetry were used to examine the reduction of Cu(II)GHK with glutathione (GSH), the most abundant biological thiol. A semistable GSH-Cu(II)GHK reaction intermediate was discovered, with properties suitable for delivering Cu(I) to biological transport proteins.