Activity of metal-responsive transcription factor 1 by toxic heavy metals and H2O2 in vitro is modulated by metallothionein

Engineering a synthetic gene circuit for high-performance inducible expression in mammalian systems

Inducible gene expression systems can be used to control the expression of a gene of interest by means of a small-molecule. One of the most common designs involves engineering a small-molecule responsive transcription factor (TF) and its cognate promoter, which often results in a compromise between minimal uninduced background expression (leakiness) and maximal induced expression. Here, we focus on an alternative strategy using quantitative synthetic biology to mitigate leakiness while maintaining high expression, without modifying neither the TF nor the promoter. Through mathematical modelling and experimental validations, we design the CASwitch, a mammalian synthetic gene circuit based on combining two well-known network motifs: the Coherent Feed-Forward Loop (CFFL) and the Mutual Inhibition (MI). The CASwitch combines the CRISPR-Cas endoribonuclease CasRx with the state-of-the-art Tet-On3G inducible gene system to achieve high performances. To demonstrate the potentialities of the CASwitch, we apply it to three different scenarios: enhancing a whole-cell biosensor, controlling expression of a toxic gene and inducible production of Adeno-Associated Virus (AAV) vectors.

Deep learning enables the discovery of a novel cuproptosis-inducing molecule for the inhibition of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common and deadly cancers in the world. The therapeutic outlook for HCC patients has significantly improved with the advent and development of systematic and targeted therapies such as sorafenib and lenvatinib; however, the rise of drug resistance and the high mortality rate necessitate the continuous discovery of effective targeting agents. To discover novel anti-HCC compounds, we first constructed a deep learning-based chemical representation model to screen more than 6 million compounds in the ZINC15 drug-like library. We successfully identified LGOd1 as a novel anticancer agent with a characteristic levoglucosenone (LGO) scaffold. The mechanistic studies revealed that LGOd1 treatment leads to HCC cell death by interfering with cellular copper homeostasis, which is similar to a recently reported copper-dependent cell death named cuproptosis. While the prototypical cuproptosis is brought on by copper ionophore-induced copper overload, mechanistic studies indicated that LGOd1 does not act as a copper ionophore, but most likely by interacting with the copper chaperone protein CCS, thus LGOd1 represents a potentially new class of compounds with unique cuproptosis-inducing property. In summary, our findings highlight the critical role of bioavailable copper in the regulation of cell death and represent a novel route of cuproptosis induction.

Structural motifs in the early metallation steps of Zn(II) and Cd(II) binding to apo-metallothionein 1a

Many proteins require a metal cofactor to function and these metals are often involved in the protein folding process. The protein metallothionein (MT) has a dynamic structure capable of binding to a variety of metals with different stoichiometries. The most well-understood structure is the seven-metal, two domain structure formed upon metallation using Zn(II) or Cd(II). However, the partially metallated states and the pathways to form these clusters are less well-understood, although it is known that the pathways are pH dependent. Using stopped flow methods, it is shown that the metallation rates of the less cooperative Zn(II) binding pathway is much more impacted by low pH conditions that that of the more cooperative Cd(II) binding pathway. Electrospray ionization mass spectrometry (ESI-MS) methods reveal specific mixtures of bridging and terminally bound MxSy structures form in the first few metallation steps. Using a combination of methods, the data show that the result of unfolding this intrinsically disordered apo-MT structure using guanidinium chloride is that the formation of preliminary bridging structures that form in the first few metallation steps is impeded. The data show that more terminally bound structures form. Our conclusion is that the compact conformation of the native apo-MT at physiological pH allows for rapid formation of complex metal-thiolate structures with high affinity that provides protection from oxidation, a function that is suppressed upon unfolding. Overall, these results highlight both the importance of the apo-MT structure in the metallation pathway, but also the differences in Zn(II) and Cd(II) binding under different conditions.

Pb exposure causes non-linear accumulation of Pb in D. melanogaster controlled by metallothionein B and exerts ecological effects

Pb pollution can harm human health and the ecosystem. Therefore, it is worthwhile to study the metabolic processes of heavy metals in individual bodies and their influence on ecological systems. In this work, we analyzed the genetic responses and physiological changes of D. melanogaster which took diets exposed to different doses of Pb using transcriptomic analysis, ICP-MS, and various other physiological methods. We found that the Pb accumulated in D. melanogaster in a nonlinear pattern with the increase of Pb content in food. Metallothioneins (Mtns), especially the MtnB directly affects the accumulation and excretion of metal Pb in D. melanogaster, and causes the nonlinear accumulation. Metal regulatory transcription factor-1 (MTF-1) is involved in the regulation of Pb-induced high expressions of Mtns. Furthermore, an interaction between the metal metabolism pathway and xenobiotic response pathway leads to the cross-tolerances of Pb-exposed D. melanogaster to insecticides and other toxins. The oxidative stress induced by Pb toxicity may be the bridge between them. Our findings provide a physiological and molecular genetic basis for further study of the accumulation and metabolism of Pb in D. melanogaster.

α-lipoic acid ameliorates consequences of copper overload by up-regulating selenoproteins and decreasing redox misbalance

α-lipoic acid (LA) is an essential cofactor for mitochondrial dehydrogenases and is required for cell growth, metabolic fuel production, and antioxidant defense. In vitro, LA binds copper (Cu) with high affinity and as an endogenous membrane permeable metabolite could be advantageous in mitigating the consequences of Cu overload in human diseases. We tested this hypothesis in 3T3-L1 preadipocytes with inactivated Cu transporter Atp7a; these cells accumulate Cu and show morphologic changes and mitochondria impairment. Treatment with LA corrected the morphology of Atp7a-/- cells similar to the Cu chelator bathocuproinedisulfonate (BCS) and improved mitochondria function; however, the mechanisms of LA and BCS action were different. Unlike BCS, LA did not decrease intracellular Cu but instead increased selenium levels that were low in Atp7a-/- cells. Proteome analysis confirmed distinct cell responses to these compounds and identified upregulation of selenoproteins as the major effect of LA on preadipocytes. Upregulation of selenoproteins was associated with an improved GSH:GSSG ratio in cellular compartments, which was lowered by elevated Cu, and reversal of protein oxidation. Thus, LA diminishes toxic effects of elevated Cu by improving cellular redox environment. We also show that selenium levels are decreased in tissues of a Wilson disease animal model, especially in the liver, making LA an attractive candidate for supplemental treatment of this disease.

ZnO-NPs alleviate aflatoxin B1-induced hepatoxicity in ducklings by promoting hepatic metallothionein expression

Aflatoxin B₁ (AFB₁) is a mycotoxin widely present in animal feed and human food, posing a serious threat to animal and human health. This study was aim to illustrate the mechanism of the protective role of MT against AFB₁-induced hepatotoxicity, as well as to explore the feasibility of enhancing the tolerance of poultry to AFB₁ by upregulating the expression of hepatic MT. After being exposed to AFB₁ (50 ng/kg) primary duckling hepatocytes, the cell viability, the antioxidant index (SOD and GPx) and the mRNA levels of MT downstream genes (PTGR, p53, TrxR, AR and Bcl-2) significantly (p < 0.05) decreased, while the intracellular formation of (AFBO)-DNA adduct content, apoptosis, and MDA content significantly (p < 0.05) increased. Interestingly, overexpression of MT in primary duckling hepatocytes markedly (p < 0.05) reversed the detrimental impact of AFB₁ and increased the expression of MT downstream genes. HepG2 cells were applied to study the mechanism how MT works to relieve the hepatic toxicity of AFB₁. The ZnO-NPs (20 μg/mL) + AFB₁ (20 μg/mL) group significantly (p < 0.05) increased the cell viability, the expression of NRF2, NQO1 and SOD, and expression of MT and MTF-1, as well as significantly (p < 0.05) decreased LDH, ROS and apoptotic rate, comparing with the AFB₁ group. While joint treatment with AFB₁ and ZnO-NPs, the hepatic toxicity exerted by AFB₁ alone was reversed, along with the translocation of MTF-1 from the cytoplasm to the nucleus and upregulated its expression. Duckling trails were further carried out. A total number of 96 1-day-old healthy Cherry Valley commercial ducklings were randomly allocated according to a 2 by 2 factorial arrangement of treatments with the main factors including oral administration of AFB₁ (0 vs. 40 μg/kg) and dietary supplementation of ZnO-NPs (0 vs. 60 mg/kg) for 7 days. It showed that AFB₁ exposure caused body weight loss (p < 0.05), impaired liver structure and failure in hepatic function (activity of ALT, AST and concentration of TP and GLU) (p < 0.05), and decreases in antioxidant capacity(activity of SOD, CAT and concentration of GSH) (p < 0.05), along with the decrease in hepatic concentration of Zn, increase in expression of apoptosis-related genes and protein CAS3 and mRNA Bcl-2 expression (p < 0.05), and suppressed mRNA levels of antioxidant-related genes MT, SOD1, NRF2, and NQO1 (p < 0.05). In accordance with the cell test, dietary supplementation with ZnO-NPs mitigated the toxicity exerted by AFB₁. In conclusion, ZnO-NPs has the protective effects against AFB₁-induced hepatocyte injury by activating the expression of MTF-1 and the ectopic induction of MT expression, providing detailed information on the detoxification ability of MT on AFB₁.

Cannabis-derived products antagonize platinum drugs by altered cellular transport

Cannabinoids, a class of compounds derived from Cannabis sativa L., have recently become more widely accessible for public consumption in the form of diverse cannabis products, in parallel with weakening the measures that so far restricted their availability. The US Food and Drug Administration has approved several cannabis-derived drugs for management of various diseases as well as chemotherapy-induced nausea and vomiting. Besides the attenuation of adverse effects of chemotherapy, numerous reports about cannabinoid-mediated anticancer effects further motivate cancer patients to support their therapy with such products. Here we present a set of preclinical data with human cell culture models, suggesting that cannabidiol and cannabis extracts may effectively counteract the anticancer effects of the clinically widely used standard-of-care platinum-based drugs. We show that even low concentrations of cannabinoids reduced the toxicity of cisplatin, oxaliplatin, and carboplatin, an effect which was accompanied by decreased platinum adduct formation and a set of commonly used molecular markers. Mechanistically, our results excluded the possibility that the observed enhanced survival of cancer cells was mediated transcriptionally. Instead, trace metal analyses strongly indicate an inhibitory impact of cannabinoids on intracellular platinum accumulation, thereby implicating changes in cellular transport and/or retention of these drugs as the likely cause of the observed biological effects. Our study raises the possibility that the desirable effect of counteracting adverse effects of chemotherapy might, at least for some cannabinoids, reflect impaired cellular availability, and consequently attenuation of the anticancer effects of platinum drugs. DATA AVAILABILITY: All data supporting the conclusions are available in the article and supplementary files. Raw data are available upon request from the corresponding author.

Zinc binding of a Cys2His2-type zinc finger protein is enhanced by the interaction with DNA

Zinc finger proteins specifically recognize DNA sequences and, therefore, play a crucial role in living organisms. In this study the Zn(II)-, and DNA-binding of 1MEY#, an artificial zinc finger protein consisting of three finger units was characterized by multiple methods. Fluorimetric, circular dichroism and isothermal calorimetric titrations were applied to determine the accurate stability constant of a zinc finger protein. Assuming that all three zinc finger subunits behave identically, the obtained thermodynamic data for the Zn(II) binding were ΔH_{binding site} =  - (23.5 - 28.0) kcal/mol (depending on the applied protonation state of the cysteines) and logβ'_pH 7.4 = 12.2 ± 0.1, being similar to those of the CP1 consensus zinc finger peptide. The specific DNA binding of the protein can be characterized by logβ'_{pH 7.4} = 8.20 ± 0.08, which is comparable to the affinity of the natural zinc finger proteins (Sp1, WT1, TFIIIA) toward DNA. This value is ~ 1.9 logβ' unit higher than those determined for semi- or nonspecific DNA binding. Competitive circular dichroism and electrophoretic mobility shift measurements revealed that the conditional stability constant characteristic for Zn(II) binding of 1MEY# protein increased by 3.4 orders of magnitude in the presence of its target DNA sequence.

Structural Role of Cadmium and Zinc in Metallothionein Oxidation by Hydrogen Peroxide: The Resilience of Metal-Thiolate Clusters

Oxidative stress is a state involving an imbalance of reactive oxygen species in a cell and is linked to a variety of diseases. The metal-binding protein metallothionein (MT) may play a role in protection due to its high cysteine content. Many studies have shown that oxidative stress will cause MT to both form disulfide bonds and release bound metals. However, studies on the more biologically relevant partially metalated MTs have been largely neglected. Additionally, most studies to date have used spectroscopic methods that cannot detect specific intermediate species. In this paper, we describe the oxidation and the subsequent metal displacement pathway of fully and partially metalated MTs with hydrogen peroxide. The rates of the reactions were monitored using electrospray ionization mass spectrometry (ESI-MS) techniques, which resolved and characterized the individual intermediate M_x(SH)_yMT species. The rate constants were calculated for each species formation. Through ESI-MS and circular dichroism spectroscopy, it was found that the three metals in the β-domain were the first to be released from the fully metalated MTs. The Cd(II) in the partially metalated Cd(II)-bound MTs rearranged to form a protective Cd₄MT cluster structure upon exposure to oxidation. The partially metalated Zn(II)-bound MTs oxidized at a faster rate as the Zn(II) did not rearrange in response to oxidation. Additionally, density functional theory calculations showed that the terminally bound cysteines were more negative and thus more susceptible to oxidation than the bridging cysteines. The results of this study highlight the importance of metal-thiolate structures and metal identity in MT's response to oxidation.

Interactions of an Artificial Zinc Finger Protein with Cd(II) and Hg(II): Competition and Metal and DNA Binding

Cys2His2 zinc finger proteins are important for living organisms, as they—among other functions—specifically recognise DNA when Zn(II) is coordinated to the proteins, stabilising their ββα secondary structure. Therefore, competition with other metal ions may alter their original function. Toxic metal ions such as Cd(II) or Hg(II) might be especially dangerous because of their similar chemical properties to Zn(II). Most competition studies carried out so far have involved small zinc finger peptides. Therefore, we have investigated the interactions of toxic metal ions with a zinc finger proteins consisting of three finger units and the consequences on the DNA binding properties of the protein. Binding of one Cd(II) per finger subunit of the protein was shown by circular dichroism spectroscopy, fluorimetry and electrospray ionisation mass spectrometry. Cd(II) stabilised a similar secondary structure to that of the Zn(II)-bound protein but with a slightly lower affinity. In contrast, Hg(II) could displace Zn(II) quantitatively (logβ′ ≥ 16.7), demolishing the secondary structure, and further Hg(II) binding was also observed. Based on electrophoretic gel mobility shift assays, the Cd(II)-bound zinc finger protein could recognise the specific DNA target sequence similarly to the Zn(II)-loaded form but with a ~0.6 log units lower stability constant, while Hg(II) could destroy DNA binding completely.

Comparative cisplatin reactivity towards human Zn7-metallothionein-2 and MTF-1 zinc fingers: potential implications in anticancer drug resistance

Cis-diamminedichloroplatinum(II) (cisplatin) is a widely used metal-based chemotherapeutic drug for the treatment of cancers. However, intrinsic and acquired drug resistance limit the efficacy of cisplatin-based treatments. Increased production of intracellular thiol-rich molecules, in particular metallothioneins (MTs), which form stable coordination complexes with the electrophilic cisplatin, results in cisplatin sequestration leading to pre-target resistance. MT-1/-2 are overexpressed in cancer cells, and their expression is controlled by the metal response element (MRE)-binding transcription factor-1 (MTF-1), featuring six Cys2His2-type zinc fingers which, upon zinc metalation, recognize specific MRE sequences in the promoter region of MT genes triggering their expression. Cisplatin can efficiently react with protein metal binding sites featuring nucleophilic cysteine and/or histidine residues, including MTs and zinc fingers proteins, but the preferential reactivity towards specific targets with competing binding sites cannot be easily predicted. In this work, by in vitro competition reactions, we investigated the thermodynamic and kinetic preferential reactivity of cisplatin towards human Zn7MT-2, each of the six MTF-1 zinc fingers, and the entire human MTF-1 zinc finger domain. By spectroscopic, spectrometric, and electrophoretic mobility shift assays (EMSA), we demonstrated that cisplatin preferentially reacts with Zn7MT-2 to form Cys4-Pt(II) complexes, resulting in zinc release from MT-2. Zinc transfer from MT-2 to the MTF-1 triggers MTF-1 metalation, activation, and binding to target MRE sequences, as demonstrated by EMSA with DNA oligonucleotides. The cisplatin-dependent MT-mediated MTF-1 activation leading to apo-MT overexpression potentially establishes one of the molecular mechanisms underlying the development and potentiation of MT-mediated pre-target resistance.

Is Genetic Engineering a Route to Enhance Microalgae-Mediated Bioremediation of Heavy Metal-Containing Effluents?

Contamination of the biosphere by heavy metals has been rising, due to accelerated anthropogenic activities, and is nowadays, a matter of serious global concern. Removal of such inorganic pollutants from aquatic environments via biological processes has earned great popularity, for its cost-effectiveness and high efficiency, compared to conventional physicochemical methods. Among candidate organisms, microalgae offer several competitive advantages; phycoremediation has even been claimed as the next generation of wastewater treatment technologies. Furthermore, integration of microalgae-mediated wastewater treatment and bioenergy production adds favorably to the economic feasibility of the former process—with energy security coming along with environmental sustainability. However, poor biomass productivity under abiotic stress conditions has hindered the large-scale deployment of microalgae. Recent advances encompassing molecular tools for genome editing, together with the advent of multiomics technologies and computational approaches, have permitted the design of tailor-made microalgal cell factories, which encompass multiple beneficial traits, while circumventing those associated with the bioaccumulation of unfavorable chemicals. Previous studies unfolded several routes through which genetic engineering-mediated improvements appear feasible (encompassing sequestration/uptake capacity and specificity for heavy metals); they can be categorized as metal transportation, chelation, or biotransformation, with regulation of metal- and oxidative stress response, as well as cell surface engineering playing a crucial role therein. This review covers the state-of-the-art metal stress mitigation mechanisms prevalent in microalgae, and discusses putative and tested metabolic engineering approaches, aimed at further improvement of those biological processes. Finally, current research gaps and future prospects arising from use of transgenic microalgae for heavy metal phycoremediation are reviewed.

Genetics of metallothioneins in Drosophilamelanogaster

Metallothioneins (MTs) are ubiquitous metal-chelating proteins involved in cellular metal homeostasis. MTs were found to be related with almost all the biological processes and their malfunctioning is responsible for a lot of important human diseases. Invertebrate MTs were also used broadly as biomarkers of metal contamination due to their inducible expression by metal exposure. MT system plays a significant role in maintaining human health and ecological stability. Drosophila melanogaster, the vinegar fly, is a perfect model for studying insect MT systems. Six MTs were identified in D. melanogaster, and were designated MtnA to F. All the MTs are considered as Cu-thioneins except for MtnF, which is putatively a Zn-thionein. Expression of all the MTs are regulated by MTF-1/MRE system, thus being able to be induced by heavy metal exposure. The expression pattern and function of separated MTs are partially overlapped and partially distinct. In this work, we made a summary of all the studies on D. melanogaster MTs. From this review, we noted that, compared with studies on mammalian MTs, the understanding of the MT system of D. melanogaster and other invertebrates, especially the regulation mechanism for MT expression and protein-protein interaction with them, is still in a low level.

The Hippo pathway kinases LATS1 and LATS2 attenuate cellular responses to heavy metals through phosphorylating MTF1

Heavy metals are both integral parts of cells and environmental toxicants, and their deregulation is associated with severe cellular dysfunction and various diseases. Here we show that the Hippo pathway plays a critical role in regulating heavy metal homeostasis. Hippo signalling deficiency promotes the transcription of heavy metal response genes and protects cells from heavy metal-induced toxicity, a process independent of its classic downstream effectors YAP and TAZ. Mechanistically, the Hippo pathway kinase LATS phosphorylates and inhibits MTF1, an essential transcription factor in the heavy metal response, resulting in the loss of heavy metal response gene transcription and cellular protection. Moreover, LATS activity is inhibited following heavy metal treatment, where accumulated zinc directly binds and inhibits LATS. Together, our study reveals an interplay between the Hippo pathway and heavy metals, providing insights into this growth-related pathway in tissue homeostasis and stress response.

The Bioinorganic Chemistry of Mammalian Metallothioneins

The functions, purposes, and roles of metallothioneins have been the subject of speculations since the discovery of the protein over 60 years ago. This article guides through the history of investigations and resolves multiple contentions by providing new interpretations of the structure-stability-function relationship. It challenges the dogma that the biologically relevant structure of the mammalian proteins is only the one determined by X-ray diffraction and NMR spectroscopy. The terms metallothionein and thionein are ambiguous and insufficient to understand biological function. The proteins need to be seen in their biological context, which limits and defines the chemistry possible. They exist in multiple forms with different degrees of metalation and types of metal ions. The homoleptic thiolate coordination of mammalian metallothioneins is important for their molecular mechanism. It endows the proteins with redox activity and a specific pH dependence of their metal affinities. The proteins, therefore, also exist in different redox states of the sulfur donor ligands. Their coordination dynamics allows a vast conformational landscape for interactions with other proteins and ligands. Many fundamental signal transduction pathways regulate the expression of the dozen of human metallothionein genes. Recent advances in understanding the control of cellular zinc and copper homeostasis are the foundation for suggesting that mammalian metallothioneins provide a highly dynamic, regulated, and uniquely biological metal buffer to control the availability, fluctuations, and signaling transients of the most competitive Zn(II) and Cu(I) ions in cellular space and time.

Effect of the Forth and Fifth Zinc Finger Deletions of MTF-1 on the Expression of Metal Ion Metabolism Related Gene

Metal response element binding transcription factor 1 (MTF-1) is one of the important regulatory proteins involved in the mediation of intracellular metal ion balance, which is zinc dependent. The changes of zinc finger effected its function. MTF-1 mutant 293T cell line was obtained by transferring the vector of MTF-1 4th or 5th mutant zinc finger into 293T cell line that knocked out MTF-1 gene. The results showed that the mutant of 4th zinc finger in MTF-1 protein showed a significant difference on target gene expression compared with 5th zinc finger. Further RNA-seq assay showed that 4th and 5th zinc finger of MTF-1 have a different effect on molecular biological functions, cellular components, and biological process. The mutant of 4th and 5th zinc finger in MTF-1 protein changed different signaling pathways and metal ion metabolism related to genes. The present study evaluated that 4th or 5th mutant zinc finger in MTF-1 gene were associated with the function of MTF-1 protein.

Cadmium hijacks the high zinc response by binding and activating the HIZR-1 nuclear receptor

Cadmium is an environmental pollutant and significant health hazard that is similar to the physiological metal zinc. In Caenorhabditis elegans, high zinc homeostasis is regulated by the high zinc activated nuclear receptor (HIZR-1) transcription factor. To define relationships between the responses to high zinc and cadmium, we analyzed transcription. Many genes were activated by both high zinc and cadmium, and hizr-1 was necessary for activation of a subset of these genes; in addition, many genes activated by cadmium did not require hizr-1, indicating there are at least two mechanisms of cadmium-regulated transcription. Cadmium directly bound HIZR-1, promoted nuclear accumulation of HIZR-1 in intestinal cells, and activated HIZR-1-mediated transcription via the high zinc activation (HZA) enhancer. Thus, cadmium binding promotes HIZR-1 activity, indicating that cadmium acts as a zinc mimetic to hijack the high zinc response. To elucidate the relationships between high zinc and cadmium detoxification, we analyzed genes that function in three pathways: the pcs-1/phytochelatin pathway strongly promoted cadmium resistance but not high zinc resistance, the hizr-1/HZA pathway strongly promoted high zinc resistance but not cadmium resistance, and the mek-1/sek-1/kinase signaling pathway promoted resistance to high zinc and cadmium. These studies identify resistance pathways that are specific for high zinc and cadmium, as well as a shared pathway.

Cadmium induced cerebral toxicity via modulating MTF1-MTs regulatory axis

Metal-responsive transcription factor 1 (MTF1) participates in redox homeostasis and heavy metals detoxification via regulating the expression of metal responsive genes. However, the exact role of MTF1 in Cd-induced cerebral toxicity remains unclear. Herein, we explored the mechanism of Cd-elicited cerebral toxicity through modulating MTF1/MTs pathway in chicken cerebrum exposed to different concentrations of Cd (35 mg, 70 mg, and 140 mg/kg CdCl₂) via diet. Notably, cerebral tissues showed varying degrees of microstructural changes under Cd exposure. Cd exposure significantly up-regulated the expression of metal transporters (DMT1, ZIP8, and ZIP10) with concomitant elevated Cd level, as determined by ICP-MS. Cd significantly altered other cerebral biometals concentrations (particularly, Zn, Fe, Se, Cr, Mo, and Pb) and redox balance, resulting in increased cerebral oxidative stress. More importantly, Cd exposure suppressed MTF1 mRNA and nuclear protein levels and its target metal-responsive genes, notably metallothioneins (MT1 and MT2), and Fe and Cu transporter genes (FPN1, ATOX1, and XIAP). Moreover, Cd disrupted the regulation of expression of selenoproteome (particularly, GPxs and SelW), and cerebral Se level. Overall, our data revealed that molecular mechanisms associated with Cd-induced cerebral damage might include over-expression of DMT1, ZIP8 and ZIP10, and suppression of MTF1 and its main target metal-responsive genes as well as several selenoproteins.

The transfer of trace metals in the soil-plant-arthropod system

Essential and non-essential trace metals are capable of causing toxicity to organisms above a threshold concentration. Extensive research has assessed the behaviour of trace metals in biological and ecological systems, but has typically focused on single organisms within a trophic level and not on multi-trophic transfer through terrestrial food chains. This reinforces the notion of metal toxicity as a closed system, failing to consider one trophic level as a pollution source to another; therefore, obscuring the full extent of ecosystem effects. Given the relatively few studies on trophic transfer of metals, this review has taken a compartment-based approach, where transfer of metals through trophic pathways is considered as a series of linked compartments (soil-plant-arthropod herbivore-arthropod predator). In particular, we consider the mechanisms by which trace metals are taken up by organisms, the forms and transformations that can occur within the organism and the consequences for trace metal availability to the next trophic level. The review focuses on four of the most prevalent metal cations in soil which are labile in terrestrial food chains: Cd, Cu, Zn and Ni. Current knowledge of the processes and mechanisms by which these metals are transformed and moved within and between trophic levels in the soil-plant-arthropod system are evaluated. We demonstrate that the key factors controlling the transfer of trace metals through the soil-plant-arthropod system are the form and location in which the metal occurs in the lower trophic level and the physiological mechanisms of each organism in regulating uptake, transformation, detoxification and transfer. The magnitude of transfer varies considerably depending on the trace metal concerned, as does its toxicity, and we conclude that biomagnification is not a general property of plant-arthropod and arthropod-arthropod systems. To deliver a more holistic assessment of ecosystem toxicity, integrated studies across ecosystem compartments are needed to identify critical pathways that can result in secondary toxicity across terrestrial food-chains.

Cadmium toxicity mediated by the inhibition of SLC2A4 expression in human proximal Tubule cells

Cadmium (Cd) is an environmental contaminant that causes renal toxicity. We have previously demonstrated that Cd induces renal toxicity by altering transcriptional activities. In this study, we show that Cd markedly inhibited the activity of transcription factor MEF2A in HK-2 human proximal tubule cells, which generated significant cytotoxicity in the cells. This reduction in the nuclear levels of MEF2A protein may be involved in the Cd-induced inhibition of MEF2A activity. We also demonstrate that one of the glucose transporters, GLUT4, was downregulated not only by Cd treatment but also by MEF2A knockdown. Knockdown of SLC2A4, encoding GLUT4, eliminated both cell viability and Cd toxicity. Cd treatment or SLC2A4 deficiency reduced the cellular concentration of glucose. Therefore, the suppression of SLC2A4 expression, which mediates the reduction in cellular glucose, is involved in Cd toxicity. The Cd toxicity induced by the reduction in GLUT4 may be associated with a reduction of cellular ATP levels in HK-2 cells. The levels of Slc2a4 mRNA in the kidney of mice exposed to Cd for 6 or 12 months were significantly lower than those in the control group. These results demonstrate that Cd exerts its cytotoxicity through the suppression in SLC2A4 expression and the subsequent inhibition of MEF2A transcriptional activity. Cd-induced suppression of SLC2A4 expression also reduces cellular ATP levels, partly by reducing glucose levels. This study suggests that the glucose transporter plays an important role in the renal toxicity of Cd, and provides a crucial breakthrough in our understanding of the mechanism of Cd toxicity.

Nickel oxide nanoparticles induce genotoxicity and cellular alterations in the ground beetle Blaps polycresta (Coleoptera: Tenebrionidae)

Nickel nanoparticles (Ni-NPs) have advantageous applications in the industry; however, little is known of their adverse effects on biological tissues. In the present study, the ground beetle Blaps polycresta was employed as a sensitive indicator for nickel oxide nanoparticles (NiO-NPs) toxicity. Adult male beetles were injected with six dose levels of NiO-NPs (0.01, 0.02, 0.03, 0.04, 0.05, and 0.06 mg/g body weight). Mortality was reported daily over 30 days under laboratory conditions to establish an LD₅₀. Nickel was detected in the testicular tissues of the beetles using X-ray analysis and transmission electronic microscopy. Beetles treated with the sublethal dose of 0.02 mg/g were selected to observe molecular, cellular, and subcellular changes. Gene transcripts of HSP70, HSP90, and MT1 were found to be increased >2.5-, 1.5-, and 2-fold, respectively, in the treated group compared with the controls. Decreased gene expression of AcPC01, AcPC02, and AcPC04 (≤1.5-, ≤2-, and < 2.5-fold, respectively, vs. controls) also were reported in the treated group. Under light microscopy, various structural changes were observed in the testicular tissues of the treated beetles. Ultrastructure observations using scanning and transmission electron microscopy showed severe damage to the subcellular organelles as well as deformities of the heads and flagella of the spermatozoa. Therefore, the present study postulated the impact of NiO-NPs in an ecological model.

The Enigmatic Metallothioneins: A Case of Upward-Looking Research

In the mid-1950s, Bert Lester Vallee and his colleague Marvin Margoshes discovered a molecule referred to today as metallothionein (MT). Meanwhile, MTs have been shown to be common in many biological organisms. Despite their prevalence, however, it remains unclear to date what exactly MTs do and how they contribute to the biological function of an organism or organ. We investigate why biochemical research has not yet been able to pinpoint the function(s) of MTs. We shall systematically examine both the discovery of and recent research on Dr. Vallee's beloved family of MT proteins utilizing tools from philosophy of science. Our analysis highlights that Vallee's initial work exhibited features prototypical of a developing research tradition: it was upward-looking, exploratory, and utilized mere interactions. Since the 1960s, MT research has increasingly become intervention- and hypothesis-based while it remained largely upward-looking in character. Whilst there is no reason to think that upward-looking research cannot successfully yield structure-function mappings, it has not yet been successful in the case of MTs. Thus, we suggest it might be time to change track and consider other research strategies looking into the evolution of MTs. Recent studies in mollusks render research in this direction worthy of pursuit.

Metal-metal interaction and metal toxicity: a comparison between mammalian and D. melanogaster

1. Non-essential heavy metals such as mercury (Hg), arsenic (As), cadmium (Cd), and aluminium (Al) are useless to organisms and have shown extensive toxic effects. Previous studies show that two main molecular mechanisms of metal toxicity are oxidative stress and metal-metal interaction which can disrupt metal homeostasis.2. In this paper, we mainly illustrate metal toxicity and metal-metal interaction through examples in mammalians and D. melanogaster (fruit fly).3. We describe the interference of metal homeostasis by metal-metal interactions in three aspects including replacement, cellular transporter competition, and disruption of the regulation mechanism, and elaborate the mechanisms of metal toxicity to better deal with the challenges of heavy metal pollution and related health problems.

Copper Toxicity Is Not Just Oxidative Damage: Zinc Systems and Insight from Wilson Disease

Essential metals such as copper (Cu) and zinc (Zn) are important cofactors in diverse cellular processes, while metal imbalance may impact or be altered by disease state. Cu is essential for aerobic life with significant functions in oxidation-reduction catalysis. This redox reactivity requires precise intracellular handling and molecular-to-organismal levels of homeostatic control. As the central organ of Cu homeostasis in vertebrates, the liver has long been associated with Cu storage disorders including Wilson Disease (WD) (heritable human Cu toxicosis), Idiopathic Copper Toxicosis and Endemic Tyrolean Infantile Cirrhosis. Cu imbalance is also associated with chronic liver diseases that arise from hepatitis viral infection or other liver injury. The labile redox characteristic of Cu is often discussed as a primary mechanism of Cu toxicity. However, work emerging largely from the study of WD models suggests that Cu toxicity may have specific biochemical consequences that are not directly attributable to redox activity. This work reviews Cu toxicity with a focus on the liver and proposes that Cu accumulation specifically impacts Zn-dependent processes. The prospect that Cu toxicity has specific biochemical impacts that are not entirely attributable to redox may promote further inquiry into Cu toxicity in WD and other Cu-associated disorders.

Environmental biomonitoring by snails

Background: Bio-indicator systems are vital in terms of monitoring of pollutants around the world. The impact of environmental change can be monitored by employing the responsive behaviour of snails. Heavy metal and organic pollutants affects snail reproduction, mortality, and normal metabolic activities. Various changes like a discontinuity in food intake, growth rate, twitching, and quenching of tentacles, are the biomarkers of the snails for biomonitoring. Different snails can bio-monitor eco-toxicological urban pollution, oil pollutant, terrestrial pollution, pesticide pollutants, mercury contamination, ammonia, chlorinated paraffin in soil, ethanol in water, ocean acidification pollutions. These animals can also make bio-sense about diverse environment spheres, which include the biosphere, lithosphere, anthroposphere, cryosphere, and hydrosphere.Methods: We examined the scientific literature and related articles listed in Pub-med, Google Scholar reporting on biomonitoring potential and biomarkers expression of various snail species and consequently explore the value of snails in the respective field by discussing various outcomes of a number of studies on the pollution biomonitoring and biosensing capabilities.Results: Several terrestrial, freshwater and sea snail species are characterized by the high sense of biomonitoring and biosensing potential. Various biomarkers such as expression of heat shock proteins and metallothioneins in the body are found to be the essential in-vivo biomarkers for pollution biomonitoring.Conclusion: It is observed that snails offer an environment friendly approach for the environmental bio monitoring by expressing their numerous physiological, biochemical, genetical and histological biomarkers in their body. Thus, it proved to be a critical bio monitoring tool and early warning indicators.

Interactions of zinc- and redox-signaling pathways

Zinc and cellular oxidants such as reactive oxygen species (ROS) each participate in a multitude of physiological functions. There is considerable overlap between the affected events, including signal transduction. While there is no obvious direct connection between zinc and ROS, mainly because the bivalent cation zinc does not change its oxidation state in biological systems, these are linked by their interaction with sulfur, forming the remarkable triad of zinc, ROS, and protein thiols. First, zinc binds to reduced thiols and can be released upon oxidation. Thereby, redox signals are translated into changes in the free zinc concentration, which can act as zinc signals. Second, zinc affects oxidation of thiols in several ways, directly as well as indirectly. A protein incorporating many of these interactions is metallothionein (MT), which is rich in cysteine and capable of binding up to seven zinc ions in its fully reduced state. Zinc binding is diminished after (partial) oxidation, while thiols show increased reactivity in the absence of bound metal ions. Adding still more complexity, the MT promoter is controlled by zinc (via metal regulatory transcription factor 1 (MTF-1)) as well as redox (via nuclear factor erythroid 2-related factor 2 (NRF2)). Many signaling cascades that are important for cell proliferation or apoptosis contain protein thiols, acting as centers for crosstalk between zinc- and redox-signaling. A prominent example for shared molecular targets for zinc and ROS are active site cysteine thiols in protein tyrosine phosphatases (PTP), their activity being downregulated by oxidation as well as zinc binding. Because zinc binding also protects PTP thiols form irreversible oxidation, there is a multi-faceted reciprocal interaction, illustrating that zinc- and redox-signaling are intricately linked on multiple levels.

Diversity, structure and regulation of microbial metallothionein: metal resistance and possible applications in sequestration of toxic metals

Metallothioneins (MTs) are a group of cysteine-rich, universal, low molecular weight proteins distributed widely in almost all major taxonomic groups ranging from tiny microbes to highly organized vertebrates. The primary function of this protein is storage, transportation and binding of metals, which enable microorganisms to detoxify heavy metals. In the microbial world, these peptides were first identified in a cyanobacterium Synechococcus as the SmtA protein which exhibits high affinity towards rising level of zinc and cadmium to preserve metal homeostasis in a cell. In yeast, MTs aid in reserving copper and confer protection against copper toxicity by chelating excess copper ions in a cell. Two MTs, CUP1 and Crs5, originating from Saccharomyces cerevisiae predominantly bind to copper though are capable of binding with zinc and cadmium ions. MT superfamily 7 is found in ciliated protozoa which show high affinity towards copper and cadmium. Several tools and techniques, such as western blot, capillary electrophoresis, inductively coupled plasma, atomic emission spectroscopy and high performance liquid chromatography, have been extensively utilized for the detection and quantification of microbial MTs which are utilized for the efficient remediation and sequestration of heavy metals from a contaminated environment.

Soil Saprobic Fungi Differ in Their Response to Gradually and Abruptly Delivered Copper

The overwhelming majority of studies examining environmental change deliver treatments abruptly, although, in fact, many important changes are gradual. One example of a gradually increasing environmental stressor is heavy metal contamination. Essential heavy metals, such as copper, play an important role within cells of living organisms but are toxic at higher concentrations. In our study, we focus on the effects of copper pollution on filamentous soil fungi, key players in terrestrial ecosystem functioning. We hypothesize that fungi exposed to gradually increasing copper concentrations have higher chances for physiological acclimation and will maintain biomass production and accumulate less copper, compared to fungi abruptly exposed to the highest copper concentration. To test this hypothesis, we conducted an experiment with 17 fungal isolates exposed to gradual and abrupt copper addition. Contrary to our hypothesis, we find diverse idiosyncratic responses, such that for many fungi gradually increasing copper concentrations have more severe effects (stronger growth inhibition and higher copper accumulation) than an abrupt increase. While a number of environmental change studies have accumulated evidence based on the magnitude of changes, the results of our study imply that the rate of change can be an important factor to consider in future studies in ecology, environmental science, and environmental management.

Copper-dependent ATP7B up-regulation drives the resistance of TMEM16A-overexpressing head-and-neck cancer models to platinum toxicity

Platinum-containing drugs such as cisplatin and carboplatin are routinely used for the treatment of many solid tumors including squamous cell carcinoma of the head and neck (SCCHN). However, SCCHN resistance to platinum compounds is well documented. The resistance to platinum has been linked to the activity of divalent transporter ATP7B, which pumps platinum from the cytoplasm into lysosomes, decreasing its concentration in the cytoplasm. Several cancer models show increased expression of ATP7B; however, the reason for such an increase is not known. Here we show a strong positive correlation between mRNA levels of TMEM16A and ATP7B in human SCCHN tumors. TMEM16A overexpression and depletion in SCCHN cell lines caused parallel changes in the ATP7B mRNA levels. The ATP7B increase in TMEM16A-overexpressing cells was reversed by suppression of NADPH oxidase 2 (NOX2), by the antioxidant N-Acetyl-Cysteine (NAC) and by copper chelation using cuprizone and bathocuproine sulphonate (BCS). Pretreatment with either chelator significantly increased cisplatin's sensitivity, particularly in the context of TMEM16A overexpression. We propose that increased oxidative stress in TMEM16A-overexpressing cells liberates the chelated copper in the cytoplasm, leading to the transcriptional activation of ATP7B expression. This, in turn, decreases the efficacy of platinum compounds by promoting their vesicular sequestration. We think that such a new explanation of the mechanism of SCCHN tumors' platinum resistance identifies novel approach to treating these tumors.

Partial ameliorative effect of Moringa leaf ethanolic extract on the reproductive toxicity and the expression of steroidogenic genes induced by subchronic cadmium in male rats

The impact of Moringa oleifera leaf ethanol extract (MOLEE) was assessed on the expression of the steroidogenic genes (steroidogenic acute regulatory protein (StAR) and cytochrome P450c17 subfamily a (CYP17a) and luteinizing hormone receptor (LHR) gene) as well as on the cadmium chloride (CdCl₂)-induced reproductive toxicity for 56 days in male rats. Four groups were used: control, Moringa-treated (MOLEE), CdCl₂-treated, and CdCl₂ + MOLEE groups. The reproductive toxicity of CdCl₂ was confirmed; it caused a significant decrease in the accessory sex organ weights, testosterone level, testicular GST level, elevated MDA level (lipid peroxidation indicator), and histopathological alterations in seminiferous tubules, prostate, seminal vesicles, and epididymis as well as sperm characteristics. It also induced downregulation in the expression of StAR and CYP17a genes without change in the expression LHR gene. Eleven active compounds were detected in the GC-MS analysis of MOLEE; six of them have antioxidant properties, and five new compounds presented variable activities. MOLEE alone induced a stimulatory effect on the expression of steroidogenic and LHR genes. It restored the weight of reproductive organs to the control level; however, the recovery in sperm count, motility, abnormalities, percentage of alive sperm, testosterone, and MDA level are still comparable with the control level. Similar findings were also reported at the histological structure of the testes, epididymis, and accessory sex glands. Complete recovery of the GST enzyme activity was observed. Additionally, a restoration in the expression level of the steroidogenic genes was also reported. Our results indicated that the concurrent administration of MOLEE with CdCl₂ can partially mitigate its harmful effects on male fertility.

Increased DMT-1 expression in placentas of women living in high-Cd-contaminated areas of Thailand

Cadmium (Cd) is a toxic heavy metal and contamination was reported in soil and rice in several areas of Thailand. Humans are normally exposed to environmental Cd, leading to gradual Cd accumulation in their bodies, including the placenta. DMT-1 is a divalent metal transporter which is found in placental tissue and plays a vital role in the transportation of Fe²⁺ and Cd²⁺. This study investigated DMT-1 protein and mRNA expressions in full term human placentas comparing those from high-Cd-contaminated areas (high-Cd group) and low-Cd-contaminated areas (low-Cd group), n = 6 per group. The maternal blood Cd (B-Cd) and placental Cd (P-Cd) of the high-Cd group was significantly raised in comparison with those in the low-Cd group. DMT-1 in the fetal portion of the placentas was localized in the apical and basal portions of the cytoplasm of the syncytiotrophoblastic cells, the endothelium of fetal capillaries which is functional structure of the placental barrier, and was also found in the cytoplasm of Hofbauer cells. Moreover, DMT-1 localization in the maternal portion was also detected in most decidual cells. In addition, the DMT-1 protein and mRNA expressions in the high-Cd group were significantly higher than those in the low-Cd group. Therefore, we suggest that pregnant women, who are exposed to environmental Cd, show an increased level of Cd in their maternal blood and this Cd can accumulate in the placenta. Intracellular Cd may induce DMT-1 mRNA transcription which further translates into DMT-1 protein, which can then function as a reciprocal Cd transporter in placental tissue.

Altered zinc balance in the Atp7b-/- mouse reveals a mechanism of copper toxicity in Wilson disease

Wilson disease (WD) is an autosomal recessive disorder caused by mutation in the ATP7B gene that affects copper transport in the body. ATP7B mutation damages copper transporter function, ultimately resulting in excessive copper accumulation and subsequent toxicity in both the liver and brain. Mechanisms of copper toxicity, however, are not well defined. The Atp7b-/- mouse model is well-characterized and presents a hepatic phenotype consistent with WD. In this study, we found that the untreated Atp7b-/- mice accumulate approximately 2-fold excess hepatic zinc compared to the wild type. We used targeted transcriptomics and proteomics to analyze the molecular events associated with zinc and copper accumulation in the Atp7b-/- mouse liver. Altered gene expression of Zip5 and ZnT1 zinc transporters indicated a transcriptional homeostatic response, while increased copper/zinc ratios associated with high levels of metallothioneins 1 and 2, indicated altered Zn availability in cells. These data suggest that copper toxicity in Wilson disease includes effects on zinc-dependent proteins. Transcriptional network analysis of RNA-seq data reveals an interconnected network of transcriptional activators with over-representation of zinc-dependent and zinc-responsive transcription factors. In the context of previous research, these observations support the hypothesis that mechanisms of copper toxicity include disruption of intracellular zinc distribution in liver cells. The translational significance of this work lies in oral zinc supplementation in treatment for WD, which is thought to mediate protective effects through the induction of metallothionein synthesis in the intestine. This work indicates broader impacts of altered zinc-copper balance in WD, including global transcriptional responses and altered zinc balance in the liver.

[Transport and Toxicity of Cadmium]

Cadmium is a nonessential heavy metal and an industrial and environmental pollutant. It has been known that cadmium must enter cells to cause damage. To understand the transport systems responsible for cadmium entry into cells, it is important to determine the precise mechanisms underlying cadmium toxicity. Numerous studies have sought to unravel the exact pathways by which cadmium enters various cells and the mechanisms by which it causes toxicity in the organs of human and animals. The purpose of this review is to present the progress made regarding the mechanisms of cadmium transport in various cells and the mechanisms underlying cadmium toxicity in organs.

Intersection of Iron and Copper Metabolism in the Mammalian Intestine and Liver

Iron and copper have similar physiochemical properties; thus, physiologically relevant interactions seem likely. Indeed, points of intersection between these two essential trace minerals have been recognized for many decades, but mechanistic details have been lacking. Investigations in recent years have revealed that copper may positively influence iron homeostasis, and also that iron may antagonize copper metabolism. For example, when body iron stores are low, copper is apparently redistributed to tissues important for regulating iron balance, including enterocytes of upper small bowel, the liver, and blood. Copper in enterocytes may positively influence iron transport, and hepatic copper may enhance biosynthesis of a circulating ferroxidase, ceruloplasmin, which potentiates iron release from stores. Moreover, many intestinal genes related to iron absorption are transactivated by a hypoxia-inducible transcription factor, hypoxia-inducible factor-2α (HIF2α), during iron deficiency. Interestingly, copper influences the DNA-binding activity of the HIF factors, thus further exemplifying how copper may modulate intestinal iron homeostasis. Copper may also alter the activity of the iron-regulatory hormone hepcidin. Furthermore, copper depletion has been noted in iron-loading disorders, such as hereditary hemochromatosis. Copper depletion may also be caused by high-dose iron supplementation, raising concerns particularly in pregnancy when iron supplementation is widely recommended. This review will cover the basic physiology of intestinal iron and copper absorption as well as the metabolism of these minerals in the liver. Also considered in detail will be current experimental work in this field, with a focus on molecular aspects of intestinal and hepatic iron-copper interplay and how this relates to various disease states. © 2018 American Physiological Society. Compr Physiol 8:1433-1461, 2018.

Micromolar Zinc in Annexin A5 Anticoagulation as a Potential Remedy for RPRGL3-Associated Recurrent Pregnancy Loss

Deficient expression of the placental anticoagulant annexin A5 (ANXA5) has been associated with thrombophilia-related pregnancy complications and ultimately with recurrent pregnancy loss (RPL). Carrier status of M2/ANXA5 ( RPRGL3), common ANXA5 promoter variant, has been identified as genetic cause of reduced ANXA5 levels and proposed as biomarker for successful anticoagulant treatment of RPL women. A murine model of AnxA5 loss of function displayed characteristic placental pathology and fetal loss that was alleviated through anticoagulant intervention. This study identified an alternative means of supplementing anticoagulation, through elevated ANXA5 expression. Physiological micromolar Zn²⁺ stimulated ANXA5 transcription, raising ANXA5 protein expression and surface abundance on BeWo and human umbilical vein endothelial cells (HUVEC), thus resulting in prolonged coagulation times. Zn²-fed AnxA5 functionally deficient pregnant mice showed a trend to increase litter size when primiparous that grew comparable to wild-type progeny in subsequent pregnancies. Elevated AnxA5 signal upon Zn²⁺ treatment was confirmed in murine placentae. Micromolar Zn²⁺ stimulated ANXA5 expression in cell culture directly and alleviated RPL in AnxA5 genetically deficient mice, without notable toxicity effects.

The antiviral role of zinc and metallothioneins in hepatitis C infection

Metallothioneins (MTs) are small, cysteine-rich proteins characterized by a high affinity for monovalent and divalent cations, such as copper and zinc. Of the four known MT isoforms, only, members of the MT 1 and 2 subfamilies are widely expressed, acting as metal chaperones whose primary role is to mediate intracellular zinc homoeostasis. Metallothioneins are potently induced by heavy metals and other sources of oxidative stress where they facilitate metal binding and detoxification as well as free radical scavenging. Metallothionein expression is well documented in the context of viral infection; however, it remains uncertain whether MTs possess specific antiviral roles or whether induction is merely a consequence of cellular stress. To better understand the role of MTs following hepatitis C virus (HCV) infection, we examined MT expression and localization in vitro and in vivo and used a siRNA knockdown approach to ascertain their antiviral efficacy. We confirmed HCV-driven MT induction in vitro and demonstrated MT accumulation in the nucleus of HCV-infected hepatocytes by immunofluorescence. Using a pan-MT siRNA to knock down all members of the MT1 and MT2 subfamilies, we demonstrate that they are mildly antiviral against the JFH1 strain of HCV in vitro (~1.4 fold increase in viral RNA, P < .05). Furthermore, the antiviral effect of zinc treatment against HCV in vitro was mediated through MT induction (P < .05). Our data suggest a potential benefit of using zinc as a low-cost adjunct to current HCV antiviral therapies and suggest that zinc may facilitate the antiviral role of MTs against other viruses.

Development of multi-metal interaction model for Daphnia magna: Significance of metallothionein in cellular redistribution

Despite the great progress made in metal-induced toxicity mechanisms, a critical knowledge gap still exists in predicting adverse effects of heavy metals on living organisms in the natural environment, particularly during exposure to multi-metals. In this study, a multi-metal interaction model of Daphnia manga was developed in an effort to provide reasonable explanations regarding the joint effects resulting from exposure to multi-metals. Metallothionein (MT), a widely used biomarker, was selected. In this model, MT was supposed to play the role of a crucial transfer protein rather than detoxifying protein. Therefore, competitive complexation of metals to MT could highly affect the cellular metal redistribution. Thus, competitive complexation of MT in D. magna with metals like Pb²⁺, Cd²⁺ and Cu²⁺ was qualitatively studied. The results suggested that Cd²⁺ had the highest affinity towards MT, followed by Pb²⁺ and Cu²⁺. On the other hand, the combination of MT with Cu²⁺ appeared to alter its structure which resulted in higher affinity towards Pb²⁺. Overall, the predicted bioaccumulation of metals under multi-metal exposure was consisted with earlier reported studies. This model provided an alternative angle for joint effect through a combination of kinetic process and internal interactions, which could help to develop future models predicting toxicity to multi-metal exposure.

Metallothionein: a Potential Link in the Regulation of Zinc in Nutritional Immunity

Nutritional immunity describes mechanisms for withholding essential transition metals as well as directing the toxicity of these metals against infectious agents. Zinc is one of these transition elements that are essential for both humans and microbial pathogens. At the same time, Zn can be toxic both for man and microbes if its concentration is higher than the tolerance limit. Therefore a "delicate" balance of Zn must be maintained to keep the immune cells surveilling while making the level of Zn either to starve or to intoxicate the pathogens. On the other hand, the invading pathogens will exploit the host Zn pool for its survival and replication. Apparently, different sets of protein in human and bacteria are involved to maintain their Zn need. Metallothionein (MT)-a group of low molecular weight proteins, is well known for its Zn-binding ability and is expected to play an important role in that Zn balance at the time of active infection. However, the differences in structural, functional, and molecular control of biosynthesis between human and bacterial MT might play an important role to determine the proper use of Zn and the winning side. The current review explains the possible involvement of human and bacterial MT at the time of infection to control and exploit Zn for their need.

Induced pluripotent stem cells derived from human amnion in chemically defined conditions

Fetal stem cells are a unique type of adult stem cells that have been suggested to be broadly multipotent with some features of pluripotency. Their clinical potential has been documented but their upgrade to full pluripotency could open up a wide range of cell-based therapies particularly suited for pediatric tissue engineering, longitudinal studies or disease modeling. Here we describe episomal reprogramming of mesenchymal stem cells from the human amnion to pluripotency (AM-iPSC) in chemically defined conditions. The AM-iPSC expressed markers of embryonic stem cells, readily formed teratomas with tissues of all three germ layers present and had a normal karyotype after around 40 passages in culture. We employed novel computational methods to determine the degree of pluripotency from microarray and RNA sequencing data in these novel lines alongside an iPSC and ESC control and found that all lines were deemed pluripotent, however, with variable scores. Differential expression analysis then identified several groups of genes that potentially regulate this variability in lines within the boundaries of pluripotency, including metallothionein proteins. By further studying this variability, characteristics relevant to cell-based therapies, like differentiation propensity, could be uncovered and predicted in the pluripotent stage.

Identification of ARNT-regulated BIRC3 as the target factor in cadmium renal toxicity

Cadmium (Cd) is an environmental contaminant that exhibits renal toxicity. The target transcription factors involved in Cd renal toxicity are still unknown. In this study, we demonstrated that Cd decreased the activity of the ARNT transcription factor, and knockdown of ARNT significantly decreased the viability of human proximal tubular HK-2 cells. Microarray analysis in ARNT knockdown cells revealed a decrease in the expression of a number of genes, including a known apoptosis inhibitor, BIRC3, whose gene and protein expression level was also decreased by Cd treatment. Although the BIRC family consists of 8 members, Cd suppressed only BIRC3 gene expression. BIRC3 is known to suppress apoptosis through the inhibition effect on caspase-3. Knockdown of BIRC3 by siRNA as well as Cd treatment increased the level of active caspase-3. Moreover, knockdown of BIRC3 not only triggered cell toxicity and apoptosis but also strengthened Cd toxicity in HK-2 cells. Meanwhile, the activation of caspase-3 by suppression of BIRC3 gene expression was mostly specific to Cd and to proximal tubular cells. These results suggest that Cd induces apoptosis through the inhibition of ARNT-regulated BIRC3 in human proximal tubular cells.

Cadmium effects on DNA and protein metabolism in oyster (Crassostrea gigas) revealed by proteomic analyses

Marine molluscs, including oysters, can concentrate high levels of cadmium (Cd) in their soft tissues, but the molecular mechanisms of Cd toxicity remain speculative. In this study, Pacific oysters (Crassostrea gigas) were exposed to Cd for 9 days and their gills were subjected to proteomic analysis, which were further confirmed with transcriptomic analysis. A total of 4,964 proteins was quantified and 515 differentially expressed proteins were identified in response to Cd exposure. Gene Ontology enrichment analysis revealed that excess Cd affected the DNA and protein metabolism. Specifically, Cd toxicity resulted in the inhibition of DNA glycosylase and gap-filling and ligation enzymes expressions in base excision repair pathway, which may have decreased DNA repair capacity. At the protein level, Cd induced the heat shock protein response, initiation of protein refolding as well as degradation by ubiquitin proteasome pathway, among other effects. Excess Cd also induced antioxidant responses, particularly glutathione metabolism, which play important roles in Cd chelation and anti-oxidation. This study provided the first molecular mechanisms of Cd toxicity on DNA and protein metabolism at protein levels, and identified molecular biomarkers for Cd toxicity in oysters.

Proteomic High Affinity Zn2+ Trafficking: Where Does Metallothionein Fit in?

The cellular constitution of Zn-proteins and Zn-dependent signaling depend on the capacity of Zn²⁺ to find specific binding sites in the face of a plethora of other high affinity ligands. The most prominent of these is metallothionein (MT). It serves as a storage site for Zn²⁺ under various conditions, and has chemical properties that support a dynamic role for MT in zinc trafficking. Consistent with these characteristics, changing the availability of zinc for cells and tissues causes rapid alteration of zinc bound to MT. Nevertheless, zinc trafficking occurs in metallothionein-null animals and cells, hypothetically making use of proteomic binding sites to mediate the intracellular movements of zinc. Like metallothionein, the proteome contains a large concentration of proteins that strongly coordinate zinc. In this environment, free Zn²⁺ may be of little significance. Instead, this review sets forth the basis for the hypothesis that components of the proteome and MT jointly provide the platform for zinc trafficking.

The Functions of Metamorphic Metallothioneins in Zinc and Copper Metabolism

Recent discoveries in zinc biology provide a new platform for discussing the primary physiological functions of mammalian metallothioneins (MTs) and their exquisite zinc-dependent regulation. It is now understood that the control of cellular zinc homeostasis includes buffering of Zn²⁺ ions at picomolar concentrations, extensive subcellular re-distribution of Zn²⁺, the loading of exocytotic vesicles with zinc species, and the control of Zn²⁺ ion signalling. In parallel, characteristic features of human MTs became known: their graded affinities for Zn²⁺ and the redox activity of their thiolate coordination environments. Unlike the single species that structural models of mammalian MTs describe with a set of seven divalent or eight to twelve monovalent metal ions, MTs are metamorphic. In vivo, they exist as many species differing in redox state and load with different metal ions. The functions of mammalian MTs should no longer be considered elusive or enigmatic because it is now evident that the reactivity and coordination dynamics of MTs with Zn²⁺ and Cu⁺ match the biological requirements for controlling—binding and delivering—these cellular metal ions, thus completing a 60-year search for their functions. MT represents a unique biological principle for buffering the most competitive essential metal ions Zn²⁺ and Cu⁺. How this knowledge translates to the function of other families of MTs awaits further insights into the specifics of how their properties relate to zinc and copper metabolism in other organisms.

Function of Metallothionein-3 in Neuronal Cells: Do Metal Ions Alter Expression Levels of MT3?

A study of factors proposed to affect metallothionein-3 (MT3) function was carried out to elucidate the opaque role MT3 plays in human metalloneurochemistry. Gene expression of Mt2 and Mt3 was examined in tissues extracted from the dentate gyrus of mouse brains and in human neuronal cell cultures. The whole-genome gene expression analysis identified significant variations in the mRNA levels of genes associated with zinc homeostasis, including Mt2 and Mt3. Mt3 was found to be the most differentially expressed gene in the identified groups, pointing to the existence of a factor, not yet identified, that differentially controls Mt3 expression. To examine the expression of the human metallothioneins in neurons, mRNA levels of MT3 and MT2 were compared in BE(2)C and SH-SY5Y cell cultures treated with lead, zinc, cobalt, and lithium. MT2 was highly upregulated by Zn²⁺ in both cell cultures, while MT3 was not affected, and no other metal had an effect on either MT2 or MT3.

Mammalian Metallothionein-3: New Functional and Structural Insights

Metallothionein-3 (MT-3), a member of the mammalian metallothionein (MT) family, is mainly expressed in the central nervous system (CNS). MT-3 possesses a unique neuronal growth inhibitory activity, and the levels of this intra- and extracellularly occurring metalloprotein are markedly diminished in the brain of patients affected by a number of metal-linked neurodegenerative disorders, including Alzheimer’s disease (AD). In these pathologies, the redox cycling of copper, accompanied by the production of reactive oxygen species (ROS), plays a key role in the neuronal toxicity. Although MT-3 shares the metal-thiolate clusters with the well-characterized MT-1 and MT-2, it shows distinct biological, structural and chemical properties. Owing to its anti-oxidant properties and modulator function not only for Zn, but also for Cu in the extra- and intracellular space, MT-3, but not MT-1/MT-2, protects neuronal cells from the toxicity of various Cu(II)-bound amyloids. In recent years, the roles of zinc dynamics and MT-3 function in neurodegeneration are slowly emerging. This short review focuses on the recent developments regarding the chemistry and biology of MT-3.

Zinc is a potent and specific inhibitor of IFN-λ3 signalling

Lambda interferons (IFNL, IFN-λ) are pro-inflammatory cytokines important in acute and chronic viral infection. Single-nucleotide polymorphisms rs12979860 and rs8099917 within the IFNL gene locus predict hepatitis C virus (HCV) clearance, as well as inflammation and fibrosis progression in viral and non-viral liver disease. The underlying mechanism, however, is not defined. Here we show that the rs12979860 CC genotype correlates with increased hepatic metallothionein expression through increased systemic zinc levels. Zinc interferes with IFN-λ3 binding to IFNL receptor 1 (IFNLR1), resulting in decreased antiviral activity and increased viral replication (HCV, influenza) in vitro. HCV patients with high zinc levels have low hepatocyte antiviral and inflammatory gene expression and high viral loads, confirming the inhibitory role of zinc in vivo. We provide the first evidence that zinc can act as a potent and specific inhibitor of IFN-λ3 signalling and highlight its potential as a target of therapeutic intervention for IFN-λ3-mediated chronic disease.

Origin, Function, and Fate of Metallothionein in Human Blood

Toxic heavy metals, toxic organic compounds, reactive oxygen species (ROS), infections, and temperature are well-known metallothionein (MT) inducers in human blood. The current review aims to summarize synthesis, function, and fate of human blood MT in response to the known MT inducers. Part of the MTs that are synthesized in different organs such as the liver, kidney, and spleen is transported and stored in different blood cells and in plasma. Cells of the circulatory system also synthesize MT. From the circulation, MT returns to the kidney where the metal-bound MTs are degraded to release the metal ion that in turn induces MT expression therein. The blood MTs play important roles in metal detoxification, transportation, and storage. By neutralizing ROS, MTs protect blood cells from oxidative stress-induced cytotoxicity and genotoxicity. Arguably, MTs are also involved in immune suppression. Given the permeating distribution of blood MT throughout the body as well as its diverse role in the protection against harmful environmental factors and in metal homeostasis, MT could be better recognized as a major public health protein.

Zn(2+) at a cellular crossroads

Zinc is an essential micronutrient for cellular homeostasis. Initially proposed to only contribute to cellular viability through structural roles and non-redox catalysis, advances in quantifying changes in nM and pM quantities of Zn(2+) have elucidated increasing functions as an important signaling molecule. This includes Zn(2+)-mediated regulation of transcription factors and subsequent protein expression, storage and release of intracellular compartments of zinc quanta into the extracellular space which modulates plasma membrane protein function, as well as intracellular signaling pathways which contribute to the immune response. This review highlights some recent advances in our understanding of zinc signaling.