Nitric oxide-induced changes in intracellular zinc homeostasis are mediated by metallothionein/thionein

Zinc as a potential regulator of the BCR-ABL oncogene in chronic myelocytic leukemia cells

BACKGROUND

Generally, decreased zinc in the serum of tumor patients but increased zinc in tumor cells can be observed. However, the role of zinc homeostasis in myeloid leukemia remains elusive. BCR-ABL is essential for the initiation, maintenance, and progression of chronic myelocytic leukemia (CML). We are currently investigating the association between zinc homeostasis and CML.

METHODS

Genes involved in zinc homeostasis were examined using three GEO datasets. Western blotting and qPCR were used to investigate the effects of zinc depletion on BCR-ABL expression. Furthermore, the effect of TPEN on BCR-ABL promoter activity was determined using the dual-luciferase reporter assay. MRNA stability and protein stability of BCR-ABL were assessed using actinomycin D and cycloheximide.

RESULTS

Transcriptome data mining revealed that zinc homeostasis-related genes were associated with CML progression and drug resistance. Several zinc homeostasis genes were affected by TPEN. Additionally, we found that zinc depletion by TPEN decreased BCR-ABL mRNA stability and transcriptional activity in K562 CML cells. Zinc supplementation and sodium nitroprusside treatment reversed BCR-ABL downregulation by TPEN, suggesting zinc- and nitric oxide-dependent mechanisms.

CONCLUSION

Our in vitro findings may help to understand the role of zinc homeostasis in BCR-ABL regulation and thus highlight the importance of zinc homeostasis in CML.

Modern optical approaches in redox biology: Genetically encoded sensors and Raman spectroscopy

The objective of the current review is to summarize the current state of optical methods in redox biology. It consists of two parts, the first is dedicated to genetically encoded fluorescent indicators and the second to Raman spectroscopy. In the first part, we provide a detailed classification of the currently available redox biosensors based on their target analytes. We thoroughly discuss the main architecture types of these proteins, the underlying engineering strategies for their development, the biochemical properties of existing tools and their advantages and disadvantages from a practical point of view. Particular attention is paid to fluorescence lifetime imaging microscopy as a possible readout technique, since it is less prone to certain artifacts than traditional intensiometric measurements. In the second part, the characteristic Raman peaks of the most important redox intermediates are listed, and examples of how this knowledge can be implemented in biological studies are given. This part covers such fields as estimation of the redox states and concentrations of Fe-S clusters, cytochromes, other heme-containing proteins, oxidative derivatives of thiols, lipids, and nucleotides. Finally, we touch on the issue of multiparameter imaging, in which biosensors are combined with other visualization methods for simultaneous assessment of several cellular parameters.

Zinc homeostasis and redox alterations in obesity

Impairment of both cellular zinc and redox homeostasis is a feature of several chronic diseases, including obesity. A significant two-way interaction exists between redox metabolism and the relatively redox-inert zinc ion. Redox metabolism critically influences zinc homeostasis and controls its cellular availability for various cellular functions by regulating zinc exchange from/to zinc-binding proteins. Zinc can regulate redox metabolism and exhibits multiple pro-antioxidant properties. On the other hand, even minor disturbances in zinc status and zinc homeostasis affect systemic and cellular redox homeostasis. At the cellular level, zinc homeostasis is regulated by a multi-layered machinery consisting of zinc-binding molecules, zinc sensors, and two selective families of zinc transporters, the Zinc Transporter (ZnT) and Zrt, Irt-like protein (ZIP). In the present review, we summarize the current state of knowledge on the role of the mutual interaction between zinc and redox homeostasis in physiology and pathophysiology, pointing to the role of zinc in the alterations responsible for redox stress in obesity. Since zinc transporters primarily control zinc homeostasis, we describe how changes in the expression and activity of these zinc-regulating proteins are associated with obesity.

Superoxide-Mediated Upregulation of MMP9 Participates in BMPR2 Destabilization and Pulmonary Hypertension Development

BACKGROUND AND AIMS

we previously reported in studies on organoid-cultured bovine pulmonary arteries that pulmonary hypertension (PH) conditions of exposure to hypoxia or endothelin-1 caused a loss of a cartilage oligomeric matrix protein (COMP) stabilization of bone morphogenetic protein receptor-2 (BMPR2) function, a known key process contributing to pulmonary hypertension development. Based on subsequent findings, these conditions were associated with an extracellular superoxide-mediated increase in matrix metalloproteinase 9 (MMP-9) expression. We investigated if this contributed to PH development using mice deficient in MMP9.

RESULTS

wild-type (WT) mice exposed to Sugen/Hypoxia (SuHx) to induce PH had increased levels of MMP9 in their lungs. Hemodynamic measures from MMP9 knockout mice (MMP9 KO) indicated they had attenuated PH parameters compared to WT mice based on an ECHO assessment of pulmonary artery pressure, right ventricular systolic pressure, and Fulton index hypertrophy measurements. In vitro vascular reactivity studies showed impaired endothelium-dependent and endothelium-independent NO-associated vasodilatory responses in the pulmonary arteries of SuHx mice and decreased lung levels of COMP and BMPR2 expression. These changes were attenuated in MMP9 KO mice potentially through preserving COMP-dependent stabilization of BMPR2.

INNOVATION

this study supports a new function of superoxide in increasing MMP9 and the associated impairment of BMPR2 in promoting PH development which could be a target for future therapies.

CONCLUSION

superoxide, through promoting increases in MMP9, mediates BMPR2 depletion and its consequent control of vascular function in response to PH mediators and the SuHx mouse model of PH.

Zinc-dependent Nucleosome Reorganization by PARP2

Poly(ADP-ribose)polymerase 2 (PARP2) is a nuclear protein that acts as a DNA damage sensor; it recruits the repair enzymes to a DNA damage site and facilitates formation of the repair complex. Using single particle Förster resonance energy transfer microscopy and electrophoretic mobility shift assay (EMSA) we demonstrated that PARP2 forms complexes with a nucleosome containing different number of PARP2 molecules without altering conformation of nucleosomal DNA both in the presence and in the absence of Mg 2+ or Ca 2+ ions. In contrast, Zn 2+ ions directly interact with PARP2 inducing a local alteration of the secondary structure of the protein and PARP2-mediated, reversible structural reorganization of nucleosomal DNA. AutoPARylation activity of PARP2 is enhanced by Mg 2+ ions and modulated by Zn 2+ ions: suppressed or enhanced depending on the occupancy of two functionally different Zn 2+ binding sites. The data suggest that Zn 2+ /PARP2-induced nucleosome reorganization and transient changes in the concentration of the cations could modulate PARP2 activity and the DNA damage response.

Significance Statement

PARP2 recognizes and binds DNA damage sites, recruits the repair enzymes to these sites and facilitates formation of the repair complex. Zn 2+ -induced structural reorganization of nucleosomal DNA in the complex with PARP2, which is reported in the paper, could modulate the DNA damage response. The obtained data indicate the existence of specific binding sites of Mg 2+ and Zn 2+ ions in and/or near the catalytic domain of PARP2, which modulate strongly, differently and ion-specifically PARylation activity of PARP2, which is important for maintaining genome stability, adaptation of cells to stress, regulation of gene expression and antioxidant defense.

Macrophage metallothioneins participate in the antileishmanial activity of antimonials

Host cell functions that participate in the pharmacokinetics and pharmacodynamics (PK/PD) of drugs against intracellular pathogen infections are critical for drug efficacy. In this study, we investigated whether macrophage mechanisms of xenobiotic detoxification contribute to the elimination of intracellular Leishmania upon exposure to pentavalent antimonials (SbV). Primary macrophages from patients with cutaneous leishmaniasis (CL) (n=6) were exposed ex vivo to L. V. panamensis infection and SbV, and transcriptomes were generated. Seven metallothionein (MT) genes, potent scavengers of heavy metals and central elements of the mammalian cell machinery for xenobiotic detoxification, were within the top 20 up-regulated genes. To functionally validate the participation of MTs in drug-mediated killing of intracellular Leishmania, tandem knockdown (KD) of MT2-A and MT1-E, MT1-F, and MT1-X was performed using a pan-MT shRNA approach in THP-1 cells. Parasite survival was unaffected in tandem-KD cells, as a consequence of strong transcriptional upregulation of MTs by infection and SbV, overcoming the KD effect. Gene silencing of the metal transcription factor-1 (MTF-1) abrogated expression of MT1 and MT2-A genes, but not ZnT-1. Upon exposure to SbV, intracellular survival of Leishmania in MTF-1KD cells was significantly enhanced. Results from this study highlight the participation of macrophage MTs in Sb-dependent parasite killing.

Metallothionein-3: 63 Cu(I) binds to human 68 Zn7 -βα MT3 with no preference for Cu4 -β cluster formation

Human metallothioneins (MTs) are involved in binding the essential elements, Cu(I) and Zn(II), and the toxic element, Cd(II), in metal-thiolate clusters using 20 reduced cysteines. The brain-specific MT3 binds a mixture of Cu(I) and Zn(II) in vivo. Its metallation properties are critically important because of potential connections between Cu, Zn and neurodegenerative diseases. We report that the use of isotopically pure 63 Cu(I) and 68 Zn(II) greatly enhances the element resolution in the ESI-mass spectral data revealing species with differing Cu:Zn ratios but the same total number of metals. Room temperature phosphorescence and circular dichroism spectral data measured in parallel with ESI-mass spectral data identified the presence of specific Cu(I)-thiolate clusters in the presence of Zn(II). A series of Cu(I)-thiolate clusters form following Cu(I) addition to apo MT3: the two main clusters that form are a Cu6 cluster in the β domain followed by a Cu4 cluster in the α domain. 63 Cu(I) addition to 68 Zn7 -MT3 results in multiple species, including clustered Cu5 Zn5 -MT3 and Cu9 Zn3 -MT3. We assign the domain location of the metals for Cu5 Zn5 -MT3 as a Cu5 Zn1 -β cluster and a Zn4 -α cluster and for Cu9 Zn3 -MT3 as a Cu6 -β cluster and a Cu3 Zn3 -α cluster. While many reports of the average MT3 metal content exist, determining the exact Cu,Zn stoichiometry has proven very difficult even with native ESI-MS. The work in this paper solves the ambiguity introduced by the overlap of the naturally abundant Cu(I) and Zn(II) isotopes. Contrary to other reports, there is no indication of a major fraction of Cu4 -β-Znn -α-MT3 forming.

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.

63Cu(I) binding to human kidney 68Zn7-βα MT1A: determination of Cu(I)-thiolate cluster domain specificity from ESI-MS and room temperature phosphorescence spectroscopy

Mammalian metallothioneins (MTs) are important proteins in Zn(II) and Cu(I) homeostasis with the Zn(II) and Cu(I) binding to the 20 cysteines in metal-thiolate clusters. Previous electrospray ionization (ESI) mass spectrometric (MS) analyses of Cu(I) binding to Zn7-MT were complicated by significant overlap of the natural abundance isotopic patterns for Zn(II) and Cu(I) leading to impossibly ambiguous stoichiometries. In this paper, isotopically pure 63Cu(I) and 68Zn(II) allowed determination of the specific stoichiometries in the 68 Zn,63Cu-βα MT1A species formed following the stepwise addition of 63Cu(I) to 68Zn7-βα MT1A. These species were characterized by ESI-MS and room temperature emission spectroscopy. The key species that form and their emission band centres are Zn5Cu5-βα MT1A (λ = 684 nm), Zn4Cu6-βα MT1A (λ = 750 nm), Zn3Cu9-βα MT1A (λ = 750 nm), Zn2Cu10-βα MT1A (λ = 750 nm), and Zn1Cu14-βα MT1A (λ = 634 nm). The specific domain stoichiometry of each species was determined by assessing the species forming following 63Cu(I) addition to the 68Zn3-β MT1A and 68Zn4-α MT1A domain fragments. The domain fragment emission suggests that Zn5Cu5-βα MT1A contains a Zn1Cu5-β cluster and the Zn4Cu6-βα MT1A, Zn3Cu9-βα MT1A, and Zn2Cu10-βα MT1A each contain a Cu6-β cluster. The species forming with >10 mol. eq. of 63Cu(I) in βα-MT1A exhibit emission from the Cu6-β cluster and an α domain cluster. This high emission intensity is seen at the end of the titrations of 68Zn7-βα MT1A and the 68Zn4-α MT1A domain fragment suggesting that the initial presence of the Zn(II) results in clustered Cu(I) binding in the α domain.

Regulation of zinc-dependent enzymes by metal carrier proteins

Zn²⁺ ions are essential in many physiological processes, including enzyme catalysis, protein structural stabilization, and the regulation of many proteins. The affinities of proteins for Zn²⁺ ions span several orders of magnitude, with catalytic Zn²⁺ ions generally held more tightly than structural or regulatory ones. Metal carrier proteins, most of which are not specific for Zn²⁺, bind these ions with a broad range of affinities that overlap those of catalytic, structural, and regulatory Zn²⁺ ions and are thought to be responsible for distributing the metal through most cells, tissues, and fluid compartments. While little is known about how many proteins obtain or release these ions, there is now considerable experimental evidence suggesting that metal carrier proteins may be responsible for transferring metals to and from some Zn²⁺-dependent proteins, thus serving as a major regulatory factor for them. In this review, the biological roles of Zn²⁺ and structures of Zn²⁺ binding sites are examined, and experimental evidence demonstrating the direct participation of metal carrier proteins in enzyme regulation is discussed. Mechanisms of metal ion transfer are also offered, and the potential physiological significance of this phenomenon is explored.

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.

The Role of Zinc Homeostasis in the Prevention of Diabetes Mellitus and Cardiovascular Diseases

Zinc is an essential micronutrient for human health and is involved in various biological functions, such as growth, metabolism, and immune function. In recent years, research on intracellular zinc dynamics has progressed, and it has become clear that zinc transporters strictly control intracellular zinc localization, zinc regulates the functions of various proteins and signal transduction pathways as a second messenger similar to calcium ions, and intracellular zinc dyshomeostasis is associated with impaired insulin synthesis, secretion, sensitivity, lipid metabolism, and vascular function. Numerous animal and human studies have shown that zinc deficiency may be associated with the risk factors for diabetes and cardiovascular diseases (CVDs) and zinc administration might be beneficial for the prevention and treatment of these diseases. Therefore, an understanding of zinc biology may help the establishment of novel strategies for the prevention and treatment of diabetes and CVDs. This review will summarize the current knowledge on the role of zinc homeostasis in the pathogenesis of diabetes and atherosclerosis and will discuss the potential of zinc in the prevention of these diseases.

Impact of the Cellular Zinc Status on PARP-1 Activity and Genomic Stability in HeLa S3 Cells

Poly(ADP-ribose) polymerase 1 (PARP-1) is actively involved in several DNA repair pathways, especially in the detection of DNA lesions and DNA damage signaling. However, the mechanisms of PARP-1 activation are not fully understood. PARP-1 contains three zinc finger structures, among which the first zinc finger has a remarkably low affinity toward zinc ions. Within the present study, we investigated the impact of the cellular zinc status on PARP-1 activity and on genomic stability in HeLa S3 cells. Significant impairment of H₂O₂-induced poly(ADP-ribosyl)ation and an increase in DNA strand breaks were detected in the case of zinc depletion by the zinc chelator N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN) which reduced the total and labile zinc concentrations. On the contrary, preincubation of cells with ZnCl₂ led to an overload of total as well as labile zinc and resulted in an increased poly(ADP-ribosyl)ation response upon H₂O₂ treatment. Furthermore, the impact of the cellular zinc status on gene expression profiles was investigated via high-throughput RT-qPCR, analyzing 95 genes related to metal homeostasis, DNA damage and oxidative stress response, cell cycle regulation and proliferation. Genes encoding metallothioneins responded most sensitively on conditions of mild zinc depletion or moderate zinc overload. Zinc depletion induced by higher concentrations of TPEN led to a significant induction of genes encoding DNA repair factors and cell cycle arrest, indicating the induction of DNA damage and genomic instability. Zinc overload provoked an up-regulation of the oxidative stress response. Altogether, the results highlight the potential role of zinc signaling for PARP-1 activation and the maintenance of genomic stability.

Metal Nanoparticles in Infection and Immunity

Background Enthusiasm for the use of metal nanoparticles in human and veterinary medicine is high. Many articles describe the effects of metal nanoparticles on microbes in vitro, and a smaller number of articles describe effects on the immune system, which is the focus of this review. Methods Articles were retrieved by performing literature searches in Medline, of the National Institute of Medicine, as well as via Google Scholar. Results In vitro studies show that metal nanoparticles have antimicrobial effects. Some metal nanoparticles augment innate host immune defenses, such as endogenous antimicrobial peptides, and nitric oxide. Metal nanoparticles may also function as vaccine adjuvants. Metal nanoparticles can migrate to locations distant from the site of administration, however, requiring careful monitoring for toxicity. Conclusions Metal nanoparticles show a great deal of potential as immunomodulators, as well as direct antimicrobial effects. Before metal particles can be adopted as therapies; however, more studies are needed to determine how nanoparticles migrate though the body and on possible adverse effects.

Combinatorial roles of mitochondria and cGMP/PKG pathway in the generation of neuronal free Zn2+ under the presence of nitric oxide

BACKGROUND

Nitric oxide (NO), which possesses both protective and toxic properties, has been observed to have a complicated biphasic character within various types of tissues, including neuronal cells. NO was also found to cause the increase of another important signaling molecular Zn (termed as NZR). The molecular mechanism of NZR has been extensively investigated, but the source of Zn is present of a major candidate that is yet to be answered. The NO-protein kinase G (PKG) pathway, mitochondria, and metallothioneins (MTs), are all proposed to be the individual source of NZR. However, this hypothesis remains inconclusive. In this study, we examined the function of PKG signaling cascades, the mitochondria storage, and MT-1 during NZR of living PC12 cells.

METHODS

We applied live-cell imaging in combination with pharmacological inhibitors and activators as well as in vitro Zn assay to dissect the functions of the above candidates in NZR.

RESULTS

Two mechanisms, namely, mitochondria as the only Zn source and the opening of NO-PKG-dependent mitochondrial ATP-sensitive potassium channels (mKATP) as the key to releasing NO-induced increase in mitochondrial Zn, were proven to be the two critical paths of NZR in neuronal-related cells.

CONCLUSION

This new finding provides a reasonable explanation to previously existing and contradictory conclusions regarding the function of mitochondria/mKATP and PKG signaling on the molecular mechanism of NZR.

HaloTag-Based Hybrid Targetable and Ratiometric Sensors for Intracellular Zinc

We report a new series of small molecule-protein hybrid zinc sensors that combine genetic targetability with the spectroscopic profile of synthetic fluorophores. We functionalized the zinc sensor ZinPyr-1 (ZP1) with a chloroalkane linker (ZP1-12Cl) that reacts specifically with the engineered protein HaloTag. The resulting construct, ZP1-HaloTag, binds zinc ions with a threefold fluorescence enhancement. Through exploitation of the protein synthesis machinery of live cells, the HaloTag protein component was expressed, and the ZP1-HaloTag hybrid was assembled upon bath application of ZP1-12Cl. After fusion of HaloTag with targeting peptides or proteins, the resulting hybrid sensor could be directed to specific subcellular locales, including the nucleus, mitochondrial outer membrane, and endoplasmic reticulum. Furthermore, HaloTag was linked with the red fluorescent protein mCherry, permitting formation of a two-fluorophore system that provides not only targetable but also ratiometric sensing of cellular zinc. This system reversibly detects both exogenous and endogenous mobile Zn2+ in response to reactive nitrogen species in live HeLa cells. HaloTag-based hybrid zinc sensors offer new opportunities for visualizing and quantifying biological mobile zinc at discrete subcellular compartments.

Sublethal treatment with plasma-activated medium induces senescence-like growth arrest of A549 cells: involvement of intracellular mobile zinc

Plasma-activated medium (PAM) is a solution produced by exposing a liquid medium to non-thermal atmospheric pressure plasma (NTAPP). A number of reactive molecules, such as reactive oxygen species and reactive nitrogen species, are contained in PAM. Therefore, exposure to high doses of PAM results in cell death. We previously demonstrated that intracellular zinc (Zn²⁺) serves as an important mediator in PAM-induced cell death; however, the effects of sublethal treatment with PAM on cell functions are not fully understood. In the present study, we found that sublethal PAM treatment suppressed cell proliferation and induced senescence-like changes in lung adenocarcinoma A549 cells. Cell cycle analysis revealed that PAM induced cell cycle arrest at the G2/M phase. PAM increased the level of intracellular free Zn²⁺ and the Zn²⁺ chelator TPEN counteracted PAM-induced growth suppression, suggesting that Zn²⁺ functions in PAM-induced growth suppression. In addition, sublethal treatment with PAM induced phosphorylation of ATM kinase, accumulation of p53 protein, and expression of p21 and GADD45A, which are known p53 target genes, in a Zn²⁺-dependent manner. These results suggest that the induction of growth arrest and cellular senescence by sublethal PAM treatment is mediated by Zn²⁺-dependent activation of the ATM/p53 pathway.

Genetic biosensors for imaging nitric oxide in single cells

Over the last decades a broad collection of sophisticated fluorescent protein-based probes was engineered with the aim to specifically monitor nitric oxide (NO), one of the most important signaling molecules in biology. Here we report and discuss the characteristics and fields of applications of currently available genetically encoded fluorescent sensors for the detection of NO and its metabolites in different cell types.

LONG ABSTRACT

Because of its radical nature and short half-life, real-time imaging of NO on the level of single cells is challenging. Herein we review state-of-the-art genetically encoded fluorescent sensors for NO and its byproducts such as peroxynitrite, nitrite and nitrate. Such probes enable the real-time visualization of NO signals directly or indirectly on the level of single cells and cellular organelles and, hence, extend our understanding of the spatiotemporal dynamics of NO formation, diffusion and degradation. Here, we discuss the significance of NO detection in individual cells and on subcellular level with genetic biosensors. Currently available genetically encoded fluorescent probes for NO and nitrogen species are critically discussed in order to provide insights in the functionality and applicability of these promising tools. As an outlook we provide ideas for novel approaches for the design and application of improved NO probes and fluorescence imaging protocols.

Molecular Neuroprotection Induced by Zinc-Dependent Expression of Hepatitis C-Derived Protein NS5A Targeting Kv2.1 Potassium Channels

We present the design of an innovative molecular neuroprotective strategy and provide proof-of-concept for its implementation, relying on the injury-mediated activation of an ectopic gene construct. As oxidative injury leads to the intracellular liberation of zinc, we hypothesize that tapping onto the zinc-activated metal regulatory element (MRE) transcription factor 1 system to drive expression of the Kv2.1-targeted hepatitis C protein NS5A (hepatitis C nonstructural protein 5A) will provide neuroprotection by preventing cell death-enabling cellular potassium loss in rat cortical neurons in vitro. Indeed, using biochemical and morphologic assays, we demonstrate rapid expression of MRE-driven products in neurons. Further, we report that MRE-driven NS5A expression, induced by a slowly evolving excitotoxic stimulus, functionally blocks injurious, enhanced Kv2.1 potassium whole-cell currents and improves neuronal viability. We suggest this form of "on-demand" neuroprotection could provide the basis for a tenable therapeutic strategy to prevent neuronal cell death in neurodegeneration.

Roles for endothelial zinc homeostasis in vascular physiology and coronary artery disease

The discovery of the roles of nitric oxide (NO) in cardiovascular signaling has led to a revolution in the understanding of cardiovascular disease. A new perspective to this story involving zinc (Zn) is emerging. Zn and its associated Zn transporter proteins are important for the integrity and functions of both the large conduit vessels and the microvascular resistance vessels. The Zn and NO pathways are tightly coordinated. Zn ions are required for the dimerization of endothelial nitric oxide synthase and subsequent generation of NO while generation of NO leads to a rapid mobilization of endothelial Zn stores. Labile Zn may mediate important downstream actions of NO including vascular cytoprotection and vasodilation. Several vascular disease risk factors (including aging, smoking and diabetes) interfere with Zn homeostatic mechanisms and both hypozincaemia and Zn transporter protein abnormalities are linked to atherosclerosis and microvascular disease. Some vegetarian diets and long-term use of certain anti-hypertensives may also impact on Zn status. The available evidence supports the existence of a Zn regulatory pathway in the vascular wall that is coupled to the generation and actions of NO and which is compromised in Zn deficiency with consequent implications for the pathogenesis and therapy of vascular disease.

Isolated domains of recombinant human apo-metallothionein 1A are folded at neutral pH: a denaturant and heat-induced unfolding study using ESI-MS

Metallothioneins (MTs) are characterized by their high metal loading capacity, small molecular weight, and abundant cysteine residues. It has long been thought that metal-free, or apo-MT peptides were unstructured and only adopted as a distinct conformation upon forming the metal clusters, described as metal-induced folding. More recent studies have suggested that the presence of a globular, yet loosely defined structure actually exists that can be disrupted or unfolded. Residue modification and ion-mobility ESI (IM-ESI)-MS have been used to examine this unusual unfolding process. The structure of apo-MT plays a critical role as the starting point in the flexible metalation pathways that can accommodate numerous soft metals. ESI-MS measurements of the product species formed following the cysteine alkylation of the isolated domain fragments of recombinant human apo-MT 1A with n-ethylmaleimide (NEM) were used in the present study to monitor the denaturant- and heat-induced unfolding at physiological pH. The results indicate that these apo-MT fragments adopt distinct structures at neutral pH that react co-operatively with NEM when folded and non-cooperatively when heated or exposed to high concentrations of the denaturant guanidinium chloride (GdmCl). From these studies, we can conclude that at neutral pH, the domain fragments are folded into globular structures where some of the free cysteine residues are buried within the core and are stabilized by hydrogen bonds. Metalation therefore, must take place from the folded conformation.

Metallothionein: A Multifunctional Protein from Toxicity to Cancer

The metallothionein (MT) family is a class of low molecular weight, intracellular and cysteine-rich proteins presenting high affinity for metal ions. Although the members of this family were discovered nearly 40 years ago, their functional significance remains obscure. Four major MT isoforms, MT-1, MT-2, MT-3 and MT-4, have been identified in mammals. MTs are involved in many pathophysiological processes such as metal ion homeostasis and detoxification, protection against oxidative damage, cell proliferation and apoptosis, chemoresistance and radiotherapy resistance. MT isoforms have been shown to be involved in several aspects of the carcinogenic process, cancer development and progression. MT expression has been implicated as a transient response to any form of stress or injury providing cytoprotective action. Although MT participates in the carcinogenic process, its use as a potential marker of tumor differentiation or cell proliferation, or as a predictor of poor prognosis remains unclear. In the present review the involvement of MT in defense mechanisms to toxicity and in carcinogenicity is discussed.

Apo-Metallothionein Emerging as a Major Player in the Cellular Activities of Metallothionein

Observations of apo-metallothlonein (apo-MT) have been made under a variety of physiologic circumstances, including zinc deficiency in cell culture and in rodents, cellular induction of MT by dexamethasone with concurrent Zn deficiency, a variety of tumors under normal Zn conditions, MT induction by Zn and Bi citrate, induction of hepatic MT after tumor cell Injection into nude mice, and overexpression of cardiac MT in MT transgenic mice. Experiments demonstrating both the lability of Zn and Cu bound to MT and the cellular stability of apo-MT are described to help rationalize the widespread presence of this metal-depleted species. Finally, comparative in vitro and cellular experiments examined the relative reactivity of Zn- and apo-MT with nitric oxide species, showing that apo-MT is much more reactive chemically and that in cells it may be a principal reactive species within the MT pool.

Regional Disruptions in Endothelial Nitric Oxide Pathway Associated With Bicuspid Aortic Valve

BACKGROUND

Endothelial nitric oxide (NO) synthase (eNOS) has been implicated in the development of bicuspid aortic valve (BAV) and with differential expression in the ascending aorta of BAV patients. However, little is known about functional disruptions in the eNOS pathway and the effect on BAV-associated aortic dilatation. We tested the hypothesis that eNOS function is regionally diminished in ascending thoracic aortic aneurysms associated with BAV.

METHODS

Thoracic aortic aneurysms specimens were collected from patients with BAV (n = 21) or tricuspid aortic valve (n = 12). Tissue samples were harvested from three circumferential regions corresponding to locations above the right, left, and noncoronary sinuses. Adventitial-stripped specimens containing media and intima only were analyzed for NO synthase 3 gene expression and total eNOS protein. Indicators of eNOS activity (pSer1177-eNOS) and NO bioavailability (phosphorylation of vasodilator-stimulated phosphoprotein at Ser239) were also measured.

RESULTS

NO synthase 3 and eNOS protein were elevated in the right aortic region of BAV specimens compared with tricuspid aortic valve specimens. Activation of eNOS, as indicated by pSer1177-eNOS, was higher in BAV specimens across all regions. Despite increases in eNOS and pSer1177-eNOS, BAV specimens displayed no change in pSer239-vasodilator-stimulated phosphoprotein compared with tricuspid aortic valve specimens.

CONCLUSIONS

BAV is associated with regional disruptions in the eNOS pathway, most markedly in the right aortic region. The discrepancy between increased eNOS activity and the absence of increased NO bioavailability in this region provides insight into physiologic mechanisms potentially underlying the asymmetric dilatation pattern observed in BAV.

Fluorescence detection of intracellular cadmium with Leadmium Green

Leadmium Green is a commercially available, small molecule, fluorescent probe advertised as a detector of free intracellular cadmium (Cd(2+)) and lead (Pb(2+)). Leadmium Green has been used in various paradigms, such as tracking Cd(2+) sequestration in plant cells, heavy metal export in protozoa, and Pb(2+) absorption by vascular endothelial cells. However very little information is available regarding its affinity and selectivity for Cd(2+), Pb(2+), and other metals. We evaluated the in vitro selectivity of Leadmium Green using spectrofluorimetry. Consistent with manufacturer's claims, Leadmium Green was sensitive to Cd(2+) (KD ~600 nM) and also Pb(2+) (KD ~9.0 nM) in a concentration-dependent manner, and furthermore proved insensitive to Ca(2+), Co(2+), Mn(2+) and Ni(2+). Leadmium Green also responded to Zn(2+) with a KD of ~82 nM. Using fluorescence microscopy, we evaluated Leadmium Green in live mouse hippocampal HT22 cells. We demonstrated that Leadmium Green detected ionophore-mediated acute elevations of Cd(2+) or Zn(2+) in a concentration-dependent manner. However, the maximum fluorescence produced by ionophore-delivered Zn(2+) was much less than that produced by Cd(2+). When tested in a model of oxidant-induced liberation of endogenous Zn(2+), Leadmium Green responded weakly. We conclude that Leadmium Green is an effective probe for monitoring intracellular Cd(2+), particularly in models where Cd(2+) accumulates rapidly, and when concomitant fluctuations of intracellular Zn(2+) are minimal.

Potential interactions of calcium-sensitive reagents with zinc ion in different cultured cells

Background

Several chemicals have been widely used to evaluate the involvement of free Ca²⁺ in mechanisms underlying a variety of biological responses for decades. Here, we report high reactivity to zinc of well-known Ca²⁺-sensitive reagents in diverse cultured cells.

Methodology/Principal Findings

In rat astrocytic C6 glioma cells loaded with the fluorescent Ca²⁺ dye Fluo-3, the addition of ZnCl₂ gradually increased the fluorescence intensity in a manner sensitive to the Ca²⁺ chelator EGTA irrespective of added CaCl₂. The addition of the Ca²⁺ ionophore A23187 drastically increased Fluo-3 fluorescence in the absence of ZnCl₂, while the addition of the Zn²⁺ ionophore pyrithione rapidly and additionally increased the fluorescence in the presence of ZnCl₂, but not in its absence. In cells loaded with the zinc dye FluoZin-3 along with Fluo-3, a similarly gradual increase was seen in the fluorescence of Fluo-3, but not of FluoZin-3, in the presence of both CaCl₂ and ZnCl₂. Further addition of pyrithione drastically increased the fluorescence intensity of both dyes, while the addition of the Zn²⁺ chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine (TPEN) rapidly and drastically decreased FluoZin-3 fluorescence. In cells loaded with FluoZin-3 alone, the addition of ZnCl₂ induced a gradual increase in the fluorescence in a fashion independent of added CaCl₂ but sensitive to EGTA. Significant inhibition was found in the vitality to reduce 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide in a manner sensitive to TPEN, EDTA and BAPTA in C6 glioma cells exposed to ZnCl₂, with pyrithione accelerating the inhibition. Similar inhibition occurred in an EGTA-sensitive fashion after brief exposure to ZnCl₂ in pluripotent P19 cells, neuronal Neuro2A cells and microglial BV2 cells, which all expressed mRNA for particular zinc transporters.

Conclusions/Significance

Taken together, comprehensive analysis is absolutely required for the demonstration of a variety of physiological and pathological responses mediated by Ca²⁺ in diverse cells enriched of Zn²⁺.

Nitric oxide is a ubiquitous signal for maintaining redox balance in plant cells: regulation of ascorbate peroxidase as a case study

Oxidative and nitrosative stresses and their respective antioxidant responses are common metabolic adjustments operating in all biological systems. These stresses result from an increase in reactive oxygen species (ROS) and reactive nitrogen species (RNS) and an imbalance in the antioxidant response. Plants respond to ROS and RNS accumulation by increasing the level of the antioxidant molecules glutathione and ascorbate and by activating specific antioxidant enzymes. Nitric oxide (NO) is a free radical considered to be toxic or protective depending on its concentration, combination with ROS compounds, and subcellular localization. In this review we focus on the mechanisms of NO action in combination with ROS on the regulation of the antioxidant system in plants. In particular, we describe the redox post-translational modifications of cytosolic ascorbate peroxidase and its influence on enzyme activity. The regulation of ascorbate peroxidase activity by NO as a redox sensor of acute oxidative stress or as part of a hormone-induced signalling pathway leading to lateral root development is presented and discussed.

Selectivity and specificity of small molecule fluorescent dyes/probes used for the detection of Zn2+ and Ca2+ in cells

Fluorescent dyes are widely used in the detection of labile (free or exchangeable) Zn(2+) and Ca(2+) in living cells. However, their specificity over other cations and selectivity for detection of labile vs. protein-bound metal in cells remains unclear. We characterized these important properties for commonly used Zn(2+) and Ca(2+) dyes in a cellular environment. By tracing the fluorescence emission signal along with UV-Vis and size exclusion chromatography-inductively coupled plasma mass spectrometry (SEC-ICP-MS) in tandem, we demonstrated that among the dyes used for Zn(2+), Zinpyr-1 fluoresces in the low molecular mass (LMM) region containing labile Zn(2+), but also fluoresces in different molecular mass regions where zinc ion is detected. However, FluoZin™-3 AM, Newport Green™ DCF and Zinquin ethyl ester display weak fluorescence, lack of metal specificity and respond strongly in the high molecular mass (HMM) region. Four Ca(2+) dyes were studied in an unperturbed cellular environment, and two of these were tested for binding behavior under an intracellular Ca(2+) release stimulus. A majority of Ca(2+) was in the labile form as tested by SEC-ICP-MS, but the fluorescence from Calcium Green-1™ AM, Oregon Green® 488 BAPTA-1, Fura red™ AM and Fluo-4 NW dyes in cells did not correspond to free Ca(2+) detection. Instead, the dyes showed non-specific fluorescence in the mid- and high-molecular mass regions containing Zn, Fe and Cu. Proteomic analysis of one of the commonly seen fluorescing regions showed the possibility for some dyes to recognize Zn and Cu bound to metallothionein 2. These studies indicate that Zn(2+) and Ca(2+) binding dyes manifest fluorescence responses that are not unique to recognition of labile metals and bind other metals, leading to suboptimal specificity and selectivity.

Zinc regulates iNOS-derived nitric oxide formation in endothelial cells

Aberrant production of nitric oxide (NO) by inducible NO synthase (iNOS) has been implicated in the pathogenesis of endothelial dysfunction and vascular disease. Mechanisms responsible for the fine-tuning of iNOS activity in inflammation are still not fully understood. Zinc is an important structural element of NOS enzymes and is known to inhibit its catalytical activity. In this study we aimed to investigate the effects of zinc on iNOS activity and expression in endothelial cells. We found that zinc down-regulated the expression of iNOS (mRNA+protein) and decreased cytokine-mediated activation of the iNOS promoter. Zinc-mediated regulation of iNOS expression was due to inhibition of NF-κB transactivation activity, as determined by a decrease in both NF-κB-driven luciferase reporter activity and expression of NF-κB target genes, including cyclooxygenase 2 and IL-1β. However, zinc did not affect NF-κB translocation into the nucleus, as assessed by Western blot analysis of nuclear and cytoplasmic fractions. Taken together our results demonstrate that zinc limits iNOS-derived high output NO production in endothelial cells by inhibiting NF-κB-dependent iNOS expression, pointing to a role of zinc as a regulator of iNOS activity in inflammation.

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Zinc inhibits iNOS-dependent nitrite accumulation in endothelial cells.

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Zinc decreases cytokine-induced iNOS expression in endothelial cells.

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Zinc inhibits iNOS promoter activity.

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NF-kB silencing abolishes cytokine-induced iNOS expression.

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Zinc inhibits the transactivation activity of NF-κB.

Nebivolol: a multifaceted antioxidant and cardioprotectant in hypertensive heart disease

Cardiomyocyte necrosis with attendant microscopic scarring is a pathological feature of human hypertensive heart disease (HHD). Understanding the pathophysiological origins of necrosis is integral to its prevention. In a rat model of HHD associated with aldosterone/salt treatment (ALDOST), myocyte necrosis is attributable to oxidative stress induced by cytosolic-free [Ca]i and mitochondrial [Ca]m overloading in which the rate of reactive oxygen species generation overwhelms their rate of detoxification by endogenous Zn-based antioxidant defenses. We hypothesized that nebivolol (Neb), unlike another β1 adrenergic receptor antagonist atenolol (Aten), would have a multifaceted antioxidant potential based on its dual property as a β3 receptor agonist, which activates endothelial nitric oxide synthase to stimulate nitric oxide (NO) generation. NO promotes the release of cytosolic Zn sequestered inactive by its binding protein, metallothionein. Given the reciprocal regulation between these cations, increased [Zn]i reduces Ca entry and attendant rise in [Ca]i and [Ca]m. Herein, we examined the antioxidant and cardioprotectant properties of Neb and Aten in rats receiving 4 weeks ALDOST. Compared with untreated age-/sex-matched controls, ALDOST alone or ALDOST with Aten, Neb cotreatment induced endothelial nitric oxide synthase activation, NO generation and a marked increase in [Zn]i with associated decline in [Ca]i and [Ca]m. Attendant antioxidant profile at subcellular and cellular levels included attenuation of mitochondrial H2O2 production and lipid peroxidation expressed as reduced 8-isoprostane concentrations in both mitochondria and cardiac tissue. Myocyte salvage was expressed as reduced microscopic scarring and tissue collagen volume fraction. Neb is a multifaceted antioxidant with unique properties as cardioprotectant in HHD.

Hemoglobin Control of Cell Survival/Death Decision Regulates in Vitro Plant Embryogenesis

Programmed cell death (PCD) in multicellular organisms is a vital process in growth, development, and stress responses that contributes to the formation of tissues and organs. Although numerous studies have defined the molecular participants in apoptotic and PCD cascades, successful identification of early master regulators that target specific cells to live or die is limited. Using Zea mays somatic embryogenesis as a model system, we report that the expressions of two plant hemoglobin (Hb) genes (ZmHb1 and ZmHb2) regulate the cell survival/death decision that influences somatic embryogenesis through their cell-specific localization patterns. Suppression of either of the two ZmHbs is sufficient to induce PCD through a pathway initiated by elevated NO and Zn²⁺ levels and mediated by production of reactive oxygen species. The effect of the death program on the fate of the developing embryos is dependent on the localization patterns of the two ZmHbs. During somatic embryogenesis, ZmHb2 transcripts are restricted to a few cells anchoring the embryos to the subtending embryogenic tissue, whereas ZmHb1 transcripts extend to several embryonic domains. Suppression of ZmHb2 induces PCD in the anchoring cells, allowing the embryos to develop further, whereas suppression of ZmHb1 results in massive PCD, leading to abortion. We conclude that regulation of the expression of these ZmHbs has the capability to determine the developmental fate of the embryogenic tissue during somatic embryogenesis through their effect on PCD. This unique regulation might have implications for development and differentiation in other species.

Nitric oxide-matrix metaloproteinase-9 interactions: biological and pharmacological significance--NO and MMP-9 interactions

Nitric oxide (NO) and matrix metalloproteinase 9 (MMP-9) levels are found to increase in inflammation states and in cancer, and their levels may be reciprocally modulated. Understanding interactions between NO and MMP-9 is of biological and pharmacological relevance and may prove crucial in designing new therapeutics. The reciprocal interaction between NO and MMP-9 have been studied for nearly twenty years but to our knowledge, are yet to be the subject of a review. This review provides a summary of published data regarding the complex and sometimes contradictory effects of NO on MMP-9. We also analyse molecular mechanisms modulating and mediating NO-MMP-9 interactions. Finally, a potential therapeutic relevance of these interactions is presented.

Proton-dependent zinc release from intracellular ligands

In cultured cortical and hippocampal neurons when intracellular pH drops from 6.6 to 6.1, yet unclear intracellular stores release micromolar amounts of Zn(2+) into the cytosol. Mitochondria, acidic organelles, and/or intracellular ligands could release this Zn(2+) . Although exposure to the protonophore FCCP precludes reloading of the mitochondria and acidic organelles with Zn(2+) , FCCP failed to compromise the ability of the intracellular stores to repeatedly release Zn(2+) . Therefore, Zn(2+) -releasing stores were not mitochondria or acidic organelles but rather intracellular Zn(2+) ligands. To test which ligands might be involved, the rate of acid-induced Zn(2+) release from complexes with cysteine, glutathione, histidine, aspartate, glutamate, glycine, and carnosine was investigated; [Zn(2+) ] was monitored in vitro using the ratiometric Zn(2+) -sensitive fluorescent probe FuraZin-1. Carnosine failed to chelate Zn(2+) but did chelate Cu(2+) ; the remaining ligands chelated Zn(2+) and upon acidification were releasing it into the medium. However, when pH was decreasing from 6.6 to 6.1, only zinc-cysteine complexes rapidly accelerated the rate of Zn(2+) release. The zinc-cysteine complexes also released Zn(2+) when a histidine-modifying agent, diethylpyrocarbonate, was applied at pH 7.2. Since the cytosolic zinc-cysteine complexes can contain micromolar amounts of Zn(2+) , these complexes may represent the stores responsible for an acid-induced intracellular Zn(2+) release. This study aimed at identifying intracellular stores which release Zn(2+) when pHi drops from 6.6 to 6.1. It was found that these stores are not mitochondria or acidic organelles, but rather intracellular Zn(2+) ligands. When the pH was decreasing from 6.6 to 6.1, only zinc-cysteine complexes showed a rapid acceleration in the rate of Zn(2+) release. Therefore, the stores responsible for an acid-induced intracellular Zn(2+) release in neurons may be the cytosolic zinc-cysteine complexes.

Zinc is released by cultured astrocytes as a gliotransmitter under hypoosmotic stress-loaded conditions and regulates microglial activity

AIM

Astrocytes contribute to the maintenance of brain homeostasis via the release of gliotransmitters such as ATP and glutamate. Here we examined whether zinc was released from astrocytes under stress-loaded conditions, and was involved in the regulation of microglial activity as a gliotransmitter.

MAIN METHODS

Hypoosmotic stress was loaded to astrocytes using balanced salt solution prepared to 214-314 mOsmol/L, and then intra- and extra-cellular zinc levels were assessed using Newport Green DCF diacetate (NG) and ICP-MS, respectively. Microglial activation by the astrocytic supernatant was assessed by their morphological changes and poly(ADP-ribose) (PAR) polymer accumulation.

KEY FINDINGS

Exposure of astrocytes to hypoosmotic buffer, increased the extracellular ATP level in osmolarity-dependent manners, indicating a load of hypoosmotic stress. In hypoosmotic stress-loaded astrocytes, there were apparent increases in the intra- and extra-cellular zinc levels. Incubation of microglia in the astrocytic conditioned medium transformed them into the activated "amoeboid" form and induced PAR formation. Administration of an extracellular zinc chelator, CaEDTA, to the astrocytic conditioned medium almost completely prevented the microglial activation. Treatment of astrocytes with an intracellular zinc chelator, TPEN, suppressed the hypoosmotic stress-increased intracellular, but not the extracellular, zinc level, and the increase in the intracellular zinc level was blocked partially by a nitric oxide synthase inhibitor, but not by CaEDTA, indicating that the mechanisms underlying the increases in the intra- and extra-cellular zinc levels might be different.

SIGNIFICANCE

These findings suggest that under hypoosmotic stress-loaded conditions, zinc is released from astrocytes and then plays a primary role in microglial activation as a gliotransmitter.

Gel-based methods in redox proteomics

BACKGROUND

The key to understanding the full significance of oxidants in health and disease is the development of tools and methods that allow the study of proteins that sense and transduce changes in cellular redox. Oxidant-reactive deprotonated thiols commonly operate as redox sensors in proteins and a variety of methods have been developed that allow us to monitor their oxidative modification.

SCOPE OF THE REVIEW

This outline review specifically focuses on gel-based methods used to detect, quantify and identify protein thiol oxidative modifications. The techniques we discuss fall into one of two broad categories. Firstly, methods that allow oxidation of thiols in specific proteins or the global cellular pool to be monitored are discussed. These typically utilise thiol-labelling reagents that add a reporter moiety (e.g. affinity tag, fluorophore, chromophore), in which loss of labelling signifies oxidation. Secondly, we outline methods that allow specific thiol oxidation states of proteins (e.g. S-sulfenylation, S-nitrosylation, S-thionylation and interprotein disulfide bond formation) to be investigated.

MAJOR CONCLUSIONS

A variety of different gel-based methods for identifying thiol proteins that are sensitive to oxidative modifications have been developed. These methods can aid the detection and quantification of thiol redox state, as well as identifying the sensor protein.

GENERAL SIGNIFICANCE

By understanding how cellular redox is sensed and transduced to a functional effect by protein thiol redox sensors, this will help us better appreciate the role of oxidants in health and disease. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

The role of metallothionein in oxidative stress

Free radicals are chemical particles containing one or more unpaired electrons, which may be part of the molecule. They cause the molecule to become highly reactive. The free radicals are also known to play a dual role in biological systems, as they can be either beneficial or harmful for living systems. It is clear that there are numerous mechanisms participating on the protection of a cell against free radicals. In this review, our attention is paid to metallothioneins (MTs) as small, cysteine-rich and heavy metal-binding proteins, which participate in an array of protective stress responses. The mechanism of the reaction of metallothioneins with oxidants and electrophilic compounds is discussed. Numerous reports indicate that MT protects cells from exposure to oxidants and electrophiles, which react readily with sulfhydryl groups. Moreover, MT plays a key role in regulation of zinc levels and distribution in the intracellular space. The connections between zinc, MT and cancer are highlighted.

Functional role of intracellular labile zinc in pulmonary endothelium

After iron, zinc is the most abundant essential trace metal. Intracellular zinc ([Zn]_i) is maintained across a wide range of cells and species in a tight quota (100 to 500 μM) by a dynamic process of transport, intracellular vesicular storage, and binding to a large number of proteins (estimated at 3-10% of human proteome). As such, zinc is an integral component of numerous metalloenzymes, structural proteins, and transcription factors. It is generally assumed that a vanishingly small component of [Zn]_i, referred to as free or labile zinc, and operationally defined as the pool sensitive to chelation (by agents such as N, N, N’, N’-tetrakis [2-pyridylmethyl] ethylenediamine [TPEN]) and capable of detection by a variety of chemical and genetic sensors, participates in signal transduction pathways. Zinc deficiencies, per se, can arise from acquired (malnutrition, alcoholism) or genetic (mutations in molecules affecting zinc homeostasis, the informative and first example being acrodermatitis enteropathica) factors or as a component of various diseases (e.g., sickle cell disease, cystic fibrosis, sepsis). Hypozincemia has profound effects on developing humans, and all facets of physiological function (neuronal, endocrine, immunological) are affected, although considerably less is known regarding cardiovascular pathophysiology. In this review, we provide an update on current knowledge of molecular and cellular aspects of zinc homeostasis and then focus on implications of zinc signaling in pulmonary endothelium as it relates to programmed cell death, altered contractility, and septic and aseptic injury to this segment of the lung.

Importance of nitric oxide in cadmium stress tolerance in crop plants

Cadmium (Cd(2+)) is a widespread heavy metal pollutant in the environment with a long biological half-life, originating mainly from industrial processes and phosphate fertilizers. It is easily taken up by plants, resulting in toxicity symptoms, such as chlorosis, wilting, growth reduction, and cell death. This cellular toxicity might result from interactions with vital metabolic pathways, carboxyl or thiol groups of proteins and reactive oxygen species (ROS) burst in plants. Plant exposure even to low concentrations of Cd may lead to cell death but the mechanism of its toxicity is still debatable. Therefore, exploring various ways to improve crop productivity and/or alleviate Cd stress effects is one of the major areas of concern. Nitric oxide (NO) is a hydrophobic gaseous molecule involved in various physiological processes such as germination, root growth, stomatal closure, control of the flowering timing etc. NO also functions as cell signaling molecule in plants and play important roles in the regulation of plant responses to both abiotic and biotic stress conditions. At the molecular level, NO signaling includes protein modification by binding to critical cysteine residues, heme or iron-sulfur centers and tyrosine residue nitration via peroxynitrite formation (ONOO(-)), mobilization of secondary messengers (Ca(2+), cyclic GMP and cyclic ADP-Rib) and modulation of protein kinase activities. Significant research had been done to understand the NO biosynthesis and signaling in plants under stress, but several questions still need to be answered. The present review is focused specifically on the importance of NO as Cd stress modulator in crop plants.

Metallothionein blocks oxidative DNA damage in vitro

The role of metallothionein (MT) in mitigation of oxidative DNA damage (ODD) induced by either cadmium (Cd) or the direct oxidant hydrogen peroxide (H(2)O(2)) was systematically examined using MT-I/II double knockout (MT-null) or MT-competent wild-type (WT) cells. Both toxicants were much more lethal to MT-null cells (Cd LC(50) = 6.6 μM; H(2)O(2) LC(50) = 550 μM) than to WT cells (Cd LC(50) = 16.5 μM; H(2)O(2) LC(50) = 930 μM). Cd induced concentration-related MT increases in WT cells, while the basal levels were undetectable and not increased by Cd in MT-null cells. ODD, measured by the immuno-spin trapping method, was minimally induced by sub-toxic Cd levels (1 or 5 μM; 24 h) in WT cells, but markedly increased in MT-null cells (>430 %). Similarly, ODD was induced to higher levels by lower concentrations of H(2)O(2) in MT-null cells than WT cells. Transfection of MT-I into MT-null cells reduced both Cd- and H(2)O(2)-induced cytolethality and ODD. Cd increased the expression of the oxidant defense genes, HO-1, and GSTa2 to a much greater extent in MT-null cells than in WT. Cd or H(2)O(2) exposure increased the expression of key transport genes, Mrp1 and Mrp2, in WT cells but not in MT-null cells. MT protects against Cd- and H(2)O(2)-induced ODD in MT-competent cells possibly by multiple mechanisms, potentially including direct metal ion sequestration and sequestration of oxidant radicals by MT. MT-deficient cells appear to adapt to Cd primarily by turning on oxidant response systems, while MT-competent cells activate MT and transport systems.

Lung tissues in patients with systemic sclerosis have gene expression patterns unique to pulmonary fibrosis and pulmonary hypertension

OBJECTIVE

Pulmonary complications, including pulmonary fibrosis (PF) and pulmonary arterial hypertension (PAH), are the leading cause of mortality in patients with systemic sclerosis (SSc). The aim of this study was to compare the molecular fingerprint of lung tissue and matching primary fibroblasts from patients with SSc with that of lung tissue and fibroblasts from normal donors, patients with idiopathic pulmonary fibrosis (IPF), and patients with idiopathic pulmonary arterial hypertension (IPAH).

METHODS

Lung tissue samples were obtained from 33 patients with SSc who underwent lung transplantation. Tissues and cells from a subgroup of SSc patients with predominantly PF or PAH were compared to those from normal donors, patients with IPF, and patients with IPAH. Microarray data were analyzed using efficiency analysis for determination of the optimal data-processing methods. Real-time polymerase chain reaction and immunohistochemistry were used to confirm differential levels of messenger RNA and protein, respectively.

RESULTS

Consensus efficiency analysis identified 242 and 335 genes that were differentially expressed in lungs and primary fibroblasts, respectively. SSc-PF and IPF lungs shared enriched functional groups in genes implicated in fibrosis, insulin-like growth factor signaling, and caveolin-mediated endocytosis. Gene functional groups shared by SSc-PAH and IPAH lungs included those involved in antigen presentation, chemokine activity, and interleukin-17 signaling.

CONCLUSION

Using microarray analysis on carefully phenotyped SSc and comparator lung tissues, we demonstrated distinct molecular profiles in tissues and fibroblasts from patients with SSc-associated lung disease compared to idiopathic forms of lung disease. Unique molecular signatures were generated that are disease specific (SSc) and phenotype specific (PF versus PAH). These signatures provide new insights into the pathogenesis and potential therapeutic targets of SSc-related lung disease.

Zinc and diabetic retinopathy

Zinc (Zn) is an important nutrient that is involved in various physiological metabolisms. Zn dyshomeostasis is often associated with various pathogeneses of chronic diseases, such as metabolic syndrome, diabetes, and related complications. Zn is present in ocular tissue in high concentrations, particularly in the retina and choroid. Zn deficiencies have been shown to affect ocular development, cataracts, age-related macular degeneration, and even diabetic retinopathy. However, the mechanism by which Zn deficiency increases the prevalence of diabetic retinopathy remains unclear. In addition, due to the negative effect of Zn deficiency on the eye, Zn supplementation should prevent diabetic retinopathy; however, limited available data do not always support this notion. Therefore, the goal of this paper was to summarize these pieces of available information regarding Zn prevention of diabetic retinopathy. Current theories and possible mechanisms underlying the role of Zn in the eye-related diseases are discussed. The possible factors that affect the preventive effect of Zn supplementation on diabetic retinopathy were also discussed.

Promotion of vesicular zinc efflux by ZIP13 and its implications for spondylocheiro dysplastic Ehlers-Danlos syndrome

Zinc is essential but potentially toxic, so intracellular zinc levels are tightly controlled. A key strategy used by many organisms to buffer cytosolic zinc is to store it within vesicles and organelles.It is yet unknown whether vesicular or organellar sites perform this function in mammals. Human ZIP13, a member of the Zrt/Irt-like protein (ZIP) metal transporter family, might provide an answer to this question. Mutations in the ZIP13 gene, SLC39A13, previously were found to cause the spondylocheiro dysplastic form of Ehlers–Danlos syndrome (SCD-EDS), a heritable connective tissue disorder.Those previous studies suggested that ZIP13 transports excess zinc out of the early secretory pathway and that zinc overload in the endoplasmic reticulum (ER) occurs in SCD-EDS patients. In contrast,this study indicates that ZIP13’s role is to release labile zinc from vesicular stores for use in the ER and other compartments. We propose that SCD-EDS is the result of vesicular zinc trapping and ER zinc deficiency rather than overload.

Metallothioneins and zinc in cancer diagnosis and therapy

Metallothioneins (MTs) are involved in protection against oxidative stress (OS) and toxic metals and they participate in zinc metabolism and its homeostasis. Disturbing of zinc homeostasis can lead to formation of reactive oxygen species, which can result in OS causing alterations in immunity, aging, and civilization diseases, but also in cancer development. It is not surprising that altered zinc metabolism and expression of MTs are of great interest in the case of studying of oncogenesis and cancer prognosis. The role of MTs and zinc in cancer development is tightly connected, and the structure and function of MTs are strongly dependent on Zn²⁺ redox state and its binding to proteins. Antiapoptic effects of MTs and their interactions with proteins nuclear factor kappa B, protein kinase C, esophageal cancer-related gene, and p53 as well as the role of MTs in their proliferation, immunomodulation, enzyme activation, and interaction with nitric oxide are reviewed. Utilization of MTs in cancer diagnosis and therapy is summarized and their importance for chemoresistance is also mentioned.

NO-β-catenin crosstalk modulates primitive streak formation prior to embryonic stem cell osteogenic differentiation

Nitric oxide (NO) has been shown to play a crucial role in bone formation in vivo. We sought to determine the temporal effect of NO on murine embryonic stem cells (ESCs) under culture conditions that promote osteogenesis. Expression profiles of NO pathway members and osteoblast-specific markers were analyzed using appropriate assays. We found that NO was supportive of osteogenesis specifically during an early phase of in vitro development (days 3-5). Furthermore, ESCs stably overexpressing the inducible NO synthase showed accelerated and enhanced osteogenesis in vitro and in bone explant cultures. To determine the role of NO in early lineage commitment, a stage in ESC differentiation equivalent to primitive streak formation in vivo, ESCs were transfected with a T-brachyury-GFP reporter. Expression levels of T-brachyury and one of its upstream regulators, β-catenin, the major effector in the canonical Wnt pathway, were responsive to NO levels in differentiating primitive streak-like cells. Our results indicate that NO may be involved in early differentiation through regulation of β-catenin and T-brachyury, controlling the specification of primitive-streak-like cells, which may continue through differentiation to later become osteoblasts.

A critical role for increased labile zinc in reducing sensitivity of cultured sheep pulmonary artery endothelial cells to LPS-induced apoptosis

We previously noted an important signaling role for decreased labile intracellular zinc ([ Zn ] (i)) in LPS-induced apoptosis in cultured sheep pulmonary artery endothelial cells (SPAEC) (Tang ZL, Wasserloos KJ, Liu X, Stitt MS, Reynolds IJ, Pitt BR, St Croix CM. Mol Cell Biochem 234-235: 211-217, 2002; Thambiayya K, Wasserloos KJ, Huang Z, Kagan VE, St Croix CM, Pitt BR. Am J Physiol Lung Cell Mol Physiol 300: L624-632, 2011). In the present study, we used small interfering RNA (siRNA) to important contributors of zinc homeostasis [ SLC39A14 or Zrt/Irt-like protein 14 (ZIP14), a zinc importer; metallothionein (MT), a zinc binding protein ] to define molecular pathways by which extracellular zinc or nitric oxide (NO) increase labile [ Zn ] (i) [ e.g., zinc-sensitive fluorophore (FluoZin-3) detectable and/or chelatable by N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine ] and reduce the sensitivity of SPAEC to LPS. Addition of 10 μM zinc to serum-free medium of SPAEC increased [ Zn ] (i) and abolished LPS-induced apoptosis (e.g., increased annexin V binding). The increase in [ Zn ] (i) and the protective effect of extracellular zinc were sensitive to reduction in ZIP14 expression (by siRNA), but not affected by collectively knocking down major isoforms of sheep MT (sMT-Ia, -Ib, -Ic, and -II). Pretreatment of wild-type SPAEC with 250 μM of the NO donor S-nitroso-N-acetylpenicillamine (SNAP) increased labile zinc in a relatively similar fashion to addition of extracellular zinc and reduced sensitivity of SPAEC to LPS-induced apoptosis (e.g., caspase-3/7 activation) in a N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine-sensitive fashion. The antiapoptotic effects of SNAP were insensitive to siRNA knockdown of ZIP14, but were abolished (along with SNAP-induced increase in [ Zn ] (i)) when SPAEC were pretreated with siRNA to sheep MT. Zinc was able to directly inhibit recombinant caspase-3 activity in an in vitro assay. Collectively, these data show that increases in labile [ Zn ] (i) are an important component of ZIP14- or NO-mediated resistance to LPS-induced apoptosis. Cytoprotection via ZIP14 appeared to be secondary to transcellular movement of extracellular zinc, whereas NO-mediated protection was secondary to S-nitrosation of MT and redistribution of [ Zn ] (i).