Resveratrol–zinc combination for prostate cancer management

Zinc, an essential trace element, plays a critical role in cell signaling, and defect(s) in zinc homeostasis may contribute to adverse physiological and pathological conditions, including cancer. Zinc is present in healthy prostate at a very high concentration, where it is required for important prostatic functions. However, zinc levels are significantly diminished in cancerous tissue, and intracellular zinc level is inversely correlated with prostate cancer progression. During neoplastic transformation, zinc-accumulating, citrate-producing normal prostate cells are metabolically transformed to citrate oxidizing cells that lose the ability to accumulate zinc. Interestingly, zinc has been shown to function as chemopreventive agent against prostate cancer, albeit at high doses, which may lead to many adverse effects. Therefore, novel means to enhance bioaccumulation of sufficient zinc in prostate cells via increasing zinc transport could be useful against prostate cancer. On the basis of available evidence, we present a possibility that the grape antioxidant resveratrol, when given with zinc, may lead to retuning the zinc homeostasis in prostate, thereby abolishing or reversing malignancy. If experimentally verified in in vivo model(s) of prostate cancer, such as transgenic mouse models, this may lead to novel means toward management of prostate cancer and other conditions with compromised zinc homeostasis.     

Metals on the move: zinc ions in cellular regulation and in the coordination dynamics of zinc proteins

Homeostatic control maintains essential transition metal ions at characteristic cellular concentrations to support their physiological functions and to avoid adverse effects. Zinc is especially widely used as a catalytic or structural cofactor in about 3000 human zinc proteins. In addition, the homeostatic control of zinc in eukaryotic cells permits functions of zinc(II) ions in regulation and in paracrine and intracrine signaling. Zinc ions are released from proteins through ligand-centered reactions in zinc/thiolate coordination environments, and from stores in cellular organelles, where zinc transporters participate in zinc loading and release. Muffling reactions allow zinc ions to serve as signaling ions (second messengers) in the cytosol that is buffered to picomolar zinc ion concentrations at steady-state. Muffling includes zinc ion binding to metallothioneins, cellular translocations of metallothioneins, delivery of zinc ions to transporter proteins, and zinc ion fluxes through cellular membranes with the result of removing the additional zinc ions from the cytosol and restoring the steady-state. Targets of regulatory zinc ions are proteins with sites for transient zinc binding, such as membrane receptors, enzymes, protein–protein interactions, and sensor proteins that control gene expression. The generation, transmission, targets, and termination of zinc ion signals involve proteins that use coordination dynamics in the inner and outer ligand spheres to control metal ion association and dissociation. These new findings establish critically important functions of zinc ions and zinc metalloproteins in cellular control.     

Interaction studies to evaluate 2- carboxyphenolate analogues as inhibitor of anti-apoptotic protein Bcl-2

Apoptosis is a cellular process that leads to the death of damaged cells. Its malfunction can cause cancer and poor response to conventional chemotherapy. After being activated by cellular stress signals, pro-apoptotic proteins bind anti-apoptotic proteins, thus allowing apoptosis to go forward. An excess of anti-apoptotic proteins can prevent apoptosis. Designed molecules that imitate the roles of pro-apoptotic proteins can promote the death of cancer cells. In this work we have applied an insilico approach to study the binding of 2-carboxyphenolate analogues as potent inhibitors of anti-apoptotic protein Bcl-2. Molecular docking study was performed in order to find specific binding mode using AutoDock. From the docking results it was observed that zinc 2- carboxyphenolate showed strong inhibition with Bcl-2 with docking energy of -4.6 kcal/mol. The effects of the Zinc 2- hydroxybenzoate on apoptosis in HT-1080 cell lines were also analysed, which shows strong evidence for their apoptotic mode of action using flow cytometric analysis of Annexin-V. Our study gave valuable insights on inhibitor specificity of anti-apoptotic proteins and might be considered as potent chemopreventive agents.     

锌转运蛋白基因研究进展

锌作为一种重要的微量元素参与了植物体内广泛的生理和生化过程,本文详细介绍了涉及Zn^2＋吸收转运的ZIP基因家族（ZRT／IRT相关蛋白）和CDF（Cation　diffusion　facilitator）家族。ZIP家族转运蛋白主要负责将Zn^2＋等二价阳离子跨膜转运进细胞内,以完成细胞内多种生理生化反应。CDF家族转运蛋白主要负责将过量Zn^2＋运出细胞,或者将细胞内过量Zn^2＋进行区室化隔离,降低Zn^2＋对细胞的危害作用。ZIP家族转运蛋白和CDF家族转运蛋白的相互协调使得Zn^2＋在细胞和有机体水平上维持着稳态,进而为细胞内各种生理生化反应的进行供一种保障机制。     

Effects of the Ca ionophore A23187 on zinc-induced apoptosis in C6 glioma cells

Zinc ions are essential, but at elevated concentrations, they also have toxic effects on mammalian cells. Zinc plays a crucial role in cell proliferation and differentiation and it even protects cells against apoptosis caused by various reagents. On the other hand, zinc at high concentrations causes cell death that was characterized as apoptotic by internucleosomal DNA fragmentation, formation of apoptotic bodies, and breakdown of the mitochondrial membrane potential. In the present work, a clone of rat C6 glioma cells that was resistant to toxic effects of ZnCl₂ up to 250 μM was employed to study the effect of the ionophore A23187 on zinc-induced apoptosis. Neither 150 μM Zn²⁺ nor 100 nM A23187 alone caused apoptosis as measured by internucleosomal DNA fragmentation. However, combined exposure of C6 cells to 100 nM A23187 and 150 μM Zn²⁺ for 48 h was effective in inducing apoptosis. Because the so-called calcium ionophore A23187 is not specific for Ca²⁺ ions but also transports Zn²⁺ with high selectivity over Ca²⁺, we investigated whether this substance promoted the uptake of Zn²⁺ ions into C6 cells. Employing the zinc-specific fluorescence probe Zinquin, we observed that the very low concentration of 1.9 nM A23187 significantly and rapidly raised the intracellular mobile Zn²⁺ content. Analysis by atomic absorption spectroscopy revealed that incubation with 1.9 nM A23187 caused a doubling of the total intracellular zinc level within 60 min. We conclude that the apoptosis evoked by the combined action of Zn²⁺ and A23187 was the result of enhanced Zn²⁺ influx evoked by the ionophore, resulting in higher intracellular zinc levels.     

Apoptosis may underlie the pathology of zinc-deficient skin

The trace element zinc is essential for the survival and function of all cells. Zinc deficiency, whether nutritional or genetic, is fatal if left untreated. The effects of zinc deficiency are particularly obvious in the skin, seen as an erythematous rash, scaly plaques, and ulcers. Electron microscopy reveals degenerative changes within keratinocytes. Despite the well-documented association between zinc deficiency and skin pathology, it is not clear which cellular processes are most sensitive to zinc deficiency and could account for the typical pathological features. We used the cultured HaCaT keratinocyte line to obtain insight into the cellular effects of zinc deficiency, as these cells show many characteristics of normal skin keratinocytes. Zinc deficiency was induced by growing cells in the presence of the zinc chelator, TPEN, or by growth in zinc-deficient medium. Growth of cells in zinc-deficient medium resulted in a 44% reduction of intracellular zinc levels and a 75% reduction in the activity of the zinc-dependent enzyme, 5'-nucleotidase, relative to the control cells. Over a period of 7 days of exposure to zinc-deficient conditions, no changes in cell viability and growth, or in the cytoskeletal and cell adhesion systems, were found in HaCaT cells. At 7 days, however, induction of apoptosis was indicated by the presence of DNA fragmentation and expression of active caspase-3 in cells. These results demonstrate that apoptosis is the earliest detectable cellular change induced by zinc deficiency in HaCaT keratinocytes. Our observations account for many of the features of zinc deficiency, including the presence of degenerate nuclei, chromatin aggregates and abnormal organization of keratin, that may represent the later stages of apoptosis. In summary, a major causal role for apoptosis in the pathology of zinc deficiency in the skin is proposed. This role is consistent with the previously unexplained diverse range of degenerative cellular changes seen at the ultrastructural level in zinc-deficient keratinocytes.     

Zinc-buffering capacity of a eukaryotic cell at physiological pZn

In spite of the paramount importance of zinc in biology, dynamic aspects of cellular zinc metabolism remain poorly defined at the molecular level. Investigations with human colon cancer (HT-29) cells establish a total cellular zinc concentration of 264 microM. Remarkably, about 10% of the potential high-affinity zinc-binding sites are not occupied by zinc, resulting in a surplus of 28 muM ligands (average Kd(c) = 83 pM) that ascertain cellular zinc-buffering capacity and maintain the "free" zinc concentration in proliferating cells at picomolar levels (784 pM, pZn = 9.1). This zinc-buffering capacity allows zinc to fluctuate only with relatively small amplitudes (DeltapZn = 0.3; below 1 nM) without significantly perturbing physiological pZn. Thus, the "free" zinc concentrations in resting and differentiated HT-29 cells are 614 pM and 1.25 nM, respectively. The calculation of these "free" zinc concentrations is based on measurements at different concentrations of the fluorogenic zinc-chelating agent and extrapolation to a zero concentration of the agent. It depends on the state of the cell, its buffering capacity, and the zinc dissociation constant of the chelating agent. Zinc induction of thionein (apometallothionein) ensures a surplus of unbound ligands, increases zinc-buffering capacity and the availability of zinc (DeltapZn = 0.8), but preserves the zinc-buffering capacity of the unoccupied high-affinity zinc-binding sites, perhaps for crucial physiological functions. Jointly, metallothionein and thionein function as the major zinc buffer under conditions of increased cellular zinc.     

Intracellular zinc during cell activation and zinc deficiency

IntroductionZinc is an essential trace element having manifold functions within living cells. Zinc deficiency but also zinc excess impairs cell-specific functions whereas a balanced zinc level is required for an adequate cell behavior.Material and methodsThis study deals with the impact of cellular priming due to stimulation with interleukin (IL)-1, IL-2, IL-4, IL-6 or the chemokine CXCL12a and its subsequent influence on the intracellular free zinc concentration. Since cellular priming and activation is essential for proper immunological reactions, and across that highly cell-type specific, we investigated T cells, B cells, and peripheral blood mononuclear cells (PBMCs). Additionally, alterations of the intracellular zinc content was investigated by inducing zinc deficiency using the zinc chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine (TPEN) with subsequent re-supplementation of zinc, hence generating an intracellular zinc flux. Evaluation of zinc staining with FluoZin3-AM, Zinpyr-1 and Zinquin was done by flow cytometry or by fluorescence microscopy.ResultsOur results indicate that cellular priming for different periods of time (10 minutes/one hour) causes decreased intracellular free zinc concentrations in the FluoZin3-AM staining and increased zinc concentrations stained with Zinpyr-1. Furthermore, zinc supplementation after induced zinc deficiency leads to a fast and excessive rise of the intracellular free zinc levels in most cellular compartments.ConclusionOur study emphasizes the importance of zinc homeostasis and zinc distribution during cellular priming and for certain signaling cascades especially in T and B cells. Moreover, we demonstrated that zinc re-supplementation of zinc deficient cells results in significantly elevated intracellular free zinc concentrations compared to untreated controls. Hence, this underlines the need of a balanced zinc homeostasis for proper immune cell function.     

The ion channel TRPM7 regulates zinc-depletion-induced MDMX degradation

Zinc deficiency has been linked to human diseases, including cancer. MDMX, a crucial zinc-containing negative regulator of p53, has been found to be amplified or overexpressed in various cancers and implicated in the cancer initiation and progression. We report here that zinc depletion by the ion chelator TPEN or Chelex resin results in MDMX protein degradation in a ubiquitination-independent and 20S proteasome-dependent manner. Restoration of zinc led to recovery of cellular levels of MDMX. Further, TPEN treatment inhibits growth of the MCF-7 breast cancer cell line, which is partially rescued by overexpression of MDMX. Moreover, in a mass-spectrometry-based proteomics analysis, we identified TRPM7, a zinc-permeable ion channel, as a novel MDMX-interacting protein. TRPM7 stabilizes and induces the appearance of faster migrating species of MDMX on SDS-PAGE. Depletion of TRPM7 attenuates, while TRPM7 overexpression facilitates, the recovery of MDMX levels upon adding back zinc to TPEN-treated cells. Importantly, we found that TRPM7 inhibition, like TPEN treatment, decreases breast cancer cell MCF-7 proliferation and migration. The inhibitory effect on cell migration upon TRPM7 inhibition is also partially rescued by overexpression of MDMX. Together, our data indicate that TRPM7 regulates cellular levels of MDMX in part by modulating the intracellular Zn²⁺ concentration to promote tumorigenesis.     

Mechanism and regulation of cellular zinc transport

Zinc is an essential cofactor for the activity and folding of up to ten percent of mammalian proteins and can modulate the function of many others. Because of the pleiotropic effects of zinc on every aspect of cell physiology, deficits of cellular zinc content, resulting from zinc deficiency or excessive rise in its cellular concentration, can have catastrophic consequences and are linked to major patho-physiologies including diabetes and stroke. Thus, the concentration of cellular zinc requires establishment of discrete, active cellular gradients. The cellular distribution of zinc into organelles is precisely managed to provide the zinc concentration required by each cell compartment. The complexity of zinc homeostasis is reflected by the surprisingly large variety and number of zinc homeostatic proteins found in virtually every cell compartment. Given their ubiquity and importance, it is surprising that many aspects of the function, regulation, and crosstalk by which zinc transporters operate are poorly understood. In this mini-review, we will focus on the mechanisms and players required for generating physiologically appropriate zinc gradients across the plasma membrane and vesicular compartments. We will also highlight some of the unsolved issues regarding their role in cellular zinc homeostasis.     

植物对重金属锌耐性机理的研究进展

Zn是植物必需的营养元素,同时也是一种常见的有毒重金属元素.由于长期的环境选择和适应进化,植物相应对Zn~(2+)产生了耐性,可减轻或避免Zn~(2+)的毒害.植物对锌耐性机制有:菌根和细胞膜对Zn~(2+)吸收的阻止和控制,其中控制Zn~(2+)的细胞膜跨膜转运器主要有(ZIP)类、阳离子扩散促进器(CDF)类和B-type ATPase (HMA)类;金属硫蛋白(MTs)、植物螯合素(PCs)和有机酸等Zn~(2+)螯合物质的体内螯合解毒;体内区室化分隔以及通过抗氧化系统和渗透调节物质的代谢调节等.本文从生理和分子水平上综述了植物对Zn~(2+)耐性机理的研究进展,并在此基础上提出目前存在的问题和今后研究的重点领域,为该领域的相关研究提供资料和借鉴.     

锌的生物学功能

人体所必需的微量元素锌,是生物体内约160多种酶的辅基,与生物的生长发育、各种抗性及免疫都有重要关系。本文综述了微量元素锌在生物体内对生物膜的稳定性和抗氧化作用、基因表达调控、细胞免疫、细胞凋亡及其对生物的毒性等生理生化功能。     

锌的生物学功能

人体所必需的微量元素锌,是生物体内约160多种酶的辅基,与生物的生长发育、各种抗性及免疫都有重要关系.本文综述了微量元素锌在生物体内对生物膜的稳定性和抗氧化作用、基因表达调控、细胞免疫、细胞凋亡及其对生物的毒性等生理生化功能.     

High levels of zinc ions induce loss of mitochondrial potential and degradation of antiapoptotic Bcl-2 protein in in vitro cultivated human prostate epithelial cells

Prostate epithelial cells contain the highest levels of zinc among all organs and tissues in the human body. Zinc is accumulated primarily in the mitochondria, where it is responsible for inhibition of mitochondrial aconitase activity, thereby increasing citrate production. The present study was designed to clarify the role of zinc for human prostate epithelial cell growth and apoptosis. Apoptosis of in vitro cultivated human prostate epithelial cells exposed to ZnCl(2) was analyzed by determination of phospholipid membrane asymmetry, nuclear fragmentation, DNA strand breaks, changes of mitochondrial potential and cellular pro/antiapoptotic proteins. Zinc induced apoptosis without involvement of p53 by decreasing mitochondrial transmembrane potential (DeltaPsi(m)) and Bcl-2 protein levels in proliferating epithelial cells. Thus, the high local concentrations of zinc ions in the prostatic lumen seem to be necessary to regulate proliferative activities and to enforce epithelial differentiation processes.