1
|
Yang L, Zhang Y, Wang F, Luo Z, Guo S, Strähle U. Toxicity of mercury: Molecular evidence. CHEMOSPHERE 2020; 245:125586. [PMID: 31881386 DOI: 10.1016/j.chemosphere.2019.125586] [Citation(s) in RCA: 173] [Impact Index Per Article: 43.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Revised: 11/28/2019] [Accepted: 12/08/2019] [Indexed: 05/25/2023]
Abstract
Minamata disease in Japan and the large-scale poisoning by methylmercury (MeHg) in Iraq caused wide public concerns about the risk emanating from mercury for human health. Nowadays, it is widely known that all forms of mercury induce toxic effects in mammals, and increasing evidence supports the concern that environmentally relevant levels of MeHg could impact normal biological functions in wildlife. The information of mechanism involved in mercurial toxicity is growing but knowledge gaps still exist between the adverse effects and mechanisms of action, especially at the molecular level. A body of data obtained from experimental studies on mechanisms of mercurial toxicity in vivo and in vitro points to that disruption of the antioxidant system may play an important role in the mercurial toxic effects. Moreover, the accumulating evidence indicates that signaling transduction, protein or/and enzyme activity, and gene regulation are involving in mediating toxic and adaptive response to mercury exposure. We conducted here a comprehensive review of mercurial toxic effects on wildlife and human, in particular synthesized key findings of molecular pathways involved in mercurial toxicity from the cells to human. We discuss the molecular evidence related mercurial toxicity to the adverse effects, with particular emphasis on the gene regulation. The further studies relying on Omic analysis connected to adverse effects and modes of action of mercury will aid in the evaluation and validation of causative relationship between health outcomes and gene expression.
Collapse
Affiliation(s)
- Lixin Yang
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, 100012, Beijing, China; Center for Global Health, School of Public Health, Nanjing Medical University, 211166, Nanjing, China.
| | - Yuanyuan Zhang
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, 100012, Beijing, China
| | - Feifei Wang
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, 100012, Beijing, China
| | - Zidie Luo
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, 100012, Beijing, China
| | - Shaojuan Guo
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, 100012, Beijing, China
| | - Uwe Strähle
- Toxicology and Genetics, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
| |
Collapse
|
2
|
Batista-Duharte A, Téllez-Martínez D, Aparecida Jellmayer J, Leandro Portuondo Fuentes D, Campos Polesi M, Martins Baviera A, Zeppone Carlos I. Repeated Exposition to Mercury (II) Chloride Enhances Susceptibility to S. schenckii sensu stricto Infection in Mice. J Fungi (Basel) 2018; 4:jof4020064. [PMID: 29799450 PMCID: PMC6023541 DOI: 10.3390/jof4020064] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Revised: 05/23/2018] [Accepted: 05/24/2018] [Indexed: 01/18/2023] Open
Abstract
Sporotrichosis is a subcutaneous mycosis that has re-emerged in several tropical and subtropical regions over the last decades. Growing findings suggest that the interplay of host, pathogen, and environment has a determinant effect on the diversity, local distribution, and virulence of Sporothrix schenckii sensu lato, the etiologic agent. Among the environmental factors, we have studied the potential role of repeated exposures to mercury (Hg), a known immunotoxic xenobiotic that is widely used in gold mining regions where sporotrichosis outbreaks are frequently reported. In this study, male Swiss mice received subcutaneous injections of either 300 or 1200 µg/kg of mercury (II) chloride (HgCl2) for 14 days, three times a week. A control group was injected with the vehicle Phosphate Buffered Saline (PBS). Treatment with HgCl2 impaired several immunologic parameters that are involved in host response to Sporothrix infection, such as the production of TNFα, IL-1, and nitric oxide by macrophages, and Th1/Th2/Th17 populations and their respective cytokines. The consequences of these effects on the host resistance to S. schenckii infection were subsequently evaluated. Hg-exposed mice exhibited a higher fungal load in the fungal inoculation site associated to systemic dissemination to spleen and liver on 14 days post-infection and a higher production of specific IgG1 and mild reduction of IgG2a. These findings suggest that repeated exposition to Hg enhances susceptibility to S. schenckii infection in mice and can be a factor associated to sporotrichosis outbreaks in endemic and highly Hg-polluted areas.
Collapse
Affiliation(s)
- Alexander Batista-Duharte
- Department of Clinical Analysis, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Rodovia Araraquara-Jaú km 1, Araraquara 14800-903, Brazil.
| | - Damiana Téllez-Martínez
- Department of Clinical Analysis, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Rodovia Araraquara-Jaú km 1, Araraquara 14800-903, Brazil.
| | - Juliana Aparecida Jellmayer
- Department of Clinical Analysis, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Rodovia Araraquara-Jaú km 1, Araraquara 14800-903, Brazil.
| | - Deivys Leandro Portuondo Fuentes
- Department of Clinical Analysis, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Rodovia Araraquara-Jaú km 1, Araraquara 14800-903, Brazil.
| | - Marisa Campos Polesi
- Department of Clinical Analysis, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Rodovia Araraquara-Jaú km 1, Araraquara 14800-903, Brazil.
| | - Amanda Martins Baviera
- Department of Clinical Analysis, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Rodovia Araraquara-Jaú km 1, Araraquara 14800-903, Brazil.
| | - Iracilda Zeppone Carlos
- Department of Clinical Analysis, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Rodovia Araraquara-Jaú km 1, Araraquara 14800-903, Brazil.
| |
Collapse
|
3
|
Miljković D, Spasojević I. Multiple sclerosis: molecular mechanisms and therapeutic opportunities. Antioxid Redox Signal 2013; 19:2286-334. [PMID: 23473637 PMCID: PMC3869544 DOI: 10.1089/ars.2012.5068] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/04/2012] [Revised: 02/09/2012] [Accepted: 03/09/2013] [Indexed: 12/15/2022]
Abstract
The pathophysiology of multiple sclerosis (MS) involves several components: redox, inflammatory/autoimmune, vascular, and neurodegenerative. All of them are supported by the intertwined lines of evidence, and none of them should be written off. However, the exact mechanisms of MS initiation, its development, and progression are still elusive, despite the impressive pace by which the data on MS are accumulating. In this review, we will try to integrate the current facts and concepts, focusing on the role of redox changes and various reactive species in MS. Knowing the schedule of initial changes in pathogenic factors and the key turning points, as well as understanding the redox processes involved in MS pathogenesis is the way to enable MS prevention, early treatment, and the development of therapies that target specific pathophysiological components of the heterogeneous mechanisms of MS, which could alleviate the symptoms and hopefully stop MS. Pertinent to this, we will outline (i) redox processes involved in MS initiation; (ii) the role of reactive species in inflammation; (iii) prooxidative changes responsible for neurodegeneration; and (iv) the potential of antioxidative therapy.
Collapse
Affiliation(s)
- Djordje Miljković
- Department of Immunology, Institute for Biological Research “Siniša Stanković,” University of Belgrade, Belgrade, Serbia
| | - Ivan Spasojević
- Life Sciences Department, Institute for Multidisciplinary Research, University of Belgrade, Belgrade, Serbia
| |
Collapse
|
4
|
Silver(I), mercury(II), cadmium(II), and zinc(II) target exposed enzymic iron-sulfur clusters when they toxify Escherichia coli. Appl Environ Microbiol 2012; 78:3614-21. [PMID: 22344668 DOI: 10.1128/aem.07368-11] [Citation(s) in RCA: 187] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The toxicity of soft metals is of broad interest to microbiologists, both because such metals influence the community structures in natural environments and because several metals are used as antimicrobial agents. Their potency roughly parallels their thiophilicity, suggesting that their primary biological targets are likely to be enzymes that contain key sulfhydryl moieties. A recent study determined that copper poisons Escherichia coli in part by attacking the exposed [4Fe-4S] clusters of dehydratases. The present investigation sought to test whether other soft metals also target these enzymes. In vitro experiments revealed that low-micromolar concentrations of Ag(I) and Hg(II) directly inactivated purified fumarase A, a member of the dehydratase family. The enzyme was also poisoned by higher levels of Cd(II) and Zn(II), but it was unaffected by even millimolar concentrations of Mn(II), Co(II), Ni(II), and Pb(II). Electron paramagnetic resonance analysis and measurements of released iron confirmed that damage was associated with destruction of the [4Fe-4S] cluster, and indeed, the reconstruction of the cluster fully restored activity. Growth studies were then performed to test whether dehydratase damage might underlie toxicity in vivo. Barely toxic doses of Ag(I), Hg(II), Cd(II), and Zn(II) inactivated all tested members of the [4Fe-4S] dehydratase family. Again, activity was recovered when the clusters were rebuilt. The metals did not diminish the activities of other sampled enzymes, including NADH dehydrogenase I, an iron-sulfur protein whose clusters are shielded by polypeptide. Thus, the data indicate that dehydratases are damaged by the concentrations of metals that initiate bacteriostasis.
Collapse
|
5
|
Park HJ, Youn HS. Mercury induces the expression of cyclooxygenase-2 and inducible nitric oxide synthase. Toxicol Ind Health 2011; 29:169-74. [DOI: 10.1177/0748233711427048] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Nuclear factor-κB (NF-κB) is a transcription factor that mediates the inducible expression of a variety of genes involved in immune and inflammatory responses. NF-κB activation induces numerous proinflammatory gene products including cytokines, cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS). The divalent heavy metal mercury has been used for thousands of years. Although mercury is clearly toxic to most mammalian organ systems, especially the immune system, exposure has still increased in some areas of the world. However, the underlying toxic mechanism is not clearly identified. Here, we report biochemical evidence that mercury alone induces NF-κB activation, resulting in the induced expression of COX-2 and iNOS. The results suggest that mercury can induce inflammatory diseases by lowering host defense.
Collapse
Affiliation(s)
- Hye-Jeong Park
- Department of Biomedical Laboratory Science, College of Medical Sciences, Soonchunhyang University, Asan-Si, Chungnam, Korea
| | - Hyung-Sun Youn
- Department of Biomedical Laboratory Science, College of Medical Sciences, Soonchunhyang University, Asan-Si, Chungnam, Korea
| |
Collapse
|
6
|
Stacchiotti A, Li Volti G, Lavazza A, Rezzani R, Rodella LF. Schisandrin B stimulates a cytoprotective response in rat liver exposed to mercuric chloride. Food Chem Toxicol 2009; 47:2834-40. [DOI: 10.1016/j.fct.2009.09.003] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2009] [Revised: 08/21/2009] [Accepted: 09/03/2009] [Indexed: 11/29/2022]
|
7
|
A new coordination mode for tris(2-carboxyethyl)phosphine: Synthesis, crystal structure and characterization of the mixed-valence Co(III)/Co(II)/Co(III) complex [Co{P(CH2CH2COO)2(CH2CH2COOH)}2]2[Co(H2O)4][Na2(H2O)4]Cl2·6H2O. Polyhedron 2008. [DOI: 10.1016/j.poly.2008.02.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
8
|
Mori K, Yoshida K, Nakagawa Y, Hoshikawa S, Ozaki H, Ito S, Watanabe C. Methylmercury inhibition of type II 5'-deiodinase activity resulting in a decrease in growth hormone production in GH3 cells. Toxicology 2007; 237:203-209. [PMID: 17582671 DOI: 10.1016/j.tox.2007.05.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2007] [Revised: 05/11/2007] [Accepted: 05/14/2007] [Indexed: 11/22/2022]
Abstract
We have recently reported that methylmercury (MeHg) inhibits type II iodothyronine 5'-deiodinase (D2) activity in mouse neuroblastoma NB41A3 cells. In the present study, we determined the biological significance of D2 inhibition by MeHg. GH3 rat pituitary tumor cells were treated with MeHg and D2 activity and production of a thyroid hormone-responsive gene product, growth hormone (GH) were analyzed. MeHg inhibited D2 activity and decreased thyroxine (T4)-induced, but not 3,3',5-triiodothyronine (T3)-induced GH secretion in GH3 cells. Our results suggest that MeHg inhibition of D2 activity might be involved in the inhibition of GH production in GH3 cells. Thus, D2 inhibition could be a novel mechanism involved in MeHg toxicity.
Collapse
Affiliation(s)
- Kouki Mori
- Division of Nephrology, Endocrinology and Vascular Medicine, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan.
| | - Katsumi Yoshida
- Department of Medical Technology, Tohoku University School of Health Sciences, 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan.
| | - Yoshinori Nakagawa
- Division of Nephrology, Endocrinology and Vascular Medicine, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan.
| | - Saeko Hoshikawa
- Division of Nephrology, Endocrinology and Vascular Medicine, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan.
| | - Hiroshi Ozaki
- Division of Nephrology, Endocrinology and Vascular Medicine, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan.
| | - Sadayoshi Ito
- Division of Nephrology, Endocrinology and Vascular Medicine, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan.
| | - Chiho Watanabe
- Department of Human Ecology, Graduate School of Medical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
| |
Collapse
|
9
|
Fonfría E, Vilaró MT, Babot Z, Rodríguez-Farré E, Suñol C. Mercury compounds disrupt neuronal glutamate transport in cultured mouse cerebellar granule cells. J Neurosci Res 2005; 79:545-53. [PMID: 15635608 DOI: 10.1002/jnr.20375] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Cerebellar granule cells are targeted selectively by mercury compounds in vivo. Despite the affinity of mercury for thiol groups present in all cells, the molecular determinant(s) of selective cerebellar degeneration remain to be elucidated fully. We studied the effect of mercury compounds on neuronal glutamate transport in primary cultures of mouse cerebellar granule cells. Immunoblots probed with an antibody against the excitatory amino acid transporter (EAAT) neuronal glutamate transporter, EAAT3, revealed the presence of a specific band in control and mercury-treated cultures. Micromolar concentrations of both methylmercury and mercuric chloride increased the release of endogenous glutamate, inhibited glutamate uptake, reduced mitochondrial activity, and decreased ATP levels. All these effects were completely prevented by the nonpermeant reducing agent Tris-(2-carboxyethyl)phosphine (TCEP). Reduction of mitochondrial activity by mercuric chloride, but not by methylmercury, was inhibited significantly by 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS) and by reduced extracellular Cl- ion concentration. In addition, DIDS and low extracellular Cl- completely inhibited the release of glutamate induced by mercuric chloride, and produced a partial although significant reduction of that induced by methylmercury. We suggest that a direct inhibition of glutamate uptake triggers an imbalance in cell homeostasis, leading to neuronal failure and Cl(-)-regulated cellular glutamate efflux. Our results demonstrate that neuronal glutamate transport is a novel target to be taken into account when assessing mercury-induced neurotoxicity.
Collapse
Affiliation(s)
- Elena Fonfría
- Department of Neurochemistry, Institut d'Investigacions Biomèdiques de Barcelona, Consejo Superior de Investigaciones Científicas, CSIC-IDIBAPS, Barcelona, Spain
| | | | | | | | | |
Collapse
|
10
|
Colombo M, Hamelin C, Kouassi E, Fournier M, Bernier J. Differential effects of mercury, lead, and cadmium on IL-2 production by Jurkat T cells. Clin Immunol 2004; 111:311-22. [PMID: 15183152 DOI: 10.1016/j.clim.2004.02.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2003] [Accepted: 02/17/2004] [Indexed: 10/26/2022]
Abstract
Mercury, lead, and cadmium are widespread and highly toxic pollutants. The aim of this study was to determine the effects of sublethal doses of CH(3)HgCl, CdCl(2), and PbCl(2) on IL-2 production by T lymphocytes. Jurkat T cells were stimulated by triggering CD3 and CD28 molecules before, in conjunction with, or following heavy metal exposure. Heavy metals, individually or mixed together at equimolar concentrations, were used. Results demonstrated that low, noncytotoxic doses of metals induce tyrosine phosphorylation. Mercury and lead (1 microM) inhibit IL-2 production regardless of the state of T cell activation. Cadmium stimulated IL-2 production only in preactivated T cells. Surprisingly, a mixture of these three metals had no effect. We subsequently determined the effects of heavy metals on NFAT (nuclear factors of activated T cells) activity. When cells were stimulated by potent stimulation involving the CD3 and CD28 molecules, an increased NFAT activation was noted when the cells were exposed to mercury and to the metal mixture. Activation with PMA/calcium ionophores indicated that the target of heavy metals is located downstream from PKC and calcium mobilization. These results suggest that the state and mode of T cell activation are important parameters to consider in heavy metal toxicity.
Collapse
Affiliation(s)
- Myrian Colombo
- Centre de recherche en santé humaine, INRS-Institut Armand Frappier, Université du Québec, Pointe-Claire, QC, Canada
| | | | | | | | | |
Collapse
|
11
|
Kim SH, Johnson VJ, Sharma RP. Mercury inhibits nitric oxide production but activates proinflammatory cytokine expression in murine macrophage: differential modulation of NF-kappaB and p38 MAPK signaling pathways. Nitric Oxide 2002; 7:67-74. [PMID: 12175822 DOI: 10.1016/s1089-8603(02)00008-3] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Mercury is well known to adversely affect the immune system; however, little is known regarding its molecular mechanisms. Macrophages are major producers of nitric oxide (NO) and this signaling molecule is important in the regulation of immune responses. The present study was designed to determine the impact of mercury on NO and cytokine production and to investigate the signaling pathways involved. The murine macrophage cell line J774A.1 was used to study the effects of low-dose inorganic mercury on the production of NO and proinflammatory cytokines. Cells were treated with mercury in the presence or absence of lipopolysaccharide (LPS). Mercury (5-20 microM) dose-dependently decreased the production of NO in LPS-stimulated cells. Concomitant decreases in the expression of inducible nitric oxide synthase (iNOS) mRNA and protein were detected. Treatment of J774A.1 cells with mercury alone did not affect the production of NO nor the expression of iNOS mRNA or protein. Interestingly, mercury alone stimulated the expression of tumor necrosis factor alpha (TNFalpha), and increased LPS-induced TNFalpha and interleukin-6 mRNA expression. Mercury inhibited LPS-induced nuclear translocation of nuclear factor kappaB (NF-kappaB) but had no effect alone. In contrast, mercury activated p38 mitogen-activated protein kinase (p38 MAPK) and additively increased LPS-induced p38 MAPK phosphorylation. These results indicate that mercury suppresses NO synthesis by inhibition of the NF-kappaB pathway and modulates cytokine expression by p38 MAPK activation in J774A.1 macrophage cells.
Collapse
Affiliation(s)
- Sang Hyun Kim
- Department of Physiology and Pharmacology, Interdisciplinary Program of Toxicology, The University of Georgia, Athens, GA 30602-7389, USA
| | | | | |
Collapse
|
12
|
Dieguez-Acuña FJ, Ellis ME, Kushleika J, Woods JS. Mercuric ion attenuates nuclear factor-kappaB activation and DNA binding in normal rat kidney epithelial cells: implications for mercury-induced nephrotoxicity. Toxicol Appl Pharmacol 2001; 173:176-87. [PMID: 11437639 DOI: 10.1006/taap.2001.9195] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mercuric ion (Hg(2+)), one of the strongest thiol-binding agents known, mediates the toxicity associated with elemental, inorganic, and organic mercurial compounds. Studies of cellular events associated with Hg(2+) toxicity have focused largely on disruption of cell membranes and impairment of mitochondrial functions. In contrast, few studies have sought to define the specific molecular mechanisms through which Hg(2+) might affect toxicity via alteration of thiol-dependent signal transduction pathways that regulate cell proliferation and survival. Of particular interest in this regard is the effect of Hg(2+) on nuclear factor-kappaB (NF-kappaB), a pleiotropic transcriptional factor that is known to require reduced cysteine moieties at critical steps of activation and DNA binding. Here, we evaluated the effects of Hg(2+) on the expression of NF-kappaB in normal rat kidney epithelial (NRK52E) cells, a principal target of Hg(2+) toxicity. The lipopolysaccharide (LPS)-inducible form of NF-kappaB was readily detected in kidney cells and has been characterized as the p50p65 heterodimer. NF-kappaB-DNA binding was prevented in a dose-related manner by Hg(2+) (0-55 microM) in vitro when added to DNA binding reactions containing the nonthiol reducing agent Tris(2-carboxyethyl)phosphine hydrochloride (TCEP). Similarly, Hg(2+) at the same concentrations prevented DNA binding of a human recombinant wild-type p50p50 homodimer in binding reactions, and this effect was attenuated using a mutant form of the p50 protein containing a cys(62)-->ser(62) mutation. The inhibition of p50-DNA binding by Hg(2+) was reversible in a dose-related manner in vitro by competitive thiols DTT, GSH, and l-cysteine in binding reactions. In contrast, competitive thiols added to nuclear binding reactions were unable to reverse attenuation of LPS-mediated NF-kappaB-DNA binding affinity when cells were pretreated in vivo with Hg(2+) at concentrations as low as 2 microM prior to LPS administration. Immunoblot analyses indicted that Hg(2+) pretreatment of kidney cells substantially diminished, in a dose-related manner, the concentration of p65 translocated into the nucleus following LPS administration. Additionally, Hg(2+) pretreatment impaired both the phosphorylation and degradation of IkappaBalpha, suggesting a specific effect on NF-kappaB activation at the level of IkappaBalpha proteolysis. Finally, Hg(2+) at concentrations as low as 5 microM significantly diminished NF-kappaB-mediated transcriptional activity when administered to kidney cells transiently transfected with an NF-kappaB-driven luciferase reporter gene (pLuc-4xNF-kappaB) prior to LPS treatment. These findings demonstrate that Hg(2+), at low cellular concentrations, attenuates NF-kappaB activation at sites associated with IkappaBalpha phosphorylation and degradation, nuclear translocation of the p50p65 heterodimer, and association of p50-cys(62) with the DNA kappaB binding site. Attenuation of NF-kappaB activation by Hg(2+) through these mechanisms may underlie apoptotic or other cytotoxic responses that are known to be associated with low level Hg(2+) exposure in kidney epithelial cells.
Collapse
Affiliation(s)
- F J Dieguez-Acuña
- Center for Ecogenetics and Environmental Health, University of Washington, Seattle, Washington, 98105, USA
| | | | | | | |
Collapse
|