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Xu X, Duan L, Yu J, Su C, Li J, Chen D, Zhang X, Song H, Pan Y. Characterization analysis and heavy metal-binding properties of CsMTL3 in Escherichia coli. FEBS Open Bio 2018; 8:1820-1829. [PMID: 30410861 PMCID: PMC6212650 DOI: 10.1002/2211-5463.12520] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Revised: 08/16/2018] [Accepted: 08/29/2018] [Indexed: 11/30/2022] Open
Abstract
Members of the metallothionein (MT) superfamily are involved in coordinating transition metal ions. In plants, MT family members are characterized by their arrangement of Cys residues. In this study, one member of the MT superfamily, CsMTL3, was characterized from a complementary DNA (cDNA) library from young cucumber fruit; CsMTL3 is predicted to encode a 64 amino acid protein with a predicted molecular mass of 6.751 kDa. Phylogenetic analysis identified it as a type 3 family member as the arrangement of N-terminal Cys residues was different from that of MT-like 2. Heterologous expression of CsMTL3 in Escherichia coli improved their heavy metal tolerance, particularly to Cd2+ and Cu2+, and led to increased uptake of Cd2+ and Cu2+; increased uptake was also observed for cells expressing Arabidopsis thaliana metallothionein 3 (AtMT3) and phytochelatin-like (PCL), with greatest uptake in PCL-expressing cells. These findings demonstrate that CsMTL3 can improve metal tolerance, especially for Cd2+ ions, when heterologously expressed in E. coli, and suggest that the composition and arrangement of N-terminal Cys residues are associated with binding capacity and preference for different metal ions.
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Affiliation(s)
- Xing Xu
- Key Laboratory of Horticulture Science for Southern Mountainous RegionsMinistry of EducationSouthwest UniversityChongqingChina
- College of Horticulture and Landscape ArchitectureSouthwest UniversityChongqingChina
| | - Ling Duan
- Key Laboratory of Horticulture Science for Southern Mountainous RegionsMinistry of EducationSouthwest UniversityChongqingChina
- College of Horticulture and Landscape ArchitectureSouthwest UniversityChongqingChina
| | - Jingwen Yu
- Key Laboratory of Horticulture Science for Southern Mountainous RegionsMinistry of EducationSouthwest UniversityChongqingChina
- College of Horticulture and Landscape ArchitectureSouthwest UniversityChongqingChina
| | - Chenggang Su
- Key Laboratory of Horticulture Science for Southern Mountainous RegionsMinistry of EducationSouthwest UniversityChongqingChina
- College of Horticulture and Landscape ArchitectureSouthwest UniversityChongqingChina
| | - Jinhua Li
- Key Laboratory of Horticulture Science for Southern Mountainous RegionsMinistry of EducationSouthwest UniversityChongqingChina
- College of Horticulture and Landscape ArchitectureSouthwest UniversityChongqingChina
| | - Dan Chen
- Comprehensive Testing Center of Guangzhou Entry‐Exit Inspection & Quarantine BureauGuangzhouChina
| | - Xingguo Zhang
- Key Laboratory of Horticulture Science for Southern Mountainous RegionsMinistry of EducationSouthwest UniversityChongqingChina
- College of Horticulture and Landscape ArchitectureSouthwest UniversityChongqingChina
| | - Hongyuan Song
- Key Laboratory of Horticulture Science for Southern Mountainous RegionsMinistry of EducationSouthwest UniversityChongqingChina
- College of Horticulture and Landscape ArchitectureSouthwest UniversityChongqingChina
| | - Yu Pan
- Key Laboratory of Horticulture Science for Southern Mountainous RegionsMinistry of EducationSouthwest UniversityChongqingChina
- College of Horticulture and Landscape ArchitectureSouthwest UniversityChongqingChina
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Nielsen AE, Bohr A, Penkowa M. The Balance between Life and Death of Cells: Roles of Metallothioneins. Biomark Insights 2017. [DOI: 10.1177/117727190600100016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Metallothionein (MT) is a highly conserved, low-molecular-weight, cysteine-rich protein that occurs in 4 isoforms (MT-I to MT-IV), of which MT-I+II are the major and best characterized proteins. This review will focus on mammalian MT-I+II and their functional impact upon cellular survival and death, as seen in two rather contrasting pathological conditions: Neurodegeneration and neoplasms. MT-I+II have analogous functions including: 1) Antioxidant scavenging of reactive oxygen species (ROS); 2) Cytoprotection against degeneration and apoptosis; 3) Stimulation of cell growth and repair including angiogenesis/revascularization, activation of stem/progenitor cells, and neuroregeneration. Thereby, MT-I+II mediate neuroprotection, CNS restoration and clinical recovery during neurodegenerative disorders. Due to the promotion of cell survival, increased MT-I+II levels have been associated with poor tumor prognosis, although the data are less clear and direct causative roles of MT-I+II in oncogenesis remain to be identified. The MT-I+II molecular mechanisms of actions are not fully elucidated. However, their role in metal ion homeostasis might be fundamental in controlling Zn-dependent transcription factors, protein synthesis, cellular energy levels/metabolism and cell redox state. Here, the neuroprotective and regenerative functions of MT-I+II are reviewed, and the presumed link to oncogenesis is critically perused.
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Affiliation(s)
- Allan Evald Nielsen
- Section of Neuroprotection, Centre of Inflammation and Metabolism
- The Panum Institute, Faculty of Health Sciences, University of Copenhagen, Denmark
| | - Adam Bohr
- Section of Neuroprotection, Centre of Inflammation and Metabolism
- The Panum Institute, Faculty of Health Sciences, University of Copenhagen, Denmark
| | - Milena Penkowa
- Section of Neuroprotection, Centre of Inflammation and Metabolism
- The Panum Institute, Faculty of Health Sciences, University of Copenhagen, Denmark
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Ruttkay-Nedecky B, Nejdl L, Gumulec J, Zitka O, Masarik M, Eckschlager T, Stiborova M, Adam V, Kizek R. The role of metallothionein in oxidative stress. Int J Mol Sci 2013; 14:6044-66. [PMID: 23502468 PMCID: PMC3634463 DOI: 10.3390/ijms14036044] [Citation(s) in RCA: 497] [Impact Index Per Article: 45.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Revised: 02/14/2013] [Accepted: 02/20/2013] [Indexed: 12/15/2022] Open
Abstract
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.
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Affiliation(s)
- Branislav Ruttkay-Nedecky
- Central European Institute of Technology, Brno University of Technology, Technicka 3058/10, CZ-616 00 Brno, Czech Republic; E-Mails: (B.R.-N.); (L.N.); (J.G.); (O.Z.); (M.M.); (V.A.)
| | - Lukas Nejdl
- Department of Chemistry and Biochemistry, Faculty of Agronomy, Mendel University in Brno, Zemedelska 1, CZ-613 00 Brno, Czech Republic
| | - Jaromir Gumulec
- Central European Institute of Technology, Brno University of Technology, Technicka 3058/10, CZ-616 00 Brno, Czech Republic; E-Mails: (B.R.-N.); (L.N.); (J.G.); (O.Z.); (M.M.); (V.A.)
- Department of Pathological Physiology, Faculty of Medicine, Masaryk University, Kamenice 5, CZ-612 00 Brno, Czech Republic
| | - Ondrej Zitka
- Central European Institute of Technology, Brno University of Technology, Technicka 3058/10, CZ-616 00 Brno, Czech Republic; E-Mails: (B.R.-N.); (L.N.); (J.G.); (O.Z.); (M.M.); (V.A.)
- Department of Chemistry and Biochemistry, Faculty of Agronomy, Mendel University in Brno, Zemedelska 1, CZ-613 00 Brno, Czech Republic
| | - Michal Masarik
- Central European Institute of Technology, Brno University of Technology, Technicka 3058/10, CZ-616 00 Brno, Czech Republic; E-Mails: (B.R.-N.); (L.N.); (J.G.); (O.Z.); (M.M.); (V.A.)
- Department of Pathological Physiology, Faculty of Medicine, Masaryk University, Kamenice 5, CZ-612 00 Brno, Czech Republic
| | - Tomas Eckschlager
- Department of Paediatric Haematology and Oncology, 2nd Faculty of Medicine, Charles University and University Hospital Motol, V Uvalu 84, CZ-150 06 Prague 5, Czech Republic; E-Mail:
| | - Marie Stiborova
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, CZ-128 40 Prague 2, Czech Republic; E-Mail:
| | - Vojtech Adam
- Central European Institute of Technology, Brno University of Technology, Technicka 3058/10, CZ-616 00 Brno, Czech Republic; E-Mails: (B.R.-N.); (L.N.); (J.G.); (O.Z.); (M.M.); (V.A.)
- Department of Chemistry and Biochemistry, Faculty of Agronomy, Mendel University in Brno, Zemedelska 1, CZ-613 00 Brno, Czech Republic
| | - Rene Kizek
- Central European Institute of Technology, Brno University of Technology, Technicka 3058/10, CZ-616 00 Brno, Czech Republic; E-Mails: (B.R.-N.); (L.N.); (J.G.); (O.Z.); (M.M.); (V.A.)
- Department of Chemistry and Biochemistry, Faculty of Agronomy, Mendel University in Brno, Zemedelska 1, CZ-613 00 Brno, Czech Republic
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Shibuya K, Suzuki JS, Kito H, Naganuma A, Tohyama C, Satoh M. Protective role of metallothionein in bone marrow injury caused by X-irradiation. J Toxicol Sci 2009; 33:479-84. [PMID: 18827447 DOI: 10.2131/jts.33.479] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
In order to elucidate the role of metallothionein (MT) in preventing the adverse effects of X-ray irradiation, we examined the susceptibility of MT-I/II null mice to bone marrow injury caused by X-irradiation and effects of pretreatment with MT-inducing metals on X-ray injury. Eight-week-old male mice were exposed to a single bout of whole-body X-irradiation at a dose between 0.1 and 6.0 Gy. The numbers of leukocytes, reticulocytes with micronuclei (MNRET) in the blood, and polychromatic erythrocytes with micronuclei (MNPCE) in the bone marrow were determined 24 hr after X-irradiation. X-irradiation significantly decreased the total number of leukocytes in MT-I/II null mice and wild-type mice in a dose-dependent manner, but the total number of leukocytes was significantly lower in MT-I/II null mice than in wild-type mice at a low dose of irradiation, between 0.1 and 1.0 Gy. X-irradiation (0.1 and 0.5 Gy) significantly increased the appearance of MNRET and MNPCE in both strains, but the increase was greater in the MT-I/II null mice than in the wild-type mice. Additional groups of mice were pre-administered bismuth nitrate or zinc sulfate to induce MT in the bone marrow cells prior to X-irradiation; the X-ray injury was prevented by such treatments in wild-type mice only. Thus, the present results suggest that MT plays a protective role against a low dose of X-ray injury.
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Affiliation(s)
- Kiyoshi Shibuya
- Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan
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Moreau JL, Baudrimont M, Carrier P, Peltier G, Bourdineaud JP. Metal binding and antioxidant properties of chimeric tri- and tetra-domained metallothioneins. Biochimie 2008; 90:705-16. [PMID: 18294460 DOI: 10.1016/j.biochi.2008.01.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2007] [Accepted: 01/18/2008] [Indexed: 11/29/2022]
Abstract
An unusual tri-domained (alpha-beta-beta) natural oyster metallothionein (MT) is known, and non-oxidative MT dimers occur in vivo in mollusk species and in mammals. To assess the respective role of the MT domains, two chimeric MTs were constructed: a tetra-domained oyster MT corresponding to the alpha-beta-alpha-beta structure, in order to mimic the natural non-oxidative dimeric form, and a tri-domained alpha-beta-alpha oyster MT. Metal binding and putative antioxidant properties of these two chimeric MTs were investigated using expression of the related genes in the bacteria Escherichia coli. In a wild-type strain these MTs could efficiently bind Cd. In a superoxide dismutase (sodA sodB) null mutant, the tri-domained MT was found to exacerbate Cd toxicity whereas the tetra-domained MT efficiently protected bacteria from Cd. The paradoxical toxicity displayed by the tri-domained MT upon Cd contamination was linked to the generation of superoxide radicals generated by a mechanism which most probably involves a copper-redox cycling reaction, since a Cd-contaminated sodA sodB strain expressing this MT produced 4 times more O2(-) than the control bacteria, and MT toxicity disappeared in the presence of bathocuproine disulfonic acid, a copper chelator. In contrast, the tetra-domained form did not. Interestingly, in bacteria producing superoxide dismutase but hypersensitive to oxidative stress due to either mutations in thioredoxin and glutathione reductase pathways (WM104 mutant) or to a lack of gamma-glutamylcysteine synthetase (gshA mutant), both chimeric MTs were protecting against Cd toxicity. However, an unexpected lack of antioxidant function was observed for both chimeric MTs, which were found to enhance the toxicity of hydrogen peroxide in WM104, or that of menadione in QC1726. Altogether, our results suggest that superoxide dismutase activity counteracts the potential prooxidative effect of the tri-domained MT mediated by Cu ions and that the tetra-domained form is a very efficient protector against metal toxicity in vivo.
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Affiliation(s)
- Jean-Luc Moreau
- Université Bordeaux 1/UMR CNRS 5805, Géochimie et écotoxicologie des métaux dans les systèmes aquatiques, Place du Dr. Peyneau, 33120 Arcachon, France
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Achard-Joris M, Moreau JL, Lucas M, Baudrimont M, Mesmer-Dudons N, Gonzalez P, Boudou A, Bourdineaud JP. Role of metallothioneins in superoxide radical generation during copper redox cycling: Defining the fundamental function of metallothioneins. Biochimie 2007; 89:1474-88. [PMID: 17681660 DOI: 10.1016/j.biochi.2007.06.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2007] [Accepted: 06/12/2007] [Indexed: 10/23/2022]
Abstract
In order to demonstrate the in vivo antioxidant properties of metallothioneins (MTs), the bacteria Escherichia coli was used as a cell reactor in which we compared the metal binding and antioxidative functions of MTs from different species, with different structures and polypeptide lengths. No protective effects of cytoplasmic MTs from cadmium (Cd) or zinc (Zn) contamination were observed in a wild-type E. coli strain, although these MTs can efficiently bind both Cd and Zn. To test their antioxidant properties, MTs were expressed within the cytoplasm of a sodA sodB deficient mutated strain (QC1726). However, a paradoxical MT toxicity was found when this strain was contaminated with Cd and Zn, suggesting that in a wild-type strain, superoxide dismutase counteracts MT toxicity. The most toxic MT was the one with the strongest Cd and Zn binding capacities. This toxic effect was linked to the generation of superoxide radicals, since a Cd-contaminated QC1726 strain expressing oyster MT isoforms produced 75-85% more O(2)*(-) than the control QC1726 strain. Conversely, under anaerobiosis or in the presence of a copper chelator, MTs protected QC1726 strain from Cd and Zn contamination. A model is proposed to explain the observed MT toxicity.
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Affiliation(s)
- Maud Achard-Joris
- UMR 5805 CNRS - Université Bordeaux 1, Team Géochimie et Ecotoxicologie des Métaux dans les systèmes Aquatiques, Station Marine d'Arcachon, Place du Dr. Peyneau, 33120 Arcachon, France
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Kennette W, Collins OM, Zalups RK, Koropatnick J. Basal and zinc-induced metallothionein in resistance to cadmium, cisplatin, zinc, and tertbutyl hydroperoxide: studies using MT knockout and antisense-downregulated MT in mammalian cells. Toxicol Sci 2005; 88:602-13. [PMID: 16150881 DOI: 10.1093/toxsci/kfi318] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Metallothioneins (MTs) mediate resistance to metal and non-metal toxicants. To differentiate the role of MTs from other protective factors, resistance to zinc (Zn), cadmium (Cd), tertbutyl hydroperoxide (tBH), and cisplatin (CDDP) was compared in renal cell lines from wild type (MT-WT) and MT-1/MT-2 knockout (MT-KO) mice. MT-WT cells were more resistant to tBH than MT-KO cells but, unexpectedly, were more sensitive to Zn, Cd, and CDDP. Thus, basal expression of MT conferred resistance to tBH, but not to Cd or CDDP. Pretreatment with Zn increased MT expression and enhanced resistance to Cd and CDDP only in MT-WT cells, indicating a critical role for MT in this form of resistance. By contrast, Zn-pretreatment increased resistance to subsequent Zn exposure, but did not alter resistance to tBH, regardless of MT-status. Therefore, Zn-induced resistance to subsequent exposure to Zn (but not to Cd or CDDP) was mediated by non-MT factors, and neither Zn-induced MT nor other factors affected tBH sensitivity. Furthermore, antisense down-regulation of MT in human HeLa cells reduced basal MT levels and resistance to TBH, but not to Cd or CDDP. Therefore, basal MT alone can mediate resistance to TBH (but not to Cd or CDDP) in mouse and human cells. These data suggest that MT can mediate resistance to toxicants by different mechanisms, some of which correlate with the cellular content of MT protein. Moreover, resistance to some agents (Cd and CDDP) can be enhanced by inducing MT. Resistance to other agents (tBH) requires only basal (non-induced) MT levels.
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Affiliation(s)
- Wendy Kennette
- Cancer Research Laboratory Program, London Regional Cancer Program, London Health Sciences Centre, Ontario, Canada
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Bouzourene H, Chaubert P, Gebhard S, Bosman FT, Coucke P. Role of metallothioneins in irradiated human rectal carcinoma. Cancer 2002; 95:1003-8. [PMID: 12209683 DOI: 10.1002/cncr.10780] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
BACKGROUND Metallothioneins (MT) are low-molecular weight, metal-binding proteins that play a role in cellular proliferation and differentiation, as well as in cellular defense mechanisms. They act as scavengers of free radicals produced by irradiation. A number of in vitro and in vivo studies have linked overexpression of cellular MT with tumor cell resistance to radiation. This is the first study that investigates whether MT expression is involved in the radioresistance of rectal carcinoma. METHODS Using a mouse monoclonal antibody, MT expression was analyzed by immunohistochemistry on surgical samples (n = 85) from 85 patients with locally advanced rectal carcinoma who were treated preoperatively with a hyperfractionated and accelerated radiotherapy schedule and on tumor biopsies (n = 13) obtained before treatment. The potential correlations between MT expression and pathologic variables and survival were examined. RESULTS MT were expressed strongly in both the cytoplasm and nucleus of tumor cells in 7 biopsy and 42 surgical samples. A comparison of MT expression in biopsy and surgical specimens showed that MT expression did not change after irradiation in most cases. Against all expectations, MT were expressed more frequently in tumors from responders than in those from the nonresponders (P = 0.02). There was no correlation between MT expression and tumor stage, histology after radiotherapy, or survival. CONCLUSION These findings do not Cansupport the hypothesis that MT overexpression at the end of radiotherapy is a marker for radiation resistance.
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Davis SR, Samuelson DA, Cousins RJ. Metallothionein expression protects against carbon tetrachloride-induced hepatotoxicity, but overexpression and dietary zinc supplementation provide no further protection in metallothionein transgenic and knockout mice. J Nutr 2001; 131:215-22. [PMID: 11160536 DOI: 10.1093/jn/131.2.215] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Metallothionein and zinc have been implicated in cellular defense against a number of cytotoxic agents. With respect to the free radical-generating hepatotoxin carbon tetrachloride, conclusions about a defensive role were reached from in vitro studies, in vivo studies using inducers of metallothionein and studies using injections of pharmacological amounts of zinc. Metallothionein knockout (null) and metallothionein transgenic mice are more direct models to examine the effects of metallothionein expression on induced cytotoxicity. Similarly, zinc presented via the diet is a more physiological model than that presented via injection. We examined whether metallothionein-overexpressing mice or metallothionein knockout mice had altered sensitivity to carbon tetrachloride and whether supplemental dietary zinc reduced sensitivity to carbon tetrachloride in these genotypes. Metallothionein knockout mice produced no metallothionein and were unable to sequester additional hepatic zinc in response to elevated dietary zinc. Hepatotoxicity, as measured by serum alanine aminotransferase activity, histological analyses and hepatic thiol levels, was greater in the knockout mice than in controls 12 h after carbon tetrachloride treatment but not at later time points (up to 48 h). In contrast, metallothionein-overexpressing mice produced more metallothionein and sequestered more liver zinc than control mice, but hepatotoxicity was similar between genotypes. Supplemental dietary zinc had no effect on hepatotoxicity with either genotype. These data suggest metallothionein null mice were more susceptible to carbon tetrachloride-induced hepatotoxicity than were control mice. However, neither metallothionein overexpression nor supplemental dietary zinc provided further protection.
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Affiliation(s)
- S R Davis
- Food Science and Human Nutrition Department, Center for Nutritional Sciences, University of Florida, Gainesville, Florida 32611-0370, USA
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Conrad CC, Grabowski DT, Walter CA, Sabia M, Richardson A. Using MT(-/-) mice to study metallothionein and oxidative stress. Free Radic Biol Med 2000; 28:447-62. [PMID: 10699757 DOI: 10.1016/s0891-5849(99)00263-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mice with null mutations for metallothionein genes MT-1 and MT-2 were used to study the role that metallothionein plays in protecting cellular targets in vivo from oxidative stress. Wild-type (MT(+/+)) and MT-null (MT(-/-)) mice were treated with either saline or zinc and exposed to two types of oxidative stress: gamma-irradiation or 2-nitropropane. There was no alteration in the antioxidant defense system (superoxide dismutase, catalase, or glutathione peroxidase and glutathione levels) to compensate for the lack of the metallothionein in the MT(-/-) mice. The amount of oxidative damage to liver DNA, lipids, and proteins were similar for the MT(-/-) and MT(+/+) mice even though the levels of metallothionein in the livers of the saline- or zinc-pretreated MT(+/+) mice were 5- to 100-fold greater than found in the MT(-/-) mice. To determine if metallothionein can protect mice from the lethal effects of ionizing radiation, the mean survivals of MT(-/-) and MT(+/+) mice exposed to whole body gamma-irradiation were measured and found to be similar. However, the mean survival increased significantly after zinc pretreatment for both the MT(-/-) and MT(+/+) mice. These results demonstrate that tissue levels of metallothionein do not protect mice in vivo against oxidative stress.
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Affiliation(s)
- C C Conrad
- Department of Molecular Biology and Immunology, The University of North Texas Health Science Center at Fort Worth, Fort Worth, TX, USA
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Klaassen CD, Liu J, Choudhuri S. Metallothionein: an intracellular protein to protect against cadmium toxicity. Annu Rev Pharmacol Toxicol 1999; 39:267-94. [PMID: 10331085 DOI: 10.1146/annurev.pharmtox.39.1.267] [Citation(s) in RCA: 756] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Metallothioneins (MT) are low-molecular-weight, cysteine-rich, metal-binding proteins. MT genes are readily induced by various physiologic and toxicologic stimuli. Because the cysteines in MT are absolutely conserved across species, it was suspected that the cysteines are necessary for function and MT is essential for life. In attempts to determine the function(s) of MT, studies have been performed using four different experimental paradigms: (a) animals injected with chemicals known to induce MT; (b) cells adapted to survive and grow in high concentrations of MT-inducing toxicants; (c) cells transfected with the MT gene; and (d) MT-transgenic and MT-null mice. Most often, results from studies using the first three approaches have indicated multiple functions of MT in cell biology: MT (a) is a "storehouse" for zinc, (b) is a free-radical scavenger, and (c) protects against cadmium (Cd) toxicity. However, studies using MT-transgenic and null mice have not strongly supported the first two proposed functions but strongly support its function in protecting against Cd toxicity. Repeated administration of Cd to MT-null mice results in nephrotoxicity at one tenth the dose that produces nephrotoxicity in control mice. Human studies indicate that 7% of the general population have renal dysfunction from Cd exposure. Therefore, if humans did not have MT, "normal" Cd exposure would be nephrotoxic to humans. Thus, it appears that during evolution, the ability of MT to protect against Cd toxicity might have taken a more pivotal role in the maintenance of life processes, as compared with its other proposed functions (i.e. storehouse for zinc and free radical scavenger).
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Affiliation(s)
- C D Klaassen
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City 66160, USA.
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