Glucocorticoid regulation of metallothionein-I mRNA synthesis in cultured mouse cells

Brain and Hepatic Mt mRNA Is Reduced in Response to Mild Energy Restriction and n-3 Polyunsaturated Fatty Acid Deficiency in Juvenile Rats

Metallothioneins (MTs) perform important regulatory and cytoprotective functions in tissues including the brain. While it is known that energy restriction (ER) and dietary n-3 polyunsaturated fatty acid (PUFA) deficiency impact postnatal brain growth and development, little data exist regarding the impact of undernutrition upon MT expression in growing animals. We tested the hypothesis that ER with and without dietary n-3 PUFA deficiency reduces MT expression in juvenile rats. ER rats were individually pair-fed at 75% of the ad libitum (AL) intake of control rats provided diets consisting of either soybean oil (SO) that is α-linolenic acid (ALA; 18:3n-3) sufficient or corn oil (CO; ALA-deficient). Fatty acids (FA) and metal concentrations of liver and brain regions were analyzed. Tissue expression of MTs (Mt1-3) and modulators of MT expression including glucocorticoid receptors (Nr3c1 and Nr3c2) and several mediators of thyroid hormone regulation (Dio1-3, Mct8, Oatp1c1, Thra, and Thrb) were measured. Plasma corticosterone and triiodothyronine levels were also evaluated. ER, but not metal deficiency, reduced Mt2 expression in the cerebellum (50%) and cerebral cortex (23%). In liver, a reduction in dietary n-3 PUFA reduced Mt1, Mt2, Nr3c1, Mct8, and Thrb. ER elevated Nr3c1, Dio1, and Thrb and reduced Thra in the liver. Given MT’s role in cellular protection, further studies are needed to evaluate whether ER or n-3 PUFA deficiency may leave the juvenile brain and/or liver more susceptible to endogenous or environmental stressors.

Metallothionein, Copper and Alpha-Synuclein in Alpha-Synucleinopathies

Metallothioneins (MTs) are proteins that function by metal exchange to regulate the bioavailability of metals, such as zinc and copper. Copper functions in the brain to regulate mitochondria, neurotransmitter production, and cell signaling. Inappropriate copper binding can result in loss of protein function and Cu(I)/(II) redox cycling can generate reactive oxygen species. Copper accumulates in the brain with aging and has been shown to bind alpha-synuclein and initiate its aggregation, the primary aetiological factor in Parkinson's disease (PD), and other alpha-synucleinopathies. In PD, total tissue copper is decreased, including neuromelanin-bound copper and there is a reduction in copper transporter CTR-1. Conversely cerebrospinal fluid (CSF) copper is increased. MT-1/2 expression is increased in activated astrocytes in alpha-synucleinopathies, yet expression of the neuronal MT-3 isoform may be reduced. MTs have been implicated in inflammatory states to perform one-way exchange of copper, releasing free zinc and recent studies have found copper bound to alpha-synuclein is transferred to the MT-3 isoform in vitro and MT-3 is found bound to pathological alpha-synuclein aggregates in the alpha-synucleinopathy, multiple systems atrophy. Moreover, both MT and alpha-synuclein can be released and taken up by neural cells via specific receptors and so may interact both intra- and extra-cellularly. Here, we critically review the role of MTs in copper dyshomeostasis and alpha-synuclein aggregation, and their potential as biomarkers and therapeutic targets.

The Role of Nuclear Factor-E2-Related Factor 1 in the Oxidative Stress Response in MC3T3-E1 Osteoblastic Cells

BACKGROUND

Reactive oxygen species (ROS) and antioxidants are associated with maintenance of cellular function and metabolism. Nuclear factor-E2-related factor 1 (NFE2L1, Nrf1) is known to regulate the expression of a number of genes involved in oxidative stress and inflammation. The purpose of this study was to examine the effects of NFE2L1 on the response to oxidative stress in osteoblastic MC3T3-E1 cells.

METHODS

The murine calvaria-derived MC3T3-E1 cell line was exposed to lipopolysaccharide (LPS) for oxidative stress induction. NFE2L1 effects were evaluated using small interfering RNA (siRNA) for NFE2L1 mRNA. ROS generation and the levels of known antioxidant enzyme genes were assayed.

RESULTS

NFE2L1 expression was significantly increased 2.4-fold compared to the control group at 10 μg/mL LPS in MC3T3-E1 cells (P<0.05). LPS increased formation of intracellular ROS in MC3T3-E1 cells. NFE2L1 knockdown led to an additional increase of ROS (20%) in the group transfected with NFE2L1 siRNA compared with the control group under LPS stimulation (P<0.05). RNA interference of NFE2L1 suppressed the expression of antioxidant genes including metallothionein 2, glutamatecysteine ligase catalytic subunit, and glutathione peroxidase 1 in LPS-treated MC3T3-E1 cells.

CONCLUSION

Our results suggest that NFE2L1 may have a distinct role in the regulation of antioxidant enzymes under inflammation-induced oxidative stress in MC3T3-E1 osteoblastic cells.

Analysis of Metallothionein Brain Gene Expression in Relation to Ethanol Preference in Mice Using Cosegregation and Gene Knockouts

BACKGROUND

Metallothioneins (MTs) are ubiquitously expressed intracellular proteins that bind heavy metals and are involved in cytoprotection against several types of stress agents including chemicals, hormones, and oxidants. We have previously reported 1 isoform, MT-II, as a possible candidate gene for ethanol (EtOH) preference (EP) determination in mice.

METHODS

Semiquantitative RT-PCR was used to determine brain mRNA levels of MT-I and MT-III in 4 inbred mouse strains with variable EP. Following this, cosegregation of MT-II brain expression with EP was analyzed in F2 mice from 2 intercrosses (C57BL/6J x BALB/cJ and C57BL/6J x DBA/2J). Studies on MT-I/MT-II knockout (KO) mice were also undertaken to further explore this relationship.

RESULTS

Our results suggest that MT-I is responsive to EtOH, with no evidence of basal-level differences between strains. Conversely, MT-III shows no EtOH response, yet indicates a possible strain-specific feature with C57BL/6J having the lowest levels of brain MT-III. Metallothionein-II expression cosegregates with EP in F2 mice from a C57BL/6J (preferring) and DBA/2J (avoiding) intercross. Although F2 mice from a cross with C57BL/6J and BALB/cJ (avoiding) strains follow a similar pattern, the results are not statistically significant. Metallothionein-I/MT-II knockout (MT-KO) mice appear to have smaller litter sizes as well as higher weight compared with controls (129S1/SvImJ) and also show a slight increase in EP.

CONCLUSIONS

Metallothionein-II remains the primary candidate of the mouse MT gene family for involvement in EP. Its effect on EP appears to be dependent on the genetic background. Such conclusions are based on results from C57BL/6J, BALB/cJ, DBA/2J, and 129 inbred mouse strains. Evidence also points to shared neural pathways involved in weight gain and obesity. The complex interactions between MT-II, EP, and weight gain/obesity remain to be studied.

Physical interaction and functional synergy between glucocorticoid receptor and Ets2 proteins for transcription activation of the rat cytochrome P-450c27 promoter

We demonstrate that dexamethasone-mediated transcription activation of the cytochrome P-450c27 promoter involves a physical interaction and functional synergy between glucocorticoid receptor (GR) and Ets2 factor. Ets2 protein binding to a "weak" Ets-like site of the promoter is dependent on GR bound to the adjacent cryptic glucocorticoid response element. Coimmunoprecipitation and chemical cross-linking experiments show physical interaction between GR and Ets2 proteins. Mutational analyses show synergistic effects of Ets2 and GR in dexamethasone-mediated activation of the cytochrome P-450c27 promoter. The DNA-binding domain of GR, lacking the transcription activation and ligand-binding domains, was fully active in synergistic activation of the promoter with intact Ets2. The DNA-binding domain of Ets2 lacking the transcription activation domain showed a dominant negative effect on the transcription activity. Finally, a fusion protein consisting of the GR DNA-binding domain and the transcription activation domain of Ets2 fully supported the transcription activity, suggesting a novel synergy between the two proteins, which does not require the transactivation domain of GR. Our results also provide new insights on the role of putative weak consensus Ets sites in transcription activation, possibly through synergistic interaction with other gene-specific transcription activators.

The transcription factor MTF-1 mediates metal regulation of the mouse ZnT1 gene

Metal regulation of the mouse zinc transporter (ZnT)-1 gene was examined in cultured cells and in the developing conceptus. Zinc or cadmium treatment of cell lines rapidly (3 h) and dramatically (about 12-fold) induced ZnT1 mRNA levels. In cells incubated in medium supplemented with Chelex-treated fetal bovine serum, to remove metal ions, levels of ZnT1 mRNA were reduced, and induction of this message in response to zinc or cadmium was accentuated (up to 31-fold induction). Changes in ZnT1 gene expression in these experiments paralleled those of metallothionein I (MT-I). Inhibition of RNA synthesis blocked metal induction of ZnT1 and MT-I mRNAs, whereas inhibition of protein synthesis did not. Metal response element-binding transcription factor (MTF)-1 mediates metal regulation of the metallothionein I gene. In vitro DNA-binding assays demonstrated that mouse MTF-1 can bind avidly to the two metal-response element sequences found in the ZnT1 promoter. Using mouse embryo fibroblasts with homozygous deletions of the MTF-1 gene, it was shown that this transcription factor is essential for basal as well as metal (zinc and cadmium) regulation of the ZnT1 gene in these cells. In vivo, ZnT1 mRNA was abundant in the midgestation visceral yolk sac and placenta. Dietary zinc deficiency during pregnancy down-regulated ZnT1 and MT-I mRNA levels (4-5-fold and >20-fold, respectively) in the visceral yolk sac, but had little effect on these mRNAs in the placenta. Homozygous knockout of the MTF-1 gene in transgenic mice also led to a 4-6-fold reduction in ZnT1 mRNA levels and a loss of MT-I mRNA in the visceral yolk sac. These results suggest that MTF-1 mediates the response to metal ions of both the ZnT1 and the MT-I genes the visceral yolk sac. Overall, these studies suggest that MTF-1 directly coordinates the regulation of genes involved in zinc homeostasis and protection against metal toxicity.

Mammalian SWI-SNF complexes contribute to activation of the hsp70 gene

ATP-dependent chromatin-remodeling complexes are conserved among all eukaryotes and function by altering nucleosome structure to allow cellular regulatory factors access to the DNA. Mammalian SWI-SNF complexes contain either of two highly conserved ATPase subunits: BRG1 or BRM. To identify cellular genes that require mammalian SWI-SNF complexes for the activation of gene expression, we have generated cell lines that inducibly express mutant forms of the BRG1 or BRM ATPases that are unable to bind and hydrolyze ATP. The mutant subunits physically associate with at least two endogenous members of mammalian SWI-SNF complexes, suggesting that nonfunctional, dominant negative complexes may be formed. We determined that expression of the mutant BRG1 or BRM proteins impaired the ability of cells to activate the endogenous stress response gene hsp70 in response to arsenite, a metabolic inhibitor, or cadmium, a heavy metal. Activation of hsp70 by heat stress, however, was unaffected. Activation of the heme oxygenase 1 promoter by arsenite or cadmium and activation of the cadmium-inducible metallothionein promoter also were unaffected by the expression of mutant SWI-SNF components. Analysis of a subset of constitutively expressed genes revealed no or minimal effects on transcript levels. We propose that the requirement for mammalian SWI-SNF complexes in gene activation events will be specific to individual genes and signaling pathways.

Zinc and cadmium can promote rapid nuclear translocation of metal response element-binding transcription factor-1

Metal response element-binding transcription factor-1 (MTF-1) is a six-zinc finger protein that plays an essential role in activating metallothionein expression in response to the heavy metals zinc and cadmium. Low affinity interactions between zinc and specific zinc fingers in MTF-1 reversibly regulate its binding to the metal response elements in the mouse metallothionein-I promoter. This study examined the subcellular distribution and DNA binding activity of MTF-1 in cells treated with zinc or cadmium. Immunoblot analysis of cytosolic and nuclear extracts demonstrated that in untreated cells, about 83% of MTF-1 is found in the cytosolic extracts and is not activated to bind to DNA. In sharp contrast, within 30 min of zinc treatment (100 microM), MTF-1 is detected only in nuclear extracts and is activated to bind to DNA. The activation to bind to DNA and nuclear translocation of MTF-1 occurs in the absence of increased MTF-1 content in the cell. Furthermore, immunocytochemical localization and immunoblotting assays demonstrated that zinc induces the nuclear translocation of MTF-1-FLAG, expressed from the cytomegalovirus promoter in transiently transfected dko7 (MTF-1 double knockout) cells. Immunoblot analysis of cytosolic and nuclear extracts from cadmium-treated cells demonstrated that concentrations of cadmium (10 microM) that actively induce metallothionein gene expression cause only a small increase in the amount of nuclear MTF-1. In contrast, an overtly toxic concentration of cadmium (50 microM) rapidly induced the complete nuclear translocation and activation of DNA binding activity of MTF-1. These studies are consistent with the hypothesis that MTF-1 serves as a zinc sensor that responds to changes in cytosolic free zinc concentrations. In addition, these data suggest that cadmium activation of metallothionein gene expression may be accompanied by only small changes in nuclear MTF-1.

PF1070A, a novel and potent inducer of the synthesis of metallothionein

Using mouse Ltk(-) cells (L13-17 cells) that had been transfected with a plasmid in which the lacZ gene had been ligated downstream of 1.4 kbp of the sequence of the promoter of the mouse gene for metallothionein-I (MT-I) as a reporter gene, we examined 268 organic compounds for the ability to activate this promoter. We found that PF1070A, an antibiotic produced by Humicola sp., efficiently activated the MT promoter and caused marked enhancement of beta-galactosidase activity in L13-17 cells. The extent of activation by PF1070A was almost equivalent to that by of zinc ions, the most effective known inducer of the synthesis of MT. PF1070A also caused marked elevation of the levels of the mRNA for MT and of MT itself in L13-17 cells. A similar result was obtained in human HeLa-S3 cells. When PF1070A was added to the culture medium simultaneously with cadmium ion or dexamethasone, the level of expression of the reporter gene was markedly elevated, compared to the level of expression induced by each agent independently. The effect of PF1070A was reduced considerably by deletion of nucleotides at positions -150 and -149 from the site of initiation of transcription in the promoter region of the MT gene and also by deletion of the seven bases located at positions -49 to -43. Since no known cis element was found in these two regions, PF1070A might be a new type of inducer of MT synthesis that promotes expression of the gene for MT via a mechanism completely different from those exploited by other known agents. These results also suggest the presence of a system for control of transcription of the gene for MT that has not previously been recognized. Both cadmium ions and bismuth ions induce the synthesis of MT by acting on the metal response element (MRE). Bismuth ions had no significant effect on the promoter activity that had already reached a maximum level in response to treatment with the optimal concentration of cadmium ion. By contrast, PF1070A further and markedly increased the promoter activity. This result suggests that it is possible to increase the concentration of MT in tissue using PF1070A as an inducer even in cases where the MRE-mediated activation of the MT promoter has already been induced by the accumulation of cadmium, as is the case in a clinical setting. PF1070A may prove to be an excellent inducer of MT synthesis that is effective and clinically applicable. Moreover, use of PF1070A in combination with salts of heavy metals might be useful in controlling expression of a transfected gene that is regulated by the MT promoter since PF1070A can activate the MT promoter to an extent that cannot be achieved with heavy metal ions alone, when PF1070A is used in combination with zinc ions at a concentration of the latter considerably below the toxic level.

Metallothionein induction in response to restraint stress. Transcriptional control, adaptation to stress, and role of glucocorticoid

Metallothioneins (MT) have been implicated in the protection of cells from oxidative stress. We studied the molecular mechanism of induction of MT-I and MT-II in response to restraint stress using a mouse model system in which the animals were restrained in well ventilated polypropylene tubes for 12 h each day (one cycle). Here, we show that MT-I and MT-II mRNA levels were elevated as much as 10-20-fold after just one cycle of this simple stress. Stress-mediated MT induction occurred at the transcriptional level. The level of MT mRNA correlated with the stress-induced increase, and not with the diurnal variation, in the level of serum glucocorticoid. Treatment of the mice with RU 486, a glucocorticoid receptor antagonist, prior to restraint stress inhibited MT induction by at least 50%. Furthermore, the glucocorticoid responsive element-binding activity in the liver nuclear extracts from the stressed mice was significantly higher than that in the control mice. The complex formations between the transcription factor Sp1, MTF1, or MLTF/ARE and the respective specific oligonucleotides were not altered in the liver from the stressed mouse. The MT mRNA levels returned to the basal level at the end of nine cycles of stress, indicating habituation of the animals to restraint stress. At this stage, exposure of the animals to another type of stress, treatment with heavy metals, resulted in further induction of MT. These data indicate that glucocorticoid is the primary physiological factor responsible for MT induction following restraint stress, and the glucocorticoid receptor is the major transcription factor involved in this process.

Overexpression of the large subunit of the protein Ku suppresses metallothionein-I induction by heavy metals

Metallothioneins (MT) are involved in the scavenging of the toxic heavy metals and protection of cells from reactive oxygen intermediates. To investigate the potential role of the protein Ku in the expression of MT, we measured the level of MT-I mRNA in the parental rat fibroblast cell line (Rat 1) and the cell lines that stably and constitutively overexpress the small subunit, the large subunit, and the heterodimer of Ku. Treatment with CdS04 or ZnS04 elevated the MT-I mRNA level 20- to 30-fold in the parental cells and the cells (Ku-70) that overproduce the small subunit or those (Ku-7080) overexpressing the heterodimer. By contrast, the cells (Ku-80) overexpressing the large subunit of Ku failed to induce MT-I. In vitro transcription assay showed that the MT-I promoter activity was suppressed selectively in the nuclear extracts from Ku-80 cells. The specificity of the repressor function was shown by the induction of hsp 70, another Cd-inducible gene, in Ku-80 cells. Addition of the nuclear extract from Ku-80 cells at the start of the transcription reaction abolished the MT-l promoter activity in the Rat 1 cell extract. The transcript once formed in Rat 1 nuclear extract was not degraded by further incubation with the extract from Ku-80 cells. The repressor was sensitive to heat. The DNA-binding activities of at least four transcription factors that control the MT-I promoter activity were not affected in Ku-80 cells. These observations have set the stage for further exploration of the mechanisms by which the Ku subunit mediates suppression of MT induction.

Requirement for cooperative interaction of interleukin-6 responsive element type 2 and glucocorticoid responsive element in the synergistic activation of mouse metallothionein-I gene by interleukin-6 and glucocorticoid

Metallothionein (MT)-inducing activity of interleukin (IL)-6 depends on the presence of glucocorticoid in hepatic cells. The synergistic action of IL-6 and glucocorticoid was observed in the transcriptional activation of the mouse MT (mMT)-I gene. We found that a 281-bp promoter was sufficient for IL-6 and glucocorticoid stimulation. Our inspection of this region revealed the putative type 1 and 2 IL-6 responsive elements (REs). Functional analyses of these regions were performed using luciferase reporter constructs, and it was observed that the type 2 IL-6RE exerted the major response to the IL-6 signal. The transcriptional factor binding to type 1 IL-6RE, nuclear factor-IL-6, hardly contributed to the activation of the mMT-I promoter by IL-6 and glucocorticoid. A glucocorticoid responsive element (GRE) was also required for the synergistic activation by IL-6 and glucocorticoid. Interestingly, this synergism was not observed when the type 2 IL-6RE and the GRE were kept apart. Therefore, the synergistic activation of the mMT-I gene by IL-6 and glucocorticoid may require not only that signal transducers and activators 3 (Stat3) and the glucocorticoid receptor (GR) bind to their respective responsive elements, but also that Stat3 and the GR physically interact with one another.

Manipulation of metallothionein expression in the regenerating rat liver using antisense oligonucleotides

Metallothioneins (MTs) are low molecular weight, zinc-binding proteins that by activating zinc metalloenzymes participate in the regulation of growth and development. The present study was designed to examine the roles of MTs in cell proliferation using an in vivo model of liver regeneration following partial hepatectomy (PH) in rats. The levels of MT-I and MT-II were studied with respect to regulation of proliferative potential, cell cycle checkpoint activity, and oxidative stress in the rat PH model. We synthesized a 17-mer antisense phosphorothioate oligodeoxynucleotide (S-ODN), named aMT, complimentary to the start site of the MT-I mRNA sequence and an appropriate control. Both S-ODNs were administered intraperitoneally at the dose of 5 mg/kg following 70% PH. MT became induced 57.4 +/- 9.8-fold following PH and the said effect became attenuated dramatically following administration of aMT. In addition, PH rats treated with aMT exhibited decreased rate of liver regeneration as measured by expression of proliferating cell nuclear antigen and elevated cell cycle checkpoint activity as determined by expression of p53. The results of these studies suggest that MT isoforms with their high thiol contents do play an important role in cellular functions and especially during stressful states induced by a broad range of mediators generating free radicals.

A pair of adjacent glucocorticoid response elements regulate expression of two mouse metallothionein genes

Synthesis of mouse metallothionein (MT)-I and MT-II is transcriptionally induced by the synthetic glucocorticoid, dexamethasone (DEX) or both in vivo as well as in numerous cell lines. However, the location(s) of a glucocorticoid response element (GRE) has not been described. The observation that a marked MT-I gene, as well as heterologous genes, when placed in the context of 17 kb of flanking sequence from the MT locus, are inducible by DEX and lipopolysaccharide in transgenic mice renewed the search for the GRE. Analysis of a series of deletion constructs from this 17-kb region in cultured cells identified a single 455-bp region that conferred DEX induction on a reporter gene. This 455-bp region contains two GREs that bind to the glucocorticoid receptor as assessed by gel mobility shift. Deletion of this fragment from the 17-kb flanking region eliminates the DEX responsiveness of reporter genes. The two GREs, which are located approximately 1 kb upstream of the MT-II gene and approximately 7 kb upstream of the MT-I gene, are necessary for induction of both genes and can function independently of elements within the proximal promoter region of either gene.

Specific deactivation of the mouse mammary tumor virus long terminal repeat promoter upon continuous hormone treatment

We have studied the transcriptional behavior of the mouse mammary tumor virus long repeat (MMTV-LTR) promoter during a prolonged exposure to glucocorticoids. When integrated into XC-derived cells, MMTV-LTR expression reached its maximum during the first day of dexamethasone treatment, but longer exposure to the hormone resulted in the deactivation of the promoter. In contrast, glucocorticoid-responsive resident genes or MMTV-based transiently transfected plasmids maintained or even increased their mRNA levels during the same period of hormone treatment. An integrated chimeric construct containing the hormone-responsive elements from MMTV-LTR but in different sequence context became also deactivated after a prolonged hormone treatment but with a deactivation kinetics significantly slower than constructs containing the entire, chromatin-positioning MMTV-LTR sequence. The decrease on MMTV-LTR-driven transcription was concomitant with a parallel closure of the MMTV-LTR chromatin and with a decrease in glucocorticoid receptor (GR) concentration in the cell. We concluded that the chromatin-organized MMTV-LTR promoter is particularly sensitive to any decrease on GR levels. We propose that chromatin structure may contribute decisively to the differential expression of MMTV-LTR by two mechanisms: limiting MMTV-LTR accessibility to activating transcription factors and accelerating its shutting down upon a decrease on GR levels.

Tumor cell growth is inhibited by suppressing metallothionein-I synthesis

The effect of metallothionein (MT)-I antisense oligodeoxynucleotide (ODN) on the growth of three kinds of tumor cells was studied, since MTs may be involved in cell growth. When MT-I antisense ODN was added to leukemia P388 cells, cell growth was inhibited in a manner dependent on the dose and incubation time. MT-I antisense ODN was also inhibitory for other tumor cell lines, i.e. Ehrlich carcinoma and sarcoma 180. A significant decrease in the level of MT, but not of Zn, was observed in MT-I antisense ODN-treated cells. On the other hand, control ODN did not inhibit the cell growth appreciably. These results indicate that MT-I expression may be necessary for the growth and survival of these tumor cells.

Effects of cadmium on trophoblast calcium transport

Maternal exposure to cadmium (Cd) during pregnancy has been linked to low fetal birthweight, which may be attributed to placental damage and/or dysfunction in nutrient transport. Previous studies have suggested that Cd is accumulated in the placenta, and that placental transport of calcium (Ca) and zinc (Zn) is perturbed by Cd. To investigate the mechanism of Cd perturbation of Ca transport, we used JEG-3, a human choriocarcinoma cell line which exhibits trophoblastic properties, to analyse Cd effects in vitro. Treatment with Cd at low, physiologically relevant concentrations (e.g. 0.04 microM) did not result in obvious changes in cell morphology or integrity, whereas higher concentrations (> or = 0.16 microM) affected cell integrity. With lower concentrations of Cd treatment for 24 h, activities of cellular Ca uptake and transport, and Ca2+ binding were decreased, and intracellular [Ca2+] ([Ca2+]i) profile was also altered; however, membrane-associated Ca(2+)-activated ATPase activity remained relatively unchanged. Interestingly, cellular Ca uptake activity was unaffected by short-term (30 min) Cd pretreatment. The 24-h Cd treatment also resulted in elevated expression of the metal-binding protein, metallothionein, whereas the expression of a trophoblast-specific cytosolic Ca(2+)-binding protein (HCaBP) was drastically reduced. These results strongly suggest that Cd exposure significantly compromises the Ca handling ability of trophoblastic cells; this effect is probably not due to perturbations in Ca channel or membrane Ca pump activities, but rather a consequence of alterations in subcellular, cytosolic Ca2+ binding activities.

Colchicine-induced elevation of tissue metallothionein contents is mediated by inflammation-independent serum factor

Subcutaneous injection of colchicine caused dose-dependent and time-dependent induction of hepatic MT in mice. Other than colchicine, similar MT induction was observed in vincristine- or vinblastine-injected mice, but not in beta-lumicolchicine-injected mice. MT contents were also elevated in the kidney, spleen, lung and heart by colchicine injection. Isoforms of colchicine-induced MT in the liver were identified to be MT-I and II by immunoblot analysis. Unlike turpentine-induced MT synthesis, dexamethasone, an anti-inflammatory agent, could not block the MT-inducing activity of colchicine. Therefore, the MT-inducing activity of colchicine does not appear to be due to inflammation. Mouse serum, obtained at 4-24 h after colchicine treatment, stimulated MT induction in rat hepatoma H4IIEC3 cells. The MT-inducing activity in the serum from colchicine-treated mice was determined to be highest at 12 h after colchicine injection. The MT-inducing activity from sera of colchicine-treated mice was completely blocked by glucocorticoid antagonist, RU38486, similar to such activity in the serum from lipopolysaccharide-treated mice. The ability of sera to induce MT was abolished by heat treatment (56 degrees C, 30 min). The molecular weight of the MT-inducing factor estimated by gel filtration was approximately 20 000 Da. Thus, colchicine-induced stimulation of MT production is mediated by some humoral factor. The production of the MT-inducing factor was not blocked by dexamethasone. We conclude that the mediator is not an inflammatory cytokine or a glucocorticoid and suspect that the disruption of microtubule triggers production or release of such humoral mediator which stimulates MT induction.

Zinc depletion suppresses tumor growth in mice

The hypothesis that in tumor-bearing animals an increase of host hepatic zinc metallothionein (Zn-MT) causes a restriction of zinc in the tumor tissue was studied. Three types of tumors were induced in laboratory mice by cell transplant. Tumor growth appears to be inhibited under zinc-deficient conditions, even in cases where zinc deficiency was started after tumor cell transplant. The survival times of tumor-bearing mice were prolonged by administration of cadmium chloride, which induces the synthesis of a combined zinc-cadmium metallothionein derivative in the host liver, but not in the tumor tissue, leading to an increase of hepatic zinc in the treated animals. The uptake of 65Zn by the liver of Cd-treated, tumor bearing mice was significantly higher than that of controls whereas uptake of 65Zn by tumor cells was significantly higher in controls than in the treated animals. These results suggest that restriction of zinc intake suppresses tumor growth.

Immunohistochemical localization of metallothionein in human prostate cancer

PURPOSE

We investigated the expression of metallothionein in human prostate cancer.

MATERIALS AND METHODS

Formalin fixed and paraffin embedded tissue specimens from 45 patients with primary prostate cancer were stained for metallothionein using a standard immunohistochemical technique.

RESULTS

Metallothionein was detected in 15 of 45 prostate cancers (33.3%). Cytoplasmic and nuclear staining occurred in most cells. Additionally, metallothionein was found in basement membrane surrounding the cancer cells in 2 cases with metallothionein expression, and in secretory products of the lumen in a few cases. Statistical analysis for metallothionein expression related to tumor grade revealed a significant difference between high (7 to 10) and low (2 to 4) Gleason scores (p < 0.001), as well as between middle (5 and 6) and low scores (p < 0.05). However, no relationship was found with clinical stage.

CONCLUSIONS

Our data suggest a close correlation of metallothionein expression with tumor grade and a wide range of metallothionein expression in prostate cancer.

Analysis of the serotype-specific epitopes of avian infectious bronchitis virus strains Ark99 and Mass41

The Ark and Mass serotype-specific epitopes of infectious bronchitis virus were studied by immunofluorescence and immunoprecipitation of mutant and recombinant spike glycoproteins (S protein) expressed in mouse L cells. Serotype-specific monoclonal antibodies could bind to the recombinant proteins of Ark99 and Mass41 expressed from the chimeras in which the N-terminal thirds of the S1 sequences were reciprocally exchanged. Therefore, it appears that the respective serotype-specific epitopes of both strains were localized within the C-terminal two-thirds of the S1 proteins. Deletion and insertion of a five-amino-acid fragment on the S1 proteins of Ark99 and Mass41, altered the serotype-specific epitopes. This result implies that the five-amino-acid insertion on the S1 protein of the Ark serotype was involved in determining the conformation of the protein, probably acting as a spacer. In addition, it appears that an interaction between sequences of the N-terminal third and the remaining portion of the S1 protein determines the tertiary structure of the protein as well as the conformation of the serotype-specific epitope.

Localization of zinc and metallothionein in the rat bladder epithelium during carcinogenesis induced by N-butyl-N-(4-hydroxybutyl) nitrosamine

This study investigated the presence of zinc and expression of metallothionein (MT) in different pathological changes of the rat bladder induced by administration of N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN). Using the Timm staining method, the presence of zinc was observed in normal and benign hyperplastic epithelial cells of the rat bladder, particularly in the malignant bladder tumor, induced by the administration of BBN. Immunohistochemically, MT expression was detected only in noninvasive (30%) and invasive transitional cell carcinoma (80%) of the rat bladder where the tumor cells were rich in zinc. Our data suggest that: (1) growth and development of the rat bladder tumor, especially malignant tumors, may have a high requirement for zinc and (2) MT synthesis may be induced by a high zinc concentration in rat bladder tumor cells.

Blocking effect of anti-mouse interleukin-6 monoclonal antibody and glucocorticoid receptor antagonist, RU38486, on metallothionein-inducing activity of serum from lipopolysaccharide-treated mice

Although there is much evidence to suggest that lipopolysaccharide (LPS)-induced elevation of hepatic metallothionein (MT) contents is mediated by cytokines, the presence of MT-inducing activity in the serum of LPS-treated animals has not been examined. It was found that serum from LPS-treated mice stimulated MT induction in a hepatoma cell culture. The MT-inducing activity in serum was highest 2 h after LPS injection. Tumor necrosis factor and interleukin (IL)-6 levels in the serum were highest 1 and 2 h, respectively, after LPS injection. Anti-mouse IL-6 monoclonal antibody neutralized MT-inducing activity in serum obtained from mice 2 h after LPS injection. The MT-inducing activity in serum was blocked by the glucocorticoid antagonist, RU38486. A similar requirement for glucocorticoid was also observed in an IL-6-stimulated culture. These results show that the LPS-induced elevation of hepatic MT is mediated by IL-6, and the expression of the stimulating activity of IL-6 is dependent on the presence of glucocorticoid.

Interactions of metallothionein with murine lymphocytes: plasma membrane binding and proliferation

Metallothionein (MT) is a thiol rich protein that has been well characterized for its ability to bind and sequester heavy metal cations, free radicals and other reactive toxicants. In addition to induction by these stressors, MT gene expression is upregulated by several cytokines of the acute phase response. In previous work, we have shown that MT can alter aspects of lymphocyte function. MT alone induces modest proliferation of unfractionated splenocytes and acts synergistically with T cell- and B cell-specific mitogens. In contrast, MT inhibits humoral responsiveness in vivo and reduces in vitro T cell responses to processed antigen. In this report, we describe the effects of MT on specific lymphocyte subpopulations in order to further characterize the mechanism of MT-mediated alterations of immune activity. MT binds to the plasma membrane of both T and B lymphocytes, but, in the absence of a costimulatory agent, MT induces lymphoproliferation only in B cells. MT also enhances the capacity of naive B lymphocytes to differentiate into plasma cells. These results demonstrate differential immunomodulatory activities of MT and may explain some of the diverse immunoregulatory effects associated with exposure to environmental toxins.

Influence of cAMP-effector-agonists on the synthesis of metallothionein in rat primary hepatocytes

The model of rat primary hepatocytes incubated in DMEM/F12 (Ham) medium was used for studying the influence of the cAMP-effectors epinephrine (100 microM), norepinephrine (100 microM), glucagon (1 microM) and isoproterenol (1-1000 microM) as well as the synthetic cAMP-analogon dibutyryl-cAMP on the metabolism of metallothionein. Liver parenchymal cells isolated by a two-step collagenase perfusion were incubated with DMEM/F12 containing 5% (v/v) fetal calf serum (FCS) and 20 microM zinc in Petri dishes. Experiments were initiated after a 24 h equilibration period by adding the agonists for 18 h. MT in hepatocyte homogenates was quantified by the 109Cd-hemoglobin-binding assay. Cell viability was assessed by the activity of the cytosolic enzyme lactate dehydrogenase (LDH) liberated into the culture medium and by trypan blue exclusion. Isoproterenol and glucagon produced a significant increase of cytosolic MT about 50%. In contrast, incubation with epinephrine and norepinephrine did not lead to any significant effects in the amount of hepatic metallothionein. Simulating the influence of cAMP by dibutyryl-cAMP (500 microM) did not affect the content of hepatic metallothionein. To examine transcriptional and translational regulatory effects supplementation of cycloheximide (0.1-500 microM) and actinomycin D (0.1-100 microM) showed a total inhibition of the agonist induced amounts. Particularly in combination with isoproterenol low LDH activities reflected a high viability of hepatocytes. In conclusion, in primary hepatocyte cultures cAMP-mobilizing-agonists like isoproterenol and glucagon indicate an independent effect on the MT-metabolism. This is possibly due to the de novo synthesis of the protein because suppression by actinomycin D can be observed. However, cAMP-effectors do not seem to be involved in the induction of metallothionein because theophylline and dibutyryl-cAMP did not affect MT-metabolism by suppressing the phosphodiesterase or by stimulating the cAMP-cascade.

Functional analyses of the human metallothionein-IG gene. In vitro and in vivo studies

We have analyzed the human (h) metallothionein (MT)-IG proximal promoter region (-174 to +5) using a TATA box mutation (TATCA) and four trinucleotide mutants of the proximal MREa. Transient transfection of HepG2 cells was complemented by in vitro transcription with rat liver nuclear extracts. In both systems, mutations of the TATA box and conserved core of metal responsive element (MRE)a were detrimental to hMT-IG promoter activity suggesting that both elements make significant contributions to hMT-IG transcription. Although MRE binding factors were active in vitro, further metal activation of MT promoter activity was accomplished only by in vivo metal treatment rather than addition of zinc in vitro. Southwestern blotting identified nuclear proteins in rat liver and HepG2 cells which physically interact with MREa in a zinc-dependent manner and could be responsible for MREa function in each system. In addition, the functional effects of the TATCA mutation correlate with altered physical interaction with TATA box-binding protein as observed using DNase I protection.

Characteristic induction of hepatic metallothionein in mice by tumor transplantation

Based on the previous finding that hepatic metallothionein (MT) level was tumor-growth dependently elevated in tumor-transplanted mice, the mode of induction of hepatic MT in tumor-bearing mice was comparatively studied with inflammation-induced and stress-subjected mice. The prefeeding with zinc (Zn)-deficient diet for 1 wk suppressed both the growth of tumor and the increase of hepatic MT and Zn in tumor-bearing mice. The postfeeding with Zn-deficient diet also suppressed hepatic MT induction in the course of tumor growth. On the other hand, in the other two experimental model mice, the prefeeding with Zn-deficient diet did not suppress the increase of hepatic MT and Zn. Further, the dexamethasone treatment stimulated hepatic MT induction in tumor-bearing mice, but rather reduced that in inflammation-induced mice. These results suggest that hepatic MT was induced uniquely in tumor-bearing mice and that Zn may play a key role for the induction of hepatic MT by tumor transplantation.

Differential hepatic response of 65Zn distribution between mice bearing experimental tumor and inflammation

Discriminative detection of tumor and inflammation was tried by radio-imaging of hepatic uptake of 65Zn. This closely related to the level of metallothionein (MT) and reflected the extent of tumor growth in mice and rats transplanted with experimental tumor. The elevation of 65Zn distribution in liver of experimental tumor-bearing mice was inhibited by treatment with Zn-deficient diet, while stimulated by dexamethasone. This stimulation occurred 2 days after tumor transplantation, at which time 67Ga-citrate could not image the tumor. On the other hand, hepatic distribution of 65Zn was also elevated in mice by inducing experimental abscess, although the effect of both treatments on this elevation was different from the case of tumor; the elevation was inhibited by treatment with dexamethasone. These results suggest that radio-imaging of hepatic Zn uptake with a short-life gamma emitting isotope such as 69mZn with use of dexamethasone, if required, may be useful for a preliminary test to detect early-stage malignant disease.

Isolation of a cDNA encoding a metal response element binding protein using a novel expression cloning procedure: the one hybrid system

A new method for isolation of cDNA clones encoding sequence-specific DNA-binding proteins is described. This method, the one-hybrid system, is based on the use of reporter genes whose transcription can be activated through synthetic cis elements recognized by the sought-after DNA-binding protein. These reporter genes are used for in vivo screening of a library of cDNAs fused to a DNA fragment encoding the GAL4 activation domain. cDNA clones expressing the appropriate fusion proteins lead to activation of these reporter genes in transformed yeast cells. We have used this approach to isolate a mammalian cDNA clone encoding a sequence-specific DNA-binding protein that recognizes the metal response elements (MREs) of the metallothionein (MT) genes. The protein encoded by this cDNA, M96, shows similarity to the trithorax proteins. Expression of a functional DNA-binding form of M96 requires Zn2+ ions. The recombinant protein binds to several different MREs but fails to recognize nonfunctional mutant MREs. M96 may be involved in the activation of MT genes in response to heavy-metal ions.

Over-expression of metallothionein and drug-resistance in bladder cancer

Metallothionein (MT) in tumor cells has been implicated as one of the factors involved in mechanisms of resistance to anti-cancer drugs, including cis-diaminedichroloplatinum (CDDP) and adriamycin (ADM). The relationship between the expression of MT and chemotherapy with anti-cancer drugs was studied in CDDP- and ADM-resistant human bladder cancer cell lines and tissue samples from clinical cases. In drug-resistant cell lines (T-24/ADM, CI-7/CDDP) established in our laboratory, MT expression was studied by immunohistochemistry using the avidin-biotin peroxidase complex (ABC) method and radioimmunoassay (RIA), using anti-MT antibody. In addition, other potential mechanisms of drug resistance, such as P-glycoprotein expression were examined and the levels of reduced glutathione (GSH), oxidized glutathione (GSSG) and glutathione-S-transferase (GST) determined in these cell lines. The results of these investigations demonstrate that the expression of MT in resistant cell lines increased 2.1- and 2.5-fold when compared with parent cell lines (CI-7, T-24). GSH, GSSG and GST levels were unchanged and P-glycoprotein was not over-expressed. A total of 120 tissue samples from 35 clinical cases of bladder cancer, before and after chemotherapy, were stained for MT which was detected in 10 of the 35 cases before chemotherapy. The incidence of MT expression was significantly higher (p < 0.05) in cases with lower pathological tumor grades.(ABSTRACT TRUNCATED AT 250 WORDS)

Basal metallothionein in tumors: widespread presence of apoprotein

A survey has been conducted of solid and ascites tumors from mice and solid tumors in rats for the presence of metallothionein or metallothionein-like protein. In most tumors, a positive identification was made on the basis of Sephadex G-75 and HPLC-DEAE chromatography followed by competitive radioimmunoassay for metallothionein. Apometallothionein was revealed in a number of tumors for the first time by comparing the Sephadex G-75 chromatographic profiles of Zn in native cytosol and Cd in cytosol incubated briefly with CdCl2 to saturate free binding sites on the protein before Sephadex G-75 chromatography. In two cases unsaturation of metallothionein was correlated with a lack of zinc in the ascites fluid which supplies the tumor with zinc.

Aldosterone modulates glucocorticoid receptor binding in hippocampal cell cultures via the mineralocorticoid receptor

The regulation of corticosteroid receptor expression in the rat brain by adrenal steroids remains controversial. The results of in vivo studies [Brinton and McEwen, 1988; Luttge et al., 1989] suggest that activation of type I receptors can modulate both mineralocorticoid (MR; type I) and glucocorticoid (GR; type II) receptor binding in selected brain regions. The present study utilized primary hippocampal cell cultures from rats sacrificed at E19-20 days of gestation to examine the effects of RU 28362, corticosterone (CORT) and aldosterone (ALDO) on GR binding ([3H]dexamethasone +/- RU 28362). Four days of exposure to 10 nM RU 28362, a highly selective GR agonist, resulted in a robust (approximately 70%) decrease in GR binding. Similar exposure to 10 nM of either CORT or ALDO also produced a significant (50-55%) decrease in GR binding capacity. Scatchard analyses confirmed that the diminished GR binding capacity in response to ALDO was due to a decrease in total number of binding sites (Bmax for Control = 112 +/- 25 fmol/mg vs. ALDO = 48 +/- 12 fmol/mg) with no significant change in the affinity constant. The calculated EC50 from the ALDO concentration response curve was 3.5 nM. Competition studies demonstrated that such low nM concentrations of ALDO were unable to displace specific [3H]dexamethasone +/- RU 28362 binding. Spironolactone, a highly specific MR antagonist, inhibited the ALDO-induced down-regulation of GR binding. These findings support the hypothesis that MR activation can modulate GR binding in hippocampal cells.

Antisense profilaggrin RNA delays and decreases profilaggrin expression and alters in vitro differentiation of rat epidermal keratinocytes

Ichthyosis vulgaris is an epidermal disorder in which profilaggrin expression is decreased or absent. To determine whether the ichthyosis vulgaris phenotype could be mimicked by eliminating profilaggrin expression, a rat epidermal cell line was transfected with a plasmid that directs the constitutive expression of an RNA that is antisense to normal profilaggrin mRNA. Non-transfected and neomycin-resistant cells not containing antisense plasmid that were grown in the neomycin analogue G418 served as controls. Immunoblot and immunofluorescence analysis showed that profilaggrin protein expression and processing to filaggrin were delayed by 3 to 4 d and decreased in transfected cells. Profilaggrin mRNA was detected in both control and transfected cells only after the cells reached confluence, whereas antisense RNA was detected in transfectants at all times, even prior to confluence. Ultrastructural examination revealed that keratohyalin granules were decreased in number, globular, and heterogeneous in appearance in transfected cells in-contrast to angular structures seen in control cells. Unexpectedly, stratification was impaired, intermediate filaments were noticeably reduced, and cornified cell envelope formation was delayed in transfectants. Unlike ichthyosis vulgaris keratinocytes, where keratin expression is unaffected, appearance of K1 and K10 was delayed and K1/K10 synthesis was delayed and decreased in transfected cells. The precipitous drop in 35S-methionine incorporation into cytoskeletal protein seen at confluence in control cells was delayed by 3 d in transfected cells. We conclude that, rather than producing the ichthyosis vulgaris phenotype, antisense profilaggrin RNA has more broad-reaching effects on in vitro differentiation of rat epidermal keratinocytes.

Metallothionein and anticancer agents: the role of metallothionein in cancer chemotherapy

Metallothioneins (MTs) are intracellular proteins containing the highest amount of thiol groups within the cytoplasm. These thiol groups are able to bind several cytotoxic agents, such as platinum compounds and alkylating agents. Increased levels of MT are one mechanism of resistance to these anticancer drugs, as intracytoplasmic binding of MT prevents the active molecules from reaching their target, the intranuclear DNA of tumor cells. MT synthesis can easily be induced by physiologic heavy metals such as zinc and copper. Pharmacological modulation of MT levels has been used to increase the MT pool in normal tissues and decrease their susceptibility to the toxicity of anticancer drugs. In the case of tumors arising in the brain, where the inducibility of MT synthesis is low, this approach would allow protection of normal tissues without decreasing the antitumor activity of the cytotoxic agents. The interaction of MT with cytotoxic agents is not limited to covalent binding. A correlation between MT synthesis and amplification of oncogenes such as ras has been reported. Furthermore, the cytotoxic drugs are bound by MT after competition with zinc and copper; these metals are cofactors of numerous metalloenzymes, some of which are involved in the metabolism of nucleic acids. Competitive displacement of these metals might modify nucleic acid metabolism and influence cellular proliferation. On the other hand, increased MT levels could provide a zinc cofactor reserve that increases the cell's reparative potential when faced by DNA damage by cytotoxic agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Stress-related induction of hepatic metallothionein synthesis and increase in peripheral polymorphonuclear leukocytes in mice

This experiment examined whether hepatic metallothionein (MT) synthesis induced by stressful stimuli could reinforce the peripheral leukocyte defense mechanism in mice. A 2 x 2 cm section of dorsal skin was excised from male ICR mice (7 w.o.), then the hepatic MT concentration and superoxide anion production (SOA) in peripheral leukocytes were measured at 6 and 24 hr after the excision. The 6 hr-hepatic MT level was 6 times greater in the skin-excised mice than in the controls. SOA in the skin-excised mice was 2.3 times greater at 6 hr than in the controls, then decreased to the control level by 24 hr. Food deprivation increased the hepatic MT and SOA levels at 24 and 48 hr to a remarkably greater level than in the controls. The increases in SOA, which was measured by chemiluminescence response (CL) were found to be due to an increase in the number of polymorphonuclear leukocytes (PMNs) in the peripheral leukocytes in both the skin excision and food deprivation groups. These results suggest that skin excision causes an inflammatory response in mice that results in an acute increase in the number of PMNs concomitant with the acute activation of hepatic MT synthesis. Food deprivation might result in physiologic stress 24 hr or more after food deprivation and cause "emergency" increases in MT synthesis and PMN defense mechanisms. Thus, some unknown linked mechanisms might exist between hepatic MT synthesis and increased peripheral PMNs.

Cloning and specific polymerised-chain-reaction amplification of a third charge-separable human metallothionein isoform

Metallothionein (MT) fractions isolated from human adult liver tissue are readily separated by anion-exchange chromatography in two isoforms, MT-1 and MT-2, which differ from each other in the nature of the amino acid residue at position 11. In fetal liver tissue, the presence of a third charge-separable MT isoform has been previously reported. We determined its partial amino acid sequence and the sequence of a cDNA clone encoding this MT form. This confirmed the existence of another human MT isoform, hereafter named MT-0, which is characterized by the presence of a negatively charged amino acid at position 8, and by a Glu23 to Lys substitution in a strictly conserved region of the protein. Taking into account these substitutions, we are able to classify human MT isoforms into three instead of two charge-separable groups, based on the nature of three amino acid residues. The unique presence of Glu8 in MT-0 enabled us to develop an MT-0-specific amplification by the polymerase chain reaction, which revealed the presence of MT-0 mRNA in adult liver RNA samples, in spite of the total absence of this isoform at the protein level. This suggests the involvement of post-transcriptional regulatory mechanisms in the expression of this fetal MT form.

Relative promoter activity in human mammary epithelial cells assayed by transient expression

Chimeric DNA expression vectors containing regulatory sequences proximal to the 5' end of coding sequences for mammalian genes provide valuable tools to study gene expression. Genes coding for easily measured products (reporter genes) can be used to study promoter strength and regulation of gene expression after transient expression of promoter-reporter constructs in mammalian cells. To determine the strength of a variety of mammalian and viral promoter-enhancer sequences in primary cultures of human mammary epithelial cells (HMEC), these sequences were fused to the bacterial chloramphenicol acetyltransferase (CAT) gene and transfected into HMEC using strontium phosphate. The long terminal repeat (LTR) of the endogenous murine leukemia virus AKR-623 was the most potent promoter of transient CAT expression in HMEC. A number of commonly available promoter sequences displayed a wide range of activities in these cells. The glucocorticoid responsive LTR promoter from the murine mammary tumor virus modulated expression of CAT and was sensitive to the concentration of dexamethasone in the growth media. In a similar fashion, the regulatory sequences from the murine metallothionein-1 gene retained responsiveness to zinc concentration in the growth media.

Selection of mouse cells with amplified metallothionein genes retaining their glucocorticoid inducibility

Two new mouse cell mutants, resistant to either 80 or 100 mM CdCl2, were isolated to study the regulation of transcription by the glucocorticoid hormones. Their metallothionein mt-1% and mt-2+ genes were amplified coordinately to a maximum of 30 copies per cell. By Southern blot analysis, no gross rearrangement was detectable near the mt+ loci. Contrary to other mutants previously isolated, the metallothionein-specific mRNAs of these mutants are inducible by dexamethasone.

Metallothionein induction in cultured fibroblasts and liver of a marine flatfish, the turbot,Scophthalmus maximus

Intraperitoneal injection of turbot with Cd induced the synthesis of a low molecular weight hepatic Cd-binding protein and a 500bp mRNA, which hybridised to a plaice metallothionein (MT) cRNA probe. The Cd-binding protein displayed cross-reactivity in a competitive ELISA with antiserum raised against rainbow trout MT and had the characteristic amino acid composition, metal stoichiometry and spectral characteristics of a Class I MT. Only one isoform was apparent on ion exchange chromatography. Southern blot analysis of DNA cleaved with four restriction enzymes suggested that only a single MT gene is present in turbot.In an established turbot fibroblast cell line, Cd induced MT mRNA and MT levels in a dose and time-dependent manner. MT was also induced by Cu, Hg and Zn but not Pb exposure. Physiological concentrations of glucocorticoids and sex hormones did not induce MT synthesis, although at high concentrations a positive response to corticosterone, dexamethasone, hydrocortisone or progesterone was observedin vitro indicating the possible presence of a functional steroid regulatory element in the fish MT gene.

Glucocorticoid inhibition of inflammation-induced metallothionein synthesis in mouse liver

The effects of glucocorticoid treatment on the induction of hepatic metallothionein (MT) during inflammation initiated by turpentine oil (TUR) or endotoxin (LPS) were studied in mice. The administration of TUR increased concentrations of hepatic MT as well as that of plasma fibrinogen. Although hepatic MT was modestly induced by dexamethasone (DEX) alone, pretreatment with DEX (12.5 to 100 mg/kg, sc) inhibited the increases both in hepatic MT and in plasma fibrinogen from a subsequent dose of TUR 6 hr after DEX administration. The concentration of hepatic MT in the DEX-pretreated (25 mg/kg) group was higher than that in the nonpretreated group 4 hr after administration of TUR, but after 24 hr, the MT concentration in the DEX-pretreated group was inhibited to 20% of that in the nonpretreated group. These inhibitory effects were also observed by prednisolone (PRE) but not by salicylic acid. The inhibitory effect of DEX on the induction of MT synthesis during inflammation was observed after administration of the exudate obtained from inflamed tissue. When inflammation was initiated by an injection of LPS as well as TUR, pretreatment of either DEX or PRE inhibited the increase of hepatic MT. Pretreatment of DEX did not affect the induction of hepatic MT synthesis by cadmium. In contrast to inflammation initiated by TUR or LPS, pretreatment of DEX caused an additive increase of hepatic MT concentration after administration of zinc. These results suggest that glucocorticoids, despite being direct inducers of MT, inhibit the induction of MT synthesis during inflammation by the suppression of cytokine production.

Induction of metallothionein synthesis by menadione or carbon tetrachloride is independent of free radical production

The relationship between induction of hepatic metallothionein (MT) synthesis and lipid peroxidation by free radical production following an injection of menadione or carbon tetrachloride (CCl4) in mice was studied. The hepatic concentration of MT was increased by menadione significantly at 25 mg/kg or higher. A significant increase in thiobarbituric acid (TBA) value, indicative of lipid peroxidation, was observed in the liver at menadione doses of 62.5 mg/kg or higher. Both the MT and the TBA value in the liver were significantly increased at the low dose of CCl4. The concentration of MT was increased significantly 4-8 hr after administrations of these compounds. The increase of TBA value over time was similar to that of MT concentration after administration of CCl4, but not after administration of menadione. The MT concentration in the menadione group was higher than that in the CCl4 group, and the TBA level in the menadione group was lower than that in the CCl4 group. Pretreatment with vitamin E caused a significant reduction in the TBA value, but did not affect the MT level in the liver. The concentration of MT did not significantly correlate with the TBA value in either the menadione or the CCl4 group. Pretreatment with phenobarbital, which promotes free radical production, did not influence induction of MT synthesis following an injection of menadione or CCl4. Neither L-buthionine sulfoximine nor 2-cyclo-hexen-1-one, which decreases hepatic glutathione, influenced the induction of MT by menadione. These data suggest that induction of MT synthesis by menadione or CCl4 is independent of free radical production in the liver.

Metal redistribution in largemouth bass (Micropterus salmoides) in response to restrainment stress and dietary cadmium: Role of metallothionein and other metal-binding proteins

1. Fish stressed by restrainment displayed elevated serum cortisol, copper and zinc levels; dietary cadmium had no effect. 2. Stress/dietary cadmium increased liver copper levels in a metal pool containing metallothionein and non-metallothionein proteins but decreased intestinal zinc bound as low molecular weight forms. 3. After restrainment, zinc losses occurred in dorsal skeletal muscle, ovary and spleen: copper decreased in intestine and pyloric caecum. 4. Dietary cadmium altered intestinal zinc distribution and raised hepatic Cu-binding protein levels but did not alter plasma zinc, copper or cortisol levels. 5. Alterations in zinc and copper concentrations during stress contrast with mammalian models.

Synergistic effects of 12-O-tetradecanoylphorbol-13-acetate and dexamethasone on de novo synthesis of histidine decarboxylase in mouse mastocytoma P-815 cells

12-O-Tetradecanoylphorbol-13-acetate (TPA) markedly enhanced the increase in L-histidine decarboxylase (HDC) activity induced by dexamethasone in mouse mastocytoma P-815 cells, even with a concentration of the latter that had the maximal effect, whereas it induced a rapid and transient increase in HDC activity, which peaked after 3 h in the absence of dexamethasone. The synergistic effect of TPA on HDC activity induced by dexamethasone was detected after 4 h, a plateau level being reached by 6 h, which was similar to the time course with dexamethasone alone. TPA enhanced the induction of HDC activity by various glucocorticoids, but had no effect on the induction by dibutyryl cAMP, prostaglandin E2 or sodium butyrate. Both 1-oleoyl-2-acetylglycerol, a protein kinase C activator, and okadaic acid, a protein phosphatase inhibitor, enhanced the increase in HDC activity induced by dexamethasone, but 4 alpha-phorbol-12,13-didecanoate, an inactive derivative of TPA, did not. Protein kinase C inhibitors, such as staurosporin, H-7 and K255a, suppressed the increase in HDC activity induced by TPA with or without dexamethasone. The enhancement of HDC activity by dexamethasone was completely suppressed by cycloheximide or actinomycin D. Furthermore, TPA markedly enhanced the accumulation of HDC mRNA due to dexamethasone (5 to 10-fold, from 6 to 12 h after). TPA did not cause a significant increase in the level of either [3H]dexamethasone binding capacity or preformed HDC activity in cells. These results taken together suggest that dexamethasone-induced de novo synthesis of HDC in mastocytoma P-815 cells is up-regulated by TPA-activated protein kinase C through the mechanism involving an increased rate of transcription.

Induction of hepatic metallothionein by nonmetallic compounds associated with acute-phase response in inflammation

Induction of hepatic metallothionein (MT) synthesis by several nonmetallic compounds and its relationship to an acute-phase response in inflammation were studied in mice. Subcutaneous injections of menadione, paraquat, carbon tetrachloride (CCl4), and several organic solvents caused an increase of hepatic MT concentration. This MT contained only zinc. Menadione and n-hexane caused the greatest accumulation of hepatic MT among these nonmetallic compounds (about 13-fold). The concentration of Zn was significantly decreased in plasma in contrast to liver after an injection of these nonmetallic compounds. When 65ZnCl2 was injected iv after these injections, uptake of 65Zn to the liver was increased. This effect was not observed after treatment with cycloheximide. The association with inflammation of this induction of MT accumulation was examined by determination of acute-phase proteins. The concentration of fibrinogen in the plasma was significantly increased following injection of those nonmetallic compounds which caused marked hepatic MT accumulation. An injection of 1 N NaOH, 1 N HCl, turpentine oil, or endotoxin caused a significant increase in the plasma concentration of fibrinogen and in the hepatic MT concentration. Injections of n-hexane as well as turpentine oil significantly increased hepatic MT concentration and plasma concentration of fibrinogen and ceruloplasmin with time. The concentration of fibrinogen was significantly correlated (r = 0.789) with the concentration of hepatic MT. Neither adrenalectomy nor pretreatment with dexamethasone prevented hepatic MT accumulation caused by these compounds. These results indicate that induction of hepatic MT synthesis by these nonmetallic compounds is associated with an acute-phase response in inflammation and is independent of glucocorticoids.

Induction of metallothionein and stimulation of calcification by dexamethasone in cultured clonal osteogenic cells, MC3T3-E1

To clarify the effects of dexamethasone (Dex) on metallothionein (MT) synthesis and calcification in osteoblastic cells, a clonal osteogenic cell line (MC3T3-E1) was used in the present study. Under culture conditions designed not to cause calcification, MT synthesis of cells at 3 days after inoculation increased with increasing concentration of Dex (2.5-50 nM) for a 24-h culture period. Cells at 6 or 9 days after inoculation also synthesized MT by a 24-h exposure to Dex. These show that undifferentiated osteoblasts have the ability to synthesize MT by Dex. Under culture conditions designed to cause calcification, cells at 6 days after inoculation were cultured with 50 nM Dex in the presence of 7 mM beta-glycerophosphate (beta-GP) for 7 days. Ca content of Dex-treated cells was about 7.5 times as high as that of untreated cells. Dex-treated cells showed a high activity of alkaline phosphatase (ALP). The Zn content of the MT fraction in Dex-treated cells was about 8 times as high as that of untreated cells. These results show that Dex has the ability to induce MT synthesis in osteoblastic cells and to cause a high calcification which is due at least partly to an enhanced activity of ALP.

Mitogenicity and metallothionein induction: two separate effects of zinc ions on human mononuclear blood cells

The mitogenic effect of elevated concentrations of zinc ions on human lymphocytes was found to be inhibited by the glucocorticoid hormone dexamethasone. The effect decreased progressively from complete block to partial inhibition when the culture period before the addition of dexamethasone was prolonged. In contrast, dexamethasone did not inhibit an induced formation of metallothionein in mononuclear cells. Furthermore, dexamethasone itself was found to induce small amounts of metallothionein. Apparently, the mitogenic effect and the induction of metallothionein by zinc ions in mononuclear cells occur by mutually independent mechanisms.