Regulation of metallothionein gene expression

Methylation mediated silencing of MicroRNA-1 gene and its role in hepatocellular carcinogenesis

MicroRNAs (miR) are a class of small ( approximately 21 nucleotide) noncoding RNAs that, in general, negatively regulate gene expression. Some miRs harboring CGIs undergo methylation-mediated silencing, a characteristic of many tumor suppressor genes. To identify such miRs in liver cancer, the miRNA expression profile was analyzed in hepatocellular carcinoma (HCC) cell lines treated with 5-azacytidine (DNA hypomethylating agent) and/or trichostatin A (histone deacetylase inhibitor). The results showed that these epigenetic drugs differentially regulate expression of a few miRs, particularly miR-1-1, in HCC cells. The CGI spanning exon 1 and intron 1 of miR-1-1 was methylated in HCC cell lines and in primary human HCCs but not in matching liver tissues. The miR-1-1 gene was hypomethylated and activated in DNMT1-/- HCT 116 cells but not in DNMT3B null cells, indicating a key role for DNMT1 in its methylation. miR-1 expression was also markedly reduced in primary human hepatocellular carcinomas compared with matching normal liver tissues. Ectopic expression of miR-1 in HCC cells inhibited cell growth and reduced replication potential and clonogenic survival. The expression of FoxP1 and MET harboring three and two miR-1 cognate sites, respectively, in their respective 3'-untranslated regions, was markedly reduced by ectopic miR-1. Up-regulation of several miR-1 targets including FoxP1, MET, and HDAC4 in primary human HCCs and down-regulation of their expression in 5-AzaC-treated HCC cells suggest their role in hepatocarcinogenesis. The inhibition of cell cycle progression and induction of apoptosis after re-expression of miR-1 are some of the mechanisms by which DNA hypomethylating agents suppress hepatocarcinoma cell growth.

The influence of metallothionein on exposure to metals: an in vitro study on cellular models

In the present study, the interactions between zinc (Zn) and copper (Cu) or iron (Fe) have been examined. Rat hepatoma cell line H4-II-E-C3, fibroblast cell line mutant MT-/-, and wild-type MT+/+ cells treated with ZnSO4 or CuSO4 or FeSO4 or CuSO4+ZnSO4 or ZnSO4+FeSO4 for different times have been employed to study the effect of metallothionein (MT), glutathione (GSH) and metal (Cu, Fe and Zn) accumulation during cellular adaptation to supraphysiological metal concentrations. To investigate the different biological functions in the processes of metal homeostasis and detoxification, the levels of both MT-1 and MT-2 mRNAs have been evaluated. The three cell lines responded differently to metal treatments suggesting that the uptake and storage of these metals are affected by the specific cellular model and MT presence. In particular, Zn treatment significantly decreased Fe accumulation (p<0.05), whereas MT induced by Zn increased intracellular Cu content (p<0.05). Moreover, in H4-II-E-C3 cells administration of metals resulted in a rapid and transient induction of MT (p<0.05) and in GSH accumulation (p<0.05) suggesting synergistic interactions in which both appear essential for a protective regulatory function against the redox activity of metals. Taken together these results demonstrate that Zn affects the cellular levels of Cu and Fe by competition with the same ligand sites and/or by coordinate regulation of MT and GSH content.

Metallothionein in the central nervous system: Roles in protection, regeneration and cognition

Metallothionein (MT) is an enigmatic protein, and its physiological role remains a matter of intense study and debate 50 years after its discovery. This is particularly true of its function in the central nervous system (CNS), where the challenge remains to link its known biochemical properties of metal binding and free radical scavenging to the intricate workings of brain. In this compilation of four reports, first delivered at the 11th International Neurotoxicology Association (INA-11) Meeting, June 2007, the authors present the work of their laboratories, each of which gives an important insight into the actions of MT in the brain. What emerges is that MT has the potential to contribute to a variety of processes, including neuroprotection, regeneration, and even cognitive functions. In this article, the properties and CNS expression of MT are briefly reviewed before Dr Hidalgo describes his pioneering work using transgenic models of MT expression to demonstrate how this protein plays a major role in the defence of the CNS against neurodegenerative disorders and other CNS injuries. His group's work leads to two further questions, what are the mechanisms at the cellular level by which MT acts, and does this protein influence higher order issues of architecture and cognition? These topics are addressed in the second and third sections of this review by Dr West, and Dr Levin and Dr Eddins, respectively. Finally, Dr Aschner examines the ability of MT to protect against a specific toxicant, methylmercury, in the CNS.

Zinc, antioxidant systems and metallothionein in metal mediated-apoptosis: biochemical and cytochemical aspects

Copper, zinc and iron are essential metals for different physiological functions, even though their excess can lead to biological damage. This review provides a background of toxicity related to copper, iron and zinc excess, biological mechanisms of their homeostasis and their respective roles in the apoptotic process. The antioxidant action of metallothionein has been highlighted by summarizing the most important findings that confirm the role of zinc in cellular protection in relation to metallothionein expression and apoptotic processes. In particular, we show that a complex and efficient antioxidant system, the induction of metallothionein and the direct action of zinc have protective roles against oxidative damage and the resulting apoptosis induced by metals with redox proprieties. In addition, to emphasize the protective effects of Zn and Zn-MT in Cu and Fe-mediated oxidative stress-dependent apoptosis, some aspects of apoptotic cell death are shown. The most widely used cytochemical techniques also have been examined in order to critically evaluate the available data from a methodological point of view. The observations on the role of Zn and MT could potentially develop new applications for this metal and MT in biomedical research.

Magnetic resonance imaging and spectroscopy of transgenic models of cancer

The complexity of cancer, where a single genetic alteration can have multiple functional effects, makes it a fascinating but humbling disease to study, and the necessity of investigating it in its entirety is more imperative than ever before. Advances in transgene technology have made it possible to create cancer cells, or mice with specific genetic alterations, and the application of an array of both functional and molecular non-invasive MR methods to these transgenic cancer cells and mice to characterize their phenotypic traits is revolutionizing our understanding of cancer. With the establishment of multi-modality molecular imaging centers within barrier or pathogen-free facilities, multi-parametric and multi-modality imaging of transgenic mouse models of human cancer are becoming increasingly prevalent. In this review, we outline some of the methods currently available for generating transgenic mice and cancer cell lines. We also present examples of the application of MR methods to transgenic models that are providing novel insights into the molecular and functional characteristics of cancer and are leading to an era of "non-invasive phenotyping" of the effects of specific molecular alterations in cancer.

Metallothionein expression is suppressed in primary human hepatocellular carcinomas and is mediated through inactivation of CCAAT/enhancer binding protein alpha by phosphatidylinositol 3-kinase signaling cascade

Reactive oxygen species (ROS) resulting from chronic inflammation cause liver injury leading to transformation of regenerating hepatocytes. Metallothioneins (MT), induced at high levels by oxidative stress, are potent scavengers of ROS. Here, we report that the levels of MT-1 and MT-2A are drastically reduced in primary human hepatocellular carcinomas (HCCs) and in diethylnitrosamine-induced liver tumors in mice, which is primarily due to transcriptional repression. Expression of the transcription factor, MTF-1, essential for MT expression, and its target gene Zn-T1 that encodes the zinc transporter-1 was not significantly altered in HCCs. Inhibitors of both phosphatidylinositol 3-kinase (PI3K) and its downstream target AKT increased expression of MT genes in HCC cells but not in liver epithelial cells. Suppression of MT-1 and MT-2A by ectopic expression of the constitutively active PI3K or AKT and their up-regulation by dominant-negative PI3K or AKT mutant confirmed negative regulation of MT expression by PI3K/AKT signaling pathway. Further, treatment of cells with a specific inhibitor of glycogen synthase kinase-3 (GSK-3), a downstream effector of PI3K/AKT, inhibited MT expression specifically in HCC cells. Short interfering RNA-mediated depletion of CCAAT/enhancer binding protein alpha (C/EBPalpha), a target of GSK-3, impeded MT expression, which could not be reversed by PI3K inhibitors. DNA binding activity of C/EBPalpha and its phosphorylation at T222 and T226 by GSK-3 are required for MT expression. MTF-1 and C/EBPalpha act in concert to increase MT-2A expression, which probably explains the high level of MT expression in the liver. This study shows the role of PI3K/AKT signaling pathway and C/EBPalpha in regulation of MT expression in hepatocarcinogenesis.

Cloning and functional characterization of 5′-upstream region of metallothionein-I gene from crucian carp (Carassius cuvieri)

Metallothioneins are low molecular weight, cysteine-rich, metal-binding proteins, which can be induced by heavy metal ions, cytokines, stress, and hormones. To investigate the roles of the main cis-acting elements involved in the inducible expression of metallothionein gene in fish, the 5'-upstream region of crucian carp (Carassius cuvieri) metallothionein-I gene had been cloned and analyzed after our previous work on metallothionein-II. In its upstream region, several putative cis-acting elements, including nine metal regulatory elements (MREs), one antioxidant response element, one E-box, and three interleukin-6 responsive elements, etc. were found. The nine metal regulatory elements are confined in less than 1000 bp from ATG start codon and organized into two clusters with different roles to the induction of the metallothionein-I expression. Deletion mutant assays demonstrated that both the distal and proximal clusters of metal regulatory elements contributed to the basal expression of the metallothionein-I, but only the proximal cluster was the chief contributor to the metal fold induction. In transient luciferase reporter assays, Zn2+ and Cd2+ served as much stronger inducers than Cu2+ to the metallothionein-I expression. H2O2 also could activate the metallothionein-I promoter about two-fold, which was mediated by the antioxidant response element (TGACAACGC, -437/-445). In conclusion, our studies demonstrate the roles of metal regulatory element and antioxidant response element in the induction of crucian carp metallothionein-I gene, and provide the regulatory mechanism for the use of fish metallothionein as a biomarker for monitoring of metal contamination in waters.

Epigenetic regulation of metallothionein-i gene expression: differential regulation of methylated and unmethylated promoters by DNA methyltransferases and methyl CpG binding proteins

Metallothioneins (MTs) are a group of cysteine-rich stress response proteins that scavenge reactive oxygen species and heavy metals. Recently, we have shown that MT-I promoter is methylated and suppressed in some solid and liquid tumors and can be robustly activated following treatment with inhibitors of DNA methyltransferase (DNMT) and histone deacetylase (HDAC). Here, we have analyzed MT-I chromatin structure in active, unmethylated (Hepa cells) and in repressed, methylated state (lymphosarcoma cells). Restriction enzyme accessibility assay showed that the MT-I promoter has an open conformation in unmethylated state as opposed to refractory chromatin structure in methylated state. Positioning of nucleosomal arrays on the methylated promoter further confirmed the closed chromatin structure of the methylated promoter. Chromatin immunoprecipitation (ChIP) assay demonstrated that the unmethylated promoter is associated with K9-acetyl, K4-methyl, and S10-phospho histone H3 whereas the methylated promoter is predominantly associated with K9-methyl H3. HP1alpha that recognizes K9-methyl H3 inhibited methylated MT-1 promoter activity whereas closely related HP1gamma repressed the promoter irrespective of its methylation status. Ubiquitously expressed DNA methyltransferase 1 (DNMT1) suppressed MT-I promoter activity irrespective of its methylation status that does not require its catalytic activity. The DNMT1-mediated repression of MT-I promoter was relieved by trichostatin A, an HDAC inhibitor. Among the methyl CpG binding proteins, MBD2 and MBD4 specifically associated with the methylated promoter and inhibited its activity. In contrast, MBD1 and MeCP2 interacted with both promoters and suppressed the promoter activity irrespective of its methylation status. These results demonstrate that the methylated and unmethylated MT-I promoter are differentially regulated by DNA methyltransferase and methyl-CpG binding proteins, and DNMT1 could suppress MT promoter by a transcriptional mechanism independent of its enzymatic function. These studies suggest that the components of epigenetic machinery differentially regulate methylated and unmethylated MT-I gene expression.

Positive in vivo heterologous gene regulation by electric pulses delivery with metallothionein I gene promoter

BACKGROUND

In vivo electrotransfer is a physical method of gene delivery in various tissues and organs. It is a promising strategy for the systemic secretion of therapeutic proteins and for DNA vaccination. Nevertheless, for the success of gene therapy in clinics, it is essential to develop gene regulation systems. The existing systems described in the literature all rely on the creation of an artificial transcription factor and/or an inducer drug. New strategies based on endogenous regulatable elements are being developed. We have previously identified the murine metallothionein promoter as an endogenous promoter inducible by controlled electric stimuli applied for electrotransfer experiments. We report here a regulation strategy based on this murine metallothionein promoter in a plasmid context using electric pulses delivery as an inducer.

METHODS

Plasmids containing different constructions of the murine metallothionein I (mMT-I) promoter were transfected in mice tibialis-cranalis muscles using the simple skeletal muscle electrotransfer method. The regulation system was studied with the murine secreted alkaline phosphatase (MUSEAP) reporter gene.

RESULTS

The mMT-I promoter can be transiently induced in vivo by application of electric fields. Its inducibility was analyzed in a plasmid context. We demonstrated that the mechanism of this transcriptional induction is not mediated by the cellular entry of metal ions. The ARE (antioxidant-responsive element) sequence was identified as the element responsive to the electric field stimulation.

CONCLUSIONS

This time-control of the expression of a therapeutic gene by physical stimuli could be of value in the context of gene regulation for gene therapy.

Metallothioneins are multipurpose neuroprotectants during brain pathology

Metallothioneins (MTs) constitute a family of cysteine-rich metalloproteins involved in cytoprotection during pathology. In mammals there are four isoforms (MT-I - IV), of which MT-I and -II (MT-I + II) are the best characterized MT proteins in the brain. Accumulating studies have demonstrated MT-I + II as multipurpose factors important for host defense responses, immunoregulation, cell survival and brain repair. This review will focus on expression and roles of MT-I + II in the disordered brain. Initially, studies of genetically modified mice with MT-I + II deficiency or endogenous MT-I overexpression demonstrated the importance of MT-I + II for coping with brain pathology. In addition, exogenous MT-I or MT-II injected intraperitoneally is able to promote similar effects as those of endogenous MT-I + II, which indicates that MT-I + II have both extra- and intracellular actions. In injured brain, MT-I + II inhibit macrophages, T lymphocytes and their formation of interleukins, tumor necrosis factor-alpha, matrix metalloproteinases, and reactive oxygen species. In addition, MT-I + II enhance cell cycle progression, mitosis and cell survival, while neuronal apoptosis is inhibited. The precise mechanisms downstream of MT-I + II have not been fully established, but convincing data show that MT-I + II are essential for coping with neuropathology and for brain recovery. As MT-I and/or MT-II compounds are well tolerated, they may provide a potential therapy for a range of brain disorders.

Cloning of crucian carp (Carassius cuvieri) metallothionein-II gene and characterization of its gene promoter region

The genomic DNA of crucian carp (Carassius cuvieri) metallothionein-II (ccMT-II), with its upstream region, was obtained. The sequence analysis of its upstream region revealed several putative cis-acting elements including seven metal regulatory elements (MREs), three activator protein 1 (AP1), two glucocorticoid response elements (GREs), etc. The seven MREs locate into two clusters, a distal cluster with four MREs within -800/-600bp from the translation start site and a proximal cluster with three MREs close to TATA box. In transient luciferase gene expression assays, both of the distal and proximal cluster MREs have significantly shown synergistic effects in the transcription of ccMT-II gene; the proximal cluster of MREs serves as the major elements in metal inducing activity; Zn(2+) and Cd(2+) served as much stronger inducers than Cu(2+) shown in ccMT-II expression. The two GRE homologous sequences in ccMT-II promoter showed not to be inductive in either HepG2 or HEK293.

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.

Gene expression profiling of the PPAR-alpha agonist ciprofibrate in the cynomolgus monkey liver

Fibrates, such as ciprofibrate, fenofibrate, and clofibrate, are peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists that have been in clinical use for many decades for treatment of dyslipidemia. When mice and rats are given PPARalpha agonists, these drugs cause hepatic peroxisome proliferation, hypertrophy, hyperplasia, and eventually hepatocarcinogenesis. Importantly, primates are relatively refractory to these effects; however, the mechanisms for the species differences are not clearly understood. Cynomolgus monkeys were exposed to ciprofibrate at various dose levels for either 4 or 15 days, and the liver transcriptional profiles were examined using Affymetrix human GeneChips. Strong upregulation of many genes relating to fatty acid metabolism and mitochondrial oxidative phosphorylation was observed; this reflects the known pharmacology and activity of the fibrates. In addition, (1) many genes related to ribosome and proteasome biosynthesis were upregulated, (2) a large number of genes downregulated were in the complement and coagulation cascades, (3) a number of key regulatory genes, including members of the JUN, MYC, and NFkappaB families were downregulated, which appears to be in contrast to the rodent, where JUN and MYC are reported to upregulated after PPARalpha agonist treatment, (4) no transcriptional signal for DNA damage or oxidative stress was observed, and (5) transcriptional signals consistent with an anti-proliferative and a pro-apoptotic effect were seen. We also compared the primate data to literature reports of hepatic transcriptional profiling in PPARalpha-treated rodents, which showed that the magnitude of induction in beta-oxidation pathways was substantially greater in the rodent than the primate.

Characterization of a rice class II metallothionein gene: tissue expression patterns and induction in response to abiotic factors

Data mining the complete rice genome sequences revealed a genomic fragment encoding a characteristic metallothionein (MT) protein, and its full-length cDNA was isolated from rice developing seeds by RT-PCR. This cDNA, designated OsMT-II-1a, contains an open reading frame of 264 bp encoding a protein of 87 amino acid residues. The predicted amino acid sequence was shown to have structural features characteristic of plant class II MT proteins. By sequence analysis of its 5'-flanking region, one putative TATA box, four putative CAAT boxes, and several short sequences homologous to previously reported regulatory cis-elements were identified. Northern blot analysis showed that accumulation of OsMT-II-1a mRNA is specifically abundant in developing seeds and 2-day glumes after pollination, and OsMT-II-1a transcription can markedly be induced by H2O2, paraquat, SNP, ethephon, ABA and SA, but barely by metal ions or other exogenous abiotic factors such as low temperature and PEG. These results coincide with the prediction of existing regulatory cis-elements in its 5'-flanking region. Taken together, the above results suggest that the processes of pollination and seed development might be mediated, at least in part, by expression of the OsMT-II-1a gene that is regulated by several abiotic factors.

Induction of human metallothionein 1G promoter by VEGF and heavy metals: differential involvement of E2F and metal transcription factors

The E2F transcription factors induce the expression of many genes in response to specific extracellular stimuli. Here, we show that human metallothionein 1G (hMT1G) promoter is upregulated by E2F1 upon VEGF stimulation of human aortic endothelial cells. Analysis of the hMT1G promoter showed the presence of many potential E2F-binding sites flanked by potential SP1 sites and metal response elements (MREs). hMT1G promoter could be induced by E2F1 in transient transfections; further, deletion analysis suggested that the region spanning the E2F-binding sites was necessary for VEGF-mediated induction. E2Fs 1-5 could bind to the hMT1G promoter in a chromatin immunoprecipitation assay. VEGF stimulation led to an increased binding of E2Fs 1-3 to the endogenous hMT1G promoter; at the same time, the binding of Rb, p107 and p130 to the promoter was abolished. VEGF stimulation also led to the increased acetylation E2F1 as well as the histones in the hMT1G promoter region. Stimulation with metals or VEGF led to dissociation of histone deacetylase 1 (HDAC1) from the promoter, leading to acetylation of histones. Induction of the hMT1G promoter upon exposure to heavy metals such as Zn and Cd is mediated by the MRE. Interestingly, mutation of MRE affected the metal response, but not the VEGF response of the hMT1G promoter. In contrast, deletion of the E2F-binding sites did not affect the metal response. Based on these findings, we conclude that induction of the hMT1G promoter by VEGF and heavy metals occurs through the utilization of different transcription factors.

Exercise-induced metallothionein expression in human skeletal muscle fibres

Exercise induces free oxygen radicals that cause oxidative stress, and metallothioneins (MTs) are increased in states of oxidative stress and possess anti-apoptotic effects. We therefore studied expression of the antioxidant factors metallothionein I and II (MT-I + II) in muscle biopsies obtained in response to 3 h of bicycle exercise performed by healthy men and in resting controls. Both MT-I + II proteins and MT-II mRNA expression increased significantly in both type I and II muscle fibres after exercise. Moreover, 24 h after exercise the levels of MT-II mRNA and MT-I + II proteins were still highly increased and the MT-II mRNA expression reached a 15-fold increase. As expected, immunohistochemical detection of malondialdehyde (MDA) and nitrotyrosine (NITT) showed that formation of free radicals and oxidative stress were clearly increased in exercising muscle peaking shortly after the end of exercise in both type I and II muscle fibres. This is the first report demonstrating that MT-I + II are significantly induced in human skeletal muscle fibres following exercise. As MT-I + II are antioxidant factors that protect various tissues during pathological conditions, the MT-I + II increases post exercise may represent a mechanism whereby contracting muscle fibres are protected against cellular stress and injury.

Are zinc-bound metallothionein isoforms (I+II and III) involved in impaired thymulin production and thymic involution during ageing?

BACKGROUND: With advancing age, thymic efficiency shows progressive decline due to thymic involution allowing impaired cell-mediated immunity and the appearance of age-related diseases. The intrinsic cause of thymic involution is still undefined. Chronic inflammation and high glucocorticoids (GCs) may be involved. However, transgenic mice, with increased GC sensitivity and over expression of GC receptors, display delayed age-associated thymic involution. This fact suggests that other substances may affect thymic involution. Among them, both isoforms of metallothioneins (MTs) I+II and III are the major candidates because their increments leads to organ atrophy in constant stress and are induced by IL-6, which increases in ageing. Enhanced MTs in ageing allows constant sequester of zinc ions and no subsequent zinc release leading to low zinc ion bioavailability for thymic efficiency. This sequester is very limited in very old age. Thus, we have investigated the MTmRNA (I+II and III) in the thymus from young, old and very old mice. METHODS: MTmRNA and IL-6mRNA (RT-PCR) in the thymus from different donors were tested. Concomitantly, TECs proliferation, zinc ion bioavailability (ratio total thymulin/active thymulin), thymulin activity and corticosterone were tested from different donors. RESULTS: Both isoforms of MTmRNA and IL-6mRNA increase in old thymus coupled with low zinc ion bioavailability, reduced TECs proliferation, impaired thymulin activity and enhanced plasma corticosterone in comparison with young. Conversely, although the thymus is involuted in very old mice because of no changes in thymus weight in comparison to old mice, reduced MTmRNA, especially MT-I+II isoforms, and low IL6mRNA occur. Concomitantly, good zinc ion bioavailability, maintained TECs proliferation, satisfactory thymulin activity and reduced corticosterone are observed in very old mice. CONCLUSIONS: The concomitant increments by high IL-6 of both MT isoforms in the thymus from old mice may be involved in thymic involution because provoking low zinc ion bioavailability, which is relevant for thymic efficiency. By contrast, the limited increments of MTs by low IL-6 induce good zinc ion bioavailability and satisfactory thymic efficiency in very old mice. Therefore, abnormal increased MTs may provoke complete thymic involution during ageing and the possible appearance of age-related diseases. If their increments are instead limited by low inflammation, healthy ageing and longevity may be reached.

Copper homoeostasis in Drosophila melanogaster S2 cells

Copper homoeostasis was investigated in the Drosophila melanogaster S2 cell line to develop an insect model for the study of copper regulation. Real-time PCR studies have demonstrated expression in S2 cells of putative orthologues of human Cu regulatory genes involved in the uptake, transport, sequestration and efflux of Cu. Drosophila orthologues of the mammalian Cu chaperones, ATOX1 (a human orthologue of yeast ATX1), CCS (copper chaperone for superoxide dismutase), COX17 (a human orthologue of yeast COX17), and SCO1 and SCO2, did not significantly respond transcriptionally to increased Cu levels, whereas MtnA, MtnB and MtnD (Drosophila orthologues of human metallothioneins) were up-regulated by Cu in a time- and dose-dependent manner. To examine the effect on Cu homoeostasis, expression of several key copper homoeostasis genes was suppressed using double-stranded RNA interference. Suppression of the MTF-1 (metal-regulatory transcription factor 1), reduced both basal and Cu-induced gene expressions of MtnA, MtnB and MtnD, significantly reducing the tolerance of these cells to increased Cu. Suppression of either Ctr1A (a Drosophila orthologue of yeast CTR1) or Ctr1B significantly reduced Cu uptake from media, demonstrating that both these proteins function to transport Cu into S2 cells. Significantly, Cu induced Ctr1B gene expression, and this could be prevented by suppressing MTF-1, suggesting that Ctr1B might be involved in Cu detoxification. Suppression of DmATP7, the putative homologue of human Cu transporter genes ATP7A and ATP7B, significantly increased Cu accumulation, demonstrating that DmATP7 is essential for efflux of excess Cu. This work is consistent with previous studies in mammalian cells, validating S2 cells as a model system for studying Cu transport and identifying novel Cu regulatory mechanisms.

Identification of premycorrhiza-related plant genes in the association between Quercus robur and Piloderma croceum

•  An in vitro system with micropropagated oaks (Quercus robur) and the ectomycorrhizal fungus Piloderma croceum, which is characterized by a delayed mycorrhiza formation, was used to identify plant transcripts upregulated in the premycorrhizal phase. •  Complementary DNA (cDNA) populations of uninoculated roots and fungal mycelium were subtracted from a cDNA population of inoculated roots. Differential expression was confirmed by reverse Northern and 50 clones for different polypeptides were found to be up-regulated. Twenty-nine clones were investigated in more detail. •  For approximately half of the cDNA fragments no homologies could be identified in databases. The residual fragments code for polypeptides with homologies to known proteins involved in signal perception and transmission, stress responses, metabolism and growth. •  Since many of the identified genes have not yet been described in the context of symbiotic events, their potential roles during early phases of the recognition process are discussed.

Regulation of zinc homeostasis by inducible NO synthase-derived NO: nuclear metallothionein translocation and intranuclear Zn2+ release

Zn2+ is critical for the functional and structural integrity of cells and contributes to a number of important processes including gene expression. It has been shown that NO exogenously applied via NO donors resulting in nitrosative stress leads to cytoplasmic Zn2+ release from the zinc storing protein metallothionein (MT) and probably other proteins that complex Zn2+ via cysteine thiols. We show here that, in cytokine-activated murine aortic endothelial cells, NO derived from the inducible NO synthase (iNOS) induces a transient nuclear release of Zn2+. This nuclear Zn2+ release depends on the presence of MT as shown by the lack of this effect in activated endothelial cells from MT-deficient mice and temporally correlates with nuclear MT translocation. Data also show that NO is an essential but not sufficient signal for MT-mediated Zn2+ trafficking from the cytoplasm into the nucleus. In addition, we found that, endogenously via iNOS, synthesized NO increases the constitutive mRNA expression of both MT-1 and MT-2 genes and that nitrosative stress exogenously applied via an NO donor increases constitutive MT mRNA expression via intracellular Zn2+ release. In conclusion, we here provide evidence for a signaling mechanism based on iNOS-derived NO through the regulation of intracellular Zn2+ trafficking and homeostasis.

Transcriptional activation of the metallothionein I gene by electric pulses in vivo: basis for the development of a new gene switch system

BACKGROUND

In vivo gene transfer to skeletal muscle is a promising strategy for the treatment of muscular disorders and for the systemic delivery of therapeutic proteins. Nevertheless, for a safe and effective protein production, the spatial and temporal control of gene expression is critical. The existing regulating systems rely on the use of an exogenously regulatory protein and/or an inducer drug whose pharmacological properties are of major concerns for therapeutic applications in humans. Therefore, new strategies based on endogenous regulatable elements have been explored.

METHODS

Gene expression profiles of skeletal muscle submitted or not to electrical pulses and harvested at different times were compared using the Affymetrix GeneChip technology. The endogenous metallothionein promoter was studied by Northern blot and semiquantitative and quantitative RT-PCR. The inducibility of the metallothionein I promoter placed in a plasmid exogenous context was studied using the murine SEAP reporter gene.

RESULTS

The expression of metallothionein I mRNA is significantly increased 6 h after electric pulses delivery. This induction is transient. Identical MT-I expression level is observed after several sequential series of pulses delivery. We demonstrated as well that the MT-II promoter was sensitive to electric pulses delivery. Moreover, the metallothionein I promoter, placed in a plasmid context in front of a reporter gene, was also activated by the application of transient electric field.

CONCLUSIONS

We identified a promoter highly inducible by the controlled electric stimuli applied for electrotransfer experiments. The use of the metallothionein promoter is promising for the time-control by physical stimuli of the expression of a therapeutic gene.

Chromium(VI) down-regulates heavy metal-induced metallothionein gene transcription by modifying transactivation potential of the key transcription factor, metal-responsive transcription factor 1

The robust induction of metallothionein-I and II (MT-I and MT-II) genes by several heavy metals such as zinc and cadmium requires the specific transcription factor metal-responsive transcription factor 1 (MTF1). Chromium (VI), a major environmental carcinogen, not only failed to activate these genes but also inhibited their induction by Zn2+ or Cd2+. The heavy metal-induced expression of another MTF1 target gene, zinc transporter 1 (ZnT-1), was also down-regulated by Cr6+. By contrast, the expression of two MTF1-independent Cd2+-inducible genes, heme oxygenase 1 (HO-1) and HSP-70, was not sensitive to Cr6+. Cr6+ did not also affect the expression of housekeeping genes such as GAPDH or beta-actin. Stable cell lines overexpressing variable levels of MTF1, the key transactivator of the MT genes, demonstrated differential resistance toward the inhibitory effect of Cr6+, indicating MTF1 as a target of chromium toxicity. The basal and inducible binding of MTF1 to metal response elements was not affected by treatment of cells with Cr6+. Transient transfection studies showed that the ability of MTF1 to transactivate the MT-I promoter was significantly compromised by Cr6+. The fusion protein consisting of a Gal-4 DNA binding domain and one or more of the three transactivation domains of MTF1, namely the acidic domain, proline-rich domain, and serine-threonine rich domain, activated the GAL-4-driven luciferase gene to different degrees, but all were sensitive to Cr6+. MTF1 null cells were prone to apoptosis after exposure to Zn2+ or Cd2+ that was augmented in presence Cr6+, whereas the onset of apoptosis was significantly delayed in cells overexpressing MTF1.

Astrocyte-targeted expression of IL-6 protects the CNS against a focal brain injury

The effect of CNS-targeted IL-6 gene expression has been thoroughly investigated in the otherwise nonperturbed brain but not following brain injury. Here we examined the impact of astrocyte-targeted IL-6 production in a traumatic brain injury (cryolesion) model using GFAP-IL6 transgenic mice. This study demonstrated that transgenic IL-6 production significantly increased wound healing following the cryolesion. Thus, at 20 days postlesion (dpl) the GFAP-IL6 mice showed almost complete wound healing compared to litter mate nontransgenic controls. It seems likely that a reduced inflammatory response in the long term could be responsible for this IL-6-related effect. Thus, while in the acute phase following cryolesion (1-6 dpl) the recruitment of macrophages and T lymphocytes was higher in GFAP-IL6 mice, at 10-20 dpl it was significantly reduced compared to controls. Reactive astrogliosis was also significantly increased up to but not including 20 dpl in the GFAP-IL6 mice. Oxidative stress as well as apoptotic cell death was significantly decreased throughout the time period studied in the GFAP-IL6 mice compared to controls. This could be linked to the altered inflammatory response as well as to the transgenic IL-6-induced increase of the antioxidant, neuroprotective proteins metallothionein-I + II. These results indicate that although in the brain the chronic astrocyte-targeted expression of IL-6 spontaneously induces an inflammatory response causing significant damage, during an acute neuropathological insult such as following traumatic injury, a clear neuroprotective role is evident.

Cloning and functional study of a novel human metallothionein-I isoform induced by paraquat

Human metallothionein (hMT) is highly overexpressed in the resistant AML-2 cell line selected by paraquat, an intracellular superoxide generator. The total RNA obtained from the paraquat-resistant AML-2 cell subline was purified and reverse-transcribed into cDNA using an oligo(dT) primer. A PCR fragment for hMT was generated and cloned. Nucleotide sequence analysis revealed that the hMT transcript was a novel hMT-I isoform, which was designated hMT-Ip and showed homology with hMT-Ia (91.8%), -Ie (98.4%), -If (91.8%), -Ig (91.8%), -Ih (91.8%), -Il (86.9%), -Ir (96.7%), -Ix (86.9%), -Iy (85.2%), -IIa (91.8%), -III (83.8%), and -VI (62.9%). Polypeptide translation indicated that the hMt-Ip protein differs from the hMT-Ie protein by only one amino acid. hMT-Ip was also expressed in the peripheral lymphocytes of humans. The gastric cancer cell line SNU-601 was transfected by an expression vector harboring the hMT-Ip isoform. These stable transfected cells showed not only an inhibitory effect on dichlorofluorescin oxidation, a fluorometric probe, by hydrogen peroxide and paraquat, but also a high level of resistance to anthracyclines such as doxorubicin and pirarubicin. These results show that the novel MT-Ip isoform is closely associated with the protection against oxidative stress. Therefore, it can be utilized for preventing anthracycline-induced cardiac toxicity.

Fluconazole downregulates metallothionein expression and increases copper cytotoxicity in Microsporum canis

Azole antifungals are widely used to treat infections with dermatophyte fungi. Whereas it is well established that this class of drugs interferes with fungal ergosterol synthesis, little is known about its potential other biological effects. Here we report the isolation and structural organization of Microsporum canis metallothionein gene and demonstrate that fluconazole is able to downregulate the baseline as well as copper-induced expression of this gene. Since this effect occurred within 30 min after exposure of the fungus to fluconazole, it is unlikely that it is due to impaired ergosterol synthesis. Our additional demonstration that fluconazole enhances copper toxicity for M. canis suggests that inhibition of metallothionein expression by fluconazole is biologically relevant and may represent an important additional mode of the antifungal action of this drug. Therefore our data indicate that antifungal effects of azole derivatives might not only be due to interference with cell wall synthesis but may also affect other biological circuits within the fungal cells.

Inhibitors of histone deacetylase and DNA methyltransferase synergistically activate the methylated metallothionein I promoter by activating the transcription factor MTF-1 and forming an open chromatin structure

Inhibitors of DNA methyltransferase (Dnmt) and histone deacetylases (HDAC) synergistically activate the methylated metallothionein I gene (MT-I) promoter in mouse lymphosarcoma cells. The cooperative effect of these two classes of inhibitors on MT-I promoter activity was robust following demethylation of only a few CpG dinucleotides by brief exposure to 5-azacytidine (5-AzaC) but persisted even after prolonged treatment with the nucleoside analog. HDAC inhibitors (trichostatin A [TSA] and depsipeptide) either alone or in combination with 5-AzaC did not facilitate demethylation of the MT-I promoter. Treatment of cells with HDAC inhibitors increased accumulation of multiply acetylated forms of H3 and H4 histones that remained unaffected after treatment with 5-AzaC. Chromatin immunoprecipitation (ChIP) assay showed increased association of acetylated histone H4 and lysine 9 (K9)-acetyl H3 with the MT-I promoter after treatment with TSA, which was not affected following treatment with 5-AzaC. In contrast, the association of K9-methyl histone H3 with the MT-I promoter decreased significantly after treatment with 5-AzaC and TSA. ChIP assay with antibodies specific for methyl-CpG binding proteins (MBDs) demonstrated that only methyl-CpG binding protein 2 (MeCP2) was associated with the MT-I promoter, which was significantly enhanced after TSA treatment. Association of histone deacetylase 1 (HDAC1) with the promoter decreased after treatment with TSA or 5-AzaC and was abolished after treatment with both inhibitors. Among the DNA methyltransferases, both Dnmt1 and Dnmt3a were associated with the MT-I promoter in the lymphosarcoma cells, and association of Dnmt1 decreased with time after treatment with 5-AzaC. Treatment of these cells with HDAC inhibitors also increased expression of the MTF-1 (metal transcription factor-1) gene as well as its DNA binding activity. In vivo genomic footprinting studies demonstrated increased occupancy of MTF-1 to metal response elements of the MT-I promoter after treatment with both inhibitors. Analysis of the promoter by mapping with restriction enzymes in vivo showed that the MT-I promoter attained a more open chromatin structure after combined treatment with 5-AzaC and TSA as opposed to treatment with either agent alone. These results implicate involvement of multifarious factors including modified histones, MBDs, and Dnmts in silencing the methylated MT-I promoter in lymphosarcoma cells. The synergistic activation of this promoter by these two types of inhibitors is due to demethylation of the promoter and altered association of different factors that leads to reorganization of the chromatin and the resultant increase in accessibility of the promoter to the activated transcription factor MTF-1.

Surplus zinc is handled by Zym1 metallothionein and Zhf endoplasmic reticulum transporter in Schizosaccharomyces pombe

Homeostatic mechanisms prevent the accumulation of free zinc in the cytoplasm, raising questions regarding where surplus zinc is stored and how it is delivered to and from these stores. A genetic screen for zinc hypersensitivity in Schizosaccharomyces pombe identified a missense mutation truncating Zhf, an endoplasmic reticulum transporter. These cells were approximately 5-fold more zinc-sensitive than other independent mutants. The targeted disruption of zhf prevented growth on low zinc medium and caused hypersensitivity to elevated zinc/cobalt but resistance to cadmium. The exposure to elevated zinc but not copper also promotes the accumulation of transcripts encoding a metallothionein designated Zym1. The Sty1 pathway is required for maximal zym1 expression but is not obligatory for zinc perception. The targeted disruption of zym1 impaired cadmium tolerance but only slightly impaired zinc tolerance, whereas zym1 overexpression substantially rescued zinc hypersensitivity of zhf(-) cells. Four equivalents of zinc were displaced from Zym1 by up to 12 equivalents of p-(hydroxymercuri)phenylsulphonate. Zym1 thiols react rapidly with 5,5'-dithiobis-(2-nitrobenzoic acid) compared with bacterial zinc metallothionein (6.8 and 0.2 x 10(-4) s(-1), respectively). Zym1 is unlike known fungal metallothioneins that are induced by and sequester copper but not zinc. Less zinc but normal cadmium was accumulated by zym1Delta, consistent with zinc sequestration by Zym1 in vivo.

Role of de novo DNA methyltransferases and methyl CpG-binding proteins in gene silencing in a rat hepatoma

The expression of metallothionein-I (MT-I), a known antioxidant, was suppressed in a transplanted rat hepatoma because of promoter methylation and was induced by heavy metals only after demethylation by 5-azacytidine (5-AzaC). Treatment of the tumor-bearing rats with 5-AzaC resulted in significant regression of the hepatoma. When the inhibitor-treated tumor was allowed to grow in a new host, MT-I promoter was remethylated, which suggested de novo methylation. The activities of both de novo (3-fold) and maintenance DNA methyltransferases (DNMT) (5-fold) were higher in the hepatoma than in the host liver. The mRNA levels of the de novo methyltransferases DNMT3a and DNMT3b were 3- and 6-fold higher, respectively, in the tumor implicating transcriptional up-regulation of these two genes in this tissue. Immunohistochemical analysis showed exclusive localization of DNMT3a in the nuclei of both the liver and hepatoma, whereas DNMT3b was detected in the nuclei as well as the cytoplasm. Immunoblot assay showed that the levels of DNMT1, DNMT3a, and DNMT3b proteins in the hepatoma were 5-, 10-, and 4-fold higher, respectively, than in the liver. The mRNA level of the major methyl CpG-binding protein (MeCP2) was 8-fold higher in the tumor compared with the liver. Immunohistochemical studies showed that MeCP2 is localized exclusively in the nuclei of both tissues. A chromatin immunoprecipitation assay demonstrated that MeCP2 was associated with the MT-I promoter in the hepatoma implicating its involvement in repressing the methylated promoter. Analysis of the DNA isolated from the liver and hepatoma by RLGS-M (restriction landmark genomic scanning with methylation-sensitive enzyme) (NotI) showed that many genes in addition to MT-I were methylated in the hepatoma. These data demonstrate suppression of the MT-I gene and probably other genes in a solid tumor by promoter methylation and have provided potential molecular mechanisms for the altered methylation profile of the genes in this tumor.

Discovery of regulatory elements by a computational method for phylogenetic footprinting

Phylogenetic footprinting is a method for the discovery of regulatory elements in a set of orthologous regulatory regions from multiple species. It does so by identifying the best conserved motifs in those orthologous regions. We describe a computer algorithm designed specifically for this purpose, making use of the phylogenetic relationships among the sequences under study to make more accurate predictions. The program is guaranteed to report all sets of motifs with the lowest parsimony scores, calculated with respect to the phylogenetic tree relating the input species. We report the results of this algorithm on several data sets of interest. A large number of known functional binding sites are identified by our method, but we also find several highly conserved motifs for which no function is yet known.

Cadmium resistance conferred to yeast by a non-metallothionein-encoding gene of the earthworm Enchytraeus

The earthworm Enchytraeus is able to survive in cadmium (Cd)-polluted environments. Upon Cd exposure, the worms express a gene encoding the putative non-metallothionein 25-kDa cysteine-rich protein (CRP), which contains eight repeats with highly conserved cysteines in Cys-X-Cys and Cys-Cys arrangements exhibiting 36-53% identities to the 6-7-kDa metallothioneins of different organisms. Here, we demonstrate that the CRP protein confers a highly Cd-resistant phenotype to a Cd-hypersensitive yeast strain. Cd resistance increases with increasing numbers of expressed CRP repeats, but even one 3-kDa CRP repeat still mediates Cd resistance. Site-directed mutagenesis reveals that each single cysteine within a given repeat is important for Cd resistance, though to a different extent. However, replacement of other conserved amino acids such as Pro(136) and Asp(196) at the CRP repeat junctions does not affect Cd resistance. Our data indicate (i) that the non-metallothionein CRP protein is able to detoxify Cd and (ii) that this is dependent on the availability of sulfhydryl groups of the conserved cysteines.

Ribozyme-mediated downregulation of human metallothionein II(a) induces apoptosis in human prostate and ovarian cancer cell lines

Human metallothioneins (MTs) are low-molecular-weight, cysteine-rich, metal ion-binding proteins that constitute the majority of intracellular protein thiols. They are overexpressed in prostate and ovarian cancers and are believed to confer resistance to radiation and cytotoxic anticancer drugs. The aim of this study was to investigate the roles of MTs in prostate and ovarian cancer cells and their possible relationship with other cancer development and progression factors. The main problem in investigating the role of MT, however, is the absence of any known specific inhibitor. To this end, in a previous study, we had developed sequence-specific ribozymes (Rzs) targeting MT and had shown their in cellulo efficacy. Here we show that transient transfection of a vector carrying a hammerhead Rz (Rz4-9), designed to cleave class II MT, in the human prostate cancer cell line PC-3 and the ovarian cancer cell line SKOV-3 resulted in a dose-dependent attenuation of MT-II(a) transcripts and dramatic cell loss. Transient transfection with 2 microg of Rz4-9 vector DNA completely abolished MT-II(a) mRNA levels and induced a 94% and a 67% reduction in cell number in PC-3 cells and SKOV-3 cells, respectively. Fluorescence-activated cell sorting (FACS) showed that the Rz-induced cell loss probably was due to apoptosis, because it was associated with marked increases in the hypodiploid cell population, reaching maximums of 52% and 64% in cultures of PC-3 and SKOV-3, respectively. Additionally, annexin V-propidium iodide double-staining, followed by FACS, confirmed that Rz4-9-induced cell death was due to apoptosis and showed a vector DNA-dependent increase in late apoptotic cell numbers that reached maximums of 80% and 42%, respectively, in PC-3 and SKOV-3 cell cultures transfected with the highest concentration of vector DNA. In parallel experiments, transfection with a vector containing the enzymatically inactive mutant Rz-3-3 or the empty vector was not effective in inducing similar responses. The Rz-induced loss of MT-II(a) mRNA-associated cell death in these cancer cell lines was attended by dose-dependent downregulation of the proto-oncogene c-myc and the apoptosis inhibitory mediator bcl-2, suggesting that these signaling pathways are involved in the process. In conclusion, our data indicate that MT-II(a) is an important cell-survival or anti-apoptotic factor for prostate and ovarian cancer cells and that downregulation of its expression via transgene expression of a sequence-specific Rz is a feasible target for cancer therapy.

Induction of metallothionein-I protects glomeruli from superoxide-mediated increase in albumin permeability

Metallothioneins (MT) are low-molecular-weight, heat-stable, cysteine-rich proteins with four isoforms. MT-I and MT-II are ubiquitous and are induced by oxidative, physical, and chemical stress. MT-I is an efficient scavenger of superoxide (*O2) and hydroxyl ion (OH(-)). We have demonstrated that *O2 and hypohalous acid can cause an increase in glomerular albumin permeability (P(alb)) in vitro. The purpose of this study was to document the protective effect of MT gene product on the *O2-mediated increase in P(alb). Glomeruli from Sprague-Dawley rats in 4% BSA medium were incubated for 4 hr at 37 degrees C in duplicate tubes. Each set contained glomeruli alone or with 5 microM Cd(++), 0.3 mM Spermine-NONOate (NO donor), 0.3 mM Sulfo-NONOate (nitrous oxide donor), 0.6 mM SNP (nonspecific NO donor) and SNP + carboxy-PTIO (10 mg/ml). After incubation, one set of tubes was used to isolate total RNA for the measurement of the mRNA levels of MT-I by reverse transcriptase polymerase chain reaction (RT-PCR). Duplicate tubes were incubated for an additional 10 min with 10 nM of *O2, and P(alb) was measured using video microscopy. RT-PCR of total RNA from Cd(++) and Spermine-NONOate treated glomeruli revealed a 2-fold induction of MT-I expression at the mRNA level. *O2 caused a significant increase in P(alb) (0.8 +/- 0.06 vs. control 0.0 +/- 0.12, P < 0.05) and induction of MT-I in glomeruli by Cd(++) or by Spermine-NONOate blocked this effect (0.21 +/- 0.12 and 0.24 +/- 0.19, respectively, P < 0.05 vs. *O2). In contrast, Sulfo-NONOate and SNP did not induce mRNA for MT-I in glomeruli and did not provide protection against *O2-mediated increase in P(alb.) We conclude that MT-I gene products may play an important role in protecting the glomerular filtration barrier from the injury induced by reactive oxygen species in immune and/or nonimmune renal diseases.

Influenza virus infection induces metallothionein gene expression in the mouse liver and lung by overlapping but distinct molecular mechanisms

Metallothionein I (MT-I) and MT-II have been implicated in the protection of cells against reactive oxygen species (ROS), heavy metals, and a variety of pathological and environmental stressors. Here, we show a robust increase in MT-I/MT-II mRNA level and MT proteins in the livers and lungs of C57BL/6 mice exposed to the influenza A/PR8 virus that infects the upper respiratory tract and lungs. Interleukin-6 (IL-6) had a pronounced effect on the induction of these genes in the liver but not the lung. Treatment of the animals with RU-486, a glucocorticoid receptor antagonist, inhibited induction of MT-I/MT-II in both liver and lung, revealing a direct role of glucocorticoid that is increased upon infection in this induction process. In vivo genomic footprinting (IVGF) analysis demonstrated involvement of almost all metal response elements, major late transcription factor/antioxidant response element (MLTF/ARE), the STAT3 binding site on the MT-I upstream promoter, and the glucocorticoid responsive element (GRE1), located upstream of the MT-II gene, in the induction process in the liver and lung. In the lung, inducible footprinting was also identified at a unique gamma interferon (IFN-gamma) response element (gamma-IRE) and at Sp1 sites. The mobility shift analysis showed activation of STAT3 and the glucocorticoid receptor in the liver and lung nuclear extracts, which was consistent with the IVGF data. Analysis of the newly synthesized mRNA for cytokines in the infected lung by real-time PCR showed a robust increase in the levels of IL-10 and IFN-gamma mRNA that can activate STAT3 and STAT1, respectively. A STAT1-containing complex that binds to the gamma-IRE in vitro was activated in the infected lung. No major change in MLTF/ARE DNA binding activity in the liver and lung occurred after infection. These results have demonstrated that MT-I and MT-II can be induced robustly in the liver and lung following experimental influenza virus infection by overlapping but distinct molecular mechanisms.

Downregulation of constitutive and heavy metal-induced metallothionein-I expression by nuclear factor I

Although the existence of repressor protein(s) involved in the regulation of highly inducible metallothionein-I (MT-I) gene expression has been postulated, none has been identified to date. We considered nuclear factor I (NFL) protein as a potential repressor, as three half-sites for NFI binding are present on MT-I promoter and NFI is known to downregulate several cellular gene promoters. Overexpression of all four isoforms of mouse NFI protein (NFI-A, -B, -C, and -X) suppressed both constitutive and heavy metal-induced activation of the MT-I promoter in HepG2 cells. However, unlike other target genes of NFI, direct interaction of NFI with MT-I promoter is not necessary to mediate its repression. Point mutation of the NFI binding sites within the MT-I promoter that abrogates NFI binding in vitro could not alleviate the repression. Similarly, NFI proteins also repress activity of minimal MT-I promoter deficient in the NFI binding sites. Further, an NFI-C deletion mutant lacking the DNA binding domain continued to repress MT-I promoter. Overexpression of MTF-1, the key trails-acting factor involved in MT-I gene transcription, surmounted NFI-mediated repression of the basal and zinc-induced MT-I promoter activity. These data demonstrate that NFI is a repressor of MT-I expression, where its DNA binding activity is not essential to downregulate the MT-I promoter. Interaction of NFI with another protein(s), probably MTF-I, may be involved in this repression.