Localization of metallothionein in the genital organs of the male rat

Molecular cloning, the characterization of metallothionein and catalase, and the evaluation of testicular toxicity of Cd in the Chinese fire-bellied newt (Cynops orientalis)

Cadmium (Cd) is an environmental toxicant and a nonessential metal. Cd can attack a wide range of organs, such as the liver, kidney, lung, ovary, testis, brain, and muscle in vertebrates. Among these organs, the testis might be the most sensitive organ to Cd toxicity. Metallothionein (MT) is a cysteine-rich protein with a low molecular weight, that can bind with Cd and eliminate reactive oxygen species (ROSs). Hydrogen peroxide, which as a crucial type of ROS that is induced by Cd, can be eliminated by catalase (CAT) in the self-protection of cells and to realize Cd toxicity resistance. To investigate the functions of MT and CAT in the testis of Cynops orientalis, we cloned the full-length MT and CAT genes of C. orientalis for the first time. Immunofluorescence results demonstrated that MT and CAT were expressed in Sertoli cells and all spermatogenic cells in the testis of C. orientalis. The results of the ultrastructural damage assay demonstrated that there were various impairments, which included organelle vacuolization, abnormal chromatin distribution, and apoptotic bodies, in somatic cells that were exposed to Cd. However, the anomalies of spermatozoa were located mainly in the mid-piece and head, many of which showed severely impaired structures. The results demonstrated that MT and CAT expression had distinct patterns in response to various Cd concentrations: an increase in MT mRNA levels with elevated Cd levels and a persistent increase in CAT mRNA levels with elevated Cd levels. These results suggested that MT and CAT play roles in Cd toxicity resistance in the testis and that the expression of CAT may be a better biomarker than the expression of MT for assessing Cd pollution.

Role of metallothionein-like cadmium-binding protein (MTLCdBP) in the protective mechanism against cadmium toxicity in the testis

The role of metallothionein (MT)-like cadmium (Cd) binding protein (MTLCdBP) in protecting the testes against Cd toxicity was examined. In the acute Cd exposure treatment, cadmium chloride was intraperitoneally injected at 2 mg Cd/kg to Wistar male rats. In the chronic Cd toxicity treatments, 20 mg Cd/kg/d was orally administered for 5 d a week for 5, 10, and 15 wk. MT (-I,-II) and MTLCdBP were measured using ELISA and Cd-Hem methods, respectively. Testicular tissues were immunostained with antibodies of MT-I,-II, MT-III, and MTLCdBP. Expression of HO1, OGG, iNOS, COX2, and p53 was measured by RT-PCR. Cd concentration in the testis increased dose-dependently in response to Cd exposure. MTLCdBP concentration increased markedly with increasing Cd accumulation. Significant increases in expression of iNOS, HO1, COX2, and OGG1 were observed in the acute exposure treatment. In the chronic oral administration group, expression of MT-I, MT-II, MT-III, iNOS, HO1, and COX2 did not change. Positive immunostaining of MTLCdBP was observed in testicular interstitial tissue. In the testis protected from Cd toxicity, MTLCdBP induction increased significantly with increasing Cd accumulation. Our results suggest that MTLCdBP plays an important role in protecting the testis against Cd toxicity.

A TEM-traceable physiologically functional gold nanoprobe that permeates non-endocytic cells

Background

Nanoparticles’ intracellular fate requires proper internalization. Most cells make use of a battery of internalization pathways, but some are practically sealed, as they lack the biochemical machinery for cellular intake. Non-endocytic cells, such as mammals’ spermatozoa, challenge standard drug-delivery strategies.

Purpose

In this article, we present a gold nanoprobe that permeates the external and internal membranes of human sperm.

Methods

Our design makes use of a gold nanoparticle functionalized with a membrane-permeable cysteine-rich recombinant protein. The chimeric protein contains two units of physiologically active metallothioneins (MT) that also provide binding motifs to gold and a cell-penetrating-peptide sequence (CPP) that confers cell permeability to the nanoparticle.

Results

Transmission electron microscopy, indirect immunofluorescence, and functional assays show that the nanoprobe is readily internalized in sperm, without compromising cell integrity, while preserving MT’s physiological activity. Our findings highlight the potential of CPP-functionalized nanogold for investigating the physiology of otherwise impermeable non-endocytic cells.

Glutathione has a more important role than metallothionein-I/II against inorganic mercury-induced acute renal toxicity

Inorganic mercury is a harmful heavy metal that causes severe kidney damage. Glutathione (GSH), a tripeptide comprising L-glutamic acid, glycine and L-cysteine, and metallothionein (MT), a cysteine-rich and metal-binding protein, are biologically important protective factors for renal toxicity by inorganic mercury. However, the relationship between GSH and MT for the prevention of renal toxicity by inorganic mercury is unknown. We examined the sensitivity of the mice depleted in GSH by treatment with L-Buthionine-SR-sulfoximine (L-BSO), and MT-I/II null mice genetically deleted for MT-I and MT-II, to inorganic mercury (HgCl₂). Kidney damage was not induced in the wild-type mice treated with HgCl₂ (30 µmol/kg). In the MT-I/II null mice, renal toxicity was induced by HgCl₂ at a dose of 30 µmol/kg but not 1.0 µmol/kg. All GSH-depleted mice of both strains were dead following the injection of HgCl₂ (30 µmol/kg). GSH-depleted wild-type mice treated with HgCl₂ (1.0 µmol/kg) developed kidney damage similar to MT-I/II null mice treated with HgCl₂ (30 µmol/kg). Moreover, renal toxicity induced by HgCl₂ (1.0 µmol/kg) was more severe in GSH-depleted MT-I/II null mice compared with GSH-depleted wild-type mice. The present study found that GSH and MT-I/II play cooperatively an important role in the detoxification of severe kidney damage caused by inorganic mercury. In addition, GSH may act as a primary protective factor against inorganic mercury-induced acute renal toxicity, because GSH-depleted mice were more sensitive to inorganic mercury than MT-I/II null mice.

Unravelling the Role of Metallothionein on Development, Reproduction and Detoxification in the Wall Lizard Podarcis sicula

Metallothioneins (MTs) are an evolutionary conserved multigene family of proteins whose role was initially identified in binding essential metals. The physiological role of MT, however, has been revealed to be more complex than expected, since not only are MTs able to bind to toxic heavy metals, but many isoforms have shown specialized and alternative functions. Within this uncertainty, the information available on MTs in non-mammalian vertebrates, particularly in neglected tetrapods such as the reptiles, is even more scant. In this review, we provide a summary of the current understanding on metallothionein presence and function in the oviparous lizard Podarcis sicula, highlighting the results obtained by studying MT gene expression in most representative adult and embryonic tissues. The results demonstrate that in adults, cadmium induces MT transcription in a dose- and tissue-specific manner. Thus, the MT mRNAs appear, at least in some cases, to be an unsuitable tool for detecting environmental ion contamination. In early embryos, maternal RNAs sustain developmental needs for MT protein until organogenesis is well on its way. At this time, transcription starts, but again in a tissue- and organ-specific manner, suggesting an involvement in alternative roles. In conclusion, the spatiotemporal distribution of transcripts in adults and embryos definitively confirms that MT has deserved the title of elusive protein.

Metallothionein expression and synthesis in the testis of the lizard Podarcis sicula under natural conditions and following estrogenic exposure

Metallothionein (MT) is the main protein involved in the homeostasis of metallic micronutrients and in cellular defence against heavy metals and reactive oxygen species. Found in almost all vertebrate tissues, MT presence and localization in the testis has been controversial. In the present study, by using in situ hybridization and immunohistochemical analysis we assessed the localization of both MT transcript and protein in Podarcis sicula testes during two different phases of the reproductive cycle: the autumnal resumption and the springearly summer mating period. In addition, with the same methodological approach, we verified the effect of estradiol-1711and nonylphenol, a potent xenoestrogen, on MT expression and synthesis. These results, the first collected in a non-mammalian oviparous vertebrate, demonstrated that the expression profile of MT mRNA and protein changes during the reproductive cycle. In the fall resumption, MT transcripts are absent in spermatogonia and present in all the other cells of tubules, including spermatozoa; vice versa, the MT protein is evident only in spermatozoa and somatic cells. In the mating period, both MT transcripts and proteins are present in spermatogonia, spermatocytes and spermatids, whereas in the spermatozoa only the proteins are detected, thus suggesting that the MTs translated in the earlier germinal stages are stored up to spermatozoa. Results also demonstrated that in lizard testis the expression of MT gene undergoes a cell-specific regulation after estrogenic exposure; the possible role and the mechanism by which this regulation occurs have been discussed.

Expression and function analysis of metallothionein in the testis of stone crab Charybdis japonica exposed to cadmium

Metallothionein (MT) participates in metallic homeostasis and detoxification in living animals. Previous studies have focused mainly on the functions of MT in vertebrates, but the functions of MT during spermiogenesis in invertebrates remain unclear. In order to investigate the functions of MT during spermiogenesis in the Japanese stone crab (Charybdis japonica), we identified the C. japonica MT complete cDNA sequence from the total RNA of the testis using RT-PCR and RACE. The 587 bp MT cDNA contains: an 80 bp 5' untranslated region, a 333 bp 3' untranslated region, and a 174 bp open reading frame. MT has 57 amino acids including 19 cysteines. The protein alignment between MT sequences of C. japonica and other crabs shows a high similarity and a strong identity in cysteine residues vital for the metal-binding affinity of MT. After the cadmium (Cd) exposure, the testis displays both abnormal morphology and MT mRNA expression both of which indicate a sensitive response of testis MT to Cd. Therefore, we suggest that MT is an excellent biomarker candidate for evaluating Cd pollution.

Protective role of metallothionein in benzo[a]pyrene-induced DNA damage

Metallothionein (MT) is known to reduce chemical carcinogenesis. Carcinogenesis induced by benzo[a]pyrene (B[a]P) which is an environmental chemical carcinogen is related to DNA adduct formation and oxidative damage through metabolic activation. Ten-week-old male MT-I/II null mice and wild-type mice were given a single injection of B[a]P (250 mg/kg, p.o.), and B[a]P-induced DNA damage was evaluated at 6-48 hr later. The frequencies of micronucleated reticulocytes (MNRET) in MT-I/II null mice were significantly increased compared with that of wild-type mice at 48 hr after B[a]P administration. At 48 hr after B[a]P administration, comet scores were significantly increased in MT-I/II null mice but not in wild-type mice. 8-Hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of oxidative DNA damage, was significantly increased in liver of MT-I/II null mice at 6 and 12 hr after B[a]P administration, although that of wild-type mice was only slightly changed. Because cytochrome P450 (CYP) plays a major role in the process of B[a]P metabolic activation, we attempted to reveal the effect of MT on metabolic activation of B[a]P. Although CYP1A activities were elevated in the livers of MT-I/II null mice and wild-type mice treated with B[a]P, it was not different between both strains of mice. In addition, MT levels in the livers of wild-type mice were significantly increased by the B[a]P treatment, whereas MT was not detected in livers of MT-I/II null mice with or without B[a]P treatment. These results demonstrate that MT acts as an endogenous defensive factor against B[a]P-induced DNA damage.

Cadmium-induced testicular injury

Cadmium (Cd) is an environmental toxicant and an endocrine disruptor in humans and rodents. Several organs (e.g., kidney, liver) are affected by Cd and recent studies have illustrated that the testis is exceedingly sensitive to Cd toxicity. More important, Cd and other toxicants, such as heavy metals (e.g., lead, mercury) and estrogenic-based compounds (e.g., bisphenols) may account for the recent declining fertility in men among developed countries by reducing sperm count and testis function. In this review, we critically discuss recent data in the field that have demonstrated the Cd-induced toxicity to the testis is probably the result of interactions of a complex network of causes. This is likely to involve the disruption of the blood-testis barrier (BTB) via specific signal transduction pathways and signaling molecules, such as p38 mitogen-activated protein kinase (MAPK). We also summarize current studies on factors that confer and/or regulate the testis sensitivity to Cd, such as Cd transporters and metallothioneins, the impact of Cd on the testis as an endocrine disruptor and oxidative stress inducer, and how it may disrupt the Zn(2+) and/or Ca(2+) mediated cellular events. While much work is needed before a unified mechanistic pathway of Cd-induced testicular toxicity emerges, recent studies have helped to identify some of the likely mechanisms and/or events that take place during Cd-induced testis injury. Furthermore, some of the recent studies have shed lights on potential therapeutic or preventive approaches that can be developed in future studies by blocking or minimizing the destructive effects of Cd to testicular function in men.

Protective role of metallothionein in bone marrow injury caused by X-irradiation

In order to elucidate the role of metallothionein (MT) in preventing the adverse effects of X-ray irradiation, we examined the susceptibility of MT-I/II null mice to bone marrow injury caused by X-irradiation and effects of pretreatment with MT-inducing metals on X-ray injury. Eight-week-old male mice were exposed to a single bout of whole-body X-irradiation at a dose between 0.1 and 6.0 Gy. The numbers of leukocytes, reticulocytes with micronuclei (MNRET) in the blood, and polychromatic erythrocytes with micronuclei (MNPCE) in the bone marrow were determined 24 hr after X-irradiation. X-irradiation significantly decreased the total number of leukocytes in MT-I/II null mice and wild-type mice in a dose-dependent manner, but the total number of leukocytes was significantly lower in MT-I/II null mice than in wild-type mice at a low dose of irradiation, between 0.1 and 1.0 Gy. X-irradiation (0.1 and 0.5 Gy) significantly increased the appearance of MNRET and MNPCE in both strains, but the increase was greater in the MT-I/II null mice than in the wild-type mice. Additional groups of mice were pre-administered bismuth nitrate or zinc sulfate to induce MT in the bone marrow cells prior to X-irradiation; the X-ray injury was prevented by such treatments in wild-type mice only. Thus, the present results suggest that MT plays a protective role against a low dose of X-ray injury.

Changes of heavy metal, metallothionein and heat shock proteins in Sertoli cells induced by cadmium exposure

In this study, we examined the levels of Cadmium (Cd), iron (Fe) and zinc (Zn), which were considered to be involved in Sertoli cell damage caused by Cd exposure. We also examined metallothionein (MT), heat shock protein 70 (Hsp70) and heme oxygenase-1 (HO-1) expressions in Sertoli cells induced by Cd exposure. Evaluation by the in-air micro-particle induced X-ray emission (PIXE) method revealed that Cd and Fe distribution was increased in the cytoplasm of Sertoli cells after Cd exposure. By contrast, Zn was decreased in the cytoplasm of Sertoli cells after Cd exposure. It was suggested that the target of Cd toxicity was the cytoplasm of Sertoli cells, Fe was considered to enhance damage to Sertoli cells caused by Cd exposure. The DNA fragmentation rate was determined by ELISA after Cd exposure to Sertoli cells. It remained essentially unchanged with 2.5 microM Cd exposure of Sertoli cells; however, MT, Hsp70 and HO-1 were significantly increased by Cd exposure. As a result, Cd-induced MT was protected Sertoli cells against apoptosis, and Cd-induced HO-1 was involved in protection against oxidative stress. Incidentally, MT, Hsp70 and HO-1 showed similar responses to Cd exposure.

The changes of heavy metal and metallothionein distribution in testis induced by cadmium exposure

Cadmium (Cd) is known to cause various disorders in the testis, and metallothionein (MT) is known as a protein, which has a detoxification function for heavy metals. However, the changes of Fe, Cu, and Zn distribution in the testis induced by Cd exposure have not been well examined. Moreover, only a few studies have been reported on the localization of MT after Cd exposure. In this study, we have investigated the changes of Fe, Cu, and Zn distribution in Cd-exposed testis by a newly developed in air micro-Particle Induced X-ray Emission (PIXE) method. Also, we examined the distribution of MT expression in testis. In the testis of Cd-treated rats with significant increases of lipid peroxidation, the sertoli cell tight junction was damaged by Cd exposure, resulting from disintegration of the blood testis barrier (BTB). Evaluation by in air micro-PIXE method revealed that Cd and Fe distribution were increased in the interstitial tissues and seminiferous tubules. The histological findings indicated that the testicular tissue damage was advanced, which may have been caused by Fe flowing into seminiferous tubules followed by disintegration of the BTB. As a result, Fe was considered to enhance the tissue damage caused by Cd exposure. MT was detected in spermatogonia, spermatocytes, and Sertoli's cells in the testis of Cd-treated rats, but was not detected in interstitial tissues. These results suggested that MT was induced by Cd in spermatogonia, spermatocytes, and Sertoli's cells, and was involved in the resistance to tissue damage induced by Cd.

Influence of combined antioxidants against cadmium induced testicular damage

Acute effects of cadmium (Cd) and combined antioxidants were evaluated in Sprague-Dawley rat testes. The rats were subdivided into four groups. Cadmium chloride (2mg/kgday) injected intraperitoneally during 8 days. Vitamin C (250mg/kgday), vitamin E (250mg/kgday) and sodium selenate (0.25mg/kgday) were pretreated by gavage in both of control and cadmium injected rats. Testis lipid peroxidation and glutathione levels were determined by spectrophotometrically. In Cd treated rats, lipid peroxidation levels were increased and glutathione levels were decreased and combined antioxidants treatment was effective in preventing of lipid peroxidation and normalizing glutathione. In Cd treated animals, the degenerative changes were observed, but not observed in the administrated rats with Cd and antioxidants under the light microscope. Proliferating cell nuclear antigen, metallothionein and caspase-3 activities were evaluated by immunohistochemically. Proliferation activity was not seen in the spermatogonial cells of cadmium treated testis. Treatment with antioxidants in cadmium administrated testis leads to pronounced increase in proliferation activity. Cytoplasmic caspase-3 activity was determined in the spermatogenic cells but not spermatogonia in treatment of antioxidants with Cd. In control and treated with antioxidants animals, metallothionein expressions were localized in the cells of seminiferous tubules, although the expression only was observed in the interstitial cells of cadmium treated rats. Results demonstrated beneficial effects of combined vitamin C, vitamin E and selenium treatment in Cd toxicity.

Role of metallothionein in coagulatory disturbance and systemic inflammation induced by lipopolysaccharide in mice

Although metallothionein (MT) can be induced by inflammatory mediators, its roles in coagulatory disturbance during inflammation are poorly defined. We determined whether MT protects against coagulatory and fibrinolytic disturbance and systemic inflammation induced by intraperitoneal administration of lipopolysaccharide (LPS) in MT-I/II null (-/-) and wild-type (WT) mice. As compared with WT mice, MT (-/-) mice revealed significant prolongation of prothrombin and activated partial thromboplastin time, a significant increase in the levels of fibrinogen and fibrinogen/fibrin degradation products, and a significant decrease in activated protein C, after LPS treatment. LPS induced inflammatory organ damages in the lung, kidney, and liver in both genotypes of mice. The damages, including neutrophil infiltration, were more prominent in MT (-/-) mice than in WT mice after LPS treatment. In both genotypes of mice, LPS enhanced protein expression of interleukin (IL)-1beta, IL-6, granulocyte/macrophage-colony-stimulating factor, macrophage inflammatory protein (MIP)-1alpha, MIP-2, macrophage chemoattractant protein-1, and keratinocyte chemoattractant in the lung, kidney, and liver and circulatory levels of IL-1beta, IL-6, MIP-2, and KC. In overall trends, however, the levels of these proinflammatory proteins were greater in MT (-/-) mice than in WT mice after LPS challenge. Our results suggest that MT protects against coagulatory and fibrinolytic disturbance and multiple organ damages induced by LPS, at least partly, via the inhibition of the expression of proinflammatory proteins.

Localization and role of metallothioneins in the olfactory pathway after exposure to mercury vapor

We have investigated the localization and physiological roles of metallothioneins (MTs) in the olfactory pathway after exposure to mercury (Hg0) vapor. Male MT-null and wild-type mice were examined for the distribution of mercury, MT immunoreactivity and MT-III mRNA expression. There were no signs of histological changes in MT-null or wild-type mice. Light and electron microscopy of the samples stained with autometallography demonstrated chronological transfer of exposed mercury granules to the olfactory bulb by way of the olfactory tract. Basal expression of MT-I and -II immunoreactivity was observed in supporting cells, basal cells and acinar cells of the Bowman's gland of the olfactory mucosa in wild-type mice even without mercury exposure. In situ hybridization showed that signals for MT-III mRNA dominated in the olfactory cells of the olfactory mucosa, neurons in the olfactory bulb and those of brain in MT-null and wild-type mice. No difference in these findings was observed between samples taken at any interval after mercury exposure.

Maternal-to-fetus transfer of mercury in metallothionein-null pregnant mice after exposure to mercury vapor

This study examined the role of placenta metallothionein (MT) in maternal-to-fetal mercury transfer in MT-null and wild-type mice after exposure to elemental mercury (Hg(0)) vapor. Both strains were exposed to Hg(0) vapor at 5.5-6.7 mg/m(3) for 3 h during late gestation. Twenty-four hours after exposure to Hg(0) vapor, accumulation of mercury in the major organs, except the brain, of MT-null maternal mice was significantly lower than that in organs of wild-type mice. In contrast to mercury levels in maternal organs, fetal mercury levels were significantly higher in MT-null mice than in wild-type mice. In placenta, mercury concentrations were not significantly different between the two strains. Although MT levels in major organs, except the brain, of wild type mice were markedly elevated after the exposure to Hg(0) vapor, the placental MT levels were not elevated. However, endogenous MT level in the placenta is significantly higher than that in other organs, except the liver. Gel filtration profile of the placental cytosol in the wild-type mice revealed that a large amount of placental mercury was associated with MT. In MT-null mice, mercury in placental cytosol appeared mainly in the high-molecular-weight protein fractions. Mercury in the placenta was localized mainly in the yolk sac and decidual cells in the deep layer of the decidua in both mouse strains. The similar localization of MT was found in the placenta of wild type mice. These results suggest that MT in the placenta has a defensive role in preventing maternal-to-fetal mercury transfer.

Genetic background but not metallothionein phenotype dictates sensitivity to cadmium-induced testicular injury in mice

Sensitivity to cadmium (Cd)-induced testicular injury varies greatly among mouse strains. For instance, 129/SvJ (129) mice are highly sensitive while C57BL/6J (C57) mice are refractory to Cd-induced testicular injury. Metallothionein (MT), a Cd-binding protein, is thought to be responsible for the strain susceptibility to Cd toxicity. In this study, MT-I/II knockout (MT-null) and wild-type 129 mice were used to determine the role of MT in Cd-induced testicular injury. Two additional strains of mice (C57 and the C57 x 129 F1cross) were also used to help define the role of genetic background in Cd toxicity. Mice were given 5-20 micromol/kg ip CdCl(2) and testicular injury was examined 24 h later by histopathology and testicular hemoglobin concentration. Cd produced dose-dependent testicular injury in all strains of mice, except for C57 mice, in which testicular injury could not be produced. MT-null mice were more sensitive than C57 x 129 mice but were equally sensitive as 129 mice to Cd-induced testicular injury. Fourteen days after 15 micromol/kg ip Cd administration, testicular atrophy was evident in MT-null, 129, and C57 x 129 mice but was absent in C57 mice. The resistance of C57 mice to Cd-induced testicular injury could not be attributed solely to a decreased uptake of (109)Cd nor to a greater amount of testicular MT. Microarray analysis revealed a higher expression of glutathione peroxidase in the testes of C57 mice, as well as genes encoding antioxidant components and DNA damage/repair, but their significance to Cd-induced injury is not immediately clear. Thus, this study demonstrates that it is genetic strain, not MT genotype, that is mechanistically important in determining susceptibility to Cd-induced testicular injury.

Role of IL-6 in the induction of hepatic metallothionein in mice after partial hepatectomy

Metallothioneins (MT) are induced upon partial hepatectomy (PH), possibly mediated by various cytokines. In the present study, we studied cytokine-dependent MT synthesis in partially hepatectomized IL-6 gene knock-out (GKO) mice in the remaining lobe of the liver. We focused on IL-6, TNFalpha and IL-1beta, the major cytokines thought to be involved in MT synthesis. The IL-6 GKO mice and B6J129Sv (wild-type control) mice were subjected to 70% PH or laparotomy. We found that MT was significantly decreased in IL-6 GKO mice, although PH induced hepatic MT in both strains of mice. Laparotomy induced MT in the liver of wild-type mice but not in IL-6 GKO mice. Pretreatment of IL-6 GKO mice with rIL-6 (5 microg/mouse) restored hepatic MT synthesis. Serum IL-6 level in wild-type mice was maximal at 6 h after surgery and decreased thereafter. Serum IL-1beta was the same in both strains of mice. Serum TNFalpha basal level in IL-6 GKO mice was higher than in wild-type mice. PH caused an increase in serum TNFalpha level in both strains of mice, and it was two times higher in IL-6 GKO mice than in wild-type mice at 18 h after surgery. We conclude that IL-6 plays a predominant role in hepatic MT synthesis after PH, but that IL-6 GKO mice still reserve the capacity to synthesize MT by an as yet unidentified mechanism.

Cutaneous metallothionein induction by ultraviolet B irradiation in interleukin-6 null mice

The mediators of cutaneous metallothionein induction by ultraviolet radiation have not been defined. In this study we sought to identify cytokines that might be involved. We examined the role of interleukin-6, using the IL-6 null (IL-6-/-) mouse, which has been observed to be highly sensitive to ultraviolet radiation damage. Whereas cutaneous metallothionein concentration, measured by radioimmunoassay, began to rise in wild-type (IL-6+/+) mice by 12 h after ultraviolet irradiation, there was a significant delay in the IL-6-/- mice until 48 h after UV irradiation. Immunohistologically, metallothionein appeared in IL-6+/+ mice at 24 h in dermal fibroblasts, and then by 48 h in epidermal basal keratinocytes, with intensity increasing until 72 h, and was coincident with proliferating cell nuclear antigen-positive staining. Corresponding metallothionein expression in IL-6-/- mouse skin was significantly delayed. Serum interleukin-6 was elevated in IL-6+/+ mice following ultraviolet irradiation, with peak concentration at 4 h, but no increase in serum interleukin-1beta was found in either IL-6+/+ or IL-6-/- mice. Interestingly, tumor necrosis factor alpha concentration in serum was elevated at 12 h postirradiation in IL-6+/+ mice, but there was an earlier (at 4 and 8 h) time-dependent increase in tumor necrosis factor alpha in serum of the IL-6-/- mice. Skin zinc and copper concentrations were not altered by ultraviolet irradiation in either IL-6+/+ or IL-6-/- mice. The results suggest that interleukin-6 may be a very early mediator of cutaneous metallothionein induction by ultraviolet radiation, but that this role is possibly assumed by alternative cytokines like tumor necrosis factor alpha when interleukin-6 is deficient.

Pulmonary toxicity caused by acute exposure to mercury vapor is enhanced in metallothionein-null mice

This study examined the protective role of metallothionein (MT) against pulmonary damage caused by acute exposure to metallic mercury (Hg0) vapor using MT-null and wild-type mice. Both strains of mice were exposed to Hg0 at 6.6 to 7.5 mg/m3 for 4 hr each day for 3 consecutive days. This dosing protocol was lethal to over 60% of MT-null mice but did not kill any wild-type mice. More severe pulmonary damage was found by histopathological observation in MT-null mice than in wild-type mice. MT levels in the lung were elevated in wild-type mice after Hg0 vapor exposure, and gel filtration of the lung cytosol revealed that most of the mercury was associated with MT. In MT-null mice, MT levels were below the limit of detection (0.2 microg/g tissue) for the MT assay even after exposure. After exposure to Hg0 vapor for 3 consecutive days, the pulmonary mercury levels in wild-type mice were significantly higher than in MT-null mice. These findings suggest that MT plays a protective role against the acute pulmonary toxicity of Hg0 vapor.

Isolation and identification of metallothionein isoforms (MT-1 and MT-2) in the rat testis

It has been a long-lasting controversial issue as to whether or not the male genital organs, such as the testis and prostate, contain metallothioneins (MTs), a group of cysteine-rich heavy-metal-binding proteins that play a role in detoxifying heavy metals such as cadmium (Cd). Earlier studies reported that the rodent testis lacks MTs and concluded that this is why the testis is very susceptible to Cd, although other indirect experimental evidence suggests that MTs are present in this organ. A deficiency of MTs in the testis was originally suspected on the basis of amino acid composition analysis, since MT-like proteins isolated as Cd-binding proteins did not have a characteristic MT structure. In the present study, we demonstrate that the rat testis indeed expresses Cd-binding proteins with sequences identical to those previously described for MT-1 and MT-2, the major isoforms. To confirm that MT-1 and MT-2 are present in the rat testis, we purified and isolated Cd-binding proteins by homogenization using Cd-containing buffer, followed by sequential purification using Sephadex G-75 gel filtration chromatography and anion HPLC column chromatography, which yielded Cd-binding protein-1 (Cd-BP-1) and -2 (Cd-BP-2). After pyridylethylation, Cd-BP-1 and Cd-BP-2 were subjected to specific protein fragmentation by acids and endopeptidases, which revealed that these Cd-binding proteins have the same primary structures as MT-1 and MT-2 respectively. Thus we believe that the present results clearly resolve the long-standing debate about the presence of MTs in the testis, at least in the rodent.

Metallothionein expression and concentrations of copper and zinc are associated with tumor differentiation in hepatocellular carcinoma

Metallothionein is the carrier protein of heavy metal ions, such as copper (Cu) and zinc (Zn). In this study, the relationships among immunohistochemical expression of metallothionein, concentrations of Cu and Zn, histological differentiation and proliferative activity of hepatocellular carcinoma were investigated in 51 cases. The concentrations of Cu and Zn in both tumor and non-tumor tissues were determined using electron probe microanalysis. Immunohistochemical expression of metallothionein in tumor tissues decreased with the degree of differentiation, whereas the number of hepatocytes positive for Ki-67 increased. Furthermore, the concentrations of Cu and Zn in tumor tissues decreased with the degree of histological differentiation in human hepatocellular carcinoma.

Ultrastructural localization of zinc ions in the rat prostate: an autometallographic study

BACKGROUND

The prostate contains high amounts of free zinc ions which are excreted into the seminal fluid. The extra- and intracellular distribution of zinc ions using the highly specific autometallographical (AMG) method is described.

METHODS

Prostates from sulfide-perfused rats were excised, and the ZnS crystals were silver-enhanced to sizes detectable by the electron and light microscope.

RESULTS

AMGZnS grains were found primarily in the acinic lumen of the lateral lobes. The dorsal lobe stained only faintly, while the ventral lobe was void of grains. At ultrastructural levels, the presence of zinc ions was confined to apical secretory vesicles and lysosome-like structure of the epithelium of mainly the lateral lobes.

CONCLUSIONS

We suggest a constant secretion of zinc ions from the epithelial cells into both the acinar lumen and the intercellular canaliculi, and that the zinc enriched secretory cells in the prostate belong to a system of glandular cells that uses zinc ions to aggregate macromolecules to be excreted.

Immunohistochemical localization of metallothionein in human prostate cancer. J Urol. 1996;156:1679-1681. [PMID: 8863569 DOI: 10.1016/s0022-5347(01)65481-8]

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.

Susceptibility of metallothionein-null mice to paraquat

Using transgenic mice in which metallothionein (MT)-I and MT-II genes, we have studied a putative role of MT as a free radical scavenger against paraquat, a free radical generator. Male mice were injected s.c. with paraquat (PQ) at a single dose of 40 or 60 mg/kg of body weight (b.w.). Two of the six MT-null mice died within 16 h at the dose of 60 mg PQ/kg. b. w. PQ administration increased hepatic MT concentration in the normal mice (C57BL/6J), but not in the MT-null mice. The lipid peroxidation (LP) determined by thiobarbituric acid-reactive substance formation was increased by PQ in the liver of normal and MT-null mice, and the enhanced level was greater in the MT-null mice than in the C57BL/6J mice. Administration of PQ significantly increased blood urea nitrogen only in the MT-null mice, indicating renal damage. Without paraquat administration, the hepatic concentration of non-protein sulphydryl compounds was less in the MT-null mice than in the C57BL/6J mice, and the basal level of LP was higher in the MT-null mice than in the C57BL/6J mice. The present results support the notion that MT plays an antioxidative role against paraquat insult under physiological conditions.

Testosterone-dependent induction of metallothionein in genital organs of male rats

Metallothioneins (MTs) are a group of cysteine-rich heavy-metal-binding proteins. We have investigated MT gene expression in the ventral and dorsolateral lobes of the prostate and coagulating gland of male Wistar rats. In intact rats, both MT mRNA and MT were present in the dorsolateral lobe and coagulating gland but not in the ventral lobe. Orchidectomy caused involution of the above organs, and both MT mRNA and MT were considerably decreased or become undetectable. An injection of testosterone propionate into orchidectomized rats restored not only the size of these organs, but also MT mRNA and MT concentrations, particularly in the dorsolateral lobe and coagulating gland. In the dorsolateral lobe, no selective uptake of Zn2+ preceding the increase in MT was observed, suggesting that Zn2+ ions are not associated with the increased expression of the MT gene. The present result suggests that of the male auxiliary genital organs, the dorsolateral lobe and coagulating gland, but not the ventral lobe, contain MT, the biosynthesis of which is regulated by testosterone.

Reduced retention of cadmium in the liver of metallothionein-null mice

The distribution of cadmium (Cd) in the organs of mice was studied using metallothionein (MT)-null transgenic mice. When mice were administered with Cd chloride at a single subcutaneous dose of 1.0 mg Cd/kg body weight, Cd accumulated mainly in the liver and kidney by 6 h after injection without any significant difference between the MT-null mice and control (C57BL/6J) mice. MT was not detected in these organs of MT-null mice both before and after Cd administration whereas MT was induced mainly in these organs of the control mice. There was a marked elimination of Cd from the liver of MT-null mice by 21 days after administration, compared with a relatively slow Cd elimination in the C57BL/6J mice. Under the condition that no significant liver or kidney damage was observed, MT was considered to play a significant role in the retention of Cd in the liver but not in the uptake of this metal.

Metallothionein gene expression in testicular interstitial cells and liver of rats treated with cadmium

The rodent testes are generally more susceptible to cadmium (Cd)-induced toxicity than the liver. Cd induces predominantly testicular interstitial cell (TIC) tumors. In order to clarify the molecular mechanism underlying tissue differences in Cd sensitivity, we compared Cd-induced metallothionein (MT) gene expression, MT protein accumulation, and Cd retention in freshly isolated TICs and liver. Adult male Fischer rats received a s.c. injection of 4.0 micromol Cd/kg or vehicle and 24 h later tissues were sampled and TICs isolated. MT-I and MT-II mRNA levels were determined by slot-blot analysis followed by densitometry scanning, and MT was estimated by the Cd-heme method. Testicular lesions were not grossly or histologically observed in rats treated with 4 micromol Cd/kg. Both MT mRNA and MT (as determined by Cd-binding capacity) were constitutively present in TICs as well as the liver. TICs isolated from Cd-treated rats accumulated more Cd (4-fold), and had higher levels of MT-I (1.9-fold) and MT-II (1.4-fold) mRNAs over control, but contained less MT (30% decrease) than TICs isolated from control animals. Cd exposure substantially increased hepatic Cd content (6000-fold), MT (58-fold), and MT-I mRNA (5.3-fold), but did not increase MT-II mRNA. Thus, our findings indicate that, although low-dose Cd exposure results in increases of MT mRNA in TICs it does not enhance MT synthesis within these cells. The inability to induce the metal-detoxicating MT-protein, in response to Cd, might account for higher susceptibility of testes to Cd toxicity and carcinogenesis relative to liver.

Activation of the complete mouse metallothionein gene locus in the maternal deciduum

The mouse metallothionein (MT) gene family consists of four known members (MT-I through IV) clustered on chromosome 8. Studies reported herein examine the expression and regulation of the MT-III and MT-IV genes in specific cell types in the maternal reproductive tract, developing embryo, and fetus known to express the MT-I and -II genes. MT-III and MT-IV mRNAs were absent from the visceral yolk sac, placenta, and fetal liver, tissues with high levels of MT-I and MT-II mRNAs. In contrast, MT-III and MT-IV mRNAs were both abundant in the maternal deciduum, and in experimentally induced deciduoma on 7 and 8 days postcoitum (1 dpc = vaginal plug), as are MT-I and -II mRNAs. The abundance of each of these MT mRNAs increased coordinately during development of the deciduum (6-8 dpc), and in situ hybridization localized MT-I, MT-III, and MT-IV mRNAs to the secondary decidual zone of the antimesometrial region on 8 dpc, where in some regions all of the cells were apparently positive. Thus, all of the known mouse MT genes are co-expressed in at least some of the cells in the secondary decidual zone. Electrophoretic analysis of decidual MT suggested that the MT-I, -II, and -III isoforms are abundant proteins in the secondary deciduum. Bacterial endotoxin-lipopolysaccharide (LPS) and Zn are powerful inducers of MT-I and MT-II gene expression in many adult organs, whereas these agents apparently have little effect on MT-III and MT-IV gene expression. Neither of these agents significantly effected levels of decidual MT-III or MT-IV mRNAs in vivo or in primary cultures of decidual cells in vitro, and only modest effects of Zn on MT-I mRNA levels were noted. During 2 days of in vitro culture, decidual cell MT-I and MT-III mRNA levels remained elevated while MT-IV mRNA levels decreased. Thus, expression of the mouse MT gene locus in the deciduum appears to be developmentally regulated, and in this tissue, the MT genes are refractory to induction by Zn or inflammation.

Metallothionein binding zinc inhibits nuclear chromatin decondensation of human spermatozoa

Nuclear chromatin decondensation (NCD) of the human spermatozoa was induced by 1% sodium dodecyl sulphate (SDS). NCD of the spermatozoa induced in healthy and fertile men was significantly stronger and at higher rates than that in infertile men. In 1% SDS with 6 mM zinc chelating EDTA, metallothionein (MT) significantly enhanced NCD in a healthy man. In contrast MT alone significantly inhibited sperm NCD. Sperm NCD rate induced by 1% SDS in 10 infertile men was significantly inhibited by adding 75 or 750 micrograms ml-1 of MT. By adding 1.5 mM zinc, MT at concentrations of 0.75, 7.5, 75, or 750 micrograms ml-1, enhanced the inhibitory effect of 1.5 mM zinc. This suggested that thiols in the MT could, when liberated from zinc by zinc-chelating EDTA, induce sperm decondensation by cleaving stabilizing S-S bridges and that zinc bound to MT could exert a chromatin stabilizing effect mediated by the zinc dependent type of chromatin stability. The present study suggested that zinc bound to MT, which is secreted mainly from the prostate gland, is one factor that contributes to the chromatin stabilizing effect of human prostatic fluid.

Metallothionein in human seminal plasma

Metallothionein (MT) concentrations were measured in the seminal plasma of 4 fertile and 35 infertile men and in the hydrocele and spermatocele fluids. The relationship between MT content and sperm density, total number of sperm per ejaculate, sperm motility and abnormal form rates, leukocyte count and zinc levels in seminal plasma, as well as the relationship between MT and serum follicle-stimulating hormone, luteinizing hormone, testosterone, and prolactin were examined. MT was not detected in the hydrocele and spermatocele fluids. MT levels were related to zinc levels and to the leukocyte count in seminal plasma, but there was no correlation between MT and the other factors examined. This study supported previous findings that MT was secreted predominantly from the prostate and induced by inflammation of the prostate gland or seminal vesicles; the findings suggest that MT binds mainly to zinc and is one of the zinc-binding proteins in seminal plasma.

Immunohistochemical metallothionein expression in colorectal adenocarcinoma: correlation with tumour stage and patient survival

Metallothioneins (MTs), a set of ubiquitous low-molecular-weight proteins essential for the protection of cells against heavy metal ion toxicity, were demonstrated immunohistochemically using a monoclonal antibody (E9) against a conserved epitope of I and II isoforms in a series of 109 colorectal adenocarcinomas. In a semiquantitative analysis strong MT expression in the majority of tumour cells was observed in 34 (31%) cases, 24 (22%) tumours showed a focal MT positivity, and 51 (47%) almost completely lacked MT expression. These differences in MT expression were statistically significantly (P < 0.05) associated with the tumour stage (Dukes classification) and the lymph node involvement at the time of operation (pN stages). However, in contrast to previous findings obtained on a variety of tumours, MT positivity was associated with a favourable clinical outcome in colonic carcinoma, which may indicate their different biological behaviour. Survival curves of cases with MT-positive and MT-negative status differed from each other in a univariate analysis (Mantel-Haenszel: 8.9, P < 0.05) but lost significance when a multivariate analysis was carried out by means of the Cox proportional regression model with Dukes' stages as a stratification factor. It is concluded that immunohistochemically demonstrated MT expression is significantly associated with tumour stages but does not represent an independent prognostic variable in colorectal cancer. However, it may provide important information about some of the biological mechanisms underlying progression in colorectal cancer.

Cadmium and prostate cancer

Prostatic cancer is a common and frequently lethal malignant disease. In the United States and other countries the incidence and mortality rate of prostate cancer continue to rise. Cancer of the prostate has an extremely complex etiology and appears dependent on a variety of factors, making linkage to a single factor very difficult to detect. Cadmium is a metallic toxin of great environmental and occupational concern. Cadmium exposure has been associated with human prostatic cancer in some, but not all, epidemiologic studies. Some studies indicate that tissue levels of cadmium in the human prostate correlate with malignant disease. Any association between cadmium and prostatic cancer has been controversial, in large part because of a previous lack of relevant animal models. However, several chronic studies in rats revealing a correlation between cadmium exposure and prostatic tumors have been published over the last several years. These include a study of oral cadmium exposure, a route extremely relevant to human exposure. Several of these chronic studies indicate a hormonal dependence of cadmium-induced prostate cancer. Other supportive work continues to accumulate, such as studies showing in vitro malignant transformation of prostatic epithelial cells with cadmium exposure. In addition, there are indications that the primary biologic tolerance system for cadmium (i.e., the metallothionein gene) may be only poorly active in the specific lobes of the rat prostate in which cadmium induces tumors. The induction in rats of prostate cancer by cadmium treatment clearly supports, but does not definitively establish, a possible role for cadmium as an etiological agent in human prostate cancer. Further research, however, will be required to establish the precise role of cadmium in this important human malignancy.

Functional integrity of metallothionein genes in testicular cell lines

The presence and inducibility of the major cadmium (Cd) chelating protein metallothionein (MT) in testicular cells has been controversial. In this study, the induction and production of MT in testicular cells were studied using mouse Leydig and Sertoli cell lines. Metal accumulation was studied by subjecting the cells to increasing levels of Cd. The presence of transcription factors for MT synthesis was analyzed by transfecting the cells with a reporter gene under the control of the MT promoter. The dose- and time-dependent induction of MT were conducted by Northern analyses. Expression of MT genes occurred in both Leydig and Sertoli cells. To avoid cross hybridization of the MT probe with mRNAs encoding testicular metal binding proteins and to investigate the integrity of MT mRNA, isoMT mRNA identification and primer extension experiments were performed. Those studies show that the induced mRNA indeed encodes MT. The biosynthesis of MT was confirmed by following 35S-cysteine incorporation into the protein. Finally, cadmium tolerance of testicular cells is compared with that of fibroblast cells. By these studies, we conclude that the MT genes are functional and inducible in testicular cells.

Metallothionein mRNA in the testis and prostate of the rat detected by digoxigenin-labeled riboprobe

Metallothionein (MT), a cysteine-rich heavy metal-binding protein, has been considered to play a role in the homeostatic control and detoxification of heavy metals, such as zinc, copper, and cadmium. In the present study, we have utilized a digoxigenin-labeled riboprobe to localize MT mRNA only by bright-field optics in the testis and prostate of the rat. In the rat testis, MT mRNA was found predominantly in primary spermatocytes and also in secondary spermatocytes and spermatids, but not in the spermatogonia, Sertoli cells, and Leydig cells. On the other hand, MT protein was present in these spermatogenic cells as well as in spermatozoa and Sertoli cells. In the prostate, MT mRNA was found predominantly in the epithelium of the dorsolateral lobes, but not in the ventral lobe, which is in agreement with the observed localization of MT protein. The utilization of both in situ hybridization and immunohistochemical staining on the same tissue specimens show MT gene expression in specific cell types in the male genital organs.

The localization of mercury and metallothionein in the cerebellum of rats experimentally exposed to methylmercury

Rats were dosed with methylmercuric chloride, either by gastric gavage (5 x 10 mg kg-1 body weight over a 15-day period), or in their drinking water (20 mg methylmercuric chloride l-1 for 14 or 42 days). Localization of mercury within the cerebellum was performed with a silver physical development technique, and metallothionein with dinitrophenyl hapten-sandwich immunohistochemistry. Mercury was detected in structurally undamaged Purkinje neurones and adjacent Bergmann glial cells; no mercury was detected in granule cells even though these small cells nearest the Purkinje layer had a high incidence of pyknotic nuclei. In general, metallothionein was detected mainly in Bergmann glial cells, Purkinje cells, astrocytes and glial cells of white matter; no metallothionein was detected in granule cells. We hypothesized that the resistance of Purkinje cells to methylmercuric chloride reflects their ability to transform organic mercurials to inorganic mercury that, in turn, induces the synthesis of radical-scavenging metallothionein molecules.

The effect of zinc in the form of erythromycin-zinc complex (Zineryt lotion) and zinc acetate on metallothionein expression and distribution in hamster skin

The occurrence of zinc-induced synthesis of metallothionein in skin after topical application of the anti-acne drug Zineryt lotion was investigated in hamster ears. The dinitrophenyl hapten-sandwich immunohistochemical method involving a monoclonal anti-metallothionein (MT) antibody (E9) was used to detect and localize zinc-binding MT in the 'treated' and untreated hamster skin. Atomic absorption spectrophotometry and dithizone histochemistry indicated that zinc penetrated the skin more readily, and accumulated more efficiently within the sebaceous glands, when applied to the skin surface as the organo-zinc complex, rather than as the inorganic zinc salt. MT and zinc had similar distributions in hamster skin exposed to the metal. Thus, MT immunoreactivity was especially intense in the sebaceous glands of Zineryt lotion-treated skin, with evidence of nuclear distribution in some cells. Zinc delivered to the sebaceous glands, and released from the organo-complex under the prevailing aqueous conditions, certainly induced MT synthesis; the cysteine-rich protein may protect the pilosebaceous units during the inflammatory phase of acne by scavenging generated oxyradical species.

Involvement of metallothionein and copper in cell proliferation

Metallothionein is a low-molecular weight, cysteine-rich, metal-binding protein which has been implicated in the detoxification of toxic metals (cadmium, mercury), metabolism of zinc and copper, as well as in the scavenging of free radicals. Recent evidence suggests that the protein may also be involved in cell proliferation. Based on the experiments carried out so far, it is assumed that the fundamental role of metallothionein in cell proliferation may be to detoxify and/or transfer copper ions from the cytoplasm to the nucleus at the G1/S phase, which in turn participate in some way in nuclear DNA synthesis.

Localization of metallothionein in breast carcinomas. An immunohistochemical study

Metallothionein (MT) is a cysteine-rich, low molecular weight protein that binds zinc, copper, and cadmium. It is present in a number of normal cells including hepatocytes particularly during fetal and early postnatal life. It has been suggested that developmental profile of MT is similar to other oncofetal gene products and hence, it could be used as a marker for aggressive tumour behaviour. In order to test that hypothesis, we used a monoclonal antibody to MT and immunohistochemically evaluated formalin-fixed, paraffin-embedded tissues from 79 breast carcinomas. In non-neoplastic breast tissue, a strong nuclear and cytoplasmic staining was observed in myoepithelial cells. Positive staining for MT was present in 35 (44%) of breast carcinomas. In most positive cases, nuclear, or both nuclear and cytoplasmic staining was seen. All positive tumours were invasive ductal carcinomas, including a medullary and a metaplastic carcinoma. None of the mucinous, lobular, or intraductal papillary carcinomas reacted for MT. A statistically significant association was found between MT immunostaining and histological grade (P < 0.01) as well as with nuclear grade (P < 0.01). We also observed an inverse relationship between MT staining and oestrogen receptor content of tumours (P < 0.01). Similarly, a statistically significant association was found between moderate and strong MT immunostaining and decreased overall survival and shorter disease-free survival (P < 0.01). MT immunostaining was also predictive of a worse prognosis in the subgroup of lymph node negative (P < 0.001) and oestrogen receptor negative patients (P < 0.01). No statistically significant association was found between MT staining and size of tumour or the presence of lymph node metastasis. We conclude that MT staining may be a useful marker of less differentiated and more aggressive carcinomas of the breast.

Postnatal changes in subcellular distribution of copper, zinc and metallothionein in the liver of bank vole (Clethrionomys glareolus): a possible involvement of metallothionein and copper in cell proliferation

1. Dramatic interdependent changes in the intracellular concentrations of copper (Cu), zinc (Zn) and metallothionein (MT) in the liver of bank voles during the first 30 days of their life were observed. 2. The post-mitochondrial Cu, Zn and MT (Zn-MT) abruptly decreased between 1 and 3 days following birth but the nuclear MT (Cu-MT) and Cu increased at the same time, suggesting that Cu displaced Zn already bound to MT in the cytoplasm and subsequently the complex Cu-MT was translocated to the nuclei. 3. The nuclear Cu concentration reached the highest level (62-71% of the total tissue Cu) in the period from day 3 to day 20 post-partum, just prior to and during a rapidly growing liver. 4. The data indicate that MT and Cu may be involved in the hepatocyte proliferation.

Recent evolutionary history of the metallothionein gene Mtn in Drosophila

A new allele of one of the metallothionein genes of D. melanogaster, Mtn.3, sheds light on the recent evolution of this gene. In comparison to the previously studied Mtn1 allele found in Canton S, this new allele, Mtn.3, produces a transcript that is 49 bases longer and 65-70% less abundant. We detected Mtn.3 in several laboratory strains as well as in isofemale lines derived from natural populations. Sequence comparison showed that Mtn.3 differs from Mtn1 in that it has: (a) base-pair substitution and an extra 49 bp-segment in the 3' untranslated region, (b) a substitution in the coding region that replaces the terminal Glu40 in Mtn1 with Lys40, and (c) two base-pair substitutions in the promoter region. The Mtn.3-type was detected in six species of the melanogaster group by restriction analysis, and this result was confirmed by sequencing the D. simulans Mtn gene. Thus Mtn.3, which produces a less abundant transcript, appears to be the oldest of the two alleles. We also found that the duplications previously isolated from natural populations all derived from Mtn1, the more recent allele. Thus, two evolutionary steps: Mtn.3 to Mtn1 and Mtn1 to Dp(Mtn1), are accompanied by an overall 5- to 6-fold increase of RNA accumulation. The two changes seem to have occurred in non-African populations since Mtn.3 but not Mtn1 was detected in our sample from tropical Africa, while Mtn1 and Dp (Mtn1) are prevalent in European and North American samples.

Metallothionein mRNA stability in chicken and mouse cells

Northern blot analysis revealed that metallothionein (MT) mRNAs accumulate after inhibition of protein synthesis with cycloheximide (CHX) in primary cultures of chick embryo hepatocytes and fibroblasts, as well as in an established mouse hepatoma cell line. Inhibition of RNA synthesis with actinomycin D (AMD) led to rapid loss of MT mRNAs in these cells, whereas CHX dramatically retarded the rate of MT mRNA decay (t1/2 greater than 24 h). These results suggest that CHX causes MT mRNA accumulation primarily by increasing stability of MT mRNA. Thus, changes in MT mRNA turn-over rates may play an important role in regulating the accumulation of MT mRNA. The half-lives of MT mRNAs in chicken and mouse cells were determined by oligodeoxyribonucleotide excess solution hybridization with RNA samples extracted after different periods of exposure to AMD. The half-life of chicken MT (cMT) mRNA in uninduced chicken embryo hepatocytes was 3.6 h. Induction of cMT mRNA by pretreatment of these cells with zinc (Zn) prior to exposure to AMD, did not alter the half-life of cMT mRNA significantly. In contrast, cadmium (Cd) induction led to a 2.5-fold increase in the stability of this mRNA. In uninduced chicken embryo fibroblasts, cMT mRNA levels were too low to allow accurate determination of half-life using the methods employed here. However, the half-life of this mRNA in Zn-induced chicken embryo fibroblasts was 6.2 h, whereas it was 9.3 h in Cd-induced cells. Thus, the turn-over rate of cMT mRNA after Cd-induction is very similar in chick embryo fibroblasts and hepatocytes. These data suggest that the accumulation of MT mRNA in chicken cells may reflect, in part, metal-specific effects on MT mRNA stability. The half-lives of mouse MT-I and MT-II (mMT-I and mMT-II) mRNAs in uninduced BNL hepatoma cells were identical (9.2 h), and were not effectively altered after induction by metals (Zn, Cd) or interleukin-1 beta (IL-1 beta). However, mMT mRNAs in pachytene spermatocytes and round spermatids, freshly isolated from the adult testes, were 2.2- to 4.5-fold more stable than in hepatoma cells. These results suggest that cell-type specific accumulation of mMT mRNAs may be regulated, in part, by mRNA stability.

Localization of metallothionein in hair follicles of normal skin and the basal cell layer of hyperplastic epidermis: possible association with cell proliferation

Metallothionein is a low-molecular-weight metal-binding protein. Although it is inducible by a variety of agents and ubiquitously present in many tissues, its physiologic functions are still not clear. The present study was undertaken to determine the possible functions of metallothionein in both the proliferation and differentiation of epidermal keratinocytes. Metallothionein was detected immunohistochemically in hair matrix cells of the bulb and cells of the outer root sheath of anagen hair follicles, but not in dermal papillae in normal skin in the back of mice. In hyperplastic epidermal tissue, induced by either a phorbol ester tumor promoter or cholera toxin, the basal cells of the interfollicular epidermis stained strongly for metallothionein. Elevated expression of mRNA of the metallothionein gene was also demonstrated when the skin was stimulated by agents that induced hyperplasia. Papillomas produced by two-stage carcinogenesis protocols also stained for metallothionein. These observations suggest that metallothionein is involved in the proliferation of epidermal keratinocytes.

Immunohistochemical localization of metallothionein in the eye of rats

In order to elucidate possible physiological roles of metallothionein (MT), we have studied immunohistological localization of MT in the eye of the rat, using an avidin-biotin peroxidase complex method. As a result, strong MT immunostaining was observed in the epithelium of the lens and cornea. In the retina, considerably strong MT immunostaining was observed in the pigment cell layer while the nerve fiber layer and inner plexiform layer showed weak MT staining. Glial cells in the optic nerve were found to have marked MT staining. The present result is consistent with the hypothesis that MT may be involved not only in activation of zinc enzymes and cell proliferation through supply of zinc ions, but also in a protective mechanism in the blood-retina barrier.

Glial immunoreactivity for metallothionein in the rat brain

A series of frozen and vibratome coronal sections of the rat brain were examined by immunocytochemistry for the presence of a cysteine-rich metal binding protein, metallothionein (MT). Astrocytes throughout the brain and brainstem stained positively for MT; neurons and oligodendroglia were unstained. Ependymal cells and tanycyte processes in the hypothalamus were also immunoreactive, along with a narrow zone of immunopositivity along the margins of the area postrema. Gomori-positive astrocytes in the hypothalamus, identifiable by toluidine blue staining, metal-containing cytoplasmic granules, represented a subset of MT-positive astrocytes that may be involved in reactions to blood-borne metal compounds that penetrate into circumventricular organs of the brain.