Human metallothionein genes: structure of the functional locus at 16q13

MT1G Regulates c-MYC/P53 Signal to Inhibit Proliferation, Invasion and Migration and Promote Apoptosis in Colon Cancer Cells

INTRODUCTION

Colon cancer is a common and malignant cancer featuring high morbidity and poor prognosis.

AIMS

This study was performed to explore the regulatory role of MT1G in colon cancer as well as its unconcealed molecular mechanism.

METHODS

The expressions of MT1G, c-MYC, and p53 were assessed with the application of RT-qPCR and western blot. The impacts of MT1G overexpression on the proliferative ability of HCT116 and LoVo cells were measured by CCK-8 and BrdU incorporation assays. Additionally, transwell wound healing, and flow cytometry assays were employed to evaluate the invasive and migrative capacities as well as the apoptosis level of HCT116 and LoVo cells. Moreover, the activity of the P53 promoter region was assessed with the help of a luciferase reporter assay.

RESULTS

It was found that the expressions of MT1G at both mRNA and protein levels were greatly decreased in human colon cancer cell lines, particularly in HCT116 and LoVo cell lines. After transfection, it was discovered that the MT1G overexpression suppressed the proliferation, migration and invasion but promoted the apoptosis of HCT116 and LoVo cells, which were then partially reversed after overexpressing c-MYC. Additionally, MT1G overexpression reduced c-MYC expression but enhanced the p53 expression, revealing that the MT1G overexpression could regulate c-MYC/P53 signal. Elsewhere, it was also shown that c-MYC overexpression suppressed the regulatory effects of MT1G on P53.

CONCLUSION

To conclude, MT1G was verified to regulate c-MYC/P53 signal to repress the proliferation, migration and invasion but promote the apoptosis of colon cancer cells, which might offer a novel targeted-therapy for the improvement of colon cancer.

Early growth response 1 transcription factor is essential for the pathogenic properties of human endometriotic epithelial cells

Although a non-malignant gynecological disorder, endometriosis displays some pathogenic features of malignancy, such as cell proliferation, migration, invasion and adaptation to hypoxia. Current treatments of endometriosis include pharmacotherapy and/or surgery, which are of limited efficacy and often associated with adverse side effects. Therefore, to develop more effective therapies to treat this disease, a broader understanding of the underlying molecular mechanisms that underpin endometriosis needs to be attained. Using immortalized human endometriotic epithelial and stromal cell lines, we demonstrate that the early growth response 1 (EGR1) transcription factor is essential for cell proliferation, migration and invasion, which represent some of the pathogenic properties of endometriotic cells. Genome-wide transcriptomics identified an EGR1-dependent transcriptome in human endometriotic epithelial cells that potentially encodes a diverse spectrum of proteins that are known to be involved in tissue pathologies. To underscore the utility of this transcriptomic data set, we demonstrate that carbonic anhydrase 9 (CA9), a homeostatic regulator of intracellular pH, is not only a molecular target of EGR1 but is also important for maintaining many of the cellular properties of human endometriotic epithelial cells that are also ascribed to EGR1. Considering therapeutic intervention strategies are actively being developed for EGR1 and CAIX in the treatment of other pathologies, we believe EGR1 and its transcriptome (which includes CA9) will offer not only a new conceptual framework to advance our understanding of endometriosis but will also furnish new molecular vulnerabilities to be leveraged as potential therapeutic options in the future treatment of endometriosis.

Protein interactions with metallothionein-3 promote vectorial active transport in human proximal tubular cells

Metallothionein 3 (MT-3) is a small, cysteine-rich protein that binds to essential metals required for homeostasis, as well as to heavy metals that have the potential to exert toxic effects on cells. MT-3 is expressed by epithelial cells of the human kidney, including the cells of the proximal tubule. Our laboratory has previously shown that mortal cultures of human proximal tubular (HPT) cells express MT-3 and form domes in the cell monolayer, a morphological feature indicative of vectorial active transport, an essential function of the proximal tubule. However, an immortalized proximal tubular cell line HK-2 lacks the expression of MT-3 and fails to form domes in the monolayer. Transfection of HK-2 cells with the MT-3 gene restores dome formation in these cells suggesting that MT-3 is required for vectorial active transport. In order to determine how MT-3 imparts this essential feature to the proximal tubule, we sought to identify proteins that interact either directly or indirectly with MT-3. Using a combination of pulldowns, co-immunoprecipitations, and mass spectrometry analysis, putative protein interactants were identified and subsequently confirmed by Western analysis and confocal microscopy, following which proteins with direct physical interactions were investigated through molecular docking. Our data shows that MT-3 interacts with myosin-9, aldolase A, enolase 1, β-actin, and tropomyosin 3 and that these interactions are maximized at the periphery of the apical membrane of doming proximal tubule cells. Together these observations reveal that MT-3 interacts with proteins involved in cytoskeletal organization and energy metabolism, and these interactions at the apical membrane support vectorial active transport and cell differentiation in proximal tubule cultures.

The Bioinorganic Chemistry of Mammalian Metallothioneins

The functions, purposes, and roles of metallothioneins have been the subject of speculations since the discovery of the protein over 60 years ago. This article guides through the history of investigations and resolves multiple contentions by providing new interpretations of the structure-stability-function relationship. It challenges the dogma that the biologically relevant structure of the mammalian proteins is only the one determined by X-ray diffraction and NMR spectroscopy. The terms metallothionein and thionein are ambiguous and insufficient to understand biological function. The proteins need to be seen in their biological context, which limits and defines the chemistry possible. They exist in multiple forms with different degrees of metalation and types of metal ions. The homoleptic thiolate coordination of mammalian metallothioneins is important for their molecular mechanism. It endows the proteins with redox activity and a specific pH dependence of their metal affinities. The proteins, therefore, also exist in different redox states of the sulfur donor ligands. Their coordination dynamics allows a vast conformational landscape for interactions with other proteins and ligands. Many fundamental signal transduction pathways regulate the expression of the dozen of human metallothionein genes. Recent advances in understanding the control of cellular zinc and copper homeostasis are the foundation for suggesting that mammalian metallothioneins provide a highly dynamic, regulated, and uniquely biological metal buffer to control the availability, fluctuations, and signaling transients of the most competitive Zn(II) and Cu(I) ions in cellular space and time.

Metallothionein 1: A New Spotlight on Inflammatory Diseases

MT1 has been demonstrated to be an essential stress protein in maintaining physiological balance and regulating immune homeostasis. While the immunological involvement of MT1 in central nervous system disorders and cancer has been extensively investigated, mounting evidence suggests that MT1 has a broader role in inflammatory diseases and can shape innate and adaptive immunity. In this review, we will first summarize the biological features of MT1 and the regulators that influence MT1 expression, emphasizing metal, inflammation, and immunosuppressive factors. We will then focus on the immunoregulatory function of MT1 on diverse immune cells and the signaling pathways regulated by MT1. Finally, we will discuss recent advances in our knowledge of the biological role of MT1 in several inflammatory diseases to develop novel therapeutic strategies.

Quantification of metallothionein-III in brain tissues using liquid chromatography tandem mass spectrometry

Metallothioneins (MTs) are crucial for metal ion homeostasis in mammalian cells. Specialized mass spectrometry methods have been developed to detect MTs in tissue extracts, though facile methods with scalable throughput are lacking. To improve analytical throughput and repeatability, we developed a standardised liquid chromatography tandem mass spectrometry (LC-MS/MS) method for robust determination of metallothionein-3 (MT3) that is amenable to microplate processing. This method uses standard protein digestion conditions with commercially available reagents and commonly practiced reversed-phase chromatography, detecting MT3 at low ng/mL levels in human brain tissue extracts. We found that trypsin digestion largely underestimated MT3 levels, whereas endopeptidase Lys-C yielded vastly higher signals with low replicate variance. The choice of target peptide was critical for accurate MT3 detection - a peptide in the α-domain yielded the most robust signals. We demonstrate the utility of this method by comparing the expression of MT3 in post-mortem brain tissues of a cohort of Alzheimer's disease (AD) individuals and age-matched controls.

Metallothionein MT1M Suppresses Carcinogenesis of Esophageal Carcinoma Cells through Inhibition of the Epithelial-Mesenchymal Transition and the SOD1/PI3K Axis

Metallothionein (MT1M) belongs to a family of cysteine-rich cytosolic protein and has been reported to be a tumor suppressor gene in multiple cancers. However, its role in esophageal carcinoma carcinogenesis remains unclear. In this study, MT1M expression was correlated with tumor type, stage, drinking and smoking history, as well as patient survival. We also studied the regulation and biological function of MT1M in esophageal squamous cell carcinoma (ESCC). We have found that MT1M is significantly downregulated in ESCC tissues compared with adjacent non-cancer tissues. Furthermore, restoration of expression by treatment with the demethylation agent A + T showed that MT1M downregulation might be closely related to hypermethylation in its promoter region. Over-expression of MT1M in ESCC cells significantly altered cell morphology, induced apoptosis, and reduced colony formation, cell viability, migration and epithelial-mesenchymal transition. Moreover, based on reactive oxygen species (ROS) levels, a superoxide dismutase 1 (SOD1) activity assay and protein analysis, we verified that the tumor-suppressive function of MT1M was at least partially caused by its upregulation of ROS levels, downregulation of SOD1 activity and phosphorylation of the SOD1 downstream pathway PI3K/AKT. In conclusion, our results demonstrated that MT1M was a novel tumor-suppressor in ESCC and may be disrupted by promoter CpG methylation during esophageal carcinogenesis.

The association of blood lead levels and renal effects may be modified by genetic combinations of Metallothionein 1A 2A polymorphisms

Metallothionein (MT) is a protein with function of heavy metal detoxification. However, studies about how single nucleotide polymorphisms (SNPs) of MT genes influence lead nephropathy are relatively scarce. Therefore, our aim is to investigate the association between blood lead levels and renal biomarkers and to study whether this association is influenced by the combination of MT1A and MT2A SNPs. Blood lead, urinary uric acid (UA), and urinary N-acetyl-beta-d-glucosaminidase (NAG) levels were analyzed from 485 participants. Genotyping were performed on MT1A SNPs (rs11640851 and rs8052394) and MT2A SNPs (rs10636 and rs28366003). The combined MT1A 2A SNPs were divided into 16 groups. Among renal biomarkers, urinary UA was negatively significant associated with the time-weighted index of cumulative blood lead (TWICL), while urinary NAG was positively significant with TWICL. Furthermore, the association between urinary UA and TWICL was significantly modified by group 6 of combined SNPs (MT1A 2 A SNPs combination were AAAGGGAA, ACAGGGAA, and ACGGGGAA). In conclusion, the negative association of urinary UA and TWICL is modified by group 6, which means participants of group 6 are more susceptible to lead nephrotoxicity.

Evaluation of MT Family Isoforms as Potential Biomarker for Predicting Progression and Prognosis in Gastric Cancer

Background

Metallothioneins (MTs) family comprises many isoforms, most of which are frequently dysregulated in a wide range of cancers. However, the expression pattern and exact role of each distinct MT family isoform which contributes to tumorigenesis, progression, and drug resistance of gastric cancer (GC) are still unclear.

Methods

Publicly available databases including Oncomine, Gene Expression Profiling Interactive Analysis (GEPIA), Kaplan-Meier plotter, SurvExpress, MethHC, cBioportal, and GeneMANIA were accessed to perform an integrated bioinformatic analysis and try to detect fundamental relationships between each MT family member and GC.

Results

Bioinformatic data indicated that the mRNA expression of all MT family members was almost lowly expressed in GC compared with normal gastric tissue (P<0.05), and patients with reduced mRNA expression of each individual MT member had inconsistent prognostic value (OS, FP, PPS), which depended on the individual isoform of MT. A negative correlation between the methylation in promoter region of majority of MT members and their mRNA expression was detected from MethHC database (p<0.001). Data downloaded from TCGA revealed that MTs were rarely mutated in GC patients and MT2A was frequently regulated by other three genes (FOS, JUN, SP1) in GC patients.

Conclusion

MTs were nearly downregulated, and distinct type of MT harbored different prognostic role in GC patients. Methylation in gene promoter region of MTs partially contributed to their reduced expression in GC. Our comprehensive analyses from multiple independent databases may further lead researches to explore MT-targeting reagents or potential diagnostic and prognostic markers for GC patients.

ZNF479 downregulates metallothionein-1 expression by regulating ASH2L and DNMT1 in hepatocellular carcinoma

Decreased expression of metallothionein-1 (MT-1) is associated with a poor prognosis in hepatocellular carcinoma (HCC). Here, we found that MT-1 expression was suppressed by 14-3-3ε, and MT-1 overexpression abolished 14-3-3ε-induced cell proliferation and tumor growth. We identified that 14-3-3ε induced expression of ZNF479, a novel potential transcriptional regulator by gene expression profiling and ZNF479 contributed to 14-3-3ε-suppressed MT-1 expression. ZNF479 induced the expression of DNMT1, UHRF1, and mixed-lineage leukemia (MLL) complex proteins (ASH2L and Menin), and increased tri-methylated histone H3 (H3K4me3) levels, but suppressed H3K4 (H3K4me2) di-methylation. ZNF479-suppressed MT-1 expression was restored by silencing of ASH2L and DNMT1. Furthermore, ZNF479 expression was higher in HCC tissues than that in the non-cancerous tissues. Expression analyses revealed a positive correlation between the expression of ZNF479 and DNMT1, UHRF1, ASH2L, and Menin, and an inverse correlation with that of ZNF479, ASH2L, Menin, and MT-1 isoforms. Moreover, correlations between the expression of ZNF479 and its downstream factors were more pronounced in HCC patients with hepatitis B. Here, we found that ZNF479 regulates MT-1 expression by modulating ASH2L in HCC. Approaches that target ZNF479/MLL complex/MT-1 or related epigenetic regulatory factors are potential therapeutic strategies for HCC.

Role of Zinc and Selenium in Oxidative Stress and Immunosenescence: Implications for Healthy Aging and Longevity

Aging is a complex process that includes gradual and spontaneous biochemical and physiological changes which contributes to a decline in performance and increased susceptibility to diseases. Zn and Se are essential trace elements that play a pivotal role in immune functions and antioxidant defense and, consequently, are claimed to play also a role in successful aging trajectories. Consistently with their nature of essential trace elements, a plethora of data obtained “in vitro” and “in vivo” (in humans and animal models) support the relevance of Zn and Se for both the innate and adoptive immune response. Moreover, Zn and Se are strictly involved in the synthesis and regulation of activity of proteins and enzymes, e.g., metallothioneins (MT) and glutathione peroxidase (GPX), that are necessary for our endogenous antioxidant response. This is clearly important to protect our cells from oxidative damage and to slow the decline of our immune system with aging. Age-related changes affecting tissue levels of Zn and Se may indicate that the risk of Zn and Se deficiency increases with aging. However, it is still unclear which of these changes can be the consequence of a “real deficiency” and which can be part of our physiological compensatory response to the accumulating damage occurring in aging. Furthermore, the upregulation of antioxidant proteins (Zn and Se dependent) may be a manifestation of self-induced oxidative stress. By the way, Zn and Se dependent proteins are modulated not only by nutritional status, but also by well-known hallmarks of aging that play antagonistic functions, such as the deregulated nutrient sensing pathways and cellular senescence. Thus, it is not an easy task to conduct Zn or Se supplementation in elderly and it is emerging consistent that these kind of supplementation requires an individualized approach. Anyway, there is consistent support that supplementation with Zn using doses around 10 mg/day is generally safe in elderly and may even improve part of immune performances in those subjects with a baseline deficiency. Regarding Se supplementation, it may induce both beneficial and detrimental effects on cellular immunity depending on the form of Se, supplemental dose, and delivery matrix. The nutritional association of supplements based on “Zn plus Se” is hypothesized to provide additional benefits, but this will likely need a more complex individualized approach. The improvement of our knowledge around screening and detection of Zn and Se deficiency in aging could lead to substantial benefits in terms of efficacy of nutritional supplements aimed at ameliorate performance and health in aging.

The roles of metallothioneins in carcinogenesis

Metallothioneins (MTs) are small cysteine-rich proteins that play important roles in metal homeostasis and protection against heavy metal toxicity, DNA damage, and oxidative stress. In humans, MTs have four main isoforms (MT1, MT2, MT3, and MT4) that are encoded by genes located on chromosome 16q13. MT1 comprises eight known functional (sub)isoforms (MT1A, MT1B, MT1E, MT1F, MT1G, MT1H, MT1M, and MT1X). Emerging evidence shows that MTs play a pivotal role in tumor formation, progression, and drug resistance. However, the expression of MTs is not universal in all human tumors and may depend on the type and differentiation status of tumors, as well as other environmental stimuli or gene mutations. More importantly, the differential expression of particular MT isoforms can be utilized for tumor diagnosis and therapy. This review summarizes the recent knowledge on the functions and mechanisms of MTs in carcinogenesis and describes the differential expression and regulation of MT isoforms in various malignant tumors. The roles of MTs in tumor growth, differentiation, angiogenesis, metastasis, microenvironment remodeling, immune escape, and drug resistance are also discussed. Finally, this review highlights the potential of MTs as biomarkers for cancer diagnosis and prognosis and introduces some current applications of targeting MT isoforms in cancer therapy. The knowledge on the MTs may provide new insights for treating cancer and bring hope for the elimination of cancer.

The Expression of Metallothioneins on Imprint Smears of Prostate Carcinoma: Correlation with Clinicopathologic Parameters and Tumor Proliferative Capacity

Aims and Background

Metallothioneins are a family of metal- binding cysteine-rich proteins that play an important role in cellular processes such as proliferation and apoptosis, protection against oxidative stress and metal ion homeostasis and detoxification. Recent findings suggest that metallothioneins might play a significant role in the development and progression of prostate cancer. It has been also demonstrated that Ki-67 expression may have prognostic value for disease-free survival in cases of prostate carcinoma.

Study Design

Imprint smears samples obtained from 70 patients immediately after radical prostatectomy for prostatic carcinoma were immunostained with monoclonal antibodies against metallothioneins and Ki-67. Metallothionein expression was correlated with Ki-67 immunostaining, Gleason score, stage, preoperative prostate-specific antigen levels and biochemical recurrence.

Results

Metallothionein expression was shown to correlate strongly with Gleason score (P <0.001) and significantly with pathological staging and Ki-67 immunostaining (P <0.001, P <0.05, respectively). In contrast, no significant association between metallothioneins and preoperative PSA was demonstrated. Both of the studied markers (metallothioneins and Ki-67) correlated with recurrence (P = 0.009, P = 0.006, respectively).

Conclusions

The present findings support the independent predictive value of metallothioneins and Ki-67 in prostate cancer. However, additional data are needed in order to reveal the factors that influence the expression of metallothioneins in epithelial neoplastic cells and clarify their mechanism of action.

Metallothioneins: Emerging Modulators in Immunity and Infection

Metallothioneins (MTs) are a family of metal-binding proteins virtually expressed in all organisms including prokaryotes, lower eukaryotes, invertebrates and mammals. These proteins regulate homeostasis of zinc (Zn) and copper (Cu), mitigate heavy metal poisoning, and alleviate superoxide stress. In recent years, MTs have emerged as an important, yet largely underappreciated, component of the immune system. Innate and adaptive immune cells regulate MTs in response to stress stimuli, cytokine signals and microbial challenge. Modulation of MTs in these cells in turn regulates metal ion release, transport and distribution, cellular redox status, enzyme function and cell signaling. While it is well established that the host strictly regulates availability of metal ions during microbial pathogenesis, we are only recently beginning to unravel the interplay between metal-regulatory pathways and immunological defenses. In this perspective, investigation of mechanisms that leverage the potential of MTs to orchestrate inflammatory responses and antimicrobial defenses has gained momentum. The purpose of this review, therefore, is to illumine the role of MTs in immune regulation. We discuss the mechanisms of MT induction and signaling in immune cells and explore the therapeutic potential of the MT-Zn axis in bolstering immune defenses against pathogens.

The Functions of Metamorphic Metallothioneins in Zinc and Copper Metabolism

Recent discoveries in zinc biology provide a new platform for discussing the primary physiological functions of mammalian metallothioneins (MTs) and their exquisite zinc-dependent regulation. It is now understood that the control of cellular zinc homeostasis includes buffering of Zn²⁺ ions at picomolar concentrations, extensive subcellular re-distribution of Zn²⁺, the loading of exocytotic vesicles with zinc species, and the control of Zn²⁺ ion signalling. In parallel, characteristic features of human MTs became known: their graded affinities for Zn²⁺ and the redox activity of their thiolate coordination environments. Unlike the single species that structural models of mammalian MTs describe with a set of seven divalent or eight to twelve monovalent metal ions, MTs are metamorphic. In vivo, they exist as many species differing in redox state and load with different metal ions. The functions of mammalian MTs should no longer be considered elusive or enigmatic because it is now evident that the reactivity and coordination dynamics of MTs with Zn²⁺ and Cu⁺ match the biological requirements for controlling—binding and delivering—these cellular metal ions, thus completing a 60-year search for their functions. MT represents a unique biological principle for buffering the most competitive essential metal ions Zn²⁺ and Cu⁺. How this knowledge translates to the function of other families of MTs awaits further insights into the specifics of how their properties relate to zinc and copper metabolism in other organisms.

The unique C- and N-terminal sequences of Metallothionein isoform 3 mediate growth inhibition and Vectorial active transport in MCF-7 cells

Background

The 3rd isoform of the metallothionein (MT3) gene family has been shown to be overexpressed in most ductal breast cancers. A previous study has shown that the stable transfection of MCF-7 cells with the MT3 gene inhibits cell growth. The goal of the present study was to determine the role of the unique C-terminal and N-terminal sequences of MT3 on phenotypic properties and gene expression profiles of MCF-7 cells.

Methods

MCF-7 cells were transfected with various metallothionein gene constructs which contain the insertion or the removal of the unique MT3 C- and N-terminal domains. Global gene expression analysis was performed on the MCF-7 cells containing the various constructs and the expression of the unique C- and N- terminal domains of MT3 was correlated to phenotypic properties of the cells.

Results

The results of the present study demonstrate that the C-terminal sequence of MT3, in the absence of the N-terminal sequence, induces dome formation in MCF-7 cells, which in cell cultures is the phenotypic manifestation of a cell’s ability to perform vectorial active transport. Global gene expression analysis demonstrated that the increased expression of the GAGE gene family correlated with dome formation. Expression of the C-terminal domain induced GAGE gene expression, whereas the N-terminal domain inhibited GAGE gene expression and that the effect of the N-terminal domain inhibition was dominant over the C-terminal domain of MT3. Transfection with the metallothionein 1E gene increased the expression of GAGE genes. In addition, both the C- and the N-terminal sequences of the MT3 gene had growth inhibitory properties, which correlated to an increased expression of the interferon alpha-inducible protein 6.

Conclusions

Our study shows that the C-terminal domain of MT3 confers dome formation in MCF-7 cells and the presence of this domain induces expression of the GAGE family of genes. The differential effects of MT3 and metallothionein 1E on the expression of GAGE genes suggests unique roles of these genes in the development and progression of breast cancer. The finding that interferon alpha-inducible protein 6 expression is associated with the ability of MT3 to inhibit growth needs further investigation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3355-9) contains supplementary material, which is available to authorized users.

Gene duplication and neo-functionalization in the evolutionary and functional divergence of the metazoan copper transporters Ctr1 and Ctr2

Copper is an essential element for proper organismal development and is involved in a range of processes, including oxidative phosphorylation, neuropeptide biogenesis, and connective tissue maturation. The copper transporter (Ctr) family of integral membrane proteins is ubiquitously found in eukaryotes and mediates the high-affinity transport of Cu⁺ across both the plasma membrane and endomembranes. Although mammalian Ctr1 functions as a Cu⁺ transporter for Cu acquisition and is essential for embryonic development, a homologous protein, Ctr2, has been proposed to function as a low-affinity Cu transporter, a lysosomal Cu exporter, or a regulator of Ctr1 activity, but its functional and evolutionary relationship to Ctr1 is unclear. Here we report a biochemical, genetic, and phylogenetic comparison of metazoan Ctr1 and Ctr2, suggesting that Ctr2 arose over 550 million years ago as a result of a gene duplication event followed by loss of Cu⁺ transport activity. Using a random mutagenesis and growth selection approach, we identified amino acid substitutions in human and mouse Ctr2 proteins that support copper-dependent growth in yeast and enhance copper accumulation in Ctr1^-/- mouse embryonic fibroblasts. These mutations revert Ctr2 to a more ancestral Ctr1-like state while maintaining endogenous functions, such as stimulating Ctr1 cleavage. We suggest key structural aspects of metazoan Ctr1 and Ctr2 that discriminate between their biological roles, providing mechanistic insights into the evolutionary, biochemical, and functional relationships between these two related proteins.

Metallothionein, Copper and Alpha-Synuclein in Alpha-Synucleinopathies

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

Role of Metallothionein in Post-Burn Inflammation

Metallothioneins (MTs) are a family of low molecular-weight and cysteine-rich metalloproteins that regulate metal metabolism and protect cells from oxygen free radicals. Recent studies suggested that MTs have some anti-inflammatory effects. However, the role of MTs in post-burn inflammation remains unclear. This study is designed to investigate the role of MTs in post-burn inflammation in a mouse burn model. MT-I/II null (-/-) and C57BL/6 wild-type (WT) mice were randomly divided into sham burn, burn, Zn treated, and Zn-MT-2 treated groups. The inflammatory cytokines levels were measured by enzyme-linked immunosorbent assay (ELISA). Myeloperoxidase (MPO) activity was determined by spectrophotometry. In in vitro study, exogenous MT-2 was added to macrophages that were stimulated with burn serum in the presence or absence of a p38 MAPK inhibitor SB203580. The IL-6 and TNF-α messenger RNA (mRNA) expression were detected by quantitative real-time polymerase chain reaction. The levels of p38 expression were determined by Western blot. Burn induced increased inflammatory cytokines such as interleukin (IL)-1β, IL-6, tumor necrosis factors-α, and macrophage chemoattractant protein-1 production in burn wound and serum. The MPO activities in the lung and heart were also increased after burn. These effects were significantly more prominent in MT (-/-) mice than in WT mice. Furthermore, these effects were inhibited by administration of exogenous MT-2 to both WT and MT (-/-) mice. Exogenous MT-2 inhibited the p38 expression and abrogated the increase of IL-6 and TNF-α mRNA expression from macrophages that were stimulated with burn serum. The effect of MT-2 was not further strengthened in the presence of SB203580. MTs may have a protective role against post-burn inflammation and inflammatory organ damage, at least partly through inhibiting the p38 MAPK signaling.

Basal and copper-induced expression of metallothionein isoform 1,2 and 3 genes in epithelial cancer cells: The role of tumor suppressor p53

Metallothioneins (MTs) are a ubiquitous low-molecular weight, cysteine rich proteins with a high affinity for metal ions. The expression and induction of MTs have been associated with protection against DNA damage, oxidative stress, and apoptosis. Our past research had shown that p53 is an important factor in metal regulation of MTs. The present study was undertaken to explore further the interrelationship between p53 and MTs. We investigated whether silencing of p53 could affect expression pattern of basal and copper induced metallothioneins. The silencing of wild-type p53 (wt-p53) in epithelial breast cancer MCF7 cells affected the basal level of MT-2A RNA, whereas the levels of MT-1A and MT-1X RNA remained largely unchanged. The expression of MT-3 was undetectable in MCF7 with either functional or silenced p53. MCF7 cells with silenced wt-p53 failed to upregulate MT-2A in response to copper and showed a reduced sensitivity toward copper induced cell apoptotic death. Similarly in MCF7-E6 and MDA-MB-231 cells, the presence of inactive/mutated p53 halted MT-1A and MT-2A gene expression in response to copper. Constitutive expression of MT-3 RNA was detectable in the presence of mutated p53 (mtp53). Transient transfection of MDA-MB-231 cells with wt-p53 enabled copper induced upregulation of both MT-1A and MT-2A but not basal level of MT-2A, MT-1E, MT-1X and MT-3. Inactivation of p53 in HepG2 cells amplified the basal expression of studied MT isoforms, including MT-3, as well as copper-induced mRNA expression of MTs except MT-1H and MT-3. Presented data demonstrate a direct relation between p53 and MT-1A and MT-2A and they also indicate that wt-p53 might be a negative regulator of MT-3 in epithelial cancer cells.

Elaidate, an 18-carbon trans-monoenoic fatty acid, but not physiological fatty acids increases intracellular Zn(2+) in human macrophages

Artificial trans fatty acids promote atherosclerosis by blocking macrophage clearance of cell debris. Classical fatty-acid response mechanisms include TLR4-NF-κB activation, and Erk1/2 phosphorylation, but these may not indicate long-term mechanisms. Indeed, nuclear NF-κB was increased by 60 min treatment by 30 μM of the 18 carbon trans unsaturated fatty acid elaidic acid (elaidate), the physiological cis-unsaturated fatty acid oleic acid (oleate), and the 18 or 16 carbon saturated fatty acids stearic and palmitic acid (stearate or palmitate). However, except for stearate, effects on related pathways were minimal at 44 h. To determine longer term effects of trans fatty acids, we compared mRNA expression profiles of (trans) elaidate to (cis) oleate, 30 μM, at 44 h in human macrophages. We found that elaidate changed Zn(2+) -homeostasis gene mRNAs markedly. This might be important because Zn(2+) is a major regulator of macrophage activity. Messenger RNAs of seven Zn(2+) -binding metallothioneins decreased 2-4-fold; the zinc importer SLC39A10 increased twofold, in elaidate relative to oleate-treated cells. Results were followed by quantitative PCR comparing cis, trans, and saturated fatty acid effects on Zn(2+) -homeostasis gene mRNAs. This confirmed that elaidate uniquely decreased metallothionein expression and increased SLC39A10 at 44 h. Further, intracellular Zn(2+) was measured using N-(carboxymethyl)-N-[2-[2-[2(carboxymethyl) amino]-5-(2,7,-difluoro-6-hydroxy-3-oxo-3H-xanthen-9-yl)-phenoxy]-ethoxy]-4-methoxyphenyl]glycine, acetoxymethyl ester (FluoZin-3-AM). This showed that, at 44 h, only cells treated with elaidate had increased Zn(2+) . The durable effect of elaidate on Zn(2+) activation is a novel and specific effect of trans fatty acids on peripheral macrophage metabolism.

Metallothionein ameliorates burn sepsis partly via activation of Akt signaling pathway in mice: a randomized animal study

Introduction

Metallothioneins (MTs) are a family of cysteine-rich and low molecular-weight proteins that can regulate metal metabolism and act as antioxidants. Recent studies showed that MTs played a protective role in excessive inflammation and sepsis. However, the role of MTs in burn sepsis remains unclear. This study is designed to investigate the role of MTs in burn sepsis in an experimental mouse model.

Methods

MT-I/II knockout (−/−) mice on a C57BL/6 background and their wild-type (WT) littermates were randomly divided into sham burn, burn, burn sepsis, Zn treated and Zn-MT-2 treated groups. Levels of inflammatory cytokines were measured by enzyme-linked immunosorbent assay (ELISA). Myeloperoxidase (MPO) activity was detected by spectrophotometry. In in vitro study, exogenous MT was added to macrophages that stimulated with serum from burn sepsis mice with or without Akt inhibitor LY294002. The IL-1 β and IL-6 mRNA expression were detected by quantitative real-time polymerase chain reaction. The levels of Akt expression were determined by western blot.

Results

Burn sepsis induced significantly elevated levels of inflammatory cytokines in serum and increased inflammatory infiltration in the liver and lung. These effects were more prominent in MT (−/−) mice than in WT mice. Furthermore, exogenous MT-2 inhibited these elevated inflammatory response in both WT and MT (−/−) mice. MT-2 up-regulated Akt phosphorylation and abrogated the increase of IL-1β and IL-6 mRNA expression from macrophages that stimulated with burn sepsis serum. These effects of MT-2 were abolished in the presence of LY294002.

Conclusion

MT-2 ameliorates burn sepsis by attenuating inflammatory response and diminishing inflammatory organ damage, which is at least partly mediated by activation of Akt signaling pathway.

SPINK1 promotes colorectal cancer progression by downregulating Metallothioneins expression

Colorectal cancer (CRC) is the third most common cancer in the world, and second leading cause of cancer deaths in the US. Although, anti-EGFR therapy is commonly prescribed for CRC, patients harboring mutations in KRAS or BRAF show poor treatment response, indicating an ardent demand for new therapeutic targets discovery. SPINK1 (serine peptidase inhibitor, Kazal type 1) overexpression has been identified in many cancers including the colon, lung, breast and prostate. Our study demonstrates the functional significance of SPINK1 in CRC progression and metastases. Stable knockdown of SPINK1 significantly decreases cell proliferation, invasion and soft agar colony formation in the colon adenocarcinoma WiDr cells. Conversely, an increase in these oncogenic phenotypes was observed on stimulation with SPINK1-enriched conditioned media (CM) in multiple benign models such as murine colonic epithelial cell lines, MSIE and YAMC (SPINK3-negative). Mechanistically, SPINK1 promotes tumorigenic phenotype by activating phosphatidylinositol 3-kinase (PI3K/AKT) and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling pathways, and the SPINK1-positive WiDr cells are sensitive to AKT and MEK inhibitors. Importantly, SPINK1 silencing mediated upregulation of various Metallothionein isoforms, considered as tumor suppressors in CRC, confer sensitivity to doxorubicin, which strengthens the rationale for using the combinatorial treatment approach for the SPINK1-positive CRC patients. Furthermore, in vivo studies using chicken chorioallantoic membrane assay, murine xenograft studies and metastasis models further suggest a pivotal role of SPINK1 in CRC progression and metastasis. Taken together, our study demonstrates an important role for the overexpressed SPINK1 in CRC disease progression, a phenomenon that needs careful evaluation towards effective therapeutic target development.

Crambescin C1 Exerts a Cytoprotective Effect on HepG2 Cells through Metallothionein Induction

The Mediterranean marine sponge Crambe crambe is the source of two families of guanidine alkaloids known as crambescins and crambescidins. Some of the biological effects of crambescidins have been previously reported while crambescins have undergone little study. Taking this into account, we performed comparative transcriptome analysis to examine the effect of crambescin-C1 (CC1) on human tumor hepatocarcinoma cells HepG2 followed by validation experiments to confirm its predicted biological activities. We report herein that, while crambescin-A1 has a minor effect on these cells, CC1 protects them against oxidative injury by means of metallothionein induction even at low concentrations. Additionally, at high doses, CC1 arrests the HepG2 cell cycle in G0/G1 and thus inhibits tumor cell proliferation. The findings presented here provide the first detailed approach regarding the different effects of crambescins on tumor cells and provide a basis for future studies on other possible cellular mechanisms related to these bioactivities.

Controlling the cytotoxicity of CdSe magic-sized quantum dots as a function of surface defect density

Quantum dots are potentially very useful as fluorescent probes in biological systems. However, they are inherently cytotoxic because of their constituents. We controlled the cytotoxicity of CdSe magic-sized quantum dots (MSQDs) as a function of surface defect density by altering selenium (Se) concentration during synthesis. Higher Se concentrations reduced the cytotoxicity of the CdSe MSQDs and diminished mRNA expression of methallothionein because of the low cadmium ions (Cd(2+)) concentration adsorbed on the surface of the MSQDs. These results agree with luminescence spectra, which show that higher Se concentrations decrease the density of surface defects. Therefore, our results describe for the first time a simple way of controlling the cytotoxicity of CdSe MSQDs and making them safer to use as fluorescence probes in biological systems.

Impact of metallothionein gene polymorphisms on the risk of lung cancer in a Japanese population

Metallothioneins (MTs) are cysteine-rich proteins that act as antioxidants. A case-control study was conducted to assess the effects of gene polymorphisms in the MT region on the risk of lung cancer in Japanese subjects: 769 lung cancer cases and 939 non-cancer controls. Associations were evaluated using logistic regression models with adjustment for potential confounders (age, sex, and lifestyle factors including smoking, drinking, and green-yellow vegetable intake). We found five polymorphisms in the MT-1 gene region that showed statistically significant associations with lung cancer. Of these polymorphisms, rs7196890 showed the strongest association (odds ratio: 1.30, P = 0.004, 95% confidence interval: 1.09-1.55). The impact of the polymorphism decreased with the increase of smoking, and virtually no association with lung cancer was observed among heavy smokers whose pack-year values were 30 or more (odds ratio: 1.02, P = 0.93, 95% confidence interval: 0.67-1.55). These results suggest that polymorphisms in the MT gene are moderately associated with the risk of lung cancer and that the associations are modified by lifestyle factors.

Metallothionein polymorphisms in pathological processes

Metallothioneins (MTs) are a class of metal-binding proteins characterized by a high cysteine content and low molecular weight. MTs play an important role in metal metabolism and protect cells against the toxic effects of radiation, alkylating agents and oxygen free radicals. The evidence that individual genetic characteristics of MTs play an important role in physiological and pathological processes associated with antioxidant defense and detoxification inspired targeted studies of genetic polymorphisms in a clinical context. In recent years, common MT polymorphisms were identified and associated with, particularly, western lifestyle diseases such as cancer, complications of atherosclerosis, and type 2 diabetes mellitus along with related complications. This review summarizes all evidence regarding MT polymorphisms of major human MTs (MT1, MT2, MT3 and MT4), their relation to pathological processes, and outlines specific applications of MTs as a set of genetic markers for certain pathologies.

MT1M and MT1G promoter methylation as biomarkers for hepatocellular carcinoma

AIM: To investigate the potential of promoter methylation of two tumor suppressor genes (TSGs) as biomarkers for hepatocellular carcinoma (HCC).

METHODS: A total of 189 subjects were included in this retrospective cohort, which contained 121 HCC patients without any history of curative treatment, 37 patients with chronic hepatitis B (CHB), and 31 normal controls (NCs). DNA samples were extracted from 400 μL of serum of each subject and then modified using bisulfite treatment. Methylation of the promoters of the TSGs (metallothionein 1M, MT1M; and metallothionein 1G, MT1G) was determined using methylation-specific polymerase chain reaction. The diagnostic value of combined MT1M and MT1G promoter methylation was evaluated using the area under the receiver operating characteristic curves.

RESULTS: Our results indicated that the methylation status of serum MT1M (48.8%, 59/121) and MT1G (70.2%, 85/121) promoters in the HCC group was significantly higher than that in the CHB group (MT1M 5.4%, 2/37, P < 0.001; MT1G 16.2%, 6/37, P < 0.001) and NC group (MT1M 6.5%, 2/31, P < 0.001; MT1G 12.9%, 4/27, P < 0.001). Aberrant serum MT1M promoter methylation gave higher specificity to discriminate HCC from CHB (94.6%) and NCs (93.5%), whereas combined methylation of serum MT1M and MT1G promoters showed higher diagnostic sensitivity (90.9%), suggesting that they are potential markers for noninvasive detection of HCC. Furthermore, MT1M promoter methylation was positively correlated with tumor size (rs = 0.321, P < 0.001), and HCC patients with both MT1M and MT1G promoter methylation tended to show a higher incidence of vascular invasion or metastasis (P = 0.018).

CONCLUSION: MT1M and MT1G promoter methylation may be used as serum biomarkers for noninvasive detection of HCC.

Micronutrient-gene interactions related to inflammatory/immune response and antioxidant activity in ageing and inflammation. A systematic review

Recent longitudinal studies in dietary daily intake in human centenarians have shown that a satisfactory content of some micronutrients within the cells maintain several immune functions, a low grade of inflammation and preserve antioxidant activity. Micronutrients (zinc, copper, selenium) play a pivotal role in maintaining and reinforcing the performances of the immune and antioxidant systems as well as in affecting the complex network of the genes (nutrigenomic) with anti- and pro-inflammatory tasks. Genes of pro- and anti-inflammatory cytokines and some key regulators of trace elements homeostasis, such as Metallothioneins (MT), are involved in the susceptibility to major geriatric disease/disorders. Moreover, the genetic inter-individual variability may affect the nutrients' absorption (nutrigenetic) with altered effects on inflammatory/immune response and antioxidant activity. The interaction between genetic factors and micronutrients (nutrigenomic and nutrigenetic approaches) may influence ageing and longevity because the micronutrients may become also toxic. This review reports the micronutrient-gene interactions in ageing and their impact on the healthy state with a focus on the method of protein-metal speciation analysis. The association between micronutrient-gene interactions and the protein-metal speciation analysis can give a complete picture for a personalized nutrient supplementation or chelation in order to reach healthy ageing and longevity.

Toxicological profile of small airway epithelial cells exposed to gold nanoparticles

Gold nanoparticles (AuNPs) have diverse applications in the biomedical industry such as in diagnosis, labeling, delivering and sensing. Despite their prevalent medical use, nanotoxicity induced by AuNPs is still largely unknown. We have previously shown that AuNPs could exert cytotoxic effects on lung fibroblasts. In this study, we investigated the in vitro toxicological effects of AuNPs in small airway epithelial cells (SAECs) which are the first cells of contact for inhaled NPs and compared expression of metallothionein (MT), a reactive oxygen species scavenger, in SAECs and lung fibroblasts in vitro. Transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy study revealed cellular uptake of aggregates of AuNPs into the cytoplasm at the ultrastructural level. A significant increase in lipid peroxide as well as substantial DNA damage and cytotoxicity was observed in AuNP-treated cells. For MT expression, AuNPs induced down-regulation of the MT-1X isoform in SAECs, but up-regulation of the MT-1X and MT-2 A isoforms in MRC5 lung fibroblasts. The present study suggests that AuNPs could induce oxidative stress-related cytotoxicity and genotoxicity in SAECs.

Metallothionein 1G functions as a tumor suppressor in thyroid cancer through modulating the PI3K/Akt signaling pathway

BACKGROUND

MT1G inactivation mediated by promoter methylation has been reported in thyroid cancer. However, the role of MT1G in thyroid carcinogenesis remains unclear. The aim of this study is to examine the biological functions and related molecular mechanisms of MT1G in thyroid cancer.

METHODS

Methylation-specific PCR (MSP) was performed to analyze promoter methylation of MT1G and its relationship with clinicopathological characteristics of papillary thyroid cancer (PTC) patients. Conventional and real-time quantitative RT-PCR assays were used to evaluate mRNA expression. The functions of ectopic MT1G expression were determined by cell proliferation and colony formation, cell cycle and apoptosis, as well as cell migration and invasion assays.

RESULTS

MT1G expression was frequently silenced or down-regulated in thyroid cancer cell lines, and was also significantly decreased in primary thyroid cancer tissues compared with non-malignant thyroid tissues. Promoter methylation, along with histone modification, contributes to MT1G inactivation in thyroid tumorigenesis. Moreover, our data showed that MT1G hypermethylation was significantly positively associated with lymph node metastasis in PTC patients. Importantly, restoring MT1G expression in thyroid cancer cells dramatically suppressed cell growth and invasiveness, and induced cell cycle arrest and apoptosis through inhibiting phosphorylation of Akt and Rb.

CONCLUSIONS

We have for the first time revealed that MT1G appears to be functional tumor suppressor involved in thyroid carcinogenesis mainly through modulating the phosphatidylinositol-3-kinase (PI3K)/Akt pathway and partially through regulating the activity of Rb/E2F pathway in this study.

Metallothioneins and brain injury: What transgenic mice tell us

In rodents, the metallothionein (MT) family is composed of four members, MT-1 to MT-4. MT-1&2 are expressed in virtually all tissues including those of the Central Nervous System (CNS), while MT-3 (also called Growth Inhibitory Factor) and MT-4 are expressed prominently in the brain and in keratinizing epithelia, respectively. For the understanding of the physiological functions of these proteins in the brain, the use of transgenic mice has provided essential information. Results obtained inMT-1&2-null mice and in MT-1-overexpressing mice strongly suggeset that these MT isoforms are important antioxidant, anti-inflammatory and antiapoptotic proteins in the brain. Results inMT-3-null mice show a very different pattern, with no support for MT-1&2-like functions. Rather, MT-3 could be involved in neuronal sprouting and survival. Results obtained in a model of peripheral nervous system injury also suggest that MT-3 could be involved in the control of nerve growth.

Metallothionein MT1M is a tumor suppressor of human hepatocellular carcinomas

Members of the metallothionein (MT) family are short, cysteine-rich proteins involved in metal metabolism and detoxification, suggesting that MT proteins protect cells from damage caused by electrophilic carcinogens and thereby constitute a critical surveillance system against carcinogenesis. However, the roles of MT proteins in human hepatocellular carcinoma (HCC) are not fully understood. We identified a member of the MT family, termed MT1M. MT1M is expressed in various normal tissues with the highest level in the liver. MT1M expression can be induced by heavy metals and protect Escherichia coli from heavy metal toxicity. However, MT1M expression markedly decreased in human HCC specimens. A methylation profiling analysis indicated that the MT1M promoter is methylated in the majority of HCC tumors examined. Moreover, restored expression of MT1M in the HCC cell line Hep3B, which lacks endogenous MT1M expression, suppressed cell growth in vitro and in vivo and augmented apoptosis induced by tumor necrosis factor α. Furthermore, stable expression of MT1M in Hep3B cells blocked tumor necrosis factor α-induced degradation of IκBα and transactivation of NF-κB. We conclude that MT1M is a novel member of the MT family. Frequent downregulation of MT1M in human HCC may contribute to liver tumorigenesis by increasing cellular NF-κB activity.

Combined metallothioneins and p53 proteins expression as a prognostic marker in patients with Dukes stage B and C colorectal cancer

Our study aimed to evaluate metallothionein and p53 expression in colorectal cancer and to correlate their combined expression with selected clinical and pathologic variables of the disease, to define their prognostic significance. Colorectal cancer specimens from 99 patients were retrospectively analyzed by immunohistochemistry for metallothionein and p53 expression. Survival curves were generated according to the Kaplan-Meier method, and univariate survival distributions were compared with the use of the log-rank test. Multivariate models were computed using Cox proportional hazards regression. This research was approved by the institutional review boards of all centers. Tumors showing concomitant high metallothionein expression and negative p53 (metallothionein(H)/p53(-)) were significantly inversely related to depth of invasion, frequency of nodal metastasis, and Dukes stage (P < .01). In univariate analysis, patients with metallothionein(H)/p53(-) phenotype showed a better overall survival (hazard ratio [HR], 2.83; P < .05) and disease-free survival (HR, 2.03; P < .05). In multivariate analysis, considering staging, metallothionein, and metallothionein + p53 variables, in 83 patients with Dukes stages B and C, metallothionein(H)/p53(-) combination was the sole factor showing an independent prognostic value for overall survival (HR, 3.88; P < .1) and disease-free survival (HR, 2.56; P < .1). In conclusion, the combined analysis of metallothionein and p53 may enhance the prognostic power of each individual marker by predicting the progression of the disease and contributing to a better identification of patients at low risk for mortality, especially for those with Dukes stage B and C colorectal cancer.

An investigation of modifying effects of metallothionein single-nucleotide polymorphisms on the association between mercury exposure and biomarker levels

BACKGROUND

Recent studies have suggested that several genes that mediate mercury metabolism are polymorphic in humans.

OBJECTIVE

We hypothesized that single-nucleotide polymorphisms (SNPs) in metallothionein (MT) genes may underlie interindividual differences in mercury biomarker levels. We studied the potential modifying effects of MT SNPs on mercury exposure-biomarker relationships.

METHODS

We measured total mercury in urine and hair samples of 515 dental professionals. We also surveyed occupational and personal exposures to dental amalgam and dietary fish consumption, from which daily methylmercury (MeHg) intake was estimated. Log-transformed urine and hair levels were modeled in multivariable linear regression separately against respective exposure surrogates, and the effect modification of 13 MT SNPs on exposure was investigated.

RESULTS

The mean mercury levels in urine (1.06 μg/L) and hair (0.51 μg/g) were not significantly different from the U.S. general population (0.95 μg/L and 0.47 μg/g, respectively). The mean estimated daily MeHg intake was 0.084 μg/kg/day (range, 0-0.98 μg/kg/day), with 25% of study population intakes exceeding the current U.S. Environmental Protection Agency reference dose of 0.1 μg/kg/day. Multivariate regression analysis showed that subjects with the MT1M (rs2270837) [corrected] AA genotype (n = 10) or the MT2A (rs10636) CC genotype (n = 42) had lower urinary mercury levels than did those with the MT1M or MT2A GG genotype (n = 329 and 251, respectively) after controlling for exposure and potential confounders. After controlling for MeHg intake, subjects with MT1A (rs8052394) GA and GG genotypes (n = 24) or the MT1M (rs9936741) TT genotype (n = 459) had lower hair mercury levels than did subjects with MT1A AA (n = 113) or MT1M TC and CC genotypes (n = 15), respectively.

CONCLUSION

Our findings suggest that some MT genetic polymorphisms may influence mercury biomarker concentrations at levels of exposure relevant to the general population.

Micronutrient (Zn, Cu, Fe)-gene interactions in ageing and inflammatory age-related diseases: implications for treatments

In ageing, alterations in inflammatory/immune response and antioxidant capacity lead to increased susceptibility to diseases and loss of mobility and agility. Various essential micronutrients in the diet are involved in age-altered biological functions. Micronutrients (zinc, copper, iron) play a pivotal role either in maintaining and reinforcing the immune and antioxidant performances or in affecting the complex network of genes (nutrigenomic approach) involved in encoding proteins for a correct inflammatory/immune response. By the other side, the genetic inter-individual variability may affect the absorption and uptake of the micronutrients (nutrigenetic approach) with subsequent altered effects on inflammatory/immune response and antioxidant activity. Therefore, the individual micronutrient-gene interactions are fundamental to achieve healthy ageing. In this review, we report and discuss the role of micronutrients (Zn, Cu, Fe)-gene interactions in relation to the inflammatory status and the possibility of a supplement in the event of a micronutrient deficiency or chelation in presence of micronutrient overload in relation to specific polymorphisms of inflammatory proteins or proteins related of the delivery of the micronutriemts to various organs and tissues. In this last context, we report the protein-metal speciation analysis in order to have, coupled with micronutrient-gene interactions, a more complete picture of the individual need in micronutrient supplementation or chelation to achieve healthy ageing and longevity.

Metallothionein expression in colorectal cancer: relevance of different isoforms for tumor progression and patient survival

Metallothioneins are a family of small, cysteine-rich proteins with many functions. Immunohistochemical evaluation of all metallothionein 1 + 2 isoforms in colorectal tumors has demonstrated an important down-regulation compared with normal tissue, although its prognostic significance is unclear. Moreover, the contribution of individual isoforms to overall metallothionein down-regulation is not known. To address these important issues, we analyzed the messenger RNA expression levels of all functional metallothionein 1 + 2 isoforms by quantitative reverse transcription polymerase chain reaction in 22 pairs of normal and tumor-microdissected epithelia and correlated these to the overall immunohistochemical protein expression. Our results showed that 5 isoforms (MT1G, 1E, 1F, 1H, and 1M) were lost during the transition from normal mucosa to tumor, whereas MT1X and MT2A were less down-regulated, and their expression was correlated with overall protein positivity. Second, we showed that MT1G hypermethylation occurred in cell lines and in 29% of tumor samples, whereas histone deacetylase inhibitors are able to induce most isoforms. Furthermore, we analyzed by immunohistochemistry 107 normal mucosae, 25 adenomas, 81 carcinomas, and 19 lymph node metastases to evaluate metallothionein expression during different stages of cancer development and to assess its relationship to patient survival. A lower immunohistochemical expression was associated with poorer survival, although it was not an independent predictor. Overall, this study identifies for the first time the relevant metallothionein isoforms for colorectal cancer progression, supports the concept that their loss is associated with worse prognosis, and suggests 2 mechanisms for epigenetic repression of metallothionein expression in colorectal tumors.

Zinc-gene interaction related to inflammatory/immune response in ageing

The pivotal role played by zinc-gene interaction in affecting some relevant cytokines (IL-6 and TNF-alpha) and heat shock proteins (HSP70-2) in ageing, successful ageing (nonagenarians) and the most common age-related diseases, such as atherosclerosis and infections, is now recognized. The polymorphisms of genes codifying proteins related to the inflammation are predictive on one hand in longevity, on the other hand they are associated with atherosclerosis or severe infections. Since the health life-span has a strong genetic component, which in turn also affected by nutritional factors like zinc, the association of these polymorphisms with innate immune response, zinc ion bioavailability and Metallothioneins (MT) homeostasis is an useful tool to unravel the role played by zinc-gene interactions in longevity, especially due to the inability of MT in zinc release in ageing and chronic inflammation. In ageing, this last fact leads to depressed innate immune response for host defence. In contrast, in very old age the inflammation is lower with subsequent more zinc ion bioavailability, less MT gene expression and satisfactory innate immunity. Therefore, the zinc-gene (IL-6, TNF-alpha, Hsp70-2) interactions, via MT homeostasis, are crucial to achieve successful ageing.

Chemistry and biology of mammalian metallothioneins

Metallothioneins (MTs) are a class of ubiquitously occurring low molecular mass, cysteine- and metal-rich proteins containing sulfur-based metal clusters formed with Zn(II), Cd(II), and Cu(I) ions. In mammals, four distinct MT isoforms designated MT-1 through MT-4 exist. The first discovered MT-1/MT-2 are widely expressed isoforms, whose biosynthesis is inducible by a wide range of stimuli, including metals, drugs, and inflammatory mediators. In contrast, MT-3 and MT-4 are noninducible proteins, with their expression primarily confined to the central nervous system and certain squamous epithelia, respectively. MT-1 through MT-3 have been reported to be secreted, suggesting that they may play different biological roles in the intracellular and extracellular space. Recent reports established that these isoforms play an important protective role in brain injury and metal-linked neurodegenerative diseases. In the postgenomic era, it is becoming increasingly clear that MTs fulfill multiple functions, including the involvement in zinc and copper homeostasis, protection against heavy metal toxicity, and oxidative damage. All mammalian MTs are monomeric proteins, containing two metal-thiolate clusters. In this review, after a brief summary of the historical milestones of the MT-1/MT-2 research, the recent advances in the structure, chemistry, and biological function of MT-3 and MT-4 are discussed.

The parkin mutant phenotype in the fly is largely rescued by metal-responsive transcription factor (MTF-1)

The gene for Parkin, an E3 ubiquitin ligase, is mutated in some familial forms of Parkinson's disease, a severe neurodegenerative disorder. A homozygous mutant of the Drosophila ortholog of human parkin is viable but results in severe motoric impairment including an inability to fly, female and male sterility, and a decreased life span. We show here that a double mutant of the genes for Parkin and the metal-responsive transcription factor 1 (MTF-1) is not viable. MTF-1, which is conserved from insects to mammals, is a key regulator of heavy metal homeostasis and detoxification and plays additional roles in other stress conditions, notably oxidative stress. In contrast to the synthetic lethality of the double mutant, elevated expression of MTF-1 dramatically ameliorates the parkin mutant phenotype, as evidenced by a prolonged life span, motoric improvement including short flight episodes, and female fertility. At the cellular level, muscle and mitochondrial structures are substantially improved. A beneficial effect is also seen with a transgene encoding human MTF-1. We propose that Parkin and MTF-1 provide complementary functions in metal homeostasis, oxidative stress and other cellular stress responses. Our findings also raise the possibility that MTF-1 gene polymorphisms in humans could affect the severity of Parkinson's disease.

Zinc, metallothioneins and immunosenescence: effect of zinc supply as nutrigenomic approach

Ageing is an inevitable biological process associated with gradual and spontaneous biochemical and physiological changes and increased susceptibility to diseases. Nutritional factor, zinc, known to be involved in improving immunity, may remodel some of the age-associated changes, leading to a healthy ageing. "In Vitro" studies involving human lymphocytes exposed to endotoxins, and "in vivo" studies comparing old and young mice fed with low dietary zinc suggest that zinc is important for both innate and adaptive immune efficiency, and more optimal inflammatory/immune response. The intracellular zinc homeostasis is mainly regulated by Metallothioneins (MT), via ion release through the reduction of thiol groups in MT molecule. These processes are crucial because mediating the zinc signalling within the immune cells assigning to zinc a role of "second messenger". Zinc homeostasis is altered in ageing partly due to higher expression levels of MT, leading to an increased sequestration of zinc, resulting in less availability of free intracellular zinc. Improvement of immune functions and stress response systems occurs in elderly after physiological zinc supplementation. The main reason behind these effects seems to be related to a like "hormetic" response induced by zinc. However, the choice of old subjects for zinc supplementation has to be performed in relationship to the specific genetic background of MT and pro-inflammatory cytokine (IL-6) because the latter is involved both in MT gene expression and in intracellular zinc homeostasis. Old subjects carrying GG genotypes (termed C- carriers) in IL-6--174G/C locus display increased IL-6 production, low intracellular zinc ion availability, impaired innate immune response and enhanced MT. By contrast, old subjects carrying GC and CC genotypes (termed C+ carriers) in the same IL-6--174 locus displayed satisfactory intracellular zinc and innate immune response. Moreover, male carriers of C+ allele are more prone to reach centenarian age than C- ones. Therefore, old C- subjects are likely to benefit more from zinc supplementation restoring NK cell cytotoxicity and improving the zinc status. Plasma zinc deficiency and the altered immune response is more evident when the genetic variations of IL-6 polymorphism are associated with the genetic variations of MT1A in position +647, suggesting that the genetic variations of IL-6 and MT1A are very useful tools for the identification of old people who effectively need zinc supplementation.

Metallothionein in human immunomagnetically selected CD34(+) haematopoietic progenitor cells

Human umbilical CD34(+) immature haematopoietic cells were rapidly and efficiently obtained from light density MNC (mononuclear cells) by MACS (magnetic cell sorting). An ex vivo expanded population of CD34(+) was cultured in serum-free medium supplemented with cytokines FL (flt3 ligand), SCF (stem cell factor) and TPO (thrombopoietin) in order to obtain a sufficient number of CD34(+) cells. CD34(+) cells expanded from cord blood for 7 days were demonstrated to increase in the absolute number of CD34(+) cells by 5.12 ± 2.47-fold (mean ± S.D., n = 3). Flow cytometric analysis demonstrated that the percentage of CD34 antigen expression after expansion of the culture was 97.81 ± 1.07%, whereas it was 69.39 ± 10.37% in none-expanded CD34(+) cells (mean ± S.D., n = 3), thus defining a system that allowed extensive amplification accompanied by no maturation. MTs (metallothioneins), low molecular weight, cysteine-rich metal-binding proteins, exhibit various functions, including metal detoxification and homoeostasis. We here examined the expression pattern of functional members of the MT gene family in immature CD34(+) cells and compared it with more mature CD34(-) cells in order to strengthen the proposed function of MT in differentiation. Cells were cultured in RPMI 1640 medium, with or without different zinc supplements for 24 h. Relative quantitative expression of MT isogenes in the mature CD34(-) cells was higher than in the immature CD34(+) cells. IHC (immunohistochemical staining) revealed an increased MT protein biosynthesis in CD34(-) cells, greater than in CD34(+) cells. Therefore, the role of MT in differentiation of human haematopoietic progenitor cells from human cord blood is reported for the first time.

The two faces of metallothionein in carcinogenesis: photoprotection against UVR-induced cancer and promotion of tumour survival

Metallothionein is a multi-functional protein that protects the host against toxic heavy metals. Under stressful situations it can protect against oxidative damage, contribute to tissue repair, modulate immune responses and limit inflammatory processes. Recently, metallothionein's role in ultraviolet radiation (UVR)-induced injury has been investigated. These studies have shown that when metallothionein is upregulated following exposure to UVR, it can protect against UVR-induced damage and the subsequent development of skin cancer. We propose that this initial protection is achieved through its anti-oxidant role resulting in reduced oxidative stress, reduced apoptosis, reduced NFkappaB activation and enhanced repair of DNA damage. However, once UVR-induced neoplasia has occurred, the cancer cells can hijack metallothionein's protective functions, resulting in increased tumour progression and malignancy. These two discordant sets of attributes are context-dependent, and represent the two faces of metallothionein.