Metallothionein isoform 3 expression in the human prostate and cancer-derived cell lines

Joint forces of mass spectrometric techniques (ICP-MS and MALDI-TOF-MS) and fluorescence spectrometry in the study of platinum-based cytostatic drugs interactions with metallothionein MT2 and MT3

Herby, the interaction of metallothioneins with commonly used Pt-based anticancer drugs - cisplatin, carboplatin, and oxaliplatin - was investigated using the combined power of elemental (i.e. LA-ICP-MS, CE-ICP-MS) and molecular (i.e. MALDI-TOF-MS) analytical techniques providing not only required information about the interaction, but also the benefit of low sample consumption. The amount of Cd and Pt incorporated within the protein was determined for protein monomers and dimer/oligomers formed by non-oxidative dimerization. Moreover, fluorescence spectrometry using Zn2+-selective fluorescent indicator - FluoZin3 - was employed to monitor the ability of Pt drugs to release natively occurring Zn from the protein molecule. The investigation was carried out using two protein isoforms (i.e. MT2, MT3), and significant differences in behaviour of these two isoforms were observed. The main attention was paid to elucidating whether the protein dimerization/oligomerization may be the reason for the potential failure of the anticancer therapy based on these drugs. Based on the results, it was demonstrated that the interaction of MT2 (both monomers and dimers) interacted with Pt drugs significantly less compared to MT3 (both monomers and dimers). Also, a significant difference between monomeric and dimeric forms (both MT2 and MT3) was not observed. This may suggest that dimer formation is not the key factor leading to the inactivation of Pt drugs.

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.

Spatial Transcriptomics analysis of uterine gene expression in enhancer of Zeste homolog 2 (Ezh2) conditional knockout mice

Histone proteins undergo various modifications that alter chromatin structure, including addition of methyl groups. Enhancer of homolog 2 (EZH2), is a histone methyltransferase that methylates lysine residue 27, and thereby, suppresses gene expression. EZH2 plays integral role in the uterus and other reproductive organs. We have previously shown that conditional deletion of uterine EZH2 results in increased proliferation of luminal and glandular epithelial cells, and RNAseq analyses reveal several uterine transcriptomic changes in Ezh2 conditional (c) knockout (KO) mice that can affect estrogen signaling pathways. To pinpoint the origin of such gene expression changes, we used the recently developed spatial transcriptomics (ST) method with the hypotheses that Ezh2cKO mice would predominantly demonstrate changes in epithelial cells and/or ablation of this gene would disrupt normal epithelial/stromal gene expression patterns. Uteri were collected from ovariectomized adult WT and Ezh2cKO mice and analyzed by ST. Asb4, Cxcl14, Dio2, and Igfbp5 were increased, Sult1d1, Mt3, and Lcn2 were reduced in Ezh2cKO uterine epithelium vs. WT epithelium. For Ezh2cKO uterine stroma, differentially expressed key hub genes included Cald1, Fbln1, Myh11, Acta2, and Tagln. Conditional loss of uterine Ezh2 also appears to shift the balance of gene expression profiles in epithelial vs. stromal tissue toward uterine epithelial cell and gland development and proliferation, consistent with uterine gland hyperplasia in these mice. Current findings provide further insight into how EZH2 may selectively affect uterine epithelial and stromal compartments. Additionally, these transcriptome data might provide the mechanistic understanding and valuable biomarkers for human endometrial disorders with epigenetic underpinnings.

Dysregulation of metallothionein and zinc aggravates periodontal diseases

BACKGROUND

Periodontitis (PD) is a multifaceted inflammatory disease connected to bacterial infection that results in the destruction of tooth supporting structures and eventually tooth loss. Given their involvement in infection and inflammation, both metallothionein (MT) and zinc (Zn) might play vital roles in the development and progression of PD. More specifically, both MT and Zn are heavily involved in regulating immune functions, controlling bacterial infection, balancing inflammatory responses, and reducing oxidative stress, all of which are associated with the pathogenesis of PD.

OBJECTIVE

This review paper will explore the physiological functions of MT and Zn and hypothesise how dysregulation could negatively affect periodontal health, leading to PD.

FINDINGS

Bacterial lipopolysaccharide (LPS) derived from periodontal pathogens, namely P. gingivalis initiates the acute phase response, thus upregulating the expression of MT which leads to the subsequent deficiency of Zn, a hallmark of periodontal disease. This deficiency leads to ineffective NETosis, increases the permeability of the gingival epithelium, and disrupts the humoral immune response, collectively contributing to PD. In addition, the presence of LPS in Zn deficient conditions favours M1 macrophage polarisation and maturation of dendritic cells, and also inhibits the anti-inflammatory activity of regulatory T cells. Collectively, these observations could theoretically give rise to the chronic inflammation seen in PD.

CONCLUSION

A disrupted MT and Zn homeostasis is expected to exert an adverse impact on periodontal health and contribute to the development and progression of PD.

Metallothionein-3 promotes cisplatin chemoresistance remodelling in neuroblastoma

Metallothionein-3 has poorly characterized functions in neuroblastoma. Cisplatin-based chemotherapy is a major regimen to treat neuroblastoma, but its clinical efficacy is limited by chemoresistance. We investigated the impact of human metallothionein-3 (hMT3) up-regulation in neuroblastoma cells and the mechanisms underlying the cisplatin-resistance. We confirmed the cisplatin-metallothionein complex formation using mass spectrometry. Overexpression of hMT3 decreased the sensitivity of neuroblastoma UKF-NB-4 cells to cisplatin. We report, for the first time, cisplatin-sensitive human UKF-NB-4 cells remodelled into cisplatin-resistant cells via high and constitutive hMT3 expression in an in vivo model using chick chorioallantoic membrane assay. Comparative proteomic analysis demonstrated that several biological pathways related to apoptosis, transport, proteasome, and cellular stress were involved in cisplatin-resistance in hMT3 overexpressing UKF-NB-4 cells. Overall, our data confirmed that up-regulation of hMT3 positively correlated with increased cisplatin-chemoresistance in neuroblastoma, and a high level of hMT3 could be one of the causes of frequent tumour relapses.

Metallothionein 3 Controls the Phenotype and Metabolic Programming of Alternatively Activated Macrophages

Alternatively activated (M2) macrophages promote wound healing but weaken antimicrobial defenses. The mechanisms that enforce macrophage divergence and dictate the phenotypic and metabolic characteristics of M2 macrophages remain elusive. We show that alternative activation with interleukin (IL)-4 induces expression of metallothionein 3 (MT3) that regulates macrophage polarization and function. MT3 was requisite for metabolic reprograming in IL-4-stimulated macrophages or M(IL-4) macrophages to promote mitochondrial respiration and suppress glycolysis. MT3 fostered an M(IL-4) phenotype, suppressed hypoxia inducible factor (HIF)1α activation, and thwarted the emergence of a proinflammatory M1 program in macrophages. MT3 deficiency augmented macrophage plasticity, resulting in enhanced interferon γ (IFNγ) responsiveness and a dampened M(IL-4) phenotype. Thus, MT3 programs the phenotype and metabolic fate of M(IL-4) macrophages.

miR-325-3p Overexpression Inhibits Proliferation and Metastasis of Bladder Cancer Cells by Regulating MT3

BACKGROUND miRNAs have been widely used in cancer treatment. Our study was designed to explore the effects of miR-325-3p in bladder cancer cells. MATERIAL AND METHODS Levels ofd miR-325-3p and MT3 in bladder cancer tissues and cells were assessed by quantitative real-time polymerase chain reaction (qRT-PCR). miR-325-3p mimics were transfected into bladder cancer T24 cells, and cell migration and invasion rates and cell proliferation were assessed by transwell assay and Cell Counting Kit-8 (CCK-8). The target mRNA for miR-325-3p was predicted by Targetscan7.2 and confirmed by dual-luciferase reporter assay. More experiments were performed to confirm the effects of miR-325-3p and MT3 in T24 cells. Additionally, the levels of TIMP-2, MMP9, and E-cadherin were assessed by Western blotting to identify the effects of miR-325-3p and MT3 on epithelial-mesenchymal transition (EMT). RESULTS miR-325-3p expression was reduced and MT3 was increased in bladder cancer tissues and bladder cancer cells. miR-325-3p mimics suppressed cell proliferation ability and invasion and migration rates of T24 cells. Moreover, miR-325-3p was confirmed to target MT3. Further experiments showed that the effects of increased cell proliferation, invasion, migration, and EMT promoted by MT3 overexpression were abolished by miR-325-3p mimics, proving that miR-325-3p is a tumor suppressor through targeting MT3 in bladder cancer cells. CONCLUSIONS Downregulation of miR-325-3p in bladder cancer regulates cell proliferation, migration, invasion, and EMT by targeting MT3. Furthermore, miR-325-3p is a potential therapeutic target in treating bladder cancer.

Metallothionein 3 Is a Hypoxia-Upregulated Oncogene Enhancing Cell Invasion and Tumorigenesis in Human Bladder Carcinoma Cells

Metallothioneins have been viewed as modulators in a number of biological regulations regarding cancerous development; however, the function of metallothionein 3 (MT3) in bladder cancer is unexplored. We determined the regulatory mechanisms and potential function of MT3 in bladder carcinoma cells. Real-Time Reverse Transcriptase-Polymerase Chain Reaction (RT-qPCR) assays revealed that TSGH-8301 cells expressed more MT3 levels than RT-4, HT1376, and T24 cells. Immunoblot and RT-qPCR assays showed that arsenic (AS₂O₃) treatments enhanced the gene expression of MT3. Hypoxia induced HIF-1α, HIF-2α, and MT3 expression; furthermore, HIF-2α-knockdown attenuated hypoxic activation on MT3 expression. Ectopic overexpression of MT3 increased cell proliferation, invasion, and tumorigenesis significantly in T24 and HT1376 cells in vitro and in vivo; however, MT3-knockdown in TSGH-8301 cells had the reverse effect. Moreover, knockdown of MT3 enhanced arsenic-induced apoptosis determined by the Annexin V-FITC apoptosis assay. MT3-overexpression downregulated the gene expressions of N-myc downstream regulated gene 1 (NDRG1), N-myc downstream regulated gene 2 (NDRG2), and the mammary serine protease inhibitor (MASPIN) in HT1376 and T24 cells, whereas MT3-knockdown in TSGH-8301 cells had the opposite effect. The experiments indicated that MT3 is an arsenic- and hypoxia-upregulated oncogene that promotes cell growth and invasion of bladder carcinoma cells via downregulation of NDRG1, NDRG2, and MASPIN expressions.

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.

An insight into the complex roles of metallothioneins in malignant diseases with emphasis on (sub)isoforms/isoforms and epigenetics phenomena

Metallothioneins (MTs) belong to a group of small cysteine-rich proteins that are ubiquitous throughout all kingdoms. The main function of MTs is scavenging of free radicals and detoxification and homeostating of heavy metals. In humans, 16 genes localized on chromosome 16 have been identified to encode four MT isoforms labelled by numbers (MT-1-MT-4). MT-2, MT-3 and MT-4 proteins are encoded by a single gene. MT-1 comprises many (sub)isoforms. The known active MT-1 genes are MT-1A, -1B, -1E, -1F, -1G, -1H, -1M and -1X. The rest of the MT-1 genes (MT-1C, -1D, -1I, -1J and -1L) are pseudogenes. The expression and localization of individual MT (sub)isoforms and pseudogenes vary at intra-cellular level and in individual tissues. Changes in MT expression are associated with the process of carcinogenesis of various types of human malignancies, or with a more aggressive phenotype and therapeutic resistance. Hence, MT (sub)isoform profiling status could be utilized for diagnostics and therapy of tumour diseases. This review aims on a comprehensive summary of methods for analysis of MTs at (sub)isoforms levels, their expression in single tumour diseases and strategies how this knowledge can be utilized in anticancer therapy.

Copper metallothioneins

Metallothioneins (MTs) are a class of low molecular weight and cysteine-rich metal binding proteins present in all the branches of the tree of life. MTs efficiently bind with high affinity several essential and toxic divalent and monovalent transition metals by forming characteristic polynuclear metal-thiolate clusters within their structure. MTs fulfil multiple biological functions related to their metal binding properties, with essential roles in both Zn(II) and Cu(I) homeostasis as well as metal detoxification. Depending on the organism considered, the primary sequence, and the specific physiological and metabolic status, Cu(I)-bound MT isoforms have been isolated, and their chemistry and biology characterized. Besides the recognized role in the biochemistry of divalent metals, it is becoming evident that unique biological functions in selectively controlling copper levels, its reactivity as well as copper-mediated biochemical processes have evolved in some members of the MT superfamily. Selected examples are reviewed to highlight the peculiar chemical properties and biological functions of copper MTs. © 2016 IUBMB Life, 69(4):236-245, 2017.

Expression of metallothionein 3 in ductal breast cancer

Metallothionein 3 (MT-3) has the ability to regulate the growth of nerve cells, but the significance of MT-3 expression outside the central nervous system and its participation in carcinogenesis have not yet been clarified. The aim of our study was to investigate the expression of MT-3 in ductal breast cancer and to determine its relationship with well-defined clinicopathological factors in this type of tumor. The study was conducted on 134 cases of invasive ductal breast carcinoma (IDC), 42 samples of non-malignant breast tissue (NMBT), and 26 cases of mastopathy. Moreover, selected breast cancer cell lines (MCF-7, SKBR-3, MDA-MB-231, BO2) and normal human breast epithelial cells (hTERT-HME1) were used. The expression of MT-3 was examined on the protein level using immunohistochemistry and on the mRNA level using real-time PCR. It was shown that the MT-3 protein in cells of IDC and mastopathy appeared in the cytoplasm as well as in the cell nuclei. Both the cytoplasmic and nuclear expression of MT-3 was significantly lower in IDC than in the mastopathies (p<0.0001 and p<0.001). However, no significant correlation was demonstrated between the level of MT-3 protein and the studied clinicopathological factors. The mRNA expression of MT-3 in IDC was also lower than in non‑malignant breast tissue (p<0.0001). Furthermore, in the cases of IDC with lymph node metastasis, the level of MT-3 mRNA was significantly lower than in the cases without metastasis (p=0.0199). The expression of MT-3 mRNA in breast cancer cell lines was significantly lower than in the normal human breast epithelial cell line (p<0.001). These results suggest that MT-3 may play a role in the malignant transformation of breast epithelial cells and in tumor progression.

Metallothionein 3 expression in normal skin and malignant skin lesions

Metallothionein-3 (MT-3) has been shown to be expressed in several malignancies and to have an impact on patients’ survival in breast and urinary bladder cancer cases. However, its expression has not been determined in normal skin or in its malignant lesions. MT-3 expression was studied using immunohistochemistry in 17 cases of normal skin, 18 of actinic keratosis (AK), 39 of squamous cell carcinoma (SCC), and 23 of basal cell carcinoma (BCC). Low MT-3 expression was observed in normal skin epidermis with faint or no expression in the epidermis basal layer. Significantly higher MT-3 expression was noted in AK (P = 0.007) and SCC (P < 0.0001), as compared with normal skin epidermis. BCC cases were characterized by the lowest MT-3 expression of all the examined groups, which was significantly lower in comparison to normal skin epidermis, AK, and SCC (P = 0.009; P < 0.0001 and P < 0.0001, respectively). In conclusion, MT-3 may be involved in the development of SCC.

Metallothionein-3 Increases Triple-Negative Breast Cancer Cell Invasiveness via Induction of Metalloproteinase Expression

It has been recently found that metallothionein-3 (MT3) enhances the invasiveness and tumorigenesis of prostate cancer cells. This finding is in contrast to those of earlier studies, which indicated that overexpression of MT3 in breast cancer and prostate cancer cell lines inhibits their growth in vitro. Therefore, to clarify the role of MT3 in breast cancer progression, we analyzed the effect of MT3-overexpression on proliferation, invasiveness, migration, and tumorigenesis of breast cancer MDA-MB-231/BO2 cells. It was found that MDA-MB-231/BO2 cells overexpressing MT3 were characterized by increased invasiveness in vitro, compared to the control cells. Interestingly, this increased invasiveness correlated with a highly increased concentration of MMP3 in the culture supernatants (p<0.0001). Our data suggest that MT3 may regulate breast cancer cell invasiveness by modulating the expression of MMP3. These experimental results, obtained using triple-negative MDA-MB-231/BO2 cells, were further supported by clinical data. It was found that, in triple-negative breast cancer (TNBC), nuclear MT3 immunoreactivity in cancer cells tended to be associated with patients' shorter disease-specific survival, suggesting that nuclear MT3 expression may be a potential marker of poor prognosis of triple-negative TNBC cases.

Metallothionein gene expression is altered in oral cancer and may predict metastasis and patient outcomes

AIMS

Metallothioneins (MTs) are proteins associated with the carcinogenesis and prognosis of various tumours. Previous studies have shown their potential as biomarkers in oral squamous cell carcinoma (OSCC). Aiming to understand more clearly the function of MTs in OSCC we evaluated, for the first time, the gene expression profile of MTs in this neoplasm.

MATERIALS AND RESULTS

Tissue samples from 35 cases of tongue and/or floor of mouth OSCC, paired with their corresponding non-neoplastic oral mucosa (NNOM), were retrieved (2007-09). All tissues were analysed for the following genes using TaqMan(®) reverse transcription-quantitative polymerase chain reaction (RT-qPCR) assays: MT1A, MT1B, MT1E, MT1F, MT1G, MT1H, MT1X, MT2A, MT3 and MT4. The expression of MT1B and MT1H was seldom detected in both OSCC and NNOM. A significant loss of MT1A, MT1X, MT3 and MT4 expression and gain of MT1F expression was observed in OSCC, compared to NNOM. Cases with MT1G down-regulation exhibited the worst prognoses. The up-regulation of MT1X was restricted to non-metastatic cases, whereas up-regulation of MT3 was related to cases with lymph node metastasis.

CONCLUSIONS

Metallothionein mRNA expression is altered significantly in oral squamous cell carcinomas. The expression of MT1G, MT1X and MT3 may aid in the prognostic discrimination of OSCC cases.

Metallothionein 3: an androgen-upregulated gene enhances cell invasion and tumorigenesis of prostate carcinoma cells

BACKGROUND

Metallothioneins (MT1, MT2, MT3, and MT4) are regarded as modulators regulating a number of biological processes including cell proliferation, differentiation, and invasion. We determined the effects of androgen, cadmium, and arsenic on MT1/2 and MT3 in prostate carcinoma cells, and evaluated the functional effects of MT3 on cell proliferation, invasion, and tumorigenesis.

METHODS

We determined the expression of MT1/2 and MT3 in prostate carcinoma cells by immunoblotting assays or real-time reverse transcription-polymerase chain reactions. The effects of ectopic MT3 overexpression or MT3-knockdown on cell proliferation, invasion, and tumorigenesis were determined by (3) H-thymidine incorporation, matrigel invasion, and murine xenograft studies. The effects of androgen, cadmium, and arsenic on target genes were assessed using immunoblotting and reporter assays.

RESULTS

Androgen, cadmium, and arsenic treatments enhanced gene expression of MT1/2 and MT3 in prostate carcinoma LNCaP cells. Results of immunohistochemical staining indicated MT3 overexpression was found predominantly in the nuclear areas of PC-3 cells overexpressing MT3. Overexpression of MT3 significantly increased cell proliferation, invasion, and tumorigenic activities in PC-3 cells in vitro and in vivo. MT3 overexpression downregulated the gene expressions of N-myc downstream regulated gene 1 (Ndrg1) and maspin, and attenuated blocking effects of doxorubicin in PC-3 cells on cell proliferation. MT3-knockdown enhanced Ndrg1 and maspin expressions in LNCaP cells.

CONCLUSIONS

The experiments indicate that MT3 is an androgen-upregulated gene, and promotes tumorigenesis of prostate carcinoma cells. The downregulation of Ndrg1 and maspin gene expressions appears to account for the enhancement of proliferative and invasive functions of MT3 in PC-3 cells.

Suppression of metallothionein 3 gene expression by androgen in LNCaP prostate cancer cells

Androgen deprivation therapy is the standard treatment for prostate cancer. However, tumors often progress towards a more aggressive phenotype despite treatment. Prostate tissue has a high zinc concentration, which may correlate with prostate cancer progression. Therefore, we investigated the effect of dihydrotestosterone (DHT) on the gene expression of metallothioneins (MTs) and zinc transporters in prostate cancer with quantitative real-time polymerase chain reaction (PCR). The MT3 gene expression in LNCaP cells was suppressed by DHT in a dose-dependent manner. However, it increased in a culture medium containing androgen-deficient charcoal-stripped fetal bovine serum (FBS). Bicalutamide, an androgen receptor antagonist, increased the gene expression of MT3 and partially reversed the suppression of MT3 gene expression induced by DHT. In PC-3 cells lacking androgen receptors, DHT and bicalutamide exerted no effect on MT3 gene expression. The reporter gene assay with a luciferase reporter plasmid containing the 5'-flanking region of MT3 demonstrated a decrease in luciferase activity caused by DHT that was reversed by bicalutamide. These results suggest that MT3 gene expression is downregulated by androgen.

Role of metallothioneins in benign and malignant thyroid lesions

Recent findings in the past two decades have brought many insights into the biology of thyroid benign and malignant lesions, in particular the papillary and follicular thyroid cancers. Although, much progress have been made, thyroid cancers still pose diagnostic problems regarding differentiation of follicular lesions in relation to their aggressiveness and the treatment of advanced and undifferentiated thyroid cancers. Metallothioneins (MTs) were shown to induce cancer cells proliferation, mediate resistance to apoptosis, certain chemotherapeutics and radiotherapy. Therefore, MTs may be of utility in diagnosis and management of patients with benign and malignant lesions of the thyroid.

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.

Metallothioneins protect cytosolic creatine kinases against stress induced by nitrogen-based oxidants

The formation of intracellular nitrogen-based oxidants has important physiological and pathological consequences. CK (creatine kinase), which plays a key role in intracellular energy metabolism, is a main target of low concentrations of oxidative and nitrative stresses. In the present study, the interaction between cytosolic CKs [MM-CK (muscle-type CK) and BB-CK (brain-type CK)] and MTs [metallothioneins; hMT2A (human MT-IIA) and hMT3 (human MT-III)] were characterized by both in vitro and intact-cell assays. MTs could successfully protect the cytosolic CKs against inactivation induced by low concentrations of PN (peroxynitrite) and NO both in vitro and in hMT2A-overexpressing H9c2 cells and hMT3-knockdown U-87 MG cells. Under high PN concentrations, CK formed granule-like structures, and MTs were well co-localized in these aggregated granules. Further analysis indicated that the number of cells containing the CK aggregates negatively correlated with the expression levels of MTs. In vitro experiments indicated that MTs could effectively protect CKs against aggregation during refolding, suggesting that MT might function as a chaperone to assist CK re-activation. The findings of the present study provide direct evidence of the connection between the two well-characterized intracellular systems: the precisely balanced energy homoeostasis by CKs and the oxidative-stress response system using MTs.

Location-specific epigenetic regulation of the metallothionein 3 gene in esophageal adenocarcinomas

Background

Metallothionein 3 (MT3) maintains intracellular metal homeostasis and protects against reactive oxygen species (ROS)-induced DNA damage. In this study, we investigated the epigenetic alterations and gene expression of the MT3 gene in esophageal adenocarcinomas (EACs).

Methods and Results

Using quantitative bisulfite pyrosequencing, we detected unique DNA methylation profiles in the MT3 promoter region. The CpG nucleotides from −372 to −306 from the transcription start site (TSS) were highly methylated in tumor (n = 64) and normal samples (n = 51), whereas CpG nucleotides closest to the TSS (−4 and +3) remained unmethylated in all normal and most tumor samples. Conversely, CpG nucleotides in two regions (from −139 to −49 and +296 to +344) were significantly hypermethylated in EACs as compared to normal samples [FDR<0.001, −log10(FDR)>3.0]. The DNA methylation levels from −127 to −8 CpG sites showed the strongest correlation with MT3 gene expression (r = −0.4, P<0.0001). Moreover, the DNA hypermethylation from −127 to −8 CpG sites significantly correlated with advanced tumor stages and lymph node metastasis (P = 0.005 and P = 0.0313, respectively). The ChIP analysis demonstrated a more repressive histone modification (H3K9me2) and less active histone modifications (H3K4me2, H3K9ace) in OE33 cells than in FLO-1 cells; concordant with the presence of higher DNA methylation levels and silencing of MT3 expression in OE33 as compared to FLO-1 cells. Treatment of OE33 cells with 5-Aza-deoxycitidine restored MT3 expression with demethylation of its promoter region and reversal of the histone modifications towards active histone marks.

Conclusion

In summary, EACs are characterized by frequent epigenetic silencing of MT3. The choice of specific regions in the CpG island is a critical step in determining the functional role and prognostic value of DNA methylation in cancer cells.

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.

Roles of zinc and metallothionein-3 in oxidative stress-induced lysosomal dysfunction, cell death, and autophagy in neurons and astrocytes

Zinc dyshomeostasis has been recognized as an important mechanism for cell death in acute brain injury. An increase in the level of free or histochemically reactive zinc in astrocytes and neurons is considered one of the major causes of death of these cells in ischemia and trauma. Although zinc dyshomeostasis can lead to cell death via diverse routes, the major pathway appears to involve oxidative stress.

Recently, we found that a rise of zinc in autophagic vacuoles, including autolysosomes, is a prerequisite for lysosomal membrane permeabilization and cell death in cultured brain cells exposed to oxidative stress conditions. The source of zinc in this process is likely redox-sensitive zinc-binding proteins such as metallothioneins, which release zinc under oxidative conditions. Of the metallothioneins, metallothionein-3 is especially enriched in the central nervous system, but its physiologic role in this tissue is not well established. Like other metallothioneins, metallothionein-3 may function as metal detoxicant, but is also known to inhibit neurite outgrowth and, sometimes, promote neuronal death, likely by serving as a source of toxic zinc release. In addition, metallothionein-3 regulates lysosomal functions. In the absence of metallothionein-3, there are changes in lysosome-associated membrane protein-1 and -2, and reductions in certain lysosomal enzymes that result in decreased autophagic flux. This may have dual effects on cell survival. In acute oxidative injury, zinc dyshomeostasis and lysosomal membrane permeabilization are diminished in metallothionein-3 null cells, resulting in less cell death. But over the longer term, diminished lysosomal function may lead to the accumulation of abnormal proteins and cause cytotoxicity.

The roles of zinc and metallothionein-3 in autophagy and/or lysosomal function have just begun to be investigated. In light of evidence that autophagy and lysosomes may play significant roles in the pathogenesis of various neurological diseases, further insight into the contribution of zinc dynamics and metallothionein-3 function may help provide ways to effectively regulate these processes in brain cells.

Cadmium concentration and metallothionein expression in prostate cancer and benign prostatic hyperplasia of humans

BACKGROUND/PURPOSE

Cadmium (Cd) causes various genitourinary disorders and is a carcinogen for prostate cancer. Metallothionein (MT) is a protein that detoxifies heavy metals. We evaluated changes in Cd concentration and MT expression in human prostate cancer (CaP) and benign prostatic hyperplasia (BPH). Our goal was to clarify the relationship between Cd concentration and MT expression in prostatic diseases.

METHODS

The experimental group consisted of 18 patients who underwent radical prostatectomy for CaP. The control group consisted of 35 patients who underwent transurethral resection of the prostate for BPH. Tissue samples were acquired from the gross tumor site and from resected chips. We determined Cd concentration by atomic absorption, MT expression by immunoblotting, and immunohistochemical staining. The significance of between-group differences for these outcomes was analyzed using Student's t tests.

RESULTS

There was no statistically significant difference in Cd concentration between the CaP and BPH groups. Immunoblots from both groups revealed a single band. The relative intensity of the MT band was 0.58 +/- 0.09 in the BPH group and 0.17 +/- 0.03 in the CaP group. MT expression in patients with BPH was 3.4-fold higher than in those with CaP.

CONCLUSION

MT may bind heavy metals and protect patients from CaP. Additional studies are needed to reveal the factors that influence the expression of MT in prostate epithelial cells, and to analyze the free and compound forms of Cd at the same time.

Reaction of human metallothionein-3 with cisplatin and transplatin

Human metallothioneins, small cysteine- and metal-rich proteins, play an important role in the acquired resistance to platinum-based anticancer drugs. These proteins contain a M(II)4(CysS)11 cluster and a M(II)3(CysS)9 cluster localized in the alpha-domain and the beta-domain, respectively. The noninducible isoform metallothionein-3 (Zn7MT-3) is mainly expressed in the brain, but was found overexpressed in a number of cancer tissues. Since the structural properties of this isoform substantially differ from those of the ubiquitously occurring Zn7MT-1/Zn7MT-2 isoforms, the reactions of cis-diamminedichloridoplatinum(II) (cisplatin) and trans-diamminedichloridoplatinum(II) (transplatin) with human Zn7MT-3 were investigated and the products characterized. A comparison of the reaction kinetics revealed that transplatin reacts with cysteine ligands of Zn7MT-3 faster than cisplatin. In both binding processes, stoichiometric amounts of Zn(II) were released from the protein. Marked differences between the reaction rates of cisplatin and transplatin binding to Zn7MT-3 and the formation of the Pt-S bonds suggest that the binding of both Pt(II) compounds is a complex process, involving at least two subsequent binding steps. The electrospray ionization mass spectrometry characterization of the products showed that whereas all ligands in cisplatin were replaced by cysteine thiolates, transplatin retained its carrier ammine ligands. The 113Cd NMR studies of Pt1 113Cd6MT-3 revealed that cisplatin binds preferentially to the beta-domain of the protein. The rates of reaction of cisplatin and transplatin with Zn7MT-3 were much faster than those of cisplatin and transplatin with Zn7MT-2. The biological consequences of a substantially higher reactivity of cisplatin toward Zn7MT-3 than Zn7MT-2 in the acquired resistance to platinum-based drugs are discussed.

Interaction of dietary zinc and intracellular binding protein metallothionein in postnatal bone growth

Zinc and its binding protein, metallothionein (MT), are important in regulating growth and development, and yet it is unclear how dietary Zn and MT interact in regulating bone growth. Here, 3.5-week female MT-I&II knockout (MT(-/-)) and wild type (MT(+/+)) mice were fed diets containing 2.5 (limiting, Zn-L), 15 or 50 mg Zn/kg (Zn adequate) for 5 or 9 weeks, and effects were analysed on structure and function of growth plate and metaphysis, two structures important for bone growth. Zn limitation did not affect bone growth in MT(+/+) mice. However, MT(-/-) mice, having lower Zn concentrations in plasma and long bone, showed growth retardation as demonstrated by lower body length gain, shorter and smaller tibia/femur, lower chondrocyte proliferation, reduced metaphysis heights, but increased osteoclast densities on trabecular bone, particularly in mice fed Zn-L diet. Interestingly, mRNA expression of MT-I&II was induced in the growth plate of MT(+/+) mice fed the Zn-L diet possibly compensating for Zn limitation. Growth plate MT-III expression increased in MT(-/-) mice fed the adequate Zn diet, whereas metaphyseal MT-III was significantly upregulated in MT(-/-) mice fed Zn-L diet, possibly as a compensatory mechanism or exacerbating effects of Zn limitation. Consistent with the increased osteoclast numbers, a higher ratio of RANKL/OPG gene expression was found in bone of mutant mice fed lower Zn diets. These results indicate that interaction between dietary Zn and endogenous MT is important for maximal bone growth, and MT is particularly important in the regulation of Zn pool for bone growth during moderate Zn limitation.

Metallothionein-3, Zinc, and Copper in the Central Nervous System

Metallothionein-3 (MT-3), also known as the neuronal growth inhibitory factor, has been discovered by Uchida and coworkers in 1991 in their search for a cellular component responsible for antagonizing aberrant neuritic sprouting and increased survival of cultured neurons stimulated by Alzheimer's disease (AD) brain extract. Since this initial discovery further studies showed that MT-3 possesses peculiar structural and functional properties not shared by other members of the mammalian MT family. Several lines of evidence suggest that the metal-binding protein MT-3 plays a vital role in zinc and copper homeostasis in the brain. Although far from being understood, the unusual structural properties of MT-3 are responsible for its neuronal growth inhibitory activity, involvement in trafficking of zinc vesicles in the central nervous system, protection against copper-mediated toxicity in AD and in controlling abnormal metal-protein interactions in other neurodegenerative disorders.

Differential expression of metallothioneins (MTs) 1, 2, and 3 in response to zinc treatment in human prostate normal and malignant cells and tissues

Background

The disturbance of zinc homeostasis featured with a significant decrease of cellular zinc level was well documented to associate with the development and progression of human prostate malignancy. We have previously reported that zinc treatment induces prostate malignant cell apoptosis through mitochondrial pathway. Metallothionein (MT) is a major receptor/donor of zinc in the cells. However, the studies on the expression of MT in association with the prostate pathological and malignant status are very limited, and the zinc regulation of MT isoform expression in prostate cells remains elusive. The goals of this study were to define the expression of endogenous MTs, the isoforms of MT 1, 2, 3 at both messenger ribonucleic acid (mRNA) and protein levels; and to investigate the zinc effect on MT expression in normal prostate, benign prostatic hyperplasia (BPH) and malignant PC-3 cells, and in relevant human tissues. Cellular MT proteins were detected by immunohistochemistry, fluorescence staining and Western blot analysis; reverse transcription polymerase chain reaction (RT-PCR) was used to determine the MT isoform-specific mRNAs.

Results

Our results demonstrated a significant suppression of endogenous levels of MT1/2 in malignant PC-3 cells (95% reduction compared to the normal prostate cells) and in human adenocarcinoma tissues (73% MT1/2 negative). A moderate reduction of MT1/2 expression was observed in BPH. Zinc treatment remarkably induced MT1/2 expression in PC-3 and BPH cells, which was accordant with the restored cellular zinc level. MT 3, as a growth inhibitory factor, was detected and up-regulated by zinc mainly in BPH cells.

Conclusion

This study provided evidence of the association of attenuated MT1/2 with prostate tumor progression, and the zinc induction of MT1/2 expression resulting in cellular zinc restoration. The results suggest the potential of MT1/2 as a candidate biomarker for prostate cancer and the utilization of zinc in prostate cancer prevention and treatment.

Zinc transporter mRNA expression in the RWPE-1 human prostate epithelial cell line

The human prostate gland undergoes a prominent alteration in Zn+2 homeostasis during the development of prostate cancer. The goal of the present study was to determine if the immortalized human prostate cell line (RWPE-1) could serve as a model system to study the role of zinc in prostate cancer. The study examined the expression of mRNA for 19 members of the zinc transporter gene family in normal prostate tissue, the prostate RWPE-1 cell line, and the LNCaP, DU-145 and PC-3 prostate cancer cell lines. The study demonstrated that the expression of the 19 zinc transporters was similar between the RWPE-1 cell line and the in situ prostate gland. Of the 19 zinc transporters, only 5 had levels that were different between the RWPE-1 cells and the tissue samples; all five being increased (ZnT-6, Zip-1, Zip-3A, Zip-10, and Zip-14). The response of the 19 transporters was also determined when the cell lines were exposed to 75 microM Zn+2 for 24 h. It was shown for the RWPE-1 cells that only 5 transporters responded to Zn+2 with mRNA for ZnT-1 and ZnT-2 being increased while mRNA for ZnT-7, Zip-7 and Zip-10 transporters were decreased. It was shown for the LNCaP, DU-145 and PC-3 cells that Zn+2 had no effect on the mRNA levels of all 19 transporters except for an induction of ZnT-1 in PC-3 cells. Overall, the study suggests that the RWPE-1 cells could be a valuable model for the study of the zinc transporter gene family in the prostate.

[Heavy metal responses of the human metallothionein isoform genes]

Metallothioneins (MTs) are proteins known to be involved in defense mechanisms against heavy metals and reactive oxygen species. In human, more than ten MT isoform genes have been identified, in contrast to much fewer isoforms in other mammalian species. The increased number of isoforms in human may have some biological significance; for example, isoforms may have been functionally differentiated to deal with various environmental factors in the evolutional process. However, we know little about the functions of the individual MT isoforms. To clarify functional differences between human MT isoforms, we developed a method to determine individual isoform mRNA levels using real-time polymerase chain reaction (PCR), and studied responses of the isoform genes against heavy metals (Zn, Cd, Cu) and As in HeLa cells. These metals induced all MT isoforms except for MT-1A by Cu, though their induced levels were different. Furthermore, these metals preferentially induced isoforms MT-2A and MT-1X suggesting that these isoforms may be important in protecting from their cytotoxicity.

Enhanced expression of metallothionein isoform 3 protein in tumor heterotransplants derived from As+3- and Cd+2-transformed human urothelial cells

This laboratory has proposed that the third isoform of the metallothionein gene family (MT-3) might be a biomarker for the development of human bladder cancer. Immunohistochemical staining of MT-3 on archival diagnostic specimens showed that only 2 of 63 (3.17%) benign bladder specimens had even weak reactivity for the MT-3 protein. In contrast, 103 of 107 (96.26%) high-grade urothelial cancers and 17 of 17 (100%) specimens of carcinoma in situ stained positive for the MT-3 protein. For low-grade bladder cancer it was shown that 30 of 48 specimens (62.5%) expressed the MT-3 protein. Using a cell culture model (UROtsa), it was demonstrated that expression of the MT-3 protein was not required for malignant transformation of urothelial cells by either Cd(+2) or As(+3). In contrast, it was shown that the cells transformed by Cd(+2) and As(+3) that did not express the MT-3 gene in cell culture, gained expression of MT-3 when grown as heterotransplants in nude mice. The gain in MT-3 expression when cells were grown as heterotransplants was also shown to occur for the MCF-7, T-47D, Hs 578t, MDA-MB-231 breast cancer, and the PC-3 prostate cancer cell lines. An analysis of MT-3 mRNA and protein expression suggested that a posttranscriptional mechanism was responsible for accumulation of the MT-3 protein. The results provide strong evidence that MT-3 could be a biomarker for the development of high-grade bladder cancer and that the expression of the MT-3 gene is not involved in the in vitro malignant transformation of UROtsa cells by Cd(+2) and As(+3).

Metallothionein isoform II expression in hyperplastic, dysplastic and neoplastic prostatic lesions

BACKGROUND

Metallothionein is a low-molecular-weight cysteine-rich protein that has the ability to bind and sequestrate heavy metal ions. It is associated with metalloregulatory functions such as cell proliferation, growth and differentiation.

AIMS

To investigate the expression of metallothionein in hyperplastic, dysplastic and neoplastic prostatic lesions and to correlate its expression with histological grade of prostatic carcinoma.

METHOD

The study was carried out on formalin-fixed and paraffin-wax-embedded tissue blocks from 8 patients with benign prostatic hyperplasia, 6 patients with prostatic intraepithelial neoplasia (PIN) and 30 patients with prostatic carcinoma, using the streptavidin-biotin technique. The histological grade was defined and the carcinomas were divided into low-grade (Gleason Score 2-4), 12 moderate grade (Gleason Score 5-6) and 10 high-grade (Gleason Score 7-10) carcinomas.

RESULTS

Patchy metallothionein staining of epithelial cells was observed in normal and benign prostatic tissues. All cases of PIN and 20 of 30 patients with prostatic carcinoma showed positive staining for metallothionein. Metallothionein expression considerably increased from low-grade to high-grade tumours. The proportion of cells staining positively for metallothionein was directly correlated with histological grade of prostatic carcinoma. The epithelial cells lack uniformity in staining intensity, but the percentage of strongly positive cells increased with the histological grade of prostatic carcinoma.

CONCLUSIONS

The high incidence of metallothionein expression in PIN in our study suggests that it is associated with early prostate tumorigenesis. Also, metallothionein expression was directly correlated with the histological grade of prostatic carcinoma, suggesting that metallothionein may be a useful marker for predicting the prognosis of prostate cancer.

Expression of metallothoinein isoform 3 is restricted at the post-transcriptional level in human bladder epithelial cells

This study was designed to define the effect that overexpression of MT-3 would have on a cell culture model of bladder urothelium. Stable and inducible transfection was used to achieve overexpression of the MT-3 gene in the UROtsa cell line. When the UROtsa cells were stably transfected with the MT-3 coding sequence, there was highly elevated expression of MT-3 mRNA, but no MT-3 protein. An inducible vector showed that low basal levels of MT-3 mRNA and protein could be produced, but that induction only increased MT-3 mRNA and not protein. The clones expressing low basal levels of MT-3 protein also had reduced growth rates compared to control cells. Site directed mutagenesis was used to produce an MT-3 coding sequence where the prolines in positions 7 and 9 were converted to threonines. When this altered MT-3 was stably transfected into the UROtsa cells, the cells were able to accumulate the mutated form of the MT-3 protein. These studies show that MT-3 protein expression is inhibited by post-transcriptional control in the urothelial cell. Modifying the MT-3 protein to resemble the MT-1 isoform removes this component of post-transcriptional control and allows accumulation of the mutated MT-3 protein. The altered sequence involved in post-transcriptional control of MT-3 protein expression is the same sequence implicated in the neuronal growth inhibitory activity associated specifically with the MT-3 isoform of the MT gene family.

Identification of mouse brain proteins associated with isoform 3 of metallothionein

Using immunological approaches and mass spectrometry, five proteins associated with metallothionein-3 in mouse brains have been identified. Metallothionein-3 and associated proteins were isolated using immunoaffinity chromatography over immobilized anti-mouse brain MT3 antibody. Proteins in the recovered pool were separated by SDS-polyacrylamide gel electrophoresis, and distinct bands were excised and the proteins digested using trypsin. Peptides were extracted and analyzed using electrospray ionization mass spectrometry. Initial identification was done comparing the identified peptide mass:charge ratios to the MASCOT database. Confirmation of proteins was accomplished by sequencing of selected peptides using tandem mass spectrometry and comparison to the MASCOT database. The proteins were heat-shock protein 84 (mouse variant of heat-shock protein 90), heat-shock protein 70, dihydropyrimidinase-like protein 2, creatine kinase, and beta actin. Independently using antibodies against metallothionein-3, creatine kinase, and heat-shock protein 84 showed that all three proteins were coimmunoprecipitated from whole mouse brain homogenates with each of the three antibodies. Mixing purified samples of metallothionein and human brain creatine kinase also generated a complex that could be immunoprecipitated either by anti-metallothionein-3 or anticreatine kinase antibody. These data are consistent with metallothionein-3 being present in the mouse brain as part of a multiprotein complex providing new functional information for understanding the role of metallothionein-3 in neuronal physiology.

Stable expression of C/EBPalpha in prostate cancer cells down-regulates metallothionein and increases zinc-induced toxicity

BACKGROUND

The transcription factor C/EBPalpha regulates terminal differentiation of various cell types. C/EBPalpha is expressed in prostate epithelium but its role in prostate development and malignant transformation is unknown. In examining the effect of forced expression of C/EBPalpha on the global gene expression profile in prostate cancer cells, we found that C/EBPalpha significantly decreased the RNA level of metallothioneins (MTs).

METHODS

The prostate cancer cell lines DU145, LNCaP, and PC3 with stable overexpression of C/EBPalpha were established with a retroviral expression system. MT expression was assayed by Western blot analysis and with the MT promoter in a plasmid using luciferase as a reporter.

RESULTS

Under basal conditions and in response to zinc, forced overexpression of C/EBPalpha decreased expression of MT isoforms 1A, B, F, and H, IIA and III. Following zinc exposure C/EBPalpha inhibited MT promoter activity by 1.5-2.5-fold. Overexpression of C/EBPalpha led to increased cytotoxicity of zinc at concentration of 150 microM in DU145 and LNCaP cells.

CONCLUSIONS

Our data demonstrated that expression of MTs in prostate cancer cells is inhibited by C/EBPalpha and the effect may have functional significance in regulating the growth of prostate cancer cells and the response of these cells to environment stresses.

Stable transfection and overexpression of metallothionein isoform 3 inhibits the growth of MCF-7 and Hs578T cells but not that of T-47D or MDA-MB-231 cells

The third isoform of metallothionein (MT-3) is overexpressed in some breast cancers and its expression is associated with a poor disease outcome. In the PC-3 prostate cancer cell line, MT-3 expression has been shown to inhibit cell growth and increase drug resistance. The goal of the present study was to determine if MT-3 overexpression would influence the growth of human breast cancer cell lines. To determine this, the coding sequence of the MT-3 gene was stably transfected into two estrogen receptor positive (MCF-7 and T-47D) and two estrogen receptor negative cell lines (Hs578T and MDA-MB-231) having no basal expression of MT-3. Cell growth was determined by counting DAPI-stained nuclei, cadmium resistance by the colony formation assay, MT mRNA expression by RT-PCR, and MT protein by immuno-blot. It was demonstrated that MCF-7 and Hs578T cells that overexpress the MT-3 gene were growth inhibited compared to untransfected cells. In contrast, T-47D and MDA-MB-231 cells that overexpress MT-3 were not growth inhibited. Stable transfection of the MT-1E gene had no effect on the growth of any of the four cell lines. It was also demonstrated that the overexpression of both MT-3 and MT-1E only increased the resistance of MCF-7 cells to Cd(+2). In all instances, stable transfection of the MT-3 or MT-1E gene had no effect on the expression of the other MT isoforms. The study shows that MT-3 can influence the growth of some breast cancer cell lines.

Metallothionein isoform 3 expression inhibits cell growth and increases drug resistance of PC-3 prostate cancer cells

BACKGROUND

The third isoform of metallothionein (MT-3) is overexpressed in prostate cancers and PIN lesions. The expression of MT-3 is highly variable but appears to correlate to Gleason score. The goal of the present study was to determine the effect of MT-3 overexpression on the growth of the PC-3 prostate cancer cell line.

METHODS

PC-3 cells were stably transfected with either the MT-3 or MT-1E gene. Cell growth was determined by counting DAPI-stained nuclei, drug resistance by the colony formation assay, MT mRNA expression by reverse transcriptase-polymerase chain reaction, and MT protein by immunoblot.

RESULTS

PC-3 cells that overexpress the MT-3 gene are growth inhibited compared with either untransfected cells, cells with blank vector, or cells with similar overexpression of the MT-1E gene. Furthermore, increased chemotherapeutic drug resistance occurred in PC-3 clones derived from MT-3- and MT-1E-transfected cells.

CONCLUSION

The overexpression of MT-3 can influence the growth and chemotherapeutic drug resistance of the PC-3 prostate cancer cell line.

Identification, using cDNA macroarray analysis, of distinct gene expression profiles associated with pathological and virological features of hepatocellular carcinoma

It is still unclear as to whether the gene expression profile in HCV- or HBV-related HCC exhibits a degree of specificity and whether the development of HCC in a context of cirrhosis influences this gene profile. To address these issues, the expression profiles of 15 cases of HCC were analysed using cDNA macroarray. A global analysis and hierarchical clustering, demonstrated the heterogeneity of HCC patterns, with a majority of down-regulated genes. Statistical analysis clearly showed a distinction between the gene expression profiles of HCV- and HBV-related HCC. HBV-associated HCC exhibited involvement of different cellular pathways, those controlling apoptosis, p53 signalling and G1/S transition. In HCV-related HCC we identified a more heterogenous pattern with an over-expression of the TGF-beta induced gene. In HCC developing on non-cirrhotic tissues, beta-catenin encoding gene and genes implicated in the PKC pathway were specifically up-regulated. In addition, our investigation highlighted a distinct profiles of TGF-beta superfamily encoding genes in well, moderately or poorly differentiated HCC. Overall, our study supports the hypothesis that despite the heterogeneity of the HCC pattern, the large-scale screening of gene expression may provide data significant to our understanding of the mechanism of liver carcinogenesis.

Metallothionein isoform 3 and proximal tubule vectorial active transport

BACKGROUND

Metallothionein isoform 3 (MT-3) is expressed in the proximal tubule cells of the human kidney. The goal of the present study was to further characterize the basal expression of MT-3 in the proximal tubule and to determine if MT-3 participates in the maintenance of proximal tubule cell function.

METHODS

Expression of MT-3 mRNA was determined in the intact proximal tubule using microdissection and reverse transcription-polymerase chain reaction (RT-PCR). Basal expression of MT-3 mRNA and protein was determined in cultured human proximal tubule (HPT) cells and an immortalized proximal tubular cell line, HK-2 cells, using RT-PCR and immunoblotting. The MT-3 gene was stably transfected into the HK-2 cell line using the pcDNA3.1/Hygro (+) vector.

RESULTS

MT-3 mRNA was detected in the proximal tubule of the in situ kidney with relative expression in excess to that of the beta-actin housekeeping gene. The mortal HPT cells were shown to express both MT-3 mRNA and protein and to form domes, while immortal HK-2 cells were shown to have no expression of MT-3 mRNA and protein nor to form domes. The stable transfection of MT-3 in HK-2 restored MT-3 expression and dome formation to the HK-2 cells.

CONCLUSIONS

MT-3 mRNA is present in the human proximal tubule, and MT-3 expression is involved in the transport function of a human renal cell line that retains properties of the proximal tubule.

Transient induction of metallothionein isoform 3 (MT-3), c-fos, c-jun and c-myc in human proximal tubule cells exposed to cadmium

Cadmium (Cd(+2)) has been shown to transiently increase the expression of mRNA for the third isoform of the metallothionein (MT-3) gene family in cultured human proximal tubule (HPT) cells. The goal of the present study was to further define the expression of MT-3 in mortal (HPT) and immortal (HK-2) cultures of HPT cells when exposed to lethal and sub-lethal concentrations of Cd(+2) under both acute and chronic time periods of exposure. Expression of MT-3 mRNA and protein was determined in cultured HPT cells and HK-2 cells using reverse-transcription-polymerase chain reaction (RT-PCR) and immuno-blotting, and expression of c-fos, c-jun and c-myc mRNA by RT-PCR. The results confirmed that exposure of the HPT cells to Cd(+2) induced a transient increase in MT-3 mRNA and extended the induction to include a subsequent transient increase in the level of the MT-3 protein. The induction of MT-3 was rapid and returned to control values within 48 h of exposure despite the continued presence of lethal and sublethal concentrations of Cd(+2). It was also demonstrated that the pattern of expression of MT-3 mRNA was similar to that of the early response genes, c-fos, c-jun and c-myc. It was shown that the HK-2 cells did not express MT-3 when exposed to Cd(+2), but had similar expression of the c-fos, c-jun and c-myc genes. The results demonstrate that MT-3 expression is metal responsive in HPT cells.

Metallothionein isoform 3 overexpression is associated with breast cancers having a poor prognosis

The third isoform (MT-3) of the metallothionein gene family is unique in that it has a limited tissue distribution, is not induced by metals, has a neuronal growth inhibitory activity, and sequesters zinc more effectively under zinc-depleted conditions. The goal of the present study was to determine whether MT-3 was absent in normal breast tissue, was overexpressed in breast cancers, and if MT-3 overexpression would be associated with disease outcome. A combination of immunohistochemistry and reverse-transcription polymerase chain reaction was used to demonstrate that the normal breast had no detectable expression of MT-3 mRNA or protein. Using immunohistochemistry, it was shown that MT-3 was overexpressed in 25 of 34 cases of breast cancer. In all cases of positive staining, MT-3 was diffusely localized to the cytoplasm. The tumors from these 34 cases were divided as to outcome based on known 5-year survival, with 20 patients being disease free at 5 years (good outcome) and the other 14 having recurring disease within 5 years (bad outcome). When analyzed for MT-3 staining, it was shown that there was a trend for increased MT-3 immunoreactivity in the group having bad outcomes. However, when the tumor subgrouping was further defined on the basis of carcinoma in situ (CIS), there was a marked significant difference in MT-3 staining between patients with good and bad outcomes. Limited to DCIS, MT-3 staining was significantly increased in patients with bad outcomes compared to those with good outcomes. Thus, these studies demonstrate that MT-3 is overexpressed in selected breast cancers and that overexpression is associated with tumors having a poor prognosis.

Roles of the metallothionein family of proteins in the central nervous system

Metallothioneins (MTs) constitute a family of proteins characterized by a high heavy metal [Zn(II), Cu(I)] content and also by an unusual cysteine abundance. Mammalian MTs are comprised of four major isoforms designated MT-1 trough MT-4. MT-1 and MT-2 are expressed in most tissues including the brain, whereas MT-3 (also called growth inhibitory factor) and MT-4 are expressed predominantly in the central nervous system and in keratinizing epithelia, respectively. All MT isoforms have been implicated in disparate physiological functions, such as zinc and copper metabolism, protection against reactive oxygen species, or adaptation to stress. In the case of MT-3, an additional involvement of this isoform in neuromodulatory events and in the pathogenesis of Alzheimer's disease has also been suggested. It is essential to gain insight into how MTs are regulated in the brain in order to characterize MT functions, both in normal brain physiology, as well as in pathophysiological states. The focus of this review concerns the biology of the MT family in the context of their expression and functional roles in the central nervous system.