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

The physiological role of copper: Dietary sources, metabolic regulation, and safety concerns

Copper plays an important physiological role in the body, with both deficiency and excess potentially impacting overall health. The body maintains a stringent copper metabolism mechanism to oversee absorption, utilization, storage, and elimination. Dietary consumption serves as the principal source of copper. The dietary factors may interfere with the absorption and metabolism of copper, leading to fluctuation of copper levels in the body. However, these dietary factors can also be strategically employed to facilitate the precise regulation of copper. This paper delved into the advancements in research concerning copper in food processing, including dietary sources of copper, the regulatory processes of copper metabolism and health implications of copper. The safety and its underlying mechanisms of excess copper were also highlighted. In particular, the paper examines the influence of dietary factors on the absorption and metabolism of copper, aiming to provide direction for accurate copper regulation and the creation of functional foods and pharmaceuticals.

Dysregulation of Long Non-coding RNAs-the Novel lnc in Metal Toxicity and Carcinogenesis

PURPOSE OF REVIEW

Metals are common environmental pollutants. Acute and chronic exposures to non-essential toxic metals or excessive essential metals cause various diseases including cancer in humans. However, the underlying mechanisms have not been well understood. Long non-coding RNAs (lncRNAs) refer to RNA transcripts that have more than 200 nucleotides but do not have significant protein coding capacities. While lncRNAs were once considered transcription noise, they have become increasingly recognized as crucial players in various physiological and pathogenesis processes. The goal of this article is to review and discuss recent studies that show important roles of lncRNA dysregulations in metal toxicity and carcinogenesis.

RECENT FINDINGS

Recent studies showed that metal exposures dysregulate expression of lncRNAs in cultured cells, animals and humas. However, only a few studies determined the mechanisms of how metal exposure dysregulated expression of lncRNAs. The majority of the studies reported the association of abnormally expressed lncRNAs with various toxic effects of metal exposures, only limited studies established causal relationships demonstrating causal roles of dysregulated lncRNAs in metal toxicity and carcinogenesis. Mechanistically, most studies reported that dysregulated lncRNAs functioned as microRNA sponges to regulate gene expression, much less studies explored other mechanisms of lncRNA actions. It is evident that metal exposures dysregulate expression of lncRNAs, which may serve as novel mediators in metal toxicity and carcinogenesis. Further studies are needed to establish dysregulated lncRNAs as potential diagnostic biomarkers and therapeutic targets for metal exposure-associated diseases.

Metallothionein: A Comprehensive Review of Its Classification, Structure, Biological Functions, and Applications

Metallothionein is a cysteine-rich protein with a high metal content that is widely found in nature. In addition to heavy metal detoxification, metallothionein is well known as a potent antioxidant. The high sulfhydryl content of metallothionein confers excellent antioxidant activity, enabling it to effectively scavenge free radicals and mitigate oxidative stress damage. In addition, metallothionein can play a neuroprotective role by alleviating oxidative damage in nerve cells, have an anticancer effect by enhancing the ability of normal cells to resist unfavorable conditions through its antioxidant function, and reduce inflammation by scavenging reactive oxygen species. Due to its diverse biological functions, metallothionein has a broad potential for application in alleviating environmental heavy metal pollution, predicting and diagnosing diseases, and developing skin care products and health foods. This review summarizes the recent advances in the classification, structure, biological functions, and applications of metallothionein, focusing on its powerful antioxidant effects and related functions.

Ketogenic diet time-dependently prevents NAFLD through upregulating the expression of antioxidant protein metallothionein-2

BACKGROUND & AIMS

The past few decades have witnessed a rapid growth in the prevalence of nonalcoholic fatty liver disease (NAFLD). While the ketogenic diet (KD) is considered for managing NAFLD, the safety and efficacy of the KD on NAFLD has been a controversial topic. Here, we aimed to investigate the effect of KD of different durations on metabolic endpoints in mice with NAFLD and explore the underlying mechanisms.

METHODS

NAFLD mice were fed with KD for 1, 2, 4 and 6 weeks, respectively. The blood biochemical indexes (blood lipids, AST, ALT and etc.) and liver fat were measured. The LC-MS/MS based proteomic analysis was performed on liver tissues. Metallothionein-2 (MT2) was knocked down with adeno-associated virus (AAV) or small interfering RNA (siRNA) in NAFLD mice and AML-12 cells, respectively. H&E, BODIPY and ROS staining were performed to examine lipid deposition and oxidative stress. Furthermore, MT2 protein levels, nucleus/cytoplasm distribution and DNA binding activity of peroxisome proliferators-activated receptors α (PPARα) were evaluated.

RESULTS

KD feeding for 2 weeks showed the best improvement on NAFLD phenotype. Proteomic analysis revealed that MT2 was a key candidate for different metabolic endpoints of NAFLD affected by different durations of KD feeding. MT2 knockdown in NAFLD mice blocked the effects of 2 weeks of KD feeding on HFD-induced steatosis. In mouse primary hepatocytes and AML-12 cells, MT2 protein levels were induced by β-hydroxybutyric acid (β-OHB). MT2 Knockdown blunted the effects of β-OHB on alleviating PA-induced lipid deposition. Mechanistically, 2 weeks of KD or β-OHB treatment reduced oxidative stress and upregulated the protein levels of MT2 in nucleus, which subsequently increased its DNA binding activity and PPARα protein expression.

CONCLUSIONS

Collectively, these findings indicated that KD feeding prevented NAFLD in a time dependent manner and MT2 is a potential target contributing to KD improvement on steatosis.

Metallothionein-3 is a multifunctional driver that modulates the development of sorafenib-resistant phenotype in hepatocellular carcinoma cells

BACKGROUND & AIMS

Metallothionein-3 (hMT3) is a structurally unique member of the metallothioneins family of low-mass cysteine-rich proteins. hMT3 has poorly characterized functions, and its importance for hepatocellular carcinoma (HCC) cells has not yet been elucidated. Therefore, we investigated the molecular mechanisms driven by hMT3 with a special emphasis on susceptibility to sorafenib.

METHODS

Intrinsically sorafenib-resistant (BCLC-3) and sensitive (Huh7) cells with or without up-regulated hMT3 were examined using cDNA microarray and methods aimed at mitochondrial flux, oxidative status, cell death, and cell cycle. In addition, in ovo/ex ovo chick chorioallantoic membrane (CAM) assays were conducted to determine a role of hMT3 in resistance to sorafenib and associated cancer hallmarks, such as angiogenesis and metastastic spread. Molecular aspects of hMT3-mediated induction of sorafenib-resistant phenotype were delineated using mass-spectrometry-based proteomics.

RESULTS

The phenotype of sensitive HCC cells can be remodeled into sorafenib-resistant one via up-regulation of hMT3. hMT3 has a profound effect on mitochondrial respiration, glycolysis, and redox homeostasis. Proteomic analyses revealed a number of hMT3-affected biological pathways, including exocytosis, glycolysis, apoptosis, angiogenesis, and cellular stress, which drive resistance to sorafenib.

CONCLUSIONS

hMT3 acts as a multifunctional driver capable of inducing sorafenib-resistant phenotype of HCC cells. Our data suggest that hMT3 and related pathways could serve as possible druggable targets to improve therapeutic outcomes in patients with sorafenib-resistant HCC.

Proteomic analysis of holocarboxylase synthetase deficient-MDA-MB-231 breast cancer cells revealed the biochemical changes associated with cell death, impaired growth signaling, and metabolism

We have previously shown that the holocarboxylase synthetase (HLCS) is overexpressed in breast cancer tissue of patients, and silencing of its expression in triple-negative cancer cell line inhibits growth and migration. Here we investigated the global biochemical changes associated with HLCS knockdown in MDA-MB-231 cells to discern the pathways that involve HLCS. Proteomic analysis of two independent HLCS knockdown cell lines identified 347 differentially expressed proteins (DEPs) whose expression change > 2-fold (p < 0.05) relative to the control cell line. GO enrichment analysis showed that these DEPs were mainly associated with the cellular process such as cellular metabolic process, cellular response to stimulus, and cellular component organization or biogenesis, metabolic process, biological regulation, response to stimuli, localization, and signaling. Among the 347 identified DEPs, 64 proteins were commonly found in both HLCS knockdown clones, confirming their authenticity. Validation of some of these DEPs by Western blot analysis showed that plasminogen activator inhibitor type 2 (SerpinB2) and interstitial collagenase (MMP1) were approximately 90% decreased in HLCS knockdown cells, consistent with a 50%-60% decrease in invasion ability of knockdown cells. Notably, argininosuccinate synthase 1 (ASS1), one of the enzymes in the urea cycle, showed approximately a 10-fold increase in the knockdown cells, suggesting the crucial role of HLCS in supporting the urea cycle in the triple-negative cancer cell line. Collectively, our proteomic data provide biochemical insights into how suppression of HLCS expression perturbs global changes in cellular processes and metabolic pathways, impairing cell growth and invasion.

Methylomics and cancer: the current state of methylation profiling and marker development for clinical care

Epigenetic modifications have long been recognized as an essential level in transcriptional regulation linking behavior and environmental conditions or stimuli with biological processes and disease development. Among them, methylation is the most abundant of these reversible epigenetic marks, predominantly occurring on DNA, RNA, and histones. Methylation modification is intimately involved in regulating gene transcription and cell differentiation, while aberrant methylation status has been linked with cancer development in several malignancies. Early detection and precise restoration of dysregulated methylation form the basis for several epigenetics-based therapeutic strategies. In this review, we summarize the current basic understanding of the regulation and mechanisms responsible for methylation modification and cover several cutting-edge research techniques for detecting methylation across the genome and transcriptome. We then explore recent advances in clinical diagnostic applications of methylation markers of various cancers and address the current state and future prospects of methylation modifications in therapies for different diseases, especially comparing pharmacological methylase/demethylase inhibitors with the CRISPRoff/on methylation editing systems. This review thus provides a resource for understanding the emerging role of epigenetic methylation in cancer, the use of methylation-based biomarkers in cancer detection, and novel methylation-targeted drugs.

Chemical genomics reveals targetable programs of human cancers rooted in pluripotency

Overlapping principles of embryonic and tumor biology have been described, with recent multi-omics campaigns uncovering shared molecular profiles between human pluripotent stem cells (hPSCs) and adult tumors. Here, using a chemical genomic approach, we provide biological evidence that early germ layer fate decisions of hPSCs reveal targets of human cancers. Single-cell deconstruction of hPSCs-defined subsets that share transcriptional patterns with transformed adult tissues. Chemical screening using a unique germ layer specification assay for hPSCs identified drugs that enriched for compounds that selectively suppressed the growth of patient-derived tumors corresponding exclusively to their germ layer origin. Transcriptional response of hPSCs to germ layer inducing drugs could be used to identify targets capable of regulating hPSC specification as well as inhibiting adult tumors. Our study demonstrates properties of adult tumors converge with hPSCs drug induced differentiation in a germ layer specific manner, thereby expanding our understanding of cancer stemness and pluripotency.

Metallothionein-2: An emerging target in inflammatory diseases and cancers

Metallothionein-2 (MT-2) was originally discovered as a mediator of zinc homeostasis and cadmium detoxification. However, MT-2 has recently received increased attention because altered expression of MT-2 is closely related to various diseases such as asthma and cancers. Several pharmacological strategies have been developed to inhibit or modify MT-2, revealing its potential as drug target in diseases. Therefore, a better understanding of the mechanisms of MT-2 action is warranted to improve drug development for potential clinical applications. In this review, we highlight recent advances in determining the protein structure, regulation, binding partners, and new functions of MT-2 in inflammatory diseases and cancers.

A comprehensive review of the relationship between autophagy and sorafenib-resistance in hepatocellular carcinoma: ferroptosis is noteworthy

Patients with hepatocellular carcinoma (HCC) bear a heavy burden of disease and economic burden but have fewer treatment options. Sorafenib, a multi-kinase inhibitor, is the only approved drug that can be used to limit the progression of inoperable or distant metastatic HCC. However, enhanced autophagy and other molecular mechanisms after sorafenib exposure further induce drug resistance in HCC patients. Sorafenib-associated autophagy also generates a series of biomarkers, which may represent that autophagy is a critical section of sorafenib-resistance in HCC. Furthermore, many classic signaling pathways have been found to be involved in sorafenib-associated autophagy, including the HIF/mTOR signaling pathway, endoplasmic reticulum stress, and sphingolipid signaling, among others. In turn, autophagy also provokes autophagic activity in components of the tumor microenvironment, including tumor cells and stem cells, further impacting sorafenib-resistance in HCC through a special autophagic cell death process called ferroptosis. In this review, we summarized the latest research progress and molecular mechanisms of sorafenib-resistance-associated autophagy in detail, providing new insights and ideas for unraveling the dilemma of sorafenib-resistance in HCC.

Immunosuppressive landscape in hepatocellular carcinoma revealed by single-cell sequencing

Background/Aims

Hepatocellular carcinoma (HCC), accounting for 75-85% of primary liver cancer cases, is the third leading cause of cancer-related death worldwide. The purpose of this research was to examine the tumor immune microenvironment (TIME) in HCC.

Methods

We investigated the HCC TIME by integrated analysis of single-cell and bulk-tissue sequencing data to reveal the landscape of major immune cell types.

Results

Regulatory T(Treg) cells were found to be specifically distributed in the TIME of HCC. Several immune checkpoints, including TNFRSF4, TIGIT and CTLA4, were found to be uniquely overexpressed in Treg cells, and the glycolysis/gluconeogenesis pathway was enriched in Treg cells. We also discovered the presence of two NK-cell subsets with different cytotoxic capacities, one in an activated state with antitumor effects and another with an exhausted status. In addition, memory B cells in HCC were found to exist in a unique state, with high proliferation, low differentiation, and low activity, which was induced by overexpression of PRAP1 and activation of the MIF-CD74 axis.

Conclusions

We revealed the TIME landscape in HCC, highlighting the heterogeneity of major immune cell types and their potential mechanisms in the formation of an immunosuppressive environment. Hence, blocking the formation of the TIME could be a useful therapeutic strategy for HCC.

Metallothioneins in Dental Implant Treatment Failure and Periodontitis in Patients with Down's Syndrome: Validation of Results

Metallothioneins (MTs) are low molecular weight cysteine-rich proteins that can bind up to seven zinc ions. Among their numerous functions, MTs appear to act as protectors against oxidative and inflammatory injury. In our first published study, we reported downregulation of the isoforms MT1B (fold distance (FD) −2. 95; p = 0.0024), MT1F (FD −1.72; p = 0.0276), MT1X (FD −3.09; p = 0.0021), MT1H (FD −2.39; p = 0.0018), MT1M (FD −2.37; p = 0.0092), MT1L (FD −2. 55; p = 0.0048), MT1E (FD −2.71; p = 0.0014), MT2A (FD −2.35; p = 0.0072), MT1G (FD −2.24; p = 0.0118), and MT1A (FD −2.82; p = 0.0023) by comparing Down’s syndrome patients with periodontal disease and implant failure to those without periodontal disease and with a positive progression of their implants. In this gene validation study, we intended to verify the results of our first gene expression analysis. Materials and Methods: In our retrospective case–control study, we performed retrotranscription (RT-qPCR) of 11 RNA-to-cDNA samples using the SuperScript™ VILO™ kit (50; reference 1,176,605) from Thermo Fisher. We conducted the study using the real-time PCR technique on the q-PCR ViiA 7 platform from Thermo Fisher. We chose the format of the Taqman Array Plate 16 Plus (reference 4,413,261) from Thermo Fisher, which accommodates 12 genes plus four controls (GAPDH, 18S, ACTB, and HPRT1). We conducted the analysis of the plates using the Thermo Fisher Cloud Web Software. Results: The results obtained through gene validation analysis show that in PD+RI+ patients, the genes encoding the isoforms MT1F (FD 0.3; p = 0.039), MT1X (FD 338; p = 0.0078), MT1E (FD 307; p = 0.0358), and MT2A (FD 252; p = 0.0428) continue to show downregulation, whereas MT1B (FD 2.75; p = 0.580), MT1H (FD 281; p = 0.152), MT1L (FD 354; p = 0.0965), and MT1G (FD 336; p = 0.0749) no longer show statistically significant results.

A Novel Pseudogene Methylation Signature to Predict Temozolomide Outcome in Non-G-CIMP Glioblastomas

Objective

Alterations in the methylation state of pseudogenes may serve as clinically useful biomarkers of glioblastomas (GBMs) that do not have glioma-CpG island methylator phenotype (G-CIMP).

Methods

Non-G-CIMP GBM datasets were included for evaluation, and a RISK-score signature was determined from the methylation state of pseudogene loci. Both bioinformatic and experimental analyses were performed for biological validation.

Results

By integrating clinical information with DNA methylation microarray data, we screened a panel of eight CpGs from discovery cohorts of non-G-CIMP GBMs. Each CpG could accurately and independently predict the prognosis of patients under a treatment regime that combined radiotherapy (RT) and temozolomide (TMZ). The 8-CpG signature appeared to show opposite prognostic correlations between patients treated with RT/TMZ and those treated with RT monotherapy. The analyses further indicated that this signature had predictive value for TMZ efficacy because different survival benefits between RT/TMZ and RT therapies were observed in each risk subgroup. The incorporation of other risk factors, such as age and O-6-methylguanine-DNA methyltransferase (MGMT) promoter methylation status, with our pseudogene methylation signature could provide precise risk classification. In vitro experimental data revealed that two locus-specific pseudogenes (ZNF767P and CLEC4GP1) may modulate TMZ resistance via distinct mechanisms in GBM cells.

Conclusion

The biologically and clinically relevant RISK-score signature, based on pseudogene methylation loci, may offer information for predicting TMZ responses of non-G-CIMP GBMs, that is independent from, but complementary to, MGMT-based approaches.

MTAP-related increased erythroblast proliferation as a mechanism of polycythaemia vera

Polycythaemia vera (PV) is a haematological disorder caused by an overproduction of erythroid cells. To date, the molecular mechanisms involved in the disease pathogenesis are still ambiguous. This study aims to identify aberrantly expressed proteins in erythroblasts of PV patients by utilizing mass spectrometry-based proteomic analysis. Haematopoietic stem cells (HSCs) were isolated from newly-diagnosed PV patients, PV patients who have received cytoreductive therapy, and healthy subjects. In vitro erythroblast expansion confirmed that the isolated HSCs recapitulated the disease phenotype as the number of erythroblasts from newly-diagnosed PV patients was significantly higher than those from the other groups. Proteomic comparison revealed 17 proteins that were differentially expressed in the erythroblasts from the newly-diagnosed PV patients compared to those from healthy subjects, but which were restored to normal levels in the patients who had received cytoreductive therapy. One of these proteins was S-methyl-5′-thioadenosine phosphorylase (MTAP), which had reduced expression in PV patients’ erythroblasts. Furthermore, MTAP knockdown in normal erythroblasts was shown to enhance their proliferative capacity. Together, this study identifies differentially expressed proteins in erythroblasts of healthy subjects and those of PV patients, indicating that an alteration of protein expression in erythroblasts may be crucial to the pathology of PV.

Subacute safety assessment of recombinant Lactococcus lactis on the gut microbiota of male Sprague-Dawley rats

BACKGROUND

Lactococcus lactis strain pGSMT/MG1363 is a genetically modified microorganism (GMM) that constitutively expresses human metallothionein-I fusion protein to combine with intracellular lead. Unlike traditional probiotics, pGSMT/MG1363 lacks a history of safe use in food. Administration of microorganism could influence the gut microbial community and consequently confer health benefits or cause disadvantages to the host. To date, little has been done to assess the influence of recombinant strain pGSMT/MG1363 on the stability of gut microbiota.

RESULTS

Liver, testis and kidney sections of male Sprague-Dawley rats orally administered pGSMT/MG1363 for 6 weeks showed normal structure and no pathological damage. There were no adverse effects on the analyzed serum biochemical parameters between the pGSMT/MG1363 group and the MG1363 group. Principal coordinate analysis showed that, compared with the MG1363 group, the 6-week-old fecal gut microbiota of rats fed with pGSMT/MG1363 was not significantly different (Adonis, P = 0.802). pGSMT/MG1363 treatment for 6 weeks did not significantly change the relative abundance of gut microbiota at the phylum and genus levels in comparison with MG1363 treatment.

CONCLUSION

Compared to the non-GM strain MG1363 group, administration of the recombinant strain pGSMT/MG1363 for 6 weeks showed no adverse effects on the analyzed physiological parameters and gut microbial compositions of male Sprague-Dawley rats. The results suggested that, in terms of gut microbiota stability, pGSMT/MG1363 could be considered as safe as MG1363, at least for short-term intake. Further toxicological evaluations still need to be considered before drawing a definite conclusion concerning the safe use of pGSMT/MG1363. © 2021 Society of Chemical Industry.

Metallothioneins and Megalin Expression Profiling in Premalignant and Malignant Oral Squamous Epithelial Lesions

This study aimed to assess the relationship and possible interactions between metallothioneins (MTs) and megalin (LRP-2) in different grades of oral squamous cell carcinoma (OSCC) and premalignant lesions of the oral mucosa (oral leukoplakia and oral lichen planus). The study included archived samples of 114 patients and control subjects. Protein expression was examined by immunohistochemistry and immunofluorescence, and staining quantification was performed by ImageJ software. Protein interaction in cancer tissue was tested and visualized by proximity ligation assay. Mann-Whitney and Kruskal-Wallis tests were used to determine the significance of differences between each group, whereas Pearson correlation coefficient was performed to test correlation. Expression of both proteins differed significantly between each group showing the same pattern of gradual increasing from oral lichen planus to poorly differentiated OSCC. Moreover, MTs and megalin were found to co-express and interact in cancer tissue, and their expression positively correlated within the overall study group. Findings of prominent nuclear and chromosomal megalin expression suggest that it undergoes regulated intramembrane proteolysis upon MTs binding, indicating its ability to directly affect gene expression and cellular division in cancer tissue. The data obtained point to the onco-driving potential of MTs-megalin interaction.

Overexpressed pseudogene MT1L associated with tumor immune infiltrates and indicates a worse prognosis in BLCA

BACKGROUND

BLCA is a common cancer worldwide, and it is both aggressive and fatal. Immunotherapy (ICT) has achieved an excellent curative effect in BLCA; however, only some BLCA patients can benefit from ICT. MT1L is a pseudogene, and a previous study suggested that MT1L can be used as an indicator of prognosis in colorectal cancer. However, the role of MT1L in BLCA has not yet been determined.

METHODS

Data were collected from TCGA, and logistic regression, Kaplan-Meier plotter, and multivariate Cox analysis were performed to demonstrate the correlation between the pseudogene MT1L and the prognosis of BLCA. To identify the association of MT1L with tumor-infiltrating immune cells, TIMER and TISIDB were utilized. Additionally, GSEA was performed to elucidate the potential biological function.

RESULTS

The expression of MT1L was decreased in BLCA. Additionally, MT1L was positively correlated with immune cells, such as Tregs (ρ = 0.708) and MDSCs (ρ = 0.664). We also confirmed that MT1L is related to typical markers of immune cells, such as PD-1 and CTLA-4. In addition, a high MT1L expression level was associated with the advanced T and N and high grade in BLCA. Increased expression of MT1L was significantly associated with shorter OS times of BLCA patients (p < 0.05). Multivariate Cox analysis revealed that MT1L expression could be an independent prognostic factor in BLCA.

CONCLUSION

Collectively, our findings demonstrated that the pseudogene MT1L regulates the immune microenvironment, correlates with poor survival, and is an independent prognostic biomarker in BLCA.

Altered protein S-glutathionylation depicts redox imbalance triggered by transition metal oxide nanoparticles in a breastfeeding system

Nanosafety has become a public concern following nanotechnology development. By now, attention has seldom been paid to breastfeeding system, which is constructed by mammary physiological structure and derived substances (endogenous or exogenous), cells, tissues, organs, and individuals (mother and child), connecting environment and organism, and spans across mother-child dyad. Thus, breastfeeding system is a center of nutrients transport and a unique window of toxic susceptibility in the mother-child dyad. We applied metabolomics combined with redox proteomics to depict how nanoparticles cause metabolic burden via their spontaneous redox cycling in lactating mammary glands. Two widely used nanoparticles [titanium dioxide (nTiO₂) and zinc oxide (nZnO)] were exposed to lactating mice via intranasal administration. Biodistribution and biopersistence of nTiO₂ and nZnO in mammary glands destroyed its structure, reflective of significantly reduced claudin-3 protein level by 32.1% (P < 0.01) and 47.8% (P < 0.01), and significantly increased apoptosis index by 85.7 (P < 0.01) and 100.3 (P < 0.01) fold change, respectively. Airway exposure of nTiO₂ trended to reduced milk production by 22.7% (P = 0.06), while nZnO significantly reduced milk production by 33.0% (P < 0.01). Metabolomics analysis revealed a metabolic shift by nTiO₂ or nZnO, such as increased glycolysis (nTiO₂: fold enrichment = 3.31, P < 0.05; nZnO: fold enrichment = 3.68, P < 0.05), glutathione metabolism (nTiO₂: fold enrichment = 5.57, P < 0.01; nZnO: fold enrichment = 4.43, P < 0.05), and fatty acid biosynthesis (nTiO₂: fold enrichment = 3.52, P < 0.05; nZnO: fold enrichment = 3.51, P < 0.05) for tissue repair at expense of lower milk fat synthesis (35.7% reduction by nTiO₂; 51.8% reduction by nZnO), and finally led to oxidative stress of mammary glands. The increased GSSG/GSH ratio (57.5% increase by nTiO₂; 105% increase by nZnO) with nanoparticle exposure confirmed an alteration in the redox state and a metabolic shift in mammary glands. Redox proteomics showed that nanoparticles induced S-glutathionylation (SSG) modification at Cys sites of proteins in a nanoparticle type-dependent manner. The nTiO₂ induced more protein SSG modification sites (nTiO₂: 21; nZnO:16), whereas nZnO induced fewer protein SSG modification sites but at deeper SSG levels (26.6% higher in average of nZnO than that of nTiO₂). In detail, SSG modification by nTiO₂ was characterized by Ltf at Cys⁴²³ (25.3% increase), and Trf at Cys^386;395;583 (42.3%, 42.3%, 22.8% increase) compared with control group. While, SSG modification by nZnO was characterized by Trfc at Cys³⁶⁵ (71.3% increase) and Fasn at Cys¹⁰¹⁰ (41.0% increase). The discovery of SSG-modified proteins under airway nanoparticle exposure further supplemented the oxidative stress index and mammary injury index, and deciphered precise mechanisms of nanotoxicity into a molecular level. The unique quantitative site-specific redox proteomics and metabolomics can serve as a new technique to identify nanotoxicity and provide deep insights into nanoparticle-triggered oxidative stress, contributing to a healthy breastfeeding environment.

Integrative Analysis of Metallothioneins Identifies MT1H as Candidate Prognostic Biomarker in Hepatocellular Carcinoma

Background: Metallothioneins (MTs) play crucial roles in the modulation of zinc/copper homeostasis, regulation of neoplastic growth and proliferation, and protection against apoptosis. The present study attempted to visualize the prognostic landscape of MT functional isoforms and identify potential prognostic biomarkers in hepatocellular carcinoma (HCC). Methods: The transcriptional expression, comprehensive prognostic performances, and gene-gene interaction network of MT isoforms in HCC were evaluated via Oncomine, GEPIA, Kaplan-Meier plotter, and GeneMANIA databases. Characterized by good prognostic value in three external cohorts, MT1H was specifically selected as a potential prognostic biomarker in HCC with various clinicopathological features. Functional and pathway enrichment analyses of MT1H status were performed using cBioPortal, the Database for Annotation, Visualization, and Integrated Discovery (DAVID), and ssGSVA method. Results: MT1E/1F/1G/1H/1M/1X/2A was greatly downregulated in HCC. Prognostic analyses elucidated the essential correlations between MT1A/1B/1H/1X/2A/4 attenuation and poor overall survival, between MT1B/1H/4 downregulation and worse relapse-free survival, and between MT1A/1B/1E/1H/1M/2A/4 downregulation and diminished progression-free survival in HCC. Taken together, these results indicated the powerful prognostic value of MT1H among MTs in HCC. In-depth analyses suggested that MT1H may be more applicable to alcohol-derived HCC and involved in the downregulation of the inflammatory pathway, Jak-STAT pathway, TNF pathway, and Wnt signaling pathway. Conclusion: MT-specific isoforms displayed aberrant expression and varying prognostic value in HCC. MT1H repression in HCC was multi-dimensionally detrimental to patient outcomes. Therefore, MT1H was possibly associated with carcinogenesis and exploited as a novel prognostic biomarker and candidate therapeutic target for HCC.

Metallothionein dimerization evidenced by QD-based Förster resonance energy transfer and capillary electrophoresis

Herein, we report a new simple and easy-to-use approach for the characterization of protein oligomerization based on fluorescence resonance energy transfer (FRET) and capillary electrophoresis with LED-induced detection. The FRET pair consisted of quantum dots (QDs) used as an emission tunable donor (emission wavelength of 450 nm) and a cyanine dye (Cy3), providing optimal optical properties as an acceptor. Nonoxidative dimerization of mammalian metallothionein (MT) was investigated using the donor and acceptor covalently conjugated to MT. The main functions of MTs within an organism include the transport and storage of essential metal ions and detoxification of toxic ions. Upon storage under aerobic conditions, MTs form dimers (as well as higher oligomers), which may play an essential role as mediators in oxidoreduction signaling pathways. Due to metal bridging by Cd²⁺ ions between molecules of metallothionein, the QDs and Cy3 were close enough, enabling a FRET signal. The FRET efficiency was calculated to be in the range of 11-77%. The formation of MT dimers in the presence of Cd²⁺ ions was confirmed by MALDI-MS analyses. Finally, the process of oligomerization resulting in FRET was monitored by CE, and oligomerization of MT was confirmed.

Interplay between Carbonic Anhydrases and Metallothioneins: Structural Control of Metalation

Carbonic anhydrases (CAs) and metallothioneins (MTs) are both families of zinc metalloproteins central to life, however, they coordinate and interact with their Zn2+ ion cofactors in completely different ways. CAs and MTs are highly sensitive to the cellular environment and play key roles in maintaining cellular homeostasis. In addition, CAs and MTs have multiple isoforms with differentiated regulation. This review discusses current literature regarding these two families of metalloproteins in carcinogenesis, with a dialogue on the association of these two ubiquitous proteins in vitro in the context of metalation. Metalation of CA by Zn-MT and Cd-MT is described. Evidence for protein-protein interactions is introduced from changes in metalation profiles of MT from electrospray ionization mass spectrometry and the metalation rate from stopped-flow kinetics. The implications on cellular control of pH and metal donation is also discussed in the context of diseased states.

lncRNA STEAP3-AS1 Modulates Cell Cycle Progression via Affecting CDKN1C Expression through STEAP3 in Colon Cancer

Previous studies have reported that long noncoding RNAs (lncRNAs) have acted as new players during tumorigenesis. Metallothionein also plays an important role in tumor progression. It is mainly considered to be involved in the process of cell proliferation, oxidative stress, and multidrug resistance. However, the potential involvement of metallothionein-related lncRNAs in colon cancer remains poorly understood. In our study, we found that MT1M affected the expression of lncRNA STEAP3-AS1. STEAP3-AS1 is located in physical contiguity with STEAP3 and notably increased in colon cancer tissues and cell lines. STEAP3-AS1 expression was negatively associated with the expression of STEAP3. High levels of STEPA3-AS1 were associated with poor overall survival in colon cancer patients. In in vitro assays, STEAP3-AS1 knockdown could inhibit colon cancer cell proliferation and migration and arrest colon cancer cells at the G₀-G₁ phase. In tumorigenicity assays, STEAP3-AS1 knockdown could strongly inhibit tumor growth. Mechanistic investigations demonstrated that STEAP3-AS1 downregulation could increase the expression of cyclin-dependent kinase inhibitor 1C (CDKN1C) by STEAP3 upregulation. Overall, we identify the underlying role of MT1M-related lncRNA STEAP3-AS1 in colon cancer progression, which provides a novel strategy for colon cancer therapy.

A chemometric-assisted voltammetric analysis of free and Zn(II)-loaded metallothionein-3 states

We focused on the application of mass spectrometry and electrochemical methods combined with a chemometric analysis for the characterization of partially metallothionein-3 species. The results showed decreased Cat1 and Cat2 signals for the Zn(II)-loaded MT3 species with respect to the metal-free protein, which might be explained by the arrangement of tetrahedral metal-thiolate coordination environments and the formation of metal clusters. Moreover, there was a decrease in the Cat1 and Cat2 signals, and a plateau was reached with 4-5 Zn(II) ions that corresponded to the formation of the C-terminal α-domain. Regarding the Zn_7-xMT3 complexes, we observed three different electrochemical behaviours for the Zn_1-2MT3, Zn_3-6MT3 and Zn₇MT3 species. The difference for Zn_1-2MT3 might be explained by the formation of independent ZnS₄ cores in this stage that differ with respect to the formation of Zn_xCys_y clusters with an increased Zn(II) loading. The binding of the third Zn(II) ion to MT3 resulted in high sample heterogeneity due the co-existence of Zn_3-6MT3. Finally, the Zn₇MT3 protein showed a third type of behaviour. The fact that there were no free Cys residues might explain this phenomenon. Thus, this research identifies the major proteins responsible for zinc buffering in the cell.

The Expression Profile and Prognostic Significance of Metallothionein Genes in Colorectal Cancer

Colorectal cancer (CRC) is a heterogeneous disease resulting from the combined influence of many genetic factors. This complexity has caused the molecular characterization of CRC to remain uncharacterized, with a lack of clear gene markers associated with CRC and the prognosis of this disease. Thus, highly sensitive tumor markers for the detection of CRC are the most essential determinants of survival. In this study, we examined the simultaneous downregulation of the mRNA levels of six metallothionein (MT) genes in CRC cell lines and public CRC datasets for the first time. In addition, we detected downregulation of these six MT mRNAs’ levels in 30 pairs of tumor (T) and adjacent non-tumor (N) CRC specimens. In order to understand the potential prognostic relevance of these six MT genes and CRC, we presented a four-gene signature to evaluate the prognosis of CRC patients. Further discovery suggested that the four-gene signature (MT1F, MT1G, MT1L, and MT1X) predicted survival better than any combination of two-, three-, four-, five-, or six-gene models. In conclusion, this study is the first to report that simultaneous downregulation of six MT mRNAs’ levels in CRC patients, and their aberrant expression together, accurately predicted CRC patients’ outcomes.

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.

Metallothionein Genes are Highly Expressed in Malignant Astrocytomas and Associated with Patient Survival

Gliomas are heterogeneous, primary brain tumours that originate from glial cells. The main type of gliomas is astrocytomas. There are four grades (I-IV) of astrocytoma malignancy. Astrocytoma grade IV known as glioblastoma multiforme (GBM) is the most common and aggressive type of astrocytic gliomas. Metallothioneins (MT) are low molecular weight, cysteine rich proteins encoded by a family of metallothionein (MT) genes. MT genes play a crucial role in carcinogenesis of diverse malignancies. We proposed MT genes as prognostic markers for malignant astrocytoma. MT1A, MT1E, MT1X, MT2, MT3 gene expression was elevated in grade IV astrocytomas (glioblastomas) as compared to astrocytomas grade I-III. Statistically significant differences were reached for MT1A and MT2 genes (Mann-Whitney test, p < 0.05). High MT1A, MT1X, MT2, MT3 genes expression was associated with shorter patient survival (Log-rank test, p < 0.05). MT1A gene promoter methylation was decreased in glioblastoma (57.6%) while the gene was highly methylated in grade II-III astrocytoma (from 66.7% to 83.3%) and associated with better patient survival (p < 0.05). MT1A gene methylation showed a trend of being associated with higher mRNA expression level in astrocytomas. Increased MT genes expression in grade IV astrocytomas as compared to I-III grade astrocytomas could be associated with malignant tumour behaviour and progression.

Transcriptomic Landscape of Cisplatin-Resistant Neuroblastoma Cells

The efficiency of cisplatin (CDDP) is significantly hindered by the development of resistance during the treatment course. To gain a detailed understanding of the molecular mechanisms underlying the development of cisplatin resistance, we comparatively analyzed established a CDDP-resistant neuroblastoma cell line (UKF-NB-4CDDP) and its susceptible parental cells (UKF-NB-4). We verified increased chemoresistance of UKF-NB-4CDDP cells by analyzing the viability, induction of apoptosis and clonal efficiency. To shed more light on this phenomenon, we employed custom cDNA microarray (containing 2234 probes) to perform parallel transcriptomic profiling of RNA and identified that 139 genes were significantly up-regulated due to CDDP chemoresistance. The analyses of molecular pathways indicated that the top up-regulation scoring functions were response to stress, abiotic stimulus, regulation of metabolic process, apoptotic processes, regulation of cell proliferation, DNA repair or regulation of catalytic activity, which was also evidenced by analysis of molecular functions revealing up-regulation of genes encoding several proteins with a wide-spectrum of enzymatic activities. Functional analysis using lysosomotropic agents chloroquine and bafilomycin A1 validated their potential to re-sensitize UKF-NB-4CDDP cells to CDDP. Taken together, the identification of alterations in specific genes and pathways that contribute to CDDP chemoresistance may potentially lead to a renewed interest in the development of novel rational therapeutics and prognostic biomarkers for the management of CDDP-resistant neuroblastoma.

Mass spectrometric imaging of cysteine rich proteins in human skin

Looking insight pathological processes, metallothioneins (MTs) are considered to be potential biomarkers for monitoring of a development of various types of diseases, such as cancer. The early identification of the MTs in biological tissues could be important tool for the estimation of appropriate clinical therapy. Therefore, here we investigated the application of matrix assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) together with immunohistochemical analyses (IHC) using MT-1/2 antibody for MT detection in formalin-fixed paraffin-embedded (FFPE) biopsy specimens of human skin. Principal component analyses revealed differences in the peptide/protein profiles separating healthy skin from the carcinoma specimens. Statistically significant ion peaks at m/z 6038, 6300, 6676, and 7026 were more frequently detected in squamous cell carcinoma (SCC), basal cell carcinoma (BCC) and melanoma. Using IHC, we found that MT-1/2 was significantly higher in SCC and melanoma compared to healthy skin. Surprisingly, significantly low levels of MT-1/2 were found in BCC. On one side, the results indicate important role of MTs in melanoma occurrence and progression, as on the second side, there are hidden processes associated with MTs based on differences of the occurrence of the MS peaks, which could be associated with cycling of MTs isoforms.

Metallothionein and Superoxide Dismutase-Antioxidative Protein Status in Fullerene-Doxorubicin Delivery to MCF-7 Human Breast Cancer Cells

Doxorubicin (DOX) is one of the most frequently used anticancer drugs in breast cancer treatment. However, clinical applications of DOX are restricted, largely due to the fact that its action disturbs the pro/antioxidant balance in both cancerous and non-cancerous cells. The aim of this study was to investigate the influence of fullerene (C₆₀) in cell treatment by DOX on the proliferation of human breast cancer cells (MCF-7), concentration of metallothionein (MT) and superoxide dismutase (SOD), and SOD activity in these cells. The use of C₆₀ in complexes with DOX causes a change in the level of cell proliferation of about 5% more than when caused by DOX alone (from 60–65% to 70%). The use of C₆₀ as a DOX nanotransporter reduced the MT level increase induced by DOX. C₆₀ alone caused an increase of SOD1 concentration. On the other hand, it led to a decrease of SOD activity. C₆₀ in complex with DOX caused a decrease of the DOX-induced SOD activity level. Exposure of MCF-7 cells to DOX-C₆₀ complexes results in a decrease in viable cells and may become a new therapeutic approach to breast cancer. The effects of C₆₀ in complexes with DOX on MCF-7 cells included a decreased enzymatic (SOD activity) and nonenzymatic (MT) antioxidant status, thus indicating their prooxidant role in MCF-7 cells.

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.