Loss of metal transcription factor-1 suppresses tumor growth through enhanced matrix deposition

The Role of Zinc on Liver Fibrosis by Modulating ZIP14 Expression Throughout Epigenetic Regulatory Mechanisms

Zinc plays a pivotal role in tissue regeneration and maintenance being as a central cofactor in a plethora of enzymatic activities. Hypozincemia is commonly seen with chronic liver disease and is associated with an increased risk of liver fibrosis development and hepatocellular carcinoma. Previously favorable effects of zinc supplementation on liver fibrosis have been shown. However, the underlying mechanism of this effect is not elucidated. Liver fibrosis was induced in mice by using CCl4 injection, followed by treatment with zinc chloride (ZnCl2) both at fibrotic and sham groups, and their hepatocytes were isolated. Our results showed that the administration of ZnCl2 restored the depleted cytosolic zinc levels in the hepatocytes isolated from the fibrotic group. Also, alpha-smooth muscle actin (αSMA) expression in hepatocytes was decreased, indicating a reversal of the fibrotic process. Notably, ZIP14 expression significantly increased in the fibrotic group following ZnCl2 treatment, whereas in the sham group ZIP14 expression decreased. Chromatin immunoprecipitation (ChIP) experiments revealed an increased binding percentage of Metal-regulatory transcription factor 1 (MTF1) on ZIP14 promoter in the hepatocytes isolated from fibrotic mice compared to the sham group after ZnCl2 administration. In the same group, the binding percentage of the histone deacetylase HDAC4 on ZIP14 promoter decreased. Our results suggest that the ZnCl2 treatment ameliorates liver fibrosis by elevating intracellular zinc levels through MTF1-mediated regulation of ZIP14 expression and the reduction of ZIP14 deacetylation via HDAC4. The restoration of intracellular zinc concentrations and the modulation of ZIP14 expression by zinc orchestrated through MTF1 and HDAC4, appear to be essential determinants of the therapeutic response in hepatic fibrosis. These findings pave the way for potential novel interventions targeting zinc-related pathways for the treatment of liver fibrosis and associated conditions.

Deciphering the contributions of cuproptosis in the development of hypertrophic scar using single-cell analysis and machine learning techniques

Hypertrophic scar (HS) is a chronic inflammatory skin disease characterized by excessive deposition of extracellular matrix, but the exact mechanisms related to its formation remain unclear, making it difficult to treat. This study aimed to investigate the potential role of cuproptosis in the information of HS. To this end, we used single-cell sequencing and bulk transcriptome data, and screened for cuproptosis-related genes (CRGs) using differential gene analysis and machine learning algorithms (random forest and support vector machine). Through this process, we identified a group of genes, including ATP7A, ULK1, and MTF1, as novel therapeutic targets for HS. Furthermore, quantitative real-time polymerase chain reaction (qRT-PCR) was conducted to confirm the mRNA expression of ATP7A, ULK1, and MTF1 in both HS and normal skin (NS) tissues. We also constructed a diagnostic model for HS and analyzed the immune infiltration characteristics. Additionally, we used the expression profiles of CRGs to perform subgroup analysis of HS. We focused mainly on fibroblasts in the transcriptional profile at single-cell resolution. By calculating the cuproptosis activity of each fibroblast, we found that cuproptosis activity of normal skin fibroblasts increased, providing further insights into the pathogenesis of HS. We also analyzed the cell communication network and transcription factor regulatory network activity, and found the existence of a fibroblast-centered communication regulation network in HS, where cuproptosis activity in fibroblasts affects intercellular communication. Using transcription factor regulatory activity network analysis, we obtained highly active transcription factors, and correlation analysis with CRGs suggested that CRGs may serve as potential target genes for transcription factors. Overall, our study provides new insights into the pathophysiological mechanisms of HS, which may inspire new ideas for the diagnosis and treatment.

Cuproptosis-related gene signature stratifies lower-grade glioma patients and predicts immune characteristics

Cuproptosis is the most recently discovered type of regulated cell death and is mediated by copper ions. Studies show that cuproptosis plays a significant role in cancer development and progression. Lower-grade gliomas (LGGs) are slow-growing brain tumors. The majority of LGGs progress to high-grade glioma, which makes it difficult to predict the prognosis. However, the prognostic value of cuproptosis-related genes (CRGs) in LGG needs to be further explored. mRNA expression profiles and clinical data of LGG patients were collected from public sources for this study. Univariate Cox regression analysis and the least absolute shrinkage and selection operator (LASSO) Cox regression model were used to build a multigene signature that could divide patients into different risk groups. The differences in clinical pathological characteristics, immune infiltration characteristics, and mutation status were evaluated in risk subgroups. In addition, drug sensitivity and immune checkpoint scores were estimated in risk subgroups to provide LGG patients with precision medication. We found that all CRGs were differentially expressed in LGG and normal tissues. Patients were divided into high- and low-risk groups based on the risk score of the CRG signature. Patients in the high-risk group had a considerably lower overall survival rate than those in the low-risk group. According to functional analysis, pathways related to the immune system were enriched, and the immune state differed across the two risk groups. Immune characteristic analysis showed that the immune cell proportion and immune scores were different in the different groups. High-risk group was characterized by low sensitivity to chemotherapy but high sensitivity to immune checkpoint inhibitors. The current study revealed that the novel CRG signature was related to the prognosis, clinicopathological features, immune characteristics, and treatment perference of LGG.

Crocin inhibits the activation of mouse hepatic stellate cells via the lnc-LFAR1/MTF-1/GDNF pathway

Crocin is the main monomer of saffron, which is a momentous component of traditional Chinese medicine Lang Qing A Ta. Here, we tried to probe into the role of crocin in liver fibrosis. Hematoxylin-eosin staining and Sirius Red staining were used to observe the pathological changes of liver tissues. After hepatic stellate cells (HSCs) were isolated from liver tissues, lnc-LFAR1, MTF-1, GDNF, and α-SMA expressions were detected by qRT-PCR and western blot. Immunohistochemistry and immunofluorescence were used to detect α-SMA expression. Chromatin immunoprecipitation was used to analyze the binding of MTF-1 to the GDNF promoter. Moreover, the dual-luciferase reporter gene, RNA pull-down, and RNA immunoprecipitation were used to clarify the interaction between MTF-1 and GDNF, lnc-LFAR1 and MTF-1. The degree of liver fibrosis was more severe in the mice from the liver fibrosis model, while the liver fibrosis was alleviated by the injection of crocin. lnc-LFAR1, GDNF, and α-SMA were up-regulated, and MTF-1 was down-regulated in liver fibrosis tissues and cells, while these trends were reversed after the injection of crocin. Besides, lnc-LFAR1 negatively regulated MTF-1 expression, and positively regulated GDNF and α-SMA expressions, and MTF-1 was enriched in the promoter region of GDNF. Furthermore, the cellular direct interactions between MTF-1 and GDNF, lnc-LFAR1 and MTF-1 were verified. In vivo experiments confirmed the relief of crocin on liver fibrosis. Our research expounded that crocin restrained the activation of HSCs through the lnc-LFAR1/MTF-1/GDNF axis, thereby ameliorating liver fibrosis.

lncRNA LINC00665 Stabilized by TAF15 Impeded the Malignant Biological Behaviors of Glioma Cells via STAU1-Mediated mRNA Degradation

Glioma is a brain cancer characterized by strong invasiveness with limited treatment options and poor prognosis. Recently, dysregulation of long non-coding RNAs (lncRNAs) has emerged as an important component in cellular processes and tumorigenesis. In this study, we demonstrated that TATA-box binding protein associated factor 15 (TAF15) and long intergenic non-protein coding RNA 665 (LINC00665) were both downregulated in glioma tissues and cells. TAF15 overexpression enhanced the stability of LINC00665, inhibiting malignant biological behaviors of glioma cells. Both metal regulatory transcription factor 1 (MTF1) and YY2 transcription factor (YY2) showed high expression levels in glioma tissues and cells, and their knockdown inhibited malignant progression. Mechanistically, overexpression of LINC00665 was confirmed to destabilize MTF1 and YY2 mRNA by interacting with STAU1, and knockdown of STAU1 could rescue the MTF1 and YY2 mRNA degradation caused by LINC00665 overexpression. G₂ and S-phase expressed 1 (GTSE1) was identified as an oncogene in glioma, and knockdown of MTF1 or YY2 decreased the mRNA and protein expression levels of GTSE1 through direct binding to the GTSE1 promoter region. Our study highlights a key role of the TAF15/LINC00665/MTF1(YY2)/GTSE1 axis in modulating the malignant biological behaviors of glioma cells, suggesting novel mechanisms by which lncRNAs affect STAU1-mediated mRNA stability, which can inform new molecular therapies for glioma.

The phosphoinositide 3-kinase pathway and glycogen synthase kinase-3 positively regulate the activity of metal-responsive transcription factor-1 in response to zinc ions

Metal-responsive transcription factor-1 (MTF-1) is a metal-regulatory transcription factor essential for induction of the genes encoding metallothioneins (MTs) in response to transition metal ions. Activation of MTF-1 is dependent on the interaction of zinc with the zinc fingers of the protein. In addition, phosphorylation is essential for MTF-1 transactivation. We previously showed that inhibition of phosphoinositide 3-kinase (PI3K) abrogated Mt expression and metal-induced MTF-1 activation in human hepatocellular carcinoma (HCC) HepG2 and mouse L cells, thus showing that the PI3K signaling pathway positively regulates MTF-1 activity and Mt gene expression. However, it has also been reported that inhibition of PI3K has no significant effects on Mt expression in immortalized epithelial cells and increases Mt expression in HCC cells. To further characterize the role of the PI3K pathway on the activity of MTF-1, transfection experiments were performed in HEK293 and HepG2 cells in presence of glycogen synthase kinase-3 (GSK-3), mTOR-C1, and mTOR-C2 inhibitors, as well as of siRNAs targeting Phosphatase and TENsin homolog (PTEN). We showed that inhibition of the mTOR-C2 complex inhibits the activity of MTF-1 in HepG2 and HEK293 cells, while inhibition of the mTOR-C1 complex or of PTEN stimulates MTF-1 activity in HEK293 cells. These results confirm that the PI3K pathway positively regulates MTF-1 activity. Finally, we showed that GSK-3 is required for MTF-1 activation in response to zinc ions.

SOCS1 inhibits migration and invasion of prostate cancer cells, attenuates tumor growth and modulates the tumor stroma

BACKGROUND

The suppressor of cytokine signaling 1 (SOCS1) gene is repressed in prostate cancer (PCa) by epigenetic silencing and microRNA miR30d. Increased expression of the SOCS1-targeting miR30d correlates with higher biochemical recurrence, suggesting a tumor suppressor role of SOCS1 in PCa, but the underlying mechanisms are unclear. We have shown that SOCS1 inhibits MET receptor kinase signaling, a key oncogenic pathway in cancer progression. Here we evaluated the role of SOCS1 in attenuating MET signaling in PCa cells and tumor growth in vivo.

METHODS

MET-overexpressing human DU145 and PC3 PCa cell lines were stably transduced with SOCS1, and their growth, migration and invasion of collagen matrix were evaluated in vitro. Cells expressing SOCS1 or the control vector were evaluated for tumor growth in NOD.scid.gamma mice as xenograft or orthotopic tumors.

RESULTS

HGF-induced MET signaling was attenuated in SOCS1-expressing DU145 and PC3 cells. Compared with vector control cells, SOCS1-expressing cells showed reduced proliferation and impaired migration following HGF stimulation. DU145 and PC3 cells showed marked ability to invade the collagen matrix following HGF stimulation and this was attenuated by SOCS1. As xenografts, SOCS1-expressing PCa cells showed significantly reduced tumor growth compared with vector control cells. In the orthotopic tumor model, SOCS1 reduced the growth of primary tumors and metastatic spread. Intriguingly, the SOCS1-expressing DU145 and PC3 tumors showed increased collagen deposition, associated with increased frequency of myofibroblasts.

CONCLUSIONS

Our findings support the tumor suppressor role of SOCS1 in PCa and suggest that attenuation of MET signaling is one of the underlying mechanisms. SOCS1 in PCa cells also appears to prevent the tumor-promoting functions of cancer-associated fibroblasts.

Ras Transformation Overrides a Proliferation Defect Induced by Tpm3.1 Knockout

Extensive re-organisation of the actin cytoskeleton and changes in the expression of its binding proteins is a characteristic feature of cancer cells. Previously we have shown that the tropomyosin isoform Tpm3.1, an integral component of the actin cytoskeleton in tumor cells, is required for tumor cell survival. Our objective was to determine whether cancer cells devoid of Tpm3.1 would evade the tumorgenic effects induced by H-Ras transformation. The tropomyosin isoform (Tpm) expression profile of a range of cancer cell lines (21) demonstrates that Tpm3.1 is one of the most broadly expressed Tpm isoform. Consequently, the contribution of Tpm3.1 to the transformation process was functionally evaluated. Primary embryonic fibroblasts isolated from wild type (WT) and Tpm3.1 knockout (KO) mice were transduced with retroviral vectors expressing SV40 large T antigen and an oncogenic allele of the H-Ras gene, H-RasV12, to generate immortalized and transformed WT and KO MEFs respectively. We show that Tpm3.1 is required for growth factor-independent proliferation in the SV40 large T antigen immortalized MEFs, but this requirement is overcome by H-Ras transformation. Consistent with those findings, we found that Tpm3.1 was not required for anchorage independent growth or growth of H-Ras-driven tumors in a mouse model. Finally, we show that pERK and Importin 7 protein interactions are significantly decreased in the SV40 large T antigen immortalized KO MEFs but not in the H-Ras transformed KO cells, relative to control MEFs. The data demonstrate that H-Ras transformation overrides a requirement for Tpm3.1 in growth factor-independent proliferation of immortalized MEFs. We propose that in the SV40 large T antigen immortalized MEFs, Tpm3.1 is partly responsible for the efficient interaction between pERK and Imp7 resulting in cell proliferation, but this is overidden by Ras transformation.

Emerging pathogenic mechanisms in human myxomatous mitral valve: lessons from past and novel data

INTRODUCTION

Myxomatous mitral valve is one of the most common heart valves diseases in human and has been well characterized at a functional and morphological level. Diseased valves are thickened as a result of extracellular matrix remodeling and proteoglycans accumulation accompanied by the disruption of the stratified structures of the leaflets.

METHODS

Global transcriptomic analysis was used as a start-up to investigate potential pathogenic mechanisms involved in the development of the human idiopathic myxomatous mitral valve, which have been elusive for many years.

RESULTS

These prospective analyses have highlighted the potential role of apparently unrelated molecules in myxomatous mitral valve such as members of the transforming growth factor-β superfamily, aggrecanases of the "a disintegrin and metalloprotease with thrombospondin repeats I" family, and a weakening of the protection against oxidative stress. We have integrated, in this review, recent transcriptomic data from our laboratory [A. Hulin, C.F. Deroanne, C.A. Lambert, B. Dumont, V. Castronovo, J.O. Defraigne, et al. Metallothionein-dependent up-regulation of TGF-beta2 participates in the remodelling of the myxomatous mitral valve. Cardiovasc Res 2012;93:480-489] and from the publication of Sainger et al. [R. Sainger, J.B. Grau, E. Branchetti, P. Poggio, W.F. Seefried, B.C. Field, et al. Human myxomatous mitral valve prolapse: role of bone morphogenetic protein 4 in valvular interstitial cell activation. J Cell Physiol 2012;227:2595-2604] with existing literature and information issued from the study of monogenic syndromes and animal models.

CONCLUSION

Understanding cellular alterations and molecular mechanisms involved in myxomatous mitral valve should help at identifying relevant targets for future effective pharmacological therapy to prevent or reduce its progression.

The taste of heavy metals: gene regulation by MTF-1

The metal-responsive transcription factor-1 (MTF-1, also termed MRE-binding transcription factor-1 or metal regulatory transcription factor-1) is a pluripotent transcriptional regulator involved in cellular adaptation to various stress conditions, primarily exposure to heavy metals but also to hypoxia or oxidative stress. MTF-1 is evolutionarily conserved from insects to humans and is the main activator of metallothionein genes, which encode small cysteine-rich proteins that can scavenge toxic heavy metals and free radicals. MTF-1 has been suggested to act as an intracellular metal sensor but evidence for direct metal sensing was scarce. Here we review recent advances in our understanding of MTF-1 regulation with a focus on the mechanism underlying heavy metal responsiveness and transcriptional activation mediated by mammalian or Drosophila MTF-1. This article is part of a Special Issue entitled: Cell Biology of Metals.

Zinc balance is critical for NFI-C mediated regulation of odontoblast differentiation

Zinc is trace element essential for diverse metabolic and cellular signaling pathways for the growth, development, and maintenance. Zinc deficiency is involved in bone malformations and oral disease. Mice deficient in zinc transporter Zip13 show connective tissue and skeletal disorders, abnormal incisor teeth, and reduced root dentin formation in the molar teeth and share a morphologically similar phenotype to nuclear factor I-C (NFI-C)-deficient mice. However, the precise function of zinc in NFI-C signaling-mediated odontoblast differentiation and dentin formation remains unclear. Here, we show that zinc stimulated the expression of metal transcription factor-1, but decreased NFI-C expression in odontoblastic MDPC-23 cells. Zinc also enhanced the phosphorylation of Smad2/3 (p-Smad2/3) and increased the binding efficiency of NFI-C and p-Smad2/3 in the cytoplasm. In contrast, zinc deficiency resulted in the accumulation of NFI-C into nucleus. Consequently, NFI-C had the biologic properties of a transcription factor, including DNA binding affinity for metallothionein-1 and the dentin sialophosphoprotein (DSPP) promoter, and transcriptional activation of the DSPP gene. Furthermore, zinc deficiency condition promoted DSPP expression in odontoblasts and dentin mineralization, while zinc sufficiency condition decreased DSPP expression and slightly delayed dentin mineralization. These data suggest that zinc equilibrium is required for odontoblast differentiation and dentin formation during dentinogenesis through the nuclear accumulation and modulation of NFI-C.

Zinc-induced Dnmt1 expression involves antagonism between MTF-1 and nuclear receptor SHP

Dnmt1 is frequently overexpressed in cancers, which contributes significantly to cancer-associated epigenetic silencing of tumor suppressor genes. However, the mechanism of Dnmt1 overexpression remains elusive. Herein, we elucidate a pathway through which nuclear receptor SHP inhibits zinc-dependent induction of Dnmt1 by antagonizing metal-responsive transcription factor-1 (MTF-1). Zinc treatment induces Dnmt1 transcription by increasing the occupancy of MTF-1 on the Dnmt1 promoter while decreasing SHP expression. SHP in turn represses MTF-1 expression and abolishes zinc-mediated changes in the chromatin configuration of the Dnmt1 promoter. Dnmt1 expression is increased in SHP-knockout (sko) mice but decreased in SHP-transgenic (stg) mice. In human hepatocellular carcinoma (HCC), increased DNMT1 expression is negatively correlated with SHP levels. Our study provides a molecular explanation for increased Dnmt1 expression in HCC and highlights SHP as a potential therapeutic target.

Metallothionein-dependent up-regulation of TGF-β2 participates in the remodelling of the myxomatous mitral valve

AIMS

Although an excessive extracellular matrix remodelling has been well described in myxomatous mitral valve (MMV), the underlying pathogenic mechanisms remain largely unknown. Our goal was to identify dysregulated genes in human MMV and then to evaluate their functional role in the progression of the disease.

METHODS AND RESULTS

Dysregulated genes were investigated by transcriptomic, immunohistochemistry, and western blot analyses of the P2 segment collected from human idiopathic MMV during valvuloplasty (n = 23) and from healthy control valves (n = 17). The most striking results showed a decreased expression of two families of genes: the metallothioneins-1 and -2 (MT1/2) and members of the ADAMTS. The mechanistic consequences of the reduced level of MT1/2 were evaluated by silencing their expression in normal valvular interstitial cells (VICs) cultures. The knock-down of MT1/2 resulted in the up-regulation of transforming growth factor-beta 2 (TGF-β2). Most importantly, TGF-β2 was also found significantly increased in MMV tissues. The activation of VICs in vitro by TGF-β2 induced a down-regulation of ADAMTS-1 and an accumulation of versican as observed in human MMV.

CONCLUSION

Our studies demonstrate for the first time that MMV are characterized by reduced levels of MT1/2 accompanied by an up-regulation of TGF-β2. In turn, increased TGF-β2 signalling induces down-regulation of aggrecanases and up-regulation of versican, two co-operating processes that potentially participate in the development of the pathology.

Hypoxia acts through multiple signaling pathways to induce metallothionein transactivation by the metal-responsive transcription factor-1 (MTF-1)

Metal-responsive transcription factor-1 (MTF-1) is essential for the induction of genes encoding metallothionein by metals and hypoxia. Here, we studied the mechanism controlling the activation of MTF-1 by hypoxia. Hypoxia activation of Mt gene transcription is dependent on the presence of metal regulatory elements (MREs) in the promoter of Mt genes. We showed that MREa and MREd are the main elements controlling mouse Mt-1 gene induction by hypoxia. Transfection experiments in Mtf-1-null cells showed that MTF-1 is essential for induction by hypoxia. Chromatin immunoprecipitation analysis showed that MTF-1 DNA-binding activity was strongly enhanced in the presence of zinc but not by hypoxia. Notably, hypoxia inducible factor- (HIF) 1α was recruited to the Mt-1 promoter in response to hypoxia but not to zinc. MTF-1 activation was inhibited by PKC, JNK, and PI3K inhibitors and by the electron transport chain inhibitors rotenone and myxothiazol, but not by the antioxidant N-acetylcysteine. We showed that prolyl-hydroxylase inhibitors can activate MTF-1, but this activation requires the presence of HIF-1α. Finally, HIF-dependent transcription is enhanced in the presence of MTF-1 and induction of an MRE promoter is stimulated by HIF-1α, thus indicating cooperation between these 2 factors. However, coimmunoprecipitation experiments did not suggest direct interaction between MTF-1 and HIF-1α.

The zinc-sensing transcription factor MTF-1 mediates zinc-induced epigenetic changes in chromatin of the mouse metallothionein-I promoter

Metallothionein (MT) is a small, cysteine-rich protein active in zinc homeostasis, cadmium detoxification, and protection against reactive oxygen species. Mouse MT-I gene transcription is regulated by metal response element-binding transcription factor-1 (MTF-1), which is recruited to the promoter by zinc. We examined alterations in the chromatin structure of the MT-I promoter associated with enhanced transcriptional activation. MTF-1 proved essential for zinc-induced epigenetic changes in the MT-I promoter. Chromatin immunoprecipitation assays demonstrated that zinc treatment rapidly decreased Lys⁴-trimethylated and Lys⁹-acetylated histone H3 in the promoter and decreased total histone H3 but not histone H3.3. Micrococcal nuclease sensitivity of the MT-I promoter was increased by zinc. Thus, the chromatin structure in the promoter may be locally disrupted by zinc-induced nucleosome removal. Without MTF-1 these changes were not observed, and an MTF-1 deletion mutant recruited to the MT-I promoter by zinc that did not recruit the coactivator p300 or activate MT-I transcription did not affect histone H3 in the MT-I promoter in response to zinc. Interleukin-6, which induces MT-I transcription independently of MTF-1, did not reduce histone H3 levels in the promoter. Rapid disruption of nucleosome structure at the MT-I promoter is mediated by zinc-responsive recruitment of an active MTF-1-coactivator complex.

Induction of FPN1 transcription by MTF-1 reveals a role for ferroportin in transition metal efflux

Ferroportin (Fpn) is the only known iron exporter in vertebrate cells and plays a critical role in iron homeostasis regulating cytosolic iron levels and exporting iron to plasma. Ferroportin1 (FPN1) expression can be transcriptionally regulated by iron as well as other transition metals. Fpn can also be posttranslationally regulated by hepcidin-mediated internalization and degradation. We demonstrate that zinc and cadmium induce FPN1 transcription through the action of Metal Transcription Factor-1 (MTF-1). These transition metals induce MTF-1 translocation into the nucleus. Zinc leads to MTF-1 binding to the FPN1 promoter, while iron does not. Silencing of MTF-1 reduces FPN1 transcription in response to zinc but not in response to iron. The mouse FPN1 promoter contains 2 MTF-1 binding sites and mutation of those sites affects the zinc and cadmium-dependent expression of a FPN1 promoter reporter construct. We demonstrate that Fpn can transport zinc and can protect zinc sensitive cells from high zinc toxicity.

The metal-responsive transcription factor-1 protein is elevated in human tumors

We previously identified metal-responsive transcription factor-1 (MTF-1) as a positive contributor to mouse fibrosarcoma growth through effects on cell survival, proliferation, tumor angiogenesis and extracellular matrix remodeling. In the present study, we investigated MTF-1 protein expression in human tissues by specific immunostaining of both normal and tumor tissue samples. Immunohistochemical (IHC) staining of a human tissue microarray (TMA), using a unique anti-human MTF-1 antibody, indicated constitutive MTF-1 expression in most normal tissues, with liver and testis displaying comparatively high levels of expression. Nevertheless, MTF-1 protein levels were found to be significantly elevated in diverse human tumor types, including breast, lung and cervical carcinomas. IHC analysis of a separate panel of full-size tissue sections of human breast cancers, including tumor and normal adjacent, surrounding tissue, confirmed and extended the results of the TMA analysis. Taken with our previous findings, this new study suggests a role for MTF-1 in human tumor development, growth or spread. Moreover, the study suggests that MTF-1 could be a novel therapeutic target that offers the opportunity to manipulate metal or redox homeostasis in tumor cells.

Metal transcription factor-1 is involved in hypoxia-dependent regulation of placenta growth factor in trophoblast-derived cells

Placenta growth factor (PlGF) is a placental angiogenic factor. Metal-responsive transcription factor (MTF)-1 was reported to take part in the hypoxic induction of PlGF in RAS-transformed mouse fibroblasts. We contrarily showed that PlGF mRNA and protein levels decreased under hypoxia in a choriocarcinoma BeWo cell line derived from trophoblast. In this report, we examined whether hypoxia-dependent regulation of the PlGF gene in these cells also depends on MTF-1. We analyzed the effect of hypoxia on MTF-1 expression, and it was revealed to be decreased. Moreover, MTF-1 small interfering RNA treatment decreased PlGF mRNA level. To investigate the transcription of PlGF under hypoxia, we cloned promoter region of the human PlGF. Promoter deletion analysis suggested that triple repeats of metal-responsive element located between -511 and -468 bp in the promoter are important for the hypoxic regulation of PlGF. Treatment with MTF-1 small interfering RNA resulted in the significant decreased luciferase activity in PlGF reporter constructs. Chromatin immunoprecipitation showed the binding of the MTF-1 protein to the promoter region. We examined MTF-1 immunoreactivity in trophoblasts of term placental tissue from patients with normal pregnancies and preeclampsia, which represents a condition of placental hypoxia. Immunoreactivity of the MTF-1 protein was decreased in placentas from pregnant women with preeclampsia when compared with those from normal pregnant women. Taken together, these findings suggest that MTF-1 is involved in hypoxia-dependent regulation of PlGF in trophoblast-derived cells.

Zinc-controlled gene expression by metal-regulatory transcription factor 1 (MTF1) in a model vertebrate, the zebrafish

There is a growing appreciation for the diverse roles of zinc as a signalling substance in biological systems. Zinc signalling is brought about by changes in intracellular concentrations of labile Zn(2+), resulting in both genomic and non-genomic effects. The genomic responses are largely mediated by MTF1 (metal-regulatory transcription factor 1), which binds to MREs (metal-response elements) in the 5' regulatory region of genes in response to zinc. Treatment of cultured zebrafish ZF4 cells with siRNA (small interfering RNA) to MTF1 changed the transcriptional response to zinc for over 1000 genes, as assessed using an oligonucleotide microarray. From this primary list of MTF1-dependent genes, we identified a relatively small cohort that showed a configuration of MREs in their 5' regulatory regions similar to known MTF1 targets. This group showed a remarkable dominance of nucleic acid-binding proteins and other proteins involved in embryological development, implicating MTF1 as a master regulator of gene expression during development.

Metallothionein induction by hypoxia involves cooperative interactions between metal-responsive transcription factor-1 and hypoxia-inducible transcription factor-1alpha

Mammalian metallothionein (MT) genes are transcriptionally activated by the essential metal zinc as well as by environmental stresses, including toxic metal overload and redox fluctuations. In addition to playing a key role in zinc homeostasis, MT proteins can protect against metal- and oxidant-induced cellular damage, and may participate in other fundamental physiologic and pathologic processes such as cell survival, proliferation, and neoplasia. Previously, our group reported a requirement for metal-responsive transcription factor-1 (MTF-1) in hypoxia-induced transcription of mouse MT-I and human MT-IIA genes. Here, we provide evidence that the protumorigenic hypoxia-inducible transcription factor-1alpha (HIF-1alpha) is essential for induction of MT-1 by hypoxia, but not zinc. Chromatin immunoprecipitation assays revealed that MTF-1 and HIF-1alpha are both recruited to the mouse MT-I promoter in response to hypoxia, but not zinc. In the absence of HIF-1alpha, MTF-1 is recruited to the MT-I promoter but fails to activate MT-I gene expression in response to hypoxia. Thus, HIF-1alpha seems to function as a coactivator of MT-I gene transcription by interacting with MTF-1 during hypoxia. Coimmunoprecipitation studies suggest interaction between MTF-1 and HIF-1alpha, either directly or as mediated by other factors. It is proposed that association of these important transcription factors in a multiprotein complex represents a common strategy to control unique sets of hypoxia-inducible genes in both normal and diseased tissue.

[Molecular mechanism involved in chromium(VI) toxicity]

Chromium exists in many different oxidation states in the environment, Cr(VI) and Cr(III) being the most stable forms. Chromium has been known for over 100 years to be a human carcinogen. The greatest risk of cancer from chromium exposure is associated with Cr(VI). Cr(VI) enters cells via the sulfate anion transporter system and is reduced to intermediate oxidation states, such as Cr(V) and Cr(IV), in the process of forming stable Cr(III) forms. It is known that Cr(VI) affects expression of various genes. Metal responsive element-binding transcription factor-1 (MTF-1) is involved in sensing heavy metal load and the induced transcription of several protective genes, including metallothionein (MT)-I, MT-II, zinc transporter-1, and gamma-glutamylcysteine synthetase. Cr(VI) inhibits zinc-induced MT transcription via modifying transactivation potential of MTF-1. However, the molecular mechanism for the Cr(VI)-mediated inhibition of MTF-1 has not been fully elucidated. In this review, I briefly summarize the previous studies and discuss the current status of research on Cr(VI) toxicity and Cr(VI)-mediated inhibition against transcription.

Role of metal-responsive transcription factor-1 (MTF-1) in EGF-dependent DNA synthesis in primary hepatocytes

Metal-responsive transcription factor-1 (MTF-1), which is involved in sensing heavy metal load, induces the transcription of several protective genes. The mouse Mtf-1 gene is essential, and Mtf-1(-/-) embryos die from liver degeneration. We showed that DNA synthesis induced in hepatocytes by epidermal growth factor (EGF) was delayed by inhibition of MTF-1. To inhibit MTF-1 activity, MTFDeltaC, a C-terminal deletion mutant of MTF-1, was expressed by infection with the virus Ad5MTFDeltaC. Lactate dehydrogenase (LDH) release and/or caspase-3/7 activation was not observed under our experimental conditions. The inhibitory effect of MTFDeltaC on EGF-dependent DNA synthesis in hepatocytes was not eliminated by zinc addition. EGF-dependent extracellular signal-related kinase (ERK) phosphorylation, an essential reaction for EGF-dependent DNA synthesis, was decreased in MTF-1-inhibited hepatocytes. Moreover, decrease of ERK phosphorylation was observed by using siRNA in MTF-1-downregulated hepatocytes. These results indicate that MTF-1 is particularly important for proper hepatocyte proliferation. This is the first report to suggest the function of MTF-1 in the ERK pathway.

The metal-responsive transcription factor-1 contributes to HIF-1 activation during hypoxic stress

Hypoxia-inducible factor-1 (HIF-1), the major transcriptional regulator of the mammalian cellular response to low oxygen (hypoxia), is embedded within a complex network of signaling pathways. We have been investigating the importance of another stress-responsive transcription factor, MTF-1, for the adaptation of cells to hypoxia. This article reports that MTF-1 plays a central role in hypoxic cells by contributing to HIF-1 activity. Loss of MTF-1 in transformed Mtf1 null mouse embryonic fibroblasts (MEFs) results in an attenuation of nuclear HIF-1alpha protein accumulation, HIF-1 transcriptional activity, and expression of an established HIF-1 target gene, glucose transporter-1 (Glut1). Mtf1 null (Mtf1 KO) MEFs also have constitutively higher levels of both glutathione (GSH) and the rate-limiting enzyme involved in GSH synthesis--glutamate cysteine ligase catalytic subunit--than wild type cells. The altered cellular redox state arising from increased GSH may perturb oxygen-sensing mechanisms in hypoxic Mtf1 KO cells and decrease the accumulation of HIF-1alpha protein. Together, these novel findings define a role for MTF-1 in the regulation of HIF-1 activity.

Two major branches of anti-cadmium defense in the mouse: MTF-1/metallothioneins and glutathione

Metal-responsive transcription factor 1 (MTF-1) regulates expression of its target genes in response to various stress conditions, notably heavy metal load, via binding to metal response elements (MREs) in the respective enhancer/promoter regions. Furthermore, it serves a vital function in embryonic liver development. However, targeted deletion of Mtf1 in the liver after birth is no longer lethal. For this study, Mtf1 conditional knockout mice and control littermates were both mock- or cadmium-treated and liver-specific transcription was analyzed. Besides the well-characterized metallothionein genes, several new MTF-1 target genes with MRE motifs in the promoter region emerged. MTF-1 is required for the basal expression of selenoprotein W, muscle 1 gene (Sepw1) that encodes a glutathione-binding and putative antioxidant protein, supporting a role of MTF-1 in the oxidative stress response. Furthermore, MTF-1 mediates the cadmium-induced expression of N-myc downstream regulated gene 1 (Ndrg1), which is induced by several stress conditions and is overexpressed in many cancers. MTF-1 is also involved in the cadmium response of cysteine- and glycine-rich protein 1 gene (Csrp1), which is implicated in cytoskeletal organization. In contrast, MTF-1 represses the basal expression of Slc39a10, a putative zinc transporter. In a pathway independent of MTF-1, cadmium also induced the transcription of genes involved in the synthesis and regeneration of glutathione, a cadmium-binding antioxidant. These data provide strong evidence for two major branches of cellular anti-cadmium defense, one via MTF-1 and its target genes, notably metallothioneins, the other via glutathione, with an apparent overlap in selenoprotein W.

NF-kappaB contributes to transcription of placenta growth factor and interacts with metal responsive transcription factor-1 in hypoxic human cells

Placenta growth factor (PlGF) is a member of the vascular endothelial growth factor family of cytokines that control vascular and lymphatic endothelium development. It has been implicated in promoting angiogenesis in pathological conditions via signaling to vascular endothelial growth factor receptor-1. PlGF expression is induced by hypoxia and proinflammatory stimuli. Metal responsive transcription factor 1 (MTF-1) was shown to take part in the hypoxic induction of PlGF in Ras-transformed mouse embryonic fibroblasts. Here we report that PlGF expression is also controlled by NF-kappaB. We identified several putative binding sites for NF-kappaB in the PlGF promoter/enhancer region by sequence analyses, and show binding and transcriptional activity of NF-kappaB p65 at these sites. Expression of NF-kappaB p65 from a plasmid vector in HEK293 cells caused a substantial increase of PlGF transcript levels. Furthermore, we found that hypoxic conditions induce nuclear translocation and interaction of MTF-1 and NF-kappaB p65 proteins, suggesting a role for this complex in hypoxia-induced transcription of PlGF.