Activation of the Metallothionein-I Gene Promoter in Response to Cadmium and USFin Vitro

Datta, Prasun K.; Jacob, Samson T.

doi:10.1006/bbrc.1996.5655

Cited by 19 publications

(10 citation statements)

References 25 publications

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“…There is a paucity of information regarding the molecular mechanism of MT transcriptional activation by other transition metals and environmental stressors. A combination of mutational and transcriptional analyses clearly show that cadmium activation of MT transcription is dependent on MTF-1 and MREs (18,29). MTF-1 binding to MREs and the activation of MT transcription is also induced by oxidative stress (25,30).…”

Section: Metallothioneins (Mt)mentioning

confidence: 95%

Regulation of Metallothionein Transcription by the Metal-responsive Transcription Factor MTF-1

Saydam¹,

Adams²,

Steiner³

et al. 2002

Journal of Biological Chemistry

153

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Every living organism must detoxify nonessential metals and carefully control the intracellular concentration of essential metals. Metallothioneins, which are small, cysteine-rich, metal-binding proteins, play an important role in these processes. In addition, the transcription of their cognate genes is activated in response to metal exposure. The zinc finger transcription factor MTF-1 plays a central role in the metal-inducible transcriptional activation of metallothionein and other genes involved in metal homeostasis and cellular stress response. Here we report that the phosphorylation of MTF-1 plays a critical role in its activation by zinc and cadmium. Inhibitor studies indicate that multiple kinases and signal transduction cascades, including those mediated by protein kinase C, tyrosine kinase, and casein kinase II, are essential for zinc-and cadmium-inducible transcriptional activation. In addition, calcium signaling is also involved in regulating metal-activated transcription. In contrast, cAMP-dependent protein kinase may not be directly involved in the metal response. Contrary to what has been reported for other transcription factors, inhibition of transcriptional activation does not impair the binding of MTF-1 to DNA, suggesting that phosphorylation is not regulating DNA binding. Elevated phosphorylation of MTF-1 is observed under condition of protein kinase C inhibition, suggesting that specific dephosphorylation of this transcription factor contributes to its activation. Metallothioneins (MT)1 are a family of evolutionarily conserved, low molecular weight, cysteine-rich metal-binding proteins (1, 2). The precise physiological function of MT has not been fully elucidated. However, proposed roles include (a) participation in maintaining the homeostasis of essential transition metals; (b) sequestration of toxic metals, such as cadmium and mercury; and (c) protection against intracellular oxidative damage (1-4).Metallothionein expression is primarily controlled at the level of transcription. Transcription can be induced by a variety of physiological agents and environmental stressors such as transition metals, glucocorticoids, cAMP, phorbol esters, alkylating agents, oxidizing agents, ultraviolet and ionizing radiation, and hypoxia (1, 5-12). The activation of MT transcription by transition metals is mediated by regulatory elements, designated metal-responsive elements (MREs). MREs contain a 7-bp core sequence (TGCRCNC) and are present in multiple copies in the promoter/enhancer regions of almost all metalinducible MTs (13,14). Inducible transcription is mediated by a variety of other regulatory elements located in promoter/ enhancer regions of MT genes, which include glucocorticoid response elements, cAMP response elements, AP-1 elements, and antioxidant response elements (1,5,15,16).Metal-inducible MT transcription is regulated by the transcription factor MTF-1 (metal transcription factor-1) (17, 18). MTF-1 is an evolutionarily conserved protein that specifically binds to MREs and has been characterize...

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Section: Metallothioneins (Mt)mentioning

confidence: 95%

Regulation of Metallothionein Transcription by the Metal-responsive Transcription Factor MTF-1

Saydam¹,

Adams²,

Steiner³

et al. 2002

Journal of Biological Chemistry

153

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“…MREd is the strongest, MREa and MREc are 50 -80% weaker, MREb is very weak, and MREe is apparently non-functional (14). In addition to MTF-1, several other proteins interact with the mouse MT-1 promoter, including USF-1, USF-2 (15)(16)(17)(18)(19), Sp1 (9, 19 -21), c-Fos (19), and c-Jun (9). However, the mechanism by which these factors contribute to MT gene expression in not known.…”

Section: Metallothioneins (Mts)mentioning

confidence: 99%

“…Phosphorylation is also involved in the activation of MTF-1 (32). Several other proteins interact with the mouse MT-1 promoter, including USF-1, USF-2 (15)(16)(17)(18)(19), Sp1 (9, 19 -21), c-Fos (19), and c-Jun (9). These transcription factors may be essential for maintenance of adequate basal promoter activities and for maximum induction in response to inducers (8).…”

Section: Nf1 Binds To and Activates The Mouse Metallothionein-1mentioning

confidence: 99%

Nuclear Factor-1 and Metal Transcription Factor-1 Synergistically Activate the Mouse Metallothionein-1 Gene in Response to Metal Ions

LaRochelle¹,

Labbé²,

Harrisson³

et al. 2008

Journal of Biological Chemistry

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Metal activation of metallothionein (MT) gene transcription is dependent on the presence of metal regulatory elements (MREs), which are present in five non-identical copies (MREa through MREe) in the promoter of the mouse MT-1 gene and on the capacity of metal transcription factor-1 (MTF-1) to bind to the MREs in the presence of zinc. We detected a protein, distinct from MTF-1, specifically binding to the MREc region. DNA binding competition experiments using synthetic oligonucleotides and specific anti-NF1 antibodies showed that this protein binds to an NF1 site overlapping the MREc element as well as to a second site upstream of the Sp1a site and corresponds to NF1 or a related protein. Transfection experiments showed that loss of the two NF1 sites decreased metal-induced MT promoter activity by 55-70% in transiently transfected cells and almost completely abrogated metal and tert-butylhydroquinone (tBHQ) induction in stably transfected cells. Similarly, expression of an inactive NF1 protein strongly inhibited MT-1 promoter activity. Using synthetic promoters containing NF1 and MRE sites fused to a minimal MT promoter, we showed that these NF1 sites did not confer metal induction but enhanced metal-induced promoter activity. Chromatin immunoprecipitation assays confirmed that NF1 binds to the mouse MT-1 promoter in vivo and showed that NF1 binding is zinc-inducible. In addition, zinc-induced NF1 DNA binding was MTF-1-dependent. Taken together, these studies show that NF1 acts synergistically with MTF-1 to activate the mouse MT-1 promoter in response to metal ions and tert-butylhydroquinone and contributes to maximal activation of the gene. Metallothioneins (MTs)3 are small metal-binding stress proteins grouped into four classes, MT-1 through MT-4 (1, 2).MTs have been identified in a wide range of species and are present in various tissues and cell types from yeast to human. In mice, MT-1 and MT-2 are ubiquitous and coordinately expressed in all tissues, whereas MT-3 is mainly expressed in the brain (3) and in the organs of the reproductive system (4), and MT-4 is restricted to stratified squamous epithelia (5). MTs have no enzymatic function but appear to play important roles in metal ion homeostasis, as an active donor of zinc to other sites within the cell, in detoxification of toxic metals, and in protection against oxidative damage, ionizing radiation, and xenobiotics (1, 2).MT genes are inducible at the transcription level by hormones, cytokines, and a variety of stress conditions that include exposure to transition metal ions, UV irradiation, hypoxia, and reactive oxygen species (2). Metals are the most general and potent of these inducers. Metal activation of MT gene transcription depends on the presence of regulatory DNA sequences termed metal regulatory elements (MREs) and involves metal-responsive transcription factor-1 (MTF-1) interacting with the MREs in a zinc-dependent manner (6, 7). MTF-1 is also involved in the response to hypoxia (8), reactive oxygen species (9), and amino acid starvation (10)...

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“…MTF-1 plays a key role in this process (26), although other transcription factors may contribute to this activation as well (3,18,36). By contrast, binding of MTF-1 to DNA in a cell-free system responds to zinc but not to any other heavy metal added (7,80).…”

Section: Promoter Induction By Cadmium and Copper Depends On The Presmentioning

confidence: 99%

Activity of Metal-Responsive Transcription Factor 1 by Toxic Heavy Metals and H₂O₂ In Vitro Is Modulated by Metallothionein

Zhang

Georgiev

Hagmann

et al. 2003

Molecular and Cellular Biology

220

152

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Metallothioneins are small, cysteine-rich proteins that avidly bind heavy metals such as zinc, copper, and cadmium to reduce their concentration to a physiological or nontoxic level. Metallothionein gene transcription is induced by several stimuli, notably heavy metal load and oxidative stress. Transcriptional induction of metallothionein genes is mediated by the metal-responsive transcription factor 1 (MTF-1), an essential zinc finger protein that binds to specific DNA motifs termed metal-response elements. In cell-free DNA binding reactions with nuclear extracts, MTF-1 requires elevated zinc concentrations for efficient DNA binding but paradoxically is inactivated by other in vivo inducers such as cadmium, copper, and hydrogen peroxide. Here we have developed a cell-free, MTF-1-dependent transcription system which accurately reproduces the activation of metallothionein gene promoters not only by zinc but also by these other inducers. We found that while transcriptional induction by zinc can be achieved by elevated zinc concentration alone, induction by cadmium, copper, or H 2 O 2 additionally requires the presence of zinc-saturated metallothionein. This is explained by the preferential binding of cadmium or copper to metallothionein or its oxidation by H 2 O 2 ; the concomitant release of zinc in turn leads to the activation of transcription factor MTF-1. Conversely, thionein, the metal-free form of metallothionein, inhibits activation of MTF-1. The release of zinc from cellular components, including metallothioneins, and the sequestration of zinc by newly produced apometallothionein might be a basic mechanism to regulate MTF-1 activity upon cellular stress.All living organisms are able to cope with a variety of stress situations by immediately adapting their gene expression program to the stress stimulus. For example, metallothioneins, small cysteine-rich proteins, are strongly upregulated upon heavy metal load (2,27,29,49,63,70,71). They have the ability to bind and hence neutralize toxic (such as Cd and Hg) and excess nontoxic (such as Zn and Cu) heavy metal ions and also act as radical scavengers. Metal response element binding transcription factor 1, also called metal-responsive transcription factor 1 (MTF-1), plays an important role in the cellular response to heavy metal stress (2,21,38,55,75) and is essential for embryonic liver development in the mouse (24). MTF-1 contains six zinc fingers of the C 2 H 2 type. C-terminal to the zinc fingers are three distinct activation domains, an acidic, a proline-rich, and a serine/threonine-rich domain. Via the zinc fingers, it binds to DNA sequence motifs with the consensus binding site TGCRCNC, known as metal response elements (MREs). MREs are present in the promoters of metallothionein genes (41,61,64) and other target genes, including zinc transporter ZnT1 and ␥-glutamylcysteine synthetase heavy chain (24,34,37). MTF-1 is also involved in the responses to oxidative stress (16, 24), hypoxia (23, 46), and amino acid starvation (1). In quiescent cells, MTF-1 pref...

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Activation of the Metallothionein-I Gene Promoter in Response to Cadmium and USFin Vitro

Cited by 19 publications

References 25 publications

Regulation of Metallothionein Transcription by the Metal-responsive Transcription Factor MTF-1

Regulation of Metallothionein Transcription by the Metal-responsive Transcription Factor MTF-1

Nuclear Factor-1 and Metal Transcription Factor-1 Synergistically Activate the Mouse Metallothionein-1 Gene in Response to Metal Ions

Activity of Metal-Responsive Transcription Factor 1 by Toxic Heavy Metals and H₂O₂ In Vitro Is Modulated by Metallothionein

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Activation of the Metallothionein-I Gene Promoter in Response to Cadmium and USFin Vitro

Cited by 19 publications

References 25 publications

Regulation of Metallothionein Transcription by the Metal-responsive Transcription Factor MTF-1

Regulation of Metallothionein Transcription by the Metal-responsive Transcription Factor MTF-1

Nuclear Factor-1 and Metal Transcription Factor-1 Synergistically Activate the Mouse Metallothionein-1 Gene in Response to Metal Ions

Activity of Metal-Responsive Transcription Factor 1 by Toxic Heavy Metals and H2O2 In Vitro Is Modulated by Metallothionein

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Activity of Metal-Responsive Transcription Factor 1 by Toxic Heavy Metals and H₂O₂ In Vitro Is Modulated by Metallothionein