Metal-responsive elements

Xu, C. (1993). cDNA cloning of a mouse factor that activates transcription from a metal response element of the mouse metallothionein-1 gene in yeast. DNA Cell Biol. 12, 517-525. 

The metabolism of sulphur plays an important role in metal response, since most chelators, including metallothioneins and phytochelatins, contain this element. APSl encodes an ATP sulfurylase and Brassica juncea has been engineered to constitutively express this gene (Pilon-Smits et al., 1999). The plants showed increased S assimilation, higher glutathione (GSH) levels and were more tolerant to Se, accumulating 2-fold higher Se levels in the shoots. 

In many inorganic pigments, lanthanides and transition elements are responsible for color. Metal oxides and oxide hydroxides are, however, also important as colored pigments because of their optical properties, low price, and ready availability. Colored pigments based on oxides and oxide hydroxides are either composed of a single component or mixed phases. In the latter, color is obtained by incorporation of appropriate cations. 

Mammalian MT synthesis is regulated at the transcriptional level. A series of ds-acting control sequences has been identified and can be attributed to the range of effectors described above (see Hamer, 1986). Among these are sequences defined as metal-responsive elements (MREs). In the mouse MTI gene is a pair of MREs which are imperfectly duplicated 12 bp sequences, at -46 (relative to the start of transcription) and -114 further partial repeats are centred at positions -160, -134 and -62. The requirement for such sequences in metal regulation is proven for the mouse MTI promoter, Zn and Cd induction requires two or more MREs (Searle et al., 1985). 

Searle, P.F., Stuart, G.W. Palmiter, R.D. (1985). Building a metal-responsive promoter with synthetic regulatory elements. Molecular and Cellular Biology 5, 1480-9. 

Metallothionein expression is mainly regulated at the transcriptional level and is induced by various heavy metals, such as zinc. There are seven short sequence motifs located in a region within 200 base pairs upstream of the transcription start site. These cis-acting DNA elements are responsible for heavy metal induction and are thus termed metal responsive elements (MREs) (Stuart et al., 1984). Several regulatory proteins have been cloned which interact with these MREs. One of these, MRE-binding transcription factor-1 (MTF-1), is essential for the transcriptional activation of metallothionein genes by heavy metals like zinc and cadmium (Radtke et al., 1993 Palmiter, 1994 Heuchel et al., 1994 Koiszumi et al., 1999). 

Koizumi, S., Suzuki, K., Ogra, Y., Yamada, H. and Otsuka, F. (1999) Transcriptional activity and regulatory protein binding of metal-responsive elements of the human metallothionein-IIA gene. EurJ. Biochem., 259, 635-642. 

To better understand the structure and the inner workings of an environmental laboratory, we need to familiarize ourselves with laboratory functional groups and their responsibilities. Figure 4.2 shows an example of a typical full service environmental laboratory organization chart. A full service laboratory has the capabilities to perform analysis for common environmental contaminants, such as VOCs and SVOCs (including petroleum fuels and their constituents, pesticides, herbicides, and PCBs), trace elements (metals), and general chemistry parameters. Analysis of dioxins/furans, explosives, radiochemistry parameters, and analysis of contaminants in air are not considered routine, and are performed at specialized laboratories. 

The 5 end of MT-1 and MT-2 genes possess a TATA box, or core promoter element and numerous response elements that confer metal inducibility on the MT gene promoter (Figure 21.8). Some of these response elements such as API and AP2 in humans and in mouse, the antioxidant response element (ARE) and upstream stimulatory factor (USF) provide putative binding sites for MT transcription factors. The most common of these cis-acting proximal elements are the metal responsive elements (MREs), motifs that are conserved across vertebrate and invertebrate species. Multiple copies of MREs exist in the MT promoter region and act syner-gistically to enhance activity. 

Figure 21.9. Human MT promoter. (Adapted from Murphy, B. J., Andrews, G. K. Activation of metallothionein gene expression by hypoxia involves metal response elements and metal transcription factor-1. Cancer Res. 59,1315-1322, 1999.)...

Chu, W. A., Moehlenkamps, J. D., Bittel, D., Andrews, G. K., and Johnson, J. A. Cadmium-mediated activation of the metal response element in human neuroblastoma cells lacking functional metal response element-binding transcription factor-1. J. Bio. Chem. 274(9), 5279-5284,1999. 

Dalton TP, Li Q, Bittel D, Liang L, Andrews GK (1996) Oxidative stress activates metal-responsive transcription factor-1 binding activity. Occupancy in vivo of metal response elements in the metallothionein-I gene promoter. J Biol Chem 271 26233-26241 Danscher G, Howell G, Perez-Clausell J, Hertel N (1985) The dithizone, Timm s sulphide silver and the selenium methods demonstrate a chelatable pool of zinc in CNS. A proton activation (PIXE) analysis of carbon tetrachloride extracts from rat brains and spinal cords intravitally treated with dithizone. Histochemistry 83 419 22 Danscher G, Jensen KB, Frederickson CJ, Kemp K, Andreasen A, Juhl S, Stoltenberg M, Ravid R (1997) Increased amount of zinc in the hippocampus and amygdala of Alzheimer s diseased brains a proton-induced X-ray emission spectroscopic analysis of cryostat sections from autopsy material. J Neurosci Methods 76 53-59... 

The modem process of electrodeposition can thus be described as a combination of three basic elements (a) Electrophoresis - migration of charged polymer particles to metal surface (b) Deposition - colloidal de-stabilization of particles at the metal-bath interface and (c) Insulation - formation of an adherent, non-conductive layer of resin on the metal surface. The last named element is responsible for the high throwing power which can be achieved with the electrocoating process. 

Evidence suggests that the regulation of metallothionein levels by metal ions results from the binding of zinc (or other metal ions) to a special transcription factor (molecular weight = 105 kDa, with the subsequent binding of the zinc/transcription factor complex to d promoter that resides near the metallothionein gene. The zinc/transcription factor complex actually binds to the metal response element that resides in the promoter The sequence of the metal response element is ... 

Bittel, D., T. Dalton, S.L. Samson, L. Gedamu and G.K. Andrews. The DNA binding activity of metal response element-binding transcription factor-1 is activated in vivo and in vitro by zinc, but not by other transition metals. J. Biol. Chem. 273 7127-7133, 1998. 

Samson, S.L. and L. Gedamu. Metal-responsive elements of the rainbow trout metallothionein-B gene function for basal and metal-induced activity. J. Biol. Chem. 270 6864—6871, 1995. 

The synthesis of MTs has been examined in several cell lines. Most studied have been two rainbow trout cell lines, RTH-149 and RTG-2, and the Chinook embryo cell line, CHSE-214151 160 229 231. Heavy metals induced MTs in RTH-149 and RTG-2 but not in CHSE-214. Methylation of the MT genes appeared to account for the failure of MTs to be induced in CHSE-214161. MTF-1, the metal response element (MRE)-binding transcription factor-1, has been demonstrated in RTH-149 and RTG-2 and in a zebrafish cell line, ZEM2S62. ZEM2S had a single isoform of MTF-1, whereas RTH-149 and RTG-2 contained two isoforms. Zn but not Cd activated MTF-1 binding to MRE in cells from both species. A cell line from at least one marine species has been studied for MT expression. In a turbot fibroblast cell line, Cd, Cu, Hg and Zn but not Pb induced MT mRNA and MT levels89. 

The regulatory regions of mammalian and yeast MTs have been studied in detail, but less is known about fish MT promoter regions. A hallmark of MTs is the rapid transactivation through multiple copies of metal responsive elements (MREs) within... 

Dalton, T., R.D. Palmiter and G.K. Andrews. Transcriptional induction of the mouse metallothionein-I gene in hydrogen peroxide-treated Hepa cells involves a composite major late transcription factor/antioxidant response element and metal response promoter elements. Nucleic Acids Res. 22 5016—5023, 1994. 

Dalton, T.P., D. Bittel and G.K. Andrews. Reversible activation of mouse metal response element-binding transcription factor 1 DNA binding involves zinc interaction with the zinc finger domain. Mol. Cell. Biol. 17 2781-2789, 1997. 

Dalton, T.P., Q. Li, D. Bittel, L. Liang and G.K. Andrews. Oxidative stress activates metal-responsive transcription factor-1 binding activity. Occupancy in vivo of metal response elements in the metallothionein-I gene promoter. J. Biol. Chem. 271 26233—26241, 1996. 

Solis, W.A., N.L. Childs, M.N. Weedon, L. He, D.W. Nebert and T.P. Dalton. Retrovirally expressed metal response element-binding transcripton factor-1 normalizes metallothionein-1 gene expression and protects cells against zinc, but not cadmium, toxicity. Toxicol. Appl. Pharmacol. 178 93-101, 2002. 

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