Regulation of Metallothionein Gene Transcription: IDENTIFICATION OF UPSTREAM REGULATORY ELEMENTS AND TRANSCRIPTION FACTORS RESPONSIBLE FOR CELL-SPECIFIC EXPRESSION OF THE METALLOTHIONEIN GENES FROM CAENORHABDITIS ELEGANS

Lori H Moilanen,Tetsunari Fukushige,Jonathan H Freedman

doi:10.1074/jbc.274.42.29655

Lori H Moilanen, Tetsunari Fukushige + Show 1 more

Open Access

https://doi.org/10.1074/jbc.274.42.29655

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Abstract

Metallothioneins are small, cysteine-rich proteins that function in metal detoxification and homeostasis. Metallothionein transcription is controlled by cell-specific factors, as well as developmentally modulated and metal-responsive pathways. By using the nematode Caenorhabditis elegans as a model system, the mechanism that controls cell-specific metallothionein transcription in vivo was investigated. The inducible expression of the C. elegans metallothionein genes, mtl-1 and mtl-2, occurs exclusively in intestinal cells. Sequence comparisons of these genes with other C. elegans intestinal cell-specific genes identified multiple repeats of GATA transcription factor-binding sites (i.e. GATA elements). In vivo deletion and site-directed mutation analyses confirm that one GATA element in mtl-1 and two in mtl-2 are required for transcription. Electrophoretic mobility shift assays show that the C. elegans GATA transcription factor ELT-2 specifically binds to these elements. Ectopic expression of ELT-2 in non-intestinal cells of C. elegans activates mtl-2 transcription in these cells. Likewise, mtl-2 is not expressed in nematodes in which elt-2 has been disrupted. These results indicate that cell-specific transcription of the C. elegans metallothionein genes is regulated by the binding of ELT-2 to GATA elements in these promoters. Furthermore, a model is proposed where ELT-2 constitutively activates metallothionein expression; however, a second metal-responsive factor prevents transcription in the absence of metals.

Highlights

Metallothioneins are small, cysteine-rich proteins that function in metal detoxification and homeostasis
We report on the identification of UREs and a transcription factor that binds to these elements, which control intestinal cell-specific transcription of C. elegans MT genes
Deletion Analysis of the mtl-1 and mtl-2 Promoters—Deletion analysis was used as the initial step in identifying cis regulatory elements that control the intestinal cell-specific transcription of the C. elegans MT genes

Summary

Regulation of Metallothionein Gene Transcription

IDENTIFICATION OF UPSTREAM REGULATORY ELEMENTS AND TRANSCRIPTION FACTORS RESPONSIBLE FOR CELL-SPECIFIC EXPRESSION OF THE METALLOTHIONEIN GENES FROM CAENORHABDITIS ELEGANS*. Mtl-2 is not expressed in nematodes in which elt-2 has been disrupted These results indicate that cell-specific transcription of the C. elegans metallothionein genes is regulated by the binding of ELT-2 to GATA elements in these promoters. We report on the identification of UREs and a transcription factor that binds to these elements, which control intestinal cell-specific transcription of C. elegans MT genes. Significant levels of intestinal cell transcription are not observed in the absence of stress [22] These observations suggest that both tissue-specific and metalloregulatory factors control C. elegans MT expression. The results presented in this report provide novel insights into the complex mechanisms that govern the expression of MT genes

EXPERIMENTAL PROCEDURES

RESULTS

CTGATAA TTCTCAGb TTATCAGb TTATCAGb

DISCUSSION