The transcription factor MTF-1 is essential for basal and heavy metal-induced metallothionein gene expression.
We have described and cloned previously a factor (MTF-1) that binds specifically to heavy metal-responsive DNA sequence elements in the enhancer/promoter region of metallothionein genes. MTF-1 is a protein of 72.5 kDa that contains six zinc fingers and multiple domains for transcriptional activation. Here we report the disruption of both alleles of the MTF-1 gene in mouse embryonic stem cells by homologous recombination. The resulting null mutant cell line fails to produce detectable amounts of MTF-1. Moreover, due to the loss of MTF-1, the endogenous metallothionein I and II genes are silent, indicating that MTF-1 is required for both their basal and zinc-induced transcription. In addition to zinc, other heavy metals, including cadmium, copper, nickel and lead, also fail to activate metal-responsive promoters in null mutant cells. However, cotransfection of an MTF-1 expression vector and metal-responsive reporter genes yields strong basal transcription that can be further boosted by zinc treatment of cells. These results demonstrate that MTF-1 is essential for metallothionein gene regulation. Finally, we present evidence that MTF-1 itself is a zinc sensor, which exhibits increased DNA binding activity upon zinc treatment.
Institut für Molekularbiologie II, Universität Zürich, Switzerland.
R
R
Heuchel
F
F
Radtke
O
O
Georgiev
G
G
Stark
M
M
Aguet
W
W
Schaffner
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects*; D008668:Metallothionein / Q000096:biosynthesis* / Q000235:genetics; D008670:Metals / Q000494:pharmacology*; D051379:Mice; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000032:analysis; D011995:Recombination, Genetic; D029701:Saccharomyces cerevisiae Proteins; D013234:Stem Cells; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology
D005656:Fungal Proteins; C071720:MTF1 protein, S cerevisiae; D008670:Metals; D024101:Mitochondrial Proteins; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D008668:Metallothionein; D015032:Zinc