title: Dissection of Drosophila MTF-1 reveals a domain for differential target gene activation upon copper overload vs. copper starvation.
abstract: Metal-responsive transcription factor-1 (MTF-1) is a zinc finger protein conserved from mammals to insects. It mediates protection against heavy metal load by activating the expression of metallothionein and other genes. In Drosophila, MTF-1 serves a dual function in that it not only helps to protect against heavy metal load but also induces the expression of Ctr1B, the gene for an intestinal copper importer, upon copper starvation. By dissecting Drosophila MTF-1 function, we have identified determinants for nuclear import and export, and characterized a phosphorylation site mutant (T127A) that differentially affects MTF-1 target genes. Further, by generating a series of fusion proteins with the heterologous DNA binding domain of Gal4 we identified a strong, constitutive activation domain in the central region of MTF-1 (aa 352-540). By contrast, an extended fusion protein that includes MTF-1's C-terminus (aa 352-791) is not active in standard conditions but induced by copper load. The paramount regulatory importance of the C-terminal part, that harbors a cysteine-rich "metallothionein-like" domain, was corroborated by different experiments. Transgenic flies expressing C-terminally truncated MTF-1 variants displayed high constitutive transcription of both, the genes for metallothioneins and the copper importer Ctr1B. The indiscriminate activation of these genes that are normally induced under opposite conditions of copper load and copper starvation manifested itself in a shortened lifespan, crippled wings, and female sterility.
authors.affiliation: Institute of Molecular Life Sciences, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
authors.forename: Viola
authors.initials: V
authors.lastname: Günther
authors.forename: Dominique
authors.initials: D
authors.lastname: Waldvogel
authors.forename: Michael
authors.initials: M
authors.lastname: Nosswitz
authors.forename: Oleg
authors.initials: O
authors.lastname: Georgiev
authors.forename: Walter
authors.initials: W
authors.lastname: Schaffner
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003300:Copper / Q000378:metabolism* / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004330:Drosophila / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D008668:Metallothionein / Q000235:genetics / Q000378:metabolism; D019216:Metals, Heavy / Q000378:metabolism; D008969:Molecular Sequence Data; D010641:Phenotype; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D016335:Zinc Fingers / Q000235:genetics; D000097809:Transcription Factor MTF-1
chemical_list: D003300:Copper; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D008668:Metallothionein; D019216:Metals, Heavy; D014157:Transcription Factors; D000097809:Transcription Factor MTF-1