Metal-responsive transcription factor 1 (MTF-1) activity is regulated by a nonconventional nuclear localization signal and a metal-responsive transactivation domain

Mol Cell Biol. 2009 Dec;29(23):6283-93. doi: 10.1128/MCB.00847-09. Epub 2009 Sep 21.

Abstract

Metal-responsive transcription factor 1 (MTF-1) mediates both basal and heavy metal-induced transcription of metallothionein genes and also regulates other genes involved in the cell stress response and in metal homeostasis. In resting cells, MTF-1 localizes to both the cytoplasm and the nucleus but quantitatively accumulates in the nucleus upon metal load and under other stress conditions. Here we show that within the DNA-binding domain, a region spanning zinc fingers 1 to 3 (amino acids [aa] 137 to 228 in human MTF-1) harbors a nonconventional nuclear localization signal. This protein segment confers constitutive nuclear localization to a cytoplasmic marker protein. The deletion of the three zinc fingers impairs nuclear localization. The export of MTF-1 to the cytoplasm is controlled by a classical nuclear export signal (NES) embedded in the acidic activation domain. We show that this activation domain confers metal inducibility in distinct cell types when fused to a heterologous DNA-binding domain. Furthermore, the cause of a previously described stronger inducibility of human versus mouse MTF-1 could be narrowed down to a 3-aa difference in the NES; "humanizing" mouse MTF-1 at these three positions enhanced its metal inducibility to the level of human MTF-1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Active Transport, Cell Nucleus
  • Animals
  • Cell Line
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Humans
  • Mice
  • Nuclear Localization Signals / chemistry
  • Nuclear Localization Signals / genetics
  • Nuclear Localization Signals / metabolism*
  • Transcription Factors / chemistry
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcriptional Activation*
  • Zinc Fingers*

Substances

  • DNA-Binding Proteins
  • Nuclear Localization Signals
  • Transcription Factors
  • transcription factor MTF-1