Multiple layers of regulation of human heat shock transcription factor 1.
Upon heat stress, monomeric human heat shock transcription factor 1 (hHSF1) is converted to a trimer, acquires DNA-binding ability, is transported to the nucleus, and becomes transcriptionally competent. It was not known previously whether these regulatory changes are caused by a single activation event or whether they occur independently from one another, providing a multilayered control that may prevent inadvertant activation of hHSF1. Comparison of wild-type and mutant hHSF1 expressed in Xenopus oocytes and human HeLa cells suggested that retention of hHSF1 in the monomeric form depends on hydrophobic repeats (LZ1 to LZ3) and a carboxy-terminal sequence element in hHSF1 as well as on the presence of a titratable factor in the cell. Oligomerization of hHSF1 appears to induce DNA-binding activity as well as to uncover an amino-terminally located nuclear localization signal. A mechanism distinct from that controlling oligomerization regulates the transcriptional competence of hHSF1. Components of this mechanism were mapped to a region, including LZ2 and nearby sequences downstream from LZ2, that is clearly separated from the carboxy-terminally located transcription activation domain(s). We propose the existence of a fold-back structure that masks the transcription activation domain in the unstressed cell but is opened up by modification of hHSF1 and/or binding of a factor facilitating hHSF1 unfolding in the stressed cell. Activation of hHSF1 appears to involve at least two independently regulated structural transitions.
Zuo
J
J
Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Florida 33101, USA.
Rungger
D
D
Voellmy
R
R
D000818:Animals; D002451:Cell Compartmentation; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D006367:HeLa Cells; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D011487:Protein Conformation; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D017384:Sequence Deletion; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D014981:Xenopus
D004268:DNA-Binding Proteins; C000619706:HSF1 protein, human; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors