Title

Regulation of heat shock factor 1 (HSF1)

Date of Award

1998

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Biochemistry and Molecular Biology

First Committee Member

Richard Voellmy, Committee Chair

Abstract

Heat shock and other proteotoxic stresses trigger the activation of a heat shock transcription factor, Heat Shock Factor 1 (HSF1) in vertebrates, which binds to promoters of heat shock or stress protein (Hsp) genes and enhances transcription from these promoter.A novel in vitro system for the ATP-stimulated activation of HSF1 DNA-binding activity and trimerization by three divergent inducers of the stress response, heat shock, geldanamycin and chemically denatured protein, was developed. Characterization of this system showed that heat also induces HSF1 hyper-phosphorylation in vitro and that HSF1 trimers can revert to monomers upon depletion of calcium. This system was used to functionally examine the role of Hsps in the induction of HSF1 trimerization and HSE DNA-binding activity. It was found that addition of Hsp90 inhibits activation by mild heat shock. Reduction of the Hsp90 level results in massive activation of HSF1, which activation can be prevented by addition of purified Hsp90. In contrast, virtually quantitative depletion of other chaperones and Hsp90-associated proteins, including Hsp/c70, Hop, Hip, p23, CyP40 or Hsp40, fails to cause activation. These data demonstrate for the first time that Hsp90 is a key regulator of HSF1 activity and suggest that Hsp90, alone or in combination with other chaperones, directly interact with monomeric HSF1, preventing it from oligomerizing and from acquiring HSE DNA-binding activity.How different inducers of the stress response cause accumulation of nonnative protein was studied. It is hypothesized that inducers of the stress response may be generally capable of triggering oxidation of nonprotein thiols, particularly glutathione (GSH). Such oxidation leads to formation of protein mixed disulfides and protein-protein disulfides, which reactions are expected to affect the conformation of proteins. A representative set of different inducers was selected. It was shown that all chemical inducers as well as heat shock cause drastic oxidation of GSH under conditions under which they induce HSE DNA-binding activity of HSF1. Under the same conditions, all inducers also cause trimerization of HSF1. For several inducers, it was also shown that they enhance thiol oxdiation of proteins.

Keywords

Biology, Molecular

Link to Full Text

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