Regulation of human heat shock factor 1 (hHSF1)

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Biochemistry and Molecular Biology

First Committee Member

Richard W. Voellmy, Committee Chair


Heat shock and other proteotoxic stresses trigger the activation of heat shock transcription factor 1 (HSF1) in vertebrates, which binds to heat shock elements (HSE) in promoters of heat shock protein (hsp ) genes and enhances transcription from these promoters. The molecular mechanism of regulation of HSF1 is not fully understood at present, and one of the fundamental unresolved questions is the molecular mechanism by which stress is sensed by the cell.A novel in situ chemical cross-linking method was developed to study the regulation of HSF1 by other cellular proteins. The present study provides evidence that Hsp90-containing HSF1 complexes are present in stressed and control cells. Together with results from previous studies, further evidence was collected to suggest that the activation of HSF1 is controlled by repression of Hsp90-containing chaperone complexes at two successive steps, the conversion of nontrimeric to trimeric and HSE DNA binding but transactivation-incompetent factor, and of inactive, trimeric to transactivation-competent factor. At each step, repression appears to be mediated by (different) Hsp90-containing chaperone complexes, and relief from repression appears to require dissociation of chaperone complexes from HSF1. During stress, such dissociation occurs as a consequence of stress-induced accumulation of nonnative proteins that are capable of competing with HSF1 for chaperone complex binding.Finally, Hsp90-containing chaperone complex binding to trimeric HSF1 was mapped to a region of HSF1 known to be capable of conferring repression on a linked heterologous transcription activation domain. Therefore, it appears that the cell is dependent on Hsp90-containing chaperone complexes to sense the induced accumulation of nonnative proteins, i.e., the proteotoxic signal, during a stress. The signal is then relayed to HSF1 through the release of Hsp90-containing chaperone complexes from the factor. The unassociated factor then activates the expression of hsp genes, enabling the cell to survive a stress.


Biology, Molecular; Biology, Cell

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