Hsf1 and Hsp70 constitute a two-component feedback loop that regulates the yeast heat shock response

  1. Joanna Krakowiak
  2. Xu Zheng
  3. Nikit Patel
  4. Zoë A Feder
  5. Jayamani Anandhakumar
  6. Kendra Valerius
  7. David S Gross  Is a corresponding author
  8. Ahmad S Khalil  Is a corresponding author
  9. David Pincus  Is a corresponding author
  1. Whitehead Institute for Biomedical Research, United States
  2. Boston University, United States
  3. Louisiana State University Health Sciences Center, United States

Abstract

Models for regulation of the eukaryotic heat shock response typically invoke a negative feedback loop consisting of the transcriptional activator Hsf1 and a molecular chaperone. Previously we identified Hsp70 as the chaperone responsible for Hsf1 repression and constructed a mathematical model that recapitulated the yeast heat shock response (Zheng et al., 2016). The model was based on two assumptions: dissociation of Hsp70 activates Hsf1, and transcriptional induction of Hsp70 deactivates Hsf1. Here we validate these assumptions. First, we severed the feedback loop by uncoupling Hsp70 expression from Hsf1 regulation. As predicted by the model, Hsf1 was unable to efficiently deactivate in the absence of Hsp70 transcriptional induction. Next, we mapped a discrete Hsp70 binding site on Hsf1 to a C-terminal segment known as conserved element 2 (CE2). In vitro, CE2 binds to Hsp70 with low affinity (9 µM), in agreement with model requirements. In cells, removal of CE2 resulted in increased basal Hsf1 activity and delayed deactivation during heat shock, while tandem repeats of CE2 sped up Hsf1 deactivation. Finally, we uncovered a role for the N-terminal domain of Hsf1 in negatively regulating DNA binding. These results reveal the quantitative control mechanisms underlying the heat shock response.

Article and author information

Author details

  1. Joanna Krakowiak

    Whitehead Institute for Biomedical Research, Cambridge, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Xu Zheng

    Whitehead Institute for Biomedical Research, Cambridge, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Nikit Patel

    Department of Biomedical Engineering, Boston University, Boston, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Zoë A Feder

    Whitehead Institute for Biomedical Research, Cambridge, United States
    Competing interests
    The authors declare that no competing interests exist.
  5. Jayamani Anandhakumar

    Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, United States
    Competing interests
    The authors declare that no competing interests exist.
  6. Kendra Valerius

    Whitehead Institute for Biomedical Research, Cambridge, United States
    Competing interests
    The authors declare that no competing interests exist.
  7. David S Gross

    Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, United States
    For correspondence
    dgross@lsuhsc.edu
    Competing interests
    The authors declare that no competing interests exist.
  8. Ahmad S Khalil

    Department of Biomedical Engineering, Boston University, Boston, United States
    For correspondence
    khalil@bu.edu
    Competing interests
    The authors declare that no competing interests exist.
  9. David Pincus

    Whitehead Institute for Biomedical Research, Cambridge, United States
    For correspondence
    pincus@wi.mit.edu
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-9651-6858

Funding

National Institutes of Health (DP5 OD017941-01)

  • David Pincus

National Science Foundation (MCB-1350949)

  • Ahmad S Khalil

National Science Foundation (MCB-1518345)

  • David S Gross

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Tony Hunter, Salk Institute for Biological Studies, United States

Version history

  1. Received: September 4, 2017
  2. Accepted: February 1, 2018
  3. Accepted Manuscript published: February 2, 2018 (version 1)
  4. Version of Record published: February 12, 2018 (version 2)
  5. Version of Record updated: March 26, 2018 (version 3)

Copyright

© 2018, Krakowiak et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Joanna Krakowiak
  2. Xu Zheng
  3. Nikit Patel
  4. Zoë A Feder
  5. Jayamani Anandhakumar
  6. Kendra Valerius
  7. David S Gross
  8. Ahmad S Khalil
  9. David Pincus
(2018)
Hsf1 and Hsp70 constitute a two-component feedback loop that regulates the yeast heat shock response
eLife 7:e31668.
https://doi.org/10.7554/eLife.31668

Share this article

https://doi.org/10.7554/eLife.31668

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    Heat shock factor (Hsf1) regulates the expression of molecular chaperones to maintain protein homeostasis. Despite its central role in stress resistance, disease and aging, the mechanisms that control Hsf1 activity remain unresolved. Here we show that in budding yeast, Hsf1 basally associates with the chaperone Hsp70 and this association is transiently disrupted by heat shock, providing the first evidence that a chaperone repressor directly regulates Hsf1 activity. We develop and experimentally validate a mathematical model of Hsf1 activation by heat shock in which unfolded proteins compete with Hsf1 for binding to Hsp70. Surprisingly, we find that Hsf1 phosphorylation, previously thought to be required for activation, in fact only positively tunes Hsf1 and does so without affecting Hsp70 binding. Our work reveals two uncoupled forms of regulation - an ON/OFF chaperone switch and a tunable phosphorylation gain - that allow Hsf1 to flexibly integrate signals from the proteostasis network and cell signaling pathways.

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