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mTOR is essential for the proteotoxic stress response, HSF1 activation and heat shock protein synthesis

Shiuh-Dih Chou1, Thomas Prince, Jianlin Gong

  • 1Department of Radiation Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, United States of America.

Plos One
|July 7, 2012
PubMed

Insights

The target of rapamycin (mTOR) pathway regulates cellular responses to stress. mTORC1 directly phosphorylates heat shock factor 1 (HSF1) at serine 326, crucial for heat shock protein synthesis and cell survival under proteotoxic stress.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The target of rapamycin (TOR) pathway, particularly mTOR (mechanistic target of rapamycin), is a critical regulator of cellular processes, including growth and metabolism, in response to nutrients and growth factors.
  • Cellular stress, such as proteotoxic stress, triggers adaptive responses to maintain cellular homeostasis.
  • Heat shock proteins (HSPs) are key components of the cellular stress response, protecting cells from damage.

Purpose of the Study:

  • To investigate the role of mTOR in cellular responses to proteotoxic stress.
  • To determine if mTOR directly interacts with and regulates heat shock transcription factor 1 (HSF1).
  • To identify which mTOR complex is involved in the regulation of HSP synthesis under stress.

Main Methods:

  • RNA interference was used to reduce mTOR levels in human tissue culture cells.
  • Sensitivity to heat shock and the synthesis of HSPs (Hsp70, Hsp90, Hsp110) were assessed.
  • Direct phosphorylation of HSF1 by mTOR was examined in vitro and in vivo.
  • Site-directed mutagenesis (S326A) was employed to study the functional significance of HSF1 phosphorylation.
  • The effect of mTORC1 inhibitor rapamycin on HSF1 phosphorylation was investigated.

Main Results:

  • Reduced mTOR levels increased sensitivity to heat shock and decreased HSP synthesis.
  • mTOR was found to directly phosphorylate HSF1 at serine 326 (S326).
  • HSF1 phosphorylation at S326 occurred rapidly after heat shock and other stressors.
  • Mutation of S326 to alanine abolished HSF1-dependent transcriptional activation of HSP genes.
  • Rapamycin treatment inhibited HSF1-S326 phosphorylation, implicating mTORC1.

Conclusions:

  • mTOR plays a vital role in cellular defense against proteotoxic stress.
  • mTORC1 directly phosphorylates HSF1 at S326, a critical step for HSP gene transcriptional activation.
  • This phosphorylation event is essential for mounting an effective heat shock response and ensuring cell survival under stress.

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