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

• Published in: PloS one 2012-06, Vol.7 (6), p.e39679-e39679
• Main Authors: Chou, Shiuh-Dih, Prince, Thomas, Gong, Jianlin, Calderwood, Stuart K
• Format: Article
• Language: English
• Subjects: Adapter proteins; Alanine; Amino Acid Sequence; Amino acids; Apoptosis; Arsenite; Autophagy; Biology; Cell culture; Chemical synthesis; Deoxyribonucleic acid; DNA; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - metabolism; Fever; Gene expression; Gene Expression Regulation; Gene regulation; Gene Silencing; Genes; Heat; Heat shock factors; Heat shock proteins; Heat Shock Transcription Factors; Heat-Shock Proteins - biosynthesis; Heat-Shock Proteins - genetics; Heat-Shock Proteins - metabolism; Heat-Shock Response; HeLa Cells; HSF1 protein; HSP70 Heat-Shock Proteins - genetics; Hsp70 protein; Hsp90 protein; Humans; Hyperthermia; Kinases; Life sciences; Medical research; Medicine; Mitogens; Molecular Sequence Data; Molecular weight; Mutation; Nutrient availability; Oncology; Peptides - chemistry; Peptides - metabolism; Phosphorylation; Phosphoserine - metabolism; Phosphotransferases - metabolism; Plasmids; Promoter Regions, Genetic - genetics; Proteasome inhibitors; Protein Biosynthesis; Protein expression; Protein kinase; Protein kinases; Protein synthesis; Proteins; Rapamycin; Reduction; Ribonucleic acid; RNA; RNA-mediated interference; Serine; Signal transduction; Sodium; Sodium arsenite; Stress; Stress response; Stress, Physiological; Stresses; Substrate Specificity; Tissue culture; TOR protein; TOR Serine-Threonine Kinases - metabolism; Transcription (Genetics); Transcription activation; Transcription Factors - chemistry; Transcription Factors - metabolism; Transcription, Genetic
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0039679

The target of rapamycin (TOR) is a high molecular weight protein kinase that regulates many processes in cells in response to mitogens and variations in nutrient availability. Here we have shown that mTOR in human tissue culture cells plays a key role in responses to proteotoxic stress and that reduction in mTOR levels by RNA interference leads to increase sensitivity to heat shock. This effect was accompanied by a drastic reduction in ability to synthesize heat shock proteins (HSP), including Hsp70, Hsp90 and Hsp110. As HSP transcription is regulated by heat shock transcription factor 1 (HSF1), we examined whether mTOR could directly phosphorylate this factor. Indeed, we determined that mTOR could directly phosphorylate HSF1 on serine 326, a key residue in transcriptional activation. HSF1 was phosphorylated on S326 immediately after heat shock and was triggered by other cell stressors including proteasome inhibitors and sodium arsenite. Null mutation of S326 to alanine led to loss of ability to activate an HSF1-regulated promoter-reporter construct, indicating a direct role for mTOR and S326 in transcriptional regulation of HSP genes during stress. As mTOR is known to exist in at least two intracellular complexes, mTORC1 and mTOR2 we examined which complex might interact with HSF1. Indeed mTORC1 inhibitor rapamycin prevented HSF1-S326 phosphorylation, suggesting that this complex is involved in HSF1 regulation in stress. Our experiments therefore suggest a key role for mTORC1 in transcriptional responses to proteotoxic stress.