AKT1 mediates multiple phosphorylation events that functionally promote HSF1 activation

• Published in: The FEBS journal 2022-07, Vol.289 (13), p.3876-3893
• Main Authors: Lu, Wen‐Cheng, Omari, Ramsey, Ray, Haimanti, Wang, John, Williams, Imade, Jacobs, Curteisha, Hockaden, Natasha, Bochman, Matthew L., Carpenter, Richard L.
• Format: Article
• Language: English
• Subjects: AKT1; AKT1 protein; AKT2 protein; Deoxyribonucleic acid; DNA; heat shock; Heat shock factors; Heat shock proteins; Heat stress; Heat tolerance; HSF1; HSF1 protein; Kinases; Localization; Mass spectrometry; Mass spectroscopy; Phosphorylation; Proteomes; Residues; TOR protein; Transcription initiation factor TFIIB
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/febs.16375

The heat stress response activates the transcription factor heat shock factor 1 (HSF1), which subsequently upregulates heat shock proteins to maintain the integrity of the proteome. HSF1 activation requires nuclear localization, trimerization, DNA binding, phosphorylation and gene transactivation. Phosphorylation at S326 is an important regulator of HSF1 transcriptional activity. Phosphorylation at S326 is mediated by AKT1, mTOR, p38, MEK1 and DYRK2. Here, we observed activation of HSF1 by AKT1 independently of mTOR. AKT2 also phosphorylated S326 of HSF1 but showed weak ability to activate HSF1. Similarly, mTOR, p38, MEK1 and DYRK2 all phosphorylated S326 but AKT1 was the most potent activator. Mass spectrometry showed that AKT1 also phosphorylated HSF1 at T142, S230 and T527 in addition to S326, whereas the other kinases did not. Subsequent investigation revealed that phosphorylation at T142 is necessary for HSF1 trimerization and that S230, S326 and T527 are required for HSF1 gene transactivation and recruitment of TFIIB and CDK9. Interestingly, T527 as a phosphorylated residue has not been previously shown and sits in the transactivation domain, further implying a role for this site in HSF1 gene transactivation. This study suggests that HSF1 hyperphosphorylation is targeted and these specific residues have direct function in regulating HSF1 transcriptional activity. Activation of Heat shock factor 1 (HSF1), the master regulator of the heat shock response, requires phosphorylation at S326. AKT1 phosphorylated T142, S230 and T527 in addition to S326 and phosphorylation at these sites enhanced HSF1 transcriptional activity. T142 phosphorylation was necessary for HSF1 trimerization, whereas S230, S326 and T527 were necessary for HSF1 to interact with general transcription factor components CDK9 (pTEF‐b) and TFIIB.