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.

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 activity 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, and MEK1. mTOR, p38, and MEK1 all phosphorylated S326 but AKT1 was the more potent activator. Mass spectrometry showed that AKT1 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. This study suggests that HSF1 activity is regulated by phosphorylation at specific residues that promote different stages of HSF1 activation. Furthermore, this is the first study to identify the functional role of these phosphorylation events.

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Motivation:  Receiving radiation to the heart has been recognized as a risk factor for the development of major adverse cardiovascular events (MACEs) for many years. However, recent data suggests that radiation dosing to substructures of the heart serve as a better surrogate for evaluating the risk of developing a MACE than whole heart radiation dose. Recent papers suggest that dosing to the left anterior descending artery (LAD) can be used as a robust marker for cardiotoxicity risk; however, this association lacks corroborative data and is currently not incorporated into clinically routine care.  Problem:  In this paper we seek to investigate the relationship between radiation dose to the LAD and risk of developing a MACE in lung cancer patients treated with curative intent radiation.  Approach:  Chart review to confirm the presence of MACE events was performed in patients who were identified based on elevated troponin values to potentially have had a MACE after receiving their last dose of radiation therapy. Patients who had multiple courses of radiation therapy separated in time (>60 days) that received greater than 0.2 Gy whole heart dose during their subsequent courses before having a MACE were excluded. Selected patients were then stratified based on presence cardiovascular co-morbidities. Contours of patient’s LADs were made after patient selection, and will be verified by an expert (e.g., cardiologist or thoracic radiologist).  Results:  Dose to the LAD will be calculated and an assessment of the correlation between radiation dose and risk of having a MACE will be made. Analysis will assess the cardiac event rate at various times as well as time to MACE.  Implications:  This paper can help set a quantifiable standard with which radiation oncologists can use to minimize their patient’s risk of developing a MACE by minimizing radiation dosing to specific cardiac substructures while maintaining tumor coverage.