Feeding Drives HSF1 Transcriptional Programs Required for Global Protein Synthesis

项目总结 我们已经发现，喂食激活了肝脏和肌肉中以前未被识别的转录程序 旨在维持蛋白质折叠动态平衡，或蛋白质平衡。热休克因子1(HSF1)，主控 控制热休克反应(HSR)的转录因子，调节这些正常反应所必需的 生理反应。禁食会抑制这些程序，禁食后再喂食则会过度刺激这些程序。 禁食对肝脏和肌肉的调节、抑制和密切摄食激活的设定和模式 类似于mTOR反应。我们进一步发现，HSF1转录程序实际上位于 典型的TSC1/2-Rheb-mTORC1轴，是mTOR依赖的蛋白质合成所必需的。监管 看起来是双向的。MTOR的抑制抑制了HSF1的转录反应，而HSF1的丢失- 肝脏功能缺失抑制了mTOR的激活和蛋白质的合成。明确的MTOR监管 将HSF1馈送反应与经典的热休克反应区分开来，后者不受 MTOR。转录组范围的rna-seq结果进一步区分了肝脏的摄食反应和hsr，因为 只有不到10%的基因是两种反应的共同基因。Rna-seq结果还表明，摄食诱导 内质网中的未折叠蛋白反应(UPR)，它不同于细胞质蛋白折叠反应 (CPFR)。而细胞质和ER蛋白的折叠反应由两个亚细胞区分 分布和涉及的蛋白质/途径，它们似乎是机械联系在一起的，就像一种扰动 影响另一个(例如，XBP1s转录程序在HSF1缺失的肝脏中被抑制)。基于我们的 初步研究结果我们假设：1)进食显著增加蛋白质的合成，因此蛋白质 折叠肝脏和肌肉的负担。2)mTOR同时促进蛋白质合成和细胞 维持蛋白质平衡的机制。3)HSF1功能丧失增加胞浆蛋白折叠 负担，它抑制依赖mTOR的蛋白质合成，从而减少蛋白质折叠 胞质和内质网均有负荷。同样，XBP1功能丧失会诱导内质网应激，抑制内质网应激 MTOR依赖的蛋白质合成以及细胞质和内质网中的蛋白质折叠负荷，这表明7) 细胞质和内质网蛋白折叠反应之间的串扰。我们对比了生理性喂养 肌肉和肝脏中经典的HSR在所有水平上的反应，调节，转录程序，和 HSF1对mTOR和ER蛋白折叠反应的影响。AIMS 1-3与以下相关的测试假设 目标4询问拟议的机制是否更广泛地扩展到 依赖mTOR的蛋白质合成。因此，目标4假设，就像喂食一样，1)锻炼协调地驱动 蛋白质平衡和肌肉所需的依赖mTOR的蛋白质合成和HSF1转录程序 生长，以及2)细胞质(HSF1)和内质网(XBP1s)蛋白质折叠反应之间的串扰 运动，就像我们看到的喂食一样。拟议的研究对这些假设进行了详细的检验。

Project summary We have found that feeding activates previously unrecognized transcriptional programs in liver and muscle designed to maintain protein folding homeostasis, or proteostasis. Heat shock factor 1 (HSF1), the master transcription factor that controls the heat shock response (HSR), regulates and is required for these normal physiological responses. The programs are inhibited by fasting, and hyperstimulated by refeeding after fasting. The setting and pattern of regulation, inhibition by fasting and activation in liver and muscle by feeding closely resembles mTOR responses. We further found that the HSF1 transcriptional program is in fact downstream of the canonical Tsc1/2-Rheb-mTORC1 axis and is required for mTOR-dependent protein synthesis. Regulation appears to go both ways. Inhibition of mTOR suppresses the HSF1 transcriptional response, and HSF1 loss- of-function in liver suppresses both mTOR activation and protein synthesis. mTOR regulation clearly distinguishes the HSF1 feeding response from a classical heat shock response, which is not regulated by mTOR. Transcriptome-wide RNA-seq results further distinguish the hepatic feeding response from the HSR, as fewer than 10% of genes are common to both responses. The RNA-seq results also show that feeding induces an unfolded protein response (UPR) in the ER, which is distinct from the cytoplasmic protein folding response (cPFR) we describe. While cytoplasmic and ER protein folding responses are distinguished by both subcellular distribution and proteins/pathways involved, they appear to be mechanistically linked, as perturbations in one affect the other (e.g. the XBP1s transcriptional program is suppressed in Hsf1 null liver). Based on our preliminary findings we hypothesize: 1) Feeding acutely increases protein synthesis and therefore the protein folding burden in liver and muscle. 2) mTOR simultaneously promotes protein synthesis and the cellular machinery for maintaining proteostasis. 3) HSF1 loss of function increases the cytoplasmic protein folding burden, which 4) suppresses mTOR-dependent protein synthesis and thereby 5) reduces the protein folding burden in both cytoplasm and ER. Similarly, 6) XBP1 loss of function induces ER stress, which suppresses mTOR dependent protein synthesis and the protein folding burden in both cytoplasm and ER, which suggest 7) cross-talk between cytoplasmic and ER protein folding responses. We contrast the physiological feeding responses in muscle and liver with the classical HSR at all levels, regulation, transcriptional programs, and effects of HSF1 on both mTOR and the ER protein folding response. Aims 1-3 test hypotheses related to feeding, whereas Aim 4 asks whether the proposed mechanisms extend more broadly to other settings of mTOR-dependent protein synthesis. Aim 4 thus hypothesizes that like feeding, 1) exercise coordinately drives mTOR-dependent protein synthesis and an HSF1 transcriptional program required for proteostasis and muscle growth, and 2) cross-talk between cytoplasmic (HSF1) and ER (XBP1s) protein folding responses occurs with exercise as we had seen with feeding. Proposed studies test these hypotheses in detail.