Feeding Drives HSF1 Transcriptional Programs Required for Global Protein Synthesis

项目摘要 我们发现进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稳态或蛋白质稳态。热休克因子1（HSF 1）， 一种控制热休克反应（HSR）的转录因子，调节这些正常的 生理反应。这些程序被禁食抑制，禁食后再进食会过度刺激。 肝脏和肌肉中的调节、禁食抑制和密切喂养激活的设置和模式 类似于mTOR反应。我们进一步发现，HSF 1转录程序实际上是下游的， 典型的Tsc 1/2-Rheb-mTORC 1轴，是mTOR依赖性蛋白质合成所必需的。调控 似乎是双向的mTOR的抑制抑制了HSF 1的转录反应和HSF 1的丢失。 肝脏中的功能缺失抑制mTOR活化和蛋白质合成。mTOR调控明确 将HSF 1摄食反应与经典的热休克反应区分开来，后者不受 mTOR。全转录组RNA-seq结果进一步区分了肝脏摄食反应与HSR， 只有不到10%的基因是两种反应共有的。RNA-seq结果还表明， ER中的未折叠蛋白反应（UPR），与胞质蛋白折叠反应不同 （cPFR）我们描述。虽然细胞质和ER蛋白折叠反应是由亚细胞和细胞质两种不同的蛋白折叠反应来区分的， 分布和蛋白质/途径参与，他们似乎是机械联系，作为扰动在一个 影响另一个（例如，在Hsf 1缺失的肝脏中，XBP 1 s转录程序被抑制）。基于我们 初步研究结果，我们假设：1）喂养急剧增加蛋白质的合成，因此蛋白质 肝脏和肌肉的折叠负担。2)mTOR同时促进蛋白质合成和细胞增殖。 维持蛋白质稳态的机制。3)HSF 1功能丧失增加细胞质蛋白折叠 负荷，其4）抑制mTOR依赖性蛋白质合成，从而5）减少蛋白质折叠 在细胞质和ER中的负荷。类似地，6）XBP 1功能的丧失诱导ER应激，其抑制 细胞质和ER中的mTOR依赖性蛋白质合成和蛋白质折叠负荷，这表明7） 细胞质和ER蛋白折叠反应之间的串扰。我们将生理摄食 肌肉和肝脏中的经典HSR反应在所有水平，调节，转录程序， HSF 1对mTOR和ER蛋白折叠反应的影响。目标1-3检验假设 喂养，而目标4问是否提出的机制更广泛地扩展到其他设置， mTOR依赖性蛋白质合成。目标4因此假设，像喂养，1）运动协调驱动 mTOR依赖性蛋白质合成和蛋白质稳态和肌肉生长所需的HSF 1转录程序 生长，和2）细胞质（HSF 1）和ER（XBP 1 s）蛋白折叠反应之间的串扰发生， 就像我们在喂食中看到的那样锻炼。拟议中的研究将详细检验这些假设。

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.