Mammalian target of rapamycin (mTOR) senses changes in nutrient status and stimulates the autophagic process to recycle amino acids. However, the impact of nutrient stress on protein degradation beyond autophagic turnover is incompletely understood. We report that several metabolic enzymes are proteasomal targets regulated by mTOR activity based on comparative proteome degradation analysis. In particular, 3-hydroxy-3-methylglutaryl (HMG)-coenzyme A (CoA) synthase 1 (HMGCS1), the initial enzyme in the mevalonate pathway, exhibits the most significant half-life adaptation. Degradation of HMGCS1 is regulated by the C-terminal to LisH (CTLH) E3 ligase through the Pro/N-degron motif. HMGCS1 is ubiquitylated on two C-terminal lysines during mTORC1 inhibition, and efficient degradation of HMGCS1 in cells requires a muskelin adaptor. Importantly, modulating HMGCS1 abundance has a dose-dependent impact on cell proliferation, which is restored by adding a mevalonate intermediate. Overall, our unbiased degradomics study provides new insights into mTORC1 function in cellular metabolism: mTORC1 regulates the stability of limiting metabolic enzymes through the ubiquitin system.

哺乳动物雷帕霉素靶标 (mTOR) 感知营养状态的变化并刺激自噬过程以回收氨基酸。然而，营养胁迫对自噬周转之外的蛋白质降解的影响尚不完全清楚。我们根据比较蛋白质组降解分析报告，几种代谢酶是 mTOR 活性调节的蛋白酶体靶标。特别是，甲羟戊酸途径中的起始酶 3-羟基-3-甲基戊二酰 (HMG)-辅酶 A (CoA) 合酶 1 (HMGCS1) 表现出最显着的半衰期适应性。 HMGCS1 的降解由 LisH (CTLH) E3 连接酶的 C 端通过 Pro/N-degron 基序调节。在 mTORC1 抑制过程中，HMGCS1 在两个 C 末端赖氨酸上泛素化，细胞中 HMGCS1 的有效降解需要 muskelin 接头。重要的是，调节 HMGCS1 丰度对细胞增殖具有剂量依赖性影响，通过添加甲羟戊酸中间体可以恢复细胞增殖。总体而言，我们的公正降解组学研究为 mTORC1 在细胞代谢中的功能提供了新的见解：mTORC1 通过泛素系统调节限制代谢酶的稳定性。