Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261.
Mol Biol Cell. 2018 Nov 1;29(22):2751-2765. doi: 10.1091/mbc.E18-03-0158. Epub 2018 Aug 29.
TORC1 (target of rapamycin complex) integrates complex nutrient signals to generate and fine-tune a growth and metabolic response. Npr1 (nitrogen permease reactivator) is a downstream effector kinase of TORC1 that regulates the stability, activity, and trafficking of various nutrient permeases including the ammonium permeases Mep1, Mep2, and Mep3 and the general amino acid permease Gap1. Npr1 exerts its regulatory effects on Mep1 and Mep3 via Par32 (phosphorylated after rapamycin). Activation of Npr1 leads to phosphorylation of Par32, resulting in changes in its subcellular localization and function. Here we demonstrate that Par32 is a positive regulator of TORC1 activity. Loss of Par32 renders cells unable to recover from exposure to rapamycin and reverses the resistance to rapamycin of Δ npr1 cells. The sensitivity to rapamycin of cells lacking Par32 is dependent on Mep1 and Mep3 and the presence of ammonium, linking ammonium metabolism to TORC1 activity. Par32 function requires its conserved repeated glycine-rich motifs to be intact but, surprisingly, does not require its localization to the plasma membrane. In all, this work elucidates a novel mechanism by which Npr1 and Par32 exert regulatory feedback on TORC1.
TORC1（雷帕霉素靶蛋白复合物 1）整合了复杂的营养信号，以产生和微调生长和代谢反应。Npr1（氮渗透酶激活剂）是 TORC1 的下游效应激酶，调节各种营养渗透酶的稳定性、活性和运输，包括铵渗透酶 Mep1、Mep2 和 Mep3 以及一般氨基酸渗透酶 Gap1。Npr1 通过 Par32（雷帕霉素后磷酸化）对 Mep1 和 Mep3 发挥其调节作用。Npr1 的激活导致 Par32 的磷酸化，导致其亚细胞定位和功能发生变化。在这里，我们证明 Par32 是 TORC1 活性的正调节剂。Par32 的缺失使细胞无法从雷帕霉素暴露中恢复，并逆转了Δnpr1 细胞对雷帕霉素的抗性。缺乏 Par32 的细胞对雷帕霉素的敏感性依赖于 Mep1 和 Mep3 以及铵的存在，将铵代谢与 TORC1 活性联系起来。Par32 的功能需要其保守的重复甘氨酸丰富基序完整，但令人惊讶的是，不需要其定位于质膜。总之，这项工作阐明了 Npr1 和 Par32 对 TORC1 发挥调节反馈的新机制。
