Laboratory of Membrane Biochemistry and Biophysics, Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan.
J Biol Chem. 2010 Nov 19;285(47):36984-94. doi: 10.1074/jbc.M110.119180. Epub 2010 Sep 20.
Nitrogen starvation-mediated reduction of Ypk1 is suggested to suppress translational initiation, possibly in parallel with the target of rapamycin complex 1 (TORC1) signaling. However, the molecular mechanism that regulates Ypk1 in nitrogen-starved cells is poorly understood. Here we report that Ypk1 is a novel selective substrate for nitrogen starvation-triggered proteolysis requiring autophagy system. Among various nutrient starvation methods used to elicit autophagy, rapid Ypk1 degradation was specific to nitrogen starvation. In screening genes required for such nitrogen starvation-specific vacuolar proteolysis, we found that autophagy-related degradation of Ypk1 depended on the endosomal sorting complex required for transport (ESCRT) machinery, which is conventionally thought to function in endosomal trafficking. In microscopic analyses, the disruption of ESCRT subunits resulted in the accumulation of both Ypk1 and autophagosomal Atg8 at a perivacuolar site that was distinct from conventional endosomes. ESCRT machinery was not involved in autophagic flux induced by the TORC1 inhibitor rapamycin, thus suggesting that ESCRT represents an exclusive mechanism of nitrogen starvation-specific proteolysis of Ypk1. Overall, we propose a novel regulation of Ypk1 that is specific to nitrogen limitation.
氮饥饿介导的 Ypk1 减少被认为抑制翻译起始,可能与雷帕霉素复合物 1(TORC1)信号平行。然而,调节氮饥饿细胞中 Ypk1 的分子机制还知之甚少。在这里,我们报告 Ypk1 是一种新型的氮饥饿触发的蛋白水解的选择性底物,需要自噬系统。在用于引发自噬的各种营养饥饿方法中,快速 Ypk1 降解是氮饥饿特有的。在筛选参与这种氮饥饿特异性液泡蛋白水解所需的基因时,我们发现 Ypk1 的自噬相关降解依赖于内体分选复合物必需的运输(ESCRT)机制,该机制通常被认为在内涵体运输中起作用。在微观分析中,ESCRT 亚基的破坏导致 Ypk1 和自噬体 Atg8 在靠近液泡的位置积累,与传统的内涵体不同。ESCRT 机制不参与 TORC1 抑制剂雷帕霉素诱导的自噬通量,因此表明 ESCRT 代表 Ypk1 的氮饥饿特异性蛋白水解的独特机制。总的来说,我们提出了一种对氮限制特异的 Ypk1 的新调节。