Graduate School of Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka 422-8021, Japan.
Department of Bioscience, Faculty of Science, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka 422-8021, Japan.
J Mol Biol. 2022 Jan 30;434(2):167360. doi: 10.1016/j.jmb.2021.167360. Epub 2021 Nov 16.
Phosphatidylinositol 3-phosphate (PI3P), a scaffold of membrane-associated proteins required for diverse cellular events, is produced by Vps34-containing phosphatidylinositol 3-kinase (PI3K). PI3K complex I (PI3KCI)-generated PI3P is required for macroautophagy, whereas PI3K complex II (PI3KCII)-generated PI3P is required for endosomal sorting complex required for transport (ESCRT)-mediated multi-vesicular body (MVB) formation in late endosomes. ESCRT also promotes vacuolar membrane remodeling in microautophagy after nutrient starvation and inactivation of target of rapamycin complex 1 (TORC1) protein kinase in budding yeast. Whereas PI3KCI and macroautophagy are critical for the nutrient starvation response, the physiological roles of PI3KCII and microautophagy during starvation are largely unknown. Here, we showed that PI3KCII-produced PI3P on vacuolar membranes is required for microautophagy induction and survival in nutrient-stressed conditions. PI3KCII is required for Vps27 (an ESCRT-0 component) recruitment and ESCRT-0 complex formation on vacuolar surfaces after TORC1 inactivation. Forced recruitment of Vps27 onto vacuolar membranes rescued the defect in microautophagy induction in PI3KCII-deficient cells, indicating that a critical role of PI3P on microautophagy induction is Vps27 recruitment onto vacuolar surfaces. Finally, vacuolar membrane-associated Vps27 was able to recover survival during nutrient starvation in cells lacking PI3KCII or Vps27. This study revealed that the PI3KCII-PI3P-Vps27 axis on vacuolar membranes is critical for ESCRT-mediated microautophagy induction and nutrient stress adaptation.
磷脂酰肌醇 3-磷酸 (PI3P) 是一种膜相关蛋白的支架，对于多种细胞事件是必需的，它由含有 Vps34 的磷脂酰肌醇 3-激酶 (PI3K) 产生。PI3K 复合物 I (PI3KCI) 产生的 PI3P 是巨自噬所必需的，而 PI3K 复合物 II (PI3KCII) 产生的 PI3P 是内体分选复合物所需的，用于运输 (ESCRT) 介导的晚期内体中的多泡体 (MVB) 形成。ESCRT 还促进营养饥饿和芽殖酵母中雷帕霉素靶蛋白复合物 1 (TORC1) 蛋白激酶失活后微自噬中的液泡膜重塑。尽管 PI3KCI 和巨自噬对于营养饥饿反应是关键的，但在饥饿期间 PI3KCII 和微自噬的生理作用在很大程度上是未知的。在这里，我们表明，液泡膜上的 PI3KCII 产生的 PI3P 对于微自噬的诱导和在营养胁迫条件下的生存是必需的。PI3KCII 对于 Vps27（ESCRT-0 组件）在 TORC1 失活后在液泡表面的募集和 ESCRT-0 复合物的形成是必需的。Vps27 被强制募集到液泡膜上，挽救了 PI3KCII 缺陷细胞中微自噬诱导的缺陷，表明 PI3P 在微自噬诱导中的关键作用是 Vps27 募集到液泡表面。最后，在缺乏 PI3KCII 或 Vps27 的细胞中，液泡膜相关的 Vps27 能够在营养饥饿期间恢复生存。这项研究揭示了液泡膜上的 PI3KCII-PI3P-Vps27 轴对于 ESCRT 介导的微自噬诱导和营养压力适应是至关重要的。
