Departments of Biochemistry, University of Illinois at Chicago, Chicago, IL 60607, USA.
Proc Natl Acad Sci U S A. 2012 May 1;109(18):6981-6. doi: 10.1073/pnas.1121299109. Epub 2012 Apr 16.
The key regulators of intracellular trafficking, Ypt/Rab GTPases, are stimulated by specific upstream activators and, when activated, recruit specific downstream effectors to mediate membrane-transport events. The yeast Ypt1 and its human functional homolog hRab1 regulate both endoplasmic reticulum (ER)-to-Golgi transport and autophagy. However, it is not clear whether the mechanism by which these GTPases regulate autophagy depends on their well-documented function in ER-to-Golgi transport. Here, we identify Atg11, the preautophagosomal structure (PAS) organizer, as a downstream effector of Ypt1 and show that the Ypt1-Atg11 interaction is required for PAS assembly under normal growth conditions. Moreover, we show that Ypt1 and Atg11 colocalize with Trs85, a Ypt1 activator subunit, and together they regulate selective autophagy. Finally, we show that Ypt1 and Trs85 interact on Atg9-containing membranes, which serve as a source for the membrane component of the PAS. Together our results define a Ypt/Rab module--comprising an activator, GTPase, and effector--that orchestrates the onset of selective autophagy, a process vital for cell homeostasis. Furthermore, because Atg11 does not play a role in ER-to-Golgi transport, we demonstrate here that Ypt/Rabs can regulate two independent membrane-transport processes by recruiting process-specific effectors.
细胞内运输的关键调节因子是 Ypt/Rab GTP 酶，它受特定的上游激活剂刺激，在被激活后，招募特定的下游效应物来介导膜转运事件。酵母 Ypt1 和其人类功能同源物 hRab1 调节内质网（ER）-高尔基体运输和自噬。然而，这些 GTP 酶调节自噬的机制是否依赖于它们在 ER-高尔基体运输中的已有功能尚不清楚。在这里，我们鉴定出 Atg11，即前自噬体结构（PAS）组织者，是 Ypt1 的下游效应物，并表明 Ypt1-Atg11 相互作用是 PAS 在正常生长条件下组装所必需的。此外，我们还表明 Ypt1 和 Atg11 与 Trs85 共定位，Trs85 是 Ypt1 的激活亚基，它们共同调节选择性自噬。最后，我们表明 Ypt1 和 Trs85 在含有 Atg9 的膜上相互作用，这些膜是 PAS 膜成分的来源。总之，我们的研究结果定义了一个 Ypt/Rab 模块，包括一个激活剂、GTP 酶和效应物，它协调了选择性自噬的开始，这是细胞内稳态的一个关键过程。此外，由于 Atg11 不参与 ER-高尔基体运输，我们在这里证明 Ypt/Rabs 可以通过招募特定过程的效应物来调节两种独立的膜转运过程。
