National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, P.R. China.
National Institute of Biological Sciences, Beijing 102206, P.R. China.
Mol Cell. 2017 Sep 21;67(6):974-989.e6. doi: 10.1016/j.molcel.2017.08.005. Epub 2017 Sep 7.
During autophagosome formation in mammalian cells, isolation membranes (IMs; autophagosome precursors) dynamically contact the ER. Here, we demonstrated that the ER-localized metazoan-specific autophagy protein EPG-3/VMP1 controls ER-IM contacts. Loss of VMP1 causes stable association of IMs with the ER, thus blocking autophagosome formation. Interaction of WIPI2 with the ULK1/FIP200 complex and PI(3)P contributes to the formation of ER-IM contacts, and these interactions are enhanced by VMP1 depletion. VMP1 controls contact formation by promoting SERCA (sarco[endo]plasmic reticulum calcium ATPase) activity. VMP1 interacts with SERCA and prevents formation of the SERCA/PLN/SLN inhibitory complex. VMP1 also modulates ER contacts with lipid droplets, mitochondria, and endosomes. These ER contacts are greatly elevated by the SERCA inhibitor thapsigargin. Calmodulin acts as a sensor/effector to modulate the ER contacts mediated by VMP1/SERCA. Our study provides mechanistic insights into the establishment and disassociation of ER-IM contacts and reveals that VMP1 modulates SERCA activity to control ER contacts.
在哺乳动物细胞的自噬体形成过程中，隔离膜（自噬体前体）与内质网（ER）动态接触。在这里，我们证明了定位于 ER 的后生动物特异性自噬蛋白 EPG-3/VMP1 控制 ER-IM 接触。VMP1 的缺失导致 IMs 与 ER 的稳定结合，从而阻止自噬体的形成。WIPI2 与 ULK1/FIP200 复合物和 PI(3)P 的相互作用有助于 ER-IM 接触的形成，并且这些相互作用通过 VMP1 的耗竭而增强。VMP1 通过促进 SERCA（肌浆网内质网钙 ATP 酶）活性来控制接触的形成。VMP1 与 SERCA 相互作用并防止 SERCA/PLN/SLN 抑制性复合物的形成。VMP1 还调节 ER 与脂滴、线粒体和内体的接触。SERCA 抑制剂 thapsigargin 极大地增加了这些 ER 接触。钙调蛋白作为传感器/效应物，调节由 VMP1/SERCA 介导的 ER 接触。我们的研究为 ER-IM 接触的建立和分离提供了机制上的见解，并揭示了 VMP1 通过调节 SERCA 活性来控制 ER 接触。
