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.

在哺乳动物细胞中自噬体形成过程中，隔离膜（IM；自噬体前体）会动态接触内质网。在这里，我们证明了ER定位的后生动物特异性自噬蛋白EPG-3 / VMP1控制ER-IM接触。VMP1的丢失会导致IM与ER稳定缔合，从而阻止自噬小体的形成。WIPI2与ULK1 / FIP200复合体和PI（3）P的相互作用有助于ER-IM接触的形成，而VMP1增强了这些相互作用消耗。VMP1通过促进SERCA（肌质网钙ATPase）活性来控制接触的形成。VMP1与SERCA相互作用并阻止SERCA / PLN / SLN抑制复合物的形成。VMP1还调节与脂质滴，线粒体和内体的ER接触。SERCA抑制剂thapsigargin大大提高了这些ER接触。钙调蛋白充当传感器/效应子，以调节由VMP1 / SERCA介导的ER接触。我们的研究为ER-IM接触的建立和解除提供了机械方面的见解，并揭示了VMP1调节SERCA活性以控制ER接触。