Abstract
The ER forms contacts with other endomembrane systems to exchange materials (e.g., calcium and lipids) and also to modulate dynamic organelle processes, including fission, cargo sorting and movement. During autophagosome formation, dynamic contacts between the ER and the phagophore membrane are crucial for phagophore expansion and closure. Little is known about the mechanisms underlying the formation and disassembly of the ER contacts. We found that the ER-localized autophagy protein EPG-3/VMP1 plays an essential role in controlling ER-phagophore dissociation and also the disassembly of ER contacts with LDs, mitochondria and endolysosomes. VMP1 regulates the ER contact by activating the ER calcium channel ATP2A/SERCA (ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting). CALM (calmodulin) acts as one of the downstream calcium effectors that controls the PIK3C3/VPS34 phosphatidylinositol (PtdIns) 3-kinase (PtdIns3K) activity to maintain these contacts. Our study provides insights into the molecular mechanisms which regulate ER contacts and generate autophagosomes.