scholarly journals Spatial control of avidity regulates initiation and progression of selective autophagy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
David M. Hollenstein ◽  
Mariya Licheva ◽  
Nicole Konradi ◽  
David Schweida ◽  
Hector Mancilla ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Nuclear Membrane ◽  
Vacuolar Membrane ◽  
Phosphatidylinositol 3 Kinase ◽  
Autophagosome Formation ◽  
Spatial Control ◽  
Selective Autophagy ◽  
Phagophore Assembly Site ◽  
Assembly Site ◽  
Phosphatidylinositol 3

AbstractAutophagosomes form at the endoplasmic reticulum in mammals, and between the vacuole and the endoplasmic reticulum in yeast. However, the roles of these sites and the mechanisms regulating autophagosome formation are incompletely understood. Vac8 is required for autophagy and recruits the Atg1 kinase complex to the vacuole. Here we show that Vac8 acts as a central hub to nucleate the phagophore assembly site at the vacuolar membrane during selective autophagy. Vac8 directly recruits the cargo complex via the Atg11 scaffold. In addition, Vac8 recruits the phosphatidylinositol 3-kinase complex independently of autophagy. Cargo-dependent clustering and Vac8-dependent sequestering of these early autophagy factors, along with local Atg1 activation, promote phagophore assembly site assembly at the vacuole. Importantly, ectopic Vac8 redirects autophagosome formation to the nuclear membrane, indicating that the vacuolar membrane is not specifically required. We propose that multiple avidity-driven interactions drive the initiation and progression of selective autophagy.

scholarly journals Autophagosome formation in relation to the endoplasmic reticulum

2020 ◽  
Vol 27 (1) ◽  
Author(s):  
Yo-hei Yamamoto ◽  
Takeshi Noda
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
De Novo ◽  
Transmembrane Protein ◽  
Lipid Transfer ◽  
Membrane Structures ◽  
Autophagosome Formation ◽  
Selective Autophagy ◽  
The Relationship ◽  
Er Membrane

Abstract Autophagy is a process in which a myriad membrane structures called autophagosomes are formed de novo in a single cell, which deliver the engulfed substrates into lysosomes for degradation. The size of the autophagosomes is relatively uniform in non-selective autophagy and variable in selective autophagy. It has been recently established that autophagosome formation occurs near the endoplasmic reticulum (ER). In this review, we have discussed recent advances in the relationship between autophagosome formation and endoplasmic reticulum. Autophagosome formation occurs near the ER subdomain enriched with phospholipid synthesizing enzymes like phosphatidylinositol synthase (PIS)/CDP-diacylglycerol-inositol 3-phosphatidyltransferase (CDIPT) and choline/ethanolamine phosphotransferase 1 (CEPT1). Autophagy-related protein 2 (Atg2), which is involved in autophagosome formation has a lipid transfer capacity and is proposed to directly transfer the lipid molecules from the ER to form autophagosomes. Vacuole membrane protein 1 (VMP1) and transmembrane protein 41b (TMEM41b) are ER membrane proteins that are associated with the formation of the subdomain. Recently, we have reported that an uncharacterized ER membrane protein possessing the DNAJ domain, called ERdj8/DNAJC16, is associated with the regulation of the size of autophagosomes. The localization of ERdj8/DNAJC16 partially overlaps with the PIS-enriched ER subdomain, thereby implying its association with autophagosome size determination.

scholarly journals Phosphatidylinositol 3-Kinase/AKT Pathway Regulates the Endoplasmic Reticulum to Golgi Traffic of Ceramide in Glioma Cells

2008 ◽  
Vol 284 (8) ◽  
pp. 5088-5096 ◽  
Author(s):  
Paola Giussani ◽  
Loredana Brioschi ◽  
Rosaria Bassi ◽  
Laura Riboni ◽  
Paola Viani
Keyword(s):  
Endoplasmic Reticulum ◽  
Glioma Cells ◽  
Akt Pathway ◽  
Phosphatidylinositol 3 Kinase ◽  
Phosphatidylinositol 3

scholarly journals Hyperosmotic Stress Induces Unconventional Autophagy Independent of the Ulk1 Complex

2019 ◽  
Vol 39 (16) ◽  
Author(s):  
Naoki Tamura ◽  
Shun Kageyama ◽  
Masaaki Komatsu ◽  
Satoshi Waguri
Keyword(s):  
Hyperosmotic Stress ◽  
Adaptive Mechanism ◽  
Phosphatidylinositol 3 Kinase ◽  
Mouse Embryonic Fibroblasts ◽  
Embryonic Fibroblasts ◽  
Selective Autophagy ◽  
Membrane Markers ◽  
T24 Cells ◽  
Mtor Activity ◽  
Phosphatidylinositol 3

ABSTRACT Autophagy is considered an adaptive mechanism against hyperosmotic stress. Although the process has been reported to be triggered by the inhibition of mTORC1, the precise downstream mechanisms remain elusive. Here, we demonstrate that hyperosmotic-stress-induced autophagy is different from conventional macroautophagy in mouse embryonic fibroblasts (MEFs) and human T24 cells. Our results indicated that cytoplasmic puncta for the isolation membrane markers WIPI2 and Atg16L increased after hyperosmotic stress. They were found to partially colocalize with puncta for a selective autophagy substrate, SQSTM1/p62, and were shown to be diminished by inhibitors of phosphatidylinositol 3-kinase (PI3K) or by knockdown of human Vps34 (hVps34), a component of PI3K. In addition, flux assays showed that SQSTM1/p62 and NcoA4 were degraded by the lysosomal pathway. Surprisingly, Ulk1, which is essential for starvation-induced macroautophagy, remained inactivated under hyperosmotic stress, which was partially caused by mTOR activity. Accordingly, the Ulk1 complex was not nucleated under hyperosmotic stress. Finally, autophagy proceeded even in MEFs deficient in RB1CC1/FIP200 or Atg13, which encode components of the Ulk1 complex. These data suggest that hyperosmotic-stress-induced autophagy represents an unconventional type of autophagy that bypasses Ulk1 signaling.

scholarly journals Autophagosome formation from membrane compartments enriched in phosphatidylinositol 3-phosphate and dynamically connected to the endoplasmic reticulum

2008 ◽  
Vol 182 (4) ◽  
pp. 685-701 ◽  
Author(s):  
Elizabeth L. Axe ◽  
Simon A. Walker ◽  
Maria Manifava ◽  
Priya Chandra ◽  
H. Llewelyn Roderick ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Dynamic Equilibrium ◽  
Membrane Vesicles ◽  
Amino Acid Starvation ◽  
Autophagosome Formation ◽  
Double Membrane ◽  
Dynamic Relationship ◽  
Golgi Membranes ◽  
Membrane Compartments ◽  
Phosphatidylinositol 3

Autophagy is the engulfment of cytosol and organelles by double-membrane vesicles termed autophagosomes. Autophagosome formation is known to require phosphatidylinositol 3-phosphate (PI(3)P) and occurs near the endoplasmic reticulum (ER), but the exact mechanisms are unknown. We show that double FYVE domain–containing protein 1, a PI(3)P-binding protein with unusual localization on ER and Golgi membranes, translocates in response to amino acid starvation to a punctate compartment partially colocalized with autophagosomal proteins. Translocation is dependent on Vps34 and beclin function. Other PI(3)P-binding probes targeted to the ER show the same starvation-induced translocation that is dependent on PI(3)P formation and recognition. Live imaging experiments show that this punctate compartment forms near Vps34-containing vesicles, is in dynamic equilibrium with the ER, and provides a membrane platform for accumulation of autophagosomal proteins, expansion of autophagosomal membranes, and emergence of fully formed autophagosomes. This PI(3)P-enriched compartment may be involved in autophagosome biogenesis. Its dynamic relationship with the ER is consistent with the idea that the ER may provide important components for autophagosome formation.

scholarly journals Autophagy requires endoplasmic reticulum targeting of the PI3-kinase complex via Atg14L

2010 ◽  
Vol 190 (4) ◽  
pp. 511-521 ◽  
Author(s):  
Kohichi Matsunaga ◽  
Eiji Morita ◽  
Tatsuya Saitoh ◽  
Shizuo Akira ◽  
Nicholas T. Ktistakis ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
Embryonic Stem ◽  
Pi3 Kinase ◽  
Class Iii ◽  
Autophagosome Formation ◽  
Membranous Structure ◽  
Er Targeting ◽  
Endoplasmic Reticulum Targeting ◽  
Phosphatidylinositol 3

Autophagy is a catabolic process that allows cells to digest their cytoplasmic constituents via autophagosome formation and lysosomal degradation. Recently, an autophagy-specific phosphatidylinositol 3-kinase (PI3-kinase) complex, consisting of hVps34, hVps15, Beclin-1, and Atg14L, has been identified in mammalian cells. Atg14L is specific to this autophagy complex and localizes to the endoplasmic reticulum (ER). Knockdown of Atg14L leads to the disappearance of the DFCP1-positive omegasome, which is a membranous structure closely associated with both the autophagosome and the ER. A point mutation in Atg14L resulting in defective ER localization was also defective in the induction of autophagy. The addition of the ER-targeting motif of DFCP1 to this mutant fully complemented the autophagic defect in Atg14L knockout embryonic stem cells. Thus, Atg14L recruits a subset of class III PI3-kinase to the ER, where otherwise phosphatidylinositol 3-phosphate (PI3P) is essentially absent. The Atg14L-dependent appearance of PI3P in the ER makes this organelle the platform for autophagosome formation.

scholarly journals Vacuolar protein Tag1 and Atg1–Atg13 regulate autophagy termination during persistent starvation in S. cerevisiae

2021 ◽  
Vol 134 (4) ◽  
pp. jcs253682
Author(s):  
Shintaro Kira ◽  
Masafumi Noguchi ◽  
Yasuhiro Araki ◽  
Yu Oikawa ◽  
Tamotsu Yoshimori ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Protein Kinase ◽  
Membrane Protein ◽  
Nitrogen Starvation ◽  
Genetic Screen ◽  
Vacuolar Membrane ◽  
Phagophore Assembly Site ◽  
Vacuolar Protein ◽  
Assembly Site ◽  
Starvation Conditions

ABSTRACTUnder starvation conditions, cells degrade their own components via autophagy in order to provide sufficient nutrients to ensure their survival. However, even if starvation persists, the cell is not completely degraded through autophagy, implying the existence of some kind of termination mechanism. In the yeast Saccharomyces cerevisiae, autophagy is terminated after 10–12 h of nitrogen starvation. In this study, we found that termination is mediated by re-phosphorylation of Atg13 by the Atg1 protein kinase, which is also affected by PP2C phosphatases, and the eventual dispersion of the pre-autophagosomal structure, also known as the phagophore assembly site (PAS). In a genetic screen, we identified an uncharacterized vacuolar membrane protein, Tag1, as a factor responsible for the termination of autophagy. Re-phosphorylation of Atg13 and eventual PAS dispersal were defective in the Δtag1 mutant. The vacuolar luminal domain of Tag1 and autophagic progression are important for the behaviors of Tag1. Together, our findings reveal the mechanism and factors responsible for termination of autophagy in yeast.

scholarly journals Reconstitution of autophagosome nucleation defines Atg9 vesicles as seeds for membrane formation

Science ◽  
2020 ◽  
Vol 369 (6508) ◽  
pp. eaaz7714 ◽  
Author(s):  
Justyna Sawa-Makarska ◽  
Verena Baumann ◽  
Nicolas Coudevylle ◽  
Sören von Bülow ◽  
Veronika Nogellova ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
De Novo ◽  
Lipid Transfer ◽  
Related Protein ◽  
Membrane Formation ◽  
Selective Autophagy ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Phosphatidylinositol 3

Autophagosomes form de novo in a manner that is incompletely understood. Particularly enigmatic are autophagy-related protein 9 (Atg9)–containing vesicles that are required for autophagy machinery assembly but do not supply the bulk of the autophagosomal membrane. In this study, we reconstituted autophagosome nucleation using recombinant components from yeast. We found that Atg9 proteoliposomes first recruited the phosphatidylinositol 3-phosphate kinase complex, followed by Atg21, the Atg2-Atg18 lipid transfer complex, and the E3-like Atg12–Atg5-Atg16 complex, which promoted Atg8 lipidation. Furthermore, we found that Atg2 could transfer lipids for Atg8 lipidation. In selective autophagy, these reactions could potentially be coupled to the cargo via the Atg19-Atg11-Atg9 interactions. We thus propose that Atg9 vesicles form seeds that establish membrane contact sites to initiate lipid transfer from compartments such as the endoplasmic reticulum.

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