The ER–Golgi intermediate compartment is a key membrane source for the LC3 lipidation step of autophagosome biogenesis

Ge, Liang; Melville, D.; Zhang, Min; Schekman, Randy

doi:10.7554/elife.00947

Cited by 368 publications

(387 citation statements)

References 83 publications

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“…Ge et al [82] found that the membrane fraction from Atg5-knockout MEF cells, in which no LC3 conjugation occurs, can be conjugated with LC3 when incubated with the cytosol from wild type cells. Using this cell-free assay system, they further performed membrane fractionation and found that LC3 was preferentially conjugated with the membrane subfraction containing ERGIC marker proteins.…”

Section: The Er-golgi Intermediate Compartment (Ergic)mentioning

confidence: 99%

A current perspective of autophagosome biogenesis

2013

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Autophagy is a bulk degradation system induced by cellular stresses such as nutrient starvation. Its function relies on the formation of double-membrane vesicles called autophagosomes. Unlike other organelles that appear to stably exist in the cell, autophagosomes are formed on demand, and once their formation is initiated, it proceeds surprisingly rapidly. How and where this dynamic autophagosome formation takes place has been a long-standing question, but the discovery of Atg proteins in the 1990's significantly accelerated our understanding of autophagosome biogenesis. In this review, we will briefly introduce each Atg functional unit in relation to autophagosome biogenesis, and then discuss the origin of the autophagosomal membrane with an introduction to selected recent studies addressing this problem.

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Section: The Er-golgi Intermediate Compartment (Ergic)mentioning

confidence: 99%

A current perspective of autophagosome biogenesis

2013

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“…ATG14 and ATG5 puncta formation is associated with autophagy initiation (21,23). ATG5 puncta, which is usually used as a phagophore marker, also localized to LAPTM4B positive endosomes ( Fig.…”

Section: Significancementioning

confidence: 99%

PtdIns(4,5)P ₂ signaling regulates ATG14 and autophagy

Tan

Thapa

Liao

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Autophagy is a regulated self-digestion pathway with fundamental roles in cell homeostasis and diseases. Autophagy is regulated by coordinated actions of a series of autophagy-related (ATG) proteins. The Barkor/ATG14(L)-VPS34 (a class III phosphatidylinositol 3-kinase) complex and its product phosphatidylinositol 3-phosphate [PtdIns(3)P] play key roles in autophagy initiation. ATG14 contains a C-terminal Barkor/ATG14(L) autophagosome-targeting sequence (BATS) domain that senses the curvature of PtdIns(3)P-containing membrane. The BATS domain also strongly binds PtdIns(4,5)P 2 , but the functional significance has been unclear. Here we show that ATG14 specifically interacts with type Iγ PIP kinase isoform 5 (PIPKIγi5), an enzyme that generates PtdIns(4,5)P 2 in mammalian cells. Autophagosomes have associated PIPKIγi5 and PtdIns(4,5)P 2 that are colocalized with late endosomes and the endoplasmic reticulum. PtdIns(4,5)P 2 generation at these sites requires PIPKIγi5. Loss of PIPKIγi5 results in a loss of ATG14, UV irradiation resistance-associated gene, and Beclin 1 and a block of autophagy. PtdIns(4,5)P 2 binding to the ATG14-BATS domain regulates ATG14 interaction with VPS34 and Beclin 1, and thus plays a key role in ATG14 complex assembly and autophagy initiation. This study identifies an unexpected role for PtdIns(4,5)P 2 signaling in the regulation of ATG14 complex and autophagy.M acroautophagy (referred to as autophagy from here on) is an intracellular self-digestion process conserved in all eukaryotes that maintains cell homeostasis and protects cells from various stresses. Autophagy involves the formation of doublemembrane autophagosomes that contain target cytoplasmic contents for lysosomal degradation (1). Autophagosome formation is driven by coordinated functions of a number of autophagy-related (ATG) proteins (2). The ATG14 (also called Barkor or ATG14L)-Beclin 1 (atg6 in yeast)-VPS34 (an enzyme involved in the cellular process of autophagy; class III PI3K) complex plays essential roles in the initiation steps of autophagy by generating phosphatidylinositol 3-phosphate [PtdIns(3)P] and recruiting PtdIns(3)P effectors (3-6). ATG14 functions by recruiting VPS34 to punctate structures associated with the endoplasmic reticulum (ER) (7), and then PtdIns(3)P, the product of VPS34, in turn binds the Barkor/Atg14 autophagosome targeting sequence (BATS) domain of ATG14 and regulates its membrane curvature sensing (8). The ATG14-BATS domain also binds PtdIns(4,5)P 2 without unknown functional relevance (8).Phosphoinositides are important lipid messengers in various membrane trafficking events. PtdIns(4,5)P 2 plays multiple roles at the plasma membrane, such as in endocytosis, exocytosis, focal adhesion assembly, and so on (9). However, recently studies have argued for roles for PtdIns(4,5)P 2 at intracellular compartments (10). The majority of PtdIns(4,5)P 2 in mammalian cells are generated by the type I phosphatidylinositol 4-phosphate (PIP) 5-kinase (PIPKI), of which there are three genes (α, β, and γ) each wit...

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“…However, the identity of nascent autophagosome structures such as PAS is pivotal to several crucial questions regarding autophagosome biogenesis, including the membrane deformation mechanism and the origin of the autophagosome membrane. Membrane sources, including the endoplasmic reticulum (ER), mitochondria, ER-mitochondria contact sites, ER-Golgi intermediate compartment, Golgi apparatus, and plasma membrane have been postulated to contribute to autophagosome formation in yeast and/or mammalian cells (Axe et al, 2008;Hayashi-Nishino et al, 2010a, 2010bHailey et al, 2010;Noda et al, 2011;Ohashi and Munro, 2010;Ravikumar et al, 2010;Ge et al, 2013;Hamasaki et al, 2013). In plants, however, most observations of autophagosome-related structures have been based on the classical features of autophagosomes: their isolated double-membrane appearance, enclosed autophagic cargos, and labeling with an autophagosome marker (Rose et al, 2006;Toyooka et al, 2006;Katsiarimpa et al, 2011;Takatsuka et al, 2011;Hanamata et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

A BAR-Domain Protein SH3P2, Which Binds to Phosphatidylinositol 3-Phosphate and ATG8, Regulates Autophagosome Formation in Arabidopsis

et al. 2013

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Autophagy is a well-defined catabolic mechanism whereby cytoplasmic materials are engulfed into a structure termed the autophagosome. In plants, little is known about the underlying mechanism of autophagosome formation. In this study, we report that SH3 DOMAIN-CONTAINING PROTEIN2 (SH3P2), a Bin-Amphiphysin-Rvs domain-containing protein, translocates to the phagophore assembly site/preautophagosome structure (PAS) upon autophagy induction and actively participates in the membrane deformation process. Using the SH3P2-green fluorescent protein fusion as a reporter, we found that the PAS develops from a cup-shaped isolation membranes or endoplasmic reticulum-derived omegasome-like structures. Using an inducible RNA interference (RNAi) approach, we show that RNAi knockdown of SH3P2 is developmentally lethal and significantly suppresses autophagosome formation. An in vitro membrane/lipid binding assay demonstrates that SH3P2 is a membrane-associated protein that binds to phosphatidylinositol 3-phosphate. SH3P2 may facilitate membrane expansion or maturation in coordination with the phosphatidylinositol 3-kinase (PI3K) complex during autophagy, as SH3P2 promotes PI3K foci formation, while PI3K inhibitor treatment inhibits SH3P2 from translocating to autophagosomes. Further interaction analysis shows that SH3P2 associates with the PI3K complex and interacts with ATG8s in Arabidopsis thaliana, whereby SH3P2 may mediate autophagy. Thus, our study has identified SH3P2 as a novel regulator of autophagy and provided a conserved model for autophagosome biogenesis in Arabidopsis.

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The ER–Golgi intermediate compartment is a key membrane source for the LC3 lipidation step of autophagosome biogenesis

Cited by 368 publications

References 83 publications

A current perspective of autophagosome biogenesis

A current perspective of autophagosome biogenesis

PtdIns(4,5)P ₂ signaling regulates ATG14 and autophagy

A BAR-Domain Protein SH3P2, Which Binds to Phosphatidylinositol 3-Phosphate and ATG8, Regulates Autophagosome Formation in Arabidopsis

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The ER–Golgi intermediate compartment is a key membrane source for the LC3 lipidation step of autophagosome biogenesis

Cited by 368 publications

References 83 publications

A current perspective of autophagosome biogenesis

A current perspective of autophagosome biogenesis

PtdIns(4,5)P 2 signaling regulates ATG14 and autophagy

A BAR-Domain Protein SH3P2, Which Binds to Phosphatidylinositol 3-Phosphate and ATG8, Regulates Autophagosome Formation in Arabidopsis

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PtdIns(4,5)P ₂ signaling regulates ATG14 and autophagy