scholarly journals Atg8 Controls Phagophore Expansion during Autophagosome Formation

2008 ◽  
Vol 19 (8) ◽  
pp. 3290-3298 ◽  
Author(s):  
Zhiping Xie ◽  
Usha Nair ◽  
Daniel J. Klionsky
Keyword(s):  
Membrane Vesicles ◽  
Degradation Process ◽  
Autophagosome Formation ◽  
Multistage Model ◽  
Intracellular Degradation ◽  
Cytoplasmic Material ◽  
New Genes ◽  
Health And Disease ◽  
Time Observation ◽  
Related Proteins

Autophagy is a potent intracellular degradation process with pivotal roles in health and disease. Atg8, a lipid-conjugated ubiquitin-like protein, is required for the formation of autophagosomes, double-membrane vesicles responsible for the delivery of cytoplasmic material to lysosomes. How and when Atg8 functions in this process, however, is not clear. Here we show that Atg8 controls the expansion of the autophagosome precursor, the phagophore, and give the first real-time, observation-based temporal dissection of the autophagosome formation process. We demonstrate that the amount of Atg8 determines the size of autophagosomes. During autophagosome biogenesis, Atg8 forms an expanding structure and later dissociates from the site of vesicle formation. On the basis of the dynamics of Atg8, we present a multistage model of autophagosome formation. This model provides a foundation for future analyses of the functions and dynamics of known autophagy-related proteins and for screening new genes.

WIPI β-propellers in autophagy-related diseases and longevity

2013 ◽  
Vol 41 (4) ◽  
pp. 962-967 ◽  
Author(s):  
Daniela Bakula ◽  
Zsuzsanna Takacs ◽  
Tassula Proikas-Cezanne
Keyword(s):  
Essential Role ◽  
Mammalian Target Of Rapamycin ◽  
Membrane Vesicles ◽  
Catabolic Pathway ◽  
Autophagosome Formation ◽  
Cytoplasmic Material ◽  
Evolutionarily Conserved ◽  
Initiation Step ◽  
Conserved Amino Acids

Autophagy is a catabolic pathway in which the cell sequesters cytoplasmic material, including long-lived proteins, lipids and organelles, in specialized double-membrane vesicles, called autophagosomes. Subsequently, autophagosomes communicate with the lysosomal compartment and acquire acidic hydrolases for final cargo degradation. This process of partial self-eating secures the survival of eukaryotic cells during starvation periods and is critically regulated by mTORC1 (mammalian target of rapamycin complex 1). Under nutrient-poor conditions, inhibited mTORC1 permits localized PtdIns(3)P production at particular membranes that contribute to autophagosome formation. Members of the human WIPI (WD-repeat protein interacting with phosphoinositides) family fulfil an essential role as PtdIns(3)P effectors at the initiation step of autophagosome formation. In the present article, we discuss the role of human WIPIs in autophagy, and the identification of evolutionarily conserved amino acids of WIPI-1 that confer PtdIns(3)P binding downstream of mTORC1 inhibition. We also discuss the PtdIns(3)P effector function of WIPIs in the context of longevity and autophagy-related human diseases, such as cancer and neurodegeneration.

scholarly journals p62 targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding

2011 ◽  
Vol 192 (1) ◽  
pp. 17-27 ◽  
Author(s):  
Eisuke Itakura ◽  
Noboru Mizushima
Keyword(s):  
Endoplasmic Reticulum ◽  
Degradation Process ◽  
Related Protein ◽  
Autophagosome Formation ◽  
Intracellular Degradation ◽  
Cargo Receptor ◽  
Specific Proteins

Autophagy is an intracellular degradation process by which cytoplasmic contents are degraded in the lysosome. In addition to nonselective engulfment of cytoplasmic materials, the autophagosomal membrane can selectively recognize specific proteins and organelles. It is generally believed that the major selective substrate (or cargo receptor) p62 is recruited to the autophagosomal membrane through interaction with LC3. In this study, we analyzed loading of p62 and its related protein NBR1 and found that they localize to the endoplasmic reticulum (ER)–associated autophagosome formation site independently of LC3 localization to membranes. p62 colocalizes with upstream autophagy factors such as ULK1 and VMP1 even when autophagosome formation is blocked by wortmannin or FIP200 knockout. Self-oligomerization of p62 is essential for its localization to the autophagosome formation site. These results suggest that p62 localizes to the autophagosome formation site on the ER, where autophagosomes are nucleated. This process is similar to the yeast cytoplasm to vacuole targeting pathway.

scholarly journals The molecular basis of selective autophagy

2012 ◽  
Vol 34 (2) ◽  
pp. 24-30 ◽  
Author(s):  
Doris Popovic ◽  
Ivan Dikic
Keyword(s):  
Molecular Basis ◽  
Membrane Vesicles ◽  
Degradation Process ◽  
Degradation Pathway ◽  
Selective Autophagy ◽  
Intracellular Degradation ◽  
Selective Degradation ◽  
Evolutionarily Conserved ◽  
The Family ◽  
Cellular Components

Autophagy is an evolutionarily conserved intracellular degradation process, through which large cellular cargos are sequestered into double-membrane vesicles (autophagosomes) and delivered to the lysosome. Starvation-induced autophagy represents a general non-selective degradation pathway that breaks down cellular components for energy replenishment. Alternatively, selective autophagy targets specific organelles, protein aggregates or invading pathogens that need to be precisely removed from the cell during development or pathogenic infection. Selective autophagy receptors noncovalently bind to the family of ATG8 modifiers and can be controlled by post-translational protein modifications, including ubiquitination and phosphorylation. In this article, we review recent advances in our understanding of the molecular basis of cargo selection in autophagy.

scholarly journals TBC1D14 regulates autophagosome formation via Rab11- and ULK1-positive recycling endosomes

2012 ◽  
Vol 197 (5) ◽  
pp. 659-675 ◽  
Author(s):  
Andrea Longatti ◽  
Christopher A. Lamb ◽  
Minoo Razi ◽  
Shin-ichiro Yoshimura ◽  
Francis A. Barr ◽  
...  
Keyword(s):  
Amino Acid ◽  
Golgi Complex ◽  
Membrane Vesicles ◽  
Degradation Process ◽  
Amino Acid Starvation ◽  
Negative Regulators ◽  
Autophagosome Formation ◽  
Double Membrane ◽  
Recycling Endosomes ◽  
Guanosine Triphosphatase

Autophagy is a bulk degradation process characterized by the formation of double membrane vesicles called autophagosomes. The exact molecular mechanism of autophagosome formation and the origin of the autophagosomal membrane remain unclear. We screened 38 human Tre-2/Bub2/Cdc16 domain–containing Rab guanosine triphosphatase–activating proteins (GAPs) and identified 11 negative regulators of starvation-induced autophagy. One of these putative RabGAPs, TBC1D14, colocalizes and interacts with the autophagy kinase ULK1. Overexpressed TBC1D14 tubulates ULK1-positive recycling endosomes (REs), impairing their function and inhibiting autophagosome formation. TBC1D14 binds activated Rab11 but is not a GAP for Rab11, and loss of Rab11 prevents TBC1D14-induced tubulation of REs. Furthermore, Rab11 is required for autophagosome formation. ULK1 and Atg9 are found on Rab11- and transferrin (Tfn) receptor (TfnR)–positive recycling endosomes. Amino acid starvation causes TBC1D14 to relocalize from REs to the Golgi complex, whereas TfnR and Tfn localize to forming autophagosomes, which are ULK1 and LC3 positive. Thus, TBC1D14- and Rab11-dependent vesicular transport from REs contributes to and regulates starvation-induced autophagy.

scholarly journals Atg8a interacts with transcription factor Sequoia to control the expression of autophagy genes in Drosophila

2019 ◽  
Author(s):  
Anne-Claire Jacomin ◽  
Stavroula Petridi ◽  
Marisa DiMonaco ◽  
Ashish Jain ◽  
Zambarlal Bhujabal ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Dependent Manner ◽  
Autophagosome Formation ◽  
Regulation Of Expression ◽  
Cytoplasmic Material ◽  
Evolutionarily Conserved ◽  
Enhanced Expression ◽  
Related Proteins ◽  
Lir Motif ◽  
Nuclear Acetyltransferase

SUMMARYAutophagy is a fundamental, evolutionarily conserved, process in which cytoplasmic material is degraded through the lysosomal pathway [1–7]. One of the most important and well-studied autophagy-related proteins is LC3 [Microtubule-associated protein 1 light chain 3, (called Atg8 in yeast and Drosophila)], which participates in autophagosome formation and autophagy cargo selection in the cytoplasm, and is one of the most widely utilized markers of autophagy [8, 9]. Despite growing evidence that LC3 is enriched in the nucleus, little is known about the mechanisms involved in targeting LC3 to the nucleus and the nuclear components it interacts with [10–13]. Here we show that Drosophila Atg8a protein, homologous to mammalian LC3 and yeast Atg8, interacts with the transcription factor Sequoia in a LIR-motif dependent manner. We show that Sequoia depletion induces autophagy in nutrient rich conditions through enhanced expression of autophagy genes. We also show that Atg8a interacts with YL-1, a component of a nuclear acetyltransferase complex, and is acetylated at position K46. Additionally, we show that Atg8a interacts with the deacetylase Sir2, which deacetylates Atg8a during starvation in order to activate autophagy. Our results suggest a mechanism of regulation of expression of autophagy genes by Atg8a, which is linked to its acetylation status and its interaction with Sequoia, YL-1 and Sir2.

WIPI β-propellers at the crossroads of autophagosome and lipid droplet dynamics

2014 ◽  
Vol 42 (5) ◽  
pp. 1414-1417 ◽  
Author(s):  
Simon G. Pfisterer ◽  
Daniela Bakula ◽  
Alice Cezanne ◽  
Horst Robenek ◽  
Tassula Proikas-Cezanne
Keyword(s):  
De Novo ◽  
Membrane Vesicles ◽  
Autophagosome Formation ◽  
Droplet Dynamics ◽  
Atg Proteins ◽  
Cytoplasmic Material ◽  
Storage Reservoirs ◽  
Close Proximity ◽  
Cytoplasmic Content ◽  
Catabolic Process

Macroautophagy (autophagy hereafter) is an evolutionarily highly conserved catabolic process activated by eukaryotes in order to counteract cellular starvation. Autophagy leads to bulk degradation of cytoplasmic content in the lysosomal compartment, thereby clearing the cytoplasm and generating nutrients and energy. Upon autophagy initiation, cytoplasmic material becomes sequestered in newly formed double-membrane vesicles termed ‘autophagosomes’ that subsequently acquire acidic hydrolases for content destruction. The de novo biogenesis of autophagosomes often occurs at the endoplasmic reticulum (ER) and, in many cases, in close proximity to lipid droplets (LDs), intracellular neutral lipid storage reservoirs. LDs are targets of autophagic destruction, but have recently also been shown to contribute to autophagosome formation. In fact, some autophagy-related (Atg) proteins, such as microtubule-associated protein light chain 3 (LC3), Atg2 and Atg14L, functionally contribute to both LD and autophagosome biogenesis. In the present paper, we discuss Atg proteins, including members of the human WD-repeat protein interacting with phosphoinositides (WIPI) family that co-localize prominently with LC3, Atg2 and Atg14L to conceivably integrate LD and autophagosome dynamics.

scholarly journals Structural catalog of core Atg proteins opens new era of autophagy research

2021 ◽  
Author(s):  
Kazuaki Matoba ◽  
Nobuo N Noda
Keyword(s):  
De Novo ◽  
Structural Information ◽  
Membrane Dynamics ◽  
Autophagosome Formation ◽  
New Era ◽  
Intracellular Degradation ◽  
Atg Proteins ◽  
Biological Studies ◽  
Evolutionarily Conserved ◽  
Biological Methods

Summary Autophagy, which is an evolutionarily conserved intracellular degradation system, involves de novo generation of autophagosomes that sequester and deliver diverse cytoplasmic materials to the lysosome for degradation. Autophagosome formation is mediated by approximately 20 core autophagy-related (Atg) proteins, which collaborate to mediate complicated membrane dynamics during autophagy. To elucidate the molecular functions of these Atg proteins in autophagosome formation, many researchers have tried to determine the structures of Atg proteins by using various structural biological methods. Although not sufficient, the basic structural catalog of all core Atg proteins was established. In this review article, we summarize structural biological studies of core Atg proteins, with an emphasis on recently unveiled structures, and describe the mechanistic breakthroughs in autophagy research that have derived from new structural information.

scholarly journals Scanning Electron-Assisted Dielectric Microscopy Reveals Autophagosome Formation by LC3 and ATG12 in Cultured Mammalian Cells

2021 ◽  
Vol 22 (4) ◽  
pp. 1834
Author(s):  
Tomoko Okada ◽  
Toshihiko Ogura
Keyword(s):  
Mammalian Cells ◽  
Culture Medium ◽  
Related Gene ◽  
Autophagosome Formation ◽  
Intact Cells ◽  
Microtubule Associated Proteins ◽  
Associated Proteins ◽  
The Difference ◽  
Related Proteins ◽  
Scanning Electron

Autophagy is an intracellular self-devouring system that plays a central role in cellular recycling. The formation of functional autophagosomes depends on several autophagy-related proteins, including the microtubule-associated proteins 1A/1B light chain 3 (LC3) and the conserved autophagy-related gene 12 (Atg12). We have recently developed a novel scanning electron-assisted dielectric microscope (SE-ADM) for nanoscale observations of intact cells. Here, we used the SE-ADM system to observe LC3- and Atg12-containing autophagosomes in cells labelled in the culture medium with antibodies conjugated to colloidal gold particles. We observed that, during autophagosome formation, Atg12 localized along the actin meshwork structure, whereas LC3 formed arcuate or circular alignments. Our system also showed a difference in the distribution of LC3 and Atg12; Atg12 was broadly distributed while LC3 was more localized. The difference in the spatial distribution demonstrated by our system explains the difference in the size of fluorescent spots due to the fluorescently labelled antibodies observed using optical microscopy. The direct SE-ADM observation of cells should thus be effective in analyses of autophagosome formation.

Autophagy is required during high MUC2 mucin biosynthesis in colonic goblet cells to contend metabolic stress

2021 ◽  
Author(s):  
Sameer Tiwari ◽  
Sharmin Begum ◽  
France Moreau ◽  
Hayley Gorman ◽  
Kris Chadee
Keyword(s):  
Endoplasmic Reticulum ◽  
Essential Role ◽  
Metabolic Stress ◽  
Thick Layer ◽  
Degradation Process ◽  
Goblet Cells ◽  
Mucosal Epithelium ◽  
Intracellular Degradation ◽  
Muc2 Expression ◽  
Or Gene

Goblet cells are specialized for the production and secretion of MUC2 glycoproteins that forms a thick layer covering the mucosal epithelium as a protective barrier against noxious substances and invading microbes. High MUC2 mucin biosynthesis induces endoplasmic reticulum (ER) stress and apoptosis in goblet cells during inflammatory and infectious diseases. Autophagy is an intracellular degradation process required for maintenance of intestinal homeostasis. In this study, we hypothesized that autophagy was triggered during high MUC2 mucin biosynthesis from colonic goblet cells to cope with metabolic stress. To interrogate this, we analyzed the autophagy process in high MUC2-producing human HT29-H and a clone HT29-L silenced for MUC2 expression by lentivirus-mediated shRNA, and WT and CRISPR/Cas9 MUC2 KO LS174T cells. Autophagy was constitutively increased in high MUC2 producing cells characterized by elevated pULK1S555 expression and increased numbers of autophagosomes as compared to MUC2 silenced or gene edited cells. Similarly, colonoids from Muc2+/+ but not Muc2-/- littermates differentiated into goblet cells showed increased autophagy. IL-22 treatment corrected misfolded MUC2 protein and alleviated the autophagy process in LS174T cells. This study highlights that autophagy plays an essential role in goblet cells to survive during high mucin biosynthesis by regulating cellular homeostasis.

scholarly journals The Role of Beclin 1-Dependent Autophagy in Cancer

Biology ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 4 ◽  
Author(s):  
Silvia Vega-Rubín-de-Celis
Keyword(s):  
Dna Damage ◽  
Tumor Suppression ◽  
Protein Aggregates ◽  
Degradation Process ◽  
Beclin 1 ◽  
Cancer Type ◽  
Intracellular Degradation

Autophagy (self-eating) is an intracellular degradation process used by cells to keep a “clean house”; as it degrades abnormal or damaged proteins and organelles, it helps to fight infections and also provides energy in times of fasting or exercising. Autophagy also plays a role in cancer, although its precise function in each cancer type is still obscure, and whether autophagy plays a protecting (through the clearing of damaged organelles and protein aggregates and preventing DNA damage) or a promoting (by fueling the already stablished tumor) role in cancer remains to be fully characterized. Beclin 1, the mammalian ortholog of yeast Atg6/Vps30, is an essential autophagy protein and has been shown to play a role in tumor suppression. Here, an update of the tumorigenesis regulation by Beclin 1-dependent autophagy is provided.

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