scholarly journals Mammalian Atg2 proteins are essential for autophagosome formation and important for regulation of size and distribution of lipid droplets

2012 ◽  
Vol 23 (5) ◽  
pp. 896-909 ◽  
Author(s):  
Anoop Kumar G. Velikkakath ◽  
Taki Nishimura ◽  
Eiko Oita ◽  
Naotada Ishihara ◽  
Noboru Mizushima
Keyword(s):  
Lipid Droplet ◽  
Lipid Droplets ◽  
Autophagic Flux ◽  
Autophagosome Formation ◽  
Independent Manner ◽  
Intracellular Degradation ◽  
Atg Proteins ◽  
High Conservation ◽  
Droplet Morphology

Macroautophagy is an intracellular degradation system by which cytoplasmic materials are enclosed by the autophagosome and delivered to the lysosome. Autophagosome formation is considered to take place on the endoplasmic reticulum and involves functions of autophagy-related (Atg) proteins. Here, we report the identification and characterization of mammalian Atg2 homologues Atg2A and Atg2B. Simultaneous silencing of Atg2A and Atg2B causes a block in autophagic flux and accumulation of unclosed autophagic structures containing most Atg proteins. Atg2A localizes on the autophagic membrane, as well as on the surface of lipid droplets. The Atg2A region containing amino acids 1723–1829, which shows relatively high conservation among species, is required for localization to both the autophagic membrane and lipid droplet and is also essential for autophagy. Depletion of both Atg2A and Atg2B causes clustering of enlarged lipid droplets in an autophagy-independent manner. These data suggest that mammalian Atg2 proteins function both in autophagosome formation and regulation of lipid droplet morphology and dispersion.

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 DRAM-3 modulates autophagy and promotes cell survival in the absence of glucose

2015 ◽  
Vol 22 (10) ◽  
pp. 1714-1726 ◽  
Author(s):  
M Mrschtik ◽  
J O'Prey ◽  
L Y Lao ◽  
J S Long ◽  
F Beaumatin ◽  
...  
Keyword(s):  
Cell Survival ◽  
Membrane Trafficking ◽  
Clonogenic Survival ◽  
Autophagic Flux ◽  
Normal Tissues ◽  
Atg Proteins ◽  
Dna Damaging Agents ◽  
Evolutionarily Conserved ◽  
Starvation Conditions

Abstract Macroautophagy is a membrane-trafficking process that delivers cytoplasmic constituents to lysosomes for degradation. The process operates under basal conditions as a mechanism to turnover damaged or misfolded proteins and organelles. As a result, it has a major role in preserving cellular integrity and viability. In addition to this basal function, macroautophagy can also be modulated in response to various forms of cellular stress, and the rate and cargoes of macroautophagy can be tailored to facilitate appropriate cellular responses in particular situations. The macroautophagy machinery is regulated by a group of evolutionarily conserved autophagy-related (ATG) proteins and by several other autophagy regulators, which either have tissue-restricted expression or operate in specific contexts. We report here the characterization of a novel autophagy regulator that we have termed DRAM-3 due to its significant homology to damage-regulated autophagy modulator (DRAM-1). DRAM-3 is expressed in a broad spectrum of normal tissues and tumor cells, but different from DRAM-1, DRAM-3 is not induced by p53 or DNA-damaging agents. Immunofluorescence studies revealed that DRAM-3 localizes to lysosomes/autolysosomes, endosomes and the plasma membrane, but not the endoplasmic reticulum, phagophores, autophagosomes or Golgi, indicating significant overlap with DRAM-1 localization and with organelles associated with macroautophagy. In this regard, we further proceed to show that DRAM-3 expression causes accumulation of autophagosomes under basal conditions and enhances autophagic flux. Reciprocally, CRISPR/Cas9-mediated disruption of DRAM-3 impairs autophagic flux confirming that DRAM-3 is a modulator of macroautophagy. As macroautophagy can be cytoprotective under starvation conditions, we also tested whether DRAM-3 could promote survival on nutrient deprivation. This revealed that DRAM-3 can repress cell death and promote long-term clonogenic survival of cells grown in the absence of glucose. Interestingly, however, this effect is macroautophagy-independent. In summary, these findings constitute the primary characterization of DRAM-3 as a modulator of both macroautophagy and cell survival under starvation conditions.

scholarly journals Structural basis of Atg conjugation systems essential for autophagy

2014 ◽  
Vol 70 (a1) ◽  
pp. C302-C302
Author(s):  
Nobuo Noda
Keyword(s):  
Molecular Mechanisms ◽  
Critical Role ◽  
Amide Bond ◽  
Structural Basis ◽  
Autophagosome Formation ◽  
X Ray Crystallography ◽  
Intracellular Degradation ◽  
Atg Proteins ◽  
Evolutionarily Conserved ◽  
Biochemical Analyses

Autophagy is an evolutionarily-conserved, intracellular degradation system for which two ubiquitin-like modifiers, Atg8 and Atg12, play essential roles. After processed by Atg4, the exposed C-terminal glycine of Atg8 is activated by Atg7 (E1) and is then transferred to Atg3 (E2), and is finally conjugated with a phospholipid, phosphatidylethanolamine (PE) through an amide bond. Whereas, Atg12 is activated by the same E1, Atg7, without processing, and is then transferred to Atg10 (E2), and is finally conjugated with Atg5 through an isopeptide bond. Atg12-Atg5 conjugates, together with Atg16, function as an E3-like enzyme to facilitate the conjugation reaction between Atg8 and PE. During autophagy, Atg8-PE conjugates play a critical role in selective cargo recognition in addition to autophagosome formation. We determined the structures of all these Atg proteins and their complexes mainly by X-ray crystallography, and performed structure-based biochemical analyses on them [1,2]. These studies established the molecular mechanisms of Atg8 and Atg12 modification reactions that have many unique features compared with canonical ubiquitin-like systems. Furthermore, we found a conserved motif named the Atg8-family interacting motif (AIM), through which Atg8 recognizes specific cargoes and selectively incorporates them into autophagosomes for degradation [3].

scholarly journals Identification and Characterization of Associated with Lipid Droplet Protein 1: A Novel Membrane-Associated Protein That Resides on Hepatic Lipid Droplets

Traffic ◽  
2006 ◽  
Vol 7 (9) ◽  
pp. 1254-1269 ◽  
Author(s):  
Silvia Turró ◽  
Mercedes Ingelmo-Torres ◽  
Josep M. Estanyol ◽  
Francesc Tebar ◽  
Manuel A. Fernández ◽  
...  
Keyword(s):  
Lipid Droplet ◽  
Lipid Droplets ◽  
Hepatic Lipid ◽  
Identification And Characterization ◽  
Lipid Droplet Protein

scholarly journals Role of seipin in lipid droplet morphology and hepatitis C virus life cycle

2013 ◽  
Vol 94 (10) ◽  
pp. 2208-2214 ◽  
Author(s):  
Sophie Clément ◽  
Catherine Fauvelle ◽  
Emilie Branche ◽  
Vincent Kaddai ◽  
Stéphanie Conzelmann ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Lipid Droplet ◽  
Outer Surface ◽  
Lipid Droplets ◽  
Particle Production ◽  
Critical Factor ◽  
Infectious Hepatitis ◽  
Particle Assembly ◽  
Droplet Morphology

Infectious hepatitis C virus (HCV) particle assembly starts at the surface of lipid droplets, cytoplasmic organelles responsible for neutral fat storage. We analysed the relationship between HCV and seipin, a protein involved in lipid droplet maturation. Although seipin overexpression did not affect the total mean volume occupied by lipid droplets nor the total triglyceride and cholesterol ester levels per cell, it caused an increase in the mean diameter of lipid droplets by 60 %, while decreasing their total number per cell. The latter two effects combined resulted in a 34 % reduction of the total outer surface area of lipid droplets per cell, with a proportional decrease in infectious viral particle production, probably due to a defect in particle assembly. These results suggest that the available outer surface of lipid droplets is a critical factor for HCV release, independent of the neutral lipid content of the cell.

Thyroid Hormone Deficiency Modifies Hepatic Lipid Droplet Morphology and Molecular Properties in Lithogenic-Diet Supplemented Mice

2021 ◽  
Author(s):  
Irina Kube ◽  
Holger Jastrow ◽  
Dagmar Führer ◽  
Denise Zwanziger
Keyword(s):  
Gene Expression ◽  
Thyroid Hormone ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Molecular Properties ◽  
Hormone Deficiency ◽  
Hepatic Lipid ◽  
Lithogenic Diet ◽  
Associated Proteins ◽  
Droplet Morphology

Abstract Objective Thyroid hormones have been associated with a hepatic lipid lowering effect and thyroid function has been shown to play a substantial role in development of non-alcoholic fatty liver disease. Hepatic lipid droplets differ in the number, size and molecular properties depending on metabolic state or pathological condition. However, in how far thyroid hormone deficiency affects hepatic lipid droplet morphology and molecular properties is still poorly understood. Therefore, we performed a study in mice using a lithogenic diet model of steatohepatitis and modulated the thyroid hormone status. Methods Male and female three months old C57BL/6 mice were divided into a euthyroid (control), a lithogenic (litho) and a lithogenic+thyroid hormone deficient (litho+hypo) group and treated for six weeks. Hepatic transmission electron microscopy and gene expression analysis of lipid-droplet associated proteins were performed. Results Increased mean diameters of hepatic lipid droplets and a shift towards raised electron-density in lipid droplets was observed under thyroid hormone deficiency. Furthermore thyroid hormone deficiency altered hepatic expression of genes involved in lipophagy and triacylglycerol mobilization. Interestingly, while the impact of thyroid hormone deficiency on lipid droplet morphology seems to be sex-independent, hepatic lipid droplet-associated gene expression differed significantly between both sexes. Conclusion This study demonstrates that thyroid hormone deficiency alters hepatic lipid droplet morphology and hepatic gene expression of lipid droplet-associated proteins in a lithogenic diet mouse model of steatohepatitis.

Characterization of the lipid droplet-associated protein MLDP in human tissues and in hepatocyte steatosis

2010 ◽  
Vol 48 (01) ◽  
Author(s):  
M Hashani ◽  
M koenig ◽  
LM Pawella ◽  
P Schirmacher ◽  
BK Straub
Keyword(s):  
Lipid Droplet ◽  
Human Tissues ◽  
Hepatocyte Steatosis
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