Microtubules facilitate autophagosome formation and fusion of autophagosomes with endosomes. 2006

Robert Köchl, and Xiao Wen Hu, and Edmond Y W Chan, and Sharon A Tooze
Cancer Research UK, London Research Institute, Secretory Pathways Laboratory, 44 Lincoln's Inn Fields, London, WC2A 3PX, UK.

Nutrient deprivation of eukaryotic cells provokes a variety of stress responses, including autophagy. Autophagy is carried out by autophagosomes which sequester cytosolic components and organelles for degradation after fusion with protease-containing endosomes. To determine the role of microtubules in autophagy, we used nocodazole and vinblastine to disrupt microtubules and independently measured formation and fusion of autophagsosomes in primary rat hepatocytes. By measuring the translocation of GFP-LC3, an autophagosomal marker, to autophagosomes and the lipidation of GFP-LC3, we quantified the rate and magnitude of autophagosome formation. Starvation increased both the rate of autophagosome formation over the basal level and the total number of autophagosomes per cell. Maximal autophagosome formation required an intact microtubule network. Fusion of autophagosomes with endosomes, assayed by acquisition of protease-inhibitor sensitivity as well as overlap with LysoTracker Red-positive endosomes, required intact microtubules. Live-cell imaging demonstrated that autophagosomes were motile structures, and their movement also required microtubules. Interestingly, vinblastine stimulated autophagosome formation more than twofold before any discernable change in the microtubule network was observed. Stimulation of autophagosome formation by vinblastine was independent of nutrients and mTOR activity but was inhibited by depletion of the Autophagy proteins Atg5 and Atg6, known to be required for autophagy.

UI MeSH Term Description Entries
D008561 Membrane Fusion The adherence and merging of cell membranes, intracellular membranes, or artificial membranes to each other or to viruses, parasites, or interstitial particles through a variety of chemical and physical processes. Fusion, Membrane,Fusions, Membrane,Membrane Fusions
D008854 Microscopy, Electron Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen. Electron Microscopy
D008870 Microtubules Slender, cylindrical filaments found in the cytoskeleton of plant and animal cells. They are composed of the protein TUBULIN and are influenced by TUBULIN MODULATORS. Microtubule
D010588 Phagosomes Membrane-bound cytoplasmic vesicles formed by invagination of phagocytized material. They fuse with lysosomes to form phagolysosomes in which the hydrolytic enzymes of the lysosome digest the phagocytized material. Phagolysosomes,Phagolysosome,Phagosome
D011992 Endosomes Cytoplasmic vesicles formed when COATED VESICLES shed their CLATHRIN coat. Endosomes internalize macromolecules bound by receptors on the cell surface. Receptosomes,Endosome,Receptosome
D011993 Recombinant Fusion Proteins Recombinant proteins produced by the GENETIC TRANSLATION of fused genes formed by the combination of NUCLEIC ACID REGULATORY SEQUENCES of one or more genes with the protein coding sequences of one or more genes. Fusion Proteins, Recombinant,Recombinant Chimeric Protein,Recombinant Fusion Protein,Recombinant Hybrid Protein,Chimeric Proteins, Recombinant,Hybrid Proteins, Recombinant,Recombinant Chimeric Proteins,Recombinant Hybrid Proteins,Chimeric Protein, Recombinant,Fusion Protein, Recombinant,Hybrid Protein, Recombinant,Protein, Recombinant Chimeric,Protein, Recombinant Fusion,Protein, Recombinant Hybrid,Proteins, Recombinant Chimeric,Proteins, Recombinant Fusion,Proteins, Recombinant Hybrid
D002478 Cells, Cultured Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others. Cultured Cells,Cell, Cultured,Cultured Cell
D003470 Culture Media Any liquid or solid preparation made specifically for the growth, storage, or transport of microorganisms or other types of cells. The variety of media that exist allow for the culturing of specific microorganisms and cell types, such as differential media, selective media, test media, and defined media. Solid media consist of liquid media that have been solidified with an agent such as AGAR or GELATIN. Media, Culture
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D001343 Autophagy The segregation and degradation of various cytoplasmic constituents via engulfment by MULTIVESICULAR BODIES; VACUOLES; or AUTOPHAGOSOMES and their digestion by LYSOSOMES. It plays an important role in BIOLOGICAL METAMORPHOSIS and in the removal of bone by OSTEOCLASTS. Defective autophagy is associated with various diseases, including NEURODEGENERATIVE DISEASES and cancer. Autophagocytosis,ER-Phagy,Lipophagy,Nucleophagy,Reticulophagy,Ribophagy,Autophagy, Cellular,Cellular Autophagy,ER Phagy

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