Endosomal microautophagy is an integrated part of the autophagic response to amino acid starvation. 2019

Hallvard L Olsvik, and Steingrim Svenning, and Yakubu Princely Abudu, and Andreas Brech, and Harald Stenmark, and Terje Johansen, and Jakob Mejlvang
a Molecular Cancer Research Group, Department of Medical Biology , University of Tromsø -The Arctic University of Norway , Tromsø , Norway.

Starvation is a fundamental type of stress naturally occurring in biological systems. All organisms have therefore evolved different safeguard mechanisms to cope with deficiencies in various types of nutrients. Cells, from yeast to humans, typically respond to amino acid starvation by initiating degradation of cellular components by inducing autophagy. This degradation releases metabolic building blocks to sustain essential core cellular processes. Increasing evidence indicates that starvation-induced autophagy also acts to prepare cells for prolonged starvation by degrading key regulators of different cellular processes. In a recent study, we found that within the first hours of amino acid starvation cells elicit an autophagic response causing rapid degradation of specific proteins. The response is executed independently of both MTOR and canonical macroautophagy. Based on RNAi-mediated knockdown of essential components of the Endosomal Sorting Complex Required for Transport (ESCRT) machinery and electron microscopy we conclude that the response relies on some sort of endosomal microautophagy, hence vesicle budding into endosomes. Substantiated by the different substrates that are selectively degraded by this novel pathway we propose that the response predominantly acts to prepare cells for prolonged starvation. Intriguingly, this includes shutting down selective macroautophagy in preparation for a massive induction of bulk macroautophagy.

UI MeSH Term Description Entries
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000080551 Microautophagy A type of autophagy in which the cytoplasmic entities, such as parts of CELL NUCLEI; damaged MITOCHONDRIA; and lipid droplets, are taken up by small vesicles such as VACUOLES or MULTIVESICULAR BODIES, and degraded by lysosomal digestion. Chlorophagy,Endosomal Microautophagy,Micropexophagy,Piecemeal Microautophagy,Microautophagy, Endosomal,Microautophagy, Piecemeal
D000596 Amino Acids Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins. Amino Acid,Acid, Amino,Acids, Amino
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
D013217 Starvation Lengthy and continuous deprivation of food. (Stedman, 25th ed)
D056827 Endosomal Sorting Complexes Required for Transport A set of protein subcomplexes involved in PROTEIN SORTING of UBIQUITINATED PROTEINS into intraluminal vesicles of MULTIVESICULAR BODIES and in membrane scission during formation of intraluminal vesicles, during the final step of CYTOKINESIS, and during the budding of enveloped viruses. The ESCRT machinery is comprised of the protein products of Class E vacuolar protein sorting genes. ESCRT Complexes,ESCRT I,ESCRT II,ESCRT III,ESCRT Machinery,Endosomal Sorting Complex Required for Transport,Endosomal Sorting Complex Required for Transport I,Endosomal Sorting Complex Required for Transport II,Endosomal Sorting Complex Required for Transport III,Endosomal Sorting Complex Required for Transport Machinery,Complexes, ESCRT,Machinery, ESCRT

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