Mechanism and regulation of lysosomal sequestration and proteolysis.
Lysosomes and autolysosomes were isolated from the livers of dextran-treated and leupeptin-injected rats, respectively. The contents of sequestered cytoplasmic proteins were much higher in autolysosomes, and more than 50% of them were found in the sediment. Isolated dextran-lysosomes showed high proteolytic activity toward sequestered cytoplasmic enzymes following incubation at pH 5. E-64 caused a complete inhibition of their degradation. Leupeptin treatment caused enrichment of ubiquitin protein conjugates of high molecular mass in the sediment of autolysosomes, which is comparable to enrichment of carbamyl-phosphate synthetase as a marker of bulk cytoplasmic sequestration in autolysosomes. The results suggest that protein ubiquitination may not be a signal for sequestration of proteins into the autophagic pathway.
Ueno
T
T
Department of Biochemistry, Juntendo University School of Medicine, Tokyo, Japan.
Kominami
E
E
D000818:Animals; D001343:Autophagy / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000378:metabolism; D005634:Fructose-Bisphosphate Aldolase / Q000378:metabolism; D008025:Ligases / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D014452:Ubiquitins / Q000378:metabolism
D003598:Cytoskeletal Proteins; D011506:Proteins; D014452:Ubiquitins; D010447:Peptide Hydrolases; D005634:Fructose-Bisphosphate Aldolase; D008025:Ligases