Ubiquitin-protein conjugates accumulate in the lysosomal system of fibroblasts treated with cysteine proteinase inhibitors.
Mouse fibroblasts (3T3-L1 cells) accumulate detergent- and salt-insoluble aggregates of proteins conjugated to ubiquitin when incubated in the presence of inhibitors of lysosomal cysteine cathepsins, including E-64. These ubiquitin-protein conjugates co-fractionate with lysosomes on density gradients and are found in multivesicular dense bodies which by electron microscopy appear to be engaged in microautophagy. Both E-64 and ammonium chloride increase the intracellular concentration of free ubiquitin, but only E-64 leads to the formation of insoluble lysosomal ubiquitin-protein conjugates. The results are discussed in relation to the possible intracellular roles of ubiquitin conjugation.
Doherty
F J
FJ
Department of Biochemistry, University of Nottingham Medical School, Queen's Medical Centre, U.K.
Osborn
N U
NU
Wassell
J A
JA
Heggie
P E
PE
Laszlo
L
L
Mayer
R J
RJ
D000135:Acid Phosphatase / Q000032:analysis; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology; D006868:Hydrolysis; D007150:Immunohistochemistry; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D008854:Microscopy, Electron; D011506:Proteins / Q000378:metabolism*; D014452:Ubiquitins / Q000378:metabolism*
D015853:Cysteine Proteinase Inhibitors; D011506:Proteins; D014452:Ubiquitins; D007770:L-Lactate Dehydrogenase; D000135:Acid Phosphatase