Ubiquitinated protein conjugates are specifically enriched in the lysosomal system of fibroblasts

FEBS Lett. 1990 Feb 26;261(2):365-8. doi: 10.1016/0014-5793(90)80593-8.


Ubiquitin-protein conjugates are found by immunogold electron microscopy to be enriched (12-fold) in the lysosomal compartment of 3T3-L1 fibroblasts. Treatment of fibroblasts with the cysteine protease inhibitor E-64 leads to an expansion of the lysosomal compartment and as a result an increase in the cellular content of ubiquitin-protein conjugates. There is no change in the specific enrichment of ubiquitin-protein conjugates in the lysosomal compartment following E-64 treatment. The results suggest that some ubiquitin-protein conjugates may normally be degraded lysosomally following sequestration by microautophagy and imply that protein ubiquitination may be one of the signals for protein uptake into lysosomes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line
  • Cysteine Proteinase Inhibitors
  • Fibroblasts / ultrastructure*
  • Immunohistochemistry
  • L-Lactate Dehydrogenase / metabolism
  • Leucine / analogs & derivatives
  • Leucine / pharmacology
  • Lysosomes / drug effects
  • Lysosomes / metabolism*
  • Microscopy, Electron
  • Proteins / metabolism*
  • RNA, Messenger / metabolism
  • Ubiquitins / genetics
  • Ubiquitins / metabolism*


  • Cysteine Proteinase Inhibitors
  • Proteins
  • RNA, Messenger
  • Ubiquitins
  • L-Lactate Dehydrogenase
  • Leucine
  • E 64