Premium
Ubiquitin‐dependent and ‐independent proteasomal degradation of apoB associated with endoplasmic reticulum and golgi apparatus, respectively, in HepG2 cells
Author(s) -
Liao Wei,
Chang Benny HungJunn,
Mancini Michael,
Chan Lawrence
Publication year - 2003
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.10538
Subject(s) - endoplasmic reticulum , golgi apparatus , microbiology and biotechnology , endoplasmic reticulum associated protein degradation , ubiquitin , apolipoprotein b , proteasome , cytosol , protein degradation , secretory pathway , intracellular , organelle , chemistry , lactacystin , unfolded protein response , biology , biochemistry , proteasome inhibitor , enzyme , gene , cholesterol
Studies in hepatocyte cultures indicate that apolipoprotein (apo) B‐100 production is regulated largely by intracellular degradation and the proteasome pathway is a major mechanism for the degradation. In the present study, we have examined the detailed itinerary of apoB degradation through its secretory pathway in HepG2 cells. We found that ubiquitin‐dependent proteasomal degradation of apoB largely occurred on the cytosolic surface of rough and smooth endoplasmic reticulum (ER) and that a small proportion of apoB was dislodged from the secretory organelles into the cytosolic compartment where it underwent ubiquitination for proteasomal degradation. The transmembrane conformation of apoB persisted as the protein was transported through the Golgi apparatus. We further demonstrated that proteasomal degradation of apoB was associated the Golgi apparatus but Golgi‐associated apoB was not ubiquitinated, indicating an ubiquitin‐independent proteasomal degradation of apoB is associated with this organelle. We conclude that apoB undergoes proteasomal degradation while going through different compartments of the secretory pathway; further, ER‐associated proteasomal degradation of apoB in the ER is ubiquitin‐dependent whereas that occurring in the Golgi is ubiquitin‐independent. J. Cell. Biochem. 89: 1019–1029, 2003. © 2003 Wiley‐Liss, Inc.