Apolipoprotein E in macrophages and hepatocytes is eegraded via the proteasomal pathway.
Macrophage-derived apolipoprotein E (apoE) influences the susceptibility of the arterial wall to atherosclerosis. Previous studies have shown that production of apoE in these cells is regulated at a posttranscriptional level and is increased by inhibitors of proteasomal degradation. To further investigate this mechanism, we stably transfected RAW 264.7 macrophages and HepG2 cells with a construct overexpressing ubiquitin, the peptide targeting proteins to the proteasome, fused to an influenza virus hemagglutinin epitope tag. Ubiquitination of apoE was investigated by immunoprecipitation and Western blot analysis. In both cell types, apoE was ubiquitinated, and inhibition of proteasome function by lactacystin led to accumulation of ubiquitinated apoE. These studies provide strong evidence for proteasomal degradation of apoE in the two main cell types responsible for its production and indicate a possible new level of regulation of this important protein.
Wenner
C
C
Institute of Arteriosclerosis Research, University of Münster, Germany.
Lorkowski
S
S
Engel
T
T
Cullen
P
P
D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001057:Apolipoproteins E / Q000378:metabolism*; D001161:Arteriosclerosis / Q000209:etiology / Q000378:metabolism; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism
D001057:Apolipoproteins E; D015853:Cysteine Proteinase Inhibitors; D009097:Multienzyme Complexes; D011993:Recombinant Fusion Proteins; D014452:Ubiquitins; C067713:lactacystin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine