J Biol Chem 1998,
PMID: 9565615
Chen, Y; Le Cahérec, F; Chuck, S L
Several secretory proteins, including apolipoprotein B, have been shown to undergo degradation by proteasomes. We found that the rapid degradation of nascent apolipoprotein B in HepG2 cells was diminished but not abolished by the addition of any of three different inhibitors of proteasomes. Ubiquitin is conjugated to apolipoprotein B that is not assembled with sufficient lipids either during or soon after synthesis. In addition, we found that apolipoprotein B that has entered the endoplasmic reticulum sufficiently to become glycosylated can be degraded by proteasomes. Furthermore, we detected ubiquitin-apolipoprotein B that is associated with the Sec61 complex, the major constituent of the translocational channel. Treatment of cells with monomethylethanolamine or dithiothreitol decreased the translocation of apolipoprotein B and increased the proportion of ubiquitin-conjugated molecules associated with Sec61. Conversely, treatment of cells with oleic acid, which increased the proportion of translocated apolipoprotein B, decreased the amount of ubiquitin-apolipoprotein B in the Sec61 complex. Finally, we found that inhibition of the interaction between calnexin and apolipoprotein B decreases the translocation of apolipoprotein B, increases the ubiquitin-apolipoprotein B in the Sec61 complex, and increases the proteasomal degradation of glycosylated apolipoprotein B. Thus, ubiquitin can be attached to unassembled apolipoprotein B in the Sec61 complex, and this process is affected by factors including calnexin that alter the translocation of apolipoprotein B.
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Text Mining Data
Dashed line = No text mining data
Manually curated Databases
-
IRef Biogrid Interaction:
SEC61A1
—
APOB
(physical association, affinity chromatography technology)
-
IRef Biogrid Interaction:
APOB
—
SEC61B
(physical association, affinity chromatography technology)
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IRef Hprd Interaction:
APOB
—
SEC61A2
(in vivo)
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IRef Hprd Interaction:
APOB
—
SEC61B
(in vivo)
In total, 3 gene pairs are associated to this article in curated databases