| Ubiquitination regulates the assembly of VLDL in HepG2 cells and is the committing step of the apoB-100 ERAD pathway. | |
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MedLine Citation:
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PMID: 21421992 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Apolipoprotein B-100 (apoB-100) is degraded by endoplasmic reticulum-associated degradation (ERAD) when lipid availability limits assembly of VLDLs. The ubiquitin ligase gp78 and the AAA-ATPase p97 have been implicated in the proteasomal degradation of apoB-100. To study the relationship between ERAD and VLDL assembly, we used small interfering RNA (siRNA) to reduce gp78 expression in HepG2 cells. Reduction of gp78 decreased apoB-100 ubiquitination and cytosolic apoB-ubiquitin conjugates. Radiolabeling studies revealed that gp78 knockdown increased secretion of newly synthesized apoB-100 and, unexpectedly, enhanced VLDL assembly, as the shift in apoB-100 density in gp78-reduced cells was accompanied by increased triacylglycerol (TG) secretion. To explore the mechanisms by which gp78 reduction might enhance VLDL assembly, we compared the effects of gp78 knockdown with those of U0126, a mitogen-activated protein kinase/ERK kinase1/2 inhibitor that enhances apoB-100 secretion in HepG2 cells. U0126 treatment increased secretion of both apoB100 and TG and decreased the ubiquitination and cellular accumu-lation of apoB-100. Furthermore, p97 knockdown caused apoB-100 to accumulate in the cell, but if gp78 was concomitantly reduced or assembly was enhanced by U0126 treatment, cellular apoB-100 returned toward baseline. This indicates that ubiquitination commits apoB-100 to p97-mediated retrotranslocation during ERAD. Thus, decreasing ubiquitination of apoB-100 enhances VLDL assembly, whereas improving apoB-100 lipidation decreases its ubiquitination, suggesting that ubiquitination has a regulatory role in VLDL assembly. |
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Authors:
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Eric A Fisher; Neeraj A Khanna; Roger S McLeod |
Publication Detail:
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Type: Journal Article Date: 2011-03-18 |
Journal Detail:
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Title: Journal of lipid research Volume: 52 ISSN: 0022-2275 ISO Abbreviation: J. Lipid Res. Publication Date: 2011 Jun |
Date Detail:
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Created Date: 2011-05-16 Completed Date: 2011-09-19 Revised Date: 2012-09-19 |
Medline Journal Info:
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Nlm Unique ID: 0376606 Medline TA: J Lipid Res Country: United States |
Other Details:
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Languages: eng Pagination: 1170-80 Citation Subset: IM |
Affiliation:
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Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 1X5. |
Export Citation:
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APA/MLA Format Download EndNote Download BibTex |
| MeSH Terms | |
Descriptor/Qualifier:
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Adenosine Triphosphatases
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antagonists & inhibitors,
genetics,
metabolism* Apolipoprotein B-100* / biosynthesis, secretion Butadienes / pharmacology Cholesterol, VLDL* / metabolism Endoplasmic Reticulum / genetics, metabolism Enzyme Inhibitors / pharmacology Gene Silencing / drug effects Hep G2 Cells Humans Isotope Labeling Mitogen-Activated Protein Kinase Kinases / antagonists & inhibitors, genetics, metabolism* Nitriles / pharmacology Nuclear Proteins / antagonists & inhibitors, genetics, metabolism* Proteasome Endopeptidase Complex / genetics, metabolism Protein Biosynthesis / drug effects* RNA, Small Interfering / metabolism, pharmacology Receptors, Autocrine Motility Factor Receptors, Cytokine / antagonists & inhibitors, genetics, metabolism* Triglycerides / metabolism Ubiquitin / genetics, metabolism* Ubiquitin-Protein Ligases / antagonists & inhibitors, genetics, metabolism* Ubiquitination / drug effects |
| Chemical | |
Reg. No./Substance:
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0/Apolipoprotein B-100; 0/Butadienes; 0/Cholesterol, VLDL; 0/Enzyme Inhibitors; 0/Nitriles; 0/Nuclear Proteins; 0/RNA, Small Interfering; 0/Receptors, Cytokine; 0/Triglycerides; 0/U 0126; 0/Ubiquitin; EC 2.7.12.2/Mitogen-Activated Protein Kinase Kinases; EC 3.4.25.1/Proteasome Endopeptidase Complex; EC 3.6.1.-/Adenosine Triphosphatases; EC 3.6.1.-/p97 ATPase; EC 6.3.2.19/AMFR protein, human; EC 6.3.2.19/Receptors, Autocrine Motility Factor; EC 6.3.2.19/Ubiquitin-Protein Ligases |
| Comments/Corrections | |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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