Lipid droplets are arrested in the ER membrane by tight binding of lipidated apolipoprotein B-100.
Apolipoprotein B-100 (ApoB) is a major component of very-low-density lipoproteins, and is deposited in a region around lipid droplets (LDs) called the ;ApoB-crescent'. The ApoB-crescent is thought to be related to ApoB degradation because it drastically increases when proteasome or autophagy is inhibited. In the present study, we found that ApoB-crescents were significantly reduced when ApoB lipidation was suppressed by either the inhibition or knockdown of the microsomal triglyceride-transfer protein. By contrast, ApoB-crescents increased under conditions that are presumed to cause lipidated ApoB abnormalities in secretory compartments. By electron microscopic analyses, we identified the ApoB-crescent as a thin cholesterol-rich ER cistern fused to an LD, and - topologically - this structure is equivalent to a lipid-ester globule between the two leaflets of the ER membrane. ApoB localized in the thin cisternal lumen, and its binding to LDs was resistant to alkaline treatment. Overexpression of ADRP or TIP47 suppressed the increase in the number of ApoB-crescents, whereas knockdown of these proteins had the opposite effect. From these results, we inferred that the ApoB-crescent is formed by an LD that is arrested in the ER membrane by tight binding of lipidated ApoB to its luminal surface. We suggest that ApoB processing and LD formation are closely linked.
Ohsaki
Yuki
Y
Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Cheng
Jinglei
J
Suzuki
Michitaka
M
Fujita
Akikazu
A
Fujimoto
Toyoshi
T
D053299:Apolipoprotein B-100 / Q000378:metabolism*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism* / Q000648:ultrastructure; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D050356:Lipid Metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D000070780:Perilipin-2; D000070796:Perilipin-3; D011257:Pregnancy Proteins / Q000378:metabolism; D033921:Vesicular Transport Proteins
D053299:Apolipoprotein B-100; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C000602982:PLIN2 protein, human; C038196:PLIN3 protein, human; D000070780:Perilipin-2; D000070796:Perilipin-3; D011257:Pregnancy Proteins; D033921:Vesicular Transport Proteins; D002784:Cholesterol