Adipocyte protein S3-12 coats nascent lipid droplets.
Most animals store lipid intracellularly in protein-coated droplets. The protein coat usually contains at least one member of the PAT (perilipin, adipose differentiation-related protein, and TIP47) family. Evidence suggests that PAT proteins control access to the lipid they enclose. The protein S3-12, which has sequence similarity to the PAT proteins, was found in a screen for adipocyte-specific proteins. The adipocyte expression of S3-12 and its similarity to the PAT proteins suggest that S3-12 is involved in adipocyte lipid storage. To test this hypothesis, we supplemented 3T3-L1 adipocytes with fatty acids and assessed the distribution of S3-12 by immunofluorescence microscopy. Prior to fatty acid incubation, S3-12 was distributed diffusely throughout the cytoplasm on punctate structures of heterogeneous size. After 10 min of lipid loading, S3-12 localized to 500-nm structures concentrated at the adipocyte periphery. After longer incubations, S3-12 coated the surface of lipid droplets up to several micrometers in diameter. Initially, these droplets were distinct from those droplets surrounded by perilipin; but by 240 min, most perilipin-coated droplets had some S3-12 on the surface as well. We additionally report that the formation of S3-12-coated droplets 1) required glucose and fatty acids that can be incorporated into triacylglycerol, 2) was blocked by an inhibitor of triacylglycerol synthesis, and 3) was insulin-dependent. This study reports for the first time the early morphological events in the genesis and maturation of adipocyte lipid droplets.
Wolins
Nathan E
NE
Department of Medicine, Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Skinner
James R
JR
Schoenfish
Marissa J
MJ
Tzekov
Anatoly
A
Bensch
Kenneth G
KG
Bickel
Perry E
PE
D016475:3T3 Cells; D017667:Adipocytes / Q000737:chemistry*; D000818:Animals; D002352:Carrier Proteins; D004268:DNA-Binding Proteins / Q000032:analysis; D005260:Female; D007328:Insulin / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008055:Lipids / Q000032:analysis*; D008565:Membrane Proteins / Q000032:analysis; D051379:Mice; D008810:Mice, Inbred C57BL; D000070778:Perilipin-1; D000070780:Perilipin-2; D000070796:Perilipin-3; D010750:Phosphoproteins / Q000032:analysis; D011257:Pregnancy Proteins; D011506:Proteins / Q000032:analysis / Q000737:chemistry*; D014226:Triazenes / Q000494:pharmacology; D014280:Triglycerides / Q000378:metabolism; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D008055:Lipids; D008565:Membrane Proteins; C000602982:PLIN2 protein, human; C038196:PLIN3 protein, human; D000070778:Perilipin-1; D000070780:Perilipin-2; D000070796:Perilipin-3; D010750:Phosphoproteins; C000602983:Plin2 protein, mouse; D011257:Pregnancy Proteins; D011506:Proteins; D014226:Triazenes; D014280:Triglycerides; D033921:Vesicular Transport Proteins; C034613:triacsin C