Dynamics of lipid droplet-associated proteins during hormonally stimulated lipolysis in engineered adipocytes: stabilization and lipid droplet binding of adipocyte differentiation-related protein/adipophilin.
In mature adipocytes, triglyceride is stored within lipid droplets, which are coated with the protein perilipin, which functions to regulate lipolysis by controlling lipase access to the droplet in a hormone-regulatable fashion. Adipocyte differentiation-related protein (ADRP) is a widely expressed lipid droplet binding protein that is coexpressed with perilipin in differentiating fat cells but is minimally present in fully differentiated cultured adipocytes. We find that fibroblasts ectopically expressing C/EBPalpha (NIH-C/EBPalpha cells) differentiate into mature adipocytes that simultaneously express perilipin and ADRP. In response to isoproterenol, perilipin is hyperphosphorylated, lipolysis is enhanced, and subsequently, ADRP expression increases coincident with it surrounding intracellular lipid droplets. In the absence of lipolytic stimulation, inhibition of proteasomal activity with MG-132 increased ADRP levels to those of cells treated with 10 mum isoproterenol, but ADRP does not surround the lipid droplet in the absence of lipolytic stimulation. We overexpressed a perilipin A construct in NIH-C/EBPalpha cells where the six serine residues known to be phosphorylated by protein kinase A were changed to alanine (Peri A Delta1-6). These cells show no increase in ADRP expression in response to isoproterenol. We propose that ADRP can replace perilipin on existing lipid droplets or those newly formed as a result of fatty acid reesterification, under dynamic conditions of hormonally stimulated lipolysis, thus preserving lipid droplet morphology/structure.
Gross
Danielle N
DN
Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Miyoshi
Hideaki
H
Hosaka
Toshio
T
Zhang
Hui-Hong
HH
Pino
Elizabeth C
EC
Souza
Sandra
S
Obin
Martin
M
Greenberg
Andrew S
AS
Pilch
Paul F
PF
D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D007976:Leupeptins / Q000494:pharmacology; D050356:Lipid Metabolism; D008066:Lipolysis; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells; D010455:Peptides / Q000378:metabolism*; D000070778:Perilipin-1; D000070780:Perilipin-2; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D061988:Proteasome Inhibitors
D022763:CCAAT-Enhancer-Binding Protein-alpha; D002352:Carrier Proteins; D015853:Cysteine Proteinase Inhibitors; D006728:Hormones; D007976:Leupeptins; D008565:Membrane Proteins; D010455:Peptides; D000070778:Perilipin-1; D000070780:Perilipin-2; D010750:Phosphoproteins; C000602983:Plin2 protein, mouse; D061988:Proteasome Inhibitors; D007545:Isoproterenol; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde