Identification and characterization of leptin-containing intracellular compartment in rat adipose cells.
The major leptin-containing membrane compartment was identified and characterized in rat adipose cells by means of equilibrium density and velocity sucrose gradient centrifugation. This compartment appears to be different from peptide-containing secretory granules present in neuronal, endocrine, and exocrine cells, as well as from insulin-sensitive GLUT-4-containing vesicles abundant in adipocytes. Exocytosis of both leptin- and GLUT-4-containing vesicles can be induced by insulin; however, only leptin secretion is responsive to serum stimulation. This latter effect is resistant to cycloheximide, suggesting that serum triggers the release of a stored pool of presynthesized leptin molecules. We conclude that regulated secretion of leptin and insulin-dependent translocation of GLUT-4 represent different pathways of membrane trafficking in rat adipose cells. NIH 3T3 cells ectopically expressing CAAT box enhancer binding protein-alpha and Swiss 3T3 cells expressing peroxisome proliferator-activated receptor-gamma undergo differentiation in vitro and acquire adipocyte morphology and insulin-responsive glucose uptake. Only the former cell line, however, is capable of leptin secretion. Thus different transcriptional mechanisms control the developmental onset of these two major and independent physiological functions in adipose cells.
Roh
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Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Thoidis
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Farmer
S R
SR
Kandror
K V
KV
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001798:Blood Proteins / Q000494:pharmacology; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000096:biosynthesis; D002352:Carrier Proteins / Q000378:metabolism; D002451:Cell Compartmentation / Q000502:physiology*; D002454:Cell Differentiation / Q000187:drug effects; D002458:Cell Fractionation; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007424:Intracellular Fluid / Q000378:metabolism*; D020738:Leptin / Q000378:metabolism*; D008297:Male; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D015388:Organelles / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis; D014157:Transcription Factors / Q000096:biosynthesis
D001798:Blood Proteins; D022763:CCAAT-Enhancer-Binding Protein-alpha; D002352:Carrier Proteins; D051275:Glucose Transporter Type 4; D020738:Leptin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D018160:Receptors, Cytoplasmic and Nuclear; C495693:Slc2a4 protein, mouse; C495694:Slc2a4 protein, rat; D014157:Transcription Factors; D005947:Glucose