title: Polymerase I and transcript release factor regulates lipolysis via a phosphorylation-dependent mechanism.
abstract: OBJECTIVE
  Polymerase I and transcript release factor (PTRF) is a protein highly expressed in adipose tissue and is an integral structural component of caveolae. Here, we report on a novel role of PTRF in lipid mobilization.
  
  
  METHODS
  PTRF expression was examined in different adipose depots of mice during fasting, refeeding, and after administration of catecholamines and insulin. Involvement of PTRF during lipolysis was studied upon PTRF knockdown and overexpression and mutation of PTRF phosphorylation sites in 3T3-L1 adipocytes.
  
  
  RESULTS
  PTRF expression in mouse white adipose tissue (WAT) is regulated by nutritional status, increasing during fasting and decreasing to baseline after refeeding. Expression of PTRF also is hormonally regulated because treatment of mice with insulin leads to a decrease in expression, whereas isoproterenol increases expression in WAT. Manipulation of PTRF levels revealed a role of PTRF in lipolysis. Lentiviral-mediated knockdown of PTRF resulted in a marked attenuation of glycerol release in response to isoproterenol. Conversely, overexpressing PTRF enhanced isoproterenol-stimulated glycerol release. Mass-spectrometric analysis revealed that PTRF is phosphorylated at multiple sites in WAT. Mutation of serine 42, threonine 304, or serine 368 to alanine reduced isoproterenol-stimulated glycerol release in 3T3-L1 adipocytes.
  
  
  CONCLUSIONS
  Our study is the first direct demonstration for a novel adipose tissue-specific function of PTRF as a mediator of lipolysis and also shows that phosphorylation of PTRF is required for efficient fat mobilization.
authors.affiliation: Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Nabila
authors.initials: N
authors.lastname: Aboulaich
authors.forename: Patricia C
authors.initials: PC
authors.lastname: Chui
authors.forename: John M
authors.initials: JM
authors.lastname: Asara
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Flier
authors.forename: Eleftheria
authors.initials: E
authors.lastname: Maratos-Flier
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D002853:Chromatography, Liquid; D007328:Insulin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008066:Lipolysis / Q000187:drug effects / Q000502:physiology*; D008565:Membrane Proteins; D051379:Mice; D009928:Organ Specificity; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053719:Tandem Mass Spectrometry
chemical_list: D000318:Adrenergic beta-Agonists; C112745:Cavin1 protein, mouse; D007328:Insulin; D008565:Membrane Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D007545:Isoproterenol