title: Carboxylesterase 3 (EC 3.1.1.1) is a major adipocyte lipase.
abstract: Hydrolysis of triglycerides is central to energy homeostasis in white adipose tissue (WAT). Hormone-sensitive lipase (HSL) was previously felt to mediate all lipolysis in WAT. Surprisingly, HSL-deficient mice show active HSL-independent lipolysis, suggesting that other lipase(s) also mediate triglyceride hydrolysis. To clarify this, we used functional proteomics to detect non-HSL lipase(s) in mouse WAT. After cell fractionation of intraabdominal WAT, most non-HSL neutral lipase activity is localized in the 100,000 x g infranatant and fat cake fractions. By oleic acid-linked agarose chromatography of infranatant followed by elution in a 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid gradient, we identified two peaks of esterase activity using p-nitrophenyl butyrate as a substrate. One of the peaks contained most of the lipase activity. In the corresponding fractions, gel permeation chromatography and SDS-PAGE, followed by tandem mass spectrometric analysis of excised Coomassie Blue-stained peptides, revealed carboxylesterase 3 (triacylglycerol hydrolase (TGH); EC 3.1.1.1). TGH is also the principle lipase of WAT fat cake extracts. Partially purified WAT TGH had lipase activity as well as lesser but detectable neutral cholesteryl ester hydrolase activity. Western blotting of subcellular fractions of WAT and confocal microscopy of fibroblasts following in vitro adipocytic differentiation are consistent with a distribution of TGH to endoplasmic reticulum, cytosol, and the lipid droplet. TGH is responsible for a major part of non-HSL lipase activity in WAT in vitro and may mediate some or all HSL-independent lipolysis in adipocytes.
authors.affiliation: Division of Medical Genetics, Ste-Justine Hospital, Montréal, Québec H3T 1C5, Canada.
authors.forename: Krishnakant G
authors.initials: KG
authors.lastname: Soni
authors.forename: Richard
authors.initials: R
authors.lastname: Lehner
authors.forename: Pavel
authors.initials: P
authors.lastname: Metalnikov
authors.forename: Paul
authors.initials: P
authors.lastname: O'Donnell
authors.forename: Meriem
authors.initials: M
authors.lastname: Semache
authors.forename: Wenhui
authors.initials: W
authors.lastname: Gao
authors.forename: Keith
authors.initials: K
authors.lastname: Ashman
authors.forename: Alexey V
authors.initials: AV
authors.lastname: Pshezhetsky
authors.forename: Grant A
authors.initials: GA
authors.lastname: Mitchell
mesh_terms: D017667:Adipocytes / Q000201:enzymology* / Q000378:metabolism; D017738:Alkanesulfonic Acids / Q000737:chemistry; D000818:Animals; D015153:Blotting, Western; D043182:Carboxylesterase / Q000378:metabolism; D002784:Cholesterol / Q000737:chemistry; D002845:Chromatography; D002847:Chromatography, Agarose; D002850:Chromatography, Gel; D003600:Cytosol / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004950:Esterases / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D006868:Hydrolysis; D008049:Lipase / Q000378:metabolism / Q000502:physiology*; D050356:Lipid Metabolism; D013058:Mass Spectrometry; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D041681:NIH 3T3 Cells; D019301:Oleic Acid / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D002787:Sterol Esterase / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D013379:Substrate Specificity; D013997:Time Factors; D014280:Triglycerides / Q000737:chemistry
chemical_list: D017738:Alkanesulfonic Acids; D010455:Peptides; D014280:Triglycerides; C068559:propylsulfonic acid; D019301:Oleic Acid; D002784:Cholesterol; D004950:Esterases; D043182:Carboxylesterase; D002787:Sterol Esterase; D008049:Lipase