Mechanism of Hormone-Stimulated Lipolysis in Adipocytes: Translocation of Hormone-Sensitive Lipase to the Lipid Storage Droplet

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 89; no. 18; pp. 8537 - 8541
• Main Authors: Egan, John J., Greenberg, Andrew S., Chang, Min-Kun, Wek, Sheree A., Moos, Malcolm C., Londos, Constantine
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 15.09.1992; National Acad Sciences; National Academy of Sciences
• Subjects: activity; Adipocytes; Adipose Tissue - metabolism; Animals; Biological and medical sciences; Blotting, Western; Cells; Cellular biology; Centrifugation; Enzymes; Fats; Fundamental and applied biological sciences. Psychology; Glycols; Homogenization; hormone-sensitive lipase; Hormones; Lipase - chemistry; Lipase - metabolism; Lipid Mobilization; Lipids; Lipids. Glycolipids; Lipolysis; Male; mechanisms; Metabolisms and neurohumoral controls; Molecular Weight; Phosphorylation; Proteins; Rats; Rats, Inbred Strains; Sterol Esterase - metabolism; Subcellular Fractions - enzymology; translocation; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Translocation; Adipocyte; Rat; Enzyme; Rodentia; Triacylglycerol lipase; Lipids; Metabolism; In vitro; Lipolysis; Mechanism; Vertebrata; Mammalia; Protein kinase; Hormonal regulation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.89.18.8537

Hormone-sensitive lipase activity (HSL), which is found in the supernatant of centrifuged homogenates of lipolytically quiet isolated rat adipocytes, was greatly reduced in or absent from the supernatant of lipolytically stimulated cells. The lipase was purified 100- to 250-fold from the supernatant of lipolytically quiet cells to 10-20% purity by a single passage over phenyl-Sepharose resin with high (>70%) activity yields. Western blotting of adipocyte homogenate fractions with polyclonal antiserum raised against HSL showed that the enzyme shifted quantitatively from the supernatant of control cells to the floating "fat cake" of lipolytically stimulated cells. A similar shift to the fat cake was observed when cells were disrupted by hypotonic lysis and centrifugation rather than by homogenization. We propose that upon lipolytic activation of adipocytes and phosphorylation of HSL by cAMP-dependent protein kinase, the critical event is not an increase in catalytic activity (i.e., turnover number) but a translocation of the lipase to its substrate at the surface of the lipid storage droplet.