1. Tumor necrosis factor-alpha stimulates lipolysis in differentiated human adipocytes through activation of extracellular signal-related kinase and elevation of intracellular cAMP.
- Author
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Zhang HH, Halbleib M, Ahmad F, Manganiello VC, and Greenberg AS
- Subjects
- 3',5'-Cyclic-AMP Phosphodiesterases metabolism, Adipocytes cytology, Adipocytes drug effects, Adult, Butadienes pharmacology, Carrier Proteins, Cell Differentiation, Cells, Cultured, Cyclic AMP-Dependent Protein Kinases antagonists & inhibitors, Cyclic AMP-Dependent Protein Kinases metabolism, Cyclic Nucleotide Phosphodiesterases, Type 3, Enzyme Inhibitors pharmacology, Female, Flavonoids pharmacology, Humans, Isoquinolines pharmacology, MAP Kinase Kinase 2, Male, Middle Aged, Mitogen-Activated Protein Kinase Kinases antagonists & inhibitors, Mitogen-Activated Protein Kinase Kinases metabolism, Mitogen-Activated Protein Kinases metabolism, Nitriles pharmacology, Perilipin-1, Phosphoproteins metabolism, Phosphorylation, Protein-Tyrosine Kinases antagonists & inhibitors, Protein-Tyrosine Kinases metabolism, Adipocytes enzymology, Antineoplastic Agents pharmacology, Cyclic AMP metabolism, Lipolysis drug effects, MAP Kinase Signaling System physiology, Sulfonamides, Tumor Necrosis Factor-alpha pharmacology
- Abstract
Tumor necrosis factor-alpha (TNF-alpha) stimulates lipolysis in human adipocytes. However, the mechanisms regulating this process are largely unknown. We demonstrate that TNF-alpha increases lipolysis in differentiated human adipocytes by activation of mitogen-activated protein kinase kinase (MEK), extracellular signal-related kinase (ERK), and elevation of intracellular cAMP. TNF-alpha activated ERK and increased lipolysis; these effects were inhibited by two specific MEK inhibitors, PD98059 and U0126. TNF-alpha treatment caused an electrophoretic shift of perilipin from 65 to 67 kDa, consistent with perilipin hyperphosphorylation by activated cAMP-dependent protein kinase A (PKA). Coincubation with TNF-alpha and MEK inhibitors caused perilipin to migrate as a single 65-kDa band. Consistent with the hypothesis that TNF-alpha induces perilipin hyperphosphorylation by activating PKA, TNF-alpha increased intracellular cAMP approximately 1.7-fold, and the increase was abrogated by PD98059. Furthermore, H89, a specific PKA inhibitor, blocked TNF-alpha-induced lipolysis and the electrophoretic shift of perilipin, suggesting a role for PKA in TNF-alpha-induced lipolysis. Finally, TNF-alpha decreased the expression of cyclic-nucleotide phosphodiesterase 3B (PDE3B) by approximately 50%, delineating a mechanism by which TNF-alpha could increase intracellular cAMP. Cotreatment with PD98059 restored PDE3B expression. These studies suggest that in human adipocytes, TNF-alpha stimulates lipolysis through activation of MEK-ERK and subsequent increase in intracellular cAMP.
- Published
- 2002
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