title: Tumor necrosis factor-alpha stimulates lipolysis in differentiated human adipocytes through activation of extracellular signal-related kinase and elevation of intracellular cAMP.
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.
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D000328:Adult; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002070:Butadienes / Q000494:pharmacology; D002352:Carrier Proteins; D002454:Cell Differentiation; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D008066:Lipolysis / Q000187:drug effects*; D048370:MAP Kinase Kinase 2; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D000070778:Perilipin-1; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D013449:Sulfonamides; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D002070:Butadienes; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007546:Isoquinolines; D009570:Nitriles; D000070778:Perilipin-1; D010750:Phosphoproteins; D013449:Sulfonamides; D014409:Tumor Necrosis Factor-alpha; C113580:U 0126; D000242:Cyclic AMP; C482128:MAP2K2 protein, human; D011505:Protein-Tyrosine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048370:MAP Kinase Kinase 2; D020929:Mitogen-Activated Protein Kinase Kinases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; C517291:PDE3B protein, human; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one