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.
Publication types
-
Research Support, Non-U.S. Gov't
-
Research Support, U.S. Gov't, Non-P.H.S.
MeSH terms
-
3',5'-Cyclic-AMP Phosphodiesterases / metabolism
-
Adipocytes / cytology
-
Adipocytes / drug effects
-
Adipocytes / enzymology*
-
Adult
-
Antineoplastic Agents / pharmacology*
-
Butadienes / pharmacology
-
Carrier Proteins
-
Cell Differentiation
-
Cells, Cultured
-
Cyclic AMP / metabolism*
-
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
-
Lipolysis / drug effects*
-
MAP Kinase Kinase 2
-
MAP Kinase Signaling System / physiology*
-
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
-
Sulfonamides*
-
Tumor Necrosis Factor-alpha / pharmacology*
Substances
-
Antineoplastic Agents
-
Butadienes
-
Carrier Proteins
-
Enzyme Inhibitors
-
Flavonoids
-
Isoquinolines
-
Nitriles
-
Perilipin-1
-
Phosphoproteins
-
Sulfonamides
-
Tumor Necrosis Factor-alpha
-
U 0126
-
Cyclic AMP
-
MAP2K2 protein, human
-
Protein-Tyrosine Kinases
-
Cyclic AMP-Dependent Protein Kinases
-
Mitogen-Activated Protein Kinases
-
MAP Kinase Kinase 2
-
Mitogen-Activated Protein Kinase Kinases
-
3',5'-Cyclic-AMP Phosphodiesterases
-
Cyclic Nucleotide Phosphodiesterases, Type 3
-
PDE3B protein, human
-
N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide
-
2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one