title: Protein kinase C mediates tumor necrosis factor-alpha-induced inhibition of obese gene expression and leptin secretion in brown adipocytes.
abstract: Previously we showed that tumor necrosis factor-alpha (TNF-alpha) inhibits lipoprotein lipase (LPL) activity and its gene expression, an early marker of adipocyte differentiation, in cultured brown adipocytes. To know whether TNF-alpha also affects late events in brown adipocyte maturation, we examined the effect of TNF-alpha on obese gene expression and leptin secretion in mouse brown adipocytes differentiated in culture. TNF-alpha caused a concentration-dependent decrease in leptin accumulation in culture medium and leptin mRNA amount in brown adipocytes which constitutively express the ob gene. Time-course study showed that TNF-alpha significantly suppressed leptin secretion during incubation for 16, 24 and 48 h. Since some effect of TNF-alpha is mediated by activation of protein kinase C (PKC), the role of PKC in TNF-alpha-induced downregulation of ob gene expression and leptin secretion was studied. The suppressive effect of TNF-alpha on both ob gene expression and leptin secretion was blocked by PKC inhibitors such as bisindolylmaleimide I (BIM) and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7). Incubation of brown adipocytes with TNF-alpha (20 ng/ml, 15 min) caused a rapid shift of PKC activity from the cytosolic to the membrane fraction, suggesting an activation of PKC by TNF-alpha in brown adipocytes. This effect of TNF-alpha was blocked by a selective PKC inhibitor, BIM. These results suggest that TNF-alpha promotes dedifferentiation of the brown adipocytes as evidenced by a downregulation in ob gene expression and leptin secretion via PKC-dependent mechanisms.
authors.affiliation: Department of Pharmacology, Tokyo Women's Medical University, School of Medicine, Japan. uchiy@research.twmu.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Uchida
authors.forename: K
authors.initials: K
authors.lastname: Ohba
authors.forename: A
authors.initials: A
authors.lastname: Ogawa
authors.forename: K
authors.initials: K
authors.lastname: Wada
authors.forename: T
authors.initials: T
authors.lastname: Yoshioka
authors.forename: T
authors.initials: T
authors.lastname: Muraki
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D017667:Adipocytes / Q000166:cytology / Q000201:enzymology; D002001:Adipose Tissue, Brown / Q000166:cytology / Q000201:enzymology*; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D020738:Leptin / Q000235:genetics* / Q000378:metabolism*; D008297:Male; D008301:Maleimides / Q000494:pharmacology; D051379:Mice; D008813:Mice, Inbred ICR; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D007211:Indoles; D020738:Leptin; D008301:Maleimides; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D005993:Glycerolphosphate Dehydrogenase; D011493:Protein Kinase C; C070515:bisindolylmaleimide I