Transcription suppression of peroxisome proliferator-activated receptor gamma2 gene expression by tumor necrosis factor alpha via an inhibition of CCAAT/ enhancer-binding protein delta during the early stage of adipocyte differentiation.
TNFalpha is known to inhibit adipocyte differentiation and induce insulin resistance. Moreover, TNFalpha is known to down-regulate peroxisome proliferator-activated receptor (PPAR)gamma2, an adipocyte-specific nuclear receptor of insulin-sensitizer thiazolidinediones. To clarify molecular mechanisms of TNFalpha- mediated PPARgamma2 down-regulation, we here examined the effect of TNFalpha on transcription regulation of PPARgamma2 gene expression during the early stage of adipocyte differentiation. 3T3-L1 preadipocytes (2 d after 100% confluent) were incubated in a differentiation mixture (dexamethasone, insulin, 3-isobutyl-1-methlxanthine), with or without 50 ng/ml TNFalpha, for 24 h. TNFalpha significantly decreased PPARgamma2 expression both at mRNA and protein levels (to approximately 40%), as well as aP2 mRNA expression. The mouse PPARgamma2 gene promoter region (2.2-kb) was isolated and was used for luciferase reporter assays by transient transfection. TNFalpha significantly suppressed PPARgamma2 gene transcription (to approximately 50%), and deletion analyses demonstrated that the suppression was mediated via CCAAT/enhancer-binding protein (C/EBP) binding elements at the -320/-340 region of the promoter. Moreover, TNFalpha significantly decreased expression of C/EBPdelta mRNA and protein levels (to approximately 40%). EMSA, using 3T3-L1 cells nuclear extracts with the -320/-340 region as a probe, demonstrated the binding of C/EBPdelta to the element, which was significantly decreased by TNFalpha treatment. Overexpression of CEBP/delta prevented the TNFalpha-mediated suppression of PPARgamma2 transactivation. Taken together, TNFalpha suppresses PPARgamma2 gene transcription by the inhibition of C/EBPdelta expression and its DNA binding during the early stage of adipocyte differentiation, which may contribute to the inhibition of adipocyte differentiation, as well as the induction of insulin resistance.
Kudo
Masataka
M
Division of Nephrology, Endocrinology, and Vascular Medicine, Tohoku University Graduate School of Medicine, 1-1, Seiryo-cho, Aoba-ku, Sendai, 980-8574 Japan.
Sugawara
Akira
A
Uruno
Akira
A
Takeuchi
Kazuhisa
K
Ito
Sadayoshi
S
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology* / Q000502:physiology*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D051743:CCAAT-Enhancer-Binding Protein-delta; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D015536:Down-Regulation; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D051379:Mice; D047495:PPAR gamma / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D000970:Antineoplastic Agents; D022762:CCAAT-Enhancer-Binding Proteins; C497253:Cebpd protein, mouse; D047495:PPAR gamma; D012333:RNA, Messenger; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D051743:CCAAT-Enhancer-Binding Protein-delta