PPARγ Protein Expression is Regulated by Cited1 and Cidec in Mouse 3T3-L1 Adipocytes Treated with Troglitazone

Abstract

We previously reported that treatment with thiazolidinediones (TZDs), such as troglitazone (Tro), downregulates the protein levels of peroxisome proliferator-activated receptor gamma (PPARγ), with enhanced lipid accumulation during 3T3-L1 murine adipocyte differentiation in the presence of 3-isobutyl methylxanthine, dexamethasone, and insulin (MDI). In this study, we performed DNA microarray analysis to compare the gene expression profiles of MDI-induced and MDI/Tro-induced 3T3-L1 adipocytes to elucidate the mechanism underlying the reduction in PPARγ protein expression by Tro treatment. Apoptotic process genes of Gene Ontology were selected from the upregulated genes in MDI/Tro-induced cells and analyzed using real-time RT-PCR and western blotting. For several proteins, higher expression was detected in MDI/Tro-treated 3T3-L1 cells than in MDI-treated cells. Plasmid expression analysis using 293T cells revealed that the expression of cell death-inducing DFFA-like effector C (Cidec) or Cbp/P300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 1 (Cited1) reduced PPARγ protein expression compared with the vector control. When 3T3-L1 preadipocytes transfected with small interfering RNA targeting Cidec or Cited1 were differentiated in response to MDI or MDI/Tro treatment, the reduction in PPARγ expression in MDI/Tro-treated 3T3-L1 adipocytes was partially suppressed. Our findings indicate that the expression of PPARγ protein is regulated in part by the induction of Cidec and Cited1 in MDI/Tro-treated 3T3-L1 adipocytes.