Acute Genome-Wide Effects of Rosiglitazone on PPARγ Transcriptional Networks in Adipocytes

Peroxisome proliferator-activated receptor (PPAR) is a master regulator of adipocyte differentiation, and genome-wide studies indicate that it is involved in the induction of most adipocyte genes. Here we report, for the first time, the acute effects of the synthetic PPAR agonist rosiglitazone on the transcriptional network of PPAR in adipocytes. Treatment with rosiglitazone for 1 hour leads to acute transcriptional activation as well as repression of a number of genes as determined by genome-wide RNA polymerase II occupancy. Unlike what has been shown for many other nuclear receptors, agonist treatment does not lead to major changes in the occurrence of PPAR binding sites. However, rosiglitazone promotes PPAR occupancy at many preexisting sites, and this is paralleled by increased occupancy of the mediator subunit MED1. The increase in PPAR and MED1 binding is correlated with an increase in transcription of nearby genes, indicating that rosiglitazone, in addition to activating the receptor, also promotes its association with DNA, and that this is causally linked to recruitment of mediator and activation of genes. Notably, both rosiglitazone-activated and -repressed genes are induced during adipogenesis. However, rosiglitazone-activated genes are markedly more associated with PPAR than repressed genes and are highly dependent on PPAR for expression in adipocytes. By contrast, repressed genes are associated with the other key adipocyte transcription factor CCAAT-enhancer binding protein (C/EBP), and their expression is more dependent on C/EBP. This suggests that the relative occupancies of PPAR and C/EBP are critical for whether genes will be induced or repressed by PPAR agonist. (Molecular Endocrinology 27: 1536 -1549, 2013) A dipocyte differentiation proceeds through the activa- tion of a cascade of early and late adipogenic transcription factors (1-3). The nuclear receptor peroxisome proliferator-activated receptor (PPAR) is a late acting key regulator of adipocyte differentiation and function (4). Recent genome-wide analyses of PPAR binding sites in mouse (5-7) and human adipocytes (8, 9) have shown that PPAR binds near most genes that are induced during adipocyte differentiation, suggesting that PPAR is directly involved in the activation of the entire adipogenic gene program. Another important late-acting adipogenic transcription factor is CCAAT-enhancer binding protein (C/EBP), and several lines of evidence indicate that PPAR and C/EBP constitute key components of the second and final wave of adipogenic transcription factors. The two factors cooperate by mutually inducing the expression of each other and by jointly activating common target genes (10 -13). Interestingly, C/EBP co-occupy a high percentage (30%-60%) of all PPAR binding sites in murine 3T3-L1 and in human Simpson-Golabi-Behmel syndrome cells (5, 9), indicating that the 2 factors directly cooperate on several enhancers in the genome.