Transcriptional regulation of adipocyte lipolysis by IRF2BP2.

Adipocyte lipolysis controls systemic energy levels and metabolic homeostasis. Lipolysis is regulated by post-translational modifications of key lipolytic enzymes. However, less is known about the transcriptional mechanisms that regulate lipolysis.

Isoform-specific functions of PPARγ in gene regulation and metabolism.

Peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor that is a vital regulator of adipogenesis, insulin sensitivity, and lipid metabolism. Activation of PPARγ by antidiabetic thiazolidinediones (TZD) reverses insulin resistance but also leads to weight gain that limits the use of these drugs. There are two main PPARγ isoforms, but the specific functions of each are not established.

Cell-Intrinsic Tumorigenic Functions of PPARγ in Bladder Urothelial Carcinoma.

The role of PPAR gamma (PPARγ) has been well characterized in the developmental process of adipogenesis, yet its aberrant expression patterns and functions in cancer subtypes are less understood. Although PPARγ has been recently demonstrated to play non-cell-autonomous roles in promoting bladder urothelial carcinoma (UC) progression, underlying mechanisms of the cell-intrinsic oncogenic activity remain unknown. Here, we report robust expression and nuclear accumulation of PPARγ in 47% of samples of patients with UC, exceeding mRNA expression patterns published by The Cancer Genome Atlas.

Shared PPARα/γ Target Genes Regulate Brown Adipocyte Thermogenic Function.

Brown adipose tissue (BAT) generates heat to maintain body temperature and suppress obesity. Agonists for nuclear receptors PPARα and PPARγ both affect brown adipocyte function, yet the interplay between these factors in BAT is uncertain. Here, we report that PPARα shares most genomic binding sites with PPARγ, and these common binding sites are more related to BAT function than PPARγ-selective sites without PPARα.

Patient Adipose Stem Cell-Derived Adipocytes Reveal Genetic Variation that Predicts Antidiabetic Drug Response.

Thiazolidinedione drugs (TZDs) target the transcriptional activity of peroxisome proliferator activated receptor γ (PPARγ) to reverse insulin resistance in type 2 diabetes, but side effects limit their clinical use. Here, using human adipose stem cell-derived adipocytes, we demonstrate that SNPs were enriched at sites of patient-specific PPARγ binding, which correlated with the individual-specific effects of the TZD rosiglitazone (rosi) on gene expression. Rosi induction of ABCA1, which regulates cholesterol metabolism, was dependent upon SNP rs4743771, which modulated PPARγ binding by influencing the genomic occupancy of its cooperating factor, NFIA.

Shared nucleotide flanks confer transcriptional competency to bZip core motifs.

Sequence-specific DNA binding recruits transcription factors (TFs) to the genome to regulate gene expression. Here, we perform high resolution mapping of CEBP proteins to determine how sequence dictates genomic occupancy. We demonstrate a fundamental difference between the sequence repertoire utilized by CEBPs in vivo versus the palindromic sequence preference reported by classical in vitro models, by identifying a palindromic motif at <1% of the genomic binding sites.

PPARγ is dispensable for clear cell renal cell carcinoma progression.

Objective: Clear cell renal cell carcinoma (ccRCC) is a subtype of kidney cancer defined by robust lipid accumulation, which prior studies have indicated plays an important role in tumor progression. We hypothesized that the peroxisome proliferator-activated receptor gamma (PPARγ), detected in both ccRCC tumors and cell lines, promotes lipid storage in ccRCC and contributes to tumorigenesis in this setting. PPARγ transcriptionally regulates a number of genes involved in lipid and glucose metabolism in adipocytes, yet its role in ccRCC has not been described.

Rev-erbα dynamically modulates chromatin looping to control circadian gene transcription.

Mammalian physiology exhibits 24-hour cyclicity due to circadian rhythms of gene expression controlled by transcription factors that constitute molecular clocks. Core clock transcription factors bind to the genome at enhancer sequences to regulate circadian gene expression, but not all binding sites are equally functional. We found that in mice, circadian gene expression in the liver is controlled by rhythmic chromatin interactions between enhancers and promoters.

Histone deacetylase 3 prepares brown adipose tissue for acute thermogenic challenge.

Brown adipose tissue is a thermogenic organ that dissipates chemical energy as heat to protect animals against hypothermia and to counteract metabolic disease. However, the transcriptional mechanisms that determine the thermogenic capacity of brown adipose tissue before environmental cold are unknown. Here we show that histone deacetylase 3 (HDAC3) is required to activate brown adipose tissue enhancers to ensure thermogenic aptitude.

Nuclear Receptor Function through Genomics: Lessons from the Glucocorticoid Receptor.

Unlocking the therapeutic potential of the glucocorticoid receptor (GR) has motivated a search for small molecules that selectively modulate its ability to activate or repress gene transcription. Recently, breakthrough studies in the field of genomics have reinvigorated debate over longstanding transcriptional models explaining how GR controls tissue-specific gene expression. Here, we highlight these genomic studies with the dual goals of advancing understanding of nuclear receptor-mediated transcription and stimulating thought on the development of anti-inflammatory and immunosuppressive ligands for GR that have reduced harmful effects on metabolism.

Targeting PPARγ in the epigenome rescues genetic metabolic defects in mice.

Obesity causes insulin resistance, and PPARγ ligands such as rosiglitazone are insulin sensitizing, yet the mechanisms remain unclear. In C57BL/6 (B6) mice, obesity induced by a high-fat diet (HFD) has major effects on visceral epididymal adipose tissue (eWAT). Here, we report that HFD-induced obesity in B6 mice also altered the activity of gene regulatory elements and genome-wide occupancy of PPARγ.

The Nuclear Receptor Rev-erbα Regulates Adipose Tissue-specific FGF21 Signaling.

FGF21 is an atypical member of the FGF family that functions as a hormone to regulate carbohydrate and lipid metabolism. Here we demonstrate that the actions of FGF21 in mouse adipose tissue, but not in liver, are modulated by the nuclear receptor Rev-erbα, a potent transcriptional repressor. Interrogation of genes induced in the absence of Rev-erbα for Rev-erbα-binding sites identified βKlotho, an essential coreceptor for FGF21, as a direct target gene of Rev-erbα in white adipose tissue but not liver.

Tribbles-1 regulates hepatic lipogenesis through posttranscriptional regulation of C/EBPα.

Variants near the gene TRIB1 are significantly associated with several plasma lipid traits, circulating liver enzymes, and the development of coronary artery disease in humans; however, it is not clear how its protein product tribbles-1 regulates lipid metabolism. Here, we evaluated mice harboring a liver-specific deletion of Trib1 (Trib1_LSKO) to elucidate the role of tribbles-1 in mammalian hepatic lipid metabolism. These mice exhibited increased hepatic triglyceride (TG) content, lipogenic gene transcription, and de novo lipogenesis.

Genetic Variation Determines PPARγ Function and Anti-diabetic Drug Response In Vivo.

SNPs affecting disease risk often reside in non-coding genomic regions. Here, we show that SNPs are highly enriched at mouse strain-selective adipose tissue binding sites for PPARγ, a nuclear receptor for anti-diabetic drugs. Many such SNPs alter binding motifs for PPARγ or cooperating factors and functionally regulate nearby genes whose expression is strain selective and imbalanced in heterozygous F1 mice.

ATF4 licenses C/EBPβ activity in human mesenchymal stem cells primed for adipogenesis.

A well-established cascade of transcription factor (TF) activity orchestrates adipogenesis in response to chemical cues, yet how cell-intrinsic determinants of differentiation such as cell shape and/or seeding density inform this transcriptional program remain enigmatic. Here, we uncover a novel mechanism licensing transcription in human mesenchymal stem cells (hMSCs) adipogenically primed by confluence. Prior to adipogenesis, confluency promotes heterodimer recruitment of the bZip TFs C/EBPβ and ATF4 to a non-canonical C/EBP DNA sequence.

GENE REGULATION. Discrete functions of nuclear receptor Rev-erbα couple metabolism to the clock.

Circadian and metabolic physiology are intricately intertwined, as illustrated by Rev-erbα, a transcription factor (TF) that functions both as a core repressive component of the cell-autonomous clock and as a regulator of metabolic genes. Here, we show that Rev-erbα modulates the clock and metabolism by different genomic mechanisms. Clock control requires Rev-erbα to bind directly to the genome at its cognate sites, where it competes with activating ROR TFs.

PRDM16 binds MED1 and controls chromatin architecture to determine a brown fat transcriptional program.

PR (PRD1-BF1-RIZ1 homologous) domain-containing 16 (PRDM16) drives a brown fat differentiation program, but the mechanisms by which PRDM16 activates brown fat-selective genes have been unclear. Through chromatin immunoprecipitation (ChIP) followed by deep sequencing (ChIP-seq) analyses in brown adipose tissue (BAT), we reveal that PRDM16 binding is highly enriched at a broad set of brown fat-selective genes. Importantly, we found that PRDM16 physically binds to MED1, a component of the Mediator complex, and recruits it to superenhancers at brown fat-selective genes.

Anti-diabetic rosiglitazone remodels the adipocyte transcriptome by redistributing transcription to PPARγ-driven enhancers.

Rosiglitazone (rosi) is a powerful insulin sensitizer, but serious toxicities have curtailed its widespread clinical use. Rosi functions as a high-affinity ligand for peroxisome proliferator-activated receptor γ (PPARγ), the adipocyte-predominant nuclear receptor (NR). The classic model, involving binding of ligand to the NR on DNA, explains positive regulation of gene expression, but ligand-dependent repression is not well understood.

Integrative genomic analysis of CREB defines a critical role for transcription factor networks in mediating the fed/fasted switch in liver.

Background: Metabolic homeostasis in mammals critically depends on the regulation of fasting-induced genes by CREB in the liver. Previous genome-wide analysis has shown that only a small percentage of CREB target genes are induced in response to fasting-associated signaling pathways. The precise molecular mechanisms by which CREB specifically targets these genes in response to alternating hormonal cues remain to be elucidated.

An Evi1-C/EBPβ complex controls peroxisome proliferator-activated receptor γ2 gene expression to initiate white fat cell differentiation.

Fibroblastic preadipocyte cells are recruited to differentiate into new adipocytes during the formation and hyperplastic growth of white adipose tissue. Peroxisome proliferator-activated receptor γ (PPARγ), the master regulator of adipogenesis, is expressed at low levels in preadipocytes, and its levels increase dramatically and rapidly during the differentiation process. However, the mechanisms controlling the dynamic and selective expression of PPARγ in the adipocyte lineage remain largely unknown.

Histone deacetylase 3 is an epigenomic brake in macrophage alternative activation.

Macrophages, a key cellular component of inflammation, become functionally polarized in a signal- and context-specific manner. Th2 cytokines such as interleukin 4 (IL-4) polarize macrophages to a state of alternative activation that limits inflammation and promotes wound healing. Alternative activation is mediated by a transcriptional program that is influenced by epigenomic modifications, including histone acetylation.

Repressor transcription factor 7-like 1 promotes adipogenic competency in precursor cells.

The identification of factors that define adipocyte precursor potential has important implications for obesity. Preadipocytes are fibroblastoid cells committed to becoming round lipid-laden adipocytes. In vitro, this differentiation process is facilitated by confluency, followed by adipogenic stimuli.

Adipogenic hotspots: where the action is.

EMBO J 30 8, 1459–1472 (2011); published online March 22 2011 Transcription factors (TFs) orchestrate cell-fate decisions by programming the expression of many genes, including those of other TFs that further drive lineage specification. C/EBP proteins and glucocorticoid receptor (GR) activate transcription of the master regulator of adipocyte differentiation, PPARγ. A study in this issue of sheds light on how C/EBPs, GR, STAT5, and RXR cooperate during early adipogenesis to globally remodel the epigenome.

Propagation of adipogenic signals through an epigenomic transition state.

The transcriptional mechanisms by which temporary exposure to developmental signals instigates adipocyte differentiation are unknown. During early adipogenesis, we find transient enrichment of the glucocorticoid receptor (GR), CCAAT/enhancer-binding protein beta (CEBPbeta), p300, mediator subunit 1, and histone H3 acetylation near genes involved in cell proliferation, development, and differentiation, including the gene encoding the master regulator of adipocyte differentiation, peroxisome proliferator-activated receptor gamma2 (PPARgamma2). Occupancy and enhancer function are triggered by adipogenic signals, and diminish upon their removal.