RNA Decay in Processing Bodies is Indispensable for Adipogenesis
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ABSTRACT: The RNA decay pathway plays key regulatory roles in cell identities and differentiation processes. Although adipogenesis is transcriptionally and epigenetically regulated and has been thoroughly investigated, how RNA metabolism that contributes to the stability of phenotype-shaping transcriptomes participates in differentiation remains elusive. In this study, we investigated Ddx6, an essential component of processing bodies (PBs) that executes RNA decay and translational repression in the cytoplasm and participates in the cellular transition of reprogramming. Upon adipogenic induction, Ddx6 dynamically accumulated to form PBs with a binding partner, 4E-T, at the early phase prior to emergence of intracellular lipid droplets. In contrast, preadipocytes with Ddx6 knockout (KO) or 4E-T knockdown (KD) failed to generate PBs, resulting in significant suppression of adipogenesis. Transcription factors related to preadipocytes and negative regulators of adipogenesis that were not expressed under adipogenic stimulation were maintained in Ddx6-KO and 4E-T-KD preadipocytes under adipogenic induction. Elimination of Dlk1, a major negative regulator of adipogenesis, in 3T3L1 Ddx6-KO cells did not restore adipogenic differentiation capacity to any extent. Similar to murine cells, human primary mesenchymal stem cells, which can differentiate into adipocytes upon stimulation with adipogenic cocktails, required DDX6 to maturate into adipocytes. Therefore, RNA decay of the entire parental transcriptome, rather than removal of a strong negative regulator, could be indispensable for adipogenesis.
Project description:The synthesis and decay of mRNA in cells are carried out by influencing each other, and their balance is altered by either external or internal cues, resulting in changes in the dynamics of the cell. We have previously reported that it is indispensable that an array of mRNAs which shape a phenotype should be degraded before cellular transitions, such as cellular reprogramming and differentiation. In adipogenesis, the interaction between DDX6 and 4E-T had a definitive impact on the pathway in the processing body (PB). We screened a library of α-helix analog with an alkaloid backbone to determine a compound inhibiting the binding between DDX6 and 4E-T proteins, because the interaction is executed between α-helix of structured and internally disordered protein, respectively, and identified IAMC-00192 as a lead compound. The compound showed a direct inhibition in the interaction between DDX6 and 4E-T by using WAVE system with a KD of 774.3 nM. The compound inhibited PB formation that temporally increases during adipogenesis and epithelial-mesenchymal transition (EMT), and significantly suppressed their cellular transition. We also found that in the EMT model, the half-life of pre-existing mRNAs in PBs was extended twofold by the compound. The novel inhibitor of RNA decay will be not only a tool to analyze in detail what pathological conditions RNA decay affects and how it regulates the state, but also lead to drug discovery of the first in class as RNA decay inhibitor.
Project description:PPARγ promotes adipogenesis while Wnt proteins inhibit adipogenesis. However, the mechanisms that control expression of these positive and negative master regulators of adipogenesis remain incompletely understood. By genome-wide histone methylation profiling in preadipocytes, we find that among gene loci encoding adipogenesis regulators, histone methyltransferase (HMT) G9a-mediated repressive epigenetic mark H3K9me2 is enriched on the entire PPARγ locus. H3K9me2 and G9a levels decrease during adipogenesis, which correlates inversely with induction of PPARγ. Removal of H3K9me2 by G9a deletion enhances chromatin opening and binding of adipogenic transcription factor C/EBP-beta to PPARγ promoter, which promotes PPARγ expression. Interestingly, G9a represses PPARγ expression in an HMT activity-dependent manner but facilitates Wnt10a expression independent of its enzymatic activity. Consistently, deletion of G9a or inhibiting G9a HMT activity promotes adipogenesis. Finally, deletion of G9a in mouse adipose tissues increases adipogenic gene expression and tissue weight. Thus, by inhibiting PPARγ expression and facilitating Wnt10a expression, G9a represses adipogenesis. Examination of gene expression changes in G9a KO brown preadipocytes
Project description:Insulin and IGF-1 promote adipocyte differentiation via complex and overlapping signalling networks. Here we used microarray analysis of brown preadipocytes derived from wild-type and insulin receptor substrate (IRS) knockout (KO) animals, which exhibited progressively impaired differentiation, to define the set of genes that predict adipogenic potential in these cells. 374 genes/ESTs were identified whose expression in preadipocytes correlated with their ultimate ability to differentiate. Many of these genes were related to early adipogenic events, including genes involved in extracellular matrix, cytoskeletal organization, growth arrest, post-mitotic clonal expansion, and inhibitors of adipogenesis, including preadipocyte factor-1 and multiple members of the Wnt-signalling pathway. Reconstitution of IRS-1 KO cells with IRS-1 reversed these changes and restored the ability to differentiate. Several of these genes showed concordant changes in brown adipose tissue in vivo. Necdin was markedly increased in IRS-1 KO cells that could not differentiate, and knockdown of necdin restored brown adipogenesis with down-regulation of Pref-1 and Wnt10a expression. We demonstrated a necdin-E2F4 interaction repressing PPARg transcription. IRS proteins regulated necdin via a CREB dependent pathway, defining a signalling network involved in brown preadipocyte determination.
Project description:PPAR? promotes adipogenesis while Wnt proteins inhibit adipogenesis. However, the mechanisms that control expression of these positive and negative master regulators of adipogenesis remain incompletely understood. By genome-wide histone methylation profiling in preadipocytes, we find that among gene loci encoding adipogenesis regulators, histone methyltransferase (HMT) G9a-mediated repressive epigenetic mark H3K9me2 is enriched on the entire PPAR? locus. H3K9me2 and G9a levels decrease during adipogenesis, which correlates inversely with induction of PPAR?. Removal of H3K9me2 by G9a deletion enhances chromatin opening and binding of adipogenic transcription factor C/EBP-beta to PPAR? promoter, which promotes PPAR? expression. Interestingly, G9a represses PPAR? expression in an HMT activity-dependent manner but facilitates Wnt10a expression independent of its enzymatic activity. Consistently, deletion of G9a or inhibiting G9a HMT activity promotes adipogenesis. Finally, deletion of G9a in mouse adipose tissues increases adipogenic gene expression and tissue weight. Thus, by inhibiting PPAR? expression and facilitating Wnt10a expression, G9a represses adipogenesis. Examination of 3 different histone modification changes in 3T3-L1 preadipocytes
Project description:Here we show through genome-wide binding studies that transcription factor 7-like 1 (TCF7L1) represses structure-related genes during adipogenesis. Intriguingly, TCF7L1 is induced in a cell contact-dependent manner by confluency in preadipocytes and is required for adipocyte differentiation by repressing transcription of cell structure genes. TCF7L1 is also sufficient to bestow adipogenic potential upon non-adipogenic cells. These results implicate TCF7L1 as a novel adipogenic competency factor that uniquely determines adipogenic fate through cell structure organization required for adipocyte gene activation. Examination of TCF7L1 binding in preadipocytes treated for 24 hours with adipogenic stimuli.
Project description:Insulin and IGF-1 promote adipocyte differentiation via complex and overlapping signalling networks. Here we used microarray analysis of brown preadipocytes derived from wild-type and insulin receptor substrate (IRS) knockout (KO) animals, which exhibited progressively impaired differentiation, to define the set of genes that predict adipogenic potential in these cells. 374 genes/ESTs were identified whose expression in preadipocytes correlated with their ultimate ability to differentiate. Many of these genes were related to early adipogenic events, including genes involved in extracellular matrix, cytoskeletal organization, growth arrest, post-mitotic clonal expansion, and inhibitors of adipogenesis, including preadipocyte factor-1 and multiple members of the Wnt-signalling pathway. Reconstitution of IRS-1 KO cells with IRS-1 reversed these changes and restored the ability to differentiate. Several of these genes showed concordant changes in brown adipose tissue in vivo. Necdin was markedly increased in IRS-1 KO cells that could not differentiate, and knockdown of necdin restored brown adipogenesis with down-regulation of Pref-1 and Wnt10a expression. We demonstrated a necdin-E2F4 interaction repressing PPARg transcription. IRS proteins regulated necdin via a CREB dependent pathway, defining a signalling network involved in brown preadipocyte determination. Keywords = brown fat Keywords = preadipocyte Keywords = adipogenesis Keywords = mouse Keywords: parallel sample
Project description:Much of our knowledge on adipogenesis comes from cell culture models of preadipocyte differentiation. Adipogenesis is induced by treating confluent preadipocytes with the adipogenic cocktail, which activates transcription factors (TFs) glucocorticoid receptor (GR) and CREB within minutes and increases expression of TFs C/EBPb/d, KLF4 and Krox20 within hours. All of these TFs have been shown to be capable of promoting adipogenesis in culture when they are overexpressed. However, it has remained unclear whether endogenous KLF4 and Krox20 are required for adipogenesis in culture and in vivo. Using conditional knockout mice and derived white and brown preadipocytes, we show that endogenous KLF4 and Krox20 are dispensable for adipogenesis in culture and brown adipose tissue development in mice. In contrast, the master adipogenic TF PPARg is essential. These results challenge the existing model on transcriptional regulation in the early phase of adipogenesis and highlight the need of studying adipogenesis in vivo.
Project description:Dexamethasone (DEX), a synthetic ligand for glucocorticoid receptor (GR), is routinely used to stimulate adipogenesis in culture. GR-depleted preadipocytes show adipogenesis defects one week after induction of differentiation. However, it has remained unclear whether GR is required for adipogenesis in vivo. By deleting GR in precursors of brown adipocytes, we found unexpectedly that GR is dispensable for brown adipose tissue development in mice. In culture, GR-deficient primary or immortalized white and brown preadipocytes showed severely delayed adipogenesis one week after induction of differentiation. However, when differentiation was extended to 3 weeks, GR-deficient preadipocytes showed similar levels of adipogenesis marker expression and lipid accumulation as the wild type cells, indicating that DEX-bound GR accelerates, but is dispensable for, adipogenesis. Consistently, DEX accelerates, but is dispensable for, adipogenesis in culture. We show that DEX-bound GR accelerates adipogenesis by directly promoting the expression of adipogenic transcription factors C/EBPb, C/EBPd, C/EBPa, KLF5, KLF9 and PPARg in the early phase of differentiation. Mechanistically, DEX-bound GR recruits histone H3K27 acetyltransferase CBP to promote activation of C/EBPb-primed enhancers of adipogenic genes. These results clarify the role of GR in adipogenesis in vivo and demonstrate that DEX-mediated activation of GR accelerates, but is dispensable for, adipogenesis.
Project description:The Wnt/b-catenin signaling inhibits adipogenesis. Genome-wide profiling studies have revealed the enrichment of histone H3K27 methyltransferase PRC2 on Wnt genes. However, the functional significance of such a direct link between the two types of developmental regulators in mammalian cells, and the role of PRC2 in adipogenesis, remain unclear. Here we show PRC2 and its H3K27 methyltransferase activity are required for adipogenesis. PRC2 directly represses Wnt1, 6, 10a and 10b genes in preadipocytes and during adipogenesis. Deletion of the enzymatic Ezh2 subunit of PRC2 eliminates H3K27me3 on Wnt promoters and de-represses Wnt expression, which leads to activation of Wnt/b-catenin signaling and inhibition of adipogenesis. Ectopic expression of the wild type Ezh2, but not the enzymatically inactive F667I mutant, prevents the loss of H3K27me3 and the defects in adipogenesis in Ezh2-/- preadipocytes. The adipogenesis defects in Ezh2-/- cells can be rescued by expression of adipogenic transcription factors PPARa, C/EBPb, or inhibitors of Wnt/b-catenin signaling. Interestingly, Ezh2-/- cells show marked increase of H3K27 acetylation globally as well as on Wnt promoters. These results indicate that H3K27 methyltransferase PRC2 directly represses Wnt genes to facilitate adipogenesis, and suggest that acetylation and trimethylation on H3K27 play opposing roles in regulating Wnt expression. To identify additional PRC2-regulated genes in preadipocytes, we performed microarray analysis in Ezh2flox/flox preadipocytes infected with retroviruses expressing Cre or vector alone.
Project description:Here we show through genome-wide binding studies that transcription factor 7-like 1 (TCF7L1) represses structure-related genes during adipogenesis. Intriguingly, TCF7L1 is induced in a cell contact-dependent manner by confluency in preadipocytes and is required for adipocyte differentiation by repressing transcription of cell structure genes. TCF7L1 is also sufficient to bestow adipogenic potential upon non-adipogenic cells. These results implicate TCF7L1 as a novel adipogenic competency factor that uniquely determines adipogenic fate through cell structure organization required for adipocyte gene activation.