Induction of the acyl-coenzyme A synthetase gene by fibrates and fatty acids is mediated by a peroxisome proliferator response element in the C promoter

Johan Auwerx, Kristina Schoonjans, Walter Wahli
1995
Article

Résumé

The long-chain acyl-coenzyme A synthetase (ACS) gene gives rise to three transcripts containing different first exons preceded by specific regulatory regions A, B, and C. Exon-specific oligonucleotide hybridization indicated that only A-ACS mRNA is expressed in rat liver. Fibrate administration induced liver C-ACS strongly and A-ACS mRNA to a lesser extent. B-ACS mRNA remained undetectable. In primary rat hepatocytes and Fa-32 hepatoma cells C-ACS mRNA increased after treatment with fenofibric acid, alpha-bromopalmitate, tetradecylthioacetic acid, or alpha-linolenic acid. Nuclear run-on experiments indicated that fenofibric acid and alpha-bromopalmitate act at the transcriptional level. Transient transfections showed a 3.4-, 2.3-, and 2.2-fold induction of C-ACS promoter activity after fenofibric acid, alpha-bromopalmitate, and tetradecylthioacetic acid, respectively. Unilateral deletion and site-directed mutagenesis identified a peroxisome proliferator activator receptor (PPAR)-responsive element (PPRE) mediating the responsiveness to fibrates and fatty acids. This ACS PPRE contains three imperfect half sites spaced by 1 and 3 oligonucleotides and binds PPAR.retinoid X receptor heterodimers in gel retardation assays. In conclusion, the regulation of C-ACS mRNA expression by fibrates and fatty acids is mediated by PPAR.retinoid X receptor heterodimers interacting through a PPRE in the C-ACS promoters. PPAR therefore occupies a key position in the transcriptional control of a pivotal enzyme controlling the channeling of fatty acids into various metabolic pathways.

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Johan Auwerx, Kristina Schoonjans, Walter Wahli
1995
Article

Résumé

Official source

https://infoscience.epfl.ch/record/135422?ln=fr

À propos de ce résultat

Concepts associés (17)

Concepts associés

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Publications associées (40)

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, ,

The three peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors of the nuclear hormone receptor superfamily. They share a high degree of structural homology with all members of the superfamily, particularly in the DNA-binding domain and ligand- and cofactor-binding domain. Many cellular and systemic roles have been attributed to these receptors, reaching far beyond the stimulation of peroxisome proliferation in rodents after which they were initially named. PPARs exhibit broad, isotype-specific tissue expression patterns. PPARalpha is expressed at high levels in organs with significant catabolism of fatty acids. PPARbeta/delta has the broadest expression pattern, and the levels of expression in certain tissues depend on the extent of cell proliferation and differentiation. PPARgamma is expressed as two isoforms, of which PPARgamma2 is found at high levels in the adipose tissues, whereas PPARgamma1 has a broader expression pattern. Transcriptional regulation by PPARs requires heterodimerization with the retinoid X receptor (RXR). When activated by a ligand, the dimer modulates transcription via binding to a specific DNA sequence element called a peroxisome proliferator response element (PPRE) in the promoter region of target genes. A wide variety of natural or synthetic compounds was identified as PPAR ligands. Among the synthetic ligands, the lipid-lowering drugs, fibrates, and the insulin sensitizers, thiazolidinediones, are PPARalpha and PPARgamma agonists, respectively, which underscores the important role of PPARs as therapeutic targets. Transcriptional control by PPAR/RXR heterodimers also requires interaction with coregulator complexes. Thus, selective action of PPARs in vivo results from the interplay at a given time point between expression levels of each of the three PPAR and RXR isotypes, affinity for a specific promoter PPRE, and ligand and cofactor availabilities.

2006

Chargement

Transcriptional control of triglyceride metabolism: fibrates and fatty acids change the expression of the LPL and apo C-III genes by activating the nuclear receptor PPAR

Johan Auwerx, Kristina Schoonjans

The development of atherosclerosis is often associated with altered concentrations of systemic lipoproteins, which are determined by the concentration and/or activity of three groups of different proteins, i.e. apolipoproteins (apo), enzymes, and receptors. The effects of diet or therapeutic interventions on lipid metabolism are mediated by changes in activity or concentrations of these three components. Fibrates have been shown to activate nuclear receptors belonging to the steroid hormone receptor super-family, termed peroxisome proliferator activated receptor (PPAR). These activated PPARs are potent transcription factors which influence the expression of several target genes implicated in lipoprotein homeostasis, e.g. LPL, apo C-III and apo A-1. Fibrates decrease apo C-III transcription and increase LPL production via these PPARs resulting in a profound hypotriglyceridaemic effect. Apolipoproteins and enzymes are important in governing lipid metabolism, thus therapeutically altering the expression of these genes constitutes an efficient therapeutic option.

1996

Chargement

A Tale of Two Tumors: Unraveling the Complexities of Epigenetic Dysregulation in Cancer

Maria Christine Donaldson

Epigenetics plays an important role in cancer development and progression. Cancer cells hijack the epigenome by modifying the histone protein units responsible for packaging DNA, or by modifying the DNA itself, resulting in changes to chromatin topology and transcriptional programming within the cell. In this thesis, I report our investigation to uncover the mechanisms of epigenetic regulation and how epigenetic control of transcriptional programming goes awry in cancer. We investigate these processes in two separate contexts. In our first study, we investigate the mechanisms by which EZH2 oncogenic mutations alter structure and function of topologically associating domains in non-Hodgkin lymphoma. The process of chromatin folding leads to a systematic arrangement of hierarchical structural and regulatory elements found within the nucleus. A topologically associating domain (TAD) is a regulatory unit of self interacting DNA, where the transcription of the genes within a TAD is usually dictated by the presence of active (H3K36me3) or inactive (H3K27me3) histone marks. In cancer, the somatic point mutation in EZH2Y646X leads to a genome wide increase in H3K27me3, associated with transcriptional repression. While this alteration leads to changes in the global epigenetic status of the cell, its impact on chromatin organization and TAD-related function remain unclear. By combining transcriptomics and epigenetics with analyses of chromatin structure, we demonstrate a functional interplay between TADs and the epigenetic and transcriptional program of the genes found within them. This balance is altered by EZH2Y646X, leading to the synergistic silencing of entire domains directly targeting cell differentiation and tumor suppressive programs. A closer look reveals that the silencing of tumor suppressive TADs are coupled with structural modifications and changes in promoter interactions within EZH2Y646X target TAD6.139. Impressively, the TADâs transcriptional and epigenetic programs are restored by pharmacological inhibition of EZH2Y646X. Our results indicate that EZH2Y646X alters the topology and function of chromatin domains to promote synergistic oncogenic programs. In our second study, we dissect the epigenetic, transcriptomic, and metabolic signaling dependencies using a novel model of central nervous system primitive neural ectodermal tumors (CNS-PNETs). Central nervous system (CNS) tumors are the leading cause of cancer-associated death in children. Primitive neural-ectodermal tumors (CNS-PNETs) are a particularly aggressive subtype of embryonal CNS-tumor, with a five-year overall survival rate in less than 50% of patients. Despite sharing a similar cell of origin of other CNS tumors, CNS-PNETs have a different anatomical location, unique genetic and epigenetic features, and significantly worse clinical outcome. In addition, a lack of in vivo models for studying CNS tumors challenges the opportunity to dissect the genetic variables that underlie the origin of these tumors. We developed a novel CNS-PNET mouse model, called CNS-NPCs, using neural progenitor cells derived from human-iPS cells. Through histological, DNA methylation, and RNA sequencing analyses, we find that the CNS-NPC model recapitulates the the morphologic, epigenetic, and transcriptomic features of primary CNS-PNETs. In addition, through in vivo metabolic analyses of CNS-NPCs and the patient derived cell line, PFSK-1, we identified dysregulation in the neurotransmitter...

EPFL2019

Chargement

A Tale of Two Tumors: Unraveling the Complexities of Epigenetic Dysregulation in Cancer

Maria Christine Donaldson

EPFL2019