Regulation of Gene Expression by the NR Corepressor RIP140 in Adipocytes
Author(s)
Kiskinis, Evangelos
Type
Thesis
Abstract
Nuclear receptors (NR) are ligand-induced transcription factors that regulate the
expression of genes involved in a number of physiological processes including
metabolism. Their ability to regulate transcription is dependent on the recruitment of
specific cofactors that remodel chromatin and promote the assembly of the basal
transcriptional machinery. Receptor interacting protein 140 (RIP140) is a corepressor
for NRs that utilizes four independent repression domains to inhibit gene expression
of target genes. While RIP140-null mice develop around 70% less white adipose
tissue than wild-type littermates, the process of adipogenesis is unaffected in
RIP140-null and RIP140-expressing cells.
To elucidate the intrinsic role of RIP140 in adipocytes i used full mouse genome
arrays to compare the gene expression profiles of pre-adipocytes and adipocytes with
and without RIP140. I demonstrate that the transcriptional corepressor negatively
regulates major gene clusters in a number of metabolic pathways including
glycolysis, TCA cycle, oxidative phosphorylation, fatty acid oxidation and glycerol
metabolism. Additionally, a futile metabolic cycle of triglyceride recycling is
activated in RIP140 null adipocytes.
In order to determine the molecular mechanism of RIP140 repression i analysed the
epigenetic profile of Ucp1, a gene which is typically expressed in brown but not
white adipocytes. I utilized RIP140-null and RIP140-expressing adipocytes and
found that RIP140 is essential for both DNA and histone methylation to maintain
gene repression. RIP140 expression promotes the assembly of DNA and histone
methyltransferases on the Ucp1 enhancer and leads to methylation of specific CpG
residues and histones as judged by bisulphite genomic sequencing and chromatin
immunoprecipitation assays. These results suggest that RIP140 serves as a scaffold
for both DNA and histone methyltransferase activities to inhibit gene transcription by
two key epigenetic repression systems. RIP140 could potentially act to divert white
adipocytes from a brown fat phenotype by repressing genes involved in fatty acid
oxidation and mitochondrial respiration and by silencing genes like Ucp1.
expression of genes involved in a number of physiological processes including
metabolism. Their ability to regulate transcription is dependent on the recruitment of
specific cofactors that remodel chromatin and promote the assembly of the basal
transcriptional machinery. Receptor interacting protein 140 (RIP140) is a corepressor
for NRs that utilizes four independent repression domains to inhibit gene expression
of target genes. While RIP140-null mice develop around 70% less white adipose
tissue than wild-type littermates, the process of adipogenesis is unaffected in
RIP140-null and RIP140-expressing cells.
To elucidate the intrinsic role of RIP140 in adipocytes i used full mouse genome
arrays to compare the gene expression profiles of pre-adipocytes and adipocytes with
and without RIP140. I demonstrate that the transcriptional corepressor negatively
regulates major gene clusters in a number of metabolic pathways including
glycolysis, TCA cycle, oxidative phosphorylation, fatty acid oxidation and glycerol
metabolism. Additionally, a futile metabolic cycle of triglyceride recycling is
activated in RIP140 null adipocytes.
In order to determine the molecular mechanism of RIP140 repression i analysed the
epigenetic profile of Ucp1, a gene which is typically expressed in brown but not
white adipocytes. I utilized RIP140-null and RIP140-expressing adipocytes and
found that RIP140 is essential for both DNA and histone methylation to maintain
gene repression. RIP140 expression promotes the assembly of DNA and histone
methyltransferases on the Ucp1 enhancer and leads to methylation of specific CpG
residues and histones as judged by bisulphite genomic sequencing and chromatin
immunoprecipitation assays. These results suggest that RIP140 serves as a scaffold
for both DNA and histone methyltransferase activities to inhibit gene transcription by
two key epigenetic repression systems. RIP140 could potentially act to divert white
adipocytes from a brown fat phenotype by repressing genes involved in fatty acid
oxidation and mitochondrial respiration and by silencing genes like Ucp1.
Date Issued
2008
Date Awarded
2008-10
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Parker, Malcolm
Creator
Kiskinis, Evangelos
Publisher Department
Div of Surgery, Oncology, Reproductive Biol & Anaesthetics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)